Vehicle Rear Suspension Mechanism

The following are closely related copending U.S. patent applications:

1. Field of the Invention

This invention relates to a rear-suspension system for a vehicle, and more particularly to an improved rear-suspension system for a vehicle, exhibiting an excellent toe in effect.

2. Description of the Prior Art

As is well known, the rear-suspension system for a vehicle is desired to be arranged so that the rear wheels or the tires thereon are caused to toe in during travel, especially during cornering, in order to improve driving stability, driving comfort and the like. The centrifugal force exerted on the vehicle body during cornering acts on the rear-suspension as a lateral force. The tires are desired to counteract the lateral force with an increased resisting force in order to maximize the critical acceleration G in turning. The resisting force against the lateral force can be increased by causing the tires on the rear wheels to toe in to create a slip angle. By increasing the resisting force, the road-gripping force of the rear tires can be improved and the tendency to under-steer can be enhanced, whereby the driving stability of the vehicle is improved. When the accelerator pedal is pushed down during cornering, a driving force is exerted on the tires, while when the accelerator pedal is released during cornering, a braking force is exerted on the tires. The tires tend to toe out upon release of the accelerator pedal which has been depressed, while they tend to toe in upon depression of the accelerator pedal. This causes the tires to toe out and in during cornering, thereby adversely affecting the driving stability of the vehicle. Further, as the rubber bushings for improving driving comfort are disposed inside the treading point of the tires, the braking forces exerted on the tires when the brake pedal is depressed or an engine-brake effect occurs cause the tires to toe out and accordingly the driving stability is lowered. This means that the driving stability is lowered as the driving comfort becomes higher since the softer the rubber bushings are, the more comfortable the vehicle is to ride in. Therefore, there is a demand for a rear-suspension system which can cause the rear tires to toe in even when braking forces are exerted thereon through operation of the brake pedal or by the engine-brake effect. The ability of the rear-suspension system to always cause the tires to toe in (This ability will be referred to as "toe-in ability" hereinbelow.) ensures a good driving stability during cornering. The toe-in ability of the rear-suspension is also desirable from the viewpoint of the stability of the vehicle during straight travel at a high speed which is particularly required in the case of a sports car. Actually, roads are not completely flat but inherently have bumps and recesses of various sizes which act on the tires as external disturbances in various directions. Further, winds impinging upon the vehicle body in various directions also act on the tires as external disturbances in various directions, and in particular, side winds act on the tires as lateral forces. If the rear-suspension can maintain its toe-in ability even when these external disturbances are exerted on the tires, an understeer condition of the vehicle is always ensured, whereby the vehicle can always be stabilized. The external disturbances act as the lateral force, braking force or driving force described above irrespective of their origins.

Therefore, the rear-suspension system is desired to be able to keep its toe-in ability against any one of the lateral force, braking force (due either to operation of the brake pedal or the engine-brake effect), and driving force. The lateral force is typically a thrust load produced during cornering and comprises a force acting on the treading point of the tires from outside to inside. The braking force due to operation of the brake pedal comprises a force acting on the treading point of the tires from front to rear while the braking force due to the engine-brake effect comprises a force acting on the wheel center of the tires from front to rear. The driving force comprises a force acting on the wheel center from rear to front. The four forces, the acting point thereof and the acting direction are tabulated in the following table.

There have been developed various rear-suspension systems which can keep the toe-in ability against the lateral force produced during cornering. For example, there is disclosed in Japanese Patent Publication 52(1977)-37649 such a rear-suspension system which utilizes three rubber bushings of different hardnesses. In West German Patent Laid Open Nos. 2,158,931 and 2,355,954 there are disclosed such rear-suspension systems in which each wheel hub is supported by way of a vertical shaft and a spring. However they are fairly complicated in structure. Further, the rear-suspension systems of the type described above cannot keep their toe-in ability against all of the four forces described above, but only against the lateral force.

In view of the foregoing observations and description, the primary object of the present invention is to provide a rear-suspension system which can cause the rear wheels to toe in against lateral forces exerted thereon during cornering as well as during a straight travel and which is simple in structure.

In accordance with one preferred embodiment of the present invention, there can be provided a rear-suspension system which can cause the rear wheels to toe in against the brake force in addition to the lateral force.

In accordance with a further preferred embodiment of the present invention, there can be provided a rear-suspension system which can cause the rear wheels to toe in against the driving force or engine-brake force in addition to the lateral force and the brake force.

