4MOTION (all wheel drive)
Keeps you safely on track
4MOTION gives you great grip on the road, come rain, wind or snow. So, however treacherous the road surface, you get a sure-footed car with huge levels of traction.
Our four-wheel drive systems work hard to keep you safe, linking with other active safety systems on your Volkswagen to constantly monitor driving conditions. It reacts to even the slightest wheel slip and automatically sends the right amount of power to the wheels with the most grip. The second it detects a problem, it delivers extra traction where it's needed.
As a driver, you get reassuring stability and optimum control. And the confidence that your Volkswagen can safely tackle the roughest roads and the worst weather conditions. That lets you relax and enjoy your drive, knowing that 4MOTION is always on the alert to keep you safe and help you out of tricky situations. It will take snow and ice, slippery roads and muddy tracks in its stride, and help you get out of places where a normal car would be stuck.
Split-second action.
All this happens in milliseconds, through control units that are linked to the car's dynamic sensors, engine management system and gearbox. At the heart of the four-wheel drive system is an inter-axle differential -the design varies depending on the particular system. The differential's job is to share power between the front and rear axle, sending it where it's most needed. If the system senses a loss of traction - caused, for instance, by the wheels on one axle spinning on a slippery surface - it will split the wheels' turning power as needed - almost instantly - to correct the problem.
At the same time, the smaller differences in rotational speed, that happen when cornering or manoeuvring, have to be balanced to stop torsional stresses in the drive train. And the differential must be able to work with the car's other active safety systems such as Anti-lock Braking System (ABS) and the electronic stability programme (ESP). In order to meet all these different demands, we offer our four-wheel drive system in three differential variants. They are called:
- Haldex clutch
- Torsen differential
- Lockable centre differential
The Haldex clutch
The Haldex clutch automatically gathers information on the driver's actions, engine performance, transmission and brakes, so it can control the transfer of torque. That lets it deal swiftly with all potentially dangerous or difficult driving conditions.
Whether you need maximum torque shift in tricky situations or when accelerating - or less when taking sharp corners or parking - the system keeps you safe while offering better performance and driving comfort.
It distributes power between front and rear axles by means of an electronically controlled multi-plate clutch, set between the front and rear axles. Sensors detect slip between the front and rear wheels and apply torque to the back pair if the powered front wheels are spinning, until the two axles are moving at the same speed. Electronic pumps regulate the pressure on the clutch plates and as it rises, the plate sets are pressed against each other. Power transmission can be precisely regulated. In extreme situations, it's even possible to send almost 100% of power to the rear.
The general principle of the Haldex clutch is to always send the driving forces to the axle with the better traction. In this way, 4MOTION is able to respond swiftly and optimally to any driving situation. However, you still keep the feel of a front-wheel drive car most of the time. In normal driving conditions, 90 per cent of the engine's power is sent to the front wheels, with 10 per cent going to the rear. This results in improved fuel efficiency, compared with permanent four-wheel drive. And there's no risk of torsional stresses on the drive train during parking and manoeuvring. The Haldex clutch can be linked with all our active safety systems, including ABS and ESP.
The Torsen differential
The Torsen differential is a mechanical self-locking centre differential which regulates power between the front and rear axles, using torque sensing. It responds to varying rotational forces between the front and rear axle, sending torque between them as needed. On a Torsen differential the two output gears are connected by worm gears. They limit high differential rotation speeds, but still balance the speeds when cornering.
On the Phaeton, under normal conditions, the Torsen differential shares driving forces equally across front and rear axles. If it detects wheel slip, it instantly diverts as much as 20 per cent of the driving power to the axle with the better traction (max. 70:30, or 30:70). Its locking effect increases automatically along with the load. In contrast to a "speed sensing" viscous lock, it operates in "torque sensing" mode. The advantage is the lack of torsional stress when cornering, as it is designed to allow the differential rotational speeds the car automatically wants to use.
Lockable centre differential on the Touareg
The advanced 4xMOTION permanent four-wheel drive system on the Touareg underpins its impressive off-road capabilities. Linked to a lockable centre differential with a multi-plate clutch and low-range gear, it can transmit 100% of torque to either axle, giving your wheels the maximum amount of grip when you need it. In normal operation, torque distribution between the front and rear axles is smoothly adjusted as a function of the amount of slip. The centre differential can also be locked to maintain a fixed drive torque split. Power is sent to the front axle by way of a bevel gear.
4MOTION can also be ordered with a rear-axle differential that gives a 100 per cent locking effect between the rear wheels. The locks are activated by the driver, using a rotary switch in the Touareg's cabin. When this is used, the drive forces are no longer diverted via differentials, instead, each of the rear wheels transmits the same drive torque and turns at the same speed as the other wheel. This gives you maximum traction in extreme conditions.
If you're planning some heavy-duty off-road driving, you can select the low-range ratio (2.66:1) electrically by using the suspension control switch. This delivers maximum traction at low speeds, so the Touareg can safely tackle very steep slopes.