JP5177269B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine, and more particularly to an apparatus having a function of detecting fuel properties.

  The components of the fuel of the internal combustion engine are various, and an internal combustion engine using a mixed fuel such as an alcohol mixed fuel in which ethanol or methanol is mixed with gasoline has been put into practical use. For this reason, it is desirable that the property of the fuel can be detected on the vehicle side.

  For the purpose of detecting the fuel property on the vehicle side, the device disclosed in Patent Document 1 corrects the air-fuel ratio when a starting failure is detected, and calculates the stoichiometric air-fuel ratio (stoichiometric air-fuel ratio) from the air-fuel ratio correction amount. The octane number is estimated from this theoretical air-fuel ratio.

  Further, the apparatus disclosed in Patent Document 2 detects the fuel property by calculating the amount of heat generated in the cylinder from the detected value of the in-cylinder pressure and determining the lower heat value of the fuel.

  Further, Patent Document 3 includes storage means for storing data indicating the relationship between the alcohol concentration in the fuel, the theoretical air-fuel ratio, and the gasoline heaviness, and the alcohol concentration and the stoichiometric air-fuel ratio (stoichiometric air-fuel ratio). By comparing with the data, the severity of gasoline is detected.

JP 2000-170581 A JP-A-64-88153 Japanese Patent No. 2907594

  However, the apparatus of Patent Document 1 cannot detect the fuel property unless it is a case where a starting failure is detected, and it takes time to converge the air-fuel ratio to the stoichiometric air-fuel ratio. The device of Patent Document 2 cannot control the air-fuel ratio. The apparatus of Patent Document 3 needs to obtain the alcohol concentration and the stoichiometric air-fuel ratio by some means, and a simpler means is desired. On the other hand, there is no conventional control device that uses the relationship between the heat generation amount and the stoichiometric air-fuel ratio.

  Accordingly, an object of the present invention is to provide a novel means for performing control using a relationship between a calorific value and a stoichiometric air-fuel ratio in a control device having a function of detecting fuel properties.

One aspect of the present invention is a control device for an internal combustion engine having means for calculating a stoichiometric air-fuel ratio based on an air-fuel ratio detection value of exhaust gas, wherein the calculation is based on a known relationship between a low heating value and a stoichiometric air-fuel ratio. Means for calculating the lower heating value of the fuel from the stoichiometric air-fuel ratio , means for calculating the lower heating value based on the in-cylinder pressure detection value, the value of the lower heating value calculated based on the stoichiometric air-fuel ratio, and the in-cylinder pressure Based on the comparison with the value of the lower heating value calculated based on the detected value, the means for calculating the lower heating value based on the detected in-cylinder pressure and the stoichiometric air-fuel ratio based on the detected air-fuel ratio of the exhaust gas And a diagnostic means for diagnosing at least one of the means for performing. In this aspect, a new means for diagnosing the detection system can be provided.

In order to obtain the amount of heat generation from the detected value of the in-cylinder pressure sensor, the detected in-cylinder pressure P and the combustion chamber volume V at the time of detection of the in-cylinder pressure P are raised to a power near the specific heat ratio κ of the supplied air-fuel mixture. It is preferable to calculate a product value PV ^κ with the calculated value as the heat generation amount parameter. Equation of state of gas: PV = nRT (P: pressure, V: volume, n: number of moles of gas, R: gas constant (J / mol · K), T: temperature (K)), PV in adiabatic change ^It has been found that ^κ = constant. Therefore, the amount of change in PV ^κ (that is, the difference between two points) when fuel combustion occurs in the combustion chamber depends on the energy generated by the combustion. Therefore, PV ^κ has a high correlation with the amount of heat generated in the combustion chamber, and by determining the fuel properties using PV ^κ as a heat generation amount parameter, the properties of the fuel can be determined with higher accuracy. The in-cylinder pressure P can be directly detected by the in-cylinder pressure sensor, and the volume (in-cylinder volume) V can be uniquely determined from the crank angle by a predetermined map or function. The constant κ may be a value near the specific heat ratio of the air-fuel mixture formed in the combustion chamber, and even if it is a predetermined fixed value, it should be changed according to the intake air amount, the fuel injection amount, and the like. May be.

