JPH01311906A - Rear suspension - Google Patents

Abstract

PURPOSE:To enhance driving stability in respect of a rear suspension device for a vehicle by arranging the lower end of a spring damper unit in between the outer end of an assist arm and the outer end of a lower arm and setting the arrangement and the elasticity of each arm so as to satisfy a specified condition. CONSTITUTION:A spring damper unit 15 has its lower end SL mounted on the inside in a body cross direction of a trailing arm 4 on a coaxis with a spindle 3 and its upper end SU mounted in the forward direction of the lower end SL and in the inward direction of a body cross direction. Then, rigidities Kg, Kt, Ka in a body lateral direction of respective bushes 5, 13, 14 and distances LG, LH, LG, LB in a longitudinal perpendicular between a supporting point G of the body side of the trailing arm 4 and the outer end H of an assist arm and the outer end B of an lower arm corresponding to lines CB, CH which connect the outer end C of an upper arm to the outer end B of a lower arm and the outer end H of the assist arm respectively are set to as to satisfy an equation I. Such a constitution permits driving stability to be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to an improvement of a rear suspension used in a vehicle such as an automobile.

(Prior Art) In recent years, as the engine performance of automobiles continues to improve, there has been a demand for improved steering stability through improved suspension performance. As an element to improve handling stability rather than suspension characteristics, it is important to control cornering power (so-called grip power to maximize tire performance) through toe control, as typified by 4WS. Are known. In order to effectively generate this cornering power, it is particularly effective to set the roll steer characteristics of the suspension so that the rear wheels undergo toe-in displacement during bumps.

Conventionally, for example, according to Japanese Patent Publication No. 62-48606,
a wheel support member rotatably supporting a rear wheel; a trailing arm having a rear end connected to the wheel support member and having a front end pivotally connected to a vehicle body side member and extending substantially in the longitudinal direction of the vehicle body;
A pair of upper and lower lateral arms extending in the vehicle width direction and provided between the wheel support member and the vehicle body side member; A rear suspension is known in which the lateral arm and the assist arm are connected to the wheel support member or the vehicle body side through one pivoting means at each end of the lateral arm and the assist arm, respectively. .

In the conventional suspension described above, the assist arm is shorter than the lower lateral arm so that toe-in during bumps can be obtained by link interference during suspension stroke.

In this way, appropriately setting the toe change (roll steer) with respect to the suspension stroke is important for improving the steering characteristics and handling stability of the vehicle. It is undesirable for this to occur.

(Problems to be Solved by the Invention) However, in the configuration of the conventional example described above, if the angle of the spring damper unit is changed, the desired toe-in displacement of the rear wheel may not be obtained.

A possible reason why the desired toe-in displacement cannot be obtained is the influence of the reaction force of the spring damper unit. In other words, in the conventional example described above, the spring damper unit is installed upright, but if this spring damper unit is arranged inwardly in consideration of the body structure, the reaction force generated by the spring damper unit will have a component in the vehicle width direction. This component force may cause a deviation in the desired toe change. If this deviation occurs in the toe-in direction, the steering characteristics of the vehicle will tend to under-perform, and there is no particular problem from a safety perspective. However, if this deviation occurs in the toe-out direction, the steering characteristics will tend to exceed the setting. This is a big problem because the steering stability also deteriorates.

To solve this problem, when arranging the spring damper unit inwardly, the spring damper unit is arranged with a large offset rearward from the center of the axle, as shown in Figure 6, to reduce the reaction force of the spring damper unit. It is possible to make the vehicle width direction component act in the toe-in direction, but if such an arrangement is adopted, the reaction force of the spring damper unit will act on the bushing at the front end of the trailing arm using the axle as a fulcrum, causing vibration and There is a problem that leads to deterioration of the noise level.

In order to prevent such deterioration of vibration and noise (in order to reduce the reaction force exerted manually on the bushing at the front end of the trailing arm), a spring damper unit is installed near the center of the axle as shown in Figure 7. It is necessary to attach the bottom end of the.

