Patent ID: 8651088

Claim:
A control apparatus for an internal combustion engine comprising: an in-cylinder pressure sensor for outputting an in-cylinder pressure detection value of a predetermined cylinder at a predetermined crank angle in the internal combustion engine; in-cylinder pressure detecting means for detecting in-cylinder pressure detection values P 1 and P 2 at predetermined crank angles θ 1 and θ 2 during an adiabatic period of the predetermined cylinder from IVC to ignition timing using the in-cylinder pressure sensor; absolute pressure correction value calculating means that, when an in-cylinder volume of the predetermined cylinder at the crank angle θ 1 is V 1 , an in-cylinder volume of the predetermined cylinder at the crank angle θ 2 is V 2 , and a specific heat ratio of in-cylinder gas in the predetermined cylinder is κ, calculates a value obtained by dividing a value obtained by subtracting P 1 V 1 κ , which is PV κ at the crank angle θ 1 , from P 2 V 2 κ , which is PV κ at the crank angle θ 2 , by a value (V 1 κ −V 2 κ ) as an absolute pressure correction value; and absolute pressure correcting means for correcting the in-cylinder pressure detection value by using the absolute pressure correction value; the apparatus comprising: comparing means for comparing the adiabatic period with a predetermined period; and adiabatic period changing means for extending the adiabatic period when the adiabatic period is shorter than the predetermined period.