GB2048430A - Device absorbing energy by extrusion - Google Patents

Abstract

An energy absorbing device comprises a cylinder 1 containing an extrusion medium 2 and a piston 4 movable in the cylinder to extrude the medium 2 through an orifice 9, and the extrusion medium is a platelet structure particulate solid material chosen from the group graphite and talc. The extrusion may be back-extrusion. The energy absorbing device is relatively insensitive to temperature variations. It may be used to absorb compression or tensile forces. The talc or graphite may be held together by wax or a plastics binder. <IMAGE>

Description

SPECIFICATION Energy absorbing device This invention relates to energy absorbing devices and has particular reference to energy absorbing devices which are intended to be relatively insensitive to temperature variations.

The devices may be used to absorb energy in a variety of uses, such as helicopter legs, vehicle bumpers, railway buffers, seat belts, mine safety devices, lift cage energy absorbing devices and numerous other analogous energy absorbing uses.

Energy absorbing devices are known in which there is provided a piston and cylinder arrangement in which the cylinder contains an extrusion medium which is forced through an orifice by movement of the piston into the cylinder. It is preferred, in these earlier devices, to use a back-extrusion technique in which the material is extruded through an orifice defined by the annular gap between the walls of the cylinder and the piston. Backextrusion is to be preferred to forward-extrusion in that the force displacement characteristics for back-extrusion are relatively constant throughout the stroke of the piston into the cylinder. With forward-extrusion the force dis placement characteristics vary with the stroke of the piston in the cylinder to a much greater extent.The proposals which have been made heretofor relate to the use of liquids as an extrusion medium, for example in dampers or shock absorbers for cars or, in certain other devices, there are proposals to use solids as the energy absorbing medium. These solids have conventionally been plastics materials or readily extrudable metals such as lead. Although such devices can be tailored to absorb energy in a very efficient manner they do have one drawback, which is namely their sensitivity to temperature variations.

Thus, if a plastics extrusion slug is used on a motor vehicle it could encounter temperature variations between - 50"C and + 70"C, depending on whether it was operating in arctic conditions or in a desert. It has proved to be extremely difficult to devise a plastics medium for the extrusion slug in an energy absorbing device which is capable of coping with large variations in temperature whilst having substantially constant force displacement characteristics.

Other energy absorbing devices capable of operating at wide temperature ranges are to be found in the prior art.

British Patent Specification No 992 932 describes a recoil absorber for automatic weapons in which the extrusion medium is in the form of solid, spherical balls of steel or plastics material.

British Patent Specification No 1 469 962 describes the use of sintered iron or steel powder as a deformable porous metal in a shock absorbing device.

British Patent Specification No 1 543 340 describes the use of particulate cured silicon rubber as an energy absorbing medium.

British Patent Specification No 1 341 820 does not describe an extrusion apparatus but does describe the use of Portland cement containing a particulate vermiculite material as an energy absorbing medium.

British Patent Specification No 784 545 describes a damper in which the damping medium is a mass of bouncing putty or other damping medium having an extremely high viscosity of the order of 300 000 poises at 20"C. It also describes a shock absorber in which the shock absorbing function is accomplished by extruding a plastic or fluid medium through a restricted orifice and states that amorphous graphite has been found well suitable for such purpose. Presumably the applicants could not have meant amorphous graphite as such because graphite is a crystalline material and it is thus impossible to have amorphous graphite. It is presumed that the applicants meant graphite which had been converted to amorphous carbon, in other words amorphous carbon as the extrusion material.

By the present invention there is provided an energy absorbing device comprising a cylinder and a piston movable in the cylinder, an orifice leading from the interior of the cylinder to the exterior of the cylinder and an extrusion medium located in the cylinder extrudable through the orifice on movement of the piston into the cylinder, characterised in that the extrusion medium is a particulate solid material of platelet-like crystalline material chosen from the group talc or graphite or a compact of such a material.

The fabrication of the material into a compact may be facilitated by a binder.

The orifice may be formed between the piston and the walls of the cylinder whereby the extrusion medium may be back-extruded from the cylinder. The piston may have an extension extending into the cylinder to form a guide, the extension with the walls of the cylinder defining an annular chamber for the medium. The annular chamber may have a circular external cross-section.

The energy absorbing device may be incorporated into a vehicle to absorb energy on impact. Thus it may be incorporated into a bumper mounting or in the mountings of the engine within the vehicle. Alternatively, the device could be incorporated into a seat belt arrangement to absorb energy or into railway buffers or into the legs of helicopters or other aircraft to absorb energy in the event of landings imposing loads on the legs beyond their normal design operating levels.

