Patent Publication Number: US-2023159086-A1

Title: Corner module apparatus for vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit under 35 USC § 119(a) of of Korean Patent Application No. 10-2021-0162193, filed on Nov. 23, 2021, in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference for all purposes. 
     BACKGROUND 
     1. Field 
     The following description relate to a corner module apparatus for a vehicle, and more particularly, to a corner module apparatus for a vehicle, in which driving, braking, steering and suspension systems are integrated. 
     2. Description of the Related Art 
     In general, an electric vehicle refers to an environment-friendly vehicle which discharges no exhaust gas. The electric vehicle includes a high voltage battery configured to supply energy for driving, and a driving motor configured to generate a rotational force from power outputted from the high voltage battery, and is driven by the rotational force of the motor, transferred to a wheel through a driving shaft. 
     Recently, a middle-stage power transmission unit such as a reducer or differential gear may be omitted to reduce the weight of the vehicle, and much attention is being paid to an in-wheel motor vehicle which includes a motor installed in a wheel in order to directly transfer power of the motor to the wheel, in consideration of an advantage of the in-wheel motor vehicle which can reduce an energy loss in a power transmission process. Furthermore, a wheel in which braking, steering and suspension systems as well as a driving system are integrated is being actively developed. 
     The related art of the present disclosure is disclosed in Korean Patent Application Publication No. 10-2019-0041855 published on Apr. 23, 2019 and entitled “Steering System of In-Wheel Motor Vehicle”. 
     SUMMARY 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. 
     In one general aspect, there is provided a corner module apparatus for a vehicle, including a driver configured to provide a driving force to a wheel of a vehicle, a suspension connected to the driver, and being configured to absorb shock transferred from a road surface, and a steering unit connected to the suspension, the steering unit rotatably installed under a frame module coupled to a vehicle body, and being configured to adjust a steering angle of the wheel. 
     The steering unit may include a steering body disposed to face a bottom surface of the frame module, and being configured to support the suspension unit, and a steering driver installed in the steering body, and being configured to rotatably support the steering body with respect to the frame module. 
     The steering driver may include a power generation module configured to receive power and generate a rotational force, a rotating module spaced apart from the power generation module, and being configured to rotate around the frame module based on the rotational force generated by the power generation module, and a power transmission module provided between the power generation module and the rotating module, and being configured to transmit the rotational force, generated by the power generation module, to the rotating module. 
     The power generation module may revolve around the rotating module, in response to the rotating module rotating around the frame module. 
     A center axis of the power generation module may be disposed in parallel to a center axis of the rotating module. 
     The rotating module may include a mounting unit fixed to the bottom surface of the frame module, an input shaft rotated by the rotational force received from the power transmission module, an output shaft rotatably supported by the mounting unit, and being configured to rotate the steering body around the mounting unit based on a rotation of the input shaft, and a reducer provided between the input shaft and the output shaft. 
     A center axis of the rotating module may be disposed on a same plane as a center plane of the wheel. 
     The reducer may include a strain wave gear. 
     The steering driver may include a measurement module fixed to the mounting unit, and being configured to measure a rotation angle of the rotating module. 
     The rotating module may include a rotating module body installed to be rotatable relative to the mounting unit, and rotated with the output shaft, and a steering guide extended from the rotating module body, and being configured to rotate an inner diameter part of the measurement module in connection with a rotation of the rotating module body. 
     The power transmission module may be moved in a caterpillar manner between the power generation module and the rotating module. 
     Other features and aspects will be apparent from the following detailed description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a front view schematically illustrating a configuration of a vehicle including a corner module apparatus for a vehicle in accordance with an embodiment of the present disclosure. 
         FIG.  2    is a perspective view schematically illustrating the configuration of the vehicle including a corner module apparatus for a vehicle in accordance with the embodiment of the present disclosure. 
         FIG.  3    is a perspective view schematically illustrating a configuration of a main platform in accordance with an embodiment of the present disclosure. 
         FIGS.  4  and  5    are expanded views schematically illustrating a configuration of a main fastener in accordance with an embodiment of the present disclosure. 
         FIG.  6    is a perspective view schematically illustrating configurations of a first corner module platform and a second corner module platform in accordance with an embodiment of the present disclosure. 
         FIGS.  7  and  8    are expanded views schematically illustrating configurations of first and second corner module fasteners in accordance with the embodiment of the present disclosure. 
         FIG.  9    is a perspective view schematically illustrating a configuration of a corner module in accordance with an embodiment of the present disclosure. 
         FIG.  10    is a perspective view illustrating the configuration of the corner module in accordance with the embodiment of the present disclosure, when seen from a different point of view from  FIG.  9   . 
         FIG.  11    is a front view schematically illustrating the configuration of the corner module in accordance with the embodiment of the present disclosure. 
         FIG.  12    is a side view schematically illustrating the configuration of the corner module in accordance with the embodiment of the present disclosure. 
         FIG.  13    is an exploded perspective view schematically illustrating the configuration of the corner module in accordance with the embodiment of the present disclosure. 
         FIG.  14    is a cross-sectional view schematically illustrating a configuration of a steering driving unit in accordance with the embodiment of the present disclosure. 
         FIGS.  15 ,  16 A and  16 B  are operation diagrams schematically illustrating an operation process of the corner module in accordance with an embodiment of the present disclosure. 
         FIG.  17    is a diagram schematically illustrating a configuration of a vehicle including a corner module apparatus for a vehicle in accordance with another embodiment of the present disclosure. 
         FIG.  18    is a diagram schematically illustrating configurations of a first corner module platform and a second corner module platform in accordance with another embodiment of the present disclosure. 
         FIGS.  19  and  20    are expanded views schematically illustrating the configurations of a first corner module extension fastener and a second corner module extension fastener in accordance with another embodiment of the present disclosure. 
         FIG.  21    is a diagram schematically illustrating a configuration of a vehicle including a corner module apparatus for a vehicle in accordance with still another embodiment of the present disclosure. 
         FIG.  22    is a block configuration diagram for describing the functions of the corner module apparatus for a vehicle in accordance with an embodiment of the present disclosure. 
         FIG.  23    is a diagram illustrating a series of processes of calculating first to fourth target angles in a first application (individual steering architecture) of the corner module apparatus for a vehicle in accordance with the embodiment of the present disclosure. 
         FIG.  24    is a diagram illustrating first to fourth target angles in a front wheel steering mode in the first application (individual steering architecture) of the corner module apparatus for a vehicle in accordance with the embodiment of the present disclosure. 
         FIGS.  25  and  26    are diagrams illustrating first to fourth target angles in a four-wheel in-phase steering mode in the first application (individual steering architecture) of the corner module apparatus for a vehicle in accordance with the embodiment of the present disclosure. 
         FIGS.  27  and  28    are diagrams illustrating first to fourth target angles in a four-wheel counter-phase steering mode in the first application (individual steering architecture) of the corner module apparatus for a vehicle in accordance with the embodiment of the present disclosure. 
         FIG.  29    is a flowchart for describing an operation method of the corner module apparatus for a vehicle in accordance with the embodiment of the present disclosure, based on the first application (individual steering architecture). 
         FIGS.  30  to  33    are diagrams illustrating the positional relationship between a slope way and a vehicle in a second application (braking mechanism through individual steering) of the corner module apparatus for a vehicle in accordance with the embodiment of the present disclosure. 
         FIGS.  34  to  36    are diagrams illustrating the alignment of wheels based on a direction angle in the second application (braking mechanism through individual steering) of the corner module apparatus for a vehicle in accordance with the embodiment of the present disclosure. 
         FIG.  37    is a flowchart for describing an operation method of the corner module apparatus for a vehicle in accordance with the embodiment of the present disclosure, based on the second application (braking mechanism through individual steering). 
         FIG.  38    is a diagram illustrating a method for deciding a variable gain in a third application (posture control mechanism for improving straight driving performance) of the corner module apparatus for a vehicle in accordance with the embodiment of the present disclosure. 
         FIG.  39    is a flowchart for describing an operation method of the corner module apparatus for a vehicle in accordance with the embodiment of the present disclosure, based on the third application (posture control mechanism for improving straight driving performance). 
         FIG.  40    is a flowchart for describing an operation method of the corner module apparatus for a vehicle in accordance with the embodiment of the present disclosure, based on a fourth application (posture control mechanism for removing slip). 
         FIG.  41    is a diagram illustrating a process of calculating distance information and a center target curvature in a fifth application (target trajectory generation and following control mechanism) of the corner module apparatus for a vehicle in accordance with the embodiment of the present disclosure. 
         FIG.  42    is a diagram illustrating a process of calculating a left wheel target curvature and a right wheel target curvature in the fifth application (target trajectory generation and following control mechanism) of the corner module apparatus for a vehicle in accordance with the embodiment of the present disclosure. 
         FIG.  43    is a diagram illustrating a process of calculating a target steering angle in the fifth application (target trajectory generation and following control mechanism) of the corner module apparatus for a vehicle in accordance with the embodiment of the present disclosure. 
         FIG.  44    is a block configuration diagram illustrating a method for independently controlling steering of wheels in the fifth application (target trajectory generation and following control mechanism) of the corner module apparatus for a vehicle in accordance with the embodiment of the present disclosure. 
         FIG.  45    is a flowchart for describing an operation method of the corner module apparatus for a vehicle in accordance with the embodiment of the present disclosure, based on the fifth application (target trajectory generation and following control mechanism). 
     
    
    
     DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS 
     The following detailed description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses, and/or systems described herein. However, various changes, modifications, and equivalents of the methods, apparatuses, and/or systems described herein will be apparent after an understanding of the disclosure of this application. For example, the sequences of operations described herein are merely examples, and are not limited to those set forth herein, but may be changed as will be apparent after an understanding of the disclosure of this application, with the exception of operations necessarily occurring in a certain order. Also, descriptions of features that are known may be omitted for increased clarity and conciseness. 
     The features described herein may be embodied in different forms, and are not to be construed as being limited to the examples described herein. Rather, the examples described herein have been provided merely to illustrate some of the many possible ways of implementing the methods, apparatuses, and/or systems described herein that will be apparent after an understanding of the disclosure of this application. 
     It should be noted that the drawings are not to precise scale and may be exaggerated in thickness of lines or sizes of components for descriptive convenience and clarity only. Furthermore, the terms as used herein are defined by taking functions of the invention into account and can be changed according to the custom or intention of users or operators. Therefore, definition of the terms should be made according to the overall disclosures set forth herein. 
     The terminology used herein is for the purpose of describing particular examples only and is not to be limiting of the examples. The singular forms “a”, “an”, and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises/comprising” and/or “includes/including” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof. 
     Throughout the specification, when one element is referred to as being “connected to” or “coupled to” another element, it may indicate that the elements are “directly connected or coupled to” each other or the elements are “indirectly connected or coupled to” each other with still another element interposed therebetween. In this specification, when an element “includes or has” a component, it may indicate that the element does not exclude another component unless referred to the contrary, but can further “include or have” another component. 
     Through this specification, like reference numerals may represent the same components. Although like or similar reference numbers are not mentioned or described in a specific drawing, the reference numerals may be described with reference to other drawings. Furthermore, although a component is not represented by a reference numeral in a specific drawing, the component may be described with reference to other drawings. Furthermore, the number, shape and size of subcomponents included in the drawings of this application and the relative difference between sizes are set for convenience of description, and may not limit embodiments but may be set to various values. 
     I. Structure of Vehicle Including Corner Module Apparatus for Vehicle 
       FIG.  1    is a diagram schematically illustrating a configuration of a vehicle including a corner module apparatus for a vehicle in accordance with an embodiment of the present disclosure, and  FIG.  2    is a perspective view schematically illustrating the configuration of the vehicle including a corner module apparatus for a vehicle in accordance with the embodiment of the present disclosure. 
     Referring to  FIGS.  1  and  2   , the vehicle including the corner module apparatus for a vehicle in accordance with the embodiment of the present disclosure includes a corner module apparatus  1 , a top hat  2  and a door part  3 . 
     The corner module apparatus  1  for a vehicle in accordance with the embodiment of the present disclosure includes a frame module  100  and a corner module  200 . 
     The frame module  100  is installed at the bottom of a vehicle body, and supports the corner module  200 , a battery  400  and an inverter  500 . 
     Referring to  FIG.  2   , the frame module  100  in accordance with the embodiment of the present disclosure includes a main platform  1100 , a first corner module platform  1200 A and a second corner module platform  1200 B. 
     The main platform  1100  is installed at the bottom of the vehicle body, and has the battery  400  mounted therein, the battery  400  serving to supply power to the corner module  200  which will be described below. The main platform  1100  may be made of a high-stiffness material such as metal, in order to sufficiently withstand a load applied from the battery  400 . The battery  400  has a smaller height than the main platform  1100 . 
       FIG.  3    is a perspective view schematically illustrating a configuration of the main platform  1100  in accordance with an embodiment of the present disclosure. 
     Referring to  FIG.  3   , the main platform  1100  in accordance with the embodiment of the present disclosure includes a main plate  1110 , a main wheel housing  1120  and a main fastener  1130 . 
     The main plate  1110  forms the exterior of the central portion of the main platform  1100 , and supports the entire main wheel housings  1120  which will be described below. The main plate  1110  in accordance with the embodiment of the present disclosure may be formed in a flat plate shape and disposed in parallel to the ground surface. The battery  400  is seated on the top surface of the main plate  1110 , and the inverter  500  may be seated on the top surface of the main plate  1110 , if necessary. The area of the main plate  1110  may be varied in design depending on the size of the vehicle body, the size of the battery  400  and the like. 
     The main wheel housing  1120  is extended from the main plate  1110 , and provides a space in which the corner module  200  is housed. The main wheel housing  1120  in accordance with the embodiment of the present disclosure may have a pillar shape which is vertically extended upward from the top surface of the main plate  1110 . More specifically, the main wheel housing  1120  is disposed at each corner of the main plate  1110 , and has an open outer surface. For example, the main wheel housing  1120  may have an approximately L-shaped cross-section as illustrated in  FIG.  3   , and may be extended from the top surface of the corresponding corner of the main plate  1110 . Thus, the main wheel housing  1120  may have an internal space in which the corner module  200  is housed. 
     An upper end portion of the main wheel housing  1120  has a plate shape disposed in parallel to the main plate  1110 . Thus, the upper end portion of the main wheel housing  1120  may have a space in which the main fastener  1130  to be described below may be formed. 
     The main wheel housing  1120  may be provided as a plurality of main wheel housings. The plurality of main wheel housings  1120  may be disposed at the respective corners of the main plate  1110 . 
     The main fastener  1130  is formed in the main plate  1110  and the main wheel housing  1120 , and fastened to a second platform  1200  which will be described below. 
       FIGS.  4  and  5    are expanded views schematically illustrating a configuration of the main fastener in accordance with an embodiment of the present disclosure. 
     Referring to  FIGS.  3  to  5   , the main fastener  1130  in accordance with the embodiment of the present disclosure includes an upper main fastener  1131  and a lower main fastener  1132 . 
     The upper main fastener  1131  in accordance with the embodiment of the present disclosure may have a groove shape which is formed concavely from the outer surface of the main wheel housing  1120 . The upper main fastener  1131  is vertically extended downward from the top surface of the main wheel housing  1120 . The upper main fastener  1131  may have a stair-shaped cross-section so as to be hooked and coupled to a first corner module upper fastener  1231 A and a second corner module upper fastener  1231 B, which will be described below. The upper main fastener  1131  is disposed at an end of the main wheel housing  1120  facing the first corner module platform  1200 A or the second corner module platform  1200 B which will be described below. The upper main fastener  1131  may be provided as a plurality of upper main fasteners which are disposed at the respective main wheel housings  1120 . 
     The lower main fastener  1132  in accordance with the embodiment of the present disclosure may have a groove shape which is formed concavely from the outer surface of the main plate  1110 . The lower main fastener  1132  may have a stair-shaped cross-section so as to be hooked and coupled to a first corner module lower fastener  1232 A and a second corner module lower fastener  1232 B, which will be described below. 
     The lower main fastener  1132  is extended in the opposite direction of the upper main fastener  1131 . More specifically, the lower main fastener  1132  is vertically extended upward from the bottom surface of the main plate  1110 . Thus, when fastened to a first corner module fastener  1230 A and a second corner module fastener  1230 B which will be described below, the upper main fastener  1131  and the lower main fastener  1132  may prevent the first and second corner module fasteners  1230 A and  1230 B from separating in any one direction. 
     The lower main fastener  1132  is provided as a pair of lower main fasteners which are disposed at ends of the main plate  1110 , facing the first and second corner module platforms  1200 A and  1200 B described below, respectively. 
     The first and second corner module platforms  1200 A and  1200 B are detachably coupled to both sides of the main platform  1100 , respectively. The corner module  200  which will be described below is coupled to the bottoms of the first and second corner module platforms  1200 A and  12008 , such that the first and second corner module platforms  1200 A and  1200 B support the corner module  200 . The first and second corner module platforms  1200 A and  1200 B each have the corner module  200  and the inverter  500  mounted therein, the inverter  500  serving to convert DC power supplied from the battery  400  into AC power, and transfer the AC power to the corner module  200 . The inverter  500  has a smaller height than the first corner module platform  1200 A of a first corner module plate  1210 A. The first and second corner module platforms  1200 A and  1200 B may be made of a high-stiffness material such as metal so as to sufficiently withstand a load applied from the corner module  200  and the battery  400 . 
       FIG.  6    is a perspective view schematically illustrating configurations of the first corner module platform and the second corner module platform in accordance with an embodiment of the present disclosure. 
     Referring to  FIG.  6   , the first corner module platform  1200 A in accordance with the embodiment of the present disclosure includes the first corner module plate  1210 A, a first corner module wheel housing  1220 A and the first corner module fastener  1230 A. 
     The first corner module plate  1210 A forms the exterior of the central portion of the first corner module platform  1200 A, and supports the entire first corner module wheel housing  1220 A which will be described below. The first corner module plate  1210 A in accordance with the embodiment of the present disclosure may be formed in a flat plate shape and disposed in parallel to the ground surface. The inverter  500  may be seated on the top surface of the first corner module plate  1210 A, and the battery  400  may be seated on the top surface of the first corner module plate  1210 A, if necessary. The area of the first corner module plate  1210 A may be varied in design, depending on the sizes of the main plate  1110  and the inverter  500 . 
     The first corner module wheel housing  1220 A is extended from the first corner module plate  1210 A, and provides a space in which the corner module  200  is housed. The first corner module wheel housing  1220 A in accordance with the embodiment of the present disclosure may have a plate shape which is extended upward from the top surface of the main plate  1110 . The first corner module wheel housing  1220 A may be provided as a pair of first corner module wheel housings which are disposed at widthwise ends of the first corner module plate  1210 A, respectively. 
     The first corner module wheel housing  1220 A has a first mounting plate  1221 A to support the corner module  200 . The first mounting plate  1221 A may have a plate shape which is extended from an upper end of the first corner module wheel housing  1220 A in the widthwise direction of the first corner module plate  1210 A. The first mounting plate  1221 A is disposed in parallel to the first corner module plate  1210 A. The bottom surface of the first mounting plate  1221 A is detachably coupled to the corner module  200  through bolting or the like. 
     In this case, the first corner module wheel housing  1220 A may have an approximately L-shaped cross-section as illustrated in  FIG.  6   , and may be extended to the outside of the first corner module plate  1210 A in the widthwise direction. Thus, the first corner module wheel housing  1220 A may have an internal space in which the corner module  200  is housed. 
     The first corner module fastener  1230 A is formed on the first corner module plate  1210 A and the first corner module wheel housing  1220 A, and fastened to the main fastener  1130  disposed on one side of the main platform  1110 . When the main platform  1100  and the first corner module platform  1200 A are assembled, the first corner module fastener  1230 A is disposed at a position facing the main fastener  1130  disposed on one side of the main platform  1110 . As the first corner module platform  1200 A is brought into contact with the main platform  1100  in a direction parallel to the longitudinal direction of the vehicle, the first corner module fastener  1230 A is hooked and coupled to the main fastener  1130  disposed on one side of the main platform  1110 . Thus, the main fastener  1130  and the first corner module fastener  1230 A may improve the assembly performance between the main platform  1100  and the first corner module platform  1200 A. 
       FIGS.  7  and  8    are expanded views schematically illustrating configurations of the first and second corner module fasteners in accordance with an embodiment of the present disclosure. 
     Referring to  FIGS.  6  to  8   , the first corner module fastener  1230 A in accordance with the embodiment of the present disclosure includes the first corner module upper fastener  1231 A and the first corner module lower fastener  1232 A. 
     The first corner module upper fastener  1231 A in accordance with the embodiment of the present disclosure may have a protrusion shape that protrudes from the outer surface of the first corner module wheel housing  1220 A. More specifically, the first corner module upper fastener  1231 A is horizontally extended from a front or rear end of the first mounting plate  1221 A, or more specifically an end facing one end of the main platform  1100 . As the first corner module platform  1200 A is brought into contact with the main platform  1100  in the direction parallel to the longitudinal direction of the vehicle, the first corner module upper fastener  1231 A is inserted into the upper main fastener  1131  disposed on one side of the main platform  1110 . In this case, the first corner module upper fastener  1231 A may have an end bent in a hook shape, and thus may be hooked and coupled to the upper main fastener  1131  disposed on the one side of the main platform  1100 . The first corner module upper fastener  1231 A may be provided as a plurality of first corner module upper fasteners which are disposed at the respective first corner module wheel housings  1220 A. 
     The first corner module lower fastener  1232 A in accordance with the embodiment of the present disclosure may have a protrusion shape that protrudes from the outer surface of the first corner module plate  1210 A. More specifically, the first corner module lower fastener  1232 A is horizontally extended from any one end of front and rear ends of the first corner module plate  1210 A, or more specifically an end facing the one end of the main platform  1100 . As the first corner module platform  1200 A is brought into contact with the main platform  1100  in the direction parallel to the longitudinal direction of the vehicle, the first corner module lower fastener  1232 A is inserted into the lower main fastener  1132  disposed on the one side of the main platform  1110 . 
     The first corner module lower fastener  1232 A may have an end bent in a hook shape, and thus may be hooked and coupled to the lower main fastener  1132 . In this case, the end of the first corner module lower fastener  1232 A is bent in the opposite direction to the end of the first corner module upper fastener  1231 A. For example, the end of the first corner module upper fastener  1231 A may be bent downward, and the end of the first corner module lower fastener  1232 A may be bent upward. Thus, when fastened to the main fastener  1130 , the first corner module upper fastener  1231 A and the first corner module lower fastener  1232 A may prevent the upper main fastener  1131  and the lower main fastener  1132  from separating in any one direction. 
     The second corner module platform  1200 B in accordance with the embodiment of the present disclosure includes a second corner module plate  1210 B, a second corner module wheel housing  1220 B and the second corner module fastener  1230 B. 
     The second corner module plate  1210 B and the second corner module wheel housing  1220 B may have the same shapes as the first corner module plate  1210 A and the second corner module wheel housing  1220 A, respectively, which are described above. 
     The second corner module fastener  1230 B is formed on the second corner module plate  1210 B and the second corner module wheel housing  1220 B, and fastened to the main fastener  1130  disposed on the other side of the main platform  1110 . When the main platform  1100  and the second corner module platform  1200 B are assembled, the second corner module fastener  1230 B is disposed at a position facing the main fastener  1130  disposed on the other side of the main platform  1110 . As the second corner module platform  1200 B is brought into contact with the main platform  1100  in the direction parallel to the longitudinal direction of the vehicle, the second corner module fastener  1230 B is hooked and coupled to the main fastener  1130  disposed on the other side of the main platform  1110 . 
     The second corner module fastener  1230 B in accordance with the embodiment of the present disclosure includes the second corner module upper fastener  1231 B and the second corner module lower fastener  1232 B. 
     The second corner module upper fastener  1231 B in accordance with the embodiment of the present disclosure may have a protrusion shape that protrudes from the outer surface of the second corner module wheel housing  1220 B. More specifically, the second corner module upper fastener  1231 B is horizontally extended from a front or rear end of a second mounting plate  1221 B, or more specifically an end facing the other end of the main platform  1100 . As the second corner module platform  1200 B is brought into contact with the main platform  1100  in the direction parallel to the longitudinal direction of the vehicle, the second corner module upper fastener  1231 B is inserted into the upper main fastener  1131  disposed on one side of the main platform  1110 . In this case, the second corner module upper fastener  1231 B may have an end bent in a hook shape, and thus may be hooked and coupled to the upper main fastener  1131  disposed on the one side of the main platform  1100 . The second corner module upper fastener  1231 B may be provided as a plurality of first corner module upper fasteners which are disposed at the respective second corner module wheel housings  1220 B. 
     The second corner module lower fastener  1232 B in accordance with the embodiment of the present disclosure may have a protrusion shape that protrudes from the outer surface of the second corner module plate  1210 B. More specifically, the second corner module lower fastener  1232 B is horizontally extended from any one end of front rear ends of the second corner module plate  1210 B, or more specifically an end facing the other end of the main platform  1100 . As the second corner module platform  1200 B is brought into contact with the main platform  1100  in the direction parallel to the longitudinal direction of the vehicle, the second corner module lower fastener  1232 B is inserted into the lower main fastener  1132  disposed on the other side of the main platform  1110 . 
     The second corner module lower fastener  1232 B may have an end bent in a hook shape, and thus may be hooked and coupled to the lower main fastener  1132 . In this case, the end of the second corner module lower fastener  1232 B is bent in the opposite direction to the end of the second corner module upper fastener  1231 B. For example, the end of the second corner module upper fastener  1231 B may be bent downward, and the end of the second corner module lower fastener  1232 B may be bent upward. Thus, when fastened to the main fastener  1130 , the second corner module upper fastener  1231 B and the second corner module lower fastener  1232 B may prevent the upper main fastener  1131  and the lower main fastener  1132  from separating in any one direction. 
     The corner module  200  is supported by the frame module  100  and connected to a wheel  300  of the vehicle, and serve to perform overall operations such as driving, braking, steering and suspension operations. The corner module  200  may be provided as a plurality of corner modules which are connected to the respective wheels  300 . The plurality of corner modules  200  may each independently perform a driving, braking, steering or suspension operation on the corresponding wheel  300 . 
       FIG.  9    is a perspective view schematically illustrating a configuration of the corner module in accordance with an embodiment of the present disclosure,  FIG.  10    is a perspective view illustrating the configuration of the corner module in accordance with the embodiment of the present disclosure, when seen from a different point of view from  FIG.  9   ,  FIG.  11    is a front view schematically illustrating the configuration of the corner module in accordance with the embodiment of the present disclosure,  FIG.  12    is a side view schematically illustrating the configuration of the corner module in accordance with an embodiment of the present disclosure, and  FIG.  13    is an exploded perspective view schematically illustrating the configuration of the corner module in accordance with the embodiment of the present disclosure. 
     Referring to  FIGS.  9  to  13   , the corner module  200  in accordance with the embodiment of the present disclosure includes a driving unit  2100  (may also be referred to as a “driver’), a braking unit  2200 , a suspension unit  2300  and a steering unit  2400 . 
     The driving unit  2100  rotates the wheel  300  by providing a driving force to the wheel  300 . 
     The driving unit  2110  in accordance with the embodiment of the present disclosure includes an in-wheel motor  2110  and a knuckle  2120 . 
     The in-wheel motor  2110  is installed inside the wheel  300  and serves to generate a driving force. The in-wheel motor  2110  in accordance with the embodiment of the present disclosure may include a stator and a rotor. The stator is fixed to the inside of the wheel  300 , and serves to form a magnetic field by using power received from the battery  400 , and the rotor is rotatably installed inside the wheel  300 , and serves to rotate the wheel  300  through an electromagnetic interaction with the stator. The stator and the rotor may be disposed so that the center axes thereof are located on the same line as the center axis of the wheel  300  and the stator and the rotor are concentrically stacked inside the wheel  300 . 
     The knuckle  2120  is coupled to the in-wheel motor  2110 , and provides a mechanical connection between the driving unit  2100 , and the braking unit  2200  and the suspension unit  2300 , which will be described below. The knuckle  2120  in accordance with the embodiment of the present disclosure may be coupled to the stator of the in-wheel motor  2110  through bolting or the like, and supported by the stator. The knuckle  2120  may rotatably support the rotor of the in-wheel motor  2110  through a wheel bearing or the like. The knuckle  2120  may be manufactured through a casting process using a metallic material, in order to secure sufficient stiffness. The shape of the knuckle  2120  is not limited to that illustrated in  FIG.  13   , but may be varied in design as long as the knuckle  2120  can support the in-wheel motor  2110 . 
     The braking unit  2200  serves to apply a braking force by interfering with the rotation of the wheel  300 , or remove the braking force. 
     The braking unit  2200  in accordance with the embodiment of the present disclosure includes a brake disk  2210  and a brake caliper  2220 . 
     The brake disk  2210  is connected to the wheel  300  or the in-wheel motor  2110 , and rotated in connection with the rotation of the wheel  300 . The brake disk  2210  in accordance with the embodiment of the present disclosure is formed in a disk shape and installed inside the wheel  300 . The brake disk  2210  is disposed so that the center axis thereof is located on the same line as the center axis of the wheel  300 . The brake disk  2210  may be connected to the wheel  300  or the rotor of the in-wheel motor  2110  through bolting or the like. Thus, the brake disk  2210  may be rotated about the center axis thereof with the wheel  300 , when the wheel  300  is rotated. The diameter of the brake disk  2210  may be varied in design depending on the diameter of the wheel  300  and the size of the in-wheel motor  2110 . 
     The brake caliper  2220  serves to apply a braking force by pressing the brake disk  2210  during a braking operation of the vehicle. The brake caliper  2220  in accordance with the embodiment of the present disclosure may include a brake pad, a caliper housing and a piston. The brake pad may be disposed to face the brake disk  2210 . The caliper housing may be coupled to the knuckle  2120 , and movably support the brake pad. The piston may be installed in the caliper housing so as to move forward and backward, and serve to press the brake pad against the brake disk  2210  or separate the brake pad from the brake disk  2210 , according to the moving direction. 
     The suspension unit  2300  is connected to the driving unit  2100 , and serves to absorb shock transferred from the road surface when the vehicle is driven. 
     The suspension unit  2300  in accordance with the embodiment of the present disclosure includes a suspension arm  2310  and a shock absorber module  2320 . 
     The suspension arm  2310  is provided between the driving unit  2100  and the steering unit  2400  described below, and serves to support the wheel  300 . More specifically, the suspension arm  2310  connects the wheel  300  to the vehicle body, and simultaneously absorbs a load, applied from the wheel  300  during driving of the vehicle, through the stiffness thereof, and serves to adjust the motion of the wheel  300 . 
     The suspension arm  2310  in accordance with the embodiment of the present disclosure may include a first arm  2311  and a second arm  2312 . 
