JP2008190433A - Four cycle engine provided with misfire detection system, misfire detection and operation method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a four cycle engine provided with a plurality of cylinders capable of accurately detecting only misfire causing a problem for continuation of operation of the engine and appropriately executing a process after misfire occurrence in lean premixed combustion engines such as gas engines, and method for operating the engine. <P>SOLUTION: The multiple cylinder four cycle engine is provided with a rotation pulse number detector detecting rotation pulse number of a crankshaft, and a misfire controller calculating average rotation speed of the crankshaft from rotation pulse number detection value of the crankshaft and rotation pulse number per one rotation of the crankshaft, calculating rotation speed deviation which is a difference between average rotation speed of a cycle and average rotation speed of one cycle before the cycle, and judging misfire of the engine if the calculation value of a rotation speed drop quantity exceeds an allowable rotation speed drop quantity setting. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a four-cycle engine having a plurality of cylinders, a four-cycle engine having a misfire detection system configured to determine misfire of the engine and perform subsequent processing, and misfire detection in the four-cycle engine The present invention relates to a method and an operation method.

In general, a gas engine premixes fuel gas and air, sends them to the combustion chamber, and ignites and burns with an ignition flame generated by an ignition device. There is a high possibility of misfire and poor combustion.
That is, as shown in FIG. 5, when a misfire occurs in the gas engine, the rotational fluctuation during the steady operation at the average rotational speed NA increases in proportion to the number of misfired cylinders, and the rotational speed reduction amount ( (Rotational speed deviation) ΔN also increases in proportion to the number of misfired cylinders (in FIG. 5B, ΔN0 indicates the limit value (allowable value) of the rotational speed reduction amount (rotational speed deviation)).
Therefore, in such a gas engine, as a means for detecting misfire or abnormal combustion, many techniques such as Patent Document 1 (Japanese Patent No. 3066004) and Patent Document 2 (Japanese Patent Publication No. 61-258955) have been proposed. ing.

Among these, in the technique of Patent Document 1 (Patent No. 3060604), misfire is determined by an angular velocity fluctuation difference amount representative of rotation fluctuation, excluding rotation fluctuation due to engine load fluctuation detected by the load detection means. Explosion force that is directly connected to misfire by performing misfire detection and detecting fluctuation amount reference updating means that updates angular velocity fluctuation amount according to the angular velocity fluctuation difference amount according to the misfire judgment criterion and detecting engine angular velocity fluctuation It is characterized by accurately detecting rotational fluctuations accompanying fluctuations.
Further, in the technique of Patent Document 2 (Japanese Patent Laid-Open No. 61-258955), an engine speed detector detects a rotational fluctuation at each explosion stroke of each cylinder, and an abnormal combustion cylinder is detected based on the rotational fluctuation. Is configured to detect.

  As means for detecting engine misfire or abnormal combustion, Patent Document 3 (Japanese Patent Laid-Open No. 2-49955), Patent Document 4 (Japanese Patent Laid-Open No. 5-39746), and the like are provided.

Japanese Patent No. 3066004 JP 61-258955 A JP-A-2-49955 JP-A-5-39746

However, the prior art has the following problems to be solved.
In the technique of Patent Document 1 (Japanese Patent No. 3060604), the angular velocity deviation between the reference angular velocity waveform in the case of normal combustion and the detected actual angular velocity waveform is calculated using the angular velocity fluctuation representing rotation fluctuation. When the reference level is exceeded, it is determined that the engine has misfired.However, in order to accurately capture the angular velocity waveform, there may be a single misfire or unstable combustion that does not hinder the continued operation of the engine. Therefore, it is difficult to detect only a misfire that causes an obstacle to continued operation of the engine.

  In the technique of Patent Document 2 (Japanese Patent Laid-Open No. Sho 61-258955), the rotation fluctuation of each cylinder in each explosion stroke is detected, and the abnormal combustion cylinder is detected based on the change in the rotation fluctuation. It does not detect misfire alone.

  In view of the problems of the prior art, the present invention makes it possible to accurately detect only misfires that impede continuation of engine operation in a lean premixed combustion engine such as a gas engine, and appropriately perform processing after occurrence of misfires. It is an object of the present invention to provide a four-cycle engine having a plurality of cylinders that can be operated and a method of operating the engine.

