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The Citroën Guide Suspension: Hydractive 3 36
As usual with Citroëns, the driver can select from four
height settings (although the selector is no longer mechani
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cally coupled with the hydraulics, it is a simple electronic
switch sending signals to the computer): high, track (plus
40 mm), normal and low. The selected setting is displayed
on the multifunction screen in the dashboard. The com
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puter also prevents unsuitable settings being selected. The
high option is not available when the car is traveling faster
than 10 km/h and neither track nor low mode can be se
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lected above 40 km/h.
In addition to the manual settings, the system adjusts
the ground clearance automatically. Below 110 km/h on
well surfaced roads the ride height remains standard but as
soon as this speed is exceeded, the vehicle will be lowered
by 15 mm at the front and 11 mm at the rear. This change
lowers the center of gravity, improving stability, lowering
fuel consumption (by reducing drag) and reducing the sen
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sibility to crosswinds. The car resumes the standard ride
height when its speed drops below 90 km/h.
On poorly surfaced roads (the computer learns about
the road quality by monitoring data on vehicle speed,
height and movement of the suspension) the ride height
will be increased. The maximum increase would be 20 mm
but this setting is only used on very poor roads and with the
vehicle traveling below 60 km/h.
The general height of the vehicle (filtering out rapid
movements due to suspension travel) is checked, and if nec
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essary, adjusted every 10 seconds and when any of the
doors is opened or closed (even with the ignition switched
off).
Hydractive 3+
Just like its predecessor, this system also has two modes,
firm and soft. A stiffness regulator—an additional
sphere and a hydraulic control block per axle—isolates or
connects the corner and center spheres. Its functioning is
practically equivalent to the similar control block of the
Hydractive II: the computer controlled electro-valve 4
opens the feed pressure onto the isolation piston 2 and by
moving it, connects the center sphere 1 to the rest of the
suspension, switching the suspension to soft mode. of the
suspension. Closing the electro-valve 4 obstructs the hy
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draulic supply coming from the BHI; the residual pressure in
the center sphere 1 moves the isolation piston 2 down
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wards into a position which closes off the center sphere
completely: the suspension switches to hard mode.
The suspension has two settings the driver can choose
from, Normal and Sport. The new stiffness regulators to
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gether with the center spheres are isolated in hard mode
and re-activated in soft mode in response to the various in
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puts received and processed by the suspension ECU. The
functioning of the computer is basically similar to the
Hydractive II ECU: it uses tables and rules to set up thresh
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olds on the value on many sensor inputs to determine when
to switch to hard mode. Just like on its predecessor, the
Sport setting does not mean constant hard mode, just low
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ered, more sensitive thresholds for the switching.
The computer observes the following input parameters:
the height and sport settings specified by the driver (com
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municated by the BSI); the vehicle speed and the longitu
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dinal-lateral acceleration of the body (communicated
on the CAN), the angle and speed of rotation of the
steering wheel (the type of the sensor depends on
whether the car is equipped with ESP, in this case the sensor
connects to the multiplex network instead of directly to the
suspension ECU), the speed of suspension travel (using
the values of the front and rear height sensors), the open-
closed status of the doors (communicated by the BSI) and
the movement of the accelerator pedal or butterfly.
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