SUSPENSION DEVICE

BACKGROUND OF THE INVENTION

1. Field of the Invention [0001] The present invention relates to the structure of a stabilizer which is provided in a suspension device to prevent rolling.

2. Description of the Related Art

[0002] In general, when a vehicle turns, the vehicle body is subjected to rolling by centrifugal force and the stability of the vehicle is adversely affected. To prevent the rolling, vehicles are usually provided with a stabilizer. The opposite ends of the stabilizer are connected to members that support wheels. When rolling occurs when the vehicle turns, the right and left support members are vertically displaced in different amounts, and therefore, the stabilizer is subjected to torsion. The torsion produces a force against the rolling moment, and, consequently, rolling is controlled.

[0003] Various suggestions have been made about the installation position of the stabilizer bar in a suspension for a vehicle provided with a stabilizer as described above to improve the performance of vehicles. For example, Japanese Patent Application Publication No. 3-276812 (JP-A-3-276812) discloses a structure in which the opposite ends of a stabilizer bar are connected to suspension members which rotate together with wheels during steering. Japanese Patent Application Publication No. 2005-306254 (JP-A-2005-306254) discloses a structure in which a fixing point of the stabilizer bar is set at an intersection between the central axis of a connecting rod and a kingpin axis. Japanese Patent Application Publication No. 2006-117159 (JP-A-2006-117159) discloses a structure in which a stabilizer link is joined to a member which does not rotate relative to steering.

[0004] With the technique disclosed in JP-A-3-276812, the roll rigidity during a turn of the vehicle can be improved. However, if the right and left suspension devices are stroked in opposite phases, that is, one of the suspension devices is stroked upward and the other downward, because of unevenness of the road surface or some other reason when the vehicle is traveling straight ahead, the stabilizer bar generates a force that urges the wheels to turn and, consequently, the directional stability of the vehicle is lowered.

CONFIRiViATION COPY

SUMMARY OF THE INVENTION

[0005] The present invention provides a suspension structure which does not lower the directional stability of a vehicle even under road conditions that cause the right and left suspension devices to be stroked in opposite phases. [0006] A first aspect of the present invention provides a suspension device including: a suspension member that rotates together with a wheel when a vehicle is steered; a stabilizer bar that connects suspension members for right and left wheels to prevent rolling; and a stabilizer link that connects a component of the suspension member and an end of the stabilizer bar. In this device, the angle between a kingpin axis as an axis of steering rotation and a stabilizer link axis and the minimum distance between the kingpin axis and the stabilizer link axis are set such that the moment which is generated about the kingpin axis by wheel weight and the moment which is generated about the kingpin axis by a reaction force of the stabilizer link can equilibrate when the suspension members for the right and left wheels are stroked in opposite directions.

[0007] According to the first aspect, the stabilizer link is positioned such that the moments which are generated about the kingpin axis equilibrate even if the suspension members for the right and left wheels are stroked in opposite phases because of unevenness of the road surface or some other reason when the vehicle is traveling straight ahead. Therefore, since no difference occurs between the forces acting on the right and left wheels, the wheel are not turned. As a result, lowering of the directional stability of the vehicle can be prevented.

[0008] The suspension member to which an end of the stabilizer link is connected is not limited as long as it is a member which is turned about the kingpin axis together with the wheel, and may be a shell case of a shock absorber.

[0009] The connection of the stabilizer link may be made by means of a ball joint. The connection may be made by means of a bush or using a cushion method in which an end of the stabilizer link is connected via an elastic member made of rubber or the like. [0010] A second aspect of the present invention relates to a strut-type suspension device. The device includes: a knuckle that supports a wheel; a lower arm that connects the knuckle to a vehicle body; a shock absorber disposed between the knuckle and the vehicle body to attenuate oscillation of the lower arm; a stabilizer bar that controls rolling of the vehicle body; a stabilizer link that connects a shell case of the shock absorber and an end of the stabilizer bar; and a kingpin axis connecting the

connection point of the shock absorber to the vehicle body and the connection point between the knuckle and the lower arm. The stabilizer link is positioned such that the moment which is generated about a kingpin axis by wheel weight and the moment which is generated about the kingpin axis by a reaction force of the stabilizer link equilibrate when the shock absorbers for the right and left wheels are stroked in opposite directions.

