JPH08108853A - Impact energy absorbing construction of steering wheel - Google Patents

Abstract

PURPOSE: To appropriately absorb a plurality of impact energy of which both the magnitude of loads themselves and the acting directions arc different from each other. CONSTITUTION: A steering wheel 1 is fitted to a steering shaft 2 through spoke members, and a cover pad 7 is provided on the upper part of the fitting part to the steering shaft 2 through an impact energy absorbing member 11. The impact energy absorbing member 11 is constituted of a first deforming member capable of deforming directly downward and obliquely downward and a second deforming member 17 being on the lower position than the first deforming member by a prescribed distance and capable of deforming directly downward and obliquely downward, and deformation rigidity directly downward of the first and second respective deforming members are set higher than deformation rigidity obliquely downward.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shock energy absorbing structure for a steering wheel.

[0002]

2. Description of the Related Art Generally, in vehicles such as automobiles, various measures are required for protecting an occupant in the event of a vehicle collision, and detailed regulations are specified for each of the measures.

One of them is a collision safety measure for the steering wheel. The steering wheel is supported by the steering shaft and faces the driver's head at a certain angle.When the vehicle is in a frontal collision (or when the vehicle is in a slant), the inertia of the driver causes the upper half of the driver's upper body to lean forward and head. May collide.

Therefore, particularly in a steering wheel not provided with an airbag, an impact energy absorbing structure for absorbing the impact energy at the time of the head collision as effectively as possible has been conventionally used.

FIG. 11 shows an example thereof. In this configuration, inside the cover pad 31 in the center of the steering wheel 1,
The steering wheel 1 is attached to the tip 32a of the steering shaft 32 by interposing an impact energy absorbing member 40 made of a metal panel whose front and rear vertical walls are indented as shown in the figure.

With respect to this structure, according to the regulation of European EC countries (hereinafter referred to as the first regulation), for example, as shown in FIG. 12, a head form impactor 36 having a G sensor 37 therein and having a weight of 6.8 kg is provided. The generated deceleration G when the vehicle collides from the upper side to the lower side at a speed of 7 m / s is 120 G or less.
It is required that the time when the 0 g deceleration G occurs is 3 ms or less.

Further, the regulation to be adopted in Japan in the future (hereinafter referred to as the second regulation)
According to the above, as shown in FIG. 13, for example, in the actual vehicle collision test using the dummy head 35 having the G sensor 37 built-in, the synthetic acceleration HIC at the center of gravity of the head of the dummy head 35 obtained by the following formula is 1000 or less. Is needed.

[0008]

[Equation 1]

Here, a is a synthetic acceleration represented by a multiple of g (gravitational acceleration), and t ₁ and t ₂ are arbitrary time points during a collision.

According to this actual vehicle collision test, when the dummy head 35 collides with the steering shaft 32 at a predetermined inclination angle θ with respect to the axial direction O-O 'as shown in the figure, the composite acceleration HIC is obtained. Is required to be 1000 or less, and eventually the impact energy absorbing member 40 needs to appropriately absorb the impact energy in the slant direction so as to satisfy the above condition.

Therefore, in order to satisfy the above-mentioned first and second types of regulation at the same time, the impact energy absorbing member 40 has the steering shaft 32.
Of the impact energy of different magnitudes in two different directions, that is, the axial direction OO ′ of the steering shaft 32 and the direction having a predetermined inclination angle θ with respect to the axial direction of the steering shaft 32. Become. Moreover, due to the above regulation, the impact energy F _{1 in the} axial direction of the steering shaft is large, and the impact energy F _{2 in the} inclination direction with respect to the axial direction is smaller than that. Therefore, the impact energy absorbing member 40 must have a structure that absorbs F ₁ with sufficient deformation rigidity without bottoming the steering shaft 32 and absorbs F ₂ with soft deformation rigidity.

However, in the case of the impact energy absorbing member 40 having the structure shown in FIG. 11, if the rigidity of the front and rear vertical wall portions is increased so that the above F ₁ can be absorbed into the steering shaft 32 without bottoming, FIG. As described above, F ₂ can be suppressed below the deceleration G120g due to the first regulation, but on the other hand, F ₂ cannot be suppressed below the second regulation HIC 100 as shown in FIG.

