Brief description, TCS and ABS function: Abs

The ABS is a control system that gives modern brake systems the ability to harness the maximum braking effect of the vehicle in critical situations, regardless of the road conditions.

The main advantages of the ABS system are:

• No loss of directional stability on braking.
• Steering control retained even during heavy braking.
• Shortest possible braking distance.
• Reduced tire wear.

The Saab 9-5 had ESP 8.0; a 2-circuit, 4-channel braking system comprising the following components:

• Speed sensors, one at each wheel.
• ESP control module with the following integrated components:
  • Valve block with one inlet and one outlet valve per wheel for the ABS function.
  • One pressure increase and one pressure relief valve per front wheel for the TCS function.
  • Return pump comprising an electric motor and pump unit (common to ABS, TCS and ESP).
  • Control module with integrated main relay and pump relay. The control module controls the ABS, TCS and ESP.

A wheel speed sensor at each wheel generates an alternating current with a frequency that increases as the speed increases. The ESP control module, which receives the information on wheel speed, calculates wheel acceleration (speed increase), wheel retardation (speed reduction), vehicle speed and wheel skid (degree of lock). If any of the wheels exceeds a certain degree of lock during braking, the control unit will activate inlet and outlet valves and the return pump to regulate the wheel in question and attain maximum braking force and retain steering ability.

The control module incorporates a function known as electronic brake-force distribution (EBD), which controls the rear inlet valves so that maximum braking effect is achieved on the rear wheels under different load conditions, without the risk of their locking up before the front wheels.