JP2007120392A - Air fuel ratio control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an air fuel ratio control device for an internal combustion engine capable of accurately controlling air fuel ratio by a simple method. <P>SOLUTION: In-cylinder air quantity Mcyl is calculated based on cylinder pressure and in-cylinder air temperature T at timing of intake valve close. Heat release rate per crank angle dQ/dθ is calculated based on cylinder pressure per crank angle. Heat release quantity Q is calculated by integrating the heat release rate dQ/dθ over combustion period. Quantity of fuel supplied into the cylinder q_inj is calculated by dividing the heat release quantity by low calorific value of fuel q_fuel. In-cylinder air fuel ratio in the cylinder AFcyl is calculated by dividing the in-cylinder air quantity Mcyl by fuel quantity q_inj. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine.

  In an internal combustion engine, it is necessary to control the air-fuel ratio with high accuracy in order to achieve an object such as reduction of exhaust emission. In Japanese Patent Laid-Open No. 5-71403, the product of the in-cylinder pressure and the cylinder volume change amount is integrated over a predetermined crank angle range to calculate the indicated mean effective pressure equivalent value, and according to the indicated mean effective pressure equivalent value. A method is disclosed in which the air-fuel ratio of each cylinder is made equal by correcting the fuel injection amount. However, various factors such as the air amount, the fuel amount, and the temperature are related to the in-cylinder pressure. For this reason, if the fuel injection amount is corrected based only on the in-cylinder pressure, an accurate air-fuel ratio cannot always be realized.

  Japanese Patent Laid-Open No. 4-358735 discloses a cylinder pressure peak value Pmax for each combustion stroke and a crank angle θPmax at the time when the Pmax is generated, and an ideal air-fuel ratio is obtained based on a map prepared in advance. A method of deriving a target Pmax with respect to θPmax and correcting the fuel injection amount so as to eliminate the difference from the actual Pmax is disclosed.

  Japanese Patent Application Laid-Open No. 5-44544 discloses in-cylinder pressure Pin at 60 ° CA before top dead center and in-cylinder pressure Pex at 60 ° CA after top dead center, respectively, and their ratio Pin / Pex and empty A method of estimating the in-cylinder air-fuel ratio and correcting the fuel injection amount based on a map prepared in advance that defines the relationship with the fuel ratio is disclosed.

Japanese Patent Laid-Open No. 5-71403 JP-A-1-253543 Japanese Patent No. 2830011 Japanese Patent No. 2830012 JP-A-4-358745 JP-A-5-44544 JP-A-1-114718

  However, when the method disclosed in Japanese Patent Laid-Open No. 4-358735 and Japanese Patent Laid-Open No. 5-44544 is actually adopted, it is actually the case that an appropriate relationship is determined under all operating conditions when creating the map. The top is difficult. Moreover, even if it adapts experimentally, a huge amount of measurement work is required, and a great deal of labor is required.

  Even if the deviation between the measured value of Pmax or Pin / Pex and the value at the ideal air-fuel ratio determined in the map is known, it is not known how much the fuel injection amount should be corrected for the deviation. However, further information is required.

  The present invention has been made in view of the above points, and an object of the present invention is to provide an air-fuel ratio control apparatus for an internal combustion engine that can control the air-fuel ratio with a simple method and with high accuracy.

In order to achieve the above object, a first invention is an air-fuel ratio control apparatus for an internal combustion engine,
In-cylinder pressure detecting means for detecting the in-cylinder pressure of the cylinder;
In-cylinder temperature acquisition means for detecting or estimating the in-cylinder temperature;
An air amount calculating means for calculating the in-cylinder air amount in accordance with the gas state equation based on the in-cylinder pressure and the in-cylinder temperature at the time of closing the intake valve;
Fuel amount calculation means for calculating the amount of fuel supplied into the cylinder based on the history of in-cylinder pressure during the combustion period;
Air-fuel ratio calculating means for calculating the air-fuel ratio of the air-fuel mixture burned in the cylinder based on the in-cylinder air amount and the fuel amount;
It is characterized by providing.

The second invention is the first invention, wherein
The fuel amount calculating means includes
Based on the in-cylinder pressure value, heat generation rate calculating means for calculating the heat generation rate in the cylinder,
A heat generation amount calculating means for calculating a heat generation amount in a cylinder by integrating the heat generation rate over a combustion period;
It is characterized by including.

The third invention is the first or second invention, wherein
Control means for controlling the fuel injection amount and / or the in-cylinder intake air amount based on the air-fuel ratio calculated by the air-fuel ratio calculating means is further provided.

According to a fourth invention, in any one of the first to third inventions,
The air amount calculation means includes gas constant correction means for correcting the value of the gas constant in the gas state equation in accordance with the amount of residual gas in the cylinder.

A fifth invention is an apparatus for controlling an air-fuel ratio of an internal combustion engine having a plurality of cylinders and capable of individually adjusting the intake air amount of each cylinder in order to achieve the above object.
In-cylinder pressure detecting means for detecting the in-cylinder pressure of each cylinder;
A heat generation rate calculating means for calculating a heat generation rate in each cylinder based on the in-cylinder pressure value of each cylinder;
Inter-cylinder variation detection means for detecting the variation in the cylinder air amount and / or the amount of fuel in the cylinder by comparing the in-cylinder pressure and the heat generation rate between the cylinders after the intake valve is closed,
Variation correcting means for correcting the in-cylinder air amount and / or the in-cylinder fuel amount so as to eliminate the variation among the cylinders;
It is characterized by providing.

