In internal combustion engines, the injection masses can vary considerably between the individual cylinders owing to fabrication tolerances of the injection system and/or as a result of ageing. Any differences in the injection masses may lead to a torque difference between the cylinders which will have an adverse effect on the overall performance of the internal combustion engine. In addition, secondary assemblies may also give rise to torque fluctuations of other frequencies. These mechanically caused rotational irregularities cannot be eliminated by known cylinder balancing routines (CYBL) or closed loop combustion control routines (CLCC).
Patent DE 197 20 009 C2 discloses a method which calculates the rotational speed for the expansion and the rotational speed for the compression for each cylinder. The difference between the rotational speeds is filtered by means of a sliding mean value formation and a cylinder-selective deviation is formed on the basis of the respective rotational speed deviations. A fuel mass correction is calculated on the basis of this deviation.
Furthermore, DE 197 00 711 A1 is known. This document describes a method in which a correction value for the injection time is applied as a function of the irregular running.
DE 10 2005 047 829 B3 is known. Said document describes a method for compensating the harmonic components of the crankshaft rotational speed. In this context, a time period of at least one revolution of a camshaft or two revolutions of a crankshaft is considered. The rotational speed signal is considered here by means of a Fourier analysis.
A further possible way of separating off the effects is to use filters, such as, for example, a reject-pass filter. However, this severely degrades the signal quality.