GB2236863A

GB2236863A - Wheel tracking

Info

Publication number: GB2236863A
Application number: GB8923120A
Authority: GB
Inventors: Justin Frederick Deverau Hardy
Original assignee: Individual
Current assignee: Individual
Priority date: 1989-10-13
Filing date: 1989-10-13
Publication date: 1991-04-17
Also published as: GB8923120D0

Abstract

Wheel tracking checking apparatus includes a pair of structures, (11) one being used on each side of the vehicle. Each structure includes a pair of pointers (21, 22) which are arranged to be vertically movable and horizontally adjustable so as to be placable at the foremost and rearmost ends of a vehicle wheel rims. A scale (34) is provided on each structure for indicating the separation of the two pointers, and a further corresponding scale (35) is provided being larger than the scale (34) by a factor such as 2. With the two structures (11 and 12) arranged one at each side of the motor vehicle and the pointers touching the appropriate parts of the vehicle wheel rims, the tracking is obtained by measuring the distance separating the two scales (35) at two predetermined positions along the scales (35) and dividing the difference therebetween by the factor by which the scale (35) is greater than the scale (34). <IMAGE>

Description

WHEEL TRACKING.

This invention relates to a method of apparatus for measuring the "tracking" of the wheel of a motor vehicle.

Heretofore, measuring of the tracking of vehicle wheels has required relatively expensive equipment which can only really be afforded by large garages who charge motorists quite considerable sums. The tracking of the wheels of a motor vehicle is the amount by which the two wheels differ from absolute parallelism. In most vehicles the leading edges of the wheels are closer together than the rear edges and this is known as "toe-in". Due to wear in the various linkages involved in steerable wheels, tracking can often vary in use and during maintenance and service it is important that the tracking is checked and adjusted if necessary to be within the manufacturers specification.Usually, the toe-in is specified as being an angle (for example 1 - 2" or simply a distance say 8 - 15mm). This distance represents the difference between the separation of the front edges of the vehicle wheel and the rear edges of the vehicle wheels (exluding the tyres).

The expensive known apparatus to measure the tracking angle has included large installations in garages upon which the vehicle has to be driven and then gauges applied to the two spaced apart wheels, the gauges being electrically or electronically interconnected to give the toe-in angle either as an angle or as a distance. Another known apparatus has stands one on each side of the vehicle which are aligned with the wheels and then mirrors on the two stands are observed via a sighting tube and the tracking angle read from a scale. Because of the use of mirrors, it is always essential that the two stands are arranged to be absolutely steady (not always possible on rought garage floors) and the equipment has to be set up and adjusted quite carefully. Of course, the mirrors being fragile make the device require careful storage.These disadvantages makes the device unsuitable for use by small garages and/or by amateur mechanics who would not have the facilities for careful storage or the funds to afford a very expensive apparatus to be used relatively occasionally.

It is an object of the present invention to provide a method of and apparatus for measuring wheel tracking which is simple and cheap in construction and easy to use.

According to the invention there is provided wheel tracking checking apparatus including a matched pair of structures, each structure including a base and a pair of pointers supported by the base and being adjustable in height and separation to be capable of disposition adjacent respective front and leading edges of vehicle wheels, the two bases having correspondingly spaced markings indicating positions at which, in use, the separation of the two bases can be measured to indicate the angle between the two bases and hence the tracking angle.

The markings on each structure could be spaced apart by a distance equal to the spacing of the pointers, but this would place the markings very close to the vehicle tyre and would make measuring rather difficult. For this reason it is advantageous if the separation between the indicia on the base is greater than the separation of the pointers by a known factor. From a measurement of the separation at the markings and a knowledge of the factor the tracking separation between the two pointers can easily be ascertained. For convenience the factor is best chosen to be a simple whole number such as 2.

However, other factors such as 1i or 3 can be provided although more calculation will be necessary in those cases.

As the separation of the pointers is variable to cope with wheels of different diameters, it is convenient if one of the pointers is fixed and the other is movable along a scale relative thereto, that scale being complementary to a scale on the body which indicates the measuring points. In use, when the movable pointer has been placed to act on a particular point on the first scale, the user uses a corresponding point on the second scale to effect measurement.

In the convenient form when the second distance is twice the pointer separation, the scale on the base could conveniently be marked in the same way as the first scale in relation to the pointer but have divisions which are twice as large.

The movability of the pointers can be achieved by the base supporting an arch whose limbs are movable vertically relative to the base. A cross piece of the arch can carry a slider on which the movable pointer is carried.

The invention includes a method of measuring the tracking of a pair of vehicle wheels including positioning apparatus as aforesaid so that a respective one of said structures is arranged with its pointers in register with the medium front and rear edges of a vehicle wheel and measuring the separation of the two structures at positions spaced apart in the direction of a line interconnecting the pointers and subtracting the smaller measurement from the larger to obtain a measurement which is indicative of the tracking.

