This invention relates to ground vehicles, and, more particularly to ground vehicles that adopt a tilting attitude when cornering.

For the purposes of this application the following definitions apply:

a) the term "ground vehicle" means any vehicle that can operate on solid surfaces, including frozen surfaces, as opposed to those that operate on water or in air and includes powered and non-powered recreational vehicles and toys, such as skateboards and luges ;

b) the term "wheels" means the means by which the vehicle is propelled across the ground and includes, for example, skids and skis, caterpillar tracks and combined caterpillar tracks skids and/or skis;

c) the term "footprint" means the ground area bounded by the points of contact of the wheels with the ground; and

d) the term "virtual axle" means an imaginary line perpendicular to the longitudinal axis of the vehicle between two wheels on opposite ends of the vehicle. BACKGROUND OF THE INVENTION

Two wheeled vehicles, such as motor-cycles, must tilt when cornering because of the centrifugal forces acting thereon. If there were no tilting they would either travel in a straight line because the handlebars have little effect except at very low speed or the rider would be thrown off.

A major cause of motor cycle accidents is that, when cornering at medium to high speed, a motor cycle cannot stop or change direction so it has to follow its enforced curved path which may intersect with that of another vehicle or pedestrian. A further drawback of motor cycles is that it is impossible to provide full weather protection for the occupants because, when stopped, the rider or the passenger must have at least one foot on the ground to prevent the motor cycle from falling over.

However, motor-cycles are popular, especially in towns, because they have a narrow foot print and are very manoeuvrable in traffic at low speed.

In recent times a number of patents have been published that disclose three or four wheel vehicles that have a footprint of similar size to a motor-cycle and are intended to solve the drawbacks of motor-cycles. Some of these patents disclose vehicles with tilting wheels and some disclose vehicles with adjustable track for one pair of wheels.

EP-2388179-B discloses a vehicle comprising a frame comprising a tiltable portion tiltable about a longitudinal axis of the vehicle and coupled with a drive rear axle with a rear wheel, a non-tiltable portion coupled with a front axle with a pair of front wheels coupled with the tiltable portion. The front wheels have a track width adjustable a wide track and a narrow track by track width control means, such that for the wide track of the front wheels the wheel base is significantly longer than for the narrow track of the front wheels. The vehicle further comprises tilting means for tilting the tiltable portion when the front wheels are set to the wide track and steering means configured to control the turn of the rear wheel when the front wheels are set to the narrow track. A major disadvantage of this vehicle is that when the track is in the narrow track position the vehicle can only tilt to an angle of the order of 18 - 20° without toppling over and therefore it cannot manoeuvre rapidly when the vehicle is in this configuration and moreover the track width cannot be adjusted unless the vehicle is stationary. SUMMARY OF THE INVENTION

This invention provides a ground vehicle having a rolling chassis carried on three or more ground engaging wheels, and including a frame pivotally mounted on the chassis, the frame being tiltable about the longitudinal axis of the chassis, and a mechanism that, when the frame tilts beyond the vertical axis of the vehicle, causes the wheels of the vehicle to tilt in the same direction as the frame and the track between any pair of wheels either on the same virtual axis or on two different virtual axes to increase only to such an extent that the centre of gravity of the vehicle remains within the footprint of the vehicle, wherein the degree of tilt of the wheels and the degree of change of track is dependent on the degree of tilt of the frame and wherein wheel tilting and track change occur automatically whenever the frame tilts, whether the vehicle is stationary or moving.

The wheel tilting/track changing mechanism in one form of the invention comprises a pair of vertically spaced parallel horizontal bars pivotally attached at their midpoints to upper and lower portions of the frame and also pivotally attached to members on which the rear wheels are supported, and connected by a linkage arrangement enabling the bars to be moved horizontally relative to each other while remaining parallel but, possibly, with reduced spacing there between.

In this arrangement, when the frame tilts the two bars move in opposite directions thus causing the wheels to tilt and the track to increase. When the degree of tilt is reduced or its direction reversed the wheel tilt and the track is altered accordingly.

The linkage arrangement may comprise two assemblies each having three link members pivotally connected together at one end and with two of the links appropriately connected to the bars and the third being attached to a fixed point on the centre line between the bars such that the links can execute a scissoring motion. However, this can be replaced by either a hydraulic or electronic actuator.

In this type of mechanism the ends of the pair of bars on the left and right sides are also preferably pivotally connected by a vertical block on which are mounted horizontally pivotable and rotatable upper and lower swing arms connected at their free ends by a wheel mounting arrangement.

