GB2339743A

GB2339743A - Wheelchair drive transmission

Info

Publication number: GB2339743A
Application number: GB9815466A
Authority: GB
Inventors: Iain Robert Warner; Kenneth Brian Stedman
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-07-17
Filing date: 1998-07-17
Publication date: 2000-02-09
Anticipated expiration: 2018-07-17
Also published as: GB2339743B; GB9815466D0

Description

2339743 Wheelchair Drive Transmission This invention relates to a

wheelchair drive transmission, for enabling a wheelchair to be driven through a gearbox 5 with a choice of gear ratios.

Most conventional wheelchairs have large diameter main ground-engaging wheels driven by a hand rim which the user grips and turns to drive the wheels. The hand wheel is conventionally fixed directly to the main wheel, usually on both sides of the wheelchair and gives a satisfactory speed/effort compromise for most- situations.

There are however situations, particularly going uphill, where a lower gear ratio would-be. desirable.

Wheelchairs with variable ratio geaboxes are known in themselves. Examples are shown in US 5,482,305, US 5,486,016 and US 4,727,965.

The gearboxes hitherto proposed for this purpose have been unduly complicated, and consequently expensive.

The invention aims to provide a simple uncomplicated and therefore low cost gearbox which will facilitate the operation of a wheelchair.

According to the invention, there is provided a wheelchair drive transmission comprising a main, ground-engaging wheel, a hand wheel coaxial with the main wheel and a gearbox for transmitting drive from the hand wheel to the main wheel, the gearbox being located at the common centre of the wheels and having two different gear ratios with the hand wheel being drivingly coupled to the main wheel at all times.

2 According to a second aspect of the invention, there is provided a wheelchair drive transmission comprising a main, ground-engaging wheel, a hand wheel coaxial with the main wheel and a gearbox for transmitting drive from the hand wheel to the main wheel, the gearbox being located at the common centre of the wheels and having two different gear ratios, wherein a gear change from one ratio to the other can only be effected when the main wheel is stationary.

One gearbox ratio is preferably a direct drive, i.e., 1:1. The other gear ratio is preferably a lower gear with a ratio of, for example, 1.5:1.

The gearbox preferably comprises a circular plate secured f ast to either the main wheel or the hand wheel, and an epicyclic gear, one element of which can either be locked up relative to the plate, or can transmit a geared force through the epicyclic gear train and another element of which is non-rotatably mounted on the wheelchair. The plate and the epicyclic gear are preferably mounted side by side, and both have an outer circumferential rim for engagement with a gear selector mechanism.

The gear selector mechanism preferably comprises two independently radially movable dogs which can be moved radially into and out of engagement with the circumferentially outer rims of the plate and the epicyclic gear. When both dogs are in engagement, the to the plate for direct, 1:1 epi.cyclic gear will be locked drive. when only the dog associated with the epicyclic gear is engaged, drive will be through the epicyclic gear to the main wheel at a lower gear ratio.

The dogs are preferably spring-biased relative to a gearbox casing in the engagement direction. A gear 3 selector finger has three positions; in one position it lifts one dog out of engagement; in a central position it allows both dogs to be spring- biased into engagement, and in a third position it lifts the other dog out of 5 engagement.

The dogs may engage with the plate or the ring gear respectively by means of toothing on the outsides of the plate and the ring gear and corresponding teeth on the dog. Alternatively the periphery of the plate and the ring gear may have a series of holes, and the dogs may have one or more pins which engage in the hole. Of course this arrangement could be reversed with the pins on the plate and the ring gear, and the holes in the dogs.

The invention will now be further described, by way of example, with reference to the accompanying drawings in which:

Figure 1 is a side view of a wheelchair with a drive transmission in accordance with the invention; Figure 2 is a detail of the centre of the main wheel of the wheelchair of Figure 1, on a larger scale; Figure 3 is a cross section through the transmission in accordance with the invention; Figure 4 is a plan view of the transmission of Figure 3; Figure 5 is an exploded view showing the dogs and gear selector for use in the transmission; Figure 6 shows an alternative form oil dogs; Figures 7a, 7b and 7c show the three different gear selector positions; Figure 8 is a detail of engaging teeth of the dogs and gear mechanism; and Figure 9 is a perspective view of an anti-run back mechanism; and Figure 10 is a plan view of- the mechanism of Figure Figure 1 schematically shows a wheelchair with a seat 10, handles 12, a footrest 14 and-small diameter front wheels 16. The wheelchair also has a main, ground-engaging or road wheel 18 and, mounted on this wheel, a hand wheel 20. The hand wheel 20 is connected by spokes 22 to a gearbox 24. The gearbox 24 has an operating lever at 26. The main wheel 18 has spokes 28 connecting the wheel rim to a hub.

It will be appreciated that this arrangement will be duplicated on the other side of the wheelchair. The gearbox may be handed, for mounting on opposite sides of the wheel chair, or identical gearboxes may be mounted on both sides.