The sixth invention is the fifth invention, wherein
The inter-cylinder variation detecting means includes
First air amount variation determination that determines that the in-cylinder air amount of one cylinder is less than that of the other cylinder when the in-cylinder pressure of the one cylinder before the rise of the heat generation rate is lower than that of the other cylinders Means,
Second air amount variation determination for determining that the in-cylinder air amount of one cylinder is greater than that of the other cylinder when the in-cylinder pressure of the one cylinder before the rise of the heat generation rate is higher than that of the other cylinders Means,
It is characterized by including.

The seventh invention is the fifth or sixth invention, wherein
The inter-cylinder variation detecting means includes
When the in-cylinder pressure before the rise of the heat generation rate is not significantly different between the cylinders and the heat generation rate of one cylinder is lower than that of the other cylinders, the in-cylinder fuel amount of the one cylinder is First fuel amount variation determination means for determining that there are fewer than other cylinders;
When the in-cylinder pressure before the rise of the heat generation rate is not significantly different among the cylinders and the heat generation rate of one cylinder is higher than that of the other cylinders, the in-cylinder fuel amount of the one cylinder is Second fuel amount variation determining means for determining that there are more than the other cylinders;
It is characterized by including.

  According to the first aspect, the in-cylinder air amount and the in-cylinder fuel amount can be calculated separately based on the in-cylinder pressure detected by the in-cylinder pressure detecting means. The in-cylinder pressure during the cycle accurately reflects the values of the in-cylinder air amount and the in-cylinder fuel amount. Therefore, by calculating the in-cylinder air amount and the in-cylinder fuel amount on the basis of the actually measured values of the in-cylinder pressure, the air amount and the fuel amount actually supplied into the cylinder in the current cycle can be obtained accurately. According to the present invention, the air-fuel ratio of the air-fuel ratio actually burned in the cylinder can be obtained with high accuracy by calculating the air-fuel ratio based on the accurate in-cylinder air amount and in-cylinder fuel amount. Can do.

  According to the second invention, the heat generation rate in the cylinder at that time can be calculated based on the in-cylinder pressure value. Then, by integrating this heat generation rate over the combustion period, the amount of heat generation in the cylinder can be accurately calculated. If the amount of heat generated in the cylinder is known, it can be converted into the amount of fuel in the cylinder using the physical property value of the fuel. Therefore, according to the present invention, the in-cylinder fuel amount can be obtained more accurately.

  According to the third aspect, the fuel injection amount and the cylinder intake air amount can be controlled based on the air-fuel ratio calculated by the air-fuel ratio calculating means. As described above, the air-fuel ratio calculated by the air-fuel ratio calculating means matches the air-fuel ratio of the air-fuel mixture actually burned in the cylinder with high accuracy. Therefore, according to the present invention, the in-cylinder air-fuel ratio can be accurately controlled by controlling the subsequent fuel injection amount and in-cylinder intake air amount based on the calculated value of the air-fuel ratio calculating means.

  According to the fourth aspect of the invention, the value of the gas constant in the gas equation of state used for calculating the in-cylinder air amount can be corrected according to the residual gas amount in the cylinder. For this reason, it is possible to accurately calculate the in-cylinder air amount without being affected by it even under a situation where there is a large amount of residual gas.

  According to the fifth aspect, the in-cylinder pressure of each cylinder can be actually measured, and the heat generation rate in the cylinder of each cylinder can be calculated based on the in-cylinder pressure value of each cylinder. Then, by a simple process of comparing the in-cylinder pressure and the heat generation rate after the intake valve is closed between the cylinders, it is possible to accurately detect the in-cylinder variation in the in-cylinder air amount and the in-cylinder fuel amount. Therefore, the subsequent in-cylinder air amount and in-cylinder fuel amount can be accurately corrected so that the in-cylinder air amount and in-cylinder fuel amount do not vary between cylinders. For this reason, according to the present invention, the deviation of the air-fuel ratio between the cylinders can be minimized and made uniform.

  According to the sixth aspect of the present invention, the variation in the cylinder air amount among the cylinders can be accurately detected by a simple process.

  According to the seventh aspect, the in-cylinder fuel amount variation between cylinders can be accurately detected by a simple process.

Embodiment 1 FIG.
[Description of system configuration]
FIG. 1 is a diagram for explaining a system configuration according to the first embodiment of the present invention. As shown in FIG. 1, the system of the present embodiment includes an internal combustion engine 10. The internal combustion engine 10 is an engine having a plurality of cylinders, and FIG. 1 shows only one of the cylinders. The internal combustion engine 10 incorporates a crank angle sensor 12 that detects a crank angle. The crank angle sensor 12 is a sensor that reverses the Hi output and the Lo output each time the crankshaft rotates by a predetermined rotation angle. According to the output of the crank angle sensor 12, the crank angle (rotational position of the crankshaft), the engine speed NE, and the like can be detected.

  Further, the internal combustion engine 10 incorporates a water temperature sensor 16 that detects the coolant temperature THW, an in-cylinder temperature sensor 17, and an in-cylinder pressure sensor 18. The in-cylinder temperature sensor 17 can detect the temperature of gas in the cylinder (combustion chamber). The in-cylinder pressure sensor 18 can detect the pressure generated in the cylinder (combustion chamber).

