JP2012180817A - Device for calculating air-fuel ratio of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device for calculating an air-fuel ratio of an internal combustion engine that calculates the air-fuel ratio with high accuracy, in consideration of an effect of a characteristic change on a fuel rich side.SOLUTION: A heating value Q generated by combustion of fuel injected into a cylinder reaches the maximum around the theoretical air-fuel ratio, and decreases on both sides thereof. As a result, as showing A and B in the figure, when an evaluated heating value Q is Q, the air-fuel ratio is uncertain whether it is a value (A) on the fuel rich side or a value (B) on a fuel lean side. An amount of fuel required in the cylinder is then increased, and the air-fuel ratio is determined whether on the fuel lean side or the fuel rich side by slope of ΔQ(=Q-Q) before and after the increase.

Description

  The present invention relates to an air-fuel ratio calculation apparatus for an internal combustion engine, and more particularly to an air-fuel ratio calculation apparatus for an internal combustion engine that calculates an air-fuel ratio using in-cylinder pressure.

  Conventionally, for example, in Patent Document 1, combustion is performed in a cylinder using an in-cylinder intake air amount calculated from the in-cylinder pressure and the in-cylinder temperature at the time of closing the intake valve and a calorific value calculated using the in-cylinder pressure. An air-fuel ratio calculating device for calculating the air-fuel ratio of the air-fuel mixture is disclosed. In this air-fuel ratio calculation device, specifically, the heat generation rate in the cylinder is calculated from the in-cylinder pressure, and then the heat generation rate is obtained by integrating the heat generation rate over the combustion period, By subtracting the latent heat necessary for evaporation of moisture etc. contained in the fuel from this calorific value, the amount of fuel supplied in the cylinder is obtained, and finally, the amount of fuel supplied in the cylinder is divided by the amount of intake air in the cylinder. The air-fuel ratio is calculated.

  Further, for example, Patent Document 2 shows the relationship between the air-fuel ratio of the air-fuel mixture burned in the cylinder and the calorific value. Specifically, when the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, the heat generation amount decreases as the fuel leans. On the other hand, when the air-fuel ratio is richer than the stoichiometric air-fuel ratio, even if the air-fuel ratio changes. It is said that the calorific value hardly changes.

JP 2007-120392 A JP 2006-144643 A

  However, the actual relationship between the air-fuel ratio and the calorific value is different from the relationship shown in Patent Document 2. That is, the amount of heat generation decreases as the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio. This is because if the amount of fuel increases, the combustion deteriorates and more latent heat of vaporization is required. Therefore, the relationship between the calorific value and the air-fuel ratio is expressed by a characteristic curve having a peak, so the calorific value on the fuel lean side may be equal to the calorific value on the fuel rich side. Therefore, when trying to obtain the air-fuel ratio from the calorific value according to the method of Patent Document 1 based on such a relationship, it is calculated as the lean-side air-fuel ratio even though it is actually the rich-side air-fuel ratio. There was a possibility.

  The present invention has been made to solve the above-described problems. That is, an object of the present invention is to provide an air-fuel ratio calculation apparatus for an internal combustion engine that can calculate the air-fuel ratio with high accuracy in consideration of the effect of characteristic changes on the fuel rich side.

In order to achieve the above object, a first invention is an air-fuel ratio calculation apparatus for an internal combustion engine,
In-cylinder pressure acquisition means for acquiring the in-cylinder pressure of the internal combustion engine;
Using the in-cylinder pressure, heat generation rate calculating means for calculating the heat generation rate in the cylinder,
Fuel amount changing means for forcibly changing the in-cylinder required fuel amount of the internal combustion engine;
Using the heat generation rate in the cycle before and after the forced change of the in-cylinder required fuel amount, the air-fuel ratio of the air-fuel mixture burned in the cylinder is on the fuel rich side or on the fuel lean side with respect to the stoichiometric air fuel ratio. An air-fuel ratio region determining means for determining whether there is,
It is characterized by providing.