The wheels 18 are mounted for rotation on an axle 30 which is non-rotatably mounted in the wheelchair frame. A centre gear 32 of an epicyclic 34 (Figure 3) is f ixed on the outer end of the axle 30. The epicyclic also has a ring gear 36 and planetary gears 38. A wheel hub plate 40 and a gearbox drive plate 42 are fixed together, and can rotate through a bearing 45 on the axle 30. The spokes 28 of the main wheel are attached to the hub plate 40.

The gearbox 24 has a housing 43 connected to the hand 5 wheel spokes 22. The housing includes, at one side (see Figure 4) two parallel selector plates 44 and 46.

As can be seen from Figure 4, the selector plates 44, 46 are urged towards the adjacent surfaces of the drive plate 42 and the ring gear 36 respectively by compression springs 50.

Referring now to Figure 5, the plates 44 and 46 are shown in conjunction with a selector lever 52. Both selector plates 44, 46 have a toothed profile at their leading edge, and this profile will engage -with and block in a correspondingly toothed profile on the peripheral edge of the drive plate 42 or the ring gear 36. In particular the plate 44 is adapted to engage with the ring gear 36 and the plate 46 is adapted to engage with the periphery of the drive plate 42. Figure 8 shows tooth profiles at the outer edge of the ring gear 36 and on the selector plate 44. The tooth profiles on the drive plate 42 and the selector plate 46 will be the same as those shown for the gear 36 and the plate 44. It can be seen that the teeth on the selector plates have a trapezoidal shape whereas the teeth on the ring gear/drive plate have a top-hat shape. These different profiles ensure that the teeth mesh promptly and reliably when the selector plate is pressed against the periphery of the ring gear/drive plate, with a minimum of possible relative rotation after changing gear. The use of a top-hat section on the periphery of the ring gear/drive plate also simplifies the manufacture of the tooth profiles.

Both selector plates have an aperture 54 which is generally square as shown. The operating lever 26 is connected to a selector lever 52 which is carried in upper and lower bearing recesses 56, 58 in the housing 24 and 5 has opposite lobes 60, 62. When the operating lever 26 is in its central position, the common plane of the lobes 60, 62 lies parallel to the back face of the apertures 54 and exerts no force on the selector plates 44, 46. In this position, the selector plates are urged by the springs 50 into contact with, respectively, the ring gear 36 and the drive plate 42. This condition is shown in Figure 7b. Because the two plates are locked together, the ring gear 36 cannot rotate relative to the drive plate 42 and the whole epicyclic mechanism is therefore locked up and in particular is locked to the centre gear 32 which itself is fixed relative to the axle 30. In this position, the wheelchair is braked, and the wheef 18 cannot move in either direction.

However turning the selector lever 26 in one direction, let us say the clockwise direction as viewed in Figure 5 will cause the lower lobe 60 to press the rear face of the aperture 54 of the selector plate 46 to withdraw the plate 46 from engagement with the rim of the drive plate 42. In this position rotation of the hand wheel, which rotates the housing 24 also rotates the ring gear 36. Drive will be transferred to the drive plate 42, and thus through the spokes 28 to the main wheel 18 through the engagement of the planetary gears 38 in the drive plate 42. The epicyclic gear 34 will operate in the manner well known to those familiar with epicyclic gears, and therelative numbers of teeth on the ring gear, centre gear and planets will determine the gear ration. To achieve a 1.5:1 ratio, the planets 38 can have 12 teeth, the centre gear 32 can have 76 teeth and the ring gear 36 can have 100 teeth.

7 This is the low gear position.

To change gear, the user has to stop the wheelchair and operate the lever 26. The lever moves first of all to the locked position (the central position) and from there to a position where the upper lobe 62 now acts on the selector plate 44 to withdraw that from engagement with the ring gear, whilst releasing the effect of the lobe 60 on the selector plate 46 which is then returned by the springs into engagement with the drive plate 42. This position is shown in Figure 7c. In this position, when the hand wheel 20 is turned, the drive will be- directly through the teeth of the selector plate 46 to the drive plate 42 and thus to the wheel 18. This position therefore achieves a 1:1 drive ratio.

Note that at no stage can the viheelchair freewheel. operation of the lever 26 moves the gear mechanism from direct drive to the braked position and then to low gear, or from low gear to the braked position and then to direct drive. This is an important safety feature which ensures that the wheelchair is fully under the control of the rider at all times.

Figure 6 shows an alternative form of the selector plates. The plates 144, 146 have a projecting, tapered pin in place of a toothed profile. These pins will co-operate with the teeth on the periphery of the drive plate and of the ring gear, so that when one plate is released to be pushed by the springs 50 against the plate or gear, the respective pin will drop into the next available tooth gap which comes into register with the pin. Alternatively the periphery of the drive plate/ring gear could be formed with a series of holes in which the pins can engage.

Other types of intermeshing edge formations may also be used.

8 Because the main wheel and the hand wheel are always locked to one another, the hand wheels can never be turned without the main wheels also turning. It follows from this that the user always has control over the main wheels, and the chair cannot "'run away" with the wheels set in a neutral setting.

Experience shows that one direct drive and one lower gear are all that most wheelchair users need, and the design described here is simple and effective and easy to manufacture. It also provides in integral brake.

