JP4085817B2 - Misfire detection device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a misfire detection apparatus for an internal combustion engine that detects the occurrence of misfire in the internal combustion engine based on the rotational fluctuation of the engine output shaft.
[0002]
[Prior art]
Conventionally, focusing on the fact that the rotational fluctuation of the engine output shaft becomes large when a misfire occurs in the internal combustion engine, a misfire detection device that detects the occurrence of misfire based on the fact that the rotational fluctuation amount exceeds a predetermined threshold has been proposed, It has been put into practical use (see, for example, Patent Document 1).
[0003]
On the other hand, in the case of an internal combustion engine, during cold operation, a correction for increasing the fuel injection amount based on the engine temperature obtained based on the detection result of the water temperature sensor or the like, more precisely, the in-cylinder temperature, so-called warm-up increase correction To do. By executing such warming-up increase correction, instability of the engine combustion state is suppressed, and the rotation fluctuation amount associated therewith can be suppressed small.
[0004]
[Patent Document 1]
JP-A-5-18311 (page 6-7, FIG. 8)
[0005]
[Problems to be solved by the invention]
By the way, the engine body is cooled by the outside air after the operation is stopped, and the temperature gradually decreases to near the outside air temperature. In this process, a temperature distribution may occur in the engine body. For example, when the engine is cold, the temperature in the vicinity of the cylinder inner wall in the engine body decreases rapidly after the engine stops, while the temperature decrease tends to be relatively slow in the vicinity of the cooling water passage through which engine cooling water flows. There is. Further, for example, the engine body has a portion that is easily cooled by outside air and a portion that is difficult to cool due to the shape, layout, and the like, and the temperature distribution may occur in the engine body due to such a difference. In addition, all of these show examples in which the engine temperature decreases, but the same can occur when the engine temperature rises until the engine is completely warmed up after the engine is started. In particular, such a temperature distribution is noticeable when the operation of the internal combustion engine is stopped in an environment where the outside air temperature is extremely low, such as in a cold region.
[0006]
As a result of this temperature distribution, the cooling water temperature in the vicinity of the water temperature sensor and the cooling water temperature in the vicinity of the cylinder wall surface greatly differ, and the correlation between the detection result of the water temperature sensor and the in-cylinder temperature temporarily May fall. In such a case, if the internal combustion engine is restarted and the warm-up increase correction and the misfire detection process described above are executed together, the following inconvenience occurs.
[0007]
That is, since the fuel increase correction for each cylinder is performed based on the detection result of the water temperature sensor having a low degree of correlation with the in-cylinder temperature, the increase correction of the fuel injection amount is an amount less than an appropriate amount or an excessive amount. It will be done with quantity. This leads to instability of the combustion state, which causes rotational fluctuations. As a result, in the misfire detection process, such rotation fluctuation is erroneously detected as rotation fluctuation caused by misfire, and there is a possibility that the detection accuracy of misfire occurrence may be lowered.
[0008]
In particular, in a cold region, in order to enhance engine startability, a device for preheating engine cooling water before the start of the engine, a so-called block heater may be attached. An internal combustion engine equipped with such a block heater may be attached. In such cases, such inconvenience tends to be more noticeable.
[0009]
In Patent Document 1, in order to improve detection accuracy of misfire occurrence, for example, the threshold value for detecting misfire occurrence is further increased during transient operation such as warm-up operation or start-up operation of an internal combustion engine. A method of setting a large value is disclosed. According to such a method, it is possible to suppress the misdetection of misfire occurrence caused by the temperature difference.
[0010]
However, when such a temperature difference does not occur, in other words, even when the above-described cold correction is properly performed and the combustion state is stable, the threshold value is changed, that is, the criterion is relaxed. Therefore, a decrease in detection accuracy of misfire occurrence is unavoidable, and in this respect, there is still room for improvement.
[0011]
In recent years, there has been a demand for accurately detecting the occurrence of misfires even at extremely low temperatures due to stricter regulations, and countermeasures against such a decrease in detection accuracy are urgently needed.
[0012]
The present invention has been made in view of such circumstances, and an object of the present invention is to provide a misfire detection device for an internal combustion engine that can suitably suppress a decrease in detection accuracy of misfire occurrence.
