THE MAGIC CAR­PET RIDE

Six decades of tech­ni­cal in­no­va­tion comes to an end

Practical Classics (UK) - - CLASSIC WORLD -

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’.

Un­der pres­sure

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.

FLUID PART­NERS

Hy­dro oil by To­tal was de­vel­oped to en­sure healthy pipes and seals.

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