30-04-2012, 02:31 PM
Electronic stability control (ESC)
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Electronic stability control (ESC) is a computerized technology [1][2] that may potentially improve the safety of a vehicle's stability by detecting and minimizing skids[3]. When ESC detects loss of steering control, it automatically applies the brakes to help "steer" the vehicle where the driver intends to go. Braking is automatically applied to wheels individually, such as the outer front wheel to counter oversteer or the inner rear wheel to counter understeer. Some ESC systems also reduce engine power until control is regained. ESC does not improve a vehicle's cornering performance; instead, it helps to minimize the loss of control. According to Insurance Institute for Highway Safety and the U.S. National Highway Traffic Safety Administration, one-third of fatal accidents could have been prevented by the technology.[4][5]
History
In 1987, the earliest innovators of ESC, Mercedes-Benz and BMW, introduced their first traction control systems. Traction control works by applying individual wheel braking and throttle to keep traction while accelerating but, unlike the ESC, it is not designed to aid in steering.
Named simply TCL in 1990, the system has since evolved into Mitsubishi's modern Active Skid and Traction Control (ASTC) system. Developed to help the driver maintain the intended path through a corner, an onboard computer monitored several vehicle operating parameters through the use of various sensors. When too much throttle has been used, while taking a curve, engine output and braking are automatically regulated to ensure the proper path through a curve and to provide the proper amount of traction under various road surface conditions. While conventional traction control systems at the time featured only a slip control function, Mitsubishi developed a TCL system which had a preventive (active) safety feature.
Introduction
In 1995, automobile manufacturers introduced ESC systems. Mercedes-Benz, supplied by Bosch, was the first to implement this with their W140 S-Class model. That same year BMW, supplied by Bosch and ITT Automotive (later acquired by Continental Automotive Systems). Volvo Cars[citation needed] began to offer their version of ESC called DSTC in 1998 on the new S80. Toyota's Vehicle Stability Control system (also in 2004, a preventive system called VDIM) appeared on the Crown Majesta in 1995.[16] Meanwhile others investigated and developed their own systems.
Operation
Main article: Directional stability
During normal driving, ESC works in the background and continuously monitors steering and vehicle direction. It compares the driver's intended direction (determined through the measured steering wheel angle) to the vehicle's actual direction (determined through measured lateral acceleration, vehicle rotation (yaw), and individual road wheel speeds).
ESC intervenes only when it detects a probable loss of steering control, i.e. when the vehicle is not going where the driver is steering.[26] This may happen, for example, when skidding during emergency evasive swerves, understeer or oversteer during poorly judged turns on slippery roads, or hydroplaning. ESC may also intervene in an unwanted way during high-performance driving, because steering input may not always be directly indicative of the intended direction of travel. ESC estimates the direction of the skid, and then applies the brakes to individual wheels asymmetrically in order to create torque about the vehicle's vertical axis, opposing the skid and bringing the vehicle back in line with the driver's commanded direction. Additionally, the system may reduce engine power or operate the transmission to slow the vehicle down.