Patent Publication Number: US-2023150326-A1

Title: Suspension

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority from Japanese Patent Application No. 2021-187147 filed on Nov. 17, 2021, the entire contents of which are hereby incorporated by reference. 
     BACKGROUND 
     The disclosure relates to a suspension for a vehicle such as an automobile. 
     Vehicles such as automobiles are provided with suspensions. A suspension includes a hub bearing housing and suspension links. In the following, the hub bearing housing is simply referred to as a housing. The housing rotatably supports a wheel. The housing is strokably coupled to a vehicle body by the suspension links. 
     An end of the suspension link, i.e., a node, is swingably coupled to the housing or the vehicle body, with an elastic member such as a cylindrical rubber bush in between. 
     As an existing technique related to a suspension including an elastic member, Japanese Unexamined Patent Application Publication (JP-A) No. 2000-118220 describes an independent suspension including a trailing arm. On a front end of the trailing arm, a cylindrical rubber bush is provided. The rubber bush has a pair of voids. The voids are disposed, with a rearwardly inclined angle with respect to a vehicle longitudinal direction. This leads to a more comfortable ride and enhanced operation stability. 
     Japanese Utility Model Gazette (JP-Y2) No. H05-44162 describes a technique in which a front end of a swing arm is attached to a vehicle body, with a rubber bush in between. The swing arm protrudes forward from a rear wheel support to which a rear wheel is attached. 
     The rubber bush has a front void and a rear void. In the rubber bush, an upper metal plate and a lower metal plate are embedded. This causes a difference between longitudinal and vertical elastic support characteristics of the rubber bush. 
     SUMMARY 
     An aspect of the disclosure provides a suspension including a housing, links, a radius arm, and a radius arm bush. To the housing, a hub bearing is attached. The hub bearing rotatably supports a rear wheel of a vehicle. The links each include both ends spaced apart in a vehicle widthwise direction. The links each couple the housing to a vehicle body of the vehicle. The radius arm is unitized with the housing and protrudes from the housing toward front of the vehicle. The radius arm bush is provided on a front end of the radius arm. The radius arm bush couples the radius arm to the vehicle body, with an elastic body in between. The radius arm bush is disposed vehicle-widthwise inwardly of a wheel center contact point of the rear wheel. The radius arm bush has higher rigidity with respect to turn of the radius arm with respect to the vehicle body in a direction in which an underside of the radius arm is displaced vehicle-widthwise outwardly from an upside of the radius arm, than rigidity with respect to turn of the radius arm with respect to the vehicle body in a direction in which the underside of the radius arm is displaced vehicle-widthwise inwardly from the upside of the radius arm. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments and, together with the specification, serve to explain the principles of the disclosure. 
         FIG.  1    is a schematic plan view of a suspension according to an embodiment of the disclosure, as viewed from above. 
         FIG.  2    is a schematic side view of the suspension according to the embodiment, as viewed from sideways of a vehicle. 
         FIG.  3    is a schematic front view of the suspension according to the embodiment, as viewed from forward of the vehicle. 
         FIG.  4    is a cross-sectional view of a radius arm bush provided in the suspension according to the embodiment. 
         FIG.  5    is a cross-sectional view taken along the line V-V in  FIG.  4   , looking in the direction of the appended arrows. 
     
    
    
     DETAILED DESCRIPTION 
     Researches have been made to enhance operation stability by means of characteristics or arrangement of components of a suspension. Most of such researches have focused on a steady state after settlement of a response to a steering operation at an initial stage of cornering. 
     However, in terms of evaluation of vehicle controllability when a driver actually drives a vehicle, it is significant to notice a steering response in a transient response state before the steady state. 
     Let us focus on behavior of a rear suspension at a start of cornering. First, the behavior of the rear suspension is influenced by vertical force steering, i.e., a toe change corresponding to variations in a vertical load on a tire. In this region, a shock absorber sticks because of friction, and does not make any stroke. 
     For example, in a known radius arm suspension, a front end of a radius arm is attached to a vehicle body, with a radius arm bush in between. The radius arm is unitized with a housing and protrudes forward from the housing. 
     A radius arm suspension often has geometry in which a radius arm bush is disposed vehicle-widthwise inwardly of a wheel center contact point of a rear wheel with a road surface. 
     In such geometry, as a vertical load on a tire increases, the radius arm and the whole housing makes a torsional turn in a direction in which an underside of the radius arm is displaced vehicle-widthwise outwardly from an upside of the radius arm. 
