GB2028521A

GB2028521A - Improvements in or relating to turntables for vehicle wheels

Info

Publication number: GB2028521A
Application number: GB7926877A
Authority: GB
Original assignee: Dunlop Ltd
Current assignee: Dunlop Ltd
Priority date: 1978-08-18
Filing date: 1979-08-01
Publication date: 1980-03-05
Also published as: DE2932221A1; JPS5530697A; AU4970079A; FR2433736A1; ZA794044B

Abstract

A turntable (1) for measuring various characteristics of the steered wheels of a vehicle comprises two relatively rotatable members (2, 3) located by an axle (4) and an aperture 5 and having a substance acting between the confronting surfaces to reduce friction between the members during said relative rotation. The substance may be a PTFE coating or a grease conveniently located in a greaseway (7) formed in one or both of the cooperating surfaces of the members (2,3). The turntable (1) also includes gauge means (8, 11) for measuring relative rotation between the members (2, 3) and locking means (9) for locking the members (2, 3) at one or more predetermined positions. <IMAGE>

Description

SPECIFICATION Improvements in or relating to turntables for vehicle wheels This invention concerns improvements in or relating to turntables for vehicle wheels and in particular to turntables used for measuring various characteristics of the steered wheels, usually the front wheels.

Turntables are known which comprise a pair of relatively rotatable members with a gauge for measuring the angular movement between the members.

Various bearing assemblies have been proposed to allow the top member, on which a vehicle wheel is disposed to rotate freely relative to the base member. One such assembly includes the provision of radially extending rollers in the upper surface of the base member on which the lower surface of the top member rotates.

A disadvantage of this and other similar known bearing assemblies is that they considerably complicate the manufacture and assembly of the turntable and also require the use of some means to prevent axial separation of the members which could release the rollers. As a result such turntables are relatively expensive to produce.

A further disadvantage is that in order to accommodate the rollers or indeed any bearing assembly the base member at least has to be made relatively thick so that the turntable is relatively heavy and awkward to handle.

Furthermore because the turntable has a considerable depth it is necessary to jack up the rear wheels in order to keep the vehicle level before taking any readings to prevent errors due to the wheels being at different heights. This is a time-consuming operation which considerably increases the time taken to check each vehicle.

It is an object of the present invention to provide a turntable for vehicle wheels which reduces at least some of the above disadvantages of the known turntables.

According to the present invention we provide a turntable for a vehicle wheel comprising first and second relatively rotatable members having a substance between adjacent co-operating surfaces of the members to allow relative rotation between the members.

Preferably the substance is a viscid material, for example grease, which also holds the members together especially during handling. Alternatively or in addition the substance may comprise a coating of low friction material, for example polytetrafluoroethylene (PTFE) on one or both of the co-operating surfaces or an element of low friction material.

According to another aspect of the present invention we provide a turntable for a vehicle wheel comprising first and second relatively rotatable members at least one of which is made of material having a low coefficient of friction to allow relative rotation between the members.

One member only may be made of low friction material, for example high density polyethylene, preferably that member which in use is uppermost i.e. that on which the vehicle tyre is located.

Preferably the upper surface of the member is adapted to have a high coefficient of friction relative to a vehicle tyre to avoid relative movement between the tyre and upper surface in use of the turntable, for example the upper surface may have a coating of high friction material or the surface may be serrated or otherwise modified to increase its coefficient of friction relative to a vehicle tyre.

The turntable includes gauge means for indicating relative angular movement between the members. Preferably the gauge means comprises a reference zero on one member and a scale on the other member.

Preferably the turntable includes locking means for preventing relative angular movement between the members. Conveniently the locking means is operable to lock the members in a reference position in which the gauge means is zeroed. The locking means may be operable to lock the members at angularly offset positions.

Preferably the locking means comprises a pin in engagement with an aperture in the turntable to prevent relative angular movement between the members, the pin being removable to allow relative angular movement between the members.

