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The Citroën Guide Suspension: Hydractive II 29
Hydractive II
The second incarnation of the hydractive suspen
-
sion appeared at February 1, 1993 (ORGA 5929).
It was designed to overcome the biggest problem
of the previous system, the very uncomfortable
hard mode.
Switching to Sport does not mean sticking to a hard, un
-
comfortable ride any more. On the Hydractive II, the rela
-
tion between suspension modes and dashboard switch set
-
tings became more complicated: in both settings—Normal
(the new name of Comfort) and Sport—the computer can
switch to both hard and soft mode as it finds it necessary,
however, when set to Sport, the suspension becomes more
sensitive and will sooner and more often switch to the hard
mode.
1
2
3
4
Many models were also fitted with an anti-sink system
that locks the system when the car is not running, using yet
another sphere. Its only purpose is to keep the car from sink
-
ing when not used, it does not influence the functioning of
the suspension system in any way.
The layout of the system (front suspension)
The center sphere circuits and supports were redesigned:
they now house the electrovalves and the internal conduits
serving the sphere were modified as well; the new control
blocks connect, as previously, to the left and right corner
spheres, the height corrector, and—depending on the con
-
trol signal coming from the suspension computer—the cen
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ter sphere. The elements are practically the same as on
Hydractive I:
1
A sphere base;
2
A hydraulically controlled isolation valve;
3
A ball and piston valve;
4
Two damping elements;
5
An electrically controlled valve driven by the suspen
-
sion computer.
The front and rear suspension circuits are identical but hy
-
draulically independent. The electro-valves are driven simul
-
taneously, in parallel.
Trapped among pistons
The electro-valve 5 is energized when the suspension is in
its soft mode, hence, the default electrical position is hard.
However, due to the indirect coupling between this valve
and the isolation piston 2 inside the control block, the hy
-
draulics can stay in either position for extended periods of
time with the electric valve disconnected, depending on the
pressure differences between the strut and the main cir
-
cuits. If the main suspension circuit has nominal pressure,
the system stays in hard mode with the electric valve off or
disconnected.
The two modes are practically the same as on the previ
-
ous Hydractive system: in soft mode the electro-valve 5
opens the feed pressure onto the isolation piston 2 and by
moving it, connects the center sphere 1 to the rest of the
suspension. In hard mode, the electro-valve 5 closes and
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