A shock absorber/compensator arrangement to ensure that the ground clearance of the of the lower bar of the wheel tilting/track changing mechanism of the vehicle is substantially constant over level ground is preferably provided between the fixed ends of the swing arms, the compensator allowing up-and-down and rotational movement of the swing arms, as necessary. In an alternative arrangement, wheel tilting is also caused by tilting of the frame which causes relative movement by a pair of spaced parallel bars pivotally mounted on and extending transversely of the frame. The bars are slidably mounted on the frame and are linked by a pair of struts pivotally connected at each end to the bars and which, in the rest position, are parallel to each other and perpendicular to the bars.

In this arrangement tilting and track changing is caused by a barrel cam having a spiral groove on its surface fixedly mounted inside a rearward part of the frame which also passes through either the upper or lower bar, so that it rotates as the frame tilts. A peg attached to the inner side of bar that houses the barrel cam engages in the groove of the barrel cam. When the frame tilts, the upper and lower bars slide relative to each other, as in the previously described embodiment, to tilt the wheels. Rotation of the barrel cam as the frame tilts causes the peg or pegs to move backwards or forwards depending on the direction of rotation so that the bars slide along the frame. Appropriate links between the bars and wheel mounting members operate to cause the wheels to move apart. The barrel cam could be replaced by a hydraulic or electronic actuator to move the upper and lower bar along the longitudinal of the frame to execute the change of the track of the wheel mounted members. In this arrangement means are preferably provided for equalising the torsional forces generated during the movement of the bars to prevent twisting of the body of the vehicle in relative to the frame. These preferably comprise a number of sliding guides extending from each side of the vehicle so that the guide arrangement cannot itself twist under the applied forces. A rack-and-pinion arrangement may be incorporated to synchronise the movement and to distribute the loads of the guides for each side of the vehicle.

In both the above wheel tilt and track change mechanisms the bars are pivotally mounted on the frame so that they remain parallel to the ground when the frame tilts.

In a still further embodiment of the invention the tilting/track changing mechanism incorporates a pair of spaced parallel bars extending outwardly from the frame. In this embodiment the bars are fixedly mounted on the frame so that they tilt with the frame. Preferably, when viewed from above the ends of the bars flare outwardly and rearwards, while they are inclined downwardly relative to the longitudinal axis of the frame to form wings which present a rear surface that is inclined to the longitudinal axis of the bars and onto which a generally trapezoidal plate is pivotally mounted forming a flap that is capable of up-and-down movement.

A rocker arm mechanism is mounted on the underside of the frame and carries pivoted struts that form a link with the upper flaps on each side of the vehicle which ensures that the flaps on each side move in opposite direction. The upper and lower flaps on each side are linked by struts to ensure that their motions are synchronised. The flaps are connected to the wheel mounting arrangements of the vehicle so that, when the frame of the vehicle tilts, the pivoting movement of the flaps cause the wheels to tilt and the track to change because the axes of rotation of the flaps relative to the frame are not perpendicular to the longitudinal axis of the vehicle. In the non-titled position, the wheel mounting arrangements are preferably coplanar with the flaps to which they are attached.

Preferably, the rear axle of the vehicle is a virtual axle arranged such that the track of the rear wheels can easily change while the vehicle is in motion and the rear wheels are carried on stub axles that are mounted on parts of the tilting/track changing mechanism that are pivotal about axes perpendicular to the longitudinal axis of the vehicle. In this case the rear wheels will each be driven by a separate motor.

A single motor with an appropriate differential could also be used to propel the vehicle.

Preferably, the vehicle of the invention has an, at least partially, and desirably fully, enclosed passenger cabin. In general, for a vehicle of the invention, with a fully enclosed cabin the vehicle can be tilted up to 45° without the centre of gravity passing outside the footprint of the vehicle which gives the vehicle a higher degree of safety when cornering at speed than is achievable with other vehicles of this type. DESCRIPTION OF PREFERRED EMBODIMENTS

The invention will now be described in greater detail, by way of example, with reference to the drawings, in which Fig. 1 is a schematic view of a tilting vehicle according to the invention illustrating the change of position of the centre of gravity as the vehicle tilts;

Fig. 2 is a schematic view of one form of vehicle according to the invention;

Fig. 3 is an isometric view of one form of wheel tilting/ track changing mechanism for use in a vehicle according to the invention, in non-tilting mode;

