JP2871219B2 - Lower body structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an underbody structure of a vehicle. More specifically, the present invention relates to a vehicle body lower structure including a cross member and a subframe spanned over a rear side member.

[0002]

2. Description of the Related Art In a lower body structure, a rear side member is provided as a strength member on both sides in the vehicle width direction, and a rear cross member as a strength member is stretched over the rear side member to form a foom. The rear side member and the rear cross member are joined to a rear floor panel.

[0003] A rear suspension is mounted on this frame. The rear suspension is attached to a rear sub-frame via a suspension arm, and the rear sub-frame is bridged and connected between rear side members. As a result, the load acting on the suspension is received by the rear side member (for example, 2-511 of Japanese Utility Model Application Laid-Open No. HEI 9-313).
No. 81).

[0004]

However, due to the improvement in quietness in the cabin, a demand for further reduction of noise due to vibration of a rear floor panel due to a load transmitted through a rear suspension during a vehicle running at the rear of the vehicle body has been increased. ing.

[0005] The present invention has been made in view of the above facts, and has as its object to provide a lower body structure for reducing the vibration level generated at the rear of the vehicle.

[0006]

In order to achieve the above object, a vehicle body lower structure according to the present invention comprises a side member disposed on both sides in a vehicle width direction, and a cross frame bridged between the side members. A floor panel joined to each of the side member and the cross member, and a subframe disposed below the cross frame and mounted with a suspension, wherein the side member of the cross frame is provided. The sub-frame is connected to a connection portion of the cross member, and a middle portion of the cross member in the vehicle width direction is closer to the sub-frame by a predetermined amount than both ends in the vehicle width direction.

[0007]

The cross member and the sub-frame are joined to the side member at the same position. A floor panel is joined to the cross member, and a rear suspension is attached to the subframe.

[0008] The cross member has an intermediate portion in the vehicle width direction closer to the sub-frame than the position of attachment to the side member. That is, the intermediate portion of the cross member is lowered by a predetermined amount below the vehicle body, and the floor panel is also lowered accordingly. During traveling of the vehicle, the load from the suspension is transmitted to the side members and the cross members via the subframe. The inertial force due to the load transmitted from this sub-frame acts on the cross member so that the middle part thereof is directed upward, and the moment force due to the load is:
It acts on the cross member as a compressive force on the side member. Since the intermediate portion of the cross member is lowered below the vehicle body, the compressive force acts as a moment force for turning the intermediate portion of the cross frame downwardly of the vehicle body.

When the cross member vibrates due to the load from the suspension, the floor panel joined to the cross member also vibrates. However, the inertia force and the moment force acting on the cross member are directed in opposite directions, thereby damping each other. , The vibration of the cross member, that is, the vibration level of the floor panel is reduced.

As shown in FIG. 5A, a dimension L in the vehicle width direction is 1000 mm, a dimension S in the front-rear direction is 80 mm, and a thickness H is 30 mm.
Of a floor model 50 having a thickness T of 70 mm and a radius of curvature R of 1306.6 mm.
FIG. 5 shows the results of comparing vibration levels using the M model.
This is shown in FIG. In the concave floor model to which the present invention is applied, the floor model 50 is bent in accordance with the radius of curvature R of the subframe model 52.

As described above, it is possible to reduce the vibration level over a wide band from about 120 Hz to about 350 Hz.

[0012] By reducing the vibration level during the running of the vehicle, the occupant feels discomfort during the running of the vehicle.
And "road noise" can be reduced, and comfortable vehicle running can be provided.

[0013]

1 is a perspective view showing an embodiment of a vehicle lower structure according to the present invention.
This will be described with reference to FIG.

In the figure, the arrow RE indicates the rear of the vehicle body and the arrow IN
Indicates the inside in the vehicle width direction, and arrow UP indicates the upper side of the vehicle body.

As shown in FIG. 1, a rear floor panel 14 is disposed in a luggage compartment 12 at a rear portion of the vehicle 10. At the end of the rear floor panel 14 in the vehicle width direction, a wheel house inner 16 and a suspension tower 18 are protruded. An upper end of a shock absorber of a rear suspension (not shown) is connected to an inner upper end of the suspension tower 18.

