JP4277279B2 - Control device and control method for internal combustion engine - Google Patents

Description

  The present invention relates to a control device and a control method for an internal combustion engine including an in-cylinder pressure sensor that detects an in-cylinder pressure.

  Conventionally, a technique for predicting the amount of intake air introduced into a combustion chamber of an internal combustion engine using a fluid model related to intake air in an intake passage including a specific heat ratio as a parameter is known (for example, Patent Document 1). reference.). Further, conventionally, as a control device for a diesel engine provided with an exhaust gas recirculation system, one that calculates a parameter for engine control using a specific heat ratio is known (see, for example, Patent Document 2). In this diesel engine control device, a specific heat ratio corresponding to the gas composition of the intake air is obtained with reference to a map using the intake air amount and the actual EGR rate as parameters, and engine control is performed using the obtained specific heat ratio. The in-cylinder gas temperature at the compression top dead center, which is a parameter for use, is calculated.

JP 2001-41095 A Japanese Patent Laid-Open No. 11-200934

  Here, since the specific heat ratio of the air-fuel mixture introduced into the cylinder changes depending on the composition of the fuel supplied to the cylinder, the gas temperature, and the like, when controlling the internal combustion engine using the specific heat ratio It is preferable to calculate the specific heat ratio each time, rather than using a constant as the specific heat ratio. However, adaptation of a map or the like for obtaining a specific heat ratio requires a great amount of time and labor, and conventionally, a technique that can estimate the specific heat ratio easily and accurately is required.

  Therefore, an object of the present invention is to provide a control device and a control method for an internal combustion engine that can easily and accurately estimate a specific heat ratio used for setting various parameters for engine control.

  An internal combustion engine control apparatus according to the present invention is a control apparatus for an internal combustion engine including an in-cylinder pressure sensor for detecting an in-cylinder pressure, and corresponds to a detection value of the in-cylinder pressure sensor at a predetermined point during the intake stroke and a predetermined one point. The bias value of the in-cylinder pressure sensor is calculated on the basis of the pressure of the intake air at the time, and based on the bias value, the detected value of the in-cylinder pressure sensor at at least two predetermined points during the compression stroke, and the in-cylinder volume. And a specific heat ratio calculating means for calculating an estimated value of the specific heat ratio of the air-fuel mixture introduced into the cylinder.

  In addition, it is preferable that the control device for the internal combustion engine further includes a fuel property determination unit that determines the property of the fuel supplied into the cylinder based on the estimated value of the specific heat ratio calculated by the specific heat ratio calculation unit.

  Further, the control device for the internal combustion engine may further include means for obtaining the ratio of EGR gas in the cylinder based on the estimated value of the specific heat ratio calculated by the specific heat ratio calculating means.

  Further, the control device for the internal combustion engine determines a time corresponding to a predetermined point in the intake stroke according to the phase delay amount until the pressure of the intake air in the intake system substantially matches the in-cylinder pressure. It is preferable to further comprise means for setting.

  An internal combustion engine control method according to the present invention is a control method for an internal combustion engine including an in-cylinder pressure sensor for detecting an in-cylinder pressure. In the in-cylinder engine at a predetermined point during an intake stroke and at least two predetermined points during a compression stroke. The pressure of the intake air is detected at a time corresponding to a predetermined point in the intake stroke, and the in-cylinder pressure at the predetermined point and the pressure of the intake air at the time corresponding to the predetermined point are detected. And calculating the bias value of the in-cylinder pressure sensor, and based on the bias value and the in-cylinder pressure and the in-cylinder volume at at least two predetermined points, the specific heat ratio of the air-fuel mixture introduced into the cylinder is calculated. An estimated value is calculated.

  In this case, it is preferable to determine the property of the fuel supplied into the cylinder based on the estimated value of the specific heat ratio, and the ratio of EGR gas in the cylinder may be obtained based on the estimated value of the specific heat ratio. Further, it is preferable to set a time point corresponding to a predetermined point in the intake stroke according to the phase delay amount until the pressure of the intake air in the intake system substantially matches the in-cylinder pressure.

  ADVANTAGE OF THE INVENTION According to this invention, the control apparatus and control method of an internal combustion engine which can estimate the specific heat ratio used for the setting of the various parameters for engine control easily and accurately are realizable.

