Apparatus for detecting pressure fluctuations in the combustion chamber of an internal combustion engine

In an apparatus for detecting pressure fluctuations in the combustion chamber of an internal combustion engine, comprising:

• an ionic current sensor mounted to the engine for exposure to the gas in a combustion chamber, said ionic current sensor including:
• a measuring means connected to detect a measurement voltage;
• means defining a dead space and a connecting channel which extends between the dead space and the combustion chamber;
• a first electrode;
• and a second electrode spaced from the first electrode, between which electrodes the measurement voltage is applied, wherein said connecting channel also defines the spacing between the first and second electrodes,
• wherein the first and second electrodes are formed and associated with each other in such a way that the lines of force extending between both electrodes are substantially limited to the connecting channel, and
• wherein the first electrode is rod-like and is disposed coaxially to the axis of the connecting channel, and wherein the second electrode is formed by means of a wall by the means defining the connecting channel, and
• wherein the ionic current sensor is embodied as a spark plug, and wherein the space defined by the spark plug housing and the spark plug insulator defines the dead space and the gap lying between the first electrode of the spark plug and the spark plug housing defines the connecting channel.