[0013]
[Means for Solving the Problems]
In the following, means for achieving the above object and its effects are described.
First, the invention according to claim 1 is a misfire detection device for an internal combustion engine that detects the occurrence of misfire based on the fact that the rotational fluctuation amount of the engine output shaft exceeds a predetermined threshold value, and the attachment of the engine temperature sensor to the engine body. A determination means for determining that there is a temperature difference greater than or equal to a predetermined value between the position and another specific part of the engine body, and a determination that there is a temperature difference greater than or equal to the predetermined value by the determination means And changing means for changing the detection mode of the occurrence of misfire so that it is difficult to detect that the misfire has occurred.
[0014]
In the above configuration, when a temperature difference of a predetermined value or more is generated between the vicinity of the engine temperature sensor and other specific parts, and the degree of correlation between the detection result of the engine temperature sensor and the in-cylinder temperature is reduced. The detection mode is changed so that it is difficult to detect that there is a misfire. This suppresses erroneous detection of the occurrence of misfire when rotation fluctuation occurs due to the warm-up increase correction performed with an inappropriate increase value. Therefore, according to the said structure, the fall of the detection accuracy can be suppressed suitably about misfire generation | occurrence | production.
[0015]
According to a second aspect of the present invention, in the misfire detection apparatus for an internal combustion engine according to the first aspect, the engine temperature sensor is a water temperature sensor that detects an engine cooling water temperature, and the determination means is the water temperature sensor. When there is a temperature difference of a predetermined temperature or more between the engine coolant temperature in the vicinity of the mounting position and the engine coolant temperature in the vicinity of the cylinder wall surface, the difference between the mounting position and the other specific part exceeds the predetermined value. The gist is to determine that there is a temperature difference.
[0016]
In the above configuration, the degree of correlation between the coolant temperature detected by the water temperature sensor and the in-cylinder temperature is low, and it is difficult to detect that there is a misfire when inappropriate warm-up increase correction is performed. The detection mode is changed. This suppresses erroneous detection of the occurrence of misfire when rotation fluctuation occurs due to the warm-up increase correction performed with an inappropriate increase value. Therefore, according to the said structure, the fall of the detection accuracy can be suppressed suitably about misfire generation | occurrence | production.
[0017]
The invention according to claim 3 is the misfire detection device for an internal combustion engine according to claim 1 or 2, wherein the determination means is configured such that the temperature of the outside air of the internal combustion engine is lower than a first predetermined temperature, When the engine temperature detected by the engine temperature sensor is higher than the second predetermined temperature, it is determined that there is a temperature difference of a predetermined value or more between the mounting position and the other specific part. The gist.
[0018]
The situation where the temperature difference between the mounting position of the engine temperature sensor and another specific part in the engine body exceeds a predetermined value occurs when the following two conditions (A) and (B) are satisfied. Cheap.
(B) The ambient temperature of the engine body is extremely low, specifically, the outside air temperature is extremely low.
(B) After the engine is started, the engine body is in a transitional state until it reaches a completely warm-up state.
[0019]
According to the configuration of the third aspect, a temperature difference of a predetermined value or more is generated between the vicinity of the engine temperature sensor and other specific parts, and the degree of correlation between the detection result of the engine temperature sensor and the in-cylinder temperature is It can determine suitably that it has fallen.
[0020]
The gist of the invention according to claim 4 is that, in the misfire detection device for an internal combustion engine according to any one of claims 1 to 3, the changing means prohibits detection of the occurrence of misfire.
[0021]
According to the above configuration, when a rotational fluctuation is caused due to improper warm-up increase correction, the rotational fluctuation is more accurately suppressed from being erroneously detected as being caused by a misfire. can do.
[0022]
In addition to what is described in claim 4, when changing the detection mode so that detection of misfiring is difficult to be performed, for example, as described in claim 5, the threshold value is set to be larger. It is also possible to adopt a configuration such as changing to a value.
[0023]
In the configuration according to claim 5, the misfire occurrence detection accuracy is also set such that the threshold value is set to a larger value as the temperature difference between the mounting position of the engine temperature sensor and the other specific part is larger. This is effective in suppressing the decrease more reliably.