According to a second invention, in the first invention,
The calorific value obtained from the heat generation rate when the in-cylinder required fuel amount is not changed corresponds to an output air-fuel ratio that generates the maximum output of the internal combustion engine when the in-cylinder required fuel amount is supplied. If it is smaller than this, forcible change of the in-cylinder required fuel amount is prohibited.

According to a third invention, in the first or second invention,
The fuel amount changing means switches fuel increase and fuel decrease as a forced change of the in-cylinder required fuel amount for each cycle,
The air-fuel ratio region determining means uses a heat generation history obtained from the heat generation rate at the time of fuel increase and a heat generation history obtained from the heat generation rate at the time of fuel reduction to generate It is determined whether the air-fuel ratio of the burned air-fuel mixture is on the fuel rich side or the fuel lean side with respect to the stoichiometric air fuel ratio.

A fourth invention is any one of the first to third inventions,
The internal combustion engine has a plurality of cylinders;
The fuel amount changing means reverses fuel increase and fuel decrease as a forced change of the in-cylinder required fuel amount in one cycle between adjacent cylinders.

  According to the first invention, whether the air-fuel ratio is on the fuel-rich side or the fuel-lean side with respect to the stoichiometric air-fuel ratio, using the heat generation rate in the cycle before and after the forced change of the in-cylinder required fuel amount. Can be determined. When the air-fuel ratio in a certain cycle is on the fuel lean side with respect to the stoichiometric air-fuel ratio, if the in-cylinder required fuel amount is forcibly increased, the heat generation rate will increase by the amount of fuel in the next cycle, and the in-cylinder required fuel will increase. If the amount is forcibly reduced, the heat generation rate is reduced by the amount of fuel. On the other hand, if the air-fuel ratio in a certain cycle is fuel richer than the stoichiometric air-fuel ratio, if the in-cylinder required fuel amount is forcibly increased, the heat generation rate will decrease in the next cycle due to combustion deterioration, etc. If the amount is forcibly reduced, the effect of combustion deterioration is alleviated by the amount of fuel reduction, so the heat generation rate increases. Therefore, if the heat generation rate in the cycle before and after the forced change of the in-cylinder required fuel amount is used, the air-fuel ratio can be calculated with high accuracy in consideration of the influence of the combustion characteristic change on the fuel rich side.

  According to the second invention, when the calorific value obtained from the heat generation rate when the in-cylinder required fuel amount is not changed is smaller than the calorific value corresponding to the output air-fuel ratio, the in-cylinder required fuel amount is changed. Can be prohibited. Since the fuel exceeding the output air-fuel ratio does not contribute to the calorific value in principle, if the calorific value corresponding to the output air-fuel ratio is smaller than the calorific value on the fuel lean side, the calorific value on the fuel rich side will not be equal. Absent. Therefore, the processing burden required for determining the air-fuel ratio range can be reduced.

  If the required amount of fuel in the cylinder is forcibly changed, torque fluctuations may occur. If the amount of change in the fuel is reduced to suppress this torque fluctuation, the sensitivity of the in-cylinder pressure acquired from the in-cylinder pressure acquisition means will be reduced accordingly. To do. In this regard, according to the third aspect of the invention, since the history of the calorific value obtained from the heat generation rate at the time of fuel increase and the history of the calorific value obtained from the heat generation rate at the time of fuel reduction are used, the change amount of fuel A decrease in the sensitivity of the in-cylinder pressure due to a small amount of can be compensated. Accordingly, the calculation accuracy of the calorific value can be ensured, and it can be determined with high accuracy whether the air-fuel ratio is on the fuel rich side or the fuel lean side with respect to the stoichiometric air-fuel ratio.

  As described above, torque fluctuation may occur when the in-cylinder required fuel amount is forcibly changed. In this regard, according to the fourth aspect of the present invention, the amount of fuel required for in-cylinder in one cycle is forcibly changed, and the fuel increase and decrease are reversed between adjacent cylinders, so torque fluctuation in one cycle is reduced. Can do.