  The present invention achieves such an object, and in a four-cycle engine having a plurality of cylinders, a rotational pulse number detector for detecting the rotational pulse number of the crankshaft of the engine, and input from the rotational pulse number detector. An average rotational speed of the crankshaft is calculated from a detected value of the rotational speed of the crankshaft and a rotational pulse number per crankshaft rotation, and the average rotational speed in the cycle one cycle before the cycle and the average of the cycle are calculated. A rotational speed deviation that is a difference from the rotational speed is calculated, and a calculated value of the rotational speed reduction amount in the rotational speed deviation is compared with a preset allowable rotational speed reduction amount to obtain a calculated value of the rotational speed reduction amount. And a misfire controller for judging misfire of the engine when the allowable rotational speed reduction amount is exceeded.

  The operation method of the four-cycle engine having such a configuration is a misfire detection and operation method of the four-cycle engine having a plurality of cylinders, and detects the number of rotation pulses of the crankshaft of the engine, and this rotation pulse number detection value And the average number of revolutions of the crankshaft from the number of rotation pulses per revolution of the crankshaft, and the number of revolutions that is the difference between the average number of revolutions in the cycle one cycle before the cycle and the average number of revolutions of the cycle The deviation is calculated, and the calculated value of the rotational speed reduction amount in the rotational speed deviation is compared with a preset allowable rotational speed reduction amount, and the calculated value of the rotational speed reduction exceeds the allowable rotational speed reduction amount. And determining the misfire of the engine.

In the present invention, the following configuration is preferable.
(1) The misfire controller sets the allowable rotational speed reduction amount in a plurality of stages corresponding to the number of misfiring cylinders, and a calculated value of the rotational speed reduction amount is a first stage of the multi-stage allowable rotational speed reduction amount. When a permissible rotational speed decrease amount of 1 cylinder is exceeded, a misfire of one cylinder is determined, and when the calculated value of the rotational speed decrease amount exceeds a permissible rotational speed decrease amount of the second stage, a misfire of 2 cylinders is determined, and the rotation When the calculated value of the number reduction amount exceeds the allowable rotation number reduction amount in the nth stage (n is an integer), the misfire of the n cylinder is determined.
(2) An alarm device that oscillates in response to a misfire determination signal from the misfire controller, and a fuel control device that receives a misfire determination signal from the misfire controller and shuts off the fuel of the engine. The controller oscillates the alarm when the number of misfire occurrences exceeds a preset fixed number when it determines that one cylinder misfires, and oscillates the alarm when it determines that more than two cylinders misfire. In addition, the fuel control device is configured to cause the engine to shut off the fuel when the number of misfire occurrences exceeds a predetermined number of times set in advance.

  In the operation method of the 4-cycle engine having the configurations (1) and (2), the allowable rotational speed reduction amount is set in a plurality of stages corresponding to the number of misfiring cylinders, and the rotational speed reduction amount is calculated. When the value exceeds the first stage allowable rotational speed reduction amount of the plurality of stages of allowable rotational speed reduction amount, it is determined that one cylinder misfires, and the calculated value of the rotational speed reduction amount is the second stage allowable rotational speed reduction. 2 cylinder misfire is judged when the amount exceeds, and n cylinder misfire is judged when the calculated value of the rotational speed reduction amount exceeds the allowable rotation speed reduction amount of the nth stage (n is an integer). When the misfire occurrence is determined, the alarm device oscillates when the number of misfire occurrences exceeds a predetermined number of preset times, and when the misfire of two or more cylinders is determined, the alarm device oscillates the alarm and the number of misfire occurrences. Is preset Characterized in that occupy perform fuel cutoff of an engine fuel control device when exceeding the predetermined number of times.