[0024]
Here, even when the temperature difference as described above occurs at the time of starting the engine, the temperature difference is gradually eliminated as the engine operation continues thereafter and the engine temperature rises.
[0025]
In this regard, according to the configuration of the sixth aspect, since the change of the misfire occurrence detection mode is canceled when a predetermined period has elapsed after the engine is started, when the temperature difference is resolved in this way, The normal detection mode can be quickly restored.
[0026]
A seventh aspect of the present invention is the misfire detection device for an internal combustion engine according to any one of the first to sixth aspects, wherein the internal combustion engine includes a block heater for heating the engine body.
[0027]
According to the above configuration, in the internal combustion engine in which the temperature difference is likely to occur because the block heater is attached and the warming-up increase correction is likely to be performed appropriately, and the detection accuracy reduction of the misfire occurrence is suitably suppressed. Will be able to.
[0028]
The invention according to claim 8 is the misfire detection device for an internal combustion engine according to any one of claims 1 to 7, wherein the determination means includes an attachment position of the engine temperature sensor to the engine body and a position of the engine body. The gist is that it is determined at the time of starting the engine that there is a temperature difference of a predetermined value or more between other specific parts.
[0029]
The situation in which the temperature difference between the vicinity of the engine temperature sensor and other specific parts described above becomes equal to or greater than a predetermined value is likely to occur in the process in which the engine temperature decreases to the environmental temperature after the engine is stopped. In this regard, according to the above configuration, when the engine is started, there is a temperature difference of a predetermined value or more between the vicinity of the engine temperature sensor and other specific parts, and the correlation between the detection result of the engine temperature sensor and the in-cylinder temperature. It can be suitably determined that the degree has decreased.
[0030]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EMBODIMENTS Hereinafter, an embodiment in which a misfire detection apparatus for an internal combustion engine according to the present invention is embodied will be described.
[0031]
First, a schematic configuration of an internal combustion engine to which the misfire detection device of the present embodiment is applied and its peripheral devices will be described with reference to FIG.
As shown in FIG. 1, the internal combustion engine 10 includes a cylinder block 12 having cylinder bores 11 for six cylinders (only one cylinder is shown) and a cylinder head 13. A piston 14 provided in each cylinder bore 11 so as to be movable up and down is connected via a connecting rod 15 to a crankshaft 16 that is an output shaft of the internal combustion engine 10. In the present embodiment, the cylinder block 12 forms a part of the engine body.
[0032]
An intake passage 19 is connected to the combustion chamber 17 of each cylinder via an intake port 18, and an exhaust passage 21 is connected via an exhaust port 20. The cylinder head 13 is provided with a spark plug 23 corresponding to each combustion chamber 17. Further, in the vicinity of the intake port 18, fuel injection valves 24 are provided corresponding to the respective cylinders.
[0033]
Then, when the operation of the internal combustion engine 10 is started, the intake air is introduced into the intake passage 19 and fuel is injected from the fuel injection valve 24, whereby the intake air and the fuel are mixed, Become. The air-fuel mixture is taken into the combustion chamber 17 in the intake stroke of the internal combustion engine 10 and ignited by the spark plug 23 to explode and burn. Thereby, a rotational force (driving force) is applied to the crankshaft 16. The exhaust gas after combustion is discharged into the exhaust passage 21.
[0034]
On the other hand, a block heater 25 is attached to the cylinder block 12. The block heater 25 is attached to the cylinder block 12 such that the heating portion is located in a cooling water passage 26 formed in the cylinder block 12. The block heater 25 is operated by supplying power from an external power source.
[0035]
On the other hand, the apparatus of the present embodiment is provided with various sensors including the sensors described below as sensors for detecting the operating state of the internal combustion engine 10.
A crank angle sensor 31 for detecting the rotation angle (crank angle) and the rotation speed (engine rotation speed NE) is provided in the vicinity of the crankshaft 16. The internal combustion engine 10 is provided with a cylinder discrimination sensor 32. The cylinder discrimination sensor 32 outputs an appropriate pulse signal corresponding to the compression top dead center of a specific cylinder, for example. Further, a water temperature sensor 33 that detects the temperature (THW) of the engine coolant as a parameter highly correlated with the engine temperature, and an outside air temperature sensor 34 that detects the ambient temperature of the internal combustion engine 10, that is, the temperature of the outside air (THA). Is provided.