  The present inventor has conducted intensive research to easily and accurately estimate the specific heat ratio used for setting various parameters for engine control. In the process, first, the actual value of the in-cylinder pressure sensor and the true value of the in-cylinder pressure are calculated. Focused on the relationship. That is, the measured value of the in-cylinder pressure when the crank angle is θ (the value obtained by converting the output voltage value of the in-cylinder pressure sensor into pressure) is Pc (θ), and the true value of the in-cylinder pressure when the crank angle is θ. If the value is Pct (θ), the sensitivity (gain) of the in-cylinder pressure sensor is α, and the bias value of the in-cylinder pressure sensor is δ, the measured value Pc (θ) of the in-cylinder pressure and the true value Pct (θ In general, the relationship shown in the following equation (1) is established.

Also, for example, in the vicinity of the intake bottom dead center (when the intake valve closes (begins to close) during the intake stroke), the in-cylinder pressure (true value) and the intake air pressure in the intake system substantially coincide with each other. If the pressure (absolute pressure) of the intake air when the angle is θ is Pi (θ), and the crank angle becomes θ ₀ during the intake stroke, the in-cylinder pressure and the intake air pressure are approximately the same, Using the above equation (1), the bias value of the in-cylinder pressure sensor is

Can be expressed as The subscript “pi” indicates that the bias value is calculated based on the pressure of the intake air.

Here, “λ” in the expression (2) is the amount of phase delay until the intake air pressure in the intake system substantially matches the in-cylinder pressure (the in-cylinder pressure and the intake air pressure substantially match). Timing phase difference). That is, due to the intake pulsation or the like, for example, the in-cylinder pressure near the intake bottom dead center (when the crank angle becomes θ ₀ ) is actually slightly delayed from the intake bottom dead center (the crank angle is It almost coincides with the pressure of the intake air at the time of θ ₀ + λ. In consideration of such a phenomenon, the phase delay amount λ is introduced into the equation (2).

On the other hand, assuming that the compression stroke of the internal combustion engine is an adiabatic process, the in-cylinder volume when the crank angle is θ is V (θ), and the specific heat ratio of the air-fuel mixture introduced into the cylinder is κ. them ^{if, Pc (θ) · V κ} (θ) and cylinder volume is the product of the value V ^kappa raised to the power cylinder pressure Pc (theta) and cylinder volume V a (theta) in the specific heat ratio kappa (theta) The bias value of the in-cylinder pressure sensor is calculated using a change between _two predetermined points during the compression stroke (when the crank angle becomes θ ₁ and θ ₂ ),

Can be expressed as The subscript “pv” indicates that the bias value is calculated based on Pc (θ) · V ^κ (θ).

  Since the bias value δpi obtained from the above equation (2) and the bias value δpv obtained from the above equation (3) should be essentially equal, δpv = δpi in equation (3) If solved, the estimated value κe of the specific heat ratio κ,

Can be calculated as Thus, using the above equation (4), the detected value of the in-cylinder pressure sensor at a predetermined point during the intake stroke and the pressure of the intake air at the time corresponding to the predetermined point during the intake stroke (intake pressure sensor) The estimated value κe of the specific heat ratio κ can be easily and accurately calculated from the detected value of the in-cylinder pressure sensor and the in-cylinder volume at at least two predetermined points during the compression stroke.

That is, when obtaining the estimated value κe of the specific heat ratio κ, first, a predetermined one point during the intake stroke (when the crank angle becomes θ ₀ ) and two predetermined points during the compression stroke (the crank angle is θ ₁ , detects the cylinder pressure at theta ₂ to become time), for detecting the pressure of intake air at the time corresponding to a predetermined point in the intake stroke (when the crank angle becomes θ ₀ + λ). Further, based on the in-cylinder pressure Pc (θ ₀ ) at the predetermined one point and the intake air pressure Pi (θ ₀ + λ) at the time corresponding to the predetermined one point, the bias value δpi of the in-cylinder pressure sensor is set. After the calculation, the bias value δpi, the in-cylinder pressures Pc (θ ₁ ) and Pc (θ ₂ ) and the in-cylinder volumes V (θ ₁ ) and V (θ ₂ ) at the two predetermined points are expressed as (4 The estimated value κe of the specific heat ratio κ can be obtained by substituting it into the formula. As a result, according to the present invention, it is possible to accurately calculate the specific heat ratio κ used for setting various parameters for engine control while omitting the adaptation process such as the specific heat ratio calculation map that requires a great amount of time and labor. The estimated value κe can be easily obtained with a low load.

