GB2168014A - Power adjusted variable track wheel - Google Patents

Abstract

A power adjusted variable track wheel comprises a rim (11) which carries internally helical rails (26 to 29) and a disc (10) which carries brackets (16 to 19) of bifurcated form which engage the rails between the limbs of the bifurcations. The rails and brackets have co-operating bolt holes so that the brackets may be secured to the rails at a number of different positions therealong by bolt assemblies (41). <IMAGE>

Description

SPECIFICATION Tractor wheels This invention relates to power-adjustable-variabletrack (PAVT) wheels. These wheels find their main use on tractors whereby the track of the tractor wheels can be varied using the power of the tractor.

A number of different constructions of PAVT wheels are known, each comprising a separate disc and rim. In some designs, the rim has secured to the inner periphery thereof a plurality of part-helical rails arranged in circumferentially-spaced relation. The disc carries brackets which engage the rails whereby, upon relative rotation between the disc and the rim, they are also moved relative to one another in directions parallel to the rotary axis of the wheel as the brackets move along the rails.

Such PVAT wheels are hereinafter referred to as being "of the type described".

In PAVT wheels of the type described the locking means which are provided to hold the brackets and rails in a desired position rely on friction between a movable locking member on each bracket and the rail with which the bracket engages. Because of the tolerances between the various parts of the wheel it is often only the final locking means to be tightened into frictional engagement with the rail which actually serves any useful purpose and with high-powered tractors working at or near their maximum capacity there has been slippage of the disc relative to the rim in such wheels.

It is an object of the present invention to provide a PAVT wheel of the type described which is economical and which is secure when in operation.

Moreover, PAVT wheels embodying the invention enable one to obtain a wheel with good lateral, i.e.

in directions parallel to the rotary axis of the wheel, and radial truth.

According to the invention we provide a PAVT wheel of the type described wherein each bracket is bifurcated and engages a rail between the limbs of its bifurcation, the bracket being provided with at least one bolt hole; and wherein each rail is provided with a plurality of bolt holes, the wheel being adjusted by bringing the bolt holes in the brackets into alignment with bolt holes in the rails, inserting bolts through the aligned holes and securing the bolts in position.

Preferably there are two bolt holes in each bracket, preferably, also, the bolt hole or bolt holes is or are in one only of the limbs of the bifurcation, the other limb serving only to retain the bracket on the rail.

Because the rails are bolted to the brackets considerable lateral stiffness and truth are obtainable in the wheel.

Preferably each bracket is bolted to the disc and the disc and the bracket each have two faces at right angles which are in mutual engagement.

Preferably, the disc is in the shape of a square with its corners cut off, thus to produce an irregular octagon, having longer sides and shorter sides alternatively arranged around the periphery of the octagon, the brackets being secured to each shorter side by a pair of bolts. The edge of each shorter side may provide one of said faces.

The invention will now be described in detail by way of example with reference to the accompanying drawings in which: Figure l is a front elevation of a wheel embodying the invention; Figure 2 is a part-section on the line 2-2 of Figure 1; Figure 3 is a detail elevation showing how one of the brackets engages a rail; Figure 4 is a view of the parts in Figure 3 in the direction of the arrow 4 in Figure 3; and Figure 5 is a perspective view of one of the brackets.

Referring first to Figure 1, the PAVT wheel there shown comprises a disc 10 and a rim 11.

The disc is of uniform thickness and in elevation has the shape of an irregular octagon formed by taking a square and cutting off the corners so that the disc has four longer sides 12 and four shorter sides 13, the sides 12 and 13 being arranged alternately around the periphery of the disc. The sides 13 are arcuate. The disc has a central hole 14 to receive a vehicle hub and a ring of bolt holes 15 whereby it can be connected to the hub. The disc has a central or nave portion 11a, an inner portion 1 1b substantially perpendicular to the rotary axis of the wheel, a conical portion 11c and an outer portion ill which is also perpendicular to said rotary axis.

To each shorter side 13 of the disc is bolted a bracket, there being four brackets 16, 17, 18 and 19. These brackets are identical. Referring now to Figures 2 to 5 the bracket 17 will be described by way of example. The bracket has a flange 20 which is bolted to the disc 10 by two bolt, nut and washer assemblies 21 passing through aligned bolt holes in the bracket and the disc; the holes in the bracket are shown at 21a in Figure 5. As shown in Figure 4 the flange 20 fits closely alongside the disc 10 and lateral truth is thus ensured. The edge of the shorter side 13 of the disc closely engages a shoulder 22 provided on the bracket at the side of the flange, radial truth of the bracket relative to the disc is thus ensured.

