PRIOR ART DE-A-1 961 008 has previously disclosed a springing and damping device for damping pivotal movements of a wheel-supporting pendular arm of a tracked vehicle, the device comprising a housing with a cavity for rotatable support of a swing axle of the pendular arm; a plate pack arranged in the housing and com- prising a number of coaxially adjoining, annular disk plates, which are alterna- tely torsionally fixed but axially moveable in the housing or on the swing axle; a first annular pressure disk torsionally fixed but axially moveable on the swing axle of the pendular arm; a second annular pressure plate, torsionally fixed but axially moveable in the housing, the two pressure plates having opposing sides with members designed, on rotation of the first pressure plate, to produce an axial movement of the pressure plates in relation to one another; and compres- sion spring unit, designed to exert a compressive force on the pressure plates and the disk plates. Springing movements of the pendular arm are permitted by a torsion bar, to which the pendular arm is connected, whilst a position- dependent damping of compressive springing movements of the pendular arm is achieved in that friction disk plates are pressed against one another and against a brake disk in the housing through the action of the compression spring unit, when the pressure disks are separated from one another by means of inte- racting wedge elements in compressive springing of the pendular arm.

In extreme off-road driving conditions of a tracked vehicle with such a spring- ing and damping system, bottoming easily occurs unless the system is of very rigid design, which has an adverse affect on comfort in ordinary road driving conditions.

OBJECT OF THE INVENTION An object of the invention is to produce an improved device for damping pivo- tal movements of the wheel-supporting pendular arms of a tracked vehicle, which device will permit both position-dependent and speed-dependent dam- ping of the pendular arms in the case of compressive springing and position- dependent damping in the case of extension springing in order to produce a good, comfortable springing and damping function both in ordinary driving of the vehicle on roads and in extreme off-road driving conditions.

SOLUTION ACCORDING TO THE INVENTION With this object in view, the aforementioned device according to the invention is characterized in that it comprises an axially moveable piston, arranged bet- ween the compression spring unit and the pressure plates, and a restrictor ele- ment, which allows a hydraulic pressure medium to flow from one side of the piston to the other. A damping device is thereby obtained, which due to the supporting of the piston between the compression spring unit and the pressure disks is capable of functioning as a hydromechanical damper, which is capable of braking rapid compression springing movements of the pendular arm and preventing bottoming.

Further special features of the damping device according to the invention are specified in the following dependent claims.

The invention is described in more detail below with reference to drawings at- tached.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a side view of a torsion damper according to the invention for a motor vehicle wheel-supporting pendular arm pivoted therein; Fig. 2 is an enlarged cross-section view through the torsion damper in Fig. 1 omitting the swing axle of the pendular arm; Fig. 3 is a cross-sectional view of an upper part of the housing of the torsion damper, showing a pressure relief valve fitted therein; Fig. 4 is a perspective view of a first pressure disk for torsionally fixed moun- ting on the swing axle of the pendular arm; Fig. 5 is a perspective view of an inner annular part of a second pressure disk for torsionally fixed mounting in the torsion damper housing; Fig. 6 is a perspective view of an outer annular part of the second pressure disk; and Fig. 7 and 8 are diagrams respectively showing position and speed-dependent damping of springing movements of the pendular arm by means of a device ac- cording to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Figure 1 shows a torsion damper according to the invention, generally denoted by 10, for position and speed-dependent damping of pivotal movements of a pendular arm 12 about an axis A. At its free end the pendular arm 12 supports a carrier wheel 14, freely rotatable about an axis B and intended to bear sup- portively against the upper side of a lower running element of an endless cater- pillar track (not shown) of a tracked motor vehicle. The damper 10 has a hou- sing 16, which is intended to be firmly fixed in the side of a chassis part of the tracked vehicle, where a number of such carrier wheel-supporting pendular arms are pivoted in series.

Figure 2 shows in more detail how the torsion damper 10 according to the in- vention is constructed. The housing 16 of the torsion damper 10 has a central cavity 18 for the accommodation and rotatable support of a hollow swing axle journal (not shown) of the pendular arm 12, which is intended to be torsionally fixed to a torsion spring (not shown) in the form of a torsion bar running coaxi- ally with the axis A. A plate pack, comprising a number of coaxially adjoining, annular disk plates 20,22, is fitted in an enlarged cylindrical cavity 24 in the housing 16. In this, every other disk plate of the disk plates 20 is torsionally fixed but axially moveable on the axle journal of the pendular arm 12 by means of a splined connection, whilst the other intermediate disk plates 22 are torsio- nally fixed but axially moveable in the housing 16 by way of another splined connection. At one end the plate pack has a fixed axial stop 26 against the hou- sing 16 and at its other end an axially moveable stop in the form of a first an- nular pressure disc 28, which is connected so that it is torsionally fixed but axi- ally moveable to the shaft journal of the pendular arm by way of a splined con- nection. A second annular pressure disk 30 is fitted coaxially up against the first pressure disk 28 and is torsionally fixed but axially moveable in the hou- sing 16 also by way of a splined connection.

