The present invention relates to a wheeled conveyance, for example a self-propelled wheeled conveyance such as a motorised wheelchair, or a push-chair or wheelchair.
Self-propelled wheeled conveyances, in the form of motorised wheelchairs, are well known in which a chassis is provided with a seat for receiving a person to be transported and with two front wheels and two rear wheels. Two of the wheels (usually the rear wheels) are independently driven by separate battery-powered electric motors and the other two wheels are arranged to swivel independently. The wheels may be provided with a suspension assembly.
Steering and motion control are effected by means of a manually-operated controller, such as a joystick, which selectively controls the two electric motors. A dead man's handle arrangement is usually built into the manually-operated controller, such that when a user releases the controller, the wheelchair immediately brakes and comes to a halt.
Motorised wheelchairs have stability problems associated therewith when front wheels drop into a sudden dip, such as over a kerb or into a pothole, or when descending a slope, particularly when coming to a standstill. Such a slope may, in practice, have an angle of as great as twenty degrees.
If a user releases the controller, such as the joystick, when the wheelchair is moving, the wheelchair in coming to an immediate halt throws the weight forward when doing so. This is disadvantageous and in severe conditions can result in overturning of the wheelchair, particularly when descending a slope. The problem is exacerbated by the fact that such wheelchairs have a relatively short wheelbase and a relatively high centre of gravity. In some situations the height of the centre of gravity is increased by heavy batteries, which are used to power the wheelchair, being mounted in the chassis beneath the seat.
The problem is exacerbated with a wheelchair incorporating a suspension assembly which permits the load to tilt forward, thereby enabling the centre of gravity to move marginally forward also.
Problems in reverse arise with non-powered push-chairs and wheelchairs with suspension when the chair is tilted backwards to effect steering or to mount a large obstacle. Downwards pressure on the pushing handle must take up suspension movement before the front wheels lift off the ground. This is less precise than for a rigid chair.