superposition of the compression curve has the effect that the maximum associated with the combustion of cylinder pressure curve p cyl u03c6 or cylinder pressure gradient curve dp cyl u03c6 d u03c6 especially in the case of late potentially delayed combustions has no global but only still a local character the robust determination of this maximum which in this case is only still a local maximum can accordingly not be reliably carried out or is able to be ascertained only using an increased calculating effort for this reason a high pass element 22 is provided in order to eliminate the compression and expansion components that is the compression curve this is possible since the compression curve has a known frequency response that is a function of the rotational speed of the internal combustion engine by the use of high pass filter element 22 one obtains a signal curve of the cylinder pressure or the curve of the cylinder pressure gradient as is shown in fig4 in fig4 three curves of the cylinder pressure gradient are shown for the same combustion positions as in fig3 one may see that in the three different combustion positions shown in comparison to the diagram in fig3 even at the crankshaft angle at a very late combustion the maximum of the cylinder pressure or its gradient are still able to be determined without a problem since the cylinder pressure recording as a rule takes place in an angularly synchronous manner the high pass filtering of the high pass filter element has to be laid out relative to the scanning frequency so that the.