     The first arm  2311  and the second arm  2312  each have one end rotatably connected to a steering body  2410  of the steering unit  2400  and the other end rotatably connected to the knuckle  2120  of the driving unit  2100 . In this case, the first arm  2311  and the second arm  2312  may be rotatably coupled to the steering body  2410  and the knuckle  2120  through a bush, ball joint, pin or the like. The first arm  2311  and the second arm  2312  are spaced apart from each other in a top-to-bottom direction so as to face each other. The first arm  2311  and the second arm  2312  may have a double wishbone shape. Thus, the first arm  2311  and the second arm  2312  may establish a negative camber set-up of the wheel  300 , thereby improving the cornering performance of the vehicle, and establishing a low floor set-up capable of lowering the height of the vehicle. The first arm  2311  and the second arm  2312  may be inclined to form a predetermined angle therebetween. Thus, the length and center of an SVSA (Side View Swing Arm), corresponding to the type and driving condition of the vehicle, may be set through the relative angle between the first and second arms  2311  and  2312 . 
     The shock absorber module  2320  is provided stretchably in a longitudinal direction, and serves to absorb shock or vibration transferred from the road surface to the vehicle body through the wheel  300 . The shock absorber module  2320  in accordance with the embodiment of the present disclosure includes a cylinder  2321 , a rod  2322  and an elastic body  2323 . 
     The cylinder  2321  is extended in the top-to-bottom direction, and filled with fluid. The cylinder  2321  may have a lower end which is rotatably connected to the top surface of the second arm  2312  through the first arm  2311 . 
     The rod  2322  is extended in the longitudinal direction of the cylinder  2321 . The bottom of the rod  2322  is inserted into the upper end of the cylinder  2321 , such that the rod  2322  can slide in the longitudinal direction of the cylinder  2321 . The top of the rod  2322  is coupled to the steering body  2410  through bolting or the like. The rod  2322  is slid in the longitudinal direction of the cylinder  2321  in connection with the pressure of the fluid filling the cylinder  2321 . 
     The elastic body  2323  is disposed to cover the outer surfaces of the cylinder  2321  and the rod  2322 , and has a length that is varied in connection with the sliding movement of the rod  2322 . The elastic body  2323  in accordance with the embodiment of the present disclosure may have a coil spring shape, and thus can stretch in the longitudinal direction. The elastic body  2323  may have both ends respectively coupled to a lower sheet  2324  fixed to the cylinder  2321  and an upper sheet  2325  fixed to the rod  2322 , and may be supported by the lower sheet  2324  and the upper sheet  2325 . The elastic body  2323  may be compressed and extended to accumulate an elastic restoring force, when the rod  2322  is slid, and may offset shock applied from the road surface by using the accumulated elastic restoring force. 
     The steering unit  2400  is connected to the suspension unit  2300 , and rotatably installed at the bottom of the frame module  100 . The steering unit  2400  adjusts the steering angle of the wheel  300 , while rotated in the clockwise direction or the counterclockwise direction about the frame module  100 . The steering unit  2400  may be installed at the bottom of the frame module  100  and prevent a part of the structure of the corner module  200  from protruding upward from the frame module  100 , which makes it possible to solve space and shape problems during vehicle body mounting design and packaging and vehicle design. 
     The steering unit  2400  in accordance with the embodiment of the present disclosure includes the steering body  2410  and a steering driving unit  2420  (may also be referred to as a “steering driver”). 
     The steering body  2410  is disposed to face the bottom surface of the frame module  100 , and supports the suspension unit  2300 . The steering body  2410  in accordance with the embodiment of the present disclosure has a length that extends in a direction parallel to the height direction of the vehicle, and is disposed between the frame module  100  and the suspension unit  2300 . The upper end portion of the steering body  2410  has a larger area than the lower end portion thereof. Thus, the steering body  2410  has an approximately L-shaped cross-section. The lower end of the steering body  2410  is coupled to one ends of the first and second arms  2311  and  2312  through a bush, ball joint, pin or the like, and rotatably supports the first and second arms  2311  and  2312 . The bottom surface of the upper end portion of the steering body  2410  is coupled to the upper end portion of the rod  2322  through bolting or the like, and supports the shock absorber module  2320 . 
     The steering body  2410  has a housing part  2411  in which the steering driving unit  2420  described below is housed. The housing part  2411  in accordance with the embodiment of the present disclosure may have a groove shape that is formed concavely from the top surface of the upper end portion of the steering body  2410 . The cross-sectional shape of the housing part  2411  may be varied in design depending on the shape of the steering driving unit  2420 . 
     The steering driving unit  2420  is installed in the steering body  2410 , and serves to rotatably support the steering body  2410  with respect to the frame module  100 . The steering driving unit  2420  is rotated about the frame module  100  during steering of the vehicle, and rotates the steering body  2410  in the clockwise direction or the counterclockwise direction. Thus, the steering driving unit  2420  may adjust the steering angle of the wheel  300  connected to the steering body  2410  through the suspension unit  2300 . 
     The steering driving unit  2420  in accordance with the embodiment of the present disclosure includes a power generation module  2421 , a rotating module  2422  and a power transmission module  2423 . 
       FIG.  14    is a cross-sectional view schematically illustrating a configuration of the steering driving unit in accordance with the embodiment of the present disclosure. 
     Referring to  FIG.  14   , the steering driving unit  2420  in accordance with the embodiment of the present disclosure includes the power generation module  2421 , the rotating module  2422  and the power transmission module  2423 . 
     The power generation module  2421  serves to receive power and generate a rotational force. The power generation module  2421  in accordance with the embodiment of the present disclosure may be exemplified as various types of electric motors which convert power applied from the outside into a rotational force, and output the rotational force through a driving shaft  2421   a . The power generation module  2421  may be connected to the battery  400  installed in the frame module  100 , and receive power from the battery  400 . 
     The power generation module  2421  may be seated on one side of the housing part  2411 , and detachably fixed to the steering body  2410  through bolting or the like. The driving shaft  2421   a  of the power generation module  2421  is located coaxially with a center axis A of the power generation module  2421 . The center axis A of the power generation module  2421  may be located in parallel to a center axis B of the rotating module  2422  which will be described below. However, the power generation module  2421  is not limited to such a structure, but may be disposed perpendicular to the center axis B of the rotating module  2422  depending on the specific structure of the power transmission module  2423  which will be described below. 
     The rotating module  2422  is rotated about the frame module  100  in connection with the rotational force generated by the power generation module  2421 . As the rotating module  2422  is rotated about the frame module  100 , the power generation module  2421  is revolved around the rotating module  2422 , which make it possible to adjust the steering angle of the wheel  300 . The operation of the power generation module  2421  will be described below in detail. 
     The rotating module  2422  is seated on the other side of the housing part  2411 , and spaced apart from the power generation module  2421 . The rotating module  2422  may be detachably fixed to the steering body  2410  through bolting or the like. The rotating module  2422  is connected to the power generation module  2421  through the power transmission module  2423  which will be described below. While housed with the power generation module  2421  and the power transmission module  2423  in the same case or the like, the rotating module  2422  may be installed in the steering body  2410 , as illustrated in  FIG.  14   . Alternatively, the rotating module  2422  may be installed in the steering body  2410  separately from the power generation module  2421  and the power transmission module  2423 . 
     The center axis B of the rotating module  2422  may be disposed on the same plane as the center plane of the wheel  300 . The center plane of the wheel  300  may be exemplified as a plane which symmetrically divides the wheel  300  in the widthwise direction of the vehicle, among planes through which the center axis of the wheel  300  vertically passes. Thus, the rotation center axis of the rotating module  2422  may be matched with the steering shaft of the wheel  300 , which makes it possible to induce stable steering of the wheel  300 . 
     The rotating module  2422  in accordance with the embodiment of the present disclosure includes a mounting part  2422   a , a rotating module body  2422   b , an input shaft  2422   c , an output shaft  2422   d , a reducer module  2422   e  and a steering guide  2422   f.    
     The mounting unit  2422   a  forms the upper exterior of the rotating module  2422 , and is fixed to the bottom of the frame module  100 . The mounting part  2422   a  in accordance with the embodiment of the present disclosure may have a plate shape parallel to the frame module  100 , or more specifically the first mounting plate  1221 A or the second mounting plate  1221 B. The top surface of the mounting part  2422   a  is detachably coupled to the bottom surface of the first or second mounting plate  1221 A or  1221 B through bolting or the like. The mounting part  2422   a  is fixed to the bottom of the frame module  100 , and supports the entire corner module  200  with respect to the frame module  100 . 
     The rotating module body  2422   b  forms the lower exterior of the rotating module  2422 , and is installed so as to rotate relative to the mounting part  2422   a . The rotating module body  2422   b  in accordance with the embodiment of the present disclosure has a hollow cylindrical shape, and is installed under the mounting part  2422   a . The rotating module body  2422   b  has an upper end that is rotatably connected to a lower end of the mounting part  2422   a  through a bearing or the like. The rotating module body  2422   b  has a lower end that is seated on the other side of the housing part  2411  and supported by the housing part  2411 . The rotating module body  2422   b  may be assembled to the case in which the power generation module  2421  and the power transmission module  2423  are housed with the rotating module body  2422   b , or directly assembled and fixed to the steering body  2410 . 
     The input shaft  2422   c  is rotatably installed in the rotating module body  2422   b , and rotated by the rotational force received from the power transmission module  2423 . The input shaft  2422   c  in accordance with the embodiment of the present disclosure may have a shaft shape whose center axis is located coaxially with the center axis B of the rotating module  2422 . The input shaft  2422   c  has a lower end that protrudes from the bottom of the rotating module body  2422   c  and is connected to the power transmission module  2423 . 
     The output shaft  2422   d  is rotatably supported by the mounting part  2422   a . The output shaft  2422   d  is rotated in connection with the rotation of the input shaft  2422   c , and rotates the steering body  410  about the mounting part  2422   a . The output shaft  2422   d  in accordance with the embodiment of the present disclosure may have a shaft shape whose center axis is located coaxially with the center axis B of the rotating module  2422 . The output shaft  2422   d  has a lower end that is connected to the upper end of the input shaft  2422   c  through a bearing so as to rotate relative to the input shaft  2422   c . The output shaft  2422   d  has an upper end which is inserted into the bottom surface of the mounting part  2422   a  so as to rotate about the mounting part  2422   a . The output shaft  2422   d  is connected to the reducer module  2422   e  to be described below, and rotated by the rotational force received from the reducer module  2422   e  when the input shaft  2422   c  is rotated. 
     The reducer module  2422   e  is provided between the input shaft  2422   c  and the output shaft  2422   d , and transmits the rotational force of the input shaft  2422   c  to the output shaft  2422   d . More specifically, the reducer module  2422   e  amplifies the magnitude of the rotational force transmitted to the output shaft  2422   d  by reducing the rotation velocity of the input shaft  2422   c  at a preset reduction gear ratio, and rotates the output shaft  2422   d  with the output rotational force. The reducer module  2422   e  in accordance with the embodiment of the present disclosure may be exemplified as a strain wave gearing which includes a wave generator, a flex spline and a circular spline. 
     The steering guide  2422   f  is extended from the rotating module body  2422   b , and connected to a measurement module  2424  which will be described below. The steering guide  2422   f  in accordance with the embodiment of the present disclosure may have a hollow disk shape whose inner circumferential end portion is bent upward, and may be disposed between the rotating module body  2422   b  and the output shaft  2422   d . The outer circumferential surface of the steering guide  2422   f  is fixed to the inner circumferential surface of the rotating module body  2422   b , such that the steering guide  2422   f  is rotated about the center axis along with the rotating module body  2422   b  when the rotating module body  2422   b  is rotated. The steering guide  2422   f  has an inner circumferential end portion coupled to an inner diameter part  2424   a  of the measurement module  2424  which will be described below. The steering guide  2422   f  rotates the inner diameter part  2424   a  in connection with the rotation of the rotating module body  2422   b.    
     The power transmission module  2423  is provided between the power generation module  2421  and the rotating module  2422 , and transmits the rotational force, generated by the power generation module  2421 , to the rotating module  2422 . The power transmission module  2423  in accordance with the embodiment of the present disclosure may have a belt or chain shape to form a looped curve. Both sides of the power transmission module  2423  are connected to ends of the driving shaft  2421   a  of the power transmission module  2421  and the input shaft  2422   c  of the rotating module  2422 , respectively. In this case, as the center axis A of the power generation module  2421  is disposed in parallel to the center axis B of the rotating module  2422 , the power transmission module  2423  may be prevented from being twisted. The power transmission module  2423  is moved in a caterpillar manner when the driving shaft  2421   a  is rotated, and transmits a rotational force to the input shaft  2422   c . However, the power transmission module  2423  is not limited to such a structure, and may be implemented as various types of power transmission units, such as a worm wheel, which can transmit a rotational force, generated by the power generation module  2421 , to the rotating module  2422 . 
     The measurement module  2424  measures the rotation angle of the rotating module  2422  as the wheel  300  is steered. The measurement module  2424  in accordance with the embodiment of the present disclosure is disposed in the rotating module body  2422   b , and fixed to the bottom of the mounting part  2422   a . The measurement module  2424  has the inner diameter part  2424   a  which is formed on the inner circumferential surface thereof, and can be rotated about the center axis of the measurement module  2424 . The inner diameter part  2424   a  is connected to the steering guide  2422   f , and rotated with the steering guide  2422   f  when the output shaft  2422   d  is rotated. The measurement module  2424  measures the rotation angle of the rotating module  2422  by detecting the angle at which the inner diameter part  2424   a  is rotated from the initial position of the output shaft  2422   d , when the vehicle is steered. The detailed shape of the measurement module  2424  is not limited to any one shape, but may be exemplified as various types of steering angle sensors capable of sensing the rotation angle of the output shaft  2422   d . The measurement module  2424  transfers data on the measured rotation angle of the rotating module  2422  to a control unit (i.e. a control unit  20  to be described below) such as an ECU (Electronic Control Unit) of the vehicle, such that the control unit performs rolling control or cornering control on the vehicle. 
     Hereafter, the operation process of the corner module  200  in accordance with the embodiment of the present disclosure will be described in detail. 
       FIGS.  15 ,  16 A and  16 B  are operation diagrams schematically illustrating an operation process of the corner module in accordance with an embodiment of the present disclosure. 
     When the vehicle needs to be cornered while the vehicle is driven, the driving shaft  2421   a  is rotated by the operation of the power generation module  2421 , and generates a rotational force. 
     The power transmission module  2423  is moved in a caterpillar manner by the rotation of the driving shaft  2421   a , and transmits the rotational force of the power generation module  2421  to the rotating module  2422 . 
     The rotational force transferred to the rotating module  2422  is sequentially passed through the input shaft  2422   c  and the reducer module  2422   e , and transferred to the output shaft  2422   d.    
     More specifically, an oval cam of the wave generator of the reducer module  2422   e  is rotated by the rotational force received from the input shaft  2422   c.    
     Then, as the flex spline is elastically deformed and rotated, the position of the outer circumferential gear of the flex spline, which is partially engaged with the inner circumferential gear of the circular spline, is sequentially changed. 
     When the oval cam is rotated once, the flex spline is moved in the reverse direction to the rotation direction of the oval cam by the difference between the number of teeth included in the outer circumferential gear and the number of teeth included in the inner circumferential gear. 
     Thus, the output shaft  2422   d  coupled to the flex spline is rotated in the opposite direction to the rotation direction of the input shaft  2422   c  at an angular velocity which is reduced to a lower velocity than the angular velocity of the input shaft  2422   c.    
     The output shaft  2422   d  is rotated about the mounting part  2422   a  fixed to the first or second mounting plate  1221 A or  1221 B, or more specifically the center axis B of the rotating module  2422 . 
     As the output shaft  2422   d  is rotated about the center axis B of the rotating module  2422 , the steering body  2410  and the rotating module body  2422   b  which are connected to the output shaft  2422   d  are also rotated about the center axis B of the rotating module  2422 . 
     Thus, the power generation module  2421  which is spaced by a predetermined distance apart from the center axis B of the rotating module  2422  revolves around the center axis B of the rotating module  2422 . 
     The rotational force generated by the rotation of the steering body  2410  is sequentially passed through the suspension unit  2300  and the driving unit  2100 , and then transferred to the wheel  300 . 
     As the center axis B of the rotating module  2422  is disposed on the same plane as the center plane of the wheel  300 , the wheel  300  is rotated about the center axis B of the rotating module  2422  by the received rotational force, and the steering angle is adjusted to corner the vehicle. 
     The top hat  2  is mounted at the top of the corner module apparatus  1  for a vehicle, and has a passenger space formed therein. 
     Referring to  FIGS.  1  and  2   , the top hat  2  in accordance with the embodiment of the present disclosure may have a hollow box shape whose bottom is open. Inside the top hat  2 , various products and devices which fit the purpose of a passenger may be installed. Examples of the products and devices may include seats, a manipulation panel, a table and the like. The top hat  2  is disposed so that the open bottom thereof faces the top side of the frame module  100 , i.e. the top surfaces of the main platform  1100 , the first corner module platform  1200 A and the second corner module platform  1200 B. The lower end portion of the top hat  2  may be coupled to the top surfaces of the main wheel housing  1120 , the first corner module wheel housing  1220 A and the second corner module wheel housing  1220 B through bolting, such that the top hat  2  is detachably fixed to the frame module  100 . The area and length of the top hat  2  may be varied in design depending on the area and length of the frame module  100 . 
     The door part  3  is installed on the top hat  2  so as to be opened/closed. When the door part  3  is opened, a passenger is allowed to get into the top hat  2  through the door part  3 . 
     The door part  3  in accordance with the embodiment of the present disclosure includes a first door  3   a  and a second door  3   b.    
     The first door  3   a  is installed on one side of the top hat  2  so as to be opened/closed, and disposed at the top of the main platform  1100 . Referring to  FIGS.  1  and  2   , the first door  3   a  in accordance with the embodiment of the present disclosure is installed at a side surface of the top hat  2  in the widthwise direction thereof so as to be opened/closed. The first door  3   a  may be installed on the top hat  2  so as to be opened/closed in various manners such as a hinged door and sliding door. The first door  3   a  may be provided as a pair of first doors which are respectively installed on both sides of the top hat  2  in the widthwise direction thereof so as to be opened/closed. Both ends of the first door  3   a  are disposed between the pair of main wheel housings  1120  which are spaced apart from each other in the longitudinal direction of the main plate  1110 . The first door  3   a  has a lower end facing the top surface of the battery  400  seated on the top surface of the main plate  1110 . As the battery  400  has a smaller height than the main platform  1100 , the lower end of the first door  3   a  may be disposed close to the ground, which makes it possible to induce a passenger to smoothly get into the vehicle. 
     The second door  3   b  is installed on the other side of the top hat  2  so as to be opened/closed, and disposed at the top of at least one of the first and second corner module platforms  1200 A and  1200 B. Hereafter, the case in which the second door  3   b  is disposed at the tops of both of the first and second corner module platforms  1200 A and  1200 B will be taken as an example for description. However, the second door  3   b  is not limited to such a structure, but may be disposed on the top of any one of the first and second corner module platforms  1200 A and  1200 B. 
     Referring to  FIGS.  1  and  2   , the second door  3   b  in accordance with the embodiment of the present disclosure is provided as a pair of second doors which are installed at side surfaces of the top hat  2  in the front-to-rear direction thereof so as to be opened/closed. Thus, the second door  3   b  may be disposed in a direction perpendicular to the first door  3   a . The second door  3   b  may be installed on the top hat  2  so as to be opened/closed in various manners such as a hinged door and sliding door. Both ends of the pair of second doors  3   b  are disposed between the pair of first corner module wheel housings  1220 A and between the pair of second corner module wheel housings  1220 B, respectively. The pair of second doors  3   b  have lower ends disposed to face the top surfaces of the inverters  500  seated on the top surfaces of the first and second corner module plates  1210 A and  1210 B, respectively. As the inverter  500  has a smaller height than the first and second corner module platforms  1200 A and  1200 B, the lower end of the second door  3   b  may be disposed close to the ground, which makes it possible to induce a passenger to smoothly get into the vehicle. 
     Hereafter, a configuration of a vehicle including a corner module apparatus in accordance with another embodiment of the present disclosure will be described. 
     For convenience of description, the overlapping descriptions with the vehicle including the corner module apparatus in accordance with the embodiment of the present disclosure will be omitted herein. 
       FIG.  17    is a front view schematically illustrating a configuration of a vehicle including a corner module apparatus in accordance with another embodiment of the present disclosure. 
     Referring to  FIG.  17   , the frame module  100  in accordance with another embodiment of the present disclosure includes a plurality of first corner module platforms  1200 A and a plurality of second corner module platforms  1200 B. 
     The plurality of first corner module platforms  1200 A and the plurality of second corner module platforms  1200 B are extended from one side and the other side of the main platform  1100 , respectively, in the longitudinal direction of the vehicle. 
     More specifically, the neighboring first corner module platforms  1200 A are connected in series to each other from one side of the main platform  1100  in the longitudinal direction of a vehicle body, and the neighboring second corner module platforms  12008  are connected in series to each other from the other side of the main platform  1100  in the longitudinal direction of the vehicle body. In this case, the number of the first corner module platforms  1200 A and the number of the second corner module platforms  12008  may be equal to or different from each other. Thus, the frame module  100  in accordance with the another embodiment of the present disclosure may freely increase the installation number of the corner modules  200  installed on both sides of the main platform  1100  according to the purpose of the vehicle. 
       FIG.  18    is a diagram schematically illustrating configurations of the first corner module platform and the second corner module platform in accordance with another embodiment of the present disclosure. 
     Referring to  FIG.  18   , the first corner module platform  1200 A and the second corner module platform  1200 B in accordance with the another embodiment of the present disclosure further include a first corner module extension fastener  1240 A and a second corner module extension fastener  12408 , respectively. 
     The first corner module extension fastener  1240 A is formed in the first corner module plate  1210 A and the first corner module wheel housing  1220 A. The first corner module extension fastener  1240 A is disposed on the opposite side of the first corner module fastener  1230 A in the first corner module platform  1200 A. That is, the first corner module fastener  1230 A and the first corner module extension fastener  1240 A are disposed at both ends of the first corner module platform  1200 A, respectively. 
