JP4168792B2 - INTERNAL COMBUSTION ENGINE HAVING FUNCTION OF RECOMBURING AIR-FILLED AIR DURING MISMISTING AND INTERNAL COMBUSTION ENGINE CONTROL METHOD - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for avoiding various adverse effects when a misfire occurs in an internal combustion engine.
[0002]
[Prior art]
Since the internal combustion engine has an excellent characteristic that it can generate a large amount of power while being relatively small, it can be used as a power source for various moving means such as an automobile, a ship, an aircraft, or a stationary type such as a factory. Widely used as a power generation source. Each of these internal combustion engines has an operating principle of burning a mixture of fuel and air in a combustion chamber and converting the pressure generated at this time into mechanical work and outputting it.
[0003]
As a method of combusting the air-fuel mixture in the combustion chamber, a method of burning the spark in the combustion chamber and igniting the air-fuel mixture, a method of compressing and auto-igniting the air-fuel mixture in the combustion chamber, and an air in the combustion chamber There is a method in which only the fuel is compressed and fuel is injected into the compressed air to burn. Even when the fuel spray is injected into the compressed air, the vaporized spray burns while being mixed with the surrounding air, so that the air-fuel mixture is eventually burned.
[0004]
Since the internal combustion engine is operated under various conditions, the air-fuel mixture may not burn in the combustion chamber, or only a part of the air-fuel mixture may burn. Such a phenomenon is skipped as “misfire”. When misfire occurs, the air-fuel mixture in the combustion chamber is discharged without generating power, which causes deterioration in fuel consumption efficiency. In view of these points, when misfire is detected, a technique has been proposed that improves mixture formation and avoids misfire by retarding the ignition timing or advancing the fuel injection timing. (For example, patent document 1).
[0005]
However, with the proposed technology, unburned fuel is discharged in the cycle where misfires occur, which increases the amount of air pollutants emitted. Furthermore, in order to purify air pollutants in the exhaust gas, when a purification catalyst is provided in the exhaust passage, the unburned air-fuel mixture reacts on the purification catalyst all at once, resulting in deterioration of the catalyst performance. There is also concern about causing it.
[0006]
In view of these points, a technology for suppressing the discharge of unburned air-fuel mixture when a misfire occurs has been filed (Japanese Patent Application No. 2002-234634).
[0007]
[Patent Document 1]
Japanese Patent Laid-Open No. 11-200935
[0008]
[Problems to be solved by the invention]
However, the above-mentioned applied technology is required to be further improved in the following points. That is, it is natural that a sufficient torque is not generated in a misfired cycle, and a desired torque may not be obtained even in a cycle following the misfire cycle, which may give an uncomfortable feeling to the driver of the internal combustion engine.
[0009]
The present invention has been made in order to solve the above-described problems in the prior art. When a misfire occurs in an internal combustion engine, a desired torque is generated in a subsequent cycle, thereby causing the driver of the internal combustion engine to feel uncomfortable. The purpose is to provide technology that can alleviate the problem.
[0010]
[Means for solving the problems and their functions and effects]
In order to solve at least a part of the problems described above, the first internal combustion engine of the present invention employs the following configuration. That is,
An internal combustion engine that outputs power by burning a mixture of air and fuel in a combustion chamber,
An air-fuel mixture discharging means for discharging the air-fuel mixture burned in the combustion chamber from the combustion chamber;
Misfire detection means for detecting the occurrence of misfire, which is a phenomenon in which combustion of the air-fuel mixture does not complete normally in the combustion chamber;
An emission suppressing means for suppressing the mixture from being discharged from the combustion chamber when the misfire occurs;
Leak amount measuring means for measuring the leak amount of the air-fuel mixture that leaks out from the combustion chamber while suppressing the emission;
A mixture replenishing means for supplementing the mixture according to the measured leakage amount;
It is a summary to provide.
[0011]
The first control method of the present invention corresponding to the internal combustion engine is as follows.
A control method for an internal combustion engine that outputs power by burning a mixture of air and fuel in a combustion chamber,
A first step of discharging the air-fuel mixture combusted in the combustion chamber from the combustion chamber;
A second step of detecting the occurrence of misfire, which is a phenomenon in which combustion of the air-fuel mixture is not normally completed in the combustion chamber;
A third step of suppressing discharge of the air-fuel mixture from the combustion chamber when the misfire occurs;
A fourth step of measuring an amount of leakage of the air-fuel mixture that leaks out from the combustion chamber while suppressing the emission;
A fifth step of supplementing the air-fuel mixture according to the measured leakage amount;
It is a summary to provide.
[0012]
In the first internal combustion engine of the present invention and the control method corresponding thereto, when the occurrence of misfire is detected, the mixture is suppressed from being discharged from the combustion chamber and burned in the next cycle. . When the exhaust is suppressed in this way, the air-fuel mixture is compressed in the subsequent exhaust stroke, and a part of the air-fuel mixture may leak from the combustion chamber. When the air-fuel mixture leaks, the amount of air-fuel mixture burned in the following cycle decreases, and it becomes difficult to generate sufficient torque. Therefore, when the discharge of the air-fuel mixture is suppressed, the amount of leakage from the combustion chamber is measured, and the air-fuel mixture is supplemented by the amount of leakage. In this way, since a desired torque can be generated in the next cycle of misfire, it is possible to reduce the uncomfortable feeling given to the driver of the internal combustion engine.
[0013]
In such an internal combustion engine, the amount of air-fuel mixture leakage from the combustion chamber can be detected by the following method. For example, the concentration of unburned hydrocarbon can be measured in the crankcase and detected from the increase in concentration. Or it can also measure based on the pressure in a combustion chamber. As will be described later, it is preferable to measure the leakage amount of the air-fuel mixture based on the pressure in the combustion chamber because the leakage amount can be easily and accurately measured.
[0014]
In addition, when the air-fuel mixture is replenished in accordance with the leakage amount, the intake valve may be opened at a timing after the middle of the intake stroke. At this time, the fuel is injected into either the intake passage or the combustion chamber.
[0015]
Immediately after the start of the intake stroke following the misfire, the mixture in the misfired cycle is compressed in the combustion chamber, but expands as the intake stroke proceeds, and the pressure in the combustion chamber decreases. Therefore, it is preferable to open the intake valve after the middle of the intake stroke because it is possible to suppress the backflow of the compressed air-fuel mixture into the intake passage.
[0016]
In an internal combustion engine that replenishes the air-fuel mixture leaked in this way, the air-fuel ratio in the combustion chamber may be controlled by adjusting at least one of the air intake amount and the fuel injection amount.
[0017]
In this way, even if the operating condition of the internal combustion engine changes between the misfire cycle and the next cycle, and the air-fuel ratio setting changes, the air-fuel mixture is burned at an appropriate air-fuel ratio, A desired torque can be generated.
[0018]
The second internal combustion engine of the present invention employs the following configuration in order to solve at least a part of the problems described above. That is,
An internal combustion engine that outputs power by burning a mixture of air and fuel in a combustion chamber,
An intake passage for sucking air into the combustion chamber;
An exhaust passage for exhausting exhaust gas generated by the combustion of the air-fuel mixture in the combustion chamber;
A recirculation passage for recirculating at least part of the exhaust gas discharged from the exhaust passage into the intake passage;
A recirculation amount control means for controlling a recirculation amount of the exhaust gas;
A purification catalyst for purifying exhaust gas discharged from the exhaust passage into the atmosphere;
Misfire detection means for detecting the occurrence of misfire, which is a phenomenon in which combustion of the air-fuel mixture does not complete normally in the combustion chamber;
A catalyst inflow gas amount calculating means for calculating an exhaust gas amount flowing into the purification catalyst when the misfire occurs;
With
The gist of the recirculation amount control means is a means for controlling the recirculation amount of the exhaust gas in accordance with the amount of exhaust gas flowing into the purification catalyst.
[0019]
The second control method of the present invention corresponding to the internal combustion engine is as follows.
A mixture of fuel and air taken from the intake passage is combusted in the combustion chamber, and at least part of the generated exhaust gas is returned to the intake passage, and power is output while the remaining exhaust gas is discharged from the exhaust passage. A method for controlling an internal combustion engine, comprising:
A first step of detecting the occurrence of misfire, which is a phenomenon in which combustion of the air-fuel mixture is not normally completed in the combustion chamber;
A second step of calculating the amount of exhaust gas flowing into the purification catalyst provided in the exhaust passage when the misfire occurs;
A third step of controlling the exhaust gas recirculation amount according to the calculated exhaust gas inflow amount;
It is a summary to provide.
