Vehicle rear suspension system

Abstract: A vehicle rear suspension system having a vertically swingable arm (18) connected at the front end swingably to the vehicle body (16) and secured at the rear end to a wheel carrying member (12) which carries a rear wheel (10) for rotation. Three lateral links (20, 22, 24) are provided and have inward ends pivotably connected to the vehicle body and outward ends pivotably connected to the wheel carrying member. The points of connection (20a, 22a, 24a) of the three lateral links to the wheel carrying member (12) are not aligned in a straight line so that the orientations of the wheel carrying member can appropriately be controlled under a bump and rebounc­ ing movements of the rear wheel and under a side and longitudinal forces acting on the rear wheel.

Description: The present invention relates to a vehicle suspension system and more particularly to a rear suspension system of a motor vehicle. Conventional independent type vehicle rear suspension systems include a so-called trailing arm type and a semi-trailing arm type. These types of suspension systems include a trailing arm extending in a longitudinal direction of the vehicle body and having a front end attached to the vehicle body for vertical swinging movements, the trailing arm being secured at the rear end to a hub carrier which carries a rear wheel hub. A substantially vertically extending damping strut is provided between the rear end portion of the trailing arm and the vehicle body. The suspension systems of these types are advantageous in that they are simple in structure so that the overall weight can be decreased. There has however been recognized that the suspension systems of these types require trailing arm of substantial cross-sectional area in order to ensure an adequate lateral rigidity. Further, the front end of the trailing arm must be attached to the vehicle body at laterally spaced positions. As the results, the trailing arm must be of a substantial dimension and therefore of an increased weight. In order to solve the above problems, Japanese laid-open utility model 56-62205 proposes, in a vehicle rear suspension system including a trailing arm having a front end mounted on a vehicle body for vertical swinging movements and a rear end carrying a wheel hub, to provide a pair of vertically spaced lateral links which are pivotably connected at the laterally outward ends to the rear end portions of the trailing arm and at the laterally inward ends to the vehicle body. This type of suspension system is advantageous in that the lateral links supports the trailing arm so that the trailing arm may not be required to possess by itself a substantial lateral rigidity. It should however be noted that in this arrangement there are produced toe-out movements in the wheel when the wheel is bumped upwards with respect to the vehicle body and when the wheel is rebounced downwards with respect to the vehicle body. Such toe-out movements cause a tendency of over-steer in a curved path so that there will be a danger of steering instability. From DE-A-923 346 a vehicle rear suspension system in accordance with the preamble part of claim 1 is known. In this vehicle rear suspension system it is not possible to carry out a toe control. US-A-4 269 432 shows a vehicle rear suspension system in which a longitudinal arm is connected at a rear end with a rear wheel support member through a pivotable connection. Thus, the longitudinal member is not connected with the rear wheel support member so that a rotational moment about the axis of the rear wheel can be transmitted between these members. From DE-A-20 38 880 a vehicle rear suspension system is known in which the second lateral link means is connected at the rear end with a rear wheel support member for swingable movement about the support member. Due to the connection between these two members, the structure shown in DE-A-20 38 880 and in US-A-4 269 432 has a triangular upper arm having an inner end portion pivotably connected with the vehicle body through longitudinally spaced pivot means. The triangular upper arm used in either of the references DE-A-20 38 880 and US-A-4 269 432 is considered disadvantageous in that the vehicle body must have a space for allowing swinging movements of the arm. Providing such space is not easy because there are several link members which must be located in this area and the triangular arm must be arranged in a manner that interference with these other members can be avoided. It is the object of the invention to provide a vehicle rear suspension system according to the preamble part of claim 1 which achieves desired toe angle and camber angle control in a compact arrangement. According to the present invention, this and other objects can be accomplished in a vehicle rear suspension system in accordance with the preamble part of claim 1 by the features of the characterizing part of claim 1. The second lateral link means is located forwardly of the rotational centre of the rear wheel so that an effective control of the camber angle is possible. The shock absorbing means is located rearwardly of the second lateral link means and forwardly of the third lateral link means so that the shock absorbing means can be operated effectively. Because the shock absorbing means is located rearwardly of the second lateral link means it becomes