Backstop and gear-shift arrangement for a wheelchair wheel

A wheel assembly comprising a wheelchair wheel (5) and a backstop arrangement (10; 30; 70) configured to selectively engage and disengage a backstop function and comprising a backstop selector (15; 35; 75) and a backstop member (18; 38; 78), wherein the wheel (5) comprises an internal-gear wheel hub (11; 31; 71) comprising a number of internal gears (57, 58) and having an inner rotatable circumferential surface (13; 33; 73), and wherein the backstop member is configured to allow the inner circumferential surface to rotate in one direction and to prevent rotation in the opposite direction. The wheel assembly comprises further a gear-shift arrangement comprising a shift member (54), which is axially moveable within the internal-gear hub (31) to engage a specific gear of said number of internal gears (57, 58), and wherein the shift member (54) via a connector member (55) is operatively connected to the backstop selector.

FIELD OF THE INVENTION

The present invention relates to a combined backstop and gear-shift arrangement used in a wheelchair wheel, and particularly to a combined backstop and gear-shift arrangement for a wheelchair wheel, wherein a selectively engageable backstop mechanism is incorporated in a combined backstop and gear-shift arrangement.

BACKGROUND OF THE INVENTION

It is becoming increasingly more common for wheelchair wheels to be provided with gears in order to facilitate the use of wheelchairs by different users, especially when travelling on surfaces having varying gradients. This is especially the case for wheelchair wheels intended to be used on manually powered wheelchairs. These manually powered wheelchairs are propelled, steered and braked by a user by either turning or gripping a ring attached to each of the two main wheels of the wheelchair. By providing a gear mechanism between the gripping ring and the wheelchair wheel, the rotational speed of the gripping ring can differ from the rotational speed of the wheelchair wheel, which, for example, enables the user to reduce or increase the number of gripping ring actions for travelling a given distance.

The advantages of providing a wheelchair wheel with a gear mechanism have been recognized in several patents and patent applications. For example, the Swedish Patent No. 538008 to Didner et al. and the corresponding International Patent Publication No. WO2015167387 disclose a gear-shift arrangement comprising an internal-gear hub, which comprises a number of internal gears, a shift member, and a gear selector for selectively engage a specific gear of the number of internal gears.

Another mechanical feature that assists a wheelchair user is the backstop mechanism. A wheelchair wheel provided with a backstop mechanism allows the wheelchair user to, for example, rest a while before he or she starts a new gripping ring action without risking that the wheelchair rolls in a backward direction. A backstop mechanism is particularly useful when the user travels uphill, and a backstop arrangement for a wheelchair wheel is therefore also sometimes referred to as a hill-holder mechanism. Many of the known backstop or hill-holder arrangements are, however, permanently or automatically engaged and/or cannot be engaged unless the wheelchair wheel is brought to a standstill. A disadvantage with an engaged backstop mechanism whose backstopping function is not utilized—i.e. when the wheelchair is continuously moving forward—is that the backstop mechanism then adds to the amount of energy necessary to propel the wheelchair. An engaged backstop mechanism is also typically more subjected to wear than a disengaged backstop mechanism.

In the U.S. Pat. No. 7,124,858 to Ikegami et al., an exemplifying wheel assembly for a wheelchair is disclosed, which comprises a brake in the form of a brake shoe that can be used as a backstop. The backstop function can be selectively engaged and disengaged by a wheelchair user. The wheel assembly disclosed in this patent has no means for gear shifting.

A similar, exemplifying arrangement is shown in the U.S. Pat. No. 4,045,047 to Buckley, wherein a backstop mechanism comprises a roller, which in an engaged position is wedged between two surfaces to prevent rotation in one direction. The roller can be selectively engaged and disengaged by a wheelchair user. Also this arrangement has no means for gear shifting.

The U.S. Pat. No. 6,755,430 to Watwood et al. discloses a wheelchair drive mechanism having a transmission providing forward, rearward and neutral movement through maneuvering of a drive arm. When the drive mechanism is in a particular gear (i.e. forward gear or rearward gear), motion in the opposite direction is prevented by a specially arranged pinion, and when the neutral gear is selected, freewheeling or motion in forward or backward directions is allowed. The wheelchair drive mechanism disclosed in this patent has no means for shifting between forward gears having different gear ratios.