     The first corner module extension fastener  1240 A formed in any one of the first corner module platforms  1200 A is detachably coupled to the first corner module fastener  1230 A formed on the neighboring first corner module platform  1200 A. More specifically, as the neighboring first corner module platforms  1200 A are brought into contact with each other in a direction parallel to the longitudinal direction of the vehicle, the first corner module extension fastener  1240 A is hooked and coupled to the first corner module fastener  1230 A. Thus, the plurality of first corner module platforms  1200 A extended in series may be sequentially connected to each other in the longitudinal direction of the vehicle. 
       FIGS.  19  and  20    are expanded views schematically illustrating the configurations of the first corner module extension fastener and the second corner module extension fastener in accordance with the embodiment of the present disclosure. 
     Referring to  FIGS.  19  to  20   , the first corner module extension fastener  1240 A in accordance with the embodiment of the present disclosure includes a first corner module upper extension fastener  1241 A and a first corner module lower extension fastener  1242 A. 
     The first corner module upper extension fastener  1241 A in accordance with the embodiment of the present disclosure may have a groove shape which is formed concavely from the first corner module wheel housing  1220 A, or more specifically the outer surface of the first mounting plate  1221 A. The first corner module upper extension fastener  1241 A is vertically extended downward from the top surface of the first corner module wheel housing  1220 A. The first corner module upper extension fastener  1241 A is disposed at the other end of front and rear ends of the first corner module wheel housing  1220 A, i.e. on the opposite side of the first corner module upper fastener  1231 A. The first corner module upper extension fastener  1241 A may have a stair-shaped cross-section so as to be hooked and coupled to the first corner module upper fastener  1231 A formed on the neighboring first corner module platform  1200 A. The first corner module upper extension fastener  1241 A may be provided as a plurality of first corner module upper extension fasteners which are formed in the respective first corner module wheel housings  1220 A. 
     The first corner module lower extension fastener  1242 A in accordance with the embodiment of the present disclosure may have a groove shape that is formed concavely from the outer surface of the first corner module plate  1210 A. 
     The first corner module lower extension fastener  1242 A is extended in the opposite direction of the first corner module upper extension fastener  1241 A. More specifically, the first corner module lower extension fastener  1242 A is vertically extended upward from the bottom surface of the first corner module plate  1210 A. Thus, when fastened to the first corner module fastener  1230 A, the first corner module upper extension fastener  1241 A and the first corner module lower extension fastener  1242 A may prevent the first corner module fastener  1230 A from separating in any one direction. 
     The first corner module lower extension fastener  1242 A is disposed at the other end of the front and rear ends of the first corner module plate  1210 A, i.e. on the opposite side of the first corner module lower fastener  1232 A. The first corner module lower extension fastener  1242 A may have a stair-shaped cross-section so as to be hooked and coupled to the first corner module lower fastener  1232 A formed on the neighboring first corner module platform  1200 A. 
     The second corner module extension fastener  1240 B is formed in the second corner module plate  1210 B and the second corner module wheel housing  1220 B. The second corner module extension fastener  1240 B is disposed on the opposite side of the second corner module fastener  1230 B in the second corner module platform  1200 B. That is, the second corner module fastener  1230 B and the second corner module extension fastener  1240 B are disposed at both ends of the second corner module platform  1200 B, respectively. 
     The second corner module extension fastener  1240 B formed in any one of the second corner module platforms  1200 B is detachably coupled to the second corner module fastener  1230 B formed on the neighboring second corner module platform  1200 B. More specifically, as the neighboring second corner module platforms  1200 B are brought into contact with each other in a direction parallel to the longitudinal direction of the vehicle, the second corner module extension fastener  1240 B is hooked and coupled to the second corner module fastener  1230 B. Thus, the plurality of second corner module platforms  1200 B extended in series may be sequentially connected to each other in the longitudinal direction of the vehicle. 
     The second corner module extension fastener  1240 B in accordance with the embodiment of the present disclosure includes a second corner module upper extension fastener  1241 B and a second corner module lower extension fastener  1242 B. 
     The second corner module upper extension fastener  1241 B in accordance with the embodiment of the present disclosure may have a groove shape which is formed concavely from the second corner module wheel housing  1220 B, or more specifically the outer surface of the second mounting plate  1221 B. The second corner module upper extension fastener  1241 B is vertically extended downward from the top surface of the second corner module wheel housing  1220 B. The second corner module upper extension fastener  1241 B is disposed at the other end of front and rear ends of the second corner module wheel housing  1220 B, i.e. on the opposite side of the second corner module upper fastener  1231 B. The second corner module upper extension fastener  1241 B may have a stair-shaped cross-section so as to be hooked and coupled to the second corner module upper fastener  1231 B formed on the neighboring second corner module platform  1200 B. The second corner module upper extension fastener  1241 B may be provided as a plurality of second corner module upper extension fasteners which are formed in the respective second corner module wheel housings  1220 B. 
     The second corner module lower extension fastener  1242 B in accordance with the embodiment of the present disclosure may have a groove shape that is formed concavely from the outer surface of the second corner module plate  1210 B. 
     The second corner module lower extension fastener  1242 B is extended in the opposite direction of the second corner module upper extension fastener  1241 B. More specifically, the second corner module lower extension fastener  1242 B is vertically extended upward from the bottom surface of the second corner module plate  1210 B. Thus, when fastened to the second corner module fastener  1230 B, the second corner module upper extension fastener  1241 B and the second corner module lower extension fastener  1242 B may prevent the second corner module fastener  1230 B from separating in any one direction. 
     The second corner module lower extension fastener  1242 B is disposed at the other end of the front and rear ends of the second corner module plate  1210 B, i.e. on the opposite side of the second corner module lower fastener  1232 B. The second corner module lower extension fastener  12428  may have a stair-shaped cross-section so as to be hooked and coupled to the second corner module lower fastener  1232 B formed on the neighboring second corner module platform  1200 B. 
     The second door  3   b  in accordance with the another embodiment of the present disclosure is provided as a pair of second doors which are installed at side surfaces of the top hat  2  in the front-to-rear direction thereof so as to be opened/closed. The pair of second doors  3   b  may be disposed at the tops of the first corner module platform  1200 A and the second corner module platform  1200 B, which are disposed at the outermost positions in the longitudinal direction of the vehicle body, among the plurality of first corner module platforms  1200 A and the plurality of second corner module platforms  12008 . 
     Hereafter, a configuration of a vehicle including a corner module apparatus for a vehicle in accordance with still another embodiment of the present disclosure will be described. 
     For convenience of description, the overlapping descriptions with the vehicle including the corner module apparatus for a vehicle in accordance with the embodiment or the another embodiment of the present disclosure will be omitted herein. 
       FIG.  21    is a front view schematically illustrating a configuration of a vehicle including a corner module apparatus for a vehicle in accordance with still another embodiment of the present disclosure. 
     Referring to  FIG.  21   , the vehicle including the corner module apparatus in accordance with the still another embodiment of the present disclosure includes a main platform assembly  1000 , the first corner module platform  1200 A and the second corner module platform  1200 B. 
     The main platform assembly  1000  includes two or more main platforms  1100  and a middle module platform  1300  disposed between the main platforms. 
     The neighboring main platforms  1100  are spaced by a predetermined distance apart from each other in the longitudinal direction of the vehicle. In this case, the first corner module platform  1200 A is detachably coupled to one side (left side in  FIG.  21   ) of the main platform  1100  disposed at the outermost position on one side (left side in  FIG.  21   ), among the plurality of main platforms  1100 , and the second corner module platform  1200 B is detachably coupled to the other side (right side in  FIG.  21   ) of the main platform  1100  disposed at the outermost position on the other side (right side in  FIG.  21   ), among the plurality of main platforms  1100 . Thus, the frame module  100  in accordance with the still another embodiment of the present disclosure may distribute the weight of the battery  400  through the plurality of main platforms  1100 , and thus may also be applied to a vehicle with a relatively long vehicle body, such as a tram, bus or trailer. 
     The middle module platform  1300  includes a third corner module platform  1200 C which is disposed between the neighboring main platforms  1100  and supports the corner module  200 . 
     The third corner module platform  1200 C may be provided as one or more third corner module platforms between the neighboring main platforms  1100 . When the third corner module platform  1200 C is provided as a plurality of third corner module platforms, the plurality of third corner module platforms  1200 C may be connected in series in the longitudinal direction of the vehicle body. The third corner module platform  1200 C disposed at the outermost position among the plurality of third corner module platforms  1200 C is detachably coupled to ends of the neighboring main platforms  1100 , which are not coupled to the first corner module platform  1200 A and the second corner module platform  12008 . 
     The third corner module platform  1200 C is coupled to the corner module  200 , which will be described below, at the bottom thereof, and supports the corner module  200 . The third corner module platform  1200 C has the corner module  200  and the inverter  500  mounted therein, the inverter  500  serving to convert DC power supplied from the battery  400  into AC power, and transfer the AC power to the corner module  200 . 
     The third corner module platform  1200 C in accordance with the embodiment of the present disclosure includes a third corner module plate, a third corner module wheel housing and a third corner module fastener. 
     The third corner module plate, the third corner module wheel housing, the third corner module fastener and a third corner module extension fastener may have the same shapes as the first corner module plate  1210 A, the first corner module wheel housing  1220 A, the first corner module fastener  1230 A and the first corner module extension fastener  1240 A, which are illustrated in  FIG.  10   . 
     The third corner module extension fastener formed on the third corner module platform  1200 C disposed at any one end, among the plurality of third corner module platforms  1200 C which are disposed between the neighboring main platforms  1100  so as to smoothly couple the main platforms  1100 , may have a hook shape that protrudes from the third corner module plate and the third corner module wheel housing. 
     The top surfaces of the mounting parts  2422   a  provided on the plurality of corner modules  200  in accordance with the still another embodiment of the present disclosure may be each detachably coupled to the bottom surface of the first mounting plate  1221 A, the second mounting plate  1221 B or the third mounting plate depending on the positions at which the mounting parts are supported, through bolting or the like. 
     The top hat  2  in accordance with the still another embodiment of the present disclosure is disposed so that the open bottom thereof faces the top side of the frame module  100 , i.e. the top surfaces of the main platform assembly  1000 , the first corner module platform  1200 A and the second corner module platform  1200 B. The lower end of the top hat  2  may be coupled to the top surfaces of the main wheel housing  1120 , the first corner module wheel housing  1220 A, the second corner module wheel housing  1220 B and the third corner module wheel housing through bolting, and detachably fixed to the frame module  100 . 
     The first door  3   a  in accordance with the still another embodiment of the present disclosure may be provided as a plurality of first doors which are spaced by a predetermined distance apart from each other in the longitudinal direction of the top hat  2 , and separately disposed at the tops of the respective main platforms  1100  provided in the main platform assembly  1000 . 
     II. Application of Corner Module Apparatus for Vehicle 
       FIG.  22    is a block configuration diagram for describing the function of a corner module apparatus for a vehicle in accordance with an embodiment of the present disclosure. Referring to  FIG.  22   , the corner module apparatus for a vehicle in accordance with the embodiment of the present disclosure includes an acquisition module  10 , the control unit  20  and an output unit  30 . 
     The acquisition module  10  functions as a module for acquiring overall information required for the control unit  20  to implement first to fifth applications which will be described below. As illustrated in  FIG.  22   , the acquisition module  10  includes a steering wheel angle acquisition unit  11 , a lever ratio value acquisition unit  12 , a braking start manipulation acquisition unit  13 , a wheel velocity acquisition unit  14  and a vehicle information acquisition unit  15 . The steering wheel angle acquisition unit  11  and the lever ratio value acquisition unit  12  are related to the first application, the braking start manipulation acquisition unit  13  is related to the second application, the wheel velocity acquisition unit  14  is related to the third and fourth applications, and the vehicle information acquisition unit  15  is related to the fifth application. 
     The steering wheel angle acquisition unit  11  may be acquire a steering wheel angle, and the steering wheel angle may correspond to a steering angle formed when a driver manipulates a steering wheel, or a steering angle command from an ADAS system. Therefore, the steering wheel angle acquisition unit  11  may be implemented as a steering angle sensor mounted in the vehicle or a separate input module configured to acquire the steering angle command outputted from the ADAS system. 
     The lever ratio value acquisition unit  12  may acquire a lever ratio value. In the first application which will be described below, the lever ratio value may be defined as a parameter indicating whether the front and rear wheels of a bicycle model defined for the vehicle are in phase or out of phase and the steering angle ratio between the front and rear wheels, and have a value of −1 to 1. The sign of the lever ratio value indicates whether the front and rear wheels of the bicycle model are in phase or out of phase. For example, a positive value indicates that the front and rear wheels of the bicycle model are in phase, and a negative value indicates that the front and rear wheels of the bicycle model are out of phase. The magnitude of the lever ratio value indicates the ratio of the steering angles of the front and rear wheels of the bicycle model. For example, when the lever ratio value is 0.5, it indicates that the ratio of the front wheel steering angle to the rear wheel steering angle is 2:1. The lever ratio value may be changed by a driver&#39;s manipulation. For this operation, the lever ratio value acquisition unit  12  may be implemented as a lever structure which is provided inside the vehicle as illustrated in  FIG.  23   , or a touch screen structure provided on an instrument panel of the vehicle. Thus, the value of the lever ratio value may be changed through a lever manipulation or a touch operation on the touch screen by a driver. 
     The braking start manipulation acquisition unit  13  may acquire a braking start manipulation of the vehicle from a driver. In the second application which will be described below, braking may correspond to a concept including a braking operation while the vehicle is moving on a slope way S (e.g. emergency braking) and a braking operation for maintaining a parking or stopping state of the vehicle on the slope way S (e.g. parking brake). As will be described below, however, the braking operation is performed through a method of independently controlling the steering of four wheels of the vehicle in the second application. Thus, when the braking operation is performed while the vehicle is moving on the slope way S, the operation in accordance with the present embodiment may be applied in the case that the vehicle is moving in a preset low-velocity region for the posture stability of the vehicle. The braking start manipulation acquisition unit  13  may be implemented as a switch which is separately provided in the vehicle, and acquire a driver&#39;s manipulation for the switch as the above-described braking start manipulation. 
     The wheel velocity acquisition unit  14  may acquire the wheel velocities of the respective four wheels of the vehicle. The wheel velocity acquisition unit  14  may be implemented as a motor sensor configured to sense the number of revolutions of the in-wheel motor mounted on each of the wheels, and the wheel velocities of a left front wheel, a right front wheel, a left rear wheel and a right rear wheel of the vehicle may be acquired by the wheel velocity acquisition unit  14 . 
     The vehicle information acquisition unit  15  may acquire the driving state information and the driving environment information of the vehicle. The driving state information may include the vehicle speed and heading angle of the vehicle, and the driving environment information may include surrounding image information (e.g. forward image) of the vehicle. In order to acquire the driving state information and the driving environment information, the vehicle information acquisition unit  15  may use various sensors (e.g. vehicle sensor, gyro sensor, camera sensor and the like) mounted in the vehicle. The driving state information and the driving environment information of the vehicle, acquired by the vehicle information acquisition unit  15 , may be used for a process of calculating distance information to a target point, a target curvature and a target steering angle in the fifth application which will be described below. 
     The control unit  20  is a main part which independently controls the driving and steering of the four wheels through individual driving torques for the respective wheels of the vehicle. The control unit  20  may be implemented as an ECU (Electronic Control Unit), CPU (Central Processing Unit), processor or SoC (System on Chip), may drive an operating system or application to control a plurality of hardware or software components connected to the control unit  20 , and may perform various data processing operations. The control unit  20  may be configured to execute one or more commands stored in a memory, and store execution result data in the memory. 
     The output unit  30  may correspond to a display or speaker installed at a cluster of the vehicle or a specific position inside the vehicle. 
     Based on the above-described contents, the first to fifth applications of the corner module apparatus for a vehicle and a detailed operation method of the corner module apparatus will be described focusing on the operation of the control unit  20 . 
     1. First Application: Individual Steering Architecture 
     In the first application, the control unit  20  may calculate first to fourth target angles of the left front wheel, the right front wheel, the left rear wheel and the right rear wheel of the vehicle, respectively, on the basis of the steering wheel angle acquired by the steering wheel angle acquisition unit  11  and the lever ratio value acquired by the lever ratio value acquisition unit  12 , and then independently control the steering of the four wheels of the vehicle by using the calculated first to fourth target angles. 
       FIG.  23    briefly illustrates a series of processes in which the control unit  20  calculates the first to fourth target angles. Referring to  FIG.  23   , in process {circle around (1)}, the control unit  20  may receive the steering wheel angle acquired by the steering wheel angle acquisition unit  11  and the lever ratio value acquired by the lever ratio value acquisition unit  12 . In process {circle around (2)}, the control unit  20  may calculate a front wheel heading angle of the bicycle model from the steering wheel angle. In this case, the control unit  20  may calculate the front wheel heading angle by multiplying the steering wheel angle by a preset steering sensitivity, and the steering sensitivity may correspond to the TGR (Total Gear Ratio) of a steering gear ratio change device applied to the vehicle, for example. In process {circle around (3)}, when the front wheel heading angle is calculated, the control unit  20  may calculate a rear wheel heading angle of the bicycle model on the basis of the front wheel heading angle and the lever ratio value acquired by the lever ratio value acquisition unit  12 . In process {circle around (4)}, the control unit  20  may extend the bicycle model to a 4WD vehicle model, and calculate the first to fourth target angles of the left front wheel, the right front wheel, the left front wheel and the right rear wheel of the vehicle, respectively. 
     The process {circle around (4)} corresponding to a process of directly calculating the first to fourth target angles, among the above-described processes, may be performed through a different method depending on the lever ratio value acquired by the lever ratio value acquisition unit  12 . Specifically, a steering control mode of the control unit  20  for the steering of four wheels may be divided into a front wheel steering mode, a four-wheel in-phase steering mode and a four-wheel counter-phase steering mode. The control unit  20  may calculate the lever ratio value and the first to fourth target angles decided by the lever ratio value through a different method for each steering control mode. Hereafter, the process of calculating the first to fourth target angles according to the lever ratio value and the steering control mode will be described in detail. 
     First, the front wheel steering mode corresponds to the steering control mode when the lever ratio value is 0. That is, since the lever ratio value is 0, the rear wheel steering control is not performed, and only the general front wheel steering control is performed. In this case, the control unit  20  may calculate the first and second target angles by applying the Ackerman geometry model to the front wheel heading angle, and calculate the third and fourth target angles as a neutral angle (i.e. 0°) indicating the longitudinal direction of the vehicle because the lever ratio value is 0.  FIG.  24    illustrates an example in which the first and second target angles are calculated as predetermined values according to the center of rotation based on the Ackerman geometry model, when the front wheel heading angle is 45°. 
     Next, the four-wheel in-phase steering mode corresponds to the steering control mode when the lever ratio value is more than 0 and less than 1. That is, since the lever ratio value has a positive value, the front wheels and the rear wheels are independently controlled while the front wheels and the rear wheels are in phase. In the four-wheel in-phase steering mode, the first to fourth target angles are calculated through different methods, when the lever ratio value is ‘more than 0 and less than 1’ and when the lever ratio value is ‘1’, respectively. 
     When the lever ratio is more than 0 and less than 1, the control unit  20  may calculate the first and second target angles by applying the Ackerman geometry model to the front wheel heading angle. Then, the control unit  20  may calculate the rear wheel heading angle of the bicycle model by applying the lever ratio value to the front wheel heading angle or multiplying the lever ratio value by the front wheel heading angle, and calculate the third and fourth target angles by applying the Ackerman geometry model to the calculated rear wheel heading angle.  FIG.  25    illustrates an example in which the first to fourth target angles are calculated as predetermined values according to the center of rotation based on the Ackerman geometry model, when the front wheel heading angle is 45° and the lever ratio value is 0.5. 
     When the lever ratio value is 1, the control unit  20  may calculate the first to fourth target values as the front wheel heading angle. That is, when the lever ratio value is 1, it indicates that the center of rotation based on the Ackerman geometry model does not exist, but the steering angles are formed as the same angle while the front wheels and the rear wheels are in phase. Thus, the control unit  20  may calculate the first to fourth target angles as the front wheel heading angle.  FIG.  26    illustrates an example in which the first to fourth target angles are calculated as the front wheel heading angle, when the front wheel heading angle is 45° and the lever ratio value is 1. 
     Next, the four-wheel counter-phase steering mode corresponds to the steering control mode when the lever ratio value is −1 or more and less than 0. That is, since the lever ratio value has a negative value, the front wheels and the rear wheels are independently controlled while the front wheels and the rear wheels are out of phase. In the four-wheel counter-phase mode, the center of rotation based on the Ackerman geometry model exists at all times. Thus, the control unit  20  may calculate the first and second target angles by applying the Ackerman geometry model to the front wheel heading angle, and calculate the third and fourth target angles by applying the Ackerman geometry model to the rear wheel heading angle of the bicycle model, which is calculated by applying the lever ratio value to the front wheel heading angle.  FIG.  27    illustrates an example in which the first to fourth target values are calculated as predetermined values according to the center of rotation based on the Ackerman geometry model, when the front wheel heading angle is 45° and the lever ratio value is −0.8, and  FIG.  28    illustrates an example in which the first to fourth target values are calculated as predetermined values according to the center of rotation based on the Ackerman geometry model, when the front wheel heading angle is 45° and the lever ratio value is −1. 
     Table 1 below shows a method of calculating the first to fourth target angles according to the lever ratio value and the steering control mode. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Steering control 
                   
