Patent Publication Number: US-2020290663-A1

Title: Steering apparatus for a vehicle

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. JP2019-47308 filed on Mar. 14, 2019, the content of which is hereby incorporated by reference in its entirety into this application. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a steering apparatus for a vehicle such as an automobile. 
     2. Description of the Related Art 
     As one of steering apparatuses for vehicles such as automobiles, a steering apparatus has been known that is provided with a steering link mechanism including left and right swing arm members, left and right tie rods connecting left and right wheels and arm portions of the left and right swing arm members, respectively and a relay rod connecting the two arm portions. Steering input provided to a steering input transmission system by a driver is converted by a motion conversion device and transmitted to one of the swing arm members, and the left and right wheels are steered by means of the swing arm member being swung. This type of steering apparatus is suitable for a large vehicle such as a bus. 
     For example, Japanese Utility Model Application Laid-open Publication No. S60-150162 discloses a steering apparatus that has the above-described steering link mechanism and a rack-and-pinion device as a motion conversion device that functions as a hydraulic power steering device and extends in a longitudinal direction of a vehicle. According to this type of steering apparatus, it is possible to assist a driver&#39;s steering operation and to reduce a power transmission loss as compared to a case where a motion conversion device is a recirculating ball screw device. 
     However, the rack-and-pinion device includes a reciprocating rack bar, and the rack bar is supported by rack bushes at both ends, so that it must be long as described later in detail. Therefore, the conventional steering apparatus described in the above publication has poor mountability to a vehicle and poor degree of freedom in vehicle design as compared to where a motion conversion device is, for example, a recirculating ball screw device. 
     SUMMARY 
     The present disclosure provides a steering apparatus which has the steering link mechanism described above and is improved to enhance the mountability on a vehicle and the degree of freedom in vehicle design as compared with such a conventional steering apparatus as described in the above publication. 
     According to the present disclosure, a steering apparatus for a vehicle is provided which comprises left and right swing arm members each having an arm portion that swings about an axis extending in the vertical direction, a relay rod pivotally connected to the arm portions of the left and right swing arm members at both ends, left and one of right tie rods respectively pivotally connected to left and right steered wheels, respectively, at outer ends and the relay rods and the arm portions of the left and right swing arm members at inner ends, a rack-and-pinion device in which one end of a rack bar is connected to the arm portion of one of the swing arm members so as to swing the one of the swing arm members about the corresponding axis, and a steering input transmission system that transmits a steering input to a pinion shaft of the rack-and-pinion device, 
     The rack-and-pinion device includes a pinion that is integral with the pinion shaft and meshes with rack teeth of the rack bar, a housing that accommodates an area where the rack teeth of the rack bar are provided, and a pair of pressing devices disposed on both sides of the pinion along a longitudinal direction of the rack bar and pressing the rack bar against the pinion. 
     According to the above configuration, the rack-and-pinion device includes a pair of pressing devices disposed on both sides of the pinion along a longitudinal direction of the rack bar and pressing the rack bar against the pinion. Thus, the rack bar can be supported by the pinion and the pair of pressing devices so as to be able to reciprocate in the longitudinal direction, so that the rack bar does not have to be supported by a rack bush (for example, an annular resin member) at a portion outside the area where the rack teeth are provided. Therefore, the rack-and-pinion device can be made smaller and the degree of freedom of arrangement can be improved as compared with a structure in which outer portions on both sides of an area provided with rack teeth are supported by two rack bushes, so that the mountability to a vehicle and the degree of freedom in designing the vehicle can be improved as compared with a conventional steering apparatus. 
     In one aspect of the present disclosure, the left and right swing arm members each have first and second arm portions extending in directions different from each other with respect to the axis; the left and right tie rods are pivotally connected at their inner ends to the first arm portions of the left and right swing arm members, respectively; one end of the rack bar is pivotally connected to the second arm portion of the one of the swing arm members; and the relay rod is pivotally connected at both ends to one of the first and second arms of the left and right swing arm members. 
