Patent Publication Number: US-2022227430-A1

Title: Running Bare Chassis Assembly For Low-Floor Bus and Manufacturing Method Thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Korean Application No. 10-2021-0008131, filed on Jan. 20, 2021, which application is hereby incorporated herein by reference. 
     TECHNICAL FIELD 
     Exemplary embodiments of the present disclosure relate to a running bare chassis assembly for a low-floor bus and a manufacturing method thereof. 
     BACKGROUND 
     Electric buses and hydrogen buses are being developed domestically and globally. Among the electric buses and the hydrogen buses, low-floor double-decker electric buses are also under development. 
     A vehicle is divided into a body and a chassis, and the chassis is formed by assembling a power transmission system, a suspension, and electric vehicle parts to a frame which is a basic frame. 
     Conventionally, since a body structure of a low-floor bus is formed as a build-up body structure, a body weight is excessive and workability is very disadvantageous. 
     For example, a conventional ultra-low-floor frame assembly for a compressed natural gas (CNG) engine has a structure in which a front frame is connected to a center frame using a longitudinal member. However, since it is impossible to integrally manufacture the front frame and the center frame and separate the front frame from the center frame, assembling work is impossible and a length of the center frame is not easily changed. 
     In addition, the conventional ultra-low-floor frame assembly has a structure in which the center frame and a rear frame are connected to the longitudinal member using a connection member. However, since it is also impossible to integrally manufacture the center frame, the rear frame, and the longitudinal member and separate the center frame, the rear frame, and the longitudinal member from each other, assembling work is impossible and a length of the center frame is not easily changed. 
     In addition, when the build-up body structure is applied, a capacity of a three-axis air spring of a double-decker electric bus may not be satisfied. The capacity of the three-axis air spring of the double-decker electric bus is less than or equal to 6,700 kg. 
     The contents described in the Background are to aid understanding of the background of the present disclosure and may include what is not previously known to those skilled in the art to which the present disclosure pertains. 
     SUMMARY 
     An embodiment of the present disclosure is directed to a running bare chassis assembly for a low-floor bus, which is not excessive in weight and has excellent manufacturing workability, and a manufacturing method thereof. 
     Other objects and advantages of embodiments of the present disclosure can be understood by the following description and become apparent with reference to the embodiments of the present disclosure. Also, it is obvious to those skilled in the art to which the present disclosure pertains that the objects and advantages of embodiments of the present disclosure can be realized by the means as claimed and combinations thereof. 
     In accordance with an embodiment of the present disclosure, there is provided a running bare chassis assembly for a low-floor bus, which includes a front frame on which a front suspension is mounted, a rear frame assembly on which a battery carrier is mounted, and a center frame coupled to the front frame and the rear frame assembly through a first engagement, wherein the rear frame assembly includes a first rear frame on which a rear suspension is mounted, a second rear frame which is coupled to the first rear frame and on which a radiator is mounted, and a battery carrier frame on which the battery carrier is mounted and which is coupled to the first rear frame through a second engagement, and a stress distribution due to the first engagement is greater than a stress distribution due to the second engagement. 
     In addition, the running bare chassis assembly may further include a center bridge connected between the front frame and the rear frame assembly. 
     In addition, the front frame may include a front suspension mounting portion on which the front suspension is mounted, and an air tank mounting portion formed on the front frame to allow an air tank to be mounted above the front frame. 
     In addition, the center frame may be formed such that lengthwise frames formed and disposed to be spaced apart from each other in a lengthwise direction of the center frame, and widthwise frames formed and disposed to be spaced apart from each other in a width direction of the center frame are formed in a grid structure. 
     In addition, the first rear frame may include a lower frame which forms a lower portion and on which the rear suspension is mounted, and an upper frame forming an upper portion, wherein the upper frame may be formed such that a first upper frame formed and disposed to be spaced apart from each other in a lengthwise direction of the first rear frame, and a second upper frame formed and disposed to be spaced apart from each other in a width direction of the first rear frame are formed in a grid structure. 
     In addition, the second rear frame may be formed of a grid-shaped low-floor frame forming the lower surface, and a plurality of vertical frames formed vertically upward from the low-floor frame. 
     In addition, each of upper ends of the plurality of vertical frames may be coupled to a lower end of the first rear frame through the first engagement. 
     In addition, a module upper side engagement portion, which protrudes downward, may be formed in the first upper frame to be bolt-coupled to a radiator upper side engagement portion above the radiator, and a module lower side engagement portion, which protrudes upward, may be formed in the low-floor frame to be bolt-coupled to a radiator lower side engagement portion below the radiator. 
