JP2017128148A - Impact absorption structure of vehicle body frame - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable proper axial collapse of crash boxes at time of a vehicle collision to improve the collision energy absorption efficiency in an impact absorption structure of a vehicle body frame where a cross member is supported at middle parts of the crash boxes through support brackets in an area below the crash boxes.SOLUTION: An impact absorption structure of a vehicle body frame includes: crash boxes 2 which are respectively provided at tips of left and right side rails 1 forming a vehicle body frame so as to extend forward and cause axial collapse at time of a collision; support brackets 3, each of which is attached to a middle part of the crash box 2 and extends downward; and a cross member 4 which is attached to the support brackets 3 and extends in a vehicle width direction below the crash boxes 2. In each crash box 2, axial strength of a rear portion 2r relative to the support bracket 3 is smaller than axial strength of a front portion 2f relative to the support bracket 3.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an impact absorption structure for a vehicle body frame in which a crash box that absorbs an impact by being crushed at the time of a collision is attached to the front ends of left and right side rails constituting the vehicle body frame.

  Crash box (extension frame) that absorbs shock by collapsing rearward at the tip of the left and right side rails that make up the body frame of trucks, buses, etc. as a structure to absorb the impact when the vehicle collides Are known (see Patent Documents 1 and 2, etc.).

  The present inventors are developing the type shown in FIG. 1 (comparative example with respect to the present invention) as a shock absorbing structure for this type of vehicle body frame. As shown in FIG. 1, in this comparative example, a crash box 2j attached to the front ends of the left and right side rails 1 constituting the body frame and axially collapsing at the time of a collision, and attached in the middle of the crash box 2j and extended downward. And a cross member 4 attached to the support bracket 3 and extending in the vehicle width direction below the crash box 2j.

  The cross member 4 supports the radiator, and a pulling hook 5 is attached to the cross member 4 facing forward. Further, 6 shown in FIG. 1 is a cross member for supporting the engine, 7 is a cab mount bracket, and 8 is a bumper.

JP-A-8-169286 JP 10-167110 A

  The results of a collision test for such a comparative example are shown in FIGS. 2 (a) to 2 (d). 2 (a) to 2 (d), the vehicle body frame (side rail 1) is supported on the left side by being fixed to a gantry (not shown) so as not to move backward. An impactor X simulating a collision object is collided.

  FIG. 2A shows a moment when the impactor X hits the bumper 8, and FIG. 2B shows a state in which the bumper 8 is crushed and the crash box 2j is axially crushed (buckled) from the tip. Since the crash box 2j is generally designed so as to be axially crushed from the tip (front of the vehicle), the impactor X collides with the traction hook 5 of the cross member 4 as indicated by the arrow F when the axial crushing progresses. Then, since the traction hook 5 with which the impactor X collides is disposed below the crash box 2j that supports the reaction force, as shown in FIG. 2C, a downward moment M is applied to the crash box 2j. Occurs. As a result, the crash box 2j bends at the base, and thereafter, as shown in FIG. 2D, the axial collapse of the crash box 2j is prevented. Therefore, the crush box 2j remains uncrushed, and the collision energy cannot be absorbed appropriately.

  Even when the tow hook 5 is not provided, the crash box 2j is axially crushed from the tip by the impact of the impactor X, and the impactor X collides with the cross member 4 due to the progress of the crushing. As in the case, a downward moment M is generated in the crash box 2j. Therefore, the crash box 2j is bent at the base, and the collision energy absorption efficiency by the crash box 2j is deteriorated.

  The object of the present invention, which was created in view of the above circumstances, is to provide a shock absorbing structure for a vehicle body frame in which a cross member is supported downward via a support bracket in the middle of the crash box. An object of the present invention is to provide a shock absorbing structure for a vehicle body frame that is crushed and has improved collision energy absorption efficiency.

