JP2002104107A - Shock absorbing body for vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a crash box having a large degree of freedom for setting compressive deformation characteristic, capable of facilitating setting of performance as a shock absorbing structure, and having excellent stability of quality in mass production. SOLUTION: The crash box 20 interposed between a bumper reinforcement and a side member is formed hollow by a hydrostatic forming method taking a steel pipe as starting material. In the center of the crash box 20, a bellows part 23 is provided as a main absorbing part. In one section intersecting perpendicularly to the central axis Z, the wall part constituting the bellows part 23 is integrally closed without a seam, and the wall thickness of the wall part is made uniform.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shock absorber for a vehicle which is added to a structural member of a vehicle body skeleton to reduce a shock at the time of a collision.

[0002]

2. Description of the Related Art Left and right side members and bumper reinforcements are constituent elements of a vehicle body front portion of an automobile. Today, a shock absorber called a crash box is provided between a front end of each side member and a bumper reinforcement. The design that intervenes the body is common.
This crash box receives a load acting on the front bumper at the time of a frontal collision of the vehicle, and compresses and deforms in the axial direction to absorb the collision energy and reduce or reduce the load input to the side members. As an example of the configuration of such a crash box, for example, there is a cylinder body in which four plate-like panels are interconnected at respective ends so that a cross section orthogonal to the longitudinal direction is rectangular. Each plate-shaped panel is obtained by press molding, and at the time of pressing, a plurality of depressions called beads are provided to each panel. An overlap margin is secured at the end of each panel, and two adjacent
The panels are connected to each other by overlapping the overlapping portions of the panels and welding them. By arranging a plurality of beads on each surface of the cylindrical body having a rectangular cross section, the crash box at the time of the collision is deformed into a bellows shape while being compressed in the axial direction.

In addition, for the purpose of absorbing the same impact as described above, an inner pipe made of carbon steel is housed inside a hollow cylindrical side member, and a certain range near the tip of the inner pipe connected to the front bumper is adjusted. A side member structure having a bellows tube has also been proposed (see Japanese Utility Model Application Laid-Open No. 5-54160 filed in 1991).

[0004]

However, the above-mentioned conventional shock absorbing structure has some disadvantages. First, 4
When a crash box is composed of two plate-like panels,
When the ends of the panels are overlapped and welded, the thickness of the resulting tubular body becomes uneven. That is, the thickness of the portion other than the welding portion is the thickness of one panel, whereas the thickness of the welding portion is the thickness of two panels, and the highly rigid portions are unevenly distributed even in the same cross section orthogonal to the axis. It becomes a situation.
Further, assuming that welding is performed at four locations, it is practically difficult to exactly equalize the welding strength at each location. Thus, from the fact that unevenness of wall thickness and unevenness of welding strength in the cross section orthogonal to the axis of the cylinder cannot be avoided,
It is difficult to set the deformation characteristics (or the absorption characteristics of the collision energy) of the crash box at the time of the collision to the desired characteristics, and it is difficult to set the performance and control the quality of the shock absorbing structure.

The same disadvantages as described above can be pointed out for the side member structure disclosed in Japanese Utility Model Laid-Open No. 5-54160. At least in the state of the art in 1991,
In order to manufacture an iron inner pipe having a bellows tube portion, the inner pipe is designed to have at least two divided pieces that are divided along the radial direction, and each of the divided pieces is press-formed beforehand. The only way to form a bellows tube is to join the split pieces and weld the joint. Therefore, there is an inherent problem that the compressive deformation characteristics are unstable and the predictability is low due to the variation in welding strength. In other words, the welding location exposes a local weakness to an external load, making it difficult to set the performance and control the quality of the shock absorbing structure. In addition, due to the double pipe structure that accommodates the inner pipe with a bellows tube in the side member, it is inevitable that the rigidity of the entire double pipe structure will increase, and only the bellows tube of the inner pipe will be deformed. It could not be shrunk to absorb the impact and avoid deformation of the side members.

