The invention relates to a steering device for a tracked vehicle according to the introduction to claim 1.

In the prior art tracked vehicles are known with two juxta- positioned tracks, wherein the vehicle is steered by operating the tracks at different speeds.

Vehicles are also known which are driven by one track, where the vehicle is steered by means of other elements which are in contact with the base, e.g. wheels, runners and the like, i.e. separate steering devices which are not a part of the track.

When such known vehicles turn as a result of this steering, substantial sections of the tracks slide in the vehicle's transverse direction and directly on the base, and this can cause damage to the tracks and the base.

Furthermore vehicles are known where each track is forcibly deflected sideways, thus causing the plane in which the loop of the endless track extends to be curved.

The steering device for such tracked vehicles comprises electronic and hydraulic components and is technically mature. For small, simple vehicles such as snow scooters, snow ploughs and rotavators, etc., however, track and steering devices of this kind are extremely expensive in relation to the price of the vehicle's other components.

The object of the invention is to provide a device of the type described in the introduction which is not encumbered by the above-mentioned disadvantages.

The characteristics of the device according to the invention are evident from the claims presented.

The invention will now be described in more detail with refer¬ ence to the drawing which schematically illustrates embodiments of the device according to the invention.

Fig. 1 is a perspective view of a track for a tracked vehicle with only one track, where some of the track shoes have been omitted and the vehicle drives straight ahead.

Fig. 2 is a perspective view of the track illustrated in fig. 1, but turned through an angle α in relation to the position of the track illustrated in fig. 1.

Fig. 3 is a view of a first embodiment of a track shoe, partially cut away, and seen in the direction along the circumference of the track.

Fig. 4 shows the right-hand end section of the shoe illustrated in fig. 3 , its sole part being displaced in relation to the shoe's upper part.

Fig. 5 is a section through line V-V in fig. 4.

Fig. 6 is a side view of a second embodiment of a track shoe, partially cut away, and seen in the direction along the circumference of the track.

Fig. 7 is a section through line VII-VII in fig-. 6.

In the following description it should be understood that the track rests on a horizontal base, e.g. the ground.

On the outside of the endless track 1 which is illustrated in fig. 1, there are evenly distributed along the circumference of the track a number of elongated track shoes 2, which extend in the track's transverse direction, and which are arranged to abut against the track's base, only a few of these track shoes 2 being illustrated in the figure. The object of the shoes is, amongst other things, to provide a good grip for the track on

the vehicle's base and constitute easily replaceable wear elements.

Each shoe 2 comprises an upper part 3 which is permanently connected to the track 1, and a lower part or sole part 4 which is arranged to come into contact with the vehicle's base. The upper parts 3 are arranged symmetrically relative to a vertical, central plane PI of the track. The sole parts 4 are connected with the respective upper parts 3 in such a way that they can be moved in the direction transverse to the track relative to the upper parts 3 , the shoes having devices which are capable by means of springs or the like of centering the sole parts 4 on the upper parts 3 , so that associated sole parts and upper parts substantially overlap one another when the sole parts are not forcibly moved away from the position by other means.

It should be understood that the track is moved in the direc¬ tion of arrow V by means of driving and supporting rollers (not shown) which are provided at each end of the track loop, and which in turn are rotatably mounted in the vehicle, the vehicle being moved in the direction of arrow F during this track movement.

Reference will now be made to fig. 2.

For steering of the vehicle, i.e. turning of the track about a vertically extending axis, the device comprises an arrangement whose design will be explained in more detail below, whereby the sole part of the front shoe 5 and the rear shoe 6, calcu¬ lated in the vehicle's direction of movement, of the track section which faces downward, can be moved away from their central position and against the centering spring force, which is exerted between the upper part and the sole part, the sole parts of the front and rear shoes 5 and 6 respectively being moved simultaneously, but each to its own side in relation to the respective upper parts 3.

Since the sole parts abut against the base and it should be assumed that the friction between the sole parts 4 and the base is greater than that between the sole parts 4 and the upper parts 3, ^' during this movement, however, the sole parts 4 will remain in position in relation to the base, i.e. continue to lie in plane Pl _r while during such a movement the track 1 will be moved horizontally in the opposite direction as a result of the reaction to the force exerted on the sole part. Thus the vehicle will be turned by angle about a central point D by the lower part of the track, calculated in the track's lon¬ gitudinal direction, located in the median plane PI, the track's new median plane thus being the plane indicated by P2.

During the turning of the vehicle, the sole parts of the shoes of the lower part of the track which are hereby located between the front and the rear shoes, will be drawn away from their central position due to the frictional force exerted on them by the base during the turning of the vehicle, and against the relatively small force exerted by the centering devices, thus causing the central sections of all those sole parts 4 which abut against the base to lie in plane PI.

When the vehicle is driven and the steering arrangement is operated in this manner, the sole parts of those track shoes which at any time constitute the front and rear shoes will be moved away from the central position in relation to the respective upper parts, thus causing the track's front and rear sections to be continuously moved in the track's transverse direction, i.e. the track is moved approximately along a circle with radius R. The remaining sole parts 4 on the lower section of the track will assume positions in accordance with the track's movement in relation to the base.

