WO1987006890A1

WO1987006890A1 - Tractor wheels

Info

Publication number: WO1987006890A1
Application number: PCT/GB1986/000269
Authority: WO
Inventors: Edward Williams; Terence Roy Crowe; John Sayer
Original assignee: Gkn Sankey Limited
Priority date: 1986-05-15
Filing date: 1986-05-15
Publication date: 1987-11-19
Also published as: BR8607357A; EP0307392A1

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).

Description

TRACTOR WHEELS

This invention relates to power-adjustable-variable- track (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 PAVT 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 member 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 usual in such wheels to bolt a stop on to one or more of the rails so that, upon relative rotation of the disc and the rim during adjustment, the locking member on the bracket on that rail engages the stop. The latter is located on the rail at a position appropriate to the desired adjusted position of the wheel. A second stop may be mounted on the same rail on the other side of the bracket when the disc and rim are in the adjusted position. The stops may be secured to the rail by bolting through the latter. An example of such an arrangement is described in U.S. Patent Serial No. 3,048,443.

If two stops are used on a rail as shown in said U.S. Patent Serial No. 3,048,443 they do prevent, in the event that the locking members come loose on the rails, an excessive relative movement between the disc and the rim. However if the locking members do come loose on the rails in service, serious damage will be done to the wheel due to slippage between the rim and the disc • notwithstanding the presence of the stops since there is clearance between the locking member and the stops.

One of the most serious problems encountered in service with known PAVT wheels is their lack of radial truth, i.e. the rim is not concentric with the rotary axis of the wheel. By way of example, in the wheel shown in said U.S. Patent Serial No. 3,048,443 each bracket carries a radially disposed lug bolt which constitutes the locking member and which has a U-shaped outer end portion which engages a rail. The disc and rim are held in the desired position by frictional engagement between the rails and the outer end portions of the lug bolts. The latter are moved radially outwardly to generate said frictional engagement and it will be apparent that unequal adjustment of the lug bolts around the periphery of the disc will cause the rim to be non-concentric with the rotary axis of the wheel. This is what often happens in practice since to retain concentricity it is necessary to adjust each lug bolt repeatedly in small increments while working round the periphery of the disc a number of times. This requires time and patience.

An object of the invention is to provide a PAVT wheel which overcomes these problems, is easy and quick to adjust and which has 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.

Such a wheel has a number of advantages over prior art wheels such as exemplified by said U.S. Patent Serial No. 3,048,443.

First, adjustment of the wheel is simple and quick. It is only necessary to loosen, withdraw, replace and tighten the bolts. It is not necessary to make small and repeated adjustments around the periphery of the disc as with radially movable lug bolts.as described above.

Second, since it is not necessary to provide radial clearance between the rails and the locking members to adjust the wheel, smooth adjustment can be obtained. Where one has to generate radial clearance between the locking members or lug bolts and the rails to permit adjustment as in the prior art, relative movement between the rim and disc during adjustment causes judder and the possibility of binding between the locking members and the rails during adjustment. Even PAVT wheels which do not use lug bolts usually require radial movement between the locking members and the disc during adjustment and therefore suffer from this problem.

Third, since no radial movement between the locking members and the rails is required during adjustment there need only be minimum clearance between them so that radial truth of the wheel can easily be ensured and the major problem with PAVT wheels overcome.

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 alternately 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 1 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 11 , an inner portion 11 b substantially perpendicular to the rotary axis of the wheel, a conical portion 11 and an outer portion 11 d 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 21 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, the limbs being separated by a channel 25. The inwardly facing surface 23 a_ of the limb 23 is parallel to surfaces 24 a. on the limb 24. The longitudinal axis of the channel 25 is inclined to the flange 20 as clearly shown in Figures 2 and 4. 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 perpendicular 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 1, 2 and 3, 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 PAVT 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 and as described above. Since there is no relative radial movement between the brackets and the rails, adjustment is very smooth and each adjustment e.g. position or track setting, can be readily obtained.

The use of an octagonal disc as described is economical since it saves material as compared with a circular disc. However other shapes of disc with a different number of rails could be used if desired.

Claims

1. A power-adjustable-variable-track wheel comprising a rim, a plurality of part-helical rails secured to the inner periphery of the rim in circumferentially-spaced relation, a disc, and brackets carried by the disc and engaging the rails so that upon relative rotation between the disc and the rim they are also moved relative to one another in directions parallel to the rotary axes of the wheel as the brackets move along the rails; characterised in that each bracket (16, 17, 18, 19) is bifurcated and engages a rail (26, 27, 28, 29) between the limbs (23 and 24) of its bifurcation, the bracket being provided with at least one bolt hole (40) and wherein each rail is provided with a plurality of bolt holes (33 - 39), the wheel being adjusted by bringing holes in the brackets into alignment with holes in the rails, inserting bolts (41) through the aligned holes and securing the bolts in situ.

2. A wheel according to Claim 1 characterised in that there are two bolt holes (40) in each bracket and two bolts (41) holding the bracket to its associated rail.

3. A wheel according to Claim 1 or Claim 2 characterised in that the bolt holes (40) in each bracket are only in one limb (24) of the bifurcation.

4. A wheel according to any preceding claim characterised in that the brackets are bolted (21) to the disc (10) .

5. A wheel according to any one of the preceding claims characterised in that the disc (10) is of irregular octagonal shape formed by cutting the corners off a square so that there are four shorter sides (13) and four longer sides (12) 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 characterised in that there are inter-engaging faces (22 and 13) on the brackets and the disc whereby the brackets are located radially of the disc.

7. A wheel according to any preceding claim, characterised in that each bracket comprises a flange

(20) which lies against and is bolted to the disc and a channel (25) between the limbs (23, 24), the length of the channel being arranged at an angle to the length of the flange.

8. A wheel according to Claim 7, characterised in that each bracket has, adjacent one edge of its flange, a shoulder (22) running the length of the flange and engaging the edge of the disc.