Damping units are used in motor vehicles and prticularly in motor cycles for damping the movement of the respective steering device. More particularly they serve to damp undesired steering deflections stimulated for example by road-way irregularities. On the other hand, the damping unit should exert only small or essetially no damping effect on the steering device in normal slow steering operation.
From U.S. Pat. No. 2,310,570 a damping unit for a motor vehicle is known. A piston rod is axially movable with respect to a cylinder. A piston unit is fixed to the piston rod within the cylinder and divides the cavity within the cylinder into two working chambers. the piston unit comprises a carrier member with axial bores. Valve plates are provided on both end faces of the carrier member,. Helical compression springs are located within the bores and urge the valve plates towards respective opening positions. On fast movement of the piston rod the pressure in one of the working chambers is increased and the respective valve plate is urged towards a damping position against the action of the springs. The valve plates are star-shaped with a plurality of arms allocated to respective bores. The valve plates are prevented from rotation so that they remain in axial alignment with the bores. The valve plates are made of bimetallic material. In the damping position of the valve plates there is no definite flow resistance through the piston unit, such that the piston rod may be completely blocked with respect to the cylinder.