SsangYong Rexton. Manual - part 91

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Y220_08011

Balancing of the point to point flows

The pulse of each injector is corrected according to the difference in instantaneous speed measured between 2 succes-
sive injectors.

• The instantaneous speeds on two successive injections are first calculated.

• The difference between these two instantaneous speeds is then calculated.

• Finally, the time to be added to the main injection pulse for the different injectors is determined. For each injector,

this time is calculated according to the initial offset of the injector and the instantaneous speed difference.

Detection of an injector which has stuck closed

The cylinder balancing strategy also allows the detection of an injector which has stuck closed. The difference in instantaneous
speed between 2 successive injections then exceeds a predefined threshold. In this case, a fault is signaled by the system.

Cylinder Balancing Strategy

Accelerometer Strategy

Resetting the pilot injection

The accelerometer is used to reset the pilot injection flow in closed loop for each injector. This method allows the
correction of any injector deviations over a period of time. The principle of use of the accelerometer is based on the
detection of the combustion noises.

The sensor is positioned in such a way as to receive the maximum signal for all the cylinders. The raw signals from the
accelerometer are processed to obtain a variable which quantifies the intensity of the combustion. This variable, known
as the ratio, consists of the ratio between the intensity of the background noise and the combustion noise.

• A first window is used to establish the background noise level of the accelerometer signal for each cylinder. This

window must therefore be positioned at a moment when there cannot be any combustion.

• The second window is used to measure the intensity of the pilot combustion. Its position is such that only the

combustion noises produced by the pilot injection are measured . It is therefore placed just before the main injection.

The accelerometer does not allow any evaluation of the quantity injected. However, the pulse value will be measured
when the injector starts injection and this pulse value is called the MDP (Minimum Drive Pulse). On the basis of this
information, it is possible to efficiently correct the pilot flows. The pilot injection resetting principle therefore consists of
determining the MDP, in other words the pulse corresponding to the start of the increase in value of the ratio (increase
of vibration due to fuel combustion).

Cylinder pressure

Needle lift

Ratio

Minor pilot injection

No pilot injection

No injection

Major pilot injection

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This is done periodically under certain operating conditions. When the resetting is finished, the new minimum pulse
value replaces the value obtained during the previous resetting. The first MDP value is provided by the C2I. Each
resetting then allows the closed loop of the MDP to be updated according to the deviation of the injector.

Detection of leaks in the cylinders

The accelerometer is also used to detect any injector which may have stuck open. The detection principle is based on
monitoring the ratio. If there is a leak in the cylinder, the accumulated fuel self-ignites as soon as the temperature and
pressure conditions are favorable (high engine speed, high load and small leak).

This combustion is set off at about 20 degrees before TDC and before main injection.

The ratio therefore increases considerably in the detection window. It is this increase which allows the leaks to be
detected. The threshold beyond which a fault is signaled is a percentage of the maximum possible value of the ratio.
Because of the severity of the recovery process (engine shut-down), the etection must be extremely robust.

An increase in the ratio can be the consequence of various causes:

• Pilot injection too strong

• Main combustion offset

• Fuel leak in the cylinder

If the ratio becomes too high, the strategy initially restricts the pilot injection flow and retards the main injection. If the
ratio remains high despite these interventions, this shows that a real leak is present, a fault is signaled and the engine
is shut down.

Detection of an accelerometer fault

This strategy permits the detection of a fault in the sensor or in the wiring loom connecting the sensor to the ECU. It is
based on detection of the combustion. When the engine is idling, the detection window is set too low for the combustion
caused by the main injection. If the ratio increases, this shows that the accelerometer is working properly, but otherwise
a fault is signaled to indicate a sensor failure. The recovery modes associated with this fault consist of inhibition of the
pilot injection and discharge through the injectors.

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INDIVIDUAL INJECTOR CALIBRATION (C2I)

Injected fuel is proportional to square root of injection time and rail pressure.

It is function between pulse and rail pressure and fuel injection curve is called injector characteristics curve having the
following shape.

Common rail injectors are very accurate components. They are able to inject fuel delivery between 0.5 to 100 mg/str
under pressure varying from 150 to 1600 bar.

This high level of accuracy requires very low machining tolerances (few 

).

Nevertheless, due to the machining dispersion, the loss of charge through the functional orifices, the friction between
moving parts and electromagnetic field level are different from one injector to the other. So, the difference of fuel delivery
for the same pressure and the same pulse can reach 5 mg/str from one injector to the other. It is impossible to control
efficiently the engine with such a dispersion between the different injectors. It is necessary to add a correction that
allows injecting the demanded fuel delivery whatever the initial hydraulic characteristics of the injector is. The method
consists in correcting the pulse that is applied to the injector with an offset that depends on the initial hydraulic map of
the injector. So, the pulse should be corrected according to characteristics of each injector.

Y220_08012

Delivery (mm

3

/st)

Drive pulse (

µsec)

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C2I is composed of models on these characteristics of injectors.

C2I consists of 16-digit; composed of numbers from 1 to 9 and alphabets from A to F. ECU remembers C2I, character-
istics of each injector, to make the most optimal fuel injection.

• When replacing the injector, C2I code on the top of new injector should be input into ECU because the ECU is

remembering the injector’s C2I value. If C2I is not input, engine power drops and occurs irregular combustion.

• When ECU is replaced, C2I code of every injector should be input. If not, cannot accelerate the vehicle even when

the accelerator pedal is depressed.

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For coding of C2I, refer to “Diagnosis” section

C2I Number

(16 digits)

C2I

value