Further, if the rigidity of the vertical wall portion is lowered and the inside recess angle is increased so that F ₂ can be absorbed softly, the second regulation HIC is suppressed to 1000 or less as shown in FIG. On the other hand, F ₁ cannot be sufficiently absorbed as shown in FIG. 16, and finally bottoming of the steering shaft 32 may occur to clear the first regulation. Can not.

On the other hand, with respect to such a problem, although it is not intended to directly cope with a plurality of regulations as described above, by combining two types of impact energies having different impact energies with different load acting directions. Those that try to absorb in stages have been proposed.

As an example thereof, for example, in Japanese Utility Model Laid-Open No. 62-112665, which is a known example, in a structure of a steering wheel in which a steering wheel is attached to a steering shaft, the steering wheel is arranged at the center of the steering wheel. A cover pad (also referred to as a horn pad or a center pad) that surrounds the periphery of the mounting portion with the steering shaft, and is mounted in the cover pad, and in the load acting direction due to the impact load of the body head that collides with the cover pad. A first impact absorbing member which is deformed, and a second load which is provided inside the first impact absorbing member with a desired clearance from the front surface of the first impact absorbing member, and which is generated when the first impact absorbing member is deformed. The load is deformed in the secondary load acting direction and the load is applied from the side along the front surface of the cover pad. There is an impact energy absorbing structure provided with a second shock absorbing member deformable along the use direction.

In the structure of the impact energy absorbing structure, the first impact absorbing member 40A is composed of a cylindrical body having a quadrangular cross section extending in the left-right direction, as shown schematically in FIG. The center of the vertical wall portion is recessed inward, and the bottom side is fixed to the steering shaft 32 together with the steering wheel, while the second impact absorbing member 40B is the first impact absorbing member 4B.
It is inside 0A, has a width larger than that of the first impact absorbing member 40A, protrudes to the left and right sides, and is fixed to the steering shaft 32 while changing its direction so as to extend in the front-rear direction.

In this structure, when the cover pad receives a primary impact load F ₁ due to the collision of the driver's head with the cover pad during the vehicle collision, the first impact
The impact absorbing member 40A is deformed so as to be flattened in the acting direction of the same load F ₁ to primarily absorb the load F ₁ (see the state from the chain line to the solid line in FIG. 19).

On the other hand, the collision load F ₁ on the cover pad
Is larger than a predetermined value, and the first impact absorbing member 40A
In the case where the second impact absorbing member 40B cannot be absorbed only by the above initial deformation, the second impact absorbing member 40B is subjected to the continuous secondary load F ₁ ′ due to the further deformation of the first impact absorbing member 40A. 'deformed in the direction of action of the, whereby the secondary impact load F _1' F ₁ effectively absorb (see dashed states from the solid line in FIG. 19).

On the other hand, when the impact load acting on the cover pad is a load from the side along the front surface portion, the second impact absorbing member protruding to the left and right sides is deformed in the acting direction of the load. And absorbs the impact (not shown).

[0020]

By the way, in the impact energy absorbing member for the steering wheel as described above, as described above, the impact load F ₁ of a predetermined magnitude is applied to the cover pad portion in the axial direction of the steering shaft. The generated deceleration G when the vehicle is actuated is equal to or less than a predetermined value, and the duration of the predetermined deceleration G smaller than the predetermined value is less than or equal to a predetermined time, and the actual vehicle collision test using the dummy head is performed. In the above, it is required that the synthetic acceleration HIC with respect to the impact load F ₂ when the dummy head collides with the steering shaft at a predetermined inclination angle θ is equal to or less than a predetermined value. Then, it tends to be necessary to satisfy these two safety standards at the same time.

From such a viewpoint, the impact energy absorbing member 4 of the conventional steering wheel shown in FIG.
Looking at the structure of 0, it becomes as follows.

That is, as described above, in this structure, the second impact energy absorbing member 40B is located inside the first impact absorbing member 40A and is arranged with its axial direction changed by 90 degrees. Therefore, the steering shaft 32
As shown in FIG. 19, the large impact load F ₁ acting in the axial direction of the first and second impact absorbing members 40A and 40B is first sequentially deformed by the bending deformation in the steering shaft 32 direction. Be absorbed.

