SSANGYONG NEW ACTYON SPORTS 2012 Service Manual

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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5. SYSTEM OPERATION
1) Block Diagram of ABS HECU

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)

10-16
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.

10-18
4) ABS Control Pattern
The ABS control is performed by comparing the reference speed with each wheel speed. Firstly,
it is determined whether the vehicle is in the deceleration or acceleration state using the wheel
speed change ratio. Then, a signal is transmitted to the valve.
Finally, the brake pressure is adjusted via the signal.
△V: Vehicle speed
Vref: Vehicle speed reference
Vw: Wheel speed

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5) EBD (Electronic Brake Force Distribution) System
System description ▶
As an add-on logic to the ABS base algorithm, EBD works in a range in which the intervention
thresholds for ABS control are not reached yet.
EBD ensures that the rear wheels are sensitively monitored for slip with respect to the front axle. If
slip is detected, the inlet valves for the rear wheels are switched to pressure hold to prevent a
further increase in pressure at the rear-wheel breaks, thus electronically reproducing
a pressure-reduction function at the rear-wheel brakes.
ABS features an enhanced algorithm which includes control of the brake force distribution
between the front and rear axles. This is called Electronic Brake Distribution. In an unloading car
condition the brake efficiency is comparable to the conventional system but for a fully loaded
vehicle the efficiency of the EBD system is higher due to the better use of rear axle braking
capability.
Advantages ▶
Elimination of conventional proportioning
valve EBD utilizes the existing rear axle
wheel speed sensor to monitor rear wheel
slip.
Based on many variables in algorithm a
pressure hold, increase and/or decrease
pulsetrain may be triggered at the rear
wheels insuring vehicle stability.
Vehicle approaches the ideal brake force
distribution (front to rear).
Constant brake force distribution during
vehicle lifetime.
EBD function is monitored via ABS safety
logic (conventional proportioning valves are
not monitorable). -
-
-
-
-
Ideal distribution
EBD start point
Cut-in point
Fixed distribution 1.
2.
3.
4.

10-20
6. HYDRAULIC CIRCUIT OF ABS
1) Normal Brake Operation (ABS is not working) Mode
If the driver depress the brake pedal so that the ABS does not operate, the hydraulic pressure in
the master cylinder increases through the vacuum booster and it is delivered to the wheel via the
normal open inlet valve. At this moment, the normally-closed outlet valve is closed The speed of
the wheel that hydraulic pressure is delivered reduces gradually.
Solenoid valve Valve Open/Close Pump motor
Inlet valve - Normal open (NO) valve Open
OFF
Outlet valve - Normal close (NC) valve Close

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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