Suspension system of a vehicle

Abstract: A suspension system for a vehicle comprises a steering knuckle (1) supporting a wheel used for steering, a steering arm (15) connected to the steering knuckle at one end and to a tie rod (14) of a steering device at the opposite end, an upper arm for connecting an upper portion of the steering knuckle to the frame of the vehicle, a lower arm (3) for connecting a lower portion of the steering knuckle to a frame of the vehicle, at least one of said arms comprising two link members (6, 7), each of said link members being pivotally connected to the frame of the vehicle at one end and to the steering knuckle at the opposite end, said link members (6, 7) being so disposed as to increase the distance (L) between the connection point (16) of the steering arm with the tie rod and the kingpin axis (KL) in response to an increase of the turning angle of the wheel in a turn wherein the wheel is located radially outwardly in relation to a turning circle, and reduce the distance (L) in response to an increase of the turning angle of the wheel in a turn wherein the wheel is located radially inwardly in relation to the turning circle.

Description: BACKGROUND OF THE INVENTION 1. Field of the invention The present invention relates to a suspension system for anchoring wheels used for steering to a frame of a vehicle. 2. Description of the prior art Hereinafter, a fore to aft direction of the vehicle is called a longitudinal direction, and a side to side direction of the vehicle is called a transverse direction. Also, a location near to a centerline of the vehicle is called inside, and a location distant from a centerline of the vehicle is called outside. There has been known a double pivot type suspension system for a vehicle. For example, Japanese Utility Model Laid-Open Publication No. 64-26507 shows such a type of suspension system according to the preamble of claim 1. This type of suspension system comprises a steering knuckle for supporting a wheel, and an upper arm and a lower arm respectively connecting an upper portion and a lower portion of the steering knuckle to a frame of a vehicle. At least one of the arms comprises two link members, each of which is pivotally connected to the frame at a respective one end thereof, and to the steering knuckle at a respective opposite end thereof. In this type of suspension system, a kingpin axis, which is an axis around which a wheel used for steering is turned, extends through a cross point between the axes of the two link members. The kingpin axis moves in response to the movement of the cross point in a horizontal plane during steering of the vehicle. When the vehicle is turned, a wheel which is located radially inwardly in relation to a turning circle must be turned more sharply than a wheel which is located radially outwardly in relation to the turning circle. This principle is known as the ACKERMAN PRINCIPLE. The ACKERMAN PRINCIPLE has previously been achieved by differentiating a transverse inclination in a horizontal plane of a tie rod for the wheel which is located radially inwardly in relation to a turning circle from that of a tie rod for the wheel which is located radially outwardly in relation to the turning circle. But the above measures cause a problem wherein the length of the tie rod and the position of a rack for driving the tie rod is restricted, so that the degree of design freedom regarding the steering system is reduced. SUMMARY OF THE INVENTION It is therefore the object of the present invention to provide a double pivot type suspension system for a vehicle wherein the ACKERMAN PRINCIPLE is achieved by using the movement of the kingpin axis during steering of the vehicle so that the degree of design freedom regarding the steering system is increased. In accordance with the present invention, there is provided a suspension system for a vehicle which comprises a steering knuckle supporting a wheel used for steering, a steering arm connected to the steering knuckle at one end and to a tie rod of a steering device at the opposite end, an upper arm for connecting the upper portion of the steering knuckle to a frame of the vehicle, a lower arm for connecting a lower portion of the steering knuckle to the frame of the vehicle, at least one of said arms comprising two link members, each of said link members being pivotally connected to the frame of the vehicle at one end and to the steering knuckle at the opposite end, said suspension system being characterised in that said link members are so disposed as to increase a distance between the connection point of the steering arm with the tie rod and a kingpin axis in response to an increase in the turning angle of the wheel used for steering when the wheel is turned in a direction