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INTRODUCTION

There are basically two types of safety systems,
Passive Safety Systems
Systems that protect you once a crash has occurred, by reducing the risk and severity of injury. Examples of passive safety systems include:
• Airbag
• Seatbelt
Active Safety Systems
Systems that improve driving safety through technology designed to prevent crashes before they happen. Examples of active safety systems include:
• ABS - Antilock Braking System
• TCS - Traction Control System


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.
In 1990, Mitsubishi released the Diamante (Sigma) in Japan. It featured a new electronically controlled traction system called traction control system, developed by Mitsubishi, the first of it kind in the world. Simply named 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 TCL system had a preventive (active) safety feature, which improved the course tracing performance by automatically adjusting the traction force, and thereby restraining the development of excessive lateral acceleration, while turning. Although not a ‘true’ modern stability control system, trace control monitors steering angle, throttle position and individual wheel speeds and there is no yaw rate input. The TCL system's standard wheel slip control function improves traction on slippery surfaces or during cornering. In addition to the TCL's traction control feature, it also works together with Diamante's electronic controlled suspension and four-wheel steering that Mitsubishi had equipped to improve total handling and performance.
BMW, working with Robert Bosch GmbH and Continental Automotive Systems, developed a system to reduce engine torque to prevent loss of control and applied it to the entire BMW model line for 1992. From 1987 to 1992, Mercedes-Benz and Robert Bosch GmbH co-developed a system called Elektronisches Stabilitätsprogramm (Ger. "Electronic Stability Programme" trademarked as ESP) a lateral slippage control system, the electronic stability control (ESC).
GM worked with Delphi Corporation and introduced its version of ESC called "StabiliTrak" in 1997 for select Cadillac models. StabiliTrak was made standard equipment on all GM SUVs and vans sold in the U.S. and Canada by 2007 except for certain commercial and fleet vehicles. While the "StabiliTrak" name is used on most General Motors vehicles for the U.S. market, the "Electronic Stability Control" identity is used for GM overseas brands, such as Opel, Holden and Saab, except in the case of Saab's 9-7X which also uses the "StabiliTrak" name. Ford's version of ESC, called AdvanceTrac, was launched in the year 2000. Ford later added Roll Stability Control to AdvanceTrac[11] which was first introduced in Volvo XC90 in 2003 when Volvo Cars was fully owned by Ford and it is now being implemented in many Ford vehicles.

ESC - Electronic Stability Controller
These safety-enhancement systems maintain vehicle stability and steering response in critical situations. Electronic Stability Controller is an active safety system that assists the driver to keep the vehicle on the intended path and thereby helps to prevent accidents. ESC is especially effective in keeping the vehicle on the road and mitigating rollover accidents, which account for over 1/3 of all fatalities in single vehicle accidents.
In 1995 Bosch was the first supplier to introduce Electronic Stability Control (ESC) for the Mercedes-Benz S-Class Sedan. Since then, Bosch has produced more than 10 million systems worldwide, which are marketed as ESP - Electronic Stability Program.
In this report, Bosch will present ESC contributions to active safety and the required adaptations to support four wheel driven vehicles and to mitigate rollover situations

Operation

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 loss of steering control, i.e. when the vehicle is not going where the driver is steering. This may happen, for example, when skidding during emergency evasive swerves, understeer or oversteer during poorly judged turns on slippery roads, or hydroplaning. 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.
ESC can work on any surface, from dry pavement to frozen lakes. It reacts to and corrects skidding much faster and more effectively than the typical human driver, often before the driver is even aware of any imminent loss of control. In fact, this led to some concern that ESC could allow drivers to become overconfident in their vehicle's handling and/or their own driving skills. For this reason, ESC systems typically inform the driver when they intervene, so that the driver knows that the vehicle's handling limits have been approached. Most activate a dashboard indicator light and/or alert tone; some intentionally allow the vehicle's corrected course to deviate very slightly from the driver-commanded direction, even if it is possible to more precisely match it.
Indeed, all ESC manufacturers emphasize that the system is not a performance enhancement nor a replacement for safe driving practices, but rather a safety technology to assist the driver in recovering from dangerous situations. ESC does not increase traction, so it does not enable faster cornering (although it can facilitate better-controlled cornering). More generally, ESC works within inherent limits of the vehicle's handling and available traction between the tires and road. A reckless maneuver can still exceed these limits, resulting in loss of control. For example, in a severe hydroplaning scenario, the wheel(s) that ESC would use to correct a skid may not even initially be in contact with the road, reducing its effectiveness.
In July 2004, on the Crown Majesta, Toyota offered a Vehicle Dynamics Integrated Management (VDIM) system that incorporated formerly independent systems, including ESC. This worked not only after the skid was detected but also to prevent the skid from occurring in the first place. Using electric variable gear ratio steering power steering this more advanced system could also alter steering gear ratios and steering torque levels to assist the driver in evasive maneuvers.


Effectiveness
Numerous studies around the world confirm that ESC is highly effective in helping the driver maintain control of the car, thereby saving lives and reducing the severity of crashes. In the fall of 2004 in the U.S., the National Highway and Traffic Safety Administration confirmed the international studies, releasing results of a field study in the U.S. of ESC effectiveness. The NHTSA in United States concluded that ESC reduces crashes by 35%. Additionally, Sport utility vehicles (SUVs) with stability control are involved in 67% fewer accidents than SUVs without the system. The United States Insurance Institute for Highway Safety (IIHS) issued its own study in June 2006 showing that up to 10,000 fatal US crashes could be avoided annually if all vehicles were equipped with ESC. The IIHS study concluded that ESC reduces the likelihood of all fatal crashes by 43%, fatal single-vehicle crashes by 56%, and fatal single-vehicle rollovers by 77-80%.
ESC is described as the most important advance in auto safety by many experts. including Nicole Nason, Administrator of the NHTSA, Jim Guest and David Champion[] of Consumers Union of the Fédération Internationale de l'Automobile (FIA), E-Safety Aware, Csaba Csere, editor of Car and Driver, and Jim Gill, long time ESC proponent of Continental Automotive Systems The European New Car Assessment Program (EuroNCAP) "strongly recommends" that people buy cars fitted with stability control.
The IIHS requires that a vehicle must have ESC as an available option in order for it to qualify for their Top Safety Pick award for occupant protection and accident avoidance.

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