The invention relates to transmission and steering apparatus for a tracked vehicle according to the ingress part of claim 1.

In a conventional motor sled like that presented in the patent publication US 3568786, the forward driving element is a moving rubber track mat rotated by track wheels which mat moves on a slide bogie and is located under the seat. Steering of the motor sled occurs by means of a bar by turning the skis or corresponding guide means located in front of the track. The motor sled of this kind has as a transmission device a transmission shaft fixed to a secondary variator from one end of which tansmission shaft the torsional force is transmitted by means of a chain to the driving track wheels of the track unit. A motor sled which has a turning track is also known wherein the steering is accomplished by extending one side of the track and, in a corresponging way, shortening the other side. In addition, there are known motor sleds with two parallel track mats, which are of the same length as the sled and the steering of which occurs by decelerating the rotation of one track mat. Also a motor sled of this kind has a chain transmission to the driving wheels or the transmission shaft of the the track wheels.

It is known to use such a transmission apparatus in tracked vehicles where the rotational motion of the transmission shaft is transmitted through a first bevel gear to an intermediate shaft and further from the intermediate shaft through a second bevel gear to the track unit which drives the tracked vehicle. This kind of solution is presented e.g. in the patent publication US 4415055.

The drawback in tracked vehicles of prior art and in motor sleds in particular is their poor steerability and poor suspension. These drawbacks affect the driving characteristics. The objective of the invention is to obtain a tracked vehicle which has much better steerabi¬ lity than conventional tracked vehicles and which has better driving characteristics. Another objective is to obtain an effective suspension of the front part. These objectives are achieved by a tracked vehicle which is primarily characterized by the features mentioned in the characterizing part of claim 1.

By means of the transmission apparatus according to the invention it is possible to replace the skis in the front of an existing motor sled with a turning track unit which acts as a driving track unit for the tracked vehicle.

According to one embodiment of the invention, the track unit can be connected to the frame of the motor sled by shock absorbers whereby a significant improvement is obtained in the suspension of the track unit. The track unit can also tilt in a plane which is perpendicular to the travel direction. The most important advantage of the invention is that it allows one to replace the skis in existing motor sleds with a turning, spring loaded and shock absorbed front track unit with minor changes and at small costs.

In the following the invention will be described in detais with reference to the enclosed drawings in which

figure 1 shows a top view of the transmission apparatus of a motor sled and the bevel gear and the shaft thereof, figure 2 shows schematically a vertical cross-section of a transmission and steering apparatus of the invention seen from the front,

figure 3 is a schematic cross-section at the joint of figure 2 along the line A - A and figure 4 shows a side view of a motor sled with a front track unit installed.

Figures 1 and 2 show a transmission and steering appara¬ tus according to the invention comprising a transmission shaft 4, a first bevel gear 5 connected with the drive shaft 8 of the front track unit 2 and a second bevel gear 7 connected with the transmission shaft 4 and an inter e- diate shaft 13 between the said bevel gears 5 and 7. By means of these members the rotational motion of the motor 3 is transmitted to the common drive shaft 8 of the front track units 2. The steering members of the apparatus comprise a steering shaft 9, a steering ring 10 and a steering lever 12 linked thereto. By means of these steering members, the steering motions of the vehicle i.e. turning of the handlebar, for example, is transmit¬ ted to corresponding turning motions of the front track units 2 for steering the tracked vehicle.

The front track units 2 mounted at both ends of the drive shaft 8 in the front part of the tracked vehicle function as the drive track unit of the tracked vehicle. The drive shaft 8 turns round the rotational axis of the interme¬ diate shaft 13 and, in particular, round the rotational axis of the end part of the intermediate shaft 13 which is connected to the first bevel gear 5. The point about which the drive shaft turns is located at the intersecti¬ on of the rotational axis of the intermediate shaft 13 and that of the drive shaft 8 i.e. in the first bevel gear 5 in the centre of the drive shaft 8.

Figure 1 shows, seen from above, the motor 3 mounted on the frame 1 of the motor sled, the transmission shaft 4 and the second bevel gear 7 belonging thereto. The motor

3 rotates a primary variator from which the rotational movement is transmitted via a V-belt to a secondary variator. To the secondary variator there is fixedly coupled a shaft 6, on which a gear wheel is mounted so that it transmits force via a chain to a gear. The gear is mounted on the transmission shaft 4 so that the gear rotates the transmission shaft 4, on one end of which there is mounted the second bevel gear 7. The other end of the transmission shaft 4 is rotatably pivoted on the frame 1 of the sled.

Figure 2 shows a vertical cross-section of a transmission and steering apparatus of the invention seen from the front of the sled. Figure 2 shows the leading-through of the transmission and steering apparatus through the bottom plate 24 in the front part of the motor sled, on which plate a protective tube 16 is attached e.g. by welding, whose one end is mounted rigidly on the body of the second bevel gear 7. A circular recess 11 is made inside the protective tube 16 so that a steering ring 10 can freely turn in the recess 11. The recess has an opening for the movement of a steering lever 12. The steering lever 12 is rigidly attached to the steering ring 10, on the inside of which there are grooves for the longitudinal projections on the outside of the steering shaft 9. Hence, upon turning the steering ring 10 the steering motion is transmitted to the steering shaft 9. However, the steering shaft 9 can simultaneously move freely in vertical direction. The steering shaft 9 is fitted to move inside the protective tube 16 so that the upper part of the steering shaft 9 cannot touch the body of the second bevel gear 7.

