This invention relates generally to track laying vehicles and more particularly in one aspect to a track assembly and in another aspect a drive wheel suitable for use in such a vehicle.

Track laying vehicles of this type may comprise a main body having a longitudinal axis extending between forward and rearward ends thereof and a pair of track assemblies disposed on opposite sides of the main body. Each track assembly may comprise first and second wheels which are spaced apart in the direction of the longitudinal axis with at least one of the wheels defining a drive wheel. An example of one such vehicle and track assembly therefor is described in applicant's international application no.

According to one aspect of the present invention there is provided a track assembly suitable for use with a track laying vehicle, the vehicle comprising a vehicle body having a longitudinal axis extending between forward and rearward ends of the vehicle, and having two such track assemblies which are disposed on opposite sides of the vehicle body, each track assembly comprising at least first and second wheels which, in use, are spaced apart in the direction of the longitudinal axis with at least one of the wheels defining a drive wheel, a continuous elastomeric belt or track having a ground engaging surface and an opposite wheel engaging surface with a plurality of power transmission elements projecting from the wheel engaging surface, said belt or track extending at least partially around said wheels so that a section thereof comprises an engagement section which is in engagement with drive wheel, said drive wheel comprising a hub and a plurality of circumferentially spaced apart drive members at or near the radially outer

periphery of the drive wheel, the space between adjacent drive members forming receiving recesses for the transmission elements in the engagement section of the belt wherein the pitch of the drive members on the drive wheel is different to the pitch of the transmission elements of the engagement section of the belt such that the maximum transmission force applied to belt by the drive wheel is at the engagement section of the belt in the region where it leaves the drive wheel.

The engagement section of the belt with the drive wheel has an entry side and an exit side and the maximum driving force may be arranged to be applied to the transmission elements by the drive members on the drive wheel at or towards the exit side. The arrangement may be such that the belt and drive wheel are arranged so that when the belt first contacts the drive wheel the transmission elements are positioned relative to the drive members such that there is little or no driving force applied to the transmission members at this stage. Because of the pitch differential between the transmission elements and the drive members there will be a relative movement between the two parts until at some stage along the engagement section the transmission elements will be engaged by the drive elements so as to apply a transmission force thereto. This force will continue to increase until that part of the belt leaves the drive wheel.

Preferably the pitch of the drive members on the drive wheel is greater than that of the transmission elements on the section of the belt engaging the drive wheel. It will be appreciated that because of the nature and contraction of the elastomeric belt the pitch of the transmission elements on the belt where it is not in contact with the drive wheel (the straight sections) will be different to that curved section extending partially around the drive wheel. The compressibility of the transmission elements enables the driving force applied by the drive wheel to be progressively taken up by the transmission elements on the engagement

section of the belt as the belt passes over the drive wheel. As the transmission elements leave the drive wheel they tend to open out to ensure that the contact with the drive member at that point is broken relatively cleanly.

The arrangement as described above reduces the problems of wear on the transmission elements on the belt because at the entry side, the driving members do not tend to slide down the profile of the transmission elements because of the pitch differential. This is not the case where the respective pitches are substantially the same.

The drive wheel may include spaced apart outer rim surfaces with the drive members extending therebetween. The general construction of the drive wheel may be similar to that described in applicant's international application no. PCT/AU90/00542. The drive wheel of the present invention may be modified from that described in the aforementioned patent specification in that the drive members, which may be in the form of drive bars, project radially outwardly from the outer rim surfaces. By this arrangement the drive members tend to seat better in between the transmission elements when a section of the belt is engaging the drive wheel.

Similarly the belt may be generally in the form described in the aforementioned international application no. PCT/AU90/00542. The section of the belt which is in engagement with the drive wheel may be any suitable angle such as for example 180° or more or less depending upon the working requirement of the vehicle.

The belt may comprise reinforcing members therein which can take any suitable form. Because of the nature of the elastomeric belt the position of the reinforcing members determines the pitch of that section of the belt which is in engagement with the drive wheel. Advantageously the reinforcing members are disposed in a plane adjacent the wheel engaging surface.

