ESP plus steering impulse intervenes when it gets slippery

ESP plus steering impulse intervenes when it gets slippery  
Filed under:
Technology, Volkswagen
on 10/24/2006

Source: Volkswagen AG

Just a little “tug” on the steering wheel, “carried out” by the electromechanical power steering, “commanded” by the electronic stabilisation program. But it’s all that is needed for the driver to do the right thing intuitively: countersteer. In very specific situations; during emergency braking on roads with different friction coefficients (for example damp leaves or snow on the right and dry on the left).

Countersteering contributes towards shortening the stopping distance in such cases by up to ten percent. But to do this, the car “needs” steering that can be actuated electronically. And this is installed in the Volkswagen Golf, Golf Plus, Jetta, Eos, Touran, Passat and Passat estate as standard – in the same way as the ESP plus steering impulse. Best to be safe.

ESP plus steering impulse in practice: Surroundings as previously described, autumn or winter, one half of the road surface is dry, the other is frequently covered with damp leaves or even snow. Until now, the scenario on the surface described with different friction coefficients (called "μ-split" in engineering terms) during emergency braking with ESP would end in an ideal case as follows: Thanks to ESP, the car will not skid out of control, the driver can keep it on course and avoid any possible obstacles. Since the braking effect has to be based on the wheel with the poorest friction coefficient in order to prevent the vehicle from breaking out, the wheels cannot be braked as sharply as they would actually permit on a dry surface. The reason for this: without countersteering in the correct direction, the vehicle would break out by overbraking of a wheel, as the unsymmetrical braking forces caused as a result would bring about a tendency of the vehicle to rotate in the direction of the road surface with greater traction. Sounds complicated and it really is. But just at this point is when ESP plus steering impulse intervenes.

ESP determines the right direction: The system "detects" the direction in which the driver has to countersteer to decelerate the vehicle optimally without it breaking out. This is why the unit gives the command to the electromechanical power steering to send a steering impulse in the required direction. This is perceived by the driver in the steering wheel, who then follows this signal intuitively and carries out the classic countersteer. As a result of this stabilising intervention, the brake pressure at the wheels can be increased with the greatest amount of grip. The consequence: a shortening of the stopping distance by the aforementioned 10 percent.

The driver keeps everything under control: The ESP plus steering impulse does not take on the job to actually steer the vehicle. The sovereignty with regards to handling the vehicle remains completely with the driver at all times. On the contrary, the system gives just a recommendation to steer, even if barely noticeable, with a torque of no more than three Newton metres. This is therefore as far as it ever goes: ESP thinks, the person steers – it’s just more effective.

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