GB2480467A - Pneumatic tyre damping means - Google Patents

Abstract

The invention provides for a damping means for a pneumatic tyre 21, 30 said tyre forming an annular chamber when in use, said damping means comprising a plurality of dividing members located within the annular chamber, thereby creating one or more sub-chambers, said dividing members being formed so as to substantially restrict but not prevent air flow between the sub-chambers. The dividing members may comprise a single orifice 20 or a plurality of valves 32.

Description

Pneumatic lyre Damping Means -Description

This invention relates to pneumatic tyres and improvements thereto.

Pneumatic tyres are used on the wheels of most automotive and other vehicles. They reduce vibrations due to surface imperfections and thereby contribute to ride comfort and reduce wear and tear of the vehicle. They also increase the contact area of the tyre with the ground leading to improved grip and consequently improved control of the vehicle.

A conventional tyre and wheel combination comprises a metal wheel with a rim and a rubber or synthetic tyre that fits around the wheel so as to create an annular chamber.

The annular chamber is accessed by a valve and is airtight so that when it is pressurised, the air does not escape, and the pressure remains substantially constant inside the tyre.

For convenience the term air is used in this description to describe the working fluid inside the tyre. It is to be understood that where any other gas is used, the term air is intended to cover this.

Some tyres contain inner tubes so that the tyre itself does not need to be airtight, the inner tube being a sealed unit which contains the valve.

A pneumatic tyre functions by the outer tyre surface conforming to the irregular ground.

It is this mechanism that results in the reduction of effect of irregular ground surface and increase in ground contact area. Air under pressure is used as the medium to transfer forces from the tyre to the inner wheel and subsequently to the vehicle.

The dynamic nature of the forces applied to the tyre from the ground can generate oscillatory motion within the tyre/wheel and/or the vehicle. The oscillations can be high frequency such and sounds waves, low frequency such as the vehicle bouncing or any vibration within this range. Some examples of low frequency vibrations are: rolling caravans, bouncing tractors, trailers and racing cars. This oscillatory motion can lead to a reduction in control of the vehicle.

Pneumatic tyres inherently have limited damping properties. In fact the standard tyre mathematical models for conventionally suspended vehicles (i.e. with spring damper suspension) assume zero damping in tyres, see Figure 1. Therefore, any oscillatory motion persists and can be detrimental to the performance of the vehicle.

The forces acting on the tyre, including those due to oscillations can result in temporary pressure variations within the tyre chamber. The air flows within the tyre in order to equalise the pressure variations. By restricting this flow of air and reducing its kinetic energy, the oscillatory motion can effectively be damped.

It is an object of the present invention to overcome some of the deficiencies by providing effective damping for tyres.

Accordingly the present invention provides a damping means for a pneumatic tyre, said tyre forming an annular chamber when in use, said damping means comprising a plurality of dividing members located within the annular chamber, thereby creating one or more sub-chambers, said dividing members being formed so as to substantially restrict but not prevent air flow between the sub-chambers.

This invention enables the restriction of the airflow within the pressurised tyre and this in turn dampens the oscillatory motion. This is achieved by dividing the air chamber into multiple separate sub-chambers. Continuous pressure variation within the tyre will now be discrete between the sub-chambers. Orifices or valves between the individual sub-chambers will be able to restrict air flow, thus removing energy from the system and dampen the oscillatory motion. The air path between sub-chambers might be achieved through a single orifice or multiple orifices. However, it must be of of such dimensions as to sufficiently constrict the air flow between the sub-chambers thereby causing internal energy in the fluid to be removed as it is forced through the constricted region.

A range of means for forming the chamber boundaries might be employed. It is to be understood that this list is illustrative and that any suitable means that achieves the end could be considered by a person skilled in the art.

The chamber boundary or boundaries might be: 1. Attached between tyre and wheel (see Figure 2); 2. Attached only to the tyre so that this is placed onto a conventional wheel; 3. Attached only to the wheel so that a range of conventional tyres can be used to achieve the object of the invention; 4. Attached to an inner tube (see Figure 3); 5. Free-floating within the annular chamber (see Figure 4); 6. Attached to one or more other boundaries; 7. Formed as integral part of a continuous material through the annular chamber, for example foam (see Figure 5).