     In this case, the rear wheel may sometimes exhibit the following behavior. First, the rear wheel tends to toe out because of vertical force steering, and thereafter, the rear wheel returns to a toe-in direction by roll steering, i.e., a toe change in accordance with a suspension stroke. 
     As described, there is a time delay between a start of cornering and the time when the toe change in the toe-in direction occurs in the rear wheel on outer side of the cornering. A long time delay may cause lowered vehicle controllability. 
     It is desirable to provide a suspension that makes it possible to enhance responsiveness at an initial stage of cornering. 
     In the following, some example embodiments of the disclosure are described in detail with reference to the accompanying drawings. Note that the following description is directed to illustrative examples of the disclosure and not to be construed as limiting to the disclosure. Factors including, without limitation, numerical values, shapes, materials, components, positions of the components, and how the components are coupled to each other are illustrative only and not to be construed as limiting to the disclosure. Further, elements in the following example embodiments which are not recited in a most-generic independent claim of the disclosure are optional and may be provided on an as-needed basis. The drawings are schematic and are not intended to be drawn to scale. Throughout the present specification and the drawings, elements having substantially the same function and configuration are denoted with the same reference numerals to avoid any redundant description. In addition, elements that are not directly related to any embodiment of the disclosure are unillustrated in the drawings. 
     A suspension according to one embodiment of the disclosure may be, for example, a rear suspension that supports a rear wheel of an automobile such as a passenger car. 
       FIG.  1    is a schematic plan view of the suspension of the embodiment, as viewed from above. 
       FIG.  2    is a schematic side view of the suspension of the embodiment, as viewed from sideways of a vehicle. 
       FIG.  3    is a schematic front view of the suspension of the embodiment, as viewed from forward of the vehicle. 
     The suspension  1  supports a rear wheel RW. The suspension  1  may include, for example, a rear subframe  10 , a housing  20 , a radius arm  30 , a front lateral link  40 , a rear lateral link  50 , an upper link  60 , a shock absorber  70 , and a spring  80 . 
     The rear subframe  10  is attached to an underside of a rear part of an unillustrated vehicle body. The rear subframe  10  is a member that serves as a base of the suspension  1 . 
     The rear subframe  10  may include, for example, a front member  11 , a rear member  12 , a side member  13 , a front bush  14 , a rear bush  15 , a front lateral link bracket  16 , and an upper link bracket  17 . 
     The front member  11  is a beam-shaped member provided in a front part of the rear subframe  10  and extended in the vehicle widthwise direction. 
     The rear member  12  is a beam-shaped member provided in a rear part of the rear subframe  10  and extended in the vehicle widthwise direction. 
     The front member  11  and the rear member  12  are spaced apart from each other in a longitudinal direction. 
     On both ends of the front member  11  and the rear member  12  in the vehicle widthwise direction, cylindrical portions are provided. In the cylindrical portions, the front bush  14  and the rear bush  15  are press-fitted. 
     The side member  13  is a beam-shaped member extended in the vehicle longitudinal direction. The side member  13  couples a rear portion of a vehicle-widthwise middle part of the front member  11  to a front portion of a vehicle-widthwise middle part of the rear member  12 . 
     The side member  13  is provided in a pair, in spaced relation to each other in the vehicle widthwise direction. In  FIG.  1   , one of the side members  13  is illustrated. 
     The front member  11 , the rear member  12 , and the side member  13  include, for example, panels of press-molded steel plates assembled and welded together. Thus, the front member  11 , the rear member  12 , and the side member  13  have a closed cross-section as taken on a plane orthogonal to the longitudinal direction. 
     The front bush  14  and the rear bush  15  are members that couple the rear subframe  10  to the unillustrated vehicle body, with an elastic body such as rubber in between. The elastic body has an anti-vibration effect. 
     The front bush  14  is provided on both ends of the front member  11  in the vehicle widthwise direction. 
     The rear bush  15  is provided on both ends of the rear member  12  in the vehicle widthwise direction. 
     The front bush  14  and the rear bush  15  may each include, for example, a cylindrical rubber bush. The cylindrical rubber bush is disposed with its central axis aligned with the vertical direction. 
     The front bush  14  and the rear bush  15  may each include, for example, an inner cylinder and an outer cylinder disposed in a concentric double-tube shape, with rubber filling space therebetween. The rubber is vulcanization-bonded to between the inner cylinder and the outer cylinder. 
     The outer cylinders of the front bush  14  and the rear bush  15  are press-fitted into the cylindrical portions on both ends of the front member  11  and the rear member  12 . 