possible to decrease the stroke of the second lateral link means under a vertical swinging movement of the swing arm means because the second lateral link means can be located closer to the swing axis of the swing arm means than in an arrangement wherein the second lateral link means is located rearward the shock absorbing means. Further, it is possible to increase the stroke of the shock absorbing means. According to the present invention a vehicle rear suspension system is provided which can suppress toe-out movements of the wheel under vertical bumping movements to thereby improve stability of the vehicle. Axial forces applied to the lateral links can be minimized. Toe-in movements are produced in the rear wheel under braking forces. The vehicle rear suspension system according to the invention can suppress toe-out movements of the rear wheel under vertical bumping movements and can produce desirable changes in toe-angles under side forces which are applied to the wheel when the vehicle is running through a curved path. Both the camber angle and the toe- angle of the rear wheel can be controlled. The rear suspension system according to the invention can minimize the tread change in upward bouncing and downward rebouncing of the rear wheel. According to the arrangement of the present invention, the orientation of the wheel carrying means and therefore that of the rear wheel is determined only by the three lateral link means. Therefore, it becomes possible to control the toe-angle and the camber angle of the rear wheel in a desired manner under either or all of upward bumping and downward rebouncing of the rear wheel and side and longitudinal forces applied to the rear wheel by simply determining the arrangements of the lateral link means. For example, the inclination of each lateral link means in a horizontal plane and that in a vertical plane may appropriately be determined. In addition or alternatively, the lengths of the respective lateral link means, the positions of connections of the lateral link means to the wheel carrying means and the lateral rigidity of the connections between the lateral link means to the wheel carrying means may appropriately be determined to obtain desired results. The swing arm means may simply possess strength and rigidity sufficient for transmitting longitudinal forces and rotating forces about a lateral axis. It is necessary that the swing arm means does not constrain the wheel carrying means so that the orientation of the wheel carrying means be controlled by the three lateral link means. For this purpose, the swing arm means may have low lateral rigidity so that the swing arm means be capable of deflecting in lateral directions under upward bouncing and downward rebouncing of the rear wheel. Alternatively, the swing arm means may be connected with the wheel carrying means so that a rotation about a vertical axis or a lateral relative displacement is permitted. In one mode of the present invention, one of the lateral link means is connected to the wheel carrying means at a position higher than positions where the other two lateral link means are connected with the wheel carrying means, the said positions being so located that a cornering force acting point on the rear wheel is between imaginary lines passing through the first mentioned position and respective ones of the second mentioned positions. With this arrangement, it is possible to decrease the axial forces on the lateral link means under a cornering force. Preferably, the first mentioned position is located above the rotation axis of the rear wheel and the second mentioned positions are located below the rotation axis. The aforementioned other two link means are preferably arranged so that projections in a horizontal plane of extensions of their longitudinal axes intersect each other outward said rear wheel. This particular arrangement is effective to produce a toe-in movement of the rear wheel under a braking force. In a specific feature of the present invention, the second lateral link means is connected to the wheel carrying means at a position above the rotation axis of the rear wheel, the first lateral link means being connected at a position below and forward the rotation axis and the third lateral link means being connected at a position below and rearward the rotation axis, the second lateral link means being shorter than the third lateral link means. This arrangement is effective to suppress toe-out movements of the rear wheel under upward bumping and downward rebouncing of the rear wheel. The first lateral link means is preferably connected to the wheel carrying means forward a line passing through the cornering force acting point on the rear wheel and the position where the second lateral link is connected to the wheel carrying means, the third lateral link means being connected to the wheel carrying means rearward of the aforementioned line, the distance between the position of connection of the second lateral link means and the aforementioned line being smaller than that between the position of connection of the third lateral link means and the aforementioned line. The arrangement is effective to produce a toe-in movement of the rear wheel under an inwardly directed side force. In a further mode of the present invention, the second and third link means are arranged rearward the first link means, the