Spherical suspense

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(Design Engineering, 13 February) surprised me inasmuch that there was no recognition given to Citroen which pioneered the Hydropneumatic suspension system on its revolutionary DS model in 1955.

This system basically comprised a steel sphere at each suspension strut containing a nitrogen-filled gas bag surrounded by high-pressure oil fed from a pump, and an accumulator to regulate the pressure.

Height sensors maintained a constant ride height regardless of load. A manual height-adjusting lever was also incorporated which would allow a wheel to be changed without having to use a jack. And all of this was achieved without the use of any electronics.

In 1989 Citroen unveiled the 'Hydractive' system, which had all the functions of the earlier set-up, plus the option of a driver-selected 'sport' setting which stiffened the suspension.

By this time the company was using electronics, which enabled the Xantia Activa model to quickly detect when it was being driven into a corner and actively control the suspension to reduce body roll to about a degree — however hard the vehicle was being driven.

Paul Scrase
Burgess Hill, West Sussex