ONE: CITROËN AT THE GENEVA MOTOR SHOW: THIRD-GENERATION HYDRACTIVE TECHNOLOGY

Innovation in suspension systems

• Electronically controlled hydraulic suspension
• Changes its settings to the driving style and road conditions automatically
• Automatically lowers the car at speed and raises it on rough roads
• No suspension servicing for five years or 200,000 km

Citroën is demonstrating its new Third-Generation Hydractive suspension for the first time at the 2000 Geneva Motor Show.

Click this banner for a large image showing the 3rd Generation Hydractive Suspension system

The new suspension incorporates a range of innovations that enhance comfort and roadholding while illustrating Citroën's expertise in running gear technology.

Combining the latest developments in electronics with a revised and simplified hydraulic architecture, Third-Generation Hydractive sets new standards in efficiency, reliability and comfort.

Controlling vehicle movement at any speed and on any type of road surface, Third-Generation Hydractive keeps a reassuringly stable and firm grip on the road to ensure passenger comfort. Endowed with new electronic sensors linked by the multiplexed network to the built-in systems interface (BSI), the new "auto-adaptive" suspension is able to make a precise analysis of the state of the road and the driving style of the person behind the wheel. The suspension system packs considerable computing power but it functions in a natural and logical way.

Click this banner for a large image showing the height variations of the 3rd Generation Hydractive Suspension system

The driver has a choice of two settings: comfort or dynamic. Each setting is managed independently by the smart suspension system, which varies flexibility and damping simultaneously. Third-Generation Hydractive is uncompromising in its quest for superlative roadholding and comfort. Moreover, the driver can activate the sports setting manually in order to switch more frequently to dynamic mode, and to remain in this mode for longer periods.

This new suspension features an innovative function: the height of the vehicle varies automatically according to its speed. This function enhances stability by lowering the centre of gravity by 15 mm and reduces consumption by improving CdA. On badly damaged road surfaces, Third-Generation Hydractive can increase vehicle height by 20 mm.

The driver can also modify clearance manually by means of an electronic push button.

Third-Generation Hydractive is also exceptionally reliable, thanks to a number of new structural parts including a built-in hydroelectronic unit, a nerve centre that regulates and manages the pressure of the hydraulic system and also controls the suspension. This unit is dedicated to the suspension system., the suspension spheres, which are built using new technology, gain an exceptionally long service life. The fluidity of the new synthetic hydraulic fluid reduces friction. A system of innovative design, Third-Generation Hydractive requires no maintenance for the first five years or 200,000 km.

Third-Generation Hydractive illustrates Citroën's commitment to enhancing customer benefits. Responsive, reliable and robust, Third-Generation Hydractive combines superlative comfort with maximum safety.

THE ALLIANCE OF ELECTRONICS AND HYDRAULICS

Citroën has always excelled in its ability to strike the balance between roadholding and comfort. With Third-Generation Hydractive - a hydraulic suspension system of completely revised architecture and parts - the Marque has taken a new step forward in its quest to improve active safety and driving pleasure.

Third-Generation Hydractive suspension comprises:

• a built-in hydroelectronic unit, at the heart of the system, comprising a powerful electronic unit, a stand-alone hydraulic pressure generator and an electric motor,
• four carrier elements with new suspension spheres,
• front and rear stiffness regulators with their sphere,
• electric height sensors linked to the anti-roll bars,
• a fluid reservoir,
• a simplified hydraulic network with new-generation connections.

This innovative and simplified design is based on the alliance of advanced electronics and hydraulics in the hydroelectronic unit. Third-Generation Hydractive is the first suspension system to offer two settings (comfort/dynamic) adapting automatically to vehicle speed and the state of the road, and requiring no maintenance for the first five years or 200,000 km.

Third-Generation Hydractive adapts automatically, instantly and continuously to the occupant's driving style and to the state of the road. The system adapts damping force and flexibility through its two settings: comfort suspension and dynamic suspension. Each axle is equipped with a third sphere and a stiffness regulator. The operating principle of the hydractive system is to isolate the third sphere in dynamic mode or to bring it into service in comfort mode. To do this, the system receives data from the height sensor and steering wheel sensor and also from the multiplexed network, which supplies information on brake pressure and engine speed.

