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What is the Citroën HYDRACTIVE system?
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Citroën cars are equipped with a hydractive suspension system. This system allows the car to automatically adjust to the road and driving conditions. However, there are advantages and disadvantages to this system. In this article, we explain everything you need to know about Citroën's hydractive system. What is his role ?
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What is the Hydractive system?
When we talk about optimal driving comfort, we always think of Citroën. The double chevron brand has always been ahead of its time when it comes to innovations related to comfort. Both in the passenger compartment and when driving and connecting to the ground.
The hydraulic spheres make it possible to absorb shocks and irregularities in the road surface while driving, as we saw in a previous article.
The term "hydractive" is actually an abbreviation of the term "hydropneumatic active". The principle of hydractive suspension adds an additional sphere per axle, further reducing the impression of rolling and obtaining better handling. We therefore go from 5 or 6 spheres to 7 or 8. It is by definition a system for modifying the state of the suspension when moving your car. It stiffens the chassis if necessary and allows you to turn completely flat.
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How does the hydractive (hydropneumatic active) suspension work ?
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Hydractive I
The 1st hydractive version appeared on the Citroën XM in 1989. This system makes it possible to obtain two suspension modes in the same vehicle. The rigidity of sports cars and the comfort of sedans. Just like competition vehicles, the hydractive system makes it possible to obtain a comfortable suspension while having the possibility of automatically modifying the suspension and anti-roll settings, when the Citroën finds itself in a situation which requires hard adjustments (blows of steering wheel, sharp turn or hard braking).
The flexibility and the damping rate are defined in such a way as to completely isolate the passengers from the shocks and vibrations of the road, adopting an oscillation frequency between 0.9 and 1.2 Hertz, while at the same time limiting the vertical accelerations a 0.25g (2.45m/s2). The passage from the "comfort" state to the "sporty" state is controlled by a computer, which acts directly on the suspension settings. This suspension is soft by default, so in comfort mode. When a shock occurs, the suspension switches to firm mode, then switches back to soft mode (in less than 3 seconds) when the disturbance has passed.
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Hydractive II
The improvements added compared to the first version are:
- 2 solenoid valves (front and rear), each directly integrated and connected to the stiffness regulators.
- a new calculator for switching from comfort mode to sport mode
- a flow regulator (with additional sphere on each axle)
- a steering wheel angle sensor
- a body displacement sensor, on the torsion bar
- 3 additional sensors (speed, brake, accelerator pedal)
- an on/off switch for the driver to manually control the mode change.
Installed as standard on the Xantia VSX (phase1), on the Exclusive (phase2), on all V6 and XM 2nd generation, from 1993. Its computing power is doubled compared to the hydractive 1, its response is 20% higher than the old model. That is a reaction of the stiffness regulators of 5/100th of a second! No more seasickness caused by the old version of the system!
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Hydractive III and 3+
The 3rd version of the hydractive system is the most successful. Installed on the Citroën C5 and C6 (on the V6, 2.2 HDi, 2.0 HPi and 2.0i 16V engines) in 2000, it consists of 3 spheres per axle, compared to 2 on the hydractive II system. Composed of an Integrated Hydro Electronic Block (BHI in French), this novelty incorporates an electronic box, an autonomous hydraulic pressure generator and an electric motor. The BHI controls the descent (therefore the center of gravity) of the vehicle by 15 mm past 110 Km/H, which allows the improvement of the stability of the vehicle, the reduction of consumption and the reduction of the sensitivity to side wind. the BHI also manages the vehicle in the high position (+ 20 mm) below 60 km/h with a deformed road surface. The ground clearance increases to allow more travel.
The hydraulic pump is abandoned to make way for an "electric pump-accumulator" unit. Assisted braking is replaced by hydraulic suspension fluid. LHM liquid is replaced by LDS (Synthetic Liquid). As for the Citroën C5 spheres and the Citroën C6 spheres, they become oval instead of round and change color (gray instead of green).
In short, your Citroën adapts its height automatically according to road conditions and/or your driving style. The hydractive III system takes the driver's driving style into account. It is therefore possible to personalize the comfort state/sport state transition threshold to achieve the right balance between flexibility and road holding. In addition, thanks to the manual switch, it is possible to activate the sport control in order to favor the firm mode, and therefore to optimize the sporty behavior of the vehicle. In comfort mode, the 3rd sphere cut off at the stiffness regulator is isolated for sports mode, or activated for comfort mode.