A propulsion system for a wheelchair is presented in the U.S. Pat. No. 8,931,796 to Nasser et al. Embodiments of the propulsion system comprise one or more planetary gears, and a wheelchair user shifts gear by rotating or pulling a gear-shift lever. The propulsion system can further be provided with a backstop mechanism in the form of a ratcheting mechanism, which a user selectively can engage or disengage by rotating an anti-rollback lever arranged at the wheel hub. In this system, the gear-shift mechanism and the backstop mechanism are operated as separate functions by two separate levers.

A backstop mechanism, which sometimes is referred to as a hill-holder mechanism, for a wheelchair wheel is typically engaged by a wheelchair user when he or she—while using the gear with lowest available gear ratio—has traveled a distance uphill and is in a more or less exhausted state, to prevent the wheelchair from rolling backwards in case he or she no longer is able to maintain the forward motion. It is therefore paramount that the backstop mechanism is easy to engage with a familiar operation that requires a minimum of force. In this respect, the known backstop and gear-shift arrangements can be improved.

The object of the present invention is therefore to provide an improved backstop and gear-shift arrangement for a wheelchair wheel, which arrangement both allows shifting between gears having different gear ratios and a selective engagement of a backstop function. The backstop and gear-shift arrangement should further be easy to operate in a reliable and user-friendly way.

SUMMARY OF THE INVENTION

The above-mentioned objects are achieved by the present invention according to the independent claims. Preferred embodiments are set forth in the dependent claims.

The present invention is based on the insight about the close relation between the engagement of a backstop function and the use of the lowest available gear in a geared wheel assembly. That is, when a wheelchair user travels uphill, he or she typically engages the lowest available gear, i.e. the gear having the lowest gear ratio, and when he/she becomes tired and no longer is confident that a forward motion can be maintained, the backstop function, if available, is engaged, to thereby provide the possibility for the wheelchair user to rest between muscle-based propulsion actions without risking that the wheelchair rolls backwards and downhill. In a sense, an engaged backstop function can therefore be regarded as a supplement to the lowest available gear. Alternatively, an engaged backstop function can even be regarded as the lowest available gear, i.e. the lowest available gear is the gear having the lowest gear ratio and an engaged backstop function, while the second lowest available gear is the gear having the lowest gear ratio and a disengaged backstop function. The present invention reflects this connection between a gear-shift mechanism and a backstop mechanism by providing an arrangement wherein the engagement of a backstop function is performed with the same type of maneuvering that is used for shifting gears.

The invention relates to a wheel assembly comprising a wheel for a wheelchair and a backstop arrangement, the wheel being provided with a wheel hub and a wheel axle, the backstop arrangement being configured to selectively engage and disengage, respectively, a backstop function, the backstop arrangement comprising a backstop selector and a backstop member, wherein the wheel hub has an inner rotatable circumferential surface, which faces the wheel axle and is arranged with a radial space therefrom, and the backstop selector is operatively connected to the backstop member, which is radially moveable within the radial space, to, upon movement of the backstop selector, be selectively engaged with or disengaged from the inner circumferential surface, and wherein the backstop member is configured, when in engagement with the inner circumferential surface, to allow the inner circumferential surface to rotate in a first direction and to prevent the inner circumferential surface from rotating in a second, opposite direction, wherein the wheel assembly further comprises a gear-shift arrangement and the wheel hub is an internal-gear hub comprising a number of internal gears, and the gear-shift arrangement comprises a shift member, which is axially moveable within the internal-gear hub to engage a specific gear of said number of internal gears, and wherein the shift member via a connector member is operatively connected to the backstop selector.

By this arrangement, the backstop arrangement is effectively a gear-shift and backstop arrangement and the backstop selector is effectively a gear and backstop selector, which allows a wheelchair user to engage a backstop function with the same familiar type of movement that was used to shift between gears, i.e. the engagement of a backstop function is done with the same type of rotational movement that was used to shift, e.g., from a higher gear to the lowest available gear.

The backstop arrangement can accomplish the backstop function in a reliable way by utilizing a cam curve, and in one embodiment, the backstop selector comprises a base portion comprising a contour, which extends a circumferential distance in the base portion and which comprises at least two positions with different radial distances from the wheel axle, and the backstop arrangement comprises a sliding element, which can slide in the contour, to, upon movement of the backstop selector, be positioned in one of said at least two positions, and wherein the sliding element is operatively connected to the backstop member.

