JPH0532145A - Energy absorbing member for car bumper - Google Patents

Abstract

PURPOSE:To provide an energy absorbing member for bumper, which has a large shock absorbing ability even for load applied aslant, is free from generation of stresses exceeding a certain level when deformation is made with collision, and which can absorb a large energy for a specific amount of deformation. CONSTITUTION:A filament is coiled so as to present a ring-shaped section and is formed cylindrically with a fiber-reinforced composite material hardened with a resin, wherein the wall thickness varies in the axial direction. Thereby inter-layer exfoliation due to compressive deformation is generated gradually from the part with larger wall thickness, and no sudden change of stress will arise. Thus a smooth deformation is made with a comparatively small stress to enable absorption of large energy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bumper energy absorbing member used as a shock absorbing member for a bumper mounted on an automobile.

[0002]

2. Description of the Related Art In order to protect a vehicle body and an occupant at the time of a collision, an automobile is generally provided with a bumper in front of and behind the vehicle body for absorbing impact energy at the time of a collision. The bumper needs to irreversibly absorb energy against a large load applied when the vehicle collides with an obstacle. In order to increase the absorbed energy, various improvements have been made to the material and structure of the support member that supports the bumper body.

For example, a German patent (3626150) published on February 18, 1988 discloses that a bumper 22 is attached to a stay 23 of a vehicle body via an elliptical annular damping molded body 21 as shown in FIG. Has been done. The damping molded body 21 is formed of FRP (fiber reinforced plastic) in which fibers are arranged in the circumferential direction, and is attached such that the elliptical long side surfaces contact the bumper 22 and the stay 23, respectively.

Further, Japanese Patent Application Laid-Open No. 57-124142 discloses an energy absorbing structural material used in a bumper as shown in FIG.
As shown in FIG. 1, there is proposed a structure 25 formed in a cylindrical shape with a network structure made of a strip 24 made of a fiber composite material (for example, epoxy resin-impregnated glass fiber). The structure 25 is used in a state in which a compressive load is applied in the axial direction of the cylinder, and when an axial load is applied to the structure 25, delamination occurs at the opposing node points 26 of the network, and shear yield occurs between the fiber and the matrix. Energy is absorbed stepwise by being generated at the interface of. Also, each node 26
Is formed of about 10 layers of fiber composite strip 24.

[0005]

The above German patent discloses the use of an FRP damping molding 21 in which fibers are arranged in the circumferential direction as an energy absorbing member, but a load is applied to the member. There is no mention of the stress that occurs when it strikes, its fluctuations, absorbed energy, etc. As a method of manufacturing an FRP annular structure in which long fibers are arranged in the circumferential direction, a filament winding (FW) is performed in which a filament is impregnated (adhered) with a resin, wrapped around a mandrel (core material) in multiple layers, and then cured by heating. The method is commonly used. When the structure manufactured by the FW method is compressed by the load from the side surface, the stress increases simultaneously with the intensive deformation of the curved surface, and when it exceeds a certain limit, delamination of the fiber occurs and the stress suddenly increases. Fall to. In the initial stage of compression, this severe stress fluctuation is repeated and delamination progresses,
The stress gradually decreases. When the deformation is further increased and the breaking limit of the fiber is exceeded, the stress is further attenuated. The product of the stress generated in the compressive deformation process and the amount of deformation (specifically, the area between the compressive load-displacement amount curve and the axis representing the amount of displacement) becomes the absorbed energy at that time. If there is a condition to reduce the impact on the human body like a bumper support member, it is necessary to suppress the maximum value of stress to a level that has a low effect on the human body. Absorption is small. Therefore, in order to satisfy the requirements of reducing the impact on the human body and increasing the amount of energy absorption during deformation, it is important to keep the compression load-displacement amount curve constant at the lowest possible level.

Similar to the one disclosed in the German patent, an elliptic ring-shaped structure made of FRP in which glass fibers are arranged in the circumferential direction and having a constant thickness is manufactured, and is compressed by a load from an elliptical longitudinal side surface. When the relationship between the load and the displacement amount was measured, the results shown in FIG. 10 were obtained. In this case, a sudden change in load occurs at the point where delamination first occurs, and the fluctuation is extremely severe.Therefore, if the maximum load value is suppressed to a level that has a low effect on the human body, the amount of energy absorbed will decrease. However, it is insufficient as an energy absorbing member for bumpers.

On the other hand, the tubular energy absorbing structural material disclosed in JP-A-57-124142 exhibits its function when a compressive load is applied in the axial direction of the tube.
Almost no load can be accommodated from diagonal directions.
Further, as described above, in order to increase the absorbed energy, it is important that the load is maintained at a constant level even if the displacement amount increases. Is gradually attenuated, and there is a problem that it is difficult for the amount of energy absorption to increase.

