ABS/TCS/ESP TRAINING GUIDE

ABS/TCS/ESP
TRAINING GUIDE

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CONTENTS
1. HYDRAULIC FUNDAMENTALS ---------------------------------------------------------------1.1 PASCAL’S LAW ----------------------------------------------------------------------------------------1.2 FORCE ----------------------------------------------------------------------------------------------------1.3 PRESSURE ----------------------------------------------------------------------------------------------1.4 PRESSURE ON A CONFINED FLUID ------------------------------------------------------------1.5 FORCE MULTIPLICATION ---------------------------------------------------------------------------1.6 PISTON TRAVEL----------------------------------------------------------------------------------------1.7 HYDRAULIC SYSTEM --------------------------------------------------------------------------------1.8 THE FLUID RESERVOIR -----------------------------------------------------------------------------1.9 THE PUMP -----------------------------------------------------------------------------------------------1.10 VALVE MECHANISM --------------------------------------------------------------------------------1.11 AN ACTUATING MECHANISM ---------------------------------------------------------------------

2. ABS GENERAL -----------------------------------------------------------------------------------------2.1 A BRIEF HISTORY OF ABS -------------------------------------------------------------------------2.2 ADVANTAGES OF ABS ------------------------------------------------------------------------------2.3 ABS TYPES ----------------------------------------------------------------------------------------------2.4 ABSCM ----------------------------------------------------------------------------------------------------2.5 TYPICAL ABS CONTROL CYCLES --------------------------------------------------------------2.6 PHYSICAL PRINCIPLES -----------------------------------------------------------------------------2.7 SELECT LOW CONTROL FOR THE REAR WHEEL -----------------------------------------2.8 ABS GENERAL CONSTRUCTION ----------------------------------------------------------------2.9 WHEEL SPEED SENSOR -----------------------------------------------------------------------------

2.10

FEATURE

OF
3

G-SENSOR

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--------------------------------------------------------------------------2.11 G SENSOR ----------------------------------------------------------------------------------------------2.12 SYSTEM LINE-UP -------------------------------------------------------------------------------------

3. LUCAS (F2, WITHOUT EBD) --------------------------------------------------------------------3.1 LUCAS ABS CONTENTS ----------------------------------------------------------------------------3.2 LUCAS ABS HCU & ABSCM -----------------------------------------------------------------------3.3 LUCAS ABS CONSTITUTION ----------------------------------------------------------------------3.4 SPECIFICATIONS --------------------------------------------------------------------------------------3.5 LOCATION -----------------------------------------------------------------------------------------------3.6 COMPONENTS -----------------------------------------------------------------------------------------3.7 LUCAS ABS OPERATION ---------------------------------------------------------------------------3.8 LUCAS ABS HYDRAULIC CIRCUIT --------------------------------------------------------------3.9 LUCAS ABS OPERATION ---------------------------------------------------------------------------3.10 CONNECTORS ----------------------------------------------------------------------------------------3.11 SRI LAMP FLASH CODE ---------------------------------------------------------------------------3.12 INPUTS / OUTPUTS ---------------------------------------------------------------------------------3.13 LUCAS ABS TROUBLESHOOTING ------------------------------------------------------------3.14 LUCAS ABS WIRING DIAGRAM 1 (KEY OFF) ----------------------------------------------3.15 LUCAS ABS WIRING DIAGRAM 2 (KEY ON) -----------------------------------------------3.16 LUCAS ABS WIRING DIAGRAM 2 --------------------------------------------------------------3.17 LUCAS ABS WIRING DIAGRAM 3 (ABS FAILURE) ---------------------------------------3.18 LUCAS ABS WIRING DIAGRAM 3 ---------------------------------------------------------------

4. INTEGRATED ABS/TCS ---------------------------------------------------------------------------4

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4.1 HYDRAULIC CONTROL UNIT(HCU) -------------------------------------------------------------4.2 HCU OPEATION ----------------------------------------------------------------------------------------4.3 EBD OPERATION --------------------------------------------------------------------------------------4.4 ACTIVE WARNING LAMP MODULE --------------------------------------------------------------

