GB2273785A - Wheel alignment measuring system - Google Patents

Abstract

A wheel alignment measuring system has front wheel clamps (17, 18) each carrying a forwardly projecting arm (22) having an angle sensor bracket (23, 24) having dual operation. Inwardly directed toe tracking arms (32, 33) extend towards each other across the front of the vehicle and are linked by an elastic cord (34). Rearwardly projecting arms (29) are linked by elastic side cords (30, 31) to forwardly projecting tracking arms (28) of rear angle sensors (26, 27) clamped to the rear wheels (13, 14). Conventional angle sensors (26, 27) detect the angle of tracking arms (28). The dual function angle sensors (23,24) on the front of the vehicle each comprise a potentiometer (55) journalled in a movable body (62) which can be raised or lowered by a solenoid (67), thereby causing either an upper drive finger (60) or a lower drive finger (61) to engage a drive connector (65 or 66). Thus, potentiometer measurements can be made in response to rotation of the upper drive connector (65) connected to the elastic front cord (34) or to the lower drive connector (66), influenced by one of the elastic side cords (31). The advantage of the arrangement is that all the elastic cords (31, 34) are left in position throughout the measuring of the wheel alignment measurements, specific readings being taken by selecting appropriate function of the dual function angle sensor. <IMAGE>

Description

WHEEL ALIGNMENT MEASURING SYSTEM This invention relates to a wheel alignment measuring system.

For good road handling and safety and to reduce wear on the tyres and suspension of a vehicle, accurate wheel alignment is required. Many individual angles and combinations of angles must be measured precisely and compared with manufacturers specifications and tolerances, to enable adjustment to suspension elements to be made where necessary. Adjustments may then need to be checked to ensure that they have corrected any misalignments originally measured.

In a basic wheel alignment measurement system, the vehicle is mounted with the steerable wheels on measuring turntables, each wheel has a clamp secured to it and angle sensors are attached to the clamps to take the necessary measurements.

For example it is necessary to measure the amount of toe-in or toe-out of the front and rear wheels, the camber and castor angles and the deviation of the thrust axis from the axis of symmetry of the vehicle. Some of these measurements are calculable from readings taken relative to a line from one front wheel to the rear wheel on the same side of the vehicle.

Others require readings to be taken between the front wheels of the vehicle.

A major problem with a conventional wheel alignment measurement system is that, as the operator proceeds through the measurement procedure, the angle sensors have physically to be connected by elastic cords stretched between them. For some measurements the cords need to be stretched between the left front and left rear wheel, and the right front and right rear wheel. For other measurements, a cord needs to be stretched from the left to the right front wheel. Each different reading requires connection of some and disconnection of other elastic cords. The necessary sequence of taking the measurement is such that the operator has repeatedly to attach and detach the elastic cords which is time consuming, tiring and requires a skilled operator. If the connections are incorrectly made, the measurement resulting will be nonsensical.

It has been proposed to make a wheel alignment measuring system in which the elastic cords are kept in place permanently throughout the measuring procedure. However it has hitherto not been possible to achieve this desirable result without the use of six angle sensors. Each rear wheel carries a single angle sensor and each front wheel carries two angle sensors, one of which is connected by an elastic cord to the rear wheel angle sensor on the same side of the vehicle and the other of which is connected across the vehicle to the opposite side front wheel angle sensor.

It is an object of the present invention to provide a wheel alignment measuring system which overcomes or reduces these disadvantages.

According to the invention there is provided a wheel alignment measuring system comprising a pair of rear wheel measuring units, each adapted to be clamped to the respective rear wheels of a vehicle and a pair of front wheel measuring units each adapted to be mounted on a mounting arm, the mounting arm projecting forwardly in use from a clamp attached to a respective front wheel, the four wheel measuring units being adapted to be connected throughout the period of use by two elastic side cords extending from the front to the rear wheel measuring units and by an elastic front cord extending between the front wheel measuring units.

The rear wheel measuring units may each have a forwardly projecting tracking arm and the front wheel measuring units may have a rearwardly projecting tracking arm connected by the side cord to the forwardly projecting tracking arm on the same side of the vehicle.

The front wheel measuring units may also have respective laterally inwardly extending toe tracking arms connected by the front cord.

Each wheel measuring unit may comprise an angle sensor.

Preferably, the angle sensor comprises a potentiometer.

It is an object of a further aspect of the invention to provide a potentiometer for use in a wheel alignment measuring system.

According to this aspect of the invention the potentiometer is provided with a pair of rotary input shafts, the potentiometer being selectively connectable to one or the other of said shafts but not to both.

The potentiometer may be journalled for rotation on a journal member selectively movable between extreme conditions in which one or the other of the input shafts is connected to the potentiometer.

The journal member may be movable by a solenoid.