In accordance with a still further preferred embodiment of the present invention, there can be provided a rear-suspension system which can cause the rear wheels to toe in against all of the four forces described above.

The rear-suspension system of the present invention is characterized in that a body side support member a part of which is connected to the vehicle body and the wheel hub of each rear wheel are connected with each other by way of a single ball joint and a pair of rubber bushings, the single ball joint being disposed in quadrant I, one of the rubber bushings being disposed in quadrant IV and the other rubber bushing being disposed in quadrant II or III, as viewed from the left hand side of the vehicle body, on a coordinate plane having its origin on the center of a rear wheel, its abscissa on the horizontal line passing through the center of the rear wheel and its ordinate on the vertical line passing through the center of the rear wheel.

Said quadrants are numbered anticlockwise beginning from the upper right quadrant as viewed from the left hand side of the vehicle body and each of the quadrants should be interpreted, in this specification, to include the part of the abscissa and the ordinate separating the quadrant from the other quadrants. For example, quadrant I should be interpreted to include the right side half of the abscissa and the upper half of the ordinate.

The present invention can be applied to any type of rear-suspension system insofar as it can support the rear tires to permit them to toe in. For example, the rear-suspension systems to which the present invention can be applied include those of the semi trailing type, strut type, wishbone type and De Dion type. The term "body side support member" should be interpreted as a general term which refers to a support member mounted on the side of the vehicle body, such as a semi trailing arm in the case of a semi trailing type rear-suspension system, a strut in the case of a strut type rear-suspension system, upper and lower arms in the case of a wishbone type rear-suspension system and a De Dion tube in the case of a De Dion type rear-suspension system.

By connecting the body side support member and the wheel hub by way of a single ball joint and a pair of rubber bushings disposed as described above, the rear tires can effectively toe in when a lateral force is exerted thereon, as will be described in more detail referring to the attached drawings hereinbelow. Further, the rear tires can effectively toe in overcoming various external forces exerted thereon by further selecting the arrangement of the ball joint and the rubber bushings and the position of the rubber bushings. This is accomplished through pivotal movements of the wheel hub about the vertical axis passing through the center of the ball joint and a horizontal axis passing through the center of the ball joint which are permitted by virtue of deformation of the rubber bushings, as will be also described in more detail hereinbelow.

FIG. 1 is a perspective view showing a part of a semi trailing type rear-suspension system in accordance with an embodiment of the present invention,

FIG. 2 is a perspective view showing a part of a strut type rear-suspension system in accordance with another embodiment of the present invention,

FIG. 3 is a perspective view of a part of a De Dion type rear-suspension system in accordance with still another embodiment of the present invention,

FIGS. 4, 5A to 5D, 6 and 7 are schematic views for illustrating the principle of the present invention,

FIG. 8 is a plan view of a part of a semi trailing type rear-suspension system in accordance with a practical embodiment of the present invention, with a part of the tire cut away,

FIG. 9 is a side elevational view of FIG. 8,

FIG. 10 is an end elevational view of FIG. 8 as viewed from the rear of the vehicle body,

FIG. 11A is a sectional view of the first resilient bushing assembly employed in the embodiment shown in FIGS. 8 to 10,

FIG. 11B is a sectional view taken along line A'--A' in FIG. 11A,

FIG. 12A is a sectional view of the second resilient bushing assembly employed in the embodiment shown in FIGS. 8 to 10,

FIG. 12B is a sectional view taken along line B'--B' in FIG. 12A, and

FIG. 13 is a sectional view of the ball joint employed in the embodiment shown in FIGS. 8 to 10.

FIG. 1 is a perspective view showing a part of a semi trailing type rear-suspension system in accordance with an embodiment of the present invention. In FIG. 1, a semi trailing arm 11 is connected to a wheel hub 12 for the left rear wheel by way of a pair of rubber bushings 2 and 3 and a single ball joint 4. In the present invention, a coordinate plane having its origin on the center of the rear wheel, its abscissa on the horizontal line passing through the center of the rear wheel and its ordinate on the vertical line passing through the center of the rear wheel is imagined as viewed from the left hand side of the vehicle body. Then the ball joint 4 is disposed in quadrant I on the imaginary coordinate plane, while one rubber bushing 3 is disposed in quadrant IV and the other rubber bushing 2 is disposed in quadrant II or III. (In the particular embodiment shown in FIG. 1, the other bushing 2 is disposed in quadrant III.) The operation of the ball joint 4 and the rubber bushings 2 and 3 will be described in detail later.