In one preferred form the drive members may include a rotatable contact section which engages the belt. This feature constitutes a separate aspect of the invention and will be described in more detail later. This rotatable contact section may, for example, be effected by mounting each of the drive members for rotation about their longitudinal axes. In one preferred arrangement each drive member has a sleeve section thereon which can rotate relative to the drive member. This provides a rolling surface which tends to assist in alleviating wear of the belt.

The adjacent drive members and the adjacent power transmission members may be disposed at a selected circumferential pitch and there is a differential between the pitch of the drive members and power transmission elements such that the force carried by the last transmission element engaging the wheel during rotation thereof carries the highest drive force.

Advantageously the circumferential pitch of transmission elements is smaller than the circumferential pitch of the drive members. Preferably there is no contact between the drive members and the transmission elements when the belt first engages the drive wheel. Because of the pitch differential there is a relative movement between that section of the belt and their associated transmission elements such that the transmission elements contact the drive members towards the end of the travel of the track over the drive wheel.

The power transmission elements may act as guides for locating the elastomeric track or belt on the wheels. For example, the power transmission elements may be arranged so as to inhibit lateral movement of the belt relative to the wheels to try and ensure that the belt does not slip off the wheels.

The drive wheel may comprise a hub and a plurality of rim supports operatively connected to the hub. The rim supports may be circumferentially spaced apart and extending radially from the hub with an outer support portion and opposed side portions and at least one pair of said rim sections operatively connected to the outer support portion in spaced apart relation to one another so as to form a gap therebetween with open sides between each rim section and the side portions of the adjacent rim supports.

The hub may comprise a disc-like member and each rim support may include a plate like body which extends generally transversely of the disc-like member with an outer edge defining the outer support portion. The side portions of each rim support plate may be inclined inwardly from the outer edge towards a region which is operatively connected to the hub. Advantageously the facing edges of the rims are inclined inwardly from the outer face.

In one advantageous form, two rims are provided however in certain applications it may be desirable to have more than two rims. For example, the power transmission elements may be arranged in two or more generally parallel lines extending in the direction of the longitudinal axis and, as such, more than two rims may be provided so that there are sets of rims with drive members therebetween for each of the lines of power transmission elements.

The drive members may comprise cross members extending between the rims. The cross members may be in the form of rods, tubes or bars.

According to another aspect of the present invention there is provided a drive wheel suitable for use with a track assembly for a vehicle of the general type referred to above the drive wheel comprising a hub, spaced apart outer rim sections and a plurality of circumferentially spaced apart drive members extending between the rim sections the space between adjacent drive members forming receiving

recesses for the transmission elements in an engagement section of the belt which is in. engagement with the drive wheel. This aspect of the invention is characterised in that the outer rim sections and/or the drive members include a rotatable belt contact surface portion which engages the belt. The contact surface portion of the outer rim sections may be rotatable relative to the wheel hub about the axis of rotation of the wheel and the contact sections of the drive members are rotatable about the longitudinal axis of the respective drive member. It is to be understood that the drive wheel of this aspect of the invention may comprise either one of the contact surface portions on the rim sections or drive members alone or provide them in combination. These rotatable contact surface portions tend to alleviate wear of the belt.

In one form the drive members may be mounted for rotation about their respective longitudinal axes. In this form of the invention, the outer surface of each drive member defines the contact surface portions. Preferably each drive member includes a rotatable sleeve section which can rotate relative to a main body section of the drive member. In this case the outer surface of the sleeve of each drive member defines the contact surface portion. Preferably the drive members are disposed at or in the region of the outer periphery of the drive wheel.

Each rim section may comprise an inner main body and an outer sleeve section rotatable relative thereto. It will be appreciated however that other arrangements could be utilized. For example, the rims may comprise a plurality of spaced apart bars which are rotatable relative to their longitudinal axes. Another arrangement could comprise balls or rollers mounted for rotation in, for example, a main body part of each rim, the belt being adapted to engage the rollers or balls. It will further be appreciated that not all of the drive members need to have a rotatable contact surface portion associated therewith. In yet another arrangement the wheel may comprises, for example, three

separate sections the outer two sections being rotatable relative to a central drive section.

