Patent Publication Number: US-2023143158-A1

Title: Brake for vehicle and control method therefor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2021-0153081, filed on Nov. 9, 2021, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present disclosure relates to a vehicle brake and a method of controlling the same. 
     2. Discussion of Related Art 
     The contents described herein provide only background information and do not constitute the related art. 
     An electronic stability control (ESC) integrated brake system is a conventional brake system (CBS) which includes an ESC and to which active braking is applied. While a vehicle is traveling, when stability of a vehicle is degraded, the ESC integrated brake system performs an anti-lock brake system (ABS) function, a vehicle dynamics control (VDC) function, a traction control system (TCS) function, and the like to secure stability. 
     The ESC integrated brake system includes a master cylinder, a pedal simulator, a motor, a screw, a nut, a hydraulic circuit, and a plurality of valves. The master cylinder is a member which generates a hydraulic pressure required for braking a vehicle and is divided into a single-acting master cylinder and a double-acting master cylinder according to a direction in which a hydraulic pressure is generated. 
     The double-acting master cylinder generates a hydraulic pressure whenever a piston moves in a forward or backward direction. When a movement direction of the piston is changed, the double-acting master cylinder takes time to generate a hydraulic pressure behind the piston, and thus the double-acting master cylinder has a problem in that braking efficiency is reduced when emergency braking is required. 
     When the single-acting master cylinder is used in order to solve such a problem of the double-acting master cylinder, since the master cylinder, of which a cross-sectional area is small and a length is long, should be manufactured in order to generate a high pressure of about 200 bar, there is a problem of increasing a package size of a brake system. 
     BRIEF SUMMARY OF THE INVENTION 
     The present disclosure is directed to providing a vehicle brake capable of enhancing braking efficiency during emergency braking using a single-acting master cylinder including a piston of which a pressurizing area is changed. 
     The present disclosure is directed to providing a vehicle brake allowing a package size of a braking system to be reduced using a single-acting master cylinder including a piston of which a pressurizing area is changed. 
     Objectives to be solved by the present disclosure are not limited to the above-described objectives, and the other objectives, which are not described above, will be clearly understood by those skilled in the art through the following descriptions. 
     According to at least one aspect, the present disclosure provides a vehicle brake comprising: a reservoir configured to store a fluid therein; a hydraulic circuit configured to transfer a hydraulic pressure to a wheel of a vehicle; a plurality of valves disposed to regulate a flow of the fluid in the hydraulic circuit; and a master cylinder including a cylinder body, a main piston which is movably disposed within the cylinder body and in which a receptacle is formed at one side thereof, and a center piston which is disposed within the cylinder body and in which a penetration hole is formed in at least a part thereof, wherein the penetration hole is formed to have a size smaller than a cross-sectional area of the receptacle, and as the main piston moves, at least a part of the center piston is inserted into the receptacle, and thus a pressurizing area of the main piston decreases. 
     According to another aspect, the present disclosure provides a method of controlling a vehicle brake including a main piston in which a receptacle is formed at one side thereof and a center piston in which a penetration hole having a size smaller than a cross-sectional area of the receptacle is formed, the method comprising: moving the main piston in a forward direction; determining whether the main piston reaches one side end of the center piston; determining whether a wheel of a vehicle is in a slip state; determining whether an anti-lock brake system (ABS) function is performed when it is determined that the wheel of the vehicle is in the slip state; and opening a first valve disposed between the penetration hole and a reservoir and moving the main piston in the forward direction again when it is determined that the ABS function is not being performed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present disclosure will become more apparent to those of ordinary skill in the art by describing exemplary embodiments thereof in detail with reference to the accompanying drawings, in which: 
         FIG.  1    is a view illustrating a structure of a master cylinder according to one embodiment of the present disclosure; 
         FIG.  2    is a hydraulic circuit diagram illustrating a vehicle brake according to one embodiment of the present disclosure; 
         FIG.  3    is a view illustrating a working principle of a low pressure conventional brake system (CBS) of the vehicle brake according to one embodiment of the present disclosure; 
         FIG.  4    is a view illustrating a working principle of a high pressure CBS of the vehicle brake according to one embodiment of the present disclosure; 
         FIG.  5    is a view illustrating a working principle of an anti-lock brake system (ABS) of the vehicle brake according to one embodiment of the present disclosure; 
         FIG.  6    is a view illustrating a working principle when a hydraulic circuit of the vehicle brake according to one embodiment of the present disclosure is leaking; 
         FIG.  7    is a view illustrating a working principle when backup braking is performed by the vehicle brake according to one embodiment of the present disclosure; 
         FIG.  8    is a graph showing a relationship between displacement of a main piston of the vehicle brake according to one embodiment of the present disclosure and a current applied to a motor; and 
         FIG.  9    is a flowchart illustrating a method of controlling the vehicle brake according to one embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, some exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the following description, like reference numerals preferably designate like elements, although the elements are shown in different drawings. Further, in the following description of some embodiments, a detailed description of known functions and configurations incorporated therein will be omitted for the purpose of clarity and for brevity. 
