GB2373561A

GB2373561A - An energy dissipating road wheel tether

Info

Publication number: GB2373561A
Application number: GB0106950A
Authority: GB
Inventors: Michael Tate
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-03-20
Filing date: 2001-03-20
Publication date: 2002-09-25
Also published as: GB0106950D0

Abstract

A road wheel tether 4 has an energy dissipating component 1, 2, 3 ,5 , 7 so that the road wheel assembly 6, to which the tether 4 is attached, can be controllably restrained in the event of it becoming detached from the vehicle body in an accident. The energy dissipating assembly contains a deformable component 2 that deforms by collapse or crushing under the force exerted by the tensile loading of a flexible tether 4. The energy dissipating assembly is contained within a housing 1, 3, 7 that is rigidly attached to the vehicle body.

Description

An Energy-Dissipating Road-Wheel Tether Field This invention relates to the field of motor racing In particular it relates to safety devices intended to reduce the level of risk of personal injury resulting from motorracing accidents.

Background In motor-vehicle racing, high-speed accidents are an accepted risk During such accidents, debris is often detached from the vehicle or vehicles involved and can travel at high speed along uncontrolled trajectories This can result in serious injury to spectators, drivers, track officials, technicians or bystanders who may be accidentally struck by such debris A common occurrence is for road-wheels, complete with brake assemblies and associated suspension components (hereafter referred to as road-wheel assemblies), to become detached which, because of their large quantities of stored kinetic-energy are particularly dangerous This energy results from both the vehicle translation speed and the associated wheel rotational speed. This combination therefore causes the road-wheel assemblies to possess

kinetic-energy that is greater, per unit of mass (a quantity known as the'specific energy'), than any other part of the vehicle, with the possible exception of some internal engine/transmission components Attempts have been made to retain the described road-wheel assemblies from complete detachment, by means of'tethers', which consist of flexible, high-strength, straps-typically of aramid fibre. However, experience has shown that, in high-speed accidents, such tethers are easily broken, so that they are made ineffective in the very type of accident for which they are required.

The fundamental problem is that a detached road-wheel assembly will separate from the vehicle body at high-speed because of its high specific-energy. Subsequently, any attempt to restrain the wheel relative to the vehicle body by the use of a conventional tether, will produce very large forces because of the extremely high accelerations produced by the attempted restraint. It can be shown that a typical wheel assembly could produce loads, in a suitably strong tether, in the order of 50 tonnes in extreme accidents It should therefore be apparent that both the tether itself and the attachments to vehicle body and wheel assembly are likely to fail in the described accident The method of using a road-wheel assembly tether can be made to work if the loads experienced by the tether and its attachment system can be controlled to levels that are of lower magnitude than the failure loads of the tether system. It is also beneficial to reduce loading to a practical minimum in order to minimise the size and weight of the tether itself and to minimize the structural demands at the points of attachment in the racing-car body A further issue is the use of a'webbing'tether-such as those made of aramid fibres This particular tether construction is driven by the demands of structural flexibility, across the suspension system and also by the fact that webbing types of tether offer some'stretch'in an impact This effect will slightly reduce the maximum loading when compared, for example, with a steel cable alternative. The aramid material itself, however, is susceptible to damage from the harder materials of the racing-car construction such as steel, carbon composites, titanium components etc, so that secondary damage from these sources can lead to premature failure when the tether system is loaded It should be particularly noted that the simple substitution of a metallic cable for a webbing type of tether (whether that webbing consists of aramid, carbon, glass or any other fibre) would result in increased loading of the tether system because of the reduced'stretch' (or'elongation') due to the tether construction.

These problems can be largely overcome by the use of some form of energy dissipation, in the tether system. This facility can be employed to significantly reduce the maximum loading on the system and therefore also allows the optional use of a steel-construction tether.

Description The invention consists of two functional elements-a flexible tether and an energydissipating part The tether can be in the form of steel cable or other metallic construction or can be in the form of rope or webbing made from fibrous materials such as aramid fibre, carbon fibres, glass fibres or other suitable high-strength material-including strong natural fibres such as flax The essential features of the tether are that it is sufficiently flexible for its purpose and that it has high tensile strength Typically, the breaking strength of the tether would be in the region of 10 tonnes or more. The tether must be capable of achieving equally high-strength connections at its ends.

The energy-dissipating component consists of a hollow bodv or'housing'that is long in comparison with its cross-section dimensions This housing is of high, axial, compressive-strength to react the applied loads without significant deformation The housing is provided with means for its rigid attachment to the vehicle body. Such attachments being adequate to react the maximum design loading applied to the energy-dissipating system, without failure.

