JP2020037892A - Failure diagnosis device for cylinder internal pressure sensor - Google Patents

Abstract

To enhance accuracy in failure diagnosis of a cylinder internal pressure sensor.SOLUTION: A failure diagnosis device 100 for a cylinder internal pressure sensor includes a cylinder internal pressure sensor SW6, and a diagnosis section 111. The diagnosis section 111 includes an operation state determination section 1111 for determining that an engine continues steady operation for a prescribed period, an estimation section 1114 for estimating a pressure in a combustion chamber at after-top timing delayed by a specified crank angle with respect to a compression top dead center, a reading section 1113 for reading a signal of the cylinder internal pressure sensor at the after-top timing, and a failure determination section 1112 for determining the failure of the cylinder internal pressure sensor on the basis of the comparison between the pressure estimated by the estimation section 1114 and the value of the signal read by the reading section 1113.SELECTED DRAWING: Figure 13B

Description

  The technology disclosed herein relates to a failure diagnosis device for an in-cylinder pressure sensor.

  Patent Literature 1 discloses an abnormality detection device for an in-cylinder pressure sensor that detects a pressure in a combustion chamber of an engine. This device detects an abnormality of the in-cylinder pressure sensor based on an output signal of the in-cylinder pressure sensor when the engine is performing a fuel cut operation.

JP 2010-127172 A

  Incidentally, the in-cylinder pressure sensor abnormality detection device described in Patent Document 1 detects an abnormality in the in-cylinder pressure sensor only when the engine is performing a fuel cut operation. Therefore, this device has room for improvement with respect to the frequency of detecting abnormalities.

  Therefore, it is conceivable to apply the technology disclosed in Patent Document 1 even when the engine is not performing the fuel cut operation. However, in this case, the output signal of the in-cylinder pressure sensor fluctuates under the influence of, for example, the combustion pressure of the air-fuel mixture, the temperature of the wall of the combustion chamber, and the amount of EGR gas introduced into the combustion chamber. Would.

  As described above, the present inventors have noticed that when the in-cylinder environment is unstable, the output of the in-cylinder pressure sensor varies even if the in-cylinder pressure sensor does not fail. Only expanding the range of application of the technology described in Patent Document 1 has a problem in the accuracy of failure diagnosis of the in-cylinder pressure sensor.

  The technology disclosed herein increases the accuracy of the failure diagnosis of the in-cylinder pressure sensor.

  The technology disclosed herein relates to a failure diagnosis device for an in-cylinder pressure sensor. The failure diagnosis device is disposed facing a combustion chamber of an engine mounted on an automobile, and outputs a signal corresponding to a pressure in the combustion chamber, and a signal of the cylinder pressure sensor is input thereto. A diagnosing unit for diagnosing a failure of the in-cylinder pressure sensor based on a signal of the in-cylinder pressure sensor.

  The diagnostic unit includes: a first determination unit that determines that the engine has continued the steady operation for a predetermined period; and a first determination unit that determines that the steady operation is continued. An estimating unit for estimating a pressure related to the pressure in the combustion chamber at a specific timing delayed by a specific crank angle with respect to the compression top dead center based on the operating state of the cylinder; and a signal of the in-cylinder pressure sensor at the specific timing. And a second determining unit that determines that the in-cylinder pressure sensor has a failure based on a comparison between the pressure estimated by the estimating unit and a value of a signal read by the reading unit. are doing.

  According to this configuration, the diagnosis unit compares the estimated value of the pressure in the combustion chamber at a specific timing with the value of the in-cylinder pressure sensor at the same timing when the engine is in the steady operation. Based on this comparison, the diagnosis unit determines that the in-cylinder pressure sensor is out of order.

  In this specification, the “pressure in the combustion chamber” is also referred to as “in-cylinder pressure”. Further, "the engine is operating steadily" refers to a state in which the operating state of the engine is kept constant or substantially constant.

  It is considered that the in-cylinder environment is stable while the engine is in the steady operation, for example, compared to when the engine is in the transient operation. Therefore, the inventors of the present application have noticed that when the failure diagnosis of the in-cylinder pressure sensor is performed at this time, the variation in the output of the in-cylinder pressure sensor is suppressed.

  Furthermore, as a result of intensive studies, the present inventors have obtained new knowledge about the gain of the output value of the in-cylinder pressure sensor. Specifically, when the in-cylinder pressure sensor is damaged by the influence of heat or the like and breaks down, the detailed mechanism is unknown, but a timing (specific timing) at which the cylinder is retarded by a predetermined crank angle with respect to the compression top dead center. The value of the signal of the in-cylinder pressure sensor greatly increases and decreases as compared with the value of the signal of the in-cylinder pressure sensor at a timing (a second specific timing described later) advanced by the same crank angle with respect to the compression top dead center. This is newly found. Therefore, if the in-cylinder pressure sensor fails, the value of the signal of the in-cylinder pressure sensor at the specific timing becomes the estimated value of the in-cylinder pressure at the same timing, that is, the value of the in-cylinder pressure sensor predicted to reach normal time (non-failure time). It will be relatively largely shifted from the value of the signal.

  As described above, while the variation in the output unrelated to the failure is suppressed, the failure diagnosis of the in-cylinder pressure sensor can be performed more accurately by performing the diagnosis at a timing at which the output remarkably increases or decreases at the time of the failure.

  Further, the reading unit reads the signal of the in-cylinder pressure sensor at a second specific timing advanced by the specific crank angle with respect to the compression top dead center, and the estimating unit reads the signal at the second specific timing. The pressure in the combustion chamber at the specific timing may be estimated based on a signal value of the in-cylinder pressure sensor.

  According to the study by the present inventors, in a cylinder pressure sensor, a piezoelectric element that converts pressure into an electric signal, and an insulating portion provided around an electrode or the like connected to the piezoelectric element are damaged by heat or the like. It is newly found that, when the insulation becomes abnormal, the theory is not clear, but the symmetry of the change of the signal of the in-cylinder pressure sensor is broken. In this case, the value of the signal of the in-cylinder pressure sensor at a specific timing delayed by a specific crank angle with respect to the compression top dead center and the value of the signal at the second specific timing advanced by the same specific crank angle with respect to the compression top dead center The difference from the value of the signal of the in-cylinder pressure sensor increases.

  In other words, when the in-cylinder pressure sensor has not failed, the above-described difference is smaller than that at the time of failure. Therefore, when estimating the in-cylinder pressure at the specific timing, it is possible to use the value of the signal of the in-cylinder pressure sensor at the second specific timing.

  The estimating unit may be configured to determine whether or not the amount of air charged into the combustion chamber and the amount of EGR gas contained in the air-fuel mixture in the combustion chamber are different from each other in the combustion chamber at the specific timing. The pressure may be estimated.

  According to this configuration, the estimation unit considers at least one of the amount of air charged into the combustion chamber and the amount of EGR gas as the operating state of the engine. Thus, it is possible to accurately estimate the in-cylinder pressure at a specific timing, and to accurately diagnose a failure of the in-cylinder pressure sensor.

