BACKGROUND OF THE INVENTION When being transported by a wheelchair outdoor it happens that steps such as curbs must be passed, in both directions, i. e. the wheelchair is both to climb the step and the wheelchair must be capable of running down the step. Wheelchairs are allowed to be capable of passing such steps for a maximum height which for example can comprise 8 cm. In particular when passing down such a step there may exist a risk that the wheelchair tips forwards and this risk can be largest for the type of wheelchairs having relatively large wheels placed in the front. When climbing a step the wheelchair can have a difficulty in advancing up a sharp step if it has a height which is a significant portion of the diameter of the front wheels of the wheelchair, and therefore there may exist a need for devices facilitating the climbing of such a step.

In U. S. patent 5,848,658 an anti-tip device for a wheelchair is disclosed which comprises elastically suspende, front stabilizer wheels. Helical compression springs are used together with link arms. In the published International patent application WO 98/46184 also front stabilizer wheels are disclosed which are attache to an articulated frame that is retained in its position by a centrally placed helical compression spring. In the published French patent application 2 727 012 also a wheelchair having front anti-tip wheels is disclosed which are rotatably mounted at the front end of arms which by an elastic bearing are connecte to the frame of the wheelchair.

DESCRIPTION OF THE INVENTION It is an object of the invention to provide a device which in a relatively simple way can reduce the risk of tipping forwards when being transported by a wheelchair down a step or similar thing.

It is another object of the invention to provide a device which facilitates for a wheelchair to climb sharp steps.

It is another object of the invention to provide a simple design of elastically mounted, front anti-tip wheels.

An anti-tip device for a wheelchair which also facilitates climbing comprises stabilizer wheels that normally have no contact with the base material or ground over which the wheelchair passes and that are rotatably mounted to bars which project forwards, beyond the front wheels of the wheelchair. The stabilizer wheels are thus placed in front of the ordinary wheels of the wheelchair and their lower sides or edges are located in a plane which is located above the plane passing through the lower sides or surfaces of the ordinary. support wheels of the wheelchair. The bars are designed as springs making the stabilizer wheels be elastically mounted so that they can move

upwards in a vertical plane when contacting an obstacle. The bars are relatively long in order to obtain sufficient elasticity and they are attache to the base of the wheelchair at places located rather far to the rear of the base, such as at a significant distance behind the rotational axis of the front ordinary wheels of the wheelchair. The elasticity of the bars laterally. i. e. in a horizontal plane, is restricted by guides. They can comprise slots made in suitably placed parts projecting from the base. The stabilizer wheels can suitably be incorporated in stabilizer assemblies shaving a simple design which comprise a guide plate shaving an elongated shape including a fange or bent portion at its front end, an elastic bar passing through a slot in the lange and attache to the rear portion of the guide plate, and a stabilizer wheel mounted to be freely rotatable at the free, front end of the bar. An adjustment device for limiting the elastic movement of the bar upwards and hence the movement of the stabilizer wheel upwards can be provided at the fange.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described as an non limiting embodiment of the invention with reference to the accompanying drawings in which -Fig. 1 is a perspective view seen a little from above and from the side of a motor driven wheelchair having a front mounted, anti-tip device, -Fig. 2 is a view from above of a wheel chassis for a wheelchair, -Fig. 3 is a side view of only an anti-tip device, and -Fig. 4 is a view from above of only an anti-tip device.

A PREFERRED EMBODIMENT In Fig. 1 a wheelchair 1 is shown including the support wheels which when running the wheelchair support the wheelchair and comprises front support wheels 3 which are driven by a motor and rear non-drive supporting wheels 5. The front wheels 3 have a considerably larger diameter than the rear, freely rotating wheels 5 which are the caster type and thus are also freely movable around vertical axes. Furthermore, a seat 2 and a wheel base or chassis 9 are provided to which thus said wheels are rotatably mounted. To reduce the risk of the wheelchair tipping in a forward direction when it for instance passes down a step, stabilizer assemblies 11 are provided, see also the view from above of the wheel base in Fig. 2 and the views of only a stabilizer assembly in Figes. 3 and 4. A stabilizer assembly is arrange at each side of the wheelchair, close to the front. large support wheels 3. In Fig. 2 motors 12 are visible which individually drive the front wheels so that the direction of the wheelchair can be changed and controlled when being transported thereby.