     In addition, the module upper side engagement portion and the radiator upper side engagement portion may be coupled by a bolt passing through the rear frame assembly in a width direction thereof, and the module lower side engagement portion and the radiator lower side engagement portion may be coupled by a bolt passing through the rear frame assembly in a height direction thereof. 
     Meanwhile, a plate-shaped forklift mounting guide, which extends in a width direction of the battery carrier frame, may be formed in a lower end portion of the battery carrier frame. 
     In addition, a guide plate may be coupled to the second upper frame so as to extend in a lengthwise direction of the second upper frame and to protrude upward from the second upper frame. 
     In addition, a stopper may be coupled to the first upper frame so as to protrude upward from the first upper frame, and a guide pin seated on the first upper frame may be coupled to one side of the stopper. 
     In addition, the first engagement may be a welding engagement method, and the second engagement may be a bolting engagement method. 
     In addition, the front suspension may be an independent suspension, and the rear suspension may be a rigid axle. 
     Next, a manufacturing method of a running bare chassis assembly for a low-floor bus includes manufacturing a front frame on which a front suspension is mounted, manufacturing a rear frame assembly including coupling a second rear frame on which a radiator is mounted to a first rear frame on which a rear suspension is mounted through a first engagement and coupling a battery carrier frame on which a battery carrier is mounted to the first rear frame through a second engagement, manufacturing a center frame configured to connect the front frame to the rear frame assembly, and coupling the front frame, the rear frame assembly, and the center frame through the first engagement, wherein a stress distribution due to the first engagement is greater than a stress distribution due to the second engagement. 
     In addition, the manufacturing method may further include connecting a center bridge between the front frame and the rear frame assembly. 
     In addition, the first engagement may be a welding engagement method, and the second engagement may be a bolting engagement method. 
     In addition, a front suspension may be an independent suspension, and a rear suspension may be a rigid axle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a running bare chassis assembly for a low-floor bus according to embodiments of the present disclosure. 
         FIGS. 2 to 5  are diagrams illustrating a coupling relationship between portions of the running bare chassis assembly for a low-floor bus according to embodiments of the present disclosure. 
         FIG. 6  is a diagram illustrating a state in which various components are mounted on a rear frame assembly of a running bare chassis for a low-floor bus according to embodiments of the present disclosure. 
         FIG. 7  is a diagram illustrating a part of  FIG. 6 . 
         FIG. 8  is a diagram illustrating a coupling relationship between portions of the running bare chassis assembly for a low-floor bus according to embodiments of the present disclosure. 
         FIG. 9  is a diagram illustrating a partial cross-sectional shape of a battery carrier frame of the running bare chassis for a low-floor bus according to embodiments of the present disclosure. 
         FIG. 10  is a diagram illustrating a partial shape of a first rear frame of the running bare chassis for a low-floor bus according to embodiments the present disclosure. 
         FIGS. 11 and 12  are diagrams illustrating stress analysis results of the running bare chassis for a low-floor bus according to embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     Reference should be made to the accompanying drawings that illustrate exemplary embodiments of the present disclosure and to the description in the accompanying drawings in order to fully understand the present disclosure and operational advantages of embodiments of the present disclosure and objects attained by practicing embodiments of the present disclosure. 
     In describing exemplary embodiments of the present disclosure, known technologies or repeated descriptions may be reduced or omitted to avoid unnecessarily obscuring the gist of the present disclosure. 
       FIG. 1  is a diagram illustrating a running bare chassis assembly for a low-floor bus according to embodiments of the present disclosure, and  FIGS. 2 to 5  are diagrams illustrating a coupling relationship between portions of the running bare chassis assembly for a low-floor bus according to embodiments of the present disclosure. 
     Hereinafter, a running bare chassis assembly for a low-floor bus and a manufacturing method of a running bare chassis assembly according to one embodiment of the present disclosure will be described with reference to  FIGS. 1 to 5 . 
     Embodiments of the present disclosure relate to a running bare chassis assembly of a low-floor bus, for example, a double-decker electric bus, and relate to minimizing an overall weight and improving assemblability by separately manufacturing a front frame  110 , a center frame  120 , and a rear frame assembly and then coupling the front frame  110 , the center frame  120 , and the rear frame assembly. 
     The front frame  110  is a chassis module corresponding to a front side of the low-floor bus and has a structure on which an independent suspension and an air tank are mounted. 