It is a schematic block diagram which shows the internal combustion engine to which the control apparatus by this invention was applied. It is a graph which shows the structural example of a stoichi air fuel ratio / low heating value ratio map. It is a flowchart which shows the fuel property discrimination | determination process in 1st Embodiment. It is a graph which shows the execution example of the air fuel ratio feedback control in 2nd Embodiment. It is a flowchart which shows the fuel property discrimination | determination process in 2nd Embodiment. It is a flowchart which shows the diagnostic process of the in-cylinder pressure detection system in 3rd Embodiment.

  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 to which a control device according to the present invention is applied. 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. The internal combustion engine 1 can be operated with gasoline and with a mixed fuel of gasoline and alcohol. 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, for example, a 4-cylinder engine.

  The intake port of each combustion chamber 3 is connected to an intake pipe (intake manifold) 5, and the exhaust port of each combustion chamber 3 is connected to an exhaust pipe 6 (exhaust manifold). In addition, an intake valve Vi and an exhaust valve Ve are provided for each combustion chamber 3 in the cylinder head of the internal combustion engine 1. Each intake valve Vi opens and closes a corresponding intake port, and each exhaust valve Ve opens and closes a corresponding exhaust port. Each intake valve Vi and each exhaust valve Ve are opened and closed by a valve operating mechanism VM including a variable valve timing mechanism. 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 line L1 is connected to the surge tank 8, and the air supply line L1 is connected to an air intake port (not shown) via an air cleaner 9. A throttle valve (in this embodiment, an electronically controlled throttle valve) 10 is incorporated in the middle of the air supply line L1 (between the surge tank 8 and the air cleaner 9). On the other hand, as shown in FIG. 1, for example, 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.

  Furthermore, the internal combustion engine 1 has a plurality of injectors 12, and each injector 12 is disposed in the cylinder head so as to face the corresponding combustion chamber 3 as shown in FIG. 1. Each piston 4 of the internal combustion engine 1 is configured as a so-called deep dish top surface type, and has a concave portion 4a on its upper surface. 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. 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.

  The internal combustion engine 1 has in-cylinder pressure sensors (in-cylinder pressure detecting means) 15 including semiconductor elements, piezoelectric elements, magnetostrictive elements, optical fiber detecting 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 outputs the pressure (in-cylinder pressure) applied to the pressure receiving surface in the combustion chamber 3 as a relative value to the atmospheric pressure, and corresponds to the pressure (in-cylinder pressure) applied to the pressure receiving surface. A voltage signal (a signal indicating a detected value) is supplied 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 also 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 detected values of the crank angle sensor 14 and the intake pressure sensor 16 are sequentially given to the ECU 20 every minute time, and are stored and held in a predetermined storage area (buffer) of the ECU 20 by a predetermined amount. Further, the detection value (in-cylinder pressure) of each in-cylinder pressure sensor 15 is subjected to absolute pressure correction based on the detection value of the intake pressure sensor 16, and then stored and held in a predetermined storage area (buffer) of the ECU 20 by a predetermined amount. Is done.

Furthermore, the internal combustion engine 1 has an A / F sensor 17 that detects the air-fuel ratio in the exhaust pipe 6 and an O ₂ sensor 18 that detects the oxygen concentration in the exhaust pipe 6 in the front stage of the front catalyst device 11a. The A / F sensor 17 and the O ₂ sensor 18 provide detection signals to the ECU 20, respectively. A
The / F sensor 17 is a full-range air-fuel ratio sensor (linear air-fuel ratio sensor) that generates an output voltage proportional to the air-fuel ratio of the air-fuel mixture burned in the internal combustion engine 1. The O ₂ sensor 18 detects whether the air-fuel ratio of the air-fuel mixture burned in the internal combustion engine 1 is rich or lean with respect to the stoichiometric air-fuel ratio.