     The inner cylinders of the front bush  14  and the rear bush  15  are fastened to the vehicle body, by mechanical fastening, e.g., with the use of bolts. 
     The front lateral link bracket  16  is a base to which a front inner bush  42  of the front lateral link  40  is attached. 
     The front lateral link bracket  16  protrudes vehicle-widthwise outwardly from an underside of a longitudinally middle part of the side member  13 . 
     The upper link bracket  17  is a base to which an upper inner bush  62  of the upper link  60  is attached. 
     The upper link bracket  17  protrudes vehicle-widthwise outwardly from an upside of the longitudinally middle part of the side member  13 . 
     Strictly, the rear subframe  10  exhibits a minute displacement with respect to the vehicle body because of elastic deformation of the front bush  14  and the rear bush  15 . However, in the specification and the claims, the rear subframe  10  is considered as a part of the vehicle body, i.e., a bracket where components such as links of the suspension  1  are attached to the vehicle body. 
     The housing  20  is a hub knuckle, i.e., a member that houses and holds an unillustrated hub bearing. The hub bearing rotatably supports an unillustrated hub to which the rear wheel RW is fastened. 
     The housing  20  is strokably supported in a direction in which the rear wheel RW moves vertically with respect to the vehicle body, by the radius arm  30 , the front lateral link  40 , the rear lateral link  50 , and the upper link  60  described below. 
     The radius arm  30  is an arm-shaped member unitized with the housing  20 . The radius arm  30  protrudes from a front part of the housing  20  toward front of the vehicle. 
     On a front end of the radius arm  30 , a radius arm bush  31  is provided. 
     The radius arm bush  31  may include, for example, an elastic bush such as a cylindrical rubber bush having the central axis aligned with the vehicle widthwise direction. 
     The radius arm bush  31  includes an inner cylinder  311  and an outer cylinder  312 . The outer cylinder  312  is fixed to the front end of the radius arm  30 . The inner cylinder  311  is fastened to the unillustrated vehicle body at a position forward of a front edge of the rear wheel RW. 
     The radius arm  30  and the housing  20  are swingable with respect to the vehicle body about the central axis of the radius arm bush  31 . 
     As illustrated in  FIG.  2   , in a steady state of the vehicle, or a so-called 1G state, the center C 2  of the radius arm bush  31  is disposed at a higher position than the rotatory center of the rear wheel RW. 
     As illustrated in  FIGS.  1  and  3   , the center C 2  of the radius arm bush  31  is disposed vehicle-widthwise inwardly of a wheel center contact point C 1  of the rear wheel RW with an unillustrated road surface. In the following, the wheel center contact point C 1  with the road surface is also simply called the wheel center contact point C 1 . 
     In the specification and the claims, the center of the radius arm bush  31  means the center of rigidity, i.e., the rigidity center. With the configuration of the radius arm bush  31  of this embodiment, the rigidity center coincides with the axial center of the inner cylinder  311  and the outer cylinder  312  of the radius arm bush  31 . 
     The configuration of the radius arm bush  31  is described in detail below. 
     The front lateral link  40  is a link, or a suspension arm, extended in the vehicle widthwise direction between an underside of the front part of the housing  20  and the front lateral link bracket  16  of the rear subframe  10 . 
     In the specification and the claims, the term “extended in the vehicle widthwise direction” is not limited to a case where a longitudinal direction of each link strictly coincides with the vehicle widthwise direction, but includes a case where the longitudinal direction of each link is inclined to the vehicle widthwise direction. 
     The front lateral link  40  is disposed, with both ends spaced apart in the vehicle widthwise direction. 
     An end of the front lateral link  40  on side on which the housing  20  is disposed is swingably coupled to the underside of the front part of the housing  20 , with a front outer bush  41  in between. 
     An end of the front lateral link  40  on side on which the rear subframe  10  is disposed is swingably coupled to the front lateral link bracket  16 , with the front inner bush  42  in between. 
     The front lateral link  40  is disposed forwardly of the rotatory center of the rear wheel RW. 
     The rear lateral link  50  is a link extended in the vehicle widthwise direction between an underside of a rear part of the housing  20  and an unillustrated bracket provided in an underside of the rear member  12  of the rear subframe  10 . 
     The rear lateral link  50  is disposed, with both ends spaced apart in the vehicle widthwise direction. 
     An end of the rear lateral link  50  on the side on which the housing  20  is disposed is swingably coupled to the underside of the rear part of the housing  20 , with a rear outer bush  51  in between. 