     Additionally, various terms such as first, second, A, B, (a), (b), etc., are used solely to differentiate one component from the other but not to imply or suggest the substances, order, or sequence of the components. Throughout this specification, when a part ‘includes’ or ‘comprises’ a component, the part is meant to further include other components, not to exclude thereof unless specifically stated to the contrary. The terms such as ‘unit’, ‘module’, and the like refer to one or more units for processing at least one function or operation, which may be implemented by hardware, software, or a combination thereof. 
       FIG.  1    is a view illustrating a structure of a master cylinder according to one embodiment of the present disclosure. 
       FIG.  2    is a hydraulic circuit diagram illustrating a vehicle brake according to one embodiment of the present disclosure. 
     Referring to  FIGS.  1  and  2   , the vehicle brake according to one embodiment of the present disclosure may include a master cylinder  100 , a reservoir  210 , a hydraulic circuit  220 , a plurality of valves, a pedal simulator  260 , and a control unit (not shown). 
     The master cylinder  100  may include a cylinder body  110 , a main piston  120 , a receptacle  122 , a center piston  130 , a penetration hole  132 , a motor  140 , a screw  150 , a nut  160 , and sealing members  170 . 
     The master cylinder  100  generate a hydraulic pressure required for braking a vehicle. The master cylinder  100  is connected to the reservoir  210  and wheels FR, FL, RR, and RL of the vehicle. The master cylinder  100  may transfer the hydraulic pressure to the wheels FR, FL, RR, and RL using the hydraulic circuit  220 . The master cylinder  100  may operate in a single-acting manner. 
     The cylinder body  110  may be formed as a hollow cylinder. A brake oil required for generating the hydraulic pressure flows into the cylinder body  110 . The main piston  120 , the center piston  130 , the sealing members  170 , and the like are disposed in the cylinder body  110 . The cylinder body  110  is connected to the reservoir  210  and the wheels FR, FL, RR, and RL using the hydraulic circuit  220 . 
     The main piston  120  is moveably disposed within the cylinder body  110 . The receptacle  122  is formed at one side of the main piston  120 . The main piston  120  may be formed as a hollow cylinder. The main piston  120  is connected to the nut  160  and moved with the nut  160  according to movement of the nut  160 . The main piston  120  generates the hydraulic pressure required for braking the vehicle by moving from one end of the cylinder body  110  in a direction toward the other end (hereinafter, referred to as a forward movement). As the main piston  120  moves in a forward direction, the center piston  130  may be inserted into the receptacle  122 . The receptacle  122  is formed to have a cross sectional area greater than a cross sectional area of the penetration hole  132 . As at least a part of the center piston  130  is inserted into the receptacle  122 , a pressurized area of the main piston  120  decreases. At least one sealing member  170  may be disposed between an outer surface of the main piston  120  and an inner surface of the cylinder body  110 . 
     The center piston  130  is disposed at the other end of an inner side of the cylinder body  110 . The center piston  130  may be formed as a hollow cylinder. The penetration hole  132  is formed in at least a part of the center piston  130 . The penetration hole  132  is connected to the reservoir  210 , and a first valve  231  is disposed between the penetration hole  132  and the reservoir  210 . The penetration hole  132  is formed to have a size smaller than the cross-sectional area of the receptacle  122 . As the main piston  120  moves, the center piston  130  may be inserted into the receptacle  122 . As the center piston  130  is inserted into the receptacle  122 , a pressurizing area of the main piston  120  decreases. At least one sealing member  170  may be disposed on an outer surface of the center piston  130 . The center piston  130  may be formed to have one of various lengths according to a desired pressure required for braking the vehicle. 