If the inner pipe is made of aluminum, it is possible to integrally form a bellows pipe which does not require a post welding by an aluminum die-casting method, but the aluminum-based material is expensive. For that reason, aluminum shock absorbing structures are not very practical. On the other hand, it is practically impossible to die-cast an iron-based material such as carbon steel due to the inherent elongation characteristics of the iron-based material.

In recent years, there has been an increasing demand in the automobile industry to prevent the airbag device from being inadvertently activated by a relatively small impact. In other words, there is a problem that the airbag is inflated and deployed even in a minor collision where the protection of the occupant by the airbag is not required. In addition, there is a situation in which the cost for repairing and regenerating the activated airbag increases the economic burden on the user. For this reason, for energy loads that are much smaller than the impact load that the airbag protection really requires, the sharp energy absorption characteristics ensure that the collision energy is absorbed and unnecessary operation of the airbag is avoided. There is a demand for a shock absorber having Furthermore, it is desired that repair of the vehicle can be completed only by replacing the shock absorber, which is relatively inexpensive compared with other parts, at the time of a minor collision.

An object of the present invention is to provide a large degree of freedom in setting the compressive deformation characteristics of the shock absorber or the energy absorption characteristics at the time of collision, so that the performance as a shock absorbing structure can be easily set and the stability of quality during mass production. Another object of the present invention is to provide an excellent vehicle shock absorber. In addition, at the time of a small impact collision, a shock absorber that can reliably absorb the collision energy by itself and can avoid damage to the structural material of the body frame and unnecessary operation of the airbag device beforehand. To provide.

[0009]

SUMMARY OF THE INVENTION The invention of claim 1 is a shock absorber for a vehicle which is added to a structural material of a vehicle body skeleton to reduce a shock at the time of a collision. It has a hollow main absorbing portion that can be compressed and deformed in the axial direction when a load is applied substantially in the axial direction, and the main absorbing portion in one section orthogonal to the axial direction of the hollow main absorbing portion. The wall portion constituting the portion has a closed shape that is seamlessly integrated, and the thickness of the wall portion of the main absorption portion is substantially equalized within the same cross section.

According to this configuration, the wall constituting the hollow main absorbing portion of the shock absorber has a closed shape that is seamlessly integrated in a cross section orthogonal to the axis, and has a substantially uniform thickness. Therefore, the entire closed wall portion can bear the external load input in the axial direction almost equally, and does not expose a local weak point to the external load. For this reason, the stability and predictability of the compressive deformation characteristics with respect to an external load increase, and the compressive deformation characteristics at the time of external load input are considerably free by appropriately selecting the material, wall thickness, shape or structure of the main absorbing portion. Can be tuned. Therefore, the degree of freedom in setting the compression deformation characteristics of the shock absorber or the energy absorption characteristics at the time of collision is increased, and the performance setting as the shock absorbing structure is facilitated, and the quality stability during mass production is excellent. .

According to a second aspect of the present invention, in the shock absorber for a vehicle according to the first aspect, at least the main absorbing portion has a cylindrical shape in which the wall thickness in a cross section orthogonal to the axis is substantially equalized. It is characterized by being formed by a hydraulic forming method using a metal material as a starting material. As described above, according to the hydraulic forming method using a cylindrical metal material as a starting material, it is possible to make the wall constituting the main absorbing portion a substantially uniform thickness and a seamlessly integrated closed shape. it can. In addition, the hydraulic forming method is very excellent in reproducibility of processing conditions, there is almost no variation in quality among manufacturing lots, and the yield can be improved.

According to a third aspect of the present invention, in the vehicle shock absorber according to the first or second aspect, the main absorbing portion has a bellows shape including one or a plurality of swelling units. I do. In this case, the impact absorbing ability of the main absorption section can be increased. In particular, due to a synergistic effect with the constituent features described in claim 1, the compression reaction force when the external load is relatively small can be minimized, and the transmission of the load to the structural material of the vehicle body skeleton can be reduced. It is possible to prevent the structural material from being damaged by a minor collision.

According to a fourth aspect of the present invention, in the vehicle shock absorber according to any one of the first to third aspects, at least the main absorbing portion is made of an iron-based material. . According to this configuration, in addition to reducing the manufacturing cost of the shock absorber, it is possible to optimize the maximum energy absorption amount of the main absorbing portion and the compression deformation characteristics up to that in relation to the hydraulic forming method. It will be easier.