[0020]
In the second internal combustion engine of the present invention and the second control method corresponding thereto, a part of the exhaust gas is recirculated into the intake passage, and the remaining exhaust gas is purified by the purification catalyst and then released to the atmosphere. To do. In this way, if not all, the unburned air-fuel mixture can be recirculated into the combustion chamber and burned, so that adverse effects such as deterioration of fuel consumption efficiency can be avoided. In addition, since a new air-fuel mixture is also supplied into the combustion chamber, good combustion can be realized even in the next cycle of misfire. Here, when a misfire occurs, the amount of exhaust gas flowing into the purification catalyst is calculated, and the recirculation amount to the intake passage is controlled according to the amount of exhaust gas flowing in.
[0021]
When a misfire occurs, the unburned mixture is discharged, increasing the load on the purification catalyst and exhausting part of the exhaust gas to the atmosphere without being purified, or the catalyst deteriorating early. May cause such problems. Therefore, when misfire occurs, the amount of inflow into the purification catalyst is calculated, and the amount of recirculation into the intake passage is controlled according to the obtained amount of inflow. For example, when the inflow amount to the purification catalyst is too large, the inflow amount to the catalyst can be reduced by increasing the recirculation amount. Conversely, if there is a margin in the amount of inflow to the catalyst, it is possible to reduce the amount of recirculation to the intake passage. In this way, when misfire occurs, if the amount of exhaust gas flowing into the purification catalyst is controlled by controlling the amount of recirculation into the intake passage, a part of the exhaust gas cannot be completely purified and released to the atmosphere. Alternatively, it is possible to avoid early deterioration of the purification catalyst, which is preferable.
[0022]
Of course, in such an internal combustion engine, an allowable value is set for the amount of exhaust gas flowing into the purification catalyst, and when this allowable value is exceeded, the amount of recirculation to the intake passage is increased to reduce the amount of inflow to the catalyst. It is good also as suppressing within an allowable value.
[0023]
In this way, the amount of reflux only needs to be controlled when the allowable value is exceeded, so that the control content can be simplified, which is preferable.
[0024]
In such an internal combustion engine, the amount of exhaust gas flowing into the purification catalyst may be calculated based on the operating conditions of the internal combustion engine and the recirculation amount of the exhaust gas.
[0025]
If the operating conditions of the internal combustion engine are determined, the total amount of exhaust gas discharged from the combustion chamber is determined automatically. Therefore, if the recirculation amount of the exhaust gas to the intake passage is known, the amount of exhaust gas flowing into the purification catalyst can be obtained. This is preferable because the amount of exhaust gas flowing into the catalyst can be easily obtained.
[0026]
Alternatively, the amount of exhaust gas flowing into the purification catalyst may be calculated based on the operating conditions of the internal combustion engine and the amount of air taken into the combustion chamber.
[0027]
When a part of the exhaust gas is recirculated into the intake passage, newly sucked air and the recirculated exhaust gas are sucked into the combustion chamber. When the operating conditions of the internal combustion engine are determined, the amount of gas sucked into the combustion chamber, that is, the total amount of newly sucked air and recirculated exhaust gas is almost determined, so if the amount of sucked air is measured, Thus, the recirculation amount of the exhaust gas can be obtained, and by extension, the exhaust gas amount flowing into the purification catalyst can be obtained. This is also preferable because the amount of exhaust gas flowing into the purification catalyst can be easily obtained.
[0028]
Alternatively, the amount of exhaust gas flowing into the purification catalyst can be obtained based on the pressure difference between the pressure in the combustion chamber during the exhaust stroke and the pressure in the combustion chamber during the intake stroke as follows. That is, since the exhaust gas recirculated from the exhaust passage is recirculated to the intake passage due to the pressure difference between the exhaust passage and the intake passage, the recirculation amount can be estimated from the pressure difference. As described above, since the total amount of exhaust gas discharged from the combustion chamber is substantially determined by the operating conditions of the internal combustion engine, if the amount of exhaust gas recirculated to the intake passage can be obtained based on the pressure difference, the purification catalyst The amount of exhaust gas flowing into can also be obtained. Such a method is also preferable because the amount of flow into the catalyst can be easily obtained.
[0029]
In the internal combustion engine described above, it is desirable to consider at least the rotational speed of the internal combustion engine as an operating condition.
[0030]
The amount of exhaust gas per unit time tends to increase with the rotational speed of the internal combustion engine. Accordingly, it is preferable that the calculation amount of the exhaust gas can be appropriately obtained by considering at least the rotational speed as the operating condition of the internal combustion engine.
[0031]
The third internal combustion engine of the present invention employs the following configuration in order to solve at least a part of the problems described above. That is,
An internal combustion engine that outputs power by burning an air-fuel mixture in which air and fuel are mixed at a predetermined air-fuel ratio in a combustion chamber,
An intake passage for sucking air into the combustion chamber;
A fuel injection valve that injects fuel into either the combustion chamber or the intake passage;
An exhaust passage for exhausting exhaust gas generated by the combustion of the air-fuel mixture in the combustion chamber;
A recirculation passage for recirculating at least part of the exhaust gas discharged from the exhaust passage into the intake passage;
A recirculation amount control means for controlling a recirculation amount of the exhaust gas;
Misfire detection means for detecting the occurrence of misfire, which is a phenomenon in which combustion of the air-fuel mixture does not complete normally in the combustion chamber;
Air-fuel ratio fluctuation amount calculating means for calculating the fluctuation amount of the air-fuel ratio caused by recirculating the exhaust gas when the misfire occurs based on the operating conditions of the internal combustion engine and the recirculation amount of the exhaust gas;
With
The summary of the recirculation amount control means is a means for controlling the recirculation amount of the exhaust gas in accordance with the calculated air-fuel ratio fluctuation amount.
[0032]
The third control method of the present invention corresponding to the internal combustion engine is as follows.
A combustion chamber for burning an air-fuel mixture in which fuel and air are mixed at a predetermined air-fuel ratio; an intake passage for sucking air into the combustion chamber; an exhaust passage for discharging exhaust gas generated by the combustion; A control method for an internal combustion engine comprising a recirculation passage for recirculating at least part of exhaust gas to the intake passage,
A first step of injecting fuel into either the intake passage or the combustion chamber to form the air-fuel mixture;
A second step of detecting the occurrence of misfire, which is a phenomenon in which combustion of the air-fuel mixture is not normally completed in the combustion chamber;
A third step of calculating, based on the operating conditions of the internal combustion engine and the recirculation amount of the exhaust gas, the variation amount of the air-fuel ratio caused by recirculating the exhaust gas when the misfire occurs;
A fourth step of controlling the recirculation amount of the exhaust gas according to the calculated variation amount of the air-fuel ratio;
It is a summary to provide.
[0033]
In the third internal combustion engine and the third control method corresponding to the third internal combustion engine of the present invention, at least a part of the exhaust gas is recirculated from the exhaust passage to the intake passage and is supplied into the combustion chamber together with the air-fuel mixture. In this way, if not all, the unburned air-fuel mixture can be recirculated into the combustion chamber and burned, so that adverse effects such as deterioration of fuel consumption efficiency can be avoided. In addition, since a new air-fuel mixture is also supplied into the combustion chamber, good combustion can be realized even in the next cycle of misfire. Here, when a misfire occurs, not the exhaust gas but the unburned air-fuel mixture is returned to the intake passage, so that the air-fuel ratio in the combustion chamber may change. In such a case, even if misfire does not occur continuously, the desired torque cannot be obtained, and there is a risk of giving the driver of the internal combustion engine a greater sense of discomfort.
[0034]
In view of these points, when a misfire occurs, the variation amount of the air-fuel ratio in the combustion chamber is calculated based on the operating conditions of the internal combustion engine and the recirculation amount of the exhaust gas, and according to the calculated variation amount. The amount of exhaust gas recirculated to the intake passage is controlled. For example, when the fluctuation amount of the air-fuel ratio becomes too large, the fluctuation amount is suppressed by reducing the recirculation amount. On the contrary, when there is a margin in the fluctuation amount, the exhaust gas recirculation amount can be increased. Thus, when misfire occurs, if the recirculation amount of the exhaust gas is controlled in accordance with the amount of fluctuation of the air-fuel ratio in the combustion chamber, a desired torque can be generated in the cycle following the misfire. It is possible to reduce the uncomfortable feeling given to the driver.