FIG. 2 is a perspective view showing a part of a strut type rear-suspension system in accordance with another embodiment of the present invention. A wheel hub 13 for the left rear wheel is connected to the lower end of a strut 14 by way of a pair of rubber bushings 2 and 3 and a ball joint 4 in a manner similar to that of the embodiment shown in FIG. 1. In this embodiment the ball joint 4 is in quadrant I, while one rubber bushing 3 is in quadrant IV and the other rubber bushing 2 is in quadrant II.

In FIG. 3, which is a perspective view of a part of a De Dion type rear-suspension system in accordance with still another embodiment of the present invention, a wheel hub 15 for the left rear wheel is connected to a bracket 18, which is mounted on an end of a De Dion tube 16 and supported by a leaf spring 17, by way of a pair of rubber bushings 2 and 3 and a ball joint 4. In this embodiment the ball joint 4 is in quadrant I, while one rubber bushing 3 is in quadrant IV and the other rubber bushing 2 is in quadrant III.

Although only the left side of the rear-suspension systems is shown in FIGS. 1 to 3, the right side of each rear-suspension system is identical to the left side. The present invention is not limited to those systems shown in FIGS. 1 to 3 and can also be applied to wishbone type and torsion beam axle type rear-suspension systems. Generally speaking, the present invention can be applied to rear-suspension systems of any type except those in which the rear wheels are rigidly mounted on a suspension arm or axle and are not permitted to toe in.

Now the principle of operation of the rear-suspension system of the present invention will be described referring to FIGS. 4, 5A to 5D, 6 and 7.

FIG. 4 is a combined schematic view for illustrating the principle of operation of the rear-suspension system in accordance with an embodiment of the present invention, where the ball joint 4 is positioned in quadrant I, and the rubber bushings 2 and 3 are positioned in quadrant III and quadrant IV, respectively. A schematic perspective view of the right rear tire of a vehicle as viewed from the left rear quarter is shown in the middle of FIG. 4, and projections from the rear, left side and above are positioned on the left and right sides of the perspective view and below it, respectively. In FIG. 4, the abscissa and the ordinate of said imaginary coordinate plane having its origin on the wheel center W are indicated at H and V, respectively, and quadrants I to IV of the coordinate plane are indicated at I to IV, respectively.

As described above, the lateral force acts on the treading point G of the tire from outside to inside as indicated at S, the brake force acts on the treading point G from front to rear as indicated at B, the engine-brake force acts on the wheel center W from front to rear as indicated at E, and the driving force acts on the wheel center W from rear to front as indicated at K.

In order to explain the principle of operation of the rear-suspension system of the present invention, a vertical axis L passing through the ball joint 4, a horizontal axis M passing through the ball joint 4 in parallel to the axle, and a horizontal axis N passing through the ball joint 4 in the direction of the vehicle body are imagined.

When the lateral force S acts on the treading point G from outside to inside, a turning moment in the direction of toe-in is generated about the imaginary vertical axis L by virtue of the fact that the ball joint 4 is in quadrant IV, i.e., the ball joint 4 is positioned to the rear of the wheel center W, and thereby the tire is caused to toe in. This is because the moment M.sub.1 about the ball joint 4 at the forward rubber bushing 2 (positioned in quadrant III) is larger than that M.sub.2 at the rearward rubber bushing 3 (positioned in quadrant IV), and therefore the former is more displaced than the latter as shown by characters A(large) and B(small) in FIG. 5A. When the forward rubber bushing 2 is less hard than the rearward rubber bushing 3, the tire can be caused to toe in more easily. Thus, the rear tire can be effectively caused to toe in against the lateral force S acting on the treading point G thereof by positioning the ball joint 4 in quadrant I and positioning one of the rubber bushings in quadrant IV and the other rubber bushing in quadrant II or III. Although the rubber bushing 2 is in quadrant III in the above description, it will be apparent for those skilled in the art that it may instead be positioned in quadrant II in order to cause the rear tire to toe in against the lateral force S.

As described above, in accordance with the present invention, the rear tire can be caused to toe in against external forces other than the lateral force S, i.e., the brake force B, the engine-brake force E and the driving force K, by appropriately selecting the arrangement of the ball joint 4 and the rubber bushings 2 and 3, and the position of the rubber bushings 2 and 3. In order to make clear the principle on which the rear tire is caused to toe in against the brake force B, the engine-brake force E and the driving force K in accordance with the present invention, the position of the plane including the centers of the ball joint 4 and the rubber bushings 2 and 3 with respect to the wheel center W and the treading point G must be first discussed. The plane is represented by a line 10 in the projection from the rear in FIG. 4. In other words, the line 10 represents the intersectional line between the plane including the centers of the ball joint 4 and the rubber bushings 2 and 3, and the vertical plane including the central axis of the rear wheel.

