JPH115559A - Car subframe - Google Patents

Abstract

(57) [Problem] To provide a subframe of an automobile capable of effectively reducing road noise generated due to unevenness of a road surface during traveling. A subframe (1) extends in a vehicle front-rear direction connecting a right front mounting point to a right rear mounting point, and extends in a vehicle front-rear direction connecting a left front mounting point to a left rear mounting point. Having a substantially H-shaped configuration composed of a portion 4 extending in the vehicle width direction and a portion 5 connecting the two portions, and a vertical separation distance from the center of gravity 6 of the subframe to the same side front-rear mounting position. The spring constant in the vehicle longitudinal direction of the elastic body set at the attachment point on the same side front and rear is determined to increase or decrease according to the increase or decrease.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a subframe of a motor vehicle, and more particularly, to a subframe of a motor vehicle capable of effectively reducing road noise caused by unevenness of a road surface during running.

[0002]

2. Description of the Related Art A subframe is provided between a suspension and a vehicle body to interrupt transmission of vibration to the vehicle body due to unevenness of a road surface, and elastic bodies are provided between suspension links and the subframe, and between the subframe and the vehicle body. Is generally set. In order to cut off vibration transmission, it is desirable that the elastic constants of these elastic bodies be low. On the other hand, in order to improve the kinetic performance of the vehicle, it is desirable that the change in the geometry of the suspension be small, which is a conflicting performance. .

Therefore, the elastic body set between the suspension link and the sub-frame has a high spring constant, and the elastic body set between the sub-frame and the vehicle body has a low spring constant in the vertical direction, the front-rear direction, and the left-right direction. The direction is often set with a high spring constant to ensure both performances. Further, the subframe is set as lightweight and as rigid as possible (see Japanese Patent Application Laid-Open No. 5-213039).

[0004]

However, such a conventional subframe has the following problems.
A sufficient road noise reduction effect was not obtained. Since a tire that forms a part of a vibration transmission system from a road surface has cavity resonance, a peak occurs at a specific frequency and transmission characteristics deteriorate. Problems caused by this phenomenon are unavoidable in automobiles using tires. In addition, since sub-frames have various resonances and transfer characteristics deteriorate in these frequency ranges, how to control the resonance frequency of the sub-frame and increase the amount of deterioration by moving away from the inevitable tire-induced transfer characteristics deterioration frequency Is an important issue.

[0005] The sub-frame includes a rigid body resonance in which an elastic body set between the sub-frame and the vehicle body is a spring, the sub-frame itself serves as a mass, and an elastic resonance caused by elastic deformation of the sub-frame. In a vehicle, the rigid body resonance frequency is lower and exists near the cavity resonance frequency of the tire.

Rigid body resonance of the sub-frame includes three translations in the vertical direction, the vehicle longitudinal direction, and the horizontal direction.
There are three rotations around the longitudinal axis and around the left and right axes. this house,
The resonance frequency of the sub-frame around the vehicle vertical axis is coupled with the torsional elastic resonance of the sub-frame around the vehicle left-right axis, and is significantly affected by the rigidity of the sub-frame itself. In order to secure the rigidity of the frame, the weight and the cost often increase, and the road noise performance often deteriorates.

The present invention has been made in view of such a conventional problem. In order to improve road noise performance in a vehicle cabin, a spring constant of an elastic body set between a vehicle body and a subframe is set. It is an object of the present invention to solve the above-described problem by making it easier to control the resonance frequency of the subframe around the vertical axis of the vehicle by increasing or decreasing.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, according to the first aspect of the present invention, the same invention is applied in accordance with the increase or decrease of the vertical separation distance from the center of gravity of the sub-frame to the same-side front and rear mounting position. The elastic body set at the attachment points on the front and rear sides is configured to decrease the spring constant in the vehicle front-rear direction.

According to a second aspect of the present invention, in the automobile sub-frame according to the first aspect of the invention, the ratio of the spring constant of the elastic body at the front and rear mounting points on the same side in the vehicle front-rear direction is determined by the vertical distance between the center of gravity and the rear mounting position. And the ratio of the vertical separation distance of the front mounting position from the center of gravity.