Figures 4, 9 and 10 show an anti-run back mechanism. This mechanism takes the form of two side by side pawls 66a, 66b, both of which are pivoted on a spindle at 68 and pulled by springs 70a, 70b against the periphery of the drive plate 42 and the ring gear 36 respectively. The pawls can engage separately in the resDective toothed peripheral surfaces, depending on the particular relative positions of each pawl and the teeth with which it must engage. In the 'pawl engaged, position, teeth 72 on the pawls engage in the teeth 53 of the drive plate and ring gear 42,36 and clockwise rotation (as seen in Figure 10) is prevented. Thus the wheel of the wheelchair cannot move in reverse. The wheel can however turn in the anti clockwise direction, by the pawl riding over the teeth 53.

The anti-run back mechanism can be disengaged. A plunger 74 (Figure 9) with a tapered shaft 76 can be pushed in to lift the pawls, against the force of the springs 70a,70b, away from the periphery of the drive plate/ring gear 42,36, so that the teeth of the pawls do not interfere with rotation of the drive plate/ring gear 42,36. Lifting the plunger 74 as indicated by the arrow 78 allows the spring 70 to once again urge the pawl against the teeth 53 and to reset the anti-run back mechanism.

The anti-run back mechanism is an important safety feature which ensures that the wheelchair will not run backwards, even if the rider lets go of the hand wheel without applying a brake.

Claims

1. A wheelchair drive transmission comprising a main, ground-engaging wheel, a hand wheel coaxial with the main wheel and a gearbox for transmitting drive from the hand wheel to the main wheel, the gearbox being located at the common centre of the wheels and having two different gear ratios with the hand wheel being drivingly coupled to the main wheel at all times.

2. A wheelchair drive transmission comprising a main, ground-engaging wheel, a hand. wheel coaxial with the main wheel and a gearbox for transmitting drive from the hand wheel to the main wheel, the gearbox being located at the common centre of the wheels and having two different gear ratios, wherein a gear change from one ratio to the other can only be effected when the main wheel is stationary.

3. A mechanism as claimed in Claim I or Claim 2, wherein one gearbox ratio is a direct drive and the other gear ratio is a lower gear.

4. A mechanism as claimed in Claim 3, wherein the lower gear ratio is substantially 1.5:1.

5. A mechanism as claimed in any preceding claim, wherein the gearbox comprises a circular plate secured f ast to either the main wheel or the hand wheel, and an epicyclic gear, one element of which can either be locked up relative to the plate or can transmit a geared force through the epicyclic gear train, and another element of which is non-rotatably mounted on the wheelchair.

6. A mechanism as claimed in Claim 5, wherein the plate and the epicyclic gear are mounted side by side, and both have an outer circumferential rim for engagement with a gear selector mechanism.

7. A mechanism as claimed in Claim 6, wherein the gear selector mechanism comprises two independently radially movable dogs which can be moved radially into and out of engagement with the circumferentially outer rims of the plate and the epicyclic gear.

8. A mechanism as claimed in Claim 7, wherein when both dogs are in engagement, the epicyclic gear is locked to the plate for direct, 1:1 drive, and when only the dog associated with the epicyclic gear is engaged, drive will be through the epicyclic gear to the main wheel at a lower gear ratio.

9. A mechanism as claimed in Claim or Claim 8, wherein the dogs are spring-biased relative to a gearbox casing in the engagement direction.

10. A mechanism as claimed in any one of Claims 7 to 9, wherein a gear selector finger has three positions; in one position it lifts one dog out of engagement; in a central position it allows both dogs to be springbiased into engagement, and in a third position it lifts the other dog out of engagement.

11. A mechanism as claimed in any one of Claims 7 to 10, wherein the dogs engage with the plate or the ring gear respectively by means of toothing on the periphery of the plate and of the ring gear and corresponding teeth on the dog.

12. A wheelchair a main, ground-engaging wheel and a hand wheel coaxial with the main wheel, wherein a ratchet mechanism is mounted between a non-rotating part of the wheelchair, and a main, ground-engaging wheel of the wheelchair, to allow rotational movement of the wheel in a forward direction but to prevent rotational movement in a reverse direction.

13. A wheelchair as claimed in Claim 12, wherein the ratchet mechanism can be selectively engaged and disengaged.

14. A wheelchair as claimed in Claim 12 or Claim 13, wherein the ratchet mechanism has a pawl mounted on a nonrotating part of the wheelchair and a toothed wheel mounted for rotation with the wheel.

15. A wheelchair as claimed in any one of Claims 12 to 13, incorporating a drive mechanism as claimed in any one of Claims I to 11.

16. A wheelchair as claimed in Claim 15 when dependent on Claims 7 and 14, wherein toothed wheels of the ratchet mechanism are formed on the circumferentially outer rims of the plate and the epicyclic gear, and a ratchet pawl is provided for engaging with each rim, the pawls being mounted on a common spindle.

17. A wheelchair drive mechanism substantially as herein described with reference to the accompanying drawings.

18. A wheelchair substantially as herein described with reference to the accompanying drawings.