Vehicle undercarriage

Abstract

To reduce vibration of a vehicle body caused by rotation of an air-conditioning compressor.SOLUTION: A vehicle lower part structure includes a pair of side members 1 arranged on both sides in a vehicle width direction and extending in a longitudinal direction, a cross member 2 extending in the vehicle width direction and having both ends in the vehicle width direction respectively fixed to the side members 1, and an air-conditioning compressor 3 having one end in the vehicle width direction attached to the cross member 2 through a first elastic member 5 and the other end in the vehicle width direction attached to the cross member 2 through a second elastic member 8. The air-conditioning compressor 3 is arranged in a position deviated in the vehicle width direction from a vehicle width center of a vehicle body so that the one end attached to the cross member 2 through the first elastic member 5 is closer to the vehicle width center of the vehicle body than the other end attached to the cross member 2 through the second elastic member 8. A spring constant of the first elastic member 5 is smaller than that of the second elastic member 8.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a vehicle underbody structure in which an air-conditioning compressor is attached to a cross member extending in the vehicle width direction.

Background Art

[0002] Patent Document 1 discloses a vibration isolation device that suppresses vibration transmission from an air-conditioning compressor to a support member by adopting a structure in which the air-conditioning compressor is supported by the support member via a vibration isolation rubber.

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a vehicle equipped with an air-conditioning compressor, vibrations and noises generated by the rotation of the air-conditioning compressor lead to an increase in discomfort and fatigue of vehicle occupants. Particularly in an electric vehicle without an engine, since vibrations and noises caused by engine rotation do not occur, vibrations and noises caused by the rotation of the air-conditioning compressor become prominent.

[0005] As measures for suppressing vibrations caused by the rotation of such an air-conditioning compressor, measures on the control side to prevent resonance by restricting the operating range of the rotational speed, and measures on the hardware side such as attaching a weight to the air-conditioning compressor are implemented. And as a method different from these measures, a measure for suppressing vibration transmission by attaching the air-conditioning compressor to the vehicle body via an elastic member, like the vibration isolation device disclosed in Patent Document 1, is also conceivable.

[0006] However, even if the air conditioning compressor is mounted to the vehicle body via an elastic member, vibrations may be amplified near the vehicle body's resonant frequency and transmitted to the vehicle's occupants due to the vehicle body's transmission sensitivity. In particular, if the air conditioning compressor is mounted on the cross member of the vehicle body frame and positioned off-center in the vehicle width direction from the vehicle body's center, vibrations may be amplified near the vehicle body's resonant frequency, potentially resulting in insufficient vibration damping.

[0007] Therefore, the present invention aims to provide a vehicle understructure that can reduce vehicle body vibrations caused by the rotation of an air conditioning compressor in a vehicle in which the air conditioning compressor is mounted on a cross member of the vehicle frame and positioned off-center in the vehicle width direction from the center of the vehicle width direction. [Means for solving the problem]

[0008] The vehicle understructure according to the present invention comprises a pair of side members arranged on both sides in the vehicle width direction and extending in the front-rear direction, a cross member extending in the vehicle width direction and having both ends in the vehicle width direction fixed to the side members, and an air conditioning compressor having one end in the vehicle width direction attached to the cross member via a first elastic member and the other end in the vehicle width direction attached to the cross member via a second elastic member, wherein the air conditioning compressor is positioned offset in the vehicle width direction from the vehicle width direction center of the vehicle body such that the one end attached to the cross member via the first elastic member is closer to the vehicle width direction center of the vehicle body than the other end attached to the cross member via the second elastic member, and the spring constant of the first elastic member is smaller than the spring constant of the second elastic member.

