Operation Of System

The hydraulic unit incorporates eight ABS solenoid valves, two (IN, OUT) for each front wheel (driving wheel).

Described below is the functioning of these components when one of the front wheels is about to slip.

1. When the TCL is inactive 

   The TCL valve (OUT) and ABS solenoid valve (IN) are open while ABS solenoid valve (OUT) is closed? The TCL valve (IN) closes when the brake pedal is depressed, and opens when it is released. If the brake pedal is depressed, the fluid pressure in the master cylinder flows through the TCL valve (OUT), check valve (1) and ABS solenoid valve (IN) to the wheel cylinder, operating the brake.

   If the brake pedal is released, the fluid pressure in the master cylinder falls, and the fluid returns through the ABS solenoid valve (IN), check valve (2) and TCL valve (OUT) to the master cylinder, releasing the brake.

   ABS SOLENOID VALVE OPERATION (TCL IS INACTIVE)
   
   

   COMPONENT		CURRENT SUPPLY	VALVE POSITION	COMPONENT		CURRENT SUPPLY	VALVE POSITION
   ABS solenoid valve	IN	OFF	Open	TCL valve	IN	-	The brake pedal is depressed: Closed The brake pedal is released: Open
   	OUT	OFF	Closed		OUT	OFF	Open

   Fig 1: TCL Fluid Flow Direction Chart (TCL Is Inactive)

   Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
2. When the TCL is active 
   1. Pressure increasing mode 

      If the ABS-ECU determines that either of the front wheels is slipping due to abrupt acceleration, etc., it commands the TCL valve (OUT) to close. At this time, the TCL valve (IN) is open because the brake pedal has not been depressed. Furthermore, it energizes the motor to drive the pump. The pump then sucks out the fluid in the master cylinder through the TCL valve (IN) and the inlet valve, then sends it through the outlet valve (IN) to the wheel cylinder, increasing the fluid pressure in that cylinder.

      ABS SOLENOID VALVE OPERATION (TCL IS ACTIVE)
      
      

      COMPONENT		CURRENT SUPPLY	VALVE POSITION	COMPONENT		CURRENT SUPPLY	VALVE POSITION
      ABS solenoid valve	IN	OFF	Open	TCL valve	IN	-	Open
      	OUT	OFF	Closed		OUT	ON	Closed

      Fig 2: TCL Fluid Flow Direction Chart (TCL Is Active)

      Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
   2. Pressure holding mode 

      If the ABS-ECU determines that the fluid pressure has been increased to the optimum level, it stops supplying power to the motor. This causes the pump to stop its operation. As a result, the fluid pressure in the wheel cylinder is retained.

      ABS SOLENOID VALVE OPERATION (PRESSURE HOLDING MODE)
      
      

      COMPONENT		CURRENT SUPPLY	VALVE POSITION	COMPONENT		CURRENT SUPPLY	VALVE POSITION
      ABS solenoid valve	IN	OFF	Open	TCL valve	IN	-	Open
      	OUT	OFF	Closed		OUT	ON	Closed

      Fig 3: TCL Pressure Holding Mode

      Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
   3. Pressure reducing mode 

      If the ABS-ECU determines that wheel slipping has been prevented, it commands the TCL valve (OUT) to open. This causes the fluid in the wheel cylinder to flow through the ABS solenoid valve (IN), check valve (2) and TCL valve (OUT) back to the master cylinder, reducing the fluid pressure in the brake circuit.

      ABS SOLENOID VALVE OPERATION (PRESSURE REDUCING MODE)
      
      

      COMPONENT		CURRENT SUPPLY	VALVE POSITION	COMPONENT		CURRENT SUPPLY	VALVE POSITION
      ABS solenoid valve	IN	OFF	Open	TCL valve	IN	-	Open
      	OUT	OFF	Closed		OUT	OFF	Open

      Fig 4: TCL Pressure Reducing Mode

      Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.