Great Wall Florid. Manual — part 27

GWFLORID Maintenance Manual

106

4. Remove the dust cover.

If necessary to replace the dust cover, replace it using the

following steps.

(a) Twist off the rod clevis.

(b) Screw off the nut.

(c) Pull out the split ring.

(d) Pull out the dust cover.

Removal of the vacuum booster with brake cylinder

assembly is now complete.

Vacuum booster with brake cylinder assem-
bly installation

1. Install the brake cylinder assembly.

Tighten the cover of the brake reservoir, place the outlet

port of the brake reservoir against the master cylinder inlet,

push the brake reservoir assembly into the master cylinder

assembly, and then insert the cylindrical pin to complete the

installation.

Caution: Check and ensure the cleanliness of the

reservoir outlet port and master cylinder inlet. Do not

lose the sealing ring inside the master cylinder inlet.

2. Installation of the vacuum booster assembly.

Install each part of booster using the following steps.

(a) Install the check valve seat.

(b) Install the check valve.

(c) Install the dust cover.

(d) Install the split ring.

(e) Install the lock nut.

(f) Install the rod clevis.

3. Installaion of the vacuum booster assembly and brake

cylinder assembly.

(a) Install the rectangular sealing ring, and then place the

brake pump assembly into the front case’s housing. Pay

attention when pushing the booster's push rod head into

the first piston hole.

(b) Put the two holes of the cylinder body’s flange surface

into the front case bolts of the vacuum booster, and

then tighten the nuts with a torque wrench.

Tightening torque: 20-26 N·m

4. The installation of the vacuum booster with brake

cylinder assembly is the reversed procedure of its

removal. Hence no more elaboration will be provided

here.

Tightening torque of the four lock bolts on the brake

pedal: 23±3 N·m

Tightening torque of master cylinder outlet port rigid

pipe: 15 N·m

Rod clevis

Nut

Split ring

Dust cover

Elastic cylindrical pin

Check valve Check valve seat

Lock nut

Rod clevis

Split ring

Dust cover

Rectangular sealing ring

First piston

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

GWFLORID Maintenance Manual

108

4. EBD working process

The EBD comes into effect when the wheel brakes are lightly applied. The wheel speed sensor detects the speed

of the wheels, and the ECU calculates the speed. If the rear wheel's slip ratio increases, adjust the brake pressure

to maintain or reduce the rear wheel's braking force. The EBD guarantees the rear wheel's lateral force and even

brake force distribution. If the ABS fails to respond, the electronic brake distribution system can still adjust the

rear wheel's braking force to guarantee the rear wheels do not lock before the front wheels, in order to ensure

vehicle safety.

The EBD's working process for lifting and holding pressure is completely the same as it of the ABS working

process. However, the process for lowering pressure is quite different. When the rear wheel has a tendency to

lock up, the normally open valve of the rear wheel closes, the normally closed valve opens, and the rear wheel

pressure reduces. The difference with ABS is that the hydraulic pump does not operate at this time, and the brake

fluid released during depressurization is temporarily stored in the low pressure accumulator. After braking,the brake

pedal is loosened, and the brake pressure inside the pump drops to zero. Open the normally closed valve one more

time at this point. The brake fluid inside the low pressure accumulator returns to the pump by passing through the

normally closed valve and normally open valve. Empty the low pressure accumulator to prepare for the next brake.

ABS installation

1. Install the ABS controller assembly.

(a) Use three hexagon bolts for flange face (Q1840825) to

fix the ABS bracket assembly onto the vehicle body.

(b) Fix the shock pad of the ABS hydraulic pump onto the

mounting holes of the ABS bracket assembly.

(c) Insert the mount pin of the ABS controller assembly

into the shock pad holes by simply inserting the two

anchor pins into the bracket.

2. Install the ABS front wheel speed sensor with bracket

assembly.

(a) Use a hexagon head bolt, spring washer, and flat

washer subassembly to connect the sensor and the

steering knuckle.

(b) Use a hexagon head bolt and a flat washer subassembly

(M8) to connect the sensor bracket and the damper.

(c) Use a hexagon head bolt and a flat washer subassembly

(M6) to connect the sensor bracket and vehicle body.

ABS controller

assembly

ABS hydraulic pressure

pump shock pad

ABS mounting

bracket assembly

Wheel speed sensor

with bracket assembly

Steering knuckle

Propeller shaft

Wheel slippage

Vehicle speed

Wheel speed

Master cylinder

pressure

Wheel cylinder

brake pressure

109

Brake System

3. Installing the ABS rear wheel speed sensor with brack-

et assembly.

Use three hexagon head bolts, spring washers, and flat

washer subassembly connecting pieces to connect the sensor

to the rear hub unit, rear twist beam, and vehicle body.

ABS General Problem Maintenance and Areas of Importance

Common problems and solutions

1. When braking, the ABS hydraulic pressure unit noise is overly loud.

When the ABS is working, the motor inside the hydraulic pressure unit is ceaselessly rotating. At this time the

driver can feel the brake pedal bouncing back. However, this bounce back feeling will be entirely different

depending on the speed and road condition. Also, when performing an actuator movement test, the sound of the

running motor may also be sensed. When the vehicle is being driven and the brake is off, the sound of the motor

running can still occasionally be heard. This is the ABS undergoing component inspection, not a malfunction.

If the ABS hydraulic pressure unit noise is irregular, a movement test can be initiated. Compare the noise to that

of normal vehicles to determine if ABS hydraulic pressure unit noise is abnormal.

2. Inlet and outlet solenoid valve failure.

Once the ignition switch is ON, the ABS control unit automatically initiates a self-check. If an inlet and outlet solenoid

valve short circuit or open circuit is found, it will record the failure, light up the fault light, and abort the operation. If using a

scanner to adjust the problem code, make sure to use the movement test to confirm that the solenoid valve has a problem and

then replace the hydraulic pressure unit directly.

X431 data flow: While the ABS is functioning, the inlet and outlet solenoid valves rapidly change operating

conditions.

EVFL - Front inlet valve LH

Off / On

AVFL - Front outlet valve LH

Off / On

EVFR - Front outlet valve RH

Off / On

AVFR - Rront outlet valve RH

Off / On

EVRR - Rear inlet valve LH

Off / On

AVRR - Rear outlet valve LH

Off / On

EVRR - Rear inlet valve RH

Off / On

AVRR - Rear outlet valve RH

Off / On

3. Wheel speed sensor malfunction.

With the engine running, use a oscilloscope to measure the voltage between the sensor's signal line and the

ground.

Output signal when wheel is stationary:

Output signal when the wheels are rotating: signal type is 0.44 V and 1.26 V square wave signal, duty cycle: 50: 50.

Rear hub unit

assembly

Rear wheel speed sensor

with bracket assembly

Hexagon head bolt,

spring washer,

and flat washer

subassembly

Hexagon head bolt,

spring washer, and flat

washer subassembly

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