  According to the present invention created to achieve the above-described object, it is a shock absorbing structure for a vehicle body frame that is attached to the front ends of the left and right side rails constituting the vehicle body frame and absorbs shock by being crushed during a collision. A crash box that extends forward at the front end of the side rail and collapses axially in the event of a collision, a support bracket that is attached in the middle of the crash box, extends downward, and is attached to the support bracket and below the crash box The crash box is characterized in that the axial strength of the rear portion of the crash box is smaller than the axial strength of the front portion of the support bracket. A shock absorbing structure for a vehicle body frame is provided.

  In the shock absorbing structure for a vehicle body frame according to the present invention, the crash box has a cross-sectional shape, a plate thickness, and At least one bead number may be different.

  In the shock absorbing structure for a vehicle body frame according to the present invention, the cross member may be provided with a tow hook extending forward.

  In the shock absorbing structure for a vehicle body frame according to the present invention, the length of the rear portion of the crash box may be longer than the length of the front portion.

  In the shock absorbing structure for a vehicle body frame according to the present invention, the cross member is supported downward via a support bracket in the middle of the crash box, and the axial strength of the rear portion of the crash box is supported by the support bracket. It is smaller than the axial strength of the front portion of the bracket. For this reason, when the collision object collides from the front end side of the crash box, the crash box is first crushed from the rear part, the rear part is crushed, the front part is axially crushed, and then the collision member is collided with the cross member. A shock is applied. That is, after the rear portion and the front portion of the crash box are axially crushed, an impact is applied to the cross member, and a downward moment is generated in the crash box. In this way, the generation time of the downward moment generated in the crash box at the time of the collision can be delayed as much as possible, so that the crash box is appropriately axially collapsed over almost the entire area, and the collision energy absorption efficiency Can be enhanced.

It is a perspective view of the shock absorption structure of the vehicle body frame which shows the comparative example which is not the Example of this invention. It is a side view showing a collision test for a comparative example, (a) is the moment when the impactor collides, (b) when the impactor collides with the tow hook, (c) is a state in which a downward moment is generated in the crash box, (D) It is explanatory drawing which each shows a mode that the crash box bent. 1 is a perspective view of a shock absorbing structure for a vehicle body frame showing an embodiment of the present invention. FIG. 4 is a perspective view of the crash box shown in FIG. 3. It is a side view which shows the impact test about one Embodiment of this invention, (a) is the moment when an impactor collided, (b) is a mode that a crash box axially collapses from a rear end, (c) is the back of a crash box It is explanatory drawing which shows a mode that a part is axially crushed and (d) the front part of a crash box is axially crushed. It is a graph which shows the relationship between the displacement amount of an impactor, and energy absorption amount about one Embodiment (invention product) of this invention, and a comparative example (comparative product).

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in the embodiment are merely examples for facilitating understanding of the invention, and do not limit the present invention unless otherwise specified. In the present specification and drawings, elements having substantially the same function and configuration are denoted by the same reference numerals, and redundant description is omitted, and elements not directly related to the present invention are not illustrated. To do.

(Body frame shock absorption structure)
FIG. 3 shows a shock absorbing structure for a vehicle body frame according to this embodiment. The shock absorbing structure of the vehicle body frame is provided to extend forward at the front ends of the left and right side rails 1 constituting the vehicle body frame, and is attached in the middle of the crash box 2 and a crash box 2 that is axially crushed at the time of collision. And a cross member 4 which is attached to the support bracket 3 and extends in the vehicle width direction below the crash box 2. The crash box 2 is provided by the support bracket 3. Also, the axial strength of the rear portion 2 r is smaller than the axial strength of the front portion 2 f than the support bracket 3. The cross member 4 supports the radiator, and a pulling hook 5 is attached to the cross member 4 facing forward. In FIG. 3, 6 is a cross member for supporting the engine, 7 is a cab mount bracket, and 8 is a bumper.