When a predetermined impact load F ₂ acts on the impact energy absorbing member 40 with an inclination angle θ in the axial direction of the steering shaft 32, the impact energy absorbing member 40 is deformed as shown in FIG. It is expected that it will absorb the load.

However, in the above structure, both the first and second shock absorbing members 40A and 40B are formed by a single wide plate member, and the first and second shock absorbing members 4 are formed.
0A and 40B are fixed to the steering shaft 32 directly in a cross state integrally with a spoke plate (not shown).

Therefore, even if, for example, as shown in FIG. 19 above, the primary and secondary deformations due to the impact load F ₁ absorption in the axial direction of the steering shaft 32 occur, it is difficult to control the deformed state, and the safety as described above is achieved. It is difficult to realize a highly accurate shock absorbing action corresponding to the standard.

Further, when an impact load such as F _{2 which is} inclined at a predetermined angle with respect to the axial direction of the steering shaft 32 is applied, since the front and rear rigidity is equal, the deformation as shown in FIG. difficult. Moreover, in that state, the subsequent rigidity is increased, and soft load energy absorption is impossible.

The present invention has been made for the purpose of solving such a problem, and an object of the present invention is to provide an energy absorbing structure for a steering wheel that can surely clear both of the above-mentioned two safety standards. To do.

[0028]

The present invention comprises the following problem solving means in order to achieve the above object.

That is, the energy absorbing structure for a steering wheel according to the present invention is attached to the steering shaft via the spoke member, and the cover pad is provided on the upper portion of the attaching portion to the steering shaft via the impact energy absorbing member. In the steering wheel consisting of
The first deformable member is capable of being deformed immediately below and obliquely below, and the second deformable member is located at a predetermined distance below the first deformable member and is deformable immediately below and obliquely below. The deformation rigidity of the first and second deformation members in the immediately downward direction is set higher than the deformation rigidity in the obliquely downward direction.

Further, the first and second deforming members having the same structure, which are deformed obliquely downward, are arranged so that they can be deformed obliquely downward without interfering with each other.

Further, the first and second deformable members in each of the above-mentioned configurations are formed as an integral structure by combining separate members or by punching and molding a sheet metal member into a three-dimensional shape.

Further, the deformed state of them can be controlled appropriately by arbitrarily changing the plate thickness and the plate width.

[0033]

The energy absorbing structure for a steering wheel according to the present invention has the following actions corresponding to the above-mentioned configurations.

That is, as described above, in the energy absorption structure for a steering wheel according to the present invention, the steering wheel is attached to the steering shaft via the spoke member,
Further, in a steering wheel in which a cover pad is provided on an upper portion of a mounting portion for the steering shaft via an impact energy absorbing member, the impact energy absorbing member can be deformed directly downward and obliquely downward.
And a second deformable member which is located below the first deformable member by a predetermined distance and can be deformed immediately downward and obliquely downward, and the first and second deformable members. The downward deformation rigidity of is set to be higher than the oblique downward deformation rigidity.

Therefore, in this structure, for example, when a front collision of the vehicle occurs and an impact load F _{1 in the} axial direction of the steering shaft is generated, first, the pair of left and right first deforming plates of the first deforming member is covered. With the pad, the upper and lower surfaces are substantially parallel to each other and are deformed inwardly into a V-shape.
Descends until it abuts the upper part of the deforming member, and thereby primarily absorbs the impact load.

When the impact load is larger than a predetermined value and cannot be absorbed only by the primary deformation of the first deformable member as described above, the left and right sides of the first deformable member. The pair of first deforming plates further bend in the flat direction, and the pair of left and right second deforming plates of the second deforming member deforms like a dogleg. And
As a result, the impact load is finally secondarily absorbed with a slightly higher rigidity than the above predetermined value. Therefore, also in this case, the top portions of the first and second deformable members do not bottom out on the steering shaft.

As a result, the impact load acting in the axial direction of the steering shaft can be suppressed to G which is equal to or less than the above-mentioned required standard of the first regulation.

On the other hand, if an impact load F ₂ is applied to the cover pad in a state where the cover pad is inclined at a predetermined angle with respect to the axial direction of the steering shaft, the first deformable member of the impact absorbing member is first inclined. It deforms rearward and absorbs the impact load as a primary soft.

