Hydractive 3 - CITROEN DS series Technical Manual

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The Citroën Guide

Hydractive 3

The new C5 has a new suspension system, doing
away with many solutions used on Citroëns for
several decades, yet offering the same or even
better comfort than before. Recent developments
in electronics and computics made it possible to
delegate many functions previously solved by me-
chanical-hydraulical components to electronic
units.
This third generation suspension system retains the same
basic functioning as the previous systems. It also comes in
two flavors: a simpler Hydractive 3 reminiscent of the origi-
nal hydropneumatic suspension of the DS–GS–BX–CX and
a slightly more complicated Hydractive 3+, building upon
the former Hydractive I and II (actually, Hydractive 3 is not
hydractive in the sense we used this term before, its only
special activity is to adjust the road clearance depending on
speed and road condition).
Although the basic functioning is practically the same,
the actual layout underwent significant changes. Most im-
portantly, the previously mechanically operated height
correctors became electronically controlled hydraulic units.
And all hydraulic units except for the spheres—which were
redesigned to give unlimited life expectancy—are now
housed in a single unit, the Built-in Hydroelectronic In-
terface (BHI). This compact unit has three main parts:
U the high pressure for the new synthetic fluid (called LDS,
orange in color) is generated by a five-piston hydraulic
pump 1, driven by an electric motor (rotating at 2,300
rear strut & sphere
Engine ECU
height setting
button
instrument
panel
doors and
tailgate
Sport switch
(3+ only)
brake
rear strut & sphere
Suspension: Hydractive 3
ABS ECU
BSI
LSD feed
front suspension
rear suspension
operational return
leakage return
rpm) operating independently of the engine, running
only when necessary;
the hydraulic units, including an accumulator 2 to even
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out the pressure pulsations of the pump, four electro-
valves 3 and 4 and two hydraulic valves 8 serving the
height regulation and anti-sink behavior, some in-line fil-
ters 5 and an overpressure valve 7 (taking the role of the
pressure regulator of previous systems).
the electronic computer 6, communicating with other
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computers across the multiplex network to read the in-
puts of various sensors and to control both the HP pump
motor and the electrovalves.
In contrast to the height correctors of previous systems, op-
erated mechanically via a linkage coupled to the anti-roll
bars, the new system used electronic sensors to learn the ac-
tual height of the suspension and electric actuators to mod-
ify the ground clearance whenever needed. The main advan-
tage of using them is that the ECU can implement very so-
phisticated algorithms to derive and apply height correc-
tion, what were impossible with the mechanically linked
feedback with simple thresholds.
The computer 6 is connected to the CAN multiplex net-
work, providing access to the messages sent by the BSI and
its fellow computers controlling the engine and the ABS.
The inputs the suspension ECU uses comprise of rear and
front body height, brake pedal, vehicle speed and accelera-
tion, open-closed status of the doors (including the tail-
gate), plus the steering steering wheel angle and rotating
speed on the Hydractive 3+.
steering wheel rear
angle sensor height
(3+ only) sensor
6
5
3 4
5 5 5
7
anti-sink valves???
inlet valves with non-return valve???
front
front strut & sphere
height
sensor
5
4 3
BHI
5
1
2
reservoir
front strut & sphere
35