Engine misfire detection with digital filtering

An apparatus for detecting misfire in individual cylinders of an internal combustion engine in a motor vehicle, comprising:

• means for sensing rotation of a crankshaft;
• measuring means connected to the sensing means for determining changes in angular velocity corresponding to each of a plurality of cylinder firings;
• means for analyzing frequency response of the engine in a frequency domain and determining a cut off frequency between misfire signals and noise-related signals;
• means for determining filter coefficients as a function of said frequency analysis;
• digital filtering means for receiving said changes in angular velocity and filter coefficients and filtering out noise-related signals from said changes in angular velocity in a real time domain so as to provide a filtered output;
• and
• means for comparing the filtered output of said filtering means with a threshold value to detect the occurrence of a misfire for a selected cylinder as a result of said comparison.

An apparatus for detecting misfire in individual cylinders of an internal combustion engine in a motor vehicle, comprising:

• means for sensing rotation of a crankshaft and determining angular velocity;
• measuring means for measuring changes in angular velocity corresponding to each of a plurality of cylinder firings;
• a high pass digital filter for receiving said changes in angular velocity and filtering out low frequency noise-related signals, said high pass digital filter providing a filtered output only when low engine speed is detected;
• a low pass digital filter for receiving said changes in angular velocity and filtering out high frequency noise-related signals, said low pass digital filter providing a filtered output only when high engine speed is detected;
• and
• means for comparing filtered outputs of said high pass and low pass filters with threshold values so as to detect the occurrence of a misfire for a selected cylinder as a result of said comparison.

A method of detecting misfires in individual cylinders of an internal combustion engine in a motor vehicle, said method comprising the steps of:

• sensing rotation of a crankshaft;
• determining changes in crankshaft velocity;
• selecting one of the cylinders for detection;
• analyzing a frequency response of the engine in a frequency domain and determining a cut-off frequency between misfire signals and noise-related signals;
• determining filter coefficients as a function of the frequency analysis;
• digitally filtering out noise related signals from said determined changes in crankshaft velocity to provide a filtered output signal;
• comparing the filtered output signal with a predetermined threshold;
• and
• detecting a misfire of the selected cylinder depending on the result of the comparing step.

A method for detecting misfire in individual cylinders of an internal combustion engine for a motor vehicle, said method comprising the steps of:

• sensing rotation of a crankshaft;
• determining changes in angular velocity corresponding to each of a plurality of expected cylinder firings;
• digitally filtering out noise related signals from the determined changes in angular velocity to provide a filtered output signal;
• determining a threshold value dependent on engine speed and manifold pressure;
• and
• comparing the filtered output signal with the threshold value to detect the occurrence of a misfire for a selected cylinder as a result of said comparison.