JP2011220128A - Control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device of an internal combustion engine in which an output error by thermal distortion of a cylinder inner-pressure sensor can be corrected, in an internal combustion engine which can use fuel containing ethanol.SOLUTION: Energy density (q) of fuel containing ethanol is calculated (step 102). Heat generation quantity Qe (=Qmax) when injected fuel burns is calculated based on the energy density (q) and fuel injection quantity fc (step 104). A crank angle of three points during combustion and heat generation quantity Qc (=PV) is calculated, then, a function of quadratic curve passing through these three points is calculated. A crank angle Cmax, when combustion corresponding to the heat generation quantity Qe is finished, is calculated using the quadratic function (step 106). Heat generation quantity on and after crank angle Cmax is corrected. (step 108).

Description

  The present invention relates to an internal combustion engine control device, and more particularly to an internal combustion engine control device equipped with an in-cylinder pressure sensor.

  The in-cylinder pressure sensor is mounted exposed in the cylinder of the internal combustion engine. For this reason, when the sensor is exposed to a high-temperature gas, thermal distortion may occur in the constituent members, and an error may occur in the sensor output. As a countermeasure against this, for example, in Japanese Patent Laid-Open No. 6-265430, pressure measurement accuracy is improved from the viewpoint of sensor hardware.

JP-A-6-265430

  However, if the pressure measurement accuracy is improved from the viewpoint of sensor hardware like the conventional in-cylinder pressure sensor, the configuration of the sensor becomes complicated, and there is a problem that the practicality is poor. Therefore, it has been desired to solve the output error due to the thermal distortion of the in-cylinder pressure sensor on board.

  The present invention has been made to solve the above-described problems, and an internal combustion engine having an in-cylinder pressure sensor that can correct an output error due to thermal distortion of the in-cylinder pressure sensor with a simple calculation. An object of the present invention is to provide a control device.

In order to achieve the above object, the first invention provides
A control device for an internal combustion engine using an alcohol-containing fuel,
An in-cylinder pressure sensor for detecting an in-cylinder pressure at a predetermined crank angle of the internal combustion engine;
A fuel property sensor for detecting the alcohol concentration of the alcohol-containing fuel;
Energy density acquisition means for acquiring the energy density of the alcohol-containing fuel based on the alcohol concentration detected by the fuel property sensor;
A maximum heat generation amount calculating means for calculating a heat generation amount (hereinafter referred to as a maximum heat generation amount) when the in-cylinder gas is burned based on the fuel injection amount of the internal combustion engine and the energy density;
When the in-cylinder pressure detected by the in-cylinder pressure sensor is P, the in-cylinder volume at the time of detection of the in-cylinder pressure is V, and the specific heat ratio of the in-cylinder gas is κ, a value obtained by raising V with κ as an exponent PV ^κ value calculating means for calculating a multiplication value with P (hereinafter referred to as PV ^κ value);
An end-of-combustion crank angle calculating means for calculating a crank angle corresponding to the maximum heat generation amount (hereinafter referred to as an end-of-combustion crank angle) using the correlation between the PV ^κ value and the crank angle in the combustion process;
Heat generation amount correction means for correcting the heat generation amount at a predetermined crank angle in the adiabatic expansion process using the crank angle at the end of combustion and the maximum heat generation amount;
It is characterized by providing.

According to a second invention, in the first invention,
The end-of-combustion crank angle calculating means includes relational expression calculating means for calculating a relational expression that defines a correlation between the PV ^κ value and the crank angle using PV ^κ values at a plurality of points in the combustion process, The crank angle at the end of combustion is calculated using the relational expression.

According to a third invention, in the first or second invention,
The heat generation amount correction means calculates the maximum heat generation amount as an actual heat generation amount at a predetermined crank angle in the adiabatic expansion process.

A fourth invention is any one of the first to third inventions,
A variation degree obtaining means for obtaining a degree of variation in energy density of the alcohol-containing fuel;
Correction means for correcting the maximum heat generation amount so as to approach the maximum value of the PV ^κ value (hereinafter referred to as the maximum PV ^κ value) as the variation degree increases;
Is further provided.

