The Citroën C5 is an all-round innovator, featuring new solutions in the key areas of safety, comfort, driving pleasure, environmental sensitivity and running costs.
With respect to active safety, note the 3rd generation Hydractive suspension, ABS anti-lock braking, ASR accereration slip reduction, assisted emergency braking, the low tyre pressure warning sensors and the lively, responsive nature of the engines and semi-automatic sequential transmission.
To provide maximum passenger protection, the C5 is based on a new platform incorporating:

• six airbags of which two at the front adapt to the violence of impact,

• front and rear seatbelts with force limiters,

• front doors with impact bars and padding.

For comfort and driving pleasure, note the spacious cabin, the multiplex electronic circuitry and the additional functions it provides, the damping of vibration and noise, and 'of course' the engines and sequential automatic gearbox.
Citroën's commitment to protecting the environment is reflected in the presence of a particle filter (on models fitted with the 2.2 HDi engine), reduced fuel consumption, lower CO2 emissions (all engines) and the use of recycled materials.

Technical characteristics

Running gear

The C5 has a new suspension system combining advanced electronic and hydraulic technology

Highlighting significant progress in suspension system design, Citroën has equipped the C5 with 3rd generation Hydractive, the hydraulic suspension unveiled and demonstrated at the Geneva Motor Show. This system is key to the roadholding / ride comfort balance, a factor that is essential to active safety and driving pleasure.

The 3rd generation Hydractive suspension system comprises :

• a BHI ("Built-in Hydroelectronic Interface"), the core of a system that incorporates a powerful control unit, an autonomous hydraulic pressure generator (pump and electrovalves with hydraulic distribution) and an electric motor,

• four carrier elements with new suspension spheres,

• front and rear ride height regulators front and rear,

• electric height sensors linked to the anti-roll bars,

• fluid reservoir,

• a simplified hydraulic network with new-generation connections,

• and a control function and position indicator on the multifunction screen.

This simplified but innovative concept is based on the latest advances in electronic and hydraulic technology, featured by the BHI. The main characteristics are as follows.

Automatic ride height adjustment depending on vehicle speed and road surface

This technical innovation enhances comfort and safety in all circumstances by adjusting vehicle height on three levels :

• in town and on well surfaced roads at speeds of up to 110 km/h, the car’s ride height remains standard ;

• at speeds of more than 110 km/h on well surfaced roads, the BHI lowers the front of the car by 15 mm and the rear by 11 mm. This improves vehicle stability by lowering its centre of gravity, lowers fuel consumption by reducing drag and makes the car less sensitive to crosswinds. The car returns to its standard ride height when speed drops below 90 km/h ;

• on poorly surfaced roads, the BHI raises the vehicle’s ride height to increase clearance without compromising handling or comfort. If the road is in particularly poor condition, the height is raised by 13 mm – provided that the car is travelling at less than 70 km/h.

In order to determine the most appropriate ride height, the BHI monitors data on vehicle speed and on the height and movement of the suspension. The car is raised or lowered by adding or removing hydraulic fluid to or from the suspension circuitry.

The driver can also adjust vehicle height manually. Four settings are available through an electronic pulse control system :
H : high - the maximum height setting, to be used when changing a wheel.
P : raised - an intermediate setting designed for clearing obstacles at low speed. The clearance increases by 40mm in this instance.
N : normal - for ordinary driving conditions.
B : low - the minimum possible setting to facilitate loading and the coupling of trailers or caravans.

These positions are displayed on the multifunction screen.

The control system has an electronic safety device to prevent unsuitable settings being selected. The "high" option is not available when the car is travelling faster than 10 km/h and "raised" mode cannot be selected after 40 km/h.

The 3rd generation Hydractive suspension makes full use of the advantages offered by hydraulic technology, such as standard ride height regardless of vehicle load.

Auto-adaptive suspension

3rd generation Hydractive suspension adapts automatically, instantly and continuously to suit individual driving styles and the state of the road. It incorporates two settings, comfort and sport, which can be selected by adjusting the damper settings. Each axle features a third sphere (for flexibility) and a stiffness regulator (controlling damper settings and switchover to the supplementary sphere). The system is designed to isolate these elements in "sport" mode and activate them in "comfort" mode in response to the signals received from the ride height sensors and steering wheel, plus the data on brake pressure and engine revs captured by the multiplex network.

In addition, the longitudinal and lateral acceleration data calculated by the BHI are collected and filtered over a period of around one minute.

The "auto-adaptive" characteristics of the suspension allow it to identify individual driving styles. The more vigorous the driving technique, the faster the suspension will transfer to sport mode and thus become personalised to suit the driver.

The driver can express a preference for "sport" mode using a switch on the instrument panel.