  For example, when the amount of the EGR gas is large, the specific heat ratio of the air-fuel mixture and, consequently, the combustion temperature are lower than when the amount is small. In this case, it is considered that the influence of the combustion on the value of the signal of the in-cylinder pressure sensor becomes relatively small. Although this tendency has nothing to do with the failure of the in-cylinder pressure sensor, it can be an error factor in estimating the in-cylinder pressure. Therefore, in order to perform the failure diagnosis more accurately, it is effective to consider the amount of the EGR gas.

  Further, the estimating unit may estimate the pressure in the combustion chamber at the specific timing higher when the engine speed is high than when the engine speed is low.

  The in-cylinder pressure after the compression top dead center decreases under the influence of cooling loss. Although this effect is not related to the failure of the in-cylinder pressure sensor, it can be an error factor in estimating the in-cylinder pressure. In order to improve the accuracy of the failure diagnosis, it is effective to consider the influence of the cooling loss.

  On the other hand, when the rotation speed of the engine is high, the cooling loss per unit time is reduced, so that the influence of the cooling loss is reduced. As a result, it is considered that the in-cylinder pressure becomes relatively high. Therefore, at this time, by estimating the in-cylinder pressure higher than when the rotation speed is low, it is advantageous in performing more accurate failure diagnosis of the in-cylinder pressure sensor.

  Further, the diagnostic unit may estimate the pressure in the combustion chamber at the specific timing to be lower when the amount of air charged into the combustion chamber is large than when the amount is small.

  When the amount of air charged into the combustion chamber is large, leakage from the abutment of the piston ring increases during compression of the combustion chamber, so that the in-cylinder pressure after the compression top dead center decreases. Although this phenomenon has nothing to do with the failure of the in-cylinder pressure sensor, it can be an error factor in estimating the in-cylinder pressure. In order to perform a failure diagnosis more accurately, it is effective to consider the above-described leakage.

  According to the configuration described above, the estimating unit estimates the in-cylinder pressure to be lower when the amount of air charged into the combustion chamber is larger than when the amount is small. This is advantageous in performing more accurate failure diagnosis of the in-cylinder pressure sensor.

  Further, the engine is configured as a reciprocating engine, and the in-cylinder pressure sensor deforms by bending the diaphragm provided facing the combustion chamber and the diaphragm, and generates an electric current according to the deformation amount. A piezo-electric element for outputting the pressure, wherein the diagnosis unit estimates the pressure in the combustion chamber to be larger when the load on the engine is high than when the load on the engine is low.

  When the load on the engine is high, the combustion pressure becomes higher than when it is low. The inventors of the present application have confirmed that when the combustion pressure is high, the value of the signal of the in-cylinder pressure sensor appears on the low output side as a result of increased engagement between the diaphragm and the piezoelectric element. Although this phenomenon has nothing to do with the failure of the in-cylinder pressure sensor, it can be an error factor in estimating the in-cylinder pressure. In order to perform the failure diagnosis more accurately, it is effective to consider the influence of the engagement.

  According to the above configuration, the estimating unit estimates the in-cylinder pressure to be lower when the load on the engine is higher than when it is lower. This is advantageous in performing more accurate failure diagnosis of the in-cylinder pressure sensor.

  Further, the diagnosis unit may set the specific crank angle such that the specific timing is in the first half of an expansion stroke.

  Here, the “first half” of the expansion stroke may be, for example, the first half when the expansion stroke is divided into the first half, the middle half, and the second half.

  As described above, the in-cylinder pressure after the compression top dead center decreases due to the effect of cooling loss. Although this influence is not related to the failure of the in-cylinder pressure sensor, it can be an error factor in estimating the in-cylinder pressure at a specific timing. By setting the specific timing so as to be in the first half of the expansion stroke, the influence of the cooling loss can be suppressed. Thus, it is possible to accurately estimate the in-cylinder pressure at a specific timing, and to more accurately perform a failure diagnosis of the in-cylinder pressure sensor.

  Further, the first determination unit is configured to determine an amount of air charged into the combustion chamber, an amount of EGR gas contained in an air-fuel mixture in the combustion chamber, and a fuel supplied into the combustion chamber. And when at least one of the values is within a predetermined range, it may be determined that the engine is operating in a steady state.

  According to this configuration, when the fluctuations in the combustion pressure of the air-fuel mixture, the temperature of the wall surface of the combustion chamber, and the specific heat ratio of the air-fuel mixture are small, that is, when the in-cylinder environment is stable, Execute the failure diagnosis of the internal pressure sensor. This is advantageous in performing more accurate failure diagnosis of the in-cylinder pressure sensor.

  In addition, the failure diagnosis device for the in-cylinder pressure sensor is configured to receive a signal of a detection unit including at least the in-cylinder pressure sensor, and to operate the engine based on the signal of the detection unit. An ignition unit arranged to face and igniting the air-fuel mixture in the combustion chamber in response to an ignition signal from the engine control unit, and the air-fuel mixture in the combustion chamber is partially ignited by forced ignition of the ignition unit. After the air-fuel mixture starts burning with flame propagation, the remaining unburned air-fuel mixture burns by self-ignition, and the engine control unit controls the unburned air-fuel mixture to self-ignite at the target timing. The engine control unit also estimates the timing at which the unburned air-fuel mixture self-ignites based on the signal of the in-cylinder pressure sensor. It may be.

  The present applicant has proposed SPCCI (SPark Controlled Compression Ignition) combustion that combines SI (Spark Ignition) combustion and CI (Compression Ignition) combustion. SI combustion is combustion with flame propagation that is initiated by forcibly igniting an air-fuel mixture in a combustion chamber. CI combustion is combustion started by the compression ignition of the air-fuel mixture in the combustion chamber. In SPCCI combustion, when the air-fuel mixture in the combustion chamber is forcibly ignited and combustion by flame propagation is started, the unburned air-fuel mixture in the combustion chamber is generated by the heat generation of SI combustion and the pressure increase by flame propagation. Burns CI.

  CI combustion occurs when the in-cylinder temperature reaches an ignition temperature determined by the composition of the air-fuel mixture. If the in-cylinder temperature reaches the ignition temperature near the compression top dead center and CI combustion occurs, the fuel efficiency of SPCCI combustion can be maximized.

  On the other hand, in SPCCI combustion, if CI combustion occurs near the compression top dead center, the in-cylinder pressure may increase excessively and the combustion noise may become excessive. In this case, if the ignition timing is retarded, CI combustion occurs at a time when the piston is considerably lowered in the expansion stroke, so that combustion noise can be suppressed. However, the fuel efficiency of the engine decreases.

  In order to achieve both suppression of combustion noise and improvement of fuel efficiency in an engine that performs SPCCI combustion, it is necessary to control SPCCI combustion so that the combustion waveform that changes with the progress of the crank angle becomes an appropriate combustion waveform. No.