     The motor  140  generates a driving force. The motor  140  is connected to the screw  150  and transfers the driving force to the screw  150 . A position sensor (not shown) may be installed at one side of the motor  140 . The position sensor detects displacement of the main piston  120 . 
     The screw  150  is connected to one side of the motor  140 . The screw  150  rotates using the driving force transferred from the motor  140 . The screw  150  is connected to the nut  160 . The screw  150  may be a ball screw. 
     The nut  160  is connected to the screw  150 . The nut  160  moves in a longitudinal direction of the screw  150  according to rotation of the screw  150 . The nut  160  is connected to the main piston  120  to move the main piston  120 . 
     The sealing member  170  may be disposed between the outer surface of the main piston  120  and the inner surface of the cylinder body  110 . The sealing member  170  may be disposed on the outer surface of the of the center piston  130 . The sealing member  170  may be configured to allow a fluid to transfer therethrough unidirectionally. The sealing member  170  may be provided as the plurality of sealing members  170  and formed in a “V” shape. 
     The reservoir  210  is configured to store the fluid such as the brake oil. The reservoir  210  is connected to all of the wheels FR, FL, RR, and RL, the pedal simulator  260 , the cylinder body  110 , and the penetration hole  132  using the hydraulic circuit  220 . 
     The hydraulic circuit  220  is configured to transfer the hydraulic pressure generated by the master cylinder  100  and/or the pedal simulator  260  to the wheels FR, FL, RR, and RL. The hydraulic circuit  220  connects the components of the vehicle brake according to one embodiment. A plurality of valves configured to regulate a flow of the fluid are disposed in the hydraulic circuit  220 . At least one pressure sensor may be disposed in the hydraulic circuit  220 . 
     A first valve  231  is disposed between the penetration hole  132  and the reservoir  210 . In a state in which at least a part of the center piston  130  is inserted into the receptacle  122 , as the first valve  231  is opened, the pressurizing area of the main piston  120  decreases. 
     The second valve  232  is disposed between an inner portion of the cylinder body  110  and the reservoir  210 . When the main piston  120  moves in a backward direction, as the second valve  232  is opened, the brake oil may smoothly flow into the cylinder body  110 . 
     The pedal simulator  260  is a member which provides a pedal feel to a driver of the vehicle and is connected to the reservoir  210  and the wheels FR, FL, RR, and RL. The pedal simulator  260  may include a brake pedal, a pressure sensor, and the like. 
     In the vehicle brake according to one embodiment of the present disclosure, as the main piston  120  moves in the forward direction, at least a part of the center piston  130  is inserted into the receptacle  122 . The penetration hole  132  of which the size is smaller than the cross-sectional area of the receptacle  122  is formed in the center piston  130 . In a state in which the center piston  130  is inserted into the receptacle  122 , as the first valve  231  is opened and the main piston  120  moves in the forward direction, the pressurizing area of the main piston  120  decreases. Thus, braking efficiency of the vehicle during emergency braking may be enhanced, and a package size of a braking system may be reduced using the master cylinder  100  operating in a single-acting manner. 
       FIG.  3    is a view illustrating a working principle of a low pressure conventional brake system (CBS) of the vehicle brake according to one embodiment of the present disclosure. 
       FIG.  4    is a view illustrating a working principle of a high pressure CBS of the vehicle brake according to one embodiment of the present disclosure. 
     Referring to  FIGS.  3  and  4   , in a state in which the low pressure CBS operates, the control unit closes the first valve  231  and moves the main piston  120  in the forward direction in order to generate a hydraulic pressure required for braking the vehicle. As the main piston  120  moves in the forward direction, the hydraulic pressure is generated in the cylinder body  110 . The hydraulic pressure generated in the cylinder body  110  is transferred to the wheels FR, FL, RR, and RL of the vehicle using the hydraulic circuit  220 . The control unit determines the displacement of the main piston  120  using the position sensor. The vehicle brake according to one embodiment may be designed so that the desired pressure is generated in the hydraulic circuit  220  when the main piston  120  reaches one side end of the center piston  130 . In this case, one side end of the center piston  130  is an end, which is inserted into the receptacle  122 , of both ends of the center piston  130 . The desired pressure is a hydraulic pressure which is required for braking the vehicle or which is a pressure set to perform an anti-lock brake system (ABS) function. 