  A surge tank 20 is provided in the intake passage 19 of the internal combustion engine 10. In addition, an air flow meter 22 for detecting an intake air amount GA flowing through the inside of the intake passage 19 is disposed. A throttle valve 24 is disposed downstream of the air flow meter 22. The throttle valve 24 is an electronically controlled throttle valve that is driven by a throttle motor (not shown) to open and close. In the vicinity of the throttle valve 24, a throttle opening sensor 26 for detecting the throttle opening TA is assembled.

  Further, the internal combustion engine 10 is provided with a fuel injection valve 28 for directly injecting fuel such as gasoline into the cylinder, and an ignition plug 30 for igniting an air-fuel mixture in the combustion chamber. Further, an air-fuel ratio sensor 33 that outputs a signal corresponding to the air-fuel ratio of the exhaust gas flowing through the exhaust passage 32 of the internal combustion engine 10 is installed. A catalyst 34 for purifying exhaust gas is incorporated in the exhaust passage 32.

  The internal combustion engine 10 includes a variable valve mechanism 36 that changes the valve opening characteristics of the intake valve 38. According to the variable valve mechanism 36, the valve opening phase of the intake valve 38 can be shifted, and the operating angle and the lift amount can be changed. A sensor 40 that detects the operation amount of the variable valve mechanism 36 is provided in the vicinity of the variable valve mechanism 36.

  The system of this embodiment includes an ECU (Electronic Control Unit) 50. Sensor signals are supplied to the ECU 50 from the various sensors described above. The ECU 50 can control various actuators such as the throttle valve 24, the fuel injection valve 28, the spark plug 30, and the variable valve mechanism 36 based on these sensor signals.

[Features of Embodiment 1]
Next, the operation of the system in this embodiment will be described.
In the present embodiment, the air-fuel ratio of the air-fuel mixture burned in the cylinder is determined based on the in-cylinder pressure P detected by the in-cylinder pressure sensor 18 for each cycle. Then, the fuel injection amount of the next cycle is corrected in accordance with the obtained air-fuel ratio value. Hereinafter, the air-fuel ratio obtained based on the in-cylinder pressure P is referred to as “in-cylinder air-fuel ratio” and is represented by the symbol AFcyl.

  Hereinafter, a method for calculating the in-cylinder air-fuel ratio AFcyl will be described. FIG. 2 is a graph showing the relationship among the in-cylinder pressure P, the heat generation rate dQ / dθ, and the heat generation amount Q in the compression stroke and the explosion stroke. Note that θ [° CA] represents a crank angle.

  As shown in the upper part of FIG. 2, after the intake valve 38 is closed, the in-cylinder pressure P starts to increase due to the compression of the gas in the cylinder. Thereafter, when the air-fuel mixture in the cylinder is ignited, heat from combustion is generated in the cylinder. As shown in the middle part of FIG. 2, the rising point of the heat generation rate dQ / dθ corresponds to the start point of combustion. While the combustion continues, as shown in the lower part of FIG. 2, the cumulative heat generation amount Q continues to increase. When combustion ends, combustion heat is no longer generated and the heat generation rate dQ / dθ becomes zero. At this combustion end point, the heat generation amount Q takes a maximum value.

  In the present embodiment, the cylinder pressure sensor 18 can measure the history of the cylinder pressure P as shown in the upper part of FIG. Between the in-cylinder pressure P and the heat generation rate dQ / dθ, the relationship of equation (1) in FIG. 2 is established thermodynamically. In the equation (1), V represents the in-cylinder volume, and κ represents the specific heat ratio of the in-cylinder gas.

  V and dV / dθ in the above equation (1) are geometrically determined values according to the crank angle θ. The specific heat ratio κ can be approximated by taking a constant value. Therefore, if the in-cylinder pressure P for each crank angle θ is known, the heat release rate dQ / dθ for each crank angle θ can be calculated based on the above equation (1). Then, if the heat generation rate dQ / dθ is integrated, the heat generation amount Q due to combustion in the cylinder can be calculated.

  The heat generation amount Q calculated in this way is generated by the combustion of the fuel injected from the fuel injection valve 28 into the cylinder. Here, the lower heating value q_fuel when the unit amount of fuel burns is a physical property value of the fuel and is a known value. The lower calorific value q_fuel is also called a true calorific value, and is obtained by subtracting from the total calorific value the latent heat necessary to evaporate the moisture contained in the fuel and the moisture generated by combustion.

When the amount of fuel supplied from the fuel injection valve 28 into the cylinder is q_inj, a value obtained by multiplying the fuel amount q_inj and the lower heating value q_fuel corresponds to the heat generation amount Q. That is, the following equation is established.
Q = q_inj x q_fuel (2)
Therefore, by dividing the heat generation amount Q by the lower heating value q_fuel, the amount q_inj of the fuel actually injected from the fuel injection valve 28 in this cycle can be calculated.

  In the present embodiment, the mass Mcyl of the air in the cylinder can be obtained using the gas state equation PV = MRT. In this formula, M represents a gas mass, R represents a gas constant, and T represents a gas temperature. In the present embodiment, the in-cylinder air amount Mcyl can be calculated from the establishment of the gas state equation when the intake valve 38 is closed. Then, the in-cylinder air-fuel ratio AFcyl can be obtained by dividing the calculated in-cylinder air amount Mcyl by the heat generation amount Q.