2 is a diagram for describing a system configuration according to Embodiment 1. FIG. It is a graph which shows the relationship between the cylinder pressure P and the emitted-heat amount Q in a compression process and an explosion process. It is the graph which showed the correlation with the emitted-heat amount Q and an air fuel ratio. FIG. 5 is a diagram showing an example of air-fuel ratio range determination control in the first embodiment. 3 is a flowchart showing air-fuel ratio range determination control executed by an ECU 50 in the first embodiment. It is the graph which showed the correlation with combustion speed FS and an air fuel ratio. It is a figure for demonstrating the combustion speed FS. A specific example of air-fuel ratio range determination control in the second embodiment is shown. FIG. 10 is a diagram showing an example of changing the fuel to be injected in the air-fuel ratio range determination control in the second embodiment.

Embodiment 1 FIG.
[Description of system configuration]
Hereinafter, Embodiment 1 of the present invention will be described with reference to FIGS. FIG. 1 is a diagram for explaining a system configuration according to the first embodiment of the present invention. The system according to the present embodiment includes an engine 10 as an internal combustion engine. The engine 10 is an in-line four-cylinder engine (explosion order is # 1 → # 3 → # 4 → # 2). FIG. 1 shows only the cylinder 12 as one of the cylinders.

  The engine 10 includes a cylinder block 16 having a piston 14 therein. The piston 14 is connected to the crankshaft 18 via a crank mechanism. A crank angle sensor 20 is provided in the vicinity of the crankshaft 18. The crank angle sensor 20 is configured to detect the rotation angle (crank angle) of the crankshaft 18.

  A cylinder head 22 is assembled to the upper part of the cylinder block 16. A space from the upper surface of the piston 14 to the cylinder head 22 forms a combustion chamber 24. The cylinder head 22 is provided with an in-cylinder pressure sensor 26 that detects a pressure in the combustion chamber 24 (hereinafter referred to as “in-cylinder pressure P”). The cylinder head 22 is provided with an electronically controlled injector 28 that directly injects fuel into the combustion chamber 24. The cylinder head 22 is provided with a spark plug 30 that ignites the air-fuel mixture in the combustion chamber 24.

  The cylinder head 22 includes an intake port 32 that communicates with the combustion chamber 24. An intake valve 34 is provided at a connection portion between the intake port 32 and the combustion chamber 24. The intake valve 34 is driven by a variable valve timing mechanism (hereinafter referred to as “VVT mechanism”) 36. The VVT mechanism 36 is configured to be able to change the valve opening timing of the intake valve 34. More specifically, the VVT mechanism 36 is configured to be able to change the valve opening phase, the operating angle, and the lift amount of the intake valve 34 in the range from the most advanced angle to the most retarded angle determined by the structure of the mechanism. A sensor 37 that detects the operation amount of the VVT mechanism 36 is provided in the vicinity of the VVT mechanism 36. An air flow meter 38 is provided upstream of the intake port 32. The air flow meter 38 is configured to detect the intake air amount.

  The cylinder head 22 includes an exhaust port 40 that communicates with the combustion chamber 24. An exhaust valve 42 is provided at a connection portion between the exhaust port 40 and the combustion chamber 24. The exhaust valve 42 is driven by the VVT mechanism 44. Similar to the VVT mechanism 36, the VVT mechanism 44 is configured to be able to change the valve opening phase, the operating angle, and the lift amount of the exhaust valve 42. A sensor 45 that detects the operation amount of the VVT mechanism 44 is provided in the vicinity of the VVT mechanism 44. A catalyst 46 for purifying exhaust gas is disposed downstream of the exhaust port 40.

  Further, the system of the present embodiment includes an ECU (Electronic Control Unit) 50 as a control device. An injector 28, a spark plug 30, VVT mechanisms 36, 44, and the like are connected to the output side of the ECU 50. A crank angle sensor 20, an in-cylinder pressure sensor 26, an air flow meter 38, sensors 37 and 45, and the like are connected to the input side of the ECU 50. The ECU 50 can control various actuators such as the injector 28, the spark plug 30, and the VVT mechanisms 36 and 44 based on these sensor signals.

