Wheelchair frame

Abstract: A wheelchair frame comprises a base frame part (1, 2) with a plurality of wheels (2, 3). These wheels are spring mounted in the base frame part and include two front wheels (3). Each of the front wheels (3) is rotatably supported by a support arm (6). This support arm is rotatably connected to a transverse axle (2) in such a manner that the rotation axis (5) of the front wheels (3) lies ahead of the transverse axle (2) as seen in forward direction. In this manner it is obtained that the wheelchair frame does not gallop at braking. Thereby the comfort for the user is increased and the stability of the wheelchair frame is guaranteed even at braking on downwardly sloping surfaces.

Description: The invention relates to a wheelchair according to the preamble of claim 1. German patent application DE-A-34 14 204 concerns a wheelchair comprising a frame and two front wheels, wherein each front wheel is rotatably supported by a support arm rotatably connected to a transverse axle in such a manner that the rotation axis of the front wheels lies ahead of and level with the transverse axle as seen in the forward direction. German Gebrauchsmuster DE-U-90 12 188 discloses a wheelchair with a complicated suspension system comprising two support arms for each front wheel, each support arm comprising two bearings and a gas compression spring mounted between the frame of the wheel chair and the second supporting arm. International patent application WO 94/15567 is directed to a wheelchair which comprises an interconnecting device which interconnects the suspension mechanism of at least one wheel situated on the front wheel axis to the suspension mechanism of at least one wheel situated on the rear wheel axis. WO-A-94 13241 discloses a wheelchair frame of the above-mentioned type, wherein only the backwheels are spring mounted in the base frame part. The invention aims to provide an improved wheelchair frame of the above-mentioned type. To this end the wheelchair frame of the invention is defined by the characterising portion of claim 1. In this manner it is obtained that the wheelchair frame will not gallop at braking. Thereby the comfort for the user is increased and the stability of the wheelchair frame is guaranteed even at braking on downwardly sloping surfaces. According to a favourable embodiment the spring means comprises a gas spring and a helical spring which are mounted in a telescoping housing. Thereby a spring means is obtained wherein the action of the gas spring can be adjusted to absorb the own weight of the complete wheelchair and a part of the weight of the user, while the helical spring can be adjusted to an optimum spring comfort. The invention will be further explained hereinafter by reference to the drawings in which an embodiment of the wheelchair frame according to the invention is shown. Figs. 1-3 schematically show side views of an embodiment of the wheelchair frame according to the invention in different positions. Fig. 4 is a top view of the wheelchair frame of Figs. 1-3. Fig. 5 shows a cross-section of the spring means of the wheelchair frame of Fig. 1. Figs. 1-3 show side views of a wheelchair frame in different positions and Fig. 4 shows a top view of this wheelchair frame. The wheelchair frame shown comprises a central beam 1 extending in driving direction and carrying a transverse axle 2 at the front side. The central beam 1 and the transverse axle 2 together form a base frame part of the wheelchair frame. The transverse axle 2 carries at each end a front wheel 3 which can be driven by an electromotor 4. Each wheel 3 is rotatable around a schematically indicated axis 5 and is rotatably connected with the transverse axle 2 by means of a support arm 6 and a bush 7, wherein the axis 5 lies ahead of the transverse axle 2 as seen in driving direction. A coupling arm 8 is attached to each bush 7 and the coupling arm 8 is connected to a lever 10 by a pulling rod 9. As shown in the top view of Fig. 4, the levers 10 are mounted at both sides on the central beam 1 rotatably around an axis 11. The opposite end of the levers 10 is connected with one end of a spring means 12 which at its other end is connected to the central beam 1. In the described manner the spring means 12 forms a common spring means for the front wheels 3 lying centrally above the central beam 1 so that a very compact frame construction is obtained. The described construction of the wheelchair frame further shows the advantage that spaces la (see Figs. 1 and 4) for the usual batteries for the power supply of the electromotors 4 are formed at both sides of the central beam 1, said spaces la being well accessible from the sides of the wheelchair frame. Checking and maintenance of the batteries is thereby easy, wherein it is not necessary for the user to leave the wheelchair. The central beam 1 carries at its backside a castor assembly 13 comprising a swivel axle 14 slidably mounted in a bush 15 which is attached to the end of the central beam 1. The swivel axle 14 is slidable in the bush 15 against the action of a spring 16. Fig. 1 shows the wheelchair frame in a not compressed position, wherein one end of the spring means 12 presses against a stop 17 of the central beam 1. Fig. 2 shows the wheelchair frame in a compressed position as caused by a user not shown. By the suspension of the front wheels 3 as described with the common spring means 12 it is obtained that the wheelchair frame will not gallop during braking but will rather move somewhat upwardly. This increases significantly the comfort of the user and also guarantees the stability of the wheelchair frame, especially during braking on a downwardly sloping surface. In the embodiment shown the base frame part supports a seat frame part 18 with adjustable seat angle and connected to the base frame part by means of front rods 19 and back rods 20. A spindle motor 21 is provided for adjusting the seat angle of the seat frame part 18. In Figs. 1 and 2 the seat frame part is adjusted in a relatively flat position and in Fig. 3 in the most rearwardly sloping position. For a further explanation of the adjustable seat frame part reference is made to EP-A-0 512 650 of the same applicant. The central castor assembly 13 provides for a very high manoeuvrability of the wheelchair frame. In order to provide a very high straight on stability also at high driving speeds, i.e. faster than 6 km/h, the castor assembly 13 comprises means 22 which at rotation of the swivel axle 14 from a neutral straight on position exerts a rotation force on the swivel axle 14 in the direction of the straight on position. These means 22 are subject of parent application EP-A-0 714 648 and for a further explination reference is made to this application. Fig. 5 shows a cross-section of the spring means 12. As shown in Fig. 5, the spring means 12 comprises a gas spring 38 and a helical spring 39 which are mounted in the telescoping housing 40. This housing 40 on one side rests with a seating 41 on a ball 32 attached to the central beam 1. The other side of the housing 40 is rotatably connected with the levers 10. The gas spring 38 provides a force which is sufficient for taking the weight of the wheelchair frame and a part of the weight of the user so that the helical spring 39 can be adjusted for providing spring comfort for the user. The spring force of the helical spring 39 and the spring force of the spring 16 are mutually adjusted in such a manner that the central beam 1 will move substantially vertically up and down during compressing the wheelchair frame. The inventionis not restricted to the above-described embodiment which can be varied within a number of ways within the scope of the claims.