  In order to control the SPCCI combustion, for example, it is conceivable to use the CI combustion start timing θci as a parameter representing the characteristics of the SPCCI combustion. The CI combustion start timing θci is a timing at which the unburned air-fuel mixture self-ignites. If the actual θci is advanced from the target θci, the CI combustion occurs at a timing close to the compression top dead center, so that the combustion noise increases. In order to suppress the combustion noise, the engine control unit must know the actual θci.

  If the actual θci can be estimated, the engine control unit can bring the actual θci closer to the target θci by adjusting the ignition timing according to the difference between the actual θci and the target θci. For example, when the actual θci is more advanced than the target θci, the engine control unit retards the ignition timing, so that the actual θci is retarded, so that the combustion noise can be suppressed.

  The present applicant has also proposed a technique for accurately estimating θci based on the signal of the in-cylinder pressure sensor.

  Performing the failure diagnosis of the in-cylinder pressure sensor more accurately enables both the suppression of combustion noise and the improvement of fuel economy performance in an engine that performs SPCCI combustion.

  As described above, according to the failure diagnosis device for an in-cylinder pressure sensor, the accuracy of failure diagnosis can be improved.

FIG. 1 is a diagram illustrating the configuration of the engine. FIG. 2 is a view exemplifying a configuration of the combustion chamber. The upper figure is a plan view equivalent view of the combustion chamber, and the lower figure is a sectional view taken along the line II-II. FIG. 3 is a block diagram illustrating the configuration of the engine control device. FIG. 4 is a sectional explanatory view illustrating the configuration of the in-cylinder pressure sensor. FIG. 5 is a diagram illustrating a waveform of SPCCI combustion. FIG. 6 is a block diagram illustrating a functional configuration of the control unit of the engine. FIG. 7 is a diagram illustrating a change in the closing timing of the intake valve with respect to the load of the engine. FIG. 8 is a block diagram illustrating a functional configuration of the in-cylinder pressure sensor failure diagnosis device. FIG. 9 is a diagram exemplifying a waveform of a signal output when the in-cylinder pressure sensor is normal and a waveform of a signal output when a failure occurs. FIG. 10 is a diagram exemplifying a pressure difference in a normal state and a threshold value related to failure diagnosis of the in-cylinder pressure sensor. FIG. 11 is a diagram illustrating a pressure difference according to an engine load. FIG. 12 is a diagram illustrating a pressure difference according to the EGR gas amount. FIG. 13A is a flowchart illustrating a part of the procedure of the failure diagnosis of the in-cylinder pressure sensor. FIG. 13B is a flowchart illustrating another part of the procedure of the failure diagnosis of the in-cylinder pressure sensor. 14 shows the relationship between the engine speed and the delay cycle, and the lower diagram shows the relationship between the engine speed and the delay time. FIG. 15 is a time chart exemplifying a change in each parameter relating to the failure diagnosis of the in-cylinder pressure sensor. FIG. 16 is a time chart exemplifying a change in each parameter relating to the failure diagnosis of the in-cylinder pressure sensor. FIG. 17 is a flowchart illustrating another part of the procedure of the failure diagnosis of the in-cylinder pressure sensor, which is different from FIG. 13B.

  Hereinafter, embodiments of a failure diagnosis device for an in-cylinder pressure sensor will be described in detail with reference to the drawings. The following description is an example of a failure diagnosis device for an in-cylinder pressure sensor.

  FIG. 1 is a diagram exemplifying a configuration of a compression ignition type engine provided with a failure diagnosis device for an in-cylinder pressure sensor. FIG. 2 is a diagram illustrating a configuration of a combustion chamber of the engine. In FIG. 1, the intake side is on the left side of the paper, and the exhaust side is on the right side of the paper. In FIG. 2, the intake side is on the right side of the paper, and the exhaust side is on the left side of the paper. FIG. 3 is a block diagram illustrating the configuration of the engine control device.

  The engine 1 is a four-stroke reciprocating engine operated by the combustion chamber 17 repeating an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke. The engine 1 is mounted on a four-wheeled vehicle. When the engine 1 operates, the automobile runs. The fuel of the engine 1 is gasoline in this configuration example. The fuel may be a liquid fuel containing at least gasoline. The fuel may be gasoline containing, for example, bioethanol.

(Engine configuration)
The engine 1 includes a cylinder block 12 and a cylinder head 13 mounted thereon. A plurality of cylinders 11 are formed inside the cylinder block 12. 1 and 2, only one cylinder 11 is shown. The engine 1 is a multi-cylinder engine.

  The piston 3 is slidably inserted in each cylinder 11. The piston 3 is connected to a crankshaft 15 via a connecting rod 14. The piston 3 defines a combustion chamber 17 together with the cylinder 11 and the cylinder head 13. The “combustion chamber” may be used in a broad sense. That is, the “combustion chamber” may mean a space formed by the piston 3, the cylinder 11, and the cylinder head 13 regardless of the position of the piston 3. In the following description, the term “in-cylinder” may be used as a word almost synonymous with the combustion chamber.

  The lower surface of the cylinder head 13, that is, the ceiling surface of the combustion chamber 17 is constituted by an inclined surface 1311 and an inclined surface 1312 as shown in the lower diagram of FIG. The inclined surface 1311 is inclined upward from the intake side toward an axis X2 of the injector 6 described later. The slope 1312 is inclined upward from the exhaust side toward the axis X2 of the injector 6. The ceiling surface of the combustion chamber 17 has a so-called pent roof shape.

  The upper surface of the piston 3 protrudes toward the ceiling surface of the combustion chamber 17. A cavity 31 is formed on the upper surface of the piston 3. The cavity 31 is recessed from the upper surface of the piston 3. In this configuration example, the cavity 31 has a shallow dish shape. The center of the cavity 31 is shifted to the exhaust side from the center axis X1 of the cylinder 11.

  The geometric compression ratio of the engine 1 is set to 10 or more and 30 or less. As described later, the engine 1 performs SPCCI combustion that combines SI combustion and CI combustion. The SPCCI combustion controls the CI combustion by utilizing the heat generated by the SI combustion and the pressure increase. The engine 1 is a compression ignition type engine. However, in the engine 1, it is not necessary to increase the temperature of the combustion chamber 17 when the piston 3 reaches the compression top dead center. The engine 1 can set the geometric compression ratio relatively low. Reducing the geometric compression ratio is advantageous for reducing cooling loss and mechanical loss. The geometric compression ratio of the engine 1 is 14 to 17 in a regular specification (a low octane fuel having an octane number of about 91), and 15 in a high octane specification (a high octane fuel having an octane number of about 96). To 18 may be used.

  An intake port 18 is formed in the cylinder head 13 for each cylinder 11. Although not shown, the intake port 18 has two intake ports 18 of a first intake port and a second intake port. The intake port 18 communicates with the combustion chamber 17. The intake port 18 is a so-called tumble port. That is, the intake port 18 has a shape such that a tumble flow is formed in the combustion chamber 17.