second link means being above and shorter than the third lateral link means, projections in a vertical transverse plane of longitudinal axes of the second and third lateral link means intersecting each other at a point inward the rear wheel, the first link means being shorter than the second and third link means. The above and other objects and features of the present invention will become apparent from the following descriptions of preferred embodiments taking reference to the accompanying drawings, in which: Figure 1 is a diagrammatical top plan view of a rear suspension system in accordance with one embodiment of the present invention; Figure 2 is a rear view of the suspension system; Figure 3 is a sectional view of a rubber bush for connecting the lateral link to the wheel carrying member; Figure 4 is a sectional view of the rubber bush for connecting the swing arm to the vehicle body; Figure 5 (a), (b), (c) are diagrams showing respectively changes in the toe-angle, the camber angle and the tread in the rear wheel under upward bumping and rebouncing movements; Figure 6 is a side view as seen from inside of a suspension system in accordance with another embodiment; Figure 7 is a side view similar to Figure 6 but showing a further embodiment; Figure 8 is a diagrammatical illustration of a further embodiment of the present invention; and, Figure 9 is a top plan view of a rear suspension mechanism showing a further embodiment. Referring now to the drawings, particularly to Figures 1 and 2, there is shown a vehicle rear left wheel 10 which is carried by a wheel carrying member 12 for rotation about a rotation axis L4. Between the wheel carrying member 12 and a vehicle body 16, there is a rear suspension system 14 which includes a longitudinally extending swing arm 18. The swing arm 18 is connected at the front end with a bracket 29 provided on a frame 28 of the vehicle body 16 by means of a rubber bush 39 and a laterally extending pin 38 so that the arm 38 is vertically swingable about a horizontal axis. The rear end of the swing arm 18 is secured to the wheel carrying member 12 by means of bolts 30. The suspension system 14 further includes a first lateral link 20, a second lateral link 22 and a third lateral link 24. The first lateral link 20 extends substantially transversely with respect to the vehicle body 16 and has a transverse outward end connected with the wheel carrying member 12 through a rubber bush 20a for swinging movement about a substantially longitudinal axis. The transverse inward end of the first lateral link 20 is connected with the body frame 28 through a rubber bush 20b for swinging movement about a substantially longitudinal axis. The second and third lateral links 22 and 24 are connected at one ends respectively through rubber bushes 22a and 24a to the wheel carrying member 12 for swinging movements about substantially longitudinal axes, and at the other ends respectively through rubber bushes 22b and 24b to a rear sub-frame 32 of the vehicle body 16 for swinging movements about substantially longitudinal axes. In Figure 3, there is shown the rubber bush 22a as typical example of the aforementioned rubber bushes. It should be noted that the other bushes have similar structures. Between the wheel carrying member 12 and the vehicle body 16, there is disposed a substantially vertically extending strut assembly 26 which comprises a coil spring 34 and an oleo damper 36. The strut assembly 26 is pivotably connected at the lower end with the wheel carrying member 12 and connected at the upper end to the vehicle body 16 so as to allow a certain degree of angular movement. As shown in Figure 1, the first lateral link 20 is inclined rearward and downward and has a length shorter than those of the other two lateral links 22 and 24. The second lateral link 22 is inclined slightly forward and upward whereas the third lateral link 24 is inclined slightly downward. The first lateral link 20 has a longitudinal axis L1 and the third lateral link 24 has a longitudinal axis L2, the axes L1 and L2 intersecting each other at a point P which is laterally outwardly apart from a vertical line passing through the wheel center 40 by a distance ℓ1 and longitudinally rearwardly apart from the wheel rotation axis L4 by a distance ℓ2. It will further be noted that projections of the axes of the second and third lateral links 22 and 24 on a transverse vertical plane intersect each other at a point inward the wheel 10. Further, the first lateral link 20 is shorter in length than the third lateral link 24. As the wheel 10 is bumped in a vertical direction, the swing arm 18 is swung about the pin 38 so that the wheel center 40 is moved along an arcuate path having a center of arc at the axis of the pin 38. The wheel carrying member 12 is laterally supported by three lateral links 20, 22 and 24 which also swing in vertical directions to produce lateral displacements at the outward ends. In the embodiment shown in Figures 1 and 2, when the wheel 10 is upwardly bumped, the laterally outward end of the first lateral link 20 is slightly displaced outward but the displacement is small because the link 20 is inclined rearward. The outer end of the second lateral link 22 is displaced inward in response to an upward bump of the wheel. Further, the outer end of the third lateral link 24 is displaced outward, the