System Architecture Overview

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A constant measurement voltage is applied to the spark plug, after the ignition spark has been applied immediately. The chemical and temperature process of combustion produces free electrons and ions. Hence, some electrical current is flowing, which is measured and analyzed.

Fig 1: System Architecture Overview

Courtesy of BMW OF NORTH AMERICA, INC.

The V10 engine (S85) is spitted in two engine banks (five cylinders each). One ion current satellite unit is dedicated for each bank. In order to reduce SNR (Signal Noise Ratio), especially to improve the accuracy of knock detection, amplification has been introduced. The amplification is controlled by the ECU applying two different measurement voltages and two different amplification gains. The cylinder individual ion currents signals from the ignition coils are amplified and multiplexed send to the ECU (MS_S65).