[Air-fuel ratio calculation using in-cylinder pressure P]
By the way, in the present embodiment, the calorific value Q in the cylinder is calculated from the in-cylinder pressure P detected by the in-cylinder pressure sensor 26 for each cycle, and the air-fuel ratio of the burned mixture is calculated based on the calorific value Q. (A / F) is calculated. This A / F calculation method will be described with reference to FIG. FIG. 2 is a graph showing the relationship between the in-cylinder pressure P and the calorific value Q in the compression stroke and the explosion stroke.

  As shown in the upper part of FIG. 2, after the intake valve (In valve) 36 is closed, the cylinder pressure is increased because the cylinder gas is compressed as the piston 14 is raised. When the air-fuel mixture in the cylinder is ignited slightly before the top dead center TDC, the in-cylinder pressure P rapidly increases due to the combustion of the fuel and reaches a maximum value, and thereafter decreases as the piston 14 descends. . The calorific value Q is generated by the combustion of the fuel injected into the cylinder. Therefore, as shown in the lower part of FIG. 2, the calorific value Q continues to increase while the combustion continues, and becomes constant when the combustion ends. At the end of combustion, the calorific value Q takes a maximum value.

Here, from the thermodynamic relational expression established in the cylinder, the following expression (1) is established between the heat generation rate dQ and the cylinder pressure P at a certain crank angle during the combustion period.
dQ = W + dU
= PdV + nC _V dT
= PdV + (1 / κ-1) d (PV)
= (1 / κ-1) (κPdV + VdP)
= {1 / (κ-1) V ^κ-1 } d (PV ^κ ) (1)
In the above formula (1), V is the in-cylinder volume and is a value determined geometrically according to the crank angle. Κ is the specific heat ratio (constant) of the in-cylinder gas.

Here, the heat generation amount Q is a value obtained by integrating the heat generation rate dQ from when the intake valve 34 is closed to when the exhaust valve 42 is opened, and can be approximated to an integrated value of the heat generation rate dQ in this section. Therefore, the relationship of the following formula (2) is established between the in-cylinder pressure P and the heat generation amount Q.
Q = {1 / (κ-1)} Σ {Δ (PV ^κ ) / V ^κ-1 } (2)
Therefore, if the in-cylinder pressure P for each crank angle is known, the calorific value Q can be obtained using the above equation (2).

Here, if the lower heating value Q _lhv (constant) is _used as the heating value per 1 g of fuel and the intake air amount g _a sucked into the cylinder when the intake valve 34 is closed, the air-fuel ratio is expressed by the following formula ( 3).
_{A / F = (g a /} Q) Q lhv ··· (3)
Therefore, if the intake air amount g _a when the intake valve 34 is closed is known in addition to the calorific value Q obtained using the above equation (2), the air-fuel ratio can be obtained using the above equation (3). .

[Features of Embodiment 1]
FIG. 3 is a graph showing the correlation between the calorific value Q obtained using the above equation (2) and the air-fuel ratio. As shown in FIG. 3, the calorific value Q becomes maximum near the theoretical air-fuel ratio (14.7) and decreases on both sides thereof. Assuming that the intake air amount g _a is constant, the heat generation amount Q decreases if the amount of fuel injected into the cylinder is small, and therefore the heat generation amount Q decreases on the fuel lean side. On the other hand, the calorific value Q also decreases on the fuel rich side. This is because when the amount of fuel injected into the cylinder increases, the combustion deteriorates and more latent heat of vaporization is required. Accordingly, as indicated by A, B in FIG. 3, if the value of the calorific value Q obtained is Q _1, no longer know the air-fuel ratio is on the fuel-rich side value (A) or fuel-lean side of the value (B) End up.

Since the calorific value Q is generated by the combustion of the fuel injected into the cylinder as described above, it is the output air-fuel ratio (the air-fuel ratio at which the engine can generate the largest output). For example, fuel exceeding 12.5) does not contribute to the calorific value Q in principle. Therefore, in the fuel-rich side, the value of the calorific value Q is less than Q ₂ in FIG. 3, there is no above such problems. From the above, in this embodiment, if the value of the calorific value Q is Q ₂ or more 3, forcibly changing the amount of fuel injected into the cylinder, the formula at that time (2 ) To determine which region the air-fuel ratio is in from the change characteristics of the calorific value Q obtained from (Air-fuel ratio region determination control).