The overall construction of the drive wheel may be of the general type of that described earlier and the belt may also be generally in the form previously described.

Preferred embodiments of the invention will hereinafter be described with reference to the accompanying drawings, in which:

Figure 1 is a side elevation view of a typical work vehicle;

Figure 2 is a front elevation view of the work vehicle as illustrated in Figure 1;

Figure 3 is a plan view taken along line A-A of Figure

1;

Figure 4 is a schematic side elevation showing the relationship between the track and drive wheel of a track assembly according to one aspect of the present invention; and

Figure 5 is a schematic perspective view of a wheel according to an aspect of the present invention.

Figure 1 illustrates the heavy duty elastomeric track laying vehicle 1 of the type to which the various aspects of the invention are applicable. The vehicle 1 has a chassis and frame 3 with a longitudinal axis 33, an operators cabin 4 and an engine 2. Connected to frame 3 is a drawbar 17 which is used to attach draft loads. Although the vehicle illustrated would be used in the main for heavy-duty draft work, the principles inherent in this invention would also apply to a vehicle for pushing, hauling and carrying large loads. The vehicle is propelled by an elastomeric track 9 along each longitudinal side of chassis 3 in which is entrained a drive wheel 5, an idler wheel 32 and load sharing track wheels 19,20. Ground engagement of the track 9 is made by lugs 11 being part of track 9. Each track is supported by laterally spaced surfaces 16 of the wheel 5 and idler wheel 32.

Each track 9 has direct drive engagement with the drive wheel 5 by means of engagement between the cross members 7 of the drive wheel 5 and the drive lugs 11 which are part of the track 9.

The engagement between cross members 7 and drive lugs 11 is maintained by the hydraulic cylinder 31 tensioning the idler wheel 32 away from the drive wheel 5.

The drive wheel 5 shown in Figures 1 to 3 rotates around axis 18 and comprises a hub including a drive flange and a wheel knave to which is attached lateral plates or spokes 8. This is best described in applicant's international application PCT/AU90/00542. These spokes 8 support two laterally spaced rims 65 to which may be bonded a firm elastomeric cushion. The elastomeric cushion consists preferably of but not limited to a polyurethane elastomer with a hardness of approximately 85 to 90 duro. The surface 16 of the cushion 6 supports the surface of the track 9. Between the two rims 65, round drive cross members 7 are attached laterally to, the driving means of drive wheel 5. The outer surface of the cross members 7 may be flush with the outer surface 16 of the cushion. For the wheel 5 to accept the drive lugs 11 of the track 9 there is an opening bounded laterally by two cross members 7 and longitudinally by the two rims 65 and the cushion which form a guiding surface. The drive lugs 11 of the track 9 are guided into lateral registry with the drive wheel 5 by the cushion and rims 65 having inwardly angled sides that interface with the inwardly angled guiding surface 35 of lugs 11. Lateral registry is also assisted by the cross member 7 pulling in a "chain-like" action on drive lug 11 of track 9. The open area is laterally wider than the inner lateral width of drive lug 11. The angle along the lateral facing side 35 of lug 11 should be approximately 100 degrees from surface 44 to allow a sliding movement with guiding surface 68 when high lateral forces are applied to track 9.

Drive lugs 11 of track 9 also have inwardly sloping angles along the longitudinal facing sides to allow positioning of the cross drive member 7 before being fully engaged with the drive lug 11. The angle is the same as the "entry" and "exit" angle of cross drive member 7.

The idler wheels 32 which rotate around axis 40, 41 are of similar construction to that of the drive wheel 5, but without cross member 7. Each idler wheel consists essentially of a knave attached to an axle. The knave is also attached to lateral plates or spokes placed radially around the axis of rotation 40 and 41 of the idler axles. The spokes are attached to laterally spaced rims to which may be bonded an elastomeric cushion which has a surface to support surface of track 9. The spokes have been cut away to make an open area which allows random entry of the drive lugs 11 to any point around the circumference of idler wheel 32.

The drive lugs 11 of track 9 are guided into lateral registry with the idler wheel 32 in the same way as the drive wheel 5 but without the assistance of the cross members 7.