According to a fifth aspect of the present invention, there is provided a shock absorber for a vehicle, which is added to a structural material of a vehicle body skeleton to reduce a shock at the time of a collision, wherein a load is applied substantially in the axial direction of the shock absorber. It has a hollow main absorbing portion that can be compressed and deformed in the axial direction when added, and at least the main absorbing portion is formed by a hydraulic forming method using a pipe made of an iron-based material as a starting material. It is characterized by being.

According to this configuration, the hollow main absorbing portion is
In a cross section orthogonal to the axial direction, a wall constituting the main absorption section has a closed shape that is seamlessly integrated. The technical significance of the fifth aspect is almost as described above. In addition, as a pipe made of an iron-based material, which is a starting material, it is preferable to use a pipe having a substantially uniform wall thickness in a cross section orthogonal to the axis. Further, it is further preferable that the main absorption portion has a bellows shape composed of one or a plurality of swelling units.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a shock absorber used for a vehicle body front portion of an automobile will be described below with reference to the drawings. As shown in FIG. 1, a crash box 20 as a shock absorber is interposed between a side member 12 as a structural member of a vehicle body skeleton and a bumper reinforcement 13 inside a front bumper 11. As shown in FIGS. 1 and 5, the tip of the crush box 20 is fixed to the bumper reinforcement 13 by welding or the like, and a bumper reinforcing material is constituted by the two parts integrated with each other. On the other hand, the bracket 14 is fixed to the rear end of the crash box 20 by welding or the like. The bumper reinforcing material including the crash box 20 is removed from the side member 12 by joining the bracket 14 on the side of the crash box 20 and the bracket 15 fixed to the front end of the side member 12 and fastening them with bolts 16. It is connected as possible.

As shown in FIGS. 2, 3 and 5, the crush box 20 is mainly composed of a bumper reinforcement 1.
3, a front end portion 21 serving as a mounting portion for the bracket 3, a rear end portion 22 to which the bracket 14 is fixed, and a bellows portion 23 located between the both end portions 21 and 22 and functioning as a main absorbing portion. ing. Crash box 2
The inside of the hollow 0 has a hollow shape, and the wall forming the hollow crash box 20 has a substantially uniform thickness through the front end portion 21, the bellows portion 23, and the rear end portion 22.
The thickness of the wall is preferably about 1.0 to 1.5 mm. The axial length L of the crash box 20 is about 140 mm, and the bellows portion 23 is 1 /
Occupies about 3 to 1/2.

The bellows portion 23 shown in FIGS. 2 and 3 is constituted by connecting three bulging units 24,
Can be said to be a connection between a portion 24a whose diameter increases toward the rear end and a portion 24b whose diameter decreases toward the rear end. The shape of the bellows 23 in a cross section orthogonal to the center axis Z of the crush box 20 is shown in FIG.
It has a polygonal shape (octagonal shape in the present embodiment) as shown in FIG. In other words, in the cross section orthogonal to the axis, the wall forming the bellows portion 23 has a closed polygonal shape surrounding the central axis Z. The wall constituting the rear end portion 22 also has a closed polygonal shape surrounding the central axis Z in the cross section orthogonal to the axis, and the polygonal shape has a similar relationship to the polygonal shape at the bellows portion 23. .

Crash box 20 is most preferably made by hydroforming. For example, as shown in FIG. 4 (A), a pair of split molds (upper mold 41 and lower mold 42) having the desired internal shape is prepared. Upper die 41 and lower die 4
Each of 2 is provided with a shaping convex portion 43 and a shaping concave portion 44 for forming the bellows portion 23. The upper mold 41 and the lower mold 42 can be relatively moved (approached and separated) in the vertical direction. At the time of the hydroforming, a pipe 4 serving as a starting material is placed between the upper mold 41 and the lower mold 42 in the separated state.
5 is arranged. The pipe 45 is made of an iron-based material such as carbon steel, and has a cylindrical shape with a uniform wall thickness in a cross section orthogonal to the axis.

