Ignition system function

Function requirements for the ignition system, general points

 Circuit 87M (engine control ON)

Ignition system, general points

Each cylinder is fitted with a single-spark ignition coil (T1).

For the ignition system, the ME-SFI (N3/10) control unit reads in the following sensors and signals:

- Knock sensor 1 (A16/1)

- knock sensor 2 (A16/2)

- intake camshaft Hall sensor (B6/15), intake camshaft setting

- exhaust camshaft Hall sensor (B6/16), exhaust camshaft setting

- coolant temperature sensor (B11/4)

- charge air temperature sensor upstream of throttle valve (B17/7)

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- charge air temperature sensor downstream of throttle valve (B17/9)

- pressure sensor downstream of throttle valve (B28/7), engine load

- crankshaft Hall sensor (B70) (with recognition of the direction of rotation), engine rpm 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

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Function sequence for ignition system

The ME-SFI [ME] control unit sends a 5 V signal for the dwell time of the respective operating point to the ignition coil over the actuation line (circuit 3). The respective ignition coil interrupts the primary circuit by means of an integral fuse after expiration of the dwell time. The ignition voltage passes from the ignition coil to the spark plug (R4) 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.

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Operating mode for the ignition coil

Single-spark ignition

The ignition coil is usually 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 can be used to securely ignite the mixture, also in cold start conditions, which allow a long spark ignition period.

There is also the option to use many sparks instead of just one

per ignition process. This operating mode is called Multispark mode.

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Multispark - multiple spark ignition

In contrast to single spark mode many sparks are used in Multispark mode. This is not a series of a number of singlespark 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 Multispark ignition begins like a singlespark 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. However, the ignition coil is not completely discharged in Multispark mode.

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 into high voltage generation mode This produces a further spark. The following sparks are generated according to the same scheme.

P15.10-2401-76

Ideal development of the primary and secondary current for a multi-spark ignition

A Dwell time

B Spark duration

C Recharging threshold

D Discharging threshold

E Ignition timing

V Operating voltage

i1 Primary charging current

i2 Secondary current

P01.10-3026-01

Cylinder arrangement and ignition firing order

1 - 4 Cylinders 1 to 4

270 Engine 270

 Diagnosis

The ignition angles can be checked using the Xentry diagnostics