4MOTION is a brand name of Volkswagen AG for its all-wheel-drive system system developed to send power to the wheels that have the most grip.

The technology was first applied back in 1998 to the Volkswagen Bora and Golf.

The principle is based on the parallelization of the rotation of the wheels of an all-wheel drive car and the rotation of the Haldex clutch discs.

When driving in normal conditions of an asphalt road, the clutch discs, like the wheels themselves, rotate at equal speeds, without exerting any mutual influence.

When one or more wheels get into conditions other than normal (water, mud, snow), the rotation speed of the corresponding clutch discs also changes, which changes the pressure in the hydraulic system of the machine and compresses the clutch pack, which in turn optimally redistribute the torque. The change in pressure is controlled by the Haldex clutch electronic control unit, which processes data from sensors installed on each of the car's wheels, the gas pedal and other significant systems.

All-wheel drive offered by Volkswagen.

An all-wheel drive system helps to increase traction reserves and provides the comforting feeling of driving safely and in adverse weather conditions or on a road in poor condition. The system ensures improved rolling stability, outstanding straight running, and optimum stability in crosswind conditions. 4MOTION thus not only offers decisive advantages in the field of traction, but also allows the approach of cornering at higher speeds, thus offering extra safety and driving pleasure - in all cases, with adaptation to concrete road conditions.

Depending on the construction type, the central element of an all-wheel drive system is represented by a differential between the front and rear axle, it is the so-called timing differential. Its task is to variably distribute the propulsion forces to the front and rear axles. If different speeds occur between the axles, for example due to the slipping of one axle on the slippery or unconsolidated road, the system properly distributes the torque to both axles. This means that the intermediate differential transmits a corresponding dimension from the motor torque to the other axis. Simultaneously, it is necessary to compensate for small speed differences when cornering or maneuvering, in order to avoid the appearance of pretensioning of the traction system. In addition, the differential must not limit the functions of the ESP, ASR and EDS running dynamics control systems.

Volkswagen currently offers all-wheel drive on the Golf, Passat, Sharan, Touareg and Phaeton. Due to the requirements of significant differences, three types of differentials are available: Haldex coupling, Torsen central differential and electronically adjusted blade lock.

Haldex coupling

The Haldex coupling is an electronically controlled blade coupling. The distribution of the propulsion forces at the level of the axles is also variable depending on the running regime. In principle, the haldex coupling distributes the propulsion forces to the axle with better traction. In this way, 4MOTION reacts ideally and very quickly to all traffic situations. In this context, the usual rolling sensation offered by a front-wheel drive model is maintained. The risk of pretensioning the traction system when parking and maneuvering is excluded. In addition, the Haldex coupling can be combined with any running dynamics control system (ABS, EDS, ASR, EBV and ESP).

The responsibility for force contact between the front and rear axles rests with the blade coupling. Electronically controlled pumps regulate the pressure on the lamellar discs of the coupling. By increasing the pressure level exerted, the packages of lamellar discs are pressed together. In this way it is possible to fine-tune the force contact between the sets of lamellar discs and thereby the force distribution between the axes.

The task of the electronic control system is to compensate, in addition to the traction and the speed differences resulting in this way between the axles, and other adjustable variables. For example dynamic running condition or torque. The control equipment takes into account, when performing the adjustment operations, different information on the running dynamics, for example speed, cornering, pushing or towing.

Torsen differential

The Torsen differential is an intermediate differential with mechanical self-locking (differential), which adjusts, as required, the force between the front and rear axles. The notion of "Torsen" consists of the English terms "torque" and "sensoring". The differential operates "sensitive to engine torque". The system reacts to different torsional forces between the input shaft and the output shaft (front and rear shaft, respectively). Thus there is the possibility of a variable distribution of the motor torque between the axles. At the Torsen differential, the two driven wheels are connected to each other by helical transmission. They limit the high speeds of the differential, but ensure the balance needed when cornering.

In the Phaeton model, the basic setting of the Torsen differential is selected so that the propulsion forces are distributed, in normal situations, in a weight of 50:50 between the front and rear axles. In case of skidding, the Torsen differential transmits directly and immediately up to 20 percent of the drive power to the axle with better traction (max. 70:30 and 30:70, respectively). The locking effect of the Torsen differential increases automatically depending on the load, it operates "sensitive to engine torque", as opposed to the viscous differential "sensitive to speed". The advantage is the lip

In the Phaeton model, the basic setting of the Torsen differential is selected so that the propulsion forces are distributed, in normal situations, in a weight of 50:50 between the front and rear axles. In case of skidding, the Torsen differential transmits directly and immediately up to 20 percent of the drive power to the axle with better traction (max. 70:30 and 30:70 respectively). The locking effect of the Torsen differential increases automatically depending on the load, it works "sensitive to torque", unlike the viscous differential "sensitive to speed". The advantage is represented by the lack of pretensioning when cornering, considering that the differential speeds imposed by the vehicle are allowed.

All-wheel drive in Touareg - perfectly adapted for rough terrain

The permanent all-wheel drive of the Touareg model is the basis of the outstanding performance obtained on extremely rough terrain. The Touareg model benefits from a central locking differential with a blade coupling and reducer. In normal mode, a direct distribution of the moment is made, depending on the skid, towards the front and rear axle. In addition, the center differential can be locked, so that a fixed torque distribution is recorded. The deviation of the power to the front axle is achieved by means of an oblique actuation, necessary at Touareg as a result of the constructive conditions.

Optionally, a rear axle differential with a transverse locking system and a 100% locking effect can also be provided. Activation of the differential lock is performed at the request of the driver. By means of a rotary switch available in the passenger compartment, it is possible to manually activate the differential lock on the Touareg. In this way the traction is improved in rough terrain conditions: the propulsion forces are no longer deflected by means of the differentials. In this case, each rear wheel transmits the same torque and rotates at the same speed as the other wheel.

The gearbox reduction gear (2.66: 1) for heavy-duty use can be electrically activated via the running gear switch. This allows maximum propulsion force at low speeds. Thus, the Touareg model benefits from a slope climbing capacity of up to 100 percent (45 °).