Abstract:
A wheeled conveyance comprising a chassis ( 4 ), support means for a load mounted on the chassis ( 4 ), a suspension assembly mounted on the chassis ( 4 ), and at least one shock absorber means ( 38 ) acting on at least part of the suspension assembly and adapted and arranged to limit tilting of the chassis ( 4 ) relative to at least part of the suspension assembly under dynamic load conditions tending to produce such tilting. The suspension assembly comprises spring means ( 32 ) and suspension arms pivotably mounted on the chassis ( 4 ) and extending in forward and rearward directions in the region of opposite sides of the chassis ( 4 ). Each suspension arm has a wheel ( 16, 26 ) rotatably mounted at the free end.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a wheeled conveyance, for example a self-propelled wheeled conveyance such as a motorised wheelchair, or a push-chair or wheelchair. 
   Self-propelled wheeled conveyances, in the form of motorised wheelchairs, are well known in which a chassis is provided with a seat for receiving a person to be transported and with two front wheels and two rear wheels. Two of the wheels (usually the rear wheels) are independently driven by separate battery-powered electric motors and the other two wheels are arranged to swivel independently. The wheels may be provided with a suspension assembly. 
   Steering and motion control are effected by means of a manually-operated controller, such as a joystick, which selectively controls the two electric motors. A dead man&#39;s handle arrangement is usually built into the manually-operated controller, such that when a user releases the controller, the wheelchair immediately brakes and comes to a halt. 
   Motorised wheelchairs have stability problems associated therewith when front wheels drop into a sudden dip, such as over a kerb or into a pothole, or when descending a slope, particularly when coming to a standstill. Such a slope may, in practice, have an angle of as great as twenty degrees. 
   If a user releases the controller, such as the joystick, when the wheelchair is moving, the wheelchair in coming to an immediate halt throws the weight forward when doing so. This is disadvantageous and in severe conditions can result in overturning of the wheelchair, particularly when descending a slope. The problem is exacerbated by the fact that such wheelchairs have a relatively short wheelbase and a relatively high centre of gravity. In some situations the height of the centre of gravity is increased by heavy batteries, which are used to power the wheelchair, being mounted in the chassis beneath the seat. 
   The problem is exacerbated with a wheelchair incorporating a suspension assembly which permits the load to tilt forward, thereby enabling the centre of gravity to move marginally forward also. 
   Problems in reverse arise with non-powered push-chairs and wheelchairs with suspension when the chair is tilted backwards to effect steering or to mount a large obstacle. Downwards pressure on the pushing handle must take up suspension movement before the front wheels lift off the ground. This is less precise than for a rigid chair. 
   BRIEF SUMMARY OF THE INVENTION 
   It is an object of the present invention to overcome or minimise these problems. 
   According to the present invention there is provided a wheeled conveyance comprising: a chassis; support means for a load mounted on the chassis; a suspension assembly mounted on the chassis and comprising suspension arms pivotably mounted on the chassis and extending in forward and rearward directions in the region of opposite sides of the chassis, each suspension arm having a wheel rotatably mounted at the free end thereof, and two separate spring means, one disposed in the region of each side of the chassis, the free ends of the forwardly and rearwardly extending suspension arms being arranged to tend to pivot towards each other by means of the two separate spring means being provided between, and acting on, the forwardly and rearwardly extending suspension arms; and two shock absorber means separately cooperating between the chassis and each of the suspension arms extending in the forward direction, wherein the two shock absorber means are provided in a substantially horizontal plane so as to limit and dampen tilting of the chassis relative to at least part of the suspension assembly under dynamic load conditions tending to produce such tilting whilst upward and downward movement of the wheels with the suspension arms is substantially uninhibited thereby in the absence of tilting motion of the chassis. 
   The wheels mounted at the free ends of one of the forwardly extending and rearwardly extending suspension arms may be adapted to swivel about swivel means, for example about a generally upright axis, such as independently of one another. 
   The wheels provided with swivel means may be provided with limiting means permitting swivelling through a predetermined limited range. 