As shown in FIGS. 1 and 2, a rear side member 20 and a rear cross member 22 are joined to the lower surface of the rear floor panel 14.

The rear side members 20 are disposed at both ends in the vehicle width direction such that the longitudinal direction thereof is along the vehicle front-rear direction. The rear side member 20 is a strength member having a substantially hat-shaped cross-section, and is joined to the lower surface of the rear floor panel 14 with an opening facing the rear floor panel 14, and a flat cross-sectional structure is formed by the rear floor panel 14. .

The rear cross member 22 is disposed along the vehicle width direction, and both ends are joined to the rear side member 14, respectively. The rear cross member 22 is a strength member having a substantially hat-shaped cross section, and is joined to the lower surface of the rear floor panel 14 with the opening facing the rear floor panel 14, and the rear cross panel 22 forms a flat cross-sectional structure.

The rear cross member 22 is joined with its longitudinal end face abutting on the inner surface of the rear side member 20 in the vehicle width.

As shown in FIGS. 2 and 3, a through hole is formed inside the end of the rear cross member 22 and a nut 26 is coaxially joined thereto. It can be screwed. Also, two nuts 30 are joined to the inside of the rear side member 20 along the vehicle front-rear direction, and a bolt 32 can be screwed into each of these nuts 30.

An extension member 34 is provided at a joint between the rear cross member 22 and the rear side member 20. The extension member 34 is a strength member having a substantially hat-shaped cross section.
The connecting portion 36 accommodates and joins the rear cross member 22. The connecting portion 36 is connected to the rear cross member 22.
Are joined by welding after the end portions are fitted and overlapped, and a closed cross-sectional structure is formed by the rear cross member 22.

The other end of the extension member 34
A joining portion 38 is formed by notching a rectangular shape on the vehicle front-rear direction side, and a flange 40 is formed by bending. The joint 38 is connected to the rear side member 2 described above.
The flange 40 is welded and joined to the lower surface of the rear side member 20 to form a flat cross-sectional structure.

As shown in FIG. 3, the bottom plate 38A of the joint 38 of the extension member 34 has a nut 26 attached to the end of the rear cross member 22 and a nut 30 attached to the rear side member 20. Corresponding through-holes are provided, and a collar 42 is provided coaxially with these through-holes. Therefore, the collar 42 is disposed in each of the closed cross-sectional structure formed by the rear cross member 22 and the extension member 34 and the closed cross-sectional structure formed by the rear side member 20 and the extension member 34.

The joint 38 of the extension member 34
The rear sub-frame 24 is connected to the lower surface of the bottom plate 38A.

The rear sub-frame 24 is disposed below the rear cross member 22 in the vehicle width direction along the vehicle width direction. The rear sub-frame 24 is bent along the vehicle body vertical direction, and has a shape in which an intermediate portion in the vehicle width direction is lowered below the vehicle body. The rear cross member 22 is composed of an upper plate 24A and a lower plate 24B, both of which have a substantially hat-shaped cross section, and is joined by welding or the like in a state where the openings are opposed to each other to form a flat cross-sectional structure. I have.

At the end of the rear sub-frame 24, through holes are formed in the upper plate 24A and the lower plate 24B corresponding to the respective collars 42 formed in the bottom plate 38A of the joint 38 of the extension member 34. The upper plate 24A and the lower plate 24B
And a collar 44 is disposed between them. Therefore, the collars 42 and 44 and the nuts 26 and 30 are coaxially arranged and communicated.

The rear sub-frame 24 includes a collar 42,
The extension member 34 is formed by the bolt 28 inserted into the nut 4 and screwed to the nut 26 and the bolt 32 inserted into the collars 42 and 44 and screwed to the nut 30.
Through the rear side member 20 and the rear cross member 22. The joining positions of the rear cross member 22 and the rear sub frame 24 to the rear side member 20 are the same.

On the other hand, as shown in FIG. 2, an intermediate portion of the rear cross member 22 in the vehicle width direction is closer to the rear sub-frame 24 by a displacement dimension D with respect to both ends. That is, the middle portion of the rear cross member 22 in the vehicle width direction is curved by being lowered by the displacement dimension D with respect to both end portions. According to the shape of the rear cross member 22, the rear floor panel 14 also has a curved shape along the vehicle width direction. When the inside of the luggage compartment 12 is viewed from the rear of the vehicle 10, a concave portion is found at an intermediate portion of the rear floor panel 14. Is done.