5. MGH-10 (Mando, with EBD) ---------------------------------------------------------------------5.1 ABS NEW ACCENT(LC) -----------------------------------------------------------------------------5.2 PRACTICE SHEET -------------------------------------------------------------------------------------5.3 ABS (SANTA FE) ---------------------------------------------------------------------------------------5.4 BTCS (SANTA FE) --------------------------------------------------------------------------------------

6. MGH-20 (Mando, with EBD) ---------------------------------------------------------------------6.1 ABS (Hyundai coupe: GK) --------------------------------------------------------------------------6.2 BTCS Matrix(FC) ---------------------------------------------------------------------------------------6.3 FTCS (Hyundai coupe: GK) -------------------------------------------------------------------------

7. MK-20 (TEVES) -----------------------------------------------------------------------------------------7.1 ABS (EF SONATA, XG) -------------------------------------------------------------------------------7.2 FTCS (EF SONATA, XG) ------------------------------------------------------------------------------

8. BOSCH 5.3 (with EBD) ----------------------------------------------------------------------------8.1 ABS 5.3 (NEW EF SONATA) -----------------------------------------------------------------------8.2 ABD 5.3 (BTCS - NEW EF SONATA) ------------------------------------------------------------8.3 ASR 5.3 (FTCS - NEW EF SONATA) -------------------------------------------------------------

9. NISSHINBO ABS (with EBD) -------------------------------------------------------------------5


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9.1 NT20S2 (TRAJET) -------------------------------------------------------------------------------------9.2 NT20Si (TERRACAN) --------------------------------------------------------------------------------9.3 NTY3 (ATOS) ---------------------------------------------------------------------------------------------

10. ESP (Electronic Stability Program, TEVES MK25) -------------------------------10.1 MK25(CENTENNIAL) ---------------------------------------------------------------------------------

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HYDRAULIC
FUNDAMENTALS

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1. HYDRAULIC FUNDAMENTALS
1.1. PASCAL’S LAW
In the early seventeenth century, Pascal, a French scientist, discovered the hydraulic lever.
Through controlled laboratory experiments, he proved that force and motion could be transferred
by means of a confined liquid. Further experimentation with weights and pistons of varying size,
Pascal also found that mechanical advantage or force multiplication could be obtained in a
hydraulic pressure system, and that the relationships between force and distance were exactly the
same as with a mechanical lever.
From the laboratory data that Pascal collected, he formulated Pascal’s Law, which states :
“Pressure on a confined fluid is transmitted equally in all directions and acts with equal force on
equal areas.” This law is a little complex to completely understand as it stands right now. The
following illustrations and explanations break down each concept and discuss them thoroughly
enough for easy understanding and retention.

1.2. FORCE
A simplified definition of the term force is : the push or pull exerted on an object. There are two
major kinds of forces : friction and gravity. The force of gravity is nothing more than the mass, or
weight of an object. In other words, if a steel block weighing 100 kg is sitting on the floor, then it is
exerting a downward force of 100 kg on the floor. The force of friction is present when two objects
attempt to move against one another. If the same 100 kg block were slid across the floor, there is
a dragging feeling involved. This feeling is the force of friction between the block and the floor.
When concerned with hydraulic valves, a third force is also involved. This force is called spring
force. Spring force is the force a spring produces when it is compressed or stretched. The
common unit used to measure this or any force is the kilogram (kg), or a division of the kilogram
such as the gram (g).

1.3. PRESSURE

Pressure is nothing more than force (kg) divided by area (m 2), or force per unit area. Given the
same 100kg block used above and an area of 10m 2 on the floor ; the pressure exerted by the
block is : 100kg/10m2 or 10kg per square meter.