Note that, unlike the C5, on the C6 the hydractive system has taken some technologies from the activa system. This means that the damping allows up to 400 changes of state per second (the calculation is different for each wheel and a 4th sphere is fitted to the front and rear axles for more flexibility in soft mode).
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Hydractive or Activa ?
What is the "activa" system?
This is the hydractive system coupled with what Citroën has called the SC-CAR (Citroën Active Roll Control System). Your Xantia activa develops an instinctive side of directions. It can counteract centrifugal force in turns, without losing any balance or handling functionality. It therefore turns completely flat on difficult turns.
On the Xantia Activa, the hydraulic circuit had to be completely revised to integrate the SC-CAR system. The anti-roll bars are larger and firmer (diameter 28mm at the front instead of 22, and 25mm at the rear instead of 21). They are fixed to the suspension foot by a hydraulic cylinder. This SC-CAR actuator therefore erases the initial stiffness of the suspension. The Xantia Activa is able to withstand a lateral acceleration of 1.2g, against 0.9 for the best production vehicles of the time.
The SC-CAR system
The SC-CAR (Citroën Active Roll Control System) is one of a kind. Developed in 1994 on the CITROEN Xantia, this hydraulic device keeps the car horizontal to within 0.5 degrees, with the aim of improving road holding without affecting comfort. Thanks to two hydraulic cylinders, rolling in curves is eliminated, and the tires maintain maximum efficiency and an optimum grip coefficient.
Coupled with the Hydractive II system, the SC-CAR benefits from sensors and electronics, and shares the same computer. However, the comfort/sport management of the hydractive is independent of that of the SC-CAR despite the common computer. In a straight line, the famous SC-CAR actuators (which we mentioned above) provide the rigid anti-roll bars with the flexibility they lack to maintain comfort by introducing a sphere calibrated at 30 bar into the circuit which acts as a spring. When cornering, the SC-CAR sphere is isolated from the cylinders and the anti-roll bars become rigid.
Common points and differences between hydractive and activa:
- Both have a 62 bar accumulator RP62DP
- The 2 also have 2 basic front and rear suspensions
- The hydractive vehicles have 7 or 8 spheres, the activa has 9 or even 10.
- The hydractives have 2 stiffness regulators (front and rear) when the activa has a front and rear anti-roll.
- In both cases, the 50 bar rear anti-sag (A50RU) is optional
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How do I know if my vehicle is hydractive or not?
There are several methods to know if your vehicle is hydractive or not. The first is to check the number of spheres on your vehicle:
- assembly 5 or 6 spheres: it is a non-hydractive.
- assembly 7 or 8 spheres: it is a hydractive.
The second method consists of looking at the diameter of the hoses which reach the front suspension spheres in the engine compartment.
If the diameter is about 3 mm, it is not a hydractive:
On the other hand, if the diameter is about 8 mm, it is a hydractive:
(pictures found on forum-auto.com).
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How do I know if the Xantia or XM spheres are HS?
Do you have the impression that your Citroën spheres have a problem? Your handling is no longer the same or your hydractive suspension is hardening? So it may be time to check and/or change the spheres of your car. To understand their fault, their condition and how to replace them, see our article entirely devoted to the maintenance of CITROEN suspension spheres.
The maintenance of the hydractive system must be scrupulous. If the hydraulic pressure is completely drained, your Citroën will be completely blocked and will no longer be able to drive.
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Where can I find new spheres / hydraulic suspensions for my Citroën C5 hydractive 3?
At www.sphere-discount.com, you will find a wide choice of hydraulic spheres for Citroen C5 Hydractive 3 or 3+
Do not hesitate to call on our teams for as much information as possible and the choice of the right product. Our contact details appear at the bottom of each of our pages.
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I am looking for spheres for my Citroen C6?
Of course, you just need to follow the following link to get satisfaction! A complete range of quality spheres at terribly low prices: Spheres for CITROEN C6
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I need LDS or LHM type hydraulic fluid:
The hydraulic circuit consists of approximately 4.8 liters of fluid. Whether LHM or LDS, your hydractive system needs it! You will find everything you need in our special category entirely dedicated to hydraulic fluids for CITROEN. In 1L or 5L packaging, our quality products are at your disposal. Order now!