According to a fifth invention, in any one of the first to fourth inventions,
The variation degree obtaining means obtains a coefficient (hereinafter referred to as a weight coefficient) that approaches 1 as the variation degree of the energy density of the alcohol-containing fuel is lower and approaches 0 as the variation degree is higher, based on the alcohol concentration. Means,
When the weighting coefficient is K, the correction means adds a value obtained by adding a value obtained by multiplying the maximum heat generation amount by K and a value obtained by multiplying the maximum PV ^κ value by (1-K). The maximum heat generation amount is obtained.

According to the first invention, the heat generation amount (maximum heat generation amount) during combustion of the in-cylinder gas is calculated based on the alcohol concentration of the alcohol-containing fuel. During combustion of the in-cylinder gas, the thermal distortion error superimposed on the PV ^κ value (in-cylinder pressure P, in-cylinder volume V, specific heat ratio κ) calculated using the detection value of the in-cylinder pressure sensor is small. Therefore, according to the present invention, the crank angle at the end of combustion corresponding to the maximum heat generation amount can be accurately calculated using the correlation between the PV ^κ value of the combustion section and the crank angle. Thereby, the heat generation amount at a predetermined crank angle in the heat insulation process after the end of combustion can be corrected with high accuracy.

According to the second invention, a relational expression of a function that defines the correlation between the PV ^κ value and the crank angle is calculated using the PV ^κ values at a plurality of points in the combustion section. For this reason, according to the present invention, the crank angle at the end of combustion corresponding to the maximum heat generation amount can be accurately calculated using such a relational expression.

According to the third invention, the PV ^κ value in the adiabatic expansion process after the end of combustion is theoretically constant. For this reason, according to the present invention, the maximum heat generation amount can be estimated as the actual heat generation amount at a predetermined crank angle in the adiabatic expansion process.

According to the fourth aspect of the invention, the degree of variation in energy density of the alcohol-containing fuel is acquired, and the value of the maximum heat generation amount is corrected so as to approach the maximum PV ^κ value as the degree of variation increases. The greater the degree of variation in energy density, the greater the maximum heat generation error. For this reason, according to this invention, the correction | amendment according to the magnitude | size of the difference | error of the maximum heat generation amount is attained.

  According to the fifth aspect of the invention, the weighting coefficient K for reflecting the energy density variation degree in the error correction of the maximum heat generation amount is acquired according to the alcohol concentration. There is a correlation between the alcohol concentration and the degree of variation. For this reason, according to the present invention, by using the weighting coefficient K, it is possible to perform correction according to the degree of variation in energy density, that is, according to the magnitude of the error of the maximum heat generation amount.

It is a figure for demonstrating the system configuration | structure of Embodiment 1 of this invention. It is a figure which compares and shows the heat generation amount Q with respect to a crank angle by a calculated value and a true value. It is a flowchart which shows the routine performed in Embodiment 1 of this invention. It is a figure for demonstrating the method to calculate the function of the curve of a combustion area. It is a figure which shows the relationship between the ethanol density | concentration in a fuel, and energy density q. It is an example which shows the relationship between ethanol concentration and the weighting coefficient K. It is a flowchart which shows the routine performed in Embodiment 2 of this invention.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted. The present invention is not limited to the following embodiments.

Embodiment 1 FIG.
[Configuration of Embodiment 1]
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 configured as a spark ignition engine, and is used as a power source of a vehicle, for example. Although the internal combustion engine 10 of this embodiment shall be an in-line 4 cylinder type, the number of cylinders and cylinder arrangement | positioning of an internal combustion engine in this invention are not specifically limited. FIG. 1 shows a cross section of one cylinder of the internal combustion engine 10.

  The internal combustion engine 10 can be operated using gasoline as a fuel, and can also be operated using a fuel obtained by mixing alcohol such as ethanol or methanol and gasoline (hereinafter also referred to as “mixed fuel”). In this case, the mixed fuel can be used from a low concentration (for example, about several percent) to a high concentration (for example, 80% or more) of the alcohol component (ratio of the alcohol component). In the system of the present embodiment, a description will be given on the assumption that a mixed fuel of gasoline fuel and ethanol is used, but the usable fuel is not limited to this, and other alcohol fuel may be used.

