Method for determining the current compression ratio of an internal combustion engine during operation

A method for determining the current compression ratio of an internal combustion engine during operation, comprising:

• measuring dynamic pressure oscillations, assignable to one cylinder of the internal combustion engine, in an intake tract or in an outlet tract of the internal combustion engine at a defined operating point during normal operation, generating a corresponding pressure oscillation signal from the measured dynamic pressure oscillations, and at the same time, determining a crankshaft phase angle signal of the internal combustion engine,
• from the pressure oscillation signal and using discrete Fourier transformation, determining at least one actual value of at least one characteristic of at least one selected signal frequency of the measured pressure oscillations in relation to the crankshaft phase angle signal, and
• determining a current compression ratio of the internal combustion engine on the basis of the at least one determined actual value of the at least one characteristic, based on reference values of the respectively corresponding characteristic of the respectively identical signal frequency for different compression ratios.