Through the real-time management of these two settings, the system is able to control roll, pitch, heave and yaw. Moreover, the longitudinal and transversal acceleration values calculated by the built-in hydroelectronic unit are collected and filtered over a period of around one minute. The self-adapting suspension is thereby able to define the criterion of "driving style". For a dynamic style of driving, the suspension will adopt the dynamic setting more frequently, thus providing a customised response.

The driver can choose to give priority to the dynamic setting (sports position) by means of a button on the driver's station.

Third-Generation Hydractive offers a range of new functions. For example, it automatically adapts the height of the vehicle according to its speed and the state of the road.

Designed to increase comfort and safety in all circumstances, this innovation adapts the vehicle height as required. Three levels exist:

• In towns and on well surfaced roads at speeds of up to 110 km/h, the vehicle remains at the reference height.
• On well surfaced roads at speeds of above 100 km/h the built-in hydroelectronic unit lowers the vehicle by 15 mm. In this way, it improves stability by lowering the centre of gravity and cuts fuel consumption by reducing the CdA of the projected frontal area and so lessening sensitivity to side winds. The vehicle returns to its reference height for a speed of less than 70 km/h.
• When the road surface is uneven, the built-in hydroelectronic unit raises the vehicle in order to increase clearance while continuing to optimise roadholding and comfort. On badly damaged road surfaces, vehicle height is increased by 20 mm provided that it is travelling at a speed of less than 60 km/h.

To determine the most suitable vehicle height, the built-in hydroelectronic unit uses information on speed, height and movement. The car is raised or lowered by adding or withdrawing hydraulic fluid in the suspension system.

Vehicle height can also be controlled manually by the driver. An electronic push button offers four positions:

H: high position to change a wheel
P: a position to clear obstacles at low speed. In this case, clearance is increased by 40 mm.
N: reference position
B: low position for loading or hooking up caravans or trailers.

The selector switch automatically returns to position N as soon as the car reaches a speed of 10 km/h.

Third-Generation Hydractive Suspension maintains the advantages of hydraulics such as, for example, the constant reference height, whatever the vehicle load.

Characteristics of the suspension system
The built-in hydroelectronic unit combines hydraulics with advanced electronics. This highly compact unit comprises three parts:

An electronic unit with a host of control laws stored in its memory, controlling the electric motor and the stand-alone pressure generator in accordance with the information delivered by:

• two new electric height sensors positioned on the front and rear anti-roll bars, which precisely measure variations in the body's height and speed of movement,
• a sensor measuring the steering wheel angle and velocity of angular displacement,
• the multiplexed network and built-in systems interface (BSI) concerning the speed at which the accelerator pedal is pressed down or released, vehicle speed, pressure on the brake pedal and engine speed.

An electric motor driving the pump in the stand-alone pressure generator. It comes into service solely when required, at rotation speeds of 2,300 rpm.

A stand-alone pressure generator designed to group flow, safety and anti-dive/anti-squat functions, and equipped with a pump and four electrovalves.

The five-piston pump supplies fluid (0.7 l/mn at 2,300 rpm) and operates at pressure of between 80 and 140 bars. At the end of the pump, a hydropneumatic accumulator shaves pressure pulsations and minimises operating noise.

The front and rear suspension circuits each have two electrovalves, one dedicated to intake and the other to exhaust of hydraulic fluid. Only the exhaust electrovalves are equipped with a non-return valve for the anti-dive/anti-squat function. Electromagnetic power ensures a virtually instantaneous switch (15 ms).

The spheres are fitted with new multi-layer diaphragms that are not nitrogen-permeable. The pressure of the nitrogen (calibration) in the spheres therefore remains constant over time, ensuring that the suspension maintains all its properties.. The new exterior shape of the spheres (modified diameter/height ratio) has been optimised by computer calculations for a longer service life.

The new hydraulic fluid is 100% synthetic. This composition gives it long-term stability while maintaining a high level of viscosity (low friction).

Third-Generation Hydractive uses high-quality parts that require no maintenance for the first five years or 200,000 km.

For further information please
e-Mail Miles Williams - General Manager on
100250.3324@compuserve.com

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