[0035]
In such an internal combustion engine, an allowable value is set for the fluctuation amount of the air-fuel ratio, and if the fluctuation amount calculated at the time of misfire exceeds the allowable value, the recirculation amount of the exhaust gas is increased to keep the fluctuation amount within the allowable value. It is also possible to suppress it.
[0036]
This is preferable because it is only necessary to control the recirculation amount of the exhaust gas only when the allowable value is exceeded, so that the control content can be simplified.
[0037]
Further, when calculating the fluctuation amount of the air-fuel ratio, at least the rotational speed of the internal combustion engine may be taken into consideration as the operating condition of the internal combustion engine.
[0038]
The fluctuation of the air-fuel ratio generated at the time of misfire is affected by the delay of the exhaust gas. That is, the exhaust gas recirculated from the exhaust passage flows into the combustion chamber through the recirculation passage and the air passage, so that a delay occurs with respect to newly sucked air and fuel, and this delay causes the air-fuel ratio fluctuation. It is one of the factors. Since the influence of this delay increases as the rotational speed of the internal combustion engine increases, the amount of fluctuation that occurs during a misfire is affected by the rotational speed of the internal combustion engine. Therefore, when calculating the fluctuation amount of the air-fuel ratio, if at least the rotational speed is taken into consideration, the fluctuation amount at the time of misfiring can be accurately estimated, and further, sufficient torque can be generated. preferable.
[0039]
In such an internal combustion engine, the air-fuel ratio in the combustion chamber may be controlled by adjusting at least one of the amount of air or the amount of fuel drawn into the combustion chamber according to the recirculation amount of the exhaust gas.
[0040]
If the air-fuel ratio is positively controlled in this way, it is preferable that a desired torque can be reliably generated in the cycle following the misfire, and further, the uncomfortable feeling of the driver of the internal combustion engine can be reduced.
[0041]
DETAILED DESCRIPTION OF THE INVENTION
In order to more clearly describe the operation and effect of the present invention, examples of the present invention will be described in the following order.
A. First embodiment:
A-1. Device configuration:
A-2. Overview of engine operation:
A-3. Engine operation control of the first embodiment:
A-4. Misfire detection method:
B. Second embodiment:
[0042]
A. Device configuration:
A-1. Device configuration:
FIG. 1 is an explanatory diagram conceptually showing the structure of the engine 10 of this embodiment. The engine 10 burns the air-fuel mixture in the combustion chamber while repeating the four steps of intake, compression, expansion, and exhaust, converts the pressure generated by the combustion into mechanical work, and outputs power. In FIG. 1, in order to show the structure of the engine 10, a cross section is shown at the approximate center of the combustion chamber. As shown in the figure, the main body of the engine 10 is configured by assembling a cylinder head 130 on top of a cylinder block 140. A cylindrical cylinder 142 is provided in the cylinder block 140, and a piston 144 is slidably provided in the cylinder 142. A space surrounded by the cylinder 142, the piston 144, and the lower surface of the cylinder head 130 is a combustion chamber.
[0043]
The piston 144 is connected to the crankshaft 148 via a connecting rod 146, and the piston 144 slides up and down in the cylinder 142 as the crankshaft 148 rotates.
[0044]
The cylinder head 130 includes an intake passage 12 for taking intake air into the combustion chamber, a fuel injection valve 14 for injecting fuel into the combustion chamber, an ignition plug 136 for igniting an air-fuel mixture in the combustion chamber, and a combustion chamber. An exhaust passage 16 for discharging the combustion gas generated in is connected. The cylinder head 130 is provided with an intake valve 132 and an exhaust valve 134, and the intake valve 132 and the exhaust valve 134 are driven by electric actuators 152 and 154, respectively. These electric actuators 152 and 154 have a structure in which a plurality of disk-shaped electrostrictive elements are stacked, and by applying a voltage, the intake valve 132 and the exhaust valve 134 can be opened and closed at an arbitrary timing. ing. In the following embodiment, the fuel injection valve 14 is described as injecting fuel into the combustion chamber. Of course, the fuel injection valve 14 is provided in the intake passage 12 to inject fuel into the intake passage. Is also possible.
[0045]
An air cleaner 20 is provided on the upstream side of the intake passage 12, and the air cleaner 20 incorporates a filter for removing foreign substances in the air. The air sucked into the engine 10 is sucked into the combustion chamber after foreign matters are removed by a filter when passing through the air cleaner 20. The intake passage 12 is provided with an air flow sensor 18 and a throttle valve 22. If the electric actuator 24 is driven to control the throttle valve 22 to an appropriate opening, the amount of air taken into the combustion chamber can be controlled. The air flow sensor 18 detects the flow rate of air flowing through the intake passage 12.
[0046]
Further, the engine 10 is provided with an EGR passage 160 that connects the exhaust passage 16 and the intake passage 12. A part of the exhaust gas discharged from the exhaust valve 134 and passing through the exhaust passage 16 flows into the intake passage 12 via the EGR passage 160 and is supplied into the combustion chamber together with the air in the intake passage. Thus, the recirculation of the exhaust gas into the combustion chamber is called EGR, and the exhaust gas to be recirculated is called EGR gas. An on-off valve called an EGR valve 162 is provided in the middle of the EGR passage 160, and the flow rate of EGR gas can be controlled by adjusting the opening degree of the EGR valve 162.
[0047]
A purification catalyst 26 is provided downstream of the exhaust passage 16 and can purify air pollutants contained in the exhaust gas.
[0048]
The operation of the engine 10 is controlled by an engine control unit (hereinafter, ECU) 30. The ECU 30 is a well-known microcomputer configured by connecting a CPU, a RAM, a ROM, an A / D conversion element, a D / A conversion element, and the like with a bus. The ECU 30 detects the engine rotational speed Ne and the accelerator opening degree θac, and controls the throttle valve 22 and the EGR valve 162 to appropriate opening degrees based on these. The engine speed Ne can be detected by a crank angle sensor 32 provided at the tip of the crankshaft 148. The accelerator opening degree θac can be detected by an accelerator opening degree sensor 34 incorporated in the accelerator pedal. Further, the ECU 30 drives the electric actuators 152 and 154 or the fuel injection valve 14 and the spark plug 136 based on the outputs of the air flow sensor 18 and the crank angle sensor 32. Thus, while synchronizing with the movement of the piston 144, the intake valve 132 and the exhaust valve 134 are opened and closed, fuel is injected to form an air-fuel mixture in the combustion chamber, and the air-fuel mixture is ignited to operate the engine 10. be able to.
[0049]
Further, the ECU 30 can detect the pressure in the combustion chamber by the pressure sensor 23 provided in the cylinder block 140. Note that the pressure sensor 23 can be provided not on the cylinder block 140 but on the cylinder head 130.
[0050]
A-2. Overview of engine operation:
As described above, the engine 10 outputs power by repeatedly performing the four strokes of the intake stroke, the compression stroke, the expansion stroke, and the exhaust stroke. FIG. 2 is an explanatory diagram conceptually showing how the engine 10 outputs power while repeating these four strokes. In FIG. 2, the intake stroke, the compression stroke, the expansion stroke, and the exhaust stroke are conceptually shown in order from the left. The position of the piston is shown at the top in the figure. “TDC” displayed in the figure indicates that the piston is at the highest position (top dead center). “BDC” indicates that the piston is at the lowest position (bottom dead center). 2, the opening / closing timing of the intake valve 132 and the exhaust valve 134 and the driving timing of the fuel injection valve 14 and the spark plug 136 are displayed. Further, at the bottom of the drawing, the operation of the engine 10 in each stroke is conceptually represented.
[0051]
First, the intake stroke shown at the left end of FIG. 2 will be described. As shown in the middle of FIG. 2, in the intake stroke, the piston 144 is lowered from the TDC with the intake valve being opened. In this way, air can be sucked into the combustion chamber from the intake valve 132. When the piston 144 reaches the BDC and stops descending, the air cannot be sucked any further, so the intake valve 132 is closed. Thus, the intake stroke is a stroke in which air is sucked into the combustion chamber by opening the intake valve 132 and lowering the piston 144. In the engine 10, as described above, the fuel injection valve 14 is provided in the combustion chamber, and fuel is directly injected into the combustion chamber during the intake stroke. The period during which the fuel injection valve 14 injects fuel is displayed at the position of the middle fuel injection valve in FIG. 2 by hatching a rectangle.
