Motor vehicles – Special wheel base – Five or more wheels
Reexamination Certificate
1999-10-25
2001-03-06
Rice, Kenneth R. (Department: 3611)
Motor vehicles
Special wheel base
Five or more wheels
C180S907000
Reexamination Certificate
active
06196343
ABSTRACT:
This invention relates generally to wheelchairs, and in particular to an improved mid-wheel drive wheelchair which incorporates a novel suspension structure.
Wheelchairs have in the past been designed with various types of suspensions for the purpose of improving passenger comfort and ride during travel over uneven surfaces. While there has been emphasis on the design of the actual seating arrangement for improving passenger comfort and ride, very little attention has been given to the suspension system for the wheelchair, nor its manoeuvrability in confined areas.
One of the problems for occupants of wheelchairs is the severe shock vibrations that are transmitted from the wheels of the wheelchair through its frame to the seat when the wheelchair travels across uneven terrain thereby causing discomfort to the wheelchair occupant. In some cases, riding the wheelchair over such terrain can be quite dangerous and often results in the wheelchair toppling over.
Several attempts have been made to improve the suspension of wheelchairs, and one example of this is to independently spring each of the rear wheels to the underframe of the wheelchair. Another example employs independent shock absorber suspensions for the rear wheels as well as the pair of front wheels. In this regard, reference is made to U.S. Pat. Nos. 5,540,297, 3,917,312, 4,861,056 and 4,455,031. In each case it will be noted that the wheelchair is restricted to a pair of rear drive wheels and a pair of front castor wheels.
In recent times, wheelchairs have been designed with a mid-wheel drive configuration which employs a pair of rear wheels, a pair of intermediate drive wheels, and a pair of anti-tipping front wheels which are normally held clear of the ground, for the purpose of improving the chair's turning ability and manoeuvrability. Common to mid-wheel drive chairs is a “teeter-totter” motion which occurs when the wheelchair rocks forward over the drive wheels. This motion will normally occur when the vehicle is going down inclines, stopping, or slowing. Any unsafe forward tilting or tipping movement of the chair is avoided by virtue of the front anti-tipper wheels which ensure that the chair does not topple. It is also known for the anti-tipper wheels to be located at the rear of the base frame of the wheelchair (rather than at the front thereof), with the pair of front castor wheels being mounted to, remain in permanent contact with the ground. An example of this is shown in U.S. Pat. No. 5,540,297.
It has now been found that considerable improvement in wheelchair ride and comfort, as well as wheelchair manoeuvrability, can be achieved by employing a wheelchair having a mid-wheel drive configuration in association with a pair of front castor wheels and a pair of rear castor wheels which remain in constant contact with the ground, and wherein the front and mid-drive wheel on each side of the chair frame are independently sprung with respect to the base frame of the wheelchair.
It is the main object of the present invention therefore to provide a mid-wheel drive wheelchair which has a novel underframe which includes three sets of ground engaging wheels and which incorporates a very simple and inexpensive suspension arrangement for improving rider comfort, stability and manoeuvrability of the wheelchair.
It is another object of the present invention to provide a mid-wheel drive wheelchair which has improved driving wheel traction properties.
Broadly according to this invention therefore, a mid-wheel drive wheelchair comprises:
a central base frame,
a seat or chair frame attachable to the base frame,
a pair of leading pivot arms pivotally supported on opposite sides of said base frame for independent pivotal movement relative to the base frame about a common transverse pivot axis, each said pivot arm extending forwardly of the front end of the base frame,
a mid-drive wheel mounted for rotation on each of said pivot arms adjacent its trailing end, with the axle of each drive wheel being located a short distance rearwardly of the pivot axis of the pivot arms,
a pair of ground-engaging front castor wheels respectively mounted at the leading ends of said pivot arms,
spring means respectively acting between each said side pivot arm and an adjacent side portion of the base frame, said spring means, in use, being arranged to resist pivotal movement of its associated said pivot arm and to allow the base frame to tilt under spring pressure with respect to the pivot arms, and
a pair of ground engaging rear castor wheels preferably located on opposite sides of the base frame and spaced rearwardly therefrom, said rear castor wheels being movably supported with respect to the base frame.
Desirably the rear castor wheels are respectively rotatably mounted at opposite ends of a rigid transverse support arm which extends across the width of the wheelchair and is pivotally connected to the rear end of the base frame, centrally thereof, for rotation about a central longitudinal axis.
Preferably each of the mid-drive wheels is coupled to an electric drive motor so that the wheelchair can be power driven.
Preferably each said spring means comprises a pair of coil compression springs respectively located fore and aft of the pivot axis of their associated pivot arm.
In a preferred embodiment of the invention, the chair or seat frame is releasably attached to said base frame by releasable spring-loaded locking means.
Preferably the distance between the pivot axis and the axis of each of the drive wheel axles is small relative to the length of the pivot arm, so as to provide a mechanical advantage for each of the pivot arms when the front castor wheel is vertically displaced, eg when travelling over uneven terrain. This in turn also minimises vertical displacement of the base frame and thereby improves rider comfort over uneven terrain.
Preferably the chair or seat of the wheelchair is attached to the base frame in a manner so that substantially the whole weight of the wheelchair rider is distributed over the mid-drive wheels, so as to provide better traction for the drive wheels, and avoid undesirable loading of the front castors. With conventional rear wheel drive wheelchairs, the weight distribution tends to be too far back and the chair can become unstable, eg by tipping backwards.
REFERENCES:
patent: 3917312 (1975-11-01), Rodaway
patent: 4861056 (1989-08-01), Duffy, Jr. et al.
patent: 5435404 (1995-07-01), Garin, III
patent: 5540297 (1996-07-01), Meier
patent: 5848658 (1998-12-01), Pulver
patent: 5944131 (1999-08-01), Schaffner et al.
Klauber & Jackson
Rice Kenneth R.
Rollerchair Pty Ltd.
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