The arrangement of the ball joint 4 and the rubber bushings 2 and 3 can be classified into four cases depending on the position of the plane including their centers or the line 10 with respect to the wheel center W and the treading point G. In the first case, the relevant plane or the line 10 is outwardly offset from the treading point G at the height of the treading point G (This condition is symbolized by G- in this specification and the drawings.) and at the same time is outwardly offset from the wheel center W at the height of the wheel center W (This condition is symbolized by W-, and the first case is symbolized by G-W-.). In the second case, the relevant plane is outwardly offset from the treading point G at the height thereof (G-) but is inwardly offset from the wheel center W at the height thereof (W+). That is, the second case is symbolized by G-W+. Similarly, the third and fourth cases are symbolized by G+W+and G+W-, respectively.

When the relevant plane is outwardly offset from the treading point G at the height thereof (G-), a turning moment in the direction of toe-in is generated about the imaginary vertical axis L when a force is exerted on the treading point G from front to rear. Thus, by outwardly offsetting the relevant plane from the treading point G at the height thereof, the rear tire can be effectively caused to toe in against the brake force B which acts on the treading point G from front to rear.

Further when the relevant plane is inwardly offset from the wheel center W at the height thereof (W+), a turning moment in the direction of toe-in is generated about the vertical axis L when a force is exerted on the wheel center W from rear to front, and a turning moment in the direction of toe-out is generated about the vertical axis L when a force is exerted on the wheel center W from front to rear. On the other hand, when the relevant plane is outwardly offset from the wheel center W at the height thereof (W-), a turning moment in the direction of toe-in is generated about the vertical axis L when a force is exerted on the wheel center W from front to rear, and a turning moment in the direction of toe-out is generated about the vertical axis L when a force is exerted on the wheel center W from rear to front. Accordingly when the relevant plane is inwardly offset from the wheel center W at the height thereof (W+), the rear tire is effectively caused to toe in against the driving force K which acts on the wheel center W from rear to front. However, in this case, the rear tire will be caused to toe out when the engine-brake force E is exerted on the wheel center W from front to rear. On the other hand, when the relevant plane is outwardly offset from the wheel center W at the height thereof (W-), the rear tire is caused to toe in when the engine-brake force E is exerted on the wheel center W, while the rear tire is caused to toe out when the driving force K is exerted on the wheel center W.

Thus, in the rear-suspension system in which the ball joint 4 and the rubber bushings 2 and 3 are positioned in quadrants I, III and IV, respectively, and at the same time the plane including the centers of the ball joint 4 and the rubber bushings 2 and 3 is outwardly offset from the treading point G at the height thereof (G-) with the plane being offset from the wheel center W at the height thereof outwardly or inwardly, the rear tire can be caused to toe in against three of said four forces, i.e., the lateral force S, the brake force B and the engine-brake force E, or the lateral force S, the brake force B and the driving force K, depending on the direction of the offset of the plane from the wheel center W at the height thereof. However, it is possible to realize a rear-suspension system in which the rear tire can be caused to toe in against all of the four forces by utilizing a turning moment generated about said horizontal axis M passing through the ball joint 4 in parallel to the axle, as can be seen from the description hereinbelow.

In the embodiment shown in FIG. 4, the plane including the centers of the ball joint 4 and the rubberbushings 2 and 3 (This plane will be referred to as "the plane 10", hereinbelow.) is outwardly offset from the treading point G at the height thereof and is inwardly offset from the wheel center W at the height thereof (G-W+), and at the same time the central axis of the rubber bushing 2 in quadrant III (This bushing will be referred to as "the first bushing" hereinbelow.) along which the first rubber bushing 2 is deformed most easily is inclined inwardly toward the rear in a horizontal plane, while the central axis of the rubber bushing 3 in quadrant IV (This bushing will be referred to as "the second bushing" hereinbelow.) along which the second bushing 3 is deformed most easily is inclined inwardly toward the front in a horizontal plane.