  According to the present invention, the number of rotation pulses of the crankshaft is detected by the number of rotation pulses generated by the movement of teeth formed along the outer periphery of the flywheel directly connected to the crankshaft accompanying the rotation of the crankshaft, The average rotational speed of the crankshaft is calculated from the detected rotational pulse number and the rotational pulse number per crankshaft rotation, and the difference between the average rotational speed in the cycle one cycle before the cycle and the average rotational speed of the cycle is calculated. The engine speed is judged to be misfired when the calculated value of the engine speed reduction amount exceeds the allowable engine speed decrease amount by comparing the engine speed decrease amount in the engine speed deviation calculated from the above and the preset allowable engine speed decrease amount. The change in the number of rotation pulses accompanying the rotation of the crankshaft is detected for each cycle, and the amount of decrease in the number of rotation pulses is used as the amount of decrease in the crankshaft rotation number. The occurrence of misfire can be detected by a simple means of monitoring the amount of decrease in the number of rotation pulses, that is, determining the occurrence of misfire when the amount of decrease in the amount exceeds the allowable amount of decrease in the rotational speed. The occurrence of misfire can be detected with very simple processing that consumes less elements and memory.

Further, since the occurrence of misfire is detected only by monitoring the amount of decrease in the number of rotation pulses, the engine operation is performed in order to accurately capture the angular velocity waveform as in the technique of Patent Document 1 (Japanese Patent No. 3066004). Even a single misfire or unstable combustion that does not interfere with continuation can be avoided by detecting that a misfire has occurred, and it is possible to detect only misfires that hinder continued operation of the engine. .
As a result, it is possible to avoid the occurrence of a situation in which a single misfire or unstable combustion that does not hinder the continued operation of the engine is judged as misfire, and the engine is stopped. Can be prevented.

  In the present invention, the allowable rotational speed reduction amount is set in a plurality of stages corresponding to the number of misfiring cylinders, and when the calculated value of the rotational speed reduction amount exceeds the allowable rotational speed reduction amount in the first stage, A misfire is determined, and when the calculated value of the rotational speed reduction amount exceeds the allowable rotational speed reduction amount in the second stage, a misfire of two cylinders is determined, and the calculated value of the rotational speed reduction amount is the nth stage (n is 3). When the permissible rotational speed decrease of (integer) is exceeded, n-cylinder misfire is judged. When one-cylinder misfire is judged, an alarm is issued to the alarm device when the number of misfires exceeds a preset number. When the misfire of two cylinders or more is determined, the alarm device is made to oscillate, and the fuel control device is configured to shut off the fuel of the engine when the number of misfire occurrences exceeds a predetermined number of times. If When an allowable value for the rotational speed reduction amount corresponding to the number of fire cylinders is set in advance by experimental results or simulation calculation, and the calculated rotational speed reduction amount exceeds the allowable rotational speed reduction amount corresponding to misfire of one cylinder It is determined that a misfire has occurred in one cylinder, and if the calculated value of the rotational speed drop exceeds the allowable rotational speed drop equivalent to a misfire of 2 cylinders, a misfire has occurred in 2 cylinders. Further, when the calculated value of the rotational speed reduction amount exceeds the allowable rotational speed reduction amount corresponding to misfire of n cylinders of 3 cylinders or more, it is judged that misfire has occurred in the n cylinder. In addition, the number of misfiring cylinders can be determined from the amount of decrease in the rotational speed.

  As a result, when a misfire has occurred in one cylinder, an alarm is oscillated by an alarm device when the number of misfire occurrences exceeds a preset number of times, and adjustments such as advancing the fuel injection timing of the cylinder are made. The operation can be continued without stopping the engine, and when misfiring has occurred in two or more cylinders, an alarm is oscillated by the alarm device in the same manner as described above when the number of misfirings is less than a preset number. Only when adjustments such as the fuel injection timing of the cylinder are advanced, and when the number of misfires exceeds a preset number of times, the engine is stopped only by shutting off the fuel in the fuel control device. Depending on the number of cylinders and the number of occurrences, it is possible to use either misfire alarm oscillation or engine stop. Sometimes required becomes possible minimal engine stop, with a reduction rate of operation of the engine at the time of occurrence of misfire can be suppressed to a minimum, thereby improving the maintainability.

  Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the component parts described in this example are not intended to limit the scope of the present invention only to specific examples unless otherwise specified. Only.

