Method and device for detecting misfiring cylinder of reciprocating internal-combustion engine using torsional vibration signal

A misfire detection apparatus for a reciprocating internal-combustion engine, comprising:

• a torsional vibration sensor arranged at a shaft line of the engine for detecting rotational speed fluctuations, the torsional vibration sensor outputting a torsional vibration signal;
• a camshaft position sensor, optionally included for a 4-stroke engine, arranged at a camshaft of the engine for detecting a reference signal indicative of a top dead center of a reference cylinder, the camshaft positon sensor outputting a camshaft position signal;
• a signal processing unit configured to obtain amplitudes and phases of a fundamental frequency component and harmonic components by performing a Fast Fourier Transform (FFT) on the torsional vibration signal;
• an application processing unit configured to detect a misfiring event and determine a misfiring cylinder position by;
• detecting the misfiring event when the amplitude of the fundamental frequency component exceeds a preset threshold;
• and
• identifying the misfiring cylinder position by calculating an explosion angle (FAi) of the misfiring cylinder according to the relation;
• FAi=ixmax·dx−(1/k)(3π/2−β(k)),
• wherein ixmax·dx is a crank-angle value obtained by multiplying ixmax, an index corresponding to a sample at which the amplitude of the fundamental frequency component of the torsional vibration signal reaches a maximum while a fundamental frequency component of the excitation force attains a minimum having a phase angle β(k), by dx, a fixed crank-angle increment between successive torsional vibration signal samples;
• wherein ρ(k) is calculated from torque harmonic coefficients and an explosion order supplied by an engine manufacturer;
• wherein, k is 1.0 for a 2-stroke engine and 0.5 for a 4-stroke engine;
• and
• wherein, for the 4-stroke engine, a crank-angle reference is synchronized to the top dead center of a reference cylinder using the camshaft position signal;
• a transmission unit connected the application processing unit and configured to transmit the result of the detected misfiring cylinder;
• and
• a display device configured to receive and display the detected misfiring cylinder.