RACQ Car Safety Fact Sheet

Stability Control Systems

Mercedes-Benz introduced ESC as standard equipment in 1999 and found that it reduced driver error related crashes by 42 percent. Later research by Monash University has shown similar reductions in single vehicle crashes.  It’s fitment to Australian passenger cars has been mandatory since 2011. 

Diagram of stability control system components in car

Components of the Electronic Stability Program ESP ® from Bosch

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

How it works

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

Sensors provide information about the vehicle’s:
  • speed and acceleration
  • steering input 
  • the G-forces acting on the vehicle
  • the vehicle’s rotation around its perpendicular axis 
  • its lateral and longitudinal deceleration
By analysing these inputs, the system’s computer can calculate the curve or line the vehicle should be travelling along. Some 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. This can involve reducing engine power and applying the brake on one or more wheels to realign the vehicle.

Critical manoeuvre with and without ESP

Vehicle without ESP ®

  1. Vehicle approaches an obstacle 
  2. Vehicle goes off course, enters oncoming traffic lane and driver loses control 
  3. Countersteering causes the vehicle to go into a skid 

Vehicle with ESP ®

  1. Vehicle approaches an obstacle 
  2. Vehicle threatens to break away.  ESP intervenes and restores full steerability 
  3. Countersteer results in threat of renewed breakaway, ESP intervenes again 
  4. Vehicle is stabilised 
Different systems have differing thresholds of intervention and vehicle manufacturers tailor the stability control system’s operation to match the vehicle’s desired handling characteristics. Some systems are switchable so the driver can choose if assistance is provided.

Note that the preceding explanation is a general overview of the topic. Different vehicle manufacturers use different terminology and may achieve the 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.

Images used in this fact sheet are courtesy of Bosch.

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