The gear-shift arrangement can accomplish the gear-shift function in a reliable way by also utilizing a cam curve, and in an embodiment, the backstop selector comprises a second cam curve having a number of fixed positions having different radial distances and wherein a shift member is connected to a sliding element which can slide in the second cam curve by movement of the backstop selector.

In one embodiment of the invention, a backstop arrangement comprises a ratcheting mechanism, which in a further embodiment is arranged such that the inner circumferential surface is provided with teeth and the backstop member comprises a pivotally arranged rod having a first end portion configured to, upon movement of the backstop selector, be in contact with said teeth, wherein the rod is configured such that the teeth of the inner rotatable circumferential surface are dragged over the first end portion of the rod when the inner circumferential surface rotates in a first direction and wherein one tooth abuts the first end portion of the rod when the inner circumferential surface rotates in a second, opposite direction, and wherein the rod comprises a second end portion, which is connected to the sliding element, and wherein the backstop arrangement further comprises a spring, which is connected to the first end portion of the rod and strives to push the first end portion towards the inner circumferential surface or is connected to the second end portion of the rod and strives to pull the second end portion away from the inner circumferential surface. Such a ratcheting mechanism is a simple and reliable way of providing a backstop function.

In an another embodiment of the invention, the backstop arrangement comprises a freewheel mechanism, and is in a further embodiment arranged such that the inner circumferential surface is provided with teeth and the backstop member comprises a pivotally arranged rod having a first end portion provided with a cogged freewheel and being configured such that, upon movement of the backstop selector, the cogged freewheel is engaged with said teeth, wherein the cogged freewheel permits the inner circumferential surface to rotate in a first direction and prevents the inner circumferential surface from rotating in a second, opposite direction, and wherein the rod comprises a second end portion, which is connected to the sliding element, and wherein the backstop arrangement further comprises a spring, which is connected to the first end portion and strives to push the cogged freewheel towards the inner circumferential surface or is connected to the second end portion and strives to pull the second end portion away from the inner circumferential surface. A freewheel mechanism of this type allows a quick engagement of the backstop function and a freewheel is also less exposed to wear than, for example, a ratcheting mechanism.

In another embodiment of the invention, the backstop function is accomplished by a roller, and the backstop arrangement comprises a support structure provided with an inclined recess, which together with the inner circumferential surface forms a space that narrows towards the inner circumferential surface and wherein the backstop member comprises a rotatable roller, which is arranged in the narrowing space and is connected to a spring, which strives to push the rotatable roller towards the inner circumferential surface, and wherein the sliding element constitutes a central axle for the rotatable roller. Because of their robust constructions, a roller and an inclined recess provide a very durable backstop mechanism.

As used herein, the term “forward direction”, when used in relation to the rotation of a wheel, refers to the rotational direction that moves a wheelchair provided with the wheel in question in a forward direction; and, similarly, the term “backward direction”, when used in relation to the rotation of a wheel, refers to the rotational direction that moves a wheelchair provided with the wheel in question in a backward direction, or alternatively the rotational direction that would have moved the wheelchair in a backward direction if the backstop arrangement had not prevented such motion.

The backstop arrangement according to the present invention is to be used in a geared wheelchair wheel, and embodiments of the invention will be described with reference to such a geared wheelchair wheel. In particular when used in combination with the gear-shift arrangement disclosed in the aforementioned patent publication WO2015167387, the benefits of the present backstop arrangement are advantageously exploited, because then a backstop selector is advantageously combined with a gear selector, such that a combined backstop and gear selector is provided; and the user can then repeat or continue the manoeuvre which was used to select a specific, preferably the lowest gear to—if he or she so wishes—also engage a backstop mechanism.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention relates to a wheelchair and more specifically to the main driving wheels of a wheelchair. An exemplifying wheelchair is depicted inFIG. 1, wherein a wheelchair1essentially comprises a seat2, a back3, a foot support4, and two wheels5. Each of the two wheels5is provided with an outer gripping ring6and an internal backstop arrangement7. InFIG. 1only one of the two backstop arrangements7is visible. By providing the wheels5with backstop arrangements7, a wheelchair user can rest without risking that the wheelchair1moves backwards, which is a feature that is extremely helpful when, for example, travelling uphill. As will be demonstrated below, the backstop arrangement7is selectively engageable, which provides the advantages of a backstop function without impairing the user's ability to, e.g., maneuver the wheelchair1in narrow spaces and without preventing the user from moving backwards when the user so wishes, something which is more or less necessary when, for example, negotiating an obstacle such as a pavement edge or a curb. A selectively engageable backstop arrangement7has also positive effects on the amount of energy needed to propel the wheelchair1and reduces the wear of the backstop arrangement7, as was explained above.