[0009] In one embodiment of the vehicle understructure according to the present invention, the air conditioning compressor may be located under the floor of the passenger compartment. [Effects of the Invention]

[0010] The present invention makes it possible to reduce vibrations of the vehicle body caused by the rotation of the air conditioning compressor in a vehicle in which the air conditioning compressor is mounted on a cross member of the vehicle body frame and positioned off-center in the vehicle width direction from the center of the vehicle body in the vehicle width direction. [Brief explanation of the drawing]

[0011] [Figure 1] This is a top view of the vehicle understructure of the embodiment disclosed herein. [Figure 2] This is a cross-sectional view along line AA in Figure 1. [Figure 3] This is a cross-sectional view along line BB in Figure 1. [Figure 4] This diagram compares the vibration inertance generated in the floor under the driver's seat when the left frame bracket of the air conditioning compressor is vibrated, with the vibration inertance generated in the floor under the driver's seat when the right frame bracket of the air conditioning compressor is vibrated. [Figure 5] This diagram compares the vibration inertance generated in the floor of the vehicle's left-side entrance when the left-side frame bracket of the air conditioning compressor is vibrated, with the vibration inertance generated in the floor of the vehicle's left-side entrance when the right-side frame bracket of the air conditioning compressor is vibrated. [Figure 6] This diagram illustrates the effect of reducing vibration in the frame-side bracket by using a bush with a spring constant of less than half that of the second elastic member as the first elastic member. [Modes for carrying out the invention]

[0012] The vehicle understructure 10 of this embodiment will be described below with reference to Figures 1 to 6. The arrows FR, UP, and RH shown in the following drawings indicate the forward (direction of travel), upward, and rightward directions of the vehicle, respectively. The opposite directions of each arrow FR, UP, and RH indicate the rear, downward, and leftward directions of the vehicle, respectively. When the directions front / back, left / right, and up / down are simply used in the following description, unless otherwise specified, they refer to the front / back direction of the vehicle, the left / right direction of the vehicle (vehicle width direction), and the up / down direction of the vehicle.

[0013] Figure 1 is a top view of the vehicle understructure 10. As shown in Figure 1, the vehicle understructure 10 comprises a pair of left and right side members 1, a pair of front and rear cross members 2, and an air conditioning compressor 3. The side members 1 are located on both sides in the vehicle width direction and extend in the front-rear direction. The cross members 2 extend in the vehicle width direction, and both ends of the cross members 2 in the vehicle width direction are fixed to the side members 1. Both the side members 1 and the cross members 2 are part of the vehicle body frame. The air conditioning compressor 3 is a compressor used in the air conditioning system of the passenger compartment. The side members 1, cross members 2, and air conditioning compressor 3 are all located under the floor of the passenger compartment.

[0014] Figure 2 is a cross-sectional view along line AA in Figure 1. As shown in Figure 2, the cross member 2 comprises a left upper section 21, a left section 22, a lower section 23, a right section 24, and a right upper section 25. The left upper section 21 extends in the vehicle width direction and connects the upper end of the left section 22 to the side member 1. The left section 22 extends in the vertical direction and connects the right end of the left upper section 21 to the left end of the lower section 23. The lower section 23 extends in the vehicle width direction and connects the lower end of the left section 22 to the lower end of the right section 24. The right section 24 extends in the vertical direction and connects the right end of the lower section 23 to the left end of the right upper section 25. The right upper section 25 extends in the vehicle width direction and connects the upper end of the right section 24 to the side member 1.

[0015] Figure 3 is a cross-sectional view along line BB in Figure 1. As shown in Figures 2-3, a compressor-side bracket 4 is fixed to the left end of the air conditioning compressor 3. The compressor-side bracket 4 is attached to the frame-side bracket 6 via first elastic members 5 at both the front and rear ends. The frame-side bracket 6 is fixed to the lower part 23 of the cross member 2.

[0016] Similarly to the left end of the air-conditioning compressor 3, a compressor-side bracket 7 is fixed to the right end of the air-conditioning compressor 3. And the compressor-side bracket 7 is attached to the frame-side bracket 9 via second elastic members 8 on the front side and the rear side, respectively. The frame-side bracket 9 is fixed to the lower part 23 of the cross member 2.

[0017] In this way, the air-conditioning compressor 3 is attached to the lower part 23 of the cross member 2 via two first elastic members 5 on the left side, and is attached to the lower part 23 of the cross member 2 via two second elastic members 8 on the right side. And the air-conditioning compressor 3 is supported by two first elastic members 5 and two second elastic members 8. Both the first elastic member 5 and the second elastic member 8 are rubber bushings.