[0052]
2 conceptually shows the operation of the engine 10 during the intake stroke. As shown in the drawing, in the intake stroke, the intake valve 132 is opened and the piston 144 is lowered to suck air into the combustion chamber. The black arrows in the figure conceptually show how air is sucked into the combustion chamber through the intake valve 132. The fuel is injected from the fuel injection valve 14 in accordance with such inflow of air. In the figure, the injected fuel spray is shown with hatching. The injected fuel spray is agitated in the combustion chamber by the flow of air that has flowed in, and is dispersed with a substantially uniform density in the combustion chamber to form an air-fuel mixture.
[0053]
When the piston 144 reaches BDC, the intake valve 132 is closed and the compression stroke is started. In the compression stroke, the air-fuel mixture formed in the combustion chamber during the intake stroke is compressed by raising the piston 144. As shown in the middle part of FIG. 2, both the intake valve 132 and the exhaust valve 134 are closed during the compression stroke. Further, the second diagram from the left in the lower part of FIG. 2 conceptually shows the operation of the engine 10 during the compression stroke. The rough hatching attached to the combustion chamber in the lower diagram indicates that an air-fuel mixture is formed. The compression stroke continues until the piston is fully raised from the BDC position to the TDC position.
[0054]
In the vicinity of the piston in the latter half of the compression stroke almost reaching the top dead center, a spark is blown from the spark plug 136 and the mixture is ignited. An asterisk indicated at the position of the ignition plug in the middle of FIG. 2 indicates that the ignition is performed immediately before the end of the compression stroke. If a spark is blown from the spark plug 136 at such timing, the flame spreads in the combustion chamber at once, and the air-fuel mixture in the combustion chamber can be burned quickly. The diagram in the lower center of FIG. 2 conceptually shows how the air-fuel mixture in the combustion chamber burns quickly near the top dead center in the second half of the compression stroke.
[0055]
When the air-fuel mixture burns, the pressure in the combustion chamber rises significantly and tries to push down the piston 144. In the expansion stroke following ignition, the pressure received by the piston while lowering the piston 144 is converted into mechanical work and output to the outside as power. The second diagram from the right in the lower part of FIG. 2 conceptually shows that the piston 144 is pushed down by the pressure in the combustion chamber and power is generated outside. The fine hatching attached to the combustion chamber in the figure conceptually indicates that the combustion chamber is filled with combustion gas generated by combustion of the air-fuel mixture. The expansion stroke continues until the piston 144 reaches BDC.
[0056]
When the piston 144 reaches bottom dead center, the piston 144 cannot be lowered further to extract power. Therefore, as shown in the middle part of FIG. 2, the exhaust valve 134 is opened to raise the piston 144. In the exhaust stroke following the expansion stroke, the exhaust valve 134 is thus opened and the piston 144 is raised. If it carries out like this, combustion gas can be discharged from a combustion chamber like pushing out with a piston. The diagram on the right side of the lower part of FIG. 2 conceptually shows how the combustion gas in the combustion chamber is discharged from the exhaust valve 134 during the exhaust stroke. When the piston 144 reaches TDC, the exhaust valve 134 is closed to complete the exhaust stroke.
[0057]
As described above, when the four strokes of the intake stroke, the compression stroke, the expansion stroke, and the exhaust stroke are completed, the operation returns to the intake stroke again and the same operation is repeated. While repeating such operations, the engine 10 outputs power by igniting at a timing near the TDC in the latter half of the compression stroke and burning the air-fuel mixture.
[0058]
However, since the engine 10 is operated under various conditions, the air-fuel mixture in the combustion chamber does not burn or burns very little even though a spark is blown near the TDC in the latter half of the compression stroke. Can occur. As described above, this phenomenon is called misfire. When misfire occurs, the air-fuel mixture in the combustion chamber is discharged without being converted into motive power, causing various adverse effects such as a reduction in fuel consumption efficiency and deterioration of the purification catalyst 26. This will be described below with reference to FIG.
[0059]
FIG. 3 is an explanatory diagram conceptually showing how the air-fuel mixture is discharged from the combustion chamber without burning when misfire occurs. From left to right, the intake stroke and compression of the engine 10 are shown. Four strokes are shown: a stroke, an expansion stroke, and an exhaust stroke. As described above, after the piston 144 is raised in the compression stroke to compress the air-fuel mixture in the combustion chamber and then a spark is blown from the spark plug 136, normally, the air-fuel mixture immediately completes combustion and the expansion stroke continues. Then, it tries to push down the piston 144.
[0060]
However, as conceptually shown in the center diagram in the lower part of FIG. 3, there is a case where the air-fuel mixture cannot be ignited even if a spark is blown by the spark plug 136. Or, although the ignition is performed, the flame may not burn quickly and spread, and the flame may disappear midway. That is, when the flame does not spread quickly after ignition, the lowering speed of the piston 144 increases at an accelerated rate, so that the temperature of the mixture in the combustion chamber rapidly decreases due to the action of adiabatic expansion and the flame disappears. Sometimes. Such a phenomenon called misfire occurs when the fuel concentration around the spark plug 136 happens to be low at the time of ignition, or when a spark is blown off by the spark plug 136, the flow velocity in the vicinity increases and the spark is blown away. This can occur due to various factors such as Since the engine is used under various conditions, it is possible that these conditions are satisfied during operation and a misfire occurs.
[0061]
When a misfire occurs, in the subsequent expansion stroke, the air-fuel mixture in the combustion chamber does not burn, and as the piston 144 descends and the combustion chamber volume increases, the volume of the air-fuel mixture increases and the pressure decreases. . When the air-fuel mixture has not burned at all, this stroke is a stroke in which the piston 144 is raised to follow the compression stroke in which the air-fuel mixture is compressed in the opposite direction. The second diagram from the lower right of FIG. 3 conceptually shows how the air-fuel mixture in the combustion chamber expands following the change opposite to the compression stroke as the piston 144 descends. The rough hatching attached to the portion of the combustion chamber conceptually represents that the air-fuel mixture is expanded as it is without being converted into combustion gas.
[0062]
When the piston 144 reaches BDC, the expansion stroke is finished and the exhaust stroke is started. As described above, in the exhaust stroke, the exhaust valve 134 is opened to raise the piston 144. Normally, the air-fuel mixture in the combustion chamber is converted to combustion gas, and in the exhaust stroke, the combustion gas is discharged. However, if a misfire occurs, the air-fuel mixture in the combustion chamber is not converted to combustion gas. Therefore, the air-fuel mixture is discharged in the exhaust stroke. The lower right diagram in FIG. 3 conceptually shows that the air-fuel mixture is discharged from the exhaust valve 134 as the piston 144 rises.
[0063]
As described above, when misfire occurs, the air-fuel mixture in the combustion chamber is discharged without burning. That is, since the air-fuel mixture is discarded without generating power, the fuel consumption efficiency is lowered accordingly. Further, the air-fuel mixture discharged in this way reacts at once on the purification catalyst 26 provided in the exhaust passage 16 and deteriorates the purification catalyst 26. In order to avoid such a situation, the engine 10 of the present embodiment performs the following control.
[0064]
A-3. Engine operation control of the first embodiment:
In the following, the engine operation control of the first embodiment will be described in detail, but for the sake of convenience of understanding, the operation of the engine 10 when a misfire occurs will be roughly described first. FIG. 4 is an explanatory diagram showing an outline of the operation of the engine 10 when a misfire occurs. In FIG. 4, the above-described four strokes of the engine are displayed for two cycles from left to right. It is assumed that misfire occurred in the first cycle. 2 and 3, the operation of the engine 10 is conceptually displayed at the bottom of FIG. 4, but in order to avoid complicated illustration, FIG. Only one part of the strokes for two cycles is displayed. That is, the leftmost diagram at the bottom indicates the intake stroke of the first cycle, and the second to fourth diagrams from the left indicate the expansion stroke of the first cycle to the intake stroke of the second cycle. . The remaining three figures show the ignition timing, expansion stroke, and exhaust stroke in the second cycle, respectively.
[0065]
It is assumed that a misfire has occurred despite the fact that a spark has been blown from the spark plug 136 in the latter half of the compression stroke of the first cycle. Then, in the subsequent expansion stroke, as described with reference to FIG. 3, the air-fuel mixture in the combustion chamber does not burn, and the volume of the air-fuel mixture increases as the piston 144 descends and the combustion chamber volume increases. The pressure will drop. The second diagram from the left in the lowermost stage of FIG. 4 conceptually shows how the volume of the air-fuel mixture in the combustion chamber increases as the piston 144 descends.
