Step-climbing attachment for a wheeled chair

1. A step-climbing attachment for a wheeled chair, the attachment including:

a wheel-mounting chassis for mounting wheels;

a first wheel and a second wheel mounted on the wheel-mounting chassis for rotation about their axes;

the first and second wheels each being adapted to move relative to the other, the relative movement in use being between a ground engaging position and a step-engaging position so that in use at least one of the first or second wheels engages a step; and

respective link arms connected to the chassis so as to mount the first wheel and the second wheel to the chassis and allow each wheel to independently swing from the ground engaging position to the step-engaging position;

at least one of the first and second wheels having a hub and said at least one of the first and second wheels having a motor and gearbox mounted within the hub, said motor and gearbox being connected to the respective link arms so as to pivot the other of the first and second wheels into a step engaging position.

2. The step-climbing attachment in accordance with claim 1 wherein the attachment is mounted to a stub axle on a wheel chair so that the wheel-mounting chassis pivots thereabout.

3. The step-climbing attachment in accordance with claim 1 wherein the link arms are linked so as to form a four bar linkage.

4. The step-climbing attachment in accordance with claim 3 wherein the four bar linkage is arranged so that first and second links of the four bar linkage are pivotally mounted at spaced-apart locations on the wheel-mounting chassis and are connected at their distal ends by a connecting arm.

5. The step-climbing attachment in accordance with claim 4 wherein at least one link includes a spring and/or damper arrangement to provide an at least partially suspended chassis.

6. The step-climbing attachment in accordance with claim 3 wherein the hub connects to a distal end of the first link of the four-bar linkage.

7. The step-climbing attachment in accordance with claim 3 wherein a motor plate is provided and mounts to a distal end of the second link of the four-bar linkage.

8. The step-climbing attachment in accordance with claim 1 wherein one of the first or second wheels is disposed in use on the chassis in a position relatively forward of the other of the first or second wheels so as to facilitate step climbing or descending.

9. The step-climbing attachment in accordance with claim 8 wherein the chassis is disposed between first and second wheels.

10. The step-climbing attachment in accordance with claim 1 wherein the first wheel is a powered wheel assembly to provide propulsion to the chassis.

11. The step-climbing attachment in accordance with claim 10 wherein the second wheel is in the form of a planetary wheel assembly and is mounted so as to orbit the first powered wheel assembly.

12. The step-climbing attachment in accordance with claim 11 wherein an idler wheel is provided and is disposed to be in contact with the tread of the first wheel, and in operation is disposed between the first and second wheels.

13. The step-climbing attachment in accordance with claim 11 wherein two planetary wheels are provided.

14. The step-climbing attachment in accordance with claim 13 wherein a differential or belt system is used so that a drive motor may be used for propulsion and climbing.

15. The step-climbing attachment in accordance with claim 14 wherein a two stage planetary gearbox is provided with a third stage reduction so as to isolate and engage a wheel arm to cause the movement of the planetary wheel into a step-engaging position.

16. A self-propelled wheeled chair including a step-climbing attachment according to claim 1 .