The present invention has been made in view of the above problems, and its purpose is to reduce the impact at the time of a collision of an automobile and to reduce the transmission of the impact to the human body. An energy-absorbing member for bumpers that does not generate stress, absorbs a large amount of energy for a certain amount of deformation, has a high impact-absorbing capacity even with a load from an oblique direction, and is lighter than metal. To provide.

[0009]

In order to achieve the above object, the energy absorbing member of the present invention is a tube made of a fiber reinforced composite material in which filaments are circumferentially wound so as to form an annular cross section and cured with a resin. It is formed into a shape and its thickness changes in the axial direction.

[0010]

The energy absorbing member for the bumper of the present invention is attached so as to receive a compressive load from the side surface of the tubular portion. The deformation of the energy absorbing member due to the compressive load is compression on the inner layer side and extension on the outer layer side, and the amount of deformation increases as the distance from the neutral layer increases. Delamination is more likely to occur in a portion having a larger amount of deformation, so that delamination occurs gradually from a thicker portion, and the deformation stress does not change drastically, and it smoothly deforms with a relatively small stress and absorbs large energy.

[0011]

【Example】

(First Embodiment) A first embodiment of the present invention will be described below with reference to FIGS. As shown in FIG. 1, the energy absorbing member 1 is formed in a cylindrical shape having a constant outer diameter, and the thickness thereof is formed so as to change gently from the axial center toward both ends.

The energy absorbing member 1 is made of FRP in which synthetic resin is reinforced by endless long fibers (filaments), and the filaments are wound in the circumferential direction. In this example, glass fiber was used as the filament and epoxy resin was used as the synthetic resin. As a manufacturing method, a filament winding (FW) method was used in which the resin was attached to the glass fiber and wound around a mandrel, and then the resin was heated and cured. A mandrel that can be split in the axial direction from the center was used to enable separation from the energy absorbing member 1 after heat curing.

FIG. 2 shows the result of measuring the relationship between the load and the displacement amount when a compressive load is applied from the side surface of the energy absorbing member 1 configured as described above.
As is clear from the figure, the maximum load is smaller than in the case where the wall thickness shown in FIG. 10 is uniform, but the sudden change of the load in the initial stage of compression is significantly reduced, and the load in the latter half of the plastic deformation is reduced. The decrease is also small. this is,
When the wall thickness is uniform, the amount of deformation due to the compressive load becomes constant in the axial direction, and when the compression energy is accumulated and exceeds a certain limit, delamination occurs at once, whereas this energy absorbing member 1 It is considered that since the thickness changes from the central portion in the axial direction toward both ends, delamination occurs sequentially from the thick central portion. That is, in the thick portion, the inner layer of the cylindrical portion has a smaller amount of fiber winding and a larger amount of deformation, so that delamination occurs sequentially from the portion. Therefore, the energy absorbing member 1 has a small load fluctuation and a larger ratio of the energy absorbing amount to the maximum load than the conventional one, and is preferable as an energy absorbing member for a bumper. The material of the energy absorbing member 1 has a specific gravity of about 2
Since it is an FRP in the vicinity, it is much smaller than that of metal and can be made lighter.

(Second Embodiment) Next, a second embodiment will be described with reference to FIGS.
Follow the instructions below. Energy absorbing member 1 of this embodiment
Is different from the above-mentioned embodiment in that it is formed in a tubular shape having a substantially elliptical cross section, and its inner diameter is changed stepwise. When the energy absorbing member 1 of this embodiment is formed by the FW method and a metal mandrel is used, it becomes difficult to remove the mandrel after the resin is heated and cured. Therefore, in this example, the mandrel was made of expanded polypropylene and left in the molded energy absorbing member 1. The mandrel made of expanded polypropylene may be destroyed and removed without being left. When the mandrel made of expanded polypropylene is left, when the compressive load acts on the energy absorbing member 1, the expanded polypropylene is also deformed, which contributes to the improvement of the absorbed energy amount and the suppression of the load fluctuation.

FIG. 4 shows a result of measuring the relationship between the load and the displacement amount when a compressive load is applied from the side surface of the energy absorbing member 1 in which the mandrel made of expanded polypropylene is left. Also in this case, the sudden change of the load is significantly reduced, and the decrease of the load in the latter half of the plastic deformation is small. (Third Embodiment) Next, a third embodiment will be described with reference to FIGS. The energy absorbing member 1 of this embodiment is formed in a cylindrical shape with a constant outer diameter, and has thin-walled portions at both ends and a thick-walled portion at the central portion in the axial direction. Is formed in a shape that changes gently. When manufacturing this energy absorbing member 1,
As in the first embodiment, a mandrel that is axially separable from the center is used. FIG. 6 shows the result of measuring the relationship between the load and the displacement amount when a compressive load is applied to the energy absorbing member 1 from the side surface thereof. Also in this case, the sudden change of the load is reduced, and the decrease of the load in the latter half of the plastic deformation is small.