     According to the above aspect, the left and right swing arm members have the first arm portions and second arm portions extending in directions different from each other with respect to the axes. The left and right tie rods are pivotally connected at inner ends to the first arm portions of the left and right swing arm members, respectively. One end of the rack bar is pivotally connected to the second arm portion of one of the swing, arm members, and the relay rod is pivotally connected at both ends to one of the first and second arms of the left and right swing arm members. 
     Therefore, the degree of freedom of pivotal attachment of the rack bar and the relay rod can be increased as compared to where each of the left and right swing arm members has only one arm portion. This also improves mountability of the steering apparatus on a vehicle and the degree of freedom in designing the vehicle. in particular, the extension direction of the rack-and-pinion device can be freely set by setting the extension direction of the second arm portions with respect to the first arm portions. 
     In another aspect of the present disclosure, the rack bar is supported reciprocably in the longitudinal direction by the pinion and the pair of pressing devices, and no bush device is provided between the rack bar and the housing. 
     According to the above aspect, the rack bar can be supported reciprocably in the longitudinal direction by the pinion and the pair of pressing devices, and hence, there is no need to provide any bush device between the rack bar and the housing. Therefore, the length of the rack bar and the housing can be reduced, and the size of the rack-and-pinion device can be reduced. 
     In another aspect of the present disclosure, the rack bar extends out from the housing on the side of one end and does not extend out from the housing on the side of the other end. 
     According to the above aspect, the rack bar extends out from the housing at one end, but does not extend out from the housing at the other end, so that the housing may be dosed at the other end. Therefore, since a member for sealing between the rack bar and the housing is unnecessary on the other end side, the number of parts of the rack-and-pinion device can be reduced and the structure thereof can be simplified as compared to where the rack bar extends out from the housing also on the other end side. 
     Further, in another aspect of the present disclosure, the pair of pressing devices are configured to press the rack bar against the pinion along center lines extending perpendicularly to the longitudinal direction of the rack bar on a side opposite to the pinion with respect to the rack bar. 
     According to the above aspect, the rack bar is pressed by the pair of pressing devices against the pinion along the center lines extending perpendicularly to the longitudinal direction of the rack bar on the side opposite to the pinion with respect to the rack bar. Therefore, the rack bar can be satisfactorily pressed against the pinion to maintain their good meshing state, and the rack bar can be supported by the pinion and the pair of pressing devices so as to stably reciprocate in the longitudinal direction. 
     Further, in another aspect of the present disclosure, the center lines of the pair of pressing devices are equidistantly spaced apart from a meshing portion between the rack teeth of the rack bar and the pinion. 
     According to the above aspect, the pair of pressing devices press the rack bar against the pinion at positions equidistantly spaced apart from the meshing portion between the rack teeth of the rack bar and the pinion. Therefore, as compared to where the center lines of the pair of pressing devices are spaced apart from each other by different distances from the meshing portion between the rack teeth of the rack bar and the pinion, it is possible to reduce a possibility that a moment around the meshing portion acts on the rack bar due to the pressing by the pair of pressing devices. 
     Other objects, other features and attendant advantages of the present disclosure will be readily understood from the description of the embodiments of the present disclosure described with reference to the following drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic plan view showing an embodiment of a steering apparatus according to the present disclosure applied to a right-hand traffic vehicle in a straight traveling state of the vehicle; 
         FIG. 2  is an enlarged sectional view showing a rack-and-pinion device in the embodiment shown in  FIG. 1 ; 
         FIG. 3  is an enlarged sectional view showing one pressing device by cutting the rack-and-pinion device along line III-III in  FIG. 2 ; 
         FIG. 4  is an illustrative sectional view showing a rack-and-pinion device in which a rack bar is supported by one end bush and extends through a housing. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure will now be described with respect to an embodiment in detail with reference to the accompanying drawings. 
     Embodiment 
     In  FIG. 1 , reference numeral  10  indicates a steering apparatus according to the embodiment of the present disclosure. The electric steering apparatus  10  is applied to a so-called left-hand drive vehicle  12 , that is, a right-hand traffic vehicle, and is configured to steer left and right front wheels  14 L and  14 R that are steered wheels of the vehicle  12 . The steering device  10  includes left and right swing arm members  16 L and  16 R, left and right tie rods  18 L and  18 R, a relay rod  20 , a rack-and-pinion device  22 , and a steering input transmission system  24 . 
