JP2004100520A - Misfire detector of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a misfire detector of internal combustion engine for performing reliable misfire detection in the operation under a low-temperature condition as cold starting. <P>SOLUTION: A secondary air supplying system 40 has the function of supplying the air taken from the outside of an engine 1 to each exhaust port as secondary air. An electric air pump 41 operates based on the instruction signal of an ECU 50 to suck air from the middle of an intake pipe 21 through an inlet passage 42 (a portion corresponding to the up stream of a throttle valve 23 and the down stream of an air cleaner 25), and force-feeds the sucked air to a main supply pipe 44 through a force-feed passage 43. The air force-fed to the main supply pipe 44 is supplied to each exhaust port 31 through for branched pipes 45. When the secondary air is supplied, the ECU 50 detects the misfire of the engine 1 based on the waveform of the detection signal of a pressure sensor 66 provided in the force-feed passage 43. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an apparatus for detecting misfire of an internal combustion engine.
[0002]
[Prior art]
Conventionally, as a method of detecting misfire of an internal combustion engine, a method of indirectly detecting misfire by detecting an abnormality in engine speed caused by misfire is known.
[0003]
For example, the device described in Japanese Patent Application Laid-Open No. 2000-4936 monitors the amount of change in the engine speed of the internal combustion engine per unit time (change in the speed), and if the change exceeds a predetermined level, a misfire occurs. It is determined that the
[0004]
[Patent Document 1] Japanese Patent Application Laid-Open No. 2000-4936 [Patent Document 2] Japanese Patent Application Laid-Open No. 9-21213 [Patent Document 3] Japanese Patent Application Laid-Open No. 9-125946 [0005]
[Problems to be solved by the invention]
By the way, under the condition that the combustion state of the internal combustion engine tends to be unstable such as at the time of a cold start, the engine speed tends to fluctuate. It has been difficult to distinguish between fluctuations in engine speed due to stability and fluctuations in engine speed due to misfire.
[0006]
As a result, under conditions where the combustion state of the internal combustion engine becomes unstable, such as during a cold start, the accuracy of misfire detection has been poor.
[0007]
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 perform highly reliable misfire detection even in a cold state. .
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides an air pump for pumping air, an air passage for introducing air pumped by the air pump into an exhaust system of a multi-cylinder internal combustion engine, and a passage provided in the middle of the air passage. A control valve that opens and closes, a pressure detection unit that detects a pressure in the air passage upstream of the control valve in the air passage, and a control valve of the internal combustion engine based on a local change in a transition waveform of the detected pressure. A misfire detection means for detecting misfire is provided.
[0009]
Here, the secondary air means air that is supplied again to the gas that has undergone the combustion process in the combustion chamber of the internal combustion engine. Further, the control valve may be a valve that selectively opens and closes the flow path of the air passage, or may be one that adjusts the area of the flow path in multiple steps or steplessly. You may.
[0010]
As in the same configuration, an air pump for pumping air, an air passage for introducing the air pumped by the air pump into an exhaust system of a multi-cylinder internal combustion engine, and an air amount provided in the middle of the air passage and flowing through the passage. An internal combustion engine having a control valve for controlling and a pressure detecting means for detecting a pressure in the air passage upstream of the control valve in the air passage, by introducing secondary air into an exhaust system of the engine, It has a function to optimize the exhaust characteristics of the engine.
[0011]
Particularly under conditions where the engine temperature is relatively low (at a cold time), immediately after the start of the engine (a warm-up period), unburned components of the fuel are removed from the exhaust system as the amount of fuel supplied for engine combustion increases. The secondary air introduced into the exhaust system acts very effectively in promoting the oxidation reaction of such unburned components.
[0012]
On the other hand, when the engine is cold, the engine combustion tends to be unstable, so that misfire easily occurs, and high accuracy is also required for misfire detection.
[0013]
When an abnormality occurs in each element for introducing air into the exhaust system of the internal combustion engine, such as the air pump, the control valve, or the air passage, an abnormality appears in a pressure value and a transition waveform of the pressure in the air passage. Further, when a misfire occurs in the internal combustion engine, the transition waveform of the pressure in the air passage locally changes.
[0014]
According to the above configuration, by observing the pressure in the air passage, whether or not each element for introducing air into the exhaust system of the internal combustion engine, such as the air pump, the control valve, or the air passage, functions normally. In addition to monitoring whether or not the misfire has occurred, misfire of each cylinder of the internal combustion engine can be detected. Therefore, highly accurate misfire detection can be performed without increasing the manufacturing cost.
[0015]
In the above-described apparatus configuration, it is preferable that the apparatus further includes a cylinder specifying unit that specifies the misfired cylinder based on a timing at which misfire of the internal combustion engine is detected. Here, the term “timing” means not only a specific time but also a predetermined period including the specific time.