When the arrangement of the pipe 45 between the upper and lower dies 41 and 42 is completed, the opening at the front end and the rear end of the pipe 45 is closed with a pair of sealing materials 46 also for the purpose of shape retention.
5 is sealed. Subsequently, the drain cock 48 provided at the end of the pipe 47 communicating with the inside of the pipe 45 is closed, and the pipe 45 is filled with a pressurized liquid (for example, water) using the pump P, and the internal pressure of the pipe is reduced to a preliminary pressure. The pressure is increased to Ps1 (for example, 20 MPa). This preliminary pressure Ps1
Is such a pressure that the pipe 45 alone cannot be expanded in the radial direction. From this state, the upper mold 41 and the lower mold 42 are relatively approached to each other, and the preforming is performed by pressing the tip of the shaping projection 43 of each mold against the wall surface of the pipe 45. At this time, the pressurized liquid in the pipe appropriately supports the inner wall surface of the pipe, thereby preventing the load from being locally concentrated on the outer wall surface of the pipe and preventing excessive deformation and cracking. Further, since the pipe 45 is filled with the liquid, the pipe wall facing the shaping recess 44 is formed in the shaping recess 44 as the shaping projection 43 cuts into the pipe wall based on the principle of Pascal. Deforms to bulge toward it.
However, in this preforming step, a slight gap is left between the bottom of the shaping recess 44 of each mold and the pipe wall surface.

After the preforming, the upper mold 41 and the lower mold 42
Is fixed, the internal pressure of the pipe is increased to the main molding pressure Ps2 (for example, 100 MPa) by increasing the capacity of the pump P. The main molding pressure Ps2 is a pressure that is sufficient by itself to expand the pipe 45 in the radial direction. Due to the further increase in the internal pressure of the pipe, the pipe 45 expands until the gap left between the shaping recess 44 of each die and the wall of the pipe is almost completely filled, and the inner die provided by the upper die 41 and the lower die 42. The pipe 45 is deformed until it almost fits the shape. Thereafter, the drain cock 48 is opened, the pressurized liquid is discharged to the outside, and the upper and lower dies 41 and 42 are separated from each other, whereby the hydraulic forming is completed, and the crush box 20 having a desired shape is obtained. In the crash box 20, at least in the cross section orthogonal to the axis, at least the wall of the bellows portion 23 has a seamlessly integrated closed shape, and the wall thickness in the same cross section is substantially uniform. Needless to say.

(Compression Deformation Characteristics) The graphs of FIGS. 7 and 8 show an example of the deformation characteristics of the crash box 20 when an external load F is applied to the bumper reinforcement 13 from the front side as shown in FIG. . FIG. 7 shows the relationship between the amount (stroke) of compression deformation of the crash box in the axial direction in response to the external load F and the compression reaction force at that time. FIG. 8 shows the amount (stroke) by which the crash box is compressed and deformed in the axial direction in response to the external load F;
The relationship with the amount of absorbed energy at that time is shown. The solid line in each graph shows the case of the crash box 20 shown in FIGS. 2, 3 and 5, and the broken line in each graph shows the case of the crash box shown in FIGS. 9 and 10 described later.

The horizontal dashed line in FIG. 7 indicates the magnitude of the reaction force corresponding to the impact required to deploy the airbag for protecting the occupant, and indicates the set reaction force Tg, which is the target value for airbag operation. . In the present embodiment, the set reaction force Tg is set to about 150
00N (Newton). According to FIG. 7, the stroke corresponding to the set reaction force Tg is about 50 mm, and the slope of the solid line is steep before and after the stroke of 50 mm. That is, in the crash box 20 of the present embodiment, when the stroke is in the range of 0 to about 40 mm, the magnitude of the reaction force is relatively stable and the stroke is 4 mm.
The reaction force suddenly increases from around 0 mm. Then, when the stroke is in the range of about 50 to 100 mm, the reaction force tends to stay high, exceeding the set reaction force Tg. That is, since the reaction force is relatively small in the early stage of the collision, 0 to 40 m
About the collision energy that can be absorbed by a stroke (compression deformation amount) of about m, as shown in FIG.
Only the compressive deformation of No. 3 absorbs the collision energy. In this case, the front end 21 and the rear end 22 of the crash box 20 are hardly deformed, much less the side members 12.
Does not transmit enough load to deform it.

