Hydropneumatic suspension
The purpose of this system is to provide a sensitive, dynamic and high-capacity suspension that offers superior ride quality on a variety of surfaces.
The suspension system usually features both self-leveling and driver-variable ride height, to provide extra clearance in rough terrain.
The principles illustrated by the successful use of hydropneumatic suspension are now used in a broad range of applications, such as aircraft oleo struts and gas filled automobile shock absorbers.
[1][2] The system was also used under licence by other car manufacturers, notably Rolls-Royce (Silver Shadow), Bmw 5-Series e34 Touring, Maserati (Quattroporte II) and Peugeot.
The purpose of this system is to provide a sensitive, dynamic and high-capacity suspension that offers superior ride quality on a variety of surfaces.
[4] The suspension system usually features both self-leveling and driver-variable ride height, to provide extra clearance in rough terrain.
[5] Hydropneumatic suspension has a number of natural advantages over steel springs, generally recognized in the auto industry.
[6] In a hydropneumatic system, gas absorbs excessive force, whereas liquid in hydraulics directly transfers force, which combines the advantages of two technological principles: Suspension and springing technology is not generally well understood by consumers, leading to a public perception that hydropneumatics are merely "good for comfort".
[citation needed] They also have advantages related to handling and control efficiency, solving a number of problems inherent in steel springs that suspension designers have previously struggled to eliminate.
First, it was patented by the inventor, and second it had a perceived element of complexity, so automakers like Mercedes-Benz, British Leyland (Hydrolastic, Hydragas), and Lincoln sought to create simpler variants using a compressed air suspension.
[10] France was noted for the poor quality of its roads after World War II, but the hydropneumatic suspension as fitted to the Citroën ID/DS and later cars reportedly ensured a smooth and stable ride there.
There have been many improvements to the system over the years, including steel anti-roll bars, variable ride firmness (Hydractive), and active control of body roll (Citroën Activa).
[17] Other modifications followed, with design changes such as the 1960 "Double stage oleo-pneumatic shock absorber" patented by Peter Fullam John and Stephan Gyurik.
The top is filled with nitrogen at high pressure, up to 75 bar, the bottom connects to the car's hydraulic fluid circuit.
Consequently, each time the suspension would rise, the fluid level in the reservoir dropped, drawing in fresh moisture-laden air.
Spheres are not subject to mechanical wear, but suffer pressure loss, due to the pressurised nitrogen diffusing through the membrane.
When Citroën designed their Hydractive 3 suspension they redesigned the spheres with new nylon membranes, which greatly slow the rate of deflation.
With no springing other than the (slight) flexibility of tyres, hitting a pothole with a flat sphere can bend the suspension parts or dent a wheel rim.
The principles illustrated by the successful use of hydropneumatic suspension are now used in a broad range of applications, such as aircraft oleo struts and gas filled automobile shock absorbers, first patented in the U.S. in 1934[31] by Cleveland Pneumatic Tool Co.
Sensors in the steering, brakes, suspension, throttle pedal and gearbox feed information on the car's speed, acceleration, and road conditions to an on-board computer, which in turn activates or deactivates an extra pair of suspension spheres on the circuit, to enable either a more smooth supple ride or tighter handling in corners.
Whenever the Hydractive 1 or 2 computers received abnormal sensor information, often caused by malfunctioning electrical contacts, the car's suspension system would be forced into its firm setting for the remainder of the ride.
Compared to earlier cars, the C5 stays at normal ride height even when the engine is turned off for an extended period, through the use of electronics.
Hydractive 3+ systems contain additional spheres that can be engaged and disengaged via a Sport button, resulting in a firmer ride.
