Abstract:
A lean-induced steerable wheel assembly has a pair of parallel wheel hub carriers arranged on either side of a leanable chassis spine. A linkage connects the wheel hub carriers to the chassis spine so that the wheels lean in unison with the chassis spine. A steering mechanism couples the wheel hub carriers to the chassis spine so that an induced lean on the chassis spine steers the wheel hub carriers through a steering angle dependent on the angle of induced lean.

Description:
CROSS REFERENCE TO RELATE APPLICATIONS  
       [0001]    This application claims the benefit under 35 USC 119(e) of U.S. provisional application serial No. 60/344,811, filed Jan. 7, 2002. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates to the field of personal transport, and in particular to a lean-induced steerable wheel assembly for multi-wheel assemblies, as well as to a vehicle including one or more such assemblies.  
           [0004]    2. Description of Related Art  
           [0005]    Two-wheeled vehicles, such as bicycles or motorcycles are well known for their dynamic characteristic to lean into corners. The rider shifts weight to induce the lean position and this has the effect of steering the vehicle round a corner. Such vehicles, however, only have a single wheel on each axle.  
           [0006]    Four wheeled vehicles are inherently more stable than two-wheeled vehicles, but such vehicles are not currently susceptible to lean-induced steering. Such vehicles, as in the case of a conventional automobile, must be steered with a manually operated steering wheel, which is not suitable for scooter like vehicles where the rider stands on a platform with one foot and powers the vehicle with the other foot.  
         SUMMARY OF THE INVENTION  
         [0007]    The invention provides a steering assembly that can be used in association with scooters and like vehicles with more than one wheel on at least one of its axles. The steering assembly is actuated by the rider inducing a lean onto the vehicle, which results in the vehicle being steered in the intended direction without out the need for manual intervention.  
           [0008]    According to the present invention there is provided a lean-induced steerable wheel assembly, comprising a pair of parallel wheel hub carriers arranged on either side of a leanable frame member; a linkage connecting said wheel hub carriers to said frame member so that said wheel hub carriers lean in unison with said frame member; and a steering mechanism coupling said wheel hub carriers to said frame member so that an induced lean on said frame member steers said wheel hub carriers through a steering angle dependent on the angle of induced lean.  
           [0009]    This invention is suitable for vehicles, such as bicycles, personal scooters and the like, with two or more pairs of wheels mounted on the wheel hub carriers. It is also suitable for a vehicle with one pair of wheels, for example at the front, and a single wheel at the rear.  
           [0010]    The frame member may be a chassis spine extending longitudinally along the length of the vehicle, or alternatively it could be in the form of one or more lugs capable of supporting the suspension beams and the elbow arm.  
           [0011]    The wheels assume a lean angle, which is normally parallel to the central vertical axis of the leaning chassis platform. The front and rear pair of wheels preferably assume steering angles proportional to the lean angles of the wheels and chassis platform.  
           [0012]    The present invention allows four wheeled vehicles, namely vehicles having two front wheels and two rear wheels, to achieve a similar leaning position, while automatically causing all wheels to steer on a common turn centre. Such steering action is fully induced by the lean angles of the wheels and chassis platform. The lean angles are achieved by the rider shifting weight in a manner consistent with centrifugal forces just as in a conventional standard two-wheeled vehicle.  
           [0013]    In a preferred embodiment the linkage is a parallelogram linkage comprising a pair of upper and lower suspension beams. An elbow member acts pivoted at its midpoint below the upper suspension beam acts as a steering arm to pull the wheels through the desired steering angle dependent on the lean angle of the chassis.  
           [0014]    The invention also provides a vehicle comprising a leanable chassis platform for supporting a rider and having front and rear wheel assemblies; and at least one of said wheel assemblies comprising a pair of parallel wheel hubs arranged on either side of a longitudinal frame member; a linkage connecting said wheel hubs to said frame member so that said wheel hubs lean in unison with said frame member; and a steering mechanism coupling said wheel hub carriers to said frame member so that an induced lean on said frame member steers said wheel hubs through a steering angle dependent on the angle of induced lean. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings, in which:  
         [0016]    [0016]FIG. 1 is a plan view of a vehicle chassis platform;  
         [0017]    [0017]FIG. 2 is a side view of the vehicle chassis platform;  
         [0018]    [0018]FIG. 3 is a cross sectional view of the vehicle chassis platform;  
         [0019]    [0019]FIG. 4 is a plan view of a wheel bogie for the vehicle chassis platform shown in FIG. 1;  
         [0020]    [0020]FIG. 5 is a side view of the wheel bogie;  
         [0021]    [0021]FIG. 6 is an end view of the wheel bogie in the static vertical position;  
         [0022]    [0022]FIG. 7 is an end view of the wheel bogie in the dynamic leaning position; and  
         [0023]    [0023]FIG. 8 shows the force vectors present when the vehicle is in the leaning position. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]    The invention will be described with reference to a personal scooter of the type having a platform on which the rider normally stands, an upright steering column and front and rear wheel assemblies. Unlike a conventional scooter, each wheel assembly consists of a pair of wheels so that the scooter as a whole has four wheels instead of the usual two. The vehicle could have more than two pairs of wheels, on in the alternative one pair of wheels and a single wheel. It will be appreciated that the invention has application to other types of vehicle, such as a “bicycle” having the usual single front and rear wheels replaced by wheel pairs as described.  