[0011] According to the second aspect, the stabilizer link is positioned such that the moments which are generated about the kingpin axis equilibrate even if the shock absorbers for the right and left wheels are stroked in opposite phases because of unevenness of the road surface or some other reason when the vehicle is traveling straight ahead. Therefore, since no difference occurs between the forces acting on the right and left wheels, the wheel are not turned. As a result, lowering of the directional stability of the vehicle can be prevented.

[0012] According to the suspension device of the present invention, the stabilizer link is positioned such that the moment about the kingpin axis which is generated by a stroke of the suspension device is cancelled even under road conditions that cause the right and left suspension devices to be stroked in opposite phases. Therefore, the directional stability of the vehicle is not lowered.

[0013] In the first aspect and second aspect of the present invention, the stabilizer bar may be a generally U-shaped torsion bar extending toward the rear of the vehicle or may be a generally U-shaped torsion bar extending toward the front of the vehicle.

[0014] Since the stabilizer link is positioned such that the moments about the kingpin axis which is generated by a stroke of the suspension device is cancelled even under road conditions that causes the right and left suspension devices to be stroked in opposite phases regardless of whether the stabilizer bar is a generally U-shaped torsion bar extending toward the rear of the vehicle or a generally U-shaped torsion bar extending toward the front of the vehicle, the directional stability of the vehicle is not lowered.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The foregoing and further features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements, and wherein: FIG. 1 is a perspective view illustrating the general structure of a strut-type

suspension device according to one embodiment of the present invention; FIGs. 2A and 2B are views illustrating a kingpin axis;

FIG. 3 is a schematic view showing the equilibrium of moments acting on the kingpin axis and the stabilizer link axis of the suspension device; FIG. 4 is a graph showing the change in tensile reaction force of a tie rod according to stroke amount of the suspension device; and

FIG. 5 is a graph showing the difference between the reaction forces of the right and left tie rods at a time when the right and left suspensions are stroked in opposite phases.

DETAILED DESCRIPTION OF EMBODIMENTS

[0016] FIG. 1 is a perspective view illustrating the structure of a strut-type suspension device 10. The strut-type suspension device 10 has a lower arm 30, a knuckle 12 that rotatably supports a wheel, and a strut 20. At the center of the knuckle 12 is formed an axle that supports the wheel. The lower arm 30 has a proximal portion bifurcated into two portions, each of which is pivoted on the vehicle body via a bush, and a distal portion extending outward in the vehicle width direction from the proximal portion and pivoted on a lower part of the knuckle 12 via a ball joint. A tie rod 41 is connected to the knuckle 12 so that the wheel can be rotatably operated about a kingpin axis.

[0017] In the suspension structure shown in FIG. 1, a shock absorber 25 serves also as the strut of the suspension. The strut 20 is constructed of a shock absorber 25 having a shell case 25a as an outer cylinder; and a piston rod as an inner cylinder connected to a piston (not shown) received in the shell case 25a and protruding from the shell case 25a. The lower end of the shell case 25a is connected to an upper part of the knuckle 12 by a housing bracket 27 extending outward in the vehicle width direction. An upper spring seat 22 is attached to the upper end of the piston rod, and a lower spring seat 24 is attached to an axial intermediate portion of the shell case 25a. A coil spring 23 is interposed between the upper spring seat 22 and the lower spring seat 24. An upper mount 21 is attached to an end of the piston rod, and the shock absorber 25 is attached to the vehicle body via the upper mount 21.

