Misfire-detecting system for an internal combustion engine

Claim 1

A system for detecting abnormality in combustion of an internal combustion engine based on fluctuations in the rotational speed of said engine, comprising: signal-outputting means for outputting a signal corresponding to the rotational speed of said engine; frequency-analyzing means for subjecting said signal from said signal-outputting means to frequency analysis to thereby detect amplitudes of components of said signal at respective predetermined frequencies; comparing means for calculating a difference between an amplitude of a component of said signal at each of said respective predetermined frequencies and an amplitude of a component of said signal at one of said respective predetermined frequencies as a reference frequency, said amplitude of said component of said signal at said each of said respective predetermined frequencies and said amplitude of said component of said signal at said one of said respective predetermined frequencies as said reference frequency being detected by said frequency-analyzing means on the same occasion of operation of said engine; and abnormality-determining means for determining that there is abnormality in combustion of said engine when said difference is smaller than a predetermined value.

Claim 2

A system for detecting abnormality in combustion of an internal combustion engine based on fluctuations in the rotational speed of said engine, comprising: signal-outputting means for outputting a signal corresponding to the rotational speed of said engine; frequency-analyzing means for subjecting said signal from said signal-outputting means to frequency analysis to thereby detect amplitudes of components of said signal at respective predetermined frequencies; comparing means for calculating a difference between an amplitude of a component of said signal at each of said respective predetermined frequencies and an amplitude of a component of said signal at one of said respective predetermined frequencies as a reference frequency, said amplitude of said component of said signal at said each of said respective predetermined frequencies and said amplitude of said component of said signal at said one of said respective predetermined frequencies as said reference frequency being detected by said frequency-analyzing means on the same occasion of operation of said engine; and abnormality-determining means for determining that there is abnormality in combustion of said engine when said difference is smaller than a predetermined value.

Claim 8

A system according to any of the preceding claims, wherein said abnormal cylinder-determining means further comprises second determining means for counting a number of times said first determining means determines that there is a possibility of spontaneous occurrence of abnormality in combustion in said selected one of said cylinders, and finally determining that abnormality in combustion spontaneously occurs in said selected one of said cylinders, when said number of times is larger than a predetermined value.

Claim 13

A system for detecting abnormality in combustion of an internal combustion engine based on fluctuations in the rotational speed of said engine, said engine including a plurality of cylinders, said system comprising: signal-outputting means for outputting a signal corresponding to the rotational speed of said engine; frequency-analyzing means for subjecting said signal from said signal-outputting means to frequency analysis; comparing means for calculating a difference between amplitudes of each of components of said signal at respective predetermined frequencies and an amplitude of a component of said signal at a predetermined reference frequency, said components of said signal at said respective predetermined frequencies and said component at said predetermined reference frequency being obtained by said frequency analysis; abnormality-determining means for determining that there is abnormality in combustion of said engine when said difference is smaller than a predetermined value; abnormality-forcing means for forcing combustion in a selected one of said cylinders to be abnormal; and abnormal cylinder-detecting means for determining whether or not said selected one of said cylinders is a cylinder in which abnormality in combustion occurs based on amplitude of said components of said signal at said respective predetermined frequencies, said components being obtained by said frequency analyzing means as a result of operation of said abnormality-forcing means.

Claim 14

A system for detecting abnormality in combustion of an internal combustion engine based on fluctuations in the rotational speed of said engine, said engine including a plurality of cylinders, said system comprising: signal-outputting means for outputting a signal corresponding to the rotational speed of said engine; frequency-analyzing means for subjecting said signal from said signal-outputting means to frequency analysis; comparing means for calculating a difference between amplitudes of each of components of said signal at respective predetermined frequencies and an amplitude of a component of said signal at a predetermined reference frequency, said components of said signal at said respective predetermined frequencies and said component at said predetermined reference frequency being obtained by said frequency analysis; abnormality-determining means for determining that there is abnormality in combustion of said engine when said difference is smaller than a predetermined value; abnormality-forcing means for forcing combustion in a selected one of said cylinders to be abnormal; and abnormal cylinder-detecting means for determining whether or not said selected one of said cylinders is a cylinder in which abnormality in combustion occurs based on amplitude of said components of said signal at said respective predetermined frequencies, said components being obtained by said frequency analyzing means as a result of operation of said abnormality-forcing means.

Claim 15

A system for detecting abnormality in combustion of an internal combustion engine based on fluctuations in the rotational speed of said engine, said engine including a plurality of cylinders, said system comprising: signal-outputting means for outputting a signal corresponding to the rotational speed of said engine; frequency-analyzing means for subjecting said signal from said signal-outputting means to frequency analysis; comparing means for calculating a difference between amplitudes of each of components of said signal at respective predetermined frequencies and an amplitude of a component of said signal at a predetermined reference frequency, said predetermined reference frequency being determined based on the rotational speed of said engine and the number of said cylinders, said components of said signal at said respective predetermined frequencies and said component at said predetermined reference frequency being obtained by said frequency analysis; and abnormality-determining means for determining that there is abnormality in combustion of said engine when said difference is smaller than a predetermined value.

Claim 16

A system for detecting abnormality in combustion of an internal combustion engine based on fluctuations in the rotational speed of said engine, said engine including a plurality of cylinders, said system comprising: signal-outputting means for outputting a signal corresponding to the rotational speed of said engine; frequency-analyzing means for subjecting said signal from said signal-outputting means to frequency analysis; comparing means for calculating a difference between amplitudes of each of components of said signal at respective predetermined frequencies and an amplitude of a component of said signal at a predetermined reference frequency, said predetermined reference frequency being determined based on the rotational speed of said engine and the number of said cylinders, said components of said signal at said respective predetermined frequencies and said component at said predetermined reference frequency being obtained by said frequency analysis; and abnormality-determining means for determining that there is abnormality in combustion of said engine when said difference is smaller than a predetermined value.