Ignition System: Description and Operation
GF15.15-P-3000MOS ECI Ignition System, Function
ENGINE 275.953 in MODEL 216.376, 221.176 as of Model Year 09 /AEJ 08
ENGINE 275.982 in MODEL 216.379, 221.179 as of Model Year 09 /AEJ 08
Function requirements for the ignition system, general points
^ Circuit 87M ON (engine control ON)
Ignition system, general points
The short name for the AC ignition system ECI means:
E = Energy
C = Controlled
I = Ignition
The ECI ignition system initiates combustion by generating sparks at the spark plug (R4). To do this, it must provide a sufficiently high voltage to cross the spark gap and sufficient energy to ignite the fuel-air mixture.
The ignition system is impervious to spark plug carbon fouling and ensures long service life for the spark plugs.
The ignition system ECI consists of:
- ECI ignition system power pack (N91)
- ECI ignition module, RH cylinder bank (N92/1)
- ECI ignition module, LH cylinder bank (N92/2)
- ME-SFI control unit (N3/10) (for evaluation of ionic current, actuation at "tml. 1", ignition maps)
- Spark plugs
No spark tests can be carried out on the ECI ignition system.
ECI ignition system function sequence
The ECI ignition system is divided into the following subfunctions:
^ Ignition voltage generation function sequence
^ Ignition spark control function sequence
^ Ionic current measurement function sequence
Ignition voltage generation function sequence
The power pack generates the required ignition voltages (AC voltages) of 2 x 180 V approx. and the auxiliary voltages of 2 X 23 V approx. for ionic current measurement..
One output stage per spark plug is provided in the ignition modules. The ignition coils are integrated in the spark plug connectors. The output stages generate the ignition voltage from about 180 V.
The ignition voltage is generated in two steps:
1. Transistor closed in the ECI power pack - 180 V voltage transferred to the secondary side.
2. Transistor open in the ECI power pack - the negative half-wave of the AC voltage is generated and is also transferred to the secondary side.
Control of the transistor can theoretically allow generation of an AC voltage of any desired duration and energy level.
However, the maximum spark duration is limited by the rated output of the ECI power pack (2 x 55 W) to between about 0.15 and 1.5 ms, depending on rpm. A spark duration of about 0.1 ms is sufficient to ignite the mixture.
The rapid increase in ignition voltage makes the
The ECI ignition system is impervious to carbon fouling of the spark plugs, for example due to frequent cold starts.
Ignition spark control function sequence
The ignition sparks are triggered by the ME-SFI control unit according to the ignition map.
Spark duration control
Adaptation of the spark energy by spark duration to the actual energy requirement for ignition of the fuel-air mixture is map- controlled by ME-SFI control unit
The spark plugs enjoy 4 times their usual working life due to spark duration control. Combining this at the same time with the use of spark plugs with platinum electrodes allows the working life to be extended even further.
Ignition offset and ignition change
In the lower part load range up to approx. 2000 rpm both ignition sparks of a cylinder are triggered simultaneously. At medium and high loads ignition is displaced by up to 10° CKA (Crank Angle).
The actuation sequence is changed every 720° crank angle, to ensure even wear on the two spark plugs in the cylinder and prevent single-sided deposits in the combustion chamber.
Ionic current measurement function sequence
When the ignition spark has ended, ionic current measurement is started and the ionic current at the spark plug is measured with the auxiliary voltage of about 23 V. Evaluation of the ionic current signals takes place in the ME control unit. The signals are used for detection of combustion misfires at high rpms.
Ionic current measurement at the spark plug delivers a signal directly from the combustion chamber without the use of any additional components such as combustion chamber pressure sensors.
The measurement is taken after a successful ignition at both spark plugs and a brief waiting time. The measurement is only taken on the spark plug which first sparked. The electrode gap has no effect on the ionic current signal.
During combustion, ions are created at the flame front (particles with different electrical charges), which are balanced out again in the burnt fuel-air mixture.
By applying a relative low measurement voltage to the spark plug (about 23 V) after the spark has ended, the ionic current can be measured through the flame.
The measurement voltage is applied to the primary side of the ignition coils. On the secondary side, this produces an AC voltage of about 1 kV at 65 kHz at the spark plug electrodes. The ionic current modulates this voltage.
Decoupling and filtering allows one to obtain an ionic current signal. The ionic current signal gives information about cylinder pressure characteristics, with some accuracy, and can therefore be used to detect combustion misfires.
The ionic current signal is transferred to the control unit ME for every 3 cylinders. The cylinder concerned in each case is allocated in the control unit ME with the help of measuring windows.
Ionic current signal and cylinder pressure
A Behavior pattern of the ionic current signal
B Behavior pattern of the cylinder pressure
c Knock vibrations
d Measuring window position for ionic current measurement
The characteristics of the ionic current signal and cylinder pressure are the same during combustion.
The ionic current can thus be used to securely detect combustion misfires in all operating conditions and at all engine speeds.
The ionic current signal is also used to control spark duration, and for spark plug diagnosis, diagnosis (as in on-board diagnosis (OBD) or EURO4) and cylinder-specific fuel shutoff.