Still with reference toFIG. 1, the backstop arrangement7comprises further a wheel hub8with a wheel axle (not visible in the figure) and a backstop selector9, which, due to the present invention, effectively works as a combined gear and backstop selector9. As will be seen and explained below, a combination of a backstop arrangement, such as backstop arrangement7, and a gear-shift arrangement provides several advantages; and in such a case the wheel hub8is preferably an internal-gear hub8comprising a planetary gear system, which as such is well-known in the art.

Suitable internal-gear hubs are, for example, commercially available from the company Sturmey-Archer, e.g. the model S3X.

InFIGS. 2a-2h, a first embodiment of a backstop arrangement according to the present inventions is illustrated. This embodiment shows both a backstop arrangement and illustrates how a backstop arrangement can be integrated into and combined with a gear-shift arrangement.

Focusing first on the backstop function of this embodiment,FIGS. 2dand 2eas well asFIGS. 2gand 2hshow a first embodiment of a backstop arrangement30, which is arranged at a wheel hub31, which comprises a wheel axle32and has an inner circumferential surface33, which faces the wheel axle32and is arranged with a radial distance from the wheel axle32, such that a radial circumferential space34is provided between the wheel axle32and the inner circumferential surface33. The inner circumferential surface33, which alternatively can be arranged as an attachable inner ring or cylinder33, is rotatable in both clockwise direction and counter-clockwise direction when the backstop arrangement30is not engaged, and is, when the backstop arrangement30is engaged, only rotatable in a counter-clockwise direction (as seen in the figures), which will be explained and demonstrated below. As depicted inFIGS. 2d-2eand 2g-2h, a counter-clockwise direction corresponds to a forward direction for a wheelchair provided with a wheel comprising the backstop arrangement30. The backstop arrangement30comprises further an axially movable backstop selector35, which is axially movably attached to the wheel axle32and has a lower or inner base portion36and an upper or outer portion in the shape of a handle37. The backstop arrangement30comprises further a backstop member38, which is pivotally arranged on a support structure48in the radial space34provided between the wheel axle32and the inner rotatable surface33, and is in this embodiment essentially a rod39having a first end portion40provided with a small cogged freewheel41and a second end portion42provided with a sliding element43in the form of a pin44, which inFIGS. 2a-2b, 2d-2eand 2g-2hextends towards the viewer.

The second end portion42of the pivotally arranged backstop member38is attached to a stretched spring45, which strives to pull the second end portion42inwardly and which, because of the pivotal arrangement of the backstop member38, simultaneously strives to push the first end portion40outwardly, such that the small cogged freewheel41comes into contact with the inner circumferential surface33. The base portion36of the backstop selector35comprises a first or upper contour46, on which the sliding element43slides, i.e. the pin44follows the upper contour46as the backstop selector35is moved axially by a user who wishes either to engage the backstop function or disengage the backstop function. The upper contour46may alternatively be regarded and referred to as the upper cam curve46, since it has the controlling function typically associated with a cam curve.

InFIG. 2dandFIG. 2e, the backstop member38is schematically illustrated in a disengaged position; and more particularly, inFIG. 2dthe backstop selector35has been removed to more clearly show the operation of the backstop member38, while the backstop selector35is present inFIG. 2eto show the functioning of the upper contour46in the base portion36of the backstop selector35in combination with the sliding element43.

FromFIG. 2dit can be seen that the inner circumferential surface33is provided with a number of teeth47and that the stretched spring45strives to pull the second end portion42of the rod39inwardly and thereby simultaneously strives to force the small cogged freewheel41, which is rotatably arranged at the first end portion40of the rod39, into engagement with the teeth47arranged on the inner circumferential surface33. FromFIG. 2eit can be seen that the upper contour46has a circumferential shape with varying radial distance to the wheel axle32; and in the disengaged position depicted inFIG. 2e, the sliding element43, which here is in the form of the pin44, is resting on the upper contour46at a position where there is a relatively long radial distance to the wheel axle32, such that the second end portion42is forced to remain at a relatively long distance from the wheel axle32, and simultaneously such that the small cogged freewheel41, which is arranged at the first end portion40of the rod39, is prevented from coming into engagement with the teeth47of the inner circumferential surface33.

