Citroën Activa

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Citroën
Activa I..jpg

Activa I (1988)

Activa
Presentation year: 1988: Activa
1990: Activa 2
Vehicle fair: Mondial de l'Automobile
Class : Upper class
Body shape : Coupe
Production model: none

Citroën Activa and Activa 2 were two concept vehicles from Citroën with the purpose of testing and showing innovative technologies for future series vehicles.

Both cars were presented at the Mondial de l'Automobile in Paris in 1988 and 1990 .

Citroën Activa has developed roll stabilization . In German it was called Active Chassis Stabilization (AFS), in French SC.CAR = Systems Citroën de Contrôle Actif du Roulis .

Later the system (and the name) went into series production in the Citroën Xantia Activa .

Activa

Activa I (1988) with all-wheel steering

Activa had all-wheel steering , active suspension , anti-lock braking system and traction control . The study had a center console with a screen and a non-circular multifunction steering wheel .

Activa 2

Activa II (1990)

Activa 2 was first as a successor to the sports coupe Citroën SM from the upper class provided, but did not go into series .

Active chassis stabilization SC.CAR

With this system, the lateral inclination is reduced to a minimum (−0.2 ° to 1 °) through mechanical control with hydraulic cylinders that act on the anti-roll bars. This technology enables lateral accelerations of up to 1.2 g on a non-slip road surface and still offers above-average suspension comfort and thus safe road holding. For more lateral support, the Activa has seats with reinforced side bolsters, which are also pneumatically adjustable in the first series (X1).

How AFS / SC.CAR works

Both (relatively thick) cross stabilizers (front 28 mm, rear 25 mm diameter ) are diagonally opposite (front-left and rear-right) via a differential - hydraulic cylinder connected to the check rails.

These cylinders are connected to a control valve that is actuated directly by the front wishbones via push rods and a spring-lever mechanism. Any roll moment that occurs (lateral inclination) acts in the opposite direction on the wishbones - one wheel compresses, the other rebounds. As a result, the control valve - the inclination corrector - is pulled or pushed out of its rest position (straight-ahead position) in one direction by the push rods, whereby it sets a pressure in the hydraulic cylinders proportional to the roll moment.

The hydraulic units change their length and thus counteract the tension in the anti-roll bar. They "push" the body back into the horizontal position against the roll moment acting on the anti-roll bars, which enables cornering of up to 0.6 g lateral acceleration with a lateral inclination of −0.2 to 0.5 °. From 0.6 g of lateral acceleration, the actuating cylinders come to their stop, from here the Activa tilts up to 1 ° into the curve until it reaches the cornering limit, which corresponds to the value of a good sports car with a correspondingly tight set-up.

Since this active roll stabilizer works independently of the Hydractive II chassis, its suspension travel is almost completely retained even when cornering and thus ensures a significantly better road holding in these situations than conventional wheel suspensions. When driving straight ahead, a solenoid valve is actuated via the control unit of the hydractive suspension, which switches an additional spring ball into the hydraulic control circuit of the actuating cylinder. As a result, on the one hand, the rigidity of the hard-tuned stabilizer rods is "virtually" reduced by the gas filling of the spring ball in order to reduce copying movements and thus increase comfort. In addition, its storage effect has a dampening effect on the control loop, so that when driving straight ahead, no undesired control oscillations occur due to brief actuation of the inclination corrector caused by the suspension.

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