Patent ID: 7568562

Claim:
A self pumping hydropneumatic spring strut, comprising: an oil-filled working cylinder having a working piston dividing said cylinder into two working spaces and a hollow piston rod carrying said working piston and which is moveable back and forth within the cylinder; a first high-pressure chamber comprising a first gas cushion with a first gas volume, and a second high-pressure chamber comprising a second gas cushion with a second gas volume, said first and second high-pressure chambers being arranged in parallel, one of the working spaces being connected to the first high-pressure chamber by an opening and to the second high-pressure chamber by a connection with a shut-off valve such that the first gas cushion and the second gas cushion are both acted on in parallel when the shut-off valve is open a piston pump comprising a pump cylinder and a hollow pump rod having a control channel connected to a low-pressure chamber, the pump cylinder being defined by the hollow piston rod, the pump rod having a first end attached to the working cylinder and a second end inserted into the hollow piston rod, the pump rod having an inlet valve arranged at the second end; and a control opening connecting the one of the working spaces to the control channel as a function of the position of the working piston in the working cylinder, wherein the piston pump is driven by movements of the piston rod to convey oil from the low-pressure chamber to the one of the working spaces so that the spring strut is extended by the piston pump when said control opening is closed to a partial spring strut extension position at which the control opening opens.