[0016]
Further, in the above configuration, the engine further includes a rotation speed detection unit that detects an engine rotation speed of the internal combustion engine, and the cylinder identification unit detects any one of the cylinders when misfire of the internal combustion engine is detected. A response delay time between a misfire timing and a timing at which a local change occurs in a pressure transition waveform at a pressure detection portion in the air passage is estimated based on the detected engine speed. Preferably, the misfired cylinder is specified based on the estimated response delay time. Here, the engine rotation speed means the rotation speed of the engine output shaft per unit time.
[0017]
The time required for the pulsation of the exhaust gas discharged from each cylinder of the internal combustion engine to reach the pressure detecting means (response delay time) varies depending on the engine speed. According to the above configuration, the response delay time can be accurately calculated (estimated) based on the engine speed quantitatively corresponding to the response delay time. Therefore, the pulsation of the exhaust gas discharged from each cylinder can be distinguished from each other. As a result, when the misfire of the internal combustion engine is detected based on the local change of the detected pressure transition waveform, it is possible to accurately recognize in which cylinder the misfire has occurred.
[0018]
It should be noted that the above configurations can be employed in combination as much as possible.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described.
[Basic configuration of engine]
As shown in FIG. 1, a gasoline engine system (hereinafter, referred to as an engine) 1 includes an engine body (internal combustion engine) 10 forming four combustion chambers (cylinders) 11 arranged in series, an intake system 20, and exhaust gas. A system 30, a secondary air supply system 40, an electronic control unit (hereinafter, referred to as an ECU) 50, and the like are configured as main components.
[0020]
The engine main body 10 includes four combustion chambers 11 arranged in series inside the cylinder block and the cylinder head as outer members. An intake port 23 for introducing a mixture of air and fuel into each combustion chamber 11 and an exhaust port 31 for discharging exhaust gas from each combustion chamber 11 are formed in the cylinder head. A fuel injection valve 12 is provided at an intake port 23 corresponding to each combustion chamber 11. The fuel injection valve 12 is an electromagnetic valve provided with an electromagnetic solenoid (not shown) therein, and is appropriately opened according to a command signal from the ECU 50 to inject and supply fuel into the combustion chamber 11.
[0021]
The intake system 20 forms a passage (intake passage) for intake air introduced into each combustion chamber 11, and is formed by sequentially connecting an intake pipe 21, an intake manifold 22, and an intake port 23 from upstream to downstream of the air flow path. Is done.
[0022]
The throttle valve 24 provided in the intake pipe 21 is an electronically controlled butterfly valve whose opening is changed in accordance with a command signal from the ECU 50 to adjust the flow area (flow rate) of the intake air. The opening of the throttle valve 24 is determined in consideration of the amount of depression of an accelerator pedal (not shown) and various parameters that reflect the operating state of the engine 1. Similarly, in the intake pipe 21, an air cleaner 25 provided upstream of the throttle valve 24 is a filter for removing dust and the like contained in the intake air.
[0023]
The exhaust system 30 forms a passage (exhaust passage) for exhaust gas discharged from each combustion chamber 11, and is formed by sequentially connecting an exhaust port 31, an exhaust manifold 32, and an exhaust pipe 33 from the upstream to the downstream of the exhaust passage. Is done. A catalyst casing 34 is provided in the exhaust pipe 33. The catalyst casing 34 incorporates a well-known three-way catalyst having a function of purifying hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) contained in exhaust gas.
[0024]
The secondary air supply system 40 has a function of supplying air introduced from outside the engine 1 to each exhaust port as secondary air. An electric air pump (hereinafter, referred to as an air pump) 41 operates based on a command signal from the ECU 50, and passes through the introduction passage 42 from the middle of the intake pipe 21 (a portion that is upstream of the throttle valve 24 and downstream of the air cleaner 25). The air is sucked and sent to the main supply pipe 44 through the feed passage 43. The air sent to the main supply pipe 44 is supplied to each exhaust port 31 through four distribution pipes 45.
[0025]
A secondary air control valve 46 that opens and closes a flow path of air flowing between the pressure feeding passage 43 and the main supply pipe 44 is provided at a connection portion between the pressure feeding passage 43 and the main supply pipe 44.
