Misfire detection in automobile engine

Claim 1

A real-time automobile engine misfiring detection system, applicable to an exhaust gas pressure of an exhaust manifold means of an engine which, except for small magnitude fluctuations, is normally substantially constant or within a narrow range, comprising: exhaust gas pressure transducer means for converting pressure changes into time-varying electrical signals, Said transducer means comprising a capacitive pressure transducer attached to a bleeder pipeline substantially equidistantly from each point where the exhaust manifold means is attached to the engine, said transducer means including an insulating plate and an insulating diaphragm, having facing sides coated with a conductive layer, said transducer means having a time constant in a range of 8 to 12 milliseconds; low-pass filter means, said time-varying electrical signals being applied to said low-pass filter means, for suppressing high-frequency oscillations of said time-varying electrical signals to produce a filtered signal; DC blocking means, coupled to an output of said low-pass filter means, for substantially removing a direct current component of said filtered signal to produce a DC-blocked filtered signal; AC amplifying means, coupled to an output of said DC blocking means, for amplifying an alternating current component of said DC-blocked filtered signal to produce an AC signal voltage; reference voltage producing means, coupled to an output of said AC amplifying means, for generating a DC reference voltage proportional to an average magnitude of said alternating current component during a normal continuous variation of the exhaust gas pressure, said reference voltage producing means including AC-to-DC conversion means for converting said AC signal voltage into a DC reference signal which is a function of said average magnitude and level-adjusting means for adjusting said DC reference signal to produce said DC reference voltage to be smaller in magnitude than said average magnitude; comparator means, having one input coupled to said AC amplifying means and another input coupled to said reference voltage producing means, for comparing said AC signal voltage of said AC amplifying means with said DC reference voltage, including a detection of an algebraic sign of a difference between said AC signal voltage and said DC reference voltage and a production of an output signal whose magnitude is not zero when said difference has a selected sign and whose magnitude is zero when said difference has an opposite sign, and for providing an output pulse whenever said magnitude of said output signal changes from zero to a selected polarity, thereby indicating an occurrence of a significant pressure discontinuity; bistable switch means for providing an on-off signal, coupled to an output of said comparator, and providing an output signal of preselected duration when said output pulse is received from said comparator; and detection use means, coupled to said bistable switch means, for providing a detection use signal upon an operation of said bistable switch means.