If the following conditions apply for the lower track section: aO = introductory displacement of the sole part of the front shoe = the distance between the front and the rear shoes

R = the vehicle's turning radius,

the turning radius will be approximately R = L ² /4a0.

When the vehicle is driven and a front sole is moved by a distance aO, the sole located immediately behind it is moved by a smaller distance al in the same direction, and the sole behind this moved by an even smaller distance a2, etc. A sole located at the centre of the track is not moved, since the vehicle will rotate about this sole, and soles behind the centre of the track will be moved in the opposite direction in relation to the direction of movement of those soles which are located in front of the centre.

Thus once a sole is moved by means of the steering device by a distance aO, as a result of contact with the ground 7 it is also moved by distances al, a2 , etc. with the length decreasing each time a new front sole is moved a distance aO, until it reaches the centre of the track, whereafter it will be moved in the opposite direction.

If the maximum steered movement of the front sole is aO, the shoe will have to have a maximum possible path of movement for the sole of aO + al + a2 .. an (where an indicates the movement of the sole which is located immediately in front of the centre of the track) in order to prevent the sole from reaching its sideways limit in the upper part before it reaches the centre of the track, whereafter it is moved in the other direction.

Fig. 3 illustrates schematically an embodiment of a shoe, viewed in the track's circumferential direction, where the shoe is illustrated in the position it occupies when the sole part is resting on the ground 7. Moreover, the wall of one of two vertically extending holes which extend through the upper part's 3 end sections is cut away.

This shoe's sole part 4 is substantially U-shaped, viewed in the track's circumferential direction, and the sole part's legs 10 project vertically upward and extend with a large clearance

through respective holes 11- in the upper part's 3 end sections, calculated in the track's transverse direction. The holes 11 are provided symmetrically in relation to a transverse mid plane of the upper part.

The upper end of each leg 10 is linked via a first pivot 13 with the upper section of two elongated members 12 which are provided on each side of the leg 10, calculated in the circumferential direction for the adjacent track section. The lower end section of the member 12 is linked via a second pivot 14 with the shoe's upper part 3, the pivots 13, 14 extending approximately in this circumferential direction. The distance between the longitudinal axes of the holes 11 corresponds to the distance between the longitudinal axes of the legs 10, and the longitudinal axis of the other pivots 14 intersects the longitudinal axis of the respective holes 11.

In the illustrated position where the ground 7 exerts an upward-directed force on the sole part 4, this force will cause a centering of each leg 10 in its respective hole 11 and thereby a centering of the sole part 4 in relation to the upper part 3. The sole parts 4 of those shoes which are located on the upper section of the track will also be centred in relation to the respective upper parts 3 due to the weight of the sole parts.

Fig. 4 shows the right-hand end section of the shoe illustra¬ ted in fig. 3, its sole part being moved to the right, away from the central position according to fig. 3, and fig. 5 shows a section along the line V-V through this end section.

Fig. 6 illustrates a second embodiment of a track shoe.

In the same way as the track shoe which is illustrated in fig. 3, the shoe illustrated in fig. 6 comprises a U-shaped sole part 24. In the upper part 23, however, there are provided two downwardly open cut-outs 31, where the distance between the

longitudinal axes of the sole parts' 24 leg 30 corresponds to the distance between the longitudinal axes of the cut-outs 31.

The upper end section of the legs 30 has a longitudinal track 35 which extends in the longitudinal direction of the shoe. In a pair of transverse, aligned holes in the side walls of each track there is mounted a shaft 33, on which there is rotatably provided a roller 32, which is arranged to abut against the bottom 36 of the respective cut-outs 31 when the legs 30 are inserted into the cut-outs. As is also illustrated in fig. 7 a pin or screw 34 extends in the shoe's longitudinal direction under the roller 32. The pin extends through and is attached to wall sections of the cut-out 31, and acts as a surface for the rollers and prevents the legs from being moved out of the cut-outs 31.

The steering device for the sole parts 4, 24 can be designed in the same way as in known per se devices whereby objects which are moved continuously on a track or the like, are moved in the track's transverse direction. Such devices are used, e.g. in sawmills. In this connection the sole parts can have one or more sections 15, 35 which project through or past the upper part, and with which the steering device can be connected for sideways movement of the sole parts.

It has been stated above that the steering device can be arranged for movement of the sole part for the front shoe and the rear shoe, in such a way that the vehicle turns about a point located between these shoes. It is obvious, however, that the device can comprise instead a steering device for only the front sole part, the rear sole part, e.g., being secured in a central position. In this case, however, the total path which must be available for the free movement of sole parts which are located behind the front, steered sole part must be larger, but the steering device can be simpler.

Alternatively, more than the front and rear shoe sole parts can, of course, be forcibly moveable, which leads to more

reliable steering, but also a more complicated steering device. Moreover, one group of shoe soles can be moveable in one direction and a second group can be simultaneously moveable in the opposite direction, since the number of shoes in the groups can be equal or unequal.

It will be understood that for a vehicle more tracks can be provided to comprise the device according to the invention, thus making it possible to coordinate the steering of the tracks so that they are steered simultaneously.