Four-wheel steering for an exceptional drive
The Active Drive chassis with four-wheel steering brings many benefits, starting with improved manoeuvrability, sharpened dynamic response, and unrivalled steering precision giving the driver truly intuitive control over the cornering line, achieving new heights in driveability and active safety. In town and on country roads, the car is easy to drive: highly manoeuvrable and precise. Laguna GT corners with very little body roll and a precise line is achieved with small steering inputs.
The Active Drive
chassis with four-wheel steering also excels in active safety, both under difficult braking conditions (with a good control over asymmetrical grip and with the ESP matched to a more sporting driving style), and during avoidance manoeuvres at speed ('elk' test).
Four-wheel steering systems of the 1980s were essentially mechanical, with the front and rear wheels linked and pre-determined angles aimed at making up for shortcomings in the vehicle's handling (e.g. a tendency to understeer). Such systems were gradually superseded by the advent of ESP.
Meanwhile, towards the end of the 1990s, manufacturers such as Nissan were beginning to develop solutions based on electrically- and even hydraulically-operated actuators to take the dynamic performance of their vehicles forward. Electronic control of rear wheel steering has enabled handling to be fine-tuned even further, notably in the case of rear-wheel drive vehicles.
The Active Drive system builds on this approach by ensuring a more dynamic and more reactive response to make the most of the inherent qualities of Laguna GT's chassis and consequently deliver even greater driving enjoyment. In addition to the complex modelling of the vehicle's handling, real-time response to the driver's instructions (every 10 milliseconds) and its ability to adapt to different conditions, Laguna GT's Active Drive four-wheel steering system means that active safety systems are only required as a very last resort, which means drivers benefit from more efficient and even more reassuring reactions when faced with an unexpected hazard.
Impressive low-speed manoeuvrability
The Active Drive chassis with four-wheel steering makes Laguna GT exceptionally easy to handle in town and agile on winding roads. At speeds of less than 38mph, 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 reduced steering wheel input required thanks to the more direct, specially calibrated steering.
With four-wheel steering on the Active Drive chassis, Laguna GT has a 10 per cent smaller turning circle than with two-wheel steering: 10.80 metres, incredibly the same as Clio, instead of 12.05m. Enhanced manoeuvrability is especially noticeable in tight parking situations.
With front and rear wheels turning in opposite directions, the car effectively pivots, which means smaller steering angles are needed for the same turning effect. Whereas it takes a 16° steering wheel angle to produce a 1° turn in the front wheels on New Laguna, it takes just 13.5° with the Active Drive chassis.
And this drops to 12° when the rear wheels are turned at the maximum 3.5° angle in the opposite direction to the front wheels. Because the steering is more direct, with less need for large steering wheel angles, the impression of manoeuvrability and agility is greatly enhanced. For any given bend, the driver will need less input on the steering wheel, making for more effective avoidance.
Ultra-precise steering control
From 38mph, the emphasis is on steering precision. The rear wheels turn simultaneously in the same direction as the front wheels, to enhance stability. 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 of less than 2° in most situations, for stability. The Active Drive chassis with four-wheel steering enhances dynamic handling, with a 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 involvement of the ESP system, specially configured for a more sporting driving style, is delayed, so that the manoeuvre can be performed both safely and more swiftly. ESP only deploys when necessary, and is applied gradually because it is synchronized with the rear-wheel turn action. Via the ESP/ABS unit, the four-wheel steering control unit also detects asymmetrical braking situations, such as on mixed surfaces, 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
The Active Drive chassis with four-wheel steering has been developed jointly by Renault and Renault Sport Technologies and implements electronic control of the vehicle dynamics. A sensor on the steering column sends steering wheel angle information via the CAN (controller area network) to the four-wheel steer control unit, located behind the rear axle. The four-wheel steer control unit also inputs vehicle speed from the ESP/ABS unit and tracks steering wheel angle information to detect sharp steering wheel movements symptomatic of a sporting 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.