Impressive manoeuvrability

he Active Drive chassis with four-wheel steering makes Renault Laguna GT exceptionally easy to handle in town and superbly agile on winding roads. At speeds of less than 60kphh, the rear wheels turn in the opposite direction to the front wheels, up to an angle of 3.5°. This brings two advantages: a smaller turning circle, for easy manoeuvring; and smaller steering wheel angles thanks to the more direct, specially calibrated steering With four-wheel steering on the Active Drive chassis, Renault Laguna GT has a 10 per cent smaller turning circle than with two-wheel steering: 10.80 metres (with 18-inch tyres) instead of 12.05m. The greater the rear-wheel steering angle, the smaller the turning circle. Enhanced manoeuvrability is especially remarkable in tight parking situations and along narrow city streets.

Ultra-precise steering

From 60kph, the emphasis is on steering precision. The rear wheels turn simultaneously in the same direction as the front wheels, to enhance stability, almost as if the car were running on rails. The Active Drive system with four-wheel steering counters the centrifugal force that tends to push the rear end outwards round bends, and thus raises the safe cornering speed. The rear axle is set on the ideal trajectory, with a rear-wheel angle usually below 2°, for stability and efficacy. The Active Drive chassis with four-wheel steering enhances dynamic handling, with sound, reassuring response for outstanding driving pleasure.

Unparalleled active safety

The Active Drive chassis with four-wheel steering also improves safety for heightened reassurance during avoidance manoeuvres. In an emergency situation, the rear-wheel angle can rise to 3.5°. The 4WS control unit monitors steering wheel angles to detect avoidance situations (recognized by a sudden increase in steering wheel angle) and adapt the rear-wheel turn angle accordingly. Cut-in of the ESC (Electronic Stability Control) system, specially configured for a sportslike driving style, is delayed, so that the manoeuvre can be performed both safely and more swiftly. ESC only switches in when necessary, and is applied gradually because it is synchronized with the rear-wheel turn action. Via the ESC/ABS unit,the 4WS control unit also detects asymmetrical braking situations, adapting the rear-wheel turn angle automatically to keep the car stable with no driver action required. This helps the driver keep control during critical situations, and ensures uninterrupted peace of mind during everyday driving conditions.

Dynamic control logic

Developed jointly by Renault and Renault Sport Technologies, the Active Drive chassis with four-wheel steering implements electronic control of vehicle dynamics. A sensor on the steering column sends steering wheel angle information via the CAN network to the 4WD control unit, located behind the rear
axle. The 4WD control unit also inputs vehicle speed from the ESP/ABS unit. And it tracks steering wheel angle information to detect sharp steering wheel movements symptomatic of a sports driving style or avoidance situation. All these parameters are analysed to determine the required rear-wheel turn angle,which is implemented by means of an electric actuator on the rear axle. Dynamic vehicle behaviour is precisely modelled to set the ideal vehicle trajectory at each instant, on the basis of the driver’s input and the actual situation of the vehicle. The controller and electric actuator are supplied by Aisin, a Japanese equipment supplier reputed for its experience in four-wheel steering systems.