In one preferred construction the members comprise a pair of discs one of which has a central stub axle on which the other disc, having a centre aperture to receive the stub, is rotatably mounted.

The turntable preferably has a handle which is conveniently secured to that disc which in use comprises the lower or base member.

The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings wherein Figure 1 is a perspective view of a turntable according to the invention; Figure 2 is a side view of the turntable shown in Figure 1, and Figure 3 is a plan view of the base member of the turntable shown in Figures 1 and 2.

The turntable 1 shown in the accompanying drawings comprises a base member 2 and a top member 3 each in the form of an annular disc. The base member 2 has an upstanding stub axle 4 received in a central aperture 5 in the top member.

A suitable grease is provided between the adjacent co-operating surfaces of the members to allow the top member 3 to rotate freely relative to the base member 2. As shown in Figure 3 the cooperating surface 6 of the base member has a greaseway 7 which comprises inner and outer annular grooves 7a and 7b respectively connected by plurality of uniformly spaced radially extending grooves 7c. The greaseway 7 channels excess grease from any area of contact between the cooperating surfaces and ensures the grease is applied substantialiy evenly over the entire area of contact. The grease is selected so as to be sufficiently viscid that the members 2, 3 are held together by the presence of the grease only and no other retaining means is necessary.However the members 2, 3 can easily be prised apart by inserting a thin blade, for example a screw-driver, between the members to allow the grease to be replenished as necessary.

The turntable 1 further comprises gauge means 8, locking means 9 and a handle 10.

The gauge means 8 comprises a reference zero (not shown) on the circumferential edge of the base member 2 and a scale 11 on the top member 3. The scale 11 is marked in degrees from 0 to 90 to either side of a central zero.

The locking means 9 comprises a pin 1 2 which is located in a radially extending aperture 1 3 in the turntable 1. As shown the aperture 13 is formed by aligned, radially extending grooves 1 3a, 1 3b in the adjacent co-operating surfaces of the members 2, 3. When the pin 12 is in the locked position shown in the drawings the members 2, 3 are held against relative rotation in a reference position in which the reference zero on the base member 2 is aligned with the central zero of the scale 11 on the top member.

The pin 1 2 is attached to the turntable by a length of wire 14 secured to the handle 10 to prevent the pin being lost when removed from the aperture.

The above described turntable facilitates the measurement of the differential angles of vehicle wheels. In use, each front wheel of the vehicle is centrally positioned on a respective turntable 1.

The turntables 1 are held in the reference position by the pins 12 which prevents relative rotation between the members 2, 3, when the vehicle wheels are positioned. The pin 12 is then removed and the conventional steering checking procedure can be carried out by steering the wheels to the right or left and checking the angles by taking the reading of the scale 11 against the reference zero.

In this way toe in/toe out, wheel lock angle and full lock measurements can be made as is well known to those skilled in the art and further description is not necessary.

It will be appreciated that the above described turntable is relatively simple and inexpensive to manufacture since no complicated bearing assembly is required to allow relative rotation between the members. The turntable can therefore be made thinner than the known turntables. As a result a vehicle can be driven onto the turntables and it is often possible to check the front wheels disposed on the turntables without having to raise the rear wheels to level the vehicle prior to taking any readings, since the errors introduced by having the wheels at different heights will be considerably reduced, especially for relatively long vehicles such as lorries.

Furthermore the turntable can be made from any suitable metal, for example steel, or alloy, for example aluminium alloy or even plastics material so that the turntable can be made relatively light in weight and is easily handled.

Additionally it will be appreciated that the selecting a viscid material which allows the members to rotate freely relative to one another but prevents axial separation of the members even if the turntable is turned over or dropped during handling, the turntable according to the invention is considerably more robust than the known turntables in which the complicated bearing assemblies can be easily damaged if the turntable is dropped.

It will be understood that the above-described turntable can be modified in a number of ways.