In the engaged position illustrated inFIG. 2gandFIG. 2h, a wheelchair user has moved the backstop selector35axially in a circumferential direction, such that the sliding element33, i.e. the pin34, has followed the upper contour46and is now in a position in the upper contour46with a relatively shorter distance to the wheel axle32. This means that the spring45now is able to pull the small cogged freewheel41, which is rotatably arranged at the first end portion40of the pivotally arranged rod39, into engagement with the teeth47of the inner circumferential surface33. The small cogged freewheel41can rotate in a first direction and is locked in a second, opposite direction. Such freewheels are known in the art, and are, for example, commercially available from the company Schaeffler. The interior functioning of the freewheel41will therefore not be described herein. Thus, when the cogged freewheel41is in engagement with the teeth47of the inner circumferential surface33, the circumferential surface33can rotate in a first direction as permitted by the cogged freewheel41, while the circumferential surface33is prevented to rotate in a second, opposite direction as prevented by the cogged freewheel41. Apparently, a first direction corresponds to a forward direction for a wheelchair having a wheel provided with the backstop arrangement30, while a second, opposite direction corresponds to a backward direction for a wheelchair having a wheel provided with the backstop arrangement30. It should further be understood that a spring, such as spring45, can optionally be arranged as a compressed and pushing spring or a stretched and pulling spring by choosing attachment side of a pivotally arranged backstop member.

An advantage with the backstop arrangement30, which is described in conjunction withFIGS. 2a-2h, is that the backstop arrangement30is very silent in operation. A freewheel, such as the small cogged freewheel41, is also resistant to wear and can provide a direct and reliable action, because the cogged freewheel41is, when the backstop function is engaged, always in engagement with the teeth41, such that the backstopping function immediately comes into action when the wheelchair attempts to go in a backward direction.

Focusing now on the gear-selection function of this first embodiment,FIGS. 2a-2cshow the backstop selector35, which, when combined with a gear-selection function, alternatively can be referred to as the gear and backstop selector35, in a first position; and more precisely, inFIG. 2athe gear and backstop selector35has been removed to more clearly show the operation of a guide member51and a sliding element52, while the gear and backstop selector35is present inFIG. 2bto show the functioning of a second or lower contour53, which is provided as a cam curve53that extends a circumferential distance, in combination with the sliding element52, andFIG. 2cshows how the gear-selecting function is executed by a shift member54, which is located in the gear hub31and is connected to a connector member55. The backstop arrangement30, which, when combined with a gear-shift arrangement, can be referred to as the backstop and gear-shift arrangement30, comprises the sliding element52, which can slide radially within a guide slot56provided in the guide member51and can also move circumferentially within the lower cam curve53. In the first position illustrated inFIGS. 2a-2c, the sliding element52is in a first position in the cam curve53and has in this position a relatively short radial distance to the wheel axle32.FIG. 2cillustrates that in this first position, the shift member54, which has a cogged outer surface, is in engagement with a first cogged internal gear57. FromFIGS. 2aand 2bit can also be inferred that in this position the upper contour46prevents the backstop member38(i.e. in this embodiment the small cogged freewheel41) to come into engagement with the teeth47arranged at the inner circumferential surface33, i.e. the backstop function is not engaged.

FIGS. 2d-2fshow the backstop and gear-shift arrangement30in a second position, wherein a wheelchair user has moved the gear and backstop selector35axially to engage a second internal gear58. More precisely, by axially moving the gear and backstop selector35in a counter-clockwise direction (as seen inFIG. 2e), the sliding element52has moved in the cam curve53into a position with a relatively longer distance to the wheel axle32, as is best seen inFIG. 2d. By moving the gear and backstop selector35and thereby the sliding element52, which is connected to the shift member54via the connector member55, the shift member54has moved out of engagement with the first internal gear57and into engagement with a second internal gear58. A connector member, such as connector member55, which preferably is a flexible member, can be provided in the form of a chain or a wire. FromFIG. 2eit can also be seen that in this position, the upper contour46still prevents the backstop member38(i.e. in this embodiment the small cogged freewheel41) to come into engagement with the inner circumferential surface33, i.e. the backstop function is still not engaged. In this exemplifying embodiment, only two internal gears are provided, but it should be understood that more internal gears can easily be arranged, and are engageable by a cam curve having more positions with different radial distances for a sliding element which slides within this cam curve.

