JP2010174745A - Device for determining deterioration in sensitivity of cylinder internal pressure sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To determine deterioration of a cylinder internal pressure sensor provided in an internal combustion engine by a simpler calculation. <P>SOLUTION: This device for determining deterioration in sensitivity of the cylinder internal pressure sensor 56 provided in the internal combustion engine 10 in order to detect cylinder internal pressure includes: a specific heat ratio calculation means calculating a specific heat ratio κ in an adiabatic expansion stroke after cylinder internal pressure peak; and a determination means comparing the specific heat ratio κ calculated by the specific heat ratio calculation means with a predetermined threshold β, and determining abnormality of sensitivity of the cylinder internal pressure sensor 56 based on a comparison result. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a sensitivity deterioration determination device for an in-cylinder pressure sensor provided in an internal combustion engine for detecting an in-cylinder pressure.

  Patent Document 1 discloses a control device for an internal combustion engine that controls a control amount such as an ignition timing using in-cylinder information detected by an in-cylinder information detection unit. This device may be provided with a detecting means for detecting an abnormality of the in-cylinder information detecting means. According to the description in Patent Document 1, the in-cylinder information detecting means may be an in-cylinder pressure sensor that detects in-cylinder pressure as in-cylinder information, and the detecting means is an in-cylinder pressure sensor at a predetermined point during the intake stroke. , The intake air pressure at a time corresponding to a predetermined point during the intake stroke, the detected value of the in-cylinder pressure sensor and the in-cylinder volume at at least two predetermined points during the compression stroke or the expansion stroke. On the basis of the calculation means for calculating the estimated value of the sensitivity of the in-cylinder pressure sensor, and the abnormality of the in-cylinder pressure sensor is determined based on the comparison result between the estimated value of the sensitivity of the in-cylinder pressure sensor calculated by this and a predetermined threshold value Determination means.

JP 2007-40207 A

  In the apparatus described in Patent Literature 1, as described above, after calculating the estimated value of the sensitivity of the in-cylinder pressure sensor, abnormality of the in-cylinder pressure sensor, specifically, deterioration of the sensitivity, is calculated using the estimated value. To be judged. The estimated value of the sensitivity of the in-cylinder pressure sensor is calculated by detecting the in-cylinder pressure sensor at a predetermined point during the intake stroke, the pressure of the intake air at the time corresponding to the predetermined point, and the compression Detection values of the in-cylinder pressure sensor at at least two predetermined points during the stroke or the expansion stroke are used. Therefore, it is expected to simplify the calculation required for the determination.

  Accordingly, the present invention has been made in view of such a point, and an object thereof is to more easily determine the deterioration of an in-cylinder pressure sensor provided in an internal combustion engine.

  In order to achieve the above object, an in-cylinder pressure sensor sensitivity deterioration determination apparatus according to the present invention is an in-cylinder pressure sensor sensitivity deterioration determination apparatus provided in an internal combustion engine for detecting in-cylinder pressure. The specific heat ratio calculating means for calculating the specific heat ratio during the expansion stroke and the specific heat ratio calculated by the specific heat ratio calculating means are compared with a predetermined threshold, and based on the comparison result, the sensitivity abnormality of the in-cylinder pressure sensor is detected. And determining means for determining.

  Preferably, the specific heat ratio calculating means performs a predetermined calculation using the in-cylinder pressure and the in-cylinder volume at two points, a point when a predetermined crank angle is advanced from when the cylinder pressure peak is shown and a point when the exhaust valve is opened. The specific heat ratio is calculated.

1 is a schematic configuration diagram of an internal combustion engine to which an embodiment of the present invention is applied. It is a conceptual graph showing the example of a relationship between the sensor output of a cylinder pressure sensor, and a true cylinder pressure. 6 is a graph conceptually showing an example of a change in in-cylinder pressure with respect to a crank angle. 6 is a graph conceptually showing an example of a relationship between in-cylinder pressure and in-cylinder volume in an arbitrary cycle in an arbitrary cylinder. 3 is a flowchart according to an embodiment of the present invention. 5 is a graph conceptually showing an example of a relationship for obtaining a predetermined threshold value.