Suspension characteristics

The BHI ("Built-in Hydroelectronic Interface") features the latest electronic and hydraulic technology. The compact unit comprises three parts :
a control 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 take precise measurements on variations in the body’s height and rate of movement,

• a sensor measuring the steering wheel angle and the speed at which it is turning,information on the rate of throttle application (or deactivation), vehicle speed, brake pedal pressure and engine speed ; 

• an electric motor to power the pump housed in the stand-alone pressure generator. Active only when necessary, it operates independently of engine speed at 2,300 rpm;

• a stand-alone pressure generator houses all the safety, output and anti-dive controls. It incorporates a pump and four electrovalves.

The five-piston pump supplies fluid (0.7 litres per minute at 2,300 rpm) and operates at pressure of between 80 and 140 bars. At the end of the pump, a hydropneumatic accumulator evens out pressure pulsations and keeps noise levels to a minimum.

The suspension circuitry has two electrovalves, front and rear, one for the hydraulic fluid intake, the other for the fluid exhaust. The intake electrovalves are equipped with a non-return valve. Electromagnetic force ensures an operational response that is almost instantaneous (17 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).

All the parts used by 3rd generation Hydractive suspension are of high quality, manufactured and assembled in extremely clean conditions. The system requires requires no maintenance for the first five years or 200,000 km.

Front suspension

The hydraulic front suspension features a MacPherson-type set-up. It comprises a sub-frame attached to the body in four places by new flexible mountings, designed to filter vibration from the road, new forged steel wishbones, iron pivots and an anti-roll bar linked directly to the strut bodies by rods.

Rear suspension

The innovative rear suspension features an innovative cross-beam with cast iron trailing arms, self-steering elastic bushes and an anti-roll bar.
The cross-beam comprises an aluminium section with cast aluminium supports welded on at either end. This concept is 13 kg lighter than more conventional suspension systems. And it also creates less vibration.
Attached to the trailing arms and axle supports, the sphere-bearing carrier elements are horizontal to avoid any part of the axle assembly intruding into the designated load area. This ensures the best possible use of space to maximise boot capacity.

Wheels and tyres

The C5 features cast aluminium wheels in either 15- or 16-inch diameter. The 2.2 HDi version is fitted with "Imola" aluminium wheels and 205 / 65 R15 H tyres, at trim level 2, or "Monza" aluminium wheels and 215 / 55 R16 W tyres at trim level 3. These last tyres are also standard on models powered by the 3.0i V6.A full-size spare wheel is housed within the rear floor.

Low tyre pressure warning system

A sensor-transmitter, located within each tyre valve, sends a continuous high-frequency signal to a receiver housed within the upper part of the steering column in order to monitor tyre pressure. If the pressure drops more than 0.3 bar below the recommended standard setting, the driver is alerted by an audible alarm and a message on the multifunction display unit.

Brakes

All C5 models are fitted with ABS anti-lock braking and EBD (electronic brakeforce distribution), as well as emergency braking aids and automatic engagement of the hazard warning lights.
Operating independently from the suspension, the braking system is of conventional design with its X-shaped layout, master cylinder, amplifier and the use of discs all round (ventilated at the front, solid at the rear).

Emergency braking assistance

In the event of an emergency, many motorists do not instantly apply sufficient pressure to the brake pedal. In these circumstances, Citroën’s emergency braking assistance increases brake pressure in relation to the speed at which the pedal is applied. When the car is travelling at 100 km/h, stopping distance is reduced by 25 per cent. Twin pistons located upstream of the emergency system actuate the process mechanically. When the brake pedal is pressed at a speed faster than 450 mm / s2, the primary piston sets off a secondary piston that exerts maximum pressure on the braking system up to the point that the ABS comes in.
Considerable attention has been paid to the ergonomy and progressiveness of the parking brake, which operates on the front wheels.
The same reservoir is used to house brake fluid and supply the hydraulic clutch system.

Automatic hazard warning lights

The ECU in the ABS system calculates the rate of deceleration and, once a certain threshold has been reached, activates the hazard warning lights via the BSI.

Acceleration slip reduction (ASR)

The C5 has an acceleration slip reduction (ASR) system.
The ABS computer uses the wheel sensors to assess the possibility of wheelspin whenever the car pulls away on a low-grip surface, and automatically brakes the wheel (or wheels) concerned.

Steering

The C5 is fitted with hydraulic variable-assistance power steering with a built-in ram, totally independent of the suspension. Variable power is provided by an engine-driven hydraulic pump that reduces flowrate progressively as the engine speed increases. This means steering is lighter at low engine speeds (when parking for example) but firms up at high speed.

Maximum steering assistance is provided at engine speeds of between 600 and 1 000 rpm, with a pump flowrate of 10 l / min. Assistance falls off steadily as engine speed rises, with a pump flowrate of 6 l / min at 2 600 rpm.

In models fitted with the 3.0i V6 engine, variable-assistance power steering is determined directly by vehicle speed.

An electronic controller adapts the level of pressure in the hydraulic circuit in accordance with a predefined profile controlled by a solenoid valve.

The steering column is height-adjustable through 40 mm and reach-adjustable through 27 mm. The column will collapse progressively in the event of impact and is damped to absorb vibration before it reaches the driver.