Now, returning once again toFIGS. 2gand 2h, wherein a wheelchair user has moved the backstop and gear selector35to a third position, it can be appreciated that the sliding element52has assumed a third position in the cam curve53, as seen inFIG. 2h. However, as seen inFIG. 2g, the radial distance for the sliding element52has not changed and is the same as in the second position shown inFIG. 2d. This means that the second internal gear58is still engaged, but now also the backstop function is engaged, as was thoroughly explained above. Thus, by moving the backstop and gear selector35back and forth in a circumferential direction, a wheelchair user can engage and disengage, respectively, a backstop function while still having the same gear engaged. It is believed that a selectively engageable backstop function is best utilized in combination with the lowest gear, when arranged in combination with a geared wheel hub, since the lowest gear available is presumably already selected and engaged under the circumstances in which a backstop function is most needed, such as when travelling uphill or maneuvering the wheelchair over obstacles.

FIGS. 3aand 3bas well asFIGS. 3cand 3dshow a second embodiment of a backstop arrangement10, which is arranged at a wheel hub11, which comprises a wheel axle12and has an inner circumferential rotatable surface13, which faces the wheel axle12and is arranged with a radial distance from the wheel axle12, such that a radial circumferential space14is provided between the wheel axle12and the inner circumferential surface13. The inner circumferential surface13, which alternatively can be arranged as an attachable inner ring or cylinder13, is rotatable in both clockwise direction and counter-clockwise direction when the backstop arrangement10is not engaged, and is, when the backstop arrangement10is engaged, only rotatable in a counter-clockwise direction (as seen in the figures), which will be explained and demonstrated below. As depicted inFIGS. 3a-3d, a counter-clockwise direction corresponds to a forward direction for a wheelchair provided with a wheel comprising the backstop arrangement10. The backstop arrangement10comprises further an axially movable backstop selector15, which is axially movably attached to the wheel axle12and has a lower or inner base portion16and an upper or outer portion in the shape of a handle17. The backstop arrangement10comprises further a backstop member18, which is pivotally arranged on a support structure28in the radial space14provided between the wheel axle12and the inner circumferential surface13, and is in this embodiment essentially a rod19having a first end portion20comprising a lip21and a second end portion22provided with a sliding element23in the form of a pin24, which inFIGS. 3a-3dextends towards the viewer. The lip21at the first end portion20of the pivotally arranged rod19is attached to a compressed spring25, which strives to push the first end portion20outwardly, i.e. towards and into contact with the inner circumferential surface13, and which, because of the pivotal arrangement of the rod19, simultaneously strives to push the second end portion22inwardly. The base portion16of the backstop selector15comprises a contour26, on which the sliding element23slides, i.e. the pin24follows the contour26as the backstop selector15is moved axially in a circumferential direction by a user who wishes either to engage the backstop function or disengage the backstop function.

The contour26, which extends a circumferential distance in the base portion16, can alternatively be regarded and referred to as a cam curve26, since it has the controlling function typically associated with a cam curve.

InFIG. 3aandFIG. 3b, the backstop member18is schematically illustrated in a first position; and more precisely, inFIG. 3athe backstop selector15has been removed to more clearly show the operation of the backstop member18, while the backstop selector15is present inFIG. 3bto show the functioning of the contour26provided in the base portion16of the backstop selector15in combination with the sliding element23.

FromFIG. 3ait can be seen that the inner circumferential surface13is provided with a number of teeth27and that the compressed spring25strives to push the first end portion20of the backstop member18into contact with the teeth27arranged on the inner circumferential surface13, and that, at the same time, the spring25strives to force the second end portion22of the pivotally arranged backstop member18inwardly. FromFIG. 3bit can be seen that the contour26has a circumferential shape with varying radial distance to the wheel axle12; and in the first position depicted inFIG. 3b, the sliding element23, which here is arranged in the form of the pin24, is resting on the contour26at a position where there is a relatively long radial distance to the wheel axle12, such that the second end portion22of backstop member18, which here is arranged in the form of the rod19, is forced to remain at a relatively long distance from the wheel axle12, and, simultaneously, such that the first end portion20of the backstop member18is prevented from coming into engagement with the teeth27of the inner circumferential surface13.