[0018] As shown in FIGS. 1 to 2, the air-conditioning compressor 3 is arranged at a position offset to the right of the center in the vehicle width direction of the vehicle body. Therefore, the left end of the air-conditioning compressor 3 attached to the cross member 2 via the first elastic member 5 is arranged closer to the center in the vehicle width direction of the vehicle body than the right end of the air-conditioning compressor 3 attached to the cross member 2 via the second elastic member 8.

[0019] Due to the influence of the air-conditioning compressor 3 being attached at a position offset to the right of the center in the vehicle width direction of the vehicle body, the inertia of the vibration generated in the vehicle body by the vibration of the frame-side bracket 6 on the left side of the air-conditioning compressor 3 is greater than the inertia of the vibration generated in the vehicle body by the vibration of the frame-side bracket 9 on the right side of the air-conditioning compressor 3.

[0020] FIG. 4 is a diagram showing a comparison of the inertance of vertical vibrations generated on the floor under the driver's seat when the frame side bracket 6 on the left side of the air conditioner compressor 3 is vibrated and the inertance of vertical vibrations generated on the floor under the driver's seat when the frame side bracket 9 on the right side of the air conditioner compressor 3 is vibrated. In FIG. 4, the measurement results when the frame side bracket 6 on the left side of the air conditioner compressor 3 is vibrated are shown by a solid line, and the measurement results when the frame side bracket 9 on the right side of the air conditioner compressor 3 is vibrated are shown by a dotted line. The range R1 shown in FIG. 4 is a frequency range corresponding to the rotational speed at which the air conditioner compressor 3 is frequently used. As shown in FIG. 4, within the range R1, the inertance of the vibrations generated on the floor under the driver's seat when the frame side bracket 6 on the left side of the air conditioner compressor 3 is vibrated is greater than the inertance of the vibrations generated on the floor under the driver's seat when the frame side bracket 9 on the right side of the air conditioner compressor 3 is vibrated. The driver's seat is arranged at the front right part of the vehicle interior.

[0021] FIG. 5 is a diagram showing a comparison of the inertance of vertical vibrations generated on the floor of the vehicle left side entrance when the frame side bracket 6 on the left side of the air conditioner compressor 3 is vibrated and the inertance of vertical vibrations generated on the floor of the vehicle left side entrance when the frame side bracket 9 on the right side of the air conditioner compressor 3 is vibrated. In FIG. 5, the measurement results when the frame side bracket 6 on the left side of the air conditioner compressor 3 is vibrated are shown by a solid line, and the measurement results when the frame side bracket 9 on the right side of the air conditioner compressor 3 is vibrated are shown by a dotted line. The range R1 shown in FIG. 5 is a frequency range corresponding to the rotational speed at which the air conditioner compressor 3 is frequently used. As shown in FIG. 5, at the frequencies within the range R1, the inertance of the vibrations generated on the floor of the vehicle left side entrance when the frame side bracket 6 on the left side of the air conditioner compressor 3 is vibrated is greater than the inertance of the vibrations generated on the floor of the vehicle left side entrance when the frame side bracket 9 on the right side of the air conditioner compressor 3 is vibrated. The vehicle left side entrance is arranged behind the driver's seat.

[0022] As described above, the inertance of vibrations generated in the vehicle body due to the excitation of the frame-side bracket 6 on the left side of the air conditioning compressor 3 is greater than the inertance of vibrations generated in the vehicle body due to the excitation of the frame-side bracket 9 on the right side of the air conditioning compressor 3. Therefore, in order to suppress the vibrations of the vehicle body caused by the rotation of the air conditioning compressor 3, it is necessary to reduce the vibration of the frame-side bracket 6 on the left side of the air conditioning compressor 3 in particular. For this reason, in the vehicle understructure 10 of this embodiment, the first elastic member 5 uses a bush with a spring constant of half or less of the spring constant of the second elastic member 8. Furthermore, by using a bush with a spring constant of half or less of the spring constant of the second elastic member 8 in the first elastic member 5 in this way, the function of the air conditioning compressor 3 as a dynamic damper is also improved. As a result, the vehicle understructure 10 can further suppress vibrations of the vehicle body by improving the function of the air conditioning compressor 3 as a dynamic damper.

