A hydropneumatic suspension system for a wheeled vehicle comprising:
- a source of hydraulic fluid under pressure;
- a hydraulic fluid reservoir;
- first and second pairs of hydropneumatic suspension units disposed between a body and wheel supporting means of the vehicle, each of said suspension units including a cylinder body having a cylinder chamber, a piston slidably accommodated in the cylinder chamber and dividing the cylinder chamber into upper and lower cylinder compartments and self-levelling valve means operative to alternatively communicate said source and said reservoir to said upper cylinder compartment through inlet and outlet ports of the suspension units for thereby maintaining the level of the vehicle body above the ground substantially constant;
- a first pair of conduits, one of which interconnects the upper cylinder compartment of one of said first pair of suspension units and the lower cylinder compartment of one of said second pair of suspension units and the other of which interconnects the upper cylinder compartment of said one of said second pair of suspension units and the lower cylinder compartment of said one of said first pair of suspension units;
- a second pair of conduits, one of which interconnects the upper cylinder compartment of the other of said first pair of suspension units and the lower cylinder compartment of the other of said second pair of suspension units and the other of which interconnects the upper cylinder compartment of said other of said second pair of suspension units and the lower cylinder compartment of said other of said first pair of suspension units;
- a first fluid supply passageway communicating with the inlet ports of said first pair of suspension units;
- a second fluid supply passageway communicating with the inlet ports of said second pair of suspension units;
- a third fluid supply passageway hydraulically connecting said first and second fluid supply passageways to said source;
- a first drain passageway communicating with the outlet ports of said first pair of suspension units;
- a second drain passageway communicating with the outlet ports of said second pair of suspension units;
- a third drain passageway hydraulically connecting said first and second drain passageways to said reservoir;
- first electrically controlled normally open valve means disposed in said first fluid supply and drain passageways and operative to obstruct fluid flow through said first fluid supply and drain passageways when actuated to close;
- second electrically controlled normally open valve means disposed in said second fluid supply and drain passageways and operative to obstruct fluid flow through said second fluid supply and drain passageways when actuated to close;
- third electrically controlled normally open valve means disposed in said third fluid supply passageway and operative to obstruct communication between said source and said first and second fluid supply passageways when actuated to close;
- fourth electrically controlled normally open valve means disposed in said third drain passageway and operative to obstruct communication between said reservoir and said first and second drain passageway when actuated to close;
- a shunt passageway interconnecting said third fluid supply passageway and said third drain passageway in such a manner that the junction between said shunt passageway and said third fluid supply is located upstream of said third valve means and that the junction between said shunt passageway and said third drain passageway is located downstream of said fourth valve means;
- electrically controlled normally closed valve means disposed in said shunt passageway and operative to allow fluid flow through said shunt passageway when actuated to open;
- and
- in which said electrically controlled valve means are actuated such that hydraulic fluid under pressure is supplied to the upper cylinder compartments of the first and second pairs of suspension units through the outlet ports thereof from said source and thereafter hydraulic fluid in the upper cylinder compartments of one of the first and second pairs of suspension units is supplied to the lower cylinder compartments of the other pair.