US3529688A - Wheelchair - Google Patents

Description

Sept. 22, 1970v ,w, BR CE 3,529,688

WHEELCHAIR Filed Nov. 7. 1968 5 Sheets-Sheet 1 Ivan/'01: T g ,1, 4/. 8/2 a a, -m/r. 0km

J. W. BRUCE WHEELCHAIR Sept; 22, 1970 Sheets-Sheet 5 Filed Nov. '2, 1968 FIG. 9

I I 2b 2b b 9b b 6b 370 30a 60 32a 50a 20" FIG. 73

J. W. BRUCE Sept. 22, 1970 WHEELCHAIR 5 Sheets-Sheet 4.

Filed NOV. 7, 1968 II II II L I I00 0/2 700M l-flllarzr 0774 14 f/wln Sep -22,1910 J.W.BRUE 3,5 9,688

WHEELCHAIR Filed Nov. 7, 1968 v 5 Sheets-Sheet s 20 24 20' \7 J: o 72a,

United States Patent 3,529,688 WHEELCHAIR John W. Bruce, 3853 Red Fox Drive NW., Roanoke, Va. 24017 Filed Nov. 7, 1968, Ser. N0. 774,090 Int. Cl. B6211 55/04; B62b 9/02 U.S. Cl. 180-9.24 16 Claims ABSTRACT OF THE DISCLOSURE A wheelchair has a seat frame which has mounted thereon ground-contacting wheels located at opposite sides and turnable about a first axis extending transversely to the direction of movement of the wheelchair. A pair of endless-belt traction assemblies are connected with the frame located below the same and projecting in mutually opposite directions. The assemblies have respective first ends which are mounted for tilting movement about a second axis common to them both and paralleling the first axis, and each having a second end remote from the respective first end. First actuating means is associated with the assemblies and serves for moving the first ends in unison between a raised position in which they are out of contact with the ground and the frame is supported on the wheels, and a lowered position in which the wheels are out of contact with the ground and the frame is supported on the assemblies. Second actuating means is associated with the respective second ends and serves for tilting the assemblies individually about the second axis in a plane normal to the same. Drive means is alternatively operative for driving the wheel means when the chair is to be propelled on substantially level ground, and for driving the traction assemblies when the chair is to be propelled over inclines and obstacles.

BACKGROUND OF THE INVENTION The present invention relates generally to motorized wheelchairs, and more particularly to a motorized wheelchair capable of locomotion not only on level ground but also over inclines and obstacles.

It is already known to provide motorized wheelchairs, usually electrically-driven chairs, for use by invalids. In fact, it is known to provide chairs which are capable of ascending and decending stair-ways and inclined surfaces as well as travelling over level horizontal surfaces. The known constructions do not, however, provide the desired safety of operation and ease of operation and it is therefore desirable to provide a wheelchair which incorporates these advantageous features.

Accordingly, it is an object of the present invention to provide an improved driven wheelchair of the type capable of locomotion not only on level surfaces but also on inclines.

A further object of the present invention is to provide such a wheelchair which is highly maneuverahle and which is very readily and in a most simple manner controllable by the user.

SUMMARY OF THE INVENTION In accordance with the above objects, and others which will become apparent hereafter, one feature of my invention resides in the provision of a wheelchair which includes a seat frame and ground-contacting wheel means on opposite sides of the seat frame, such wheel means being turnable about a first axis which extends transversely of the direction of movement of the wheelchair. A pair of elongated endless-belt traction assemblies is connected with the frame and projects from below the same in mutually opposite directions. The assemblies have respective first ends mounted for tilting movement about a second axis which is common to them both and parallels the first axis, and they each have a second end remote from the respective first end. First actuating means is associated with the assemblies and is operative for moving the first ends in unison between a raised position in which they are out of contact with the ground and in which the frame is supported on the wheel means, and a lowered position in which the wheel means are out of contact with the ground and the frame is supported on the assemblies. Second actuating means is associated with the respective second ends and is operative for tilting the assemblies individually about the second axis in a plane normal to the same. Finally, I provide drive means which is alternatively operative for driving the wheel means when the chair is to be propelled on substantially level ground, or for driving the traction assemblies when the chair is to be propelled over inclines and obstacles.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIGS. l6 illustrate in diagrammatic manner various phases of the negotiation of a stairway with the wheelchair according to the present invention;