The track 9 and drive lugs 11 maintain lateral registry with the load sharing wheels 19 and 20 because these wheels form a channel in a longitudinal line between the drive wheel 5 and idler wheel 32. As with the drive wheel 5 and idler wheel 32, lateral movement of the track 9 is restricted to lateral movement of the drive lugs 11 within the angled guiding surfaces of each pair of load sharing wheels 19 and 20.

The elastomeric track 9 may be of the type having no joints and is therefore continuous and has an endless characteristic.

While the elastomeric track 9 can be manufactured from a range of elastomers, the preferred track 9 would be a

fully moulded track manufactured from polyurethane have a hardness of approximately 85 DURO. This material has the properties to allow "rolling-out" of flowable debris in gested between the track 9 surface 44 and the support surfaces 16 of the drive wheel 5, idler wheel 32 and load sharing wheels 19 and 20. Non-flowable material between these surfaces will do little or no damage because of the characteristics of polyurethane. Because the track 9 is directly driven by the drive wheel 5 there is no relative movement between the wheel 5 and track 9 to cause an abrasive action by non-flowable material or debris.

Flowable debris ingested into the track drive area and idler wheel area is returned to the environment by a "squeezing" action of the tensioned track 9 surface 44 against the support surfaces 16 of the drive wheel 5, idler wheel 32 and load sharing wheels 19 and 20. Flowable debris when being "squeezed" or "rolled" will be returned to the environment either at each lateral side of the track 9 or through the open area of either the drive wheel 5 or idler wheel 32. There is therefore a continued cleaning action of the track-drive system without loss of engagement between track 9 and drive wheel 5.

As mentioned previously the preferred elastomeric track 9 would be of continuous construction and fully moulded from a polyurethane elastomer. The track 9 may be of the general type described in applicant's international application PCT/AU90/00542 or PCT/AU91/00029. It will be appreciated that other tracks would also be suitable.

Figure 4 shows the novel relationship between the belt lugs 11 and the drive members 7 of the drive wheel 5. The drive wheel 5 and belt or track 9 are shown schematically in order to explain the phenomena.

As shown in Fig. 4 the belt or track 9 as shown according to this aspect of the invention a pitch P„ of the transmission elements or lugs 11 in that section of the

belt around the drive wheel 5 differs from the pitch P.. in the straight section of the belt. The pitch P« is less than the pitch P-. between adjacent drive members 7 on the drive wheel 5. As can be seem the drive members 7 do not contact the lugs 11 at the entry side of the track (i.e. where it first contacts the drive wheel). Because of the pitch differential there is relative movement between the two members until the drive members eventually contact the lugs 11. In Fig. 4 this first occurs at lug and drive member 11A and 7A. The transmission force increases until the belt leaves the wheel. As the belt straightens the lug 11 at this point tends to move away from the drive member with which it is associated thereby ensuing that contact between the parts is broken cleanly with minimum sliding between the two parts.

As mentioned previously the normal unstressed pitch P.. between adjacent lugs 11 is greater than the pitch P~ between adjacent lugs as the belt passes around the drive wheel. As shown reinforcing members 12 are positioned in a plane adjacent the wheel engaging surface of the belt or track.

Figure 5 illustrates a modified form of drive wheel which is in accordance with another aspect of the present invention.

Referring specifically to Figure 5, according to this aspect of the present invention the drive wheel comprises a hub which includes a pair of discs 67 (only one being shown) to which are operatively connected spaced apart rims 65. Rim supports 15 are operatively connected between the discs 67 and the rims 65 to provide additional support for the rims. Drive members 7 extend between the two rims in similar fashion to that described earlier.

The drive members 7 include an outer sleeve 89 which is rotatable about the longitudinal axis of each drive member. In addition the rims 65 have a sleeve section 88 rotatable

relative to a main body part thereof about the wheel axis.

It will be appreciated because of the surfaces 88 and 89 being freely rotatable relative to the main section of the drive wheel wear on the belt can be reduced.

The steps, features, compositions and compounds referred to or indicated in the specification and/or claims of this application, individually or collectively, and any and all combinations of any two or more of said steps or features.