  This air-fuel ratio range determination control is a fuel amount calculated based on the intake air amount, engine speed, engine coolant temperature, etc. in the fuel injection control that is being performed separately (hereinafter referred to as “in-cylinder required fuel amount”). Is forcibly increased or decreased. Here, the amount of fuel to be increased or decreased is set in advance within a range of ± 10% to ± 100% of the in-cylinder required fuel amount.

FIG. 4 is a diagram showing an example of air-fuel ratio range determination control in the present embodiment. In the present embodiment, as shown in each upper stage of FIGS. 4A to 4C, the amount of fuel injected into the cylinder is forcibly increased. If it does so, as shown to each middle stage of the figure (A)-(C), calorific value Q will change to three kinds with the forced increase of fuel. Among these, as shown in the lower part of FIG. 4 (A), when the slope of ΔQ (= Q _after −Q _before ) _{before and after the} increase is positive, the air-fuel ratio becomes the fuel lean side according to the explanation of FIG. It can be judged that. On the other hand, as shown in the lower part of FIG. 4B, when the slope of ΔQ before and after the increase is negative, it can be determined that the air-fuel ratio is on the fuel rich side. Further, as shown in the lower part of FIG. 4C, when ΔQ does not change before and after the increase, it can be determined that the air-fuel ratio is the output air-fuel ratio.

  When the amount of fuel injected into the cylinder is forcibly reduced, the inclination of ΔQ before and after the decrease is determined to be opposite to the inclination of ΔQ before and after the increase. That is, when ΔQ becomes negative, it can be determined that the air-fuel ratio is on the fuel lean side, and when the slope of ΔQ is positive, it can be determined that the air-fuel ratio is on the fuel rich side. When ΔQ does not change before and after the increase, it can be determined that the air-fuel ratio is the output air-fuel ratio, similar to ΔQ before and after the increase.

[Specific Processing in Embodiment 1]
Next, a specific process for realizing the above-described air-fuel ratio range determination control will be described with reference to FIG. FIG. 5 is a flowchart showing air-fuel ratio range determination control executed by the ECU 50 in the present embodiment. Note that the routine shown in FIG. 5 is periodically and repeatedly executed when the engine 10 is in operation.

In the routine shown in FIG. 5, first, ECU 50 is the calorific value Q is equal to or _{Q 2} or more (step 100). In the process of this step, the ECU 50 first calculates the calorific value Q. Specifically, ECU 50 obtains the detected value of the air flow meter 38, based on the detected value, to calculate the intake air amount g _a at time of closing of the intake valve 34. At the same time, the ECU 50 acquires the in-cylinder pressure P from when the intake valve 34 is closed to when the exhaust valve 42 is opened. In the present embodiment, the in-cylinder pressure P is acquired, for example, every 1 ° crank angle from when the intake valve 34 is closed to when the exhaust valve 42 is opened. Note that the closing timing of the intake valve 34 and the opening timing of the exhaust valve 42 are grasped based on the operation amounts of the VVT mechanisms 36 and 44 detected by the sensors 37 and 45, respectively. The ECU 50 calculates the calculated intake air amount g _a , the acquired in-cylinder pressure P, the in-cylinder volume V determined for each crank angle, and κ (a constant value) stored in the ECU 50 in advance by the above formula. are substituted into (2) to calculate the calorific value Q, it is compared with Q _2. Here, Q ₂ corresponds to the threshold described in FIG. 3, and is stored in advance in the ECU50 on determined for each the required fuel quantity cylinder.

In step 100, when the calorific value Q is determined to be smaller than Q ₂ are the air-fuel ratio is the value of the fuel-lean side, so further processing can be judged to be unnecessary, ECU 50 ends the present routine To do. On the other hand, when the calorific value Q is determined to be Q ₂ or more, ECU 50 forcibly increasing the amount of fuel injected into the cylinder (Step 110). Here, as the fuel value to be increased, a value stored in the ECU 50 in advance is used.