  The intake port 18 is provided with an intake valve 21. The intake valve 21 opens and closes between the combustion chamber 17 and the intake port 18. The intake valve 21 opens and closes at a predetermined timing by a valve operating mechanism. The valve operating mechanism may be a variable valve operating mechanism that changes valve timing and / or valve lift. In this configuration example, as shown in FIG. 3, the variable valve mechanism has an intake electric S-VT (Sequential-Valve Timing) 23. The intake electric S-VT 23 continuously changes the phase of the intake camshaft within a predetermined range. The valve opening timing and the valve closing timing of the intake valve 21 change continuously. Note that the intake valve operating mechanism may have a hydraulic S-VT instead of the electric S-VT.

  An exhaust port 19 is formed in the cylinder head 13 for each cylinder 11. The exhaust port 19 also has two exhaust ports 19, a first exhaust port and a second exhaust port. The exhaust port 19 communicates with the combustion chamber 17.

  The exhaust port 19 is provided with an exhaust valve 22. The exhaust valve 22 opens and closes between the combustion chamber 17 and the exhaust port 19. The exhaust valve 22 opens and closes at a predetermined timing by a valve operating mechanism. This valve operating mechanism may be a variable valve operating mechanism that changes valve timing and / or valve lift. In this configuration example, as shown in FIG. 3, the variable valve mechanism has an exhaust electric S-VT24. The exhaust electric S-VT 24 continuously changes the phase of the exhaust camshaft within a predetermined range. The valve opening timing and the valve closing timing of the exhaust valve 22 change continuously. The exhaust valve mechanism may have a hydraulic S-VT instead of the electric S-VT.

  The intake electric S-VT 23 and the exhaust electric S-VT 24 adjust the length of the overlap period during which both the intake valve 21 and the exhaust valve 22 are opened. When the length of the overlap period is increased, the residual gas in the combustion chamber 17 can be scavenged. By adjusting the length of the overlap period, an internal EGR (Exhaust Gas Recirculation) gas can be introduced into the combustion chamber 17. The intake electric S-VT 23 and the exhaust electric S-VT 24 constitute an internal EGR system. Note that the internal EGR system is not always configured by the S-VT.

  The injector 6 is attached to the cylinder head 13 for each cylinder 11. The injector 6 injects fuel directly into the combustion chamber 17. The injector 6 is an example of a fuel injection unit. The injector 6 is provided at a portion where the inclined surfaces 1311 and 1312 intersect. As shown in FIG. 2, the axis X2 of the injector 6 is located closer to the exhaust side than the center axis X1 of the cylinder 11. The axis X2 of the injector 6 is parallel to the central axis X1. The axis X2 of the injector 6 coincides with the center of the cavity 31. The injector 6 faces the cavity 31. Note that the axis X2 of the injector 6 may coincide with the center axis X1 of the cylinder 11. In the case of this configuration, the axis X2 of the injector 6 may be coincident with the center of the cavity 31.

  Although not shown in detail, the injector 6 is configured by a multi-injection type fuel injection valve having a plurality of injection ports. The injector 6 injects the fuel such that the fuel spray spreads radially from the center of the combustion chamber 17 as shown by a two-dot chain line in FIG. In the present configuration example, the injector 6 has ten injection holes, and the injection holes are arranged at equal angles in the circumferential direction.

  A fuel supply system 61 is connected to the injector 6. The fuel supply system 61 includes a fuel tank 63 and a fuel supply path 62 that connects the fuel tank 63 and the injector 6 to each other. The fuel tank 63 stores fuel. A fuel pump 65 and a common rail 64 are provided in the fuel supply path 62. The fuel pump 65 pumps fuel to the common rail 64. The fuel pump 65 is a plunger pump driven by the crankshaft 15 in this configuration example. The common rail 64 stores the fuel pumped from the fuel pump 65 at a high fuel pressure. When the injector 6 opens, the fuel stored in the common rail 64 is injected into the combustion chamber 17 from the injection hole of the injector 6. The fuel supply system 61 can supply the fuel at a high pressure of 30 MPa or more to the injector 6. The pressure of the fuel supplied to the injector 6 may be changed according to the operating state of the engine 1. Note that the configuration of the fuel supply system 61 is not limited to the above configuration.

  An ignition plug 25 is attached to the cylinder head 13 for each cylinder 11. The spark plug 25 forcibly ignites the mixture in the combustion chamber 17. The spark plug 25 is an example of an ignition unit. In this configuration example, the spark plug 25 is disposed closer to the intake side than the center axis X1 of the cylinder 11. The spark plug 25 is located between the two intake ports 18. The ignition plug 25 is attached to the cylinder head 13 so as to be inclined downward from the upper side toward the center of the combustion chamber 17. As shown in FIG. 2, the electrode of the ignition plug 25 faces the inside of the combustion chamber 17 and is located near the ceiling surface of the combustion chamber 17. Note that the ignition plug 25 may be arranged on the exhaust side of the center axis X1 of the cylinder 11. Further, the spark plug 25 may be arranged on the central axis X1 of the cylinder 11.

  An intake passage 40 is connected to one side of the engine 1. The intake passage 40 communicates with the intake port 18 of each cylinder 11. Gas entering the combustion chamber 17 flows through the intake passage 40. An air cleaner 41 is provided at an upstream end of the intake passage 40. The air cleaner 41 filters fresh air. A surge tank 42 is provided near the downstream end of the intake passage 40. The intake passage 40 downstream of the surge tank 42 forms an independent passage that branches off for each cylinder 11. The downstream end of the independent passage is connected to the intake port 18 of each cylinder 11.

  A throttle valve 43 is provided between the air cleaner 41 and the surge tank 42 in the intake passage 40. The throttle valve 43 adjusts the amount of fresh air introduced into the combustion chamber 17 by adjusting the opening degree of the valve.

  In the intake passage 40, a supercharger 44 is disposed downstream of the throttle valve 43. The supercharger 44 supercharges gas entering the combustion chamber 17. In this configuration example, the supercharger 44 is a mechanical supercharger driven by the engine 1. The mechanical supercharger 44 may be of a Roots type, a Richolm type, a vane type, or a centrifugal type.

  An electromagnetic clutch 45 is interposed between the supercharger 44 and the engine 1. The electromagnetic clutch 45 transmits a driving force from the engine 1 to the supercharger 44 between the supercharger 44 and the engine 1 or interrupts the transmission of the driving force. As will be described later, the supercharger 44 switches between on and off when the ECU 10 switches between disconnection and connection of the electromagnetic clutch 45.

  An intercooler 46 is provided downstream of the supercharger 44 in the intake passage 40. The intercooler 46 cools the gas compressed by the supercharger 44. The intercooler 46 may be configured, for example, as a water-cooled type or an oil-cooled type.

