Saturday, February 12, 2011

Stability Control Systems

Stability Control Systems

Some safety experts rate Electronic Stability Control (ESC) as the most important vehicle safety innovation since the introduction of seat belts.

Mercedes-Benz introduced ESC as standard equipment in 1999 and found that stability control equipped vehicles were involved in 42% fewer driver error related crashes than vehicles that did not have the system. Recent research by Monash University has shown similar significant reductions in single vehicle crashes.

ESC systems very effectively control understeer and oversteer by sensing the vehicle’s attitude and altering engine power and brake application to correct it when necessary.

Electronic Stability Program ESP ®

Electronic Stability Program car

Components of the Electronic Stability Program ESP ® from Bosch

  1. ESP-Hydraulic unit with integrated ECU
  2. Wheel speed sensors
  3. Steering angle sensor
  4. Yaw rate sensor with integrated acceleration sensor
  5. Engine-management ECU for communication

To do this wheel speed sensors provide information about the vehicle’s speed and acceleration, steering input and G-forces acting on the vehicle. The vehicle’s rotation around its perpendicular axis and its lateral and longitudinal deceleration is also measured.

By analysing these inputs the system’s computer can calculate the appropriate curve or line the vehicle should be travelling along. Some manufacturers call this the “Target Yaw Rate”.

By comparing the vehicle’s actual yaw rate to the target yaw rate the computer can identify to what degree it is understeering or oversteering, and what corrective action, if any, is needed. Corrective action can involve reducing engine power and applying the brake on one or more wheels to realign the vehicle.

Current stability systems work hand-in-hand with the vehicle’s Antilock Braking System (ABS) and in fact the two systems usually share wheel speed sensors and other hardware, while the ABS unit is used to apply the brakes as required.

Different systems have differing thresholds of intervention and vehicle manufacturers tailor the stability control system’s operating characteristics to match the vehicle’s desired handling characteristics. Some systems are switchable so the driver can choose if assistance is wanted.

Stability control is a worthwhile feature and is likely to become a mandatory safety feature on all new vehicles in the near future.

Note that the preceding explanation is a general overview of the topic. Different vehicle manufacturers have different terms for components and their operation and may achieve the desired outcome in slightly different ways. There are also various names for the systems. Vehicle Stability Control, Vehicle Stability Enhancement, Dynamic Stability Control, Active Stability Control, Vehicle Dynamic Control, Vehicle Stability Assist and Electronic Stability Control are some.

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