[0066]
Thus, when misfire occurs, the combustion chamber after completion of the expansion stroke is filled with the air-fuel mixture. Therefore, in the first embodiment, the driving of the exhaust valve 134 in the subsequent exhaust stroke is stopped. In FIG. 4, in the portion indicating the drive timing of the exhaust valve during the exhaust stroke of the first cycle, a rectangle with a thick broken line instead of hatching is normally the timing at which the exhaust valve is driven. This shows that the drive is stopped due to a misfire. As a result of stopping the driving of the exhaust valve 134 in this way, in the exhaust stroke of the first cycle, the piston 144 rises while the intake valve 132 and the exhaust valve 134 are closed. Eventually, in the exhaust stroke following the misfire, the air-fuel mixture in the combustion chamber is compressed by the piston 144 just as in the compression stroke. The third diagram from the left in the lowermost stage of FIG. 4 conceptually shows how the air-fuel mixture is compressed in the combustion chamber as the piston 144 rises.
[0067]
In the exhaust stroke following the misfire, the piston 144 is raised while the exhaust valve 134 is closed, so that the combustion chamber is filled with the air-fuel mixture. Therefore, the driving of the intake valve 132 and the fuel injection valve 14 is stopped in the first half of the subsequent intake stroke, and the intake valve 132 and the fuel injection valve 14 are driven only for a short period after the second half of the intake stroke. In FIG. 4, in the first half of the intake stroke of the second cycle, the portion indicating the drive timing of the intake valve and the fuel injection valve is indicated by a thick broken line instead of hatching. Although it is the timing at which the injection valve is driven, it represents that the drive is stopped due to a misfire. In addition, a hatched rectangle in the portion indicating the drive timing of the intake valve and the fuel injection valve in the latter half of the intake stroke represents that the intake valve and the fuel injection valve are driven for a short period of time.
[0068]
Thus, the reason why the intake valve and the fuel injection valve are driven for a short period in the latter half of the intake stroke is as follows. As described above, when misfire occurs, the piston 144 is raised without opening the exhaust valve 134 in the subsequent exhaust stroke, so the unburned mixture is compressed to a high pressure in the combustion chamber. For this reason, the compressed air-fuel mixture leaks little by little from the sliding surface between the piston 144 and the cylinder 142 over the exhaust stroke and the intake stroke after the misfire. If the air-fuel mixture leaks, even if the air-fuel mixture is ignited in the next cycle to burn the air-fuel mixture, it is difficult to generate torque as usual. Therefore, in order to replenish the leaked mixture, the intake valve and the fuel injection valve are driven for a short period in the second half of the intake stroke. Here, if the intake valve is driven in the first half of the intake stroke, the air-fuel mixture compressed in the combustion chamber flows backward from the intake valve 132 into the intake passage 12, so that the intake valve 132 is in the second half of the intake stroke. To drive. In the latter half of the intake stroke, since the piston 144 is lowered and the pressure in the combustion chamber is reduced, it is possible to prevent the air-fuel mixture from flowing backward from the combustion chamber even if the intake valve 132 is opened. Further, the leak amount of the air-fuel mixture can be detected by a method described later.
[0069]
In the example shown in FIG. 4, the drive timing of the fuel injection valve 14 is set while the intake valve 132 is open. This is intended to promote mixing in the combustion chamber by causing the spray of injected fuel to flow into the combustion chamber on the flow of air flowing from the intake valve 132. However, it is not always necessary to set the drive timing of the fuel injection valve 14 while the intake valve 132 is opened. For example, fuel may be injected before the valve is opened. If the fuel is injected at an early timing, there is an advantage that it is easy to secure a sufficient time for the fuel to vaporize.
[0070]
In this way, when the leaked air-fuel mixture is replenished, when the piston 144 reaches the BDC (that is, at the end of the intake stroke of the second cycle), it returns to a state almost the same as at the end of the intake stroke of the first cycle.
[0071]
After the end of the intake stroke of the cycle after the misfire (second cycle in FIG. 4), the state is almost the same as that at the end of the intake stroke of the cycle thus misfired (first cycle in FIG. 4). If the air-fuel mixture in the combustion chamber is compressed in the compression stroke and a spark is blown from the spark plug 136 at an appropriate timing later in the compression stroke, the air-fuel mixture in the combustion chamber can be burned quickly. Even if a misfire occurs in the first cycle ignition, the air-fuel mixture in the combustion chamber is sufficiently stirred between the expansion stroke in the first cycle and the intake stroke in the second cycle. Since the flow of the air-fuel mixture is also attenuated, it is possible to reliably ignite the air-fuel mixture in the combustion chamber by blowing a spark from the spark plug 136 in the second cycle. The third diagram from the right end of the lowermost stage in FIG. 4 conceptually represents the state in which the air-fuel mixture in the combustion chamber is rapidly burned by ignition in the second cycle.
[0072]
When ignition is successful, the air-fuel mixture in the combustion chamber is quickly converted into high-pressure combustion gas, and in the subsequent expansion stroke of the second cycle, the piston 144 is pushed down to generate power. When the piston 144 reaches the BDC, the exhaust valve 134 is opened, and then the piston 144 is raised to discharge the combustion gas in the combustion chamber. The diagram at the right end of the lowermost stage in FIG. 4 conceptually shows how the combustion gas in the combustion chamber is discharged from the exhaust valve 134 while raising the piston 144. Thus, when the piston 144 reaches TDC while exhausting the combustion gas from the exhaust valve 134, the intake stroke is started, and thereafter, the same operation as the normal operation is repeated.
[0073]
In this way, even if misfire occurs, the air-fuel mixture is not discharged as it is, but it can be discharged after being burned in the following cycle and the power is taken out, so that the fuel consumption efficiency deteriorates or the purification catalyst 26 deteriorates. Can be avoided. Also, even if the air-fuel mixture compressed in the combustion chamber leaks during the exhaust stroke after misfire, the same torque as in the normal operation state is output by replenishing the leaked air-fuel mixture in the subsequent intake stroke It is possible. Hereinafter, control for performing such an operation will be described.
[0074]
FIG. 5 is a flowchart showing a flow of an engine control routine performed by the ECU 30. The ECU 30 controls the operation of the engine 10 by performing control according to the routine shown in FIG. Hereinafter, it demonstrates according to a flowchart.
[0075]
When the engine control routine is started, the ECU 30 first detects engine operating conditions (step S100). As operating conditions, the engine speed Ne and the accelerator opening θac are detected. As described above with reference to FIG. 1, the engine rotational speed Ne is detected based on the output of the crank angle sensor 32 provided at the tip of the crankshaft 148, and the accelerator opening θac is the accelerator opening built in the accelerator pedal. It can be detected by the sensor 34.
[0076]
Next, it is determined whether or not a misfire has been detected (step S102). A method for detecting misfire will be described later. When such a determination is made for the first time, such as immediately after the operation of the engine 10 is started, it is determined that no misfire has been detected (step S102: no), and EGR control is started (step S104). In the EGR control, a process of setting the opening of the EGR valve 162 to an appropriate opening according to the operating condition of the engine is performed. The ROM built in the ECU 30 stores in advance the opening degree of the EGR valve appropriate for the operating conditions in the form of a map using the engine speed Ne and the accelerator opening degree θac as parameters. In step S104, referring to the map stored in the ROM, the opening degree with respect to the operating condition detected in step S100 is read, and the opening degree of the EGR valve 162 is set.
[0077]
Following the EGR control, the valve control is started (step S106). In the valve control, the opening and closing timings of the intake valve 132 and the exhaust valve 134 are set, and the electric actuators 152 and 154 are controlled at the set timing. By doing so, as shown in FIG. 2, the intake valve 132 and the exhaust valve 134 can be opened and closed at an appropriate timing synchronized with the movement of the piston.
[0078]
Following the valve control, the ECU 30 performs fuel injection control (step S108). In this control, the amount of fuel injected into the combustion chamber and the injection timing are calculated, and the drive timing of the fuel injection valve 14 is set. The fuel injection amount is calculated so as to have an air-fuel ratio appropriate for the amount of air taken into the combustion chamber. The amount of air taken into the combustion chamber can be detected by the air flow sensor 18. The air-fuel ratio is preset in the form of a map with respect to the engine operating conditions. The drive timing of the fuel injection valve 14 is set based on the fuel amount calculated from the air amount and the air-fuel ratio. When the fuel injection amount is large, the drive time is long, and when the fuel injection amount is small, the drive time is short. In this embodiment, the drive start timing of the fuel injection valve 14 is fixed at a predetermined timing after the intake valve 132 is opened, and the drive end timing is automatically determined when the drive time is determined. Of course, the drive start timing of the fuel injection valve 14 may be changed in accordance with the operating conditions of the engine. In step S108 of FIG. 5, the drive timing of the fuel injection valve 14 is thus set. By doing so, fuel can be injected from the fuel injection valve 14 into the combustion chamber at an appropriate timing in synchronization with the movement of the piston 144.
