Ignition System Function - GF07.10-S-1005TRJ
Engine 274 in model 447.6/7
with code XM0 (Facelift)
Function requirements for the ignition system, general points
- Circuit 87M (Engine management ON)
Ignition system, general points
Each cylinder is equipped with a directly inserted ignition coil. To control the ignition system, the ME-SFI [ME] control unit (N3/34) reads in the signals of the following sensors over the direct line to control the ignition system:
- Knock sensor 1 (A16/8)
- Knock sensor 2 (A16/9)
- Intake camshaft Hall sensor (B6/29)
- Exhaust camshaft Hall sensor (B6/30)
- Coolant temperature sensor (B11/21)
- Intake manifold pressure sensor (B28/24)
- Crankshaft Hall sensor (B70/2)
- Charge air temperature sensor upstream of throttle valve (B17)
- Charge air temperature sensor downstream of throttle valve (B17/16)
The requirements of the torque coordination function are also taken into account.
For the following partial functions, ignition angle adjustment in the direction "retarded" or "advanced" takes place:
- Idle speed control
- Inertia fuel shutoff
- Transmission overload protection
- Knock sensor system
- Torque coordination
Function sequence for ignition system
The ME-SFI [ME] control unit outputs the signal for the dwell time (A) of the respective operating point to the ignition coil via the actuation line (circuit 4). The respective ignition coils interrupts the primary circuit after expiration of the dwell time (A). The ignition voltage passes from the ignition coil to the spark plug and causes arcing in the air gap between the center and ground electrodes.
Determination of the ignition angle takes place dependent on a characteristics map according to the input signals from the ME-SFI [ME] control unit.
Operating mode of ignition coil
Single spark ignition
The ignition coil is generally charged for an engine running at its normal operating temperature once per ignition cycle and an ignition spark is generated. Ignition coils (T1) can be used to securely ignite the mixture, also in cold start conditions, which allow a long spark ignition period.
Multi-spark ignition
In contrast to single spark ignition more sparks are generated for multi-spark ignition. This is not a series of a number of single sparks occurring one after the other but instead the ignition coil is recharged in-between in order to again provide sufficient energy for sparks. A multi-spark ignition begins like a single spark ignition. The ignition coil is supercharged at the beginning up to a desired target primary current (i1). The charging current (E) is interrupted at the ignition timing whereby the ignition sparks are created. The ignition coil is not fully discharged for multi-spark ignition.
The flowing secondary current (i2), which directly depends on the charge level of the ignition coil is measured in the ignition coil. If it drops below the secondary current threshold (D), the coil electronics switch the power amplifier to conducting, whereby the charging current flows again.
The level of the flowing primary current (i1) is also monitored. If the primary current threshold (C) is reached, the power amplifier closes the primary circuit and it comes again into high voltage generation mode This produces a further spark. The next sparks are also generated according to the same scheme.
Ideal development of the primary and secondary current for a multi-spark ignition
The arrow designates the direction of travel.
Engine configuration and ignition firing order
| Function schematic for ignition system | PE15.10-S-2500-97TRH | ||
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