  As shown in FIG. 4, the crush box 2 is formed of a hollow body having a rectangular cross section in which U-shaped cross-section members 2x and 2y are welded facing each other in the middle, but is not limited to this structure. A cross-sectional material may be used. The crash box 2 includes a rear portion 2r and a front portion so that the axial strength of the rear portion 2r of the portion to which the support bracket 3 is attached (attachment portion 3a) is smaller than the axial strength of the front portion 2f of the attachment portion 3a. 2f is different in at least one of the cross-sectional shape, the plate thickness, and the number of beads. In the present embodiment, the crash box 2 has a portion 2a having the smallest cross-sectional height disposed behind the mounting portion 3a of the support bracket 3, and axial crushing is applied to the rear portion 2r including the portion 2a. A bead (crush bead, axial crush promoting bead) 9 for inducing is provided, and the portion 2a is configured to be a starting point of axial crush when compressed from the axial direction.

  As shown in FIG. 5 (a), the crash box 2 has a constant cross-sectional height from the front portion 2f to the middle of the rear portion 2r, but the lower surface of the rear portion 2r rises from the middle toward the rear. And the cross-sectional height of the rear portion 2r is reduced. In addition, in the upper surface and the lower surface of the rear portion 2r of the crash box 2, depressions forming the beads 9 are formed with a space in the front-rear direction (longitudinal direction). The number of the beads 9 is not limited to two spaced apart in the longitudinal direction as in the present embodiment, and may be three or more, or may be one. In the present embodiment, the cross-sectional width of the crash box 2 is constant in the longitudinal direction, but the axial strength may be reduced by making the rear portion 2r narrower than the front portion 2f.

  The configuration for making the axial strength of the rear portion 2r of the crash box 2 smaller than the axial strength of the front portion 2f is not limited to that described above. For example, the thickness of the rear portion 2r of the crash box 2 is set to the front portion. It may be thinner than 2f, and the material of the rear part 2r may be softer than the material of the front part 2f. In the case of these configurations, it is also conceivable to connect the rear part 2r and the front part 2f as separate parts by bolts and nuts or welding. Moreover, you may combine some of the some structure mentioned above.

(Action / Effect)
FIG. 5A to FIG. 5D show the results of a collision test performed on the shock absorbing structure of the vehicle body frame according to the present embodiment. 5 (a) to 5 (d), the vehicle body frame (side member 1) is fixed to the gantry (not shown) on the left side and is supported so as not to move backward. An impactor simulating a collision object) collides (offset collision or full lap collision).

  In the shock absorbing structure for a vehicle body frame according to the present embodiment, the cross member 4 is supported downwardly via the support bracket 3 in the middle of the crash box 2, and the crash box 2 is a rear portion of the support bracket 3. The axial strength of 2r is set to be smaller than the axial strength of the front portion 2f than the support bracket 3.

  Therefore, as shown in FIG. 5 (a), when the impactor X collides from the front end side of the crash box 2 and the bumper 8 is crushed, the crash box 2 is first moved backward as shown in FIG. 5 (b). As shown in FIG. 5 (c), the axial crushing starts from the minimum cross-sectional height portion 2a (see FIG. 4) of the portion 2r and the rear portion 2r is crushed, as shown in FIG. 5 (d). The portion 2f is axially crushed, and finally, the impactor X hits the tow hook 5 and an impact is applied.

  That is, after the rear portion 2r and the front portion 2f of the crash box 2 are axially crushed, an impact is applied to the traction hook 5 and a downward moment is generated in the crash box 2. As described above, since the generation time of the downward moment generated in the crash box 2 at the time of the collision can be delayed as much as possible, the crash box 2 is appropriately axially collapsed over almost the entire region, and the collision energy is reduced. Absorption efficiency can be increased (see comparative example in FIG. 2). Even when the tow hook 5 is omitted, the impactor X collides with the cross member 4 as the front portion 2f is crushed in FIG.