[Specific Processing in Embodiment 1]
FIG. 3 is a flowchart of a routine executed by the ECU 50 in the present embodiment in order to realize the above function. This routine is intended for one cylinder of the internal combustion engine 10 and is executed for each cycle of the cylinder in synchronization with the crank angle. Then, the same routine as this routine is separately executed for the other cylinders.

  According to the routine shown in FIG. 3, first, the in-cylinder pressure P when the intake valve 38 is closed is acquired based on the output of the in-cylinder pressure sensor 18 (step 100). The closing time of the intake valve 38 varies depending on the state of the variable valve mechanism 36. The ECU 50 can grasp the valve closing time of the intake valve 38 based on the operation amount of the variable valve mechanism 36 detected by the sensor 40.

  Further, the ECU 50 acquires the temperature T of the air sucked into the cylinder when the intake valve 38 is closed (step 102). This in-cylinder temperature T can be acquired based on the output of the in-cylinder temperature sensor 17.

  Next, the in-cylinder air amount Mcyl is calculated based on the gas state equation established in the cylinder when the intake valve 38 is closed (step 104). Specifically, the calculation process is performed based on the formula Mcyl = PV / RT. In this calculation process, the in-cylinder pressure P acquired in step 100 is substituted for P in this equation, and the in-cylinder temperature T acquired in step 102 is substituted for V. Further, the in-cylinder volume V when the intake valve 38 is closed is geometrically determined according to the crank angle θ when the intake valve 38 is closed. The value of the cylinder volume V when the intake valve 38 is closed is substituted for V in the above equation. In addition, a value of a gas constant R corresponding to fresh air (air) stored in advance is substituted for R in the above formula.

  After the intake valve 38 is closed, the ECU 50 takes in the cylinder pressure P detected by the cylinder pressure sensor 18 at predetermined crank angle intervals. At this time, the interval at which the in-cylinder pressure P is acquired is preferably about several degrees CA or less. In the present embodiment, the in-cylinder pressure P is acquired every 1 ° CA. By substituting the in-cylinder pressure P into the equation (1), the heat release rate dQ / dθ is calculated every 1 ° CA after the intake valve 38 is closed (step 106). In this calculation process, a value geometrically determined according to the crank angle θ is substituted for V and dV / dθ, and a predetermined value stored in advance is substituted for the specific heat ratio κ.

  Next, the heat generation amount Q is calculated by integrating (integrating) the heat generation rate dQ / dθ for each 1 ° CA calculated in step 106 (step 108). This integration process may be performed up to a crank angle at which the value of dQ / dθ is substantially zero.

Next, the fuel amount q_inj is calculated by the following equation based on the heat generation amount Q calculated in step 108 and the lower heating value q_fuel of the fuel stored in advance (step 110).
q_inj = Q / q_fuel (3)

The q_inj calculated in step 110 represents the amount of fuel supplied into the cylinder in the current cycle, that is, the amount of fuel injected from the fuel injection valve 28. The in-cylinder air-fuel ratio AFcyl of this cycle is calculated by dividing the in-cylinder air amount Mcyl obtained in step 104 by the fuel amount q_inj (step 112). That is, the in-cylinder air-fuel ratio AFcyl is expressed by the following equation.
AFcyl = Mcyl / q_inj (4)

  Next, based on the calculated in-cylinder air-fuel ratio AFcyl, the target value of the fuel injection amount for the next cycle of this cylinder is corrected (step 114). Specifically, this correction can be performed as follows, for example. When performing control targeting the stoichiometric air-fuel ratio, it is determined whether the in-cylinder air-fuel ratio AFcyl is richer or leaner than the stoichiometric air-fuel ratio. The deviation is calculated, and the fuel injection amount of the next cycle is corrected according to the deviation width.

  In step 114, the tendency of deviation from the target air-fuel ratio of the in-cylinder air-fuel ratio AFcyl calculated in each cycle is learned, and the in-cylinder air-fuel ratio AFcyl and the target air-fuel ratio are determined according to the learning result. The fuel injection amount of the next cycle may be corrected so as to eliminate the deviation.

  As described above, in this embodiment, both the in-cylinder air amount Mcyl and the in-cylinder fuel amount q_inj are obtained, and the in-cylinder air-fuel ratio AFcyl is calculated based on them. According to such a calculation process, the air-fuel ratio of the air-fuel mixture actually burned in the cylinder, that is, the in-cylinder air-fuel ratio AFcyl can be accurately estimated. Then, by correcting the fuel injection amount in the next cycle based on the accurately obtained in-cylinder air-fuel ratio AFcyl, the target air-fuel ratio can be realized accurately.

  By the way, in Embodiment 1 mentioned above, although the apparatus which controls the internal combustion engine 10 which injects a fuel directly in a cylinder was demonstrated, the internal combustion engine which this invention makes object is not limited to this. The present invention can also be applied to an internal combustion engine that injects fuel into an intake port and an apparatus that controls an internal combustion engine that injects fuel into both a cylinder and an intake port.