[0036]
In addition, the apparatus according to the present embodiment includes an electronic control unit 30 including, for example, a microcomputer. The electronic control unit 30 takes in the output signals of the various sensors and executes various calculations, and engine control such as fuel injection control and ignition timing control including the warm-up increase correction described above based on the calculation results. Various controls related to the above are executed.
[0037]
Hereinafter, the misfire detection method according to the present embodiment will be described.
First, in the combustion stroke of each cylinder, a time T required for the crankshaft 16 to rotate 30 ° CA starting from the compression top dead center is detected. Then, the difference (= T−Ti) between this time T and the previously detected time (Ti) is calculated as the rotation fluctuation amount ΔT. Then, when the rotational fluctuation amount ΔT exceeds a predetermined threshold Lvs, it is determined that misfire has occurred.
[0038]
FIG. 2 is a plan view of the cylinder block 12.
As shown in the figure, in the cylinder block 12, the block heater 25 and the water temperature sensor 33 are attached at relatively close positions. For this reason, when the operation of the internal combustion engine 10 is stopped in a very low temperature environment and the block heater 25 is operated after the temperature becomes extremely low, the temperature of the cooling water is quickly raised. On the other hand, the temperature of the cooling water at a position away from the block heater 25 does not rise easily. As a result, in the cylinder located in the vicinity of the block heater 25, the in-cylinder temperature (temperature in the combustion chamber 17) is high, and the in-cylinder temperature of the cylinder located away from the block heater 25 is relatively low. As described above, a temperature difference (temperature distribution) occurs between the respective parts.
[0039]
At this time, when the internal combustion engine 10 is started and the warming-up increase correction is executed, the correction amount calculated by the correction becomes an appropriate correction amount in the cylinder located near the block heater 25. On the other hand, the amount of correction is insufficient in the cylinder located away from the block heater 25.
[0040]
This correction amount may be an inappropriate amount even in the following cases.
That is, in the process in which the operation of the internal combustion engine 10 is stopped from the completely warmed-up state and the engine temperature is lowered to near the outside air temperature, there may be a temperature difference between the outside and the inside of the internal combustion engine 10. . In particular, when the warm-up increase correction is executed when the temperature difference between the coolant temperature in the vicinity of the water temperature sensor 33 and the coolant temperature in the vicinity of each cylinder is large, the water temperature having a low correlation with the actual in-cylinder temperature. Based on the detection result of the sensor 33, the fuel increase correction for each cylinder is performed. For this reason, the fuel injection amount is increased so that the increase correction of the fuel injection amount is performed with an amount smaller than an appropriate amount or an excessive amount.
[0041]
In any case, if the correction amount calculated by the warm-up increase correction is an inappropriate amount, the combustion state becomes unstable, causing an increase in rotational fluctuation, and the detection accuracy for the occurrence of misfire is described below. To lower.
[0042]
As shown in FIG. 3A, when the increase correction amount is an appropriate correction amount for each cylinder during the stable operation of the internal combustion engine 10 and no misfire has occurred, the rotation fluctuation amount ΔT is expressed as A value near “0” is calculated. On the other hand, as shown in FIG. 3B, when misfire occurs during such stable operation, the rotation fluctuation amount ΔT is a relatively large value, and a value near a certain value is detected. Accordingly, during such a stable operation, the rotational fluctuation amount ΔT at the time of misfire occurrence and the rotational fluctuation amount ΔT at the time when no misfire has occurred are calculated as greatly different values. It is possible to accurately determine an increase in the rotational fluctuation amount ΔT.
[0043]
On the other hand, at the time of unstable operation of the internal combustion engine 10 where the increase correction amount becomes an inappropriate amount, the engine speed NE fluctuates as the combustion state becomes unstable. For this reason, as shown in FIG. 3C, the variation of the rotational fluctuation amount ΔT calculated when no misfire has occurred increases. Even though no misfire has occurred at this time, a value exceeding the threshold value Lvs may be calculated as the rotational fluctuation amount ΔT, which causes a decrease in the accuracy of detection of misfire occurrence.