In accordance with figures 2 and 3, to the lower end of the steering shaft 9 there are rigidly fixed support plates 26 which are joined by means of fixed joining pins

28 and detachable locking pins 29 to underlying support plates 27. By removing the locking action of the locking pins 29, at least the support plates 27 can freely turn round the concentric gravitational axes of the joining pins 28. Neither is the operation of a cardan joint 17 prevented by the turning of the support plates 27. The support plates 27 are rigidly attached to the body 21 of the first bevel gear, on whose round upper part there is rigidly attached a lower annular support flange 35 and a detachable support flange 31. Between the support flanges 31 and 35 there is pivoted a mounting flange 32 for the suspension and the shock absorber so that it can freely rotate between the support plates 31 and 35 round the upper part of the body 21 of the first bevel gear. The support flange 31 and the mounting flange 32 are locked in place by a special locking nut 30.

The rotating steering motion of the steering shaft 9 in the transmission and steering apparatus of the invention turns the body 21 of the first bevel gear 5 and, being rigidly attached thereto by means of fixing elements, the protective tubes 22 of the drive shaft 8 whose motion in turn turns the front track unit 2. Due to the way the steering shaft 9 is mounted, the first bevel gear 5 can also move vertically. For dampening vertical movements and shocks of the first bevel gear 5, there are mounted a suspension and shock absorbers 19 on the mounting flange 32. Figure 2 shows schematically such shock absorbers 19 which also comprise a supension element. Furthermore, for limiting the movement of the steering shaft 9 and for dampening adrupt vigorous shocks, a rubber cushion 20 is mounted on top of a fixed flange of the lower end of the steering shaft 9. The shock absorbers 19 are led through the bottom plate 24 of the sled and fixed by means of an auxiliary bar to the frame 1 of the sled. At the leading- through point, the shock absorbers 19 are protected by

means of rubber collars fixed to the bottom plate 24 of the sled. The leading-through openings of the shock absorbers 19 are fitted to allow the lower ends of the shock absorbers 19 to move to such an extent as caused by the turning of the first bevel gear 5 round the joining pins 28. When it is desireable to prevent the first bevel gear 5 from turning round the joining pins 28 and thereby make the joint rigid, locking pins 29 must only be mounted in place and lock them in place with locking elements 36.

The transmission and steering apparatus of the invention operates best when the first bevel gear 5 is capable of turning round the joining pins 28. In this case, e.g. the suspension of the front track units is at its best since they are able to move according to the terrain up and down nearly independent of each other. The apparatus of the invention has to be provided with such shock absor¬ bers which limit the vertical movement of the first bevel gear 5 suitably, taking into account the allowed vertical movements of the steering shaft 9 and the intermediate shaft 13.

As shown in figure 2, the second bevel gear 7 transmits the rotating motion of the transmission shaft 4 to the intermediate shaft 13. The intermediate shaft 13 is composed of two shafts 14 and 15 one within the other, the first shaft 14 being connected to the first bevel gear 5 and the second shaft 15 to the second bevel gear 7. The second shaft 15 is hollow and the first shaft 14 is fitted by means of a sliding slot joint to move freely in the longitudinal direction of the hollow shaft . At the lower end of the intermediate shaft 13, there is a cardan joint 17 which is situated inside the tilting joint 18.

The steering elements of the transmission and steering apparatus according to the invention comprise a tubular steering shaft 9 with a circular cross-section which surrounds the intermediate shaft 13, and is, at its lower part, connected to the drive shaft 8 for transmitting steering motions to the drive shaft 8. The steering elements additionally comprise a steering ring 10 for transmitting steering motions to the steering shaft 9. The steering ring 10 is fitted to the steering shaft to allow a longitudinal motion of the steering shaft 9 inside the steering ring 10. Steering motion from the handlebar of the motor sled is transmitted to the steering ring 10 by means of a steering lever 12. The steering shaft 9 is, at its lower end, connected to the drive shaft 8 via the tilting joint 18 for enabling a tilting motion. The steering shaft 9 is fitted to move inside the protective tube 16 which is rigidly fixed to the frame 1 of the tracked vehicle. The protective tube 16 comprises a recess 11 for the steering ring 10. The springing motion of the track unit is possible because the intermediate shaft 13 enables a longitudinal sprin¬ ging motion and because the steering shaft 9 is able to move longitudinally inside the protective tube 16.

The steering shaft 9 and the intermediate shaft 13 are fitted to allow the steering shaft 9 to turn freely and move round the intermediate shaft 13. Figure 3 shows how the intermediate shaft 13 is connected through the cardan joint 17 to the first bevel gear 5. Hence the first bevel gear 5 can turn round the joining pins 28 of the titing joint 18 if necessary. The first bevel gear 5 transmits the turning motion of the intermediate shaft 13 is transmitted to the drive shaft 8 which rotates the drive wheels of the front track units 2.

Figure 4 shows schematically, seen from the side, a motor

sled wherein the skis have been replaced with driving and turning front track units 2 by utilizing the apparatus according to the invention. This kind of vehicle is superior as compared with motor sleds with skis or the like because it can move in the terrain both in summer and winter conditions.

The invention is not limited to the above embodiment but it can be varied within the limits of the enclosed claims. For example, the steering shaft 9 can be connec- ted to the first bevel gear 5 or the drive shaft 8 via any member which transmits the turning motion of the steering shaft 9 to a turning motion of the drive shaft 8. This member can be a folding joint which is connected to the steering shaft, on one hand, and to the drive shaft, on the other hand, and which transmits turning motion and allows a vertical motion of the intermediate shaft 13.