Relative compression measurement method for internal combustion engine

摘要

The method involves detecting the relative compression of an internal combustion (IC) engine from the measured a.c. component of a current of an electric starter motor during restricted fuel feed, and in which the difference of the starter current to a straight line joining the starter current values at the integration limits (1" to 6"), is integrated with respect to time in partial regions of at least one complete engine cycle. The integration limits (1" to 6") are selected by evaluation of an auxiliary signal which indicates the occurrence of at least one repeating event in each complete engine cycle. Each cylinder is associated with a section of the complete engine cycle, based on the engine type, and the cycle sections are translated so that the sum of currents is minimised at the integration limits. The results of the cylinder-specific integration are normalised to the largest value, and the relative compression is determined based on a engine-specific calibration curve.