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

  FIG. 1 is a schematic configuration diagram illustrating an internal combustion engine to which the embodiment is applied. The internal combustion engine 10 shown in FIG. 1 generates power by burning a fuel / air mixture in a combustion chamber 14 formed in a cylinder block 12 and reciprocating a piston 18 in the cylinder 16. It is. Although only one cylinder is shown in FIG. 1, the internal combustion engine 10 is preferably configured as a multi-cylinder engine, and the internal combustion engine 10 of the present embodiment is configured as a four-cylinder engine, for example.

  An intake port facing each combustion chamber 14 is connected to an intake manifold 20. A surge tank 22 and an intake pipe 24 are sequentially connected to the upstream side of the intake manifold 20. The intake pipe 24 is connected to an air intake (not shown) via an air cleaner 26. A throttle valve (in this embodiment, an electronically controlled throttle valve) 28 is incorporated in the middle of the intake pipe 24 (between the surge tank 22 and the air cleaner 26). For example, each of the intake port, the intake manifold 20, and the intake pipe 24 defines a part of the intake passage 29.

  On the other hand, an exhaust port facing each combustion chamber 14 is connected to an exhaust manifold 30, and an exhaust pipe 32 is connected to the exhaust manifold 30 on the downstream side. Connected to the exhaust pipe 32 are a front-stage catalyst device 34 including a three-way catalyst and a rear-stage catalyst device 36 including a NOx storage reduction catalyst. For example, each of the exhaust port, the exhaust manifold 30 and the exhaust pipe 32 defines a part of the exhaust passage 37.

  The internal combustion engine 10 of the present embodiment is provided with an exhaust gas recirculation (EGR) device (external EGR device) that guides part of the exhaust gas flowing through the exhaust passage 37 to the intake passage 29, but in FIG. Not shown. The external EGR device includes an EGR passage defined by an EGR pipe so that a part of the exhaust gas flowing through the exhaust passage 37 is guided to the intake passage 29, and an EGR valve (here, an electronically controlled EGR valve) provided in the EGR passage. ).

  In the cylinder head of the internal combustion engine 10, an intake valve Vi that opens and closes an intake port and an exhaust valve Ve that opens and closes an exhaust port are disposed for each combustion chamber 14. Each intake valve Vi and each exhaust valve Ve are opened and closed by a valve operating mechanism (not shown) having a variable valve timing and / or a variable lift function. Further, the internal combustion engine 10 has a number of spark plugs 40 corresponding to the number of cylinders, and the spark plugs 40 are disposed in the cylinder head so as to face the corresponding combustion chambers 14.

  Further, as shown in FIG. 1, the internal combustion engine 10 includes an injector 42, and the injector 42 is disposed in the cylinder head so as to face the corresponding combustion chamber 14. In the internal combustion engine 10, fuel such as gasoline is directly injected from the injectors 42 toward the recesses 18 a of the pistons 18 in the combustion chambers 14 in a state where air is sucked into the combustion chambers 14. As a result, in the internal combustion engine 10, it is possible to form (stratify) an air-fuel mixture layer of fuel and air in the vicinity of the spark plug 40 in a state separated from the surrounding air layer. Can be used to perform stable stratified combustion.

  The throttle valve 28, each spark plug 40, each injector 42, and the valve mechanism are electrically connected to an ECU 50 that substantially functions as a control device for the internal combustion engine 10. The ECU 50 includes a CPU, a ROM, a RAM, an input / output port, a storage device, etc., all not shown. Various sensors are electrically connected to the ECU 50 via an A / D converter or the like, for example, an air flow meter 52 for detecting an intake air amount. The ECU 50 uses the various maps stored in the storage device and the throttle valve 28 and the spark plug 40 so that a desired output can be obtained based on detection values obtained based on output signals from various sensors. The injector 42, the valve mechanism, and the like are controlled.

  As shown in FIG. 1, the sensors connected to the ECU 50 include a crank angle sensor 54. The crank angle sensor 54 is a magnetic sensor or a photoelectric sensor including a rotor plate (signal plate) fixed to the crankshaft, and the like, and gives a pulse signal indicating the rotation angle of the crankshaft to the ECU 50 every minute time. In addition, the internal combustion engine 10 has in-cylinder pressure sensors 56 including semiconductor elements, piezoelectric elements, optical fiber detection elements, and the like corresponding to the number of cylinders. Each in-cylinder pressure sensor 56 is disposed on the cylinder head so that the pressure receiving surface faces the corresponding combustion chamber 14, and is electrically connected to the ECU 50 via an A / D converter (not shown). Each in-cylinder pressure sensor 56 outputs an electric signal corresponding to the pressure in the combustion chamber 14, that is, the in-cylinder pressure. An output signal from each in-cylinder pressure sensor 56 is sequentially given to the ECU 50 every predetermined time (predetermined crank angle) to obtain a pressure value (for example, absolute pressure), and is then stored in the ECU 50 in association with the crank angle. A predetermined amount is stored and held in the area (buffer). Further, an intake pressure sensor 58 is provided for detecting the intake pressure in the intake passage 29. Here, the intake pressure sensor 58 is provided in the surge tank 22.

