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Citroën Xantia Activa in action

Anti-roll suspension  

Between February 1955 - barely six months after the launch of the DS - and November 1968, six DS were successively fitted with anti-roll suspensionsystems and covered more than 6 000 km.  The studies were intended to improve on both comfort and roadholding (neither of which could hardly be called bad!) compared to the production car. 

The two pictures above demonstrate the system in action - the car on the left is a normal production vehicle, the one on the right is fitted with antiroll - same bend, same speed.  The picture on the right gives little indication of the speed - until you notice how the left front tyre is deformed.

The system could have been put into production in the late sixties but the team was forced to abandon its research to concentrate on the soon-to-be launched GS.  A prototype SM with zero roll suspension was also developed in 1973.

Paul Magès had intended such a system to be part of the design of the suspension system and as early as 1944, he had sketched just such a system, a derivation of which was fitted to a prototype 2CV in 1946.

It was not until the launch of the Xantia Activa below that such a system was put into production
1  Steering wheel angle
2  Rate of steering wheel rotation
3  Vehicle velocity

A  High pressure pump
B  Anti roll regulator
C  Electro valve
D  Regulator
E  Activa accumulator
F  Front stabiliser cylinder
G  Rear stabiliser cylinder
H  Stabiliser
I  Suspension computer


1. Front stabiliser bar

2. Front stabiliser (anti-roll) bar


3. Rear stabiliser cylinder (hydraulic ram)

4. Rear stabiliser (anti-roll) bar

5. Rear stabiliser (anti-roll) bar

6. Rear stabiliser cylinder (hydraulic ram)

Other developments 

Electro-hydraulic gearbox
Anti-roll suspension was not the only project being developed by Paul Magès' team.  Amongst the ideas being contemplated were electro-hydraulic control of the gearbox which employed electronics to change gear, making use of the following parameters: vehicle speed, engine speed, throttle depression and rate of throttle movement.  The result was an improvement of 10% in economy and improved performance.  This project never made it into production.
Hydrostatic transmission
Hydrostatic transmission was yet another idea that was abandoned.  As early as1908, Louis Renault had proposed just such a system.  The idea is relatively simple; the engine drives a pump which sends fluid under pressure to four hydraulic pumps in each wheel hub.  There is no need for different gear ratios and transmission is therefore continuous, the clutch being dispensed with also.  Furthermore there was no need for a separate braking system.  Magès and his colleagues worked on this project for twenty eight years and some thirty prototypes were fitted with the system (2 CVs, GSs and a CX) between 1958 and 1973 and covered a total distance of 1 130 000 km.  However there were major problems with noise and when Peugeot took control in 1974, the project was killed off. Hydrostatic transmissions are used in vehicles such as forklift trucks and some specialist earth moving vehicles.
1. hydraulic pump
2. hydraulic motors
3. hydraulic pipes - forward rotation
4. hydraulic pipes - backwards rotation
5. conventional engine
Joystick steering
Magès also worked on the project that led to the DIRAVI steering system - powered return of the wheel to the straight ahead position coupled with both variable ratio (movements around the straight ahead position result in small deflections while moving away from this position results in larger deflections) and variable assistance (as velocity increases, assistance diminishes).  A DS was fitted with a system which was 100% assisted and the steering wheel was replaced with an aircraft type joystick - one steered with tiny movements of a finger and with one's eyes.  It was felt that despite the undoubted advantages such a system would offer (unrestricted view ofthe instrument panel and removal of the injury potential of a wheel and column), the clients would dislike it.
Hydraulic motors
Hydraulic motors weigh one sixth of an equivalent electric motor.  Since the DS was already fitted with a high pressure hydraulic system, it was logical to look at other applications including an hydraulically powered cooling fan (30% reduction in weight and 30% reduction in radiator volume, thereby freeing up some much needed under bonnet space and allowing the radiator to be mounted at an angle); hydraulically powered windscreen wipers which had much higher starting torque than electric ones and could be steplessly variable in speed; an hydraulically powered alternator which would supply power on demand; hydraulically powered window lifters, hydraulically powered starter motor...

...and probably most bizarre of all, a roof mounted, hydraulically powered air brake which not only employed wind resistance to slow the car but also increased the rear wheel downforce thereby reducing the tendency for the rear brakes to lock up.  As early as the beginning of the sixties, an anti-lock braking system had also been perfected.

©1999 Julian Marsh