Misfire detecting device and method for internal combustion engine

A misfire detecting device for an internal combustion engine, the internal combustion engine including cylinders, the misfire detecting device including circuitry, wherein the circuitry is configured to execute:

• a stopping process that stops a combustion operation for air-fuel mixture in a cylinder subject to the stopping process among the cylinders;
• a combustion variable obtaining process that obtains values of a combustion variable, the combustion variable being determined by a detected value of a sensor that detects physical quantities corresponding to combustion states of air-fuel mixture in the respective cylinders, and the combustion variable representing the combustion state in each of the respective cylinders;
• and
• a determination process that
• when the stopping process is executed, defines one of cylinders in which the combustion operation is performed as a cylinder subject to misfire determination as to whether there is a misfire,
• sets, as a reference value, the value of the combustion variable of the cylinder subject to the stopping process, the reference value not reflecting the values of the combustion variable of the cylinders in which the combustion operation is performed, and
• determines that a misfire has occurred in the cylinder subject to the misfire determination in response to a degree of deviation of the value of the combustion variable of the cylinder subject to the misfire determination in relation to the reference value being less than or equal to a specified value.

A misfire detecting method for an internal combustion engine, the internal combustion engine including cylinders, the misfire detecting method comprising:

• stopping a combustion operation for air-fuel mixture in a cylinder subject to the stopping process among the cylinders;
• obtaining values of a combustion variable, the combustion variable being determined by a detected value of a sensor that detects physical quantities corresponding to combustion states of air-fuel mixture in the respective cylinders, and the combustion variable representing the combustion state in each of the respective cylinders;
• and
• determining that includes
• when the stopping process is executed, defining one of cylinders in which the combustion operation is performed as a cylinder subject to misfire determination as to whether there is a misfire,
• sets, as a reference value, the value of the combustion variable of the cylinder subject to the stopping process, the reference value not reflecting the values of the combustion variable of the cylinders in which the combustion operation is performed, and
• determining that a misfire has occurred in the cylinder subject to the misfire determination in response to a degree of deviation of the value of the combustion variable of the cylinder subject to the misfire determination in relation to the reference value being less than or equal to a specified value.