wherein the wheel is located radially outwardly in relation to a turning circle, and reduce said distance in response to an increase in the turning angle of the wheel when the wheel is turned in a direction wherein the wheel is located radially inwardly in relation to the turning circle. In a preferable embodiment of the present invention, said upper arm comprises said two link members, one of the link members being disposed in a transverse direction, the other link member being disposed in a longitudinal direction, the two link members being disposed such that, in a plan view, a forwardly extended portion of an axis of the longitudinally disposed link member crosses an axis of the transversely disposed link member, with the cross point between the axis of the longitudinally disposed link member and the axis of the transversely disposed link member being located, during the turning of the wheel used for steering, in front of a vertical plane which includes the connection point of the steering arm with the tie rod and extends in a transverse direction, said steering arm being located to the rear of the center of the wheel used for steering. In another preferable embodiment of the present invention, said upper arm comprises said two link members, one of the link members being disposed in a transverse direction, the other link member being disposed in a longitudinal direction, the two link members being disposed such that, in a plan view, an axis of the longitudinally disposed link member crosses an axis of the transversely disposed link member when the wheel used for steering is in a neutral position, with the cross point between the axis of the longitudinally disposed link member and the axis of the transversely disposed link member being located, during the turning of the wheel used for steering, in front of a vertical plane which includes the connection point of the steering arm with the tie rod and extends in a transverse direction, said steering arm being located to the rear of the center of the wheel used for steering. In still another preferable embodiment of the present invention, said lower arm comprises said two link members, one of the link members being disposed in a transverse direction, the other link member being disposed in a longitudinal direction, the two link members being disposed such that, in a plan view, a forwardly extended portion of an axis of the longitudinally disposed link member crosses a portion of an axis of the transversely disposed link member extended toward the outside of the vehicle, with the cross point between the axis of the longitudinally disposed link member and the axis of the transversely disposed link member being located, during the turning of the wheel used for steering, to the rear of a vertical plane which includes the connection point of the steering arm with the tie rod and extends in a transverse direction, said steering arm being located in front of the center of the wheel used for steering. In another preferable embodiment of the present invention, said lower arm comprises said two link members, one of the link members being disposed in a transverse direction, the other link member being disposed in a longitudinal direction, the two link members being disposed such that, in a plan view, an axis of the longitudinally disposed link member crosses a portion of an axis of the transversely disposed link member extended toward the outside of the vehicle when the wheel used for steering is in a neutral position, with the cross point between the axis of the longitudinally disposed link member and the axis of the transversely disposed link member being located, during the turning of the wheel used for steering, to the rear of a vertical plane which includes the connection point of the steering arm with the tie rod and extends in a transverse direction, said steering arm being located in front of the center of the wheel used for steering. According to the features of the present invention, the two link members are so disposed as to increase a distance between the connection point of the steering arm with the tie rod and a kingpin axis in response to an increase in a turning angle of the wheel used for steering when the wheel is turned toward an outward direction wherein the wheel is located radially outwardly in relation to a turning circle, and reduce the distance in response to an increase in a turning angle of the wheel when the wheel is turned toward an inward direction wherein the wheel is located radially inwardly in relation to the turning circle. As a result, the turning angle of the wheel which is located radially inwardly in relation to a turning circle becomes larger than that of the wheel which is located radially outwardly in relation to a turning circle, that is the wheel which is located radially inwardly in relation to a turning circle is turned more sharply than a wheel which is located radially outwardly in relation to the turning circle. Thus, the ACKERMAN PRINCIPLE is achieved. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a plan view of a suspension system in accordance with a first embodiment of the present invention. Figure 2 is a front view of a suspension system in accordance with the first embodiment of the present invention. Figure 3 is a schematic perspective view showing a general arrangement of the suspension system of a first embodiment of the present invention. Figure 4 is a schematic plan view of the arrangement of Figure 3. Figure 5 is a side view showing a movement of a kingpin axis in the first embodiment. Figure 6 is a diagram showing variations in a distance between a kingpin axis and a connection point of a steering arm with a tie rod. Figure 7 is a schematic plan view of a general arrangement of a suspension system of a second embodiment of the present invention. Figure 8 is a side view showing a movement of a kingpin axis in the second embodiment. Figure 9 is a schematic plan view of a general arrangement of a suspension system of a third embodiment of the present invention. Figure 10 is a side view showing a movement of a kingpin axis in the third embodiment. Figure 11 is a schematic plan view of a general arrangement of a suspension system of a fourth embodiment of the present invention. Figure 12 is a side view showing a movement of a kingpin axis in the fourth embodiment. DESCRIPTION OF THE PREFERED EMBODIMENTS Referring to Figures 1 to 3, there is shown a suspension system according to a first embodiment of the present invention. The suspension system is for anchoring a right front wheel W, which is a wheel used for steering, of a FF (front-engine-front-drive) vehicle, to the frame of the vehicle. In Figures 1 to 3, a steering knuckle 1 supporting the wheel W is connected to and supported by the frame of the vehicle ( not shown) at an upper portion thereof through an upper arm 2, while being connected to and supported by the frame of the vehicle ( not shown) at a lower portion thereof through a lower arm 3. The lower arm 3 has an A shaped configuration. Two end points of the A shaped lower arm 3 are aligned in substantially a longitudinal direction of the vehicle, and respectively connected to and supported by the frame of the vehicle for vertical pivotal motion through rubber bushings 4a, 4b. The apex of the A shaped lower arm 3 is rotatably connected to the steering knuckle 1 through a ball joint 5. The upper arm 2 comprises two link members 6, 7. The link member 6 is disposed in substantially a transverse direction of the vehicle. The link member 6 is connected to the frame of the vehicle through a rubber bush 8 at one end thereof and pivotally connected to the steering knuckle 1 through a ball joint 9 at an opposite end thereof. The link member 7 is disposed above the link member 6 and in substantially a longitudinal direction of the vehicle. The link member 7 is connected to the frame of the vehicle through a rubber bush 10 at one end thereof and pivotally connected to the steering knuckle 1 through a ball joint 11 at an opposite end thereof. As shown in Figure 1, in a plan view, the link member 7 is disposed such that its axis, when extended forward, crosses an axis of the link member 6 at point P on the axis of the link member 7. More over, the link member 7 is located to the rear of the cross point P in relation to the longitudinal direction of the vehicle. Though not shown in Figure 1, the rubber bushes 8, 10 respectively comprise an inner cylinder, an outer cylinder and a rubber placed into a space between the two cylinders. Thus, the link members 6, 7 can pivot horizontally within a limited angle determined by the resiliency of the rubber bushes 8, 10, and they can rotate around the axes of the rubber bushes 8, 10, that is they can pivot upward and downward. In Figure 1, there is also shown a drive shaft 12 and a shock absorber 13. The shock absorber 13 is connected to the lower arm 3 at a lower end thereof and, to the frame of the vehicle at an upper end thereof. A tie rod 14 of the steering system is connected to a steering arm 15 protruding rearwardly from the steering knuckle 1 through a ball joint 16. Thus, under a steering force provided through the tie rod 14, the front wheel W, integrally with the steering knuckle 1, turns around a kingpin axis KL. The kingpin axis KL extends from a cross point between the lower arm 3 and the steering knuckle 1, ie., the center of the ball joint 5, to the point P on the axis of the link member 7 where, in a plan view, the axis of the link member 6 and the axis of the link