FIG. 1 is an overall configuration diagram showing a misfire detection system for a four-cycle gas engine according to an embodiment of the present invention.
In FIG. 1, an engine denoted by reference numeral 100 is a multi-cylinder four-cycle engine, a piston 102 fitted in a cylinder 102a so as to be reciprocally slidable, and a crankshaft 112 for converting reciprocating motion of the piston 102 into rotation. A flywheel 113 coupled to the crankshaft 112, a combustion chamber 101 defined between an upper surface of the piston 102 and an inner surface of the cylinder 102a, an intake port 103 connected to the combustion chamber 101, and the intake port An intake valve 104 that opens and closes 103, an exhaust port 105 connected to the combustion chamber 101, an exhaust valve 106 that opens and closes the exhaust port 106, and the like.

A gas mixer 110 is installed in the middle of the intake port 103, and the fuel gas supplied from the fuel gas pipe 111 through the gas amount adjusting valve 109 and the compressed air supplied from a supercharger (not shown) are used in the gas mixer 11. The mixed gas is supplied to the combustion chamber 101 through the intake port 103 and the intake valve 104.
In this example, the ignition device denoted by reference numeral 107 is composed of a pilot injection device that injects pilot fuel such as light oil into the auxiliary chamber to ignite and combust it, and injects the combustion flame into the combustion chamber 101.

A plurality of teeth for generating rotation pulses are formed on the outer periphery of the flywheel 113 along the circumferential direction, and the rotation pulse detector 1 detects a rotation pulse due to the movement of the teeth by the rotation of the flywheel 113. It has become.
Then, a detection signal of a rotation pulse by the teeth of the flywheel 113 by the rotation pulse detector 1, that is, a rotation pulse of the crankshaft 112 is inputted to the misfire controller 10. The misfire controller 10 performs calculation and control as described later based on the detection signal of the rotation pulse, and outputs the output signal to the fuel control device 3 that controls the opening degree of the alarm device 2 and the gas amount adjusting valve 109. To do.

Next, the operation of this embodiment will be described with reference to FIGS.
A detection signal of the rotation pulse number of the crankshaft 112 from the rotation pulse detector 1 is input to the average rotation number calculation means 11 of the misfire controller 10. In the average rotational speed calculation means 11, one cycle of rotation of the crankshaft 112 is performed based on the detected value of the rotational pulse number and the number of teeth of the entire circumference of the flywheel 113 set in the rotational pulse tooth number setting means 12. Calculate the average number of revolutions per cycle.
That is, as shown in FIG. 3A, for example, when the number of teeth of the flywheel 113 is Z1 and the number of rotation pulses is Z1, in a four-cycle engine, the number of rotation pulses in one cycle is 2Z1. When misfire occurs, the average rotational speed decreases from NA1 to NA11, NA00, and from NA2 to NA21, as shown in FIG. 3B.

The calculated value of the average rotational speed for each cycle is input to the one-cycle rotational speed deviation calculating means 13. In the one-cycle rotational speed deviation calculating means 13, the difference between the average rotational speed calculated value in the cycle one cycle before a certain cycle and the average rotational speed calculated value in the cycle (average rotational speed NA1 in the previous cycle−the cycle concerned). The average rotational speed NA2) is calculated. This rotational speed deviation is the rotational speed reduction amount associated with the possibility of misfire occurrence, and the calculated value of the rotational speed reduction amount is input to the misfire determination means 15.
In the misfire rotation speed deviation setting means indicated by reference numeral 14, a minimum rotation speed reduction amount at which misfire occurs, that is, an allowable rotation speed reduction amount determined by an experimental result or the like is set.
Accordingly, the misfire determination means 15 calculates the rotation speed reduction amount by comparing the calculated value of the rotation speed reduction amount with the allowable rotation speed reduction amount set in the misfire rotation speed deviation setting means 14. When the value exceeds the allowable rotational speed reduction amount, it is determined that an engine misfire has occurred.

  In this case, more specifically, a misfire occurs when the number of times that the calculated value of the rotational speed reduction amount exceeds the allowable rotational speed reduction amount exceeds a preset allowable number based on experimental results or the like within a certain period. When it is less than the allowable number of times, it is determined that no misfire has occurred.

