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Electronic Stability Control won't be so well-known without Mercedes A-Class. After the roll-over incident, Mercedes fitted ESP to this car as standard equipment. |
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Electronic Stability Control won't be so well-known without Mercedes A-Class. After the roll-over incident, Mercedes fitted ESP to this car as standard equipment. |
To understand the purpose of Electronic Stability Control, we must learn some basic steering theory first.
When a driver turns the steering wheel, he would expect the car steers exactly the same direction as he has already inputed, no less and no more. However, in reality, this so-called "neutral steering" is very difficult to obtain. Weight distribution, FWD / RWD / 4WD, suspension geometry, choice of tyres etc. can introduce non-neutral steering. If you won't to know the exact theory behind them, please read the Handling section of technical school.
Electronic Stability Control appeared in just several years ago. It was (again) pioneered by Bosch, helped by its first client, Mercedes-Benz, as they tested the ESC-equipped 600SEC coupe extensively in snow. Its objective is to correct extreme understeering and oversteering when the car corners too fast or on slippery surfaces. In other words, it ensures cornering stability.
Stability control is the next logical evolution of ABS and Traction Control. It has ABS's hardware and two additonal sensors: steering-wheel angle sensor, which measures the rate the steering wheel is turning, and yaw sensor, which measures the rate the vehicle is actually turning. By comparing them, computer will know if the vehicle is oversteering or understeering.
On slippery surfaces or aggressive maneuver, if the car understeer seriously, the computer will actuate the brakes on the inside rear wheel, just hard enough and just long enough to correct the steering behaviour. Some systems like Bosch's can also reduce the engine output to cooperate.
When the car oversteer seriously, the outside front wheel will be braked instead.
Unlike 4WD and 4WS, Electronic Stability Control cannot raise cornering limit. It just prevent the car from exceeding the limit through intelligent control of individual wheels. Therefore, it is a security system for unexpected conditions.
Unless you are a novice driver or your car is very unbalanced, ESC cannot help you to corner faster. By opposite lock and cooperation of braking, human can do better than computer, at least until today. Therefore, most good drivers like to switch off ESC for weekend driving. As a safety backup device for daily drive, however, ESC is worthwhile.