FIG. 7 illustrates, in a diagrammatic view, the locomotion of the Wheelchair according to the present invention on a level surface;

FIG. 8 is side-elevational view, partly illustrated in phantom lines, of a wheelchair according to the present invention;

FIG. 9 is a plan view of the chair illustrated in FIG. 8 as seen from the line IX-IX in FIG. 8;

FIG. 10 is a rear-elevational view of the wheelchair shown in FIG. 8;

FIG. 11 is a front-elevational view of the wheelchair shown in FIG. 8;

FIG. 12 is a transverse section through a traction assembly as taken on the line XII-XII of FIG. 8; and

FIG. 13 is a top-plan view of the associated front and rear traction assemblies at one side of the wheelchair.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Discussing now firstly the embodiment of the wheelchair as illustrated in FIGS. 8-12, it will be seen that the chair is generally identified with reference numeral 1. While the term wheelchair has been used as the expression most commonly employed for designating this type of con veyance, this is not to be construed as precluding any other type of locomotion, but is to be understood as a term used for the sake of convenience.

At opposite sides of the chair 1 are provided the wheels 2a and 2b on each of which there is mounted in known manner a hand wheel, designated with reference numerals 2a and 2b, respectively, which may be gripped by the user for manually actuating the chair.

Arm rests 1a and 1b are provided and the wheels 2a and 2b are mounted on a shaft 3 extending transversely below the chair seat 10. The diameters of the wheels 2a and 2b are of course so selected that the seat of chair will be sufiiciently elevated above the ground to avoid interference with the latter particularly when going over obstacles.

Below the front part of the chair which constitutes the foot rest 1d, there are provided two vertical shafts 4a and 4b turnable about their respective axis and each provided with a supporting roller a and 5b which thus can turn about the axis defined by the shafts 4a and 4b.

Two electric motors 6a and 6b respectively are associated with the wheels 2a and 2b in the manner still to be described in more detail later on. A suitable battery, such as a storage battery 7, is provided for energizing the electric motors (compare FIG. 9) and a rectifier 8 may be provided for the purpose of recharging the battery 7 when necessary.

A drive wheel 30a is associated with the wheel 2a and a drive wheel 30b is associated with the wheel 2b, the drive wheels respectively being provided on the output shafts of the electric motors 6a and 6b in known manner. The drive wheels 30a and 30b respectively mesh with the gears 32a and 32b (compare FIG. 9) which are provided at the inwardly facing side of the wheels 2:: and 2b, respectively. Levers 1e and 1e (see FIG. 11) are provided by means of which the motors 6a and 6b may be disengaged from their meshing collection with gears 32a and 32b. The levers 1e and 1e are provided at the sides of the chair seat 10 and are associated with the motors 6a and 6b respectively via linkages 1 and 1f which are so arranged that, when the levers 1e and 1e are respectively actuated, the motor 6a or 6b are respectively tiltable about bolts 6c and 60' from a position of meshing engagement into a position of disengagement. This is necessary so that the user may manually operate the chair.