[0018] A strut bearing (not shown) is attached to the upper mount 21. The strut bearing is a bearing which allows rotation in the steering direction. The strut 20 is therefore rotatably supported on the vehicle body. [0019] Steering torque input from a steering wheel (not shown) is transmitted to a

gear box 40 via a steering column (not shown). The gear box 40 converts the rotational motion from the steering wheel into linear motion in the vehicle width direction and transmits the linear motion to the tie rod 41. The tie rod 41 is joined to the knuckle 12 via a ball joint 42. With the above structure, when the driver steers the steering wheel, the wheel is turned by the tie rod 41.

[0020] In the above structure, the piston rod of the shock absorber 25 is incapable of rotating relative to the vehicle body, and the shell case 25a of the shock absorber 25 is capable of rotating relative to the vehicle body. That is, when the driver steers the steering wheel, the shell case 25 a rotates but the piston rod does not rotate. An axis extending through the upper end of the shock absorber 25 and the lower end of the knuckle 12 is the kingpin axis.

[0021] A stabilizer includes a stabilizer bar 51, a bush 52, and a stabilizer link 53. The stabilizer bar 51 is a generally U-shaped torsion bar. The roll rigidity is increased by the restoring force of the stabilizer bar 51 against torsion, and the rolling during a turn of the vehicle can be controlled. The stabilizer bar 51 is attached to the vehicle body by right and left bushes 52.

[0022] The stabilizer link 53 is a rod-like member, and ball joints are attached to the opposite ends of the stabilizer link 53. The lower end of the stabilizer link 53 is connected to an end of the stabilizer bar 51 via a ball joint. The upper end of the stabilizer link 53 is connected to a stabilizer bracket 26 extending from an outer periphery of the shell case 25a via a ball joint.

[0023] The general operation of the stabilizer is next described. The stabilizer has a U-shaped torsion bar connecting right and left suspension arms. When the vehicle is turned by steering input to the steering wheel from the driver, a centrifugal force acts on the vehicle. The centrifugal force generates a rolling load, and the suspension on the side of the outer wheel compresses and the suspension on the side of the inner wheel expands, causing a difference in position between the right and left suspensions. Thus, one end of the stabilizer bar 51 is twisted upward and the other downward. Then, a restoring force against the torsion is generated in the stabilizer bar 51, and the restoring force is transmitted to the knuckle 12 via the stabilizer link 53. As a result, the outer wheel side, which has compressed, is lifted up and rolling is prevented. That is, the tilt of the vehicle is controlled by the restoring force of the stabilizer. When the right and left suspensions are stroked in the same direction, the spring effect, which is produced by torsion of the stabilizer bar 51, is not produced. As described above, when a stabilizer is adopted, rolling of the vehicle can be

prevented without restricting the strokes of the suspensions.

[0024] FIGs. 2A and 2B are views illustrating a kingpin axis. FIG. 2A is a view of the left wheel side of a front suspension, viewed from a rear side of the vehicle, and FIG. 2B is a view of the left wheel, viewed from a left side of the vehicle body. The kingpin axis of a strut-type suspension device is determined by a connection point X where the shock absorber is connected to the vehicle body and a connection point Y where the lower arm is connected to the knuckle. As can be understood from FIGs. 2A and 2B, the kingpin axis of a front suspension usually extends inside the center of the tire and is inclined outwardly to the lower side and forwardly toward the front of the vehicle. Therefore, a tensile load is applied to the tie rod 41 when the weight of a wheel is supported. However, when the vehicle is traveling straight ahead, the tires are stable without being steered because the forces acting on the right and left tie rods are equilibrated.

[0025] When the right and left suspensions are stroked in opposite phases because of unevenness of the road surface or some other reason, the reaction force of the coil spring increases and therefore the reaction force of the tie rod increases on the side where the suspension is bounded and its stroke is compressed. On the other hand, the reaction force of the spring decreases and therefore the reaction force of the tie rod decreases on the side where the suspension is rebounded and its stroke is expanded. This results in a difference between the reaction forces of the right and left tie rods, and a force that urges the tires to turn is generated. That is, the difference between the reaction forces of the right and left tie rods adversely affects the directional stability of the vehicle.