By way of example embodiments of the present invention will now be described with reference to the accompanying drawings, oi: which: Figure 1 is a cross-section of one form of energy absorbing device; Figure 2 is a cross-section of an alternative form of device; Figure 3 is a side view of a helicopter; Figure 4 is a view of a helicopter leg suspension system; Figure 5 is a side view of a car; Figure 6 is a perspective view of a railway buffer; and Figure 7 is a perspective view of a seat belt installation.

Referring to Fig. 1 this shows a cylinder 1 which contains a solid extrusion slug 2. The extrusion slug is in the form of a cylinder having a longitudinal hole therethrough which accommodates a rod 3 having a piston 4 formed at one end. Connected to the end 5 of the cylinder is a stirrup 6 terminating in an eye 7 to which a wire rope 8 can be connected.

The material of the extrusion slug 2 is talc which has been compressed so as to form a substantially solid item. In use the device absorbs energy when the rod 3 is puiled so as to force the piston 4 into the slug thereby displacing the talc through the orifice 9 defined between the walls of the cylinder 1 and the piston 4.

Because talc has a plate-like structure it is believed that the material flows in the manner of a solid and the movement of the piston through the slug 2 requires energy which is, therefore, dissipated by the device.

In an alternative form of construction as shown in Fig. 2 the cylinder 10 again has a solid slug 11 of material which has a bore through which passes a nose 1 2 of a piston 1 3 connected to a piston rod 14. When the rod 14 is pushed in the direction of the cylinder 10 the piston 1 3 displaces the medium 11 to absorb energy. Again the material is back-extruded through the orifice 1 5 defined between the cylinder 10 and the piston 13.

The material of the slug may be talc or may be graphite, both of which are crystalline solid materials having a platelet-type structure. In order that the material does not fall to pieces prior to its being called upon to absorb energy it may be held together with a suitable binding material such as a wax or plastics material or any other suitable binder.

The energy absorbing device may be used in the legs of a helicopter as is shown in Figs.

3 and 4. The helicopter 1 6 has four legs, two of which 1 7 and 1 8 are shown, and these legs are connected to the helicopter by means of a suitable linkage arrangement as is shown in Fig. 4. The linkage comprises a four-rod system 19, 20, 21, 22 in which rod 21 is formed of part of the fuselage of the helicopter. The wheel 23 is suspended from the lower end of the linkage arrangement. The energy absorbing device 24 is connected to pivots 25 and 26 and is only activated when the wheel is moved upwardly relative to the helicopter body and the link 21 beyond that permitted by the normal movement of the dampers. Thus unit 24 is normally inoperative and can be regarded as a lost motion device.

Illustrated in Fig. 5 is a vehicle, a car 27, in which bumpers 28 and 29 are joined to the vehicle by means of energy absorbing devices 30 and 31 which would be similar to those illustrated in Fig. 2.

The engine of the motor vehicle may also be connected into the car by means of an energy absorbing device if required.

Illustrated in Fig. 6 is a railway buffer system in which buffers 32 and 33 are mounted on a block 34 by means of energy absorbing devices 35 and 36 similar in construction to that illustrated in Fig. 2.

Fig. 7 illustrates a seat belt system in which an inertia reel seat belt 38 is located in the car and incorporates an energy absorbing device 39 which is similar in construction to that illustrated in Fig. 1.

Because the energy is absorbed by the device of the invention by extrusion of a solid particulate material it is relatively insensitive to variations in temperature and is particularly much less sensitive than the solid plastics material or solid metal devices proposed heretofor.

Solid particulate materials are less susceptible than plastics material to ageing bio-degrading attack by termites, moisture and other environmental surroundings.

In order that the solid particulate material may be easily handled it may be held together by a binder.

Claims (8)

1. An energy absorbing device comprising a cylinder and a piston movable in the cylinder, an orifice leading from the interior of the cylinder to the exterior of the cylinder and an extrusion medium located in the cylinder extrudable through the orifice on movement of the piston into the cylinder, characterised in that the extrusion medium is a particulate solid material of platelet-like crystalline material chosen from the group talc or graphite or a compact of such a material.

2. A device as claimed in Claim 1 in which there is provided a binder to facilitate fabrication of the particulate solid material into a compact.

3. A device as claimed in any one of Claims 1 or 2 in which the orifice is formed between the piston and the walls of the cylinder whereby the extrusion medium is back-extruded from the cylinder.

4. A vehicle incorporating an energy absorbing device as claimed in any one of Claims 1 to 3.

5. A helicopter or other aircraft including a landing leg incorporating an energy absorbing device as claimed in any one of Claims 1 to 3.

6. A helicopter as claimed in Claim 5 in which two or more landing legs incorporate energy absorbing devices as claimed in any one of Claims 1 to 3.

7. An energy absorbing device substantially as described herein with reference to and as illustrated by Figs. 1 or 2 of the accompanying drawings.

8. A helicopter incorporating an energy absorbing device substantially as described herein with reference to and as illustrated by Figs. 1 to 4 of the accompanying drawings.