The misfire determination result in the misfire determination means 15 is input to the misfire cylinder number calculation means 17.
In the misfire cylinder number / rotational speed deviation setting means indicated by reference numeral 16, the allowable rotational speed reduction amount is set in a plurality of stages corresponding to the misfire cylinder number for each engine load.
That is, in the misfire cylinder number / rotational speed deviation setting means, as shown in FIG. 4A, for example, when the engine load is 0 to 50%, in the case of one cylinder (1 cylinder) misfire, the rotational speed reduction amount Is -A1 rotational speed (A1 rotational speed lower than the average rotational speed), and in the case of 2-cylinder misfire, the rotational speed reduction amount is -2A1 rotational speed which is twice that of the single-cylinder misfire. The rotational speed reduction amount is -3A1 rotational speed that is three times that in the case of one cylinder misfire, and although not shown, in the case of n cylinder (n cylinder) misfire, the rotational speed reduction amount is n times that in the case of one cylinder misfire. The number of misfire cylinders corresponding to the amount of decrease in the rotational speed is set for each engine load, such as -nA1 rotational speed.

  Accordingly, the misfire cylinder number calculating means 17 is set to the rotation speed reduction amount calculation value when the misfire occurrence means determines the misfire occurrence and the misfire cylinder number / rotational speed deviation setting means 16. The number of misfire cylinders (FIG. 4A) is matched to calculate (select) the number of misfire cylinders corresponding to the calculated value for decrease in the number of revolutions in the engine load, and input to the misfire number calculating means 18.

In the misfire number calculation means 18, when the misfire cylinder number calculation means 17 calculates the number of misfire occurrence cylinders as one cylinder, when the number of misfire occurrences within a predetermined period exceeds a predetermined number. The alarm device 2 is caused to generate an alarm. On the other hand, if the number of misfire occurrences is less than or equal to the predetermined number, the alarm does not oscillate because there is no continuous occurrence of misfire.
That is, as shown in FIG. 4B, for example, when it is determined that misfire has occurred more than M1 times (twice) during the N1 cycle (100 cycles), the alarm device 2 oscillates an alarm, and M1 times If it is less than (once), the alarm does not oscillate.

In the misfire number calculation means 18, when the misfire cylinder number calculation means 17 calculates that the number of misfire occurrence cylinders is 2 cylinders or more, the alarm device 2 is caused to oscillate and within a preset fixed period. When the number of misfire occurrences exceeds the predetermined number of times set in advance, the fuel control device 3 is made to shut off the fuel of the engine and the engine is stopped.
That is, as shown in FIG. 4 (B), for example, when it is determined that the misfire has occurred M3 times (three times) or more during the N2 cycle (100 cycles), the alarm device 2 oscillates an alarm, The fuel control device 3 causes the engine to shut off and stops the engine. On the other hand, for example, when it is determined that the number of misfires has occurred M2 times (may be once or twice) during the N2 cycle (100 cycles), the alarm device 2 oscillates the alarm and the fuel of the misfired cylinder is generated. It only takes measures to prevent misfires, such as earlier injection timing, and does not stop the engine.

  According to the embodiment of the present invention as described above, according to the number of rotation pulses generated by the movement of teeth formed along the outer periphery of the flywheel 113 directly connected to the crankshaft 11 as the crankshaft 112 rotates, The average rotational speed of the crankshaft 112 is calculated from the rotational speed of the crankshaft 112, and the rotational speed deviation calculated from the difference between the average rotational speed in the previous cycle of the cycle and the average rotational speed of the cycle is calculated. Since the engine speed is determined by comparing the engine speed reduction amount with a preset allowable engine speed decrease quantity and the calculated value of the engine speed decrease exceeds the engine speed reduction amount, the crankshaft 112 By detecting a change in the number of rotation pulses for each cycle accompanying rotation, the amount of decrease in the rotation number of the crankshaft is defined as the amount of decrease in the number of rotations of the crankshaft. The occurrence of misfire can be detected simply by monitoring the amount of decrease in the number of rotation pulses, that is, the occurrence of misfire is judged when the allowable number of revolutions is exceeded. It is possible to detect the occurrence of misfire by simple processing.

