Ignition System Function - GF07.10-D-1005TSB

Engine 274 in model 907 

Block diagram 

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. The ME-SFI [ME] control unit (N3/36) reads in the following signals for 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)
• Charge air temperature sensor upstream of throttle valve (B17)
• Charge air temperature sensor downstream of throttle valve (B17/16)
• Intake manifold pressure sensor (B28/24), engine load
• Crankshaft Hall sensor (B702), engine speed and crankshaft position

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 of the respective operating point for the ignition coil via the actuation line.

The respective ignition coil interrupts the primary circuit after expiry of the dwell time. 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 with high energies, which allow a long spark ignition period, are used to securely ignite the fuel/air mixture, even in cold start conditions.

Multi-spark ignition 

There is also the option of using several sparks for each ignition process instead of just one spark. This operating mode is called multi-spark ignition.

In contrast to single-spark ignition, multi-spark ignition does not involve a series of single sparks occurring one after the other, but instead the ignition coil is recharged in-between in order to provide sufficient energy for sparks again.

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. The charging current is interrupted at the ignition timing whereby the ignition spark is created. The ignition coil is not fully discharged for multi-spark ignition.

The flowing secondary current 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, the coil electronics switches the power amplifier to conducting again, whereby the charging current flows again.

The level of the flowing primary current is also monitored. If the primary current threshold is reached, the power amplifier closes the primary circuit and it comes again to generation of a high voltage. This produces a further spark. The subsequent sparks are generated according to the same scheme.

Electrical function schematic for ignition system	PE07.10-D-2705-97TSA
Overview of system components for gasoline injection and ignition system with direct injection	GF07.70-D-9998TSB