GB2089466A - Energy absorbing devices - Google Patents

Abstract

An energy absorbing device (1) which may be incorporated in a vehicle under-run protector (3) comprises at least one resilient first element (4) and at least one second element (5) arranged so that compression of the first and second elements (4, 5) at or above a predetermined level causing plastic deformation of the second elements (5) to absorb part or all of the energy of the applied load. Compression loads below this level are absorbed by the first element(s). As described the device is associated with an under-run protector 21 and comprises a stack of elastomeric first elements (4) and interleaved dish shaped elements (5) of mild steel. <IMAGE>

Description

SPECIFICATION Energy absorbing device This invention relates to a device which partially or wholly absorbs the energy of an applied load when compressed.

It is known to provide energy-absorbing devices in the form of shock-absorbers in which a fluid is displaced by the actuation of a piston within a cylinder, the displacement of this fluid together with the heat thereby generated acting to absorb part or all of the energy of the applied load. Such energy-absorbing devices may, for example, be incorporated within a vehicle under-run protector, the arrangement being such that when a following vehicle is in collision with the vehicle on which the under-run protector is mounted, the piston is moved within the cylinder and a suitable fluid contained within the cylinder is displaced through a small orifice, which may be in the piston, to absorb the energy of the impact.Such energyabsorbing devices may also incorporate a return spring arrangement, the whole assembly being relatively complicated in construction and hence can therefore be expensive to manufacture.

It is an object of the present invention to provide an energy-absorbing device of relatively simple construction and which is capable of partially or wholly absorbing the energy of an applied load, the arrangement being such that the device acts as a resilient shock-absorber when a relatively light load is applied to it and the device being plastically deformable when the applied load reaches or exceeds a pre-determined level. A further object of the invention is to provide a vehicle under-run protector incorporating such an energy-absorbing device.

According to the invention we provide an energy-absorbing device comprising, at least one resilient first element capable of elastic deformation under load, at least one second element adjacent the or each resilient first element, said second element being plastically deformable at or above a pre-determined pressure applied by said first element to said second element when the or each siad first element is elastically deformed under load.

Conveniently, each first element may be a rubber or synthetic plastics material of annular cross-section which resiliently deforms under load.

Conveniently each second element may be dish shaped and of a metal which plastically deforms under load.

The energy-absorbing device may comprise a plurality of said first and second elements sandwiched with respect to each other and mounted on a centre bolt, the assembly forming a stack having the above stated energy-absorbing characteristics.

In a preferred embodiment the energyabsorbing device is incorporated in a vehicle under-run protector and is pivotally mounted such that arcuate movement of the under-run protector causas compression of the resilient first elements and, if a pre-determined load is exceeded, the pressure exerted on the resilient first elements is transmitted to the second elements to cause plastic deformation therein.

These and other aspects of the invention will become apparent with reference to the accompanying drawings in which, Figure 1 is a cross-sectional side view of an energy-absorbing device according to the invention incorporated in a vehicle under-run protector, showing both the normal and the fully deformed conditions of the device; and Figure 2 is an end view of the device in the direction of arrow 2 in Figure 1.

Referring to the drawings, an energy-absorbing device 1 is pivotally mounted at one end to a chassis member 2 of a vehicle and connected at its other end to part of a vehicle under-run protector 3 also pivoted to the chassis member 2.

The energy absorbing device 1 comprises four elastically deformable tubular resilient first elements 4, of rubber or synthetic plastics material, arranged in two pairs, each pair of which is sandwiched between a pair of dish-shaped second elements 5 facing inwardly with respect to each other to form an enclosure 6 within which is contained a pair of the resilient first elements 4.

Adjacent first elements 4 in each enclosure 6 are separated by a flat metal disc 7 through the centre of which is provided a hole of diameter corresponding to the diameter of complementary holes in each of the first elements 4 and the second elements 5. The first and second elements 4 and 5 and discs 7 are axially located on a centre bolt 8 which extends through the holes in the middle of each of the first and second elements 4 and 5 and through the hole in each disc 7. One end of the centre bolt 8 extends through an aperture in a bracket 9 such that bracket 9 abuts a spring 10, retained on the bolt 8 by a washer 11 and pin 12. A nut 13 is welded to a threaded end of the bolt 8 and serves to allow rotation of the bolt 8 during assembly or dis-assembly of the energy-absorbing device.At the other end of the centre bolt 8 a threaded portion 14 is received within a threaded bore of a cast steel collar 15, itself pivotally fixed to the chassis member 2 by pivot pin 1 6.

Centre bolt 8 and the energy-absorbing elements 4 and 5 mounted thereon are thus capable of pivotal movement with respect to chassis member 2.

A hollow spacing member 1 7 is received on the bolt 8 between the lowermost element 5 and the bracket 9 and is provided at the end adjacent such lowermost element 5 with a bearing flange 1 8.

The end of the spacing member abutting the bracket 9 is curved in the plane of pivotal movement of the bolt 8 and is arranged to embrace a correspondingly shaped surface on the bracket 9 such that pivotal movement of the bracket 9 and relative to the spacing member 1 7 is possible.

