Suspension Explanation - CITROEN XM Internet Reference

Suspension

86 Suspension Explanation

86 Suspension Explanation
Citroen hydractive suspension
Citroen was a pioneer of sophisticated suspension design, launching their
unique self-levelling hydropneumatic system on the DS model of 1955.
Hydropneumatic suspension works on the principle of having a nitrogen gas
spring (very similar in construction to the accumulator used in an ABS
actuator unit) connected to the suspension arm by means of a hydraulic ram.
The ram can be lengthened or shortened (and hence the ride height altered)
by changing the pressure of the fluid supplied to it. Pressurized fluid is
provided by an engine-driven pump and supplied to each spring through a
network of small-diameter pipes. Pressure, and therefore ride height, is
regulated by mechanical control valves that sense the body-to axle
displacement at each end of the vehicle and distribute the fluid
accordingly.
Although hydropneumatic suspension was a spectacular success when first
launched, its superiority became less evident as conventional suspension
systems were progressively improved. To restore the appeal of their
hydropneumatic system, Citroen took the decision to add computer control.
This system, first seen on the XM model, is called Hydractive suspension. It
gives exceptional ride comfort, combined with precise wheel control when the
need arises.
Hydractive operation
The major components of the Hydractive system are illustrated in Figure
7.24. It is a semi-active suspension system that offers two spring rates
('Sport' and 'Comfort') and two damping forces ('Soft' and Firm').
Hydractlve uses hydraulic rams acting on, nitrogen gas springs. The big
difference is the inclusion of a third gas spring for each axle. During
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