The separation of the two measuring positions can be equal to the separation of the two pointers so that said difference measurement is the tracking measurement. Alternatively, said measuring distance can be a factor greater than the interpointer distance so that said difference measurement is greater than the tracking measurement by said factor.

Preferably said factor is a convenience factor such as 1.5, 2, 2.5 or 3. A factor of 2 has been found to be particularly satisfactory.

The apparatus will be described further, by way of example, with reference to the accompanying drawings wherein : - Fig. 1 is a schematic side elevation illustrating part of preferred apparatus of the invention in use; Fig. 2 is a plan view, comparable to Fig. 1, illustrating the apparatus of the invention; and Fig. 3 is a partial perspective view illustrating apparatus of the invention in use in a practical form.

Referring to the drawings, it will be seen that preferred apparatus 10 of the invention includes a pair of structures 11,12. These structures 11,12 are complementary, being essentially mirror images of each other. The structure 11 is adapted for use with a front offside wheel 13 of a vehicle and the structure 12 is adapted for use with a front near side wheel 14 of the vehicle. Because of possible variations in tyre diameter due to the use of different types of tyre, it is normal for tracking to be measured in relation to the wheel rim. In the drawings, the wheel rims are indicated by reference numeral 15 and 16 and their associated tyres by reference numberal 17,18.

the front of the vehicle is to the left in Fig. 2.

Each structure 11, 12 (see Fig. 3) includes an elongated base 19,20. Each base 19,20 mounts a pair of pointers 21,22,23,24. Each base 19,20 has a transverse stabiliser 25,26.

Figs. 1 and 2 illustrate the apparatus 10 of the invention schematically and are best suited to the description of the method of the apparatus and how the apparatus of the invention enables the method to be carried out. However, Fig. 3 best describes the physical characteristics of the two structures 11,12 and they will now be described in some detail. It will be seen that Fig. 3 illustrates only the structure 11 in detail. However, structure 12 is simply a mirror image of the structure 11 and does not need to be illustrated. The structure 11 includes a base 19 which is in the form of a flat piece of steel. At one end the base 19 has a transverse bar which constitutes a stabiliser 25. This discourages the structure 11 from tilting in use. Upstanding from the base 19 are a pair of hollow columns 27. Slidably received in the columns 27 are the parallel limbs 28 of an arch 29 whose cross piece 30 has at one end a fixed stub 31 which carries the fixed pointer 21 and along which cross piece 30 can travel a slider 32 which carries movable pointer 22. The movability of the pointers 21 and 22 in order that their height above the base 19 and their separation can be varied is provided in order that the apparatus can be used with wheels whose rims have different diameters. When using the apparatus, the height and separation of the pointers 21, 22, 24, 25 are first set to suit the wheels in question and the clamping screws (generally indicated at 33) or other comparable means are operated to prevent movement of the pointers.

The cross piece 30 bears a first scale 34. When separation of the pointers 21, 22 has been adjusted in order to match the rim diameter of the wheel in question a reading is taken from the scale 34 which determines the separation of the pointers 21 and 22.

A second scale 35 is provided on the base 19 as it is extended away from the arch 29 and its associated structure. Its zero or comparable base point 36 is provided on the base 19 and the scale 35 is so chosen that its length is a known multiple of the length between the pointer 21 and the poiner 22 on the scale 34. Conveniently, the distance between the zero point 36 and the point on the scale 35 is chosen to be twice the distance a between the pointer 21 and the pointer 22. The scales 34 and 35 can be very conveniently graduated such that the divisions on the scale 35 are double those of the scale 34. This means that calculations to determine the tracking angle is very simple. However, for various applications factors of 1.5, 2.5, 3 or other factors could be used.

However, they are far less convenient for the normal user.

The actual use of a tape measure 38 to determine the separation of the two structures 11 and 12 at the respective zero points 36 and at some place on the scale 35 is illustrated in Fig. 3. Each and every amateur mechanic has access to and is capable of using such a tape.

Figs. 1 and 2 illustrate how the apparatus is used in practice. As best seen in Fig. 2, the structure 11 is placed on the ground (supported by the stabiliser 25) adjacent the offside wheel 13. The structure 12 is disposed similarly adjacent the other offside wheel 14. The separation and height of the pointers 21, 22,23,24 is adjusted to be level with the leading and rear edges of the vehicle rim (best seen in Fig. 1). The structures 11,12 are then moved up until the pointers 21, 22 are touching the appropriate edges of their associated rims. In this condition the bases 19,20 extend parallel to their respective wheels 13,14. Thus, by measuring the separations of the two bases 19, 20 (or indeed any other comparable member or members forming part of structures 11,12) it is easy to ascertain the relative inclinations of the two wheels.