distance of displacement being larger than that of the outer end of the first lateral link 20. Since the outer ends of the first and second lateral links 20 and 24 are located forward the outer end of the third lateral link 24, there is produced a slight toe-in movement. Further, there is produced a decrease in the camber angle. Under a downward rebouncing of the wheel, there are produced a slight toe-out movement and a slight increase in the camber angle. Speaking more specifically, the toe-angle of the wheel is changed as shown by a curve a in Figure 5(a). The toe-angle change in the prior art suspension system of the laid-open Japanese utility model 56-62205 is shown by a curve b in Figure 5 (a). Thus, the advantage of the present invention will be apparent from this diagram. Where the third lateral link 24 has a length sufficiently large as compared with the first lateral link 20, there will be no noticeable displacement in the outer end of the third lateral link 24 so that the toe-angle change will be as shown by a curve c. It will be understood that the camber angle is changed as shown by a curve M₁ in Figure 5(b) due to the arrangements of the second and third lateral links 22 and 24 as described previously. As the wheel 10 bumps upward, the wheel carrying member 12 is displaced inward and there may be produced a decrease in tread between the rear wheels. However, in the arrangement described above, the camber angle is decreased in response to an upward bumping of the wheel and the decrease in the camber angle causes an increase in the tread. As the result, the tread changes as shown by a curve M₂ in Figure 5(c). Where the second and third lateral links 22 and 24 are inclined so that projections of their axes on a transverse vertical plane intersect outward the wheel 10, the camber angle will change as shown by a curve N₁ in Figure 5(b). Then, the tread will change as shown by a curve N₂ in Figure 5(c). Since the swing arm 18 is of a cross-sectional configuration which provides a certain degree of deflection in lateral direction of the vehicle body, the swing arm 18 is laterally deflected as necessary as the wheel carrying member 12 is displaced as described above. Further, the rubber bush 39 permits a certain amount of lateral displacement of the swing arm. Referring to Figure 4, it will be noted that the rubber bush 39 includes an outer tube 39a and an inner tube 39. A resilient rubber 39c is disposed between and adhered to the outer and inner tubes 39a and 39b. The pin 38 is inserted into the inner tube 39b to secure the inner tube 39b to the bracket 29 of the frame 28. The outer tube 39a is welded to the swing arm 18. It will be understood in Figure 5 that the rubber bush 39 is deflected as shown by phantom lines to permit a lateral displacement of the swing arm 18. When a braking force is applied to the wheel 10, the rubber bush 39 is deformed to allow a slight rearward displacement of the swing arm 18. Thus, there will be produced in the wheel carrying member 12 a turning displacement about the point P of intersection of the lines L₁ and L₂. Therefore, a slight toe-in displacement is produced in the rear wheel 10. When a forwardly directed traction force is applied to the wheel 10, there may be produced a toe-out displacement in the wheel 10. However, such toe-out displacement can be prevented by providing the rubber bush 39 with a stopper which restricts forward deflection of the rubber bush 39. When a side force or a cornering force F is applied to the rear wheel 10 as shown in Figure 1, there will be produced a slight toe-in displacement due to reaction forces applied from the lateral links 20, 22 and 24 to the wheel carrying member 12 since the side force acting point on the wheel 10 is forward the point P of intersection of the lines L₁ and L₂. Thus, a steering stability is ensured in operations through curved paths. It is also possible to obtain a slight toe-in displacement under an inwardly directed side force and a slight toe-out displacement under an outwardly directed side force by appropriately determining the lateral rigidity of the rubber bushes 20a, 22a and 24a connecting the lateral links 20, 22 and 24 to the wheel carrying member 12. Referring now to Figure 6, the embodiment shown therein is different from the previous embodiment in that the second lateral link 22 is connected to the wheel carrying member 12 at a location above and forward of the wheel center 40. In either of the previously described arrangements, it is possible to substantially equalize the axial forces produced in the lateral links 20, 22 and 24 under a side force F. In Figure 6, considering the balance of moment about a line L₅ passing through centers of the rubber bushes 20a and 22a, a moment produced by the side force F acting on a point P₁ is balanced by a moment produced by an axial compression force F₃ in the third lateral link 24. Similarly, considering the balance of moment about a line L₆ passing through centers of the rubber bushes 22a and 24a, a moment produced by the side force F is balanced by a moment produced by an axial compression force F₁ in the first lateral link 20. In order to counterbalance these axial compression forces F₁ and F₃, there will be produced an axial tensile force F₂ in the second lateral link 22, the sum of the forces F₁ and F₃ being substantially equal to the sum of the