  A piston 12 that reciprocates inside the cylinder of the internal combustion engine 10 is provided. Further, the internal combustion engine 10 includes a cylinder head 14. A combustion chamber 16 is formed between the piston 12 and the cylinder head 14. One end of an intake passage 18 and an exhaust passage 20 communicates with the combustion chamber 16. An intake valve 22 and an exhaust valve 24 are disposed at a communication portion between the intake passage 18 and the exhaust passage 20 and the combustion chamber 16, respectively.

  An air cleaner 26 is attached to the inlet of the intake passage 18. A throttle valve 28 is disposed downstream of the air cleaner 26. The throttle valve 28 is an electronically controlled valve that is driven by a throttle motor based on the accelerator opening.

  A spark plug 30 is attached to the cylinder head 14 so as to protrude into the combustion chamber 16 from the top of the combustion chamber 16. The cylinder head 14 is provided with a fuel injection valve 32 for injecting the mixed fuel into the cylinder. Further, the cylinder head 14 incorporates an in-cylinder pressure sensor 34 for detecting the in-cylinder pressure.

  The ethanol concentration of the mixed fuel supplied to the fuel injection valve 32, that is, the mixed fuel stored in a fuel tank (not shown) increases or decreases according to the ethanol concentration of the fuel selected by the user. In the present embodiment, the ethanol concentration of the fuel can be detected by a fuel property sensor 46 provided in the middle of a fuel pipe (not shown) communicating from the fuel tank to the fuel injection valve 32. As the fuel property sensor 46, for example, a sensor that detects the ethanol concentration by measuring the dielectric constant, refractive index, etc. of the mixed fuel can be used. The installation position of the fuel property sensor 46 is not limited to the configuration shown in the fuel pipe. For example, the fuel property sensor 46 may be installed in a fuel tank or a delivery pipe. In the present invention, the method for detecting the ethanol concentration of the fuel in the tank is not limited to the method using the fuel property sensor 46. For example, the ethanol concentration of the fuel may be detected (estimated) from the learned value in the air-fuel ratio feedback control. That is, since the value of the theoretical air-fuel ratio differs between gasoline and ethanol, the value of the theoretical air-fuel ratio of the mixed fuel varies depending on the ethanol concentration. For this reason, the ethanol concentration of the mixed fuel can be detected (estimated) based on the value of the theoretical air / fuel ratio learned by feeding back a signal from an air / fuel ratio sensor (not shown) provided in the exhaust passage 20. Is possible.

  The system according to the present embodiment includes an ECU (Electronic Control Unit) 40 as shown in FIG. In addition to the in-cylinder pressure sensor 34 and the fuel property sensor 46 described above, various sensors such as a crank angle sensor 42 for detecting the rotational position of the crankshaft and a water temperature sensor 44 for detecting the water temperature are provided at the input portion of the ECU 40. It is connected. Further, various actuators such as the throttle valve 28, the spark plug 30, and the fuel injection valve 32 described above are connected to the output portion of the ECU 40. The ECU 40 controls the operating state of the internal combustion engine 10 based on various types of input information.

[Operation of Embodiment 1]
(About the thermal distortion error of the cylinder pressure sensor)
The in-cylinder pressure sensor 34 is a very effective sensor in that the in-cylinder combustion state can be directly detected. For this reason, the output of the in-cylinder pressure sensor 34 is used for various controls. For example, the detected in-cylinder pressure P is used for calculations such as calculation of exhaust energy and fluctuations in the indicated torque. For this reason, the detection accuracy of the in-cylinder pressure P greatly affects catalyst warm-up control using these parameters, torque demand control, and the like. In addition, the heat generation amount PV ^κ (cylinder volume V, specific heat ratio κ of cylinder gas) and MFB (combustion mass ratio) calculated using the detected in-cylinder pressure P are calculated. These are used for misfire detection and optimal ignition timing control.

