Patent ID: 8091870

Claim:
A self-pumping hydropneumatic spring strut with internal level control for a motor vehicle, the spring strut comprising: an outer tube having one end sealed by a piston rod guide; a working cylinder received inside the outer tube; a hollow piston rod extending into the working cylinder through the piston rod guide, the piston rod carrying a piston which is operable to travel axially inside the working cylinder in a sealing manner and separates the working cylinder into first and second working spaces, the first working space being under a high-pressure from a high-pressure chamber and acting as a spring, and the second working space being located on a piston rod-side; and a pump rod received inside the hollow piston rod; wherein the pump rod and the hollow piston rod form a piston pump configured to convey a damping medium from a low-pressure chamber into the first working space connected to the high-pressure chamber, wherein the high-pressure chamber and the low-pressure chamber are each connected to the atmosphere by a filling connection formed in the piston rod guide, each of the filling connections including a check valve operable to selectively communicate the high-pressure or the low-pressure chamber to the atmosphere, wherein the filling connection to the low-pressure chamber is in the form of a filling bore, which is normally closed to prevent the escape of pressure from the low-pressure chamber to the atmosphere, and wherein the filling bore opens into a pressure relief bore opening into the low-pressure chamber, the pressure relief bore having one end provided with an O-ring check valve.