force F₂ and the side force F. Figure 7 shows another embodiment of the present invention in which corresponding parts are designated by the same reference numerals. Referring to Figure 7, there is drawn an imaginary line L₇ which passes through the center of the rubber bush 22a and the side force acting point P₁ on the wheel 10. In this embodiment, the distance ℓ1 between the center of the rubber bush 20a and the imaginary line L₇ is smaller than the distance ℓ₂ between the center of the rubber bush 24a and the imaginary line L₇ . In this arrangement, the axial compression force F₁ produced in the first lateral link 20 under the side force F becomes greater than that F₃ in the third lateral link 24. Such difference in the axial forces F₁ and F₃ produces a difference in deformations of the rubber bushes 20a and 24a and causes a slight toe-in movement of the wheel 10. Figure 8 shows a modification of the arrangement of Figure 7 and a similar toe-in movement of the wheel 10 is produced under a side force F. Referring now to Figure 9, the embodiment shown therein is different from the previously described embodiments in that the rubber bush 39 for connecting the front end of the swing arm 18 has an axis 39ℓ which is inwardly and rearwardly inclined with respect to a transverse direction of the vehicle body. With this arrangement, when the wheel 10 is bumped, the swing arm 18 is deflected inward as shown by phantom lines to permit inward displacement of the wheel carrying member 12. At the same time, an axial deformation is produced in the rubber bush 39 causing a slight rearward displacement of the swing arm 18 and therefore a corresponding rearward displacement of the wheel carrying member 12. As the result, there will be produced a slight toe-in movement as described with reference to Figure 1. The invention has been shown and described with reference to specific embodiments, however, it should be noted that the invention is in no way limited to the details of the illustrated structures but changes and modifications may be made without departing from the scope of the appended claims.

Claims: A vehicle rear suspension system comprising swing arm means (18) extending substantially longitudinally and having one front portion resiliently connected to the vehicle body for vertical swinging movements about a substantially horizontal transverse axis (391) and for permitting a certain lateral displacement of said swing arm, wheel carrying means (12) for carrying a rear wheel (10) for rotation about a rotation axis (L4), said wheel carrying means (12) being rigidly connected to the rear end of said swing arm means (18) such that a rotational moment about the axis of the rear wheel can be transmitted between the swing arm means (18) and the wheel carrying means (12), first (20), second (22) and third (24) lateral link means extending in substantially lateral direction of the vehicle body and controlling the attitude of the rear wheel (10), said second lateral link means (22) being above a rotational center (40) of the rear wheel (10), said third lateral link means (24) being located downward and rearward of said rotational centre (40) of the rear wheel (10), said first lateral link means (20) being located forwardly of said third lateral link means (24), and whereby each of said lateral link means (20, 22, 24) comprises a transverse inner end connected to the vehicle body about a single pivotal connection, shock absorbing means (26) located between said wheel carrying means and said vehicle body for absorbing vertical vibratory loads, characterized in that said second lateral link means (22) is located forwardly of the rotational centre (40) of the rear wheel (10), said first lateral link means (20) has a length shorter than those of the other two lateral links (22, 24) and in that said shock absorbing means (26) is located rearwardly of the second lateral link means (22) and forwardly of said third lateral link means (24). A vehicle rear suspension system in accordance with claim 1 in which said third lateral link means (24) is located downward and rearward of said second lateral link means (22). A vehicle rear suspension system in accordance with claim 1 or 2 in which said first lateral link means (20) is arranged so that the outer end is located rearwardly with respect to the inner end and has an axis of which extension intersects with an extension of the axis of the third lateral link means (24). A vehicle rear suspension system in accordance with any one of claims 1 through 3 in which said inner end of the third lateral link means (24) is connected with a subframe (32) provided on the vehicle body (16) to extend in a lateral direction of the vehicle body (16). A vehicle rear suspension system in accordance with any one of claims 1 through 4 in which said third lateral link means (24) has a length which is longer than any one of lenghts of the second (22) and first (20) lateral link means.

Inventors: ARAKI NOBUHIRO C O MAZDA MOTOR, KANAI SEITA C O MAZDA MOTOR CO, TAKATA NAOTO C O MAZDA MOTOR C, UDO TADASHI C O MAZDA MOTOR CO, ARAKI, NOBUHIRO C/O MAZDA MOTOR CORPORATION, KANAI, SEITA C/O MAZDA MOTOR CORPORATION, TAKATA, NAOTO C/O MAZDA MOTOR CORPORATION, UDO, TADASHI C/O MAZDA MOTOR CORPORATION
Applicants: MAZDA MOTOR, MAZDA MOTOR CORPORATION
Application year: 1984
Main classification: B60G3
IPC codes: B60G3