ABS 16 ANTI-LOCK BRAKES B. Pressure Reduction Phase Even after the pressure hold phase, if already the existing pressure in the wheel cylinder is too much, by which the wheel is further tending to lock, then the ECU activates outlet solenoid valve and lets some amount of brake fluid to reach the accumulator, which serves the purpose of temporary storage. ECU activates both Inlet & Outlet solenoid valves. The closed Inlet solenoid valve shuts the liquid channel from master cylinder. The outlet valve opens and connects the wheel circuit to the reservoir. Refer Fig. 7. Brake f luid gets discharged into the accumulator. The recirculation pump (which is driven by a motor which is not shown in the figure) pumps the brake fluid back to the master cylinder through the damping chamber. The damping chamber avoids the pulsations of the returning brake fluid from getting transferred to the driver’s foot. The pressure reduction is continued till the wheel speed recovers to the vehicle reference speed. Solenoid valve Electricity status Valve open-close Open-close channel INLET ON CLOSE Master cylinder-Wheel cylinder OUTLET ON OPEN Wheel cylinder-reservoir Fig. 7 (Open)
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