Subsequently, the ECU 50 calculates ΔQ from the heat generation amount Q before and after the increase of the injection amount (step 120). In this step, the value calculated in step 100 is used as the heat generation amount Q _before before the injection amount is increased. Further, the calorific value Q _after after the increase in the injection amount is calculated by the same processing as in Step 100. Then, ΔQ is calculated by obtaining these differences.

  Subsequently, the ECU 50 determines whether or not the absolute value of ΔQ calculated in step 120 is equal to or less than a threshold value (step 130). In this step, a value stored in advance in the ECU 50 is used as the threshold value, which is 0 or 0 including a predetermined error. If it is determined that the absolute value of ΔQ is equal to or less than the threshold value, it can be determined that the air-fuel ratio is the output air-fuel ratio (step 140).

  On the other hand, when it is determined that the absolute value of ΔQ is larger than the threshold value, it is determined whether ΔQ is a positive value or a negative value (step 150). When it is determined that ΔQ is a positive value, the air-fuel ratio is a value on the fuel lean side (step 160), and when it is determined that ΔQ is a negative value, the air-fuel ratio is It can be determined that the value is on the fuel rich side (step 170).

As described above, according to the routine shown in FIG. 5, it is possible to determine whether the air-fuel ratio is in the fuel rich side (including the output air-fuel ratio) or the fuel lean side using the calculated ΔQ. Therefore, the air-fuel ratio can be calculated with high accuracy. Further, according to the routine shown in FIG. 5, ΔQ is calculated when the calorific value Q is equal to or greater than Q _2, so that the processing load on the ECU 50 due to the calculation of ΔQ when less than Q ₂ can be reduced.

  In the first embodiment described above, the calorific value Q is used in the air-fuel ratio region determination control, but the combustion rate FS may be used instead of the calorific value Q. The combustion speed FS has a correlation with the air-fuel ratio, and as shown in FIG. 6, the tendency of the combustion speed FS with respect to the air-fuel ratio shows the same tendency as the calorific value Q with respect to the air-fuel ratio. Further, as shown in FIG. 7, the combustion speed FS can be expressed as a change amount of the heat generation amount Q (that is, a heat generation rate dQ) from after the fuel ignition to when the exhaust valve 42 is opened. Therefore, the air-fuel ratio range can be determined in the same manner as in the present embodiment by using the difference in the amount of change in the calorific value Q before and after the forced change of the injected fuel. Thus, as long as the air-fuel ratio range determination control is executed using the heat generation rate dQ, the present embodiment can be applied as a modification of the present embodiment.

  In the first embodiment described above, the in-cylinder pressure sensor 26 corresponds to the “in-cylinder pressure acquisition means” in the first invention. In the first embodiment described above, the ECU 50 calculates the heat generation amount Q in the process of step 100 of FIG. 5 so that the “heat generation rate calculating means” in the first aspect of the present invention is the same as step 110 of FIG. By executing the process, the “fuel amount changing means” in the first invention performs the series of processes in steps 130 to 170 in FIG. Each is realized.

Embodiment 2. FIG.
[Features of Embodiment 2]
Next, a second embodiment of the present invention will be described with reference to FIGS. As described in the first embodiment, the air-fuel ratio region determination control forcibly changes the amount of fuel injected into the cylinder. Therefore, there is a high possibility that torque fluctuation will occur. However, if the change amount of the fuel injected at the time of forced change is reduced in order to reduce the torque fluctuation, the S / N of the in-cylinder pressure P detected by the in-cylinder pressure sensor 26 is deteriorated, and the calorific value Q is calculated accurately. It will be lower.

  Therefore, in the present embodiment, the fuel amount is forcibly changed a plurality of times, and the determination of the air-fuel ratio region is executed after the ΔQ data is accumulated. Specifically, as shown in FIG. 8, ΔQ data is accumulated for each cylinder by distinguishing between when the fuel is increasing and when the fuel is decreasing (for example, 10 times when increasing and decreasing, 10 times when decreasing and a total of 20 times). In other words, it is determined in which region the air-fuel ratio is based on the average value of each data. Thereby, since the deterioration of the S / N of the in-cylinder pressure P caused by reducing the change amount of the injected fuel can be compensated, the calculation accuracy of the calorific value Q can be ensured.

