Control device for compression-ignition engine

A control device for a compression-ignition engine in which partial compression-ignition combustion including spark ignition (SI) combustion performed by combusting a portion of a mixture gas inside a cylinder by spark ignition followed by compression ignition (CI) combustion performed by causing the remaining mixture gas inside the cylinder to self-ignite is executed at least within a part of an operating range of the engine, comprising:

• an EGR (exhaust gas recirculation) controller configured to change an EGR ratio that is a ratio of exhaust gas recirculated into the cylinder;
• and
• a combustion controller configured to control the EGR controller during the partial compression-ignition combustion to switch a combustion mode between a first mode and a second mode in which the EGR ratio is higher than the first mode,
• wherein after the combustion mode is switched from the first mode to the second mode, the combustion controller is configured to cause the resumption to the first mode upon first determining that both of the following are satisfied:
• a noise index value has fallen below an allowable limit, and
• a given period of time has elapsed from the switching to the second mode.