  FIG. 6 is a graph showing the relationship between the amount of displacement of the impactor X and the amount of energy absorption for the present embodiment (the invention, see FIG. 5) and the comparative example (the comparison, see FIG. 2). In FIG. 6, (a) on the horizontal axis is the moment when the impactor X contacts the bumper 8, and corresponds to FIGS. 5 (a) and 2 (a). The displacement amount of the impactor X in this state is 0 mm. To do. 6B corresponds to FIG. 5B and FIG. 2B, FIG. 6C corresponds to FIG. 5C and FIG. 2C, and FIG. d) corresponds to FIG. 5 (d) and FIG. 2 (d).

  As shown in FIG. 6, when the impactor X moves 300 mm after contacting the bumper 8, the energy absorption amount of the invention increases by 18% compared to the comparative product, and similarly, when the impactor X moves by 400 mm, it increases by 33% and increases by 500 mm. Increases by 36% when moved. Such an increase in the amount of energy absorption occurs when the ratio of axial crushing to the entire crash box 2 is higher in the invention shown in FIG. 5 (d) than in the comparison product shown in FIG. 2 (d). In addition, in the invention product, when the amount of energy absorption equivalent to that of the comparative product is ensured, the plate thickness of the crash box 2 can be reduced, so that weight reduction and material cost reduction can be promoted.

  Further, focusing on the vertical axis in FIG. 6, for example, when the kinetic energy (collision energy) of the impactor (collision vehicle) X is 50 kJ, the impactor X stops at a position of about 380 mm from the bumper 8 in the invention. The comparative product moves to a position of about 470 mm and stops. As a result, the impactor (collision vehicle) X of the invention product does not bite more than the comparison product, and it is easy to secure the occupant's living space.

  By the way, in the invention, from FIG. 5C to FIG. 5D, the axial crushing of the front portion 2f of the crash box 2 proceeds in accordance with the movement of the impactor X, and the impactor X moves to the towing hook 5 (towing hook). If 5 is omitted, a collision with the cross member 4) may cause a downward moment in the crash box 2 and bend the front portion 2f. Therefore, although the rear portion 2r of the crash box 2 is almost completely axially crushed, there is a possibility that a slight crush remains in the front portion 2f.

  Here, in this embodiment, as shown in FIG. 4, the length of the rear portion 2r of the crash box 2 is longer than the length of the front portion 2f. The amount of absorption can be made larger than the amount of collision energy absorbed by the axial crush of the front portion 2f, and even if a slight crushing residue occurs in the front portion 2f, the necessary amount of collision energy absorption can be ensured for the entire crash box 2.

  The preferred embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the above-described embodiments, and various modifications within the scope described in the claims. Needless to say, the modified examples also belong to the technical scope of the present invention.

  In the present invention, a crash box that absorbs an impact by being crushed at the time of collision is attached to the end of a side rail that constitutes the body frame, and the impact of the body frame in which the cross member is supported downward via a support bracket in the middle of the crash box. Available for absorption structure.

1 Side rail 2 Crash box 2f Front part 2r Rear part 3 Support bracket 4 Cross member 5 Towing hook 9 Bead

Claims (4)

It is attached to the tip of the left and right side rails that make up the body frame, and is a shock absorbing structure for the body frame that absorbs shock by being crushed at the time of collision,
A crash box that is provided to extend forward at the tip of the side rail and axially collapses in the event of a collision, a support bracket that is attached in the middle of the crash box, and that extends downward, is attached to the support bracket, With a cross member extending in the vehicle width direction below the crash box,
The shock absorbing structure for a vehicle body frame, wherein the crash box has an axial strength at a rear portion smaller than the support bracket, which is smaller than an axial strength at a front portion of the support bracket.   In the crash box, in order to make the axial strength of the rear portion smaller than the axial strength of the front portion, at least one of the cross-sectional shape, the plate thickness, and the number of beads differs between the rear portion and the front portion. The shock absorbing structure for a vehicle body frame according to claim 1, wherein:   The shock absorbing structure for a vehicle body frame according to claim 1 or 2, wherein a pulling hook extending forward is provided on the cross member.   4. The shock absorbing structure for a vehicle body frame according to claim 1, wherein a length of the rear portion is longer than a length of the front portion. 5.

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