When the brake force B is exerted on the treading point G from front to rear, a turning moment in the direction of toe-in is generated about the vertical axis L by virtue of the fact that the plane 10 is outwardly offset from the treading point G at the height thereof, and at the same time a turning moment to displace the tire counterclockwisely (as seen from the left of FIG. 4) about the horizontal axis M. The turning moment to displace the tire counterclockwisely is converted into a force to inwardly displace the forward part of the tire and to outwardly displace the rearward part of the same as shown by the arrows A' and B' in FIG. 5B through a guiding effect of the bushings 2 and 3 due to the inclination of their central axes, thereby causing the tire to toe in together with the turning moment about the vertical axis L. This effect increases with increasing outward offset of the plane 10 from the treading point G at the height thereof and with decreasing hardness of the bushings 2 and 3.

When the engine-brake force E is exerted on the wheel center W from front to rear, a turning moment to counterclockwisely displace the tire about the horizontal axis M is generated. This turning moment is converted into a force to cause the tire to toe in through the guiding effect of the bushings 2 and 3 as shown in FIG. 5C, whereby the tire toes in overcoming the turning moment in the direction of toe-out generated about the vertical axis L.

When the driving force K is exerted on the wheel center W from rear to front, a turning moment to displace the tire in the clockwise direction is generated about the horizontal axis M. This turning moment is converted into a force to cause the tire to toe out through the guiding effect of the bushings 2 and 3 since the driving force K acts on the wheel center W in the direction opposite to the enginebrake force E. The force tending to cause the tire to toe out overcomes the turning moment in the direction of toe-in generated about the vertical axis L, whereby the tire toes out. However, the tire can be caused to toe in by providing a stopper 5 in front of one of the bushings 2 and 3 as shown in FIG. 5D. When the stopper 5 is provided in front of one of the bushings 2 and 3, a turning moment to turn the tire in the direction of toe-in is generated about the line connecting the ball joint 4 and the bushing provided with the stopper 5, whereby the tire is caused to toe in when the driving force K is exerted on the wheel center W.

In the embodiment shown in FIG. 6, the plane 10 is outwardly offset from both the treading point G and the wheel center W (G-W-), and at the same time the central axis of the first bushing 2 is inclined outwardly toward the rear in a horizontal plane and the central axis of the second bushing 3 is inclined inwardly toward the rear in a horizontal plane.

In this case a turning moment to rotate the tire in the direction of toe-in is generated about the vertical axis L by virtue of the fact that the plane 10 is outwardly offset from both the wheel center W and the treading point G when either the brake force B or the engine-brake force E is exerted on the tire. However this turning moment is converted into a force to cause the tire to toe out through the guiding effect of the rubber bushings 2 and 3 which are inclined in the direction opposite to the direction of the inclination of the two rubber bushings in the embodiment shown in FIG. 4. This can be avoided by providing a stopper behind one of the bushings 2 and 3. When the driving force K is exerted on the wheel center W from rear to front, there is generated a turning moment to displace the tire in the clockwise direction about the horizontal axis M which is converted into a force to cause the tire to toe in through the guiding effect of the bushings 2 and 3. Thus, by selecting the position of the rubber bushings 2 and 3, the tire can be caused to toe in even against the driving force K which acts on the tire only to cause it to toe out in the case that the plane 10 is outwardly offset from both the treading point G and the wheel center W.

In the above embodiments, the ball joint 4 is positioned in quadrant I, and the first bushing 2 is positioned in quadrant III with the second bushing in quadrant IV. However, the first bushing 2 may be in quadrant II insofar as the second bushing 3 is in quadrant IV. Now, referring to FIG. 7, another embodiment of the present invention in which one bushing is in quadrant II and the other bushing is in quadrant IV with the ball joint being in quadrant I and the plane 10 including the centers of the ball joint and the bushings being offset from the treading point G outwardly and from the wheel center W inwardly (G-W+). In FIG. 7, the bushing in quadrant II is indicated at 1. Also in this embodiment, the lateral force S acting on the treading point G causes the tire to rotate about the vertical axis L in the direction of toe-in since the ball joint 4 is positioned in quadrant I. The brake force B acting on the treading point G from front to rear generates a turning moment in the direction of toe-in about the vertical axis L by virtue of the fact that the plane 10 is butwardly offset from the treading point G at the height thereof, and at the same time generates a turning moment to counterclockwisely displace the tire about the horizontal axis M.

