Electronic four-wheel steering from Renault
April 9, 2008 Renault is set to introduce its new Active Drive chassis with four-wheel steering next month with the European introduction of the new high-performance GT versions of the new Laguna Hatch and Sport Tourer. Four-wheel steering systems of the 1980s were essentially mechanical, with the wheels linked at pre-determined angles to make up for a vehicle's tendency to understeer. Such systems were gradually superseded by the advent of ESP. 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. We look at the new Renault system …
Developed jointly by Renault and Renault Sport Technologies, the Active Drive chassis with four-wheel steering brings many benefits, starting with improved manoeuvrability, sharpened dynamic response, and unrivaled steering precision giving the driver superb 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).
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.
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 meters, 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.
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.
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.
The Active Drive chassis 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 analyzed to determine the required rear-wheel turn angle, which is implemented by means of an electric actuator on the rear axle. Dynamic vehicle behavior is precisely modeled 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.
The new chassis and technology will be exclusively available with a choice of two engines in the New Laguna – a 205hp two-litre turbo petrol engine or 180hp two-litre turbo diesel.
The diesel version is a new 2.0 dCi engine, offering peak power of 180hp at 3,750rpm. Peak torque of 400Nm is available from 2,000rpm, with a consistent build-up through to 5,000 rpm. A reduced-inertia variable-vane turbocharger enhances dynamic response at low revs to achieve excellent performance: 29.6 seconds for the 1,000m standing start, and 0 to 62mph in 8.5 seconds. This new unit is fitted with a particulate filter and an exhaust gas regeneration valve with enhanced cooling to maximize environmental protection: combined-cycle fuel consumption is just 43.4mpg, which translates into CO2 emissions of just 172g/km. With its ultra-fast glow plugs, the 180hp 2.0 dCi unit fires into action instantly the Start button is pressed, even in conditions of extreme cold (down to -23°C).
The petrol version of Laguna GT is powered by a turbo-charged two-liter 16-valve unit (205hp at 5,000rpm and 300Nm from 3,000rpm) derived from Renault Sport technology as featured on the Mégane Renaultsport, and specifically reworked for Laguna GT, to yield the best in performance, handling and driving pleasure. Laguna GT 205 accelerates from 0 to 62mph in 7.8 seconds and takes 28 seconds to cover 1,000 meters from standstill. Fuel consumption is 34.4mpg, with CO2 emissions of just 194g/km.
The car's sporting character is underpinned by lateral air-intakes in the front bumper, a larger front grille and black background to the headlamps. Laguna GT sits on specific 225/45 Bridgestone Potenza tyres with new 18-inch ‘Celsium’ alloy wheels. Braking power is provided by larger 320mm diameter discs at the front and 300mm discs at the rear.
GT attributes run through to every last detail, such as the gloss black door mirrors and smoked rear lights. Externally visible on the ‘B’ pillar, the GT logo is also embossed on the light grey alcantara centre sections of the seats. As on all New Laguna versions, the interior design exudes comfort and quality for all occupants. Sports design details abound highlighting the GT version: special three-spoke leather sports steering wheel with grey stitching, drilled aluminum pedals, GT gearshift knob, sports front seats with increased lateral support and dark charcoal Riviera leather upholstery. Close attention has been paid to materials and finish, in keeping with the car’s commitment to pure motoring pleasure
Nothing has been left to chance on active and passive safety. New Laguna, and the GT version in particular, excels in terms of active safety performance as demonstrated by the latest EuroNCAP test results. Its principal innovation concerns improved side impact protection thanks to a twin impact sensor system and new-generation double thorax/groin airbags.