lock SSANGYONG NEW ACTYON SPORTS 2012 Service Manual

10-14
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.

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Slip ▶
The brake slip is the difference between the vehicle speed and the wheel circumference speed. If
the wheel locks, the slip is greatest, that is 100 %. If the wheel is running freely and un-braked,
the slip is the lowest, equal to 0 %. Slip can be calculated from the vehicle speed Vveh and the
wheel speed Vw. The equation for this is:
Vveh = 100 km/h, Vw = 70 km/h
Slip ratio (S) = X 100%
S = 30%Vveh - Vw
Vveh
Typical Slip Curves ▶
For the various road conditions, the friction
coefficients were plotted. The typical course
of the curves is always the same. The only
special feature is shown by the curve for
freshly fallen snow, for this curve increases
at 100 % slip. In a vehicle without ABS, the
wheel locks on braking and therefore
pushes a wedge before it. This wedge of
loose surface or freshly fallen snow means
and increased resistance and as a result the
stopping distance is shorter. This reduction
in stopping distance is not possible with a
vehicle with ABS, as the wheel does not
lock. On these surfaces the stopping
distance with ABS is longer than without
ABS. The reason for this is based in physics
and not in the Anti-Lock System.
However, as mentioned before, ABS is not
about the stopping distance, but
maneuverability and driving stability, for the
vehicle with locking wheels without ABS
cannot be steered. Ex)

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KAMM circle ▶
Before we go into the Kamm circle, you
should know that a tire offers a maximum of
100 % transmissibility. It is all the same for the
tire whether we require 100 % in the direction
of braking or in the direction of the acting
lateral force, e.g. when driving round curves. If
we drive into a curve too fast and the tire
requires 100 % transmissibility as cornering
force, the tire cannot transmit any additional
brake force. In spite of the ABS the car is
carried out of the curve. The relationship
between brake force B and cornering force S
is shown very clearly in the Kamm circle. If we
put a vehicle wheel in this circle, the
relationship becomes even clearer. In this
relationship: as long as the acting forces and
the resulting force remain within the circle, the
vehicle is stable to drive. If a force exceeds
the circle, the vehicle leaves the road.
Brake force
When depressing the brake pedal the brake
force increases to the maximum, then the
brake force decreases until the wheel locks.
Cornering force
The cornering force is a maximum when the
wheel is turning freely with zero slip. When
braking the cornering force falls to zero if the
wheel locks (slip 100 %).
ABS operating range
The operating range starts just before the
maximum brake force and ends in maximum,
for the unstable range then begins, in which
no further modulation is possible. The ABS
controls the regulation of the brake pressure
so that the brake force only becomes great
enough for a sufficient proportion of cornering
force to remain. With ABS we remain in the
Kamm circle as long as the car is driving
sensibly. We will leave driving physics with
these statements and turn to the braking
systems with and without ABS. -
-
- Brake and cornering force ▶

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3) Basic ABS Control
Operation of ABS control unit ▶
Applications of the ABS control unit The
signals produced by the wheel sensors are
evaluated in the electronic control unit. From
the information received, the control unit
must first compute the following variables:
Wheel speed
Reference speed
Deceleration
Slip -
-
-
-
Reference speed ▶
The reference speed is the mean, I.e. average speed of all wheel speeds determined by simple
approximation.
Simplified ABS control ▶
If, during braking, one wheel speed deviates from the reference speed, the ABS control unit
attempts to correct that wheel speed by modulating the brake pressure until it again matches the
reference speed. When all four wheels tend to lock, all four wheels speeds suddenly deviate from
the previously determined reference speed. In that case, the control cycle is initiated again in
order to again correct the wheel speed by modulating the brake pressure.

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2) DUMP (ABS is working) Mode
Even when the hydraulic pressure on each circuit is constant, the wheel can be locked as the
wheel speed decreases. This is when the ABS HECU detects the wheel speed and the vehicle
speed and gives the optimized braking without locking the wheels. In order to prevent the
hydraulic pressure from increasing, the inlet valve will be closed, the outlet valve will be opened
and the oil will flow into the low pressure chamber. In addition, the ABS HECU operates the pump
to circulate the oil in the low pressure chamber to the master cylinder. This may make the driver to
feel the brake pedal vibration and some
Solenoid valve Valve Open/Close Pump motor
Inlet valve - Normal open (NO) valve Close
ON
Outlet valve - Normal close (NC) valve Open

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3) HOLD (ABS is working) Mode
As hydraulic pressure on each wheel increases, the wheel tends to lock. In order to prevent the
wheel from locking, the hydraulic valve modulator operates the inlet valve control solenoid to stop
increasing the hydraulic pressure by closing the inlet valve. At this moment, the outlet valve is
closed. This procedure helps the wheel to maintain a constant hydraulic pressure.
Solenoid valve Valve Open/Close Pump motor
Inlet valve - Normal open (NO) valve Close
OFF
Outlet valve - Normal close (NC) valve Close

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4) RISE (ABS is working) Mode
As the wheel speed increases, the inlet valve opens and the wheel's pressure increases due to
the master cylinder pressure. In addition, the pump circulates the oil in the low pressure chamber
to the wheel. As the hydraulic pressure to the wheel increases, the wheel speed will reduce. This
operation continues repetitively until there are no signs that the ABS HECU tends to lock the
wheels. Since the ABS hydraulic pressure control process takes place repeatedly for a short time,
there may be some vibration and noises at the brake pedal.
Solenoid valve Valve Open/Close Pump motor
Inlet valve - Normal open (NO) valve Open
ON
Outlet valve - Normal close (NC) valve Close

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1. SPECIFICATION
1) Specification of Active Wheel Sensor
Description Specification Remark
Supplying voltage 4.5 ~ 16.0V
Output current (at 2.75 km/h of
vehicle speed)7mA(Lo) ~ 14mA(Hi)
Tightening torqueFront: 7.8 to 11.8 Nm
Rear: 7.8 to 11.8 Nm
Operating temperature-40 ~ 150℃
Operating frequency 1 ~ 2,500Hz
UnitDescription
Specification
ABS ESP
HECU Clock frequency: 32 MHz Clock frequency: 50 MHz
Memory: 128 KB Memory: 256 KB
Wheel speed
sensorActive type Active type Output: 7~14
mA
Steering wheel
angle sensorNone Max. detection angle speed:
1500 °/SecPulse duty:
50±10%
Operating voltage: 9 to 12 V
Sensor cluster None Yaw rate sensor + lateral G
sensor + longitudinal G sensor
(4WD)Mounting
direction should
be kept (CAN
communcation)
Longitudinal G
sensor4WD only None
Pressure
sensorNone HECU integrated

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5. SYSTEM DESCRIPTION
1) Block Diagram of ESP HECU

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2) DUMP (ESP is working) Mode
The pressure decreases just before the wheel speed drops and the wheels are locked.
The inlet valve closes and the outlet valve opens as in the ABS HECU and the oil is gathered at
the low pressure chamber while no additional oil is being supplied. Then the pump operates to
allow fast oil drainage. The shuttle valve and the separation valve do not operate while
decompression.