     An end of the rear lateral link  50  on the side on which the rear subframe  10  is disposed is swingably coupled to the underside of the rear member  12 , with a rear inner bush  52  in between. 
     The rear lateral link  50  is disposed rearwardly of the rotatory center of the rear wheel RW. 
     The front lateral link  40  and the rear lateral link  50  are configured to perform, for example, positioning of a toe angle of the rear wheel RW. 
     The rear lateral link  50  is lengthened with respect to the front lateral link  40 . This imparts a roll steering characteristic to the suspension  1 . The roll steering characteristic means that the rear wheel RW is steered in a toe-in direction during a bumpwise stroke of the suspension  1 , or a shrinkwise stroke. 
     The upper link  60  is a link extended in the vehicle widthwise direction between an upside of the housing  20  and the upper link bracket  17  of the rear subframe  10 . 
     The upper link  60  is disposed, with both ends spaced apart in the vehicle widthwise direction. 
     An end of the upper link  60  on the side on which the housing  20  is disposed is swingably coupled to the upside of the housing  20 , with an upper outer bush  61  in between. 
     An end of the upper link  60  on the side on which the rear subframe  10  is disposed is swingably coupled to the upper link bracket  17 , with the upper inner bush  62  in between. 
     The upper link  60  is disposed at a position in the vehicle longitudinal direction upward of the rotatory center of the rear wheel RW. 
     The upper link  60  is configured to perform, for example, positioning of a camber angle of the rear wheel RW in cooperation with the front lateral link  40  and the rear lateral link  50 . 
     Each of the outer bushes and the inner bushes described above may include, for example, an elastic bush such as a cylindrical rubber bush having a central axis aligned with the vehicle longitudinal direction. 
     For example, each of the outer bushes and the inner bushes may include an outer cylinder and an inner cylinder, with an elastic material such as rubber filing space therebetween. The elastic material such as rubber is vulcanization-bonded to between an inner circumferential surface of the outer cylinder and an outer circumferential surface of the inner cylinder. The outer cylinder is press-fitted into a cylindrical portion provided in each link. The inner cylinder is fastened to the rear subframe  10  or the housing  20 . 
     The shock absorber  70  is a damping element configured to generate a damping force during a stroke of the suspension  1 . The damping force increases in accordance with an increase in a stroke speed, i.e., an expansion or shrink speed. 
     The shock absorber  70  may include, for example, a hydraulic shock absorber including an orifice through which hydraulic oil passes during a stroke. 
     An upper end  71  of the shock absorber  70  is attached to, for example, the vehicle body, with an anti-vibration rubber mount in between. 
     A lower end  72  of the shock absorber  70  is swingably coupled to, for example, the housing  20 , with an elastic bush such as a cylindrical rubber bush in between. 
     The spring  80  is a spring element configured to generate a reaction force corresponding to an amount of stroke of the suspension  1 . 
     The spring  80  may include, for example, a compression coil spring. 
     The spring  80  is disposed rearwardly of the shock absorber  70 , with a line of axis of expansion and shrink aligned with the vertical direction. The line of axis of expansion and shrink of the spring  80  is the center of coil winding. 
     An upper end and a lower end of the spring  80  abut on unillustrated spring sheets provided respectively on the vehicle body and on the rear lateral link  50 . 
     In the following, description is given of more details of the configuration of the radius arm bush  31  in this embodiment. 
       FIG.  4    is a cross-sectional view of the radius arm bush provided in the suspension of this embodiment. 
       FIG.  5    is a cross-sectional view taken along the line V-V in  FIG.  4   , looking in the direction of the appended arrows. 
       FIG.  4    is a cross-sectional view of the radius arm bush  31  taken on a plane orthogonal to the vehicle widthwise direction.  FIG.  4    illustrates a cross-section taken through a lower protrusion  315  described later. In other words,  FIG.  4    is a cross-sectional view taken along the line IV-IV in  FIG.  5   , looking in the direction of the appended arrows. 
     The radius arm bush  31  includes, for example, the inner cylinder  311 , the outer cylinder  312 , an elastic body  313 , an upper protrusion  314 , the lower protrusion  315 , a front cavity  316 , and a rear cavity  317 . 
     The inner cylinder  311  is a cylindrical member. 
     The inner cylinder  311  includes, for example, a metal material such as steel, or a harder material, or a material of higher hardness, having a higher elastic modulus than the elastic body  313 , e.g., engineering plastic. 