  In the state where the internal combustion engine 10 is operated, the deterioration determination of the in-cylinder pressure sensor 56 according to the present embodiment is performed. This will be described below. First, the technical idea will be described with reference to FIGS.

  FIG. 2 is a graph showing an example of the relationship between the sensor output (in-cylinder pressure based on the sensor output signal) and the true value (true in-cylinder pressure) of the in-cylinder pressure sensor in which sensitivity abnormality occurs in any one cylinder. It is. In FIG. 2, the relationship regarding when the in-cylinder pressure sensor 56 is normal, that is, when no sensitivity abnormality has occurred in the cylinder pressure sensor 56 is represented by a dotted line. An example of the relationship with respect to time is represented by a solid line. As apparent from FIG. 2, when a sensitivity abnormality occurs in the in-cylinder pressure sensor 56 in the high pressure side region A, in the high pressure side region A, the sensor output decreases with respect to the true value. This relationship is shown in FIG.

  FIG. 3 is a graph conceptually showing a change example (corresponding to the sensor output example of FIG. 2) of the in-cylinder pressure (corresponding to the sensor output example of FIG. 2) in any one cylinder with respect to the crank angle. is there. In FIG. 3, the crank angle 0 ° corresponds to when the piston 18 is at the compression top dead center, and the crank angle 180 ° corresponds to when the piston 18 is located at the bottom dead center. As shown in FIG. 3 as an example by a line B, when the sensitivity abnormality occurs in the in-cylinder pressure sensor 56, the maximum value of the in-cylinder pressure (in-cylinder pressure peak) detected using the sensitivity abnormality is about 3.2 MPa. . On the other hand, when the in-cylinder pressure sensor 56 is normal, the maximum value of the in-cylinder pressure detected using the in-cylinder pressure sensor 56 is about 3.6 MPa (see line C).

  Thus, when the in-cylinder pressure cannot be accurately detected by the in-cylinder pressure sensor 56 in the high-pressure side region A, the in-cylinder pressure in the high-pressure side region A obtained by using the in-cylinder pressure sensor 56 is used. It is not preferable to control 10. Therefore, it is required to appropriately determine such sensitivity abnormality of the in-cylinder pressure sensor 56, that is, deterioration thereof. Therefore, the present inventor has paid attention to the fact that the specific heat ratio κ related to the in-cylinder pressure P and the in-cylinder volume V is constant in the adiabatic change in the combustion expansion stroke.

  FIG. 4 shows an example of the relationship between the in-cylinder pressure P and the in-cylinder volume V in a certain cycle in any one cylinder, and the example of the relationship when the in-cylinder pressure sensor 56 is normal shows the line D. In addition, a relationship example when the sensitivity abnormality occurs in the in-cylinder pressure sensor 56 in the high pressure side region is represented by a line E. Further, in FIG. 4, a straight line DL is drawn in a portion substantially corresponding to the adiabatic change in the combustion expansion stroke with respect to the line D, and a straight line EL corresponding to the straight line DL is drawn with respect to the line E. These straight lines DL and EL relate to the maximum value of the in-cylinder pressure, that is, the in-cylinder pressure peak DPM and the adiabatic expansion stroke after the EPM. It corresponds to. The adiabatic expansion stroke after the in-cylinder pressure peak substantially corresponds to the period from the in-cylinder pressure peak to the exhaust valve opening in the combustion expansion stroke.

