Motor vehicles – Steering by driving – Combined with manual steering
Patent
1994-06-03
1996-01-09
Hurley, Kevin T.
Motor vehicles
Steering by driving
Combined with manual steering
180 65, 180 655, 180907, B62D 900
Patent
active
054821258
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a steerable four wheel drive vehicle and in particular to the use of such a vehicle as a wheelchair.
BACKGROUND ART
It is known to provide a wheelchair with drive to each of its four wheels. Such vehicles are conventionally steered by the skid steer principle or by providing that some or all of the wheels are steered by a positive steering mechanism. The skid steer principle provides a high degree of manoeuvrability to a four wheel drive vehicle and is for this reason used in tractors, armoured personnel carriers and the like. This system is not satisfactory for wheelchairs which are likely to be used indoors as the skid steering of the wheelchair would damage flooring surfaces such as carpets. The provision of positive steering mechanisms on wheelchairs adds to the weight, complexity and cost of wheelchairs. The present invention is directed to a four wheel drive vehicle incorporating an alternative steering mechanism.
DISCLOSURE OF THE INVENTION
The present invention consists of a vehicle having a frame, a pair of front wheels and a pair of rear wheels mounted on the frame, a steering means wherein at least one of the pairs of wheels are castor mounted on the frame so that each wheel of that pair freely pivots about a respective vertical axis, the steering means further comprising a linkage means connecting the pair of castor mounted wheels so that the castor mounted wheels pivot generally in unison, a motor drivably connected to each wheel for rotating that wheel in its vertical plane, and control means to control power to be independently delivered to each one of at least one of the pairs of wheels.
Preferably, each castor mounted wheel is rotatable in a generally vertical plane which is laterally spaced from the vertical pivotal axis of that wheel.
Preferably, the linkage means is a rigid elongate bar pivotably connected to the castor mounting of each one of the pair of castor mounted wheels to thereby interconnect the pair of castor mounted wheels, the pivotal connections of the elongate bar being in each case about another vertical axis laterally spaced from the vertical pivotal axis of the respective castor mounted wheels
In a preferred embodiment of the invention the vehicle is a wheelchair having a chair mounted on the frame. The control means are preferably mounted on an arm of the chair but may be mounted remotely of it.
The vehicle is preferably an electric vehicle using a battery or batteries to drive an electric motor connected to each of the four wheels of the vehicle. These motors are preferably printed circuit motors which deliver high torque at low speeds.
The castor mounted wheels may have either a positive or a negative trail. A positive trail means that the horizontal axis of rotation of the wheel lies behind the vertical axis of rotation of the castor mechanism relative to the frame. A negative trail implies that the axis of rotation of the wheel is in front of the castor axis.
In order to provide a wheelchair with a tight turning circle and minimum physical dimensions it is preferred that the front wheels of the wheelchair are castor mounted and are given a positive trail by an amount less than the radius of the wheel. This allows the front wheels to arc around the respective ends of the front frame member of the wheelchair while still leaving sufficient space between the full lock positions of the wheels for a footrest to be provided between the wheels in front of a front frame member. In this respect it is also desirable that the free end portions of the front frame member are angled forwardly on either side of the footrest. It is, of course, a requirement that the wheels do not contact either the footrest or the feet of a user resting thereon. The stop members must therefore be positioned to stop such contact.
In the simplest embodiment of the invention the rear wheels will be non-steerable. In this arrangement the drive means of the left hand wheels should be coupled to drive in the same direction and similarly the right ha
REFERENCES:
patent: 2122924 (1938-07-01), Ammen et al.
patent: 4483405 (1984-11-01), Noda et al.
patent: 4805712 (1989-02-01), Singleton
patent: 5311957 (1994-05-01), McLaurin et al.
Hurley Kevin T.
J. Pagett Industries Pty Limited
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