[0044]
Therefore, in the present embodiment, in order to suppress such a decrease in detection accuracy, it is determined that the temperature difference between the cooling water temperature in the vicinity of the water temperature sensor 33 and the cooling water temperature in other specific parts is a predetermined value or more. When the same determination is made, detection of the misfire occurrence itself is prohibited.
[0045]
Hereinafter, a specific processing procedure of the processing for prohibiting detection of the occurrence of misfire will be described with reference to the flowchart shown in FIG.
The series of processes shown in the flowchart of FIG. 4 is a process executed by the electronic control device 30 at predetermined intervals.
[0046]
As shown in FIG. 4, in this process, it is first determined whether or not all of the following (condition A) to (condition C) are satisfied (steps S10, S20, and S30).
(Condition A): The outside air temperature (starting outside air temperature THast) when the engine start is started is lower than the first predetermined temperature α (step S10).
(Condition B): The coolant temperature (starting coolant temperature THWst) when the engine start is started is higher than a second predetermined temperature β that is higher than the first predetermined temperature α (step S20).
(Condition C) The cooling water temperature THW is lower than a third predetermined temperature γ that is higher than the second predetermined temperature β (step S30). The third predetermined temperature γ is a temperature for determining that the warm-up operation of the internal combustion engine 10 has not yet been completed.
[0047]
In the present embodiment, the process of steps S10 and S20 is performed by the internal combustion engine 10 when the “temperature difference between the cooling water temperature in the vicinity of the water temperature sensor 33 and the cooling water temperature in other specific parts becomes a predetermined value or more. It functions as a determination unit that determines that the state is a specific state.
[0048]
Here, the specific state is likely to occur when the following conditions are satisfied.
-The ambient temperature of the internal combustion engine 10 is extremely low. This can be determined by the fact that the outside air temperature THA is extremely low.
[0049]
The internal combustion engine 10 is in a transitional state from when the operation is stopped until the temperature of each part drops to the environmental temperature. This can be determined by the fact that the coolant temperature THW detected by the water temperature sensor 33 is higher than the outside air temperature THA.
[0050]
Therefore, by satisfying both of the above (Condition A) and (Condition B), it can be determined that there is a high possibility that the internal combustion engine 10 is in a specific state at least when the engine is started.
[0051]
On the other hand, even when the internal combustion engine 10 is in a specific state at the start of starting, the temperature difference is gradually eliminated as the engine temperature rises due to the heat generated by itself when the operation is continued. The In particular, when the warm-up operation of the internal combustion engine 10 is completed, it can be said that the temperature difference is almost eliminated. Under the above (Condition C), it is determined that the warm-up operation of the internal combustion engine 10 has not yet been completed and the temperature difference has not been eliminated.
[0052]
Accordingly, when all of the above (Condition A) to (Condition C) are satisfied (Steps S10, S20, S30: YES), it is highly likely that the internal combustion engine 10 is in the specific state at this time. In order to suppress a decrease in detection accuracy, the detection is prohibited (step S40). In the present embodiment, the processing shown in step S40 functions as changing means for changing the detection mode of occurrence of misfire.
[0053]
Then, when the cooling water temperature THW rises as the internal combustion engine 10 continues to operate and the above (Condition C) is not satisfied (Step S30: NO), the temperature difference is eliminated, and the detection accuracy decreases. Otherwise, detection of the occurrence of misfire is started (step S40).
[0054]
On the other hand, when the above (Condition A) or (Condition B) is not satisfied (Step S10 or S20: NO), it is unlikely that the internal combustion engine 10 is in the specific state when the internal combustion engine 10 is started. Assuming that accurate detection is possible, detection of the occurrence of misfire is started (step S40).
[0055]
In this way, after the execution prohibition of the detection of misfire occurrence (step S40) or the execution of the detection (step S50) is selected based on the above (condition A) to (condition C), this processing is temporarily ended. The
[0056]
By performing such processing, as shown in FIG. 5 as an example of the processing mode, when the internal combustion engine 10 is likely to be in the specific state at the start of the operation, the operation is performed. The detection of the misfire occurrence is prohibited over a predetermined period (time t11 to t12) after the start. Therefore, when the internal combustion engine 10 is in a specific state and the rotational fluctuation amount ΔT is large due to improper warming-up correction, this is erroneously detected as a misfire occurrence. That is suppressed, and as a result, a reduction in detection accuracy for the occurrence of misfire is suppressed.
