The present invention is concerned with a tractor with slip steering, comprising a bogie-borne frame, which carries a driving cab and a drive package for the transmission of the drive power to the wheels of the vehicle.

Slip-steered tractors known in prior art are, as a rule, provided with two wheels per side only, which said wheels have no spring system at all, so that no individual movement of any of the wheels in the vertical direction is permitted. This results in the circumstance that all irregularities in the road are transferred to the tractor body. Moreover, attempts have been made to place the wheels at the same side as close to each other as possible in order to reduce the effect of the counter- force that always acts upon the wheels of a slip-steered tractor during a turning maneuver. As a result of this, a tractor with highly unstable and shaky running is obtained. For example, when the tractor runs over an irregularity in the ground, it is readily set in a strong swinging movement, whereby its front wheels and its rear wheels rise off the ground alternatingly. If the swinging becomes excessively intensive, there is a risk of over- turning of the tractor. Moreover, as long as the tractor is in such a swinging movement, it is practically com¬ pletely unmaneuverable. The only mode of eliminating such a swinging movement is complete stopping of the tractor. Owing to these drawbacks, such a tractor may be driven only at a very low speed on a public highway.

The object of the present invention is to eliminate these problems, which is achieved by means of a tractor with slip steering, which is characterized in that, at each side, the tractor is provided with two driven wheels suspended on a longitudinal bogie, and additionally with at least one wheel per side, suspended at the respective ends of one and the same transverse axle,

which said axle is, approximately at the middle, vertically pivotably, suspended on an extra frame rigidly connected to one end of the frame proper of the tractor, the free end of the said extra frame being provided with fastenings for working implements. Such a tractor has a very stable run without any tendency of swinging, and a relatively good spring action because both of the longitudinal bogies and the vertically pivotable axle absorb road irregula¬ rities in a satisfactory way. The other characteristics of the invention come out from the accompanying patent claims.

In the following, the invention will be described in more detail with reference to the accom¬ panying drawing, wherein .Pig. 1 shows an example of a tractor in accord¬ ance with the invention as viewed from the side.

Fig. 2 shows the tractor of Fig. 1 as viewed from the right, and

Fig. 3 shows another example of a tractor in accordance with the invention as viewed from the side.

The slip-steered tractor comprises a bogie- borne frame 1 , which carries the driving cab 2 and a drive package that supplies the vehicle wheels 3, and possibly 4, with drive power. The drive package comprises preferably a diesel engine, which drives either two ad¬ justable hydraulic pumps or possibly one or two electric generators. The hydraulic pumps or the electric gener¬ ators are supposed to transmit the drive power to the hydraulic or electric motors of the tractor, which are arranged so that they drive their respective wheels or wheel groups. The tractor is provided either with one motor per bogie 5 or one motor per wheel 3, depending on the magnitude of the drive power that is desired and required per wheel 3. It is characteristic of the tractor in accordance with the invention that, at each side, the tractor is provided with two driven wheels 3 suspended on a longitudinal bogie 5 , and additionally with at

least one wheel 4 per side, suspended at the respective ends of one and the same transverse axle 6. The trans¬ verse axle 6 is, approximately at the middle, vertically freely pivotably suspended on an extra frame 7, which is rigidly connected to one end of the frame 1 proper of the tractor. The extra frame 7 is, at its free end, provided with fastenings 8 for working implements of different kinds, such as agricultural implements, excavators, trailers, front loaders, and equivalent. The slip-steered tractor is steered thereby that the driving wheels 3 at one side of the tractor are made to revolve at a higher or lower speed of rotation as compared with the wheels 3 at the other side, depending on the direction in which the tractor is to be turned. The maneuvering of the vehicle takes place appropriately by means of a T-shaped maneuver lever, which acts, e.g., upon the two hydraulic pumps of the tractor so that they feed hydraulic fluid in one direction when the maneuver lever is moved forwards, and in the opposite direction when the lever is moved rearwards, whereby the magnitude of the volumetric flow depends on the extent to which the maneuver lever is shifted from its starting position in the direction concerned. By turning the maneuver lever around its longitudinal axis, volumetric flows of different magnitudes and possibly of opposite directions are produced through the two hydraulic pumps. Thus, the speeds of rotation of the hydraulic motors and, thus, of the wheels 3 are proportional to the said volumetric flows. The coupling member between the frame 1 proper of the tractor and the extra frame 7 is preferably of a quick-coupling type. By providing both ends of the frame 1 proper with identical quick coupling members 9, it is possible to couple the extra frame 7 either at the front or at the rear of the tractor. By means of this arrangement, the possibilities of use of the tractor are increased remarkably, as the stabilizing extra frame 7 can be coupled to the end of the tractor at which a higher