[0079]
Next, the ECU 30 performs ignition control, and sparks are discharged from the spark plug 136 at an appropriate timing (step S114). In a normal case, the air-fuel mixture in the combustion chamber can be burned by blowing off the spark in this way.
[0080]
Following the ignition control, misfire is detected (step S116). In the engine 10 of this embodiment, detection is performed based on the output of the pressure sensor 23 provided in the cylinder block 140 as shown in FIG. A method for detecting misfire will be described later.
[0081]
If misfire is detected, it is confirmed whether or not an instruction to stop the engine is given (step S118). If the engine driver has instructed the engine 10 to be stopped, the engine control routine is terminated as it is. If the stop of the engine 10 is not instructed, the process returns to step S100 to continue the control.
[0082]
If it is determined in step S100 that the occurrence of misfire has been detected (step S100: yes), driving of the exhaust valve 134 is stopped so that the air-fuel mixture is not discharged from the exhaust valve 134 in the subsequent exhaust stroke. To do. When the piston 144 is raised while the drive of the exhaust valve 134 is stopped, the unburned air-fuel mixture is gradually compressed in the combustion chamber, and the air-fuel mixture slightly leaks from the sliding portion between the cylinder 142 and the piston 144. Therefore, in step S110 in FIG. 5, a process for detecting the amount of air-fuel mixture leakage is performed. A method for detecting the leakage amount will be described later.
[0083]
Next, the ECU 30 performs control to replenish the leaked mixture (step S112). That is, as described above with reference to FIG. 4, the intake valve 132 is driven for a predetermined period after the middle of the intake stroke to suck in an amount of air corresponding to the leaked amount, and the fuel injection valve 14 is driven. Then, an amount of fuel corresponding to the amount of air is injected into the combustion chamber. The fuel injection amount, that is, the drive period of the fuel injection valve 14 is calculated based on the leakage amount detected in step S110. Of course, the intake air amount may be directly measured by the air flow sensor 18 and the fuel injection amount may be calculated based on the measured value.
[0084]
In this manner, during the period from the exhaust stroke to the intake stroke following the occurrence of misfire, the amount of air-fuel mixture leakage is detected, and after the leaked air-fuel mixture is replenished, the piston 144 is raised again and ignited at a predetermined timing. Timing control is performed (step S114). As described above with reference to FIG. 4, even if a misfire occurs, the ignition can be reliably performed in the next cycle.
[0085]
Thus, if the engine 10 is controlled according to the engine control routine shown in FIG. 5, even if a misfire occurs, it can be reliably burned in the next cycle. As a result, the air-fuel mixture in the combustion chamber is not discharged without generating power, so that it is possible to avoid deterioration in fuel consumption efficiency. Further, since the air-fuel mixture is not discharged into the exhaust passage 16 without being combusted, the purification catalyst 26 is not deteriorated.
[0086]
In addition, in the engine control described above, the air-fuel mixture leaking from the combustion chamber is detected during the exhaust stroke following the misfire, and after the replenished air-fuel mixture is replenished in the intake stroke, it is compressed and ignited by the piston 144. In this way, in the next cycle that misfires, a torque equivalent to that in the normal cycle can be generated, so that it is possible to reduce the uncomfortable feeling given to the engine driver.
[0087]
A-4. Misfire detection method:
Here, how the engine 10 detects misfire will be briefly described. As described above, the engine 10 detects the occurrence of misfire based on the output of the pressure sensor 23 provided in the cylinder block 140. FIG. 6 conceptually shows how the pressure in the combustion chamber measured by the pressure sensor 23 changes according to the crank angle. As described above, in the compression stroke, as the crankshaft rotates, the piston 144 rises and compresses the air-fuel mixture in the combustion chamber. Accordingly, the pressure in the combustion chamber gradually increases. When the piston reaches approximately TDC, a spark is blown from the spark plug 136 and the air-fuel mixture in the combustion chamber is ignited. Normally, after ignition, the air-fuel mixture burns quickly, and as a result, the pressure in the combustion chamber rapidly increases as shown by the broken line in FIG. However, when misfire occurs, the pressure in the combustion chamber gradually decreases without increasing after TDC, as indicated by the solid line in FIG. From this, the pressure in the combustion chamber is detected at a predetermined timing before the spark is blown by the spark plug 136 and at a predetermined timing after the spark is blown, and the presence or absence of misfire is detected by comparing these. can do. That is, if the pressure in the combustion chamber does not increase to a predetermined value before or after the spark is blown, it can be determined that a misfire has occurred.
[0088]
Alternatively, it is possible to detect the occurrence of misfire by measuring the rotational speed of the engine. Such a principle will be briefly described with reference to FIG. Even when the engine is operated in a steady state, the rotational speed of the engine actually varies with the crank angle. Such fluctuations occur because the intake stroke, the compression stroke, the expansion stroke, and the exhaust stroke are repeatedly performed while the phases are slightly different in the respective combustion chambers. FIG. 7 is an explanatory diagram showing how the rotational speed of the engine fluctuates in a so-called four-cylinder engine having four combustion chambers. The uppermost stage of the figure shows how the engine speed fluctuates with respect to the crank angle, and immediately below that are the four strokes for the first cylinder and the pressure in the combustion chamber for each cylinder. It is shown. First, paying attention to the first cylinder, the piston is raised against the pressure in the combustion chamber in the compression stroke, so the engine speed gradually decreases. When the air-fuel mixture is compressed and ignited in the vicinity of the top dead center, the piston is pushed down due to the pressure in the combustion chamber, and the engine speed increases. As is clear from this, the engine rotational speed shows a fluctuation that gradually decreases during the compression stroke of the first cylinder and increases during the subsequent expansion stroke.
[0089]
In a four-cylinder engine having four combustion chambers, the expansion stroke of the first cylinder corresponds to the compression stroke of the third cylinder. From this, the engine rotation speed continues to increase for a while after entering the expansion stroke of the first cylinder, but when the pressure in the combustion chamber of the third cylinder increases, the engine rotation speed gradually decreases. When the air-fuel mixture in the third cylinder is ignited and the expansion stroke starts, the engine speed increases again. The expansion stroke of the third cylinder corresponds to the compression stroke of the fourth cylinder, the expansion stroke of the fourth cylinder corresponds to the compression stroke of the second cylinder, and the expansion stroke of the second cylinder corresponds to the compression stroke of the first cylinder. ing. In this way, the compression stroke and the expansion stroke are performed while the phases are slightly different for each cylinder, and therefore the engine rotational speed exhibits fluctuations as shown in FIG.
[0090]
Here, it is assumed that misfire occurs in a certain cylinder. For example, consider a case where the first cylinder misfires. Then, the piston is not pushed down with a large force in the subsequent expansion stroke. In addition, the expansion stroke of the first cylinder corresponds to the compression stroke of the third cylinder, and the third cylinder raises the piston against the pressure in the combustion chamber, so misfire occurs in the first cylinder. Then, the engine rotation speed is greatly reduced during the expansion stroke of the cylinder. As described above, when the misfire occurs, the engine rotation speed is drastically reduced. Therefore, if it is detected which cylinder expansion stroke corresponds to the timing at which the rapid decrease in the rotation speed occurs, the misfire has occurred. It is possible to detect the cylinder.
[0091]
In FIG. 7, it has been described that the occurrence of misfire is detected based on a decrease in the engine speed. However, when an increase in the engine speed when the air-fuel mixture burns is detected and this increase is not detected. It is also possible to determine that a misfire has occurred.
[0092]
Next, referring to FIG. 6 again, a method for detecting the leak amount of the air-fuel mixture that leaks in the next cycle of misfire will be described. As described above, when misfire occurs, the pressure in the combustion chamber gradually decreases so as to follow the compression stroke in reverse, and when the piston 144 is fully lowered, the pressure is almost the same as that immediately before the start of compression. In the exhaust stroke after the occurrence of misfire, the piston 144 is raised while the exhaust valve 134 is closed, so that the air-fuel mixture in the combustion chamber is compressed again and rises. At this time, leakage of the compressed air-fuel mixture occurs from the sliding surface between the cylinder 142 and the piston 144. For this reason, the pressure in the combustion chamber from the exhaust stroke after the misfire to the intake stroke is slightly lower than the pressure from the compression stroke to the expansion stroke at the time of misfire shown by the solid line in FIG. In FIG. 6, the pressure in the combustion chamber from the exhaust stroke after the misfire to the intake stroke is represented by a one-dot chain line. A hatched area in the figure corresponds to a pressure drop due to leakage of air-fuel mixture from the combustion chamber. Therefore, the amount of air-fuel mixture leakage can be detected by comparing the pressure in the combustion chamber at the time of misfire and the pressure in the combustion chamber after the misfire at a predetermined crank angle and measuring the amount of pressure decrease. . In step S110 of FIG. 5, the amount of air-fuel mixture leakage is detected in this way.