  In addition, the phase delay amount λ until the intake air pressure in the intake system substantially matches the in-cylinder pressure is introduced into the above equation (2), and the time when the intake air pressure is detected (during the intake stroke) By setting the time point corresponding to one predetermined point) according to the phase delay amount λ, the in-cylinder pressure sensor bias value δpi can be accurately calculated. If the estimated value κe of the specific heat ratio κe calculated as described above is used, as will be described later, the fuel properties such as the degree of heavyness of the fuel supplied into the cylinder, and the EGR gas in the cylinder It is possible to easily and accurately grasp the ratio and the like.

  Hereinafter, the best mode for carrying out the present invention will be specifically described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram showing an internal combustion engine according to the present invention. The internal combustion engine 1 shown in FIG. 1 generates power by burning a fuel / air mixture in a combustion chamber 3 formed in a cylinder block 2 and reciprocating a piston 4 in the combustion chamber 3. Is. Although only one cylinder is shown in FIG. 1, the internal combustion engine 1 is preferably configured as a multi-cylinder engine, and the internal combustion engine 1 of the present embodiment is configured as a four-cylinder engine, for example.

  The intake port of each combustion chamber 3 is connected to the intake pipe 5 via an intake manifold, and the exhaust port of each combustion chamber 3 is connected to the exhaust pipe 6 via an exhaust manifold. In addition, an intake valve Vi that opens and closes an intake port and an exhaust valve Ve that opens and closes an exhaust port are provided for each combustion chamber 3 in the cylinder head of the internal combustion engine 1. Each intake valve Vi and each exhaust valve Ve are opened and closed by a valve mechanism VM having a variable valve timing function. Further, the internal combustion engine 1 has a number of spark plugs 7 corresponding to the number of cylinders, and the spark plugs 7 are disposed in the cylinder heads so as to face the corresponding combustion chambers 3.

  The intake pipe 5 is connected to a surge tank 8 as shown in FIG. An air supply pipe L1 is connected to the surge tank 8, and the air supply pipe L1 is connected to an air intake port (not shown) via an air cleaner 9. A throttle valve (electronically controlled throttle valve in this embodiment) 10 is incorporated in the middle of the supply pipe L1 (between the surge tank 8 and the air cleaner 9). On the other hand, as shown in FIG. 1, a front-stage catalyst device 11 a including a three-way catalyst and a rear-stage catalyst device 11 b including a NOx storage reduction catalyst are connected to the exhaust pipe 6.

  Further, as shown in FIG. 1, the internal combustion engine 1 has a plurality of injectors 12, and the injectors 12 are arranged in the cylinder head so as to face the corresponding combustion chambers 3. Each piston 4 of the internal combustion engine 1 is configured as a so-called deep dish top surface type, and a recess 4a is formed on the upper surface thereof. In the internal combustion engine 1, fuel such as gasoline is directly injected from each injector 12 toward the recess 4 a of the piston 4 in each combustion chamber 3 in a state where air is sucked into each combustion chamber 3. As a result, in the internal combustion engine 1, the fuel / air mixture layer is formed (stratified) in the vicinity of the spark plug 7 so as to be separated from the surrounding air layer. And stable stratified combustion can be performed. The internal combustion engine 1 of the present embodiment is described as a so-called direct injection engine, but is not limited to this, and the present invention can be applied to an intake pipe (intake port) injection type internal combustion engine. Not too long.

  Each of the spark plugs 7, the throttle valve 10, the injectors 12, the valve operating mechanism VM, and the like described above are electrically connected to the ECU 20 that functions as a control device for the internal combustion engine 1. The ECU 20 includes a CPU, a ROM, a RAM, an input / output port, a storage device, and the like, all not shown. As shown in FIG. 1, various sensors including the crank angle sensor 14 of the internal combustion engine 1 are electrically connected to the ECU 20 via an A / D converter or the like (not shown). The ECU 20 uses the various maps stored in the storage device and the spark plug 7, the throttle valve 10, the injector 12, and the valve mechanism VM so that a desired output can be obtained based on detection values of various sensors. Control etc.

