Tham khảo tài liệu 'advanced vehicle technology episode 3 part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Normal braking conditions Fig. a Under normal braking conditions the solenoid is disengaged and the armature valve is held in its lowest position by the return spring. When the brakes are applied fluid flows unrestricted from the master cylinder to the wheel cylinder via the solenoid piston armature type valve central passage. This continues until the required pressure build-up against the caliper piston produces the desired retardation to the vehicle. Pressure hold Fig. b When the wheel deceleration approaches some predetermined value the speed sensor signals to the computer control unit the danger of the wheel locking. The control unit immediately responds by passing a small electric current to the appropriate solenoid valve. Accordingly the solenoid coil is partially energized. This raises the armature valve until it blocks the flow of fluid passing from the master cylinder to the wheel cylinder pipe line. The fluid pressure in the pipe line is now held constant Fig. . Pressure reducing Fig. c Should the wheel sensor still signal an abnormally rapid speed reduction likely to cause the wheel to lock the control unit increases the supply of current to the solenoid coil causing the armature valve to lift Fig. Typical antilock brake system ABS pressure wheel and vehicle speed characteristics with respect to time still further to a position where it uncovers the return flow passage. The hold line pressure collapses instantly because the highly pressurized fluid is able to escape into the pressure reducer accumulator. At the same time as the accumulator is being charged surplus fluid is drawn from the accumulator into the return flow pump via the inlet valve whence it is discharged back into the appropriate pressurized master cylinder output pipe line. Consequently the reduction in pressure Fig. permits the wheel to accelerate once again and re-establish its grip with the road surface. During the time fluid is pumped back into the .