  The inclination of the straight line DL when the in-cylinder pressure P is appropriately detected using the in-cylinder pressure sensor 56 is different from the inclination of the straight line EL when the in-cylinder pressure sensor 56 is deteriorated. Is also big. From this relationship, when the adiabatic change in the combustion expansion stroke, that is, the magnitude of the slope of the portions of lines D and E substantially corresponding to the adiabatic expansion stroke after the in-cylinder pressure peak, that is, the specific heat ratio κ is below a predetermined threshold value. It is understood that it can be determined that the in-cylinder pressure sensor 56 has deteriorated. Therefore, in the present invention, the deterioration of the in-cylinder pressure sensor 56 is determined by paying attention to the change in the specific heat ratio. Hereinafter, the deterioration determination of the in-cylinder pressure sensor in the embodiment of the present invention will be described based on the flowchart of FIG. Here, the calculation according to the flowchart of FIG. 5 is performed at a predetermined time. However, the flowchart of FIG. 5 may be repeated for various periods, for example, only for a predetermined period.

  However, in the determination based on FIG. 5, deterioration determination of the in-cylinder pressure sensor 56 is performed in the low pressure side region F (see FIG. 2), and after it is determined that it is normal, the cylinder in the high pressure side region A is determined. Deterioration determination of the internal pressure sensor 56 is performed. However, in the present invention, only the deterioration determination of the in-cylinder pressure sensor 56 in the high pressure side region A, that is, only steps S511 to S517 (or S519) described later may be executed for the determination of the in-cylinder pressure sensor 56.

Note that the deterioration determination of the in-cylinder pressure sensor 56 in the low pressure side region F is performed by paying attention to the following relationship. The change width (compression pressure) ΔP of the in-cylinder pressure between two predetermined points in the compression stroke is proportional to the intake air amount KL _AFM, and the proportional coefficient is constant regardless of the intake air amount. However, as the in-cylinder pressure sensor 56 deteriorates, the proportional coefficient in the proportional relationship between the intake air amount KL _AFM and the compression pressure ΔP changes. Therefore, the deterioration of the in-cylinder pressure sensor 56 in the low pressure side region F is determined by paying attention to the change in the proportional coefficient.

  The ECU 50 determines the deterioration of the in-cylinder pressure sensor 56 in the low pressure side region F at a predetermined time. The predetermined time is a time at which the influence of the variation in the compression pressure ΔP due to the difference in the intake fresh air amount and the residual gas amount can be substantially eliminated. Steps S501 and S503 are provided to determine whether or not it is the time. In order to substantially eliminate the influence of the variation in the compression pressure ΔP between the cylinders, the valve lift is set to a predetermined value L or more, the valve overlap is zero, and the EGR valve opening (EGR opening) is zero. It is desirable.

  In step S501, it is determined whether or not the valve lift amount is equal to or greater than a predetermined value L. As the valve lift amount, a value calculated by reading a control value of the valve mechanism is used. Note that the valve lift amount may be derived from the engine operating state.

  If an affirmative determination is made in step S501, it is determined in step S503 whether or not the EGR gas amount is zero. The EGR gas referred to here includes internal EGR gas derived from valve overlap and external EGR gas via the external EGR device. Therefore, the determination in step S503 can be made up of two determinations: a determination as to whether the valve overlap is zero and a determination as to whether the EGR opening is zero. In this case, when the valve overlap is zero and the EGR opening is zero, it is determined that the EGR gas amount is zero. When the valve overlap and the EGR opening are controlled based on the engine operating state, it is determined whether or not the engine operating state is a predetermined engine operating state in which they are both zero, and an affirmative determination is made here. Sometimes an affirmative determination may be made in step S503.

  If a positive determination is made in step S503, the process proceeds to step S505. If a negative determination is made in step S501 or step S503, the process does not proceed to step S505. That is, when the lift amount of the intake valve Vi or the like does not exceed a predetermined value or when EGR gas is introduced into the cylinder through the external EGR device, the deterioration determination of the in-cylinder pressure sensor 56 is not performed (prohibited) )

In step S505, the intake air amount KL _AFM is detected. The intake air amount KL _AFM is obtained by performing a predetermined calculation based on an output signal from the air flow meter 52. Note that the intake air amount may be obtained based on an output signal from the intake pressure sensor 58.

