English Translation to figure 1: Electronic Stability Program ESP
1 ESP hydraulic power unit with integrated control unit
2 Wheel speed sensors
3 Steering angle sensor
4 Rotational rate sensor with integrated acceleration sensor
5 Engine management control unit for communication

The modern regulation of braking and drive-train torques is based on a network which is more or less shown in the above pictures. This includes the actuators, which can individually adjust the braking pressure for each wheel. Thereby, it is irrelevant, whether the necessary brake pressure comes from the brake pedal, or from an additional unit which produces pressure.

So, where the pressure comes from, doesn't concern us at the moment. We'll move directly onto the Traction Control System, which automatically includes the engine. The calculated torques, their increase or decrease in the generating engine and their distribution to the individual wheels, will be looked at.

If one also reduces the engine torque, as is usual nowadays, together with a specific braking intervention, this can occur much more gently. By the way, the instability of a vehicle, e.g., yawing, is perceived by the passengers much more than, for example, a spinning wheel is. Although the torque-flow is being controlled, the emphasis is on stability.

The driver's wishes must thus, play second fiddle to the physical circumstances. Nevertheless of course, at full acceleration, everthing will still be done to move the car forwards as fast as possible. However,the controling systems keep a constant eye on the situation, to avoid taking all the fun out of driving, they only intervene a little later. Thus, the switching off of the ESP-button is no guarantee that this is completely switched off, what remains, is a little more security than there would be without any ESP at all.

This is of course, also the case when you abruptly take your foot off the gas-pedal. In the past, and not only in wintry conditions, this could have caused the car to go into a skid. Nowadays, the engine management immediately but gently compensates for something like this. Indeed, this part of the ESP can possibly, not be swithed off completely. There's no reason for a complete deactivation. It would however, go into action, in the event of a braking maneuver making the car otherwise uncontrolllable.

As the above shown systems clearly show, both an increased yawing and too great a deviation from the forwards movement of the car and the sideways drifting-angle caused by the steering, should be prevented. One can easily imagine, that the engineers have, for some time now, been working on a method of combining this control with the roll-stabilisation or the electronic influence on the suspension.

Something that's often forgotten when braking with ESP, is the posibility, perhaps through specific acceleration, of achieving the same necessary rotary effect of the vehicle. Instead of braking the outside front wheel to avoid overstreering, the same effect could also be achieved by increasing the torque to the inside front wheel, if it has sufficient traction, ie, not too much drift-angle. This assumes at least, an modulatable amount of torque distribution to the front axle.

Whatever the case may be, this method requires a genuine limited-slip differential, with a hydraulically controllable clutch for the left- and the right hand side. For four wheels, this can be achieved by an all-wheel drive, where e.g., Porsche uses a magnetic clutch between the front and the rear. As a reward for the high amount of effort, the handling can be similar to that of driving on rails. 08/13