[0057]
In addition, when the coolant temperature THW becomes higher than the third predetermined temperature γ, in other words, when the predetermined period elapses after the operation of the internal combustion engine 10 is started, the warm-up operation of the internal combustion engine 10 is completed. Assuming that the temperature difference is eliminated, detection of the misfire occurrence is started.
[0058]
As described above, according to the present embodiment, the effects described below can be obtained.
(1) When starting the engine, if there is a temperature difference of a predetermined value or more between the cooling water temperature near the mounting position of the water temperature sensor 33 and the cooling water temperature of other specific parts, it is difficult to detect that there is a misfire. Thus, the detection mode of misfire occurrence is changed. As a result, when the correlation between the detection result of the water temperature sensor 33 and the in-cylinder temperature is reduced due to the temperature difference, in other words, the warm-up increase correction is performed with an inappropriate increase value. In the case where the rotation fluctuation is caused by the occurrence of misfire, it is suppressed that this is erroneously detected as being due to the occurrence of misfire. Accordingly, it is possible to suitably suppress a decrease in detection accuracy of misfire occurrence.
[0059]
(2) Also, when (Condition A) and (Condition B) are satisfied, it is determined that the temperature difference is equal to or greater than a predetermined value. It can be suitably determined that the degree of correlation between the detection result 33 and the actual in-cylinder temperature is reduced.
[0060]
(3) The misfire occurrence detection itself is prohibited in order to change the misfire occurrence detection mode so that it is difficult to detect the misfire occurrence. As a result, when a rotational fluctuation occurs due to improper warm-up increase correction, it is possible to accurately suppress the rotational fluctuation being erroneously detected as being caused by a misfire. it can.
[0061]
(4) When the predetermined period has elapsed after the engine is started, the change in the misfire occurrence detection mode is canceled. For this reason, when the temperature difference disappears as the engine operation continues and the engine temperature rises, it is possible to quickly return to the normal detection mode.
[0062]
(5) In the internal combustion engine 10 in which the temperature difference is likely to occur because the block heater 25 is attached, and an inappropriate warm-up increase correction is easily performed, and a reduction in detection accuracy of misfire occurrence is suitably suppressed. be able to.
[0063]
The embodiment described above may be modified as follows.
In place of (Condition A) in the above embodiment, a condition such as “the outside air temperature THA immediately after the operation of the internal combustion engine 10 is started is higher than the first predetermined temperature” may be set.
[0064]
-Instead of (Condition C) in the above-described embodiment, “the amount of increase in the coolant temperature THW from the startup coolant temperature THWst is less than the predetermined temperature Ta, as in the process of step S60 shown in FIG. It is also possible to set a condition such as Even with such a configuration, it is possible to determine that the operation of the internal combustion engine 10 has continued for a predetermined period. Also, with this configuration, it is possible to particularly accelerate the execution start timing of the misfire occurrence detection, and it is possible to maintain the execution frequency of the detection as much as possible.
[0065]
In addition to the above (Condition C), other conditions described below can be used. The integrated value of the intake air amount after the start of the internal combustion engine 10 is less than a predetermined value (the process shown in step S70 of FIG. 7). The integrated value of the engine speed NE after the start of the internal combustion engine 10 is less than a predetermined value (processing shown in step S80 in FIG. 8). The integrated value of the fuel injection amount after the start of the internal combustion engine 10 is less than a predetermined value.
[0066]
In the above embodiment, it is determined based on (Condition A) and (Condition B) that the internal combustion engine 10 is in a specific state when the engine is started. These (Condition A) and (Condition B) are changed to conditions for determining that the internal combustion engine 10 is in a specific state in the transition period until the internal combustion engine 10 reaches a fully warmed-up state after the engine is started. Also good. According to such a configuration, when there is a rotation fluctuation due to the increase correction during warm-up with an inappropriate increase value during the transition period, this is erroneously detected as a misfire occurrence. Thus, it is possible to suitably suppress a decrease in detection accuracy of misfire occurrence.