member 7 cross each other. A distance L between the kingpin axis KL and the center of the connection point between the steering arm 15 and the tie rod 14, ie., the center of the ball joint 16, varies as the cross point P moves in response to the turning of the front wheel W. The variation of the distance L in response to the turning of the front wheel W will be described hereinafter with reference to Figures 4 and 5. In Figures 4 and 5, the link members 6, 7 are indicated by solid lines when the front wheel W is in the neutral position, by dashed lines when the front wheel W is turned in a direction wherein the wheel W is positioned radially outwardly in relation to a turning circle of the vehicle, that is the front wheel W is turned so as to turn the vehicle to the left in this embodiment, hereinafter said direction bing called an outward direction, by two-dot chain lines when the front wheel W is turned in a direction wherein the wheel W is positioned radially inwardly in relation to a turning circle of the vehicle, that is the front wheel W is turned so as to turn the vehicle to the right in this embodiment, hereinafter said direction being called an inward direction. As understood from Figure 4, the link members 6, 7 of the upper arm 2 horizontally pivot around their respective connection points to the frame of the vehicle, ie., the rubber bushes 8, 10, in response to the turning of the front wheel W. Thus the cross point P between the link members 6 and 7 moves along the axis of the link member 6. More specifically, when the front wheel W is turned to the outward direction from the neutral position, the cross point P moves to the outside of the vehicle along the link member 6 ( P₀ to P₁ ). When the front wheel W is turned to the inward direction from the neutral position, the cross point P moves to the inside of the vehicle along the link member 6 ( P₀ to P₂ ). Link members 6, 7 are so disposed as to, during the turning, locate the cross point P in front of a vertical plane which includes the connection point 16 between the steering arm 15 and the tie rod 14 and extends in a transverse direction. Thus, as shown in Figure 5, the kingpin axis KL longitudinally pivots around the center of the connection point of the lower arm 3 with the steering knuckle 1, ie., the center of the ball joint 5, in response to the turning of the wheel W. The distance L between the kingpin axis and the connection point 16 increases when the front wheel W is turned to the outward direction from the neutral position ( L₀ to L₁ ) , while it decreases when the front wheel W is turned to the inward direction from the neutral position ( L₀ to L₂ ). As a result, as shown in Figure 6, the distance L gradually increases in response to the increase in the turning angle when the front wheel is turned to the outward direction, while it gradually decreases in response to the increase in the turning angle when the front wheel is turned to the inward direction. As described above, link members 6, 7 are so disposed as to increase the distance L between the kingpin axis KL and the connection point 16 between the steering arm 15 and the tie rod 14 in response to the increase in the turning angle when the front wheel W is turned to the outward direction and decrease the distance L in response to the increase in the turning angle when the front wheel W is turned to the inward direction. As a result, the turning angle of the wheel which is located radially inwardly in relation to a turning circle becomes larger than that of the wheel which is located radially outwardly in relation to a turning circle, that is the wheel which is located radially inwardly in relation to a turning circle is turned more sharply than a wheel which is located radially outwardly in relation to the turning circle. Thus, the ACKERMAN PRINCIPLE can be achieved wihout differentiating the transverse inclinations of the tie rods, so that the degree of design freedom regarding the steering system can be increased. Figure 7 shows a second embodiment of the present invention. The arrangement of the suspension system in this embodiment is almost the same as in the first embodiment. But, in this embodiment, the link members 6, 7 which define the upper arm 2 are disposed such that, in a plan view, the axis of the link member 7 crosses the axis of the link member 6 when the front wheel W is in the neutral position. By this arrangement, the cross point P between the link members 6 and 7 moves along the axis of the link member 6 in the same manner as the first embodiment, so that, as shown in Figure 8, the kingpin axis KL longitudinally pivots around the center of the connection point of the lower arm 3 with the steering knuckle 1, ie., the center of the ball joint 5, in response to the turning