Claims: Wheelchair frame, comprising a base frame part (1, 2) with a plurality of wheels (2, 3), said wheels being spring mounted in the base frame part and including two front wheels (3), wherein each front wheel (3) is rotatably supported by a support arm (6) rotatably connected to a transverse axle (2) in such a manner that the rotation axis (5) of the front wheels (3) lies ahead of and below the transverse axle (2) as seen in forward direction characterized in that a common spring means (12) is provided for both front wheels (3), said spring means being connected to the base frame part (1, 2) at one end and to both support arms (6) at the other end. Wheelchair frame according to claim 1, wherein the base frame part (1, 2) comprises a central beam (1) extending in the centre from the front side to the back side and carrying the transverse axle (2) at the front side, wherein the spring means (12) is mounted in the centre above the central beam and is connected to one end of levers (10) pivotably mounted at each side of the central beam, said levers being connected to a corresponding support arm (6) at their other end. Wheelchair frame according to claim 2, wherein each support arm (6) is rotatably mounted on the transverse axle (2) by means of a bush (7), wherein a coupling arm (8) is attached to each bush (7), said coupling arm being connected to the corresponding lever (10) by means of a pulling rod (9). Wheelchair frame according to claim 1 or 2, wherein the spring means (12) comprises a gas spring (38) and a helical spring (39) which are mounted in a telescoping housing (40) which on one side rests with a seating (41) against a ball (42) mounted on the central beam (1) and on the other side is rotatably connected to the levers (10). Wheelchair frame according to anyone of the preceding claims, wherein each of the front wheels (3) can be driven by an electromotor. Wheelchair frame according to anyone of the preceding claims, wherein the base frame part (1, 2) carries a central castor assembly (13) at the back side.

Inventors: SCHEULDERMAN PETRUS JOHANNES, SCHEULDERMAN, PETRUS, JOHANNES
Applicants: SEENUS NL BV R VAN, RICHARD VAN SEENUS NEDERLAND B.V.
Application year: 1995
Main classification: A61G5
IPC codes: A61G5, B62K5, A61G7