Fig. 4 is an isometric view of the wheel tilting/track changing mechanism of Fig. 3 in tilting mode;

Fig. 5 is a further view of the rear portion of the vehicle shown in Fig. 2 on a larger scale and showing a shock absorber/ compensator arrangement;

Fig. 6 is a schematic view of a luge board fitted with a wheel tilting/ track changing mechanism according to the invention; and

Fig.7 is a schematic view of a child's scooter fitted with a wheel tilting/ track changing mechanism according to the invention:

Fig. 8 is a schematic view of a second form of wheel tilting/track changing mechanism for use in a vehicle according to the invention, in non-tilting mode;

Fig. 9 is a schematic view of wheel the tilting/track changing mechanism shown in Fig. 8, in tilting mode;

Fig.10 is a schematic view from the rear showing the tilting/track changing mechanism of Figs 8 and 9 in the rest position;

Fig. 11 is a schematic view from the rear showing the tilting/track changing mechanism of Figs 8 and 9 in the tilted position;

Fig. 12 is a schematic view showing one form of torsion equalising means in the mechanism shown in Figs. 9 to 11 ;

Fig. 13 s a schematic view of a third form of wheel tilting/track changing mechanism for use in a vehicle according to the invention, from the rear in non-tilting mode;

Fig. 14 is a schematic view of the tilting/track changing mechanism shown in Fig. 13, in tilting mode;

Fig. 15 is an isometric view of the tilting/track changing mechanism shown in Fig. 13 in non-tilting mode; Fig. 16 is an isometric view of the tilting/track changing mechanism shown in Fig. 13 in tilting mode; and

Fig 17 is an isometric view of the tilting/track changing mechanism shown in Fig. 13 in non-tilting mode including detail of one method of mounting the wheel.

As shown in Fig. 1, the centre of gravity of a tilting vehicle 1 in a non-tilted orientation lies on the longitudinal axis 2 of the vehicle. During a tilting operation, to compensate for the centrifugal force that occurs while the vehicle turns, the centre of gravity moves towards position 2a, which as shown may be outside the footprint of a fixed track 56 vehicle. If, in such circumstances, cornering of the vehicle is interrupted and the vehicle has to be brought to an emergency halt, there are two possible scenarios. First, if the centre of gravity of the vehicle falls within the footprint 56, the tilted cabin can return to its upright position. Secondly, if the centre of gravity of the vehicle falls outside the footprint, the vehicle will become unsteady and topple over.

To counteract toppling of the vehicle, in the vehicle of the invention, the rear wheels of the vehicle are caused to move apart to increase their track and increase the footprint of the vehicle 57 when the vehicle tilts. This allows the vehicle to tilt to a greater angle while still remaining within the footprint of the vehicle. At the same time, while the vehicle track is expanding, the mechanism also causes the rear wheels to tilt in the same direction as the body of the vehicle. Such extension has increased the safety tilting angle of the vehicle and the safety speed of vehicle while performing a turn. The track width will also automatically reduce to its original width when the vehicle returns to an upright orientation.

As shown in Fig. 2, one form of vehicle according to the invention has a rolling chassis 3 and a tiltable frame 4 forming part of the chassis. The vehicle has a pair of front wheels 5 carried on stub axles 6 pivotally mounted between upper 7 and lower 8 parallel plates that are fixedly attached to frame 4.

Wheels 5 are connected to steering gear (not shown) and steering wheel 9. At the rear of the vehicle a wheel tilting and track changing mechanism 10 to be described in detail in relation to Figs. 3 and 4 is attached to frame 4 so that, when frame 4 tilts, mechanism 10 is activated. A pair of rear wheels 11 are mounted on stub axles 12 carried on plates 13 that are mounted for generally vertical motion between the free ends 14, 15 of upper and lower pairs of arms 16, 17. The other ends 18, 19 of arms 16, 17 are mounted for rotation about horizontal axes on opposite sides of mechanism 10.

As shown in Figs. 3 and 4, wheel tilting and track changing mechanism 10 comprises a pair of parallel members 20, 21, mounted on the upper and lower surfaces of frame 4. Upper members 20 are also connected to ends 18 of arms 16 by a joint 22 that allows rotation in the horizontal and vertical plane. On the front sides of members 20, 21 are left and right linkages 23 that allow a scissoring motion and that each comprise three links 24, 25, 26. Link 24 is connected to member 20 and to link 25, link 25 is connected to member 21 and to link 24, and link 25 is connected to the junction of links 24 and 26 and to a point on the front end surface of a further member 27 connecting arms 16, 17.