The solenoid may be operated under operator control or may be controlled according to a preselected programme under the influence of a central processing unit.

The journal member may be mounted on a pair of swinging limbs so as to achieve the same lateral position of the potentiometer in the two extreme positions of the journal member.

An embodiment of the invention will now be described in more detail by way of example only with reference to the accompanying drawings in which Figure 1 is a diagrammatic plan view of a wheel alignment measuring system embodying the invention attached to a vehicle, Figure 2 is a side elevational view of the system of Figure 1, Figure 3 is a sectional view through an angle sensor of a front wheel measuring unit.

Referring to Figures 1 and 2 of the drawings a four wheeled vehicle is diagrammatically represented at 10, the front wheels being shown at 11 and 12 and the rear wheels at 13 and 14. The steering wheel is represented at 15.

A wheel alignment measurement system generally indicated at 16 includes four wheel clamp devices 17, 18, on the front wheel and 19, 20 on the rear wheels. Each wheel clamp device 17 to 20 is of any suitable known type capable of making a secure fixing to a vehicle wheel.

On each of the front wheel clamps 17, 18, a mounting means 21 carries a forwardly projecting arm 22 which is provided with suitable means such as a spirit level (not shown) for levelling it. The mount 21 and arm 22 form part of a wheel measuring unit which also includes an angle sensor 23, 24 associated with the wheels 11 and 12 respectively.

Each of the rear wheels 13, 14 also has a mounting means 25 forming part of a wheel measuring unit incorporating another angle sensor 26, 27 associated with the wheels 13 and 14.

The rear angle sensors 26 and 27 each have a forwardly projecting tracking arm 28. A rearwardly projecting tracking arm 29 is provided on each of the forward angle sensors 24, and is linked by an elastic cord 30, 31, running along the right and left hand sides of the vehicle respectively.

Measurements taken from the angle sensors therefore enable the position and orientation of the front and rear wheels to be measured relative to each other.

In addition to the tracking arms 29, each of the front wheel measuring unit angle sensors 23, 24 has a toe tracking arm 32, 33 extending towards each other and linked by an elastic front cord 34 in use.

Throughout the use of the wheel alignment measurement system 16, all three of the elastic cords 30, 31 and 34 are connected in place and are not removed. A series of measurements is taken indicating for example the toe-in or toe-out of the front or rear wheels, the amount of toe-out on turns measured as the steerable front wheels 11 and 12 are turned first to one side and then to the other and other required angles are measured without removal of the cords.

This is achieved because each of the angle sensors 23 and 24 is a dual function angle sensor, capable of measuring angles detected both by the rearwardly projecting tracking arms 29 and by the toe tracking arms 32 and 33.

Referring to Figure 3 of the drawings one of the angle sensors 23 is illustrated in more detail and comprises a rigid housing 50 having bearings 51 and 52 which receive upper and lower rotary input shafts 53 and 54. The upper rotary input shaft 53 is connected to the toe tracking arm 32 and the lower rotary input shaft 54 is connected to the rearwardly extending tracking arm 29.

A potentiometer 55 of conventional construction is mounted within the housing 50. Its input shaft 56 is mounted in a cross piece 57 which in turn has upper and lower actuating limbs 58, 59 rigidly secured to it. The actuating limbs have respective fingers 60, 61 which are arranged to be coaxial with the shaft 56 of the potentiometer.

The potentiometer shaft 56 is journalled in a movable body 62 which can swing upwardly or downwardly on a pair of parallel leaf springs 63 bolted at 64 to one side wall of the casing.

The arrangement is such that the movable body 62, in a central neutral condition, corresponds with the leaf spring 63 being parallel and at right-angles to the wall of the housing.

Upward movement of the leaf springs brings the finger 60 into engagement with a forked drive connector 65 rotatable with the upper input shaft 53. Downward movement of the leaf springs causes the finger 60 to clear the drive connector 65 and causes the finger 61 simultaneously to engage a drive connector 66 rotatable with the lower input shaft 54.

Thus, according to whether the leaf springs are turned upwardly or downwardly, the movable body 62 carries the potentiometer into driven engagement with either the upper drive shaft53 or the lower drive shaft 54. At no time can both shafts be connected to the potentiometer.

The movable body 62 is caused to move upwardly or downwardly by the operation of a solenoid 67 under operator control.

If desired, the movable body 62 can be spring loaded for example by means of the spring 68 to adopt one condition of engagement in the absence of a signal from the solenoid 67.

In view of the parallelogram type linkage using the two leaf springs 63, the upper and lower positions of the potentiometer 55 are aligned with the axis of rotation of the upper and lower drive shafts 53 and 54, although at intermediate positions, the potentiometer may swing slightly out of line.

However during this out of line portion of the movement, the fingers 60 and 61 are both disengaged from their respective drive formations 65 and 66.