1.4. PRESSURE ON A CONFINED FLUID

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Pressure is exerted on a confined fluid by applying a force to some given area in contact with the
fluid. A good example of this would be if a cylinder is filled with a fluid, and a piston is closely fitted
to the cylinder wall having a force applied to it, thus, pressure will be developed in the fluid. Of
course, no pressure will be created if the fluid is not confined. It will simply “leak” past the piston.
There must be a resistance to flow in order to create pressure. Piston sealing, therefore, is
extremely important in hydraulic operation. The force exerted is downward (gravity) ; although, the
principle remains the same no matter which direction is taken.
The pressure created in the fluid is equal to the force applied ; divided by the piston area. If the
force is 100 kg, and the piston area is 10m 2, then pressure created equals 10kg/m 2 =
100kg/10m2. Another interpretation of Pascal’s Law is that : “Pressure on a confined fluid is
transmitted undiminished in all directions.” Regardless of container shape or size, the pressure will
be maintained throughout, as long as the fluid is confined. In other words, the pressure in the fluid
is the same everywhere.
The pressure at the top near the piston is exactly same as it is at the bottom of the container, thus,
the pressure at the sides of the container is exactly the same as at top and bottom.

1.5. FORCE MULTIPLICATION
Going back to the previous figure and using the 10kg/m 2 created in the illustration, a force of

1,000kg can be moved with another force of only 100kg. The secret of force multiplication in
hydraulic systems is the total fluid contact area employed. The figure shows an area that is ten
times larger than the original area. The pressure created with the smaller 100kg input is 10kg/m 2.
The concept “Pressure is the same everywhere”, means that the pressure underneath the larger
piston is also 10 kg/m2. Reverting back to the formula used before : Pressure = Force/Area or P =
F/A, and by means of simple algebra, the output force may be found. Example : 10kg/m2 = F(kg) /
100m2. This concept is extremely important as it is used in the actual design and operation of all
shift valves and limiting valves in the valve body of the transaxle. It is nothing more than using a
difference of area to create a difference in pressure in order to move an object.

1.6. PISTON TRAVEL
Returning to the small and large piston area discussion. The relationship with a mechanical lever is
the same, only with a lever it’s a weight-to-distance output rather a pressure-to-area output.
Referring to following figure, using the same forces and areas as in the previous example ; it is
shown that the smaller piston has to move ten times the distance required to move the larger
piston 1m. Therefore, for every meter the larger piston moves, the smaller one moves ten meters.
This principle is true in other instances, also. A common garage floor jack is a good example. To
raise a car weighing 1,000kg, an effort of only 25kg may be required. But for every meter the car
moves upward, the jack handle moves many times that distance downward.
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A hydraulic ram is another good example where total input distance will be greater than the total
output distance. The forces required in each case are reversed. That is, very little effort is required
to produce a greater effort.

1.7. HYDRAULIC SYSTEM

Now that some of the basic principles of hydraulics have been covered and understood, it is time to
explore hydraulic systems and see how they work. Every pressure type hydraulic system has
certain basic components. This discussion will center on what these components are and what
their function is in the system. Later on, the actual systems in the transaxle will be covered in
detail. The figure reveals a basic hydraulic system that can be used in almost any situation
requiring work to be performed. The basic components in this system are : Reservoir, Pump,
Valving, Pressure lines, Actuating mechanism or mechanisms.

1.8. THE FLUID RESERVOIR
Since almost all fluids are nearly incompressible, the hydraulic system needs fluid to function
correctly. The reservoir or sump, as it is sometimes called, is a storehouse for the fluid until it is
needed in the system. In some systems, (also in the automatic transaxle), where there is a
constant circulation of the fluid, the reservoir also aids in cooling of the fluid by heat transfer to the
outside air by way of the housing or pan that contains the fluid. The reservoir is actually a fluid
source for the hydraulic system. The reservoir has a vent line, pressure line, and a return line. In
order for the oil pump to operate correctly, the fluid must be pushed up from the reservoir to the
pump. The purpose of the vent line is to allow atmospheric pressure to enter the reservoir. As the
pump rotates, an area of low pressure results from the pump down to the reservoir via the pressure
line. The atmospheric pressure will then push the oil or fluid up to the pump due to a pressure
difference existing in the system.
The return line is important because with a system that is constantly operating, the fluid has to be
returned to the reservoir for re-circulation through the system.

1.9. THE PUMP
The pump creates flow and applies force to the fluid. Remember flow is needed to create pressure
in the system. The pump only creates flow. If the flow doesn’t meet any resistance, it’s referred to
as free flow, and there is no pressure built up. There must be resistance to flow in order to create
pressure.
Pumps can be the reciprocating piston type (as in a brake master cylinder) or, they can be of the
rotary type. The figure shows three major types of hydraulic oil pumps employing the rotary design.