  Further, the internal combustion engine 1 has a number of in-cylinder pressure sensors 15 including semiconductor elements, piezoelectric elements, optical fiber detection elements, and the like corresponding to the number of cylinders. Each in-cylinder pressure sensor 15 is disposed on the cylinder head so that the pressure receiving surface faces the corresponding combustion chamber 3, and is electrically connected to the ECU 20 via an A / D converter (not shown). Each in-cylinder pressure sensor 15 detects the in-cylinder pressure (relative pressure) in the corresponding combustion chamber 3 and gives a signal indicating the detected value to the ECU 20. Furthermore, the internal combustion engine 1 has an intake pressure sensor 16 that detects the pressure (intake pressure) of intake air in the surge tank 8 as an absolute pressure. The intake pressure sensor 16 is electrically connected to the ECU 20 via an A / D converter (not shown) or the like, and gives a signal indicating the detected absolute pressure of the intake air in the surge tank 8 to the ECU 20. The detection values of the crank angle sensor 14, each in-cylinder pressure sensor 15 and the intake pressure sensor 16 are sequentially given to the ECU 20 every minute time, and stored in a predetermined storage area (buffer) of the ECU 20 by a predetermined amount.

  Next, a procedure for calculating the estimated value κe of the specific heat ratio κ in the internal combustion engine 1 and controlling the ratio of the EGR gas in the cylinder will be described with reference to FIG. The routine shown in FIG. 2 is executed by the ECU 20 of the internal combustion engine 1 every predetermined time. When the execution timing of this routine is reached, the ECU 20 first rotates the internal combustion engine 1 based on the detected value of the crank angle sensor 14. The number is acquired (S10). When the engine speed is acquired, the ECU 20 sets the phase delay amount λ corresponding to the speed acquired in S10 using a predetermined map or function equation stored in the storage device (S12).

  Here, in the present embodiment, the phase delay amount λ is substantially equal to the time when the intake bottom dead center is reached (when the intake valve is closed during the intake stroke), and the cylinder pressure at the intake bottom dead center is the intake air pressure. Although it is an angle according to the difference from the substantially coincident time, according to the study of the present inventor, the phase delay amount λ increases as the engine speed increases and is approximately proportional to the engine speed. Has been found to increase. For this reason, in S12, a map or a function formula that defines the correlation between the engine speed and the phase delay amount λ as shown in FIG. 3 is used. Note that when creating the map or the function expression used in S12, it is preferable to consider the opening / closing timing and lift amount of the intake valve Vi and the exhaust valve Ve, and also the back pressure in the internal combustion engine 1.

When the phase delay amount λ is set in S12, the ECU 20 determines the in-cylinder pressure Pc (θ ₀ ) when the crank angle is θ ₀ (for example, −180 °) for each combustion chamber 3 from a predetermined storage area. Then, the pressure Pi (θ ₀ + λ) of the intake air (in the vicinity of the intake bottom dead center) when the crank angle becomes θ ₀ + λ (for example, −180 ° + λ) is read (S14). Further, the ECU 20 substitutes the read in-cylinder pressure Pc (θ ₀ ) and the intake air pressure Pi (θ ₀ + λ) into the above-described equation (2) for each combustion chamber 3, so that the in-cylinder pressure sensor 15. And an average value δpia of the bias values δpi for all the combustion chambers 3 is calculated (S16). In the present embodiment, the sensitivity α of the in-cylinder pressure sensor 15 in the equation (2) used in S16 is set to a constant value assuming that there is almost no sensitivity change (sensitivity deviation).

