Hydropneumatic

Hydropneumatic is the name given to a suspension system invented by Citroën and fitted to Citroën cars, as well as being adapted by other car manufacturers, notably Mercedes-Benz and Peugeot. It was also used on Berliet trucks. Similar systems are also used on some millitary vehicles.

Related Topics:
Suspension system - Citroën - Mercedes-Benz - Peugeot - Berliet

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This system uses a belt driven pump from the engine to pressurise special LHM fluid around the hydraulic system to the brakes, suspension and power steering.

Related Topics:
Brake - Power steering

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It can also power any number of features such as the clutch, turning headlamps and even power windows.

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LHM stands for Liquide Minéral Hydraulique and is a mineral oil, quite close to automatic transmission oils. The suspension setup is referred to as 'oléopneumatique' in early literature, pointing to oil and air as its main components.

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As well as powering the brakes, the suspension system features self-leveling and variable ride height. The height can be set in an extra high position to facilitate wheel changing, or just raised mode to give some off-road ability.

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There have been many improvements to this system over the years, including variable ride firmness and active control of body roll. The latest incarnation features single pump-sphere combinations on each wheel.

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