BACKGROUND OF THE INVENTION: One problem associated with vehicles for travel on soft ground surfaces, such as snow, is to provide sufficient traction to propel the vehicle even if the surface is very loose, ie. it cannot support large surface pressures without giving in and collapsing.

On known vehicles of the snowmobile type, generally, two steerable front skis are provided together with a rear mounted and suspended drive belt. The vehicle is pressed down into the ground surface by its own heavy weight in order to provide any traction, resting upon the front skis and the drive belt. Thus, if the ground surface is suffi- ciently soft, the snowmobile will risk sinking too deeply into the surface and it may become stuck. A vehicle of this type is disclosed in US Patent 4,133,400 (Shiraishi).

Other known motorized vehicles for utilization on snow surfaces, or similar, are of the type having one steerable front ski together with a rear mounted and suspended drive belt. The full weight of the vehicle rests on the ski and drive belt, comparable to a snowmobile mentioned above.

These vehicles are usually of lighter weight than the snowmobile type, but, because of their lighter and smaller construction, lack the relatively large belt drive surface area of the snowmobile. This impedes their traction on soft ground surfaces. Known vehicles of this type are disclosed in the US Patents 4,613,006 (Moss et al.), 4,307,788

(Shelton), 4,286,682 (Stewart et al.) and 4,244,436 (Condon et al.).

Other motorized vehicle types for utilization on snow surfaces, or similar, are of the variety where a tradi- tional skiboard has been equipped with a motorized drive belt having some type of drive profiles arranged perpendicularly to the direction of travel and protruding some distance into the snow. This drive belt is not sus- pended and has its drive surface substantially level with the gliding surface of the skiboard, to also enable tradi- tional downhill skiing with this type of skiboard, because the drive profiles can be folded back to a position flush with the drive belt. This results in a vehicle having sufficient traction for motorized travel only on relatively hard packed snow or similar. Vehicles of this type are disclosed in the US Patent 4,984,648 (Strzok) and in the French Patent Application 2 688 701 (Martinez).

Still a further vehicle type claimed to be utilizable on soft ground surfaces consists of a motorized trackboard having propelled tracks on each side of a main body portion. This type of vehicle rests solely on its tracks during use. A preferred embodiment has a front and a rear belt pair, where the rear pair is motorized and the front pair is made steerable. A vehicle of this type is disclosed in US Patent 5,305,846 (Martin). Vehicles like these, which rely on tracks for all its ground surface contact, require relatively large and heavy belts resulting in vehicles having a large total weight. Thus, if the ground surface is sufficiently soft, the vehicle will sink too deeply into the surface and lose all traction (compare snowmobile type vehicles above).

SUMMARY OF THE INVENTION: The object of the present invention is to provide a vehicle which has improved traction on soft ground surfaces, such as snow, combined with a mechanically simple construction to keep manufacturing costs low.

Said object is achieved by the arrangement according to the present invention, whose features are detailed in appended claim 1.

Preferred embodiments of the present invention are detailed in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS: The invention will be described in greater detail in the following with reference to the accompanying drawings, in which Fig. 1 is a partially sectioned elevational view of a vehicle according to the present invention, Fig. 2 is a partially sectioned plan view of a vehicle according to the invention, whilst Fig. 3 shows a view from below of a vehicle according to the invention.

PREFERRED EMBODIMENTS: Figs. 1 and 2 show a motorized vehicle having a body unit 1 in which a propulsion unit 2 is carried. Any known power source which is light and powerful enough can be used as a propulsion unit, e. g. small i. c. engines, electric motors or similar. Speed regulation of the propulsion unit 2 is accomplished via a hand-held throttle device 13. The throttle device 13 is rigidly attached to a front part of the vehicle by a combined throttle cable/support hose 15, thus enabling the driver to hold onto the throttle device 13, by pulling backwards, which enhances the driver's balance.

As is shown in Fig. 3, the body unit 1 comprises gliding surfaces 5 arranged on the bottom of the body unit, ie. facing the ground. The gliding surfaces are preferably covered with some type of coating which enhances the sliding properties of the gliding surfaces by lowering the friction between the gliding surfaces and the soft ground surfaces.

The propulsion unit 2 is connected to a drive unit 3 which is held and guided by a suspension unit 4. The drive unit 3 comprises an endless belt 6 having a traction surface 7 facing the soft ground surface. The total surface area of the gliding surfaces 5 constitutes approximately 50 % or more of the total vehicle-to-ground surface (ie. the sum of the gliding surfaces 5 and the traction surface 7). The relatively large gliding surfaces 5 make it possible to use lower output engines, and thus smaller, quieter and less polluting engines. The endless belt rotates over a forward driving roller 18 and a rearward roller 19 whilst gliding on a slide frame 20. This slide frame 20 may have gliding strips arranged between it and the endless belt to lower friction.

The endless belt 6 may comprise standard profile snowmobile belts, i. e. no special demands are placed on the construc- tion of the belt because the vehicle of the invention has a relatively low total weight. The endless belt 6 may have a typical width of approximately 230 mm. Similarly to a snowmobile construction, the endless belt 6 can be lubricated by the snow when the vehicle is used on snowy ground surfaces.

The propulsion unit 2 may advantageously be equipped with sealing discs arranged on both sides of the propulsion unit on its drive shafts, to prevent the ingress of snow, or other lose material, into the engine compartment inside the body unit 1 as the snow is thrown from the drive belt 6.

The endless belt traction surface 7 has a forward part 22 and a rearward part 17, where the forward part is angled upwards in the travel direction of the vehicle so that loose ground material, eg. snow, is packed under the forward part. The rearward part 17 is substantially parallel to the ground surface and is held in a lower

position than the forward part 22, i. e. it sinks lower into the soft ground material. The rearward part 17 is longer relative to the forward part 22. The traction surface 7 may have a length which corresponds to approximately 2/3 of the total length of the vehicle, which typically may be around 1700 mm.