In the second position illustrated inFIG. 3candFIG. 3d, a wheelchair user has moved the backstop selector15axially in a circumferential direction, such that the sliding element23, i.e. the pin24, has followed the contour26and is now in a position in the contour26having a relatively shorter distance to the wheel axle12. This means that the spring25now is able to push the first end portion20of the pivotally arranged backstop member18, which here is arranged as the rod19, into engagement with the teeth27of the inner circumferential surface13. And since the rod19is arranged with an inclination to the circumferential surface13, the teeth27can slip over the lip21at the first end portion20of the rod19when the circumferential surface13rotates in a first direction (inFIG. 3c, in a counter-clockwise direction), but when the circumferential surface13rotates—or rather tries to rotate—in a second, opposite direction (inFIG. 3c, in a clockwise direction), the lip21at the first end portion20abuts and locks with one tooth27of the toothed inner circumferential surface13and prevents rotation in this second direction. In other words, in this embodiment, the backstop member18works as a ratchet in combination with the tooted inner circumferential surface13.

In the second embodiment of a backstop arrangement illustrated inFIGS. 3a-3d, it can be seen that the backstop function is combined with a gear-shift arrangement, which comprises a guide member51, a sliding element52, and a second or lower contour or cam curve53. Thus, the wheel hub11is an internal-gear hub11, and the function of the gear-shift arrangement is identical to the gear-shift arrangement that was thoroughly described above in conjunction withFIGS. 2a-2h. The gear-shift arrangement provided for the second embodiment described in conjunction withFIGS. 3a-3dwill therefore not be further described, but it is to be understood that the backstop arrangement10comprises a gear-shift arrangement, and also the backstop arrangement10can be regarded as a gear-shift and backstop arrangement10, and the backstop selector15can be regarded as a gear and backstop selector15.

FIGS. 4aand 4bas well asFIGS. 4cand 4dshow a third embodiment of a backstop arrangement70, which is arranged at a wheel hub71, which comprises a wheel axle72and has an inner circumferential rotatable surface73, which faces the wheel axle72and is arranged with a radial distance from the wheel axle72, such that a radial circumferential space74is provided between the wheel axle72and the inner circumferential surface73. The inner circumferential surface73, which alternatively can be arranged as an attachable inner ring or cylinder73, is rotatable in both clockwise direction and counter-clockwise direction when the backstop arrangement70is not engaged, and is, when the backstop arrangement70is engaged, only rotatable in a clockwise direction (as seen in the figures), which will be explained and demonstrated below. As depicted inFIGS. 4a-4d, a counter-clockwise direction corresponds to a forward direction for a wheelchair provided with a wheel comprising the backstop arrangement70. The backstop arrangement70comprises further an axially movable backstop selector75, which is axially movably attached to the wheel axle72and has a lower or inner base portion76and an upper or outer portion in the shape of a handle77. The backstop arrangement70comprises further a backstop member78, which is arranged in the radial space74provided between the wheel axle72and the inner rotatable circumferential surface73, and is in this embodiment a rotatable roller79. The backstop arrangement70comprises further a sliding element80, which is provided in the form of a central axle81for the rotatable roller79. The central axle81has an end portion82(not seen in the figures), which faces the backstop selector75and extends outside the roller79. The roller79is arranged in an inclined recess83, which faces the inner circumferential surface73and is provided in a support structure84. The roller79is further connected to a spring85and is arranged such that it can rotate and roll, i.e. move inwards and outwards, in the inclined recess83. The shape of the inclined recess83is such that it together with the inner circumferential surface73creates a space which narrows towards the inner circumferential surface73. That is, the spring-loaded roller79is free to rotate in a clockwise direction (as seen in the figures) and can then roll inwards (or at least strive to roll inwards against the action of the spring85) within the space provided between the inclined recess83and the inner circumferential surface73, but when the spring-loaded roller79rotates in a counter-clockwise direction (as seen in the figures) it rolls outwards and will, because of the narrowing space provided between the inclined recess83and the inner circumferential surface73, eventually be wedged in and get stuck and lock with the inner circumferential surface73, thereby preventing also the inner circumferential surface73from rotating in this direction. In other words, the spring-loaded roller79arranged in a narrowing recess constitutes together with the rotatable inner surface73an example of a conventional freewheel. The base portion76of the backstop selector75comprises a contour86, which extends a distance in the circumferential direction and is arranged as a cam curve86, into which the end portion82of the central axle81of the roller79reaches and in which the end portion82can slide. The cam curve86extends a circumferential distance in the base portion76and comprises two different radial distances to the wheel axle72.