   The wheeled conveyance may be self-propelled or may be non-powered. 
   The self-propelled wheeled conveyance may comprise a motorised wheelchair, having a support means comprising a seat, and a load such as a person to be transported. 
   Where the wheeled conveyance is self-propelled, the wheels mounted at the free ends of the suspension arms extending in the rearward direction may each be motor-driven and the wheels mounted at the free ends of the suspension arms extending in the forward direction may be provided with swivel means adapted to allow the wheels to swivel. 
   Alternatively, the wheels mounted at the free ends of the suspension arms extending in the forward direction may each be motor-driven and the wheels mounted at the free ends of the suspension arms extending in the rearward direction may be provided with swivel means adapted to allow the wheels to swivel. 
   The motor-driven wheels may be powered by separate motors, which may be electric motors, which may be powered by one or more batteries which may be mounted on the chassis. 
   A manually-operated controller, such as a joystick, may be provided for controlling the motors whereby motion and steering of the conveyance is controlled. 
   The two shock absorber means may be provided with adjustment means to effect a desired extent of limitation of the tilting of the chassis. 
   The two shock absorber means may be provided with adjustment means adapted to substantially minimise tilting of the chassis. 
   Each of the two shock absorber means may be of elongate telescopic form, having one end thereof pivotably secured to the chassis and an opposite end thereof pivotably secured to the associated forwardly extending suspension arm or to a strut extending upwardly from the associated forwardly extending suspension arm. Each of the two shock absorber means of elongate telescopic form may be adapted to pivot during corresponding pivoting of its associated forwardly extending suspension arm. 
   The two shock absorber means may be arranged to operate simultaneously and collectively to limit the forward tilting of the chassis, with each shock absorber means acting independently on its associated forwardly extending suspension arm. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     For a better understanding of the present invention and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: 
       FIG. 1  is a side view of an embodiment of a self-propelled wheeled conveyance according to the present invention, in the form of a motorised wheelchair; 
       FIG. 2  is a top plan view of the self-propelled wheeled conveyance of  FIG. 1 ; 
       FIG. 3  is an end view of a chassis for use in the self-propelled wheeled conveyance of  FIGS. 1 and 2 ; 
       FIG. 4  is a side view of another embodiment of a self-propelled wheeled conveyance according to the present invention, in the form of a motorised wheelchair; 
       FIG. 5  is a top plan view of the self-propelled wheeled conveyance of  FIG. 4 ; 
       FIG. 6  is a side view of an embodiment of a chassis forming part of a non-powered wheeled conveyance; 
       FIG. 7  is a top plan view of the wheeled conveyance chassis of  FIG. 6 ; and 
       FIG. 8  is an end view of the wheeled conveyance chassis of  FIGS. 6 and 7 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIGS. 1 ,  2  and  3 , a motorised wheelchair  2  has a tubular metal chassis  4 , which is shown in detail in  FIG. 3 , on which is secured a seat  6  for supporting a person to be transported in the wheelchair. 
   A suspension assembly is mounted on the chassis  4  and comprises two suspension arms  8  pivotably mounted at ends  10  thereof on lower portions  12  of T-shaped brackets  14  provided at opposite sides of the chassis  4 . The suspension arms  8  extend in a forward direction and have ground-engaging wheels  16 , rotatably mounted and arranged to swivel about a generally upright axis, at free ends  18  thereof. 
   Two further suspension arms  20  are pivotably mounted at ends  22  thereof on upper portions  24  of the T-shaped brackets  14  at opposite sides of the chassis  4 . The suspension arms  20  extend in a rearward direction and have ground-engaging wheels  26  rotatably mounted at free ends  28  thereof. Each wheel  26  is independently driven by a separate electric motor  30  mounted on each of the suspension arms  20 . 
   The electric motors  30  are energised by one or more batteries (not shown) mounted on the chassis  4 , such as below the seat  6 . Power to the motors  30  is independently controlled through a joystick controller (not shown) of well-known form and by means of which steering and motion control of the wheelchair are effected. 