[0023] Figure 6 illustrates the effect of reducing vibrations of the frame-side bracket 6 and frame-side bracket 9 by using a bush with a spring constant of half or less than that of the second elastic member 8 in the first elastic member 5. In the evaluation experiment shown in Figure 6, the magnitude of vibrations of the frame-side bracket 6 and frame-side bracket 9 was measured while varying the rotational speed of the air conditioning compressor 3. In Figure 6, the vibration level of the frame-side bracket 6 in the vehicle understructure 10 of this embodiment, in which the first elastic member 5 uses a bush with a spring constant of half or less than that of the second elastic member 8, is shown by the dotted line L1, and the vibration level of the frame-side bracket 9 is shown by the dotted line L2. The vibration level of the frame-side bracket 6 in a comparison vehicle understructure, in which the first elastic member 5 uses the same bush as the second elastic member 8, is shown by the solid line L3, and the vibration level of the frame-side bracket 9 is shown by the solid line L4. The range R2 shown in Figure 6 is the range of rotational speeds in which the air conditioning compressor 3 is frequently used.

[0024] As shown by the dotted line L1 and solid line L3 in Figure 6, at rotational speeds within range R2, using a bush with a spring constant of half or less than that of the second elastic member 8 in the first elastic member 5 reduces the vibration of the frame-side bracket 6. Furthermore, as shown by the dotted line L2 and solid line L4 in Figure 6, at rotational speeds within range R2, using a bush with a spring constant of half or less than that of the second elastic member 8 in the first elastic member 5 reduces the vibration of the frame-side bracket 9. In other words, the vehicle understructure 10 of this embodiment, which uses a bush with a spring constant of half or less than that of the second elastic member 8 in the first elastic member 5, can reduce the vibration of the frame-side bracket 6 and frame-side bracket 9 at rotational speeds within range R2 where the air conditioning compressor 3 is frequently used, compared to a vehicle understructure that uses the same bush as the second elastic member 8 in the first elastic member 5.

[0025] Thus, in this embodiment, the vehicle understructure 10 can suppress the transmission of vibrations from the air conditioning compressor 3 to the vehicle body more effectively than when the same bush as the second elastic member 8 is used for the first elastic member 5, by using a bush with a spring constant of half or less of the spring constant of the second elastic member 8 for the first elastic member 5. Therefore, the vehicle understructure 10 can suppress vibrations of the passenger compartment floor caused by the rotation of the air conditioning compressor 3, thereby reducing discomfort and fatigue for the vehicle occupants.

[0026] <Supplement to the embodiment> The vehicle understructure of this disclosure is not limited to the above-described form and can be implemented in various forms within the scope of the gist of this disclosure. For example, the air conditioning compressor may be positioned to the left of the center of the vehicle body in the vehicle width direction. [Explanation of Symbols]

[0027] 1 Side member, 2 Cross member, 3 Air conditioning compressor, 4 Compressor side bracket, 5 First elastic member, 6 Frame side bracket, 7 Compressor side bracket, 8 Second elastic member, 9 Frame side bracket, 10 Vehicle understructure, 21 Upper left side, 22 Left side, 23 Lower side, 24 Right side, 25 Upper right side.

Claims

1. A pair of side members are positioned on both sides in the vehicle width direction and extend in the front-rear direction, A cross member extending in the vehicle width direction, with both ends in the vehicle width direction fixed to the side member, An air conditioning compressor, with one end in the vehicle width direction attached to the cross member via a first elastic member, and the other end in the vehicle width direction attached to the cross member via a second elastic member, A vehicle understructure equipped with, The air conditioning compressor is positioned offset in the vehicle width direction from the vehicle width direction center of the vehicle body, such that one end attached to the cross member via the first elastic member is closer to the vehicle width direction center of the vehicle body than the other end attached to the cross member via the second elastic member. A vehicle understructure characterized in that the spring constant of the first elastic member is smaller than the spring constant of the second elastic member.

2. The vehicle understructure according to claim 1, A vehicle understructure characterized in that the aforementioned air conditioning compressor is located beneath the floor of the passenger compartment.

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