[0093]
B. Second embodiment:
In the first embodiment described above, when the misfire occurs, the exhaust valve 134 is stopped to keep the unburned mixture in the combustion chamber. However, the unburned air-fuel mixture may not be confined in the combustion chamber, but may be recirculated as EGR through the intake passage into the combustion chamber. Hereinafter, such a second embodiment will be described.
[0094]
FIG. 8 is a flowchart showing a flow of an engine control routine of the second embodiment performed by the ECU 30. Hereinafter, it demonstrates according to a flowchart.
[0095]
When starting the engine control routine of the second embodiment, the ECU 30 first detects the engine operating conditions (step S200). As the operating conditions, the engine speed Ne and the accelerator opening θac are detected as in the first embodiment.
[0096]
Next, it is determined whether or not a misfire has been detected (step S202). When determining for the first time, such as immediately after starting the operation of the engine 10, it is determined that no misfire has been detected (step S202: no), EGR control (step S208) described later, fuel injection control (step S210), After performing ignition control (step S212) and misfire detection (step S214), the process returns to step S200 again to perform a series of processes unless the engine is stopped.
[0097]
If the occurrence of misfire is detected in step S202 (step S202: yes), EGR misfire correction processing is performed (step S204). This is the following process. When misfire occurs, unburned air-fuel mixture is discharged instead of combustion gas. Part of the exhausted and unburned air-fuel mixture is recirculated to the intake passage 12 via the EGR passage 160, but the remaining air-fuel mixture flows into the purification catalyst 26 via the exhaust passage 16 and is purified by the catalyst. Released into the atmosphere. Since the unburned air-fuel mixture is purified in this way, a large load is applied to the purification catalyst 26 when a misfire occurs, and the deterioration of the catalyst is promoted when the inflowing air-fuel mixture increases. In this sense, it is preferable to recirculate as much air-fuel mixture as possible as EGR so that the air-fuel mixture flowing into the purification catalyst 26 does not increase so much.
[0098]
On the other hand, when the air-fuel mixture is recirculated, fuel is contained in the EGR gas, unlike normal EGR, so that the air-fuel ratio in the combustion chamber may shift. If the air-fuel ratio cannot be maintained at an appropriate value, various adverse effects such as fluctuation of generated torque or unstable combustion state occur. Therefore, in this sense, it is not preferable that the amount of air-fuel mixture to be recirculated as EGR gas is too large. As described above, when EGR is performed when misfire occurs, the amount of EGR gas recirculated into the intake passage 12 is set to an appropriate value in order to prevent the purification catalyst 26 from deteriorating and suppress adverse effects due to the deviation of the air-fuel ratio. It is desirable to control. In step S204 in FIG. 8, a process for correcting the EGR gas amount at the time of misfire in this way so as to be an appropriate gas amount is performed.
[0099]
Here, the content of the EGR misfire correction process will be described. FIG. 9 is a flowchart showing the flow of the EGR misfire correction process. As shown in the figure, when the EGR misfire correction process is started, first, the amount of exhaust gas generated is calculated based on the operating conditions of the engine (step S300). As the operating conditions, the engine rotational speed Ne and the accelerator opening degree θac detected in step S200 of the engine control routine shown in FIG. 8 are used. If these values are known, the amount of exhaust gas generated per unit time can be easily calculated.
[0100]
Next, the EGR rate is calculated (step S302). The EGR rate is a value indicating the ratio of the amount of EGR gas to the amount of exhaust gas generated. In the present embodiment, the EGR rate is calculated as follows using the output of the pressure sensor 23 provided in the combustion chamber. Since the pressure in the combustion chamber becomes equal to the pressure in the intake passage 12 while the intake valve 132 is opened, the pressure in the intake passage 12 can be measured from the output of the pressure sensor 23 provided in the combustion chamber. Similarly, while the exhaust valve 13 is open, the pressure in the combustion chamber becomes equal to the pressure in the exhaust passage 16, so that the pressure in the exhaust passage 16 can be measured using the pressure sensor 23. Therefore, by taking these differences, the pressure difference between the intake passage 12 and the exhaust passage 16 can be obtained. Since the EGR gas recirculates in the EGR passage 160 due to this pressure difference, the EGR gas amount increases as the pressure difference increases, that is, the EGR rate increases, and the EGR rate decreases as the pressure difference decreases.
[0101]
FIG. 10 is an explanatory diagram conceptually showing the relationship between the pressure difference between the exhaust passage 16 and the intake passage 12 and the EGR rate. In the region where the pressure difference is too large, the influence of throttling by the EGR passage 160 or the EGR valve 162 appears, but in other regions, the EGR rate has a substantially linear relationship with the pressure difference. Therefore, if the EGR rate for the pressure difference between the exhaust passage 16 and the intake passage 12 is obtained in advance by an experimental method, the EGR rate can be calculated from the pressure difference. In step S302 of FIG. 9, the relationship between the pressure difference and the EGR rate is stored in the ROM of the ECU 30 as a map, and the EGR rate is calculated from the output of the pressure sensor 23 during the intake stroke and the exhaust stroke. In the present embodiment, the EGR rate is calculated from the pressure difference between the exhaust passage 16 and the intake passage 12, but more simply, the EGR rate may be obtained based on the opening degree of the EGR valve 162.
[0102]
When the EGR rate is thus obtained, the EGR amount (that is, the amount of gas recirculated into the intake passage 12) and the amount of exhaust gas flowing into the purification catalyst 26 are calculated (step S304). The EGR amount can be calculated by multiplying the exhaust gas generation amount obtained in step S300 by the EGR rate. The amount of exhaust gas flowing into the purification catalyst 26 can be calculated by subtracting the EGR amount from the amount of exhaust gas generated.
[0103]
Next, it is determined whether or not the load of the purification catalyst 26 is within an allowable range (step S306). As described above, when misfire occurs, an unburned air-fuel mixture flows into the purification catalyst 26, so that a large load is applied to the catalyst. Therefore, if the amount of exhaust gas flowing into the catalyst determined in step S304 is larger than a predetermined threshold, it is determined that the allowable range is exceeded (step S306: no), and the load on the catalyst is allowed by reducing the EGR amount. The correction coefficient K1 is set so as to be in the range (step S308).
[0104]
On the other hand, when the amount of exhaust gas flowing into the purification catalyst 26 is smaller than the predetermined threshold (step S306: yes), the process immediately calculates the air-fuel ratio after mixing without setting the correction coefficient K1 (step S306). S310). That is, as described above, when EGR is performed in the event of a misfire, the fuel once supplied into the combustion chamber is recirculated and supplied again into the combustion chamber, so that the air fuel ratio in the combustion chamber is shifted by that amount. There are things to do. Therefore, at the time of misfire, the air-fuel ratio of the air-fuel mixture formed in the combustion chamber is calculated by mixing the air-fuel mixture newly supplied into the combustion chamber and the air-fuel mixture recirculated as EGR gas. If the flow rate and air-fuel ratio of the newly supplied air-fuel mixture and the flow rate and air-fuel ratio of the air-fuel mixture recirculating as EGR gas are known, the air-fuel ratio after mixing can be easily obtained by proportional calculation. Here, the flow rate of the newly supplied air-fuel mixture is measured by the air flow sensor 18, and the flow rate of the EGR gas has already been obtained. Since the ECU 30 knows any of these air-fuel ratios, the ECU 30 can easily calculate the air-fuel ratio after mixing.
[0105]
After calculating the air-fuel ratio after mixing, it is then determined whether or not the air-fuel ratio fluctuation is within an allowable range (step S312). That is, if the calculated air-fuel ratio after mixing is greatly deviated from the target air-fuel ratio, the amount of torque generated will be different, which may cause a great sense of discomfort to the engine driver. Therefore, if the deviation amount of the air-fuel ratio is larger than the predetermined threshold value, it is determined that the air-fuel ratio fluctuation exceeds the allowable range (step S312: no), and the EGR amount is reduced so that the air-fuel ratio fluctuation falls within the allowable range. The correction coefficient K2 is set to (step S314). If the air-fuel ratio fluctuation is within the allowable range, the EGR misfire correction process shown in FIG. 9 is skipped without setting the correction coefficient K2, and the process returns to the engine control routine of FIG.
