Single speed gear assembly for a wheelchair

A single speed gear assembly suitable for use in a wheelchair is disclosed. The assembly incorporates a sun gear together with a plurality of planet gears which reduces the amount of torque required by the user in order to effect rotation of the wheel to which the assembly is attached. Specific ratios for the diameter of the sun gear to the each planet gear is taught. The assembly conveniently eases the use of a wheelchair by those confined to using same.

FIELD OF THE INVENTION 
The present invention relates to a gear assembly for use in a wheelchair 
and more particularly, the present invention relates to a single speed 
gear assembly capable of reducing the torque necessary by the user to 
effect rotation of the wheel. 
BACKGROUND OF THE INVENTION 
Geared hub arrangements and gear assemblies for wheelchair use have been 
previously proposed in the art. Typical of the references known is U.S. 
Pat. No. 4,729,965 issued to Zach et al., Mar. 1, 1988. In the reference, 
geared hub with a free wheel especially for wheelchairs is provided 
wherein the system has at least one forward speed with an active hub brake 
and one reverse speed. The system is fairly complicated and employs a 
ratchet gear assembly. In view of the number of moving parts in such an 
assembly, the same not only would be fairly expensive to manufacture but 
also would appear to be maintenance intensive. 
Seol, in U.S. Pat. No. 4,762,332, issued Aug. 9, 1988, discloses a 
wheelchair having a propulsion and velocity change mechanism in which the 
mechanism provides a clutch with a cam clutch, a cylindrical fly wheel, 
both of which are installed on a hub of a shaft of the main wheel of the 
chair. A forward and backward selector is additionally provided to direct 
the operation and this is actuated via a wire. 
U.S. Pat. No. 5,167,168, issued Dec. 1, 1992 to Beumer, provides a driving 
gear for a wheelchair in which the arrangement is drivable via a lever 
coupled to at least two free wheel clutches. Although the arrangement is 
useful, it relies on a lever to operate in the reverse direction and thus 
adds complication to the system. 
It would be desirable if there were an arrangement whereby the assembly was 
simple and reduced the amount of torque required to produce a relatively 
high degree of work at the output. The present invention is directed to 
satisfying this need and overcomes the limitations of the prior art. 
SUMMARY OF THE INVENTION 
According to one object of the present invention, there is provided a 
torque reducing gear assembly suitable for use in a wheelchair, 
comprising: 
a hollow hub; 
axle extending through the hub, the axle having an inner end and an outer 
end and means rotatably mounting the hub on the axle; 
a sun gear fixed to the axle; 
a plurality of planet gears in spaced relation relative to one another and 
in meshing contact with the sun gear; and 
a drive gear for driving the planet gears, the drive gear meshing with the 
planet gears, whereby a reduced torque is required to effect rotation of 
the drive gear of the hub. 
It has been found that by making use of a plurality of planet gears about a 
sun gear, in a single speed gear assembly reduces the amount of work or 
torque required to rotate the wheel shaft. This is of significant 
advantage to persons who must use a wheelchair since less strain and 
muscle power is required to move the chair. This is particularly 
advantageous when the user must go up a positive incline where a 
significnt amount of energy is demanded by the user. 
As an added advantage, the entire assembly or portions thereof, may be 
composed of suitable plastics or other lightweight materials, e.g., metals 
and/or composites. This has the obvious advantage of reducing the mass of 
the overall apparatus and therefore the burden on the user. 
As will be appreciated, there is a significant amount of variation that can 
take place with respect to the sun and planet gears. Typically, the ratio 
of the diameter of the sun gear relative to the planet gear will be 
anywhere from about 1:0.7 to about 1:0.55. As will be appreciated by those 
skilled in the art, the greater the diameter of the planet gear relative 
to the sun gear, the greater the reduction in torque required to effect 
rotation. A preferred range in ratio is from about 1:0.69 to about 1:0.57. 
According to a further object of the present invention, there is provided a 
wheel assembly for a wheelchair having a frame member on each side of the 
seat, comprising: 
a hollow hub; 
a wheel mounted on the hub; 
axle extending through the hub, the axle having an inner end and an outer 
end and means rotatably mounting the hub on the axle; 
means for fixedly mounting the axle at its inner end on a frame member of a 
wheelchair; 
a single speed gear assembly including: 
a sun gear fixed to the axle; 
a plurality of planet gears in spaced relation relative to one another and 
in meshing contact with the sun gear; 
a drive gear meshing with the planet gears, the drive gear for driving the 
planet gears; and 
a hand wheel mounted on the drive gear, whereby a reduced torque is 
required at the handwheel to effect rotation of the wheel. 
Any number of planet gears may be incorporated in the assembly and this 
will only be limited by the available space between the ring gear 
associated with the drive gear and the sun gear. By the ratios indicated, 
the most effective assembly can be manufactured resulting in an easy to 
use and inexpensive arrangement. Where the assembly is used with a motor 
drive, less demand is experienced by the motor in terms of its duty cycle 
and therefore the wear is significantly reduced. 
A further object of the invention is to provide a torque reducing single 
speed gear assembly suitable for use in a wheelchair, comprising: 
a hollow hub; 
axle extending through the hub, the axle having an inner end and an outer 
end and means rotatably mounting the hub on the axle; 
a sun gear fixed to the axle; 
a plurality of planet gears in spaced relation relative to one another and 
in meshing contact with the sun gear, the sun gear having a diameter 
relative to a planet gear of the planet gears in a ratio of about 1:0.7 to 
about 1:0.55; and 
a drive gear for driving the planet gears, the drive gear meshing with the 
planet gears, whereby a reduced torque is required to effect rotation of 
the drive gear of the hub. 
Having thus described the invention, reference will now be made to the 
accompanying drawings illustrating preferred embodiments.