As shown in more detail in Figure 4, the first pressure disk 28, on one side fa- cing the second pressure disk 30, has three wedge-shaped cams 32 running in a circumferential direction, which are designed to interact with three comple- mentary cams 34, formed on the opposite side of the second pressure disk 30 (Fig. 5). This second pressure disk 30, as shown in Figures 5 and 6, comprises an inner ring 30a with cams 34, and an outer ring 30b, the rings 30a, 30b ha- ving three interlocking recesses 36 and 38 for receiving a spherical element 40 (Fig. 2), which couples the rings together so that they are torsionally fixed but allows an axial movement in relation to one another.

A compression spring unit in the form of a pair of annular disk springs 42,44, in which one spring 44 is thicker and stiffer than the other, exerts a pretensio- ning force on the pressure disks 28,30 and on disks 20,22 of the plate pack under the action of a piston 46, which is situated between the pressure disks and the spring unit and bears against the inner ring 30a, and is axially moveable in a cylindrical part 48 in the housing 16. The piston 46 has a fixed restriction 50, which allows a hydraulic medium (oil) to flow through from one side of the pi- ston to the other, when the piston 46 is moved axially. The piston 46 also has a return valve 52, which together with the restriction 50 permits a more rapid displacement (return movement) of the piston 46 to the left than to the right in Figure 2, that is to say it permits a greater flow of oil from the left-hand side of the piston to the right in a return movement of the piston 46, assisted by the compression spring unit 42,44 in the case of a return movement or extension springing of the pendular arm by means of the torsion bar. The space to the : of the piston 46 is further connected to the space to the right of the piston by way of a chamber 54 in a superstructure 56 of the housing 16. Ducts 58 and 60 connect the respective sides of the piston 46 to the chamber 54. Co-ordinated with the duct 58 is a pressure relief valve 62 (Fig. 3), which is designed to open the connection between the chamber 54 and the space to the right of the piston 46 when a predetermined oil pressure in the latter chamber is exceeded, which occurs in the event of rapid compressive springing of the pendular arm 12.

The damping device according to the invention functions as follows: When driving a tracked vehicle the pendular arms are compressively sprung to a different degree and at differing rates depending on the irregularities of the ground and the speed of the vehicle. In the case of relatively slow compressive springing (position-dependent damping), the pendular arm 12 turns the first pressure disk 28, which then by means of the cams 32 and 34 presses the se- cond pressure disk 30 and the piston 46 away from itself, against the action of the disk springs 42,44, the first pressure disk 28 at the same time pressing the disk plates 20,22 operating in oil towards one another and against the fixed stop 26 in the housing 16, so that the compressive springing of the pendular arm 12 is friction damped ever more strongly the further the arm compresses, as shown in the graph in Figure 7. After passing a specific angular position (com- pressive springing) of the pendular arm 12, in which the weaker disk spring 42 is pressed to a limit stop, the stiffer disk spring 44 is activated, a change to the steeper damping curve in Figure 7 then occurring. At the same time oil flows from the right-hand side of the piston 46 to the left-hand side by way of the re- striction 50, a speed-dependent damping moment being exerted on the pendular arm 12 in accordance with the left-hand sloping curve in Figure 8.

In extreme off-road driving conditions, in which the pendular arm 12 is made to perform a rapid compressive springing movement in excess of a predetermined angular velocity, the pressure relief valve 62 opens due to the oil pressure inc- rease, thereby allowing the oil on the right-hand side of the piston 46 also to flow through the valve 62 to the chamber 54 and the opposite side of the piston 46. An instantaneously dynamic pivotal damping of the pendular arm 12 is the- reby achieved according to the horizontal curve in Figure 8. In the event of ra- pid extension springing of the pendular arm 12 the return valve 52 opens, the oil flowing rapidly back to the right-hand side of the piston 46 by way of the return valve 52 and the fixed restriction 50.

It is also possible, without departing from the scope of the present invention, to locate the valve elements 50 and 52, like the pressure relief valve 62, in the su- perstructure 56 of the housing 16 rather than in front of the piston 46, making the valves more easily accessible for inspection and servicing. Owing to the double action of the damping device with static and dynamic (po- sition and speed-dependent) damping of the pendular arm 12 in compressive springing and position-dependent damping in extension springing, improved comfort and ride characteristics are obtained in the vehicle with a reduced risk of bottoming in the spring suspension system