DIRAVI

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The DIRAVI (" DI rection assistée à RA ppel asser VI ", German "assisted steering with dependent feedback") is a hydraulic steering system for motor vehicles developed by the French car manufacturer Citroën .

Steering assistance

The steering is connected to the vehicle's central hydraulics, which also feeds the suspension ( hydropneumatics ) and the high-pressure brake. A mechanical connection in the steering gear intended for emergencies only works if the hydraulics should fail. In normal operation, the movements of the steering wheel are transmitted to the tie rods purely hydraulically .

For this purpose there is a piston in the steering gear that is actuated from two sides with hydraulic fluid. One side is connected directly to the high pressure. Only the pressure on the other side of the piston is controlled by means of a slide that is connected to the steering wheel via a second shaft. Depending on the position of the slide, hydraulic fluid flows from the high pressure system into the piston or from the piston back into the hydraulic reservoir. No hydraulic fluid flows in the middle position of the slide; this is the case when holding the steering wheel. Because of this control, the steering wheel is very easy to turn (when stationary).

The principle means that external influences have no influence on the position of the wheels. Even with strong cross winds or a sloping road, it is not necessary to correct the straight line. The position of the steering wheel alone determines the position of the wheels. In addition, the DIRAVI principle prevents potholes, curbs, etc. from being transferred to the steering wheel.

Provision

A second mechanism in the DIRAVI resets the steering to the center position. The restoring force is dependent on the steering wheel angle and the speed of the vehicle.

Dependence on steering wheel angle

A contour disk is attached to a shaft that is directly connected to the steering shaft, which is also called a heart disk because of its shape. A steel roller presses this disk by means of a spring. Due to the shape of the disc, the restoring force of the steering is greater, the further the steering is turned from the center. This means that the further the steering wheel is turned, the higher the restoring force.

Dependence on the speed

The dependence of the restoring force on the vehicle speed is controlled as follows: A speedometer cable controls a centrifugal governor, which in turn actuates a hydraulic valve that in turn moves a piston that presses the spring that presses the roller against the heart disc. The faster the governor turns, the greater the hydraulic pressure on the piston and thus the mechanical pressure on the heart disc.

The DIRAVI does not become more difficult to move at higher speeds, but only increases the restoring force, which of course means that the driver needs more force to move the steering wheel from the central position. The steering assistance itself is constant. However, the higher restoring force at higher speeds feels as if the steering is more difficult to move.

Steering geometry

Because the steering is reset, it is neither necessary nor possible for the wheels - as in most cars - to turn straight while driving. The Diravi enables a steering scrub radius of 0, which means that external influences do not affect the steering. So a car with Diravi stays very well on the right and left even when braking sharply on different surfaces, even without an anti-lock braking system .

vehicles

The DIRAVI was installed in the following vehicles - depending on the equipment:

Individual evidence

  1. ↑ Olivier de Serres: La Citroën SM. ETAI, Boulogne-Billancourt.
  2. ↑ Tuninglexikon DIRAVI tuningdirekt.com ( Memento of the original from January 7th, 2009 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.  @1@ 2Template: Webachiv / IABot / www.tuningdirekt.com