Further, in this case, when the impact load is an impact load of a predetermined value or more that cannot be absorbed only by the primary deformation of the first deformable member, the first deformable member is further added. Is greatly deformed obliquely rearward from the above state, and at the same time, the second deformable member is also deformed together in the same direction, and secondarily and reliably absorbs an impact load larger than the predetermined value.

As a result, the collision safety rule of the second regulation as described above can also be cleared.

In the above structure, when the first and second deforming members which are further deformed obliquely downward are arranged so that they can be deformed obliquely downward without interfering with each other, each of them is Since the deformation is appropriately performed as designed without being affected by other deformation members, the load absorbing action is realized more reliably and effectively.

Further, in each of the above-mentioned constitutions, if the first and second deformable members are integrally formed by bending one sheet metal member punched and molded into a three-dimensional structure, the impact energy absorbing member is welded when manufactured. No work is required, which simplifies processing and assembly.

In each of the above cases, the first,
If the plate thickness and plate width of the second deformable member are appropriately and arbitrarily variably controlled, more effective load absorbing performance can be realized.

[0044]

As a result of the above, according to the present invention, it is possible to properly absorb a plurality of impact energies having different magnitudes and different directions of action of the load itself, and the deformation control is also highly accurate and easy. Will be things.

[0045]

【Example】

(Embodiment 1) FIGS. 1 to 7 show the structure and operation of an impact energy absorption structure for a steering wheel according to Embodiment 1 of the present invention.

In the drawing, reference numeral 1 is a ring-shaped steering wheel. The steering wheel 1 is formed by welding and integrating a T-shaped spoke plate 3 inside a pipe ring 1a which is a core material, and outside the pipe ring 1a. It is configured by covering the rubber member 1b.

On the other hand, reference numeral 2 is a steering shaft (column shaft) supported and fixed to the vehicle body side, and the tip end portion of the steering shaft 2 has a boss portion 2a and a boss portion 2a.
The spoke plate 3 has a thread groove 2b at its tip and is formed in the fitting fixing portion (mounting bolt portion) of the spoke plate 3, and the flat center portion 3a side center of the spoke plate 3 with respect to the spoke plate fitting fixing portion. The thick fitting portion 4a is fitted in a state orthogonal to the axis, and is fastened and fixed by the nut 5.
The spoke plate 3 is configured to have a tapered portion 3c between the welding end portion 3b on the pipe ring 1a side and the base portion 3a.

Reference numeral 7 is a cover pad provided above the spoke plate mounting portion of the steering shaft 2, and the cover pad 7 is a shock absorbing member 11 supported by an elastic support piece 10. It is supported by.

A lower cover 12 is fitted to the lower portion of the spoke plate 3 from below, and a base end portion 12a of the lower cover 12 is attached to a taper portion 3c of the spoke plate 3 by a bolt 14A and a nut 14B. The distal end side peripheral edge portion 12b is fitted inside the peripheral edge portion 7a of the cover pad 7.
The central portion 12c of the lower cover 12 is also fitted and fixed to the lower portion of the boss portion 2a of the spoke plate fitting and fixing portion of the steering shaft 2.

The shock absorbing member 11 is, as shown in the drawing,
The cover panel 7 is located inside the cover pad 7 and is erected at predetermined intervals in both left and right directions.
B and the first deformable member 16 composed of a pair of left and right deformable plates 16a, 16a to which the cushion member 21 is attached to the cover panel 21B via fasteners 22, and the first deformable member 16a.
Pair of left and right deformation plates 16a, 16a of the deformation member 16 of FIG.
A pair of left and right deformation plates 16a, 16a located between
And a second deformable member 17 including a pair of left and right second deformable plates 17a, 17a provided at a height lower than the predetermined distance R by a predetermined distance R.

The pair of left and right first deformable plates 16a, 16a forming the first deformable member 16 are vertically bent as a side face dogleg from the rear side of the vehicle body toward the front side of the first deformable plate 16a. It has an upper and lower piece 18 and a second upper and lower piece 19 whose upper side is bent toward the rear side of the vehicle body in a U-shape. Then, the cover panel 2 connecting the upper end portions thereof
The rear end portion 7b of the cover pad 7 is locked to the rear end portion of the vehicle body 1B via a screw screw 23.

