GB2132954A

GB2132954A - Wheelchairs

Info

Publication number: GB2132954A
Application number: GB08334624A
Authority: GB
Inventors: Bryan Oliver Shepherd
Original assignee: STANSGATE ENGINEERING Ltd
Current assignee: STANSGATE ENGINEERING Ltd
Priority date: 1983-01-07
Filing date: 1983-12-30
Publication date: 1984-07-18
Also published as: GB8334624D0; GB2132954B

Abstract

An easily steerable tiller-steered battery-driven wheelchair has the axle (20) of the or each steerable wheel (6) disposed in front of the kingpin (17), giving oversteer which is not detrimental at the very low speeds to which it is restricted, the or each kingpin (17) preferably being offset laterally from the centre plane (23) of wheel, whereby the wheel turns by running around the kingpin, and a four-wheeled wheelchair (as shown) preferably has the driven wheels (5) carried by an axle carrying beam (24) extending laterally and pivoted centrally on a horizontal axis (25) on the fore-and-aft centre line of the wheelchair, to maintain driving and steering contact with uneven ground or when negotiating kerbs or steps. <IMAGE>

Description

SPECIFICATION Wheelchairs This invention relates to wheelchairs, more particulaly tiller steered battery driven wheelchairs, and has for its object the provision of improved tiller steered battery driven wheelchairs well suited to outdoor use. The expression "wheelchairs" also embraces invalid carriages.

Many invalids are weak in the arms and find the steering of tiller steered battery driven wheelchairs to be beyond their capability, because such wheel.

chairs resist very strongly any deviation from a straight line and so when cornering there is a strong tendency to pull outwards on the bends. It is not generally understood amongst designers of electric wheelchairs, that this is caused by the electric drive.

The simplest and most popular way of propelling the wheelchair is to put two small permanent magnet DC motors and reduction gearboxes, one on each back wheel. These motors have a stalled torque up to ten times their rated running torque, and the slowing down of the inside wheel when cornering results in a large increase in torque causing the wheelchair to try to return to a straight line.

According to one aspect of the present invention, therefore, a tiller steered battery driven wheelchair has the or each steerable wheelaxle disposed in front of the kingpin or the respective kingpin. This is applicable to either a three-wheeled wheelchair with one steerable wheel, which may be at the front or the back, orto a four-wheeled wheelchair with two steerable wheels, which may be at the front or at the back.

This aspect of the present invention is in complete contrast to the usual practice with vehicles, which is to have the or each steerable axle disposed behind the kingpin or the respective kingpin and which enables the vehicle to continue in a straight line if the hands are taken off the steering wheel (or tiller).In other words a wheelchair in accordance with this aspect of the invention is inherently directionally unstable and tends to oversteer into a corner, but this is not detrimental with a wheelchair restricted to very low speeds, such as a maximum of four miles per hour, and - indeed - proves beneficial if, as is preferred, the distance between the axes of the axle and the kingpin is no more than one inch, the specific distance being that which is required for the unbalanced torque of the driven wheels to be exactly neutralised, thus producing a very light and easy steering, both for holding it straight and for guiding it into and out of corners or bends.

According to another aspect of the present invention, a tiller steered wheelchair has the or each kingpin offset laterally from the centre plane of the steerable wheel or the respective steerable wheel, whereby steering of the wheelchair when stationary or substantially stationary requires but little effort, because the or each steerable wheel turns by running around the axis of the kingpin or the respective kingpin, instead of being rotated on the spot against considerable friction forces between the tyre of the wheel and the ground.

The greater the width of the or each steerable wheel the greater should be the lateral offset of the or each kingpin from the centre plane of the steerable wheel or the respective steerable wheel, but the axis of the or each kingpin is preferably about 4 inches from the adjacent side of the rim of the hub of the steerable wheel or the respective steerable wheel.

According to a further aspect of the present invention, a battery driven wheelchair has a pair of steerable wheels and a pair of driven wheels (usually respectively the front and back pairs), with the driven wheels carried by an axle beam extending laterally and pivoted centrally on a horizontal axis on the fore-and-aft centre line of the wheelchair, whereby when negotiating uneven ground (and including negotiating kerbs and steps) the driven wheels maintain driving contact and the steerable wheel maintain steering contact, and also helps to smooth out any change in attitude of the wheelchair, without the need for springs, which may be so deflected by a heavy occupant that there is little or nothing in reserve to accommodate ground that is only slightly uneven.

