Abs Control

When braking, the hydraulic pressure in the TMC is increased. The pressure reaches the wheel brake via the current less open inlet valve IV. The current less closed outlet valve 0V is closed. For the sake of simplicity the diagram is limited to only the solenoid valve pair of one brake circuit. The wheel speed is reduced as the brake pressure increases, in the extreme case until the wheel locks.

Fig 1: ABS Operation Diagram - Normal Braking Without ABS

Courtesy of HYUNDAI MOTOR CO.

1. DUMP MODE 
   SOLENOID VALVE SPECIFICATION
   
   

   Solenoid	State	Valve	Passage	Pump motor
   Inlet valve (NO)	ON	CLOSE	Master cylinder <=> Wheel cylinder	ON
   Outlet valve (NC)	ON	OPEN	Wheel cylinder <=> Reservoir

   If the wheel speed decreases, there is still a tendency to lock; the brake pressure on the corresponding wheel must be reduced accordingly. For this, the outlet valve 0V is opened, the inlet valve IV remains closed.

   The brake pressure to the low-pressure accumulator is reduced. The wheel in danger of locking gains speed again.

   Fig 2: ABS Operation Diagram - With ABS

   Courtesy of HYUNDAI MOTOR CO.
2. HOLD MODE 
   SOLENOID VALVE SPECIFICATION
   
   

   Solenoid	State	Valve	Passage	Pump motor
   Inlet valve (NO)	ON	CLOSE	Master cylinder <=> Wheel cylinder	OFF
   Outlet valve (NC)	OFF	CLOSE	Wheel cylinder <=> Reservoir

   When a wheel (or several) tends to lock the inlet valve IV is first closed to avoid a further increase in brake pressure. The outlet valve 0V remains closed: the brake pressure is kept constant.

   Fig 3: ABS Operation Diagram - Hold Mode

   Courtesy of HYUNDAI MOTOR CO.
3. INCREASE MODE 
   SOLENOID VALVE INCREASE MODE SPECIFICATION
   
   

   Solenoid	State	Valve	Passage	Pump motor
   Inlet valve (NO)	OFF	OPEN	Master cylinder <=> Wheel cylinder	ON
   Outlet valve (NC)	OFF	CLOSE	Wheel cylinder <=> Reservoir

   For optimum brake from the certain wheel acceleration a brake pressure increase is necessary. For this, the inlet valve IV is opened and the outlet valve 0V is closed. The pump of the unit starts to run and aspirates the necessary quantity of fluid from the Low-pressure accumulator, in order to produce the necessary brake pressure for the pressure increase phase in seconds.

   With an increase in the brake pressure the wheel speed is reduced. These control phases are repeated until the ABS control unit no longer detects any tendency of the wheels to lock.

   NOTE: During ABS control function, the brake pedal only moves in accordance with the volume requirement of the wheels. Because of a sudden change in friction coefficient this pedal movement may increase slightly.
   Fig 4: ABS Operation Diagram - Increase Mode

   Courtesy of HYUNDAI MOTOR CO.

If there is a problem with the ABS system, the Fail-safe function operates, turning off the relay which supplies the power to the solenoid valve, stopping the output of the control signal, and turning on the ABS warning lamp in order to warn the user of malfunction of the ABS system.

Conventional brake system operates under the circumstance.