THE MAGIC CARPET RIDE
Six decades of technical innovation comes to an end
André Citroën’s legacy was bolstered by his successor, CEO Pierre Boulanger, who made his intentions clear in 1937: ‘Study all possibilities. Even the impossible.’ Five years later, he introduced designer Paul Magès to aeronautical engineer André Lefebvre and sculptor Flaminio Bertoni (the stylist responsible for the Traction Avant, 2CV, H Van, DS and Ami 6). Paul’s design brief was to enable ‘fast travel on poor road surfaces.’
What he came up was a high-pressure gas and oil system, enabling suspension, steering, brakes, clutch and gearshift to work in harmony and operating from an engine-driven pump. With a conventional spring having the same stiffness whether compressed or not, it was realised the harder gas is compressed, the stiffer the spring becomes. It was known as ‘infinite rising rate suspension’.
The concept was actually quite simple, according creator of
Citroënet.org, Julian Marsh: ‘The nitrogen gas acts as a spring and is housed in a metal sphere at each wheel, each of which contains a flexible diaphragm. When a wheel hits a bump, it rises and via a mechanical link it pushes the suspension piston back and this squeezes fluid through a tiny hole (effectively a damper valve) in the sphere to let the gas absorb the energy of the bump. Once the car is over the bump, the gas pushes the diaphragm back out, pushing the fluid down and thereby pushing the wheel down to the ground.’
There’s a fifth sphere, known as the accumulator, which
evens out pressure caused by whichever part of the system is being used at that time – be it steering, brakes or suspension. It also acts as a pressure reserve if engine power is lost.
Additional features of the system include automatic ride height. Corrector valves respond to the road surface or load by letting more fluid into the suspension cylinders. Both SM and CX (and LHD XMS) got fully powered (not power assisted) self-centring steering which varied in weight, depending on speed.
All of this was made possible by the bright green Liquide Hydraulique Minéral (LHM) fluid – the lifeblood of any hydro-citroën. It was developed by the company with Total Lubricants and unlike standard brake fluid, it’s non-corrosive and hydrophobic.
Coupled with new innovations such as adaptive headlights, plastic bodywork panels and fingertip interior ergonomics, Citroën was decades ahead with technology now in widespread use across the industry. The impossible had become possible.
Hydro oil by Total was developed to ensure healthy pipes and seals.