TRANSMISSION

FIELD OF THE INVENTION

This invention relates to a planetary drive mechanism for an electrically powered vehicle such as a wheelchair or similar vehicle for transport of a handicapped person, a robot base, or any vehicle

requiring up to 360 degrees turning ability without linear displacement

of the vehicle. More particularly, this invention relates to an improved

planetary drive system for an electrically powered vehicle over that disclosed in my prior U.S. Patent No. 5,275,248.

BACKGROUND OF THE INVENTION

My aforesaid prior patent disclosed a novel drive mechanism for a powered wheelchair utilizing two reversible motors, one for driving the wheelchair and the second for effecting the steering of the

wheelchair. The driving motor effects the concurrent rotation of the two primary ground engaging wheels in an operator selected direction through two separate planetary gear systems respectively operatively

connected to such wheels by a tubular extension provided on the

mounting housing for the planet gears of the respective planetary system. The operator controlled steering motor effects an opposite

rotation of the ring gears of the planetary systems, which results in one

wheel rotating at a different speed than the other, thereby steering the wheelchair.

While the operation of the wheelchair driving and steering mechanism disclosed in my aforesaid patent represented a significant improvement over prior art mechanisms, continued development

activities have resulted in improvements to such planetary drive and

steering mechanism to provide further benefits and increased safety for the handicapped operator. For example, prior art powered wheelchairs have generally required a separate driving motor for each primary

ground engaging wheel. The primary reason for the duplication of driving motors for the primary ground engaging wheels of a wheelchair

arises from the fact that a single motor drive would require the primary

ground engaging wheels to be connected for corotation. This would

then require that steering be effected by the relatively small secondary ground engaging wheel or wheels.

Steering a power operated wheelchair, or any other wheeled vehicle requiring sharp turning ability, by the secondary ground

engaging wheel or wheels inherently results in a large turning radius for the wheelchair. This presents serious problems when the wheelchair is operated in a congested area, such as the typical home or

department store.

Turning "on a dime" by rotating the two primary ground

engaging wheels in opposite directions is prevented except by

disengaging in driving connection between the two wheels and

manually rotating the wheels in opposite directions, if the wheelchair occupant has sufficient strength to do so.

The use of two driving motors for the two primary ground

engaging wheels of any electrically powered vehicle, which are not mechanically interconnected, necessarily requires complex electronic

controls for maintaining the two driving motors in synchronism.

Considering the variable torque requirements separately required by the primary ground engaging wheels by variations in the terrain

encountered by each wheel, this means that the motor speeds are

continually being adjusted and true synchronism of the primary ground

engaging driving wheels is seldom attained. Thus the prior art wheelchairs move along a wobbling path.

Additionally, safety regulations that will soon be applicable to

all powered wheelchairs limited the maximum speed of the wheelchair to about six miles per hour. The maximum speed of the wheel driving motor or motors are therefore limited to that necessary to drive the wheelchair at about six miles per hours on a level floor or ground.

As is well known, the maximum torque and horsepower

output of a reversible electric motor (as well as an internal combustion engine) is obtained when the motor rotational speed is on the order of

1800 to 3000 rpm, hence many times higher than the customary

rotational speed of the primary ground engaging wheels of wheelchairs

and similar vehicles at a vehicle speed of six miles per hour. Thus the

rotational speed ration of the electric motor to the rotational speed of the driving wheels is on the order of 20-50 to 1, depending on the

diameter of such driving wheels. With two motors, this required two

gear boxes to chain drives of significant size and weight compared to other components of the wheelchair.

In the mechanism disclosed in my aforesaid U.S. patent, a single driving motor is connected by a belt drive, having an essentially

one to one gear ration, to a transfer shaft having a small pinion secured thereto and driving a large gear of substantially the same size as the ring gears of two planetary gear systems. This large gear has the two

sun gears of the two planetary systems integrally formed on its opposite sides to provide a large gear ratio belt drive. This gear ratio, plus that

inherent in the planetary gear systems provides a large reduction in wheel rotational speed relative to the optimum motor rotational speed

without increasing the size of the planetary gear systems to an

intolerable dimension. Thus the motor may be operated at an optimum motor speed level without exceeding any prescribed 6 miles per hour

maximum speed of the wheelchair.

However, when an upgrade of soft terrain was encountered,

this optimum motor speed was not capable of maintaining the desired

speed of the wheelchair. On severe grades, stalling and thermal deactivation of the motor could occur. On down grades, the wheelchair

speed could exceed the six miles per hour limitation and, unless the handicapped operator took action to reduce the motor speed, or apply

hand operated brakes, a speed responsive safety switch would operate

to cut off power to the driving motor.