In addition, since the occurrence of misfire is detected only by monitoring the amount of decrease in the number of rotation pulses, the conventional method does not hinder the continuation of operation of the engine 100 in order to accurately capture the angular velocity waveform. A single misfire or unstable combustion can be prevented from being detected as a misfire occurrence, and only a misfire that hinders the continuation of the operation of the engine 100 can be detected.
As a result, it is possible to avoid the occurrence of a situation in which a single misfire or unstable combustion that does not hinder the continuation of the operation of the engine 100 is determined to be a misfire and the engine is stopped. Can be prevented.

  Further, the allowable rotational speed reduction amount is set in a plurality of stages corresponding to the number of misfiring cylinders, and when the calculated value of the rotational speed reduction amount exceeds the allowable rotational speed reduction amount in the first stage, the misfire of one cylinder is determined. When the calculated value of the rotational speed reduction exceeds the allowable rotational speed reduction amount of the second stage, it is determined that two cylinders have misfired, and the calculated value of the rotational speed reduction amount is the nth stage (n is an integer of 3 or more). N cylinder misfire is determined when the permissible rotational speed decrease amount is exceeded, and when one cylinder misfire is determined, an alarm is generated in the alarm device 2 when the number of misfire occurrences exceeds a predetermined number of times. Since it is configured to cause the alarm device 2 to oscillate when a misfire exceeding the cylinder is determined, and to cause the fuel control device 3 to shut off the fuel of the engine when the number of misfire occurrences exceeds a preset number of times. Misfire cylinder An allowable value of the rotational speed reduction amount corresponding to the above is preset by an experimental result or simulation calculation, and when the calculated value of the rotational speed reduction amount exceeds the allowable rotational speed reduction amount corresponding to misfire of 1 cylinder, one cylinder It is determined that a misfire has occurred in the cylinder, and if the calculated value of the rotational speed reduction exceeds the allowable rotational speed reduction amount corresponding to the misfire of the two cylinders, it is determined that a misfire has occurred in the two cylinders. Further, when the calculated value of the rotational speed reduction amount exceeds the allowable rotational speed reduction amount corresponding to misfire of n cylinders of 3 cylinders or more, it is determined that misfire has occurred in the n cylinder. The number of misfired cylinders can be ascertained from the amount of decrease in the number.

  As a result, when a misfire has occurred in one cylinder, an alarm is generated by the alarm device 2 when the number of misfire occurrences exceeds a preset number of times, and the fuel injection timing of the cylinder is advanced. The operation can be continued without stopping the engine 100, and when the misfire has occurred in two or more cylinders, the alarm device 2 warns in the same manner as described above when the misfire occurrence number is less than a predetermined number. The engine 100 is stopped only when the fuel control device 3 shuts off the fuel when the misfire occurrence number exceeds a predetermined number of times. Depending on the number of cylinders and the number of occurrences of misfire, the misfire alarm oscillation or engine stop can be used properly It becomes ability becomes possible requires only minimum engine stop when a misfire occurs, with a reduction rate of operation of the engine at the time of occurrence of misfire can be suppressed to a minimum, thereby improving the maintainability.

  According to the present invention, in a lean premixed combustion engine such as a gas engine, it is possible to accurately detect only a misfire that hinders the continuation of engine operation, and a plurality of cylinders that can appropriately perform processing after the misfire has occurred. The provided four-cycle engine and a method for operating the engine can be provided.

It is a whole lineblock diagram showing the misfire detection system of the 4 cycle gas engine concerning the example of the present invention. It is a control block diagram of the misfire detection system in the said Example. (A), (B) is explanatory drawing of the rotation pulse detection method in the said Example. (A), (B) is explanatory drawing of the misfire determination in the said Example, and a subsequent process. (A), (B) is explanatory drawing of the rotation speed change at the time of misfire generation | occurrence | production.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rotation pulse detector 2 Alarm apparatus 3 Fuel control apparatus 10 Misfire controller 11 Average rotation speed calculation means 13 1-cycle rotation speed deviation calculation means 15 Misfire determination means 17 Misfire cylinder number calculation means 18 Misfire number calculation means 100 Engine 101 Combustion chamber 102 Piston 102a Cylinder 103 Intake port 104 Intake valve 105 Exhaust port 106 Exhaust valve 107 Ignition device 109 Gas amount adjustment valve 110 Gas mixer 111 Fuel gas pipe 112 Crankshaft 113 Flywheel

