Hydropneumatic suspension Hydractive III
Besides the original design, Citroen is also famous for its unique gas-liquid suspension system. The system is truly unique and provides suspension comfort that competitors at this price level can only dream of. It is true that the first generations of this system showed a higher failure rate, but the fourth generation used in the C5 I generation model, known as the Hydractive III, is pretty reliable except for a few details, and of course there is no need to worry too much about more high failure rate.
The first generation Hydractive first appeared in the legendary XM, where it replaced the previous classic hydropneumatic suspension. The hydraulic system combines hydraulics with complex mechanics. The next generation Hydractive was first introduced on the successful Xantia model, where it again underwent some improvements that led to increased reliability and comfort (pressure tanks with fall protection). The unique Activa system was also introduced for the first time in Xantia, where, in addition to a comfortable suspension, the system also provided the elimination of car tilts when cornering. However, due to the extreme complexity, the manufacturer did not continue development and did not make it to the C5.
The Hydractive III used in the C5 has been improved again, although it doesn't inspire much orthodox fans as it has undergone some simplifications and the electronics have become more widely used as well. The simplification is, in particular, that the main system is only responsible for the vehicle's suspension. This means that the brakes no longer operate according to the high pressure control principle and are connected to a hydropenumatic system, but are classic brakes with standard hydraulic distribution and vacuum booster. It's the same with the power steering, which is hydraulic with the addition of a pump driven directly from the engine. As with previous generations, the car's suspension itself uses a common reservoir of hydraulic fluid, but the red LDS instead of the green LHM that was previously used. Of course, liquids are different and do not mix with each other. Another difference between the Hydractive III and its predecessors is that it cannot automatically change the suspension stiffness from comfortable to sporty as standard. If you wanted this convenience, you had to pay extra for the Hydractive III Plus version or order a car with a 2,2 HDi or 3,0 V6 engine, for which it was supplied as standard. It differed from the basic system by two more balls, that is, it contained only six, three for each axis. There was also a difference in the interior, where there was also a Sport button between the arrows to change the ride height. The very regulation of stiffness occurs by connecting (soft mode) or disconnecting (harder sport mode) an additional pair of balls.
The Hydractive III system consists of a BHI (Built in Hydroelectronic Interface) control unit, pressure is provided by a powerful five-piston pump driven by an electric motor, independent of the engine running. The hydraulic unit itself consists of a pressure reservoir, four solenoid valves, a pair of hydraulic valves, a fine cleaner and a pressure relief valve. Based on the signals from the sensors, the control unit changes the pressure in the hydraulic system, which leads to a change in ground clearance. For comfortable loading of luggage or cargo, the station wagon version is equipped with a button in the fifth door, which further reduces the car's ground clearance at the rear. The C5 is equipped with hydraulic locks, which means the car does not lower after parking, as it did with older models. In truth, a lot of fans are missing this unique post-launch uplift. In the case of C5, there is no more spontaneous pressure leakage from the system and, moreover, if there is a drop after a long period of inactivity, the electric pump automatically replenishes the pressure when the car is unlocked, bringing the car to the exact position and ready to drive.
The extremely technical Activa system is no longer used in the C5, but the manufacturer has used electronics to add sensors to the hydropneumatics so that the control electronics can eliminate roll and roll to some extent, helping to drive a sportier or more agile car. crisis situations. However, this is definitely not for sports. The advantage of the hydropneumatic suspension is also in the change in ground clearance, that is, the C5 chassis is not afraid of even lighter off-road conditions. Manual or fully automatic ride height adjustment has only four positions. The highest is the so-called service, which is used, for example, when changing a wheel. If necessary, in this position, you can move at speeds up to 10 km / h, while the ground clearance is up to 250 mm, which allows you to overcome even more difficult terrain. In second place in height is the so-called Track, which is most suitable for driving on bad roads. In this position on the ground, it is possible to achieve a clear height of up to 220 mm at speeds up to 40 km/h. Another 40 mm lower is the normal position, followed by the so-called low position (Low). Both the working and lowering positions are only manually adjustable up to a driving speed of up to 10 km/h. The system usually operates in fully automatic mode, when exceeding 110 km/h on a good road reduces the ride height by 15 mm in front and 11 mm in the rear, which improves not only aerodynamics, but also the stability of the car. at high speeds. The car returns to the "normal" position when the speed drops to 90 km / h. When the speed drops below 70 km / h, the body increases by another 13 millimeters.
As already mentioned, the system is really reliable with regular and quality maintenance. This is also evidenced by the fact that the manufacturer did not hesitate to provide a worthy guarantee of 200 km or five years for hydraulics. Practice has shown that the suspension also works significantly more kilometers. Problems with springing, or rather with spring assemblies (balls), can be found on special shock absorbers even on small irregularities. The nitrogen pressure above the membrane is too low. Unfortunately, re-purging, as in previous generations, is not possible with the C000, so the ball itself must be replaced. A more frequent failure of the Hydractive III system was a small fluid leak from the rear suspension assemblies, fortunately, only in the early years, which was mainly eliminated by the manufacturer during the warranty period. Sometimes fluid also leaks from the rear return hose, which then needs to be replaced. Very rarely, but even more expensive, the ride height adjustment fails, the cause of which is a bad BHI control unit.
