JPH08164868A - Car body front part structure - Google Patents

Abstract

PURPOSE: To reduce oscillation of a car body front part and to reduce weight of the car body front part by installing a pair of left and right lower arm rear end parts on a cross member on the bar body rear side and installing front end parts in the neighbourhood of a front end part of side rails. CONSTITUTION: Integrated left and right side rails 16, 18 of a pipe member thinner than a pair of a front cross member 12 and a rear cross member 14 in diameter are arranged between those front cross member 12 and rear cross member 14. Thereafter, rear side installation parts 40A are inserted into both ends of the rear cross member 14 and axially supported by bolts 34. Thereafter, arm front side installation parts 40B of the lower arm 40 are installed on connecting parts with the front cross member 12 of each of front end parts 16A, 18A of the side rails 16, 18 through brackets 42. Consequently, offset L along the car body longitudinal direction of these installation parts and installation parts 12A, 12B of both left and right end parts of the front cross member 12 to a car body becomes small. Consequently, a sectional secondary moment of the side rails 16, 18 becomes small, and resonance is hardly caused.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle body front structure, and more particularly to a vehicle body front structure having a cross member and side rails at the vehicle body front portion.

[0002]

2. Description of the Related Art Conventionally, in a vehicle body front structure, a structure is known in which a front suspension is attached to a front subframe composed of a cross member and side rails, one example of which is Japanese Patent Laid-Open No. 6-8846. Is shown in.

As shown in FIG. 10, in this vehicle body front structure, a pair of strong left and right side rails 80 arranged along the longitudinal direction of the vehicle body and these side rails 8 are provided.
A pair of front and rear cross members 82 arranged between 0 form a well-shaped front sub-frame 84 in a plan view, and a pair of left and right lower arms 86 are attached to the front sub-frame 84.

[0004]

However, in the vehicle body front structure of this automobile, the attachment portion 80A of the front end of the side rail 80 to the vehicle body and the front attachment portion 8 of the lower arm 86 are formed.
The offset amount L1 along the vehicle body front-rear direction with the portion 80B to which 6A is attached is large. Therefore, the bending force applied to the side rail 80 by the input of the lower arm 86 is increased. Therefore, in the side rail 80, it is necessary to increase the cross-sectional area in order to obtain the required bending rigidity. Further, since a large lateral force acts on the cross member 82, it is necessary to increase the cross-sectional area of the cross member 82. As a result, the difference in cross-sectional area between the side rail 80 and the cross member 82 becomes small, the vibration characteristics become similar to each other, and the front portion of the vehicle body easily vibrates due to resonance.

In view of the above facts, an object of the present invention is to obtain a vehicle body front structure capable of reducing the vibration of the vehicle body front portion.

[0006]

A vehicle body front structure of the present invention comprises a pair of front and rear cross members extending substantially along the vehicle width direction and attached to the vehicle body at both left and right ends, and between these cross members. A pair of left and right side rails, and a pair of left and right lower arms whose rear end is attached to a cross member on the rear side of the vehicle body and whose arm front end is attached near the front end of the side rail. It is characterized by having.

[0007]

In the vehicle body front structure of the present invention, the lower arm
Since the front end of the side rail is mounted in the vicinity of the front end of the side rail, the offset between this mounting part and the mounting parts at the left and right ends of the cross member on the front side of the vehicle body to the vehicle body becomes small along the vehicle body front-rear direction. Therefore, the bending force acting on the side rail due to the input from the lower arm is reduced, and the rigidity of the side rail can be reduced. That is, the cross-sectional area of the side rail can be made smaller than that of the cross member. As a result, the secondary moment of inertia of the side rail is smaller than the secondary moment of cross section of the cross member, so the natural frequency of the side rail becomes smaller than the natural frequency of the cross member, and the side rail and the cross member resonate. It will be difficult.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a vehicle body front structure according to the present invention is shown in FIG.
~ It demonstrates using FIG.