FIG. 11 illustrates that there are provided two traction assemblies each of which consists of a front portion and a rear portion, as will be developed in more detail. The traction assemblies comprise an endless belt 12a and 12b consisting of a heavy strip of rubber or other material having inwardly facing teeth or projections and having at the respectively outwardly facing surface strong transversely extending projections or cleats 13. The inwardly projecting teeth are identified with reference numeral 12c. Cords of steel net cables or other reinforcement material may be imbedded in the respective belts and the latter are of course of requisite width. The traction assemblies, and accordingly the belts 12a and 12, are spaced apart from one another in transverse direction as far as possible to provide the maximum possible stability for the chair. They are located between the wheels 2a and 2b and, when the chair is supported on the wheels 2a and 2b, the enclosed belts 12 and 12b are maintained in a retracted position upwardly above the ground in substantially horizontal position by means of a hydraulically operated cylinder and piston arrangement. Reference numeral 14 identifies a hydraulic cylinder whose piston, including the piston rod 15, are movable within the cylinder 14. The latter is secured to the underside of the chair seat 10 and the piston rod 15 which extends downwardly from the cylinder 14, is journalled to a horizontal shaft 16 extending in substantial parallelism with the shaft 3 and which supports the traction unit frames 17 and 18 in the manner to be still described. The traction unit frames 17 and 18 are tiltable about the shaft 16 and each consists of a front pair of rails 20, 20 and a rear pair of rails 19, 19'.

The drive wheels 27 and 21, 21' for the endless belts 12a and 12b, as well as rollers 22, 23, 24, 25 and 26 which support the endless belts and also the forward guide roller 28 are arranged between the pairs of rails in suitable manner to be described. The front pair of rails 20, 20 is advantageously longer than the rear pair of rails 19, 19', with the length differential being on the order of 4:3. Each rail of each pair of wheels is tiltable about the shaft 16 which connects the two traction unit frames 17 and 18 with one another, and axial movement on the shaft 16 is prevented with respect to the rails 19, 19 and 20 and 20 in known manner, such as by means of setting or snap rings. The ends of lead pair 20, 20 of rails which are secured to the shaft 16 are so offset that at each side the rails extend in one plane. A shaft 29 connects the front ends of the rails 20, 20' and thereby the traction unit frames 17 and 18. The guide roller 28 is freely turnable on the shaft 29 in each traction unit frame 17 and 18. This roller is provided for guiding the respective endless belts 12a and 12b; its diameter corresponds to the diameter between the upper and lower stringers of the respective endless belts 12a and 12b.

The rollers 24, 25, 26 are arranged between the rails 20, 20' and in identical spacing between the shafts 16 and 29. Their diameter is smaller than that of the guide roller 28 and they only engage the inside of the lower groundcontacting stringers of the endless belts 12a and 12b.

Timing or V belts 47a and 4712 (FIG. 11) serve to drive the endless belts 12a and 12b in that they are convoluted about the pulleys 48a and 48b on the one hand and the pulleys 31a and 31b on the other hand, as shown in FIG. 11. The latter pulleys are provided on the shaft of the electric motors 6a and 6b, respectively, next to the drive gears 30a and 30b. As illustrated, a motor 6a drives the wheel 2a via a gear drive and the endless belts 12a via a V belt, as soon as the wheels 2a and 2b are raised from the ground. Similarly, motor 6b drives the wheel 2b and the endless belts 12b in the same manner.

When the traction unit frames 17, 18 are raised as shown in FIG. 7, the belts 47a and 47b are normally loose, that is a certain amount of slack develops. A portion of this slack is taken up by a tightening device 49a and 49b, respectively. As soon as the cylinder 14 which is connected with the shaft 16 is lowered, thereby lifting the wheels 2a and 2b off the ground, the V belts 47a and 47b are sufficiently tensioned to assure motion transmission and driving of the endless belts 12a and 1217. This is so because the belt pulleys 48a and 48b are provided at the gear wheels 27a and 27b which in turn are secured on the shaft 16 via suitable bearings. The wheels 27a and 27b are located substantially at the center of the belts 12a and 12b, and a second set of V belts 10a and 10b (see FIG. 10) connects the wheels 27a and 27b with the rear drive wheels 21 and 21, being convoluted about the belt pulleys 11a and 11b which are bolted to the wheels 27a and 27b, respectively, and being further convoluted about belt pulleys 9a and 9b each of which is bolted to one of the wheels 21 and 21', respectively. In other words, the pulleys 11a and 11b are also secured on the shaft 16, whereas the pulleys 9a and 9b are secured on the shaft 33. Since the shafts 16 and 33 always are identically spaced from one another because they are secured on the rails 19 and 19, the pulleys 10a and 10b are always tensioned for driving the belts 12a and 12b and transmit motion from the wheels 27a and 27b to the wheels 21a and 21b, respectively. This prevents slippage of the belts and enables a much more precise guidance and control of the wheelchair than otherwise possible because it is always the lowermost element, that is either the wheels 2a and 2b or the belts 12a and 12b, which drives the wheelchair 1.

