Control device for internal combustion engine

A control device for an internal combustion engine comprising a processor that

• operates a first combustion timing or a first combustion period in a cylinder of an internal combustion engine from a crank angle detected by a crank angle sensor,
• operates a heat generation rate based on the first combustion timing or the first combustion period,
• operates an in-cylinder pressure and an in-cylinder unburned gas temperature based on the heat generation rate,
• operates a first combustion speed based on the in-cylinder pressure and the in-cylinder unburned gas temperature,
• learns a correspondence relationship between the first combustion speed and the first combustion timing or the first combustion period, and
• using the learned correspondence relationship to determine a combustion state of the internal combustion engine, wherein
• the processor compares the first combustion speed, the first combustion timing, or the first combustion period with a threshold value for determining a fault state based on a learning result of the correspondence relationship, and diagnoses a fault based on a comparison result, or
• predicts a period until reaching a fault state based on a temporal change in a learning result of the correspondence relationship and a threshold value for determining the fault state.