Shock absorber unit

A shock absorber unit comprising

• a shock absorber including a strut cylinder, a piston which divides the internal space of the strut cylinder into a first and a second chamber, and a gas spring bladder unit;
• a source of pressurized liquid;
• switching valve means including a first port which receives a pressurized liquid from the source, a second port receiving a drain pressure, and a third and a fourth port which selectively deliver the pressurized liquid and the drain pressure, and also including means movable among a first position in which a communication between the first and the second port on one hand and the third and the fourth port on the other hand is interrupted, a second position in which a communication between the first and the third port as well as a communication between the second and the fourth port are established and a third position in which a communication between the first and the fourth port as well as communication between the second and the third port are established, thus selectively establishing an interconnection among the first to the fourth port;
• first open/close valve means for opening or closing a flow path between the third port of the switching valve means and the first chamber;
• second open/close valve means for opening or closing a flow path between the fourth port of the switching valve means and the second chamber;
• third open/close valve means for opening or closing a flow path between the liquid chamber of the gas spring bladder unit and the first chamber;
• mode selection signal generating means responsive to the deceleration and the acceleration of a vehicle and a change in the direction in which the vehicle runs for determining if a compressive or tensile load is applied to the shock absorber and for generating a second mode selection signal in response to the compressive load, a third mode selection signal in response to the tensile load and a first mode selection signal when no substantial load is applied;
• and drive means responsive to the first mode selection signal for driving the switching valve means to its first position and driving the third open/close valve means to its open position;
• responsive to the second mode selection signal for driving the switching valve means to its second position and for driving the first open/close valve means to its open position;
• and responsive to the third mode selection signal for driving the switching valve means to its third position, driving the second open/close valve means to its open position and driving the third open/close valve means to its closed position.

A method for controlling a shock absorber unit of the type having a strut cylinder, a piston which divides the internal space of the strut cylinder into a first and second chamber and a gas bladder unit, the method comprising:

• connecting a source of pressurized liquid to a switching valve means;
• detecting acceleration and deceleration of a vehicle and a change in the direction in which the vehicle is moving for determining if a compressive or tensile load is applied to the shock absorber and providing signals indicative thereof to a control unit;
• generating a first mode selection signal when no substantial load is applied to the shock absorber, generating a second mode selection signal in response to a compressive load and generating a third mode selection signal in response to a tensile load;
• and
• controlling said switching valve means and additional valve means intermediate said switching valve means and said first and second chambers and said gas bladder unit in response to the specific mode selection signal.