In order to effectively cause the tire to toe in by converting the latter turning moment into a force to cause the tire to toe in, the central axis of the bushing 1 in quadrant II (which is substantially perpendicular to the line connecting the ball joint and the rubber bushing 1) is inclined downwardly inwardly (In other words, the lower or front end of the bushing 1 is directed inwardly.) so that the forward part of the tire is inwardly displaced when the tire rotates about the horizontal axis M, while the bushing 3 in quadrant IV is inclined outwardly toward the rear (In other words, the upper end or the rear end of the bushing 3 is directed outwardly.) so that the rearward part of the tire is outwardly displaced when the tire rotates the horizontal axis M.

As for the engine-brake force, the tire can be caused to toe in totally by making the force to cause the tire to toe in obtained, by virtue of the inclination of the bushings 1 and 3, from the turning moment generated about the horizontal axis M larger than the turning moment in the direction of toe-out generated about the vertical axis L due to the inward offset of the plane 10 from the wheel center W (W+). With respect to the driving force K, the tire can be effectively caused to toe in by providing a stopper in front of the bushing 3 in quadrant IV so that a turning moment to cause the tire to toe in is generated about a line connecting the ball joint 4 and the bushing 3.

Although the plane 10 is outwardly offset from the treading point G at the height thereof and is inwardly offset from the wheel center W at the height thereof (G-W+) in the embodiment shown in FIG. 7, the tire can be effectively caused to toe in against all of the four forces in a similar manner even when the plane 10 is outwardly offset from both the treading point G and the wheel center W (G-W-).

Now a more practical embodiment of the present invention will be described referring to FIGS. 8 to 13. In the embodiment shown in FIGS. 8 to 13, the present invention is applied to a semi trailing type rear-suspension.

FIG. 8 is a plan view of a part of the rear-suspension system associated with the right rear tire, FIG. 9 is a side elevational view of FIG. 8 as viewed from the right hand side of the vehicle body, and FIG. 10 is an elevational view thereof as viewed from the rear of the vehicle body. In FIG. 8, a semi trailing arm 30 has a bifurcated end forming an inner arm 30a and an outer arm 30b. The inner and outer arms 30a and 30b are mounted on the vehicle body (not shown) to pivot about a common axis 31. The other or rear end 30c of the semi trailing arm 30 is connected to a wheel hub 32 (on which a wheel 33 for the right rear tire 34 is mounted) by way of first and second resilient bushing assemblies 21 and 23 and a single ball joint 24 so that the wheel hub 32 can move about the ball joint 34 relative to the semi trailing arm 30 with a slight resiliency. More particularly, three arms 35a, 35b and 35c (FIGS. 9 and 10) are provided on the wheel hub 32. The first arm 35a is resiliently supported on the first resilient bushing assembly 21 mounted in a first bushing pivoting portion 36a provided on the rear end 30c of the semi trailing arm 30. The second arm 35b is resiliently supported on the second rubber bushing assembly 23 mounted in a second bushing pivoting portion 36b provided on the rear end 30c of the semi trailing arm 30. The third arm 35c is supported for rotation about a point on the ball joint 24 mounted in a ball joint supporting portion 36c provided on the rear end 30c. The first bushing pivoting portion 36a is positioned in quadrant III and is inclined downwardly inwardly while the second bushing pivoting portion 36b is positioned in quadrant IV and is inclined upwardly outwardly. The ball joint supporting portion 36c is positioned in quadrant I.

The first and second resilient bushing assemblies 21 and 23 include rubber bushings 21a and 23a, respectively, as shown in FIGS. 11A, 11B and 12A, 12B. The rubber bushings 21a and 23a permit displacement in the direction of their axes and a direction perpendicular to their axes. However, the rubber bushing 21a of the first resilient bushing assembly 21 in quadrant III is provided with a rigid material 21b on the outer side thereof so as to be permitted to deform only inwardly. The rubber bushing 23a of the second resilient bushing assembly 23 in quadrant IV is provided with a stopper 23b which serves to limit the forward displacement. The ball joint 24 has a spherical portion 24a which permits pivotal movement about a point but does not permit an axial displacement as shown in FIG. 13. Said third arm 35c is supported for rotation about the spherical portion 24a.

This embodiment corresponds to the embodiment shown in FIG. 4 and causes the rear tire to toe in against all of the external forces on the principle described above in conjunction with FIGS. 4 and 5A to 5D.

Further by relatively increasing the rigidity of the first bushing toward the outside of the vehicle body by providing the rigid material on the outer side of the first bushing, the tendency of the tire to toe-out can be prevented. The same effect can be obtained by relatively increasing the rigidity of the second bushing toward the inside of the vehicle body.