of the wheel W. As a result, the distance L between the kingpin axis and the connection point 16 increases when the front wheel W is turned to the outward direction from the neutral position ( L₀ to L₁ ), while it decreases when the front wheel W is turned to the inward direction from the neutral position ( L₀ to L₂ ). Thus, the ACKERMAN PRINCIPLE can be achieved. Figure 9 shows a third embodiment of the present invention. In this embodiment, the upper arm 2 has an A shaped configuration. Two end points of the A shaped upper arm 2 are aligned in substantially a longitudinal direction of the vehicle, and respectively connected to and supported by the frame of the vehicle for vertical pivotal motion through rubber bushings 24a, 24b. The apex of the A shaped upper arm 2 is rotatably connected to the steering knuckle 1 ( not shown ) through a ball joint 25. The lower arm 3 comprises two link members 26, 27. The link member 26 is disposed in substantially a transverse direction of the vehicle. The link member 26 is connected to the frame of the vehicle through a rubber bush 28 at one end thereof and pivotally connected to the steering knuckle 1 through a ball joint 29 at an opposite end thereof. The link member 27 is disposed longitudinally and obliquely. The link member 27 is connected to the frame of the vehicle through a rubber bush 30 at one end thereof and pivotally connected to the steering knuckle 1 through a ball joint 31 at an opposite end thereof. As shown in Figure 9, in a plan view, the link members 26 and 27 are disposed such that, when the link member 27 is extended forwardly and the link member 26 is extended toward the outside of the vehicle, they crosse each other at point P. More over, the link member 27 is located to the rear of the cross point P in relation to the longitudinal direction of the vehicle. A tie rod 34 of the steering system is connected to a steering arm 35 protruding forwardly from the steering knuckle 1 through a ball joint 36. Link members 26, 27 are so disposed as to, during turning, locate the cross point P to the rear of a vertical plane which includes the connection point of the steering arm 35 with the tie rod 34, ie., the ball joint 36, and extends in transverse direction. Thus, as understood from Figure 9, the cross point P between the link members 26 and 27 moves rearwardly ( P₀ to P₁ ) when the front wheel W is turned to the outward direction. When the front wheel W is turned to the inward direction, the cross point P moves forward ( P₀ to P₂ ). As a result, as shown in Figure 10, the kingpin axis KL longitudinally pivots around the center of the connection point of the upper arm 2 with the steering knuckle 1, ie., the center of the ball joint 25, in response to the turning of the wheel W, so that the distance L between the kingpin axis and the connection point 36 increases when the front wheel W is turned to the outward direction from the neutral position ( L₀ to L₁ ), while it decreases when the front wheel W is turned to the inward direction from the neutral position ( L₀ to L₂ ). Thus, the ACKERMAN PRINCIPLE can be achieved wihout differentiating the transverse inclinations of the tie rods, so that the degree of design freedom regarding the steering system can be increased. Figure 11 shows a fourth embodiment of the present invention. The arrangement of the suspension system in this embodiment is almost the same as in the third embodiment. But, in this embodiment, the link members 26, 27 which define the lower arm 3 are disposed such that, in a plan view, the axis of the link member 26, when extended toward the outside of the vehicle, crosses the axis of the link member 27 in the neutral position. By this arrangement, as understood from Figure 11, the cross point P between the link members 26 and 27 moves rearwardly ( P₀ to P₁ ) when the front wheel W is turned to the outward direction in the same manner as in the third embodiment. When the front wheel W is turned to the inward direction, the cross point P moves forward ( P₀ to P₂ ). As a result, as shown in Figure 12, the kingpin axis KL longitudinally pivots around the center of the connection point of the upper arm 2 with the steering knuckle 1, ie., the center of the ball joint 25, in response to the turning of the wheel W, so that the distance L between the kingpin axis and the connection point 36 increases when the front wheel W is turned to the outward direction from the neutral position ( L₀ to L₁ ), while it decreases when the front wheel W is turned to the inward direction from the neutral position ( L₀ to L₂ ). Thus, the ACKERMAN PRINCIPLE can be achieved wihout differentiating the transverse inclinations of the tie rods, so that the degree of design freedom regarding the steering system can be increased.

