Power operated wheelchair

A power-driven and steered wheelchair comprises a pair of ground-engaging wheels mounted in laterally-spaced relationship to a frame carrying a seat for an occupant and supporting the power source and a transaxle transmission for imparting parting both driving and steering power to the ground-engaging wheels. Steering is accomplished by employing separate planetary drive mechanisms for each of the primary ground-engaging wheels and imparting rotation in opposite directions to the ring gears of such planetary drive mechanisms to effect the rotation of one wheel at a greater speed than the other wheel in either a forward or rearward direction, thus producing power steering of the wheelchair.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to a wheelchair for invalids, and particularly for 
individuals having a permanent handicap, which utilizes battery driven, 
combustion driven, hydraulically driven or generator driven motors for 
effecting the driving of the main wheels of the wheelchair and the 
steering thereof. 
2. Summary of the Prior Art 
Power operated wheelchairs have long been known in the prior art. The vast 
majority of previously issued patents, however, disclosed power operated 
wheelchairs wherein a separate driving motor was provided for each of the 
two driving wheels of the wheelchair. 
As is well known to wheelchair occupants, whenever a conventional power 
operated wheelchair, having two power driven wheels and two castering 
wheels for steering, is driven along the side of a slope, the wheelchair 
will always tend to turn from a desired direction relative to the slope 
due to the tendency of the castering wheels to turn downwardly regardless 
of whether the castering wheels are forwardly or rearwardly located 
relative to the power driven wheels. The maintenance of steering in a 
desired direction becomes a difficult task, particularly to seriously 
handicapped individuals who may have to resort to the use of finger 
operated electrical switches, or in severe cases, to switches operated by 
movements of the head. Another difficulty with the conventional powered 
wheelchair lies in the fact that such wheelchairs generally have the power 
wheels mounted rearwardly of the center of gravity of the wheelchair when 
the occupant is sitting in the wheelchair. If, by inadvertence, full 
forward power is supplied to the driving wheels, or when climbing a steep 
slope, there is a definite tendency for the wheelchair to tilt backwardly, 
and in many cases to overturn, due to the location of the center of 
gravity of the wheelchair assemblage and occupant just forward and well 
above the power driven wheels. 
Wheelchairs are also known to have power driven wheels located forwardly of 
the center of gravity of the wheelchair and castering or steerable wheels 
are provided rearwardly of the center of gravity. These wheelchairs are 
extremely difficult to steer due to the fact that the non steerable wheels 
will only find directional equilibrium when trailing the center of 
gravity. Manufacturers of this type of wheelchair have resorted to power 
steering of the castering wheels with limitations normally imposed with 
this system. 
It is therefore obvious that improvements are sorely needed in the art of 
power driven, steerable wheelchairs in order to overcome each of the 
aforementioned disadvantages of the prior art wheelchair designs. 
SUMMARY OF THE INVENTION 
A power operated wheelchair embodying this invention employs a pair of 
primary ground-engaging wheels which are concurrently driven by a single 
motor through a unique planetary transaxle. The frame of the wheelchair 
defines a seat for the occupant, a support for batteries or another motive 
source, and a mounting for a gearbox casing for housing the transaxle. The 
frame further defines two laterally spaced bearing mounts for axles upon 
which the two laterally spaced driving wheels are mounted. One, or 
preferably, two castering wheels are provided on the frame rearwardly of 
the primary power driven wheels. The design is such that the center of 
gravity of the wheelchair, including the occupant, is located rearwardly 
of the power driven wheels. As mentioned, the wheels are driven by a motor 
through a unique planetary transaxle having a common input gear driving 
two separate sets of planet gears. The driving motor has a geared 
connection to the common input gear of the two planetary systems. The 
input gear has two oppositely axially projecting shafts, each with an 
integral pinion sun gear, which shafts are respectively mounted in 
bearings provided in the inner ends of the two axles which support the 
primary ground-engaging wheels. Additionally, the driving axles are each 
provided with radial flanges upon which are mounted a plurality of planet 
gears in radially spaced relationship which engage the sun gear teeth 
provided on opposite sides of input gear. 
A pair of ring gears having both internal and external teeth are provided. 
