Tài liệu đào tạo HYUNDAI ABS TCS ppt

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ABS/TCS/ESP
TRAINING GUIDE


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HYDRAULIC
FUNDAMENTALS


HYDRAULIC FUNDAMENTALS
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.

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HYDRAULIC FUNDAMENTALS

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PASCAL’s Law
100 kgf
10 kgf

Area : 1m2

Area : 10m2

P1=10kgf/m2

Hydraulic fluid


HYDRAULIC FUNDAMENTALS
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).

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HYDRAULIC FUNDAMENTALS
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
10m2 on the floor ; the pressure exerted by the block is : 100kg/10m 2 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

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HYDRAULIC FUNDAMENTALS
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/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.

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HYDRAULIC FUNDAMENTALS
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/m2. The concept “Pressure is the same everywhere”,
means that the pressure underneath the larger piston is also 10 kg/m 2.
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.

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HYDRAULIC FUNDAMENTALS
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-todistance 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.
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.

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HYDRAULIC FUNDAMENTALS
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

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HYDRAULIC FUNDAMENTALS
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.

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HYDRAULIC FUNDAMENTALS
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.

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HYDRAULIC FUNDAMENTALS
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.

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HYDRAULIC FUNDAMENTALS
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.

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HYDRAULIC FUNDAMENTALS
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


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

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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
② If the rear wheels lock
▶ the car can become unstable and can start to skid sideways

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ADVANTAGES OF ABS

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Braking at cornering
[Without ABS]

[With ABS]


ADVANTAGES OF ABS

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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]

Low μ road

[Braking with ABS]

Low μ road
High μ road
surface

High μ road
surface


ABS TYPES
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.

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ABS TYPES

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System Evaluation
Evaluation Item
System Type

4-Sensor 4-Channel

Brake line

X line
or H line

Control Logic
All wheels independent
control

Steerability Stability

Stopping
distance

Good

Fair

Good

Good

Good

Fair

Good

Good

Fair

Good

Good

Fair

NO

Fair

No

Front: Independent control
Rear: Select Low
Front: Independent control

4-Sensor 3-Channel

H line
Rear: Select Low
Front: Independent control

3-Sensor 3-Channel

H line
Rear: Select Low

1-Sensor 1-Channel

H line

Rear: Select Low


ABS TYPES

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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]


ABS TYPES
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
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 lock-up tendency.
This control concept is called ‘Select-low control’.

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ABS TYPES

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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.

[FF car, H-line brake system]

[FR car, H-line brake system]