When the motors 6a and 6b drive the belts 12a and 12b in the manner already described above, the wheels 30a and 30b each drive one of the wheels 2a and 2b and mesh with the wheels 32a and 32b so as to rotate while the wheelchair is propelled on the belts 12a and 12b. This is necessary to assure smooth transfer of traction from the belts 12a and 12b to the wheels 2a and 2b, or vice versa, at the beginning or at the end of a climbing episode, that is when the chair begins or ends the negotiation of an obstacle.

The emergency brakes 50a and 50b (see FIG. 11) serve to brake turning of the wheels 2a, 2b in acting upon the wheels 32a and 32b when utilized. These brakes 50a and 50b are hydraulically operated so-called spot brakes which are already known in the art and therefore are not more specifically illustrated. They not only serve to prevent further turning of the wheels 2a and 2b when actuated, but also switch off the motors 6a and 6b via a microswitch adjacent the brake-operating handgrip 52 so that the belts 12a and 12b undergo braking action via the V belts 47a, 47b and a, 10b.

The rollers 22 and 23 are located between the rails 19 and 19 and the drive wheels 27 and 21 which latter are mounted on the shafts 16 and 33, respectively, with suitable bearings. They always have the same diameter as the rollers 24, 25, 26 and engage only the lower stringer of the belts 12a and 12b.

A non-illustrated piston has a piston rod 34 which is connected at the center of the rearmost shaft 33. This piston is reciprocal in a cylinder 35 and is double-acting for hydraulic operation. The end of the cylinder 35 is tiltably secured via ' bolts 37a and 37b and a connecting member 36 into the bearings 36a and 36b. The bolts are arranged on the cylinder 14, which serves to raise and lower the traction assemblies, diametrically opposite one another. The tilting axis of the cylinder 35 is parallel to the axis of the shaft 3 and all four shafts 3, 16, 29 and 33 are always parallel to one another and with the ground.

When the piston in the cylinder 35 is operated, the pairs of rails 19 and 19' of each traction assembly frame can be tilted about the shaft 16 so that the rearmost portion of the belts 12a and 12b can be tilted through a desired angle with respect to the remaining foremost portion. Levers 38, 38' are provided at the opposite ends of the shaft 16 which extends from the pairs of rails 19, 19' and 20, 20', and the length of the levers 38 and 38' are so selected that a roller 39, which is mounted on a pin 40 and connects the lever ends with one another, engages the outer surface of the uppermost stringer of the respective belts 12a and 12b. The purpose of the roller 39 is to assure that the portions of the upper most stringers which are associated with the foremost and rearmost pair of rails, will remain in parallelism with the corresponding portion of the respective lowermost stringer when the foremost pair of rails is turned about the shaft 16 so as to assume an angle with respect to the rearmost pair of rails. The particular configuration of the roller 39 is illustrated in FIG. 12 and makes it possible for the ' belts 12a and 12b to pass below the roller 39 without interference by the cleats 13.

The piston rod 41 of a double-acting hydraulic piston is connected at the center of the shaft 29 which connects the front ends of the two pairs of rails 20*, 20. This piston reciprocates ni a cylinder 42 one end of which is connected to a shaft 43 which is secured below the chair seat 10 in parallelism with the shaft 29 and therefore also with the shaft 16. Movement of the piston in the cylinder 42 effects tilting of the forward portion of the respective belts 12a and 12b about the shaft 16, which connects the forward pair 20, 20- of rails tiltably with the rearward pair of rails 19, 19'.