[0067]
In the above embodiment, when it is determined that there is a high possibility that the internal combustion engine 10 is in the specific state, execution of misfire occurrence detection is prohibited. At this time, the threshold value Lvs is set to be larger. After changing to the value, detection of misfire occurrence may be executed. According to such a configuration, when the rotational fluctuation amount ΔT is increased due to the temperature distribution, it is possible to relax the criterion for detecting misfire by the increase, and the increase is due to the occurrence of misfire. It is possible to suppress erroneous detection. In addition, an increase in the rotational fluctuation amount ΔT exceeding the relaxed determination standard can be detected as a misfire.
[0068]
-Moreover, in the said structure, you may make it set the threshold value Lvs to a larger value, so that the temperature difference between the attachment position of the water temperature sensor 33 and another specific site | part is large. Thereby, more reliable suppression about the detection accuracy fall of misfire occurrence can be aimed at.
[0069]
As shown in the flowchart of FIG. 9, it is also possible to execute a combination of a method for prohibiting execution of misfire detection and a method for executing detection of misfire after changing the threshold value Lvs.
[0070]
In the process shown in FIG. 9, first, when it is determined that the internal combustion engine 10 is likely to be in the specific state, for example, until a predetermined condition such as a predetermined time Tb has elapsed after the start of the engine is satisfied. During this period (steps S10 and S20: YES, S91: NO), detection of misfire occurrence is prohibited (step S40). Further, in the period from when the period of synchronization elapses until the coolant temperature THW becomes higher than the third predetermined temperature γ (steps S91 and S92: YES), the threshold value Lvs is changed to a larger predetermined value Lv1. (Step S93). Then, detection of misfire occurrence based on the predetermined value Lv1 is executed (step S94). Furthermore, after the coolant temperature THW becomes higher than the third predetermined temperature γ (step S92: NO), detection of the occurrence of misfire based on the threshold value Lvs is executed (step S95).
[0071]
FIG. 10 shows an example of the processing mode of such processing. As shown in FIG. 10, when the outside air temperature THA at the start of operation of the internal combustion engine 10 (time t21) is extremely low (FIG. [A]) and the coolant temperature THW is relatively high (FIG. [B]). ), The misfire detection itself is prohibited immediately after the engine is started ([c] in the figure). Thereby, even when the possibility that the internal combustion engine 10 is in a specific state is high, when the temperature difference is large and the rotational fluctuation amount ΔT is remarkably increased, the misfire occurrence detection is prohibited and the misfire occurrence occurs. Can be accurately suppressed. Moreover, after the operation of the internal combustion engine 10 has been continued for a predetermined time Tb (time t21 to t22), in other words, after the temperature difference has become relatively small, the criteria for detecting misfire are relaxed. (FIG. [D]), the detection of misfire occurrence is started (FIG. [C]). Accordingly, at this time, it is possible to execute the detection while suitably suppressing the erroneous detection of the misfire occurrence, and it is possible to maintain the misfire detection function. Furthermore, when the coolant temperature THW becomes higher than the third predetermined temperature γ (time t23) and the warm-up operation of the internal combustion engine 10 is completed, after that, detection of misfire occurrence based on the threshold value Lvs, that is, normal Detection is performed.
[0072]
In addition, the processing of step S91 in the above configuration is performed by, for example, “the cooling water temperature THW has risen by a predetermined temperature or more from the starting cooling water temperature THWst” or “the cooling water temperature THW is a predetermined temperature δ (where δ <γ It is also possible to change the processing to be determined based on the cooling water temperature.
[0073]
In the misfire detection device that detects the occurrence of misfire when the ratio of the “number of times that the rotational fluctuation amount ΔT exceeds the threshold Lvs” in the “number of times the detection of misfire occurrence is detected” exceeds a predetermined ratio. Instead of changing the threshold value Lvs, the predetermined ratio can be changed to a larger value. In short, when the internal combustion engine 10 is in the specific state, the detection mode may be changed so that misfire is hardly detected.
