WHEELCHAIR

Abstract: Wheelchair with four wheels, with two side frames (1,2) and a middle frame (3,4) carrying the seat, both side frame (1,2) being connected to each other by means of the middle frame (3,4) in such a way that tilting of one of the side frames in one direction is followed by tilting of the other side frame through the same angle in the other direction, while the middle frame remains stationary.

Description: The invention relates to a wheelchair with four wheels, with two side frames and a middle frame carrying the seat, the two left and the two right wheels being connected to each other in each case by one of the side frames. Such wheelchairs are generally known in practice. The two side frames are then rigidly connected to the middle frame. The seat forms a rigid unit with a top frame, which is again connected to the middle frame. In order to obtain a certain flexibility in the underframe, it is possible to connect the side frames to the middel frame via shock absorbers. Another possibility is to make the seat itself somewhat flexible, as disclosed in EP-A-0,011,812. This known wheelchair does not have a middle frame with which the wheels are connected. A disadvantage of the wheelchair according to EP-A-0,011,812 is that the seat deforms during travel, which is uncomfortable for the person in it. The working of the frame according to EP-A-0011812 is such that when a wheel is lifted, the point with which the seat is fixed to the frame is making a proportional movement. The seat is directly connected to that part with which also the wheel is connected. A first reason for making a wheelchair frame flexible is to prevent the wheelchair with its passenger from wobbling. On account of their functional limitations, most wheelchair users have poor trunk stability. The movements which the wheelchair makes when following an uneven road surface therefore have to be limited as much as possible. The "pivoting effect" is important here. This effect means that, due to the short wheelbase and narrow track width of a wheelchair compared with the total height of structure and passenger, the highest point makes a relatively great horizontal movement as the result of a vertical displacement of a wheel. It has been found in practice that spring suspension of the wheels does not produce the desired results. A wheelchair is provided with two swivel wheels and two rigid wheels. The rigid wheels are the driven wheels in a manually operated wheelchair and an electric wheelchair. The problem with the swivel wheels is often that they start "shimmying" at a particular speed through a decrease in the wheel pressure. This shimmying depends, inter alia, on the wheel pressure. If a wheelchair is provided with a rigid frame, deformation of said frame can easily cause one of the wheels to have less contact with the road surface, which then results in shimmying and poor directional stability. In order then to ensure that the wheelchair retains good directional stability and that the wheels do not shimmy during its service life, the frame is made somewhat flexible. However, these measures are not sufficient to ensure constant contact between the wheels and the road surface, which is never flat in practice. The object of the invention is to improve the flexibility of a wheelchair, and this is achieved according to the invention in that both side frames are pivotably connected to a horizontal cross shaft of the middle frame and are connected to each other by a straight, two-armed lever disposed at a distance to the horizontal cross shaft, of which the point of rotation is connected to the middle frame, so that pivoting of one of the side frames in one direction causes pivoting of the other side frame through the same angle in the opposite direction. This connection between left and right side frames can be achieved in various ways. As a result of this connection, the seat always undergoes less angular displacement than the side frames. Besides, the vertical movements of the four wheels are linked together, with the result that the weight of the wheelchair with passenger is always borne on the four wheels, which in fact gives the wheelchair greater stability than in the case of a frame such as that described in DE-OS-27,31,952 and as great stability as the frame described in EP-A-0,011,812. Compared with the frame described in this European patent application, this principle has the advantage that the wheel pressure is distributed more uniformly over the four wheels. The invention relates also to a wheelchair with four wheels and two side frames of a seat, the two left and right wheels being connected to each other in each case by one of the side frames of the underframe, which wheelchair is characterized in that each side frame of the underframe is rigidly connected to a circular arc-shaped pivoting part, relative to which the seat can be moved, each pivoting part being displaceable in a circular arc-shaped groove in each side frame of the seat, each pivoting part being provided with a gear rack with which a pinion mounted on a shaft meshes the two shafts lying in line with each other and being connected to each other by a differential mechanism which is capable of converting the rotary movement of one shaft to an equally great rotary movement of the other shaft in the opposite direction. Two embodiments of the wheelchair according to the invention are shown in perspective in the drawing, in which: Fig. 1 shows the embodiment with direct connection; and Fig. 2 shows the embodiment used with a pivoting mechanism. In Fig. 1 the left side frame is indicated by 1. It comprises a horizontal part 1a with a suspension for a drive wheel (not shown), a vertical part 1b, and a horizontal part 1c. The suspension 1d is connected to the end of the horizontal part 1c for the vertical swivel axle of a swivel wheel, not shown. The right side frame is indicated by 2 and comprises the corresponding parts 2a, 2b, 2c and 2d. Each side frame 1, 2 is freely pivotable about a horizontal cross shaft 3. This cross shaft is rigidly connected to the top frame (not shown) of the seat (not shown). An arm 4 running horizontally and in the lengthwise direction is fixed to said cross shaft 3, and is thus also rigidly connected to the seat. The coupling mechanism, which in the embodiment shown comprises a cross bar 5 which is pivotably connected to the wheel suspensions 1d and 2d, is connected to the free end of this shaft 4. The various connections are formed, for example by ball-and-socket joints 6, 7 and 8. When the left drive wheel now moves upwards, the side frame 1 will pivot to the right about the cross shaft 3, and the left swivel wheel will move downwards. Since the arm 4 remains in place, the right swivel wheel will move up and the right drive wheel will move down over the same distance. The seat follows approximately half the angle of the road surface; see also figs. 9-12, EP-A-0,011,812. The seat now makes a smaller movement than is the case with a rigid frame or a frame of the type described in DE-OS-27,31,952. The embodiment according to Fig. 2 will now be discussed. The underframe is not shown here, but it also comprises a left side frame 1 and a right side frame 2. The left side frame 1 is rigidly connected, in a manner not shown, to the arc-shaped pivoting part 10, while the right side frame 2 is connected to the pivoting part 11. The two pivoting parts 10 and 11 form part of a circular arc and are provided with a gear rack, of which only the gear rack 10a is shown. The side frames of the seat which are rigidly connected to each other are indicated by 12 and 13 and are each provided with circular arc-shaped grooves, of which only the groove 13a is shown. The pivoting parts 10, 11 are displaceable in the grooves. When the user of the wheelchair wishes to assume a different posture, he moves the seat relative to the pivoting parts 10, 11. This is the subject of Dutch Patent Application 86,01457. A pinion 14, 15, fixed on shafts 16, 17 lying in line with each other, meshes each of the gear racks. These shafts come together in a differential mechanism, which consists of sun gears 18 connected to the shaft 16, 17 and having between them at least one planet gear 19 which is supported in a housing 20. If this housing 20 is held fast, the shaft 16 will turn in a certain direction when the left side frame 1 and thus the pivoting part 10, turns. As a result of the differential mechanism, the shaft 17 will turn through the same angle, but in the opposite direction, and the pivoting part 11, and thus the right side frame 2, will thus be turned in the opposite direction. The housing 20 can be kept immobile by, for example, fixing a toothed wheel 21 on the housing 20. A toothed belt 23 can run round said wheel 21 and round a second wheel 22. This second wheel 22 is non-rotatably mounted on a shaft 24, which is supported in self-braking fashion in the side frame of the seat. During deliberate pivoting of the seat by the passenger, the shaft 24 is rotated, so that the two shafts 16, 17 drive the pinions 14, 15.

