Incline anti-rollback system for wheelchairs

[0002] This application claims the benefit of U.S. Provisional Application Ser. No. 60/088,769 filed Jun. 10, 1998.

[0003] This invention relates generally to wheelchairs and, more particularly, to an anti-rollback system which acts to prevent bi-directional rollback of manually operated wheelchairs when positioned on inclines.

[0004] Many people who use wheelchairs experience difficulty when negotiating inclines and ramps because of the gravitational forces acting on the wheelchair when the user releases his or her grip on the propulsion ring while repositioning the hands for the next thrust of motion.

[0005] The present invention provides an anti-rollback system that allows wheelchair users the freedom of travelling up and down inclines without enlisting the assistance of others to do so. The anti-rollback system of the present invention includes a pair of non-rotatable axles fixed to the frame of a wheelchair, a pair of wheel hubs, each of which includes two sprags or one-way clutches mounted in opposing rotational directions therein, and a means for selectively engaging either or neither sprag with the associated axle. The user may thereby select normal operation of the wheelchair or anti-rollback in either the forward or reverse direction.

[0006] FIG. 1 is a general pictorial diagram illustrating a conventional wheelchair equipped with the incline anti-rollback system of the present invention.

[0007] FIG. 2 is an exploded view of one of the wheel hub assemblies and its associated shifiting mechanism employed in the incline anti-rollback system of the present invention.

[0008] FIG. 3 is a cross-sectional diagram illustrating one of the wheel hub assemblies of the present invention after being shifted into the forward postion.

[0009] FIG. 4 is a cross-sectional diagram illustrating one of the wheel hub assemblies of the present invention after being shifted into the reverse position.

[0010] FIG. 5 is a cross-sectional diagram illustrating one of the wheel hub assemblies of the present invention in the neutral position.

[0011] Referring now to FIGS. 1 and 2, there is shown a conventional wheelchair 100 equipped with the incline anti-rollback system of the present invention. A hollow axle 14 is non-rotatably secured to the frame of wheelchair 100 by means of a pair of nuts 22, 23. A hub 5 is coaxially mounted about axle 14 and includes a multiplicity of holes around the periphery of inner and outer flanges thereof through which the spokes of one of the main wheels of wheelchair 100 are conventionally attached. Two sprags or one-way clutches 4, 6 are mounted in opposite rotational directions within hub 5, which serves as an outer reaction ring for the two sprags 4, 6. Sprag 4 reacts on a sprag center 3 that is mounted coaxially over axle 14 with a bushing 27 to reduce friction. Similarly, sprag 6 reacts on sprag center 7 that is mounted coaxially over axle 14 with bushing 28. Hub 5 is supported on axle 14 by means of hub supports 2, 8 that are secured to hub 5 with a plurality of fastener screws 10. Hub supports 2 and 8 contain bearings 1 and 9 and are retained to axle 14 by means of a retaining nut 21. A shift rod 12 fits into a central opening in axle 14. A pair of springs 13, 20 are positioned coaxially over a smaller portion of shift rod 12 and are retained by means of a spring retainer 19. A shift lug 18 is positioned over shift rod 12, sandwiched between springs 13, 20, and inserted in a slot in axle 14. An outer housing of a shift cable 11 is secured to axle 14 by way of a set screw 24 to provide a means for adjusting the position of shift rod 12. An inner wire of shift cable 11 is connected to shift rod 12 by way of a set screw 26. A distal end of shift cable 11 is connected to a shift lever 25 that may be mounted at a location on the frame of wheelchair 100 convenient to the user.

[0012] Sprag centers 3 and 7 are slotted to receive shift lug 18 to thereby provide a means for selectively engaging either sprag center 3 or 7 with axle 14. The position of shift rod 12 is lightly held with pressure from a detent spring 16 on a detent ball 15. Detent spring 16 is secured within axle 14 by means of a screw-plug 17. As may be understood with reference to FIG. 3, when shift cable 11 is actuated by shift lever 25 to engage shift lug 18 within sprag center 3, rotation of hub 5 in one direction is prevented by sprag 4. As may be similarly understood with reference to FIG. 4, when shift cable 11 is actuated by shift lever 25 to engage shift lug 18 within sprag center 7, rotation of hub 5 in the opposite direction is prevented by sprag 6. When shift cable 11 is actuated by shift lever to the neutral position illustrated in FIG. 5 such that shift lug 18 is not engaged with either of sprag centers 3 or 7, hub 5 may freely rotate in either direction.

[0013] It should be understood that hub 5 and the structure associated therewith depicted in FIG. 2 and described in detail above in connection with one main wheel of wheelchair 100 is duplicated in connection with the other main wheel. Thus, the user may independently control the forward and reverse braking action of each of the main wheels of wheelchair 100 when negotiating an incline. Alternatively, he may choose to leave either or both of the main wheels in the neutral or freewheeling position.