     The rear frame assembly is a chassis model corresponding to a rear side of the low-floor bus, to which a first rear frame  130 , a second rear frame  140 , a first battery carrier frame  150 , a second battery carrier frame  160 , and an air conditioner mounting frame  170  are coupled, and has a structure on which an in-wheel motor, a low-floor rigid axle, a PE room, a battery carrier, and the like are mounted. 
     In addition, the center frame  120  may be connected between the front frame  110  and the rear frame assembly, and a center bridge  180  may be connected between the front frame  110  and the rear frame assembly to prevent deformation during driving. 
     That is, the center frame  120  is connected to a lower end of a rear side of the front frame  110  and connected to a lower end of a front side of the rear frame assembly. 
     As shown in  FIG. 2 , an air tank mounting portion  111  and a front suspension mounting portion  112  are formed on the front frame  110 , and an air tank and a front suspension are mounted on the air tank mounting portion  111  and the front suspension mounting portion  112 , respectively. The front suspension mounting portion  112  has an arch-shaped structure, and the air tank mounting portion  111  is formed in a hexahedral shape on an upper side of the front frame  110 . The front suspension may be an independent suspension. 
     The center frame  120  is formed in a structure in which lengthwise frames  121  are disposed to be spaced apart from each other in a lengthwise direction of a bare chassis, and widthwise frames  122  are disposed to be spaced apart from each other in a width direction of the bare chassis. 
     The lower end of the rear side of the front frame  110  and the front side of the center frame  120 , that is, a front side of the lengthwise frame  121 , are coupled by welding which is a first engagement method. 
     Since the connection between the front frame  100  and the center frame  120  is a connection between main members which are subjected to high stress, the front frame  110  and the center frame  120  are members which are coupled by welding so as to distribute stress. This welding is possible since the members do not need be separated in the field after the welding, e.g., for maintenance. Such a stress distribution due to the first engagement method is greater than a stress distribution due to a second engagement method which will be described below. 
     A conventional ultra-low-floor frame assembly for a compressed natural gas (CNG) engine has a structure in which a front frame is connected to a center frame using a longitudinal member. However, since it is impossible to integrally manufacture the front frame and the center frame and separate the front frame from the center frame, assembling work is impossible and a length of the center frame is not easily changed. 
     However, according to embodiments of the present disclosure, it is achieved a structure in which the front suspension is capable of being mounted with only the front frame  110  of embodiments of the present disclosure. In addition, such a structure is also applicable to 13M electric vehicles, 18M electric vehicles, hydrogen vehicles, and the like. 
     In addition, since a workspace is reduced and a work range is simplified, workability is more advantageous when the front suspension is assembled. 
     In addition, the conventional ultra-low-floor frame assembly for a CNG engine has a structure in which the center frame and a rear frame are connected to the longitudinal member using a connection member. However, since it is also impossible to integrally manufacture the center frame, the rear frame, and the longitudinal member and separate the center frame, the rear frame, and the longitudinal member from each other, assembling work is impossible and a length of the center frame is not easily changed. 
     However, the center frame  120  according to embodiments of the present disclosure has a structure which has an advantage of being easily changed in length. In addition, the center frame  120  is also applicable to 13M electric vehicles, 18M electric vehicles, hydrogen vehicles, and the like. 
     That is, in consideration of a stress measurement result which will be described below, it is possible to set a length of the center frame  120  by separating or extending the widthwise frame  122 . 
     Next,  FIGS. 3 to 5  illustrate a coupling relationship of the rear frame assembly. 
     Referring to  FIG. 3 , the first rear frame  130  and the second rear frame  140  may be coupled first. 
     The first rear frame  130  forms a lower portion, and an in-wheel motor and a low-floor rigid axle, as an example of a rear suspension, are mounted on the first rear frame  130 . To this end, the first rear frame  130  is formed of a lower frame  131  including an arch-shaped structure and an upper frame forming an upper portion, and the upper frame is formed in a shape in which first upper frames  132  and second upper frames  133  are formed in a grid shape. 
     That is, the upper frame is formed in a structure in which the first upper frames  132  are disposed to be spaced apart from each other in the lengthwise direction of the bare chassis, and the second upper frames  133  are disposed to be spaced apart from each other in the width direction of the bare chassis. 
     The second rear frame  140  is formed of grid-shaped low-floor frames  141  forming a lower surface and a plurality of vertical frames  142  vertically formed upward from the low-floor frames  141 . 