For example the substance may comprise a coating of material having a low coefficient of friction, for example polytetrafluoroethylene (PTFE), on one or both of the co-operating surfaces or an element, for example a disc, made of material having a low coefficient of friction between the members. The coating or disc may be provided in addition to the viscid material so as to further reduce friction between the co-operating surfaces or may be provided in place of the viscid material. The stub axle may comprise a stem portion releasably secured to one member and an enlarged head portion which is received in a stepped bore of the other member so as to prevent axial separation of the members whilst allowing relative rotation.

One of the members 2, 3 may be provided with addtional radially extending grooves so that the turntable can be locked at predetermined angular positions by aligning a groove with the groove in the other member and then inserting the pin.

The scale 8 could be on the base member 2 and the reference zero on the top member 3.

Alternatively the top member could have a reference mark or scale which is aligned with a scale or reference mark on the surface on which the turntable is used.

The pin and aperture (s) in the turntable may have any complementary cross-sections for example, rectangular, round, oval etc.

The aperture in the turntable may be formed by aligning axially extending holes in the members.

The locking means may be of any appropriate type, for example friction means such as an axially extending screw in the top member which can be tightened to frictionally engage the base member.

In an alternative construction (not shown) the turntable is substantially similar to that described above comprising two relatively rotatable members except that at least one of the members is made of material having a low coefficient of friction to allow relative rotation between the members. Preferably that member which in use is uppermost i.e.that on which the tyre is located, is made of low friction material, for example high density polyethylene, and the upper surface thereof is adapted to have a high coefficient of friction relative to the vehicle tyre to avoid slippage between the tyre and member in use of the turntable. For example the upper surface may have a coating of high friction material or may be serrated.

Claims

1. A turntable for a vehicle wheel comprises first and second relatively rotatable members having a substance between adjacent co operating surfaces of the members to allow relative rotation between the members.

2. A turntable according to claim 1 wherein the substance comprises a viscid material.

3. A turntable according to claim 1 or claim 2 wherein the substance comprises a coating of material having a low coefficient of friction on one or both of said co-operating surfaces.

4. A turntable according to claim 1 or claim 2 wherein the substance comprises an element made of material having a low coefficient of friction.

5. A turntable for a vehicle wheel comprises first and second relatively rotatable members at least one of which is made of material having a low coefficient of friction to allow relative rotation between the members.

6. A turntable according to claim 5 wherein that member which in use of the turntable is upper most is made of low friction material and the upper surface thereof is adapted to have a high coefficient of friction relative to a vehicle tyre.

7. A turntable according to claim 6 wherein said upper surface has a coating of material having a high coefficient of friction.

8. A turntable according to claim 6 wherein said upper surface is serrated.

9. A turntable according to any one of the preceding claims including gauge means for indicating relative angular movement between the members.

10. A turntable according to claim 9 wherein the gauge means comprises a reference zero on one member and a scale on the other member.

11. A turntable according to any one of the preceding claims including locking means for preventing relative angular movement between the members.

12. A turntable according to claim 11 wherein the locking means comprises a locking member located in an aperture in the turntable.

1 3. A turntable according to claim 12 wherein the aperture is defined by a pair of radially extending aligned grooves in the co-operating surfaces of the members and the locking member comprises a removable pin.

14. A turntable according to claim 1 3 wherein the co-operating surface of one of the members is formed with a plurality of radially extending grooves to allow the members to be locked in a plurality of angularly spaced positions.

15. Aturntable according to claim 2 wherein one or both of the co-operating surfaces is formed with a greaseway.

1 6. A turntable according to claim 1 5 wherein the greaseway comprises a network of interconnected grooves.

17. A turntable according to any one of the -.

preceding claims wherein the members comprise a pair of discs one of which has a central stub axle received in a central aperture in the other member to allow relative rotation between the members.

18. A tu mtabie substantially as hereinbefore described with reference to the accompanying drawings.