Misfiring cylinder diagnosis through crankshaft torsional vibration measurement

When each cylinder in an internal combustion engine fires, a torque pulse is applied to the crankshaft. These torque pulses contain significant energy for the first twenty-four harmonics of engine cycle speed, resulting in dynamic torsional excitation and response of the crankshaft and drivetrain in both rigid body and flexible modes. If a cylinder misfires, the excitation torque for that cylinder is altered, resulting in an altered dynamic torsional system response.; This research presents a new method for diagnosing and identifying misfiring cylinders in an internal combustion engine. A system dynamic model, system boundary conditions, and measured crankshaft torsional response are used to characterize the dynamic input at each engine cylinder. Current methods of misfire diagnosis using crankshaft torsional response as an indicator rely on several key assumptions to form a solvable equation set relating measured response to the system input at each cylinder. Chief among these assumptions are non-overlapping firing pulses and rigid crankshaft behavior. These assumptions limit diagnostic success with current methods to engines with six or fewer cylinders operating at low to moderate engine speeds.; The proposed diagnostic method does not rely on these assumptions. Rather, a set of linear constraint equations are added to the otherwise unsolvable equation set that relates the measured torsional crankshaft response to individual cylinder input. The constraint equations relate the magnitude and phase of the harmonics of the forcing function for each cylinder to the peak pressure and location of peak pressure for each cylinder pressure curve. Thus, the harmonics of the excitation torque for each cylinder are no longer independent. The constraint equations are introduced into the diagnostic equation set through the simultaneous consideration of multiple frequencies of excitation and response.; A series of test cases are presented which show that the diagnostic process should work with engines with overlapping firing pulses operating with significant crankshaft deflection. An error sensitivity analysis shows the process is viable with reasonable levels of noise and error associated with all key assumptions and measurements. In addition, a new signal processing technique is proposed which promises to significantly reduce torsional vibration measurement error compared to current state of the art techniques.