Hydro-pneumatic suspension systems improve comfort and productivity of vehicles by isolating the vehicle’s chassis and cab - and thus the driver and the payload/implements - from the undesired vibrations from the ground.
According to many automotive experts, the automotive industry is owed to the designers and engineers of Citroën. The Citroën French company has today introduced many of the technologies and mechanical systems into the automobile world and has made the industry progress in different directions. One of the most significant inventions of this French company is Hydropneumatic Suspension. Hydropneumatic suspension is a type of motor vehicle suspension system, designed by Paul Magès, invented by Citroën. This system is the first type of Active suspension in the modern automotive industry. The system takes advantage of the fact that you can compress a gas but cannot compress a fluid. Thus gas acts as the springing medium while the hydraulic fluid does all the clever things such as providing damping and levelling. Unlike the hydrolastic system fitted to certain BMC and BLMC cars, the Citroën system relies on an engine-driven pump to pressurise the hydraulic system and it is this power source which enables self-levelling, variable ride height, assisted jacking and zero roll and also allows for fully powered braking systems and power steering too. Citroën first introduced this system in 1954 on the rear suspension of the Traction Avant. The first four-wheel implementation was in the advanced DS 19 in 1955.
How Hydropneumatic suspension works?
Hydro-pneumatic suspension systems improve comfort and productivity of vehicles by isolating the vehicle’s chassis and cab – and thus the driver and the payload/implements – from the undesired vibrations from the ground. This is done by hydraulic means – a cylinder and an accumulator act as a combination of spring and damper. With the regulation of oil fl ow and preload pressure an optimal suspension performance can be achieved. The health and safety directive 2002/44/EG implements high standards for the daily permissible vibration exposure to the driver. Particularly during off-road work, the usage of our hydro-pneumatic suspension extends the possible working time. It increases comfort and driving safety. At the rear the wheels were mounted on swinging arms joined to a stabilising torsion bar, which acted as a first spring. This was a radically different damping principle of the shock absorbers that gave the car its incredible stability. The shocks were filled with Lockheed-type hydraulic fluid, supplied under pressure from a seven-piston pump, belt-driven off the engine. Each of them was topped by a metal sphere that contained a rubber ball filled with inert gas and floating freely in the fluid. The shock-absorber piston was actuated by a lever at the pivoting end of the swinging arm (just under the stabilising bar). Its upstroke, acting through the fluid, compressed the gas-filled ball, damping out the initial shock; further damping was obtained by forcing the fluid through a series of calibrated openings. In the absence of coil springs or other solid supports, the rear of the car would ride entirely on the combination of gas and liquid. This explained the softness of the ride. It also meant that the car’s level and road clearance depended on the amount of pressure exerted on the fluid – but here uniformity was assured by a pressure regulator and an additional apparatus which automatically corrected any variations that may have occured. When the car remained stationary for some time, the driver turned a hand control on the dashboard; this locked up the pressure inside the suspension system and prevented the fluid returning to the reservoir via the recovery line, so that the car would not settle back on its haunches.