     The inner cylinder  311  is fastened to an unillustrated bracket by mechanical fastening, e.g., with the use of bolts and nuts. The unillustrated bracket protrudes downward from an unillustrated side frame of the vehicle body. 
     The inner cylinder  311  is disposed, with its central axis aligned with the vehicle width direction. 
     The outer cylinder  312  is a cylindrical member having an inner diameter larger than an outer diameter of the inner cylinder  311 . 
     The outer cylinder  312  includes, for example, a metal material such as steel, or a harder material, or a material of higher hardness, having a higher elastic modulus than the elastic body  313 , e.g., engineering plastic. 
     The inner cylinder  311  is inserted into inside the inner circumferential surface of the outer cylinder  312 . 
     The outer circumferential surface of the inner cylinder  311  and the inner circumferential surface of the outer cylinder  312  are spaced apart from each other in their radial directions. 
     The inner cylinder  311  may be disposed concentrically with the outer cylinder  312  in a neutral state in which no load is applied to the radius arm bush  31 . 
     Both ends of the inner cylinder  311  in an axial direction are disposed to protrude in the axial direction of the inner cylinder  311  from both ends of the outer cylinder  312 . 
     The outer cylinder  312  is fixed to the front end of the radius arm  30 . 
     The outer cylinder  312  may be press-fitted into and fixed to a cylindrical portion provided on the front end of the radius arm  30 , for example. 
     The outer cylinder  312  is disposed, with its central axis aligned with the vehicle widthwise direction in the steady state of the vehicle. The steady state of the vehicle is a state without any remarkable behavior such as pitch, roll, bounce. 
     The elastic body  313  fills the space between the outer circumferential surface of the inner cylinder  311  and the inner circumferential surface of the outer cylinder  312 . 
     The elastic body  313  includes a softer material, or a material of lower hardness, having a lower elastic modulus than the material of the inner cylinder  311  and the outer cylinder  312 . 
     The elastic body  313  may include, for example, a rubber-based material such as synthetic rubber or natural rubber, or various materials having elasticity such as an elastomer or urethane. 
     For example, in a case with the use of a synthetic rubber-based material, the elastic body  313  may be formed by putting unvulcanized fluidic rubber into the space between the outer circumferential surface of the inner cylinder  311  and the inner circumferential surface of the outer cylinder  312  and heating the rubber for vulcanization. At this occasion, the elastic body  313  is vulcanization-bonded to each of the inner cylinder  311  and the outer cylinder  312 . 
     The upper protrusion  314  and the lower protrusion  315  may be block-shaped members protruding from the outer circumferential surface of the inner cylinder  311 . 
     The upper protrusion  314  and the lower protrusion  315  may include, for example, a harder material having a higher elastic modulus than the material of the elastic body  313 , e.g., an engineering plastic or a metal material. 
     The upper protrusion  314  and the lower protrusion  315  may be formed as separate parts from the inner cylinder  311  and fixed to the inner cylinder  311 . 
     The upper protrusion  314  and the lower protrusion  315  may be unitized with the inner cylinder  311 . 
     The upper protrusion  314  and the lower protrusion  315  are provided in advance on the inner cylinder  311  before the material of the elastic body  313 , e.g., the unvulcanized rubber, fills the space between the inner cylinder  311  and the outer cylinder  312 . Thus, the upper protrusion  314  and the lower protrusion  315  are embedded in the elastic body  313 . Surfaces of the upper protrusion  314  and the lower protrusion  315  are vulcanization-bonded to the elastic body  313 . 
     A portion of the elastic body  313  is interposed between tips of the upper protrusion  314  and the lower protrusion  315 , and the inner circumferential surface of the outer cylinder  312 . The tips of the upper protrusion  314  and the lower protrusion  315  are upsides of the upper protrusion  314  and the lower protrusion  315  protruding from the inner cylinder  311 . However, a thickness of the interposed portion of the elastic body  313  in a radial direction of the inner cylinder  311  is locally reduced with respect to other portions. 
     Here, the reference characters C 1  denotes the wheel center contact point of the rear wheel RW. The reference characters C 2  denotes the center of the radius arm bush  31 . The center of the radius arm bush  31  is the rigidity center but coincides with the axial center of the inner cylinder  311 , or the vehicle-widthwise midpoint of the inner cylinder  311 . The reference characters L 1  denotes a straight line coupling the wheel center contact point C 1  of the rear wheel RW and the center C 2  of the radius arm bush  31 . The straight line L 1  serves as a central axis of torsional turn of the radius arm  30  in accordance with the variations in the vertical load on the tire of the rear wheel RW. 