A rear suspension is mounted on a middle portion of the rear sub-frame 24 in the vehicle width direction via a suspension arm or the like (not shown), and a load from these rear suspensions is applied to the rear sub-frame 24.
Through the rear side member 20 and the rear cross member 2
2.

In the lower body structure of the vehicle 10 having the above-described structure, the load from the rear subframe 24 during running of the vehicle acts on the joint between the rear side member 20 and the rear cross member 22, and the rear side member 20 and the rear cross member 22 are connected. Communicate to

The action of the load from the rear sub-frame 24 on the rear cross member 22 as the inertial force acts so that the intermediate portion of the rear cross member 22 in the vehicle width direction is directed upward of the vehicle body (see FIG. 2). Arrow F direction). Further, the compressive force applied to the rear side member 20 by the load received from the rear sub-frame 24 acts on the rear cross member 22 as a moment force in the direction of arrow A about the rear side member 20.

With respect to this moment force, since the intermediate portion of the rear cross member 22 in the vehicle width direction is displaced downward by a displacement dimension D with respect to both ends, the rear cross member 22 in the vehicle width direction is displaced downward. The intermediate portion is lowered below the vehicle body (the direction of arrow M in FIG. 2).

Since the rear floor panel 14 is joined to the rear cross member 22, the rear cross member 2
2 and one. For this reason, the rear cross member 2
2 is applied to the rear floor panel 14 in the same manner. That is, the inertial force and the moment force act on the rear floor panel 14 while buffering them in opposite directions, and reduce the vibration level of the rear floor panel 14.

FIGS. 4 (A) and 4 (B) show the characteristics of the underbody structure according to the present invention using the FEM model.
This is a comparison with a conventional rear floor panel provided flat. FIG. 4A shows a vibration level (dB) corresponding to the vibration frequency (Hz), and FIG. 4B shows a range from 80 Hz to 200 Hz with respect to the descending amount (mm) of the rear floor panel 14. The average vibration level (dB) of the vibration frequency is shown.

As shown in FIG. 4 (A), the vibration level is set at a frequency of around 100 Hz, and between 150 Hz and 200 Hz.
At z, it is clearly lower than before. Especially 150H
The vibration of the rear floor panel 14 in a frequency band near 200 Hz from z gives discomfort to the occupant as "muffled sound" or "road noise" accompanying the traveling of the vehicle. By lowering the level, it is possible to provide an optimal driving state.

As shown in FIG. 4 (B), a favorable effect can be obtained when the downward displacement dimension D of the rear floor panel 14 is in a range of 5 mm to 40 mm, and particularly, an optimum effect is obtained in the vicinity of 25 mm. Can be obtained.

[0037]

As described above, according to the lower body structure of the present invention, the vibration level of the floor panel can be reduced, and an excellent effect of eliminating discomfort to the occupant during running of the vehicle can be obtained. I was able to.

[Brief description of the drawings]

FIG. 1 is a perspective view of a main part showing a rear part of a vehicle according to an embodiment.

FIG. 2 is a cross-sectional view of a main part along line 2-2 in FIG.

FIG. 3 is a main part plan view showing a joint between a rear side member and a cross member according to the embodiment.

FIG. 4 is a characteristic diagram illustrating a relationship between a vibration level and a frequency in the vehicle body lower structure according to the embodiment.

FIG. 5 is a characteristic diagram showing a relationship between an average vibration level and a descending amount of a cross member.

[Explanation of symbols]

 Reference Signs List 10 vehicle 14 rear floor panel 20 rear side member 22 rear cross member 24 rear subframe 34 extension member

Claims (1)

(57) [Claims] 1. A side member disposed on both sides in a vehicle width direction, a cross frame bridged between the side members, and a floor panel joined on each of the side member and the cross member. And a sub-frame to which a suspension is mounted, which is disposed below the vehicle body of the cross frame, and wherein the sub-frame is connected to a connection portion of the cross frame to the side member, and A lower body structure in which a middle portion in a vehicle width direction is closer to the subframe by a predetermined amount than both end portions in a vehicle width direction.