                   
               
               
                 mode 
                 Lever ratio value 
                 Target angle calculation method 
               
               
                   
               
             
            
               
                 Front wheel 
                 0 
                 First and second target angles: 
               
               
                 steering mode 
                   
                 Ackerman geometry model 
               
               
                   
                   
                 Third and fourth target angles: 
               
               
                   
                   
                 Neural angle 
               
               
                 Four-wheel in- 
                 0 &lt; R &lt; 1 
                 First to fourth target angles 
               
               
                 phase steering 
                   
                 Ackerman geometry model 
               
               
                 mode 
                 R = 1 
                 First to fourth target angles: 
               
               
                   
                   
                 Front wheel heading angle 
               
               
                 Four-wheel counter- 
                 −1 ≤ R ≤ 0  
                 First to fourth target angles 
               
               
                 phase steering 
                   
                 Ackerman geometry model 
               
               
                 mode 
               
               
                   
               
            
           
         
       
     
     As described above, the lever ratio value may be changed through a driver&#39;s manipulation. Thus, when a sudden transition of the steering control mode is caused by the change in lever ratio value while the vehicle is driven, the driving stability of the vehicle may be degraded. For example, a vehicle tire slip or a turnover of the vehicle may occur. In order to prevent the above-described problem, when the transition of the steering control mode is caused by the change in lever ratio value, the control unit  20  may control the change speed of the steering angles of the four wheels to a preset control speed, thereby performing the transition of the steering control mode during a predetermined transition time. The control speed may be preset to a sufficiently low value in the control unit  20 , on the basis of a designer&#39;s experimental result, within a range in which a sudden transition of the steering control mode is not caused and the driving stability of the vehicle is secured, and the above-described transition time may also be preset as a value corresponding to the control speed in the control unit  20 . For specific example, when a driver changes the lever ratio value to −0.5 such that the steering control mode transitions to the four-wheel counter-phase steering mode, while the vehicle is driven in the four-wheel in-phase steering mode, the control unit  20  may change the current rear wheel steering angle to the target angle (i.e. the third and fourth target angles in the four-wheel counter-phase steering mode). In this case, the control unit  20  may slowly change the rear wheel steering angle to the third and fourth target angles according to the control speed, in order to secure the driving stability of the vehicle. 
       FIG.  29    is a flowchart for describing an operation method of the corner module apparatus for a vehicle in accordance with the embodiment of the present disclosure, based on the first application. Referring to  FIG.  29   , the operation method of the corner module apparatus for a vehicle in accordance with the embodiment of the present disclosure will be described. Hereafter, the detailed descriptions of contents overlapping the above-described contents will be omitted herein, and the following descriptions will be focused on a time series configuration. 
     First, the steering wheel angle acquisition unit  11  acquires a steering wheel angle in step S 10   a , and the lever ratio value acquisition unit  12  acquires a lever ratio value indicating a steering angle ratio and information on whether the front and rear wheels of a bicycle model defined for the vehicle are in phase or out of phase, in step S 20   a . The lever ratio value has a value of −1 to 1, the sign of the lever ratio value indicates whether the front and rear wheels of the bicycle model are in phase or out of phase, and the magnitude of the lever ratio value indicates the steering angle ratio between the front and rear wheels of the bicycle model. 
     Then, the control unit  20  calculates the front wheel heading angle of the bicycle model from the steering wheel angle acquired in step S 10   a , and calculates the rear wheel heading angle of the bicycle model on the basis of the calculated front wheel heading angle and the lever ratio value acquired in step S 20   a . In step S 30   a , the control unit  20  calculates the front wheel heading angle by multiplying the steering wheel angle by a preset steering sensitivity. 
     Then, the control unit  20  extends the bicycle model to a 4WD vehicle model, and calculates the first to fourth target angles of the left front wheel, the right front wheel, the left rear wheel and the right rear wheel of the vehicle, respectively, in step S 40   a . The calculation method of the first to fourth target angles in step S 40   a  is differently decided according to the lever ratio value acquired in step S 20   a . Specifically, the first to fourth target values are calculated through a different method for the lever ratio value and the steering control mode decided through the lever ratio value. The steering control mode includes the front wheel steering mode corresponding to the case in which the lever ratio value is 0, the four-wheel in-phase steering mode corresponding to the case in which the lever ratio value is more than 0 and less than 1, and the four-wheel counter-phase steering mode corresponding to the case in which the lever ratio value is −1 or more and less than 0. 
     When the steering control mode of the vehicle is the front wheel steering mode, the control unit  20  calculates the first and second target values by applying the Ackerman geometry model to the front wheel heading angle, and calculates the third and fourth target values as the neutral angle indicating the longitudinal direction of the vehicle, in step S 40   a.    
     When the steering control mode of the vehicle is the four-wheel in-phase steering mode or the four-wheel counter-phase steering mode while the lever ratio value is more than 0 and less than 1, the control unit  20  (i) calculates the first and second target angles by applying the Ackerman geometry model to the front wheel heading angle, (ii) calculates the rear wheel heading angle of the bicycle model by applying the lever ratio value to the front wheel heading angle, and (iii) calculates the third and fourth target angles by applying the Ackerman geometry model to the calculated rear wheel heading angle, in step S 40   a.    
     When the steering control mode of the vehicle is the four-wheel in-phase steering mode while the lever ratio value is 1, the control unit  20  calculates the first to fourth target angles as the front wheel heading angle in step S 40   a.    
     When the first to fourth target angles are calculated through step S 40   a , the control unit  20  independently controls the steering of the four wheels of the vehicle by using the first to fourth target angles, in step S 50   a . If a transition of the steering control mode is caused by a change in the lever ratio value, the control unit  20  may control the change speed of the steering angles of the four wheels to the preset control speed in step S 50   a , such that the transition of the steering control mode is performed during the preset transition time. 
     According to the first application, the steering of the four wheels of the vehicle may be independently controlled, which is advantageous for the expandability and degree of freedom thereof compared to the existing front wheel steering method or the rear wheel steering method (RWS). Further, the transition of the steering control mode may be continuously implemented, which makes it possible to perform safe four-wheel independent control even in not only the parking and stopping states of the vehicle but also the driving of the vehicle. 
     2. Second Application: Braking Mechanism Through Individual Steering 
     In the second application, when a braking start manipulation is acquired by the braking start manipulation acquisition unit  13 , the control unit  20  may independently control the steering of four wheels of the vehicle, thereby braking the vehicle. 
     In the case of the structure for independently controlling four wheels, the brakes of the respective corner modules may be removed, and the method for performing braking through the in-wheel motor may be applied. In this case, since the in-wheel motor cannot be controlled while the vehicle is powered off, braking control cannot be performed. Therefore, there is a need for new braking logic. The present embodiment suggests a method for braking a vehicle through a process of controlling the alignments of four wheels by independently controlling the steering of the four wheels, in consideration of the design expandability of a four-wheel independent driving apparatus and the need for braking logic, and the method will be hereafter described in detail. In order to promote understandings of the embodiment, an example in which a braking operation (i.e. parking brake) for maintaining a parking or stopping state of the vehicle on a slope way S is performed will be taken for description. 
     In the present embodiment, when a braking start manipulation is acquired by the braking start manipulation acquisition unit  13  while the vehicle is located on the slope way S, the control unit  20  may brake the vehicle by independently controlling the steering of four wheels of the vehicle according to an angle (acute angle) between the slope direction of the slope way S and the longitudinal direction of the vehicle. In the present embodiment, the angle is defined as a direction angle.  FIG.  30    illustrates an example in which the vehicle is located on the slope way S, and  FIGS.  31  to  33    illustrate the posture of the vehicle when the vehicle and the slope way S are seen from a direction ‘A’ of  FIG.  30   .  FIG.  31    illustrates the case in which the direction angle is 0°,  FIG.  32    illustrates the case in which the direction angle is 40, and  FIG.  33    illustrates the case in which the direction angle is 80. 
     At this time, the control unit  20  may align the four wheels by applying different rules to lower wheels DW located at a lower position of the slope way S and upper wheels UW located at a higher position of the slope way S, respectively, among the four wheels of the vehicle. In the example of  FIG.  31    in which the direction angle is 0°, a relatively large load is applied to the lower wheels DW located at a lower position of the slope way S with respect to the slope direction of the slope way S, and a relatively small load is applied to the upper wheels UW located at a higher position of the slope way S with respect to the slope direction of the slope way S. Therefore, when the lower wheels DW to which a relatively large load is applied are aligned in a direction for restricting the vehicle from moving in the slope direction of the slope way S and the upper wheels UW to which a relatively small load is applied are aligned in a direction for suppressing the vehicle from moving in a direction perpendicular to the slope direction, the vehicle may be effectively prevented from moving in the vertical and horizontal directions of the vehicle on the slope way S, while the parking and stopping state of the vehicle is effectively maintained. 
     Therefore, when the steering control rule for the lower wheels DW and the steering control rule for the upper wheels UW are represented by a first rule and a second rule, respectively, the first rule may be defined as a rule for restricting the vehicle from moving in the slope direction of the slope way S, and the second rule may be defined as a rule for restricting the vehicle from moving in the direction perpendicular to the slope direction on the slope sway S. The first and second rules may be predefined in the control unit  20 . 
     The process of aligning the lower wheels DW and the upper wheels UW according to the first and second rules will be described in detail with reference to  FIG.  34    illustrating the example in which the direction angle is 0°. When the direction angle is 0°, the lower wheels DW are defined as two wheels located at a lower position on the slope way S among the four wheels, and the upper wheels UW are defined as the other two wheels located at a higher position on the slope way S. The lower wheels DW and the upper wheels UW are defined in a different manner depending on the direction angle, which will be described below in detail. 
     In the present embodiment, a reference point which is defined as a point spaced by a preset distance apart from a gravity center GC of the vehicle in the reverse direction to the slope direction is employed as a reference for aligning the lower wheels DW and the upper wheels UW. When a circle passing through the gravity center GC of the vehicle on the basis of the reference point is defined as a parking circle, the reference point may be named a CPC (Center of Parking Circle), and the wheels may be aligned on the basis of the CPC, such that the vehicle may be converged on a stable state with respect to the slope way S. The preset distance may be expressed as N*WB, where WB represents the distance between the front wheel axle and the rear wheel axle, and N represents a value which is set according to the inclination of the vehicle (for example, the control unit  20  may set N to a larger value as the inclination increases. In  FIGS.  34  to  36   , N is 1.5). An algorithm for defining the reference point CPC may be preset in the control unit  20 . 
     When the reference point CPC is defined as described above, the first rule may be defined as a rule for aligning the lower wheels DW such that straight lines connecting the reference point CPC to the center points of the lower wheels DW are perpendicular to the major axes of the lower wheels DW, respectively, and the second rule may be defined as a rule for aligning the upper wheels UW such that the major axes of the upper wheels UW and straight lines connecting the reference point CPC to the center points of the upper wheels UW are located on the same lines, respectively. 
     Thus, as illustrated in  FIG.  34   , the control unit  20  may align the lower wheels DW through the first rule such that the straight lines connecting the reference point CPC to the center points of the lower wheels DW are perpendicular to the major axes of the lower wheels DW, respectively, and align the upper wheels UW through the second rule such that the major axes of the upper wheels UW and the straight lines connecting the reference point CPC to the center points of the upper wheels UW are located on the same lines, respectively. 
     In the above example, it has been described that, among the four wheels, the lower wheels DW correspond to two wheels located at a lower position on the slope way S, and the upper wheels UW correspond to the other two wheels at a higher position on the slope way S. As described above, in the present embodiment, the lower wheels DW and the upper wheels UW may be defined differently depending on the direction angle. Before the present embodiment is described in more detail, first to third regions are defined as follows.
         First region is defined as a region where the direction angle is 0° or more and less than a first reference angle.   Second region is defined as a region where the direction angle is the first reference angle or more and less than a second reference angle.   Third region is defined as a region where the direction angle ranges from the second reference angle to 90°.       