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The internal-external type of pump design is used almost exclusively in today’s automatic
transaxle.

1.10. VALVE MECHANISM
After the pump has started to pump the oil, the system needs some sort of valving, which will direct
and regulates the fluid. Some valves interconnect passages, directing the fluid where to go and
when. On the other hand, other valves control or regulate pressure and flow. The pump will pump
oil to capacity all the time. It is up to the valves to regulate the flow and pressure in the system.
One important principle to learn about valves in automatic transaxle hydraulics is that the valves
can move in one direction or the other in a passage, opening or closing another passage.
The valve may either move left or right, according to which force can overcome the other. When
the spring force is greater than the hydraulic force, the valve is pushed to the left, closing the
passage.
When the hydraulic force builds up enough force to overcome the spring force, the hydraulic force
will push the valve to the right compressing the spring even more, and re-directing the fluid up into
the passage. When there is a loss of pressure due to the re-direction of oil, the spring force will
close the passage again. This system is called a balanced valve system. A valve that only opens
and closes passages or circuits, is called a relay valve.

1.11. AN ACTUATING MECHANISM
Once the fluid has passed through the lines, valves, pump, etc., it will end up at the actuating
mechanism. This is the point where the hydraulic force will push a piston causing the piston to do
some sort of mechanical work. This mechanism is actually the dead end that the oil pump flow will
finally encounter in the system. This dead end causes the pressure to build up in the system.

The pressure works against some surface area (piston) and causes a force to be applied. In
hydraulics and transaxle technology, the actuating mechanism is also termed a servo. A servo is
any device where an energy transformation takes place causing work as a result. The clutch
assemblies found in the alpha automatic transaxle are actually servos, but they are termed “clutch”
for ease of identification

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ABS GENERAL

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2. ABS GENERAL

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2.1. A BRIEF HISTORY OF ABS
▪ 1952 ABS for aircraft by Dunlop
▪ 1969 Rear-wheel-only ABS by Ford & Kelsey Hayes
▪ 1971 Four-wheel ABS by Chrysler & Bendix
▪ 1978 Mass production of Bosch ABS Systems with Mercedes Benz
▪ 1984 Integrated ABS system by ITT-Teves
▪ Since the early 1990s
ABS began to be offered on the mid-size and compact cars due to a significant cost reduction
and increased efficiency of the system

2.2. ADVANTAGES OF ABS
Anti-lock Brake Systems are designed to prevent wheel lockup under heavy braking conditions on
any type of road condition.
The result is that, during heavy braking, the driver :
• retains directional stability(Vehicle Stability)
• stops faster (Shortened Stopping distance, except gravel, fresh snow..)
• retains maximum control of vehicle (Steerability)
① If the front wheels lock
▶ it is no longer possible to steer the car
<Braking without ABS>

② If the rear wheels lock


<Braking with ABS>

▶ the car can become unstable and can start to skid sideways
BRAKING AT CORNERING

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If a car on the different conditions of surface brakes, the wheels on the slippery surface easily lock
up and the vehicle begins to spin. But ABS provides vehicle stability until it stops.
<Braking without ABS>

<Braking with ABS>

Low μ road
Low μ road

High
μ road
Surface

High μ road
Surface

2.3. ABS TYPES
2.3.1. 4-SENSOR 4-CHANNEL TYPE

This type is generally used for FF(Front engine Front driving) car which has X-brake lines. Front
wheels are independently controlled and rear wheel control usually follows a select-low logic for

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vehicle stability while ABS operation.
2.3.2. 4-SENSOR 3-CHANNEL TYPE
This type is generally used for FR(Front engine Rear driving) car which has H-brake lines. Front
wheels are independently controlled and rear wheels are controlled together by on brake pipe on
the basis of select-low logic.
2.3.3. 3-SENSOR 3-CHANNEL TYPE
Front wheels are controlled independently but rear wheels are controlled together by one wheel
speed sensor(ex. On the differential ring gear).
2.3.4. 1-SENSOR 1-CHANNEL TYPE
Only control the rear wheel pressure by one sensor.
2.3.5. SYSTEM EVALUATION
System Type