It should be emphasized here that this particular method does not give the tracking in the form of an angle. However, as the vehicle wheel tracking is invariably specified in makers specifications as being a distance as well as an angle this lack of an angular indication is not significant. In any case, most manufacturers, relying on standard sizes of wheels, can give a range of trackings measured by way of distance which are equivalent to various angles. If the angular tracking is needed it can easily be ascertained.

As will be appreciated from a look at Fig. 1, the tracking distance could be measured exactly by measuring at the points generally indicated at 39,40.

However, these points are very close to the tyre and there could be difficulty for the user in placing his tape measure 38 closely in the gap between the tyres and the ground. The tyre would block his view and placing the tape accurately could be a difficulty.

With the preferred method illustated in Figs. 2 and 3, the scales on the cross piece 30 and the base 19 are used to good effect. Measuring markings on the bases are provided at opposite ends of the chain dotted line 41. These measurements constitute a base or datum line indicated at 36. The second measurement is made on the scale 35 (Fig.3) at a position indicated by the second line 42. The separation between the line 41 and the line 42 is chosen (using the scale 35) to be a distance A which is twice the distance a which separates the pointers.

When the length of the line 41 and that of the line 42 have been ascertained, the smaller is subtracted from the larger and the difference is divided by 2 to give the tracking as a distance. This will normally be from, say, 0.75 to 2mm.

A very interesting result of using a distance A which is greater than the distance a is that the accuracy of the measurement is doubled. If the tracking were measured solely at points 39, 40 an accuracy of perhaps x% could be expected. However, by measuring the distances at lines 41 and 42 wherein A is double a, an accuracy of x/2% can be achieved.

This can be quite an important factor wherein measurements made by an amateur mechanic on relatively simple apparatus would be expected to be less accurate than measurements made under very controlled and professional conditions. It will be appreciated here, of course, that in vehicles wherein the tracking is of very significant accuracy bases 19, 20 of considerable length, (for example 3 or more times the separation of the pointers 21,22) could be used to achieve greater accuracy.

The apparatus can be constructed very cheaply and simply from readily available mild steel sections and at a price which can be afforded by even amateur mechanics.

Of course, the precise construction of the apparatus need not be as described. The two structures can be of any convenient configuration provided that they are stable and can be arranged so that their pointers are in register with the relevant portions of a vehicles wheels.

Many other variations can be made within the scope of the invention.

Claims

1. Wheel tracking checking apparatus including a matched pair of structures, each structure including a base and a pair of pointers supported by the base and being adjustable in height and separation to be capable of disposition adjacent respective front and leading edges of vehicle wheels, the two bases having correspondingly spaced markings indicating positions at which, in use, the separation of the two bases can be measured to indicate the angle between the two bases and hence the tracking angle.

2. Apparatus as claimed in Claim 1 wherein the markings on each structure are spaced apart by a distance equal to the spacing of the pointers.

3. Apparatus as claimed in Claim 1 wherein the separation between the indicia on the base is greater than the separation of the pointers by a known factor so that from a measurement of the separation at the markings and a knowledge of the factor the tracking separation between the two pointers can easily be ascertained.

4. Apparatus as claimed in Claim 4 wherein the factor is chosen to be a simple whole number such as 2 or 3.

5. Apparatus as claimed in Claims 1-4, wherein one of the pointers is fixed and the other is movable along a scale relative thereto, that scale being complementary to a scale on the body which indicates the measuring points.

6. Apparatus as claimed in Claim 4, wherein the factor is 2, and the scale on the base marked in the same way as the first scale in relation to the pointer but has divisions which are twice as large.

7. Apparatus as claimed in Claim 6, wherein movability of the pointers is achieved by the base supporting an arch whose limbs are movable vertically relative to the base, a cross piece of the arch carrying a slider on which the movable pointer is carried.

8. Wheel tracking apparatus substantially as described with reference to the accompanying drawings.

9. A method of measuring the tracking of a pair of vehicle wheels including positioning apparatus as claimed in any of claims 1 - 8 so that a respective one of said structures is arranged with its pinters in register with the medium front and rear edges of a vehicle wheel and measuring the separation of the two structures at positions spaced apart in the direction of a line interconnecting the pointers and subtracting the smaller measurement from the larger to obtain a measurement which is indicative of the tracking.

10. A method as claimed in Claim 9, wherein the separation of the two measuring positions is equal to the separation of the two pointers so that said difference measurement is the tracking measurement.

11. A method as claimed in Claim 9, wherein said measuring distance is a factor greater than the inter-pointer distance and said difference measurement is obtained by multiplying the tracking measurement by said factor.

12. A method Qf checking the tracking of a pair of vehicle wheels substantially as described with reference to the drawings.