BACKGROUND OF THE INVENTION 1. Field of the Invention THIS INVENTION relates to an improved drive system, and to vehicles incorporating the drive system.

The invention is particularly suitable for, but not limited to, a drive system which enables vehicles to negotiate steps, stairs, escalators or like surfaces.

2. Prior Art Through the years, there have been many proposals to enable vehicles to negotiate steps or stairs. Examples include climbing hand trolleys, which have three wheels at the apexes of rotating triangular brackets; and crawler type tracks which have been proposed to enable wheelchairs to negotiate stairways.

There is a need for a simple, yet efficient, drive or support system to enable a wide range of vehicles to negotiate steps or stairs.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a bracket assembly, mountable on a chain, which can be incorporated

into a drive system to enable a vehicle to negotiate steps or stairs.

It is a preferred object of the present invention to provide such a drive system incorporating one or more of the bracket assemblies.

It is a further preferred object of the present invention to provide a vehicle incorporating such a drive system.

It is a still further preferred object to provide such bracket assemblies which are relative inexpensive and easy to manufacture and which can be easily fitted to existing chains with minimal modification.

Other preferred objects of the present invention will become apparent from the following description.

In a first aspect, the present invention resides in a bracket assembly, mountable on a chain of the type having a plurality of interconnected links, the bracket assembly including: a pair of spaced, substantially parallel, bracket plates, with (optional) spacer means therebetween; wheel or roller means rotatably mounted on axle or shaft means interconnecting distal ends of the bracket plates; and at the proximal end, at least two spaced pairs of aligned holes in the bracket plates to receive shafts or pins interconnecting an adjacent pair of the links, and at least two spaced pairs of (optionally) aligned, curved slots to receive the shafts or pins of the preceding

and succeeding links, so arranged that the shafts or pins are movable within the slots as the links pass around a sprocket or travel in a non- linear path.

In a second aspect, the present invention resides in a chain assembly fitted with at least one of the bracket assemblies as hereinbefore described.

In a third aspect, the present invention resides in a vehicle having first and second pairs of head and tail, or driving and driven, sprockets; a respective chain assembly interconnecting the sprockets of each pair; and a plurality of the bracket assemblies, as hereinbefore described, provided at equally spaced intervals along the chains.

Preferably, the bracket assemblies are provided in aligned pairs on the chains.

Preferably, four, five, six, eight or n brackets are provided at equal spacings on each chain where n is an even number greater than eight.

Preferably, at least one chain guide assembly is provided between the sprockets of each pair.

The driving sprocket of each pair may be connected to a manual, electrical, internal combustion, hydraulic (or hydrostatic) or other suitable propulsion means.

BRIEF DESCRIPTION OF THE DRAWINGS To enable the invention to be fully understood, preferred embodiments will now be described with reference to the accompanying drawings in which: FIG. 1 is a side view of a drive system incorporating four bracket assemblies in accordance with the present invention; FIGS. 2, 3 & 4 are respective side elevation, end elevation and top plan views of one of the bracket assemblies; FIG. 5 is a schematic side view of a hand cart provided with the drive system of the present invention; FIGS. 6 and 7 are similar views showing the hand cart negotiating a set of steps; FIG. 8 is a similar view of a iuggage carrier; FIG. 9 is a similar view of a wheelchair; and FIG. 10 is a similar view of a child carrier.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, the drive system 10 has a chain 11 passing around a driving sprocket 12 and a driven sprocket 13, the lower run of the chain 11 being supported by a chain guide 14 intermediate the sprockets 12, 13. The sprockets 12, 13 are provided on respective driving and driven shafts 15, 16 rotatably journalled in bushes or bearings (not shown) at respective ends of a crawler frame 17 on which is also mounted the chain guide 14.

Four bracket assemblies 20, to be hereinafter described in more detail with reference to FIGS. 2 to 4, are provided at equal spacings about the chain 11, and each bracket assembly 20 is provided with a ground engaging wheel 21 rotatably journalled on an axle 22 between a pair of bracket plates 23, 24 mounted on the chain 11 via shaft pins 25.

Referring now to FIGS. 2 to 4, each bracket assembly 20 has a pair of bracket plates 23, 24 interconnected by a spacer 26. A wheel 21 is rotatably mounted on an axle 22 which interconnects the bracket plates 23, 24 at the distal end of the bracket assembly 20.

The chain 11 is received between the bracket plates 23, 24 at the proximal end of the bracket assembly 20, and a pair of extended shaft pins 25 pass through two pairs of aligned holes in the bracket plates 23, 24. A second pair of extended shaft pins 26, connecting the links preceding and succeeding the chain links interconnected by shaft links 25, are received in respective pairs of curved slots 27 in the bracket plates 23, 24.

The curved slots 27 allow the adjacent chain links to hingedly move so that the chain 11 can pass around the sprockets 12,13 or follow a non-linear path. Without the curved slots 27, the chain links would tend to pull free from the teeth of the sprockets 12, 13 as the chain 11 passes around the sprockets 12, 13.

Referring to FIG. 5, a hand cart 140 has a load supporting frame 141 and a handle 142. The cart 140 is supported by a pair of the drive systems 110, each having six wheels 121.

To travel along a substantially even surface, the drive systems are locked, so that three of the ground wheels 121 on each drive system 110 engage the supporting surface 150.

As shown in FIG. 6, to move up or down a stairway 160, the sprockets 112, 113 are allowed to rotate and allow the frame 117 and chain guides 1 14 to move relative to the chains 111, as the wheels 121 are blocked by the risers 161 on the stairway 160.

When the cart 140 is moving, the six wheels 121 on each side of the cart (six pairs of wheels in total) will be in contact with the treads 162 and risers 161 on the stairway 160.

As shown in FIG. 7, three pairs of the wheels 121 are shown in contact with the stairway 160.

FIG. 8 shows a small luggage trolley 240 where four wheels 221 are provided on each drive system 210 on the trolley 240.

Again, when moving on a flat floor, the sprockets 212, 213 are locked against rotation and the wheels 221 roll over the floor and climb the stairway 260. The sprockets 212, 213 are allowed to rotate to allow the drive systems 210 to operate to thereby enable the trolley 242 to negotiate the stairs.

Referring to FIG. 9, a wheelchair 340 has a seat 345, and a crank or handle 346 is operably connected (eg., by a chain or chains) to the driven sprockets 312 of the drive systems 310 to enable the person using the wheelchair to negotiate the stairs 360.

It will be readily apparent to the skilled addressee that the wheelchair 340 may be provided with, eg., an electric motor or other suitable propulsion sources to propel the drive systems 310, to enable the wheelchair 340 to negotiate the stairway 360.

FIG. 10 illustrates a child carrier 440 where each drive system 410 has five ground wheels 421.

It will be readily apparent to the skilled addressee that the drive systems of the present invention enable the vehicles, to which the drive systems are fitted, to easily negotiate both flat surfaces and to climb steps or stairways. As hereinbefore described, propulsion for the drive systems may be manual, eg., by pushing or hand-operated crank, by electric motor or other suitable propulsion means.

The number of bracket assemblies provided for each drive system can be varied to suit the intended load capacity of the vehicle to which the drive systems are fitted.

Various changes and modifications may be made to the embodiments described and illustrated without departing from the present invention.