Brake
line

Control Logic

Evaluation Item
Steerability


Stability

Stopping
Distance

4-Sensor 4-Channel

X line

All wheels independent control

Good

Fair

Good

Front : Independent control

Good

Good

Fair

Rear : Select Low
Front : Independent control

Good


Good

Fair

Good

Good

Fair

No

Fair

No

or H Line

4-Sensor 3-Channel

H Line

Rear : Select Low
3-Sensor 3-Channel

H Line

Front : Independent control
Rear : Select Low


1-Sensor 1-Channel

H Line

Rear : Select Low

1) 4-Sensor 4-Channel type ( Independent control type )
This type has four wheel sensors and 4 hydraulic control channels and controls each wheel
independently. Steering safety and stopping distance maintains optimum condition on the
homogeneous road surface.
However, on the split-μ road surface, uneven braking force between left wheels
and right wheels generates a Yawing Moment of the vehicle body resulting in vehicle instability.
Therefore, most of vehicles with a 4 channel ABS incorporates a select low logic on rear wheels to
maintain the vehicle stability at any road conditions.

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2) 4-Sensor 3-Channel type (Front wheels: independent control, Rear wheels: Select low
control )
In case of FF(Front engine Front driving) car, most vehicle weight concentrated on front wheels
and the center of the mass of vehicle also moves forward while braking allowing almost 70% of
braking force to be controlled by front wheels.
This means that most braking power is generated by front wheels and to get a maximum braking
efficiency while ABS operation, independent control of front wheels is necessarily required.
However, rear wheels which performs relatively less braking force are very important to guarantees

vehicle safety while braking. That is, while ABS operation of rear wheels on the split road surface,
independent control of rear wheel generates uneven braking force resulting in vehicle yawing
moment.
To prevent this yawing and to maintain vehicle safety with ABS operation on any kinds of road
surface, rear wheel braking pressure is managed according to the wheel which shows more lockup tendency. This control concept is called ‘Select-low control’.
3) 4-Sensor 3-Channel type (Front wheels;indendent control,Rear wheels ; Select contnrol )
Vehicle with H-bake line system has this ABS control system. 2 channels are for front wheels and
the other one is for rear wheel control. Rear wheels are controlled together by a select low control
logic.
In case of X-brake line system, 2 channels (2 brake ports in the ABS unit) are required to control
rear wheel pressure because each rear wheel belongs to different brake line.

4) 1-Sensor 1-Channel type ( Rear wheels: Select low control )
Vehicle with H-bake line system. Only controls rear wheel pressure.
One wheel speed sensor is installed on a rear differential detecting rear wheel speed. Front wheels
are locked up while heavy braking, vehicle loses its steering stability and stopping distance on a
low-μ road surface also increases. This system helps vehicle have a straight stop.

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2.4. ABSCM
ABS consists of wheel speed sensors which detects a wheel lock-up tendency, on the basis of
wheel speed sensor signal a ABSCM(Control Module) which outputs control signal and
HCU(Hydraulic Control Unit) which supplies brake pressure to each wheel according to the
ABSCM output signals.


