Patent ID: 8646419

Claim:
A control apparatus for an internal combustion engine that is provided in a vehicle, and that includes a compression ratio change device that changes an actual mechanical compression ratio, wherein the mechanical compression ratio is a ratio of a maximum value of a volume of a combustion chamber to a minimum value of the volume of the combustion chamber, and the volume of the combustion chamber is changed according to reciprocating movement of a piston, the control apparatus comprising: a compression ratio control device that controls the compression ratio change device so that the actual mechanical compression ratio is equal to the mechanical compression ratio set based on a load of the internal combustion engine; a cooling device that cools a wall surface that constitutes the combustion chamber using a cooling medium, by supplying the cooling medium to an area near the wall surface, and that adjusts cooling efficiency that indicates a magnitude of heat energy transferred to the supplied cooling medium from the wall surface per unit time; an index value obtaining device that obtains an index value relating to occurrence of knocking; and a knocking suppression device that determines whether a knocking determination condition which includes at least one of a condition that knocking occurs and a condition that there is a possibility that knocking will occur, is satisfied based on the obtained index value, wherein when the knocking suppression device determines that the knocking determination condition is satisfied, the knocking suppression device controls the cooling device to increase the cooling efficiency, and controls the compression ratio change device so that the actual mechanical compression ratio is equal to a low mechanical compression ratio that is lower than the mechanical compression ratio set based on the load, in a predetermined low compression ratio control period that starts at a knocking determination time point at which it is determined that the knocking determination condition is satisfied, wherein the knocking suppression device sets the low mechanical compression ratio to a first low mechanical compression ratio during a first period from the knocking determination time point to a predetermined first time point, in the low compression ratio control period, the knocking suppression device sets the low mechanical compression ratio to a second low mechanical compression ratio that is higher than the first low mechanical compression ratio during a second period after the first time point, in the low compression ratio control period, the knocking suppression device maintains the first low mechanical compression ratio at a constant value during the first period, and the knocking suppression device gradually increases the second low mechanical compression ratio toward the mechanical compression ratio set based on the load, as time elapses, during the second period.