A further problem encountered with the powered wheelchair driving and steering mechanism of my aforesaid U.S. patent is the complicated design of the mechanism for effecting the connection of a

reversible steering motor to the two planetary gear drive systems to effect a speed differential between the two planetary wheel driving housings to produce steering of the wheelchair in a desired direction by

varying the speed of one ground engaging wheel relative to the other. The minimum turning radius is then the lateral spacing of the primary

ground engaging wheels, when one wheel is maintained stationary as the other wheel rotates. In place turning of the vehicle, where one

primary ground engaging wheel is selectively rotated in one direction

while the other primary ground engaging wheel is rotated in the opposite direction, required an extra reversing shaft and gear to be incorporated in the gear train driven by the steering motor.

Lastly, a more rapid connection of the steering motor to the driving wheels is desirable.

SUMMARY OF INVENTION

The object of this invention is to provide an improved driving

and steering mechanism for electrically powered wheelchairs, or similar

electric motor driven, wheeled vehicles, that overcomes the above stated

problems of prior art mechanisms.

Two reversible electric motors are employed, one for

synchronously driving the two primary ground engaging wheels of the

vehicle and the second for effecting the power steering of the

wheelchair by producing a differential in rotational speeds of the two ground engaging wheels.

In a first embodiment of the invention, the driving motor is

operatively connected to the ring gears of two planetary gear systems.

In a second embodiment, the driving motor is operatively connected to the sun gears of the two planetary gear systems.

In both embodiments, the planetary gear housings are

respectively operatively connected to the ground engaging wheels of the wheelchair to rotate same at equal speeds by utilizing a worm gear

operated by the steering motor to prevent relative rotation of the sun gears in the first embodiment of the invention, or to prevent relative

rotation of the ring gears in the second embodiment, when the steering motor is not activated.

In both embodiments, the driving motor is connected to a

transfer shaft by an automatic transmission mechanism which, in my preferred embodiment, may comprise two belt connected, adjustable diameter, V-shaped pulleys. In the first embodiment of this invention,

the transfer shaft is connected by small gears or chain sprockets to

enlarged gears or sprockets respectively formed on the exterior of the ring gears of the two planetary gear systems. In the second

embodiment, a single enlarged gear or sprocket may be integrally

formed or otherwise corotatably connected to the sun gears of the two planetary gear systems.

In the first embodiment, the planetary gear mounting

housings of the two planetary gear systems each have a shaft with a

pinion thereon that drives a larger gear secured to the respective inwardly projecting end of a shaft which mounts a primary ground engaging wheel. In the second embodiment, the planetary gear

mounting housings respectively directly drive the shafts on which the ground engaging wheels are mounted.

In both embodiments, the adjustable diameter V-shaped

pulley on the electric driving motor shaft has an axially adjustable side which is shifted in response to motor speed or torque transmitted to

increase the motor speed relative to the ground engaging wheels, if the ground engaging wheels encounter an upgrade or a soft surface, or

conversely, to decrease the motor speed relative to the ground engaging

wheels when a downgrade or improved surface is encountered. In both the first and second embodiments of this invention, the steering motor is operatively connected to a first bevel gear having an axis perpendicular to the axis of the planetary drive system. Such

first bevel gear is axially shiftable by the operator.

In the first embodiment, as stated above, the driving motor is

operatively connected to the ring gears of the two planetary gear drive systems by an automatic transmission mechanism. A pair of bevel gears are secured to the two opposed sun gears in spaced, opposed

relationship. The first bevel gear is then axially shifted by the operator into engagement with said pair of bevel gears. When the steering motor is energized in an operator selected direction, the sun gears of

the two planetary gear systems are oppositely rotated in selected directions, thus producing a variation in rotational speed of the two

planetary gear housings, hence varying the speed of the two primary ground engaging wheels to effect steering in an operator selected direction.

If the driving motor is deenergized, the operation of the steering motor will produce equal and opposite rotations of the two

ground engaging wheels, resulting in the vehicle turning in place.

In the second embodiment, the driving motor is operatively

connected by an automatic transmission mechanism to the sun gears of the two planetary systems. A second transfer shaft is provided in parallel relationship to the axis of the planetary drive systems and a

pair of bevel gears are mounted on the second transfer shaft in spaced,

opposed relationship. These bevel gears respectively have two integral gears that are respectively engagable with gear teeth formed on the

external periphery of each ring gear of the two planetary gear systems.