ABSCM(CONTROL MODULE)
From the wheel speed sensor signals, ABSCM calculates an estimated acceleration, deceleration
and slip ratio. This controls solenoid valves and return pumps to prevent a wheel lock-up.
Moreover, ABSCM manages a system monitoring circuit and turn off itself to protect the system if a
system faulty is detected. Driver can recognize a system malfunction when ABS warning lamp
comes on.
1) Basic Composition of ABSCM
Once ABS fails, ABSCM should inhibit the system operation to guarantee the system safety.
Because abnormal solenoid valve operation can affect the brake pressure on wheels. With this
reason, ABSCM can analyze and prepare all kinds of possible faulty causes.
To install the ABSCM directly on the HCU(Hydraulic Control Unit), semiconductors inside ABSCM
should resist at the temperature range of –40 ~ +125 degrees Celsius. Owing to the enhanced
technology on semiconductor and size reduction, Integrated type (ABSCM+HCU) is popularly used
worldwide. For example, Bosch ABS version 5.0 or higher, version MK-20i or higher of TEVES and
EBC 325 of Kelsey Hayes are representative integrated ABS.
All inputs are double-monitored and double-calculated. Inputs are also double-monitored.
Moreover, to prevent a improper operation of ECU, two microprocessors compare and monitors
their results And ECU is additionally monitored by SAS(Safety Assurance System) or intelligent
Watch-Dog to prevent a ECU’s wrong operation. One IC controls solenoids at each channel and a
Power MOSFET with a very reliable protect circuit is substituted for relays which handled solenoid
operation and big current while motor operation. Furthermore, motor speed control is being
employed to reduce excessive pumping and Kick-Back. 16 bit of microprocessor is used for the
better ABS performance and wheel speed calculation which requests around 5msec of one cycle
operating time.
ABSCM consists of several basic circuits below
a) Wheel Speed Sensor Input Amplification circuit
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From each wheel speed sensors installed each wheel, alternating current waveforms in proportion
to the vehicle speed come in the circuit. The waveforms are amplified and converted into the
square waveforms, and are sent to the Microcontroller. According to ABS types, the number
ofwheel speed sensors changes and the number of amplification circuit also changes.
b) Microcontroller
From each wheel speed information, this calculates a Reference Speed, Slip Ratio,
Acceleration/Deceleration rates and performs solenoid valve & motor operation. This circuit detects
the wheel speed sensor waveforms generated by the teeth of sensor rotor at every moment.
Microcontroller calculates a reference speed by integrating a momentary wheel speed and then
compares the reference speed and a momentary wheel speed to estimate a slip ratio and an
acceleration/deceleration rates.
Solenoid valve activation circuit outputs pressure dump, hold, increasing signals to the lock-up
wheels’ solenoids according to the estimated control signals like a slip ratio, acceleration/decelerration rates.
c) Solenoid Valve activation circuit
This circuit controls the solenoid valve current and turns it on or off on the basis of the pressure
dump, hold, increasing signal from the Microcontroller.
d) Voltage Regulator, Motor Relay & Failsafe Relay Driver circuit, Lamp Driver circuit,
Communication circuit
Monitors the supply voltage(5V, 12V) being used for ABSCM is stable within the threshold voltage
range. This detects a system failure and activates valve relay, motor relay. System faulty is
detected, ABS system is down because a valve/motor relay comes off and ABS warning lamp turns
on to inform the driver of system failure. While ABS failure, normal braking is available.

ABS ECU Block Diagram
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- ABS ECU Block Diagram
Solenoid

VCC

IGNITION

Voltage
Reg.

8 × Valve Driver
Valve
Relay

BATT 1

Processor 2
(8bit)

Processor 1
(16bit)

BATT 2

EBD W/L

Interface Circuit


M
Motor
Relay

A/D Monitor Circuit

Lamp Driver Circuit

Motor relay & FSR Driver Circuit

Communicaion Circuit

Wheel signal conditioning Circuit

Swtich Control/Clamp Circuit

Wheel Sensors FR Speed Out

ABS W/L

K-Line

BLS

BTCS ECU Block Diagram
- BTCS ECU Block Diagram
Solenoid

VCC


IGNITION

Voltage
Reg.

8 × Valve Driver

2 × Valve Driver

Processor 1
(16bit)

Processor 2
(8bit)

Valve
Relay

BATT 1
BATT 2

M

Interface Circuit
Motor
Relay

BTCS Lamp


A/D Monitor Circuit

Lamp Driver Circuit

Motor relay & FSR Driver Circuit

Communicaion Circuit

Wheel signal conditioning Circuit

Swtich Control/Clamp Circuit

Wheel Sensors FR Speed Out

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EBD W/L
ABS W/L
K-Line

BLS

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2) Safety Circuit
Ignition switch turns on, ABSCM performs a self-test until the vehicle speed reaches certain speed
and also monitors system while driving. When a system failure is detected, firstly stops the ABS

function and illuminates ABS warning lamp to inform the driver of system breakdown. Even in case
of an ABS breakdown, conventional brake is still available. After turn the IG off and turn it on, if a
system faulty is not detected, warning lamp turns off and system comes normal.
a) Initial Self-Testing after the IG on,(vehicle stops)
When the IG switch turns on and the voltage comes in ABSCM, followed procedures performs.
▪ Microprocessor function check