[0026] In an actual vehicle, a difference between the reaction forces of the right and left tie rods does not directly leads to a turn of the wheels and is controlled to some extent because there is friction about each kingpin axis and in the steering system. Even so, when the wheel rate or the roll rigidity is high, the moment about each kingpin axis which is generated by an opposite phase stroke may be so large that the tires can be steered. [0027] The above phenomenon could be prevented from occurring when each kingpin axis is not inclined but set perpendicular with respect to the ground. However, such geometric setting is not practical. It is considered to reduce the steering amount of the tires by increasing friction about each kingpin axis and in the steering system, but it is difficult in reality to employ such a measure because it may adversely affect the steering feel and deteriorate vehicle performance.

[0028] Therefore, in this embodiment, the position of the stabilizer link with respect to the strut is reconsidered to prevent the above phenomenon. When the stabilizer link is positioned with respect to the strut such that the relation described later is satisfied, the moment which is generated about the kingpin axis by the stabilizer link as the suspension is stroked can be generated in the tie rod with a magnitude generally equal to that of the moment caused by the wheel weight. As a result, the reaction forces of the tie rods can be equilibrated between the right and left wheels and unintentional steering of the tires can be prevented.

[0029] FIG. 3 is a schematic view showing equilibrium of forces acting on the components of the suspension. FIG. 3 shows the right wheel, viewed from rear right side. In the drawing, each component is shown in a simplified fashion, and KP, SB, SL, and W represent the kingpin axis, stabilizer bar, stabilizer link, and wheel, respectively. Also, a junction Jl represents where the shock absorber 25 is attached to the vehicle body, and a junction J2 represents the ball joint connecting the lower arm 30 and the knuckle 12. A junction J3 represents the ball joint at the connection between the upper end of the stabilizer link 53 and the shell case 25a, and a junction J4 represents the ball joint at the connection between the stabilizer link 53 and the stabilizer bar 51.

[0030] In FIG. 3, the geometry of the kingpin axis and a stabilizer link axis are set such that the load variation on the coil spring and the load variation on the stabilizer which are generated as the suspension is stroked equilibrate. That is, the angle between the kingpin axis KP and the stabilizer link axis SL and the minimum distance between the kingpin axis KP and the stabilizer link axis SL are defined as θs and Ls, respectively, and the relation which they should satisfy is discussed. [0031] When the moment about the kingpin axis which is generated by the wheel weight F is defined as Mk, the following equation holds:

Mk = IK-θk-F (1) where IK is the distance between the kingpin axis and the axis of rotation of the tire, and θk is the angle between the kingpin axis and the vertical axis of the tire. Since θk is sufficiently small, it may be assumed that sinθk « θk.

[0032] The increase δMk in the moment caused by a suspension stroke x can be obtained using the following equation:

δMk = IK-θk-K-x (2) where K is the wheel rate, which is determined in view of the efficiencies of transmission between members and so on.

[0033] The moment Ms which is generated about the kingpin axis KP by the reaction force P of the stabilizer link is represented by the following equation: Ms = Ls-θs-P (3) [0034] The increase δMs in the moment caused by the suspension stroke can be obtained using the following equation:

δMs = Ls-θs-Ks-x (4) where Ks is the stabilizer rate, which is determined in view of the fact that the difference between the right and left stabilizer bars is twice their displacement and the efficiencies of transmission between members and so on. [0035] The wheel rate K and the roll rigidity (K + Ks) can be calculated for each vehicle based on the specifications and motion performance of the vehicle. Therefore, Ls and θs are determined from equations (2) and (4) such that the relation δMk = δMs is satisfied, and the installation position of the stabilizer link 53 is determined according to the values. More specifically, the location of attachment between the upper end of the stabilizer link 53 and the shell case 25a and the location of attachment between the lower end of the stabilizer link 53 and an end of the stabilizer bar 51 are determined. Then, the difference between the reaction forces of the right and left tie rods can be zero even at a time of an opposite phase stroke. Therefore, unintentional steering of the tires due to unevenness of the road surface can be prevented and the vehicle can be kept in the straight direction.

