Abstract: An auxiliary suspension unit for mounting parallel to a standard shock absorber comprises a cylinder receiving a piston which includes a piston head mounted to a piston rod and defining in the cylinder first and second chambers filled with oil. The first chamber is on the rod side of the piston head. A spring structure comprises a floating piston and a high pressure accumulator contained in a third chamber with the floating piston being slidable therein. The working fluid from the second chamber exerts pressure on the floating piston and is opposed by the high-pressure accumulator of the third chamber. The auxiliary unit also comprises an actuator for positioning a valve provided on the piston into first and second positions thereof and further comprises a control device for the actuator. In the first position of the valve and upon compression of the auxiliary unit, a bypass allows fluid transfer from the second to the first chamber.