  A bypass passage 47 is connected to the intake passage 40. The bypass passage 47 connects an upstream portion of the supercharger 44 and a downstream portion of the intercooler 46 in the intake passage 40 to each other. The bypass passage 47 bypasses the supercharger 44 and the intercooler 46. An air bypass valve 48 is provided in the bypass passage 47. The air bypass valve 48 adjusts the flow rate of gas flowing through the bypass passage 47.

  The ECU 10 fully opens the air bypass valve 48 when the supercharger 44 is turned off (that is, when the electromagnetic clutch 45 is disconnected). The gas flowing through the intake passage 40 bypasses the supercharger 44 and enters the combustion chamber 17 of the engine 1. The engine 1 operates in a non-supercharged state, that is, in a state of natural intake.

  When the turbocharger 44 is turned on, the engine 1 operates in a supercharged state. The ECU 10 adjusts the opening of the air bypass valve 48 when the supercharger 44 is turned on (that is, when the electromagnetic clutch 45 is connected). Part of the gas that has passed through the supercharger 44 flows back to the upstream of the supercharger 44 through the bypass passage 47. When the ECU 10 adjusts the opening of the air bypass valve 48, the pressure of the gas entering the combustion chamber 17 changes. That is, the supercharging pressure changes. It should be noted that the supercharging time is defined as a time when the pressure in the surge tank 42 exceeds the atmospheric pressure, and the non-supercharging time is defined as a time when the pressure in the surge tank 42 becomes equal to or less than the atmospheric pressure. Is also good.

  In this configuration example, a supercharging system 49 is configured by the supercharger 44, the bypass passage 47, and the air bypass valve 48.

  The engine 1 has a swirl generator that generates a swirl flow in the combustion chamber 17. The swirl flow flows as shown by white arrows in FIG. The swirl generator has a swirl control valve 56 attached to the intake passage 40. Although not shown in detail, the swirl control valve 56 is provided in a secondary passage among a primary passage connected to one of the two intake ports 18 and a secondary passage connected to the other intake port 18. It is arranged. The swirl control valve 56 is an opening control valve that can narrow the cross section of the secondary passage. If the opening degree of the swirl control valve 56 is small, the intake air flow entering the combustion chamber 17 from one intake port 18 is relatively large, and the intake air flow entering the combustion chamber 17 from the other intake port 18 is relatively small. The swirl flow in the combustion chamber 17 becomes stronger. If the degree of opening of the swirl control valve 56 is large, the flow rate of intake air entering the combustion chamber 17 from each of the two intake ports 18 becomes substantially equal, so that the swirl flow in the combustion chamber 17 becomes weak. When the swirl control valve 56 is fully opened, no swirl flow occurs.

  An exhaust passage 50 is connected to the other side of the engine 1. The exhaust passage 50 communicates with the exhaust port 19 of each cylinder 11. The exhaust passage 50 is a passage through which the exhaust gas discharged from the combustion chamber 17 flows. Although not shown in detail, an upstream portion of the exhaust passage 50 constitutes an independent passage branched for each cylinder 11. The upstream end of the independent passage is connected to the exhaust port 19 of each cylinder 11.

  An exhaust gas purification system having a plurality of catalytic converters is provided in the exhaust passage 50. Although not shown, the upstream catalytic converter is disposed in the engine room. The upstream catalytic converter has a three-way catalyst 511 and a GPF (Gasoline Particulate Filter) 512. The downstream catalytic converter is located outside the engine room. The downstream catalytic converter has a three-way catalyst 513. Note that the exhaust gas purification system is not limited to the configuration shown in the figure. For example, the GPF may be omitted. Further, the catalytic converter is not limited to one having a three-way catalyst. Furthermore, the arrangement order of the three-way catalyst and the GPF may be appropriately changed.

  An EGR passage 52 is connected between the intake passage 40 and the exhaust passage 50. The EGR passage 52 is a passage for returning a part of the exhaust gas to the intake passage 40. EGR passage 52 constitutes an external EGR system. The upstream end of the EGR passage 52 is connected between the upstream catalytic converter and the downstream catalytic converter in the exhaust passage 50. The downstream end of the EGR passage 52 is connected to an upstream portion of the supercharger 44 in the intake passage 40. The EGR gas flowing through the EGR passage 52 enters the intake passage 40 upstream of the supercharger 44 without passing through the air bypass valve 48 of the bypass passage 47.

  The EGR passage 52 is provided with a water-cooled EGR cooler 53. The EGR cooler 53 cools the exhaust gas. An EGR valve 54 is also provided in the EGR passage 52. The EGR valve 54 adjusts the flow rate of the exhaust gas flowing through the EGR passage 52. By adjusting the opening of the EGR valve 54, it is possible to adjust the amount of recirculated exhaust gas, that is, the amount of external EGR gas.

  The engine 1 has an external EGR system and an internal EGR system as the EGR system 55. The external EGR system can supply exhaust gas having a lower temperature than the internal EGR system to the combustion chamber 17.

  The control device of the compression ignition type engine includes an ECU (Engine Control Unit) 10 for operating the engine 1. The ECU 10 is a control unit based on a well-known microcomputer. As shown in FIG. 3, the ECU 10 includes a microcomputer 101 including a central processing unit (CPU) for executing a program, and a RAM (Random Access Memory), for example. The memory 102 includes a memory 102 configured by an access memory (ROM) and a read only memory (ROM) and stores programs and data, and an I / F circuit 103 that inputs and outputs electric signals.

  Various sensors SW <b> 1 to SW <b> 17 are connected to the ECU 10 as shown in FIGS. 1 and 3. The sensors SW1 to SW17 output signals to the ECU 10. The sensors include the following sensors.

