ABS (Anti-Lock Brake System)

Components and Component Location

Components

1. ABS control unit (HECU) 2. Front wheel speed sensor

3. Rear Wheel Speed Sensor

Description and Operation

Description

This specification applies to the HCU (Hydraulic Control Unit) and ECU (Electronic Control Unit) of the HECU (Hydraulic and Electronic Control Unit). This specification is intended for the wiring design and installation of the ABS ECU. This unit has the following functions.

• Input of the signal from the wheel speed sensors attached to each wheel.
• Brake force control.
• Fail-safe function.
• Self-diagnosis function.
• Interface with external diagnostic tester.

Installation location: Engine compartment

• The length of the brake pipe from the master cylinder port to the HECU inlet port must be max. 1 m.
• The position must not be close to the engine block and not lower than the wheel.

The ECU operation is activated by turning on the operating voltage (IGN). After completion of the initialization phase, the ECU must be ready for operation. In the operating state, the ECU must be ready within the specified limits (voltage and temperature) to process signals provided by the various sensors and switches according to the control algorithm defined by the software, and to control the hydraulic and electrical actuators. Wheel sensor signal processing: the ECU must receive the wheel rotation speed signal from the four active wheel sensors. The wheel signals are converted into a voltage signal by the signal conditioning circuit after receiving the current signal from the active wheel sensors and are supplied to the MCU input. Solenoid valve control: when one side of the valve coil is connected to positive voltage, i.e. supplied through the valve relay, and the other side is connected to ground via a semiconductor circuit, the solenoid valve operates. The electrical function of the coils is always monitored by a valve test pulse under normal operating conditions. Voltage limits

• Overvoltage: When an overvoltage is detected (above 16.8 V), the ECU turns off the valve relay and disables the system. When the voltage returns to the operating range, the system returns to normal after the initialization phase.
• Undervoltage: When an undervoltage is detected (below 9.3 V), ABS control is inhibited and the warning lamp is turned on. When the voltage returns to the operating range, the warning lamp turns off and the ECU returns to normal operation.

Pump motor check: the ECU performs a check of the pump motor at 30 km/h speed once after the ignition is switched on. Diagnostic interface: Faults detected by the ECU are coded in the ECU, stored in EEPROM and read out by diagnostic equipment with the ignition on. The diagnostic interface can also be used to test the ECU during production and to operate the HCU (air bleeding line or roll and brake test line). Warning lamp module

1. 1
   ABS warning lamp: The ABS warning lamp indicates the ABS self-check and fault status. The ABS warning lamp must come on:

   • During the initialization phase after IGN ON (continuously for 3 seconds).
   • In case of ABS operation failure during braking.
   • In diagnostic mode.
   • When the ECU connector is disconnected from the ECU.
2. 2
   The EBD/parking brake warning lamp: The active EBD warning lamp indicates a self-check and a malfunction state of EBD. However, if the parking brake switch is ON, the EBD warning lamp is always illuminated regardless of EBD function. The EBD warning lamp illuminates under the following conditions:

   • During the initialization phase after IGN ON (continuously for 3 seconds).
   • When the parking brake switch is on or the brake fluid level is low.
   • When the EBD function has failed.
   • In diagnostic mode.
   • When the ECU connector is disconnected from the ECU.

ABS Control

1. 1
   Normal Braking without ABS

   	Inlet Valve (IV)	Outlet Valve (OV)	Return Pump
   Operation	Open	Close	OFF

   
   

   

2. 2
   Decrease Mode

   	Inlet Valve (IV)	Outlet Valve (OV)	Return Pump
   Operation	Close	Open	ON (engine speed control)

   
   

   

3. 3
   Hold Mode

   	Inlet Valve (IV)	Outlet Valve (OV)	Return Pump
   Operation	Close	Close	ON (engine speed control)

   
   

   

4. 4
   Increase Mode

   	Inlet Valve (IV)	Outlet Valve (OV)	Return Pump
   Operation	Open	Close	ON (engine speed control)