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How exactly does ESC work?



Assistance systems help prevent accidents. In a new series on VisionZeroWorld we explain how ABS, airbags and other safety systems work. This time it’s the turn of Autonomous Emergency Braking.

The fateful test took place on October 21, 1997, at a site just outside Stockholm. At the time, no one taking part could have had any inkling that this day would become a turning point in the history of mobility, arguably on a par with the moon landing, or the invention of the wheel by an unknown but inspired individual back in ancient times. When one of the cars taking part – a new Mercedes A-Class – overturned, the news traveled fast around the globe, and the term “moose test” became famous overnight. But this mishap had a silver lining. Because in retrospect it can be seen as the catalyst that transformed Daimler’s newly developed Electronic Stability Program (ESP), launched a short while before in the Mercedes S-Class, into an international bestseller. Today, Electronic Stability Control, as this system is also known, is a standard feature on all new cars. And Continental is one of the leading manufacturers of this eminently important safety technology.

ESC owed its rapid rise in popularity not least to the Swedish car magazine “Teknikens Värld. The above incident in October 1997 took place in the course of the magazine’s annual “Car of the Year” tests. These included a double lane-change maneuver, in which the vehicle was steered abruptly out of and back into its lane, replicating a sudden swerve to avoid an obstacle such as – typical for Swedish roads – a moose. When it was time for the A-Class, the latest model from the Stuttgart stable, to perform this maneuver, test driver Robert Collin, deputy editor in chief of “Teknikens Värld”, promptly flipped the “Baby Benz” onto its roof. This led to all Mercedes A-Class models being recalled for modifications. The track-width was increased, the suspension was firmed up and Daimler’s Electronic Stability Program (ESP) was fitted. The company later went a stage further, fitting this assistance system as standard on all its other models as well. In the meantime, all new passenger car and commercial vehicle models registered in the European Union have to be equipped with ESC. Since 2014, this goes for all new vehicles, regardless of when the model was first introduced.

Small component with a big impact: The MK 100® ESC High Plus from Continental meets the high standards of comfort required for driver assistance functions while also delivering the highly dynamic pressure build-up required by Autonomous Emergency Braking (AEB) systems. In this way the system helps to prevent accidents and mitigate injuries. Photo: Continental


Over the years that followed the Electronic Stability Program – whose manufacturers include Continental, where it is known as Electronic Stability Control (ESC) – has delivered significant improvements in road safety. But how does the system work? Essentially, ESC is an electronically controlled driver assistance system that helps to prevent skids or slides by selectively braking one or more wheels and by intervening in the vehicle’s engine management. As a combination of the Anti-lock Braking System (ABS), the Traction Control System (TCS), Electronic Brake Force Distribution and Active Yaw Control, this assistance system helps prevent drivers losing control of their vehicle in critical situations such as sudden evasive maneuvers. This is achieved by selective wheel braking when under- or oversteer is detected, and by adjusting engine output via the engine management interface. The system operates by comparing the actual status of the vehicle with what the driver is asking it to do – up to 150 times a second. A sensor in the steering column measures how far the steering wheel is turned in either direction. This information is used to determine what the driver wants the vehicle to do. High-precision sensors – used to control systems like the engine management or the ESC system itself – simultaneously supply information about what the vehicle is actually doing, and the two sets of data are compared. The central component of the system is a yaw sensor, which measures the rotation of the vehicle about its vertical axis. Up until 1995, use of such sensors was confined to the aerospace sector. ESC automatically intervenes whenever its electronics detect a significant deviation between the driver’s intentions and the computed actual dynamic status of the vehicle. In fractions of a second the system then takes corrective action to counter oversteer or understeer, by braking the outside front wheel, or inside rear wheel respectively. This keeps the vehicle stable and on track.

ESC significantly improves safety in critical situations. Graphic: Continental


So the introduction of ESC has led to a significant improvement in road safety, and in part, this progress can be traced back directly to the moose test on October 21, 1997. One of many people who see that test as a turning point in the history of the auto industry is Peter Fuss from consultancy firm Ernst & Young. Writing in the Frankfurter Allgemeine Zeitung, Fuss puts it like this: “In retrospect, the A-Class rollover proved to be a blessing in disguise. After all, the accident only occurred during testing, and not in an everyday driving situation, so there were no serious injuries.” The test drivers escaped with only minor cuts and bruises, he adds, and ESC went on to become standard equipment throughout the industry – and has delivered a lasting improvement in road safety.