Such ring gears are respectively mounted in bearing relationship around 
the exterior of the inner ends of the axle shafts supporting the primary 
ground-engaging wheels. The internal teeth on the ring gears respectively 
engage the adjacent set of planetary gears. If no restraints are imposed 
on the rotation of the ring gears, then the primary ground engaging wheels 
are effectively disposed in a free wheeling condition and rotation of the 
driving motor will not result in any rotation of the primary wheels, 
permitting the wheelchair to be manually pushed in the event of a driving 
motor failure. 
In accordance with this invention, the outer gear teeth provided on the two 
ring gears are normally engaged with a reversible steering motor by a gear 
train which includes a worm gear. The worm gear is preferably connected to 
the shaft of the reversible steering motor. The gearing connection is such 
that rotation of the steering motor effects rotation of the two ring gears 
in opposite directions. This results in an immediate turning action of the 
wheelchair due to the opposite rotation of the two primary wheels relative 
to each other. Even if no power is concurrently supplied to the primary 
ground-engaging wheels from the driving motor, the operation of the 
steering motor in a selected direction will cause the wheelchair to 
effectively rotate by opposite rotation of the primary ground-engaging 
wheels. If the driving motor is energized, then the relative speed of the 
steering motor determines how fast the turn will be made. Suitable 
conventional motor controls may be incorporated in the control circuit for 
the steering motor, or the gearing may be proportioned to prevent the gear 
train from the steering motor from reaching a speed which would cause a 
wheelchair to turn too rapidly while it is progressing either forwardly or 
rearwardly under power supplied by the driving motor. 
When no power is supplied to the steering motor, the wheelchair will track 
in a positively straight direction since the two shafts driving the 
primary ground-engaging wheels are effectively locked together for 
co-rotation by virtue of the gearing connection to the steering motor 
which includes a worm gear preventing backward transmission of rotation to 
the steering motor. 
Thus, the problem of maintaining the direction of the wheelchair when 
moving along a side slope is completely overcome since both primary 
ground-engaging wheels will automatically turn at the same speed and 
prevent the castering wheels from turning down the slope, particularly 
when the castering wheels are disposed in trailing relation to the primary 
wheels. 
Additionally, the sudden application of forward movement to the power 
wheelchair will not result in a rearward tipping of the wheelchair due to 
the location of the castering wheels and the center of gravity of the 
wheelchair in a position rearwardly of the power driving wheels. 
Other advantages of the invention will become readily apparent to those 
skilled in the art from the following detailed description, taken in 
conjunction with the annexed sheets of drawings on which is schematically 
shown a preferred embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENT 
Referring to FIG. 1, there is schematically shown a wheelchair 1 
incorporating a preferred embodiment of this invention. Wheelchair 1 
comprises an articulated frame 2, having the various frame elements 
conventionally secured together by welding or by mechanical fasteners. 
Frame 2 defines a battery compartment 2a within which batteries 3 are 
mounted. Frame 2 incorporates a transaxle gearbox 8. Gearbox 8 
incorporates a pair of laterally spaced axle-mounting bearings 8a (FIGS. 
2a, 2b, 3, 4, & 5) which respectively rotatively support a pair of similar 
hollow axle shafts 4 for rotation about a horizontal axis. Ground-engaging 
wheels 5 of sufficient size are mounted on the outer ends of the axles 4 
that project laterally beyond frame 2. 
Projecting rearwardly from frame 2 are a pair of upper links 2b and a lower 
swing arm 2c which form a parallelogram and terminate into a cross-member 
6b which incorporates two vertical axis hubs 6a for journaling two 
laterally-spaced, castering rear wheels 6. The vertical position of rear 
wheels 6 relative to the frame 2 may be varied by a spring/shock absorber 
link 7 mounted between the parallelogram links 2b to the lower swing arm 
2c and the upper rear portion of the frame 2. Link 7 may be either a gas 
cylinder or a spring, depending on the preference of the operator 
propelling the wheelchair 1. The gas cylinder or spring may incorporate a 
viscous damped cylinder. 
A seat structure 9, having a seat element 9a which may be cushioned, a back 
portion 9b which may be reclinable, a forwardly and downwardly projecting 
leg support 9c and conventional foot supports 9d are conventionally 
mounted on the frame 2. It will be particularly noted that with the 
described configuration, the center of gravity of the structure, including 
the weight of the occupant of the seat, is disposed rearwardly of the 
horizontal axis of rotation of the primary ground-engaging wheels 5 due to 
the weight of the battery, or other power source to be later discussed, 
being disposed rearwardly of the axis of the ground-engaging wheels 5. 
