Abnormal combustion detection apparatus and control unit of internal combustion engine

A control unit of an internal combustion engine comprising:

• an abnormal combustion detection apparatus for detecting an abnormal combustion of the internal combustion engine based on a vibration waveform from a vibration sensor attached to the internal combustion engine, the apparatus including:
• a gain circuit for amplifying or attenuating the vibration waveform from the vibration sensor,
• an abnormal combustion determination period setting unit for setting an abnormal combustion determination period synchronizing with a rotation of a crank of the internal combustion engine,
• an AD conversion circuit for converting a waveform provided by the gain circuit to digital data,
• a determination unit for determining an abnormal combustion based on the digital data, and
• a gain switching unit for switching a gain of the gain circuit from a small gain value to a large gain value at a gain switch timing in the abnormal combustion determination period;
• and
• a detection unit for determining whether an amplitude of the waveform from the vibration sensor exceeds a fixed value, wherein
• the gain switching unit does not perform gain switching when the detection unit detects the amplitude of the waveform greater than or equal to the fixed value at the gain switch timing, and
• multiple control inputs of the internal combustion is controlled according to a detected magnitude of the abnormal combustion detected by the abnormal combustion detection apparatus.

An abnormal combustion detection apparatus detecting an abnormal combustion of an internal combustion engine based on a vibration waveform from a vibration sensor attached to the internal combustion engine, the apparatus comprising:

• a gain circuit for amplifying or attenuating the vibration waveform from the vibration sensor;
• an abnormal combustion determination period setting unit for setting an abnormal combustion determination period synchronizing with a rotation of a crank of the internal combustion engine;
• an AD conversion circuit for converting a waveform provided by the gain circuit to digital data;
• a determination unit for determining an abnormal combustion based on the digital data;
• a gain switching unit for switching a gain of the gain circuit from a small gain value to a large gain value at a gain switch timing in the abnormal combustion determination period;
• a digital filter for selecting a predetermined frequency band in the digital data derived from the AD conversion circuit;
• and
• a correction unit for outputting, to the digital filter, the digital data from the AD conversion circuit in a corrected state for canceling a gain difference between gains before and after the gain switching, wherein
• the AD conversion circuit performs an oversampling of the waveform from the gain circuit, and
• the digital filter stops an operation for a predetermined time from the gain switch timing.