[0026]
Inside the secondary air control valve 46, a diaphragm 46a and a valve body 46b operated by deformation of the diaphragm 46a are provided. The valve body 46b releases the flow path of the air flowing between the pressure feeding passage 43 and the main supply pipe 44 only when the diaphragm 46a is deformed. The secondary air control valve 46 is connected to a negative pressure passage 47 for applying a negative pressure (attraction force) generated in the intake system 20 to the diaphragm 46a. The negative pressure passage 47 communicates between the intake manifold 22 and the secondary air control valve 46, and from the side of the intake manifold 22 to the side of the secondary air control valve 46, a check valve 47 a, A negative pressure tank 47b and a negative pressure control valve 47c are sequentially provided. The check valve 47a allows only the air flow from the negative pressure tank 47b to the intake manifold 22, and regulates the air flow from the intake manifold 22 to the negative pressure tank 47b. The negative pressure tank 47b is a pressure-resistant container capable of holding the inside thereof at a gas pressure lower than the atmospheric pressure. The negative pressure control valve 47c is an electromagnetically driven on-off valve. The negative pressure control valve 47c is normally in a closed state, but is opened appropriately in response to a command signal from the ECU 50.
[0027]
During the operation of the engine 1, a negative pressure is generated in the intake manifold 22, so that the pressure in the negative pressure tank 47b decreases and falls below the atmospheric pressure (maintained at the negative pressure). When the ECU 50 opens the negative pressure control valve 47c under such conditions, the negative pressure (suction force) in the negative pressure tank 47b deforms the diaphragm 46a in the secondary air control valve 46. The valve body 46b operates by the deformation of the diaphragm 46a, and releases the flow path of the air flowing between the pressure feeding passage 43 and the main supply pipe 44. When the air pump 41 is operated at this time, air (secondary air) introduced from outside the engine 1 is pressure-fed from the air pump 41 to the main supply pipe 44 and supplied to the exhaust port 31 through the distribution pipe 45.
[0028]
In addition, various sensors 61 to 66 are attached to each part of the engine 1, and output signals relating to environmental conditions of the part and an operation state of the engine 1. For example, the air flow meter 61 provided in the intake pipe outputs a detection signal corresponding to the flow rate (intake amount) of the intake air. The throttle opening sensor 62 is attached to the throttle valve 24, and outputs a detection signal corresponding to the opening of the throttle valve 24. The crank angle sensor 63 outputs a detection signal (pulse) every time the output shaft (crank shaft) of the engine 1 rotates by a certain angle. Further, oxygen concentration sensors 64 and 65 provided upstream and downstream of the catalyst casing 34 of the exhaust pipe 33 output detection signals that continuously change in accordance with the oxygen concentration in the exhaust gas at the respective locations. The detection signals from the oxygen concentration sensors 64 and 65 reflect the air-fuel ratio of the air-fuel mixture supplied to the engine combustion, and include oxidizing components (oxygen (O ₂ )) and reducing components (hydrocarbon (HC)) in the exhaust gas. Is an index that directly indicates the amount of Further, the pressure sensor 66 outputs a detection signal corresponding to the pressure P in the pressure supply passage 43 in the secondary air supply system 40. These sensors 61 to 66 are electrically connected to the ECU 50.
[0029]
The ECU 50 includes a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), a backup RAM, a timer counter, an external input circuit including an A / D converter, an external output circuit, and the like. Prepare. The CPU, the ROM, the RAM, the backup RAM, the timer counter, and the like, and the external input circuit, the external output circuit, and the like are connected by a bidirectional bus, and constitute a logical operation circuit as a whole.
[0030]
The ECU 50 configured as described above controls the supply of fuel to each intake port 23 through the opening / closing operation of the fuel injection valve 12 (fuel injection control) and the negative pressure based on the detection signals of the various sensors 61 to 66. Various controls relating to the operating state of the engine 1 such as a control (secondary air supply control) for supplying secondary air to each exhaust port 31 through the opening / closing operation of the control valve 47c and the driving of the air pump 41 are performed.
[0031]
The ECU 50 configured as described above, together with the secondary air supply system 40, constitutes a misfire detection device for the engine 1 according to the present embodiment.
[Secondary air supply control]
Next, the secondary air supply control will be described in detail.
[0032]
In the engine 1, when the engine is operated under a condition in which the temperature of the engine main body 10 is not sufficiently high (at a cold time), such as when the engine is started, the amount of fuel supplied into the combustion chamber 11 through the fuel injection valve 12 (Enrichment of the air-fuel mixture supplied to engine combustion) to stabilize engine combustion and promote warm-up. However, if the air-fuel mixture supplied for engine combustion is enriched, the amount of unburned fuel (HC, CO, etc.) in the exhaust gas increases. In addition, under such a condition that an increase in the amount of fuel is required, the temperature of the three-way catalyst provided in the exhaust system 30 is also low, and the temperature does not reach the temperature (activation temperature) at which the catalyst is sufficiently activated. Normal.