     As illustrated in  FIG.  4   , the upper protrusion  314  and the lower protrusion  315  are disposed to be aligned with a straight line that passes through the center C 2  of the radius arm bush  31  and is orthogonal to the straight line L 1 , as viewed in the axial direction of the inner cylinder  311 , i.e., as viewed in the vehicle widthwise direction. 
     The upper protrusion  314  is provided in a region upward of the straight line L 1 . 
     The lower protrusion  315  is provided in a region downward of the straight line L 1 . 
     Because the straight line L 1  is inclined to lower toward rear of the vehicle, the upper protrusion  314  is disposed, with its center position offset rearward of the central axis of the inner cylinder  311 . The lower protrusion  315  is disposed, with its center position offset forward of the central axis of the inner cylinder  311 . 
     As illustrated in  FIG.  5   , the upper protrusion  314  is provided in a region vehicle-widthwise inward of the axial center of the inner cylinder  311 . The axial center of the inner cylinder  311  is the vehicle widthwise midpoint of the inner cylinder  311 . 
     The lower protrusion  315  is provided in a region vehicle-widthwise outward of the axial center of the inner cylinder  311 . 
     As illustrated in  FIG.  4   , the front cavity  316  and the rear cavity  317  are hollows, or bores, that extend through the elastic body  313  in an axial direction of the radius arm bush  31 . 
     The front cavity  316  and the rear cavity  317  each have, for example, a planar shape of an ellipse, as viewed in the axial direction of the radius arm bush  31 , having a long-axis direction orthogonal to a radial direction of the radius arm bush  31 . 
     As viewed in the axial direction of the radius arm bush  31 , the front cavity  316  is positioned, or phased, around the central axis of the inner cylinder  311 , between the upper protrusion  314  and the lower protrusion  315 , and in a region on front side of the vehicle. 
     The center of the front cavity  316  is disposed upward and forward of the central axis of the inner cylinder  311 . 
     As viewed in the axial direction of the radius arm bush  31 , the rear cavity  317  is positioned, or phased, around the central axis of the inner cylinder  311 , between the upper protrusion  314  and the lower protrusion  315 , and in a region on rear side of the vehicle. 
     The center of the rear cavity  317  is disposed downward and rearward of the central axis of the inner cylinder  311 . 
     The front cavity  316  and the rear cavity  317  are disposed to be aligned with the straight line L 1 , as viewed in the axial direction of the radius arm bush  31 . 
     With the configuration described above, in the state illustrated in  FIG.  5   , the radius arm bush  31  has higher torsional rigidity with respect to clockwise turn of the outer cylinder  312 , with the inner cylinder  311  fixed, than torsional rigidity with respect to counterclockwise turn of the outer cylinder  312 . Clockwise means a direction in which the protrusions  314  and  315  are compressed. 
     Moreover, in the state illustrated in  FIG.  4   , the radius arm bush  31  has lower rigidity in a case where the inner cylinder  311  is fixed and the outer cylinder  312  is displaced in an obliquely longitudinal direction along the straight line L 1 , than rigidity without the front cavity  316  and the rear cavity  317 . 
     In the following, description is given of workings and effects of the suspension  1  of this embodiment including the radius arm bush  31  as described above. 
     At a start of cornering of the vehicle, first, a steering angle is generated on a front wheel by, for example, a steering operation by a driver who drives the vehicle. Thereupon, a slip angle is given to a front wheel tire, and the front wheel tire generates a lateral force, i.e., a cornering force, corresponding to the slip angle. 
     The cornering force acting on the front wheel causes yaw behavior of the vehicle body, or rotation about a vertical axis. A part of the force generated by the front wheel is transmitted to the suspension  1  on side on which the rear wheel RW is disposed, while involving torsion of the vehicle body. 
     Immediately after the start of the cornering of the vehicle, the suspension  1  on the side on which the rear wheel RW is disposed is in a stuck state in which friction of, for example, the shock absorber  70  inhibits behavior in a stroke direction. 
     In this state, an increase in the vertical load on the tire of the rear wheel RW on outer wheel side of the cornering causes a toe change called vertical force steering in the rear wheel RW because of geometric displacement, or geometry, and rigidity balance of the links of the suspension  1 . 
     In the geometry of the suspension  1  of this embodiment, as illustrated in  FIGS.  1  and  3   , the wheel center contact point C 1  of the rear wheel RW is disposed vehicle-widthwise outwardly of the center C 2  of the radius arm bush  31 . 