     The swing arm members  16 L and  16 R are disposed at positions spaced apart in the lateral direction of the vehicle  12 , and are supported by a vehicle body  30  of the vehicle  12  so as to be able to swing about vertical axes  28 L and  28 R at boss portions  26 L and  26 R, respectively. In the illustrated embodiment, the swing arm members  16 L and  16 R have first arm portions  32 L and  32 R and second arm portions  34 L and  34 R, respectively. The first arm portions  32 L and  32 R respectively extend from the boss portions  26 L and  26 R substantially to the rear of the vehicle  12  when the vehicle is in a straight traveling state, and the second arm portions  34 L and  34 R respectively extend from the boss portions  26 L and  26 R in the inboard direction of the vehicle across the longitudinal direction of the vehicle. 
     The relay rod  20  extends in the lateral direction of the vehicle  12 , and is pivotally connected at both ends to the first arm portions  32 L,  32 R of the left and right swing arm members  16 L,  16 R by joints  36 L,  36 R, respectively. The left and right tie rods  18 L,  18 R are pivotally connected at theft outer ends to knuckle arms (not shown) of the left and right front wheels  14 L,  14 R by joints  38 L,  38 R, respectively, and are pivotally connected at their inner ends to neighbors of the corresponding ends of the relay rod  20  by joints  40 L,  40 R, respectively. Therefore, in the illustrated embodiment, the inner ends of the left and right tie rods  18 L,  18 R are pivotally connected to the first arm portions  32 L,  32 R of the left and right swing arm members  16 L,  16 R, respectively via the relay rod  20 . Notably, the inner ends of the left and right tie rods  18 L,  18 R may be pivotally connected directly to the first arm portions  32 L,  32 R, respectively. 
     The rack-and-pinion device  22  is disposed on the left side of the vehicle  12  and extends substantially in the longitudinal direction of the vehicle  12 . As shown in  FIG. 2 , the rack-and-pinion device  22  includes a housing  42  and a rack bar  44  extending along an axis  43 , and the rack bar  44  extends out from the housing  42  toward the rear of the vehicle on the side of the rear end. The housing  42  is closed at the front end, and the rack bar  44  does not extend out toward the front of the vehicle from the housing  42  on the side of the front end. 
     One end of a connection link  48  is pivotally connected to the rear end of the rack bar  44  by a joint  46 , and the other end of the connection link  48  is pivotally connected to the second arm  34 L of the left swing arm member  16 L by a joint  50 , Accordingly, the rear end of the rack bar  44  is connected to the second arm portion  34 L of the left swing arm member  16 L via the connection link  48  so as to swing the swing arm member  16 L about the corresponding axis  28 L. Therefore, a reciprocating motion of the rack bar  44  is converted into a swing motion about the axis  28 L by the connection link  48  and transmitted to the swing arm member  16 L. Conversely, the swing motion of the swing arm member  16 L about the axis  28 L is converted into a reciprocating motion by the connection link  48  and transmitted to the rack bar  44 . 
     Although joints such as the joint  36 L are not shown in detail in  FIG. 1 , any joint known in the art can be used as long as the corresponding two members can be relatively pivotally connected. For example, a ball joint, a pillow ball, a combination of a pivot and a bush may be used, 
     Although not shown in detail in  FIG. 1 , the steering input transmission system  24  includes a known steering shaft  52  including an upper steering shaft, a lower steering shaft, universal joints, and the like. A steering wheel  54  operated by a driver is connected to an upper end of the steering shaft  52 , and a lower end of the steering shaft  52  is connected to a pinion shaft  56  of the rack-and-pinion device  22 . Thus, the steering input transmission system  24  transmits a steering input given to the steering wheel  54  by the driver to the pinion shaft  56 . 
     In the illustrated embodiment, a worm wheel  58  is provided integrally with the pinion shaft  56 , and a worm  60  is screwed to the worm wheel  58 . The worm  60  is connected to an output shaft of an electric motor  62 . Torque of the electric motor  62  is transmitted to the pinion shaft  56  by the worm  60  and the worm wheel  58  as steering assist torque. Therefore, the electric motor  62  functions as an electric steering assist force applying device  64  that applies steering assist torque to the rack-and-pinion device  22  in cooperation with the worm wheel  58  and the worm  60 . 