[0033]
For this reason, in the engine 1, when enriching the air-fuel mixture to be used for engine combustion under conditions in which the temperature of the three-way catalyst has not reached the activation temperature, such as during a cold start, the secondary air supply control must be performed. As a result, air is mixed into the exhaust gas immediately after being discharged from each combustion chamber 11, thereby promoting the oxidation reaction of unburned fuel components (HC, CO) contained in the exhaust gas. As a result, the purification of the unburned fuel component is promoted upstream of the three-way catalyst, and the heat of the reaction accelerates the activation of the three-way catalyst.
[0034]
FIG. 2 is a schematic diagram schematically illustrating the functions of the secondary air control valve 46, the negative pressure control valve 47c, and the air pump 41 that constitute the secondary air supply system 40.
[0035]
The interior of the secondary air control valve 46 is partitioned into three spaces S1, S2, S3. The first space S1 communicates with the negative pressure passage 47, the second space S2 communicates with the pressure feed passage 43, and the third space S3 communicates with the main supply pipe 44. The diaphragm 46a that partitions between the first space S1 and the second space is formed integrally with the valve body 46b. A communication hole 46d is provided at the boundary between the second space S2 and the third space S3 to allow the two spaces S2 and S3 to communicate with each other. The spring 46c housed in the first space S1 urges the diaphragm 46a toward the second space S2 so that the valve body 46b closes the communication hole 46d.
[0036]
Therefore, as shown in FIG. 2A, when the negative pressure control valve 47c is in the closed state, the second space S2 (the pressure supply passage 43) and the third space S3 (the main supply pipe 44) are shut off from each other. Is done.
[0037]
On the other hand, as shown in FIG. 2 (b), when the negative pressure control valve 47c is in the open state, the first space S1 becomes negative pressure (below the atmospheric pressure), and the diaphragm 46a is moved to the second position. A suction force is generated in the one space S1 side. Then, the force for sucking the diaphragm 46a toward the first space S1 exceeds the urging force of the spring 46c, and the valve body 46b is separated from the communication hole 46d. As a result, the second space S2 (the pressure feeding passage 43) and the third space S3 (the main supply pipe 44) communicate with each other. When the secondary air supply control is performed, the opening of the negative pressure control valve 47c and the operation of the air pump 41 are simultaneously performed based on a command signal from the ECU 50, so that the air pumped from the air pump 41 is mainly transmitted from the pressure feeding passage 43 through the pressure feeding passage 43. It is transferred to the supply pipe 44 and further supplied to each exhaust port 31 through each distribution pipe 45.
[0038]
The reed valve 46e provided in the third space S3 allows the flow of air from the second space S2 to the main supply pipe 44 via the third space S3, while allowing the third space S3 to flow from the main supply pipe 44. The flow of the air toward the second space S2 is regulated. In the case where the valve body 46b is fixed while being separated from the communication hole 46d for some reason, the reed valve 46e prevents the backflow of gas from the main supply pipe 44 to the pressure feed passage 43 (FIG. 2C).
(Secondary air supply system abnormality diagnosis)
The ECU 50 monitors the transition of the pressure in the pressure feed passage 43 based on the detection signal of the pressure sensor 66, and diagnoses whether the secondary air supply system 40 is abnormal based on the transition of the pressure.
[0039]
FIGS. 3A and 3B show pressure transitions in the pressure feed passage 43 that vary depending on the state of energization of the negative pressure control valve 47c and the air pump 41.
[0040]
For example, FIG. 3A shows a difference in a change in pressure in the pressure feeding passage observed when the air pump 41 is operated and when the air pump 41 is stopped under the condition that the negative pressure control valve 47c is closed. . When the negative pressure control valve 47c is kept closed, the second space S2 and the third space S3 in the secondary air control valve 46 are shut off from each other (see FIG. 2A), so that the exhaust port 31 is closed. The pressure pulsation of the exhaust gas generated inside does not propagate to the pressure feed passage 43. When the air pump 41 operates under such a condition, the pressure P in the pressure feed passage 43 increases from an initial value P0 to a predetermined value P1, and holds this value P1. Here, when the air pump 41 is not functioning properly or has deteriorated in function, the pressure P in the pressure feed passage 43 changes from the initial value P0 even though the air pump 41 is energized. Or rises only to a value below the predetermined value P1. The ECU 50 can diagnose a malfunction of the air pump 41 from such an abnormal change in pressure.
