Early Mercedes-Benz ESP stability control description
Suppose you enter a right-hand turn too quickly. The car oversteers and threatens to go into a spin. ESP stability control immediately springs into action, applying the brakes to the front left wheel. The car is back on track.
What happens if the car understeers in the same curve and threatens to plow on straight ahead? ESP stability control applies the brakes to the right rear wheel, bringing the car back on track (see animated version). Like a world champion in water sports, ice skating and slalom the Electronic Stability Program follows the ideal line like an athlete. With ESP, a computer continually monitors a car's handling, comparing the data it receives with pre-programmed ideal data. The moment the car deviates from its ideal line, ESP takes over to nip a potential spin in the bud.
The car is brought back on course in two ways. Firstly, ESP stability control precisely regulates the braking action on one or more wheels. ESP can individually brake each wheel as if you had four feet to apply four brake pedals. Secondly, it automatically adjusts engine output if necessary. ESP stability control thus corrects an incipient spin caused by an abrupt dodging maneuver for instance, within milliseconds .
But ESP stability control doesn't just stabilize the vehicle on dry surfaces. It handles icy, wet, gravelly and other adverse road surfaces too; conditions in which even the best of drivers would hardly be able to keep the car on the road. Mercedes-Benz engineers designed ESP to be ready when you need it whether you're braking, accelerating or even coasting. A light on the instrument panel advises caution whenever ESP stability control intervenes.
However, even if ESP has often been referred to as a technical wonder, it cannot suspend the laws of physics. In other words, ESP doesn't give you a license to speed.
Although ESP stability control comes from the aerospace industry, it keeps you on the ground. The heart of ESP stability control is a yaw velocity sensor which resembles the ones used in aircraft and space vehicles. Like a compass, it constantly monitors the exact attitude of the car and registers every incipient spin. Other sensors report how high the current brake pressure is, what the position of the steering wheel is, how great the lateral acceleration is, what the speed is and how big the difference in wheel speed is. Whenever handling becomes instable, the necessary commands are executed and the vehicle is brought under control in a fraction of a second.
Sensor monitoring occurs every 20 milliseconds.
The main ESP control device is comprised of two computers with 56 KB of memory a piece. By comparison, ABS requires only a quarter of that. ESP uses this computer capacity to constantly monitor individual system components. For instance, the crucial sensor that reads wheel speeds is itself checked at 20-millisecond intervals. ESP has proven its effectiveness and reliability in numerous tests.
Development engineers had already tested its application and acceptance in 1994. Eighty Mercedes owners drove on an imaginary road at 60 mph in a Mercedes simulator. Suddenly, an icy situation was simulated in four curves where traction was reduced by more than 70 percent within a few feet. The result: without ESP, 78 percent of the drivers would have not had a chance of holding their car on the road. Furthermore, they would have suffered up to three consecutive accidents caused by spins. All simulated test drives with the help of ESP stability control ran spin and accident free.