     As shown in  FIG. 2 , the rack-and-pinion device  22  further includes a pinion  66  and a pair of pressing devices  68 . The pinion  66  is formed integrally with the pinion shaft  56  via a torsion bar and meshes with rack teeth  70  of the rack bar  44 . The housing  42  accommodates a main portion of the rack bar  44  including an area where the rack teeth  70  are provided. The pair of pressing devices  6 $ are arranged on both sides of the pinion  66  along the longitudinal direction of the rack bar  44 , and press the rack bar  44  against the pinion  66 . 
     As shown in  FIG. 3 , each pressing device  68  includes a rack guide  72  and a compression coil spring  74  arranged on the side opposite to the pinion  66  with respect to the rack bar  44 . Each rack guide  72  is supported by the housing  42  so as to reciprocate along a center line  76  extending perpendicular to the axis  43  of the rack bar  44 . Each compression coil spring  74  presses the rack guide  72  against the rack bar  44  along the center line  76 . Thus, the rack bar  44  is supported by the pinion  66  and the pair of pressing devices  68  so as to be able to reciprocate in the longitudinal direction, and no rack bush or the like is provided between the rack bar  44  and the housing  42 . 
     In particular, in the illustrated embodiment, as shown in  FIG. 2 , the to center lines  76  of the pair of pressing devices  68  are spaced apart from a center P of a meshing portion  78  between the rack teeth  70  of the rack bar  44  and the pinion  66  by equal distances L along the axis  43 . Notably, the distances L between the center ones  76  of the pair of pressing devices  68  and the center P may be different from each other. [ 0035 ] 
     As shown in FIG,  1 , the steering assist force applying device  64  further includes an electronic control unit  82 , The steering input transmission system  24  is provided with a torque sensor  84  for detecting steering torque Ts generated in the steering input transmission system. The electronic control unit $ 2  controls the steering assist torque by controlling output torque of the electric motor  62  based on steering torque Ts detected by the torque sensor  84  and a vehicle speed V detected by a vehicle speed sensor  86 . 
     As can be understood from the above description, according to the embodiment, the rack-and-pinion device  22  includes a pair of pressing devices  68  that are disposed on both sides of the pinion  66  along the longitudinal direction of the rack bar  44  and press the rack bar against the pinion, The rack bar  44  is supported by the pinion  66  and the pair of pressing devices  68  so as to be able to reciprocate in the longitudinal direction, and no bush device is provided between the rack bar  44  and the housing  42 . 
     Thus, the rack and pinion device  22  can be reduced in size and weight, and the degree of freedom of arrangement can be improved, as compared, for example, with a structure in which the rack bar is supported by two bush devices on both sides of an area where rack teeth are provided. Therefore, as compared with a conventional steering apparatus having the above--described steering link mechanism, the mountability of the steering apparatus on a vehicle and the degree of freedom in designing a vehicle can be improved, and a weight of the steering apparatus can be reduced. 
     Further, instead of the conventional general structure in which a rack bar is supported by two bush devices, a structure in which the rack bar  44  is supported by one bush device  41  can be considered as shown in  FIG. 4 . In  FIG. 4 , a double-headed arrow S indicates a rack stroke. However, in this structure, at least a supported area  44 A having a length corresponding to the rack stroke S must be provided on the rack bar  44 , and, accordingly, a total length of the rack bar  44  and the housing  42  must be longer, so that the steering apparatus cannot be reduced in size and weight. 
     The left and right swing arm members  16 L,  16 R have the first arm portions  32 L,  32 R and second arm portions  34 L,  34 R extending in directions different from each other with respect to the axes  28 L,  28 R, respectively. The left and right tie rods  181 .,  18 R are pivotally connected at inner ends to the first arm portions  32 L,  32 R of the left and right swing arm members  16 L,  16 R, respectively, via the relay rod  20 . The rear end of the rack bar  44  is pivotally connected to the second arm portion  34 L of the left swing arm member  32 L, and the relay rod  20  is pivotally connected at both ends to the first arm portions  32 L,  32 R of the left and right swing arm members. 