     In a state in which the high pressure CBS operates, the control unit closes the first valve  231  and moves the main piston  120  in the forward direction. The control unit determines the displacement of the main piston  120  using the position sensor. When a pressure generated in the hydraulic circuit  220  is lower than the desired pressure even though the main piston  120  reaches one side end of the center piston  130 , the control unit opens the first valve  231  and moves the main piston  120  in the forward direction again. As a pressurizing area of the main piston  120  decreases and the main piston  120  moves in the forward direction, a pressure higher than the desired pressure may be generated in the hydraulic circuit  220 . 
       FIG.  5    is a view illustrating a working principle of an ABS of the vehicle brake according to one embodiment of the present disclosure. 
     The working principle of the ABS of the vehicle brake according to one embodiment will be described with reference to  FIG.  5   . 
     When the ABS function of the vehicle is being performed, the control unit determines displacement of the main piston  120 . When the main piston  120  moves by as much as a maximum displacement in the forward direction, the control unit controls hydraulic pressures generated at the wheels FR, FL, RR, and RL using inlet valves  241 ,  242 ,  243 , and  244  and outlet valves  251 ,  252 ,  253 , and  254 . The control unit moves the main piston  120  in the backward direction so that the brake oil flows into the cylinder body  110 . The control unit moves the main piston  120  in the forward direction again to generate a hydraulic pressure in the cylinder body  110 . 
     When the ABS function is being performed, the control unit determines a state of a ground surface on which the vehicle is traveling. The control unit may determine the state of the ground surface using a pressure (hereinafter, “wheel control pressure”) required for controlling the wheels FR, FL, RR, and RL. The control unit compares the wheel control pressure and a preset pressure. When the wheel control pressure is lower than the preset pressure, the control unit determines that the ground surface is in a low friction state. When the control unit determines that the ground surface is in the low friction state, the control unit controls the main piston  120  to move in the backward direction by as much as the maximum displacement and to move in the forward direction again. When the wheel control pressure is higher than the preset pressure, the control unit determines that the ground surface is in a high friction state. When the control unit determines that the ground surface is in the high friction state, the control unit moves the main piston  120  in the backward direction to one side end of the center piston  130  and moves the main piston  120  in the forward direction again. 
       FIG.  6    is a view illustrating a working principle when the hydraulic circuit of the vehicle brake according to one embodiment of the present disclosure is leaking. 
     Referring to  FIG.  6   , when the control unit determines that a brake oil of the hydraulic circuit  220  of a side of the rear wheel leaks, the control unit opens a front wheel valve  233  and closes a rear wheel valve  234 . The control unit moves the main piston  120  in the forward direction to supply a hydraulic pressure to the front wheels FR and FL so as to brake the vehicle. 
       FIG.  7    is a view illustrating a working principle when backup braking is performed by the vehicle brake according to one embodiment of the present disclosure. 
     Referring to  FIG.  7   , when backup braking of the vehicle is performed, the control unit closes the first valve  231 , the front wheel valve  233 , and the rear wheel valve  234  and closes a front wheel backup valve  235  and a rear wheel backup valve  236 . The control unit transfers a hydraulic pressure generated by the pedal simulator  260  to the wheels FR, FL, RR, and RL to brake the vehicle. 
       FIG.  8    is a graph showing a relationship between the displacement of the main piston of the vehicle brake according to one embodiment of the present disclosure and a current applied to the motor. 
     Referring to  FIG.  8   , as the main piston  120  moves in the forward direction, a current applied to the motor  140  and a pressure generated in the cylinder body  110  increase. When the main piston  120  reaches one side end of the center piston  130  (piston displacement=x), as the first valve  231  is opened, the pressurizing area of the main piston  120  decreases. As the pressurizing area of the main piston  120  decreases, a force required for generating a pressure having the same magnitude decreases, and thus a current applied to the motor  140  decreases. As the main piston  120  moves in the forward direction again, the current applied to the motor  140  and the pressure generated in the cylinder body  110  increase. Thus, the vehicle brake according to one embodiment of the present disclosure has an effect of generating a high pressure using a low current. 