The first bevel gear is manually shiftable into engagement with the two bevel gears on the second transfer shaft.

In the second embodiment of this invention, the rotation of

the first bevel gear in an operator selected direction by the steering

motor then effects opposite rotational speed changes of the ring gears of the planetary gear system, hence producing a selected speed variation

of the two primary ground engaging wheels to effect steering of the

vehicle. Turning in place is thus possible by deengerizing the driving motor and using only the steering motor. The afore described driving mechanism provides an adequate gear ratio between the electric driving motor and the primary ground

engaging wheels to permit the motor to operate at an optimum speed at any operator setting of a conventional motor speed control. In both

embodiments the automatic transmission incorporated in the driving connection between the driving motor and the primary ground engaging

wheels automatically changes the gear ratio to maintain optimum motor speed and operator selected ground speed irrespective of variations in the ground terrain.

Further objects and advantages of this invention will be

readily apparent to those skilled in the art from the following detailed description, taken in conjunction with the annexed sheets of drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic, side elevational view of a wheelchair having a power driving and steering mechanism embodying this invention.

Figure 2 is a vertical sectional view of the wheelchair of

Figure 1 with portions of the transaxle case and other parts removed for clarity of illustration and showing one embodiment of the invention

with the driving motor operatively connected to the two ring gears of

the two planetary gear systems. Figure 2 A is a view similar to Figure 2 but showing the steering motor disconnected from the sun gears of the two planetary gear systems.

Figure 3 is a view Similar to Figure 2 but showing a second embodiment of the invention with the driving motor operatively

connected to the sun gears of the two planetary gear systems.

Figure 3A is a view similar to Figure 3 but showing the

steering motor disconnected from the ring gears of the two planetary

gear systems.

Figure 4 is a schematic view of a preferred embodiment of an

automatic transmission connected between the driving motor and the two planetary gear systems of Figures 2, 2 A, 3 and 3 A.

Figure 5 is a schematic circuit diagram of the electrical

controls for the driving and steering electric motors.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Referring to Figure 1, there is schematically shown an

electrically powered wheeled vehicle incorporating this invention. The

specific vehicle shown is a wheelchair 1, but the invention may be

applied to any other type of electric motor driven wheeled vehicle requiring the ultimate in maneuverability.

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 also mounts a pair of laterally spaced bearing supports 2b (Figure 2) which respectively

provide bearing supports for the inner ends of axle shafts 4. Primary ground engaging wheels 5 are respectively mounted on the outwardly

projecting ends of axle shafts 4. 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

form 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 27 mounted between the parallelogram links 2b to the lower swing arm 2c and the upper rear portion of the

frame 2. Link 27 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, has 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, all of which are conventionally mounted to 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 housing 8 is supported between the two bearing supports 2b and a cover element 2e secured to frame 2 completes the enclosure of each end of transaxle gear housing 8 and

also defines a chamber 2f in which a large gear 4a, formed on, or secured to each inner end of the axle shafts 4, is housed.

The transaxle housing 8 defines at each end recesses to receive bearings 8a. Bearings 8a respectively journal a shaft end 12c of a planetary gear housing 12b. The outer end of shaft 12c has pinion teeth 12d formed thereon which mesh with the large gear 4a.

Planetary gear housing has an enlarged inner end 12a which rotatably

mounts three angularly spaced planet gears 12. Thus, rotation of

planet gear housing 12b results in a lower speed rotation of the ground

engaging wheels 5.

The inner ends of the planetary gear housings 12b are respectively provided with axial recesses which provide a rotatable

mounting for the two ends of a sun gear shaft 11a. Two sun gears 11

are respectively mounted on sun gear shaft 11a in radial alignment

with the two sets of three planetary gears 12 and meshing therewith.

Two ring gears 13 are provided to respectively cooperate with the two sets of planetary gears 12. The internal teeth 13e of each ring

gear 13 are formed on the enlarged inner end of a hollow frusto-

conically shaped ring gear mounting 13a. The small outer ends 13b of each ring gear mounting 13a are rotatably supported by bearings 13c and 13d mounted in transaxle gear housing 8. The internal teeth 13e

of each ring gear 13 mesh with the respective teeth of the planetary

gears 12 in conventional fashion. Thus two conventional planetary gear systems 15a and 15b are provided in gear housing 8 in transversely spaced, coaxial relationship.

Referring to Figure 2, and assuming that a battery powered, reversible motor is to be utilized to drive the powered wheelchair, such

electric motor 10 is conventionally supported on either frame 2 or transaxle gear box 8 by straps 10b with its axis horizontal and parallel

to the axis of primary ground engaging wheels 5.