The suspension unit 4 comprises automatic height adjusting means 8,9,16 for adjusting the position of the drive unit 3 relative to the body unit 1. The automatic height adjustment means 8,9,16 comprise forward and rearward automatic height adjustment means.

In a preferred embodiment, the suspension unit 4 comprises front and rear dampers 8, advantageously of the gas-filled type, affixed at one end of each damper to mounting struts 16 and at another end to the body unit 1. The dampers at all times (except when the drive unit 3 is in a retracted transport position) press the drive unit into the soft ground surfaces in order to achieve good traction. The gas- filled dampers 8 thus regulate the height of the endless belt 6, relative to a length axle 10 of the vehicle, according to the softness of the ground surfaces. One, possibly two or more, dampers may be used in each of the front and rear positions. Also gas-filled dampers of the adjustable type may be used.

The suspension unit 4 further comprises parallel link arms 9 which are arranged so that the movement of the suspension unit 4 is limited to one plane perpendicular to the general plane of the soft ground surfaces. The parallel link arms 9 may be attached to each other via a bridge 23. The front damper's mounting strut is affixed to the parallel link arms 9 and the rear damper's mounting strut is affixed to the drive unit 3. The gas-filled dampers 8 may be mounted in a plurality of mounting holes 11, or similar, arranged

on the mounting struts 16, in order to make it possible to change the geometry of the drive unit/suspension unit assembly for achieving the desired turning properties of the vehicle. Factors to consider in this context are, for example, the weight of the driver and the ground conditions.

The gliding surfaces 5 advantageously extend on both sides of the endless drive belt 6 to enhance the turning capabilities of the vehicle according to the invention. The drive belt 6 is thus limited to a relative movement essentially perpendicular to a general plane of the gliding surfaces 5, which contributes to the good traction properties of the vehicle.

The driver stands or sits on the body unit 1 which also may comprise foot ledges 12 on which the driver's feet can rest. These ledges may advantageously be equipped with some type of friction surface to enhance grip, e. g. angular profiles of aluminium or similar having a friction-enhanc- ing pattern on the surface. The ledges also strengthen the body unit 1 construction. It is also possible to provide some type of foot straps on these foot ledges 12 to further increase grip.

The dampening/downwards pressing effect of the gas-filled dampers 8 is essential to make it possible to turn the vehicle since it does not have any steering means as such.

Turning is accomplished by shifting the driver's body weight from side to side, and possibly from fore to aft and vice versa. To further facilitate turning, small cutoffs 14 may be incorporated into the outer and rearmost portion of the gliding surfaces 5.

The whole suspension unit 4/driving unit 3 assembly may be arranged to be foldable into a stowage position where the

traction surface 7 of the endless belt 6 is situated completely inside the lower edge 21 of the body unit 1, thus enabling the vehicle to glide freely on the ground surface. This can be used, for example, to glide down hills without the need for added propulsion. Typically, the suspension unit 4/driving unit 3 assembly may be located 30-50 mm above the lower edge of the body unit 1 in this stowage position, compared to a maximum downward position of typically 150-200 mm at the rear roller 19 and 50-100 mm below the lower edge 21 of the body unit 1 at the forward roller 18. The suspension unit 4/driving unit 3 assembly may also advantageously be in the stowage position during transportation of the vehicle, eg. on or in a car.

A handle may be affixed to the front of the body unit to facilitate the carrying or dragging of the vehicle and also to double as a collision bumper. Splash guards may also be arranged on the back of the body unit 1.

A small sleigh can be pulled by the vehicle, this sleigh may also be used to store the vehicle during transport. Any snow remaining on the vehicle would then run down into the sleigh if and when the snow would melt.

The operational range of the vehicle according to the invention depends i. a. on the propulsion unit and the size of its fuel reservoir, but is generally shorter than that of a traditional snowmobile, typically 20-50 km compared to 150 km. The total weight of the vehicle according to the invention may be approximately 30-50 kg compared to more than 200 kg for a traditional snowmobile. It is thus possible for one person to lift the vehicle up onto a cart or similar. The turning radius of the vehicle is also smaller than that of a traditional snowmobile. The vehicle according to the invention is thus smaller and lighter than a traditional snowmobile, which means it should cause lower

wear and tear to the environment in which it is used. It also utilises smaller and therefore quieter and less fuel consuming engines, possibly also electric motors. The lower weight combined with the gliding surfaces makes the vehicle according to the invention very suitable for soft and deep snow conditions, conditions which are extremely unsuitable for traditional snowmobiles. The vehicle has an approximate bearing surface towards the ground of 0.85 m2 which translates into a pressure of approximately 1.4 kg/dm2 (including a person weighing 80 kg). A normal snowmobile weighing 225 kg and having a bearing surface of 0.75 m2 causes a pressure of 4.1 kg/dm2 (including a person weighing 80 kg). The same person on a pair of normal skis has a pressure towards the ground of approximately 2.9 kg/dm2. The low weight of the vehicle according to the invention combined with the small dimensions also facili- tates storage of the vehicle.

The invention is not limited to the description above nor to the examples shown on the drawings, but may be varied within the scope of the appended claims. For example, a possible alternative to gas-filled dampers are standard springs and shocks, but these are generally heavier and provide a bouncy ride which might not be desirable.

Advantageously, the propulsion unit is connected to the drive unit via a variator drive because this provides the smoothest running characteristics of the vehicle, but a cheaper alternative is an ordinary centrifugal clutch although it may provide a jerkier power transmission.