     The first and second reference angles may be preset in the control unit  20 , on the basis of the specification of the vehicle and experimental results of the designer. For example, the first reference angle may be set to 20°, and the second reference angle may be set to 70°. 
     Thus, when the direction angle is present in the first or third region, the lower wheels DW may be defined as two wheels located at a lower position on the slope way S, among the four wheels, and the upper wheels UW may be defined as the other two wheels located at a higher position on the slope way S, among the four wheels. Furthermore, when the direction angle is present in the second region, the lower wheels DW may be defined as three wheels located at lower positions on the slope way S, among the four wheels, and the upper wheel UW may be defined as the other one wheel located at a higher position on the slope way S, among the four wheels. Since the case in which the direction angle exists in the first region has been described with reference to  FIG.  34   , the case in which the direction angle exists in the second and third regions will be described. 
       FIGS.  32  and  35    each illustrate an example in which the direction angle is 40°, and exists in the second region. The control unit  20  may align the lower wheels DW through the first rule, such that straight lines connecting the reference point CPC to the center points of the respective lower wheels DW (i.e. three lower wheels DW) are perpendicular to the major axes of the respective lower wheels DW, respectively. Furthermore, the control unit  20  may align the upper wheel UW through the second rule, such that the major axis of the upper wheel UW and a straight line connecting the reference point CPC to the center point of the upper wheel UW (i.e. the other one upper wheel UW) are located on the same line. 
       FIGS.  33  and  36    each illustrate an example in which the direction angle is 80°, and exists in the third region. The control unit  20  may align the lower wheels DW through the first rule, such that straight lines connecting the reference point CPC to the center points of the respective lower wheels DW (i.e. two lower wheels DW) are perpendicular to the major axes of the respective lower wheels DW, respectively. Furthermore, the control unit  20  may align the upper wheels UW through the second rule, such that the major axes of the upper wheels UW and straight lines connecting the reference point CPC to the center points of the respective upper wheels UW (i.e. the other two upper wheels UW) are located on the same lines, respectively. 
     The above-described braking process through the steering control and alignment for the wheels may suppress the vehicle from moving in the vertical and horizontal directions of the vehicle on the slope way S, and effectively maintain the parking and stopping state of the vehicle. 
       FIG.  37    is a flowchart for describing an operation method in the second application of the corner module apparatus for a vehicle in accordance with the embodiment of the present disclosure. Referring to  FIG.  37   , the operation method of the corner module apparatus for a vehicle in accordance with the embodiment of the present disclosure will be described. Hereafter, the detailed descriptions of contents overlapping the above-described contents will be omitted herein, and the following descriptions will be focused on a time series configuration. 
     First, the control unit  20  determines whether a braking start manipulation for a vehicle by a driver was acquired, through the braking start manipulation acquisition unit  13 , in step S 10   b.    
     Then, when the braking start manipulation was acquired while the vehicle is located on the slope way S, the control unit  20  brakes the vehicle by independently controlling the steering of the four wheels of the vehicle according to the direction angle defined as an angle between the slope direction of the slope way S and the longitudinal direction of the vehicle, in step S 20   b.    
     In step S 20   b , the control unit  20  aligns the four wheels by applying the first and second rules to lower wheels DW located at a lower position of the slope way S and upper wheels UW located at a higher position of the slope way S, respectively, among the four wheels of the vehicle. At this time, the lower wheels DW and the upper wheels UW may be defined on the basis of the direction angle. Thus, when the direction angle exists in the first or third region, the lower wheels DW may be defined as two wheels located at a lower position on the slope way S, among the four wheels of the vehicle, and the upper wheels UW may be defined as the other two wheels located at a higher position on the slope way S, among the four wheels of the vehicle. Furthermore, when the direction angle exists in the second region, the lower wheels DW may be defined as three wheels located at lower positions on the slope way S, among the four wheels of the vehicle, and the upper wheel UW may be defined as the other one wheel located at a higher position on the slope way S, among the four wheels of the vehicle. 
     The first rule may be defined as a rule for restricting the vehicle from moving in the slope direction, and the second rule may be defined as a rule for restricting the vehicle from moving in a direction perpendicular to the slope direction on the slope way S. The first and second rules may be preset in the control unit  20 . Specifically, when a point spaced by a preset distance apart from the gravity center GC of the vehicle in the reverse direction to the slope direction is defined as the reference point CPC, the first rule is defined as a rule for aligning the lower wheels DW such that straight lines connecting the reference point CPC to the center points of the lower wheels DW are perpendicular to the major axes of the lower wheels DW, respectively, and the second rule is defined as a rule for aligning the upper wheels UW such that the major axes of the upper wheels UW and straight lines connecting the reference point CPC to the center points of the upper wheels UW are located on the same lines, respectively. Thus, in step S 20 , the control unit  20  aligns the lower wheels DW through the first rule, such that straight lines connecting the reference point CPC to the center points of the lower wheels DW are perpendicular to the major axes of the lower wheels DW, respectively, and aligns the upper wheels UW through the second rule, such that the major axes of the upper wheels UW and straight lines connecting the reference point CPC to the center points of the upper wheels UW are located on the same lines, respectively. 
     According to the second application, it is possible to control the alignments of the four wheels by independently controlling the steering of the four wheels, thereby safely braking the vehicle regardless of whether the vehicle is powered on/off. 
     3. Third Application: Posture Control Mechanism for Improving Straight Driving Performance 
     In the case of an existing vehicle with an internal combustion engine structure, a driving force is transferred through engine-drive shaft-differential-axle shaft. In the case of the four-wheel independent driving method premised in the present embodiment, the respective wheels are individually and independently driven with no axle shaft. Thus, a speed difference may occur between the respective wheels. The speed difference between the respective wheels is a risk factor which may cause a spin or turnover of the vehicle while the vehicle goes straight. Thus, the third application suggests a method capable of improving the straight driving performance of the vehicle, in a driving control aspect of wheels, not a mechanical or additional steering control aspect of a vehicle 
     For this method, the control unit  20  may detect an abnormal wheel which causes the degradation in straight driving performance of the vehicle, on the basis of four wheel velocities acquired by the wheel velocity acquisition unit  14 , calculate a compensation parameter for compensating for deviations between the respective wheel velocities, on the basis of the wheel velocity of the detected abnormal wheel, decide target driving torque for driving the abnormal wheel on the basis of the calculated compensation parameter, and then control the driving of the abnormal wheel through the decided target driving torque. Hereafter, the operation method in accordance with the present embodiment will be described in detail for each operation of the control unit  20 . 
     First, in order to detect the abnormal wheel, the control unit  20  may calculate a first average value of the four wheel velocities, and determine whether differences between the calculated first average value and the respective wheel velocities are equal to or greater than a preset threshold value. When the wheel velocities of the left front wheel, the right front wheel, the left rear wheel and the right rear wheel of the vehicle are represented by V fl , V fr , V rl  and V rr , respectively, the first average value V avg  may be expressed as (V fl +V fr +V rl +V rr )/4, and an abnormal wheel detection method may be expressed as a condition expression of “V avg −V i ≥threshold value, where i=fl, fr, rl, rr”. For example, when a wheel satisfying the above conditional expression corresponds to the left front wheel fl, the left front wheel may be specified as the abnormal wheel. When a plurality of wheels satisfy the conditional expression, the wheel having the lowest wheel velocity among the plurality of wheels may be specified as the abnormal wheel. Thus, a wheel which has a lower wheel velocity by a predetermined value or more than the other wheels when the vehicle goes straight and thus degrades the straight driving performance of the vehicle is specified as the abnormal wheel. In the conditional expression, the threshold value may be defined as a different value depending on the first average value. For example, the threshold value may be defined as a larger value as the first average value increases. Thus, in a high-velocity region, an abnormal wheel may be decided according to the more reinforced standards for the driving stability of the vehicle. 
     When an abnormal wheel is detected, the control unit  20  may calculate a compensation parameter for compensating deviations between the respective wheel velocities on the basis of the wheel velocity of the detected abnormal wheel. The compensation of the deviations between the respective wheel velocities indicates reducing the deviations in wheel velocity between the abnormal wheel and the other wheels by increasing the driving torque of the abnormal wheel or increasing the wheel velocity of the abnormal wheel. 
     At this time, the control unit  20  may calculate a second average value of the wheel velocities of the three wheels excluding the abnormal wheel, and calculate the compensation parameter by using, as factors, a difference between the second average value and the wheel velocity of the abnormal wheel and a variable gain based on the second average value. In an example where the left front wheel is detected as the abnormal wheel, the second average value V target  may be expressed as (V fr +V rl +V rr )/3, and the compensation parameter may be expressed as α*V target *(V target −V fl ). In the expression of the compensation parameter, the second term V target  functions as a target wheel velocity which is the following target, and the third term V target −V fl  functions as a term for considering the deviation between the wheel velocity of the abnormal wheel and the target wheel velocity in the compensation parameter calculation process. The first term α represents a variable gain, and functions as a scaling factor for scaling the magnitude of the compensation parameter. 
     As illustrated in  FIG.  38   , when the second average value Vtarget is located in a predetermined middle-low velocity region (e.g. a region where the second average value Vtarget is equal to or lower than a predetermined threshold velocity Vth), the variable gain may be decided as a value that decreases as the second average value increases. On the other hand, when the second average value Vtarget is located in a predefined high-velocity region (e.g. a region where the second average value Vtarget exceeds the predetermined threshold velocity Vth), the variable gain may be decided as a predefined fixed value. That is, when the compensation parameter functioning as a value for compensating for the driving torque of the abnormal wheel is calculated as a smaller value as the second average value Vtarget functioning as the target wheel velocity increases, the compensation parameter does not rapidly change the current driving control state of the vehicle, and is suitable for securing the driving stability of the vehicle. If the second average value Vtarget exceeds the threshold value, the compensator parameter may be calculated as the lowest value (i.e. the above-described fixed value), which is suitable for maintaining the driving stability of the vehicle. Therefore, as illustrated in  FIG.  38   , the control unit  20  may calculate the compensation parameter which has a different value depending on the second average value. 
     When the compensation parameter is calculated, the control unit  20  may decide the target driving torque for driving the abnormal wheel on the basis of the calculated compensation parameter. In this case, the control unit  20  may decide the target driving torque by applying the compensation parameter to the current driving torque (i.e. existing driving torque) for driving the abnormal wheel (that is, target driving torque=current driving torque*compensation parameter). Then, the control unit  20  may control the driving of the abnormal wheel through the target driving torque decided through the above-described method. As the driving torque for driving the abnormal wheel is increased more than the existing driving torque, the straight driving performance of the vehicle may be improved. 
     The control unit  20  may recalculate the first average value of the four wheel velocities while controlling the driving of the abnormal wheel through the target driving torque. When the difference between the recalculated first average value and the wheel velocity of the abnormal wheel is equal to or greater than the threshold value, the control unit  20  may output an alarm through the output unit  30 . That is, the control unit  20  may determine whether the straight driving performance of the vehicle has been improved, by determining whether the difference between the recalculated first average value and the wheel velocity of the abnormal wheel is less than the threshold value. When it is determined that the deviation between the recalculated first average value and the wheel velocity of the abnormal wheel is equal to or more than the threshold value even though the control unit  20  calculated the target driving torque through the above-described process and controlled the driving of the abnormal wheel, it indicates that a risk element such as a spin or turnover of the vehicle exists, because the deviation in wheel velocity between the respective wheels is still equal to or more than the threshold value. Therefore, the control unit  20  may output an alarm through the output unit  30  such that a driver can recognize the corresponding situation. 
       FIG.  39    is a flowchart for describing an operation method of the corner module apparatus for a vehicle in accordance with the embodiment of the present disclosure, based on the third application. Referring to  FIG.  39   , the operation method of the corner module apparatus for a vehicle in accordance with the embodiment of the present disclosure will be described. Hereafter, the detailed descriptions of contents overlapping the above-described contents will be omitted herein, and the following descriptions will be focused on a time series configuration. 
     First, the control unit  20  acquires four wheel velocities of the vehicle through the wheel velocity acquisition unit  14  in step S 10   c.    
     Then, in step S 20   c , the control unit  20  detects an abnormal wheel that causes the degradation in straight driving performance of the vehicle, on the basis of the four wheel velocities acquired in step S 10   c . In step S 20   c , the control unit  20  may calculate the first average value of the four wheel velocities, and determine whether a difference between the calculated first average value and the respective wheel velocities is equal to or greater than the preset threshold value, in order to detect the abnormal wheel. 
     Then, the control unit  20  calculates the compensation parameter for compensating for the deviation between the respective wheel velocities on the basis of the wheel velocity of the abnormal wheel, detected in step S 20   c , in step S 30   c . In step S 30   c , the control unit  20  calculates the second average value of the wheel velocities of the three wheels except the abnormal wheel, and calculates the compensation parameter by using, as factors, a difference between the calculated second average value and the wheel velocity of the abnormal wheel, a variable gain based on the second average value, and the second average value. The variable gain is decided as a value that decreases as the second average value increases, when the second average value is located in a predefined middle-low velocity region, and decided as a predefined fixed value when the second average value is located in a predetermined high velocity region. 
     Then, the control unit  20  decides target driving torque for driving the abnormal wheel, on the basis of the compensation parameter calculated in step S 30   c , in step S 40   c . Specifically, the control unit  20  decides the target driving torque by applying the compensation parameter to the current driving torque for driving the abnormal wheel. 
     Then, the control unit  20  controls the driving of the abnormal wheel through the target driving torque decided in step S 40   c , in step S 50   c . The other wheels except the abnormal wheel are controlled according to the existing driving torque. 
     The control unit  20  recalculates the first average value of the four wheel velocities, and compares a difference between the recalculated first average value and the wheel velocity of the abnormal wheel to the threshold value in step S 60   c . When it is determined in step S 60   c  that the difference between the recalculated first average value and the wheel velocity of the abnormal wheel is equal to or more than the threshold value, the control unit  20  outputs an alarm through the output unit  30  in step S 70   c.    
     According to the third application, it is possible to compensate for the deviation between the respective wheel velocities only through the driving torque control for the wheels without a mechanical or additional steering control of the vehicle, thereby improving the straight driving performance of the vehicle. 
     4. Fourth Application: Posture Control Mechanism for Removing Slip 
     The existing forward wheel drive vehicle has a limitation in that the battery consumption of the vehicle is increased because the posture control of the vehicle is performed through electronic control systems such as ABS (Anti-lock Brake System), ESP (Electronic Stability Program) and ECS (Electronic Controlled Suspension). In the present embodiment, since the four-wheel independent driving method is applied to independently control the driving of the respective wheels, the posture control of a vehicle can be performed through a method of controlling the driving and steering of the respective wheels, compared to a conventional vehicle posture control system. Hereafter, a specific configuration for performing the posture control of a vehicle by controlling the driving and steering of the respective wheels will be described focusing on the operation of the control unit  20 . 
     In the fourth application, the control unit  20  determines whether a predefined slip condition is satisfied, on the basis of the wheel velocities of the respective wheels, acquired by the wheel velocity acquisition unit  14 . When it is determined that the slip condition is satisfied, the control unit  20  may perform the vehicle posture control through a driving torque control process of controlling the driving torques of the respective wheels. 
     The slip condition indicates that a slip occurred in a wheel, and corresponds to a condition for determining whether posture control is required for the driving stability of the vehicle. In this case, the control unit  20  may calculate the slip rates of the respective wheels on the basis of the wheel velocities of the respective wheels, decide the maximum slip rate having a maximum value among the calculated slip rates of the respective wheels, and determine that the slip condition is satisfied when the decided maximum slip rate is equal to or more than a preset threshold value. As well known, the slip rate of each wheel may be calculated as the ratio of ‘difference between vehicle velocity and wheel velocity’ to ‘vehicle velocity.’ 
     When determining that the slip condition is satisfied, the control unit  20  may perform the vehicle posture control through the above-described driving torque control. In this case, the control unit  20  may control the driving of the wheels through the target driving torque having a lower value than the current driving torques of the respective wheels. The target driving torque may be decided as a value which is lower than the minimum value among the current driving torques of the respective wheels, which are currently applied to drive the wheels. That is, the control unit  20  may perform the control of reducing the driving torques of the wheels, in order to remove the current slips of the wheels, and the driving of the wheels may be controlled through the same target driving torque. At this time, as the maximum slip rate increases, the driving torque of the wheel needs to be reduced to a lower value in order to remove the slip. Thus, the target driving torque may be decided as a smaller value as the maximum slip rate increases. For example, the target driving torque and the maximum slip rate may be defined in the control unit  20  so as to have a negative linear relation. 
     After performing the driving torque control, the control unit  20  may determine whether the slip was removed through the driving torque control, by re-determining whether the slip condition is satisfied. When determining that the satisfaction of the slip condition is maintained or the slip is not removed, the control unit  20  may subsequently perform the steering control process for controlling the steering of the wheels, thereby performing the vehicle posture control. 
     The control unit  20  may perform the steering control by steering two wheels, located on the opposite side of the wheel having the maximum slip rate in the horizontal direction, by the target steering angle. For example, when the wheel having the maximum slip rate corresponds to the right front wheel, the control unit  20  may perform the steering control by steering the left front wheel and the left rear wheel by the target steering angle. In the above example, the steering control on the left front wheel and the left rear wheel may be performed to induce the braking effect of the vehicle, thereby removing the slip of the right front wheel. Therefore, the steering direction thereof may be any one of the left and the right. At this time, as the maximum slip rate increases, the steering angles of the two wheels located on the opposite side in the horizontal direction need to be increased, in order to remove the slip. Thus, the target steering angle may be decided as a larger value as the maximum slip rate increases. For example, the target steering angle and the maximum slip rate may be defined in the control unit  20  so as to have a positive linear relation. In order to prevent an unstable behavior of the vehicle, which may occur due to the rapid steering control on the two wheels on the opposite side in the horizontal direction, the control time required until the steering angles of the two wheels on the opposite side in the horizontal direction reach the target steering angle may be selected as a sufficient time based on an experimental result of the designer, and set in the control unit  20 . 
       FIG.  40    is a flowchart for describing an operation method the corner module apparatus for a vehicle in accordance with the embodiment of the present disclosure, based on the fourth application. Referring to  FIG.  40   , the operation method of the corner module apparatus for a vehicle in accordance with the embodiment of the present disclosure will be described. Hereafter, the detailed descriptions of contents overlapping the above-described contents will be omitted herein, and the following descriptions will be focused on a time series configuration. 
     First, the control unit  20  acquires wheel velocities of four wheels through the wheel velocity acquisition unit  14  in step S 10   d.    
     In step S 20   d , the control unit  20  determines whether the predefined slip condition is satisfied, on the basis of the wheel velocities of the respective wheels, acquired in step S 10   d . In step S 20   d , the control unit  20  calculates the slip rates of the respective wheels on the basis of the wheel velocities of the respective wheels, decides the maximum slip rate having a maximum value among the calculated slip rates of the respective wheels, and determines that the slip condition is satisfied, when the decided maximum slip rate is equal to or more than the preset threshold value. 
     When it is determined in step S 20   d  that the slip condition is satisfied, the control unit  20  performs the vehicle posture control through the driving torque control process of driving the driving torques of the respective wheels, in step S 30   d . In step S 30   d , the control unit  20  may control the driving of the wheels through the target driving torque having a lower value than the current driving torques of the respective wheels. At this time, the target driving torque may be decided as a smaller value as the maximum slip rate increases. 
     After step S 30   d , the control unit  20  re-determines whether the slip condition is satisfied, in step S 40   d.    
     When it is determined in step S 40   d  that the satisfied slip condition is maintained, the control unit  20  performs the vehicle posture control through a steering control process of controlling the steering of the wheels, in step S 50   d . In step S 50   d , the control unit  20  may steer the two wheels, located on the opposite side of the wheel having the maximum slip rate in the horizontal direction, by the target steering angle. At this time, the target steering angle may be decided as a larger value as the maximum slip rate increases. 
     Steps S 40   d  and S 50   d  may be repeatedly performed within a predetermined repetition number, until it is determined in step S 40   d  that the slip condition is not satisfied or the slip is removed. 
     According to the fourth application, it is possible to remove the dependency on the existing vehicle posture control system, and perform the vehicle posture control only through the method of controlling the driving and steering of the wheels. Thus, it is possible to reduce the battery consumption required for the vehicle posture control, thereby improving the available battery capacity. 
     5. Fifth Application: Target Trajectory Generation and Following Control Mechanism 
     In the four-wheel independent driving method, the wheels of the vehicle need to be independently controlled because the wheels are not mechanically connected to each other. In particular, in order to secure the driving stability of the vehicle during cornering, a quantitative control mechanism for steering control on each of the wheel needs to be provided. Thus, the fifth application suggests a method of independently controlling the steering of four wheels by differently calculating the target steering angles of the respective wheels, when a vehicle to which the four-wheel independent driving method is applied travels along a curved road having a predetermined curvature, or specifically when no slips occur in the respective wheels while the vehicle travels along a curved road at low velocity which is less than a preset velocity. 
     In the fifth application, the control unit  20  may calculate information on the distance to a target point to which the vehicle is to move, on the basis of driving state information and driving environment information which are acquired by the vehicle information acquisition unit  15 , calculate a target curvature, defined as the curvature of a target trajectory to the target point, on the basis of the calculated distance information, calculate the target steering angles of the four wheels, respectively, on the basis of the calculated target curvature, and then independently control the steering of the four wheels according to the calculated target steering angles. Hereafter, the configuration in accordance with the present embodiment will be described in detail for each operation of the control unit  20 . 
     First, the control unit  20  may calculate the information on the distance to the target point by using the vehicle velocity of the vehicle, an offset distance of the vehicle from the center ({circle around (4)} of  FIG.  41   ) of the road, calculated from surrounding image information, and the curvature radius of the road based on the center of the road. The offset distance and the curvature radius of the road may be calculated through the analysis on the lane and the road, included in the surrounding image information. The distance information may include a straight distance from the current location (C of  FIG.  41   ) of the vehicle to the target point (A of  FIG.  41   ), a vertical distance and a horizontal distance. 
     Specifically, the control unit  20  may calculate the straight distance to the target point by applying the velocity of the vehicle to a predefined distance calculation algorithm. The distance calculation algorithm is an algorithm to calculate a straight distance that has a larger value as the vehicle velocity increases, and may be predefined in the control unit  20 . For example, the distance calculation algorithm may be defined as a one-dimensional equation of (L=A*Vx+B) where L represents a straight distance, Vx represents a vehicle velocity, and A and B represent constant values which are designed on the basis of experimental results of the designer. 
     When the straight distance to the target point is calculated, the control unit  20  may calculate the vertical distance and the horizontal distance to the target point by using the offset distance, the heading angle of the vehicle, the curvature radius of the road, and the straight distance to the target point. Referring to  FIG.  41   , Equation 1 below may be induced. 
     