(Fourth Embodiment) Next, a fourth embodiment will be described with reference to FIGS.
Follow the instructions below. Energy absorbing member 1 of this embodiment
Is greatly different from each of the above-described embodiments in that it has a structure in which a plurality of annular tubular portions are combined. The energy absorbing member 1 has two cylindrical portions 2 having the same shape as those of the first embodiment, which are arranged in parallel with each other with a space therebetween, and an elliptic cylindrical portion 3 is externally integrated with the cylindrical portions 2 circumscribing both cylindrical portions 2. Is formed in. In the energy absorbing member 1, first, a cylinder corresponding to the cylindrical portion 2 is manufactured by the FW method, and then two cylinders are arranged in parallel with each other at intervals, and glass fibers having a resin adhered to the outer peripheral portion thereof are processed by the FW method. It is produced by winding and heating and curing the resin.

FIG. 8 shows the result of measuring the relationship between the load and the displacement amount when a compressive load is applied to the energy absorbing member 1 from the side surface thereof. The sudden change in the load is reduced, the load becomes almost constant until the latter half of the plastic deformation, and the ratio between the energy absorption amount and the maximum load becomes larger than that in each of the embodiments. It is considered that this is because the loads are averaged because there are a plurality of cylindrical portions 2.

The present invention is not limited to the above-mentioned embodiment, and for example, the cross-sectional shape of the cylindrical portion of the energy absorbing member 1 is not limited to circular or elliptical, but a combination of arcs having different curvatures is substantially used. Any ring shape will do. Further, the resin forming the FRP of the material is not limited to epoxy resin, but thermosetting resin such as phenol resin and unsaturated polyester may be used, or high elasticity such as carbon fiber or aramid fiber may be used as the reinforcing fiber instead of glass fiber. Although various functional fibers having high-strength physical properties are used, in the case of automobile bumper applications, glass fibers are preferable in terms of heat resistance in terms of cost. Further, in the case of the structure in which a plurality of cylinders are combined as in the fourth embodiment, the number of cylinders may be increased or the diameters of the cylinders may be different.

[0019]

As described above in detail, according to the present invention, since the energy absorbing member is formed in an annular cross section and used in a state of receiving a compressive load from its side surface, it is possible to cope with a load from an oblique direction. Also has a high shock absorption capacity. In addition, since the thickness of the energy absorbing member formed in a tubular shape changes in the axial direction, delamination due to compressive deformation does not gradually occur and sudden stress change does not occur, and the human body is not affected by a car collision. The impact given can be relaxed and a large amount of energy can be absorbed.

[Brief description of drawings]

FIG. 1 shows an energy absorbing member of a first embodiment,
(A) is the sectional view on the AA line of (b), (b) is a side view.

FIG. 2 is a compression load of the energy absorbing member of the first embodiment-
It is a displacement curve.

FIG. 3 shows an energy absorbing member of a second embodiment,
(A) is a BB line sectional view of (b), (b) is a side view.

FIG. 4 is a compression load of the energy absorbing member of the second embodiment-
It is a displacement curve.

FIG. 5 shows an energy absorbing member of a third embodiment,
(A) is the CC sectional view taken on the line of (b), (b) is a side view.

FIG. 6 is a compressive load of the energy absorbing member according to the third embodiment-
It is a displacement curve.

FIG. 7 is a schematic perspective view of an energy absorbing member of a fourth embodiment.

FIG. 8 is a compressive load of the energy absorbing member according to the fourth embodiment-
It is a displacement curve.

FIG. 9 is a schematic plan view showing a bumper support state by a conventional bumper support member.

FIG. 10 is a compression load-displacement amount curve of a conventional bumper support member.

FIG. 11 is a schematic perspective view showing a conventional energy absorbing structural material.

[Explanation of symbols]

 1 ... Energy absorbing member, 2 ... Cylindrical part.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshiharu Yasui 2-chome Toyota-cho, Kariya city, Aichi stock company Toyota Industries Corporation (72) Inventor Yasumi Miyashita 2-chome Toyota-cho, Kariya city, Aichi stock Incorporated company Toyota Industries Corporation (72) Inventor Toshiro Kondo 2-chome Toyota Town, Kariya City, Aichi Stock Company Toyota Industries Corporation (72) Inventor Naohiro Tada 1 Toyota Town, Aichi Prefecture Toyota Automobile Within the corporation

Claims (1)

Claim: What is claimed is: 1. A filament is wound in the circumferential direction so as to have an annular cross section, and is formed into a tubular shape from a fiber-reinforced composite material cured by a resin, and its wall thickness changes in the axial direction. Energy absorbing member for bumpers.