   Two springs  32  are provided, only one of which is shown in the drawings. 
   The springs  32  are disposed in the region of each side of the chassis  4  and act between the forwardly and rearwardly extending suspension arms  8  and  20  in such a way that the free ends  18  and  28  of the suspension arms  8  and  20  tend to pivot towards each other. 
   The suspension arms  8 ,  20  and the springs  32  may incorporate features as described and claimed in EP-A-0 836 979. 
   The wheelchair  2  is arranged to move forward in the direction of arrow  34 , the swivelling wheels  16  being at the front. 
   If the joystick controller (not shown) is released while the wheelchair  2  is in motion, a dead man&#39;s handle arrangement incorporated in the controller shuts off the power to the motors  30  and the wheelchair is braked and comes to an immediate halt. When this happens, the chassis  4  will tend to tilt forward as shown by the arrow  36 . This is undesirable and in severe conditions, particularly when the wheelchair  2  is located on downward-sloping ground, could result in overturning of the wheelchair  2 . Such tendency for the chassis  4  to tilt forward may also occur when the wheelchair descends a gradient, or drops over a kerb or into a pothole, and is reduced or minimised in the present invention. 
   A shock absorber  38  is provided at each side of the chassis  4 . The shock absorbers  38  are suitably of elongate telescopic form and each has one end  40  thereof pivotably secured to a mounting  42  on the chassis  4  and an opposite end  44  pivotably secured to a strut  46  extending upwardly from an associated forwardly extending suspension arm  8 . The shock absorbers  38  are disposed in a substantially horizontal plane. 
   The two shock absorbers  38  act simultaneously to damp any forward tilting movement of the chassis  4 , such as when power to the motors  30  is interrupted and the wheelchair  2  comes to an abrupt halt. The shock absorbers  38  are preferably adjustable whereby their damping action can be tuned such that forward tilting movement of the chassis  4  is minimised. 
   Although the two shock absorbers  38  operate simultaneously and collectively to limit the forward tilting movement of the chassis  4 , each shock absorber  38  acts independently on its associated suspension arm  8  as when the suspension travels along an irregular surface. 
   The shock absorbers  38  undergo pivoting about their ends  40 ,  44  during corresponding pivoting of their associated forwardly extending suspension arms  8 . Upward and downward movement of the wheels  16  on the suspension arms  8  is substantially uninhibited by the shock absorbers  38  in the absence of forward tilting motion of the chassis  4 . 
   The shock absorbers  38  are arranged such that articulation of the suspension system is retained. Such articulation is important to ensure that the driving wheels  26  maintain contact with ground surface. If a driving wheel  26  were to undesirably leave the ground, the wheelchair  2  would veer away from its intended direction of travel. 
     FIGS. 4 and 5  show an alternative embodiment of a motorised wheelchair according to the present invention. The motorised wheelchair  2  in  FIGS. 4 and 5  differs from that of  FIGS. 1 ,  2  and  3  in that the motor-driven wheels  26  are provided at the front of the wheelchair and the swivelling wheels  16  are provided at the rear of the wheelchair. 
   In  FIGS. 4 and 5 , parts fulfilling the same or similar functions as those in  FIGS. 1 ,  2  and  3  are given the same reference numerals as those in  FIGS. 1 ,  2  and  3 . 
   Accordingly, the motorised wheelchair  2  shown in  FIGS. 4 and 5  has a tubular metal chassis  4 , constructed as shown in  FIG. 3 , and on which is secured a seat  6  for supporting a person to be transported in the wheelchair. 
   A suspension assembly is mounted on the chassis  4  and comprises two suspension arms  8  pivotably mounted at ends  10  thereof at opposite sides of the chassis  4 . The suspension arms  8  extend in a forward direction and have wheels  26  rotatably mounted at free ends  18  thereof. Each wheel  26  is independently driven by a separate electric motor  30  mounted on each of the suspension arms  8 . 