       
         
           
             
               
                 
                   
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                 ε 
               
               - 
               
                 2 
                 ⁢ 
                 ε 
                 ⁢ 
                 R 
               
               + 
               
                 L 
                 2 
               
               - 
               
                 y 
                 2 
               
             
           
         
       
       
         
           
             
               ⇒ 
               
                 2 
                 ⁢ 
                 
                   y 
                   ⁡ 
                   ( 
                   
                     R 
                     - 
                     ε 
                   
                   ) 
                 
               
             
             = 
             
               
                 ε 
                 2 
               
               - 
               
                 2 
                 ⁢ 
                 ε 
                 ⁢ 
                 R 
               
               + 
               
                 L 
                 2 
               
             
           
         
       
       
         
           
             
               ⇒ 
               y 
             
             = 
             
               
                 
                   
                     L 
                     2 
                   
                   + 
                   
                     ε 
                     2 
                   
                   - 
                   
                     2 
                     ⁢ 
                     ε 
                     ⁢ 
                     R 
                   
                 
                 
                   2 
                   ⁢ 
                   
                     ( 
                     
                       R 
                       - 
                       ε 
                     
                     ) 
                   
                 
               
               = 
               
                 
                   
                     
                       ρ 
                       k 
                     
                     ( 
                     
                       
                         L 
                         2 
                       
                       + 
                       
                         ε 
                         2 
                       
                     
                     ) 
                   
                   - 
                   
                     2 
                     ⁢ 
                     ε 
                   
                 
                 
                   2 
                   ⁢ 
                   
                     ( 
                     
                       1 
                       - 
                       
                         
                           ρ 
                           k 
                         
                         ⁢ 
                         ε 
                       
                     
                     ) 
                   
                 
               
             
           
         
       
       
         
           
             
               ⇒ 
               y 
             
             = 
             
               
                 
                   
                     L 
                     2 
                   
                   - 
                   
                     ε 
                     2 
                   
                   - 
                   
                     2 
                     ⁢ 
                     
                       ε 
                       ⁡ 
                       ( 
                       
                         R 
                         - 
                         ε 
                       
                       ) 
                     
                   
                 
                 
                   2 
                   ⁢ 
                   
                     ( 
                     
                       R 
                       - 
                       ε 
                     
                     ) 
                   
                 
               
               = 
               
                 
                   
                     
                       ρ 
                       k 
                     
                     ( 
                     
                       
                         L 
                         2 
                       
                       - 
                       
                         ε 
                         2 
                       
                     
                     ) 
                   
                   
                     2 
                     ⁢ 
                     
                       ( 
                       
                         1 
                         - 
                         
                           
                             ρ 
                             k 
                           
                           ⁢ 
                           ε 
                         
                       
                       ) 
                     
                   
                 
                 - 
                 ε 
               
             
           
         
       
     
     When Equation 1 is summarized with respect to x and y, Equation 2 below is established. 
     
       
         
           
             
               
                 
                   x 
                   = 
                   
                     
                       
                         L 
                         2 
                       
                       - 
                       
                         y 
                         2 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                         
                     2 
                   
                   ] 
                 
               
             
           
         
       
       
         
           
             y 
             = 
             
               
                 
                   
                     
                       ρ 
                       k 
                     
                     ( 
                     
                       
                         L 
                         2 
                       
                       + 
                       
                         ε 
                         2 
                       
                     
                     ) 
                   
                   - 
                   
                     2 
                     ⁢ 
                     ε 
                   
                 
                 
                   2 
                   ⁢ 
                   
                     ( 
                     
                       1 
                       - 
                       
                         
                           ρ 
                           k 
                         
                         ⁢ 
                         ε 
                       
                     
                     ) 
                   
                 
               
               = 
               
                 
                   
                     
                       ρ 
                       k 
                     
                     ( 
                     
                       
                         L 
                         2 
                       
                       - 
                       
                         ε 
                         2 
                       
                     
                     ) 
                   
                   
                     2 
                     ⁢ 
                     
                       ( 
                       
                         1 
                         - 
                         
                           
                             ρ 
                             k 
                           
                           ⁢ 
                           ε 
                         
                       
                       ) 
                     
                   
                 
                 - 
                 ε 
               
             
           
         
       
     
     In Equations 1 and 2, L, x and y represent the straight distance, the vertical distance and the horizontal distance to the target point, respectively, R represents the curvature radius of the road, ρ k  represents the curvature (1/R) of the road, and ε represents the offset distance. 
     When the distance information to the target point is calculated as described above, the control unit  20  may calculate a target curvature defined as the curvature of the target trajectory to the target point, on the basis of the calculated distance information. In the present embodiment, the target curvature may be sorted into a center target curvature defined as the curvature of a target trajectory based on the center of the vehicle (i.e. the moving target trajectory of the center of the vehicle, indicated by {circle around (1)} in  FIGS.  41  and  42   ), a left wheel target curvature defined as the curvature of a target trajectory based on the left wheel of the vehicle (i.e. the moving target trajectory of the left wheel of the vehicle, indicated by {circle around (2)} of  FIG.  42   ), and a right wheel target curvature defined as the curvature of a target trajectory based on the right wheel of the vehicle (i.e. the moving target trajectory of the right wheel of the vehicle, indicated by {circle around (3)} of  FIG.  42   ). The control unit  20  may preferentially calculate the center target curvature, and then extend the center target curvature to the left wheel target curvature and the right wheel target curvature by using the tread information of the vehicle. 
     Referring to  FIGS.  41  and  42   , the center target curvature may be calculated by Equation 3 below. 
     
       
         
           
             
               
                 
                   
                     
                       R 
                       c 
                     
                     ⁢ 
                     
                       cos 
                       ⁡ 
                       ( 
                       
                         ϕ 
                         + 
                         α 
                       
                       ) 
                     
                   
                   = 
                   
                     
                       
                         
                           R 
                           c 
                         
                         L 
                       
                       ⁢ 
                       
                         ( 
                         
                           
                             y 
                             ⁢ 
                             cos 
                             ⁢ 
                             ϕ 
                           
                           - 
                           
                             x 
                             ⁢ 
                             sin 
                             ⁢ 
                             ϕ 
                           
                         
                         ) 
                       
                     
                     = 
                     
                       L 
                       2 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                         
                     3 
                   
                   ] 
                 
               
             
           
         
       
       
         
           
             
               
                 ρ 
               
               c 
             
             = 
             
               
                 1 
                 
                   R 
                   c 
                 
               
               = 
               
                 
                   2 
                   
                     L 
                     2 
                   
                 
                 ⁢ 
                 
                   ( 
                   
                     
                       y 
                       ⁢ 
                       cos 
                       ⁢ 
                       ϕ 
                     
                     - 
                     
                       x 
                       ⁢ 
                       sin 
                       ⁢ 
                       ϕ 
                     
                   
                   ) 
                 
               
             
           
         
       
     
     In Equation 3, R c  represents the curvature radius of the moving target trajectory of the center of the vehicle, φ represents the heading angle of the vehicle, a represents the angle between the vehicle and the target point, L represents the straight distance to the target point, and ρ c  represents the center target curvature (1/R c ). 
     When the center target curvature is calculated, the control unit  20  may calculate the left wheel target curvature and the right wheel target curvature from the center target curvature by using the tread information of the vehicle. Referring to  FIG.  42    illustrating an example in which the vehicle is cornering to the left, the left wheel target curvature and the right wheel target curvature may be calculated by Equations 4 and 5 below, respectively. 
     
       
         
           
             
               
                 
                   
                     R 
                     L 
                   
                   = 
                   
                     
                       R 
                       C 
                     
                     - 
                     
                       w 
                       L 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                         
                     4 
                   
                   ] 
                 
               
             
           
         
       
       
         
           
             
               P 
               L 
             
             = 
             
               
                 1 
                 
                   R 
                   L 
                 
               
               = 
               
                 
                   1 
                   
                     
                       R 
                       C 
                     
                     - 
                     
                       w 
                       L 
                     
                   
                 
                 = 
                 
                   
                     ρ 
                     c 
                   
                   
                     1 
                     - 
                     
                       
                         ρ 
                         c 
                       
                       ⁢ 
                       
                         w 
                         L 
                       
                     
                   
                 
               
             
           
         
       
       
         
           
             
               
                 
                   
                     R 
                     R 
                   
                   = 
                   
                     
                       R 
                       C 
                     
                     + 
                     
                       w 
                       R 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                         
                     5 
                   
                   ] 
                 
               
             
           
         
       
       
         
           
             
               ρ 
               R 
             
             = 
             
               
                 1 
                 
                   R 
                   R 
                 
               
               = 
               
                 
                   1 
                   
                     
                       R 
                       C 
                     
                     + 
                     
                       w 
                       R 
                     
                   
                 
                 = 
                 
                   
                     ρ 
                     c 
                   
                   
                     1 
                     + 
                     
                       
                         ρ 
                         c 
                       
                       ⁢ 
                       
                         w 
                         R 
                       
                     
                   
                 
               
             
           
         
       
     
     In Equation 4, R L  represents the curvature radius of the moving target trajectory of the left wheel of the vehicle, R C  represents the curvature radius of the moving target trajectory of the center of the vehicle, w L  represents a half of the tread value of the vehicle (w/2, w represents tread), and ρ L  represents the left wheel target curvature. In Equation 5, R R  represents the curvature radius of the moving target trajectory of the right wheel of the vehicle, RC represents the curvature radius of the moving target trajectory of the center of the vehicle, w R  represents a half of the tread value of the vehicle (w/2), and ρ R  represents the right wheel target curvature. 
     Through  FIG.  42    and Equations 4 and 5, the case in which the vehicle is cornering to the left has been described. When the vehicle is cornering to the right, the left wheel target curvature and the right wheel target curvature are calculated by Equation 6 below because the inner wheels and the outer wheels are set in the opposite way. 
     
       
         
           
             
               
                 
                   
                     ρ 
                     L 
                   
                   = 
                   
                     
                       ρ 
                       c 
                     
                     
                       1 
                       + 
                       
                         
                           ρ 
                           c 
                         
                         ⁢ 
                         
                           w 
                           L 
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                         
                     6 
                   
                   ] 
                 
               
             
           
         
       
       
         
           
             
               ρ 
               R 
             
             = 
             
               
                 ρ 
                 c 
               
               
                 1 
                 + 
                 
                   
                     ρ 
                     c 
                   
                   ⁢ 
                   
                     w 
                     R 
                   
                 
               
             
           
         
       
     
     When the left wheel target curvature and the right wheel target curvature are calculated, the control unit  20  may calculate the target steering angles of the respective four wheels on the basis of the calculated target curvatures. 
     Specifically, the target yaw rates of the left wheel and the right wheel may be expressed as in Equation 7 below, on the basis of the calculated left wheel target curvature and the calculated right wheel target curvature. 
       YR des,L =ρ L   v   x  
 
       YR des,R =ρ R   v   x   [Equation 7]
 
     In Equation 7, YR des,L  represents the target yaw rate of the left wheel, ρ L  represents the left wheel target curvature, YR des,R  represents the target yaw rate of the right wheel, ρ R  represents the right wheel target curvature, and v x  represents vehicle velocity. 
       FIG.  43    illustrates an example of a vehicle dynamics model having a degree of freedom. For convenience of description,  FIG.  43    illustrates only the front and rear left wheels. According to the vehicle dynamics model of  FIG.  43   , the slip angles of the respective wheels may be expressed by Equation 8 below. 
     
       
         
           
             
               
                 
                   
                     α 
                     fl 
                   
                   = 
                   
                     
                       δ 
                       fl 
                     
                     - 
                     
                       
                         
                           
                             β 
                             cg 
                           
                           ⁢ 
                           
                             v 
                             x 
                           
                         
                         + 
                         
                           
                             l 
                             f 
                           
                           ⁢ 
                           
                             YR 
                             
                               des 
                               , 
                               L 
                             
                           
                         
                       
                       
                         v 
                         x 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                         
                     8 
                   
                   ] 
                 
               
             
           
         
       
       
         
           
             
               α 
               fr 
             
             = 
             
               
                 δ 
                 fr 
               
               - 
               
                 
                   
                     
                       β 
                       cg 
                     
                     ⁢ 
                     
                       v 
                       x 
                     
                   
                   + 
                   
                     
                       l 
                       f 
                     
                     ⁢ 
                     
                       YR 
                       
                         des 
                         , 
                         R 
                       
                     
                   
                 
                 
                   v 
                   x 
                 
               
             
           
         
       
       
         
           
             
               α 
               rl 
             
             = 
             
               
                 δ 
                 rl 
               
               - 
               
                 
                   
                     
                       β 
                       cg 
                     
                     ⁢ 
                     
                       v 
                       x 
                     
                   
                   - 
                   
                     
                       l 
                       r 
                     
                     ⁢ 
                     
                       YR 
                       
                         des 
                         , 
                         L 
                       
                     
                   
                 
                 
                   v 
                   x 
                 
               
             
           
         
       
       
         
           
             
               α 
               rr 
             
             = 
             
               
                 δ 
                 rr 
               
               - 
               
                 
                   
                     
                       β 
                       cg 
                     
                     ⁢ 
                     
                       v 
                       x 
                     
                   
                   - 
                   
                     
                       l 
                       f 
                     
                     ⁢ 
                     
                       YR 
                       
                         des 
                         , 
                         R 
                       
                     
                   
                 
                 
                   v 
                   x 
                 
               
             
           
         
       
     
     In Equation 8, α fl , α fr , α rl  and α rr  represent the slip angle of the left front wheel, the slip angle of the right front wheel, the slip angle of the left rear wheel, and the slip angle of the right rear wheel, respectively, β cg  represents the slip angle of the center of the vehicle, v x  represents the vehicle velocity, I f  represents the distance between the front wheel axle and the center cg of the vehicle, I r  represents the distance between the rear wheel axle and the center cg of the vehicle, YR des,L  and YR des,R  represent the target yaw rates of the left and right wheels, respectively, and δ fl , δ fr , δ rl  and δ rr  represent the target steering angle of the left front wheel, the target steering angle of the right front wheel, the target steering angle of the left rear wheel, and the target steering angle of the right rear wheel, respectively, which are calculation targets. 
     As described above, the present embodiment is premised on the case in which the vehicle corners at low velocity and no slips occur in the respective wheels. Thus, in Equation 8, α fl , α fr , α rl , α rr  and β cg  may be approximated to 0, and the target steering angle of the left front wheel, the target steering angle of the right front wheel, the target steering angle of the left rear wheel, and the target steering angle of the right rear wheel may be calculated by Equation 9 below. 
     
       
         
           
             
               
                 
                   
                     δ 
                     fl 
                   
                   = 
                   
                     
                       
                         
                           l 
                           f 
                         
                         ⁢ 
                         
                           YR 
                           
                             
                               d 
                               ⁢ 
                               e 
                               ⁢ 
                               s 
                             
                             , 
                             L 
                           
                         
                       
                       
                         v 
                         x 
                       
                     
                       
                     = 
                     
                       
                         l 
                         f 
                       
                       ⁢ 
                       
                         ρ 
                         L 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                         
                     9 
                   
                   ] 
                 
               
             
           
         
       
       
         
           
             
               δ 
               fr 
             
             = 
             
               
                 
                   
                     l 
                     f 
                   
                   ⁢ 
                   
                     YR 
                     
                       des 
                       , 
                       R 
                     
                   
                 
                 
                   v 
                   x 
                 
               
                 
               = 
               
                 
                   l 
                   f 
                 
                 ⁢ 
                 
                   ρ 
                   R 
                 
               
             
           
         
       
       
         
           
             
               δ 
               rl 
             
             = 
             
               
                 - 
                 
                   
                     
                       l 
                       r 
                     
                     ⁢ 
                     
                       YR 
                       
                         des 
                         , 
                         L 
                       
                     
                   
                   
                     v 
                     x 
                   
                 
               
               = 
               
                 
                   - 
                   
                     l 
                     r 
                   
                 
                 ⁢ 
                 
                   ρ 
                   L 
                 
               
             
           
         
       
       
         
           
             
               δ 
               rr 
             
             = 
             
               
                 - 
                 
                   
                     
                       l 
                       r 
                     
                     ⁢ 
                     
                       YR 
                       
                         
                           d 
                           ⁢ 
                           e 
                           ⁢ 
                           s 
                         
                         , 
                         R 
                       
                     
                   
                   
                     v 
                     x 
                   
                 
               
               = 
               
                 
                   - 
                   
                     l 
                     r 
                   
                 
                 ⁢ 
                 
                   ρ 
                   R 
                 
               
             
           
         
       
     
     The above-described case indicates the process of calculating the target steering angles in a state in which the front wheel and the rear wheel are out of phase. The target steering angles in a state in which the front wheel and the rear wheel are in phase may be calculated through the following process. 
     First, the vehicle dynamics model in a state in which the front wheel and the rear wheel are in phase may be expressed by Equation 10 below. 
     
       
         
           
             
               
                 
                   
                     
                       d 
                       
                         d 
                         ⁢ 
                         t 
                       
                     
                     [ 
                     
                       
                         
                           β 
                         
                       
                       
                         
                           Ψ 
                         
                       
                     
                     ] 
                   
                   = 
                   
                     
                       
                         [ 
                         
                           
                             
                               
                                 a 
                                 11 
                               
                             
                             
                               
                                 a 
                                 12 
                               
                             
                           
                           
                             
                               
                                 a 
                                 21 
                               
                             
                             
                               
                                 a 
                                 
                                   2 
                                   ⁢ 
                                   2 
                                 
                               
                             
                           
                         
                         ] 
                       
                       [ 
                       
                         
                           
                             β 
                           
                         
                         
                           
                             Ψ 
                           
                         
                       
                       ] 
                     
                     + 
                     
                       
                         [ 
                         
                           
                             
                               
                                 b 
                                 11 
                               
                             
                             
                               
                                 b 
                                 12 
                               
                             
                           
                           
                             
                               
                                 b 
                                 21 
                               
                             
                             
                               
                                 b 
                                 
                                   2 
                                   ⁢ 
                                   2 
                                 
                               
                             
                           
                         
                         ] 
                       
                       [ 
                       
                         
                           
                             
                               δ 
                               f 
                             
                           
                         
                         
                           
                             
                               δ 
                               r 
                             
                           
                         
                       
                       ] 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                         
                     10 
                   
                   ] 
                 
               
             
           
         
       
       
         
           where 
         
       
       
         
           
             
               a 
               
                 1 
                 ⁢ 
                 1 
               
             
             = 
             
               
                 
                   
                     
                       C 
                       f 
                     
                     + 
                     
                       C 
                       r 
                     
                   
                   
                     mv 
                     x 
                   
                 
                 ⁢ 
                     
                 
                   a 
                   12 
                 
               
               = 
               
                 
                   - 
                   1 
                 
                 - 
                 
                   
                     
                       
                         C 
                         f 
                       
                       ⁢ 
                       
                         l 
                         f 
                       
                     
                     - 
                     
                       
                         C 
                         r 
                       
                       ⁢ 
                       
                         l 
                         r 
                       
                     
                   
                   
                     mv 
                     x 
                     2 
                   
                 
               
             
           
         
       
       
         
           
             
               a 
               
                 2 
                 ⁢ 
                 1 
               
             
             = 
             
               
                 
                   - 
                   
                     
                       
                         
                           C 
                           f 
                         
                         ⁢ 
                         
                           l 
                           f 
                         
                       
                       - 
                       
                         
                           C 
                           r 
                         
                         ⁢ 
                         
                           l 
                           r 
                         
                       
                     
                     I 
                   
                 
                 ⁢ 
                     
                 
                   a 
                   
                     2 
                     ⁢ 
                     2 
                   
                 
               
               = 
               
                 - 
                 
                   
                     
                       
                         C 
                         f 
                       
                       ⁢ 
                       
                         l 
                         f 
                         2 
                       
                     
                     - 
                     
                       
                         C 
                         r 
                       
                       ⁢ 
                       
                         l 
                         r 
                         2 
                       
                     
                   
                   I 
                 
               
             
           
         
       
       
         
           
             
               b 
               11 
             
             = 
             
               
                 
                   
                     C 
                     f 
                   
                   
                     mv 
                     x 
                   
                 
                 ⁢ 
                     
                 
                   b 
                   12 
                 
               
               = 
               
                 
                   C 
                   r 
                 
                 
                   mv 
                   x 
                 
               
             
           
         
       
       
         
           
             
               b 
               
                 2 
                 ⁢ 
                 1 
               
             
             = 
             
               
                 
                   
                     
                       C 
                       f 
                     
                     ⁢ 
                     
                       l 
                       f 
                     
                   
                   I 
                 
                 ⁢ 
                     
                 
                   b 
                   
                     2 
                     ⁢ 
                     2 
                   
                 
               
               = 
               
                 
                   
                     C 
                     r 
                   
                   ⁢ 
                   
                     l 
                     r 
                   
                 
                 I 
               
             
           
         
       
     
     In Equation 10, β and Ψ represent the slip angle and direction angle of the center of the vehicle, respectively, and factors defining a matrix parameter are shown in Table 2 below. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
             
            
               
                   
                 v x   
                 Vehicle speed 
               
               
                   
                 m 
                 Vehicle mass 
               
               
                   
                 I 
                 Yaw moment of Inertia 
               
               
                   
                 I f   
                 Distance from front axle to center of gravity 
               
               
                   
                 I r   
                 Distance from rear axle to center of gravity 
               
               
                   
                 C f   
                 Front cornering coefficient 
               
               
                   
                 C r   
                 Rear cornering coefficient 
               
               
                   
                   
               
            
           
         
       
     
     Since Equation 10 is premised on the case in which the slip angle of the vehicle is 0, the left side of Equation 10 and β become 0, thereby inducing Equation 11. 
     