The bracket 9 is welded to an "L" shaped hanger 20, which extends downwardly from the chassis 2. A horizontal beam 21 of generally channel section extends across a pair of the hangers 20 and is fixed thereto by means of mounting bracket 22.

One end of each hanger 20 is pivotally mounted on chassis member 2 by pivot bolt 23 which extends through a pivot tube 24, extending through a suitable orifice in each hanger 20 and chassis member 2.

In operation it will be apparent that the underrun protector 3 is capable of pivotal movement with respect to the chassis member 2 and that the energy-absorbing device 1 is also capable of pivotal movement with respect to the chassis member 2 and the bracket 9. Consequently when a horizontal load is applied to the beam 21 in, for example a collision, the under-run protector 3 can swing along the arcuate line shown by the letter "A". However, since the energy-absorbing device is pivotally mounted at pivot pin 16, this component can only swing along the arcuate path shown by the letter "B" and it therefore foilows that axial movement of the spacing member 1 7 towards the collar 1 5 occurs whenever the underrun protector 3 is loaded in a collision.The spacing member 1 7 exerts pressure through flange 18 to compress the resilient first elements 4 against the collar 1 5. For relatively small arcuate movements of the under-run protector such compression of the first resilient elements 4 is entirely'elastic and when this small load is relieved the under-run protector 3 swings back to its original position with the first resilient elements 4 returning to their original shape.

However, in a serious collision the under-run protector 3 and the energy absorbing device 1 swings to a greater arcuate position such as is shown schematically on the left of Figure 1. It can be seen that the individual first resilient elements have been considerably reduced in their axial dimension with respect to the centre bolt 8 and an increase in their width has occured. It can also be seen that the dish-shaped second elements have become flattened at 25 due to pressure exerted on them by the compressed rubber first elements. It will be understood that the flattening of the dishshaped second elements is caused by plastic deformation and it is this plastic deformation that absorbs a substantial part of the energy of the load imposed in a collision.

The dish-shaped elements 5 are formed of a suitable ductile material such as, for example, mild steel of thickness corresponding to the desired level of energy-absorbtion required.

The first resilient elements can be formed of rubber or rubber-like material capable of withstanding the relatively large compressive forces applied under load. In principle, the first resilient elements convert the axial force applied by the spacing member 1 7 into a multi-axial component force, the pressure of which is capable of plastically deforming the dish-shaped elements 5 when under load.

It is envisaged that the energy-absorbing device as herein described would be disposable after plastic deformation of the dish-shaped elements 5 and possible destruction of the rubber elements 4 in a collision has occured. A fresh stack of elements 4 and 5 could be located on the centre bolt 8 after unscrewing the bolt via the fixed nut 1 3 and withdrawing the centre bolt 8 part way.

A shock absorbing device according to the invention may comprise, instead of a series of dish-shaped second elements 5, a convolute tube surrounding a single inner first resilient element, compression of which may tend to flatten out the convolutions in the tube, the plastic deformation of which would absorb part or all of the energy of compression.

The scope of the present invention is intended to cover all possible combinations whereby a resilient member is compressed and after a predetermined level of compression has been reached or exceeded the pressure is transmitted to adjacent, plastically deformable members which absorb a substantial part of the load imposed. It is further intended to cover applications other than those incorporated within a vehicle under-run protector and such may for example, be included in a railway buffer system or any like device wherein a relatively simple and inexpensive energy absorbing device is required.

Claims (9)

1. An energy absorbing device comprising, at least one resilient first element capable of elastic deformation under load, at least one second element adjacent the or each resilient first element, said second element being plastically deformable at or above a pre-determined pressure applied by said first element to said second element when the or each said first element is elastically deformed under load.

2. An energy absorbing device as claimed in claim 1 in which said first element is of a rubber or synthetic plastics material of annular cross-section which resiliently deforms under load.

3. An energy absorbing device according to claim 1 or claim 2 in which said second element is of a metal of dish-shape which plastically deforms under load.

4. An energy absorbing device according to any preceding claim comprising a plurality of said first and second elements comprising a plurality of said first and second elements sandwiched with respect to each other and mounted on a centre bolt, the assembly forming a stack having energy absorbing characteristics.

5. An energy absorbing device according to claim 1 in which said second element comprises a convolute tube which surrounds a single first resilient element, compression of which causes plastic deformation of the convolute second element to absorb part or all of the energy of compression.

6. A vehicle under-run protector incorporating the energy absorbing device according to any preceding claim.

7. An under-run protector incorporating the energy absorbing device according to any one of claims 1 to 5 in which the under-run protector is pivotally mounted with respect to a chassis member of the vehicle, the energy-absorbing device also being pivotally mounted on the chassis member of a vehicle and a bracket forming part of the under-run protector, such that upon arcuate movement of the under-run protector, compression of the energy absorbing device as herein described results.

8. An energy absorbing device substantially as herein described with reference to and as shown in the accompanying drawings.

9. An under-run protector incorporating the energy absorbing device of claim 1 substantially as herein described with reference to and as shown in the accompanying drawings.