     Accordingly, on the outer wheel side at the start of the cornering of the vehicle, as illustrated in  FIG.  3   , an increase ΔF in the vertical load on the tire causes a rotatory moment M in the radius arm  30  around the straight line L 1  coupling the wheel center contact point C 1  of the rear wheel RW and the center C 2  of the radius arm bush  31 . The rotatory moment M is generated in a direction in which the underside of the radius arm  30  is displaced vehicle-widthwise outwardly from the upside of the radius arm  30 . 
     In a case with considerable torsional behavior of the whole radius arm  30  and the whole housing  20 , this rotatory moment M causes an increase in the toe change of the rear wheel RW in the toe-out direction at the start of the cornering, or the vertical force steering. 
     Generally, in a suspension for a rear wheel, roll behavior of a vehicle occurs, causing a shrinkwise stroke, or a bumpwise stroke, of a suspension on the outer wheel side. Thereupon, a toe change in a toe-in direction, i.e., roll steering, occurs, depending on setting of, for example, lengths and angles of the front lateral link  40  and the rear lateral link  50 . 
     To allow the tire of the rear wheel RW to generate a lateral force, i.e., a cornering force, causing the vehicle to corner, the rear wheel RW on the outer wheel side has to toe in appropriately, generating a slip angle. 
     However, in a case with a large toe change in the toe-out direction because of the vertical force steering mentioned above, there occurs a long delay in the response until the rear wheel RW on the outer wheel side makes the toe change in the toe-in direction. 
     In contrast, in this embodiment, the upper protrusion  314  and the lower protrusion  315  are provided. This makes it possible to allow the radius arm bush  31  to have the higher rigidity with respect to the turn in the direction in which the underside of the radius arm  30  is displaced vehicle-widthwise outwardly from the upside of the radius arm  30 , than the rigidity with respect to reverse turn. The reverse turn means turn in the direction in which the underside of the radius arm  30  is displaced vehicle-widthwise inwardly from the upside of the radius arm  30 . 
     Thus, in the rear wheel RW on the outer wheel side on which the vertical load on the tire increases, it is possible to suppress the turn in the direction in which the underside of the radius arm  30  is displaced vehicle-widthwise outwardly from the upside, i.e., in the direction of the rotatory moment M illustrated in  FIG.  3   . Hence, it is possible to suppress the toe change in the toe-out direction at the initial stage of the cornering, and advance the time when the toe change in the toe-in direction occurs. This leads to reduction in the delay in the response of the vehicle to the steering operation. 
     Meanwhile, in the rear wheel RW on inner wheel side on which the vertical load on the tire decreases, the turn in the direction in which the underside of the radius arm  30  is displaced vehicle-widthwise inwardly from the upside, i.e., in the reverse direction to the rotatory moment M illustrated in  FIG.  3   , is less likely to be inhibited. Hence, it is possible to promote the toe change in the toe-out direction, leading to effective utilization of a grip force of the tire. 
     As described, according to this embodiment, it is possible to obtain the following effects. 
     (1) On the outer wheel side of the cornering, as the vertical load on the tire increases, the radius arm  30  makes the torsional turn accompanied by the toe change in the toe-out direction, i.e., the vertical force steering. Suppressing such torsional turn makes it possible to advance the toe change in the toe-in direction by the roll steering. This leads to reduction in the time delay in the response of the vehicle behavior to the driver&#39;s operation of the steering wheel. 
     Hence, it is possible to accelerate the cycle of the operation, the response, and the correction operation between the driver and the vehicle, leading to enhanced operation accuracy. 
     On the inner wheel side of the cornering, as the vertical load on the tire decreases, the radius arm  30  makes the torsional turn accompanied by the toe change in the toe-in direction. Permitting such toe change in the toe-in direction makes it possible to promote the toe change in the toe-out direction, leading to effective utilization of the grip of the tire on the inner wheel side. 
     (2) The radius arm bush  31  may include the upper protrusion  314  and the lower protrusion  315  between the outer circumferential surface of the inner cylinder  311  and the inner circumferential surface of the outer cylinder  312 . The upper protrusion  314  and the lower protrusion  315  include the harder material than the elastic body  313 . The upper protrusion  314  is provided in the region upward and vehicle-widthwise inward of the straight line L 1 . The lower protrusion  315  is provided in the region downward and vehicle-widthwise outward of the straight line L 1 . Hence, it is possible to effectively enhance the rigidity of the elastic body  313  against the deformation in the direction in which the protrusions  314  and  315  are compressed. 