It will be seen that if the wheels 2a and 2b engage the ground for horizontal movement of the chair, then the piston of both cylinders 35 and 42 are withdrawn to positions closest to shaft 43 with which cylinder 42 is connected, as well as closest to the connections 37a, 37b with the cylinder 35. This maintains the front portion of each of the traction unit frames 17, 18, which is controlled by the rails 20, 20" in horizontal position while the rear portion, which is controlled by the rails 19, 19', is maintained at an upward angle with respect to the front portion, with the shaft 16 being raised 'by the piston in the cylinder 14, as illustrated in FIG. '8 in broken line.

The hydraulic arrangements 14, 35 and 42 are known per se in the art and are therefore not described in more detail except for being shown in FIG. 8. They have double-acting pistons which are respectively connected to piston rods 15, 35a and 41. The pistons are separately actuated through known types of controls which are provided on the armrests 1a and 1b and which include a microswitch located next to the controls which actuates the electric drive motor 44 when the control levers are moved forwardly or rearwardly. The motor 44 is energized by the battery 7 via a suitable connection which is not illustrated, and drives a hydraulic pump 46 whose shaft is connected with the output shaft of the motor 44. Pump 46 supplies hydraulic pressure to the cylinders and the hydraulic brake arrangements 50a and 50b. A container 45 is provided and accommodates a quantity of hydraulic fluid sufiicient for actuating the cylinders and brake arrangements.

The control means for actuation of the hydraulic cylinders and brake arrangements are so-called four-way controls, two for inlet and two for outlet purposes, and when actuated will operate as follows: to lower the shaft 29 which is connected with the front portion of the traction assemblies, the control lever 53 is moved forwardly thereby actuating the microswitch and via this the motor 44. This actuates the hydraulic pump 46 supplying hydraulic fluid to the upper inlet of the cylinder 42 whereby the piston and the piston rod 41 is driven downwardly in the cylinder 42. ecause the piston rod 41 is connected with the shaft 29, the front ends of the belts 12a and 12b are lowered until they engage the ground, continued lowering and resulting in a raising of the rollers 5a and 5b off the ground. The operator may control to what extent he wishes to raise rollers 5a and 5b from the ground and the lever 53 is spring biassed, so that when it is disengaged, it will return to inoperative position. This movement to the off position terminates further movement of the piston and stops the operation of the motor 44 via the aforementioned (non-illustrated) microswitch. To raise the shaft 29, on the other hand, the control lever 53 is moved rearwardly, thereby actuating the motor 44 via the pump 46, so that hydraulic fluid is pressed by the latter from the other side of the cylinder to the lower inlet whereby the piston is moved upwardly with concomitant raising of the shaft 29 until the rollers 5a and 5b are engaged with the ground. The same type of control is true of the shaft 16, and this control is initiated via the control lever 54 provided on the arm rest 1b. Similarly, control of the shaft 33 is effected by the control lever 55 which is also provided on the arm rest 1b.

Additional control levers 51a and 51b are provided on the arm rest 1a and 1b, respectively, and control operation of the motors 6a and 6b. These controls are of known construction and are not further illustrated, it being suf- -ficient to point out that they are provided with variable resistors so that the rotations permitted of the motors 6a and 6b can be adjused. If control levers 510 or 51b are moved slightly forwardly, a microswitch (not illustrated) is actuated which starts the motors 6a or 6b, respectively, and causes the chair 1 to slowly advance in forward direction. The farther the levers 51a and 51b are advanced in forward direction, the faster the chair will be propelled. To propel the chair rearwardly, the control levers 51a and 51b are moved rearwardly and again the speed of rearward movement of the chair is controlled in dependence upon the extent to which the levers 51a and 51b are moved rearwardly from their off or center position. To bring the chair to a halt, it is simply necessary to move the levers 51a and 51b to their center position in which case the motors 6a and 6b are stopped by the microswitches. To effect a turning of the chair, one of the levers 51a or 51b is set to center position whereas the other one is either moved forwardly or rearwardly so that the chair will turn about the wheel associated with the non-energized motor. In the event that a handicapped user of the chair should have only one hand or one arm, all controls may be provided on a control panel which may be mounted at a suitable location, or for instance tiltably arranged as to be readily accessible. This is not illustarted but is clearly a possibility within the scope of the present invention.

