Winter Driving Fun In The Mercedes-Benz GLK - PART II

Winter Driving Fun In The Mercedes-Benz GLK - PART II

As is the case with 4MATIC鈥檚 fine-tuning on a dry or wet road, directional stability and therefore the active safety of the GLK models is always to the fore when wintry conditions prevail, too. The basic 4MATIC mechanism with a 45:55 percent torque split between the front and rear axles along with the multiple-disc limited-slip centre differential with a basic locking torque of 50 Nm adds up to an ideal solution. This basic design delivers high traction since, on the one hand, the dynamic shift in axle load toward the rear axle that occurs during acceleration is used to deliver more drive torque to the rear. Meanwhile, the multiple-disc limited-slip centre differential can also variably shift the drive torque from 30 to 70 or 70 to 30 percent between the front and rear axle, whenever the road conditions so dictate. As such, the electronic control systems ESP, 4ETS or ASR can intervene as late as possible; the bulk of the torque is converted into traction on slippery roads. All interventions go virtually unnoticed, but the drivers are still informed immediately if they are driving on the limit.

In this case a yellow warning light flashes in the instrument panel - a clear signal to adjust their driving style to the road conditions. The arrangement featuring a permanent design mechanism has key advantages over other systems that first need to diagnose a lack of traction before activating their 4x4 all-wheel drive. The 4MATIC on the GLK will have already made use of this valuable time to transmit drive torque via the wheels to the road. Just like any all-wheel-drive system, 4MATIC in the GLK has to abide by the laws of physics, a fact clearly illustrated in what is known as the 鈥淜amm circle鈥? The fundamental rule is that a tyre is only able to transfer a certain level of overall force to the road surface. If a large amount of force is required in a longitudinal direction, for example when accelerating or braking, the lateral forces available are reduced. When cornering the reverse applies.

In this case a particularly high degree of lateral force is needed for directional stability, whilst the longitudinal force potential is restricted. When designing the drive mechanism and fine-tuning the control systems, engineers鈥?skills are called upon to use this correlation in such a way that the very best possible handling is ensured in any conditions. The frictional coefficient 碌 describes the physical grip between the tyres and the road surface. Despite the engineers鈥?best efforts, it is ultimately the drivers themselves who determine how safe they are on the road. They should always adapt their driving style in accordance with wintry conditions and ensure that their vehicle is suitably equipped; winter tyres are absolutely essential. The employees at the Mercedes-Benz Technology Centre have a wealth of experience at their fingertips in this respect. The first all-wheel-drive system was created over 100 years ago, and the engineers also occupy a leading position where the fine-tuning of all-wheel-drive control systems is concerned.

4ETS celebrated its world premiere in 1997 in the first generation of the M-Class, development work having begun as far back as 1993. Mercedes-Benz thus enjoys the most extensive experience of all car manufacturers with these systems. When pulling away in wintry conditions the engineers use the off-road algorithms on the GLK 4MATIC to develop optimum traction. Certain road conditions are automatically detected and the interventions of the 4ETS electronic traction control system adjusted so that as much acceleration as possible can be achieved with minimal wheel slip, providing optimum directional stability in the process. So when starting off on 碌-split one side of the GLK is on snow or ice and the other on asphalt. There are major differences in the coefficient of friction between the left and right-hand side of the vehicle. On all vehicles with open axle differentials the wheel with the lowest coefficient of friction limits the maximum transferable driving power.

If the driving power rises above the maximally transferable power, the wheels on snow or ice start to spin, and the GLK would not be able to start off. This situation is immediately registered by 4ETS and the spinning wheels are baked by precisely the right amount of pressure build-up in the wheel brakes. As the wheel with the higher coefficient of friction is now supported via the brake force of the wheel with the lower coefficient of friction, the GLK starts to move. Following the start-off process, the wheel characteristics are observed very closely and the brake pressure controlled in such a way that, as far as possible, there is no difference in speed between the individual wheels. The braking force applied by 4ETS simulates, as it were, a higher coefficient of friction on the side with ice or snow, which, in an ideal case, corresponds to the coefficient of friction on the asphalt side. This produces an optimal transverse locking effect on the axle differentials, resulting in the maximum possible acceleration on 碌-split.