Anti-lock Braking System(ABS) 12 ii. HYDRAULIC CONTROL UNIT (HCU) / HYDRAULIC MODULATOR : MC1 - Primary brake circuit MC2 - Secondary Brake circuit RP1 - Recirculating Pump of circuit MC1 RP2 - Recirculating Pump of circuit MC2 M - Motor For driving recirculating pumps X1EV - Inlet solenoid valve of Rear Left wheel X2EV - ??? X3EV - ??? X4EV - ??? A1 - Accumulator of Circuit MC1 A2 - Accumulator of circuit MC2 X1AV - Outlet solenoid valve of Rear Left wheel X2AV - ??? X3AV - ??? X4AV - ??? X1 - Rear Left X2 - Front Right X3 - Front Left X4 - Rear Right It consists of a Return Pumps, Solenoid Valves, Damping Chamber, Accumulator, Non-Return Valve and Motor. It forms the link between the TMC and the foundation brakes. It implements the commands issued by the ECU by using solenoid valves to control the pressure at the foundation brakes. There are four pairs (4-channel system) of Inlet and Outlet valves located in the modulator. Solenoid valves are responsible for modulating the pressure in the wheel brake during active ABS control. The Return Pump element is installed in the center of the modulator and is driven by an electric Motor. The pump transfers the brake fluid emerging from the wheel brakes through the accumulator on its way back to the TMC. The pump and valve actuation can be felt on the foot pedal as pulsations. In order to prevent damage to the TMC primary seals from the compensating port, the design of TMC is changed to central valve type (CV/CV). The accumulator absorbs the surge in brake fluid that accompanies the pressure reduction phase. The Damping Chamber suppresses pressure oscillations within the hydraulic system, preventing them from being propagated back to the brake pedal and reduces noise levels in the system.
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