US Patent 7520494 Spring element

A spring element with a hydropneumatic strut are positioned between the bogie and the body of a rail car, with the strut having a sliding piston in a cylinder, whereby the piston or the cylinder can be connected with the bogie and the other component can be connected with the body, and the piston area of the cylinder is connected with a hydraulic accumulator. A strut that is easy to service and maintain and does not accumulate any appreciable amount of dirt is created by virtue of the fact that the hydropneumatic strut has a hydraulic height regulator valve or a height sensor connected or connectable with a feedback loop, whereby the position of the piston in the cylinder can be adjusted or determined.