Simplified Basic Layout of Ion Current Monitoring

Fig 1: Basic Layout Of Ion Current Monitoring

Courtesy of BMW OF NORTH AMERICA, INC.

INDEX EXPLANATION REFERENCE CHART

Index	Explanation
1	Microcontroller ignition
2	Output amplifier of the ignition signal
3	Ion current input amplifier
4	Digital signal processor for ion current measurement signal
5	MSS60 Engine control system
6	Ignition suppression capacitor (one per cylinder bank for 4 cylinders)
7	Input amplifier for ignition signal
8	Output amplifier of the ion current measurement signal
9	Ignition coil with integrated ion current electronics
10	Ignition output stage
11	Capacitor for storing measured flow
12	Zener diode for limiting the measured voltage
13	Primary and secondary coil
14	Spark plugs

The following diagrams show the ion current curve (bottom) in relation to the development of combustion pressure (top). This curve is used for the evaluation of combustion quality and the identification of misfiring.

Fig 2: Combustion Curve (Top) And Ionic Current (Bottom)

Courtesy of BMW OF NORTH AMERICA, INC.

Fig 3: MSS60 Representation Of Normal Combustion And Combustion Knock Graph

Courtesy of BMW OF NORTH AMERICA, INC.

INDEX EXPLANATION REFERENCE CHART

Index	Explanation
1	Ionic current maximum by induction of ignition coil
2	Ionic current maximum due to ignition (flame front directly in area of spark plugs)
3	The ionic current progression is a function of the pressure curve

INDEX EXPLANATION REFERENCE CHART

Index	Explanation
A	Ionic current (mA)
B	Section of measuring window
1	Normal combustion (no knocking)
2	Combustion knock

Depending on the engine load, the level of the ionic current generated at the spark plug lies in the range 50-500 μA and is only measured by the electronic system in the mA range.

Combustion knock is identified in the ionic current measurement signal in the form of oscillations within a defined measuring window. The measuring window is after position 3 of the above diagram.