GB2199291A

GB2199291A - Wheelchair with kerb climbing ability

Info

Publication number: GB2199291A
Application number: GB08630613A
Authority: GB
Inventors: John Bernard Chant
Original assignee: Everest & Jennings Ltd
Current assignee: Everest & Jennings Ltd
Priority date: 1986-12-22
Filing date: 1986-12-22
Publication date: 1988-07-06
Anticipated expiration: 2006-12-22
Also published as: GB8630613D0; GB2199291B

Abstract

A wheelchair of the type having large powerable front wheels (1) and relatively small rear caster wheels (2) has an additional caster protecting wheel means (3) disposed between the rear caster wheels and journalled for rotation or pivoting about a fixed horizontal axis. The additional wheel means (3) has its lower surface clear of the ground in normal travel and its forward facing surface adapted to contact a kerb before a caster wheel, in whatever swivelling orientation, can do so. Alternatively each of the caster wheels (2) is mounted for swivelling about a non-vertical axis, said axis being inclined forwardly of vertical, preferably in the region of 3 DEG from the vertical. <IMAGE>

Description

WHEELCHAIR The present invention relates to wheelchairs and similar vehicles such as prams, pshchairs and the like, all of which are encompassed by the term wheelchair.

More particularly, the invention relates to wheelchairs having relatively large powerable front wheels and relatively small rear wheels mounted, e.g. on casters, to be swivellable. Such wheelchairs will hereinafter be referred to as wheelchairs of the type described.

It is conventional for wheelchairs to have the large wheels, optionally powered, at the rear and small caster wheels at the front. This arrangement gives required. degree of stability and enables them to be easily steered. However, there is one great disadvantage of this arrangement. It is that the wheelchair cannot negotiate kerbs, steps and other upstanding obstacles (hereinafter referred to generically as kerbs). Much ingenuity has been exercised in attempting to overcome this disadvantage. Among others, there may be mentioned British patent specifications nos. 1569166, 2111000, and 2145983, and European patent specification no. 0127929.

There is also our copending application no. 8617532.

These all provide a quadrant arm or additional wheel mounted to the front of the wheelchair higher than the caster wheel or wheels and adapted to strike the kerb before the caster does. The kerb climbing attachment then either pivots or rotates as the wheelchair advances, and in so doing, lifts the caster wheels to a height where they can run onto the upper surface of the kerb. These kerb climbing attachments, while useful, are often mechanically complex and since they take the shock of the impact, there is a possibility of breakage. Also, since the attachments necessarily project beyond the front of the caster wheels, they may interfere with the comfort of the user.

One other method of overcoming the problem is shown in U.K. patent specification no. 2043554 in which the large driving wheels are placed at the front and caster wheels at the back, in other words it is a wheelchair of the type described. Such wheelchairs can negotiate kerbs, or at least those kerbs less high than the radius of the large front wheels. However, steering wheelchairs of the type described is extremely difficult, or at least it has been until the advent of sophisticated electronic feedback for speed control for each driving wheel. They are then compensated automatically, and virtually instantaneously, to the power required to maintain the chosen speed and direction of travel. This feedback control negates the effect of the casters following every slight variation in the running surface and every defect in the exact trueness and smoothness of the caster wheels.However, problems arise with the caster wheels during the climbing of a kerb. Once the large front wheels are on the upper surface, the angle of the wheelchair changes and the weight of the wheelchair on the rear caster wheels causes them to tend to swivel.

Once they have swivelled, they are no longer in a position to follow up the kerb and in the great majority of cases, they finish by striking the kerb when they are at right angles to their intended direction of travel, i.e. they are sideways on. This causes great damage to the casters, not to mention the occupant of the wheelchair whose progress is suddenly and possibly violently halted.

One way of overcoming this problem is to dispense with the caster wheels at the rear and instead provide steerable rear wheels, either by mechanical means or by electromechanical means. However this adds to the weight and cost of the wheelchair.

It is an object of the present invention to provide a wheelchair of the type described in which the rear caster wheels are protected from the effects of their swivelling when climbing kerbs.

According to a first aspect qf the present invention there is provided a wheelchair of the type described comprising an additional caster protecting wheel means disposed between the rear caster wheels and journalled for rotation or pivoting about a fixed horizontal axis, the additional wheel means having its lower surface clear of the ground in normal travel and its forward facing surface adapted to contact a kerb before a caster wheel, in whatever swivelling orientation, can do so.

Preferably the wheel means is a freely rotatable wheel, optionally of similar diameter to the caster wheels and mounted centrally therebetween. Alternatively, it may comprise two freely rotatable wheels spaced along the horizontal axis.

According to a second aspect of the present invention, there is provided a wheelchair of the type described in which each of the caster wheels is mounted for swivelling about a non-vertical axis, said axis being inclined forwardly of vertical.