stability is required, or if it is desirable to distribute the gravitational effect of the vehicle in a different way.

In order to improve the carrying capacity of the vehicle and to reduce its wheel load, it is possible to suspend a longitudinal bogie 14 at each end of the transverse axle 6, so that the tractor receives four wheels 3, 4 per side.

As required, the wheels 4, which are directly or indirectly mounted at the end of the transverse axle 6, may be driven or non-driven. In particular if the wheels 4 are also suspended on a bogie 14, it is appropriate that all the wheels of the tractor are driven, which also increases the running capability of the vehicle in difficult terrain. By at each side mounting a hydraulic cylinder- piston device 10 between the frame 1 of the tractor and, e.g., the front end of the longitudinal bogie 5 at the side concerned, a possibility's obtained to adjust and to lock the bogie 5 at the side concerned in different * angular positions. When the cylinder-piston devices 10 are connected free, they have a spring action. With the aid of these cylinder-piston devices 10, an even higher stability and better maneuverability are obtained for the tractor. When the tractor, e.g. with a working implement coupled at the rear, is to turn on a field, both of the hydraulic cylinder-piston devices 10 are first activated so that the front ends of the two longitudinal bogies 5 are pulled upwards, whereby the rear wheel of each bogie is, at the same time, pressed down so that the weight of the tractor is concentrated on these wheels, whereupon the turning meneuver itself is performed. In this way, it is possible to make the tractor turn around practically on the spot when speeds of rotation of different magni¬ tudes and possibly of opposite directions are applied to the said two wheels. The cylinder-piston devices 10 may also be utilized in order to obtain a desired distri¬ bution of weight when work is performed by means of some

working implement coupled to the tractor. The separately maneuverable cylinder-piston devices 10 may also be used when the tractor is to be coupled to a working implement. In view of increasing the driving comfort of the vehicle further, the extra frame 7 may be suitably provided with an articulated joint 12, which permits piv¬ oting of this extra frame 7 in the vertical direction in relation to the frame 1 proper of the tractor. In such a case, a substantially horizontal cylinder-piston device 13 is connected between the two frames 1 and 7, whereby a so-called parallellogram coupling is obtained. In the free position, this cylinder-piston device 13 acts as a spring counteracting the swinging of the joint 12, but by activating the device 13, it is possible to lock the frame 7 in different angular positions relative the frame 1.

When the tractor is used as a piste machine or for collecting of peat, it is appropriate to provide it with crawler belts 15 which enclose all the wheels 3 and 4 at each side. In Fig. 2, it is shown with broken lines how the tractor can be provided with wheels of different dimensions and with crawler belts.

As a result of the peculiar mode of operation of the tractor, it can be driven with an equally high speed both forwards and rearwards. In order to facilitate the maneuvering of the tractor in this connection, it is appropriate to provide it with a driver's seat rotable around a vertical axis, to which said seat the maneuver lever of the vehicle is also coupled. Such a construction facilitates the driver's work considerably also in the case of plowing and equivalent, as the driver, with the seat in the tranverse direction, may look both forwards and rearwards.

The transverse axle 6 has preferably the shape of an inverted V, whereby the axle 6 is pivotably attached 5 to the extra frame 7 by means of a shaft passing through the tip of the V in the longitudinal direction of the tractor.