IGNITION TIMING CONTROL DEVICE FOR LEAN BURN ENGINE

摘要

PROBLEM TO BE SOLVED: To suppress knocking and a torque shock at the time of transition from the stoichiometric operation to the lean burn operation. SOLUTION: When the engine operating condition has made transition from the stoichiometric to the lean burn mode, the fundamental correction value ALEANFFB is set with a lean burn delay angle correction value KALEANF1 (S23), and the pressure correction factor ALEANFFP to correct the fundamental correction value ALEANFFB is set by reference to a table on the basis of a suction pipe pressure PMXL as the representation of the engine load (S31), and the fundamental correction value ALEANFFB is corrected with the pressure correction factor ALEANFFP so that the at-lean-switching advance angle correction value ALEANFF is calculated (S32). The fundamental ignition timing is subjected to subtraction with the at-lean-switching advance angle correction value ALEANFF, and the ignition timing immediately after the lean burn operation switching is set, an then the fundamental correction value ALEANFFB is subjected to subtractions at certain intervals until it nullifies so that transition to the lean burn operation is made. Because of setting of ALEANFFP on the basis of engine load, the delay angle amount of the ignition timing can be adapted accurately to knocking and a torque shock.