  The ROM of the ECU 20 stores a stoichiometric air-fuel ratio / low heating value ratio map as shown in FIG. The map stores a known relationship between the stoichiometric air-fuel ratio and the lower heating value ratio, and is configured so that the other value can be retrieved from one of these values. The stoichiometric air-fuel ratio here is an air-fuel ratio when oxygen in the air and fuel react with each other without excess or deficiency and complete combustion. Here, the lower heating value ratio is a ratio that the lower heating value of the fuel makes with respect to the lower heating value of the reference gasoline fuel. As shown in FIG. 2, the stoichiometric air-fuel ratio and the lower heating value ratio are approximately proportional.

The ROM of the ECU 20 stores two types of fuel injection amount maps, two types of injection timing maps, and two types of ignition timing maps created in advance. One of each of the two types of maps corresponds to gasoline fuel, and the other corresponds to gasoline / alcohol mixed fuel. Each map is configured such that, for example, the intake air amount and the engine speed are input variables, and the fuel injection amount, the injection timing, and the ignition timing can be read according to these values. Further, the ROM of the ECU 20 further includes other various parameters indicating the operation state such as the intake air temperature, the throttle opening degree, and the engine water temperature with respect to the fuel injection amount, the injection timing and the ignition timing read from each of these maps. A function and a program for performing correction based on this are stored.

  In this embodiment, air-fuel ratio feedback control is performed to control the fuel injection amount so that the air-fuel ratio approaches the target stoichiometric air-fuel ratio. Specifically, the air-fuel ratio feedback control calculates a deviation between a preset target stoichiometric air-fuel ratio A / Ftgt and a detected value of the A / F sensor 17, and sets an amount corresponding to the deviation and a fuel injection amount. It is executed by changing the deviation in a direction approaching zero.

  Next, a procedure for determining the fuel property in the internal combustion engine 1 will be described with reference to FIG. When an ignition key (not shown) is operated so as to start the internal combustion engine 1, the ECU 20 repeatedly executes the fuel property determination process shown in FIG. 3 at predetermined intervals. In FIG. 3, the ECU 20 first reads parameters indicating engine conditions (S10). The parameters read here are the in-cylinder pressure P, the crank angle θ, and the fuel injection amount Tau. These parameters are acquired for a plurality of predetermined crank angles θ for each cylinder and stored in a predetermined storage area of the ECU 20.

Next, the ECU 20 determines the value of PV ^κ from the in-cylinder pressure P at the predetermined reference crank angle, the in-cylinder volume V, and the specific heat ratio κ determined in advance as described above or a value in the vicinity thereof as a heat generation amount parameter. The cylinder is calculated (S20) and stored in a predetermined storage area of the ECU 20.

The detection and computation of all the cylinders is completed, ECU 20 calculates the lower calorific value ratio R _Q (S30). The lower calorific value ratio here is a ratio that the lower calorific value of the fuel to be detected forms with respect to the lower calorific value of the reference gasoline fuel. Specifically, the ECU 20 regards the amount of increase ΔPV ^κ from the intake bottom dead center of PV ^κ calculated in step S40 as the indicated calorific value Qind of the fuel according to the following equation (1), and this is the reference gasoline fuel. A lower heating value ratio _RQ is calculated by dividing by the lower heating value Qref per predetermined unit, the fuel injection amount Tau in the detection period, and the conversion coefficient x for converting to the lower heating value.

The value of the lower calorific value ratio R _Q are different depending on the nature of the fuel, in the case of an alcohol blended fuel, it becomes smaller than the case of gasoline fuel.

Then, the lower calorific value ratio R _Q, with reference to the stoichiometric air-fuel ratio / lower calorific value ratio map as described above (FIG. 2), and calculates the stoichiometric air-fuel ratio AFtgt corresponding thereto (S40). The stoichiometric air-fuel ratio AFtgt calculated here is used as a target stoichiometric value in air-fuel ratio feedback control described later.

  Next, the ECU 20 compares the calculated stoichiometric air-fuel ratio AFtgt with a threshold value determined in advance as a value corresponding to the reference gasoline fuel (S50). Then, a predetermined mixed fuel use flag is set (S60). If the stoichiometric air-fuel ratio AFtgt is greater than or equal to the threshold value, it is determined as gasoline fuel and the mixed fuel use flag is reset (S80).