[0074]
In the above embodiment, the method for detecting the occurrence of misfire can be arbitrarily changed as long as the method detects the occurrence of misfire based on the fact that the rotational fluctuation amount of the crankshaft 16 of the internal combustion engine 10 exceeds a predetermined threshold. is there.
[0075]
In the above embodiment, the water temperature sensor 33 for detecting the temperature of the engine cooling water in which the same temperature is suitably reflected is used as the engine temperature sensor. Instead, the engine temperature is directly detected. You may make it use what you do.
[0076]
The present invention can be applied to an internal combustion engine in which the block heater 25 is not provided.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an internal combustion engine to which an embodiment of the present invention is applied and its peripheral structure.
FIG. 2 is a plan view of a cylinder block.
FIG. 3 is a graph showing a trend of rotational fluctuation amount.
FIG. 4 is a flowchart showing a processing procedure when detecting the occurrence of misfire.
FIG. 5 is a timing chart showing an example of a processing mode of the processing.
FIG. 6 is a flowchart showing a modification example of the processing procedure when detecting the occurrence of misfire.
FIG. 7 is a flowchart showing an example of a change in the processing procedure when detecting the occurrence of misfire.
FIG. 8 is a flowchart showing an example of a change in the processing procedure when detecting the occurrence of misfire.
FIG. 9 is a flowchart showing a modification example of the processing procedure when detecting the occurrence of misfire.
FIG. 10 is a timing chart showing an example of a processing mode of the modification example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 11 ... Cylinder bore, 12 ... Cylinder block, 13 ... Cylinder head, 14 ... Piston, 15 ... Connecting rod, 16 ... Crankshaft, 17 ... Combustion chamber, 18 ... Intake port, 19 ... Intake passage, 20 ... Exhaust Port, 21 ... Exhaust passage, 23 ... Spark plug, 24 ... Fuel injection valve, 25 ... Block heater, 26 ... Cooling water passage, 30 ... Electronic controller, 31 ... Crank angle sensor, 32 ... Cylinder discrimination sensor, 33 ... Water temperature Sensor 34 ... Outside air temperature sensor.

Claims (8)

In the misfire detection device for an internal combustion engine that detects the occurrence of misfire based on the fact that the rotational fluctuation amount of the engine output shaft exceeds a predetermined threshold,
A determining means for determining that there is a temperature difference of a predetermined value or more between an attachment position of the engine temperature sensor to the engine body and other specific parts of the engine body;
And changing means for changing the misfire occurrence detection mode so that it is difficult to detect that the misfire has occurred when the determination means determines that there is a temperature difference equal to or greater than the predetermined value. A misfire detection device for an internal combustion engine. The engine temperature sensor is a water temperature sensor that detects an engine cooling water temperature,
The determination means is configured such that when there is a temperature difference of a predetermined temperature or more between the engine coolant temperature near the mounting position of the water temperature sensor and the engine coolant temperature near the cylinder wall surface, the mounting position and the other specific part The misfire detection device for an internal combustion engine according to claim 1, wherein a determination is made that there is a temperature difference equal to or greater than the predetermined value. The determination means is configured such that when the temperature of the outside air of the internal combustion engine is lower than a first predetermined temperature and the engine temperature detected by the engine temperature sensor is higher than a second predetermined temperature, the attachment position and the other The misfire detection device for an internal combustion engine according to claim 1 or 2, wherein it is determined that there is a temperature difference of a predetermined value or more between the specific portion. The misfire detection device for an internal combustion engine according to any one of claims 1 to 3, wherein the changing unit prohibits detection of the occurrence of misfire. 4. The misfire detection apparatus for an internal combustion engine according to claim 1, wherein the changing means changes the threshold value to a larger value. 6. The misfire detection apparatus for an internal combustion engine according to claim 1, wherein the changing means cancels the change of the detection mode when a predetermined period has elapsed after the engine is started. The misfire detection device for an internal combustion engine according to any one of claims 1 to 6, wherein the internal combustion engine includes a block heater for heating the engine body. The determination means determines that there is a temperature difference of a predetermined value or more between a position where the engine temperature sensor is attached to the engine body and another specific part of the engine body when starting the engine. The misfire detection apparatus for an internal combustion engine according to any one of claims 7 to 9.

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