Editing Electronic stability control (section)

== Components and design ==
ESC incorporates yaw rate control into the anti-lock braking system (ABS). Anti-lock brakes enable ESC to slow down individual wheels. Many ESC systems also incorporate a traction control system (TCS or ASR), which senses drive-wheel slip under acceleration and individually brakes the slipping wheel or wheels and/or reduces excess engine power until control is regained. However, ESC serves a different purpose from that of ABS or traction control.<ref name=autogenerated3/>

The ESC system uses several [[sensor]]s to determine where the driver intends to travel. Other sensors indicate the actual state of the vehicle. The control algorithm compares driver input to vehicle response and decides, when necessary, to apply brakes and/or reduce throttle by the amounts calculated through the [[state space (controls)|state space]] (set of equations used to model the dynamics of the vehicle).<ref>{{cite journal|url=http://www.sae.org/technical/papers/2000-01-1633 |title=Anton Van Zanten, "Bosch Esp Systems: 5 Years of Experience," SAE 2000-01-1633 |publisher=Sae.org |date=2000-05-15 |doi=10.4271/2000-01-1633 |access-date=2011-11-13|last1=Zanten |first1=A. T. van |url-access=subscription }}</ref> The ESC controller can also receive data from and issue commands to other controllers on the vehicle such as an [[all-wheel drive]] system or an [[active suspension]] system to improve vehicle stability and controllability.

The sensors in an ESC system have to send data at all times in order to detect a loss of traction as soon as possible. They have to be resistant to possible forms of interference, such as [[precipitation]] or [[pothole]]s. The most important sensors are as follows:
*A steering wheel angle sensor that determines where the driver wants to steer. This kind of sensor often uses [[magnetoresistance|AMR elements]].
*A [[yaw rate sensor]] that measures the rotation rate of the car. The data from the yaw sensor is compared with the data from the steering wheel angle sensor to determine regulating action.<ref>{{citation |url=https://catdrivertraining.co.uk/car-blog/what-is-esp-on-a-car/ |title=What is ESP on a car and how does it work? |publisher=catdrivertraining.co.uk |date=2022-02-28 }}</ref>
*A lateral acceleration sensor that measures the vehicle's lateral acceleration. This is often called an [[accelerometer]].
*Wheel speed sensors that measure wheel speed.

Other sensors can include:
*A longitudinal acceleration sensor that is similar to the lateral acceleration sensor in design, but provides additional information about road pitch, as well as being another sensor for vehicle acceleration and speed.
*A roll rate sensor that is similar to the yaw rate sensor in design, but improves the fidelity of the controller's vehicle model and provides more accurate data in combination with the other sensors.

ESC uses a hydraulic modulator to assure that each wheel receives the correct brake force. A similar modulator is used in ABS. Whereas ABS reduces hydraulic pressure during braking, ESC may increase pressure in certain situations, and an active vacuum brake booster unit may be utilised in addition to the hydraulic pump to meet these demanding pressure gradients.

At the centre of the ESC system is the [[electronic control unit]] (ECU), which contains various control techniques. Often, the same ECU is used for different systems at the same time (such as ABS, traction control, or climate control). The input signals are sent through an input circuit to the digital controller. The desired vehicle state is determined based upon the steering wheel angle, its gradient, and the wheel speed. Simultaneously, the yaw sensor measures the vehicle's actual yaw rate. The controller computes the needed brake or acceleration force for each wheel and directs the valves of the hydraulic modulator. The ECU is connected with other systems via a [[Controller Area Network]] interface in order to avoid conflicting with them.

Many ESC systems have an override switch so the driver can disable ESC, which may be used on loose surfaces such as mud or sand, or if using a small [[spare tire]], which could interfere with the sensors. Some systems also offer an additional mode with raised thresholds, so that a driver can utilize the limits of their vehicle's grip with less electronic intervention. However, the ESC reactivates when the ignition is restarted. Some ESC systems that lack an off switch, such as on many recent Toyota and Lexus vehicles, can be temporarily disabled through an undocumented series of brake pedal and handbrake operations.<ref>{{cite magazine | url = http://www.automobilemag.com/features/news/0601_lexus_gs430_vsc/index.html | title = How to switch off VSC on a Lexus GS430 | magazine = Automobile Magazine | access-date = 2008-05-13 | archive-date = 2007-10-18 | archive-url = https://web.archive.org/web/20071018161851/http://www.automobilemag.com/features/news/0601_lexus_gs430_vsc/index.html | url-status = dead }}</ref> Furthermore, unplugging a wheel speed sensor is another method of disabling most ESC systems.  The ESC implementation on newer Ford vehicles cannot be completely disabled, even through the use of the "off switch".  The ESC will automatically reactivate at highway speeds, and below such speeds if it detects a skid with the brake pedal depressed.