Claims (5)

  In a four-cycle engine having a plurality of cylinders, a rotation pulse number detector for detecting the number of rotation pulses of the crankshaft of the engine, and a rotation pulse number detection value of the crankshaft inputted from the rotation pulse number detector and a crank An average rotation speed of the crankshaft is calculated from the rotation pulse number per rotation of the shaft, and a rotation speed deviation which is a difference between the average rotation speed in the cycle one cycle before the cycle and the average rotation speed of the cycle is calculated. When the calculated value of the rotational speed reduction amount exceeds the allowable rotational speed reduction amount by comparing the calculated value of the rotational speed reduction amount in the rotational speed deviation with a preset allowable rotational speed reduction amount A four-cycle engine having a misfire detection system characterized by comprising a misfire controller for judging misfire of the engine.   The misfire controller sets the allowable rotational speed decrease amount in a plurality of stages corresponding to the number of misfiring cylinders, and the calculated value of the rotational speed decrease amount is a first stage allowable rotational speed of the multiple stages of allowable rotational speed decrease amount. When the number reduction amount is exceeded, the misfire of one cylinder is determined. When the calculated value of the rotation number reduction exceeds the allowable rotation number reduction amount in the second stage, the misfire of two cylinders is determined, and the rotation number reduction amount is determined. The misfire detection system according to claim 1, wherein the misfire detection system is configured to determine misfire of n cylinders when the calculated value exceeds an allowable rotational speed reduction amount of the nth stage (n is an integer). 4-cycle engine.   The misfire controller includes an alarm device that oscillates in response to a misfire determination signal from the misfire controller, and a fuel control device that receives a misfire determination signal from the misfire controller and shuts off the engine fuel. When the misfire of the cylinder is determined, the alarm device oscillates when the number of misfire occurrences exceeds a preset fixed number of times, and when the misfire of two or more cylinders is determined, the alarm device oscillates the alarm and the misfire 3. A four-cycle engine equipped with a misfire detection system according to claim 2, wherein the fuel control device is configured to cause the fuel to be cut off when the number of occurrences exceeds a predetermined number of times set in advance.   A misfire detection and operation method for a four-cycle engine having a plurality of cylinders, wherein the number of rotation pulses of the crankshaft of the engine is detected, and the crankshaft is detected from the detected number of rotation pulses and the number of rotation pulses per crankshaft rotation. Calculate the average rotational speed of the shaft, calculate the rotational speed deviation that is the difference between the average rotational speed in the cycle one cycle before the cycle and the average rotational speed of the cycle, and decrease the rotational speed in the rotational speed deviation Comparing the calculated value of the amount with a preset allowable rotational speed reduction amount, and determining the misfire of the engine when the calculated value of the rotational speed reduction amount exceeds the allowable rotational speed decrease amount Misfire detection and operation method of a 4-cycle engine.   The allowable rotational speed reduction amount is set in a plurality of stages corresponding to the number of misfiring cylinders, and the calculated value of the rotational speed reduction amount exceeds the allowable rotational speed reduction amount in the first stage of the allowable rotational speed reduction amount in the plurality of stages. 1 cylinder misfire is determined, and when the calculated value of the rotational speed reduction exceeds the allowable rotational speed reduction amount in the second stage, it is determined that 2 cylinders are misfiring, and the calculated rotational speed reduction amount is When the number of allowable rotation speed reductions in n stages (n is an integer) is exceeded, the misfire of n cylinders is determined. When the misfire of one cylinder is determined, the alarm device is activated when the number of misfire occurrences exceeds a preset number of times. An alarm is oscillated, and when the misfire of two or more cylinders is judged, the alarm device is oscillated, and when the number of misfires exceeds a predetermined number of times, the fuel control device is made to shut off the fuel of the engine. Special Misfire detection and a method of operating a four-stroke engine according to claim 4,.

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