6.6.2 Description and operation 

6.6.2.1 Description and operation 

This vehicle is equipped with an anti-lock braking system(ABS) and electronic brake force distribution (EBD) 
system and the following components are added on the basis of the original brake system: 

Hydraulic electronic control unit (HECU) 

Notes: 

A rubber damping pad is equipped between the mounting bolt of the hydraulic electronic control unit and the 
bracket and plays the role in preventing the hydraulic electronic control unit from being affected by the vibration 
of the vehicle; the hydraulic electronic control unit is unable to decompose as assembly replacement. 

The hydraulic electronic control unit (HECU) controls the system function and detects the fault. When the ignition 
switch is on and the fault diagnosis code of the antilock brake system is absent, the system electrifies the relay, so 
as to provide battery positive voltage to the electromagnetic valve and pump. The hydraulic electronic control unit 
(HECU) continues to detect the state of the wheel to control the wheel slip rate within a certain range, thereby 
maintaining the stability of the vehicle. The hydraulic control pipeline is configured in a diagonal branching rod, 
so that one branch of the oil of the brake master cylinder is flowed to the left front wheel and the right rear wheel 
and the other branch thereof is flowed to the right front wheel and the left rear wheel. Diagonal branch on the 
hydraulic control is isolated, so that the other branch can ensure the continuous braking capacity when one main 
braking pipeline leaks or is broken down. Hydraulic electronic control unit (HECU) comprises the following main 
components: 

–   ABS control module 

–    ABS pump and its relay 

–    Fuel inlet valve. Each fuel inlet valve control an wheel 

–    Oil drain valve: each oil drain valve controls one wheel. 

–   Electromagnetic coil relay 

Wheel speed sensor: 

The wheel speed sensor is a Hall type rotating speed sensor. As the wheel revolves, the ABS control module 
calculates the wheel speed from the wheel speed signal. The wheel speed sensor can be separately replaced, but 
the signal panel (gear ring) must be replaced together with the axle shaft as it is embedded on the axle shaft. 

Brake lamp switch 

Illuminate the brake lamp when depressing the brake pedal and at the same time send to the ABS control module 
the braking signal. 

ABS warning lamp: 

Locate on the combination instrument and remind the driver of malfunction of the ABS by turning on. When 
happen the following events, the dashboard combination instrument will turn on the ABS warning lamp: 

–    ABS control module inspect fault of ABS system, combination instrument is connect to an request light-up 

message by ABS control module 

Combination instrument carries out self-inspection test at the beginning of each ignition cycle, and the indicator 
lamp will light up for 3s. 

The combination instrument detects the missing of communication between ABS control modules. 

EBD warning lamp: 

Locate on the combination instrument and remind the driver of malfunction of the EBD by turning on. When an 
ABS warning lamp turns on but an EBD warning lamp does not turn on, there is still EBD function; and when 
both the ABS warning lamp and the EBD warning lamp turn on, both the ABS and EBD functions become 
invalid. 

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Self-diagnostic test: 

The antilock brake system performs self-diagnosis under the following two conditions: 

–    When each ignition switch is ON. ABS control module carried out one self-diagnostic test. 

–    After starting the engine, when vehicle travels about 15km/h, conduct a self-diagnosis test, and a buzz sound 
will be produced. This is the normal sound during ABS self-inspection. 

The performance will be monitored as long as the ABS is in the working condition. In the case of discovering the 
error, give an alarm immediately until the error is eliminated. Error code keep in the ABS memory until manual 
clear thems  。 

 

6.6.3 System operating principle 

6.6.3.1 System operating principle 

Schematic diagram of hydraulic pipeline of antilock brake system (ABS) 

AV

EV

FL

RR

RL

FR

AV

M

LPA

节流孔

EV

AV

EV

AV

EV

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1.    AV-oil inlet electromagnetic valve 

2 .  EV- oil exhaust electromagnetic valve 

3 .  LPA- lower pressure battery 

4.   M-motor 

5.    FL-Front left wheel 

6.   RR-right rear wheel 

7.   RL-Rear left wheel 

8.    FR-Front right wheel 

Antilock brake system (ABS) 

In the course of antilock brake, the antilock brake system controls the oil pressure in the wheel oil passage to 
prevent the wheel from sliding. Each wheel is equipped with independent hydraulic oil path and special 
electromagnetic valve. The antilock brake system can reduce, maintain or increase the oil pressure of the wheel 
brake. However, the oil hydraulic pressure does not exceed the pressure provided in the course of brake through 
the antilock brake system. During anti-lock braking, a series of pulsation may be sensed on the brake pedal. When 
an ABS control module perceives a vehicle speed sensor input and try to prevent the wheel-slip, various 
electromagnetic valves are quickly continuously changed in a circular manner, and an ABS pump works to 
generate pulse. Pedal pulsation only appears during the anti-lock braking and disappears after restoring the 
conventional brake or parking. For the vehicle with the antilock brake system, normal force is applied to the brake 

th

ro

ttles

 

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pedal to stop. The vehicle with an antilock brake system can effectively shorten a brake distance and maintains its 
stability. During anti-lock braking, the pressure adjustment of the brake system can be divided into 3 stages. 

Pressure kept 

In case of wheel-slip, the ABS control module closes an oil filling valve and keeps an oil draining valve closed, so 
as to isolate the system. In this way, the oil pressure in the brake can be maintained, so that the oil pressure is 
neither increased nor reduced. 

Pressure reduced 

In case of wheel-slip, the ABS control module reduces the pressure supplied to each wheel in the course of 
deceleration. Close the oil filling valve and open the oil draining valve. The excessive oil is stored in the 
accumulator until the ABS oil return pump return the oil to the master cylinder. 

Pressure increased 

If the wheels do not slip, the ABS control module gradually increases the brake pressure of each wheel to reduce 
the wheel speed. Open the oil filling valve and close the oil draining valve. The pressure increased is provided by 
the brake master cylinder. 

Electric brake force distribution (EBD) 

As the ground condition attached to each wheel may be different, the attachment coefficient provided by the 
ground may be different; in addition, when the vehicle brakes, its center of gravity will be changed; thus, it is easy 
to produce slippage, incline and rollover when braking. 

The function of the EBD is to rapidly calculate the friction difference resulted in by difference in adhesion 
coefficients between four wheel tires and then adjust the solenoid valve within the hydraulic unit at a high speed 
to match the braking force with the frictional force (adhesional force) for ensuring the stability and safety of the 
vehicle. Under the condition of emergency brake, the effective ground traction of each wheel has been balanced 
by the EBD prior to ABS action, thereby preventing drifting and lateral displacement. Actually the EBD is an 
additional function of the ABS. It can automatically adjust the allocation of the braking force according to the 
road surface condition and load and thus can improve the function of the ABS. 

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6.6.4 Component position 

6.6.4.1 Component position 

1

2

3

5

4

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1.    right front speed sensor 

2 .  Right rear speed sensor 

3 .  Left rear speed sensor 

4.    Left front speed sensor 

5.    Hydraulic electronic control unit (HECU) 

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