  Here, the pressure receiving diaphragm of the in-cylinder pressure sensor 34 is exposed to the combustion chamber 16. For this reason, exposure to the high-temperature burned gas (combustion flame) in the combustion chamber 16 may cause a phenomenon (thermal distortion) in which the pressure receiving diaphragm is thermally expanded and deformed. When the pressure receiving diaphragm expands due to thermal strain, the amount of pressure on the transmission rod decreases, and as a result, the output value of the in-cylinder pressure sensor 34 may be smaller than the output value corresponding to the actual pressure. .

FIG. 2 is a diagram showing the heat generation amount Q with respect to the crank angle by comparing the calculated value with the true value. In this figure, the curve indicated by the dotted line is the PV ^κ value calculated using the detected in-cylinder pressure (hereinafter referred to as “heat generation amount Qc”), and the curve indicated by the solid line is the true value of the heat generation amount Q. Respectively. As shown in this figure, the heat generation amount Qc is shifted to a value lower than the true value from the vicinity of the end of combustion to the subsequent heat insulation process due to the influence of thermal strain on the in-cylinder pressure sensor 34. This is because the pressure-receiving diaphragm exposed to the high-temperature burned gas starts to be distorted with a delay when the combustion is almost finished.

  Further, what should be noted about FIG. 2 is that the P ′ point (maximum heat generation amount Q′max, crank angle C′max), which is the combustion end point of the heat generation amount Qc, is the combustion end point at the true value. This is a point shifted from (maximum heat generation amount Qmax and crank angle Cmax). For this reason, there is a possibility that the error of the heat generation amount Q due to the thermal distortion cannot be accurately corrected by the method of correcting the error of the subsequent heat insulation process on the assumption that no thermal distortion error has occurred at the point P ′. is there.

(Characteristic operation of this embodiment)
As described above, in order to accurately correct the thermal distortion error of the heat generation amount Qc, it is first required to calculate the maximum heat generation amount Qmax and its crank angle Cmax with high accuracy. Therefore, in the system of the present embodiment, the maximum heat generation amount Qmax and its crank angle Cmax are accurately calculated using the heat generation amount calculated from the ethanol concentration in the mixed fuel. Hereinafter, further detailed description will be given along the routine shown in FIG.

  FIG. 3 is a flowchart showing a routine in which the ECU 40 corrects the thermal distortion error. In the routine shown in FIG. 3, it is first determined whether or not a correction condition is satisfied (step 100). Specifically, it is determined whether or not the internal combustion engine 10 is in a steady state after completion of warming up. As a result, if the correction condition has not yet been established, this routine is immediately terminated.

  On the other hand, if it is determined in step 100 that the correction condition is satisfied, the process proceeds to the next step, and the energy density q is calculated (step 102). The energy density q of ethanol is less varied than that of gasoline. This is because the composition variation of ethanol is smaller than that of gasoline. Therefore, for the high-concentration ethanol mixed fuel, the heat generation amount can be accurately estimated based on the energy density q. The relationship between the ethanol concentration and the energy density q variation will be described in detail in a second embodiment to be described later. Here, specifically, the ethanol concentration in the mixed fuel is first detected by the fuel property sensor 46. Next, an energy density q corresponding to the density is calculated. The calculation of the energy density q can be realized, for example, by previously obtaining the relationship between the ethanol concentration and the energy density q through experiments or the like and storing it in the ECU 40 as map data.

  Next, a heat generation amount Qe is calculated based on the calculated energy density q and the fuel injection amount fc (step 104). Unlike the heat generation amount Qc calculated by using the in-cylinder pressure, the heat generation amount Qe is a value calculated by multiplying the energy density q by the fuel injection amount fc. Here, specifically, the heat generation amount Qe (= Qmax) when the injected fuel burns is calculated based on the energy density q calculated in step 102 and the fuel injection amount fc.

  Next, the crank angle Cmax corresponding to the heat generation amount Qe calculated in step 104 is calculated (step 106). Here, as described above, the thermal distortion error of the in-cylinder pressure sensor 34 occurs from the vicinity of the end of combustion. For this reason, as shown in FIG. 2, it can be determined that no thermal distortion error has yet occurred in the combustion section in which the heat generation amount is rapidly increasing, and that no error is superimposed on the heat generation amount Qc.