Next, in step S507, the compression pressure ΔP (= P _θ2 −P _θ1 ) is calculated. This compression pressure ΔP is a change in in-cylinder pressure between two predetermined points (two time points) in the compression stroke. Here, the two predetermined points are the two predetermined points in a state where there is no change in the in-cylinder gas amount. Here, the two predetermined points are the two predetermined points in a state where there is substantially no noise due to the closing of the intake valve Vi or ignition by the spark plug. Specifically, the crank angle θ1 is a crank angle advanced by a predetermined angle from the crank angle when the intake valve Vi is closed, for example, a crank angle delayed by 5 ° from the crank angle when the intake valve Vi is closed. . The crank angle θ2 is a crank angle that is a predetermined angle before the crank angle at the time of ignition by the spark plug 40, and is, for example, a crank angle that is 5 ° before the crank angle at the time of ignition. When the internal combustion engine 10 is a compression ignition type engine, the crank angle θ2 may be a crank angle that is a predetermined angle before the crank angle at the time of compression ignition. ECU50 reads the cylinder pressure P _.theta.1 of the crank angle .theta.1 example from the storage unit, reads the cylinder pressure P _.theta.2 of the crank angle .theta.2, calculates the compression pressure [Delta] P.

In the next step S509, it is determined whether or not the ratio (KL _AFM / ΔP) between the intake air amount KL _AFM detected in step S505 and the compression pressure ΔP calculated in step S507 is equal to or less than a predetermined threshold value α. The predetermined threshold value α can be referred to as a system compensation value, and is determined based on the required accuracy for the in-cylinder pressure sensor 56.

If the determination in step S509 is affirmative, that is, when the ratio (KL _AFM / ΔP) between the intake air amount KL and the compression pressure ΔP is equal to or less than the predetermined threshold value α, the low-pressure side sensitivity of the in-cylinder pressure sensor 56 is in the normal region. In step S511, the high-pressure side sensitivity is determined. Although a detailed description is not given here, in this case, it is assumed that the low-pressure side sensitivity is normal, the low-pressure side sensitivity normal flag is turned ON, and the low-pressure obtained based on the output signal from the in-cylinder pressure sensor 56 Various controls of the internal combustion engine 10 can be performed using the in-cylinder pressure on the side.

  In step S511, it is determined whether or not a fuel cut is in progress. This can be determined by the ECU 50 reading the control target value of the injector 42. The determination in step S511 is performed in order to determine whether or not the engine operating state is an engine operating state in which the deterioration determination in the high pressure side region of the in-cylinder pressure sensor 56 can be performed.

  In the internal combustion engine 10, when the engine rotational speed is equal to or higher than a predetermined rotational speed (fuel cut rotational speed) or the accelerator opening is 0%, that is, the accelerator pedal (not shown) is not depressed, for example, an injector The fuel injection from 42 is stopped (fuel cut). That is, the fuel cut is performed when the engine rotational speed is in a predetermined rotational speed region set in advance and the accelerator opening is fully closed while the vehicle is running. However, when such a fuel cut state continues and the engine rotational speed decreases and reaches another predetermined rotational speed (fuel cut return rotational speed), fuel injection is resumed. In addition, when the fuel cut is being performed, the fuel injection is resumed also when the accelerator pedal is depressed and the accelerator opening increases to the open side and exceeds 0%.

If a negative determination is made in step S511 that the fuel is not being cut, the process proceeds to step S513. Then, the crank angle θ _Pmax when the maximum value (maximum in-cylinder pressure) Pmax of the in-cylinder pressure is indicated is read from the storage device.

  In the next step S515, the specific heat ratio κ during the adiabatic expansion stroke after the in-cylinder pressure peak is calculated. The calculation of the specific heat ratio κ is performed based on the equation (1).

Here, P (θ _EVO ) and V (θ _EVO ) are in-cylinder pressure and in-cylinder volume when the exhaust valve is opened, and are stored based on the crank angle derived from the control target value of the exhaust valve Ve. It is obtained by searching the data of the in-cylinder pressure and the in-cylinder volume. _{Also, P (θ Pmax + δ)} , V (θ Pmax + δ) is the crank angle theta crank from _Pmax angle [delta] (e.g., 15 °) crank angle when the minute advanced theta _Pmax when the maximum cylinder pressure Pmax The in-cylinder pressure and the in-cylinder volume at + δ are similarly obtained by searching the stored in-cylinder pressure and in-cylinder volume data based on the crank angle. By substituting the in-cylinder pressure and the in-cylinder volume at the two points, the time when the predetermined crank angle is advanced from the time when the maximum in-cylinder pressure is shown and the time when the exhaust valve is opened, into the equation (1), The specific heat ratio κ during the adiabatic expansion process after the internal pressure peak is calculated. Further description will be made based on FIG. 4. P (θ _EVO ) corresponds to the pressures of DPO and EPO in FIG. P (θ _Pmax ) corresponds to the pressures of DPM and EPM in FIG. 4, and P (θ _Pmax + δ) corresponds to the pressures of DPM1 and EPM1 in FIG.