The brake assemblies 50a and 50b may be of various different types, but the so-called spot-brakes which have been mentioned and which are of the type used in aircraft, are advantageous because they are not only highly reliable but also require very little space. They are provided only for emergencies and will deactivate both motors 6a and 6b via microswitches as soon as operated. This prevents overloading of the motors and the user may effect emergency braking of the chair without any danger that the chair will run while undergoing such a braking.

Returning now to FIGS. 18, it is emphasized that the chair may be moved forwardly as well as rearwardly, and that FIGS. 1-7 illustrate the possibility of moving either upwardly or downwardly over a stair. Let it be assumed that the chair is to move upwardly over a stairway, then the chair will be backed up to the bottom step as illustrated in FIG. 7. Now the rear axial 33 is depressed so that the rear portions of the belts 12 and 12b will engage the bottom step as shown in FIG. 6. Thereupon, the axial 16 is similarly depressed until the wheels 2a and 2b are raised off the ground and the front axial or shaft 29 is depressed until the rollers 5a and 5b are also raised off the ground. This position is shown in FIG. 5. The electric motors are now actuated in a sense for propelling the chair rearwardly which is accomplished by the belts 12a and 121). At this time the front shaft 29 is further depressed slowly until the belts 12a and 12b are located in the position shown in FIG. 4. It will be noted that the seat will remain unchanged in its position relative to the ground. The chair continues to advance up the stairway until the position illustrated in FIG. 3 is reached, in which the shaft 33 at the rear of the chair is depressed.

Axle 16 can be raised independently of the front and rear axles 29 and 33, respectively, to allow the operator to make a smooth transition from stairs or slopes to level surfaces without any tilting or rocking of the chair. It will be appreciated that this is possible because the independent adjustment of the axle 16 allows the wheels 2a and 2b to contact the level surface at the top (or bottom, as the case may be) of the stair or slope, while the front and rear track sections 17 and 18 are in solid contact with the steps (or slope) and the level surface, respectively. Continued rearward advancement of the chair will then effect movement of the belts 12a and 12b in their totality onto the level ground or surface at the upper end of the stairway, as shown in FIG. 2. Now, the wheels 2a and 2b are lowered until they engage the ground, and similarly the rollers 5a and 5b. The chair is then in the position as illustrated in FIG. 7 for horizontal movement.

It will be evident that if the stairway is to be negotiated in downward direction, the procedure just outlined will be reversed, beginning with advancement of the chair in the manner shown in FIG. 7 until the upper stair is reached, is illustrated in FIG. 1, whereupon successive operations are carried out as illustrated in FIGS. 2-6.

It will be seen that my novel chair provides vastly greater control and safety, as well as versatility in the negotiations of all types of obstacles and terrain. Furthermore, my novel wheelchair is relatively simple in its construction and is therefore not only relatively inexpensive to manufacture and sell, but also less liable to mechanical breakdowns.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions difiering from the types described above.

While the invention has been illustrated and described as embodied in a motorized wheelchair, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. A wheelchair comprising, in combination, a seat frame; large diameter ground-contacting wheel means on opposite sides of said seat frame and turnable about a first axis located near the rear of said seat frame and extending transversely of the direction of movement of said wheelchair; forwardly disposed small diameter supporting roller means; a pair of elongated endless-belt traction assemblies connected with said frame and projecting from below the same in mutually opposite directions, said assemblies having respective first ends mounted for tilting movement about a second axis common to them both and paralleling said first axis, and each having a second end remote from the respective first end; first actuating means associated with said assemblies and operative for moving said first ends in unison between a raised position in which they are out of contact with the ground and the frame is supported on said wheel means, and a lowered position in which said wheel means are out of contact with the ground and said frame is supported on said assemblies; second actuating means associated with the respective second ends and operative for tilting said assemblies individually about said second axis in a plane normal to the same; and drive motor means alternatively operative for driving said wheel means when said chair is to be propelled on substantially level ground, and said traction assemblies when said chair is to be propelled over inclines and obstacles.