In the figure, the arrow FR indicates the front direction of the vehicle body, the arrow IN indicates the vehicle width inner direction, and the arrow UP indicates the vehicle body upward direction.

As shown in FIG. 2, the front sub-frame 10 has a pair of front and rear front cross members 12 and a rear cross member 14 extending substantially along the vehicle width direction. The front cross member 12 is made of a pipe material, and the left and right ends thereof are mounting portions 12A, 12 to the vehicle body.
It is B. Further, the rear cross member 14 is also made of a pipe material, and the left and right ends thereof are attached to the vehicle body.
It is A and 14B. Between the front cross member 12 and the rear cross member 14, a pair of left and right side rails 16 and 18 extending in the front-rear direction of the vehicle body are arranged. These side rails 16 and 18 are the front cross member 12 and the rear cross member. It is made of a pipe material thinner than the diameter of the cross member 14.

As shown in FIG. 1, the front end portion 16A of the left side rail 16 is welded to the vicinity of the left mounting portion 12A of the front cross member 12, and the rear end portion 16B of the left side rail 16 is It is welded in the vicinity of the left mounting portion 14A of the rear cross member 14. The front end portion 18A of the right side rail 18 is welded to the vicinity of the right side mounting portion 12B of the front cross member 12, and the rear end portion 18B of the right side rail 18 is connected to the right side mounting portion of the rear cross member 14. It is welded near 14B.

As shown in FIG. 2, the side rails 16,
The longitudinal intermediate portions 16C and 18C of 18 are bent downward in an arc shape. Also, the front cross member 12
And the longitudinal middle portion 12C of the rear cross member 14, 1
4C is located slightly lower than the left and right mounting parts,
The vicinity of both left and right mounting portions of the front cross member 12 and the rear cross member 14 is curved toward the upper side of the vehicle body.

That is, the vicinity of both the left and right mounting portions of the front cross member 12 and the rear cross member 14 is curved upward so as to avoid a lower arm described later.

As shown in FIG. 3, the rear cross member 1
A bracket 20 is welded to the lower surface side of the connecting portion between the side rail 16 and the side rail 16, and the bracket 20 has a box shape with an opening facing upward. Bracket 20
Flanges 22 and 24 are formed at the opening edge portion of the opening toward the outside of the opening. The flange 22 is the rear cross member 14
And the flange 24 is welded to the side rail 16.

As shown in FIG. 4, one end portion 26A of the connecting plate 26 is provided on the lower surface side of the bottom portion 20A of the bracket 20.
Are fixed by bolts 28 and weld nuts 30. The connecting plate 26 extends outward in the vehicle width direction, and a cut-and-raised portion 27 is formed downward at the outer peripheral edge portion. A through hole 32 is formed in the vehicle width direction outer end portion 26B of the connecting plate 26, and a bolt 34 is inserted into the through hole 32 from below. This bolt 34
Is screwed into a weld nut 36 embedded near the mounting portion 14A of the rear cross member 14. Further, the vehicle width direction outer end portion 26B of the connecting plate 26 and the rear cross member 14 are
The rear mounting portion 40A of the A-type lower arm 40 is inserted between the mounting portion 14A and the vicinity of the mounting portion 14A, and is pivotally supported by the bolt 34.

The rear mounting portion 40A of the A type lower arm 40 on the right side of the vehicle body is also pivotally supported in the same manner.

As shown in FIG. 5, a bracket 42 is welded to the lower surface of the connecting portion between the front cross member 12 and the side rail 18.