     Therefore, the degree of freedom of pivotal attachment of the rack bar  44  and the relay rod  20  can be increased as compared to where each of the left and right swing arm members  16 L and  16 R has only one arm portion. This also improves mountability of the electric power steering apparatus on a vehicle and the degree of freedom in designing the vehicle. In particular, the extension direction of the rack-and-pinion device  22  can be freely set by setting the extension direction of the second arm portions  34 L,  34 R with respect to the first arm portions  32 L,  32 R, respectively. 
     The rack bar  44  extends out from the housing  42  on the rear end side, but does not extend out from the housing on the front end side, and the housing is closed on the front end side. Therefore, a member for sealing between the rack bar  44  and the housing  42  on the front end side is unnecessary, so that the number of parts of the rack and pinion device  22  can be reduced and the structure can be simplified as compared to where the rack bar also extends out from the housing on the front end side. 
     The rack bar  44  is pressed against the pinion by the pair of pressing devices  68  on both sides of the pinion  66  along the center lines  76  extending perpendicular to the longitudinal direction of the rack bar. Therefore, the rack bar can be satisfactorily pressed against the pinion to maintain their good meshing state, and the rack bar can be stably reciprocated in the longitudinal direction by the pinion and the pair of pressing devices. 
     Further, the pair of pressing devices  68  presses the rack bar against the pinion at the positions spaced apart by an equal distance L from the meshing portion  78  between the rack teeth  70  of the rack bar  44  and the pinion  66 . Therefore, as compared to where the center lines of the pair of pressing devices are spaced apart by different distances from the meshing portion between the rack teeth of the rack bar and the pinion, it is possible to reduce the possibility that a moment around the meshing portion acts on the rack bar  44  due to the pressing by the pair of pressing devices. 
     Although the present disclosure has been described in detail with reference to a specific embodiment, it will be apparent to those skilled in the art that the present disclosure is not limited to the above-described embodiment, and various other embodiments are possible within the scope of the present disclosure. 
     For example, in the above-described embodiment, the swing arm members  16 L and  16 R have the first arm portions  32 L and  32 R and the second arm portions  34 L and  34 R, respectively, but each may have one arm portion. Further, when the vehicle  12  is in the straight traveling state, the first arm portions  32 L and  32 R extend substantially rearward from the boss portions  26 L and  26 R, respectively, and the second arm portions  34 L and  34 R extend from the bosses  26 L,  26 R, respectively, in the vehicle inboard direction across the longitudinal direction of the vehicle. However, the first arm portions  32 L,  32 R may extend substantially forward of the vehicle, and the second arm portions  34 L,  34 R may extend in a direction different from the illustrated direction including the outboard direction of the vehicle. Thus, the rack-and-pinion device  22  may extend in a direction other than the longitudinal direction of the vehicle. 
     In the above-described embodiment, the inner ends of the left and right tie rods  18 L,  18 R are pivotally connected to the relay rod  20  near corresponding ends, but may be pivotally connected to the first arm portions  32 L,  32 R of the swing arm members  16 L,  16 R, respectively. In that case, the relay rod  20  may be pivotally connected to the second arm portions  34 L,  34 R of the swing arm members  16 L,  16 R, respectively. 
     In the above-described embodiment, the steering apparatus  10  is applied to a so-called left-hand drive vehicle, that is, a right-hand traffic vehicle  12 , but may be applied to a so-called right-hand drive vehicle, that is, a left-hand traffic vehicle. In that case, the rack-and-pinion device  22  is disposed on the right side of the vehicle. 
     In the above-described embodiment, the steering apparatus  10  is configured to steer the left and right front wheels  14 L and  14 R which are the steered wheels of the vehicle  12 , but may be configured to steer the left and right rear wheels. 
     Further, in the above-described embodiment, although the electric steering assist force applying device $ 4  that applies steering assist torque to the pinion shaft  56  of the rack-and-pinion device  22  is provided, steering assist torque may be applied to the steering shaft. In addition, the electric steering assist force applying device  64  may be omitted, and the steering apparatus of the present disclosure may be configured as a steering apparatus having no power steering function,