An instrument for engine torque estimation and misfire detection.

Abstract

The subject of this work is the design of an instrument for the estimation of indicated torque and the detection of misfires in spark ignition internal combustion engines. Engine indicated torque measurement is a very important performance variable for engine testing, control and diagnostics. An estimate of indicated torque can also can be used to detect engine misfire, thus preventing potential damage to the catalytic converter, and reducing exhaust gas emission. In this study, the relationship between crankshaft angle of rotation and time is exploited to derive models describing engine torque production and the engine rotating dynamics in the angular position domain. Based on these models, an algorithm is developed to estimate engine indicated torque and a method is introduced to detect engine misfire. Processing engine related data in the crankshaft angle domain offers several advantages over conventional time domain processing. Among these advantages is a reduction in the computation time and memory size, when compared with time domain data processing, because crankshaft angle domain data processing is independent of the engine angular speed. The implementation of the algorithm is also considered in the study, leading to the design of an instrument for the estimation of engine indicated torque and the detection of engine misfire. The instrument is composed of two parts. The first is the Engine Angular Speed Variation (EASV) signal demodulator, which uses an engine angular speed driven tracking filter to realize engine crankshaft angle domain data processing. The second part is a special purpose microprocessor to implement the algorithm and detect engine misfire. A discrete implementation of the EASV demodulator has been built and used successfully at the Vehicular Electronics Laboratory at the University of Michigan. A version of the VLSI implementation and layout for the demodulator also introduced in the study. The special purpose microprocessor has its own hardware multiplier and hardware DFT unit for real time on-board misfire detection.