Preferably the axis of swivelling is in the region of 30 from the vertical.

An embodiment of the present invention will now be more particularly described by way of example and with refercnce to the accompanying drawings, in which: FIGURE 1 shows a conventional wheelchair with mechanically steered rear wheels and which does not form part of the invention; FIGURE 2 shows the wheelchair of Figure 1 surmounting a kerb; FIGURES 3 and 4 show a wheelchair embodying the second aspect of the present invention, travelling on the flat and up a kerb respectively; FIGURE 5 shows the effect of the rear caster wheels swivelling during kerb climbing; and FIGURES 6 and 7 show a wheelchair embodying the first aspect of the present invention during kerb climbing.

Referring now to the drawings, it can be seen that any wheelchair having large front wheels 1 will easily mount onto a kerb. In Figures 1 and 2, the rear wheels are held in position and no problem is experienced in their also negotiating the kerb.

Referring now to Figures 3 and 4, it can be seen in Figure 4 that once the wheelchair is on the kerb, the angle of the wheelchair changes so that the angle of the caster crown pivot assumes the negative angle as shown.

The mass of the wheelchair under gravity then tends to rotate the caster out of its normal trailing position as soon as there are any side forces induced by irregularities of driving or of the running surface. Given sufficient time, tlie caster would turn through 1800 as shown in Figure 4. but in practice turns only sufficiently for the impact with the step to turn it through 900. As stated above, this results in damage to the casters. from a sideways on impact as shown in Figure 5. This problem can be partially alleviated by mounting the rear casters 2 at a slight angle from the vertical. If the kerb to be climbed is only small, then it may be that the angle made by the wheelchair during the climbing phase is not sufficient to give a negative bias to the swivelling axis of the caster.In such cases, the non-vertical mounting will thus ensure that the casters follow up the ke.rb along the desired line. However, the angle cannot be too great since, during steering manoeuvres the rear of the wheelchair will tend to move up and down. This is clearly undesirable from the point of view of the occupant. It has been found that an angle of 30 forward of vertical will not produce this side-effect and will still help in some cases.

As can be seen from Figure 4, where the angle moved by the wheelchair is more than 30, a negative angle is produced and the caster wheel 2 will tend to swivel from a~-position shown in dotted lines in Figure 4 towards its most stable position shown in full lines.

In order to overcome this problem, an additional caster protection wheel 3 is mounted centrally of the wheelchair between the two rear caster wheels 2. It is mounted slightly clear of the ground in normal use and its forward edge is forward of the caster wheels forward edge, in whatever swivelling inclination. The caster protection wheel 3 is journalled for free rotation about a fixed horizontal axis 6 by means of a support 5 attached to the wheelchair.

As can be seen from Figure 6, the caster protection wheel 3 strikes the kerb during the kerb climbing procedure before the caster wheel may do so.

The wheelchair is thus dragged by the powered front wheels 1 onto the upper surface of the kerb by means of the caster protection wheel 3. The height at which it is set is such that, when the caster wheels 2 contact the edge of the kerb, the contact is made by the outer rounded part of the caster tyre 4. The kerb thus gently pushes the caster wheel 2 into its normal trailing position for onward forward travel. This is helped by the positive bias of the caster swivelling angle.

The caster protection wheel 3 may, in fact, be duplicated so that one wheel 3 is near each caster wheel 2, although not so near as to interfere with its swivelling action. Such pairs of protection wheels may even be outside the caster wheels although this is likely to interfere either with the usability of the wheelchair of its stability.

The caster protection wheel 3 need not in fact be a wheel. It may be a quadrant arm mounted for pivoting movement.

Claims

CLAIMS:

1. A wheelchair of the type described comprising an additional caster protecting wheel means disposed between the rear caster wheels and journalled for rotation or pivoting about a fixed horizontal axis, the additional wheel means having its lower surface clear of the ground in normal travel and its forward facing surface adapted to contact a kerb before a caster wheel, in whatever swivelling orientation, can do so.

2. A wheelchair as claimed in claim 1, wherein the wheel means is a freely rotatable wheel.

3. A wheelchair as claimed in claim 2, wherein the wheel is of similar diameter to the caster wheels and mounted centrally therebetween.

4. A wheelchair as claimed in claim 1, wherein the wheel means comprises two freely rotatable wheels spaced along the horizontal axis.

5. A wheelchair of the type described in which each of the caster wheels is mounted for swivelling about a nonvertical axis, said axis being inclined forwardly of vertical.

6. A wheelchair as claimed in claim 5, wherein the axis of swivelling is in the region of 30 from the vertical.

7. A wheelchair of the type described substantially as described herein with reference to the accompanying drawings.