[Structure of the invention]

(Means for Solving the Problems) The present invention was devised to solve the above problems, and the present invention optimizes the layout of each arm of the suspension, the rigidity of each arm system, and the arrangement of the spring damper unit. This prevents the roll steer characteristics from shifting toward the toe-out side due to the reaction force of the spring damper unit even when the spring damper unit is arranged inwardly. a trailing arm whose rear end is connected to the wheel support member and whose front end is pivoted to the vehicle body side member and extends approximately in the longitudinal direction of the vehicle body; and an upper portion of the wheel support member which extends in the vehicle width direction. an upper arm pivotally connected to the vehicle body side member; a lower arm extending in the vehicle width direction and pivotally connected between the lower part of the wheel support member and the vehicle body side member; an assist arm extending in the vehicle width direction at the front and below the upper arm and pivotally connected to the wheel support member or the trailing arm and the vehicle body side member; In a rear suspension including a trailing arm or a spring damper unit connected to the wheel support member and arranged substantially vertically, the spring damper unit has a lower end rearward of the outer end of the assist arm and outside the lower arm. The trailing arm is located forward of the end, and the upper end is located inside the vehicle body than the lower end, and the distance between the axis connecting the outer end of the upper arm and the outer end of the lower arm and the elastic center support point of the trailing arm relative to the vehicle body. LG is the component in the vertical plane in the longitudinal direction of the vehicle body, LH is the component in the vertical plane in the longitudinal direction of the vehicle body of the distance between the axis connecting the outer end of the upper arm and the outer end of the lower arm and the outer end of the assist arm. LG' is the component of the distance between the axis connecting the outer end of the assist arm and the elastic center support point of the trailing arm relative to the vehicle body in a vertical plane in the longitudinal direction of the vehicle body, and the outer end of the upper arm and the outer end of the assist arm are LB is the component of the distance between the connecting axis and the outer end of the lower arm in the vertical plane in the longitudinal direction of the vehicle body, Kg is the rigidity in the lateral direction of the vehicle body at the elastic center support point of the trailing arm relative to the vehicle body, and is Kg is the rigidity of the assist arm system in the lateral direction of the vehicle body. When the stiffness is Kt and the lateral stiffness of the lower arm system is Ka, LG'(LH' ・K t + LG" ・Kg) ≦
The arrangement and elasticity of each arm system are set to satisfy the conditions of LG (LB2 ・Ka+LG” ・Kg).

(Function) According to the present invention, the arrangement and elasticity of each arm system are set as described above, and the lower end of the spring damper unit is arranged near the center of the axle, so that the spring damper unit is arranged inwardly. Despite this, the roll steer characteristics do not shift toward the toe-out side due to the reaction force of the spring damper unit, and the desired roll steer characteristics are achieved without the reaction force of the spring damper unit acting on the bushing at the front end of the trailing arm. (Embodiment) Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

As shown in FIGS. 1 to 3, the rear wheel 1 is rotatably supported by a spindle 3 provided at the center of a knuckle 2, which serves as a wheel support member, and is supported by a rear part of a trailing arm 4 arranged approximately in the front-rear direction. The knuckle 2 is fixed by means such as welding. The front end of the trailing arm 4 is elastically supported by the vehicle body via a rubber bushing 5, and the center point of this rubber bushing 5 is represented by a point G in the drawing. Also,
The outer end of an upper arm 7 arranged in the vehicle width direction is pivotally attached to the upper part of the knuckle 2 at a position directly above the spindle 3 in a side view via a ball joint 6, and the inner end of the upper arm has a rubber bush 8. It is elastically supported by the vehicle body through the The center points of these ball joints 6 and rubber bushes 8 are represented by point 0 and point Q, respectively, in the illustration. Further, the outer end of an assist arm 9 arranged in the vehicle width direction is pivotally attached to a position forward of the spindle 3 at the bottom of the knuckle 2 via a ball joint 10, and a position rearward of the spindle 3 at the bottom of the knuckle 2. , the outer end of the lower arm 11 arranged in the vehicle width direction is connected to the ball joint 1.
It is pivotally connected via 2. The assist arm 9 is formed shorter than the lower arm II, and the inner ends of the assist arm 9 and the lower arm 11 are each provided with a rubber bush 13.
．． It is elastically supported by the vehicle body via 14. The center points of these ball joints 10.12 and rubber bushes 13.14 are represented by point H, point B, point T, and point A, respectively, in the illustration. The trailing arm 4 described above is a rigid body having a closed cross-sectional structure, and the unstretched arm, upper arm, and lower arm are rigid bodies made of iron pipes.

Further, the spring damper unit 15 is configured such that a coil spring 16 and a shock absorber 17 are integrally arranged on the same axis, and the lower end SL is located coaxially with the spindle 3 so that the trailing arm 4 It is installed on the inside in the width direction. Further, the upper end SU of the spring damper unit 15 is located forward of the lower end SL and inward in the vehicle width direction, and is attached to the vehicle body (not shown). Therefore, the spring damper unit 15 as a whole is tilted forward and inward in a substantially vertical direction, and the toe change of the suspension having the above configuration will be analyzed below.

First, as shown in FIG. 4, bush 5 (point G).