As can be seen in Fig. 4, when frame 4 tilts members 20, 21 to slide in opposite directions while remaining parallel, and the gap between them reduces. The scissoring motion of the linkage 23 pulls and rotates the bar 27 inwards which are pivoted at 22 which in effect causes wheels 11 to tilt and the distance between the wheels increases. This movement of members 20, 21 and linkage 23 are reversed when the frame 4 assumes its upright position again. Fig. 5 shows, within the region bounded by the marked circle 28, one form of compensator/shock absorber comprising spring damper 31 mounted to arms 17, and connected by links 29, which rotates horizontally to bar 20, 30 is pivotal to bar 27 which holds bars 20, 21 that allow movement about vertical and horizontal axes to control the spacing of member 21 above the ground over which the vehicle is travelling.

Figs. 6 and 7 illustrate how the wheel tilting and track changing mechanism 10 described with reference to Figs. 3 and 4 can be applied to other types of vehicle, in particular a luge board and a child's scooter to provide safer operation and manoeuvrability.

As shown in Figs 8 to 12, in the second embodiment the rear portion of the frame 4 is a tubular section 32 which houses a barrel cam (not shown) such that the barrel cam can neither move longitudinally of the frame 4 or rotate within it. Upper and lower parallel bars 33, 34, respectively are connected by pivotal struts 35. The forward end of the frame is formed as a barrel cam and passes through a bore in the upper bar 33. Pegs (no shown) in the inner side of the bore of the upper bar 33 engages in the groves of the barrel cam. The arrangement is such that when frame 4 tilts, the barrel cam is forced to rotate thus causing the peg on the upper bar 33 to move rearwards, this in turns also moves the lower bar 34 rearwards too due to the link with the pivotal struts 35 thus causing arms 36, 37 to open outwards and increases the track of the rear wheels by pushing wheel bearing members 38 outwards, and due to relative movement of the bars cause the wheels to tilt relative to the frame 4 as shown in Fig. 9.

The operation of the tilting/track changing mechanism can clearly be seen in Figs.10 As shown in Fig. 12 an arrangement for equalising the torsional forces generated by the sliding movement of the wheel bearing members 38 comprises four sliding guide rods 39a, 39b, 39c and 39d extending transversely through bores 40, only one of which is shown, in lower frame 58. Rods 39 are fixed at one end to their respective bars 59, 60 where the wheel bearing members 38 are pivoted to allow for tilt. Rods 39a and 39c being fixed to the left bar 60 and rods 39b and 39d are fixed to the right bar 59. The centre sections of bars 39b and 39c have teeth 41 on their facing sides that engage with a pinion gear 42. Bars 39 serve to prevent the body of the vehicle and wheel bearing member 38 from twisting when the tilting/track changing mechanism is operated via sliding in the bores 40 within the lower frame 58 and pinion gear 42 serves to synchronise the sliding movement of guide rods 39 and to distribute the load for both side of the wheel bearing members 38.

As shown in Figs. 13 to 17, in the third embodiment of the invention at least the rear portion of frame 4 is of rectangular configuration with its axis vertical in its non-tilted position. Upper and lower spaced parallel bars 43, 44, respectively, are fixed to and extend perpendicularly from the sides of frame 4. At their otherwise free ends bars 43, 44 have portions 45, 46 respectively, that sweep rearwards and somewhat downwardly in relation to frame 4. Generally trapezoidal flaps 47, 48 are pivotally attached to the rearward facing surfacing surfaces of portions 45, 46. Wheel carrying swing arms 49, 50 are attached by pivoted yoke members 1, 52 to the sides of flaps 47, 48 at their rear ends.

A rocker arm 53 is located at the lower edge of frame 4 and carries links 54 that are attached to the inner face of flaps 47, so that tilting of frame 4 causes movement and synchronisation of flaps 47. Links 55 are formed between the flaps 47, 48 so that the flaps 48 follow the movement of flaps 47.

The operation of the tilting/track changing mechanism can clearly be seen in Figs.13 and 14. The flaps 47, 48 are connected to the wheel mounting arrangements of the vehicle so that, when the frame 4 of the vehicle tilts, the pivoting movement of the flaps 47, 48 cause the wheels to tilt and the track to change because the axes of rotation of the flaps 47, 48 are on the rear surface of the portion 45, 46 which relative to the frame are not perpendicular to the longitudinal axis of the vehicle.