Airflow sensor SW1: disposed downstream of air cleaner 41 in intake passage 40 and outputs a signal corresponding to the flow rate of fresh air flowing through intake passage 40 First intake air temperature sensor SW2: downstream of air cleaner 41 in intake passage 40 And outputs a signal corresponding to the temperature of fresh air flowing through the intake passage 40. The first pressure sensor SW3: downstream of the connection position of the EGR passage 52 in the intake passage 40 and upstream of the supercharger 44 A second intake air temperature sensor SW4 that is arranged and outputs a signal corresponding to the pressure of gas entering the supercharger 44: downstream of the supercharger 44 in the intake passage 40 and upstream of the connection position of the bypass passage 47 The intake pressure sensor SW5 which is arranged and outputs a signal corresponding to the temperature of the gas flowing out of the supercharger 44 is provided to the surge tank 42. A cylinder pressure sensor SW6 attached to the cylinder head 13 corresponding to each cylinder 11 and corresponding to the pressure in each combustion chamber 17 is provided and outputs a signal corresponding to the pressure of the gas downstream of the supercharger 44. exhaust gas temperature sensor SW7 for outputting a signal for: disposed in the exhaust passage 50 and the linear O ₂ sensor SW8 to output a signal corresponding to the temperature of the exhaust gas discharged from the combustion chamber 17: the catalyst converter upstream of the exhaust passage 50 and is also disposed upstream lambda O ₂ sensor outputs a signal corresponding to the oxygen concentration in the exhaust gas SW9: arranged downstream of the three-way catalyst 511 upstream of the catalytic converter and corresponding to the oxygen concentration in the exhaust gas Water temperature sensor SW10: attached to engine 1 and outputs a signal corresponding to the temperature of cooling water. Link angle sensor SW11: Attached to engine 1 and outputs a signal corresponding to the rotation angle of crankshaft 15. Accelerator opening sensor SW12: Attached to the accelerator pedal mechanism and accelerator opening proportional to the operation amount of the accelerator pedal The output cam angle sensor SW13 is attached to the engine 1 and outputs a signal corresponding to the rotation angle of the intake camshaft. The exhaust cam angle sensor SW14 is attached to the engine 1 and outputs a signal corresponding to the rotation angle of the exhaust camshaft. EGR differential pressure sensor SW15 that outputs a signal corresponding to the rotation angle EGR differential pressure sensor SW15: disposed in EGR passage 52 and outputs signals corresponding to the differential pressure upstream and downstream of EGR valve 54 Fuel pressure sensor SW16: common rail of fuel supply system 61 64 and supplied to the injector 6 The third intake air temperature sensor SW17: attached to the surge tank 42 and outputs a signal corresponding to the temperature of the gas in the surge tank 42, in other words, the temperature of the intake air entering the combustion chamber 17. .

  The ECU 10 determines the operating state of the engine 1 based on the signals of the sensors SW1 to SW17, and calculates the control amount of each device according to a predetermined control logic. The control logic is stored in the memory 102. The control logic includes calculating a target amount and / or a control amount using the map stored in the memory 102.

  The ECU 10 sends an electric signal related to the calculated control amount to the injector 6, the ignition plug 25, the intake electric S-VT23, the exhaust electric S-VT24, the fuel supply system 61, the throttle valve 43, the EGR valve 54, and the supercharger 44. To the electromagnetic clutch 45, the air bypass valve 48, and the swirl control valve 56.

  For example, the ECU 10 sets the target torque of the engine 1 and determines the target supercharging pressure based on the signal of the accelerator opening sensor SW12 and the map. Then, the ECU 10 adjusts the opening degree of the air bypass valve 48 based on the target supercharging pressure and the differential pressure across the supercharger 44 obtained from the signals of the first pressure sensor SW3 and the intake pressure sensor SW5. Perform control. By this feedback control, the supercharging pressure becomes the target supercharging pressure.

  Further, the ECU 10 sets a target EGR rate (that is, a ratio of EGR gas to all gases in the combustion chamber 17) based on the operating state of the engine 1 and the map. The ECU 10 determines the target EGR gas amount based on the target EGR rate and the intake air amount based on the signal from the accelerator opening sensor SW12, and determines the differential pressure across the EGR valve 54 obtained from the signal from the EGR differential pressure sensor SW15. The feedback control for adjusting the opening degree of the EGR valve 54 is performed based on By this feedback control, the external EGR gas amount entering the combustion chamber 17 becomes the target EGR gas amount.

Further, the ECU 10 executes the air-fuel ratio feedback control when a predetermined control condition is satisfied. Specifically ECU10 includes a linear O ₂ sensor SW8 and, based on the oxygen concentration in the exhaust gas obtained from the signal of the lambda O ₂ sensor SW9, as the air-fuel ratio of the mixture becomes a desired value, the injector 6 Adjust the fuel injection amount.

  The details of other control of the engine 1 by the ECU 10 will be described later.

  A notification unit 57 is also connected to the ECU 10. The notification unit 57 is configured by, for example, a warning lamp provided on the instrument panel. As described later, when the failure diagnosis device 100 for the in-cylinder pressure sensor SW6 diagnoses the failure of the in-cylinder pressure sensor SW6, the notification unit 57 notifies the user.

(Configuration of in-cylinder pressure sensor)
FIG. 4 illustrates the configuration of the in-cylinder pressure sensor SW6. The in-cylinder pressure sensor SW6 has a diaphragm 71 disposed facing the inside of the combustion chamber 17. The diaphragm 71 is made of a flexible material. The diaphragm 71 is provided at the tip of the in-cylinder pressure sensor SW6. The peripheral edge of the diaphragm 71 is supported by the housing. The housing has an outer housing 72 and an inner housing 73. When the pressure in the combustion chamber 17 increases, the outer surface of the diaphragm 71 is pushed, so that the central portion of the diaphragm 71 that is not supported by the outer housing 72 and the inner housing 73 is bent.

  Although not shown, the outer housing 72 is fixed to the cylinder head 13 of the engine 1. The outer housing 72 has a cylindrical shape with an open end. The diaphragm 71 is attached to a distal end surface of the outer housing 72. The peripheral edge of the diaphragm 71 is fixed to the outer housing 72 by welding.

  The inner housing 73 is inserted into the outer housing 72. The inner housing 73 is located at the tip of the outer housing 72. The inner housing 73 is configured by combining a plurality of components. The inner housing 73 is also cylindrical. The periphery of the diaphragm 71 is also fixed to the inner housing 73 by welding.

  The inner housing 73 is urged by the urging member 74 toward the tip of the in-cylinder pressure sensor SW6. The biasing member 74 is provided inside the outer housing 72 at a position closer to the base end of the in-cylinder pressure sensor SW6 than the inner housing 73 (that is, the upper side in FIG. 4).

  A piezoelectric element 75 is provided inside the inner housing 73. The piezoelectric element 75 is deformed by the flexure of the diaphragm 71 and outputs a weak current according to the amount of the deformation.

  A pedestal 76 is attached to the tip of the piezoelectric element 75. The pedestal 76 has a protruding portion 761 at the center thereof, protruding toward the tip of the in-cylinder pressure sensor SW6. The protruding portion 761 is located in a through hole 731 provided at the tip of the inner housing 73.

  A central projection 711 protruding toward the base end of the in-cylinder pressure sensor SW6 is provided integrally with the diaphragm 71 at a central portion on the inner surface of the diaphragm 71. The central projection 711 of the diaphragm 71 and the projection 761 of the pedestal 76 are in contact with each other. When the central portion of the diaphragm 71 bends, the pedestal 76 is pushed toward the base end of the in-cylinder pressure sensor SW6 by the central projection 711, so that the piezoelectric element 75 is deformed.

  An electrode 77 is attached to the base end of the piezoelectric element 75. The weak current of the piezoelectric element 75 is output through the electrode 77.

  The base end of the electrode 77 is supported by an electrode support 78. The electrode support portion 78 is also formed by combining a plurality of members. The electrode support 78 is welded to the inner housing 73. A conductive portion 79 is provided inside the electrode support portion 78. The conductive portion 79 extends toward the base end of the in-cylinder pressure sensor SW6. The base end of the conductive portion 79 is connected to a charge amplifier 710 included in the in-cylinder pressure sensor SW6. The charge amplifier 710 amplifies the weak current of the piezoelectric element 75 and outputs it to the ECU 10.