The stiffness of the bushing 13 (point T) and the bushing 14 (point A) in the vehicle body lateral direction is Kg, Kt, and Ka, respectively, and the amount of deflection of each bushing in the vehicle body lateral direction is δg, δ, and δa, respectively. In addition, the components of the distances between the CB axis and the G point, H point, and SL point in the vertical plane in the longitudinal direction of the vehicle body are LG, respectively.
Let LH and L milk be the components of the distances between the CH axis and points G, B, and SL in the vertical plane in the longitudinal direction of the vehicle, respectively.
Let B and L SL '.

Here, let f be the vehicle width direction component of the input from the spring damper unit, and consider the balance of the force in one direction with respect to the human force from the spring damper unit.

First, considering the balance of the moment MCB around the CB axis, MCB= r - LSL - fH LH + fG - LG ... (1)
However, for # and #, the relationship of the human force loads to the H point and the G point in this case holds true.

Next, considering the balance of the moment MC)i around the CH axis, MCB = f - LSL' = fB - LH + fG '・LG'... (2) However, FB and fG' are the B point in this case. and the relationship between the human force load and the G point holds true.

By the way, the above-mentioned moment MCB causes a displacement in the toe-out direction, and moment )MC)I causes a displacement in the toe-in direction.

Here, we will consider rear wheel toe change (roll steer) with respect to suspension stroke.

By setting the arrangement and length of each link and the stiffness of the bush,
Assume that toe change characteristics as shown in FIG. 5 are set. In this case, the above-mentioned one-way moment) MCB.

As shown in the figure, the toe change characteristics are greatly affected by the magnitude of MCH. In addition, the reaction force of the spring damper unit increases or decreases depending on the suspension stroke, and due to differences in vehicle weight or spring constant of the spring damper system between the same car models, the above M[:B, M(:H) may increase or decrease, and the If a large difference occurs, a large deviation will occur in the roll steer characteristics.Of course, M CB=
At the time of MCH, no deviation occurs in the roll steer characteristics.

Toe change relative to stroke (roll steer) is one of the most important factors in vehicle handling stability, and as mentioned above, differences in vehicle weight and spring constant cause differences in roll steer characteristics between vehicles of the same model. I don't like that, but
In particular, if the MCB becomes large and shifts toward toe-out, this is a problem because the basic structure of the suspension has a large unstable element with regard to steering stability.

In order to generate such a shift on the stable side, M
It is also possible to place the CB axis forward of the SL point so that the CB generates a moment in the toe-in direction in the same way as the MCH, but this would result in a decrease in lateral rigidity against external forces, making it impractical. .

Therefore, in order to make the toe change of the suspension shown in FIGS. 1 to 4 stable against the human force from the spring damper unit, MC8≦MCI may be satisfied.

Substituting equations (1) and (2) above into this relationship, f H・
The relationship LH+fG -LG ≦fB -LH+fG'·LG' (3) is obtained.

Taking into account that the assist arm and the lower arm are connected to the trailing arm via a ball joint, and considering the relationship between the human load, the support rigidity, and the amount of deflection, fll=Kt・δt... (4) fG = K
g・δg...(5) fB=K
a · δ a − (6) fG'=
Kg・δg′...(7) relationship is obtained.

In addition, since the trailing arm 4 and the assist arm 9 are rigid bodies, the ratio of the amount of deflection in the lateral direction of the vehicle body between the bushings 5 and 13 is calculated based on the ratio of the amount of deflection in the vehicle body lateral direction. Considering the ratio of the amount of deflection in the lateral direction of the vehicle body between the bushing 14 and the bushing 14, δ is - δg - LH/LG (8) 682
The relationship 6g'·LH/LG' - (9) holds true.

Rearranging the above equation (3) based on the above equations (4) to (9), Kt・δg−LH2/LG +Kg・δg−LG ≦Ka・δg′−LB′/LG′ +Kg・δg′・LG′ The following relationship is obtained.

If we organize this further, (K t LH2 + Kg LG2) 6g / LG
≦(KaLB'+KgLG")δg'/LG'
Since δg-δg', (Kt-LH'+Kg-LG')LG'≦(Ka -
LB2+Kg-LG''')LG-(II above aQ
If the arrangement of each arm and the rigidity of each bushing are selected to satisfy the formula, the lower end SL point of the spring damper unit shown in Figs. ), it is possible to easily prevent the human force from the spring damper unit from affecting the roll steer characteristics in the toe-out direction.

In addition, if the same bushings 13 and 14 are used for the purpose of obtaining the cost reduction effect by sharing parts, Ka = Kt =, so from the above formula 00, Kg - LG - LG '( LG-LG')≦K (LG
-LB'-LG'・LH2)...A relationship of 0υ is obtained.

