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Hydractive 3

At the Geneva Motor Show in March 2000, CitroŽn announced details of the new Hydractive 3 suspension system which has subsequently been fitted to the Mk 1 C5, the top of the range C6 and the current C5.

Characteristics of the suspension system

The built-in hydroelectronic unit combines hydraulics with advanced electronics. This highly compact unit comprises three parts:

An electronic unit with a host of control laws stored in its memory, controlling the electric motor and the stand-alone pressure generator in accordance with the information delivered by:

  • two new electric height sensors positioned on the front and rear anti-roll bars, which precisely measure variations in the body's height and speed of movement, 

  • a sensor measuring the steering wheel angle and velocity of angular displacement, 

  • the multiplexed network and built-in systems interface (BSI) concerning the rate at which the accelerator pedal is pressed down or released, vehicle speed, pressure on the brake pedal and engine speed. 

An electric motor driving the pump in the stand-alone pressure generator. It comes into service solely when required, at rotation speeds of 2,300 rpm.

A stand-alone pressure generator designed to group flow, safety and anti-dive/anti-squat functions, and equipped with a pump and four electrovalves.
The five-piston pump supplies fluid (0.7 1/mn at 2,300 rpm) and operates at pressure of between 80 and 140 bars. At the end of the pump, a hydropneumatic accumulator regulates pressure variations and minimises operating noise.
The front and rear suspension circuits each have two electrovalves, one dedicated to intake and the other to exhaust of hydraulic fluid. Only the exhaust electrovalves are equipped with a non-return valve for the anti-dive/anti-squat function. Electromagnetic power ensures a virtually instantaneous switch (15 ms).

The spheres are fitted with new multi-layer diaphragms that are not nitrogen-permeable. The pressure of the nitrogen (calibration) in the spheres therefore remains constant over time, ensuring that the suspension maintains all its properties.. The new exterior shape of  the spheres (modified diameter/height ratio) has been optimised by computer calculations for a longer service life.

The new hydraulic fluid is 100% synthetic. This composition gives it long-term stability while maintaining a high level of viscosity (low friction).

Third-Generation Hydractive uses high-quality parts that require no maintenance for the first five years or 200,000 km. 

© 2000 Julian Marsh