[0041]
FIG. 3B shows an example of a pressure change in the pressure feed passage 43 observed when the secondary air supply system 40 is functioning normally. During execution of the secondary air supply control, the negative pressure control valve 47c is opened, so that the second space S2 and the third space S3 in the secondary air control valve 46 communicate with each other (FIG. 2B). reference). When the air pump 41 is operated, air flows from the pressure feed passage 43 toward the main supply pipe 44, so that the reed valve 46e is also opened (see FIG. 2B). As a result, the pressure feed passage 43 and the main supply pipe 44 communicate with each other, and the pressure pulsation of the exhaust gas generated in the exhaust port 31 propagates to the pressure feed passage 43. For this reason, during execution of the secondary air supply control, if various members such as the negative pressure control valve 47c, the secondary air control valve 46, and the air pump 41 function normally, they are indicated by solid lines in FIG. 3B. As described above, the regular pressure fluctuation having the predetermined value (average value) Pm as the center of the fluctuation width is observed in the pressure feeding passage 43.
[0042]
As described above, the ECU 50 of the engine 1 appropriately combines the selection of whether to output the command signal for opening the negative pressure control valve 47c and the selection of whether to output the command signal for operating the air pump 41. By observing the change in the pressure in the pressure-feeding passage 43 while performing the operation, it is diagnosed whether or not the function of the secondary air supply system 40 is abnormal.
(Misfire detection during secondary air supply control)
The ECU 50 diagnoses the function of the secondary air supply system 40 using the detection signal of the pressure sensor 66 provided in the pressure feed passage 43 as described above, and also executes the engine 1 during the execution of the secondary air supply control. Is detected for each cylinder (combustion chamber 11) that constitutes.
[0043]
FIG. 4 shows a change in the pressure in the pressure feed passage 43 during the execution of the secondary air supply control. In particular, regarding a specific cylinder of the engine 1, a change in the pressure when the engine combustion is normally performed and a misfire occurs. 6 is a time chart showing both of them in order to compare with the change in pressure in the case where the pressure change has occurred.
[0044]
As described above, during the execution of the secondary air supply control, if the engine combustion of the engine 1 is normally performed, the regular pressure fluctuation having the predetermined value (average value) Pm as the center of the fluctuation width is pumped. Observed in passage 43. On the other hand, when a misfire occurs in a specific cylinder, for example, as shown in a period from time tA to time tB, a maximum value exceeding a predetermined level should originally appear (solid line), and a relatively small maximum value appears. Phenomena such as a dashed line (dash-dotted line) or no maximum value (two-dot chain line).
[0045]
Here, the ignition timing (start of the combustion stroke) and the opening timing of the exhaust valve (start of the exhaust stroke) in each cylinder (combustion chamber 11) are determined by the timing of energization of the ignition plug and the detection of the crank angle sensor 63. Accurate grasp can be made based on signals and the like. Further, a time (response delay time) required for the exhaust pulsation generated in each combustion chamber 11 to propagate as a pressure fluctuation to a position where the pressure sensor 66 is installed can be obtained in advance by an experiment or the like. That is, by observing the pressure transition of each cylinder during a predetermined period including the exhaust stroke, and analyzing the waveform of the pressure transition (fluctuation) during this predetermined period, the occurrence of misfire in each cylinder can be detected. .
[0046]
Based on such a principle, the ECU 50 of the engine 1 determines, for each cylinder (combustion chamber 11) constituting the engine 1, from the pressure fluctuations in the pressure feed passage 43 observed during the execution of the secondary air supply control. Perform misfire detection individually.
[0047]
More specifically, during execution of the secondary air supply control, the combustion stroke of a specific cylinder (cylinder to be observed) or During a period corresponding to the exhaust stroke (hereinafter referred to as a corresponding period), a period T (hereinafter referred to as a positive pressure propagation period) T in which the pressure P in the pressure feed passage 43 exceeds a predetermined level is measured. If the positive pressure propagation period T is less than the predetermined reference value T0, it is determined that a misfire has occurred in the cylinder to be observed.
[Misfire detection routine]
Hereinafter, a specific procedure for detecting misfire of the engine 1 will be described with reference to a flowchart.
[0048]
FIG. 5 is a flowchart illustrating a processing routine of “misfire detection during secondary air supply control” executed by the engine 1. This routine is repeatedly executed at predetermined intervals through the ECU 50 while the engine 1 is operating.
[0049]
When the process proceeds to this routine, the ECU 50 first determines in step S101 whether or not the secondary air supply control is currently being performed. Incidentally, the secondary air supply control is performed in spite of the fact that the three-way catalyst in the catalyst casing 34 is not sufficiently activated, such as immediately after starting the engine 1 in a state where the temperature of the engine body 10 is lower than the predetermined value. This is carried out under such conditions that an increase in the amount of fuel supplied to engine combustion is expected. If the determination in step S101 is affirmative, the ECU 50 shifts the processing to step S102. If the determination is negative, the ECU 50 once exits this routine.
[0050]
In step S102, the ECU 50 determines, based on the current engine speed NE, the time (response delay time) required for the exhaust pulsation generated in each combustion chamber 11 to propagate to the installation site (pressure detection site) of the pressure sensor 66. Recognition is performed by referring to a preset map.
