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10-4
2. OPERATING FREQUENCY
1) Hydraulic and Electronic Control Unit (HECU)
Hydraulic and Electronic Control Unit (HECU) 1.
FL wheelRR wheelRL wheel
FR wheel
Master cylinder
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10-54892-01
2) ABS System
Sensor - front wheel speed
Sensor - rear wheel speed
Screw (7.8~11.8 Nm)
Clip - cable holder
Clip - sensor cable mounting, rear
Plug - blind
G-sensor
Nut (9.8~10.8 Nm) 1.
2.
3.
4.
5.
6.
9.
11.
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10-6
1. SYSTEM OVERVIEW
1) What is ABS?
When braking suddenly or braking on slippery roads, the vehicle keeps moving forward but the wheels
are locking and not rotating. If these happen, the vehicle may lose stability or rotate resulting in an
accident. ABS helps to maintain directional stability and control of the vehicle. ABS is designed to
secure more safety and increase the control of steering wheel during emergency braking situation. But,
ABS does not guarantee perfect safety beyond its physical limit. ABS in this vehicle contains EBD
function. In normal driving conditions, the brake system operates without ABS function.
2) What is EBD (Electronic Brake-force Distribution)?
EBD is an automobile brake technology that automatically varies the amount of force applied to each of a
vehicle's brakes, based on road conditions, speed, loading, etc. Always coupled with anti-lock braking
systems, EBD can apply more or less braking pressure to each wheel in order to maximize stopping
power whilst maintaining vehicular control. EBD does not operate when ABS is working.
ABS effect according to braking conditions ▶
Braking on split road Maneuvering while braking
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10-8
ABS warning lamp
Rear wheel speed sensor
(4WD)
Located at both ends of rear axle.
Rear discRear caliper assembly
(2WD/4WD)
Located on the knuckle.
G-sensor
Located on the floor under center
fascia.
2. COMPONENT
EBD warning lamp
(two indicators come on)
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10-94892-01
Front wheel speed sensor
(4WD)
Located on the hub assembly.
Front discFront caliper assembly
(2WD/4WD)
Located on the knuckle.
ABS hydraulic device and control unit
Located near the brake booster in engine compartment.
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10-10
3. ABS CONTROL LOGIC
The principal ABS control logic is the determination of the reference speed by choosing one wheel
meeting a certain condition, while sensing the speed information from 4 wheel speed sensors when the
vehicle is being driven.
For example, when the comparison of the reference speed with front right wheel speed shows a slip, the
control signal is determined according to whether it's deceleration or acceleration. If the control
conditions are met, the brake for the front right wheel will be got under control.
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10-12
2) EBD (Electronic Brake-force Distribution) Warning Lamp
EBD warning lamps (brake warning lamp and ABS warning lamp) come on when the system performs
the self diagnosis and when it detects the malfunction of EBD system. However, the brake warning lamp
comes on regardless of EBD system when the parking brake is applied.
EBD warning lamp ON:
When turning the ignition switch to ON position, ABS warning lamp and the brake warning lamp
comes on for 3 seconds for self diagnosis and goes off if the system is OK (initialization mode).
When applying the parking brake, the brake warning lamp comes on.
When the brake fluid is not sufficient, the brake warning lamp comes on.
When disengaging the connector, the warning lamp comes on.
When the system is defective, ABS warning lamp and the brake warning lamp come on
simultaneously. A.
B.
C.
D.
E.
When the solenoid valve is defective
When one or more wheel sensors are defective
When ABS HECU is defective
When the voltage is abnormal
When valve relay is defective a.
b.
c.
d.
e.
When the communication between warning lamp CAN modules in meter cluster is failed, the
warning lamp comes on. F.
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2) Basic Theory of ABS Function
To give you a better understanding of the tasks and functions of ABS, we will first look at the physics
principles.
(1) Stopping distance
(2) Brake force on a wheel
The maximum possible brake force on a wheel depends on the wheel load and the adhesion coefficient
between tire and carriageway. With a low adhesion coefficient the brake force, which can be obtained is
very low. You are bound to know the result already from driving on winter roads. With a high adhesion
coefficient on a dry road, the brake force, which can be obtained, is considerably higher. The brake
force, which can be obtained, can be calculated from below formula:
Maximum brake force ▶
FBmax = wheel load FR x coefficient of
frictionMh
The braking process cannot be described
sufficiently accurately with the brake forces
calculated. The values calculated only apply if
the wheel is not locked. In the case of a locking
wheel, the static friction turns into lower sliding
friction, with the result that the stopping distance
is increased. This loss of friction is termed "slip"
in specialist literature.
The stopping distance depends on the vehicle weight and initial speed when braking starts. This also
applies for vehicle with ABS, where ABS always tries to set an optimum brake force on each wheel. As
great forces are exerted between the tires and the carriageway when braking, even with ABS the wheels
may scream and rubber is left on the road. With an ABS skid mark one may be able to clearly recognize
the tire profile. The skid mark of an ABS vehicle does not however leave any hint of the speed of the
vehicle in the case of an accident, as it can only be clearly drawn at the start of braking.