CYLINDER PRESSURE PEGGING METHOD BASED ON THE LEAST SQUARES METHOD WITH A VARYING POLYTROPIC COEFFICIENT

摘要

A cylinder pressure pegging method based on an LSM(Least Squares Method) is provided to measure accurate combustion absolute pressure by estimating a polytropic coefficient varied according to the driving condition of an engine and pegging a bias of a pressure sensor. A cylinder pressure pegging method based on an LSM with a varying polytropic coefficient includes the steps of: inducing an equation for calculating a voltage measured at a crank angle by assuming that measured pressure of a pressure sensor is linearly proportional to cylinder pressure P; calculating motoring pressure of a specific crank angle; calculating measured voltage during motoring operation; calculating sensor offset(Ebias) and reference cylinder pressure(P(thetaref)) with the LSM; assuming that the polytropic coefficient in a variable between cycles and a constant in one cycle by using crank angles at two points and calculating the polytropic coefficient for one cycle; using a movement average of the assumed result to determine a sensor offset; using the assumed polytropic coefficient to calculate the sensor offset of the present cycle; and assuming the polytropic coefficient of the present cycle by using the pegged cylinder pressure.