DETAILED DESCRIPTION OF THE DRAWINGS 
Referring now to FIG. 1, shown is an exploded view of one embodiment of the 
present invention. The entire assembly is globally denoted by numeral 10. 
A wheelchair clamp is provided at one end, the clamp being denoted by 
numeral 12, into which is positioned an anti-rotation bushing 14. 
Anti-rotation bushing 14 provides a peripheral skirt and is received 
within an opening in the wheelchair clamp, while bearing 16 fits over 
anti-rotation bushing 14. An axle, globally denoted by numeral 18, 
provides an outer end 20 adapted for connection with a wheelchair wheel 
(not shown and discussed hereinafter), the outer end 20 being threaded. 
The axle includes a central flange 22 and an inner end 24, inner end 24 
being threaded for connection purposes with other elements to be discussed 
hereinafter. A sun gear 26 is provided with a series of apertures 28 
surrounding a central opening 30, the central opening 30 for positioning 
on outer end 24 of shaft 18 and more specifically directly against flange 
22. Flange 22 is provided with similar apertures 28 on sun gear 26. The 
apertures on flange 22 and those apertures 28 are register and fasteners 
32 fixedly secure the sun gear 26 to flange 22. A planet gear cage 34 is 
provided within which is coaxially disposed and extending outwardly 
therefrom planet gear 26. The planet gear cage 34, as is typical with this 
type of mechanical component, provides a generally annular slot 36 within 
which are disposed a series of four planet gears 38. The gears 38 are 
rotatably fastened within the annular slot via planet gear pins 40 which 
extend into the annular slot 36 within which is disposed apertures 42 for 
receiving the pins 40. 
A hub 44 is provided on the assembly and fits over cage 34 in order to 
protect the entire assembly discussed thus far from debris, damage, etc. 
Disposed within hub 44 is provided a bushing 46. A ring gear 48, which is 
fixedly secured within a driver 50, is in meshing contact with the planet 
gears 38. Driver 50 employs a nut portion 52, which nut portion 
additionally provides a threaded segment 54. A nut 56 cooperatively 
engages the threaded portion 54 on driver 50. A bushing 58 is positioned 
within the apertured driver member 50. FIG. 2 illustrates the arrangement 
in assembled form. 
Referring now to FIG. 3, shown is an exploded view of the assembly as 
positioned on a wheelchair wheel 60. 
In operation, the force applied to driver 50 within which is disposed ring 
gear 48 causes the planet gear 38 and hub 44 to turn about axle 18. Hub 44 
and planet cage 34 are fixed in the wheelchair wheel 60 (FIG. 3) thus 
driving the wheel upon rotation of wheel 60. 
The result of this arrangement is that the force required to induce 
rotation to the shaft or axle 18 is significantly reduced and therefore 
makes use of the wheelchair abundantly easier for persons confined to the 
chair. The arrangement effectively reduces the force required to rotate 
the wheel of the wheelchair assembly. The degree of multiplication will be 
dependent upon the ratio of a planet gear to the sun gear. As an example, 
the ratio of the sun gear diameter to the planet gear diameter may vary 
from approximately 1:0.7 to about 1:0.55 with a typical range being 1:0.69 
to about 1:0.57. In addition, it will be appreciated by those skilled in 
the art, that the number of planet gears 38 can vary and generally 
speaking, the larger the planet gear relative to the sun gear, the greater 
the degree of ease of rotation realized by the user. 
Accordingly, the present invention has provided significant utility 
relative to a gearless wheelchair wheel assembly since the same amount of 
force applied to each of these wheels would result in a greater speed 
output on the wheel incorporating the gear assembly according to the 
present invention. 
Although embodiments of the invention have been described above, it is not 
limited thereto and it will be apparent to those skilled in the art that 
numerous modifications form part of the present invention insofar as they 
do not depart from the spirit, nature and scope of the claimed and 
described invention.