Further, the pair of left and right second deformable plates 17a, 17a constituting the second deformable member 17 is a driver whose entire vertical direction is bent from the rear side of the vehicle body to the front side of the vehicle body in the shape of a lateral dogleg. Similarly to the first side upper and lower pieces 24, there is a second upper and lower piece 25 that is bent in the shape of a side face from the rear side of the vehicle body to the front side of the vehicle body in the same manner as the first upper and lower side pieces 24. It is held and arranged integrally and continuously through the top piece 26. The dogleg-shaped bending points of the first and second upper and lower pieces 24 and 25 are the same as the second upper and lower pieces 25.
Is provided at a position lower than the first bending point position.

Further, the pair of left and right first and second deformation plates 24 and 25 constructed as described above are integrated with each other at the bottom plate 27, and the bottom plate 2
7 is supported by the elastic support piece 10 on the rear end side of the vehicle body.

Next, the shock absorbing action of the shock absorbing member 11 configured as described above at the time of a vehicle collision will be described with reference to FIG.
~ It demonstrates in detail with reference to FIG.

That is, the structure of the shock absorbing member 11 described above is simplified and shown as shown in FIG.

In the structure shown in FIG. 3, for example, a head-on collision of the vehicle occurs, and an arrow shown in the figure along the axial direction of the steering shaft 2 with respect to the central portion 7C of the cover pad 7.
When the impact force F _{1 in the} (a) direction is generated, first, the pair of left and right first deformable plates 16a, 16 of the first deformable member 16 is firstly formed.
As shown by the solid line in FIG. 4 (a), the first and second upper and lower pieces 18 and 19 are each deformed into a dogleg shape inward while the upper and lower surfaces are substantially parallel to each other, and the second deformation is performed. It descends until it abuts against the upper part of the member 17, so that primarily the impact force F ₁
Absorbs.

When the impact force F ₁ is larger than a predetermined value and cannot be absorbed only by the deformation of the first deformable member 16 as shown in FIG. 4 (a), it is shown in FIG. 4 (b). As described above, the pair of left and right first deformable plates 16a, 16a of the first deformable member 16 are further bent greatly, and the pair of left and right second deformable plates 1 of the second deformable member 17 are bent.
7a and 17a are deformed into a square shape. Then, finally, the impact load of the predetermined value or more is absorbed with a slightly higher rigidity. Therefore, also in this case, the top portions (the cover panel 21B portions) of the first and second deformable members 16 and 17 do not bottom on the tip portion 2a of the steering shaft 2.

As a result, as shown in FIG. 5, G can be suppressed to the value equal to or lower than the above-mentioned first regulation requirement standard (120 g).

On the other hand, in contrast, for example, the arrow (b) in FIG.
If an impact load F ₂ smaller than F ₁ is applied in the direction, the first deformable member 1 in the impact absorbing member 11 will be described.
6 first deforms obliquely rearward as shown in FIG. 6 (a) to primarily absorb the impact load F ₂ .

Further, in this case, when the impact load F ₂ is an impact load of a predetermined value or more that cannot be absorbed only by the deformation of FIG. 6 (a), the first deformable member 1 is further added.
6 deforms largely as shown in FIG. 6 (b), and at the same time, the second deforming member 17 also deforms as shown in FIG. 6 to absorb the impact load F ₂ larger than the predetermined value reliably and softly.

In each of these cases, the first and second
Both the deformation members 16 and 17 have high deformation rigidity with respect to the impact load F _{1 in the} (a) direction and relatively low deformation rigidity with respect to the impact load F _{2 in the} (b) direction.

Therefore, with respect to the impact load F _{1 in the} (a) direction where the absolute value of the normal load value itself is large, it is stable without bottoming against the tip of the spoke plate fitting portion 2a of the steering shaft 2. The impact load F ₁ is absorbed by deforming with the supporting rigidity described above, while the impact load F _{2 in the} (b) direction in which the load value is generally smaller than that is softened diagonally backward. The shock load F ₂ is smoothly absorbed.

As a result, as shown in FIGS. 7 and 8, the collision safety rule corresponding to the above-mentioned second regulation can be cleared.

(Embodiment 2) FIGS. 9 and 10 show the structure of an impact energy absorbing member in an impact energy absorbing structure for a steering wheel according to Embodiment 2 of the present invention.