         [0025]    Referring now to FIG. 1, the personal scooter comprises a rectangular platform  1  for receiving a rider&#39;s foot with a longitudinal chassis spine  2  on the underside of the platform. In this embodiment, the spine  2  extends along the length of the chassis  1  to provide longitudinal rigidity to the vehicle. A wheel assembly comprising a pair of wheels  3  is provided at each end of the platform  1 .  
         [0026]    At each wheel assembly, an upper suspension beam  5 , a lower suspension beam  6 , extending generally parallel to the upper suspension beam  5 , and an elbow steering arm  7 , extend transversely relative to the chassis  1 . As shown in FIG. 4, the suspension beams  5 ,  6  are mounted in a fore and aft arrangement to provide a negative caster angle.  
         [0027]    The spine  2  has openings to accommodate the suspension beams and steering arm  7 . The elbow  7  passes through an opening  25  (FIG. 4) longitudinally displaced relative to the upper and lower openings  26   a,    26   b  (FIG. 6) for the upper and lower suspension beams.  
         [0028]    The suspension beams  5  and  6 , and elbow arm  7 , are rockingly mounted on spine  2  by longitudinal shafts  11 ,  12 , and  13 , which allow them to pivot in a transverse vertical plane. The shafts  11 ,  12  and  13  are fixed to the beams  5  and  6 , and arm  7  and thus rotate relative to the spine  2  as the latter pivot. The caster angle created by the fore and aft arrangement of the upper and lower suspension beams provides a self-centering effect.  
         [0029]    The ends of suspension beams  5  and  6  and steering arm  7  are coupled to hub-carriers  4  through spherical ball joints  8 , although other suitable universal couplings could be employed. The ball joints  8  of the upper suspension beam  5  are mounted on a common shaft  10  with the respective ball joints of the elbow arm  7 .  
         [0030]    The hub-carriers  4  are fitted with bearings  20  to receive axles, which are integral with the wheels  3 . The wheel axle  3  is secured into the hub wheel bearings  20  by the central lock bolt  21 . The wheels are equipped with tires  3   a.    
         [0031]    The line  50  passing through the ball joints  8  of the upper and lower suspension beams should be centrally located relative to the wheel perimeter. For this reason, the hub carrier  4  is recessed to accommodate the ball joints  8  and the end portions of the suspension beams  5 ,  6 .  
         [0032]    The geometry of the wheel assembly is such that as an induced lean is applied to the platform  1 , and hence the chassis spines  2 , the parallelogram linkage, consisting of the upper and low suspension beams  5 ,  6  and the hub carriers  4 , causes the wheel hubs  4  to lean in unison with the chassis spine  2 , preferably, though not necessarily, in equal amounts.  
         [0033]    The ball joints  8  at the ends of the steering arm  7  and suspension arm  6  are mounted on a common shaft  10  (FIG. 6). As the assembly leans, the steering arm  7  tilts and its end moves through a distance  30  (FIG. 7), which causes the wheel hub carrier  4  to turn through a steering angle α (FIG. 4), which depends on the amount and direction of lean.  
         [0034]    As shown in FIG. 5, the lower suspension beam pivot shaft  12  has an extended portion  12   a  in the form of a torsion bar lying parallel to the chassis platform  1 . The end of the extended portion  12   a  is anchored  12   b  in the central channel on the underside of the chassis 1 . As the lower suspension beam  6  pivots, the torsion bar  12  twists and thus acts to tend to restore the assembly to the vertical, no-lean attitude and thereby provide a vertical self-aligning torque for the vehicle after leaning into a turn.  
         [0035]    The front wheel assembly is identical to the rear wheel assembly except for the fact that the front and rear assemblies are mounted in 180° opposition. This causes the front and rear wheels to counter-steer around a common steering centre.  
         [0036]    The placement of the central pivot  13  of the steering arm  7  assures that the inner wheels assume greater steering angles than the outer wheels. The central pivot  13  should be below the axis of the upper suspension beam  5  to ensure steering in the direction of lean and generally be between the upper and lower suspension beams  5 ,  6 .  
         [0037]    In use, the user propels the personal scooter in a manner similar to a conventional scooter by placing one foot on the chassis platform  1  and leaving the other foot free to periodically engage the ground and propel the scooter forward. An upstanding frame (not shown) at the front end of the chassis supports a fixed handle bar for the rider to hold on to. This handle bar does not directly participate in steering the scooter and serves only to provide support to the rider.  
         [0038]    [0038]FIG. 8 shows the load distribution on the vehicle chassis platform  1  during the cornering leaning position. Weight shift on the chassis platform  1  determines the lean angle θ. This angle θ determines the steering angles α of the front and rear wheel assemblies. If the total load on the chassis platform  1  and spines  2  is low, this load is transmitted to suspension beams  5 ,  6  in equal amounts. The load is further transmitted equally to the ball-jointed ends of suspension beams  5 ,  6 , resulting in a force of 2.5 W at each ball-jointed end assuming a total load of 10 W. It can be seen that each wheel is loaded equally, regardless of lean angle.  
         [0039]    The ground load of the outer and inner wheel when cornering differs slightly due to the inward rotation of the contact point on the arc-profile tires  3   a.    
         [0040]    It should be noted that the torsion bar extension for vertical self-alignment can be either associated with the upper suspension beam or lower suspension beam. Vertical self-alignment torque arrangement by means other than torsion bar can be applied to suit the vehicle size and type.  
         [0041]    Although the invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.