InFIG. 4aandFIG. 4b, the backstop member78, i.e. the roller79, is schematically illustrated in a first position; and more precisely, inFIG. 4athe backstop selector75has been removed to more clearly show the operation of the backstop member78, while the backstop selector75is present inFIG. 4bto show the functioning of the cam curve86provided in the base portion76of the backstop selector75in combination with the sliding element80.

FromFIG. 4ait can be seen that the spring-loaded roller79is pressed inwards, i.e. into the inclined recess83, and is not in contact with the inner circumferential surface73. Hence, there is no backstop function engaged. FromFIG. 4b, it can be appreciated that the sliding element80in this position is at a relatively short radial distance from the wheel axle72, which—since the sliding element80constitutes the end portion82of the central axle81of the spring-loaded roller79—prevents the roller79from acting as a freewheel.

In the second position illustrated inFIG. 4candFIG. 4d, a wheelchair user has moved the backstop selector75axially in a circumferential direction, such that the sliding element80now is at relatively longer radial distance from the wheel axle72. Since the sliding element80constitutes the end portion82of the central axle81of the spring-loaded roller79, the roller79has in this position been forced into close contact with the inner circumferential surface73, and is now, as was explained above, only able to rotate in a clockwise direction, i.e. to roll inwards (as seen in the figures), whereas the spring-loaded roller79will be wedged in and get stuck and lock with the inner surface73if the roller79attempts to rotate in a counter-clockwise direction. In other words, since it is the rotation and rotational direction of the inner circumferential surface73that drives and controls the rotation of the spring-loaded roller79, the inner circumferential surface73is free to rotate in a clockwise direction (as seen in the figures) but is prevented to rotate in a counter clockwise direction (as seen in the figures). When the backstop arrangement70is arranged on a wheel attached to a wheelchair, the allowed rotational direction corresponds obviously to a forward direction for the wheelchair, while the prevented rotational direction corresponds to a backward direction for the wheelchair. In comparison with the small cogged freewheel provided in the second embodiment of the present invention, a freewheel function provided as a spring-loaded roller, which can rotate and roll in an inclined and narrowing recess and get into close contact with an inner circumferential surface, the latter freewheel is presumably more durable and reliable.

In the third embodiment of a backstop arrangement illustrated inFIGS. 4a-4d, it can be seen that the backstop function is combined with a gear-shift arrangement, which comprises a guide member51, a sliding element52, and a second or lower contour or cam curve53. Thus, the wheel hub71is an internal-gear hub71, and the function of the gear-shift arrangement is identical to the gear-shift arrangement that was thoroughly described above in conjunction withFIGS. 2a-2h. The gear-shift arrangement provided for the third embodiment described in conjunction withFIGS. 4a-4dwill therefore not be further described, but it is to be understood that the backstop arrangement70comprises a gear-shift arrangement, and also the backstop arrangement70can be regarded as a gear-shift and backstop arrangement70, and the backstop selector75can be regarded as a gear and backstop selector75.

A common feature of all gear-shift arrangements presented herein is that a backstop selector, or, if applicable, a combined backstop and gear selector, does not rotate as a user propels a wheelchair. It is therefore easy for a user to locate the backstop selector when he or she wants to engage a backstop function. It should further be noted that all backstop arrangements disclosed herein can be engaged by wheelchair user while the wheelchair wheels still rotate, which is an advantage since no energy is wasted when a wheelchair user otherwise would have to bring the wheelchair to an unnecessary standstill. Wear of the backstop arrangement is also minimized since the backstop function is selectively engageable and is preferably only engaged when needed. Likewise, inherent and unavoidable energy losses due to friction, which arise when a backstop mechanism is engaged and the wheelchair is moving, are minimized as the backstop mechanism is selectively engageable and is preferably only engaged when needed. The incorporation of a backstop arrangement into a gear-shift arrangement should also be appreciated by a wheelchair user who prefers a user-friendly mechanism which is easy and intuitive to operate, wherein gear shifting and backstop engagement and backstop disengagement are executed with the same type of manual movement; and as the combined gear and backstop selector is arranged with a handle in a lever-arm arrangement, the force needed to change gear and to engage a backstop function is minimized, to thereby provide a maximum of user-friendliness and safety.

Although the present invention has been described with reference to specific embodiments, also shown in the appended drawings, it will be apparent to those skilled in the art that many variations and modifications can be done within the scope of the invention as described in the specification and defined with reference to the claims below.