Apparatus and method for diagnosing occurrence of misfire in multi-cylinder internal combustion engine

Claim 3

A misfire diagnostic system for a multi-cylinder, four-stroke internal combustion engine, comprising: a first sensor for detecting an engine crankshaft rotation and outputting a first signal indicative of the engine crankshaft rotated through a predetermined angle; a second sensor for detecting an engine driving condition and outputting a second signal indicative of thereof; a control unit for receiving the first and second signals and determining misfire on any cylinder of the multi-cylinder engine, wherein the control unit generates a reference signal for each predetermined crank angular timing based on the first signal, measures a period of the generated reference signal, detects a fuel supply cutoff for each cylinder and a predetermined driving condition based on the second signal, wherein at the predetermined driving condition an engine revolution speed is relatively stably reduced at a predetermined rate after the detected fuel supply cutoff, the predetermined driving condition serving as a learning condition, learns correction values of the period for the respective engine cylinders based on the measured period during the reduction in the engine speed in the learning condition, corrects results of measurements of the period for the respective cylinders based on the learned correction values, and determines presence or absence of misfire in any cylinder of the multi-cylinder engine based on the corrected period for the respective cylinder, and outputs a third signal when misfire is detected.

Claim 4

A misfire diagnostic system for a multi-cylinder, four-stroke internal combustion engine, comprising: a first sensor for detecting an engine crankshaft rotation and outputting a first signal indicative of the engine crankshaft rotated through a predetermined angle; a second sensor for detecting an engine driving condition and outputting a second signal indicative of thereof; a control unit for receiving the first and second signals and determining misfire on any cylinder of the multi-cylinder engine, wherein the control unit generates a reference signal for each predetermined crank angular timing based on the first signal, measures a period of the generated reference signal, detects a fuel supply cutoff for each cylinder and a predetermined driving condition based on the second signal, wherein at the predetermined driving condition an engine revolution speed is relatively stably reduced at a predetermined rate after the detected fuel supply cutoff, the predetermined driving condition serving as a learning condition, learns correction values of the period for the respective engine cylinders based on the measured period during the reduction in the engine speed in the learning condition, corrects results of measurements of the period for the respective cylinders based on the learned correction values, and determines presence or absence of misfire in any cylinder of the multi-cylinder engine based on the corrected period for the respective cylinder, and outputs a third signal when misfire is detected.

Claim 5

A misfire diagnostic system according to claim 2, wherein the control unit detects the engine driving condition after a predetermined period after the fuel supply cutoff is detected.

Claim 6

A misfire diagnostic system according to claim 2, wherein the control unit detects the engine driving condition when a variation in the period for each combustion cycle increases after the fuel cutoff is detected.

Claim 7

A misfire diagnostic system according to claim 2, wherein the control unit detects the engine driving condition when a variation rate of the variation quantity of the period for each one measured combustion cycle falls within a predetermined range.

Claim 8

A misfire diagnostic system according to claim 2, wherein the control unit calculates a correction value for the period based on the measured period during the fuel supply cutoff detection and detects the engine driving condition when a variation rate of the variation quantity of the period for each one measured combustion cycle falls within a predetermined range.

Claim 9

A misfire diagnostic system according to claim 6, wherein the control unit updates and stores the correction value and inhibits the updating and storing of the correction value when deviations between the correction values for the respective cylinders calculated based on the values of the measured periods in a same crank angle range are outside a predetermined range.

Claim 10

A misfire diagnostic system according to claim 3, further comprising a ring gear for generating a unit angular signal indicative of an angular displacement of the crankshaft, wherein the first sensor is a cam shaft sensor outputting the reference signal indicative of the engine crankshaft having rotated through a predetermined angular displacement set according to a number of the engine cylinders.

Claim 11

A misfire diagnostic system according to claim 2, further comprising a warning means for warning the occurrence of misfire.

Claim 12

A misfire diagnostic system according to claim 2, wherein the control unit calculates a misfire determination value MISA for a four-cylinder, four-cycle engine using a calculation MISA=(3×(TINT4-TINT5)+(TINT4-TINT1))/TINT5 3 , where TINT4 denotes the period of the reference signal for a fourth cylinder #4, which is corrected by the corresponding learning correction value KTINT4, TINT5 denotes the period of the reference signal for a first cylinder #1, which is corrected by the corresponding learning correction value KTINTa 1 , and wherein the control unit determines presence of misfire when the value of MISA is equal to or larger than a reference value.