Further, in the third invention, in the automobile subframe according to the first invention, the spring constant ratio of the elastic body at the front and rear mounting points on the same side in the vehicle front-rear direction is determined by the vertical separation distance from the center of gravity to the rear mounting position. Is set to be approximately equal to the ratio of the product obtained by multiplying the left and right separation distance from the center of gravity to the rear mounting position and the product obtained by multiplying the vertical separation distance from the center of gravity to the front mounting position by the left and right separation distance from the center of gravity to the front mounting position.

[0011]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a subframe of an automobile according to an embodiment of the present invention;

(First Embodiment) First, the configuration of a subframe of an automobile according to a first embodiment of the present invention will be described with reference to FIGS. In the present embodiment, the subframe 1 is attached to the vehicle body at four attachment points of front, rear, left and right.
And the front and rear mounting positions on the same side are vertically separated from each other. The subframe 1 has a portion 3 extending in the vehicle longitudinal direction connecting the right front mounting point to the right rear mounting point, and a portion extending in the vehicle longitudinal direction connecting the left front mounting point to the left rear mounting point. 4 and a portion 5 extending in the vehicle width direction connecting the two portions to each other. The elastic body 2 supporting the sub-frame 1 has a vertical separation distance Lf from the center of gravity 6 of the sub-frame to a front position on the same side, and a vertical separation distance Lr from the center of gravity 6 of the sub-frame to a rear mounting position on the same side.
In accordance with the increase or decrease, the spring constant in the vehicle longitudinal direction of the elastic body set at the attachment point on the same side front and rear is reduced.

Next, the operation of the first embodiment will be described.
This will be described with reference to FIGS. Hereinafter, since the sub-frame is generally left-right symmetric, only the left half of the vehicle will be described. Further, for simplicity, a portion 3 extending in the vehicle front-rear direction connecting the right front mounting point to the right rear mounting point and a portion extending in the vehicle front-rear direction connecting the left front mounting point to the left rear mounting point. 4 linearly shows a portion 5 extending in the vehicle width direction connecting the two portions,
It was assumed that they were bonded at one point.

When the sub-frame 1 resonates around the vertical axis of the vehicle and rotates rigidly around the vertical axis by θ, the displacement of the front mounting point 7 of the sub-frame in the front-rear direction is Yf = Wf × Similarly, the displacement of the rear attachment point 8 in the front-rear direction is given by Yr = Wr × θ. That is, the force Ffy in the front-rear direction acting on the front attachment point is represented by Ffy = Kf, where Kfy is the front-rear direction spring constant of the front elastic body 9.
y × Wf × θ, front-rear force F acting on the rear mounting point
ry is given by Fry = Kry × Wr × θ, where Kry is the longitudinal spring constant of the rear elastic body 10. Actually, the front mounting point 7 and the rear mounting point 8 apply vertical forces Ffz, F
Although rz also acts, the vertical spring constant of the elastic body supporting the sub-frame 1 is much smaller than the spring constant in the front-rear direction and the left-right direction for the purpose of anti-vibration effect as the sub-frame. Can be ignored in the description of the action of.

At a connecting point 11 between a portion 3 extending in the vehicle longitudinal direction and a portion 5 extending in the vehicle width direction connecting the front mounting point 7 to the rear mounting point 8, the moment about the vehicle left-right axis is reduced with respect to the front. Moment Mf = Ffy × Lf = Kfy × Wf × Lf × θ due to longitudinal force acting on the attachment point, and moment Mr = − due to longitudinal force acting on the rear attachment point
The sum of Fry × Lr = −Kry × Wr × Lr × θ is balanced with the torsional moment of the portion 5 extending in the vehicle width direction. That is, if the moment from the front mounting point and the moment from the rear mounting point are balanced, the torsional moment does not act on the portion extending in the vehicle width direction, and the torsional rigidity of the sub-frame in the vehicle left-right direction is about the vertical axis of the sub-frame. Will not be affected.

