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Networked systems make for greater safety

Electronic Stability Control (ESC) is currently the most important active safety system of them all. It identifies critical dynamic situations as they begin to develop and intervenes automatically – if necessary – to correct the vehicle’s behavior.

“Following the invention and mandatory introduction of seat belts, the development and increasing use of Electronic Stability Control systems from 1995 onwards marked a decisive milestone en route to reducing the number of accidents in general and the numbers of fatalities and injuries in particular,” says Frank Jourdan, member of the Executive Board of Continental AG responsible for the Chassis & Safety Division, “because Electronic Stability Control prevents vehicles from skidding.” In the past it was precisely this loss of control that led to a large proportion of accidents with serious or very serious consequences.

In technical terms, Electronic Stability Control or ESC is an electronically controlled driver assistance system for motor vehicles which by selectively braking specific wheels and adjusting the engine torque acts to prevent the vehicle becoming unstable. ESC is an extension and combination of the Anti-lock Braking System (ABS) with a Traction Control System (TCS), as well as with Electronic Brake-force Distribution (EBD) and Active Yaw Control (AYC). “This assistance system,” says Jourdan, “can prevent a driver losing control of the vehicle in a hazardous situation such as when taking sudden evasive action. It does so by selectively braking individual wheels in the event of over- or understeer and regulating the engine output via the engine interface.”

To make this possible, the system compares the dynamic state of the car with the driver’s intentions up to 150 times per second. A sensor built into the steering column measures the motion of the steering wheel in both directions to provide an indication of the desired direction of travel. The data on the actual behavior of the vehicle are supplied by high-precision sensors that feed the engine management and the ESC systems, for example. At the core of the system is a yaw rate sensor that measures the rotation of the vehicle around its vertical axis and which, until 1995, was used exclusively in the aerospace sector. The system takes action as soon as the ESC electronics register a substantial deviation between the computed dynamic state of the vehicle and the driver’s intention. At this point, in just thousandths of a second ESC corrects either oversteer by braking the outer front wheel, or understeer by braking the inner rear wheel.

Studies commissioned by various automakers in 2007 showed that since they introduced Electronic Stability Control as standard equipment, the number of accidents in which their vehicles were involved had fallen by 15 percent. Other studies have shown that the number of vehicle occupants killed in road accidents would drop by around 25 percent if all vehicles were equipped with ESC. Accident researchers compare the gain in safety achieved through the advent of ESC with those brought by the introduction of seat belts and airbags. Accident research studies commissioned by the insurance companies in the German Insurance Association (GDV) have also shown that 25 percent of car accidents involving injuries and at least 35 percent of fatal car accidents could be prevented by Electronic Stability Control or at least the severity could be substantially reduced. Applying these findings to the official statistics for 2007 regarding multiple- and single-car accidents reveals that in Germany – allowing for the fact that in 2007 36 percent of all passenger cars were already equipped with Electronic Stability Control – ESC could have prevented or mitigated the consequences of some 21,000 accidents involving injuries and some 400 fatal accidents.

Against this backdrop, it came as no surprise when the European Parliament passed a resolution on March 10, 2009, whereby from November 2011 all new car models and from November 2014 all new cars in the European Union had to be equipped with ESC as standard. In taking this step, the EU was following the example set by the USA where the phasing in of mandatory ESC began as long ago as 2008. Japan and Korea followed suit in 2012. Significant room for improvement in this respect still exists in the BRIC countries in particular (Brazil, Russia, India and China) where car ownership levels are rising fast. In China, for example, at present only four new cars out of ten are fitted with ESC.

Electronic Stability Control (ESC)

ESC Oversteer: ESC intervenes when the car threatens to oversteer by braking the outer wheels of the car. As a general rule, most of the brake force goes to the front of the wheel, where wheel slip is set at about 50 percent. This gives rise to a counter torque which compensates the yawing torque that causes oversteer. At the same time, the increase in wheel slip reduces the lateral forces.

ESC Understeer: ESC intervenes when the car understeers and seeks to drift straight ahead in a curve. Here, ESC brakes the inside wheels, applying the largest brake force to the rear wheel.