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Hydropneumatics at the end: Citroën relies on a new chassis revolution

Citroen
Instead of hydropneumatics as once in the DS
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D he outcry among friends of the brand was after This decision became known in the middle of the year, because it removes a unique selling point of Citroën that has ensured unrivaled driving comfort for 60 years. The hydropneumatics has been part of the program since 1955, since the divine DS was given this special type of suspension - and enabled it to float like a sedan. But Citroën wouldn't be Citroën if the French didn't have a new, idiosyncratic technology up their sleeve. Citroën boss Linda Jackson has now revealed to the British magazine Autocar that the French will take over the legacy of hydropneumatics with a new, revolutionary suspension technology from 2017.

Chassis technology relies on hydraulic end stops

The new Citroën suspension technology is basically simple and relies on conventional suspension consisting of a shock absorber, a spring and a mechanical stop that adds two hydraulic stops that provide pressure and tension on both sides. The suspension works in two stages, depending on the load:

  • With light pressure, the spring and shock absorber jointly control the vertical movements and do not need the help of the hydraulic stops. Nevertheless, these have a function, since the engineers can achieve a greater spring deflection.
  • With greater pressure and greater relief, the spring and stop work together with the hydraulic stop, which is responsible for pushing or pulling. In contrast to a mechanical stop, which completely absorbs the energy but only partially reproduces it, the hydraulic stop absorbs the energy and dissipates it. There is no springback phenomenon.

The new chassis technology is to be offered in all segments and in all markets - from city cars to higher-quality models. In addition, the new suspension technology should be reserved exclusively for Citroën models as a unique selling point; it should not be used in other PSA models.

Balls instead of springs - gentle floating thanks to hydropneumatics

A short one Review of hydropneumatics: In short, as the name suggests, hydropneumatics combines a hydraulic system for damping with a pneumatic system for suspension. The core of the hydropneumatic system is nitrogen-filled'Spring balls' that are connected to the hydraulic system. Depending on the condition of the road surface and the degree of suspension, more or less pressure is exerted on the nitrogen filling via the hydraulic system.

Hydraulic fluid and nitrogen are separated from one another by a membrane. Depending on the wheel position and the compression of the system, sometimes more and sometimes less hydraulic fluid is required to keep the vehicle level always the same and to compensate for the road surface. This is ensured by a high-pressure pump.

Superior chassis and central hydraulics

The hydropneumatics is the otherwise common system of springs and dampers - depending on the pressure, the car height can be varied - so level control is already on board as standard. The driving behavior is litter-like and difficult to achieve with conventional systems.

In addition, Citroën also uses the existing hydraulic pressure system for the power assistance of the steering and the braking system. Although this increases the complexity of the hydropneumatics, it means a reduction in the number of components - for example, the servo pump and brake booster are no longer necessary.

By the way, the hydropneumatics are not as susceptible as is often claimed. It usually does its job for years without any major interventions outside of regular maintenance. The hydropneumatics can even temporarily compensate for a loss of pressure due to a leak in the system. The maintenance costs are only slightly higher due to the slightly increased maintenance effort. For used car buyers, the condition of the car is crucial.

Hydropneumatics saved Charles de Gaulle's life

A dramatic event proved the qualities of hydropneumatics. When the then French President Charles de-Gaulles was assassinated on August 22, 1962 in Petit-Clamart, he was able to escape thanks to his Citroën DS despite a blown rear tire - the hydropneumatics kept the car safely on the road and kept the level constant of the three wheels.

Mercedes and Rolls-Royce as licensees

Competitors have also recognized the advantages of hydropneumatics. The luxury car manufacturers in particular were quickly convinced of the increased comfort compared to a conventional chassis. Rolls-Royce /Bentley and Mercedes Benz were licensees of Citroën.

However, they used hydropneumatics in their luxury models Rolls-Royce Silver Shadow, Bentley T1 and T2 and Mercedes W116 (450 SEL 6.9) and W126 only for the chassis and level control - they did not dare to combine it with steering and brakes.

Hydropneumatics currently only available in one model

Currently, hydropneumatics are only available in Citroën C5, but there are many proven Citroën on the used market that are on the road with the unique chassis. Here areall Citroën with hydropneumatics:

  • 15CV (only on the rear axle)
  • Type H (only on the rear axle)
  • DS /ID
  • SM
  • GS /GSA
  • M35 (small series with Wankel engine)
  • CX
  • BX
  • XM ('Hydractiv' - for the first time with electronic control)
  • Xantia
  • C5 (for the first time with an electric instead of a motor-driven pump)
  • C6

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