[0036] FIG. 4 is a graph showing the change in tensile reaction force of the tie rod according to the stroke amount of the suspension in a suspension device in which the relation described with FIG. 3 is satisfied. In the drawing, E represents the initial reaction force which is measured when the wheel is in contact with the ground. The curve A represents the tensile reaction force of the tie rod at a time when the right and left shock absorbers are stroked in the same phase, and the curve B represents the tensile reaction force of the tie rod at a time when the right and left shock absorbers are stroked in opposite phases. As can be understood from the drawing, the curve B is generally bilaterally symmetric, which means that when the right and left suspensions are stroked the same amount in opposite phases, almost the same tensile reaction forces are generated therein.

[0037] FIG. 5 is a graph showing the difference between the reaction forces of the right and left tie rods in a suspension device in which the relation described with FIG. 3 is satisfied at a time when the right and left suspensions are stroked in opposite phases. In the drawing, the curve C represents the difference between the reaction

forces generated in the right and left tie rods when the right and left shock absorbers are stroked in opposite phases in the case where each suspension device is provided only with a coil spring. As shown in the drawing, when each suspension device is provided only with a coil spring, as the opposite phase stroke amount is greater, the difference between the reaction forces of the right and left tie rods is greater and therefore the force that urges the tires to turn is greater. The curve D represents the difference between the reaction forces generated in the right and left tie rods at a time when the right and left shock absorbers are stroked in opposite phases in a suspension device in which the stabilizer link is positioned such that the relation described with FIG. 3 is satisfied. As can be understood from the drawing, in this case, even when the opposite phase stroke increases, the difference between the reaction forces of the right and left tie rods hardly increases. Thus, even when an opposite phase stroke occurs because of unevenness of the road surface or some other reason, the force which urges the wheels to turn is hardly generated and the vehicle can be kept in the straight direction.

[0038] As described above, according to this embodiment, in a suspension structure having a stabilizer, the position of the stabilizer link is set such that an appropriate moment can be generated on the steer-out side with respect to the kingpin axis when the right and left suspensions are stroked in opposite phases. Thus, even when an opposite phase stroke occurs because of unevenness of the road surface or some other reason when the vehicle is traveling straight ahead, the phenomenon in which the tires are steered by moments generated about the kingpin axes can be eliminated.

[0039] The present invention has been described based on some embodiments. Those skilled in the art will recognize that the embodiments are for illustration purposes only and various modifications, including any combinations of the embodiments and any combinations of the components of the embodiments, are also included in the scope of the present invention.

[0040] The present invention is not limited to the embodiments described above, and various modifications such as design changes may be made to the embodiments based on knowledge of those skilled in the art. The structure shown in each drawing is for illustration of one example and may be changed as needed as long as the same function is accomplished.

[0041] FIG. 2 shows a suspension structure in which the stabilizer link is located on the side of the rear of the vehicle with respect to kingpin axis. However, the same

effect as in the above embodiment can be achieved in a suspension structure in which the stabilizer link is located on the side of the front of the vehicle with respect to kingpin axis, for example, when Ls and θs are set such that the equations (2) and (4) equilibrate. [0042] Although the upper end of the stabilizer link 53 is connected to the shell case 25a in the embodiments, the stabilizer link may be connected to any member which is turned together with the wheel about the kingpin axis.

[0043] In the embodiments, the present invention is described through a strut-type suspension. However, the present invention is also applicable to any independent suspension system in which a stabilizer link is attached to an axle which is stroked and turned together with a tire.