In this embodiment, the vertical distance Lf from the center of gravity of the sub-frame to the front mounting position on the same side and the vertical distance Lr from the center of gravity of the sub-frame to the rear mounting position on the same side increase or decrease. Since the spring constants Kfy and Kry in the vehicle front-rear direction of the elastic body set at the front and rear mounting points are reduced and increased, the moment from the front mounting point and the moment from the rear mounting point are in a balanced direction. The rigid resonance frequency around the vertical axis of the sub-frame can be tuned by the spring constant of the front and rear elastic bodies in the vehicle front-rear direction without being affected by the torsional rigidity.

Strictly speaking, the portion 5 extending in the vehicle width direction
The vertical distance from the torsion center to the front and rear mounting positions corresponds to Lf and Lr. However, in an actual subframe, a portion extending in the vehicle width direction occupies a large portion of the entire subframe, and the distance from the center of gravity is large. There is not much difference with distance.

FIG. 5 is a graph showing the effect of the first embodiment. The sum of the spring constants in the front-rear direction of the elastic body at the front attachment point and the rear attachment point was made constant in order to make the rigid body front-rear resonance constant as a subframe. The solid line shows the case where the subframe is an elastic body, and the broken line shows the case where it is assumed to be a rigid body, and it is better to lower the spring constant of the elastic body at the front mounting point than to make the spring constant the same before and after the vertical axis of the subframe. This shows that the surrounding rigid body resonance frequency can be increased. Also, the closer the resonance frequency between the broken line and the solid line is, the more the resonance frequency is not affected by the torsional rigidity of the subframe, and the lower the spring constant of the front mounting point, the lower the torsional rigidity of the subframe to the resonance frequency. It was also confirmed that the effect was reduced.

As described above, according to the first embodiment, the subframe 1 is a portion 3 extending in the vehicle longitudinal direction connecting the right front mounting point to the right rear mounting point.
And a portion 4 extending in the vehicle longitudinal direction connecting the left front mounting point to the left rear mounting point, and a portion 5 extending in the vehicle width direction connecting the two portions. According to the increase and decrease of the vertical separation distances Lf and Lr from the center of gravity 6 of the subframe to the front and rear mounting positions on the same side, the spring constant in the vehicle front and rear direction of the elastic body set at the front and rear mounting points on the same side is increased. It was decided as follows. For this reason, the torsional load around the vehicle left-right axis acting on the portion of the sub-frame extending in the vehicle width direction that connects the vehicle left-right direction at the time of rigid body resonance around the vertical axis of the sub-frame is reduced. The rigid body resonance frequency is less likely to be affected by the torsional rigidity of the subframe around the vehicle left-right axis. Therefore, the rigid body resonance frequency around the vertical axis of the sub-frame can be easily tuned by the spring constant of the elastic body, the necessary minimum spring constant of the elastic body can be set, and the improvement of the road noise performance can be easily achieved. Further, since the torsional rigidity of the sub-frame can be suppressed to the minimum necessary, the weight of the sub-frame can be reduced.

(Second Embodiment) A second embodiment of the present invention will be described. The second embodiment has the same configuration as that of the first embodiment, except that the spring constant ratio of the elastic body at the front and rear mounting points on the same side in the vehicle front-rear direction is the vertical separation distance from the center of gravity to the rear mounting position. And a subframe of an automobile set to be substantially equal to the ratio of the vertical separation distance of the front mounting position from the center of gravity.

Next, the operation of the second embodiment will be described. The second embodiment has the following operation in addition to the operation of the first embodiment. Since the spring constant ratio is set as described above, a value near the region A shown in FIG. 5 can be taken, and the torsional rigidity of the subframe can be made to have less influence on the rigid resonance frequency around the vertical axis of the subframe. Therefore, tuning can be easily performed, which leads to improvement in road noise performance.

As described above, according to the second embodiment, the spring constant of the elastic body set between the vehicle body and the sub-frame is set to Since the constant ratio is set so as to be substantially equal to the ratio of the vertical separation distance from the center of gravity to the rear mounting position and the vertical separation distance from the center of gravity to the front mounting position, the vehicle of the subframe relative to the rigid resonance frequency around the vertical axis of the subframe The influence of the torsional rigidity around the left and right axes is further reduced, the spring constant can be tuned more easily than in the first embodiment, and the same effect can be expected.