Motor 10 has an outwardly projecting output shaft 10a. Output shaft 10a is drivingly connected to a first transfer shaft 16 by any conventional automatic transmission mechanism 50, a preferred

form of which is illustrated in Figure 5 and which will be later

described. Automatic transmission 50 preferably provides a gear ratio between motor output shaft 10a and transfer shaft 16 ranging from about a positive 2 to 1 to a negative 1 to 2 depending upon the speed of motor shaft 10a or the torque transmitted to the transfer shaft 16.

First transfer shaft 16 is journaled in two transversely spaced bearings 16a and 16b mounted in suitable recesses provided in transaxle gear housing 8. In the first embodiment of the invention shown in Figures 2 and 2a, a pair of small gears 16c and 16d are secured to transfer shaft 16 at positions respectively aligned with external gear teeth 13f of the two ring gears 13 of the two planetary

drive systems 15a and 15b.

Accordingly, if sun gears 11 are prevented from rotating, by apparatus to be described, both sets of planetary gears 12 are synchronously rotated around their respective sun gears 11 by motor

10, hence both primary ground engaging wheels 5 are synchronously

driven, and the vehicle will move in a straight line. On the other hand, if the sun gears 11 are freely rotatable, the vehicle can be manually moved and turned by differential rotation of the wheels 5 without

energizing the motor 10.

To effect the steering of the vehicle by selectively varying the relative speeds of rotation of the two ground wheels 5, each sun gear 11

is secured to, or integrally formed with, a bevel gear 7. Bevel gears 7

are disposed in spaced, inwardly facing relationship.

A third bevel gear 7a is rotatably mounted in transaxle housing 8 for rotation about an axis that is perpendicular and radial

relative to the axis of sun gear shaft 11a. Bevel gear 7a has an axially

extending hollow shaft 7b, which is slidably mounted in the splined bore 17a of a large worm gear 17, which has hollow stub shafts 17b

respectively mounted in bearings 17c and 17d. Bearing 17c is provided

in a hollow cap structure 18 which is conventionally mounted in an opening 8f provided in transaxle housing 8. Bearing 17d is mounted in a recess 8g provided in transaxle housing 8.

The third bevel gear 7a is manually shiftable from a radially

inward position of engagement with the bevel gears 7 of the planetary system 10, as shown in Figure 2, to a radially outer position of disengagement with the bevel gears 7, as shown in Figure 2A. In the

engaged position, rotation of bevel gear 7a will effect an opposite

rotation of the sun gears 11, producing a variation of the rotational speed of planetary gear housings 12, hence a variation in the rotational speed of the primary ground engaging wheels 5, to effect steering of the vehicle.

The shifting of the bevel gear 7a between engaged and

disengaged positions relative to the bevel gears 7 is accomplished manually by a hand operated plunger 19 which passes through a seal

18a in cover 18 and traverses the bore 17a of the large worm gear 17.

Downward movement of plunger 19 effects the outward displacement of detent balls 18b, as shown in Figure 2 and locks the bevel gear 7a in its engaged position with bevel gears 7. Raising the plunger 19 will retract

the detent balls 18b and raise the third bevel gear 7a to its disengaged

position shown in Figure 2A. The steering motor 20 is then disconnected from the planetary drive systems 15a and 15b, permitting unimpeded manual movement of the wheelchair 1.

Rotation of the bevel gear 7a is accomplished by a steering

motor 20 which is suitably secured to the transaxle gear housing 8 by a strap 20a. Steering motor 20 is a reversible direct current motor energized by the batteries 3 and drives a small worm gear 21, which drives large worn gear 17. Third bevel gear 7a drives bevel gears 7,

which in turn drives the sun gears 11 in opposite directions and thus change the relative rotational speeds of the two ground engaging

wheels 5 to effect steering of the vehicle when driving motor 10 is

energized. If driving motor 10 is not engerzied, and bevel gear 7a is in its engaged position, then steering motor 20 will effect reverse rotation

of the two ground engaging wheels 5 to cause the vehicle to turn in

place.