Therefore, in the system according to the present embodiment, the curve of the combustion interval of the heat generation amount Qc is approximately expressed as a function. FIG. 4 is a diagram for explaining a method of calculating a curve function of a combustion section. In this figure, the curve indicated by the dotted line indicates the true value of the heat generation amount Q, and the curve indicated by the alternate long and short dash line indicates the heat generation amount Qc. If the curve of the combustion interval of the heat generation amount Qc shown in this figure is approximately defined as a quadratic function f (x) = ax ² + bx + c, the heat generation amount Qe (= Qmax) at the P point is the crank angle at the P point. It can be expressed by the following formula (1) using Cmax.

  When the above equation (1) is solved for the crank angle Cmax, Cmax can be expressed by the following equation (2). Although there are two solutions for Cmax, the smaller one is selected here as shown in FIG.

Next, the heat generation amount Qn and the crank angle Cn at n points before n samples before the P ′ point where the heat generation amount Qc is maximum are acquired. The n point is a point in the combustion section where no thermal distortion error is superimposed. The heat generation amount Qn can be obtained by calculating PV ^κ using the in-cylinder pressure P, the in-cylinder volume V, and the specific heat ratio κ when the crank angle is Cn. Similarly, (n-1) the heat generation amount Qn-1 and crank angle Cn-1 before the sample from the point P ', and (n-2) the heat generation amount Qn-2 and crank angle Cn- before the sample. 2 is acquired.

  Based on the values of the three points, the constants a, b, and c of the quadratic function f (x) described above can be obtained. Therefore, by substituting these constants a, b, and c and Qe (= Qmax) calculated in the above step 104 into the above equation (2), it corresponds to the heat generation amount Qe (= Qmax) at point P. The calculated crank angle Cmax can be accurately calculated.

  After the point P where the in-cylinder combustion ends, an adiabatic expansion stroke is performed. The amount of heat generated during the heat insulation process is constant. For this reason, the heat generation amount in the adiabatic expansion process after the P point is fixed at the heat generation amount Qe at the P point, and the heat generation amount is corrected (step 108).

  Thus, according to the system of the present embodiment, the function of the heat generation amount with respect to the crank angle of the combustion section is approximately calculated. For this reason, since the crank angle Cmax corresponding to the heat generation amount Qe at the end of combustion calculated based on the energy density q can be calculated based on this function, the heat generation amount at the end point of combustion and its crank angle are calculated. Can be calculated with high accuracy. This makes it possible to accurately correct the heat generation amount corresponding to the crank angle after the end of combustion.

  By the way, in the system of the present embodiment, the function f (x) is calculated by approximating the curve of the combustion section to a quadratic curve, but the function f (x) is not limited to the quadratic function. That is, it is good also as selecting according to a combustion state (the shape of the curve of a combustion area) from several functions.

  In the system of the present embodiment, the heat generation amount in the adiabatic process is assumed to be constant, and the heat generation amount after the completion of combustion is corrected as a constant value. Not limited to. That is, it is good also as combining the correction | amendment which considered the influence of the cooling loss in the heat insulation process, and another well-known correction | amendment.

In the first embodiment described above, the heat generation amount Qc is the “PV ^κ value” of the first invention, the heat generation amount Qmax is the “maximum heat generation heat amount” of the first invention, and the crank angle Cmax corresponds to the “crank angle at the end of combustion” in the first aspect of the invention. Further, when the ECU 40 executes the process of step 102, the “energy density calculating means” in the first aspect of the invention executes the process of step 104, so that the “maximum heat” in the first aspect of the invention is achieved. When the “generation amount calculation means” executes the process of step 106, the “combustion end crank angle calculation means” according to the first aspect of the invention executes the process of step 108, thereby executing the first step. The “generated heat amount correcting means” in the present invention is realized.

Embodiment 2. FIG.
[Features of Embodiment 2]
Next, features of the second embodiment will be described with reference to FIGS. The second embodiment can be realized by executing a routine shown in FIG. 6 to be described later using the hardware configuration shown in FIG.