Makes an Watchdog Error and check if the error is detected



Checks the ROM data



Checks the RAM data whether data reading, writing is normal



Checks the A/D(Analog /Digital) Converter operation



Checks the communication between two microprocessor

▪ Valve Relay function check

 Activates a valve relay and check the operation
▪ Fail Memory function check


 Checks the fail memory circuit of a microprocessor
b) Initial Self-Testing while a vehicle begins to move
A vehicle begins to move, ABSCM performs actuators’ function test.

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▪ Solenoid Valve function test

 Checks the solenoid valve function and monitors its operation
▪ Motor function test

 Operates a motor and check its condition. According to the ABS makers, the self-testing
time of motor can be considerably different. But mostly, self-testing is performs at the
beginning of vehicle driving or at the end of ABS operation.
▪ Wheel Speed Sensor signal check

 Checks whether all wheel speed sensor signals
c) System test while driving
After completing the initial self-test, ABS system is check by two microprocessor and other circuits
surrounding. If a faulty is detected, microprocessor finally confirms it and the corresponding error
code is memorized in ABSCM.
▪ Voltage test (12V, 5V)

 Checks the supplied 12 voltage and 5 voltage inside ABSCM is normal. But the
momentary voltage drop caused by ABS operation or motor operation is considered while

monitoring 12 voltage.
▪ Valve Relay operation test

 While ABS operation, valve relay is activated. ABSCM watchdogs a valve relay operation.
▪ Calculation Result comparison between two microprocessor

 Usually, there are two microprocessors inside ABSCM and they perform the same
operation at the same time. They compare their results each other and identify their
sameness. This comparison concept guarantees the system trust and can detect the
system failure at an early stage.
▪ Microprocessor operation test

 Monitors microprocessor’s normality.
▪ ROM Data check

 Performs a Check Sum of ROM data and confirms the program’s normality.
d) Display Self Diagnosis
When a system faulty is detected by a safety circuit, ABS function stops illuminating the ABS
warning lamp. ABSCM displays trouble codes via a scan tool. With the scan tool, activates
solenoid valves and motor.
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2.5. TYPICAL ABS CONTROL CYCLES

2.5.1. BRAKING CONTROL ON A HIGH-GRIP ROAD SURFACE (HIGH BRAKING FORCE

COEFFICIENT)
During initial braking, the brake pressure in the wheel brake cylinder and the each wheel
deceleration increase.
At the end of phase 1, the wheel deceleration exceeds the set threshold (-a). As a result, the
corresponding solenoid valve switches to the “pressure hold” position. The brake pressure
must not be reduced yet, because the threshold(-a) could be exceeded in the stable range of
the braking force coefficient/ brake slip curve. At the same time, the reference speed is
reduced. The value for the slip switching threshold λ1 is derived from the reference speed.
The wheel speed falls below the λ1 threshold at the end of phase 2. The solenoid valve then
switches to the “pressure drop” position, with the result that the brake pressure is reduced until
the wheel deceleration has exceeded the threshold (-a).
The speed falls below the threshold(-a) again at the end of phases 3 and a pressure hold
phase of a certain length follows. The wheel acceleration increases within this time to such an
extent that the threshold(+a) is exceeded. The pressure remains constant. At the end of phases
4, the acceleration exceeds the relatively high threshold(+A). The brake pressure then
increases as long as the threshold(+A) is exceeded.
In phase 6, the brake pressure is kept constant again because the threshold(+a) is exceeded.
At the end of this phase, the peripheral wheel acceleration falls below the threshold(+a). This is
an indication that the wheel has entered the stable range of the braking force coefficient/brake
slip curve and is slightly under-braked.
The brake pressure is now built up in stages(phase 7) until the wheel deceleration exceeds the
threshold(-a)(end of phase 7). This time, the brake pressure is decreased immediately without
generation of a λ1 signal

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