Further, when the average value δpia of the bias value δpi is calculated, the ECU 20 causes the in-cylinder pressure Pc (θ ₁ ) when the crank angle becomes θ ₁ (for example, −100 °) for each combustion chamber 3 from a predetermined storage area. ) And the in-cylinder pressure Pc (θ ₂ ) when the crank angle becomes θ ₂ (for example, −50 °), and the average value Pca of the in-cylinder pressure Pc (θ ₁ ) for all the combustion chambers 3. (Θ ₁ ) and an average value Pca (θ ₂ ) of in-cylinder pressure Pc (θ ₂ ) are calculated (S18). If the angles θ ₁ and θ ₂ are selected so as to be included in the compression stroke, the respective values can be arbitrary.

In this way, the average value of the bias value .DELTA.Pi Derutapia, calculating the average value Pca of the cylinder pressure _{Pc (θ 1) (θ 1} ) and the average value of the cylinder pressure _{Pc (θ 2) Pca (θ} 2), The ECU 20 sets these values together with the in-cylinder volumes V (θ ₁ ) and V (θ ₂ ) in the above equation (4), δpi = δpia, Pc (θ ₁ ) = Pca (θ ₁ ), Pc (θ ₂ ) = by substituting a Pca (θ _2), to calculate the estimated value κe specific heat ratio kappa (S20). Note that the values of in-cylinder volumes V (θ ₁ ) and V (θ ₂ ) used in S20 (in this embodiment, values of log V (−100 °) and log V (−50 °)) are calculated in advance. In addition, the ECU 20 reads out the values of these in-cylinder volumes V (θ ₁ ) and V (θ ₂ ) from the storage device and uses them in the processing of S20. When the estimated value κe is obtained, the ECU 20 updates the specific heat ratio κ stored for obtaining various parameters for engine control with the estimated value κe (S22), and further updates the specific heat ratio κ (= estimated value). Based on κe), an EGR rate b, which is a ratio of EGR gas in each combustion chamber 3, is calculated (S24). Here, when the specific heat ratio of _air is κ _air (for example, about 1.4) and the specific heat ratio of EGR gas is κ _egr (for example, about 1.3),

When this is solved for “b”, the EGR rate b is

Can be obtained as

When the EGR rate b is obtained, the ECU 20 reads the target EGR rate bt corresponding to the operating condition from a predetermined map or the like, and a value obtained by subtracting the target EGR rate bt from the EGR rate b (b−bt) is the target EGR rate bt. It is determined whether or not the upper limit value b ₁ corresponding to is exceeded (S26). If S26 in value (b-bt) is determined to exceed the upper limit value b _1, or ECU20 causes the opening timing of the intake valve Vi and controls the valve operating mechanism VM is retarded by a predetermined amount, And / or the valve opening timing of the exhaust valve Ve is advanced by a predetermined amount, thereby reducing the overlap between the intake valve Vi and the exhaust valve Ve (S28). As a result, the amount of high-temperature burned gas remaining in each combustion chamber 3 can be reduced, so that the EGR rate b can be reduced to approach the target EGR rate bt.

Also, if the value in S26 (b-bt) is equal to or less than the upper limit value b _1, ECU 20 further value obtained by subtracting the target EGR rate bt from the EGR rate b (b-bt) the target EGR rate It determines whether below the lower limit b ₂ corresponding to bt (S30). If S30 in value (b-bt) is determined to be below the lower limit b _2, or ECU20 causes advanced by a predetermined amount the valve opening timing of the intake valve Vi and controls the valve operating mechanism VM, And / or the opening timing of the exhaust valve Ve is retarded by a predetermined amount to increase the overlap between the intake valve Vi and the exhaust valve Ve (S32). Thus, by increasing the amount of high-temperature burned gas remaining in each combustion chamber 3, it is possible to increase the EGR rate b and approach the target EGR rate bt.

The value obtained by subtracting the target EGR rate bt from the EGR rate b at S30 (if a negative determination is made in S30, is made) (b-bt) may be determined to be the lower limit value b ₂ or more, calculated in S24 Since the EGR rate b is approximately a value near the target EGR rate bt, the control of the valve mechanism VM (valve overlap control) is not particularly executed. Then, after executing the process of S28 or S32 or making a negative determination in S30, the ECU 20 waits until the next execution timing of this routine.