Here, for example, a relationship as shown in FIG. 6 is stored on a map adopted as a relationship between the response delay time and the engine speed NE.
[0051]
In the following step S103, it is determined which cylinder the pressure fluctuation currently observed in the pressure feed passage 43 is caused by exhaust pulsation generated from the cylinder, taking into account the response delay time recognized in step S103. In this cylinder discrimination, a circuit serving as a cylinder discrimination counter is employed.
[0052]
FIG. 7 shows exhaust pulsation (FIG. 7 (a)) observed at a portion (exhaust port 31) close to the combustion chamber 11, pressure fluctuation (FIG. 7 (b)) observed within the pressure feed passage 43, and cylinders. 8 is a time chart showing changes in the count value of the discrimination counter (FIG. 7C) on the same time axis.
[0053]
The cylinder discrimination counter is a circuit included in the ECU 50, and has a function of storing a set value corresponding to each cylinder (for convenience, discriminated as cylinders # 1, # 2, # 3, and # 4). . For example, a period in which the crank angle of the cylinder # 1 is from α ° before the compression top dead center to β ° after the exhaust top dead center is a period in which the pressure fluctuation caused by the cylinder # 1 occurs in the pressure feed passage 43 (hereinafter, referred to as a cylinder). The ECU 50 sets the count value of the cylinder discrimination counter to “1” (referred to as a corresponding period of # 1) (FIG. 7C).
[0054]
Here, between the exhaust pulsation (FIG. 7 (a)) observed at a portion (exhaust port 31) close to the combustion chamber 11 and the pressure fluctuation (FIG. 7 (b)) observed within the pressure feed passage 43. Appears as a phase difference as seen between times t0 'and t0.
[0055]
For this reason, the ECU 50 appropriately adjusts the setting range (period) of the cylinder discriminating counter corresponding to each cylinder according to the engine speed NE at each time in consideration of the response delay time.
[0056]
For example, in FIGS. 7A to 7C, assuming that the times t0 'to t1' (broken lines) are the periods set without considering the fluctuation of the engine speed NE as the corresponding periods of the cylinder # 1. The times t0 to t1 correspond to a period set in consideration of the fluctuation of the engine speed NE as in the present embodiment.
[0057]
In step S104, based on the detection signal of the pressure sensor 66 and its history, the change in the pressure in the pressure feed passage 43 during a predetermined period up to the present time is recognized.
[0058]
In step S105, an average value Pm is calculated for the pressure transition recognized in step S103. When the pressure P recognized based on the detection signal of the pressure sensor 66 exceeds the average value Pm during the rising process, the ECU 50 starts measuring the positive pressure propagation period T starting from this. If the combustion state of the cylinder to be observed is normal, the pressure P exceeding the average value Pm continues to increase thereafter, and decreases when reaching the maximum value. The ECU 50 recognizes, as the end of the positive pressure propagation period T, a time at which the pressure P that has reached the maximum value falls below the average value Pm in the subsequent descending process.
[0059]
In step S106, it is determined whether or not the present time is a timing at which misfire detection should be performed. For example, the end of the corresponding period of each cylinder (time t1, t2, t3,... In FIG. 7) may be set as the timing for performing misfire detection.
[0060]
In step S107, it is determined whether or not a misfire has occurred in the cylinder that has become the target of observation this time. Specifically, when the positive pressure propagation period T measured this time exceeds a preset reference value T0, it is determined that the cylinder to be observed is in a normal combustion state. On the other hand, if the positive pressure propagation period T is equal to or less than the reference value T0, it is determined that a misfire has occurred in the cylinder to be observed. If it is determined that a misfire has occurred in the cylinder to be observed, the ECU 50 shifts the processing to step S108. On the other hand, if it is determined that no misfire has occurred, the ECU 50 once exits this routine.
[0061]
In step S108, the count values of the cylinder-specific misfire counter and the all-cylinder misfire counter are updated. The misfire counter for each cylinder and the misfire counter for all cylinders are circuits included in the ECU 50. The cylinder-by-cylinder misfire counter stores and updates the number of misfires that occur in each cylinder for each cylinder, and the all-cylinder misfire counter stores and updates the total number of misfires that occur in all cylinders that constitute the engine 1. . If a misfire is detected in step S107 of this routine, the ECU 50 increments the count value of the cylinder-by-cylinder misfire counter corresponding to the cylinder to be observed this time by “1”, and increments the count value of the all-cylinder misfire counter. Is incremented by “1”.
[0062]
For example, FIG. 8 shows the change in the pressure in the pressure feed passage during the execution of the secondary air supply control (FIG. 8A) and the change in the count value of the cylinder discrimination counter (FIG. 8B) on the same time axis. 5 is an example of a time chart shown in FIG.
