Leisure-Drive: #2 Citroen's Hydropneumatic Suspension

There are two main component which give rise to the hydropneumatic suspension:

Characteristic of both fluid used as the dampening agent:
- Nitrogen, which has a unique progressive characteristic. The harder pressure exerted on it the greater its dampening rate.
- LHM (Liquide Hydraulique Minéral), a non hygroscopic mineral oil (would not absorb moisture). Eliminating tiny bubbles that could be formed by prevailing heat and thus there is no spongy brake feeling. LHM is the recirculating agent which responsible for primary absorption on each wheel.
The green spheres as many as five units which regulate the fluid pressure through out the entire system. Each sphere has incorporated the interaction between both Nitrogen and LHM fluids. In order to regulate the pressure, the main sphere is normally driven by the engine.

Since the pressure is interactively maintained, it could be used further to equalize braking load. Say a heavy laden car would automatically get greater breaking pressures at the rear wheels, at the same brake pedal effort as an empty car would. This feature is available through out DS (late 1960s) to the compact GS model (1973 - 1983).

The feature extends further to maintain power steering effort and to maintain steering direction. Today we know electronic controlled speed sensitive power steering, as the speed rises the more effort is required to turn the wheel. The steering features are both introduced in SM model (1970 - 1974), the only Citroen car powered by 90 degrees angled V6 Maserati engine.

All Citroen cars also feature adjustable clearance height. The magic carpet ride prevails under normal driving condition. As the terrain requires higher clearance, there are two higher height adjustments by merely shifting a lever from inside.

As the car is parked overnight, its height decreases significantly. All wheels are fully concealed beneath their respective wheel arches, it looks as though hugging the ground. Parking on the level ground is a must, any object beneath the floorpan may damage its undercarriage. Once the engine is started the self levelling system gradually accumulate pressure and thus some height clearance as well, only then the car could be driven away. Thief chasing police would have a hard time to catch one!