Thus, in the internal combustion engine 1, it is possible to obtain an accurate estimated value κe of the specific heat ratio κ used for setting various parameters for engine control. If the estimated value κe of the specific heat ratio κ calculated as described above is used, the EGR rate b in each combustion chamber 3 can be easily and accurately grasped and brought close to the target EGR rate bt. Note that the estimated value κe may be calculated using an average value of the in-cylinder pressure at three or more sampling points with three or more sampling points in the compression stroke. Thereby, the calculation accuracy of the estimated value κe can be further improved. Further, omitting the intake pressure sensor 16 of the surge tank 8, a pressure Pi of the intake air (θ ₀ + λ) opening and the throttle valve 10, is estimated from the measured value of the air flow meter (not shown) for measuring the intake air amount It may be used. Further, the specific heat ratio κ and the EGR rate b may be calculated for each combustion chamber 3 without taking the average of the bias value δpi and the in-cylinder pressures Pc (θ ₁ ) and Pc (θ ₂ ).

  And although the above-mentioned internal combustion engine 1 was demonstrated as what is a gasoline engine, it is not restricted to this, It cannot be overemphasized that this invention can be applied to a diesel engine. That is, the routine for calculating the estimated value κe of the specific heat ratio κ as described above and controlling the ratio of EGR gas in each combustion chamber 3 is suitable for a diesel engine equipped with an exhaust gas recirculation system.

In this case, as shown in FIG. 4, when exceeds the upper limit value b ₁ the value obtained by subtracting the target EGR rate bt from the EGR rate b to (b-bt) is in accordance with the target EGR rate bt at S26 If determined, the amount of exhaust gas recirculated to each combustion chamber 3 may be reduced by reducing the opening of the EGR valve included in the exhaust gas recirculation system (S29). Also, after the value (b-bt) is determined to be less than the upper limit value b ₁ at S26, further, when the value (b-bt) is determined to be below the lower limit b _2, exhaust gas recirculation The amount of exhaust gas recirculated to each combustion chamber 3 may be increased by increasing the opening of the EGR valve included in the system (S33). As a result, the EGR rate b in the combustion chamber of the diesel engine can be easily and accurately grasped and brought close to the target EGR rate bt.

  FIG. 5 is a flowchart for explaining a routine for determining the properties of the fuel supplied to each combustion chamber 3 in the internal combustion engine 1 described above. As shown in FIG. 5, the fuel property determination in the internal combustion engine 1 is performed using the estimated value κe of the specific heat ratio κ calculated through the processes of S10 to S22 described with reference to FIG. Then, when the ECU 20 updates the specific heat ratio κ stored in the predetermined storage area with the estimated value κe in S22, the specific heat ratio κr (for example, κr = 1.32) in the standard state from the updated specific heat ratio κ. It is determined whether or not the value obtained by subtracting) exceeds a predetermined threshold (S23).

  Here, when the fuel supplied to each combustion chamber 3 is heavy, the specific heat ratio κ of the air-fuel mixture introduced into each combustion chamber 3 is larger than that in the standard state (a state where κ = κr). Value. Therefore, if an affirmative determination is made in S23, the degree of fuel supplied to each combustion chamber 3 is somewhat high. In this case, the ECU 20 determines the ignition timing by each spark plug 7. The valve mechanism VM is controlled so as to retard by a fixed amount (S25). Thus, when the routine of FIG. 5 is executed, the ignition timing by each spark plug 7 is optimally determined according to the fuel severity obtained based on the estimated value κe of the specific heat ratio κ calculated accurately. Will be set. The ECU 20 waits until the next execution timing of this routine after executing the process of S25.

It is a schematic block diagram which shows the internal combustion engine containing the control apparatus by this invention. 2 is a flowchart showing a routine for calculating an estimated value of a specific heat ratio in the internal combustion engine of FIG. 1 and further controlling the ratio of EGR gas in a cylinder. 4 is a graph illustrating the relationship between the rotational speed of an internal combustion engine and the amount of phase delay until the pressure of intake air in the intake system substantially matches the in-cylinder pressure. It is a flowchart which shows the modified example of the routine for calculating the estimated value of a specific heat ratio, and also controlling the ratio of EGR gas. FIG. 2 is a flowchart showing a routine for calculating an estimated value of a specific heat ratio in the internal combustion engine of FIG. 1 and determining the properties of fuel supplied into a cylinder. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Cylinder block 3 Combustion chamber 4 Piston 5 Intake pipe 6 Exhaust pipe 7 Spark plug 8 Surge tank 10 Throttle valve 12 Injector 14 Crank angle sensor 15 In-cylinder pressure sensor 16 Intake pressure sensor L1 Intake pipe Ve Exhaust valve Vi Intake valve VM Valve mechanism