[0063]
8 (a) and 8 (b), the pressure in the pressure feed passage 43 at the time t11 to t12 (corresponding period of the cylinder # 2) and at the time t16 to t17 (corresponding period of the cylinder # 3). Local depression (misfire) is observed. As a result, during the observation period on this time chart, the count value of the cylinder-specific misfire counter corresponding to cylinder # 2 and the count value of the cylinder-specific misfire counter corresponding to cylinder # 3 are each "1". Thus, the count value of the all-cylinder misfire counter is incremented twice by "1".
[0064]
Knowing the frequency of misfires occurring in each cylinder is useful for identifying defective cylinders, for example, when repairing or maintaining the engine 1. Further, grasping the frequency of misfires occurring in all cylinders is useful for overall evaluation of the exhaust characteristics of the engine 1.
[0065]
That is, in step S109, the ECU 50 diagnoses the state of each cylinder constituting the engine 1 based on the count values of the four types of cylinder-specific misfire counters updated in step S108 and the count values of the all-cylinder misfire counters. I do. For example, when the occurrence of misfire is detected with a frequency exceeding a predetermined standard for a specific cylinder, the ECU 50 notifies the driver that there is a problem with the cylinder by turning on a warning lamp or the like. Further, when the occurrence of a misfire is detected in the engine 1 as a whole at a frequency exceeding a predetermined reference, the driver is warned that the exhaust characteristics are deteriorated due to the misfire of each cylinder constituting the engine 1. Control is performed through lighting of a lamp or the like, and control (for example, adjustment of fuel injection amount, throttle opening, ignition timing, intake / exhaust valve timing, and the like) for correcting such deterioration of exhaust characteristics is performed.
[0066]
After the processing in step S109, the ECU 50 once exits this routine.
[0067]
In accordance with such a procedure, the ECU 50 detects misfire of each of the cylinders constituting the engine 1 in addition to the execution of the secondary air supply control, and determines whether there is a malfunction of the engine 1 due to the misfire of each of the cylinders. Diagnose.
[0068]
Here, in the conventional misfire detection device, for example, misfires in each cylinder are detected based on engine rotation fluctuations. For example, when an engine started under a condition where the engine temperature is relatively low performs idle operation, Under the conditions where the engine speed is high and the combustion state tends to be unstable, the engine speed fluctuates irrespective of the presence or absence of misfire, making it difficult to perform highly accurate misfire detection.
[0069]
In this regard, according to the misfire detection device of the present embodiment, during the execution period of the secondary air supply control, the pressure sensor 66 of the secondary air supply system configured to propagate the exhaust pulsation is used. Misfire occurring in each cylinder is detected based on the detection signal. When a misfire occurs in each cylinder of the engine 1, unlike the waveform of the exhaust pulsation (exhaust pressure variation) caused simply by the engine rotational variation, a characteristic waveform of the exhaust pressure variation is locally observed. Thus, highly accurate misfire detection can be performed through the detection signal of the pressure sensor 66. Originally, the secondary air supply system 40 is often used at the time of a cold start in which the rotation of the engine 1 becomes unstable. That is, according to the present embodiment, the rotation fluctuation of the engine 1 under the condition that the rotation fluctuation of the engine 1 is large and it is difficult to perform the misfire detection with high accuracy (the condition under which the secondary air supply control is performed). And a highly reliable misfire detection can be performed at low cost by using a method which is hardly affected by the misfire.
[0070]
Further, in the present embodiment, the response delay time until exhaust pulsation generated in the combustion chamber 11 reaches the pressure sensor 66 is accurately grasped (estimated) based on the engine speed NE at each time, thereby enabling observation. It is possible to accurately specify the cylinder in which the target pressure fluctuation has occurred. As a result, for example, by recognizing the frequency of occurrence of misfires in all cylinders, it is possible to not only evaluate the exhaust characteristics of the engine 1 at the time of cold start as a whole, but also determine which cylinder has a malfunction. , And effective measures can be taken through repair, maintenance, operation control by the engine 1 itself, and the like.
[0071]
In the above-described embodiment, as a control valve for opening and closing a passage for supplying air pumped from the air pump 41 to the exhaust port 31, a negative pressure generated in the intake system 20 like the secondary air control valve 46. A configuration in which the passage is opened and closed by using (suction force) as needed is applied. However, for example, instead of the secondary air control valve 46, an electromagnetically driven control valve that operates based on a command signal from the ECU 50 or the like may be provided between the pressure feeding passage 43 and the main supply pipe 44.