Each bracket is bifurcated and has, as is most clearly shown in Figure 5, a shorter limb 23 and a longer limb 24 which are separated by a channel 25. The inwardly facing surface 23 a of the limb 23 is parallel to surfaces 24a on the limb 24. The longitudinal axis of the channel 25 is inclined to the flange 20 as clearly shown in Figures 4 and 5. Each rail on the rim, which will now be described, fits in the channel 25 between the limbs of one of the brackets.

Returning now to Figures 1 and 2, there are four part-helical rails, 26, 27, 28 and 29 welded to the internal surface of the rim. The rails are circumferentially spaced about the rim with their ends in alignment. That is to say that the one ends of each of the rails is in the same plane which is perpendicular to the rotary axis of the wheel and the other ends of the rails are in a different plane per pendicular to said axis. A block such as 32 is welded to each end of each rail to act as a stop to prevent the bracket leaving the rail. As will be clearly seen from the figures, the shorter limb 23 of each bracket lies to one side of the rail whereas the longer limb 24 lies to the other side of the rail, the latter being received in the channel 25. Each of the rails, for example the rail 27 in the figures, is provided with a plurality of spaced holes indicated at 33 to 39 respectively.The spacing between each adjacent pair of the holes 33 to 39 is the same as the spacing between the holes 40 in the limb 24.

Thus each of the brackets 16 to 19 can have the holes therein aligned with an adjacent pair of holes in whichever of the rails 26 to 29 it engages and the wheel and disc can be secured in position by inserting through the aligned holes bolt, nut and washer assemblies such as 41. When these are tightened up the disc is secured to the rim via the rails and any clearance between the bracket limbs 24 and the rails is taken up thus ensuring that the rim is laterally true with respect to the disc. Radial truth is ensured as described above by the disc sides 13 engaging the shoulders 22.

To adjust the track of the wheel, the nut and bolt assemblies 41 are removed. The desired pair of holes in each of the rails 26 to 29 with which the holes in the limbs 24 of the brackets 16 to 19 are to be aligned is selected, stops 42 (see Figures 1 and 2) are arranged in appropriate positions on each of the rails 27 and 29 and held there by nut and bolt assemblies 43. Two stops are shown, one on each of the rails 27 and 29, but any number of stops from one to four may be used. Assuming that the rim with the tyre thereon is resting on the ground, the disc can be turned by engaging the tractor in gear, and the disc will turn relative to the rim, in the case shown, in a clockwise direction, until the brackets 17 and 19 engage the stops 42.The holes in the limbs 24 of the brackets will then be in alignment with the holes in the rails 27 and 29 and the nut and bolt assemblies 41 can be placed in position and tightened down, thus to lock the rim and the disc together. Similarly the brackets 13 and 18 will be bolted to the rails 26 and 28 respectively.

Each rail will be clamped against the surfaces 24 a on a bracket and thus lateral truth will be obtained.

Each wheel will be adjusted separately.

The invention thus provides a PAVQT wheel of the type described in which there is positive locking between the rim and the disc and in which lateral and radial truth is easily and accurately obtained.

The locking does not involve any radially applied force which can distort the rim and which often occurs in prior art PAVT wheels.

Moreover, the use of an octagonal disc as described with the bolt assemblies 41 arranged in pairs gives the advantage described in our British Patent Specification No. 2,058,868. However other shapes of disc with a different number of rails could be used if desired.

Claims (7)

1. A PAVT wheel of the type described wherein each bracket is bifurcated and engages a rail between the limbs of its bifurcation, the bracket being provided with at least one bolt hole and wherein each rail is provided with a plurality of bolt holes, the wheel being adjusted by bringing holes in the brackets into alignment with holes in the rails, inserting bolts through the aligned holes and securing the bolts in situ.

2. A wheel according to Claim 1 wherein there are two bolt holes in each bracket and two bolts holding the bracket to its associated rail.

3. A wheel according to Claim 1 or Claim 2 wherein the bolt holes in each bracket are only in one limb of the bifurcation.

4. A wheel according to any preceding claim wherein the brackets are bolted to the disc.

5. A wheel according to any one of the preceding claims wherein the disc is of irregular octagonal shape formed by cutting the corners off a square so that there are four shorter sides and four longer sides arranged alternately around the periphery of the disc, the brackets being secured to the shorter sides.

6. A wheel according to any one of the preceding claims wherein there are inter-engaging faces on the brackets and the disc whereby the brackets are located radially of the disc.

7. A PAVT wheel substantially as hereinbefore described with reference to the accompanying drawings.