On the other hand, if the collision energy is too large to be absorbed by a stroke (compression deformation amount) of about 0 to 40 mm, compression deformation occurs not only in the bellows portion 23 but also in the front end portion 21 and the rear end portion 22. The entire crash box 20 has a stroke of up to about 100 mm. Of course, when the external load F is excessive, the side member 12 is required to have a load of energy absorption. In such a case, an activation sensor (for example, an acceleration sensor) incorporated in the airbag device detects in advance a sign that the reaction force against the external load F is likely to exceed the set reaction force Tg, and based on the detected signal, The bag is deployed to protect the occupant's body. As shown in FIG. 8, the crash box 20 of the present embodiment is
It is designed such that the energy absorption of the entire box at the time of compressive deformation of m is about 1300 Nm (Newton meter).

(Effects) According to the present embodiment, the following effects can be obtained. -If the external load F at the time of collision is greater than the set reaction force Tg, the entire crash box 20 is compressed and deformed in the axial direction, and if necessary, the side member 12 is also deformed to produce an impact at the time of collision. As much as possible, and the operation of deploying the airbag is allowed to ensure the safety of the occupant. On the other hand, when the external load F at the time of the collision is relatively small and does not reach the set reaction force Tg, the bellows portion 23 which is the main absorption portion of the crash box 20 is compressed and deformed to absorb most of the impact at the time of the collision. , Side member 1
In the case of No. 2, not only the deformation load is not required but also the operation of deploying the airbag is avoided. That is, at the time of a small impact collision, only the crash box 20 can exhibit the impact absorbing function, and only the crash box 20 can be damaged. Therefore, the repair and the replacement of parts at that time are performed only by the crash box 20, so that the repair cost can be reduced and it becomes economical.

The crash box 20 of the present embodiment
Is manufactured by a hydraulic forming method using an iron pipe 45 as a starting material, so that the bellows portion 23 and other portions have a seamlessly integrated closed shape in a cross section orthogonal to the axis thereof. The wall thickness of the wall in the same cross section becomes substantially uniform. For this reason, the degree of freedom in setting the deformation characteristics at the time of compressive deformation is extremely large as compared with the conventional method of manufacturing a shock absorber. In other words, the deformation characteristics (specifically, the characteristics of the stroke versus the reaction force and the characteristics of the stroke versus the absorbed energy) up to the maximum absorbed energy amount (about 1300 Nm in the present embodiment).
Can be tuned quite freely only by selecting the material and thickness of the pipe 45 and setting the shape of the bellows 23. In addition, since the hydroforming method has excellent reproducibility of processing conditions, there is almost no variation in quality between production lots, and the compression deformation characteristics of the obtained product are stable, and the yield is improved.

According to the hydraulic forming method, in addition to the fact that the starting material can be an inexpensive iron pipe 45,
Since the necessity of post-processing such as welding is greatly reduced, the manufacturing cost of the crash box 20 can be reduced as compared with the related art.

(Another Example) The embodiment of the present invention may be modified as follows. In the above-described embodiment, the main absorption portion between the front end portion 21 and the rear end portion 22 of the crush box 20 is the bellows portion 23, but instead of such a structure, a main absorption portion as shown in FIGS. The absorbing unit 25 may be employed. That is, the main absorbing portion 25 slightly protrudes in the radial direction from the front end portion 21 and the rear end portion 22, and as shown in FIG. It has a vertical cross-sectional shape consisting of a diameter-reducing portion 25b. Such a structure of the main absorption portion 25 can be regarded as a bellows structure including only one swelling unit. The crash box 20 shown in FIGS.
Crash box 20 of the above embodiment except for the shape of
It has almost the same structure as that of FIGS. 1 to 6 and is made by the same hydraulic forming method. It has a compression deformation characteristic as shown by a broken line in FIGS. As can be seen from FIG. 7, the reaction force in the stroke range of 0 to 40 mm tends to be slightly unstable compared to the case of the above embodiment, but does not exceed the set reaction force Tg of the airbag operation. Therefore, the same operation and effect as in the above embodiment can be obtained for the crash box 20 of FIGS. 9 and 10.