In the next step S517, the specific heat ratio κ calculated in step S515 is compared with a predetermined threshold value β. Specifically, it is determined whether the specific heat ratio κ is equal to or less than a predetermined threshold value β. The predetermined threshold β is determined based on the required accuracy for the in-cylinder pressure sensor 56. For example, the predetermined threshold β is derived from the point where the line G indicating the transition from the initial value κ ₀ of the specific heat ratio κ and the line H of the required accuracy intersect in FIG. If a negative determination is made in step S517, the routine is terminated assuming that no abnormality in sensitivity in the high pressure side region A (high pressure side sensitivity abnormality) is recognized in the in-cylinder pressure sensor 56.

  On the other hand, if an affirmative determination is made in step S517, it is determined in step S519 that the in-cylinder pressure sensor 56 has a high-side sensitivity abnormality, and the corresponding engine operating state J (for example, the engine rotational speed NE, engine load, etc.) is indicated. The rate KL) is read from the storage area and the routine is terminated. An abnormal operating condition region related to the in-cylinder pressure sensor 56 is formed using the engine operating state J read in this way.

  Thus, the specific heat ratio κ during the adiabatic expansion process after the in-cylinder pressure peak is calculated, the specific heat ratio κ is compared with a predetermined threshold β, and the high pressure side sensitivity of the in-cylinder pressure sensor is determined based on the comparison result. Abnormality can be determined. Since this determination is performed by simple calculation using only the in-cylinder pressure and the cylinder volume at two points as described above, the calculation required for the determination can be simplified.

  It should be noted that the abnormal operation condition region is formed by using the engine operation state when it is determined that the sensitivity abnormality in the high pressure side region A exists in the in-cylinder pressure sensor 56 through the above step S519. The internal combustion engine control using the in-cylinder pressure sensor 56 is limited using the condition region. Specifically, when the engine operating state is included in the abnormal operating condition region, it is prohibited to use the in-cylinder pressure obtained based on the output signal from the in-cylinder pressure sensor 56 for controlling the internal combustion engine 10. . Therefore, the internal combustion engine 10 can be controlled more appropriately.

  As mentioned above, although this invention was demonstrated based on embodiment and its modification, this invention is not limited to these. For example, in the above embodiment, the internal combustion engine is a spark ignition engine, but it may be a compression ignition engine. Alternatively, the internal combustion engine to which the present invention is applied may be a port injection type internal combustion engine, and the present invention is applicable to various internal combustion engines.

  While the present invention has been described based on the embodiments and the like, the present invention is not limited to this. The present invention includes all modifications, applications, and equivalents included in the spirit of the present invention defined by the claims. Therefore, the present invention should not be construed as being limited, and can be applied to any other technique belonging to the scope of the idea of the present invention.

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Cylinder block 14 Combustion chamber 16 Cylinder 18 Piston 20 Intake manifold 22 Surge tank 24 Intake pipe 26 Air cleaner 28 Throttle valve 30 Exhaust manifold 32 Exhaust pipe 34 Pre-stage catalyst device 36 Rear-stage catalyst device 40 Spark plug 42 Injector 54 Crank angle sensor 56 In-cylinder pressure sensor 58 Intake pressure sensor Vi Intake valve Ve Exhaust valve

Claims (2)

In the in-cylinder pressure sensor sensitivity deterioration determination device provided in the internal combustion engine for detecting the in-cylinder pressure,
A specific heat ratio calculating means for calculating a specific heat ratio during the adiabatic expansion process after the in-cylinder pressure peak;
An in-cylinder pressure sensor comprising: a determination unit that compares the specific heat ratio calculated by the specific heat ratio calculation unit with a predetermined threshold and determines an abnormality in sensitivity of the in-cylinder pressure sensor based on the comparison result. Sensitivity degradation judgment device.   The specific heat ratio calculating means calculates the specific heat by a predetermined calculation using the in-cylinder pressure and the in-cylinder volume at two points, that is, when a predetermined crank angle is advanced from when the cylinder pressure peak is shown and when the exhaust valve is opened. The apparatus according to claim 1, wherein the ratio is calculated.

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