  In response to these fuel ignitability determinations (S60, S80), the ECU 20 switches the operation map (S70). Specifically, in accordance with the reference to the mixed fuel use flag, alcohol mixed fuel is used when alcohol mixed fuel is used among the two types of fuel injection amount maps, fuel injection timing maps, and ignition timing maps. When gasoline fuel is used, one for gasoline fuel is selected and used for control of fuel injection amount / injection timing and ignition timing, respectively.

  As a result of the above processing, when the stoichiometric air-fuel ratio AFtgt is smaller than the threshold value, the control map for the alcohol mixed fuel is selected and used for engine control.

  On the other hand, the stoichiometric air-fuel ratio AFtgt calculated in step S40 is used as a target value in the air-fuel ratio feedback control. In the air-fuel ratio feedback control, the fuel injection amount is controlled so that the detection value AF of the A / F sensor 17 installed in the exhaust passage matches the target stoichiometric air-fuel ratio AFtgt. Specifically, the target stoichiometric control is performed. A correction amount is calculated by multiplying the deviation between the air-fuel ratio AFtgt and the detected value AF by a proportional gain Kc, and this correction amount is added to or subtracted from the current fuel injection amount. In the control system in the air-fuel ratio feedback control, the operation of the adjustment unit for calculating the feedback correction amount is not only the proportional (P) operation (P term) but also the integral (I) operation having an effect of eliminating the steady-state deviation ( It is also possible to have a differential (D) operation (D term) that avoids control instability due to the introduction of an integral operation (so-called PID control). Therefore, in the present embodiment, the target stoichiometric air-fuel ratio AFtgt is changed according to the fuel property (S40), so that the operation is performed at an appropriate stoichiometric air-fuel ratio according to the fuel property.

  As described above, in the present embodiment, the lower heating value Qind of the fuel is calculated, and the target stoichiometric air-fuel ratio AFtgt is set based on the calculated lower heating value (S40). Therefore, the relationship between the heating value and the stoichiometric air-fuel ratio is determined. By utilizing this, it becomes possible to perform air-fuel ratio control according to the fuel properties.

  Further, in the present embodiment, the lower heating value Qind of the fuel is calculated using the heat generation amount obtained from the detection value P of the in-cylinder pressure sensor. Therefore, the expected effect of the present invention can be obtained with a simple configuration. .

  Next, a second embodiment of the present invention will be described. The apparatus of the second embodiment further includes means for calculating a lower heating value based on the stoichiometric air-fuel ratio in a control device for an internal combustion engine having means for calculating the stoichiometric air-fuel ratio based on components in the exhaust gas. Features. Since the mechanical configuration of the second embodiment is the same as that of the first embodiment, detailed description thereof is omitted.

In the present embodiment, separately from the fuel property determination process according to the present invention, the fuel injection amount is controlled based on the detection value of the O ₂ sensor 18 so that the air-fuel ratio is set to the lean side and the rich side every predetermined time. O ₂ feedback control is performed to maintain the air-fuel ratio at the stoichiometric air-fuel ratio while reversing. Then, the stoichiometric air-fuel ratio is calculated based on the detected value of the O ₂ sensor 18 and the detected value of the A / F sensor 17 during the execution of the control, and the fuel property is determined based on the stoichiometric air-fuel ratio.

The processing routine of FIG. 5 is executed on condition that the O ₂ feedback control is being executed. First, the ECU ₂₀ reads the output of the O ₂ sensor 18 (S110) and stores it in the memory. Next, the ECU 20 reads the output of the A / F sensor 17 (S120) and stores it in the memory. The processes in steps S110 and S120 are repeatedly executed over a predetermined period of inversion of the output signal of the O ₂ sensor (S130). The period may be counted by using an operation command output to the injector 12 or by analyzing the output signal itself of the O ₂ sensor.

When the O ₂ sensor output and the A / F sensor output of a predetermined cycle are obtained, the ECU 20 then sets the stored output value of the O ₂ sensor 18 for a plurality of cycles to 1 as the maximum value and 0 as the minimum value. Normalize to 0-1 (S140).