  Further, in the first embodiment described above, in step 102, the temperature T of the in-cylinder air when the intake valve is closed is actually measured by the in-cylinder temperature sensor 17, but a method for obtaining this in-cylinder temperature T is as follows. It is not limited to this. In the compression stroke and the explosion stroke, the actual in-cylinder temperature T varies greatly with each cycle. In contrast, the in-cylinder temperature T when the intake valve is closed is stable with little change in each cycle, and has a high correlation with the operating conditions. For this reason, the relationship between the in-cylinder temperature T and the operating condition is examined in advance, the relationship is stored in the ECU 50 in the form of a map or formula, and the in-cylinder temperature T is obtained based on the map or formula. Also good. In this case, operating conditions having a correlation with the in-cylinder temperature T include, for example, the engine speed NE, the intake air amount GA, the cooling water temperature THW, the air-fuel ratio AF of the previous cycle, the ignition timing SA, and the valve timing of the intake valve 38. Is mentioned.

In step 110, the fuel amount q_inj may be calculated in consideration of the combustion efficiency η. When all of the fuel supplied into the cylinder is completely burned, the combustion efficiency η is 1. Depending on the operating conditions of the internal combustion engine 10, not all of the fuel supplied into the cylinder is burned completely, and in that case η is smaller than 1. The combustion efficiency η correlates with the operating conditions of the internal combustion engine 10, that is, the engine speed NE, the intake air amount GA, the cooling water temperature THW, the air-fuel ratio AF of the previous cycle, the ignition timing SA, the valve timing of the intake valve 38, and the like. Therefore, if the relationship between these operating conditions and the combustion efficiency η is examined in advance and the relationship is stored in the ECU 50 in the form of a map or formula, the combustion efficiency η can be acquired based on the map or formula. . In consideration of the combustion efficiency η, the following equation is established instead of the above equations (2) and (3).
Q = η × q_inj × q_fuel (5)
q_inj = (1 / η) × Q / q_fuel (6)

  Therefore, when the fuel amount q_inj is calculated in consideration of the combustion efficiency η in step 110, the calculation process based on the above equation (6) is performed using the combustion efficiency η acquired based on the operating conditions. Good. In this case, the fuel amount q_inj can be obtained with higher accuracy.

  In the first embodiment described above, the in-cylinder pressure sensor 18 is the “in-cylinder pressure detection means” in the first invention, and the in-cylinder temperature sensor 17 is the “in-cylinder temperature acquisition means” in the first invention. , Respectively. Further, when the ECU 50 executes the processing of step 104, the “air amount calculation means” in the first invention executes the processing of steps 106 to 110, thereby “fuel amount” in the first invention. The “calculating means” executes the processing of step 112 described above, thereby realizing the “air-fuel ratio calculating means” in the first invention.

  In the first embodiment described above, the ECU 50 executes the process of step 106, so that the “heat generation rate calculating means” in the second aspect of the invention executes the process of step 108. The “heat generation amount calculation means” in the second invention realizes the “control means” in the third invention by executing the processing of step 114.

  By the way, in Embodiment 1 described above, a constant value stored in advance as the gas constant R is used in the calculation process of step 104. However, the value of the gas constant R is corrected under operating conditions with a large amount of residual gas. It is also good to do. When there is a lot of residual gas, such as when performing EGR (Exhaust Gas Recirculation), the value of the gas constant R changes according to the composition of the in-cylinder gas when the intake valve 38 is closed. When internal EGR is performed by operating the variable valve mechanism 36 to generate a valve overlap period, the amount of residual gas depends on the length of the valve overlap period. Therefore, the value of the gas constant R may be corrected based on the length of the valve overlap period calculated from the valve timing of the intake valve 38 detected by the sensor 40. In the case of correcting the gas constant R, the cylinder air amount Mcyl can be calculated more accurately without being affected even when the residual gas amount is large. In this case, the “gas constant correcting means” according to the fourth aspect of the present invention is realized by the ECU 50 executing the above processing.

Embodiment 2. FIG.
[Features of Embodiment 2]
Next, the second embodiment of the present invention will be described with reference to FIG. 4 to FIG. 8. The description will focus on the differences from the first embodiment described above, and the same matters will be described. Omitted or simplified.

  It is assumed that the internal combustion engine 10 in the present embodiment can individually adjust the intake air amount of each cylinder. As a configuration in which the intake air amount of each cylinder can be individually adjusted, a configuration in which a throttle valve is individually provided for each cylinder, or a working angle and a lift amount of the intake valve 38 can be independently changed for each cylinder. What is necessary is just to employ | adopt the structure which provides a variable valve mechanism. For other points, the hardware used in this embodiment is the same as that shown in FIG. The system of the present embodiment can be realized by causing the ECU 50 to execute a routine shown in FIG. 8 to be described later using the above hardware configuration.

  In the present embodiment, variation between cylinders in the cylinder intake air amount and fuel injection amount is detected, and the air amount and fuel injection amount are corrected so as to eliminate the variation between cylinders. 4 to 7 are diagrams for explaining a method of determining variation between cylinders in the air amount or the fuel injection amount in the present embodiment.

  4 to 7, the cylinder in which the in-cylinder air amount or the in-cylinder fuel amount varies is referred to as “variable cylinder”, and the other cylinders are referred to as “standard cylinders”. Further, the theoretical air-fuel ratio when gasoline is used as fuel is about 14.5. However, in the description of FIGS. 4 to 7, it is assumed that the theoretical air-fuel ratio is 10 for easy understanding.

