Great Wall Florid, Service Manual

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107 Brake System
Anti-lock Brake System
ABS/EBD introduction
1. Operation
The vehicle's Anti-lock Brake System (ABS) is a type of increasingly popular brake safety device. It detects the
wheel's speed using wheel speed sensor detection. After signal processing, the wheel speed will be transferred
to the computer, which controls the solenoid valve’s operating condition and the pressure inside the brake wheel
cylinder to avoid wheel locking by using certain calculations and control methods based on the wheel speed.
ABS helps the vehicle to avoid sliding, deviation, fishtailing, and losing steering control capacity. ABS improves
the vehicle’s handling capability, stability and shortens braking distance. It also helps the vehicle to avoid the
partial wear and tear of wheels, hence improves the tire's useful life.
Electronic Brake Distribution (EBD) is used to adjust the vehicle's rear wheel brake pressure by using the ABS
components when the ABS does not respond to vehicle braking. It is also used to balance the vehicle’s front and
rear wheel brake pressure, maximizing the vehicle's braking efficiency. EBD uses the ABS components, yet its
controlling logic is independent from the ABS. After the ABS responds, the EBD will disengage.
2. Basic structure
3. ABS working process
(a) Pressure rising phase: While service braking, oil pressure output from the pump passes the inlet solenoid
valve and enters the brake wheel cylinder. The brake generates braking force and the wheel speed sharply
declines until the ABS control unit detects that the wheel is starting to lock via the wheel speed sensor
detection.
(b) Pressure maintaining phase: When the ABS control unit detects that the wheel is starting to lock via wheel
speed sensor signal, the inlet solenoid valve closes, with the outlet solenoid valve shut as usual. The
pressure maintaining phase thus begins.
(c) Pressure drop phrase: During the pressure maintaining phase, the wheels tend to lock further. This brings
the ABS into the pressure drop phrase. With the inlet valve closed and the outlet valve open, the hydraulic
pump starts working, and brake fluid returns to the brake pump from the wheel cylinder by passing through
the low pressure accumulator. The brake pressure reduces and the brake pedal bounces back.
(d) Pressure maintaining phase: With the degree of wheel locking decreases and wheel speed begins to
increase, the pressure maintaining phrase begins.
(e) Next cycle’s pressure rising phase: When the wheels reach a certain speed, the ABS enters the pressure rise
phase and starts the next cycle.
Note: The ABS's pressure adjusting frequency is generally 2 to 4 cycles per second.
ABS control unit
Wheel speed sensor
Wheel speed signal
Wheel cylinder
Valve work instruction
Hydraulic modulator
Vacuum booster & master cylinder