     Moreover, for example, the arrangement and the shapes of the upper protrusion  314  and the lower protrusion  315  makes it possible to easily set the direction of deformation in which the rigidity increases, and an amount of increase in the rigidity. 
     (3) The upper protrusion  314  and the lower protrusion  315  may protrude from the outer circumferential surface of the inner cylinder  311 . This makes it possible to easily manufacture the radius arm bush  31  having the characteristic mentioned above, by filling the space between the inner cylinder  311  and the outer cylinder  312  with the material of the elastic body  313  and vulcanizing the material of the elastic body  313 . Non-limiting examples of the material of the elastic body  313  may include unvulcanized fluidic rubber. 
     (4) The elastic body  313  of the radius arm bush  31  may have the cavities  316  and  317 , as viewed in the direction of the central axis of the inner cylinder  311 . The cavities  316  and  317  are spaced apart from the upper protrusion  314  and the lower protrusion  315  in the circumferential direction of the inner cylinder  311 . Hence, it is possible to lower supporting rigidity of the radius arm  30  in the longitudinal direction, and provide a comfortable ride of the vehicle. 
     Moreover, it is possible to lower supporting rigidity of the radius arm  30  in the direction of stroke of the suspension  1 , i.e., torsional rigidity around the central axis of the inner cylinder  311 . This leads to the smoother motion of the suspension  1 . 
     As described, according to the embodiment, it is possible to provide a suspension that makes it possible to enhance responsiveness at an initial stage of cornering. 
     MODIFICATION EXAMPLES 
     Although some example embodiments of the disclosure have been described in the foregoing by way of example with reference to the accompanying drawings, the disclosure is by no means limited to the embodiments described above. It should be appreciated that modifications and alterations may be made by persons skilled in the art without departing from the scope as defined by the appended claims. The disclosure is intended to include such modifications and alterations in so far as they fall within the scope of the appended claims or the equivalents thereof. 
     (1) The configurations of the suspension and the vehicle are not limited to the forgoing embodiments, but may be changed as appropriate. 
     For example, the shapes, the structures, the materials, the manufacturing methods, the arrangements, and the quantities of the members constituting the suspension and the vehicle are not limited to the forgoing embodiments, but may be changed as appropriate. 
     For example, in the forgoing embodiments, the radius arm bush is disposed, with the central axes of the inner cylinder and the outer cylinder aligned with the vehicle widthwise direction. However, the radius arm bush may have a configuration in which the central axes of the inner cylinder and the outer cylinder have inclinations small enough not to diminish the effects of the embodiments. 
     Moreover, there are no particular limitations on configuration of other links than the radius arm in the suspension. For example, multiple upper links may be disposed in longitudinally spaced relation. 
     Furthermore, there are no particular limitations on positions of the shock absorber and the spring. 
     (2) In the embodiments, the protrusions are provided that protrude from the outer circumferential surface of the inner cylinder. In one embodiment of the disclosure, the protrusions may serve as “one or more deformation resistant members”. However, a configuration of the deformation resistant members is not limited to the configuration described in the embodiment, but may be changed as appropriate. 
     For example, protrusions may be provided that protrude from the inner circumferential surface of the outer cylinder. 
     In another example, a harder material than the elastic body may be embedded inside the elastic body by, for example, insert molding. The deformation resistant members thus embedded may be spaced apart from both the outer circumferential surface of the inner cylinder and the inner circumferential surface of the outer cylinder. 
     Furthermore, in the embodiments, the radius arm bush includes both the upper protrusion and the lower protrusion, but the radius arm bush may include either the upper protrusion or the lower protrusion. 
     (3) In the embodiments, the rear subframe includes, for example, assembled panels of press-molded steel plates, but the rear subframe may be provided by other manufacturing methods. 
     For example, the rear subframe may be formed by hydroforming. Hydroforming includes applying hydraulic pressure such as water pressure to an inside of a metal hollow body to cause plastic deformation. Alternatively, the rear subframe may include, for example, an extruded material of an aluminum-based alloy. 
     In another alternative, without the use of the rear subframe, some or all of the suspension links may be coupled to, for example, the vehicle body, or a cross member rigidly coupled to the vehicle body. 
     (4) In the embodiment, the bushes of each link of the suspension include, for example, cylindrical rubber bushes, but the disclosure is not limited thereto. For example, bushes including an elastic body other than rubber may be used. 
     Moreover, the bushes of each link of the suspension are not limited to the cylindrical bushes. Other forms of bushes such as a ball joint, or a spherical bearing, may be used.