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Electronic Stability Control System

Basic Description

Electronic Stability Control (ESC), also called Vehicle Dynamic Control (VDC), Dynamic Stability Control (DSC), Electronic Stability Program (ESP), Vehicle Stability Control (VSC) or Vehicle Stability Assist (VSA), is one of the most significant active safety systems in modern automobiles. The main function of this system is to improve the handling performance of the vehicle and prevent possible accidents during severe driving maneuvers (e.g. fast cornering or lane changing with emergency braking). Generally, these systems stabilize the vehicle by applying the necessary yaw moment (generated by individual braking force on each wheel) and regulating the side slip angle of the vehicle based on a comparison between the vehicle state and the driver's demand. Some ESC systems also reduce the power from the engine during excessive steering.

A vehicle may go in a direction different from the one the steering wheel position indicates when the driver tries to turn very hard or turn on a slippery road. In these situations, the vehicle may understeer or oversteer. In an oversteer situation, the vehicle turns more than the driver intended because the rear end loses traction and slides out. Understeer occurs when the front wheels lose traction and the vehicle turns less than the driver intended.

Electronic Stability Control Architecture

The figure above shows the architecture of a typical stability control system, incorporating three fundamental elements: the driver, the vehicle and the environment. In the normal control loop, the driver detects the deviation of the vehicle from the current road trajectory and corrects it through the steering system. When the electronic stability control system senses that the driver is about to lose control of the vehicle, it generates the necessary yaw moment automatically based on the difference between the driver's demand and actual vehicle state and helps to pull the vehicle back to the desired trajectory.

illustration of understeer
illustration of oversteer

The United States Insurance Institute for Highway Safety (IIHS) issued the results of a study in June 2006 showing that up to 10,000 fatal crashes could be avoided annually in the US 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%. Beginning with the 2012 model year, federal law requires that all cars sold in the U.S. must have an electronic stability control system.

Sensors
Steering wheel angle sensor: detects the steering wheel position and provides a reference input for the ESC controller.
Yaw rate sensor: measures the actual yaw rate of the vehicle and can also estimate the yaw angle by integrating.
Lateral acceleration sensor: measures the lateral acceleration of the vehicle (also called a G-force sensor).
Wheel speed sensor: measures the spin speed of each wheel for individual braking control.
Actuators
The main actuator of the stability control system is the application of the anti-lock brakes to each wheel individually. Electronic throttle, fuel injector and spark plugs may also be actuated in order to control the engine output.
Data Communications
High-speed CAN or FlexRay bus.
Manufacturers
Bendix, Bosch, BWI Group, Continental, Johnson Electric, Mitsubishi Electric, Nissin, TRW, Wabco
For More Information
[1] Federal Motor Vehicle Safety Standards; Electronic Stability Control Systems, NHTSA website.
[2] Electronic Stability Control, Wikipedia.
[3] Electronic Stability Control, safercar.gov.
[4] Simulated Comparison between Vehicles With and Without ESC Systems (video), CVEL video. [wmv format]
[5] Electronic Stability Control, Freescale website.
[6] How Effective is Stability Control, YouTube, Apr. 10, 2007.
[7] Electronic Stability Control (ESC) Revealed, YouTube, Dec. 28, 2010.
[8] Q&A: Electronic Stability Control, Insurance Institute for Highway Safety, May 2011.
[9] Electronic Stability Control, Cars.com, July 20, 2012.
[10] 3-Mode AdvanceTrac - ESC (Electronic Stability Control), YouTube, Nov. 6,2013.