  In the system of the first embodiment described above, the energy density q is calculated based on the ethanol concentration in the mixed fuel. However, as described above, when the degree of variation in the fuel composition is large, the degree of variation in the energy density q is also increased as a result. FIG. 5 is a diagram showing the relationship between the ethanol concentration in the fuel and the energy density q. As shown in this figure, it can be seen that the degree of variation in the energy density q increases as the ethanol concentration decreases, that is, as the proportion of gasoline increases. This is because gasoline fuel as a mixture has a larger variation in fuel composition than ethanol. For this reason, when a fuel with a low ethanol concentration is used, the energy density q cannot be calculated accurately, and as a result, the heat generation amount Qe at the end of combustion cannot be calculated accurately.

Here, the heat generation amount Qc (= PV ^κ ) calculated based on the in-cylinder pressure is calculated as a relatively stable value without being affected by the ethanol concentration in the fuel, although the thermal distortion error is somewhat superimposed. The Therefore, in the system of the present embodiment, as the ethanol concentration in the fuel is lower, the influence of the heat generation amount Qc is reflected on the heat generation amount Qe calculated based on the energy density q. Accordingly, as the variation error of the heat generation amount Qe becomes larger, the heat generation amount Qe can be corrected in a direction closer to the heat generation amount Qc. As a result, the heat generation amount Qe is effectively brought closer to a true value. Can do.

More specifically, the heat generation amount Qe is corrected based on the following equation (3).
Qx = K × Qe + (1−K) × Qc (3)
In this equation, Qx represents the heat generation amount at the end of combustion after correction, and K represents a weighting factor. The weighting coefficient K is a coefficient that defines the reflection ratio of Qe and Qc with respect to Qx, and is defined as shown in FIG. 6, for example. FIG. 6 is an example showing the relationship between the ethanol concentration and the weighting factor K. In this figure, it is specified that the weighting coefficient K = 1 when the ethanol concentration is 100%, and K = 0 when the ethanol concentration is 0% (the gasoline concentration is 100%). According to this, Qx = Qe when the ethanol concentration is 100%, and conversely, Qx = Qcps when the ethanol concentration is 0%. The weighting factor K is preferably calculated in advance through experiments or the like and stored in the ECU 40 as map data associated with the ethanol concentration. As a result, the heat generation amount Qx at the end of combustion can be accurately calculated regardless of the ethanol concentration.

[Specific Processing of Embodiment 2]
Next, specific processing of the present embodiment will be described with reference to FIG. FIG. 7 is a flowchart showing a routine in which the ECU 40 corrects the thermal distortion error.

In the routine shown in FIG. 7, first, the processes in steps 100 to 104 are executed, and the heat generation amount Qe based on the energy density q is calculated (step 200). Next, a heat generation amount Qc at the combustion end point based on the in-cylinder pressure is calculated (step 202). Specifically, the heat generation amount at the crank angle at which the heat generation amount Qc (PV ^κ value) is maximum is calculated as the heat generation amount Qc at the end of the combustion.

  Next, a weighting factor K is calculated (step 204). Here, the weighting coefficient corresponding to the ethanol concentration detected in step 102 is calculated based on the map shown in FIG. Next, the corrected heat generation amount Qx is calculated (step 206). Here, specifically, the heat generation amount Qe calculated in step 200 and the heat generation amount Qc calculated in step 202 are substituted into the above equation (3), and the corrected heat generation amount Qx is calculated. Next, a crank angle corresponding to the heat generation amount Qx is calculated (step 208). Next, the heat generation amount in the adiabatic expansion process is corrected (step 210). Here, specifically, the same processing as in steps 106 to 108 is executed.

  As described above, according to the system of the present embodiment, the heat generation amount Qe calculated based on the energy density q is corrected according to the ethanol concentration. This makes it possible to accurately calculate the amount of heat generated at the end of combustion and the crank angle even when fuel with a low ethanol concentration is used. Can be corrected.