A stabilizer assembly 11 inclues a freely rotating stabilizer wheel 13 which is rotatably mounted to a shaft that is parallel to the axes of the front, large support wheels 3. The stabilizer wheel is mounted to the front end of a cylindric, elastic bar 15 that at

its rear end is rigidly, in particular as to rotations, attache to a camping device 17 projection2 from and attache to a guide plate 19. The guide plate 19 is in turn rigidly attache to the wheel base 9, inside a front, large wheel 3. The elastic bar 15 extends substantially horizontally, i. e. substantially in parallel to the base or ground which supports the wheelchair and on which it rests, and it is so long that the stabilizer wheel 13 is located avina its front edge or surface located at a distance in front of the front edge or surface of the corresponding large support wheel 3.

The dimensioning of the stabilizer wheels and their location is made considering the largest height of steps which the wheelchair is intended to be capable of passing. If for example the wheelchair is intended to be capable of passing steps having a height of 8 cm, the guide plate 19 is placed so that the axis of the stabilizer wheel 13 is located at approximately the same height above the ground plane and somewhat thereabove, for instance at a height of between 8 and 9 cm. Furthermore, the stabilizer wheel 13 has a diameter which is significantly smaller than the diameter of the diameter of the front support wheels 3 and is smaller than the diameter of the rear support wheels 5. For said height the stabilizer wheels can have a diameter of about 10 cm which grives a distance between the lower surfaces of the stabilizer wheels and a ground plane of 3-4 cm. The position of the stabilizer wheels in the longitudinal or front direction of the wheelchair is such that their front edges or surfaces are located at a considerable distance of the front edges or surfaces of the front support wheels 3. A plane which is tangent to the periphery of both the stabilizer wheels 13 and the large support wheels 3 can extend in an angle of for example 10 and 25° to the ground plane, in particular between 15 and 25° to the same plane. The bars are designed so that the stabilizer wheels can elastically move upwards for a distance of for instance at most 3-4 cm, the largest distance of which being dependent on the position of the adjustments screws to be described hereinafter.

When climbing a step, then, if the step has a height lower than the distance between the rotational axes of the stabilizer wheels 13 and thé ground plane, surfaces of the stabilizer wheels 13 which are directe obliquely forwards will come in contact with the step. By the elasticity of the bars 15 then the stabilizer wheels are lifted and facilitate the passing of the step. The maximal elastic movement of the bars 15 can be set by ajustable adjustments screws 21 attache to fanges 23 of the guide plates 19. These flanges projet rightly to the side, i. e. they are located perpendicularly to the plane through the main portion of the guide plates and they comprise simply a bent end portion of a guide plate. Each flange 23 is in itself substantially flat and the corresponding plane extends in an oblique angle to the longitudinal direction of the corresponding elastic bar 15, in particular an angle of about 45 °. The fanges have two functions. both to receive the adjustment screws 21 passing through bores at the top

portion of the flanges and to guide the elastic bars 14 laterally by shaving them pass through elongated holes or slots 25 in the langes. The elongated guide holes 25 have a width adapted to the diameters of the elastic bars and have their longitudinal direction extending in a vertical plane so that the upward movement of the free portions of the bars is allowed.

When passing down a step, if the step has a sufficient height, the stabilizer wheels 13 can first come in contact with the ground below the step and can thereby prevent the wheelchair from tipping forwards. This risk is not entirely insignificant since a wheelchair of the type shown can have a center of gravity which is located at a rather large height and which can be offset forwards in relation to the center of the wheel base.

Each stabilizer assembly 11 is a single unit which for a suitable design of the guide plate 19 can be attache to existing wheelchairs, both motor powered wheelchairs and wheelchairs not being motor driven. The main portion of the guide plate 19 can have an elongated, strip-like shape and is mounted to the chassis of the wheelchair adjacent to the shaft of the front, large support wheels. Therefor the guide plates 19 can have recesses 27 at their upper edges : The main portions of the guide plates are mounted so that longitudinal axes of the main portions will be located approximatively horizontally.

This gives the elastic bars a rather grenat length which makes it more easy to give them a suitable elasticity. The mounting places behind the rotary axes of the large wheels can have such a distance of these axes that they are located completely behind the large wheels or close to the periphery thereof.