Referring to Figures 3 and 3A, there is illustrated a second embodiment of the invention. Similar numerals in Figures 3 and 3A

indicate components already described in connection with Figures 1, 2

and 2A. In the second embodiment of the invention, the primary ground engaging wheels 5 are respectively directly connected to the outer ends of elongated shaft portions 12c of the planetary gear

mounting housing 12'b which are respectively journaled in transversely

spaced bearings 8'a provided in transaxle gear housing 8'. The inner ends of planetary gear mounting housing 12'b have axial bores 12'd

which receive bearings 12'e which respectively rotatably support the

opposite ends of a sun gear shaft 11 ^* a on which the sun gears 11 of the two planetary gear systems 15's and 15'b are mounted and secured in

transversely spaced, co-rotatable relationship. Thus wheels 5 are directly driven by the planetary gear housings and not by an

intermediate gear connected as in the first embodiment.

The power from electric motor 10 to synchronously drive the ground engaging wheels 5, is applied to the sun gears 11 of the two

planetary gear systems 15'a and 15'b by a chain drive 30 connecting a small sprocket 16a on the first transfer shaft 16 to a large sprocket 11 'd

which is secured to the sun gear shaft 1 l's for corotation.

Alternatively, a small and large gear (not shown) may effect

the driving connection. In either case, the sun gears 11 of the two

planetary gear systems 15a' and 15b' are driven by motor 10 through an

automatic transmission 50 and a large gear ratio connection from first

transfer shaft 16.

Ring gears 13' are provided with external teeth 13'a in addition to the conventional inner teeth 13'b which engage the

planetary gears 12. To drive the ring gears 13', a pair of bevel gears 22 are rotatably mounted in axially spaced relation on a second transfer

shaft 21. Shaft 21 is mounted in suitable bearings 23 conventionally mounted in the transaxle gear housing 8'. Each bevel gear 22 is

provided with an axial extension 22a on which are formed teeth 22b, which are respectively engagable with the external teeth 13'a formed on ring gears 13'. Hence rotation of the two bevel gears 22 in opposite

directions effects rotation of the two ring gears 13' in opposite

directions, thus producing opposite variations in rotational speed of the two primary ground engaging wheels 5.

To rotate the bevel gears 22 in opposite directions, the same

mechanism is utilized as described in connection with the modification

of this invention shown in Figures 2 and 2A. Thus, steering motor 20 drives a worm gear 21 which, in turn effects the driving of a large

worm gear 17 which has a hub extension defining or mounting a bevel

gear 7a, which is engagable with both bevel gears 22 on second transfer shaft 21. A manually operable plunger 19 effects the axial

displacement of third bevel gear 7a from a position of engagement with bevel gears 22, as shown in Figure 3, to a position of disengagement

shown in Figure 3A. Thus, all of the operational characteristics of the first embodiment of the invention are available with the second embodiment.

Referring now to Figure 5, a preferred form of automatic transmission 50 is illustrated, the elements of which are commercially

available. Thus a torque responsive, adjustable diameter V pulley 60 is secured to motor shaft 10a. Such pulley has a stationary side 61 and

an axially shiftable side 62, which is axially shiftable in response to the torque being transmitted by belt 52. A second speed responsive adjustable V pulley 70 is mounted

on the transfer shaft 16. This pulley has an axially stationary side 71

and a speed responsive, axially shiftable V side 72. Thus, when the primary ground engaging wheels 5 of the electric powered vehicle

encounter an upgrade or soft terrain, the resulting increase in torque

and the slowing of the driving motor 10 will effect an increase in

effective diameter of the driven pulley 70 and a corresponding increase in effective diameter of the driving pulley 60, thus automatically increasing the gear ratio of the motor relative to the ground engaging

wheels to prevent stalling and burnout of the driving motor.

While the employment of the two described adjustable pulleys is preferred, acceptable results can be attained by using only one of such pulleys, either torque or speed responsive, plus a belt tightening

pulley to remove slack from the belt 52 produced by changes in the effective diameter of the adjustable pulley.

Each of the aforementioned adjustable pulleys is available from commercial suppliers, such as Comet Industries of Richmond, Indiana, hence further description is unnecessary.

Figure 6 schematically represents an electric circuit for controlling the operation of motors 10 and 20 at operator selected

speeds and direction. The circuit diagram is believed to be self

explanatory to any person skilled in the art of electrically driven

vehicles.

Such person would also recognize that if the apparatus of this invention is utilized for remotely controlled vehicles, such as a wheeled

base for a robot, that a solenoid can be employed for operation of the bevel gear engagement control plunger 19, and electromagnetic signals

can be employed for operating the plunger solenoid and the direction and speed controls for the driving motor 10 and the steering motor 20.

Obvious modifications of this invention can readily be made by those skilled in the art of electric motor driven vehicles and it is intended that all such modifications fall within the scope of the

appended claims.