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 (OV) 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: Normal Braking State Chart

Courtesy of KIA MOTORS AMERICA, INC.

Fig 2: Normal Braking Flow Chart

Courtesy of KIA MOTORS AMERICA, INC.

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 OV 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 3: Dump Mode State Chart

Courtesy of KIA MOTORS AMERICA, INC.

Fig 4: Dump Mode Flow Chart

Courtesy of KIA MOTORS AMERICA, INC.

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 OV remains closed and the brake pressure is kept constant.

Fig 5: Hold Mode State Chart

Courtesy of KIA MOTORS AMERICA, INC.

Fig 6: Hold Mode Flow Chart

Courtesy of KIA MOTORS AMERICA, INC.

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 OV 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.