Ignition timing controller and ignition timing control method for multi-cylinder internal combustion engine

An ignition timing controller for a multi-cylinder internal combustion engine, wherein

• the multi-cylinder internal combustion engine is configured to perform:
• an all-cylinder operation that performs combustion in all cylinders;
• and
• a partial-cylinder operation that suspends combustion in part of the cylinders while performing combustion in the remaining cylinders, the ignition timing controller comprising processing circuitry, the processing circuitry being configured to execute:
• a process that sets a knock control amount and a knock learning value as operated amounts of ignition timing for advancing the ignition timing within a range in which knocking is suppressed;
• a knock determination process that determines whether knocking is occurring based on an output signal of a knock sensor;
• a feedback correction process that
• updates the knock control amount so as to reduce the operated amounts for advancing the ignition timing when it is determined that knocking is occurring, and
• updates the knock control amount so as to increase the operated amounts for advancing the ignition timing when it is determined that knocking is not occurring;
• a learning process that updates the knock learning value such that the knock learning value gradually approaches a knock control operated amount, the knock control operated amount being an operated amount for advancing the ignition timing based on the knock control amount and the knock learning value;
• an operation process that operates ignition timing of each cylinder based on the knock control amount and the knock learning value;
• and
• a process that limits update of the knock learning value such that a followability of the knock learning value to the knock control operated amount is lower during the partial-cylinder operation than during the all-cylinder operation.