However, it is preferable to use wheels with balloon tyres to afford some resilience in the suspension and to assist the negotiating kerbs or steps.

Afour-wheeled tiller-steered battery-driven wheelchair in accordance with the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of the complete wheelchair facing to the right; Figure 2 is a plan of the complete wheelchair facing to the left; Figure 3 corresponds to Figure 2 but with the body and battery box removed; and Figure 4 is a section taken from the line IV-IV of Figure 3.

In the drawings, a wheelchair has a chassis 1 and body 2, the latter enclosing a box 3 for a battery (not shown) for driving electric motors 4 for the back wheels 5, the front wheels 6 being steerable by means of a tiller 7. The body 2 also includes a seat 8 with a backrest 9 and arms 10, wings 11 for the back wheels 5 and wings 2 for the front wheels 6, between which is disposed a footrest 13.

The chassis 1 includes a pair of longitudinal members 14 and a front wheel support beam 15, which carries steering boxes 16 whose kingpins 17 are connected to each other by arms 18 and a linkrod 19 pivoted thereto. One of the kingpins 17 is also connected directly to the tiller 7. The axle 20 of each steerable wheel 6 is disposed in front of the respective kingpin 17, whereby the wheelchair is inherently directionally unstable and tends to oversteer into a corner, but this is not detrimental with a restriction to very low speeds (e.g., four miles per hour) and is beneficial if the distance between the respective axes 21, 22 of the respective axle and kingpin is no more than one inch, the specific distance being that which is required for the unbalanced torque of the driven wheels 5 to be exactly neutralised, thus producing a very light and easy steering, both for holding it straight and for guiding it into and out of corners or bends.

Each kingpin 17 is also offset laterally from the centre plane 23 of the respective steerable wheel 6, whereby steering of the wheelchair when stationary or substantially stationary requires but little effort, because each steerable wheel turns by running around the axis 22 of the respective kingpin, instead of being rotated on the spot against considerable friction forces between the tyre and the ground.

The driven wheels 5 are carried by an axle beam 24 pivoted centrally on a horizontal axis 25 on the fore-and-aft centre line of the wheelchair, whereby when negotiating uneven ground (or kerbs or steps) and driven wheels maintain driving contact and the steerable wheels 6 maintain steering contact, and also helps to smooth out any change in attitude of the wheelchair, without the need for springs, which may be so deflected by a heavy occupant that there is little or nothing in reserve to accommodate ground that is only slightly uneven.

However, it will be seen that the wheels 5, 6 have balloon tyres to afford some resilience in the suspension and to assist in negotiating kerbs or steps.

The axle beam 24 is part of a frame 26 having a longitudinai members 27 and another transverse beam 28 also pivoted on the horizontal axis 25, with the beam 28 carrying bearings 29 for a torsional shaft 30 between brake arms 31 for the driven wheels 5, the shaft 30 being linked (by means including a flexible armoured cable 32) to a brake lever 33.

Claims

1. A tiller-steered battery-driven wheelchair having the or each steerable wheel axle disposed in front of the kingpin or the respective kingpin.

2. A wheelchair as in Claim 1, wherein the distance between the axes of the axle and the kingpin is no more than one inch.

3. A wheelchair as is Claim 1, or Claim 2 wherein, the or each kingpin is offset laterally from the centre plane of the steerable wheel or the respective steerable wheel.

4. A wheelchair as in Claim 3, wherein, the axis of the or each kingpin is about 4 inches from the adjacent side of the rim of the hub of the steerable wheel or the respective steerable wheel.

5. A wheelchair as in any one of the preceding Claims having one steerable wheel.

6. A wheelchair as in Claim 5, wherein the steerable wheel is at the front.

7. A wheelchair as in any one of Ciaims 1 to 4 having two steerable wheels.

8. A wheelchair as in Claim 7, wherein the steerable wheels are at the front.

9. A wheelchair as in Claim 7 or Claim 8, wherein the driven wheels are carried by an axle beam extending laterally and pivoted centrally on a horizontal axis on the fore-and-aft centre line of the wheelchair.

10. A wheelchair as in any one of Claims 7 to 9, wherein the wheels have balloon tyres.

11. A tiller-steered battery-driven wheelchair substantially as herein before described with reference to the accompanying drawings.