  Further, in the present embodiment, the amount of fuel injected at the time of forced change is finely changed. The amount of fuel injected into the cylinder is controlled by the energization time of the solenoid coil of the injector 28. In the present embodiment, at the time of forced change, the energization time is subdivided to inject while finely varying the amount of fuel injected into the cylinder. As a result, it is possible to perform air-fuel ratio range determination control at a high frequency (for example, about 30 Hz) where the driver cannot sense torque fluctuation.

  Furthermore, in the present embodiment, as shown in FIG. 9, the increase / decrease of fuel is switched between cycles in the same cylinder. If the fuel amount is continuously changed in the same direction (increase or decrease) in the same cylinder, the exhaust air-fuel ratio region is biased to one side, so that the purification ability of the catalyst 46 may decrease. In this respect, if the increase / decrease of the fuel is switched between cycles, a decrease in the purification ability of the catalyst 46 can be suppressed, so that the exhaust emission can be prevented from deteriorating.

  In addition, in this embodiment, as shown in the figure, the increase / decrease in fuel is reversed between adjacent cylinders in one cycle. Thereby, torque fluctuation in one cycle can be reduced. Further, if the increase / decrease in fuel between the adjacent cylinders is reversed, the exhaust air / fuel ratio region will not be biased to one side, so that a decrease in the purification ability of the catalyst 46 can be suppressed and deterioration of exhaust emissions can be prevented.

DESCRIPTION OF SYMBOLS 10 Engine 12 Cylinder 14 Piston 16 Cylinder block 18 Crankshaft 20 Crank angle sensor 22 Cylinder head 24 Combustion chamber 26 In-cylinder pressure sensor 28 Injector 30 Spark plug 32 Intake port 34 Intake valve 36, 44 VVT mechanism 37, 45 Sensor 38 Air flow meter 40 Exhaust port 42 Exhaust valve 46 Catalyst 50 ECU

Claims (4)

In-cylinder pressure acquisition means for acquiring the in-cylinder pressure of the internal combustion engine;
Using the in-cylinder pressure, heat generation rate calculating means for calculating the heat generation rate in the cylinder,
Fuel amount changing means for forcibly changing the in-cylinder required fuel amount of the internal combustion engine;
Using the heat generation rate in the cycle before and after the forced change of the in-cylinder required fuel amount, the air-fuel ratio of the air-fuel mixture burned in the cylinder is on the fuel rich side or on the fuel lean side with respect to the stoichiometric air fuel ratio. An air-fuel ratio region determining means for determining whether there is,
An air-fuel ratio calculation apparatus for an internal combustion engine, comprising:   The calorific value obtained from the heat generation rate when the in-cylinder required fuel amount is not changed corresponds to an output air-fuel ratio that generates the maximum output of the internal combustion engine when the in-cylinder required fuel amount is supplied. 2. The air-fuel ratio calculation apparatus for an internal combustion engine according to claim 1, wherein if it is smaller, the forced change of the in-cylinder required fuel amount is prohibited. The fuel amount changing means switches fuel increase and fuel decrease as a forced change of the in-cylinder required fuel amount for each cycle,
The air-fuel ratio region determining means uses a heat generation history obtained from the heat generation rate at the time of fuel increase and a heat generation history obtained from the heat generation rate at the time of fuel reduction to generate 3. The air-fuel ratio calculation apparatus for an internal combustion engine according to claim 1, wherein it is determined whether the air-fuel ratio of the burned air-fuel mixture is on the fuel rich side or on the fuel lean side with respect to the stoichiometric air-fuel ratio. The internal combustion engine has a plurality of cylinders;
4. The fuel amount changing means according to any one of claims 1 to 3, wherein a fuel increase and a fuel decrease as a forced change of the in-cylinder required fuel amount in one cycle are reversed between adjacent cylinders. The air-fuel ratio calculation device for an internal combustion engine according to the item.

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