Abstract: A suspension strut for a vehicle comprises a cylinder in which works a piston, and the piston is carried by a piston-rod which passes through an axial extension depending from a closure for one end of the cylinder. An annular chamber defined between the cylinder and the extension accommodates the whole of a volume of gas or air and a portion of a volume of hydraulic fluid which fills the remaining space in the cylinder and against which the piston works. A seal through which the piston-rod works is carried by the extension at a position which is always below the level of hydraulic fluid in the cylinder so that the gas or air is prevented from escaping past the seal by the presence of the hydraulic fluid.

Abstract: A self-pumping strut comprises radially inner and outer cylinders extending between closure members to define a reservoir space between the cylinders which is partitioned by a cylindrical elastomeric membrane into an hydraulic reservoir space and a gas space.A piston connected by a piston rod to a wheel slides in the inner cylinder to define a pump chamber and a first working chamber within the inner cylinder. Each chamber communicates with the hydraulic reservoir space by means of a respective solenoid-operated valve. A pump outlet valve incorporated into the piston controls flow of hydraulic fluid between the chambers. The first working chamber is in communication with a second working chamber by means of flap valves, the second working chamber being separated from a gas spring chamber by a diaphragm.An electronic control unit operates the solenoid-operated valves to adjust the height of the strut, which is detected by a sensor.