(Third Embodiment) A third embodiment of the present invention will be described. The third embodiment has the same configuration as that of the first embodiment, except that the ratio of the spring constant of the elastic body in the vehicle front-rear direction at the attachment point on the same side front and rear is the vertical separation distance from the center of gravity to the rear mounting position. A vehicle subframe set to be approximately equal to the ratio of the center of gravity multiplied by the left and right separation distance of the rear mounting position, and the center of gravity multiplied by the vertical separation of the front mounting position multiplied by the left and right separation distance of the front mounting position from the center of gravity. Has become. FIG. 6 schematically shows a subframe according to the present embodiment.

Next, the operation of the third embodiment will be described. The third embodiment has the following operation in addition to the operation of the first embodiment. Since the spring constant ratio is set as described above, a value near the region B shown in FIG. 5 can be taken, and the torsional stiffness of the subframe can be made to have less influence on the rigid resonance frequency around the vertical axis of the subframe. Therefore, tuning can be easily performed, which leads to improvement in road noise performance.

As described above, according to the third embodiment, the ratio of the spring constant of the elastic body in the front-rear direction of the elastic body at the front and rear mounting points on the same side is determined from the center of gravity to the vertical separation distance of the rear mounting position from the center of gravity. From the center of gravity multiplied by the left and right separation distance of the rear mounting position and from the center of gravity to the vertical separation distance of the front mounting position multiplied by the left and right separation distance of the front mounting position from the center of gravity, it is set to be approximately equal to the ratio, so that the subframe The spring constant can be tuned in consideration of the difference between the positions of the vehicle on the same side and in the left-right direction. The effect can be obtained in the same manner as in the second embodiment.

[0026]

According to the present invention, since the present invention has the above-described features, it is possible to reduce the influence of the torsional rigidity of the subframe itself on the rigid body resonance frequency around the vertical axis of the subframe. Tuning of the elastic body is facilitated, leading to improved road noise performance. Further, the rigidity of the sub-frame can be set to a necessary minimum, so that the weight can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of a subframe of an automobile according to the present invention.

FIG. 2 is a diagram illustrating a configuration of a first embodiment.

FIG. 3 is a diagram illustrating the operation of the first embodiment.

FIG. 4 is a diagram illustrating the operation of the first embodiment.

FIG. 5 is a diagram showing an effect of the first embodiment.

FIG. 6 is a diagram illustrating a configuration of a third embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sub-frame 2 Elastic body 3 Part extending in the vehicle longitudinal direction (right side) 4 Part extending in the vehicle longitudinal direction (left side) 5 Part extending in the vehicle width direction 6 Center of gravity of sub-frame 7 Front attachment point 8 Rear Attachment point 9 Front elastic body 10 Rear elastic body 11 Connection point

Claims (3)

[Claims] 1. A sub-frame of an automobile, wherein the sub-frame is supported by a vehicle body at four mounting points of front, rear, left and right via elastic bodies, and front and rear mounting positions on the same side are vertically separated, A portion extending in the vehicle longitudinal direction connecting the right rear mounting point from the right front mounting point; a vehicle extending longitudinal direction connecting the left rear mounting point from the left front mounting point; The sub-frame has a substantially H-shaped configuration composed of a portion extending in the vehicle width direction. The sub-frame has a substantially H-shaped shape. A vehicle sub-frame characterized in that a spring constant in the vehicle longitudinal direction of an elastic body set at an attachment point is reduced or increased. 2. The sub-frame of an automobile according to claim 1, wherein the spring constant ratio of the elastic body at the attachment point on the same side front and rear in the vehicle front-rear direction is the vertical separation distance from the center of gravity to the rear mounting position and the front mounting from the center of gravity. A sub-frame for an automobile, wherein the sub-frame is set to be substantially equal to a ratio of a vertical distance between positions. 3. The vehicle sub-frame according to claim 1, wherein a spring constant ratio of the elastic body in the vehicle front-rear direction of the elastic body at the front and rear mounting points on the same side is determined by a vertical separation distance from the center of gravity to a rear mounting position. A subframe for an automobile, wherein the ratio is obtained by multiplying a ratio obtained by multiplying the left-right distance between the positions and a vertical distance from the center of gravity to the front mounting position by the left-right distance of the front mounting position from the center of gravity.