In use, the potentiometer can therefore measure an angle of the toe tracking arm 32 or an angle of the rearwardly extending tracking arm 29 at the front of the vehicle. A conventional potentiometer forms the angle sensor 26 or 27 at the rear of the vehicle and is not illustrated since it is of conventional design. Angle readings can be taken separately of the angular positions of the tracking arm 29 and toe tracking arm 32, the selection of which angle is used being either under operator control or under sequenced control by a central processing unit 100 of the apparatus, which receives signals from each of the angle sensors 23, 24, 26, 27.

Throughout the operation of the wheel alignment measuring system, the elastic cords 30, 31 and 34 are all left in place and do not need to be attached or removed to take different measurements.

It will be appreciated that, as in all wheel alignment measurement systems, compensation may need to be made for wheel run out, that is the distortion of the wheel rim relative to its axle before any measurements are taken.

Claims (20)

1. A wheel alignment measuring system comprising a pair ofrear wheel measuring units each adapted to be clamped to the respective rear wheels of a vehicle and a pair of front wheel measuring units each adapted to be mounted on a mounting arm, the mounting arm projecting forwardly in use from a clamp attached to a respective front wheel, the four wheel measuring units being adapted to be connected together throughout the period of use by two elastic side cords extending from the front to the rear wheel measuring units and by an elastic front cord extending between the front wheel measuring units.

2. A wheel alignment measuring system according to claim 1 wherein each rear wheel measuring unit has a forwardly projecting tracking arm and each front wheel measuring unit has a rearwardly projecting tracking arm connected by the side cord to the forwardly projecting tracking arm of the rear wheel measuring unit on the same side of the vehicle.

3. A wheel alignment measuring system according to claim 2 wherein the front wheel measuring units also have respective laterally inwardly extending toe tracking arms connected by the front cord.

4. A wheel alignment measuring system according to any preceding claim wherein the measuring unit comprises an angle sensor.

5. A wheel alignment measuring system according to claim 4 wherein the angle sensor comprises a potentiometer.

6. A wheel alignment measuring system according to claim 5 wherein the potentiometer has a pair of rotary input shafts, the potentiometer being selectively connectable to one or the other of said rotary input shafts but not to both.

7. A wheel alignment measuring system according to claim 6 and journalled for rotation on a journal member selectively movable between extreme conditions in which one or the other of the input shafts is connected to the potentiometer.

8. A wheel alignment measuring system according to claim 7 wherein the journal member is movable by a solenoid between said extreme conditions.

9. A wheel alignment measuring system according to claim 8 wherein the solenoid is operated under operator control.

10. A wheel alignment measuring system according to claim 8 wherein the solenoid is controlled according to a pre-selected programme under the influence of a central processing unit.

11. A wheel alignment measuring system according to any one of claims 7 to 10 wherein the journal member is mounted on a pair of swinging limbs so as to achieve the same lateral position of the potentiometer in the two extreme positions of the journal member.

12. A potentiometer having a pair of rotary input shafts, the potentiometer being selectively connectable to one or the other of said shafts but not to both.

13. A potentiometer according to claim 12 and journalled for rotation on a journal member selectively movable between extreme conditions in which one or the other of the input shafts is connected to the potentiometer.

14. A potentiometer according to claim 13 wherein the journal member is movable by a solenoid.

15. A potentiometer according to claim 14 wherein the solenoid is operated under operator control.

16. A potentiometer according to claim 14 wherein the solenoid is controlled according to a preselected programme under the influence of a central processing unit.

17. A potentiometer according to any one of claims 13-16 wherein the journal member is mounted on a pair of swinging limbs, the potentiometer having the same lateral position in the two extreme positions of the journal member.

18. A vehicle wheel alignment measuring system comprising a pair of rear wheel measuring units, each adapted to be clamped to the respective rear wheels of a vehicle and a pair of front wheel measuring units each adapted to be mounted on a mounting arm, the mounting arm projecting forwardly in use from a clamp attached to a respective front wheel, the four wheel measuring units being adapted to be connected throughout the period of use by two elastic side cords extending from the front to the rear wheel measuring units and by an elastic front cord extending between the front wheel measuring units, each rear wheel measuring unit having a forwardly projecting tracking arm and each front wheel measuring unit having a rearwardly projecting tracking arm connected by a respective side cord to the forwardly projecting tracking arm on the same side of the vehicle, each front wheel measuring unit also having a respective laterally inwardly extending toe tracking arm, said toe tracking arms being connected by the front cord, wherein each front wheel measuring unit comprises an angle sensor afforded by a potentiometer having a pair of rotary input shafts, the potentiometer being selectively connectable to one or the other of said rotary input shafts but not to both.

19. A wheel alignment measuring system substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

20. A potentiometer substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.