Method and apparatus for changing the spark advance of internal combustion engines

A method of changing the spark advance characteristic of internal combustion engines, in which pulse sequences are produced, the main pulses of which are all of equal length and derived from a rotating part of the internal combustion engine, including the steps of counting the number of such pulses occurring during a pre-determined time t (reference count) this representing a desired angle of spark advance .alpha. relative to engine top dead centre, and is dependent on the speed of the internal combustion engine, deducting said count from a larger angle .psi. count (reference angle) which extends between said top dead centre and an arbitrary phase position .psi. 0 in advance thereof, said angle .psi. being represented by a predetermined number of pulses which is independent of the engine speed, starting a pulse count (trigger count) from said position .phi. 0, and generating an ignition pulse during said trigger count when the number of pulses counted from the arbitrary phase position .psi. 0 corresponds to the differential angle .psi. - .alpha., so that the ignition pulse occurs advanced by the advance angle .alpha. relatively to the engine top dead centre, wherein the dependence of the advance angle .alpha. on the speed of rotation of the internal combustion engine changes in that the number of pulses (final number) corresponding to the effective advance angle is obtained from the number of pulses which appear during the pre-determined time t (starting number) amended by at least one calculating operation applied to said starting number, said calculating operation depending on a parameter of said engine operation.