A transaxle gear box casing 8 for housing and rotatably mounting various 
driving gears is provided between the primary ground-engaging wheels 5. 
Such transaxle gear box casing is only shown schematically in FIG. 1. For 
clarity of illustration of the plurality of gear elements incorporated 
within the transaxle gear box casing, the casing is omitted in FIGS. 2a, 
2b, 3, 4, 5, and 6. The various elements contained in such casing are 
indicated by numerals 8a, 8b, etc. 
Referring to FIG. 2a, assuming that a battery-powered, reversible DC motor 
is to be utilized as the power source, such motor 10 is conventionally 
supported on either the frame 2 or the transaxle casing 8 with its axis 
parallel to the axis of wheels 5, and has a horizontal output shaft 10a on 
which is mounted a pulley or a sprocket 10b for imparting rotation to a 
horizontal transverse shaft 11 supported by laterally-spaced bearings 8c 
provided in the transaxle gearbox casing 8. Shaft 11 has a pulley or 
sprocket 11a mounted thereon which is engaged by a power-transfer belt or 
chain 11b to thus effect the driving of the shaft 11 in a forward or 
reverse direction depending upon the directional energization of the 
driving motor 10. 
On the medial portion of the shaft 11, a small gear 11c is mounted which 
drivingly engages external teeth 12a provided on an input gear 12. Input 
gear 12 has two oppositely laterally projecting coaxial shaft portions 12b 
and 12c, which are respectively journaled in a pair of bearings 4a and 
axially controlled by a pair of thrust bearings 4b provided in the bores 
of the hollow wheel-supporting axle shafts 4. 
The input gear 12 also defines two laterally-spaced sun gears 12b and 12c 
of two separate, but identical, laterally spaced planetary gear systems, 
which are respectively operatively connected to the primary 
ground-engaging wheels 5. 
Each such planetary system comprises a hollow gear mounting element 13 
(FIGS. 2a, 2b, & 3). Each mounting element 13 has a reduced diameter 
portion 13a at one end, which is supported in a bearing relationship upon 
the exterior of the internal ends of the wheel-mounting axle shafts 4 by 
laterally-spaced bearing elements 4c and 4d. Additionally, bearing 
elements 8b, provided in transaxle casing 8, respectively support the 
external surfaces of the reduced diameter portions 13a of the hollow gear 
mountings 13. 
A plurality of planetary gears 14 are mounted in angularly spaced 
relationship within the enlarged diameter inner end 13b of each planetary 
gear mounting unit 13 by shafts 14a, which are fixedly mounted in a radial 
flange 4e provided on the inner end of each wheel mounting axle 4. The 
external teeth 14b on each planetary gear 14 are in an engagement with 
internal teeth 13c provided on the interior of the large diameter end 
portion 13b of the planetary gear mounting 13, thus functioning as ring 
gears for the planetary system. Therefore, if the planetary gear mounting 
units 13 are in some manner non-rotatably secured together, rotation 
imparted to the planetary system through the input gear 12 would result in 
rotation of each of the primary ground-engaging wheels 5 at the same speed 
and in the same direction. When, however, the planetary gear mountings 13 
are not secured and allowed to rotate freely, then no driving connection 
is provided between the input gear 12 and the axles 4 (FIGS. 2b & 5), and 
the ground-engaging wheels 5 can move independently of whether the driving 
motor 10 is rotating or is stationary. This permits pushing of the 
wheelchair in the event of motor or battery failure. 
The selective interconnection of the planetary gear mountings 13, and the 
application of oppositely directed steering rotation of the planetary gear 
mountings 13 is accomplished, in accordance with this invention, to effect 
power steering of the wheelchair 1 by the primary ground-engaging wheels 
5. 
Shaft 15a (FIGS. 2a & 2b) journaled in suitable bearings 8d in the gearbox 
casing 8 has a limited length spline portion 15c which mounts an 
internally splined sliding gear 15. Sliding gear 15 is always in 
engagement with one set of external teeth 13d provided on the planetary 
gear mountings 13. In one position of its sliding movement, slidable gear 
15 also simultaneously engages the splines 15c on shaft 15a and an 
intermediate gear 16 (omitted in FIG. 2a & 2b but shown in FIG. 3 for 
clarity), which is mounted on a horizontal shaft 16a journaled in bearings 
8e, provided in transaxle casing 8, and engages the external teeth 13d on 
the other planetary gear mounting 13. Thus, rotation of shaft 15a will 
impart rotation in opposite directions to the two planetary gear mountings 
13. 