     Thus, as shown in  FIG. 4 , an upper end of the vertical frame  142  of the second rear frame  140  may be coupled to the first rear frame  130  and may be coupled to a lower end of the lower frame  131  of the first rear frame  130  or coupled to a point at which the first upper frame  132  and the second upper frame  133  intersect. 
     Since the connection between the first rear frame  130  and the second rear frame  140  is a connection between main members which are subjected to high stress, the first rear frame  130  and the second rear frame  140  are members that are coupled by welding, which is the first engagement method, so as to distribute stress. This connection is possible since the members need not to be separated in the field after the welding for maintenance. 
     Next, as shown in  FIG. 5 , the first battery carrier frame  150 , the second battery carrier frame  160 , and the air conditioner mounting frame  170  are coupled on the first rear frame  130  and the second rear frame  140  which are coupled. 
     The first battery carrier frame  150  and the second battery carrier frame  160  are formed of frames capable of accommodating components of a battery carrier, and an air conditioner is mounted on the air conditioner mounting frame  170 . 
     In addition, lower ends of the first battery carrier frame  150 , the second battery carrier frame  160 , and the air conditioner mounting frame  170  are coupled to an upper end of the first rear frame  130  through bolting which is the second engagement method, thereby complementing the rear frame assembly. Thereafter, the lower end of the front side of the rear frame assembly is welded to a rear end of the center frame  120 . 
     The coupling between the first battery carrier frame  150 , the second battery carrier frame  160 , the air conditioner mounting frame  170 , and the first rear frame  130  may require battery replacement work or maintenance of the air conditioner in the field, and the coupling is achieved through bolting, thereby facilitating coupling and disassembly. 
     In addition, positions of bolting and the number of bolts between the first rear frame  130 , the first battery carrier frame  150 , and the second battery carrier frame  160  may be selected on the basis of the stress analysis result. 
       FIG. 6  illustrates a state in which various components are mounted on the completed rear frame assembly, and  FIG. 7  illustrates a part of  FIG. 6 . 
     As shown in  FIG. 6 , a wheel motor axle  11  and a low-floor rigid axle  12  are mounted on the lower frame  131  of the first rear frame  130 , and a radiator (cooling system) and a battery carrier  40  are mounted on the second rear frame  140 . 
     In addition, an air tank  30  and the battery carrier  40  are mounted on the first battery carrier frame  150  and the second battery carrier frame  160 . 
     As described above, the battery carrier  40 , the low-floor rigid axle  12 , the radiator, and the air tank  30  may be assembled to the rear frame assembly, and thus the rear frame assembly may be extended and applied to other derivative vehicles. 
     Meanwhile, according to a related art, a radiator is mounted on a frame and a side panel, whereas according to embodiments of the present disclosure, the radiator is configured to be mounted on only the frame. 
     In addition, according to embodiments of the present disclosure, as shown in  FIG. 7 , a module upper side engagement portion  132 - 1  protruding downward is formed on the first upper frame  132  of the first rear frame  130  and bolt-coupled to a radiator upper side engagement portion  21  above a radiator  20 , and a module lower side engagement portion  141 - 1  protruding upward is formed on a low-floor frame  141  of the second rear frame  140  and bolt-coupled to a radiator lower side engagement portion  22  below the radiator  20 . 
     In particular, a bolt for connecting the module upper side engagement portion  132 - 1  to the radiator upper side engagement portion  21  is formed to pass through and couple the module upper side engagement portion  132 - 1  and the radiator upper side engagement portion  21  in the width direction of the bare chassis, and a bolt for connecting the module lower side engagement portion  141 - 1  to the radiator lower side engagement portion  22  is formed to pass through and couple the module lower side engagement portion  141 - 1  and the radiator lower side engagement portion  22  in a height direction of the bare chassis, thereby being capable of minimizing a vibration of a fan of the radiator  20 . 
     Meanwhile, the first battery carrier frame  150  and the second battery carrier frame  160  are bolt-coupled to the upper end of the first rear frame  130 . As shown in  FIG. 8 , in order to arrange the first battery carrier frame  150  and the second battery carrier frame  160  on an upper side of the first rear frame  130  or facilitate separation of the first battery carrier frame  150  and the second battery carrier frame  160  from the upper side of the first rear frame  130 , the first battery carrier frame  150  and the second battery carrier frame  160  are put into the upper side of the first rear frame  130  from a lateral direction thereof. 