  The state in which the air amount or fuel amount of only one cylinder varies can be classified into the following four types. That is, the case where the amount of air is small for one cylinder, the amount of air for one cylinder is large, the amount of fuel for one cylinder is small, and the amount of fuel for one cylinder is large. 4 to 7 show these four types, respectively.

  FIG. 4 shows a case where only one cylinder has a smaller air amount than the other cylinders. Specifically, in the standard cylinder, a theoretical air-fuel ratio with an air amount of 100 and a fuel amount of 10 is realized, whereas in a variation cylinder, the fuel amount is also 10, but the air amount becomes 90. It shall be.

  As shown in the graph of FIG. 4, in this case, due to the difference in the amount of air in the cylinder, the in-cylinder pressure of the variation cylinder is higher than the in-cylinder pressure of the standard cylinder in the compression stroke, that is, before the heat generation rate rises. Lower. By capturing this feature, the type variation shown in FIG. 4 can be detected. That is, before the heat generation rate rises, if there is a cylinder whose in-cylinder pressure is lower than that of the other cylinders, it can be determined that the air amount of that cylinder is smaller than the other cylinders. Then, after the next cycle, the air amount of all the cylinders can be made uniform by performing correction so that the air amount of the variation cylinder is larger than the current amount.

  In the situation shown in FIG. 4, since the variation cylinder has an insufficient amount of air, only a smaller amount of fuel than the standard cylinder can be burned. For this reason, the variation rate cylinder has a lower heat generation rate than the standard cylinder.

  FIG. 5 shows a case where only one cylinder has a larger air amount than the other cylinders. Specifically, in the standard cylinder, a theoretical air-fuel ratio with an air amount of 100 and a fuel amount of 10 is realized, whereas in a variation cylinder, the fuel amount is 10 but the air amount becomes 110. It shall be.

  As shown in the graph of FIG. 5, in this case, due to the difference in the amount of air in the cylinder, the in-cylinder pressure of the variation cylinder is higher than the in-cylinder pressure of the standard cylinder in the compression stroke, that is, before the heat generation rate rises. Get higher. By capturing this feature, the type variation shown in FIG. 5 can be detected. That is, before the heat generation rate rises, if there is a cylinder having a higher in-cylinder pressure than other cylinders, it can be determined that the air amount in that cylinder is greater than the other. Then, after the next cycle, the air amount of all the cylinders can be made uniform by correcting the air amount of the variation cylinders to be smaller than the present amount.

  FIG. 6 shows a case where the fuel amount of only one cylinder is smaller than that of the other cylinders. Specifically, in the standard cylinder, a theoretical air-fuel ratio with an air amount of 100 and a fuel amount of 10 is realized, whereas in a variation cylinder, the air amount is also 100, but the fuel amount becomes 9. It shall be.

  As shown in the graph of FIG. 6, in this case, the amount of air in the cylinder is the same in each cylinder. Therefore, the in-cylinder pressure before the heat generation rate rises differs between the variation cylinder and the standard cylinder. Absent. On the other hand, due to the difference in the fuel amount, the heat generation rate of the variation cylinder is lower than the heat generation rate of the standard cylinder. Due to this difference in heat generation rate, after the heat generation rate rises, the in-cylinder pressure of the variation cylinder becomes lower than the in-cylinder pressure of the standard cylinder. By capturing such characteristics, it is possible to detect variations in the types shown in FIG. That is, there is no variation in the in-cylinder pressure of each cylinder before the heat generation rate rises, and there is a cylinder whose heat generation rate and in-cylinder pressure are lower than other cylinders after the heat generation rate rises. Can be determined that the amount of fuel in the cylinder is smaller than the others. Then, after the next cycle, the fuel amount of all the cylinders can be made uniform by performing correction so that the fuel amount of the variation cylinder is larger than the current amount.

  FIG. 7 shows a case where the fuel amount of only one cylinder is larger than that of the other cylinders. Specifically, in the standard cylinder, a theoretical air-fuel ratio with an air amount of 100 and a fuel amount of 10 is realized, whereas in a variation cylinder, the air amount is also 100, but the fuel amount becomes 11. It shall be.

  As shown in the graph of FIG. 7, in this case, the amount of air in the cylinder is the same in each cylinder. Therefore, the in-cylinder pressure before the heat generation rate rises differs between the variation cylinder and the standard cylinder. Absent. On the other hand, due to the difference in the fuel amount, the heat generation rate of the variation cylinder becomes higher than the heat generation rate of the standard cylinder. Due to this difference in heat generation rate, after the heat generation rate rises, the in-cylinder pressure of the variation cylinder becomes higher than the in-cylinder pressure of the standard cylinder. By capturing such a feature, it is possible to detect the type variation shown in FIG. That is, there is no variation in the in-cylinder pressure of each cylinder before the heat generation rate rises, and there is a cylinder whose heat generation rate and in-cylinder pressure are higher than those of other cylinders after the heat generation rate rises. Can be determined that the amount of fuel in the cylinder is larger than the others. Then, after the next cycle, the fuel amount of all the cylinders can be made uniform by performing correction so that the fuel amount of the variation cylinder is made smaller than the current amount.