The power for effecting such oppositely directed rotation is derived from a 
reversible DC motor 17 which is suitably mounted on either frame 2 or the 
transaxle gearbox casing 8 with its axis perpendicular to the axis of the 
primary driving wheels 5, and has a projecting shaft 17a mounting a 
self-locking worm 17b. Worm 17b engages external teeth of worm gear 17c 
which is keyed to the shaft 15a, thus effecting rotation of the internally 
splined slidable gear 15 and the intermediately shifted motion reversing 
gear 16, resulting in opposite rotation of the two planetary gear 
mountings 13, hence opposite rotation of the power driven primary ground 
engaging wheels 5. Thus, the energization of the steering motor 17 can 
cause the steering of the wheelchair 1 to be accomplished solely by the 
power-driven primary ground-engaging wheels 5. 
If no power is being supplied to the transmission by the driving motor 10, 
the energization of the steering motor 17 will cause the wheelchair to, in 
effect, turn about its own central vertical axis. If no power is being 
supplied to the gearbox by the steering motor 17, the energization of the 
driving motor 10 will cause the wheelchair to move forward or reverse in a 
straight line. Because the worm 17b and worm gear 17c are self-locking and 
cannot be backdriven, no amount of side-load will cause the wheelchair to 
deviate from its desired direction until the main ground-engaging wheels 
are made to skid. 
When the internally splined slidable gear element 15 is laterally shifted 
to the position indicated in FIGS. 2b and 5, then slidable gear 15 will be 
out of engagement with both the external splines 15c on shaft 15a and the 
intermediate gear 16, thereby removing the connection between the two 
planetary gear mounting units 13, and thus allowing the two planetary gear 
mountings 13 to rotate freely and independently, hence the wheelchair may 
be manually moved in either direction regardless of whether the drive 
motor 10 is operating or not. The sliding of gear 15 on shaft 15a between 
its two mentioned positions can be manually accomplished by a shifting 
fork 18 journaled in a bushing 8f provided in transaxle casing 8 and 
engaging a peripheral groove 15b provided on one end of slidable gear 15. 
Shifting fork 18 may be operated manually, electrically, or hydraulically. 
For example, a link 19 is secured to the end of fork 18 and actuated by a 
cam 20 provided on the end of a shaft 21. Turning shaft 21 will shift fork 
18 between its two positions. 
If the wheelchair is stationary, and by inadvertence, full-forward power is 
applied to the primary ground-engaging wheels 5, the wheelchair will not 
tip over due to the location of the center of gravity of the entire 
structure behind the ground-engaging wheels 5 and the additional support 
provided by the trailing steerable wheels 6. 
Modifications of this invention will be readily apparent to those skilled 
in the art. For example, the battery 3 may be replaced by an internal 
combustion engine driven generator to supply power to both the driving 
motor 10 and the steering motor 17. An internal combustion engine may be 
employed to drive a fluid-pressure pump and fluid-pressure motors may then 
be utilized for the driving motor 10 and the steering motor 17. 
Those skilled in the art will also recognize that the controls for the 
driving and the steering motors have to be selected to accommodate the 
particular disability of the user of the wheelchair. For example, if the 
user has control of his fingers, then finger operated controls may be 
employed to effect the selective energization of the driving motor in 
either direction and/or the steering motor in either direction. If the 
handicapped occupant can only move his legs or alternatively, his head, 
then power controls responsive to such movement will be mounted on the 
wheelchair frame to produce selective energization of the driving motor 10 
and steering motor 17 for the primary ground-engaging wheels 5 to produce 
forward or rearward movement of the wheelchair and turning in any desired 
direction. 
The castering wheels may be mounted forwardly relative to the primary 
ground-engaging wheels without effecting the steering of the wheelchair, 
due to the fact that steering is always accomplished by the relative 
rotational speeds of the large power driven, ground-engaging wheels. All 
such modifications are intended to be included within the scope of the 
appended claims.