     As shown in  FIG. 9 , a forklift mounting guide  151  is formed in a lower end portion of the first battery carrier frame  150  and a lower end portion of the second battery carrier frame  160  so as to allow transportation of the first battery carrier frame  150  and the second battery carrier frame  160  by a forklift. That is, the forklift mounting guide  151  capable of being supported on a clamp of the forklift is formed in the form of a plate in the lower end portions of the first battery carrier frame  150  and the second battery carrier frame  160  in the width direction. 
     As shown in  FIG. 8 , the first battery carrier frame  150  and the second battery carrier frame  160  are coupled to the upper end of the first rear frame  130  through bolting which is the second engagement method, thereby complementing the rear frame assembly. Thereafter, the lower end of the front side of the rear frame assembly is welded to the rear end of the center frame  120 . 
     In addition, guide pins  191 , stoppers  192 , and a plurality of guide plates  193  are configured to transport the first battery carrier frame  150  and the second battery carrier frame  160  on the first rear frame  130  and locate the first battery carrier frame  150  and the second battery carrier frame  160  at the correct positions on the first rear frame  130 . 
     A lengthwise direction of the guide plate  193  is parallel to a lengthwise direction of the second upper frame  133 , and the guide plate  193  is coupled on an upper portion of the second upper frame  133  to protrude upward from the second upper frame  133 . Thus, the first battery carrier frame  150  and a front end and a rear end of the second battery carrier frame  160  are guided to be disposed in the plurality of guide plates  193 . 
     In addition, the stoppers  192  are coupled to protrude upward on sides of two first upper frames  132  which are disposed on outer sides among the first upper frames  132 . When the first battery carrier frame  150  and the second battery carrier frame  160  are pushed into and transported, the stoppers  192  block the first battery carrier frame  150  and the second battery carrier frame  160  and aid the first rear frame  130  to not be deviated and disposed. 
     In addition, in order to support the stopper  192 , the guide pin  191  is formed to protrude from one side of the stopper  192  to be coupled thereto and to be seated on the first upper frame  132 , thereby preventing the stopper  192  from being pushed by the first battery carrier frame  150  and the second battery carrier frame  160  which are being transported. 
     As described above, when compared to the conventional bare chassis, since a weight of the running bare chassis assembly for the low-floor bus according to embodiments of the present disclosure may be reduced, stress concentration may be minimized, and results of stress analysis are shown in  FIGS. 11 and 12 . 
     That is, it can be confirmed that, since the stress is largely distributed due to the first engagement method, there is no stress in the vicinity of a portion in which the center frame  120  is coupled to the front frame  110  and the vicinity of a portion in which the center frame  120  is coupled to the rear frame assembly. Thus, the corresponding portions may be determined as parting lines. 
     In determination of parting lines of the front frame  110 , the center frame  120 , and the rear frame assembly, it should be considered whether a response is possible without a change when a derivative vehicle is deployed, and it should select a module range in which system assembly is prior to a parting line, respectively and select a portion receiving minimum stress as the parting line. 
     Through such stress analysis results, it can be seen that the running bare chassis assembly for a low-floor bus according to embodiments of the present disclosure receives less stress when compared to the conventional chassis. 
     Thus, in the case of the conventional battery carrier frame, a thickness of a cross section ranges from 5.7 mm or 3.2 mm according to portions, whereas a thickness of a cross section of the battery carrier frame according to embodiments of the present disclosure may be changed to 2.3 mm. 
     In addition, in the case of a lower frame of a conventional rear frame, a thickness of a cross section is 5.7 mm, whereas a thickness of a cross section of the lower frame  131  of the first rear frame  130  according to embodiments of the present disclosure may be changed to 3.2 mm. 
     In addition, in the case of an upper frame of the conventional rear frame, a thickness of a cross section is 3.2 mm, whereas a thickness of a cross section of the upper frame of the first rear frame  130  according to embodiments of the present disclosure may be changed to 2.3 mm. 
     In accordance with a structure of a running bare chassis for a low-floor double-decker electric bus according to embodiments of the present disclosure, since an underbody platform is assembled with five modules to manufacture a body module structure of a bare chassis and then electric bus electronic components and a system are assembled, workability can be significantly improved and a weight can be reduced. 
     In addition, based the improved workability and the reduced weight, the running bare chassis can be additionally applied to various eco-friendly vehicle bare chassis models. 
     While embodiments of the present disclosure have been described with reference to the accompanying drawings, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present disclosure without being limited to the exemplary embodiments disclosed herein. Accordingly, it should be noted that such alternations or modifications fall within the claims of the present disclosure, and the scope of the present disclosure should be construed on the basis of the appended claims.