Within the housing, a deformable component is contained The function of this deformable part is to dissipate energy by its'progressive collapse under load The deformable component can be of composite or metallic material, but in highperformance applications, is most likely to be of composite construction It is known that composite components can provide the required energy-dissipating capability with very high efficiency; typically dissipating in excess of 3 5 joules per gram of deformed (crushed) material. This compares with steel, for example, which will typically dissipate only 6 or 7 joules per gram. Aluminium has intermediate capability and can achieve around 22 joules per gram The deformable component is retained at one end, within the housing. The tether (or an extension of the tether) passes through the deformable component from the retained end to the'free'end, where it is attached to a disc in the general form of a piston. This piston-like component (typically of metal) is guided within the housing, and is arranged to crush the deformable component when sufficient force is applied by tensile loading of the tether. The tether is attached to a road-wheel assembly at its other end, where large forces can be applied as a result of the accidental events The mathematical product of the crushing (or collapse) force and the displacement of the piston, resolves the quantity of energy-dissipation within the housing This energy-dissipation restrains the movement of the wheel-assembly relative to the vehicle body, to which the housing is strongly attached. The wheel-assembly is thereby constrained to move at the same rate as the vehicle body and to remain within a closely controlled spatial envelope drawn around the racing-car body The invention will now be described by way of example and in particular, with reference to the drawing Figure 1 Referring to figure 1 There is shown, in the form of a longitudinal section, an energy-dissipation device, a flexible tether and a road-wheel assembly.

There is a cylindrical housing 1, containing a deformable component 2. The deformable component 2 is retained by an end-cap 3. Passing approximately through the centroid of the cross-section of the deformable component is a flexible tether 4 The tether is strongly attached to a free-running piston-like component 5 and passes through the end cap 3. The tether 4 is of a length appropriate to reach the wheelassembly 6, and also to allow kinematic freedom to the wheel-assembly suspension system. The cylindrical housing 1 is closed at its opposite end by another cap 7 ; of light construction. Optionally, the tether 4 can pass through a guide plate 8.

Tensile forces occurring in the flexible tether 4 are applied to the piston-like component 5 which will thereby cause compressive loading on the deformable component 2 which will undergo progressive collapse after a critical value of loading has been exceeded. The compressive loading, on the deformable component 2, is reacted by the end-cap 3 that is strongly attached to the housing 1 that in turn is strongly attached to the racing-car body (not shown) The housing 1 can be mechanically attached to the vehicle body or it can be bonded to, or encapsulated within, the vehicle body structure In order to allow some flexibility in the choice of location of housing 1 and the energy-dissipating device contained within, a guide plate 8 can be incorporated into the path of the tether 4 so that the alignment of the housing 1 need not be exactly perpendicular with the alignment of the tether at its'point of exit from the vehicle body

Claims

What I claim i

1 A mechanically-acting, energy-dissipating device for attachment, by means of its'housing, to a racing-car body and having a flexible connection, of its energy-dissipating part, to a road-wheel assembly, the housing having means to dissipate mechanical-energy by the controlled collapse of an internal deformable component and means to apply compressive loading to that deformable component by a piston-like component displaced by the action of the flexible connection under tensile loading.

2 An energy-dissipating device, as in claim 1, in which the flexible connection to the road-wheel assembly consists of a mechanical linkage.

3 An energy-dissipating device, as in claim 1, in which the flexible connection to the road-wheel assembly consists of a'tether'in the form of a cable of steel-stranded construction.

4 An energy-dissipating device, as in claim 1, in which the flexible connection to the road-wheel assembly consists of a'tether'in the form of a cable of aramid-fibre construction

5 An energy-dissipating device, as in claim 1, in which the flexible connection to the road-wheel assembly consists of a'tether'in the form of a cable of carbon-fibre construction

6 An energy-dissipating device, as in claim 1, in which the flexible connection to the road-wheel assembly consists of a'tether'in the form of a cable of natural-fibre construction.

7 An energy-dissipating device, as in claim 1, in which the flexible connection to the road-wheel assembly consists of a'tether'in the form of webbing of steel-stranded construction.

8 An energy-dissipating device, as in claim 1, in which the flexible connection to the road-wheel assembly consists of a'tether'in the form of webbing of aramid-fibre construction.

9 An energy-dissipating device, as in claim 1, in which the flexible connection to the road-wheel assembly consists of a'tether'in the form of webbing of carbon-fibre construction

10 An energy-dissipating device, as in claim 1, in which the flexible connection to the road-wheel assembly consists of a'tether'in the form of webbing of carbon-fibre construction.

11 An energy-dissipating device, as in claim 1, in which the flexible connection to the road-wheel assembly consists of a'tether'in the form of webbing of natural-fibre construction.

12 An energy-dissipating device, as in claim 1 and any of claims 2 to 11, in which the deformable component is made of fibre-reinforced composite material.

13 An energy-dissipating device, as in claim 1 and any of claims 2 to 11, in which the deformable component is made of metallic material 14 An energy-dissipating device substantially as described herein with reference to figure 1 of the accompanying drawing