The number of the bulging units 24 constituting the bellows portion 23 of the crash box 20 does not need to be three, but may be two.
There may be one or four or more. The cross-section orthogonal to the axis of the crush box 20 in the above-described embodiment and the above-mentioned another example is not limited to an octagon or other polygonal shapes, and may be an annular shape, an ellipse or an oval shape. In addition, the external shape of the crash box is not limited to the above. For example, by providing a plurality of beads (concave portions or grooves) on each side surface of a tubular body having a rectangular cross section, it can be compressed in a bellows shape in the axial direction at the time of collision. It may have a deformable box structure.

The crash box 20 of the above-described embodiment and another example may be mounted near the rear bumper or at both ends of a cross member extending in the width direction of the vehicle body. Further, the present invention may be applied to impact parts other than the crash box. The starting material for the hydroforming need not be an iron pipe, but an aluminum or other metal pipe may be used.

[0031]

As described in detail above, according to the vehicle shock absorber described in the claims, the degree of freedom in setting the compression deformation characteristics or the energy absorption characteristics at the time of collision is large, and the performance setting as a shock absorbing structure is achieved. And the stability of quality during mass production is excellent. In particular, claims 3 and 4
According to this, at the time of a small impact collision, the collision energy can be reliably absorbed by itself, and damage to structural members of the vehicle body skeleton and unnecessary operation of the airbag device can be avoided beforehand.

[Brief description of the drawings]

FIG. 1 is a perspective view of a vehicle body front part viewed from a side.

FIG. 2 is a plan view of a crash box.

3A is a cross-sectional view taken along line XX of FIG. 2, and FIG. 3B is a cross-sectional view taken along line YY of FIG.

FIG. 4 is a cross-sectional view showing an outline of the steps of the hydroforming method.

FIG. 5 is a perspective view showing a crash box and the like before compression deformation.

FIG. 6 is a perspective view showing a crash box and the like after compression deformation.

FIG. 7 is a graph showing a relationship between a stroke (compression deformation amount) and a reaction force.

FIG. 8 is a graph showing a relationship between a stroke and absorbed energy.

FIG. 9 is a perspective view corresponding to FIG. 5, showing another example of the crash box.

FIG. 3A shows another example of a crash box.
FIG.

[Explanation of symbols]

12: side member (body structure of body frame), 20: crash box (shock absorber), 23: bellows (main absorption part), 24: swelling unit, 25: main absorption part, 45: pipe (cylindrical) , F ... external load.

Claims (5)

[Claims] 1. A shock absorber for a vehicle, which is added to a structural material of a vehicle body skeleton to mitigate a shock at the time of a collision, and is provided when a load is applied substantially in the axial direction of the shock absorber. It has a hollow main absorbing portion that can be compressed and deformed in the axial direction, and the wall constituting the main absorbing portion is seamlessly integrated in one section orthogonal to the axial direction of the hollow main absorbing portion. In the same cross section,
A shock absorber for a vehicle, wherein the thickness of the wall of the main absorber is substantially equalized. 2. The method according to claim 1, wherein at least the main absorbing portion is formed by a hydraulic forming method using a cylindrical metal material having a substantially uniform wall thickness in a cross section orthogonal to the axis as a starting material. The shock absorber for a vehicle according to claim 1, wherein: 3. The apparatus according to claim 1, wherein the main absorption section has a bellows shape including one or a plurality of swelling units.
Or the shock absorber for vehicles according to 2. 4. The shock absorber for a vehicle according to claim 1, wherein at least the main absorber is made of an iron-based material. 5. A shock absorber for a vehicle, which is added to a structural material of a vehicle body skeleton to reduce a shock at the time of a collision,
The shock absorber has a hollow main absorbing portion that can be compressed and deformed in the axial direction when a load is applied substantially in the axial direction, and at least the main absorbing portion starts from a pipe made of an iron-based material. A shock absorber for a vehicle, wherein the shock absorber is formed by a hydraulic forming method using the material.