  A compression spring 791 is provided between the electrode 77 and the conductive part 79. The compression spring 791 conducts between the electrode 77 and the conductive portion 79.

  An annular insulating portion 712 is provided between the integrated pedestal 76, piezoelectric element 75, electrode 77, and inner housing 73. The insulating portion 712 is a portion colored black in FIG.

(SPCCI combustion concept)
The engine 1 performs combustion by compression self-ignition in a predetermined operating state with a primary purpose of improving fuel efficiency and exhaust gas performance. In the combustion by self-ignition, when the temperature in the combustion chamber 17 before the start of compression varies, the timing of self-ignition greatly changes. Therefore, the engine 1 performs SPCCI combustion that combines SI combustion and CI combustion.

  In the SPCCI combustion, the ignition plug 25 forcibly ignites the air-fuel mixture in the combustion chamber 17 so that the air-fuel mixture performs SI combustion by flame propagation and generates heat in the combustion chamber 17 by the heat generated by the SI combustion. The unburned air-fuel mixture performs CI combustion by self-ignition by increasing the temperature and increasing the pressure in the combustion chamber 17 due to flame propagation.

  By adjusting the calorific value of the SI combustion, it is possible to absorb the temperature variation in the combustion chamber 17 before the start of compression. By adjusting the ignition timing by the ECU 10, the air-fuel mixture can self-ignite at the target timing.

  In SPCCI combustion, heat generation during SI combustion is more moderate than heat generation during CI combustion. As illustrated in FIG. 5, the waveform of the heat release rate (dQ / dθ) in the SPCCI combustion has a rising slope smaller than the rising slope in the CI combustion waveform. Also, the pressure fluctuation rate (dp / dθ) in the combustion chamber 17 becomes gentler during SI combustion than during CI combustion.

  When the unburned air-fuel mixture self-ignites after the start of SI combustion, the slope of the heat release rate waveform may change from small to large at the timing of self-ignition. The waveform of the heat release rate may have an inflection point X at the timing when the CI combustion starts.

  After the start of CI combustion, SI combustion and CI combustion are performed in parallel. Since the CI combustion generates more heat than the SI combustion, the heat generation rate is relatively large. However, since the CI combustion is performed after the compression top dead center, the slope of the waveform of the heat release rate is prevented from becoming too large. The pressure fluctuation rate (dp / dθ) during CI combustion also becomes relatively moderate.

  The pressure fluctuation rate (dp / dθ) can be used as an index representing combustion noise. As described above, in the SPCCI combustion, since the pressure fluctuation rate (dp / dθ) can be reduced, it is possible to prevent the combustion noise from becoming too large. The combustion noise of the engine 1 is kept below an allowable level.

  When the CI combustion ends, the SPCCI combustion ends. CI combustion has a shorter combustion period than SI combustion. SPCCI combustion has an earlier combustion end timing than SI combustion.

The waveform of the heat generation rate in SPCCI combustion, a first heat generation rate portion Q _SI formed by SI combustion, and the second heat generating section Q _CI formed by CI combustion, but so as to be continuous in this order Is formed.

  Here, the SI ratio is defined as a parameter indicating the characteristics of SPCCI combustion. The present applicant defines the SI ratio as an index relating to the ratio of the amount of heat generated by SI combustion to the total amount of heat generated by SPCCI combustion. The SI ratio is a ratio of the amount of heat generated by two combustions having different combustion modes. When the SI ratio is high, the ratio of SI combustion is high, and when the SI ratio is low, the ratio of CI combustion is high. A high ratio of SI combustion in SPCCI combustion is advantageous for suppressing combustion noise. When the ratio of CI combustion in SPCCI combustion is high, it is advantageous for improving the fuel efficiency of the engine 1.

The SI rate may be defined as the ratio of the amount of heat generated by SI combustion to the amount of heat generated by CI combustion. That is, in SPCCI combustion, the crank angle at which the CI combustion starts as CI combustion start time Shitaci, in the waveform 801 shown in FIG. 5, the area _{Q SI} the SI combustion also advance side than Shitaci, slow including Shitaci angle from the area _{Q CI} of CI combustion is a side, it may be SI index ₌ Q SI _{/ Q CI.}

(Engine control logic)
FIG. 6 is a block diagram illustrating a functional configuration of the ECU 10 that executes the control logic of the engine 1. The ECU 10 operates the engine 1 according to the control logic stored in the memory 102. Specifically, the ECU 10 determines the operating state of the engine 1 based on the signals of the sensors SW1 to SW17, and performs combustion so that the combustion in the combustion chamber 17 becomes the combustion at the SI rate according to the operating state. Calculation for adjusting the state quantity in the chamber 17, adjusting the injection amount, adjusting the injection timing, and adjusting the ignition timing is performed.

  The ECU 10 controls SPCCI combustion using two parameters, the SI ratio and θci. Specifically, the ECU 10 determines the target SI ratio and the target θci corresponding to the operating state of the engine 1 and sets the combustion chamber 17 so that the actual SI ratio matches the target SI ratio and the actual θci becomes the target θci. And the ignition timing. The temperature in the combustion chamber 17 is adjusted by adjusting the temperature and / or the amount of exhaust gas entering the combustion chamber 17.

  The ECU 10 first reads signals from the sensors SW1 to SW17 through the I / F circuit 103. Next, the target SI ratio / target θci setting unit 101a in the microcomputer 101 of the ECU 10 determines the operating state of the engine 1 based on the signals of the sensors SW1 to SW17, and also sets the target SI ratio (that is, the target heat amount ratio). And the target CI combustion start timing θci. The target SI ratio is determined according to the operating state of the engine 1. The target SI ratio is stored in a target SI ratio storage unit 1021 of the memory 102. The target SI ratio / target θci setting unit 101a sets the target SI ratio low when the load on the engine 1 is low, and sets the target SI ratio high when the load on the engine 1 is high. When the load of the engine 1 is low, the suppression of the combustion noise and the improvement of the fuel economy are compatible with each other by increasing the ratio of the CI combustion in the SPCCI combustion. When the load of the engine 1 is high, increasing the ratio of SI combustion in SPCCI combustion is advantageous for suppressing combustion noise.

  θci means the crank angle timing at which CI combustion starts in SPCCI combustion as described above (see FIG. 5). The target θci is also determined according to the operating state of the engine 1. The target θci is stored in the target θci storage unit 1022 of the memory 102. If θci is on the retard side, combustion noise is reduced. If θci is on the advance side, the fuel efficiency of the engine 1 is improved. The target θci is set on the advance side as much as possible within a range where the combustion noise can be suppressed to an allowable level or less.