Claims: A suspension system for a vehicle comprising: a steering knuckle (1) supporting a wheel used for steering; a steering arm (15) connected to the steering knuckle (1) at one end and to a tie rod (14) of a steering device at the opposite end; an upper arm (2) connecting the upper portion of the steering knuckle (1) to the frame of the vehicle; a lower arm (3) connecting the lower portion of the steering knuckle (1) to the frame of the vehicle; at least one of said arms (2,3) comprising two link members (6,7), each of said link members being pivotally connected to the frame of the vehicle at one end and to the steering knuckle at (1) at the opposite end, said suspension system being characterised in that said link members (6,7) are so disposed as to increase the distance between the connection point (16) of the steering arm (15) with the tie rod (14) and the kingpin axis in response to an increase in the turning angle of the wheel used for steering when the wheel is turned in a direction wherein the wheel is located radially outwardly in relation to a turning circle, and reduce said distance in response to an increase in the turning angle of the wheel when the wheel is turned in a direction wherein the wheel is located radially inwardly in relation to the turning circle. A suspension system for a vehicle in accordance with claim 1, wherein: said upper arm (2) comprises said two link members (6,7); one of the link members (6) being disposed in a transverse direction; the other link member (7) being disposed in a longitudinal direction; the two link members (6,7) being disposed such that, in a plan view, a forwardly extended portion of an axis of the longitudinally disposed link member crosses an axis of the transversely disposed link member, with the cross point between the axis of the longitudinally disposed link member and the axis of the transversely disposed link member being located, during the turning of the wheel used for steering, in front of a vertical plane which includes the connection point (16) of the steering arm (15) with the tie rod (14) extends in a transverse direction; said steering arm (15) being located to the rear of the center of the wheel used for steering. A suspension system for a vehicle in accordance with claim 1, wherein: said upper arm (2) comprises said two link members (6,7); one of the link members (6) being disposed in a transverse direction; the other link member (7) being disposed in a longitudinal direction; the two link members (6,7) being disposed such that, in a plan view, an axis of the longitudinally disposed link member crosses an axis of the transversely disposed link member when the wheel used for steering is in a neutral position, with the cross point between the axis of the longitudinally disposed link member and the axis of the transversely disposed link member being located, during the turning of the wheel used for steering, in front of a vertical plane which includes the connection point (16) of the steering arm (15) with the tie rod (14) and extends in a transverse direction; said steering arm (15) being located to the rear of the center of the wheel used for steering. A suspension system for a vehicle in accordance with claim 1, wherein: said lower arm (3) comprises said two link members (26,27); one of the link members (26) being disposed in a transverse direction; the other link member (27) being disposed in a longitudinal direction; the two link members (26,27) being disposed such that, in a plan view, a forwardly extended portion of an axis of the longitudinally disposed link member crosses a portion of an axis of the transversely disposed link member extended toward an outside of the vehicle, with the cross point between the axis of the longitudinally disposed link member and the axis of the transversely disposed link member being located, during the turning of the wheel used for steering, to the rear of a vertical plane which includes the connection point (36) of the steering arm (35) with the tie rod (34) and extends in a transverse direction; said steering arm (35) being located in front of the center of the wheel used for steering. A suspension system for a vehicle in accordance with claim 1, wherein: said lower arm (3) comprises said two link member (26,27); one of the link members (26) being disposed in a transverse direction; the other link member (27) being disposed in a longitudinal direction; the two link members (26,27,) being disposed such that, in a plan view, an axis of the longitudinally disposed link member crosses a portion of an axis of the transversely disposed link member extended toward an outside of the vehicle when the wheel used for steering is in a neutral position, with the cross point between the axis of the longitudinally disposed link member and the axis of the transversely disposed link member being located, during the turning of the wheel used for steering, to the rear of a vertical plane which includes the connection point (36) of the steering arm (35) with the rod (34) and extends in a transverse direction; said steering arm (35) being located in front of the center of the wheel used for steering.

Inventors: KUMADA HIROYOSHI PAREGURESU-NI, YAMAMOTO TADANOBU, KUMADA, HIROYOSHI 1015, PAREGURESU-NIHO II, YAMAMOTO, TADANOBU
Applicants: MAZDA MOTOR, MAZDA MOTOR CORPORATION
Application year: 1991
Main classification: B60G3
IPC codes: B60G3, B62D7