As shown in FIG. 6, this bracket 42
Is composed of a bracket front 44 forming a front portion of the bracket 42 and a bracket rear 46 forming a rear portion of the bracket 42. The bracket rear 46 is welded to a vertically intermediate portion (a portion indicated by an imaginary line in FIG. 6) of the rear side surface of the bracket front 44 by a flange 46A formed on an upper edge portion, and the flange 46A and the inclined surface are welded. A lower portion 46C continuous by 46B is parallel to the base portion 44A of the bracket front 44. Also,
Cut-and-raised parts 45 are formed at the vehicle width direction outer edge and the lower end part of the base part 44A of the bracket front 44 toward the front of the vehicle body, and cut-and-raised parts continuous to the flange 46A are formed at the outer peripheral edge part of the bracket rear 46. 48 are formed.

As shown in FIG. 5, the bracket rear 46
Inner portions 48A and 48B of the cut-and-raised portion 48 in the vehicle width direction are welded to the front end portion 18A of the side rail 18.

As shown in FIG. 7, the upper edge 44C of the bracket front 44 is welded to the rear outer peripheral portion of the front cross member 12. Bracket front 44
A through hole 50 is formed in the lower portion of the base portion 44A of
The lower part 4 of the bracket rear 46 facing the through hole 50
A through hole 52 is formed in the portion 6C. The bracket front 44 is provided in the through hole 50 and the through hole 52.
The bolt 54 is inserted from the front side of the. This bolt 5
4, a nut 56 is screwed from the rear side of the bracket rear 46. In addition, the base 4 of the bracket front 44
A front side mounting portion 40B of the lower arm 40 is inserted between 4A and a lower portion 46C of the bracket rear 46, and is pivotally supported by a bolt 54.

The front mounting portion 40B of the lower arm 40 on the left side of the vehicle body is also rotatably supported.

As shown in FIGS. 8 and 9, the front sub-frame 10 is disposed between a pair of left and right front side members 58 arranged along the vehicle front-rear direction in the vicinity of both ends of the front portion of the vehicle body in the vehicle width direction. The front sub-frame 10 is disposed on the side of the front side member 5 at the left and right mounting portions 12A and 12B of the front cross member 12 and the left and right mounting portions 14A and 14B of the rear cross member 14.
It is fixed to the bottom of 8.

An engine 70 and a transmission 72 are fixed above the front sub-frame 10 via brackets 60, 61, 62, 63, 64 and 65 shown in FIG. Incidentally, reference numeral 74 in FIGS.
Indicates a drive shaft, reference numeral 76 indicates a steering gear box, and reference numeral 78 in FIG. 8 indicates a front tire.

Next, the operation of this embodiment will be described.
In the vehicle body front structure of this embodiment, as shown in FIG. 1, the arm front side mounting portion 40B of the lower arm 40 is connected to the front cross members 12 of the front end portions 16A and 18A of the side rails 16 and 18, respectively. Since it is mounted via the bracket 42, the offset L between the mounting portion and the mounting portions 12A, 12B at the left and right ends of the front cross member 12 to the vehicle body along the vehicle front-rear direction is small.

Therefore, the bending force applied to the side rails 16 and 18 by the input from the lower arm 40 is reduced, and the rigidity of the side rails 16 and 18 can be reduced. That is, the cross-sectional areas of the side rails 16 and 18 can be made smaller than the cross-sectional areas of the front cross member 12 and the rear cross member 14. As a result, the geometrical moment of inertia of the side rails 16 and 18 is the geometrical moment of inertia of the front cross member 12 and the rear cross member 14.
Is smaller than the second moment of area.

Here, the natural frequencies f _n of the side rails 16 and 18, the front cross member 12, and the rear cross member 14 are given by the following formula 1.

[0027]

[Equation 1]

Here, E is the elastic modulus, I is the second moment of area, M is the mass, and L is the length.

Therefore, each natural frequency f _n is proportional to the second moment of area I. Therefore, the side rails 16, 1
8 is the second moment of area of the front cross member 12 and the second moment of area of the rear cross member 14 is 2.
When it becomes smaller than the next moment, the side rails 16 and 1
Since the natural frequency of No. 8 is smaller than the natural frequency of the front cross member 12 and the natural frequency of the rear cross member 14, the side rails 16 and 18 and the front cross member 12 and the rear cross member 14 are less likely to resonate. Vibration of the front part of the vehicle body can be reduced.

