System Overview

System Overview

Introduction

The Mark 20 brake control system
The Mark 20 brake control system is an electronic control system which prevents wheel lock up during braking (ABS). As the ABS system prevents the wheels from locking, steering control is maintained and the maximum braking effect is transferred to the road surface.

The brake control system is equipped with:
- ABS (Anti-lock Braking System)
- Electronic Brake force Distribution function, which regulates the brake force to the rear wheels.

The brake control system, as a factory installed option, can be supplemented with:
- STC (Stability and Traction Control)
- TRACS (TRAction Control System)
- DSTC (Dynamic Stability and Traction Control).

EBD
EBD (Electrical Brake force Distribution) is a function for electronically controlling the brake force on the rear wheels and is integrated with the ABS system. During electronic brake force distribution (EBD) control, the control module regulates the hydraulic pressure in the brake circuit for the rear wheels if the rear wheels tend to lock under braking. This ensures optimal and stable braking. The EBD function replaces the relief valve used in the Mark IV version to reduce the pressure in the brake circuit for the rear wheels.

TRACS
TRACS is a traction control system which is integrated with the ABS system. The traction control system distributes driven power between the wheels so that the wheel with the best road traction receives the greatest amount of driven power. The system is mainly designed to assist with moving off on slippery surfaces at speeds up to approximately 40 km/h. TRACS has only a very limited effect at speeds over 40 km/h. TRACS (traction control system) is always engaged when the ignition is switched on. TRACS (traction control system) is engaged and disengaged using a switch in the lower section of the climate control module (CCM).

STC
STC (stability and traction control) consists of two components:
- Traction Control - this function is described above under TRACS. The traction control function is always engaged when the ignition is switched on. The traction control function together with the stability function is engaged and disengaged using a switch under the climate control module (CCM)
- Stability Control - stability system which is integrated in the ABS system and stabilizes the car in the event of wheel spin. The Antilock Brake System Module (ABS) transmits a signal to the engine control module (ECM) to reduce engine torque until the slipping wheel(s) has/have stopped spinning. The stability function is always engaged when the ignition is switched on. The stability function together with the traction control function is engaged and disengaged using a switch in the lower section of the climate control module (CCM). Applies to cars equipped with STC (stability and traction control).

DSTC
DSTC (Dynamic Stability and Traction control) - a dynamic anti-slip system which is integrated in the STC (stability and traction control) system. The DSTC (dynamic stability and traction control) function is always engaged when the ignition is switched on but can be disengaged or engaged manually using the switch in the lower section of the climate control module (CCM).

The DSTC (Dynamic stability and traction control) system consists of the following:
- Traction Control - This function is described above under TRACS
- Stability Control - Described under STC above
- AYC (Active Yaw Control). The system is based upon a number of sensors which sense the driver's steering movements (steering wheel angle) and the directional, both straight and lateral, movement of the car. The information is used to correct the car in the event of oversteer or understeer.

Control module
The control module is integrated in the ABS hydraulic modulator and is located in the engine compartment. The control module contains the electrical valve coils for the different hydraulic valves.

The main function of the control module is to process the signals from the different sensors and to control the hydraulic pump and the electromagnetic hydraulic valves (inlet and outlet valves) in the ABS hydraulic modulator when controlling the:
- ABS
- EBD
- TRACS
- STC or
- DSTC.

Control modules with the DSTC (dynamic stability and traction control) function also have external sensors which sense the driver's steering wheel movements and the directional behavior of the car.

The control module communicates with directly connected components and other control modules via the Controller Area Network (CAN).

The control module checks calculations and all input and output signals via the built-in diagnostic functions. When the control module detects a fault certain functions are completely disengaged depending on the severity of the fault. At the same time a warning light comes on depending on the fault (see table). During manual disengagement of TRACS/STC/DSTC the control module stops all the functions except for the ABS, Electronic brake force distribution and vehicle speed signal. If the temperature of the brake discs is too high, certain functions are prevented from operating.







Any diagnostic trouble codes (DTC) are stored in the control module memory. This information can be read off using VADIS via the data link connector (DLC) in the car.

When the car is driven the control module checks that a signal is received from the wheel sensors. When the car reaches 20 km/h for the first time (40 km/h if the stop (brake) lamp switch is activated) the control module checks the pump motor and the hydraulic valves by quickly activating them. A noise is then heard from the hydraulic pump, this is completely normal. The ABS function first becomes available when the vehicle speed exceeds approximately 7 km/h. The ABS function is active until the vehicle speed falls below approximately 4 km/h, when the function is disengaged. Traction control is available from standstill.

Signals, ABS control module with or without STC/TRACS
The table below summarizes the input signals to and output signals from the ABS control module. The signal types are divided into directly connected signals, serial communication and Controller area network (CAN) communication. The following figures displays the same information with the Volvo component designations.










Signals ABS control module with DSTC (dynamic stability traction control)
The table below summarizes the input signals to and output signals from the ABS control module. The signal types directly connected signals, serial communication and Controller area network (CAN) communication. The following figures displays the same information with the Volvo component designations.