Where the boundaries forming the sub-chambers are free from the wall of both the wheel and the tyre they may be linked so as to maintain optimum separation between them.

Any of the boundaries may be constructed so as to be inflatable so that as the tyre inflates the boundaries form into position.

Where the air is contained in an inner tube, the inner tube itself might be formed with areas of constriction. These might be by having inelastic portions of a small diameter in between the conventional elastic portions or by having an internal constriction or by winding some constricting means around the inner tube so that it has a plurality of inflatable regions separated by narrow inelastic collars with small inner bores, connecting them.

The orifices/valves can be formed in a number of ways: 1. Individual orifces/valves between sub-chambers (see Figure 2); 2. Multiple orifices/valves between sub-chambers (see Figure 3); 3. The use of a porous material to allow air flow; 4. Air flow is around the edge of the structures used to form the sub-chambers (see Figure 4).

Note that for the purpose of this application, a valve is described as an orifice that allows air to pass through it but has a degree of control over the motion of the air, for example it only allows air to pass in one direction or it controls the air flow rate.

The invention will now be described with reference to the following drawings.

Figure 1 shows a typical automotive system with damping members, as may be found in many current text books; (10) represents the mass of the vehicle, (11) represents the mass of the wheel, (12) is the suspension damper, (13) is the suspension spring, (14) is the tyre modelled as a spring and (1 5) is the ground.

Figure 2 shows the air compartment of a tyre (21) and wheel (22) combination.

Members block a cross section of the annulus with, in this case, a single orifice (20) to permit air transfer. In this case it is simply a hole but it is to be appreciated that this could be a valve. The position of the hole is shown in this case at the centre, but this is for illustration only. Manufacturing, strength or other considerations might dictate that the hole should be placed in a different part of the member; a person skilled in the art of wheel systems would be able to determine the most efficient configuration to maxim ise damping within a dynamic system in such as way as to maintain optimum efficiency of the entire system.

Figure 3 shows the invention applied to an inner tube (33) for a pneumatic tyre (30).

There is a plurality of orifices or valves (32). It is to be appreciated in both Figure 2 and Figure 3 that the members should be selected from a material that is sufficiently durable to maintain its function in use but not so rigid as to damage the tyre or wheel should the tyre deflate.

Figure 4 shows the invention where the sub-chamber boundaries are formed by free floating members (42). In this case the air path between sub-chambers is around the outside of the free floating barriers (43).

Figure 5 shows an annular chamber which is filled with hollow cells (53). These cells have airtight walls where most or all of the cells have orifices/valves in their walls. The orifices could join directly between sub-chambers or open into the annular chamber.

Sub-chambers may be joined together, either as part of the manufacturing process of the chambers (for example, foam) or pre-formed chambers may be joined. The cells may or may not be attached to the tyre (51), wheel (52) or both. The orifices/valves could be formed in bulk before being set into the annulus, or formed once in the annulus. The cells are formed from a resilient material.

Claims (11)

1. Pneumatic lyre Damping Means -Claims 1. A damping means for a pneumatic tyre, said tyre forming an annular chamber when in use, said damping means comprising a plurality of dividing members located within the annular chamber, thereby creating one or more sub-chambers, said dividing members being formed so as to substantially restrict but not prevent air flow between the sub-chambers.
2. 2. A device as claimed in claim 1 in which the dividing member is perforated to allow air to flow through it.
3. 3. A device as claimed in claim 1 in which the dividing member is dimensioned to provide one or more air gaps at an interface with a wall of the annular chamber.
4. 4. A device as claimed in any of claims 1 to 3 in which the dividing member is fixed to the tyre.
5. 5. A device as claimed in any of claims 1 to 3 in which the dividing member is fixed to the wheel.
6. 6. A device as claimed in any of claims 1 to 3 in which the dividing member is free floating.
7. 7. A device as claimed in any of claims 1 to 3 in which the dividing member is attached to one or more other members.
8. 8. A device as claimed in claim 1 in which the air is contained within an inner tube.
9. 9. A device as claimed in claim 7 in which the inner tube comprises one or more constrictions.
10. 10. A device as claimed in claim 8 in which the constrictions are formed by adding additional members to the inner tube.
11. 11. A device substantially as described with reference to Figures 2 to 5.