Impact energy absorbing member 1 of the first embodiment
In the first configuration, the first and second deformable members 16 and 17 are configured by, for example, separate plate members. However, these are formed by press molding one sheet metal as shown in FIG. 9 may be assembled in the same manner as the structure shown in FIG. 1 as shown in FIG.

When such a structure is adopted, welding work is not required and the working and assembling work is simplified.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an impact energy absorption structure for a steering wheel according to a first embodiment of the present invention.

FIG. 2 is a plan view showing a configuration of an energy absorbing member in the same energy structure.

FIG. 3 is a schematic diagram showing a basic structure of the energy absorbing member.

FIG. 4 is a modification view showing the first impact absorbing action of the energy absorbing member, which is based on the structure of FIG.

5 is a shock absorption characteristic diagram corresponding to the modification of FIG. 4;

FIG. 6 is a modification view showing the second impact absorbing action of the energy absorbing member, which is based on the structure of FIG.

FIG. 7 is a shock absorption characteristic diagram corresponding to the first modification (a) of FIG. 6.

FIG. 8 is a shock absorption characteristic diagram corresponding to the second modification (b) of FIG. 6.

FIG. 9 is a perspective view showing the configuration of an impact energy absorbing member in the impact energy absorbing structure for a steering wheel according to the second embodiment of the present invention.

FIG. 10 is a plan view showing a plate state of the impact energy absorbing member before assembly.

FIG. 11 is a schematic diagram showing an impact energy absorption structure of a steering wheel according to a first conventional example.

FIG. 12 is an explanatory diagram showing the test content of the first regulation required in the impact energy absorption structure of the steering wheel.

FIG. 13 is an explanatory diagram showing the test content of the second regulation required in the impact energy absorption structure of the steering wheel.

FIG. 14 is a diagram showing impact energy absorption characteristics under the first structural condition of the conventional impact energy absorption structure for a steering wheel shown in FIG. 11.

FIG. 15 is a diagram showing impact energy absorption characteristics under the second structural condition of the conventional impact energy absorption structure for a steering wheel shown in FIG. 11.

16 is a diagram showing impact energy absorption characteristics under the third structural condition of the conventional impact energy absorption structure for a steering wheel shown in FIG. 11.

FIG. 17 is a diagram showing impact energy absorption characteristics under the fourth structural condition of the conventional impact energy absorption structure for a steering wheel shown in FIG. 11.

FIG. 18 is a schematic cross-sectional view showing an energy absorption structure of a steering wheel according to a second conventional example.

FIG. 19 is a diagram showing a first deformed state of the same structure.

20 is a diagram showing a second modified state of the structure of FIG.

[Explanation of symbols]

1 is a steering wheel, 1a is a pipe ring, 2 is a steering shaft, 2a is a spoke plate fitting fixing boss portion, 3 is a spoke plate, 5 is a nut, 7 is a cover pad, 10 is an elastic support piece, and 11 is impact energy. Absorbing member, 16 is a first deforming member, 16a is a deforming plate of the first deforming member, 17 is a second deforming member, and 17a.
Is a deformation plate of the second deformation member, 18 is the first upper and lower pieces of the first deformation member, 19 is the second upper and lower pieces of the first deformation member, and 24 is the first upper and lower pieces of the second deformation member. One piece, 25 is the second
It is the second upper and lower pieces of the deforming member of.

Claims (3)

[Claims] 1. A steering wheel which is attached to a steering shaft via a spoke member, and a cover pad is provided on an upper portion of a mounting portion for the steering shaft via an impact energy absorbing member, wherein the impact energy absorbing member is provided. Is composed of a first deformable member that can be deformed directly below and obliquely below, and a second deformable member that is located a predetermined distance below the first deformable member and that can be deformed immediately below and obliquely below. In addition, the impact energy absorption structure for a steering wheel is characterized in that the deformation rigidity of the first and second deformation members in the immediately downward direction is made higher than the deformation rigidity in the obliquely downward direction. 2. The steering wheel according to claim 1, wherein the first and second deformable members which are deformed obliquely downward are arranged so as to be deformed obliquely downward without interfering with each other. Impact energy absorption structure. 3. The steering wheel according to claim 1, wherein the first and second deformable members are integrally formed by bending a single punched sheet metal member into a three-dimensional shape. Impact energy absorption structure.