Claims: 1. Wheelchair with four wheels, with two side frames (1, 2) and a middle frame (3, 4) carrying the seat, the two left and the two right wheels being connected to each other in each case by one of the side frames (1, 2), characterized in that both side frames (1, 2) are pivotably connected to a horizontal cross shaft (3) of the middle frame and are connected to each other by a straight, two-armed lever (5) disposed at a distance to the horizontal cross shaft (3), of which the point of rotation is connected to the middle frame, so that pivoting of one of the side frames (1, 2) in one direction causes pivoting of the other side frame (1, 2) through the same angle in the opposite direction. 2. Wheelchair according to claim 1, characterized in that the point of rotation of the lever (5) is formed by a ball-andsocket joint bearing (6) which is supported in the arm (4) of the middle frame (3, 4). 3. Wheelchair according to claim 1, characterized in that the seat can be deliberately tilted forwards and backwards. 4. Wheelchair with four wheels and two side frames (12, 13) of a seat, the two left and right wheels being connected to each other in each case by one of the side frames (1, 2) of the underframe, characterized in that each side frame (1, 2) of the underframe is rigidly connected to a circular arc-shaped pivoting part (10, 11), relative to which the seat can be moved each pivoting part being displaceable in a circular arc-shaped groove (13a) in each side frame (12, 13) of the seat, each pivoting part (10, 11) being provided with a gear rack (10a) with which a pinion (14, 15) mounted on a shaft (16, 17) meshes the two shafts (16, 17) lying in line with each other and being connected to each other by a differential mechanism which is capable of converting the rotary movement of one shaft (16, 17) to an equally great rotary movement of the other shaft (17, 16) in the opposite direction. 5. Wheelchair according to claim 4, characterized in that the differential mechanism consists of two sun gears (18) which are disposed opposite each other and are each connected to the appropriate shaft (16, 17), and of at least one planet gear (19) at right angles thereto which connects the two sun gears (18), the shaft(s) (16, 17) of the planet gear(s) (19) being held firmly in position.

Inventors: HUTTENHUIS, ALOYSIUS GERHARDHUS, JANSSEN, HENRICUS THEODORUS JOZEF
Applicants: HUKA DEVELOPMENTS B.V.
Application year: 1988
Main classification: A61G5
IPC codes: A61G5