   Two further suspension arms  20  are pivotably mounted at ends  22  thereof at opposite sides of the chassis  4 . The suspension arms  20  extend in a rearward direction and have wheels  16 , rotatably mounted and arranged to swivel, at free ends  28  thereof. Swivelling of the wheels  16  is desirably limited to a predetermined range, for optimised steering control of the wheelchair. 
   The electric motors  30  are energised by one or more batteries (not shown) mounted on the chassis  4 , such as below the seat  6 . Power to the motors  30  is independently controlled through a joystick controller (not shown) and by means of which steering and motion control of the wheelchair are effected. 
   Two springs  32  are provided, only one of which is shown in  FIG. 4 . The springs  32  are disposed in the region of each side of the chassis  4  and act between the forwardly and rearwardly extending suspension arms  8  and  20  in such a way that the free ends  18  and  28  of the suspension arms  8  and  20  tend to pivot towards each other. 
   The wheelchair  2  is arranged to move forward in the direction of arrow  34 . 
   A shock absorber  38  is provided at each side of the chassis  4 . The shock absorbers  38  are suitably of elongate telescopic form and each has one end  40  thereof pivotably secured to a mounting  42  on the chassis  4  and an opposite end  44  pivotably secured to a strut  46  extending upwardly from an associated forwardly extending suspension arm  8 . The shock absorbers  38  are disposed in a substantially horizontal plane. 
   The shock absorbers  38  act in exactly the same way as those previously described with reference to  FIGS. 1 and 2 , to minimise forward tilting movement of the chassis  4  in the direction of arrow  36 , such as when power to the motors  30  is interrupted and the wheelchair  2  comes to an abrupt halt, or when the wheelchair  2  descends a gradient, or drops over a kerb or into a pothole. 
     FIGS. 6 ,  7  and  8  show an embodiment of a chassis of a non-powered push-chair or wheelchair. The push-chair or wheelchair chassis  2  in  FIGS. 6 to 8  differs from that of  FIGS. 1 to 3  in that the wheels are not swivelable and the shock absorber  38  is mounted in an upright configuration. 
   In  FIGS. 6 ,  7  and  8 , parts fulfilling the same or similar functions as those in  FIGS. 1 ,  2  and  3  are given the same reference numerals as those in  FIGS. 1 ,  2  and  3 . 
   Accordingly, the wheeled conveyance shown in  FIGS. 6 to 8  has a tubular metal chassis  4  adapted to receive a seat (not shown) for supporting an infant or person to be transported. A seat or other support means can readily be mounted on the chassis  4  in a manner similar to that shown in  FIGS. 1 ,  3  and  4 . 
   A suspension assembly is mounted on the chassis  4  and comprises two suspension arms  8  pivotably mounted at ends  10  thereof at opposite sides of the chassis  4 . The suspension arms  8  extend in a forward direction and have wheels  16  rotatably mounted at free ends  18  thereof. 
   Two further suspension arms  20  are pivotably mounted at ends  22  thereof at opposite sides of the chassis  4 . The suspension arms  20  extend in a rearward direction and have wheels  26  rotatably mounted at free ends  28  thereof. 
   If desired, one of the sets of wheels  26  or  16  may be able to swivel about an upright axis. 
   Two springs  32  are provided, the springs being disposed in the region of each side of the chassis  4  and act between the forwardly and rearwardly extending suspension arms  8  and  20  in such a way that the free ends  18  and  28  of the suspension arms  8  and  20  tend to pivot towards each other. 
   The wheeled conveyance  2  is adapted to move forward in the direction of arrow  34 . 
   A shock absorber  38  is provided at each side of the chassis  4 . The shock absorbers  38  are suitably of elongate telescopic form and each has one end pivotably secured to a mounting  42  on the rearwardly extending suspension arm  20  and an opposite end pivotably secured to a mounting  46  provided on the forwardly extending suspension arm  8 . The shock absorbers  38  are in a substantially upright configuration. 
   The shock absorbers  38  of the wheeled conveyance of  FIGS. 6 to 8  act to minimise forward and rearward tilting movement of the chassis  4  permitted by compressing the suspension such as when the conveyance is tilted to facilitate steering or to climb a large obstacle.