       FIG.  9    is a flowchart illustrating a method of controlling the vehicle brake according to one embodiment of the present disclosure. 
     The control unit moves the main piston in the forward direction to generate a hydraulic pressure required for braking the vehicle (S 910 ). 
     The control unit determines whether the main piston reaches one side end of the center piston (S 920 ). The control unit determines displacement of the main piston  120  using the position sensor installed in the motor  140 . Whether the main piston  120  reaches one side end of the center piston  130  may be determined on the basis of the displacement of the main piston  120 . 
     When the control unit determines that the main piston reaches one side end of the center piston, the control unit determines whether the wheel of the vehicle is in a slip state (S 930 ). The control unit may determine whether the wheels FR, FL, RR, and RL are in the slip state on the basis of whether the wheels FR, FL, RR, and RL of the vehicle rotate and whether the vehicle travels. 
     When the control unit determines that the wheel of the vehicle is in the slip state, the control unit determines whether the ABS function of the vehicle is performed (S 940 ). The control unit may determine whether the ABS function is performed by comparing a pressure generated in the hydraulic circuit  220  and a pressure set to perform the ABS function. 
     When the control unit determines that the ABS function of the vehicle is not being performed, the control unit opens the first valve (S 950 ). As the first valve  231  is opened, a pressurizing area of the main piston  120  decreases. 
     The control unit moves the main piston in the forward direction to perform the ABS function (S 960 ). In a state in which the first valve  231  is opened, as the main piston  120  moves in the forward direction, a pressure, which is higher than the pressure set to perform the ABS function, is generated in the hydraulic circuit  220 , and the ABS function of the vehicle is performed. 
     When the control unit determines that the ABS function of the vehicle is performed, the control unit determine a state of a ground surface on which the vehicle travels (S 970 ). The control unit may determine the state of the ground surface using a wheel control pressure. The control unit compares the wheel control pressure and the preset pressure. The control unit determines that the ground surface is in a low friction state when the wheel control pressure is lower than the preset pressure and determines that the ground surface is in a high friction state when the wheel control pressure is higher than or equal to the preset pressure. 
     When the control unit determines that the ground surface is in the low friction state, the control unit moves the main piston in the backward direction by as much as a maximum displacement (S 982 ). When the control unit determines the ground surface is in the low friction state, the control unit moves the main piston  120  in the backward direction by as much as the maximum displacement in order to transfer a higher hydraulic pressure to the wheel. 
     When the control unit determines that the ground surface is in the high friction state, the control unit moves the main piston to one side end of the center piston (S 984 ). When the ground surface is in the high friction state, the control unit moves the main piston  120  in the backward direction to one side end of the center piston  130  in order to rapidly transfer the hydraulic pressure to the wheel. 
     The control unit moves the main piston in the forward direction again (S 990 ). When the ABS function is performed, the control unit moves the main piston  120  in the forward direction in order to continuously supply the hydraulic pressure to the wheel of the vehicle. 
     According to one embodiment, since the vehicle brake uses a single-acting master cylinder including a piston of which a pressurizing area is changed, there is an effect of enhancing braking efficiency during emergency braking. 
     According to one embodiment, since the vehicle brake uses the single-acting master cylinder including the piston of which the pressurizing area is changed, there is an effect of reducing a package size of a braking system. 
     In the flowchart of the preset disclosure, the operations are sequentially performed but are only an example for describing the technical spirit of one embodiment of the present disclosure. In other words, since the present disclosure may be variously changed, modified, and applied by those skilled in the art including one embodiment of the present disclosure by changing the operations described in the flowchart and performing the changed operations without departing from the essential features of the embodiment of the present disclosure or performing one or more of the operations in parallel, the flowchart is not limited to a chronological order. 
     Although exemplary embodiments of the present disclosure have been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions, and substitutions are possible, without departing from the idea and scope of the claimed invention. Therefore, exemplary embodiments of the present disclosure have been described for the sake of brevity and clarity. The scope of the technical idea of the present embodiments is not limited by the illustrations. Accordingly, one of ordinary skill would understand the scope of the claimed invention is not to be limited by the above explicitly described embodiments but by the claims and equivalents thereof.