Claims (10)

In a control device for an internal combustion engine including an in-cylinder pressure sensor for detecting an in-cylinder pressure,
The detected value of the in-cylinder pressure sensor at the point where the pressure of the intake air and the in-cylinder pressure during the intake stroke coincide with each other, and the intake air pressure at the time corresponding to the point at which the pressure of the intake air and the in-cylinder pressure match in terms of calculating the bias value of the cylinder pressure sensor based on, the bias value, based on the detected value and the cylinder volume of the cylinder pressure sensor in at least two predetermined points during the compression stroke, the intake stroke The bias value obtained by using the intake air pressure and the in-cylinder pressure related to the point at which the intake air pressure and the in-cylinder pressure coincide with each other, and the in-cylinder pressure at at least two predetermined points during the compression stroke features and utilizing the relationship that is equal to the bias value is determined using in-cylinder volume, further comprising the specific heat ratio calculating means for calculating the estimated value of the specific heat ratio of the gas mixture which is introduced into the cylinder Control device for an internal combustion engine to be.   2. The internal combustion engine according to claim 1, further comprising a fuel property determination unit that determines a property of fuel supplied into the cylinder based on an estimated value of the specific heat ratio calculated by the specific heat ratio calculation unit. Engine control device.   2. The control apparatus for an internal combustion engine according to claim 1, further comprising means for obtaining a ratio of EGR gas in the cylinder based on an estimated value of the specific heat ratio calculated by the specific heat ratio calculating means. The pressure of intake air in accordance with the phase delay until the cylinder pressure and the match so in the intake system, means for setting a time corresponding to the point where the pressure and cylinder pressure of the intake air is coincident The control device for an internal combustion engine according to any one of claims 1 to 3, further comprising: The control device for an internal combustion engine according to any one of claims 1 to 4, wherein a point at which the pressure of the intake air and the cylinder pressure during the intake stroke coincide with each other is an intake bottom dead center. In a control method for an internal combustion engine including an in-cylinder pressure sensor for detecting an in-cylinder pressure,
The point at which the pressure of the intake air during the intake stroke and the in-cylinder pressure coincide with each other and the point at which at least two predetermined points during the compression stroke are detected, and the pressure of the intake air and the in-cylinder pressure coincide with each other The pressure of the intake air is detected at a time corresponding to the above, and the in-cylinder pressure, the intake air pressure, and the in-cylinder pressure at the point where the intake air pressure and the in-cylinder pressure match correspond to each other. A bias value of the in-cylinder pressure sensor is calculated on the basis of the pressure of the intake air at the time point, and then during the intake stroke based on the bias value and the in-cylinder pressure and the in-cylinder volume at the at least two predetermined points. The bias value obtained by using the intake air pressure and the in-cylinder pressure related to the point at which the intake air pressure and the in-cylinder pressure coincide with each other, and the in-cylinder pressure at at least two predetermined points during the compression stroke and Utilizing the relationship that is equal to the bias value is determined using an internal volume, a control method for an internal combustion engine, and calculates the estimated value of the specific heat ratio of the gas mixture which is introduced into the cylinder. The internal combustion engine control method according to claim 6 , wherein the property of the fuel supplied into the cylinder is determined based on the estimated value of the specific heat ratio. The internal combustion engine control method according to claim 6 , wherein the ratio of EGR gas in the cylinder is obtained based on the estimated value of the specific heat ratio. The pressure of intake air in accordance with the phase delay until the cylinder pressure and the match so in the intake system, said pressure and cylinder pressure of the intake air to set the time corresponding to the point coincident The method for controlling an internal combustion engine according to any one of claims 6 to 8 , characterized in that: 10. The control method for an internal combustion engine according to claim 6, wherein the point at which the pressure of the intake air during the intake stroke matches the in-cylinder pressure is an intake bottom dead center.

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