4MATIC all-wheel drive: Agile on the road, superior when off-road

Jun 24, 2019
Stuttgart/Salt Lake City

All versions of the new GLS are for the first time equipped with fully variable all-wheel drive (torque on demand, TonD), which regulates the torque split between the front and rear axle from 0-100 % depending on the selected drive mode. With the optional Off-Road Engineering Package, a likewise fully variable all-wheel-drive system with low and high range is available. This makes the GLS more off-road capable than ever.

The torque split is controlled by the standard-fit transfer case with electronically controlled multi-disc clutch. This allows a variable transfer of drive torque from 0-100 percent (torque on demand) between the axles. The transfer case of the Off-Road Package has an additional reduction gear for off-road driving.

The two fully networked transfer cases with torque on demand allow further improvement in driving safety and agility, especially when cornering. This is achieved by specifically influencing the yaw moment to induce vehicle oversteer or understeer.

Torque on demand: shows just how efficient an SUV can be

Depending on the driving situation, the new transfer case can feed the front axle with suitable, variable drive torque as required. This takes into account the driver's wishes and the selected driving mode, and physical factors such as the current yaw rate or actual traction are also considered.

These are used to continuously calculate the best torque distribution, so as to transfer correspondingly more drive torque to the front axle via the multi-disc clutch in the transfer case. This makes safe and sporty handling characteristics possible even on surfaces with varying friction coefficients.

When moving off either forwards or in reverse, Torque on Demand ensures the best possible traction even on ice and snow. The physical operating principle of the clutch corresponds to that of a centre differential lock familiar from purely off-road vehicles.

During dynamic driving manoeuvres such as driving slaloms, evasive action or cornering, on the other hand, maximum lateral stability at the front axle can be assured by reducing the drive torque at these wheels.

The new transfer case also has a positive effect on longitudinal dynamics and ride comfort, as the engine torque no longer requires to be reduced for the purposes of load reversal damping.

Torque on demand with off-road reduction: more power off-road

With the optional Off-Road Engineering Package, a likewise fully variable all-wheel-drive system (TonD) with low and high range is available. This variant of the transfer case has a reduction gear (known as low range, with a ratio of 1:2.93), which allows to nearly triple the torque acting on the wheel. When operating with engaged inter-axle lock, this ensures optimum traction at both drive axles when driving off-road, especially on sand and above all in rocky terrain. In addition, the power output can be controlled more finely when off-road, especially at slow and crawling speeds.

New brake control system: for even more safety on the road

The modular driving dynamics control system includes the basic functions of anti-lock braking system (ABS) and acceleration skid control (ASR), as well as yaw control, configured for the special features of 4MATIC. When the Off-Road key is pressed, the characteristic curves are adjusted accordingly. When critical driving situations are detected, traction and handling stability are preserved or restored within the physical limits much more rapidly and efficiently by interventions from the brakes and the engine control system.

This gives rise to benefits in particular during

  • evasive manoeuvres,
  • braking on surfaces with different left and right friction values,
  • ABS intervention on changing friction surfaces, 
  • when braking on bends with large changes in wheel load. 

Off-road ABS: blocking for a digging-in effect

Off-road ABS was developed specifically for off-road operations at below 40 km/h, and allows cyclical locking of the front wheels on poor surfaces. The resulting digging-in effect allows the braking distance to be reduced, depending on the surface. On extreme downhill gradients, this makes stopping possible in the first place. The transition from the normal ABS function to off-road ABS is gradual when below the threshold speed.

Off-road score: fun in terrain

Despite its superior technology, the GLS with its luxurious elegance and stately dimensions is not designed to be an extreme climber, of course. However, some drivers will get a taste for using the traction properties of the GLS for more than just occasionally pulling a trailer out of a wet pasture.

For those who dare to venture off-road for the first time or are going on such an excursion with friends, the new GLS offers an innovative app in its MBUX infotainment system, the off-road score. The app uses the information of the different sensors and control units to evaluate how skilfully the driver masters the difficulties of the terrain. The programme offers two options. Either the driver uses it alone: in this case, he can get tips from a tutorial about what he can do better. Or several drivers create their own user profiles and successively drive the same route competing against each other. The incorruptible off-road score decides who did it best.

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