[Specific Processing in Second Embodiment]
FIG. 8 is a flowchart of a routine executed by the ECU 50 in the present embodiment in order to realize the above function. Note that this routine is repeatedly executed for each cycle of the internal combustion engine 10 as a whole in synchronization with the crank angle.

  According to the routine shown in FIG. 8, first, the in-cylinder pressure P after the closing time of the intake valve 38 of each cylinder is measured based on the output of the in-cylinder pressure sensor 17 (step 120). Specifically, for each cylinder, the output of the in-cylinder pressure sensor 17 of the cylinder is taken at a predetermined crank angle interval after the timing at which the intake valve 38 of the cylinder is closed. Here, the “predetermined crank angle interval” is assumed to be 1 ° CA.

  Next, the heat generation rate of each cylinder is calculated (step 122). Specifically, the heat release rate for each 1 ° CA is calculated for each cylinder by substituting the value of the in-cylinder pressure P for each 1 ° CA acquired in step 120 in the above equation (1). The

  Through the processing in steps 120 and 122, a history of the in-cylinder pressure and the heat generation rate with respect to the crank angle as shown in the graphs of FIGS. 4 to 7 can be acquired for each cylinder.

  In the routine shown in FIG. 8, it is next determined whether or not there is a variation among cylinders in the cylinder pressure before the heat generation rate rises (step 124). As a specific determination method here, for example, the in-cylinder pressure value of the cylinder having the lowest in-cylinder pressure and the in-cylinder pressure of the other cylinders at one or a plurality of crank angles before the heat generation rate rises. It is possible to determine whether the difference is larger than a predetermined determination value by comparing with the average value.

  As a result of the determination in step 124, when it is determined that the in-cylinder pressure before one heat generation rate rises is significantly lower in one cylinder than in the other cylinders, this corresponds to the case shown in FIG. Therefore, in this case, it is determined that the cylinder has less air than the other cylinders (step 126). In this case, in order to eliminate the variation in the air amount, the air amount of the cylinder is corrected to be increased after the next cycle (step 128). The increase correction of the air amount can be performed by increasing the opening of the throttle valve dedicated to the cylinder or by increasing the operating angle and the lift amount of the intake valve 38 of the cylinder. The width of the increase correction may be changed according to the deviation width of the in-cylinder pressure of the cylinder, or may be a constant width.

  Conversely, if it is determined in step 124 that the in-cylinder pressure before one heat generation rate rises is significantly higher in one cylinder than in the other cylinders, the case shown in FIG. Equivalent to. Therefore, in this case, it is determined that the cylinder has a larger amount of air than the other cylinders (step 130). In this case, in order to eliminate the variation in the air amount, the air amount of the cylinder is corrected to decrease after the next cycle (step 132). Specifically, after the next cycle, the opening of the throttle valve dedicated to the cylinder or the operating angle and lift amount of the intake valve 38 of the cylinder are corrected to be small.

  On the other hand, if it is determined as a result of the determination in step 124 that there is no significant variation among the cylinders regarding the in-cylinder pressure before the heat generation rate rises, then the heat generation rate varies among the cylinders. Is determined (step 134). As a specific determination method here, for example, the peak value of the heat generation rate of the cylinder having the lowest heat generation rate is compared with the average value of the peak of the heat generation rate of the other cylinders, and the difference between them is predetermined. It can be determined by whether or not it is larger than the determination value.

  If it is determined in step 134 that one cylinder has a significantly lower heat generation rate than the other cylinders, this corresponds to the case shown in FIG. Therefore, in this case, it is determined that the amount of fuel in the cylinder is smaller than that in the other cylinders (step 136). In this case, in order to eliminate this variation in the fuel amount, the fuel amount of the cylinder is corrected to increase after the next cycle (step 138). The width of this increase correction may be changed according to the deviation of the heat generation rate of the cylinder, or may be a constant width.

  On the other hand, if it is determined in step 134 that there is no significant variation among the cylinders in the heat generation rate, it can be determined that there is no variation in the fuel amount of each cylinder. In this case, it is not necessary to correct the fuel amount of each cylinder, and since it has been confirmed that there is no variation in the air amount of each cylinder, it is not necessary to correct the air amount of each cylinder. That is, in this case, it can be determined that neither the air amount nor the fuel amount has variations between cylinders. Therefore, in this case, the current processing cycle is terminated as it is.

  As described above, in the present embodiment, the variation in the air amount and the fuel amount between the cylinders can be detected with a simple processing method and with high accuracy. Then, by correcting the air amount and the fuel amount for each cylinder based on the detected inter-cylinder variation, the air-fuel ratio and the combustion pressure variation among the cylinders can be reduced as much as possible, and all the cylinders can be made uniform. For this reason, it is possible to effectively prevent adverse effects caused by variations in the air-fuel ratio and the combustion pressure between cylinders, such as adverse effects such as torque fluctuation, fuel consumption deterioration, and exhaust emission increase.

  In the second embodiment described above, the in-cylinder pressure sensor 18 corresponds to the “in-cylinder pressure detecting means” in the fifth aspect of the present invention. Further, the ECU 50 executes the processing of steps 120 and 122 so that the “heat generation rate calculating means” in the fifth aspect of the invention executes the processing of steps 124, 126, 130, 134, 136 and 140. As a result, the “inter-cylinder variation detecting means” in the fifth invention realizes the “variation correcting means” in the fifth invention by executing the processing of steps 128, 132, 138 and 142, respectively. Yes.

