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ABS/TCS/ESP

TRAINING GUIDE

HYDRAULIC FUNDAMENTALS

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

PASCAL’s Law

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)

Pressure is nothing more than force (kg) divided by area (m2), or force

per unit area Given the same 100kg block used above and an area of 10m2 on the floor ; the pressure exerted by the block is : 100kg/10m2 or 10kg per square meter

Pressure On a Confined Fluid

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 10m2, then pressure created equals 10kg/m2 = 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

Going back to the previous figure and using the 10kg/m2 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/m2 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

Force Multiplication

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

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

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

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

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 The

internal-external type of pump design is used almost exclusively in

today’s automatic transaxle

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

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

ABS GENERAL

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

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

② If the rear wheels lock

▶ the car can become unstable and can start to skid sideways

[Without ABS] [With ABS]

Braking at cornering

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]

surface

Low μ road

High μ road surface

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 vehicle stability while

ABS operation

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

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)

1-Sensor 1-Channel type

Only control the rear wheel pressure by one sensor

Steerability Stability Stopping

distance All wheels independent

Front: Independent control Rear: Select Low

Front: Independent control Rear: Select Low

Front: Independent control Rear: Select Low

1-Sensor 1-Channel H line Rear: Select Low NO Fair No

Evaluation Item Brake line

System Type Control Logic

Good Good Fair Good Good Fair

System Evaluation

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

[FF car, X-line brake system]

2) 4-Sensor 4-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

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 lock-up tendency

This control concept is called ‘Select-low control’

3) 4-Sensor 3-Channel type (Front wheels: independent control, Rear wheels: Select low control )

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

[FR car, H-line brake system]

[FF car, H-line brake system]

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

[FR car, H-line brake system]

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

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

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

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 of

wheel 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/deceleration 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

Processor 2 (8bit) Solenoid

Wheel Sensors

ABS W/L EBD W/L

- ABS ECU Block Diagram

Processor 1 (16bit)

Valve Relay

IGNITION Voltage

Reg.

Processor 1 (16bit)

Processor 2 (8bit) Solenoid

ABS W/L BTCS Lamp

K-Line EBD W/L

VCC

- BTCS ECU Block Diagram

BLS Wheel Sensors FR Speed Out

8 × Valve Driver 2 × Valve Driver

M

Valve Relay

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

a.1) 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

a.2) Valve Relay function check

- Activates a valve relay and check the operation

a.3) 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

b.1) Solenoid Valve function test

- Checks the solenoid valve function and monitors its operation

b.2) 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

b.3) 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

c.1) 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

c.2) Valve Relay operation test

- While ABS operation, valve relay is activated ABSCM watchdogs a

valve relay operation

c.3) 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

c.4) Microprocessor operation test

- Monitors microprocessor’s normality

c.5) 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

Braking control on a high-grip road surface (high 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)