Description and Operation

Description

These specifications apply to the HCU (Hydraulic Control Unit) and ECU (Electronic Control Unit) of the HECU (Hydraulic and Electronic Control Unit). These specifications apply to the wiring design and installation of the ABS/ESP/ECU. This unit has the following functions.

• Input signals from the pressure sensor, steering wheel angle sensor, lateral acceleration and yaw rate sensor, and wheel speed sensors attached to each wheel.
• Brake force / driving force / yaw moment control
• Fail-Safe Function
• Self-check function
• Interface with external diagnostic tool

Installation location: Engine compartment

• The maximum length of the brake line between the master cylinder and the HECU inlet must be 1 meter.
• The position must not be close to the engine block and not lower than the wheel.

Operation: This ECU operates within the operating voltage range (ALL). After the initialization phase is complete, the ECU is ready for operation. Under operating conditions, the ECU is ready within specification (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 receives the wheel rotational speed signal from the four active wheel sensors. The wheel signals are converted to a voltage signal by the signal processing circuit after receiving the current signal from the active wheel sensors and are provided as input to the MCU. Solenoid valve control: When one side of the valve coil is connected to positive voltage through the valve relay and the other side is connected to ground through a solid-state circuit, the solenoid valve operates. The electrical function of the coils is always checked by the valve test pulse under normal operating conditions. Voltage limits

• Overvoltage: When an increased voltage is detected (above 17 ± 0.5 V), the ECU switches off the valve relay and interrupts system operation. When the voltage returns to the operating range, the system returns to normal after the initialization phase.
• Undervoltage: When a reduced voltage is detected (below 9.5 ± 0.5 V), ABS control is disabled and the warning lamp illuminates. When the voltage returns to the operating range, the warning lamp goes off and the ECU returns to normal operation.

Pump motor control: The ECU performs a single-speed pump motor check after the ignition is switched on. Diagnostic interface: Faults detected by the ECU are coded in the ECU and stored in EEPROM memory, and are read by diagnostic equipment (Hi-Scan Pro) when the ignition key is turned to the ON position. The diagnostic interface can also be used to check the ECU during production of the last unit and to enable use of the HCU on factory test lines (purge line or roller brake test line). WARNING LAMP MODULE

1. 1
   ABS WARNING LAMP MODULE: The ABS warning lamp indicates the self-check and the ABS fault status. The ABS warning lamp illuminates:

   • During the initialization phase after ALL ON (continuously for 3 seconds).
   • When ABS functions related to a fault are deactivated.
   • In diagnostic mode.
   • When the ECU connector is disconnected from the ECU.
   • The instrument cluster warning lamp illuminates when communication with the CAN module is not possible.
2. 2
   EBD / PARK WARNING LAMP MODULE: The EBD warning lamp indicates the self-check and the EBD fault status. However, if the parking brake switch is active, the EBD warning lamp illuminates regardless of EBD function status. The EBD warning lamp illuminates:

   • During the initialization phase after ALL ON (continuously for 3 seconds).
   • When the parking brake switch is on or when the brake fluid level is low.
   • When the EBD function is faulty.
   • In diagnostic mode.
   • When the ECU connector is disconnected from the ECU.
   • The instrument cluster warning lamp illuminates when communication with the CAN module is not possible.

ABS CONTROL

1. 1
   NORMAL BRAKING WITHOUT ABS: During normal braking, voltage is not applied to the solenoid valve, the inlet valve is open, and the outlet valve is closed. When the brake is applied, brake fluid is supplied to the wheel cylinder through the solenoid valve to activate the brake. When the brake is released, brake fluid returns to the master cylinder through the inlet valve and the regulating valve.

   Solenoid valve	STATUS	Valve	Communication	PUMP Motor
   Inlet valve (NO)	OFF	Open	Master cylinder → Wheel cylinder	OFF
   Outlet valve (NC)	OFF	Closed	Wheel cylinder → Reservoir

   
   

   

2. 2
   DUMP MODE: In an emergency braking situation, if the wheels begin to lock, the HECU sends a signal to the solenoid valve to reduce brake fluid pressure. Voltage is then applied to each solenoid. At this point, the inlet valve closes and brake fluid is blocked from the master cylinder. The outlet valve opens, and brake fluid circulates to the reservoir through the wheel cylinder, which causes the pressure to drop.

   SOLENOID VALVE	STATUS	Valve	Communication	PUMP Motor
   Inlet valve (NO)	WE	Closed	Master cylinder → Wheel cylinder	WE
   Outlet valve (NC)	WE	Open	Wheel cylinder → Reservoir

   
   

   

3. 3
   HOLD MODE: When brake fluid pressure in the wheel cylinder reaches the minimum level, the HECU sends a signal to the solenoid valve so that it maintains the specified pressure and the inlet valve is energized (as opposed to the outlet valve). The inlet and outlet valves are then closed, and brake fluid is held at that level inside the wheel cylinder.

   SOLENOID VALVE	STATUS	Valve	Communication	PUMP Motor
   Inlet valve (NO)	WE	Closed	Master cylinder → Wheel cylinder	OFF
   Outlet valve (NC)	OFF	Closed	Wheel cylinder → Reservoir

   
   

   

4. 4
   INCREASE MODE: If the HECU determines that the wheels are not locked, it cuts the voltage supply to the solenoid valve. Voltage is not supplied to each solenoid valve, and brake fluid flows into the wheel cylinder through the inlet valve, which increases the pressure.

   SOLENOID VALVE	STATUS	Valve	Communication	PUMP Motor
   Inlet valve (NO)	OFF	Open	Master cylinder → Wheel cylinder	WE
   Outlet valve (NC)	OFF	Closed	Wheel cylinder → Reservoir

   
   

   

   

   

ABS HECU EXTERNAL CIRCUIT / HYDRAULIC SYSTEM CIRCUIT