2. A wheelchair as defined in claim 1, said first and second actuating means respectively comprising hydraulically operable double-acting piston and cylinder arrangements.

3. A wheelchair as defined in claim 2, said drive means comprising reversible electric motor means and storage battery means associated with said motor means for supplying electric energy thereto.

4. A wheelchair as defined in claim 3, said motor means including two electric motors each provided with an output shaft having a drive gear, said drive means further comprising gear means on said wheel means, and said motors being mounted for common tilting movement between a first position in which the respective drive gears mesh with said gear means, and a second position in which said drive gears are withdrawn from said gear means.

5. A wheelchair as defined in claim 4, said drive means further comprising first pulley means provided on the respective output shafts, second pulley means associated with said endless-belt traction assemblies, and drive-belt means convoluted about said first and second pulley means and tightly engaging the same when said first ends are in said lowered position so as to drive said second pulley means and thereby said assemblies, said drive-belt being slackened so as to slip over said pulley means when said first ends are in said raised position thereof.

6. A wheelchair as defined in claim 5; further comprising take-up means for partially taking up the slack of said drive-belt means when said first ends are in said raised position.

7. A wheelchair as defined in claim 5, said traction assemblies each including two transversely spaced rails and a shaft connecting said rails at the second end of the respective assembly; further comprising an axle constituting said second axis and tiltably connecting the rails of both of said assemblies at said first ends of the latter, said pulley means being rigid with said axle; and further comprising supporting rollers provided on said axle and the respective shafts, endless belts each convoluted about the supporting rollers on one of said shafts and some of the supporting rollers on said axle, an additional pulley provided on one of said shafts rigid therewith, and additional drive belt means convoluted about said pulley means and said additional pulley.

8. A wheelchair as defined in claim 7, each of said endless belts having a ground-contacting stringer and another stringer upwardly spaced therefrom; and further comprismg a plurality of supporting rollers arranged intermediate said axle and the respective shafts between said stringers and engaging only the respective groundcontacting stringer of each belt.

9. A wheelchair as defined in claim 8; and further comprising roller means associated with the other stringers of the respective belts on said traction assemblies and operative for maintaining each other stringer in parallelism with the associated ground-contacting stringer in all angular positions of said traction assemblies relative to one another.

10. A wheelchair as defined in claim 7, one of said traction assemblies being longer than the other.

11. A wheelchair as defined in claim 1, said traction assemblies including a first and a second assembly respectively projecting from below said frame in the normally forward and the normally rearward direction of said wheelchair; and wherein said first traction assembly is longer than said second traction assembly.

12. A wheelchair as defined in claim 11, the length ratio of said first assembly to said second assembly being on the order of 4:3.

13. A wheelchair as defined in claim 3; and further comprising brake means associated with said drive means and operable at the will of a user for braking the motion of said Wheelchair.

14. A wheelchair as defined in claim 13, said brake means including a hydraulic brake assembly; and further comprising a hydraulic pump operatively associated with said hydraulic brake assembly and with said hydraulically operable piston and cylinder arrangements, an electric drive motor for said pump, and an operative connection between said drive motor and said storage battery for supplying electric energy from the latter to the former.

15. A Wheelchair as defined in claim 14; and further comprising four-way hydraulic control means operatively associated with said brake assembly and said cylinder and piston arrangements.

16. A wheelchair as defined in claim 15; and further comprising switch means associated with said control means and operative for effecting starting and stopping of said electric drive motor in response to operation of said control means.

References Cited UNITED STATES PATENTS 24,751,027 6/1956 McLaughlin 1809.24- 3,127,188 3/1964 Greub 2809.24 X 3,231,290 1/1966 Weyer 2805.22 3,276,531 10/1966 Hale l-9.24

LEO FRIAGLIA, Primary Examiner R. J. JOHNSON, Assistant Examiner US. 01. X.R rim-51; 2:20-52;

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