BACKGROUND

1. Field

The present disclosure relates to an ignition timing controller and an ignition timing control method for a multi-cylinder internal combustion engine that performs a partial-cylinder operation.

2. Description of Related Art

As disclosed in Japanese Laid-Open Patent Publication No. 2001-182601, a type of multi-cylinder internal combustion engine has been known that performs an all-cylinder operation, which performs combustion in all the cylinders, and a partial-cylinder operation, which suspends combustion in some cylinders while performing combustion in the remaining cylinders.

Many internal combustion engines such as vehicle on-board engines include a knock sensor, for example, in a cylinder block to detect vibration caused by knocking, and perform a knock control based on the detected result. The knock control advances the ignition timing within a range in which knocking is suppressed. The knock control learns, as a knock learning value, the operated amount for advancing the ignition timing, thereby improving the responsiveness of the knock control.

On the other hand, the cylinders in which combustion is suspended during the partial-cylinder operation generate vibration that is different from the vibration generated during combustion. The knock sensor may detect such vibration of the combustion-suspended cylinders and thus make an erroneous knock determination. A result of the knock control based on an erroneous knock determination during the partial-cylinder operation may be reflected on the knock learning value. This may reduce the learning accuracy of the knock learning value.

SUMMARY

This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

In one general aspect, an ignition timing controller for a multi-cylinder internal combustion engine is provided. 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 includes processing circuitry. The processing circuitry is 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; and a feedback correction process. The feedback correction process 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. The circuitry also executes a learning process and an operation process. The learning process updates the knock learning value such that the knock learning value gradually approaches a knock control operated amount. The knock control operated amount is an operated amount for advancing the ignition timing based on the knock control amount and the knock learning value. The operation process operates ignition timing of each cylinder based on the knock control amount and the knock learning value. The circuitry further executes 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.

In another general aspect, an ignition timing control method for a multi-cylinder internal combustion engine is provided. 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 control method comprises: setting 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; determining whether knocking is occurring based on an output signal of a knock sensor; updating the knock control amount so as to reduce the operated amounts for advancing the ignition timing when it is determined that knocking is occurring; updating 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; updating 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; operating ignition timing of each cylinder based on the knock control amount and the knock learning value; and limiting 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.

Other features and aspects will be apparent from the following detailed description, the drawings, and the claims.