       
         
           
             
               
                 
                   
                     [ 
                     
                       
                         
                           β 
                         
                       
                       
                         
                           Ψ 
                         
                       
                     
                     ] 
                   
                   = 
                   
                     
                       
                         
                           
                             [ 
                             
                               
                                 
                                   
                                     a 
                                     11 
                                   
                                 
                                 
                                   
                                     a 
                                     12 
                                   
                                 
                               
                               
                                 
                                   
                                     a 
                                     21 
                                   
                                 
                                 
                                   
                                     a 
                                     22 
                                   
                                 
                               
                             
                             ] 
                           
                           
                             - 
                             1 
                           
                         
                         [ 
                         
                           
                             
                               
                                 b 
                                 11 
                               
                             
                             
                               
                                 b 
                                 12 
                               
                             
                           
                           
                             
                               
                                 b 
                                 21 
                               
                             
                             
                               
                                 b 
                                 22 
                               
                             
                           
                         
                         ] 
                       
                       [ 
                       
                         
                           
                             
                               δ 
                               f 
                             
                           
                         
                         
                           
                             
                               δ 
                               r 
                             
                           
                         
                       
                       ] 
                     
                     = 
                       
                     
                       
                         [ 
                         
                           
                             
                               
                                 
                                   
                                     
                                       - 
                                       
                                         a 
                                         22 
                                       
                                     
                                     ⁢ 
                                     
                                       b 
                                       11 
                                     
                                   
                                   + 
                                   
                                     
                                       a 
                                       12 
                                     
                                     ⁢ 
                                     
                                       b 
                                       21 
                                     
                                   
                                 
                                 
                                   
                                     
                                       a 
                                       11 
                                     
                                     ⁢ 
                                     
                                       a 
                                       22 
                                     
                                   
                                   - 
                                   
                                     
                                       a 
                                       12 
                                     
                                     ⁢ 
                                     
                                       a 
                                       21 
                                     
                                   
                                 
                               
                             
                             
                               
                                 
                                   
                                     
                                       - 
                                       
                                         a 
                                         22 
                                       
                                     
                                     ⁢ 
                                     
                                       b 
                                       12 
                                     
                                   
                                   + 
                                   
                                     
                                       a 
                                       12 
                                     
                                     ⁢ 
                                     
                                       b 
                                       22 
                                     
                                   
                                 
                                 
                                   
                                     
                                       a 
                                       11 
                                     
                                     ⁢ 
                                     
                                       a 
                                       22 
                                     
                                   
                                   - 
                                   
                                     
                                       a 
                                       12 
                                     
                                     ⁢ 
                                     
                                       a 
                                       21 
                                     
                                   
                                 
                               
                             
                           
                           
                             
                               
                                 
                                   
                                     
                                       a 
                                       21 
                                     
                                     ⁢ 
                                     
                                       b 
                                       11 
                                     
                                   
                                   - 
                                   
                                     
                                       a 
                                       11 
                                     
                                     ⁢ 
                                     
                                       b 
                                       21 
                                     
                                   
                                 
                                 
                                   
                                     
                                       a 
                                       11 
                                     
                                     ⁢ 
                                     
                                       a 
                                       22 
                                     
                                   
                                   - 
                                   
                                     
                                       a 
                                       12 
                                     
                                     ⁢ 
                                     
                                       a 
                                       21 
                                     
                                   
                                 
                               
                             
                             
                               
                                 
                                   
                                     
                                       a 
                                       21 
                                     
                                     ⁢ 
                                     
                                       b 
                                       12 
                                     
                                   
                                   - 
                                   
                                     
                                       a 
                                       11 
                                     
                                     ⁢ 
                                     
                                       b 
                                       22 
                                     
                                   
                                 
                                 
                                   
                                     
                                       a 
                                       11 
                                     
                                     ⁢ 
                                     
                                       a 
                                       22 
                                     
                                   
                                   - 
                                   
                                     
                                       a 
                                       12 
                                     
                                     ⁢ 
                                     
                                       a 
                                       21 
                                     
                                   
                                 
                               
                             
                           
                         
                         ] 
                       
                       [ 
                       
                         
                           
                             
                               δ 
                               f 
                             
                           
                         
                         
                           
                             
                               δ 
                               r 
                             
                           
                         
                       
                       ] 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                         
                     11 
                   
                   ] 
                 
               
             
           
         
       
     
     Under the condition of β=0, the relationship between δ f  and δ r  is derived as in Equation 12 below. 
     
       
         
           
             
               
                 
                   
                     δ 
                     r 
                   
                   = 
                   
                     
                       
                         
                           - 
                           
                             l 
                             r 
                           
                         
                         + 
                         
                           
                             [ 
                             
                               m 
                               ⁢ 
                               
                                 l 
                                 f 
                               
                               / 
                               
                                 
                                   C 
                                   r 
                                 
                                 ( 
                                 
                                   
                                     l 
                                     f 
                                   
                                   + 
                                   
                                     l 
                                     r 
                                   
                                 
                                 ) 
                               
                             
                             ] 
                           
                           ⁢ 
                           
                             v 
                             x 
                             2 
                           
                         
                       
                       
                         
                           l 
                           f 
                         
                         + 
                         
                           
                             [ 
                             
                               m 
                               ⁢ 
                               
                                 l 
                                 r 
                               
                               / 
                               
                                 
                                   C 
                                   f 
                                 
                                 ( 
                                 
                                   
                                     l 
                                     f 
                                   
                                   + 
                                   
                                     l 
                                     r 
                                   
                                 
                                 ) 
                               
                             
                             ] 
                           
                           ⁢ 
                           
                             v 
                             x 
                             2 
                           
                         
                       
                     
                     ⁢ 
                     
                       δ 
                       f 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                         
                     12 
                   
                   ] 
                 
               
             
           
         
       
     
     The target steering angle of the left front wheel and the target steering angle of the right front wheel are calculated by Equation 9 above, and the target steering angle of the left rear wheel and the target steering angle of the right rear wheel are calculated according to the relationship with Equation 12. Thus, the target steering angle of the left front wheel, the target steering angle of the right front wheel, the target steering angle of the left rear wheel, and the target steering angle of the right rear wheel in the in-phase state may be calculated by Equation 13 below. 
     
       
         
           
             
               
                 
                   
                     δ 
                     fi 
                   
                   = 
                   
                     
                       
                         
                           l 
                           f 
                         
                         ⁢ 
                         
                           YR 
                           
                             des 
                             , 
                             L 
                           
                         
                       
                       
                         v 
                         x 
                       
                     
                     = 
                     
                       
                         l 
                         f 
                       
                       ⁢ 
                       
                         ρ 
                         L 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                         
                     13 
                   
                   ] 
                 
               
             
           
         
       
       
         
           
             
               δ 
               fr 
             
             = 
             
               
                 
                   
                     l 
                     f 
                   
                   ⁢ 
                   
                     YR 
                     
                       des 
                       , 
                       R 
                     
                   
                 
                 
                   v 
                   x 
                 
               
               = 
               
                 
                   l 
                   f 
                 
                 ⁢ 
                 
                   ρ 
                   R 
                 
               
             
           
         
       
       
         
           
             
               δ 
               rl 
             
             = 
             
               
                 
                   
                     - 
                     
                       l 
                       r 
                     
                   
                   + 
                   
                     
                       [ 
                       
                         m 
                         ⁢ 
                         
                           l 
                           f 
                         
                         / 
                         
                           
                             C 
                             r 
                           
                           ( 
                           
                             
                               l 
                               f 
                             
                             + 
                             
                               l 
                               r 
                             
                           
                           ) 
                         
                       
                       ] 
                     
                     ⁢ 
                     
                       v 
                       x 
                       2 
                     
                   
                 
                 
                   
                     l 
                     f 
                   
                   + 
                   
                     
                       [ 
                       
                         m 
                         ⁢ 
                         
                           l 
                           r 
                         
                         / 
                         
                           
                             C 
                             f 
                           
                           ( 
                           
                             
                               l 
                               f 
                             
                             + 
                             
                               l 
                               r 
                             
                           
                           ) 
                         
                       
                       ] 
                     
                     ⁢ 
                     
                       v 
                       x 
                       2 
                     
                   
                 
               
               · 
               
                 ( 
                 
                   
                     l 
                     f 
                   
                   ⁢ 
                   
                     ρ 
                     L 
                   
                 
                 ) 
               
             
           
         
       
       
         
           
             
               δ 
               rr 
             
             = 
             
               
                 
                   
                     - 
                     
                       l 
                       r 
                     
                   
                   + 
                   
                     
                       [ 
                       
                         m 
                         ⁢ 
                         
                           l 
                           f 
                         
                         / 
                         
                           
                             C 
                             r 
                           
                           ( 
                           
                             
                               l 
                               f 
                             
                             + 
                             
                               l 
                               r 
                             
                           
                           ) 
                         
                       
                       ] 
                     
                     ⁢ 
                     
                       v 
                       x 
                       2 
                     
                   
                 
                 
                   
                     l 
                     f 
                   
                   + 
                   
                     
                       [ 
                       
                         m 
                         ⁢ 
                         
                           l 
                           r 
                         
                         / 
                         
                           
                             C 
                             f 
                           
                           ( 
                           
                             
                               l 
                               f 
                             
                             + 
                             
                               l 
                               r 
                             
                           
                           ) 
                         
                       
                       ] 
                     
                     ⁢ 
                     
                       v 
                       x 
                       2 
                     
                   
                 
               
               · 
               
                 ( 
                 
                   
                     l 
                     f 
                   
                   ⁢ 
                   
                     ρ 
                     R 
                   
                 
                 ) 
               
             
           
         
       
     
     As a result, the control unit  20  may calculate the target steering angle of the left front wheel by using the distance between the front wheel axle and the center of the vehicle and the left wheel target curvature, calculate the target steering angle of the right front wheel by using the distance between the front wheel axle and the center of the vehicle and the right wheel target curvature, calculate the target steering angle of the left rear wheel by using the distance between the rear wheel axle and the center of the vehicle and the left wheel target curvature, and calculate the target steering angle of the right rear wheel by using the distance between the rear wheel axle and the center of the vehicle and the right wheel target curvature, on the basis of the predefined vehicle dynamics model. 
     When the target steering angles of the respective wheels are calculated, the control unit  20  may independently control the steering of the four wheels according to the calculated target steering angles. In this case, as illustrated in  FIG.  44   , the control unit  20  may calculate the driving torques for driving the four wheels through feedforward control (understeer gradient) and feedback control (PID control) on the target steering angle and the current steering angle of the vehicle, and control the driving of the four wheels, thereby independently controlling the steering of the four wheels. 
       FIG.  45    is a flowchart for describing an operation method of the corner module apparatus for a vehicle in accordance with the embodiment of the present disclosure, based on the fifth application. Referring to  FIG.  45   , the operation method of the corner module apparatus for a vehicle in accordance with the embodiment of the present disclosure will be described. Hereafter, the detailed descriptions of contents overlapping the above-described contents will be omitted herein, and the following descriptions will be focused on a time series configuration. 
     First, the control unit  20  acquires the driving state information and the driving environment information of the vehicle from the vehicle information acquisition unit  15  in step S 10   e . The driving state information may include the vehicle velocity and the heading angle of the vehicle, and the driving environment information may include surrounding image information (e.g. forward image) of the vehicle. 
     Then, the control unit  20  calculates information on the distance to the target point to which the vehicle is to move, on the basis of the driving state information and the driving environment information of the vehicle, in step S 20   e . In step S 20   e , the control unit  20  calculates the straight distance, the vertical distance and the horizontal distance from the vehicle to the target point as the distance information to the target point, by using the velocity of the vehicle, an offset distance of the vehicle from the center of the road, calculated from the surrounding image information, and the curvature radius of the road based on the center of the road. 
     Then, the control unit  20  calculates a target curvature defined as the curvature of a target trajectory to the target point, on the basis of the distance information calculated in step S 20   e , in step S 30   e . The target curvature may be sorted into a center target curvature defined as the curvature of a target trajectory based on the center of the vehicle (i.e. the moving target trajectory of the center of the vehicle), a left wheel target curvature defined as the curvature of a target trajectory based on the left wheel of the vehicle (i.e. the moving target trajectory of the left wheel of the vehicle), and a right wheel target curvature defined as the curvature of a target trajectory based on the right wheel of the vehicle (i.e. the moving target trajectory of the right wheel of the vehicle). Thus, in step S 30   e , the control unit  20  calculates the center target curvature by using the straight distance, the vertical distance and the horizontal distance from the vehicle to the target point and the heading angle of the vehicle, and then calculates the left wheel target curvature and the right wheel target curvature from the center target curvature by using the tread information of the vehicle. 
     Then, the control unit  20  calculates the target steering angles of the four wheels of the vehicle on the basis of the target curvature calculated in step S 30   e , in step S 40   e . In step S 40   e , the control unit  20  calculates the target steering angle of the left front wheel by using the distance between the front wheel axle and the center of the vehicle and the left wheel target curvature, calculates the target steering angle of the right front wheel by using the distance between the front wheel axle and the center of the vehicle and the right wheel target curvature, calculates the target steering angle of the left rear wheel by using the distance between the rear wheel axle and the center of the vehicle and the left wheel target curvature, and calculates the target steering angle of the right rear wheel by using the distance between the rear wheel axle and the center of the vehicle and the right wheel target curvature, on the basis of the predefined vehicle dynamics model. In this case, the control unit  20  calculates the target steering angles of the respective four wheels under the condition that the slip angles of the respective wheels of the vehicle are 0. 
     Then, the control unit  20  independently controls the steering of the four wheels according to the target steering angles calculated in step S 40   e , in step S 50   e . In step S 50   e , the control unit  20  calculates the driving torques for driving the four wheels through the feedforward control and feedback control on the target steering angles and the current steering angle of the vehicle, and controls the driving of the four wheels, thereby independently controlling the steering of the four wheels. 
     According to the fifth application, it is possible to suggest the quantitative control mechanism which differently calculates the target steering angles of the respective wheels when the vehicle to which the four-wheel independent driving method is applied travels along a curved road, and independently controls the steering of the four wheels, thereby improving the cornering performance and the cornering stability of the vehicle. 
     The term “unit” used in this specification may include a unit implemented in hardware, software or firmware. For example, the term may be used interchangeably with the term such as logic, a logical block, a part or a circuit. The “unit” may become the minimum unit or a portion of a part configured as one component or configured to perform one or more functions. For example, in accordance with an embodiment, the “unit” may be implemented in the form of ASIC (Application-Specific Integrated Circuit). Furthermore, the embodiments described in this specification may be implemented with a method or process, a device, a software program, a data stream or a signal, for example. Although a feature is discussed only in a single context (for example, discussed only in a method), the discussed feature can be implemented in another type (for example, apparatus or program). An apparatus may be implemented in suitable hardware, software or firmware. The method can be implemented in a device such as a processor which generally refers to a processing device including a computer, a microprocessor, an integrated circuit or a programmable logic device, for example. The processor also includes a communication device, such as a computer, cellular phone, PDA (Personal Digital Assistant) and another device, which facilitates information communication between end users. 
     As disclosed above, a corner module apparatus for a vehicle, which can freely adjust the number and arrangement of wheels according to the purpose of a vehicle. 
     As disclosed above, various embodiments are directed to a corner module apparatus for a vehicle, which can independently control the operations of wheels. 
     As disclosed above, the corner module apparatus can adjust the number and arrangement of the first and second platforms according to the type and purpose of a vehicle, thereby improving the degree of freedom in design, and enabling mass production of various types of PBV vehicles. 
     As disclosed above, the control module apparatus can independently adjust the operations of the respective wheels such that the vehicle can stably travel according to the driving condition, and secure a wide range of steering angle. 
     While this disclosure includes specific examples, it will be apparent after an understanding of the disclosure of this application that various changes in form and details may be made in these examples without departing from the spirit and scope of the claims and their equivalents. The examples described herein are to be considered in a descriptive sense only, and not for purposes of limitation. Descriptions of features or aspects in each example are to be considered as being applicable to similar features or aspects in other examples. Suitable results may be achieved if the described techniques are performed in a different order, and/or if components in a described system, architecture, device, or circuit are combined in a different manner, and/or replaced or supplemented by other components or their equivalents. 
     Therefore, the scope of the disclosure is defined not by the detailed description, but by the claims and their equivalents, and all variations within the scope of the claims and their equivalents are to be construed as being included in the disclosure.