HYDRAULIC VIBRATION-DAMPER WITH VARIABLE DAMPING CHARACTERISTIC

A hydraulic vibration-damper with variable damping characteristic comprises a cylinder (1) with a piston rod (2) and a piston (7; 24) which divides the volume of the cylinder (1) into two working chambers (8, 9). The piston parts which move relative to the cylinder (1) are provided with a passage arranged between the working chambers (8, 9) which can be opened or closed by a shut-off valve (17, 18; 34). The cross-section of the piston (7; 24) is less than the free cross-section of the cylinder (1), so that a gap (13; 26, 26', 32) is formed as a passage between the cylinder wall and the piston (7; 24). The piston has a groove (10'; 29, 29') in the region of the gap (13; 26, 26', 32) which extends across the whole width of the gap (13, 26, 26', 32). Arranged in said groove is an elastic expanded body (11; 31, 31') which is curved like a tyre in the direction of the cylinder wall and which closes the gap (13; 26, 26', 32) and seals the volume (12; 37, 37') of the groove (10; 29, 29') from the passage. Two channels (15, 16; 33, 33'), in each of which is arranged a shut-off valve (17, 18; 34) with a passage (19, 20; 35, 35'), lead from each working chamber (8, 9) and open into the groove (10; 29, 29').