Next, the ECU 20 normalizes the output value O2 _i (i = 1) of the O ₂ sensor 18 thus normalized.
˜k) and the output value AF _i (i) of the A / F sensor 17 acquired at the timing corresponding thereto.
= 1 to k), a weighted average stoichiometric air-fuel ratio AFst, which is a weighted average (weighted average) of AF _i weighted by O 2 _i , is calculated by the following equation (2) (S150).

The ECU20 is the calculated weighted average stoichiometric air-fuel ratio AFST, with reference to the stoichiometric air-fuel ratio / lower calorific value ratio map as described above (FIG. 2), calculates the lower calorific value ratio R _Q corresponding thereto (S160 ).

Next, the lower calorific value ratio R _Q calculated in ECU 20, and compared with a predetermined threshold as a value corresponding to the norms gasoline fuel (S170), is smaller than the threshold value, alcohol-mixed fuel And a predetermined mixed fuel use flag is set (S180). If the lower heating value ratio _RQ is greater than or equal to the threshold value, it is determined that the fuel is gasoline fuel and the mixed fuel use flag is reset (S200).

In response to these fuel ignitability determinations (S180, S200), the ECU 20 switches the operation map (S190). Specifically, in accordance with the reference to the mixed fuel use flag, alcohol mixed fuel is used when alcohol mixed fuel is used among the two types of fuel injection amount maps, fuel injection timing maps, and ignition timing maps. When gasoline fuel is used, one for gasoline fuel is selected and used for control of fuel injection amount / injection timing and ignition timing, respectively. As a result of the above processing, the lower heating value ratio R
_{If Q} is less than the threshold, the control map for the alcohol blend will be selected and used to control the engine.

  On the other hand, the weighted average stoichiometric air-fuel ratio AFst calculated in step S150 is used as a target value in the air-fuel ratio feedback control, and the detected value AF of the A / F sensor 17 installed in the exhaust passage is the target value. The fuel injection amount is controlled to coincide with the air-fuel ratio AFst.

As described above, in the second embodiment, it is possible to calculate the heat generation amount from the stoichiometric air-fuel ratio by using the relationship between the heat generation amount and the stoichiometric air-fuel ratio, and a new one for calculating the heat generation amount. Means can be provided. Accordingly, it is possible to eliminate the calculation of the amount of heat generation using the in-cylinder pressure sensor 15 itself. In the present embodiment, since a weighted average weighted by oxygen concentration is used instead of a simple average of the output of the A / F sensor 17, a stable stoichiometric point by O ₂ feedback control is not obtained. However, there is an advantage that the weighted average stoichiometric air-fuel ratio can be calculated.

Next, a third embodiment will be described. In the second embodiment described above, the lower heating value is calculated based on the stoichiometric air-fuel ratio. However, in the third embodiment, the portion related to the processing (step S110)
To S160), the lower heating value calculated based on the stoichiometric air-fuel ratio (lower heating value ratio R _Q1 ), and the lower heating value calculated based on the in-cylinder pressure (lower). The in-cylinder pressure detection system is diagnosed based on the comparison with the calorific value ratio R _Q2 ). The in-cylinder pressure detection system here includes an in-cylinder pressure sensor 15, a transmission path from the sensor to the ECU 20, a program for performing a series of processes for determining fuel properties using the in-cylinder pressure detection value, and various reference values. Since the mechanical configuration of the third embodiment is the same as that of the first embodiment, detailed description thereof is omitted.

The control of the third embodiment will be described. In FIG. 6, first, the ECU 20 calculates a value of the lower heating value (lower heating value ratio R _Q1 ) based on the stoichiometric air-fuel ratio (S210). The processing in step S210 is the same as that in steps S110 to S160.

Next, the ECU 20 calculates a value of the lower heating value (lower heating value ratio R _Q2 ) based on the in-cylinder pressure (S220). The process in step S220 is the same as that in steps S10 to S30 in the first embodiment.

