Estimation of Engine Torque and Cylinder Pressure Index Based on Crankshaft Rotation Measurement

The recent regulations for engine emissions require precise temperature control. Because high response temperature measurement is difficult, engine torque, which is closely correlated with the temperature, must be estimated. We propose a method for estimating engine torque from the crankshaft rotation speed. This method consists of four steps, (1) the measured engine speed ω is analyzed and divided into frequency components, (2) each component is multiplied by the gain, which is proportional to the frequency, (3) the phase of each component is shifted by 2π/4, (4) the combustion torque is estimated by synthesizing each component. These steps are summarized into one filter. The output of the filter is compensated for by the geometrical character of the engine link mechanism. The method was evaluated through experimentation. In the steady and transient states and under the condition that the engine speed was not greater than 1000 rpm, the estimated torque accurately follows the reference torque. However, when the engine speed increases to 2000 rpm, the pulsation in the estimated torque becomes noticeable. Based on the estimated torque, IMEP was estimated within an accuracy of 3.4% when the engine speed was not greater than 1000 rpm. When the valve timing changed, the estimated IMEP followed the change in reference IMEP.