  Incidentally, in the system of the above-described embodiment, the map shown in FIG. 6 is used when calculating the weighting factor K, but the method of calculating the weighting factor K is not limited to this. That is, the weighting coefficient K may be calculated by defining a function using the ethanol concentration as a parameter, or the weighting coefficient may be defined as a multidimensional map including the operating state of the internal combustion engine 10 and the like. .

In the second embodiment described above, the ECU 40 executes the process of step 202, so that the “PV ^κ value calculating means” in the first invention executes the process of step 208. The “combustion end crank angle calculating means” in the first invention executes the processing of step 210, thereby realizing the “generated heat amount correcting means” in the first invention.

  In the second embodiment described above, the ECU 40 executes the process of step 204, so that the “variation degree acquisition unit” in the fourth aspect of the invention executes the process of step 206. The “correction means” in the fourth aspect of the invention is realized.

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Piston 14 Cylinder head 16 Combustion chamber 18 Intake passage 20 Exhaust passage 22 Intake valve 24 Exhaust valve 26 Air cleaner 28 Throttle valve 30 Spark plug 32 Fuel injection valve 34 In-cylinder pressure sensor 40 ECU (Electronic Control Unit)
42 Crank angle sensor 44 Water temperature sensor 46 Fuel property sensor

Claims (5)

A control device for an internal combustion engine using an alcohol-containing fuel,
An in-cylinder pressure sensor for detecting an in-cylinder pressure at a predetermined crank angle of the internal combustion engine;
A fuel property sensor for detecting the alcohol concentration of the alcohol-containing fuel;
Energy density acquisition means for acquiring the energy density of the alcohol-containing fuel based on the alcohol concentration detected by the fuel property sensor;
A maximum heat generation amount calculating means for calculating a heat generation amount (hereinafter referred to as a maximum heat generation amount) when the in-cylinder gas is burned based on the fuel injection amount of the internal combustion engine and the energy density;
When the in-cylinder pressure detected by the in-cylinder pressure sensor is P, the in-cylinder volume at the time of detection of the in-cylinder pressure is V, and the specific heat ratio of the in-cylinder gas is κ, a value obtained by raising V with κ as an exponent PV ^κ value calculating means for calculating a multiplication value with P (hereinafter referred to as PV ^κ value);
An end-of-combustion crank angle calculating means for calculating a crank angle corresponding to the maximum heat generation amount (hereinafter referred to as an end-of-combustion crank angle) using the correlation between the PV ^κ value and the crank angle in the combustion process;
Heat generation amount correction means for correcting the heat generation amount at a predetermined crank angle in the adiabatic expansion process using the crank angle at the end of combustion and the maximum heat generation amount;
A control device for an internal combustion engine, comprising: The end-of-combustion crank angle calculating means includes relational expression calculating means for calculating a relational expression that defines a correlation between the PV ^κ value and the crank angle using PV ^κ values at a plurality of points in the combustion process, 2. The control apparatus for an internal combustion engine according to claim 1, wherein the combustion end crank angle is calculated using the relational expression.   3. The control apparatus for an internal combustion engine according to claim 1, wherein the heat generation amount correction means calculates the maximum heat generation amount as an actual heat generation amount at a predetermined crank angle in the adiabatic expansion process. A variation degree obtaining means for obtaining a degree of variation in energy density of the alcohol-containing fuel;
Correction means for correcting the maximum heat generation amount so as to approach the maximum value of the PV ^κ value (hereinafter referred to as the maximum PV ^κ value) as the variation degree increases;
The control device for an internal combustion engine according to any one of claims 1 to 3, further comprising: The variation degree obtaining means obtains a coefficient (hereinafter referred to as a weight coefficient) that approaches 1 as the variation degree of the energy density of the alcohol-containing fuel is lower and approaches 0 as the variation degree is higher, based on the alcohol concentration. Means,
When the weighting coefficient is K, the correction means adds a value obtained by adding a value obtained by multiplying the maximum heat generation amount by K and a value obtained by multiplying the maximum PV ^κ value by (1-K). The control apparatus for an internal combustion engine according to claim 4, wherein the maximum heat generation amount is acquired.

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