As is clear from Fig. 4, since LG>LG', the left side of the above equation 00 is greater than 0, and therefore, from the right side of the above equation 00, the relationship LG -LB'-LG'・LH>0 is derived. It will be destroyed. If we organize this, LB>LH, /”'Tteichi=
A relationship of 7τG −021 is obtained.

As mentioned above, when sharing the bushings of the vehicle width direction arms, after setting the arrangement of each arm so as to satisfy the above 0''!:J formula, By selecting the stiffness of the bushings of the width direction arm and the trailing arm, it is possible to easily prevent the human force from the spring damper unit from affecting the roll steer characteristics in the toe-out direction.

Note that the present invention is not limited to the above-mentioned embodiment at all, and for example, the assist arm may be attached to the trailing arm. Further, the trailing arm may be a temporary spring as in the conventional example. In this case, a pseudo elastic center point is calculated taking into consideration the elasticity of the trailing arm and the elasticity of the bushing, and this elastic center point is It is necessary to make each setting based on the following. Furthermore, rubber bushings may be provided at both ends of the arms arranged in the vehicle width direction, or rubber bushings may be provided only at the outer ends, but in these cases, the stiffness of each arm system as a whole in the vehicle width direction is calculated and based on this. You need to configure each setting.

〔Effect of the invention〕

As described above in detail with the embodiments, according to the present invention, the spring damper unit can be tilted inward while the spring damper unit is placed in a position where the human force from the spring damper unit does not adversely affect the riding comfort. Effects of providing a rear suspension that can reliably prevent the input to the suspension stroke from displacing the rear wheel in the toe-out direction even if the suspension stroke is arranged, improve vehicle handling stability, and facilitate design work. play.

[Brief explanation of the drawing]

Fig. 1 is a plan view showing the configuration of an embodiment of the present invention, Fig. 2 is a side view of the same, Fig. 3 is a rear view of the same, Fig. 4 is a schematic side view of the same, and Fig. 5 is a characteristic diagram of bump steer. , FIG. 6.7 is a schematic diagram showing an example of the arrangement of the spring damper unit. 2...knuckle, 4...trailing arm. 8... Upper arm, 13... Assist arm. 14...lower arm. 5.8, 13.14...Rubber bushing 6.10.12
... Ball joint applicant Mitsubishi Motors Corporation Figure 4 Figure 6 Figure 5 Figure 7

Claims (1)

[Claims] a wheel support member that rotatably supports a rear wheel; a trailing arm to which the wheel support member is connected at the rear and whose front end is pivotally connected to a vehicle body side member and extends substantially in the longitudinal direction of the vehicle body; an upper arm extending in the vehicle width direction and pivotally connected between the upper part of the wheel support member and the vehicle body side member; and an upper arm extending in the vehicle width direction and pivotally connected between the lower part of the wheel support member and the vehicle body side member. an assist arm extending in the vehicle width direction forward of the lower arm and below the upper arm and pivotally connected to the wheel support member or the trailing arm and the vehicle body side member; , a rear suspension comprising a spring damper unit whose upper end is connected to the vehicle body side member and whose lower end is connected to the trailing arm or the wheel support member and arranged approximately in the vertical direction, the spring damper unit has the lower end connected to the assist member. The trailing arm is located behind the outer end of the arm and forward of the outer end of the lower arm, and has an upper end located inside the vehicle body than the lower end, and is relative to an axis connecting the outer end of the upper arm and the outer end of the lower arm to the vehicle body. LG is the component of the distance between the elastic center support point in the vertical plane in the vehicle longitudinal direction, and LG is the component of the distance between the outer end of the assist arm and the axis connecting the outer end of the upper arm and the outer end of the lower arm in the vertical plane in the vehicle longitudinal direction. The inner component is LH, and the component in the vertical plane in the longitudinal direction of the vehicle body of the distance between the axis connecting the outer end of the upper arm and the outer end of the assist arm and the elastic center support point of the trailing arm relative to the vehicle body is LG'.
LB is the component of the distance between the axis connecting the outer end of the upper arm and the outer end of the assist arm and the outer end of the lower arm in a vertical plane in the longitudinal direction of the vehicle body, and LB is the component of the distance in the vertical plane in the longitudinal direction of the vehicle body; If the stiffness is Kg, the lateral stiffness of the assist arm system is Kt, and the lateral stiffness of the lower arm system is Ka, then LG'(
LH^2・Kt+LG^2・Kg)≦LG(LB^2・
A rear suspension characterized by setting the arrangement and elasticity of each arm system to satisfy the conditions of Ka+LG'^2・Kg)