Then, the ECU 20 determines whether or not the lower heating value ratio R _Q2 calculated based on the in-cylinder pressure matches the lower heating value ratio R _Q1 calculated based on the stoichiometric air-fuel ratio within a predetermined range (S230). In this case, it is determined that the in-cylinder pressure detection system is normal, and a predetermined in-cylinder pressure detection system abnormality flag is reset (S240). If the determination in step S230 is negative, it is determined that the in-cylinder pressure detection system is abnormal, and an in-cylinder pressure detection system abnormality flag is set (S250). The in-cylinder pressure detection system abnormality flag is referred to in other control using the in-cylinder pressure detection value or the calculation result performed using the detection value. When the flag is set, the in-cylinder pressure detection value or the same value is detected. The control itself using the calculation result performed using the detection value is stopped, or a predetermined substitute value is used as the calculation result performed using the in-cylinder pressure detection value or the detection value.

  As described above, in the third embodiment, the in-cylinder pressure detection system can be diagnosed.

In the third embodiment, the configuration for diagnosing the in-cylinder pressure detection system has been described. However, instead of such a configuration, when the lower heating value ratio R _Q2 does not match the lower heating value ratio R _Q1 within a predetermined range. The air-fuel ratio detection system may be determined to be abnormal. The air-fuel ratio detection system mentioned here includes a program for performing a series of processes for calculating the stoichiometric air-fuel ratio using the A / F sensor 17 and the transmission path from the sensor to the ECU 20, the air-fuel ratio detection value, and various reference values. Including.

Further, when the lower heating value ratio R _Q2 does not match the lower heating value ratio R _Q1 within a predetermined range, both the in-cylinder pressure detection system and the air-fuel ratio detection system are determined to be abnormal, thereby diagnosing both. It is good. Further, when the lower heating value ratio R _Q2 does not match the lower heating value ratio R _Q1 within a predetermined range, other diagnostic means (for example, a property sensor for determining the viscosity and specific gravity from the refractive index of the fuel is arranged in the fuel system) In addition, the in-cylinder pressure detection system and / or the air-fuel ratio detection system in accordance with the processing program for diagnosing the in-cylinder pressure detection system by comparing the lower calorific value calculated from the detection value of the property sensor and the lower calorific value calculated from the in-cylinder pressure By referring to the diagnosis result, it may be configured that the majority logic determines which of the in-cylinder pressure detection system and the air-fuel ratio detection system is abnormal.

  In the above embodiment, the present invention has been described with a certain degree of concreteness, but various modifications and changes can be made to the present invention without departing from the spirit and scope of the invention described in the claims. It must be understood that. That is, the present invention includes modifications and changes that fall within the scope and spirit of the appended claims and their equivalents. For example, as a method for obtaining the stoichiometric air-fuel ratio from the detection value of the A / F sensor 17, various methods other than those shown in the above embodiments can be adopted. In each of the above embodiments, an example in which the present invention is applied to an internal combustion engine of a vehicle that can use a gasoline / alcohol mixed fuel has been described. The present invention is also applicable to an engine or a hybrid vehicle including various internal combustion engines as a drive source.

1 Internal combustion engine 3 Combustion chamber 14 Crank angle sensor 15 In-cylinder pressure sensor 16 Intake pressure sensor 20 ECU Ve Exhaust valve Vi Intake valve VM Valve mechanism

Claims (1)

In a control device for an internal combustion engine having means for calculating a stoichiometric air-fuel ratio based on an air-fuel ratio detection value of exhaust gas,
Means for calculating a lower heating value of the fuel from the calculated stoichiometric air-fuel ratio based on a known relationship between the lower heating value and the stoichiometric air-fuel ratio ;
Means for calculating a lower heating value based on the in-cylinder pressure detection value;
Based on the comparison between the lower heating value calculated based on the stoichiometric air-fuel ratio and the lower heating value calculated based on the in-cylinder pressure detection value, the lower heating value is calculated based on the detected in-cylinder pressure. Diagnosing means for diagnosing at least one of the means and the means for calculating the stoichiometric air-fuel ratio based on the detected air-fuel ratio of the exhaust gas
A control device for an internal combustion engine, further comprising:

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