Further, in the vehicle body front structure of this embodiment, the side rails 16 and 18 have a small cross-sectional area, so that the side rails 16 and 18 are light in weight, and the weight of the vehicle body front portion can be reduced. Furthermore, since the cross-sectional areas of the side rails 16 and 18 are reduced, the degree of freedom in designing the side rails 16 and 18 is increased. Therefore, it becomes easy to control the bending mode of the side rails 16 and 18 at the time of frontal collision, and for example, the bending mode of the side rails 16 and 18 is set so that the front and rear crushing margin of the vehicle body becomes small at the time of frontal collision. Can be done easily.

In the vehicle body front structure of this embodiment, the arm front side attachment portion 40B of the lower arm 40 is attached to the connecting portion of the front end portions 16A and 18A of the side rails 16 and 18 with the front cross member 12. , This mounting part,
When the offset L along the vehicle body front-rear direction between the left and right end portions of the front cross member 12 and the vehicle body attachment portions 12A, 12B becomes smaller, the lower arm 40 front arm attachment portion 4 is formed.
The mounting position of 0B may be in the vicinity of the front end portions 16A and 18A of the side rails 16 and 18, respectively. Further, the arm front side attachment portion 40B of the lower arm 40 may be attached to the front cross member 12 as long as it is near the front end portions 16A and 18A of the side rails 16 and 18.

[0032]

The vehicle body front structure of the present invention is provided with a pair of front and rear cross members extending substantially along the vehicle width direction and attached to the vehicle body at both left and right ends, and between these cross members. And a pair of left and right side rails, and a pair of left and right lower arms whose rear end is attached to a cross member on the rear side of the vehicle body and whose arm front end is attached near the front end of the side rail. Therefore, the vibration of the front portion of the vehicle body can be reduced, the weight of the front portion of the vehicle body can be reduced, and the folding mode can be easily set.

[Brief description of drawings]

FIG. 1 is a plan view showing a vehicle body front structure according to an embodiment of the present invention.

FIG. 2 is a perspective view of a vehicle body front structure according to an exemplary embodiment of the present invention as seen obliquely from the front of the vehicle body.

FIG. 3 is an enlarged perspective view showing a part of a vehicle body front structure according to an embodiment of the present invention, as viewed from the diagonally left front outside of the vehicle body.

4 is a cross-sectional view taken along line 4-4 of FIG.

FIG. 5 is an enlarged perspective view showing a part of a vehicle body front structure according to an embodiment of the present invention as seen from the diagonally right front outside of the vehicle body.

FIG. 6 is an exploded perspective view showing a part of a vehicle body front structure according to one embodiment of the present invention as seen from the diagonally right front outside of the vehicle body.

7 is a cross-sectional view taken along line 7-7 of FIG.

FIG. 8 is a plan view showing a vehicle body front portion to which a vehicle body front portion structure relating to an exemplary embodiment of the present invention is applied.

FIG. 9 is a side view showing a vehicle body front portion to which a vehicle body front portion structure relating to an exemplary embodiment of the present invention is applied.

FIG. 10 is a plan view showing a vehicle body front structure according to a conventional example.

[Explanation of symbols]

 10 front sub-frame 12 front cross member 12A mounting portion to vehicle body 12B mounting portion to vehicle body 14 rear cross member 16 side rail 18 side rail 40 lower arm 40B front mounting portion

Claims (1)

[Claims] 1. A pair of front and rear cross members extending substantially along the vehicle width direction and attached to the vehicle body at both left and right ends, a pair of left and right side rails disposed between these cross members, and an arm. A front structure of a vehicle body, comprising a pair of left and right lower arms having a rear end portion attached to a cross member on a rear side of the vehicle body and an arm front end portion attached to a vicinity of a front end portion of the side rail.