  In the second embodiment described above, the ECU 50 executes the process of step 126, so that the “first air amount variation determining means” in the sixth aspect of the invention executes the process of step 130. As a result, the “second air amount variation determining means” in the sixth aspect of the present invention executes the processing of step 136 so that the “first fuel amount variation determining means” of the seventh aspect of the present invention is the above step. By executing the process 140, the “second fuel amount variation determining means” in the seventh aspect of the invention is realized.

It is a figure for demonstrating the system configuration | structure of Embodiment 1 of this invention. 6 is a graph showing the relationship among in-cylinder pressure P, heat generation rate dQ / dθ, and heat generation amount Q in a compression stroke and an explosion stroke. It is a flowchart of the routine performed in Embodiment 1 of the present invention. In Embodiment 2 of this invention, it is a figure for demonstrating the method to determine the dispersion | variation in the air quantity between cylinders. In Embodiment 2 of this invention, it is a figure for demonstrating the method to determine the dispersion | variation in the air quantity between cylinders. In Embodiment 2 of this invention, it is a figure for demonstrating the method to determine the dispersion | variation in the amount of fuel between cylinders. In Embodiment 2 of this invention, it is a figure for demonstrating the method to determine the dispersion | variation in the amount of fuel between cylinders. It is a flowchart of the routine performed in Embodiment 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Crank angle sensor 17 In-cylinder temperature sensor 18 In-cylinder pressure sensor 28 Fuel injection valve 30 Spark plug 33 Air-fuel ratio sensor 34 Catalyst 36 Variable valve mechanism 40 Sensor 50 ECU (Electronic Control Unit)

Claims (7)

In-cylinder pressure detecting means for detecting the in-cylinder pressure of the cylinder;
In-cylinder temperature acquisition means for detecting or estimating the in-cylinder temperature;
An air amount calculating means for calculating the in-cylinder air amount in accordance with the gas state equation based on the in-cylinder pressure and the in-cylinder temperature at the time of closing the intake valve;
Fuel amount calculation means for calculating the amount of fuel supplied into the cylinder based on the history of in-cylinder pressure during the combustion period;
Air-fuel ratio calculating means for calculating the air-fuel ratio of the air-fuel mixture burned in the cylinder based on the cylinder air amount and the fuel amount;
An air-fuel ratio control apparatus for an internal combustion engine, comprising: The fuel amount calculating means includes
Based on the in-cylinder pressure value, heat generation rate calculating means for calculating the heat generation rate in the cylinder,
A heat generation amount calculating means for calculating a heat generation amount in a cylinder by integrating the heat generation rate over a combustion period;
The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, comprising:   3. The internal combustion engine air conditioner according to claim 1, further comprising control means for controlling the fuel injection amount and / or the cylinder intake air amount based on the air-fuel ratio calculated by the air-fuel ratio calculating means. Fuel ratio control device.   The said air quantity calculation means contains the gas constant correction | amendment means which correct | amends the value of the gas constant in the said state equation of gas according to the amount of residual gas in a cylinder, The any one of Claim 1 thru | or 3 characterized by the above-mentioned. 2. An air-fuel ratio control device for an internal combustion engine according to the item. An apparatus for controlling an air-fuel ratio of an internal combustion engine having a plurality of cylinders and capable of individually adjusting the intake air amount of each cylinder,
In-cylinder pressure detecting means for detecting the in-cylinder pressure of each cylinder;
A heat generation rate calculating means for calculating a heat generation rate in each cylinder based on the in-cylinder pressure value of each cylinder;
Inter-cylinder variation detection means for detecting the variation in the cylinder air amount and / or the amount of fuel in the cylinder by comparing the in-cylinder pressure and the heat generation rate between the cylinders after the intake valve is closed,
Variation correcting means for correcting the in-cylinder air amount and / or the in-cylinder fuel amount so as to eliminate the variation among the cylinders;
An air-fuel ratio control apparatus for an internal combustion engine, comprising: The inter-cylinder variation detecting means includes
First air amount variation determination that determines that the in-cylinder air amount of one cylinder is less than that of the other cylinder when the in-cylinder pressure of the one cylinder before the rise of the heat generation rate is lower than the other cylinders Means,
Second air amount variation determination for determining that the in-cylinder air amount of one cylinder is greater than that of the other cylinder when the in-cylinder pressure of the one cylinder before the rise of the heat generation rate is higher than that of the other cylinders Means,
The air-fuel ratio control apparatus for an internal combustion engine according to claim 5, comprising: The inter-cylinder variation detecting means includes
When the in-cylinder pressure before the rise of the heat generation rate is not significantly different between the cylinders and the heat generation rate of one cylinder is lower than that of the other cylinders, the in-cylinder fuel amount of the one cylinder is First fuel amount variation determination means for determining that there are fewer than other cylinders;
When the in-cylinder pressure before the rise of the heat generation rate is not significantly different among the cylinders and the heat generation rate of one cylinder is higher than that of the other cylinders, the in-cylinder fuel amount of the one cylinder is Second fuel amount variation determining means for determining that there are more than other cylinders;
The air-fuel ratio control apparatus for an internal combustion engine according to claim 5 or 6, characterized by comprising:

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