Like nearly all luxury brands, Mercedes-Benz used to exclusively produce rear-wheel-drive vehicles. In fact, it pretty much went without saying that if you were a luxury car maker, your products were rear-wheel-driven. It was a defining characteristic.
Things have changed. No-one doubt that Mercedes-Benz is a luxury car maker, but four out of five of that company’s vehicles sold in Canada feature all-wheel-drive (83.5 percent in 2014; 90 percent in January, 2015). The revolution has taken place over the past 25 years or so, gathering momentum as time passed. Now one can make the argument that luxury brands are more likely to be associated with all-wheel-drive rather than rear-wheel-drive (Acura breathes a sigh of relief…).
Known as 4MATIC and introduced 30 years ago, the Mercedes-Benz all-wheel-drive system has evolved into a suite of technologies that adds only 50-70 kilograms to the vehicle, depending on the model. Its light weight means that the fuel penalty formerly associated with all-wheel drive vehicles has been almost eliminated. In fact, for the compact class Mercedes-Benz vehicles, the difference is less than 1.0 L/100 km, combined.
This model year, the 4MATIC system is offered in 37 Mercedes-Benz models and the version found in the compact class vehicles (B-Class, CLA, GLA with transverse mounted four-cylinder engines) becomes “fully variable,” providing traction in snow, grip on mud and control when cornering on dry pavement and able to move torque between front and rear axles as required. The system features a compact power take-off unit (PTU) built into the seven-speed, dual clutch transmission and a hydraulically actuated multi-disc clutch in the rear differential. Mercedes points out that this system is up to 25 percent lighter than all-wheel drive systems from competitors.
Normal drive mode sends 100 percent torque to the front axle, with the drive shaft decoupled from the rear differential. When a difference of speed is detected between the front and rear axles, the drive shaft couples, the multi-disc clutch in the rear differential closes and torque is distributed front to rear in amounts required to stabilize the vehicle (it’s fully variable between 100:0 and 50:50). If more intervention is required, the vehicle’s electronic traction system (4ETS) and electronic stability program (ESP) kicks into action, braking the wheels that are slipping, sending torque to the wheels that have grip.
As Mercedes-Benz puts it: [the] “fundamental operating principle [is that] when the multi-disc clutch is open, the car is driven exclusively by the front axle. When the clutch is closed, the rear axle comes into play. However, the drive torque can be shifted in fully variable mode between front and rear axle according to the given situation (torque on demand).”