Engine ignition timing with knock control by combustion pressure harmonic amplitude ratio

Claim 1

An ignition timing control for an internal combustion engine including a combustion chamber, means effective to ignite a combustible charge in the combustion chamber and power output apparatus including a rotating crankshaft driven in response to the expansion of the ignited combustible charge, the ignition timing control comprising, in combination: means effective to define a normal ignition timing for the engine in the absence of knock; pressure sensing means effective to sense the pressure in the combustion chamber and generate a combustion pressure signal therefrom; means effective to sense the rotational speed of the crankshaft; frequency selective filter means for generating a plurality of predetermined harmonic signals of the combustion pressure signal, the frequency selective filter means being responsive to the last means to maintain the frequencies of the harmonic signals at whole number multiples of the firing frequency of the engine as the rotational speed of the crankshaft changes; means effective to detect the relative peak amplitudes of corresponding peaks in a first predetermined pair of the harmonic signals and determine the ratio thereof; and means for selectively retarding the ignition timing of the engine from the normal ignition timing in response to the ratio.