Patent ID: 7809489

Claim:
A method for determining cylinder interior pressure (P gas ) of an internal combustion engine from a cylinder pressure model having input variables comprising at least load, speed of rotation and crank angle, the method comprising the following steps: calculating a crank-angle-dependent pressure value in the cylinder (P pressure model ), which forms a cylinder interior pressure (P gas ) when corrected with a pressure correction value (ΔP gas ), said pressure correction value (ΔP gas ) being formed from an observation of alternating moments at a crankshaft; calculating a gas alternating moment {tilde over (M)} G — pressure model that occurs at the crankshaft, on the basis of the cylinder interior pressure (P gas ), said gas alternating moment being formed from a modeled cylinder interior pressure (P gas ) as the input variable of a model of a crank drive; calculating an alternating component of the gas moment ({tilde over (M)} G ) according to M ~ G = J ⁡ ( φ ) ⁢ φ ¨ KW , meas + 1 2 ⁢ ⅆ J ⁡ ( φ ) ⅆ φ ⁢ φ . KW , meas 2 , from non-uniformity of rotation, by means of calculating a crank-angle-dependent moment of inertia (J(φ)) and a measured angular velocity ({dot over (φ)} KW,meas ) as well as an angular acceleration ({umlaut over (φ)} KW,meas ) at the crankshaft; and determining a correction value (ΔP gas ) from a difference of the gas alternating moment from a pressure model M G — pressure model and the alternating component of the gas moment ({tilde over (M)} G ), from non-uniformity of rotation.