[0106]
In the engine control routine, when returning from the EGR misfire correction process, the air-fuel ratio misfire correction process is started (step S206). This is the following process. As described above, when EGR is performed during a misfire, the air-fuel ratio of the air-fuel mixture formed in the combustion chamber may shift. In the EGR misfire correction process that is performed prior to the air-fuel ratio misfire correction process, the deviation amount of the air-fuel ratio is calculated, and when the slip amount exceeds the allowable range, the correction coefficient K2 is set so as to reduce the EGR amount to the allowable range. It was set. In the air-fuel ratio misfire correction process, a process for correcting the fuel injection amount is performed in order to correct such a deviation in the air-fuel ratio. That is, when the air-fuel ratio shifts to a smaller value (rich side) due to EGR, the fuel injection period is shortened according to the amount of deviation, and conversely, when the air-fuel ratio shifts to a larger value (lean side), the fuel injection period becomes shorter. Processing to correct the length is performed.
[0107]
Thus, when the EGR misfire correction process and the air-fuel ratio misfire correction process are completed, the EGR control is started (step S208). FIG. 11 is a flowchart showing the flow of EGR control performed in the engine control routine of the second embodiment. When the EGR control is started, first, the reference opening degree of the EGR valve is acquired (step S400). Similar to the first embodiment described above, an appropriate opening degree of the EGR valve is stored in the form of a map in the ROM of the ECU 30 in accordance with the engine operating conditions (the engine speed Ne and the accelerator opening degree θac). ing. In step S400, the reference opening of the EGR valve is acquired by referring to the map based on the operating condition detected in the engine control routine.
[0108]
Next, the reference grade is corrected using the correction coefficients K1 and K2 set in the EGR misfire correction control (step S402). Here, correction is performed by multiplying the reference opening by these correction coefficients. Of course, if the correction coefficient is set appropriately, the correction can be made by adding or subtracting the correction coefficient to the reference opening.
[0109]
When the reference opening degree of the EGR valve is corrected in this way, the EGR valve is set to the obtained opening degree (step S404), the EGR control of FIG. 11 is terminated, and the process returns to the engine control routine.
[0110]
In the engine control routine, fuel injection control is started following EGR control (step S210). In this control, the fuel injection valve 14 is driven for an appropriate period to inject fuel into the combustion chamber in substantially the same manner as the fuel control of the first embodiment described above. The fuel injection period of the second embodiment is a period reflecting the result of the air-fuel ratio misfire correction performed in advance. That is, the injection period determined based on the engine operating conditions and the output of the air flow sensor 18 is the injection period corrected by the air-fuel ratio misfire correction process described above.
[0111]
Thus, after fuel is injected into the combustion chamber to form an air-fuel mixture, a spark is blown from the spark plug 136 at a predetermined timing to ignite the air-fuel mixture (step S212), and then the presence or absence of misfire is detected (step S214). . The presence or absence of misfire is detected based on the output of the pressure sensor 23, as in the first embodiment.
[0112]
If misfire is detected, it is confirmed whether or not an instruction to stop the engine is given (step S216). If the engine driver has instructed the engine 10 to be stopped, the engine control routine is terminated as it is. If the stop of the engine 10 is not instructed, the process returns to step S200 to continue the control.
[0113]
As described above, in the engine control routine of the second embodiment, when a misfire occurs, a part of the unburned mixture is recirculated to the combustion chamber as EGR gas. At this time, the EGR gas amount is appropriately controlled so that the load applied to the purification catalyst and the deviation of the air-fuel ratio in the combustion chamber are within the allowable range, so the catalyst deteriorates early or torque fluctuation occurs. Thus, it is possible to avoid giving the engine driver a feeling of strangeness.
[0114]
Although various embodiments have been described above, the present invention is not limited to all the embodiments described above, and can be implemented in various modes without departing from the scope of the invention.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram conceptually showing the structure of an engine of the present embodiment.
FIG. 2 is an explanatory diagram conceptually showing how an engine outputs power while repeating four strokes.
FIG. 3 is an explanatory view conceptually showing how the air-fuel mixture is discharged from the combustion chamber without burning when misfire occurs.
FIG. 4 is an explanatory diagram showing an outline of the operation of the engine when a misfire occurs.
FIG. 5 is a flowchart showing a flow of an engine control routine of the first embodiment.
FIG. 6 is an explanatory diagram conceptually showing how the pressure in the combustion chamber changes according to the crank angle.
FIG. 7 is an explanatory diagram showing the principle of detecting the occurrence of misfire based on the rotational speed of the engine.
FIG. 8 is a flowchart showing a flow of an engine control routine of a second embodiment.
FIG. 9 is a flowchart showing a flow of an EGR misfire correction process performed in an engine control routine of a second embodiment.
FIG. 10 is an explanatory view conceptually showing the relationship between the pressure difference between the intake passage and the exhaust passage and the EGR rate.
FIG. 11 is a flowchart showing a flow of EGR control performed in an engine control routine of a second embodiment.
[Explanation of symbols]
10 ... Engine
12 ... Intake passage
13 ... Exhaust valve
14 ... Fuel injection valve
16 ... Exhaust passage
18 ... Air flow sensor
20 ... Air cleaner
22 ... Throttle valve
23 ... Pressure sensor
24 ... Electric actuator
26 ... Purification catalyst
30 ... ECU
32 ... Crank angle sensor
34 ... accelerator opening sensor
130 ... Cylinder head
132 ... Intake valve
134. Exhaust valve
136 ... Spark plug
140 ... Cylinder block
142 ... Cylinder
144 ... Piston
146 ... Connecting rod
148 ... crankshaft
152, 154 ... Electric actuator
160 ... EGR passage
162 ... EGR valve

Claims (6)

An internal combustion engine that outputs power by burning a mixture of air and fuel in a combustion chamber,
An air-fuel mixture discharging means for discharging the air-fuel mixture burned in the combustion chamber from the combustion chamber;
Misfire detection means for detecting the occurrence of misfire, which is a phenomenon in which combustion of the air-fuel mixture does not complete normally in the combustion chamber;
An emission suppressing means for suppressing the mixture from being discharged from the combustion chamber when the misfire occurs;
Leak amount measuring means for measuring the leak amount of the air-fuel mixture that leaks out from the combustion chamber while suppressing the emission;
An internal combustion engine comprising: an air-fuel mixture replenishing unit that supplements the air-fuel mixture according to the measured leakage amount.   The internal combustion engine according to claim 1, wherein the leakage amount measuring means is a means for measuring the leakage amount by measuring a pressure in the combustion chamber. The internal combustion engine according to claim 1,
An intake passage for sucking the air into the combustion chamber;
A fuel injection valve for injecting fuel into the intake passage;
An intake valve for opening and closing the intake passage,
The air-fuel mixture replenishing means is means for replenishing the air-fuel mixture by opening the intake valve after the middle of the intake stroke and sucking the air and fuel supplied from the fuel injection valve into the combustion chamber. An internal combustion engine. The internal combustion engine according to claim 1,
An intake passage for sucking the air into the combustion chamber;
A fuel injection valve for injecting fuel into the combustion chamber;
An intake valve for opening and closing the intake passage,
The air-fuel mixture replenishing means injects fuel from the fuel injection valve into the combustion chamber and opens the intake valve after the middle of the intake stroke to suck the air into the combustion chamber. An internal combustion engine that is a means to supplement. An internal combustion engine according to claim 3 or claim 4,
The air-fuel mixture replenishing means is a means for controlling the air-fuel ratio in the combustion chamber to a predetermined value by adjusting at least one of the air intake amount or the fuel injection amount when supplementing the air-fuel mixture. Internal combustion engine. A control method for an internal combustion engine that outputs power by burning a mixture of air and fuel in a combustion chamber,
A first step of discharging the air-fuel mixture combusted in the combustion chamber from the combustion chamber;
A second step of detecting the occurrence of misfire, which is a phenomenon in which combustion of the air-fuel mixture is not normally completed in the combustion chamber;
A third step of suppressing discharge of the air-fuel mixture from the combustion chamber when the misfire occurs;
A fourth step of measuring an amount of leakage of the air-fuel mixture that leaks out from the combustion chamber while suppressing the emission;
And a fifth step of supplementing the air-fuel mixture according to the measured leakage amount.

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