[0072]
In the above-described embodiment, an example has been described in which the misfire detection based on the detection signal of the pressure sensor 66 is performed during the execution period of the secondary air supply control. During the execution period of the secondary air supply control, while it becomes difficult to detect misfire based on the rotation fluctuation of the engine 1 and the like, it corresponds to a representative opportunity where the detection signal of the pressure sensor 66 can be effectively used. is there. However, the present invention is not limited to this. If the pressure pulsation from the exhaust system is propagated to the pressure sensor 66 (or by actively setting such a condition), the secondary air supply control may be performed during the execution period. Other than the above, the misfire detection based on the detection signal of the pressure sensor 66 can be performed, and the effect according to the present embodiment can be obtained. In addition, the opportunity to execute the secondary air supply control may be expanded (not limited to the cold start) so that the misfire detection based on the detection signal of the pressure sensor 66 is performed.
[0073]
Further, in the above-described embodiment, a period (exhaust pressure propagation period) T in which the pressure value in the pressure feed passage 43 exceeds a predetermined level is measured, and when the exhaust pressure propagation period T is lower than a predetermined reference value T0, It is now determined that a misfire has occurred in the cylinder that was the object of observation. However, the present invention is not limited to this, and it is also possible to apply another criterion for determining the abnormality of the waveform of the pressure transition in the pressure passage 43 to detect misfire. For example, when the difference between the minimum value and the maximum value of the pressure transition observed within a predetermined period is equal to or smaller than a predetermined value, it may be assumed that a misfire has occurred.
[0074]
In the above embodiment, the present invention is applied to a gasoline engine. However, the present invention is not limited to this, and may be applied to, for example, a diesel engine.
[0075]
【The invention's effect】
As described above, according to the present invention, in an internal combustion engine having a secondary air supply function, when operating under low-temperature conditions such as a cold start, highly reliable misfire detection can be performed at low cost. It can be realized by.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a basic configuration of an engine according to an embodiment of the present invention.
FIG. 2 is a schematic diagram schematically showing the function of a secondary air control valve.
FIG. 3 is a time chart showing a change in pressure in a pressure-feeding passage which varies depending on a state of energization of a negative pressure control valve and an air pump.
FIG. 4 is a time chart showing a change in pressure in a pressure feed passage during execution of secondary air supply control.
FIG. 5 is a flowchart showing a processing procedure for misfire detection during secondary air supply control.
FIG. 6 is a graph showing a relationship between a response delay time and an engine speed on a map.
FIG. 7 is a time chart showing, on the same time axis, exhaust pulsation observed at an exhaust port, pressure fluctuation observed in a pressure feed passage, and a change in a count value of a cylinder discrimination counter.
FIG. 8 is a time chart showing, on the same time axis, a change in pressure in a pressure-feeding passage and a change in a count value of a cylinder discrimination counter during execution of secondary air supply control.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Engine 10 Engine main body 11 Combustion chamber 12 Fuel injection valve 20 Intake system 21 Intake pipe 22 Intake manifold 23 Intake port 24 Throttle valve 25 Air cleaner 30 Exhaust system 31 Exhaust port 33 Exhaust pipe 34 Catalyst casing 40 Secondary air supply system 41 Air pump 42 Introductory passage 43 Compression passage (air passage)
44 Main supply pipe (air passage)
45 minute piping (air passage)
46 Secondary air control valve 46a Diaphragm 46b Valve element 46c Spring 46d Communication hole 46e Reed valve 47 Negative pressure passage 47a Check valve 47b Negative pressure tank 47c Negative pressure control valve 61 Air flow meter 62 Throttle opening sensor 63 Crank angle sensor 64, 65 oxygen concentration sensor 66 pressure sensor S1 first space S2 second space S3 third space

Claims (3)

An air pump for pumping air,
An air passage for introducing air pumped by the air pump into an exhaust system of a multi-cylinder internal combustion engine,
A control valve provided in the middle of the air passage to open and close the passage;
Pressure detection means for detecting the pressure in the air passage upstream of the control valve in the air passage;
Misfire detection means for detecting misfire of the internal combustion engine based on a local change in the detected transition waveform of pressure,
A misfire detection device for an internal combustion engine, comprising: 2. The misfire detection device for an internal combustion engine according to claim 1, further comprising a cylinder identification unit that identifies the misfired cylinder based on a timing at which the misfire of the internal combustion engine is detected. A rotational speed detecting means for detecting an engine rotational speed of the internal combustion engine, and
The cylinder specifying means includes:
When a misfire of the internal combustion engine is detected, a response delay between a timing at which any cylinder misfires and a timing at which a local change occurs in a pressure transition waveform at a pressure detection portion in the air passage. 3. The misfire detection device for an internal combustion engine according to claim 2, wherein a time is estimated based on the detected engine speed, and a misfired cylinder is specified based on the estimated response delay time.

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