  The target in-cylinder state quantity setting unit 101b sets a target in-cylinder state quantity for realizing the set target SI ratio and target θci based on the model stored in the memory 102. Specifically, the target in-cylinder state quantity setting unit 101b sets a target temperature, a target pressure, and a target state quantity in the combustion chamber 17.

  The in-cylinder state quantity control unit 101c performs the necessary opening of the EGR valve 54, the opening of the throttle valve 43, the opening of the air bypass valve 48, and the opening of the swirl control valve 56 to achieve the target in-cylinder state quantity. The degree, the phase angle of the intake electric S-VT 23 (that is, the valve timing of the intake valve 21), and the phase angle of the exhaust electric S-VT 24 (that is, the valve timing of the exhaust valve 22) are set. The in-cylinder state quantity control unit 101c sets the control amounts of these devices based on the map stored in the memory 102. The in-cylinder state quantity control unit 101c is configured to control the EGR valve 54, the throttle valve 43, the air bypass valve 48, the swirl control valve (SCV) 56, the intake electric S-VT 23, and the exhaust electric S- The control signal is output to the VT 24. When each device operates based on a signal from the ECU 10, the state quantity in the combustion chamber 17 becomes the target state quantity.

  The in-cylinder state quantity control unit 101c further calculates a predicted value of the state quantity in the combustion chamber 17 and an estimated value of the state quantity based on the set control amounts of the respective devices. The state quantity prediction value is a value that predicts a state quantity in the combustion chamber 17 before the intake valve 21 closes. The state quantity predicted value is used for setting the fuel injection amount in the intake stroke, as described later. The state quantity estimation value is a value obtained by estimating the state quantity in the combustion chamber 17 after the intake valve 21 is closed. As will be described later, the state quantity estimation value is used for setting the fuel injection amount in the compression stroke and setting the ignition timing.

  The first injection amount setting unit 101d sets the fuel injection amount during the intake stroke based on the state amount prediction value. When performing the split injection during the intake stroke, the injection amount of each injection is set. When the fuel injection is not performed during the intake stroke, the first injection amount setting unit 101d sets the fuel injection amount to zero. The first injection control unit 101e outputs a control signal to the injector 6 so that the injector 6 injects fuel into the combustion chamber 17 at a predetermined injection timing. The first injection control unit 101e also outputs a fuel injection result during the intake stroke.

  The second injection amount setting unit 101f sets the fuel injection amount during the compression stroke based on the estimated state value and the fuel injection result during the intake stroke. When the fuel injection is not performed during the compression stroke, the second injection amount setting unit 101f sets the fuel injection amount to zero. The second injection control unit 101g outputs a control signal to the injector 6 so that the injector 6 injects fuel into the combustion chamber 17 at an injection timing based on a preset map. The second injection control unit 101g also outputs a fuel injection result during the compression stroke.

  The ignition timing setting unit 101h sets the ignition timing based on the estimated state quantity and the fuel injection result during the compression stroke. The ignition control unit 101i outputs a control signal to the ignition plug 25 so that the ignition plug 25 ignites the air-fuel mixture in the combustion chamber 17 at the set ignition timing.

  Here, when the ignition timing setting unit 101h predicts that the temperature in the combustion chamber 17 will be lower than the target temperature based on the estimated state value, the ignition timing setting unit 101h performs the compression stroke so that the ignition timing can be advanced. Is advanced from the injection timing based on the map. When the ignition timing setting unit 101h predicts that the temperature in the combustion chamber 17 will be higher than the target temperature based on the estimated state quantity, the ignition timing setting unit 101h sets the ignition timing during the compression stroke so that the ignition timing can be retarded. The injection timing is retarded from the injection timing based on the map.

  In other words, if the temperature in the combustion chamber 17 is low, the timing at which the unburned air-fuel mixture self-ignites (CI combustion start timing θci) is delayed after the start of SI combustion by spark ignition, and the SI rate becomes lower than the target SI rate. It deviates from the SI rate. In this case, an increase in unburned fuel and a decrease in exhaust gas performance are caused.

  Therefore, when the temperature in the combustion chamber 17 is predicted to be lower than the target temperature, the first injection control unit 101e and / or the second injection control unit 101g advance the injection timing and set the ignition timing setting unit. 101h advances the ignition timing. Since the early start of SI combustion enables sufficient heat generation by SI combustion, it is possible to prevent the timing θci of the self-ignition of the unburned mixture from being delayed when the temperature in the combustion chamber 17 is low. Can be. As a result, θci approaches the target θci, and the SI ratio approaches the target SI ratio.

  If the temperature in the combustion chamber 17 is high, the unburned air-fuel mixture self-ignites immediately after SI combustion starts due to spark ignition, and the SI ratio deviates from the target SI ratio. In this case, combustion noise increases.

  Therefore, when it is predicted that the temperature in the combustion chamber 17 becomes higher than the target temperature, the first injection control unit 101e and / or the second injection control unit 101g delays the injection timing and sets the ignition timing setting unit. 101h retards the ignition timing. Since the start of SI combustion is delayed, it is possible to prevent the timing θci of the self-ignition of the unburned mixture from being advanced when the temperature in the combustion chamber 17 is high. As a result, θci approaches the target θci, and the SI ratio approaches the target SI ratio.

  When the ignition plug 25 ignites the air-fuel mixture, SI combustion or SPCCI combustion is performed in the combustion chamber 17. The in-cylinder pressure sensor SW6 measures a change in pressure in the combustion chamber 17.

  The measurement signal of the in-cylinder pressure sensor SW6 is input to the θci shift calculation unit 101k. The θci deviation calculating unit 101k estimates the CI combustion start timing θci based on the measurement signal of the in-cylinder pressure sensor SW6, and calculates a deviation between the estimated CI combustion start timing θci and the target θci. The θci shift calculating unit 101k outputs the calculated θci shift to the target in-cylinder state quantity setting unit 101b. The target in-cylinder state quantity setting unit 101b corrects the model based on the θci shift. The target in-cylinder state quantity setting unit 101b sets the target in-cylinder state quantity using the corrected model in the next and subsequent cycles.

  The control logic of the engine 1 is based on an SI ratio and θci by a state quantity setting device including a throttle valve 43, an EGR valve 54, an air bypass valve 48, a swirl control valve 56, an intake electric S-VT23, and an exhaust electric S-VT24. Is adjusted to correspond to the operating state of the engine 1.

  As an example of control of the state quantity setting device, FIG. 7 shows a change in the valve closing timing IVC of the intake valve 21 with respect to the load of the engine 1. In the figure, the valve closing timing IVC of the intake valve 21 is advanced as it goes upward. When the valve closing timing IVC of the intake valve 21 is advanced, the valve opening timing IVC of the intake valve 21 is also advanced, so that the positive overlap period in which both the intake valve 21 and the exhaust valve 22 are opened becomes longer. Therefore, the amount of EGR gas entering the combustion chamber 17 increases.

  Here, when the engine 1 is in a specific operating state, the A / F of the air-fuel mixture is set to the stoichiometric air-fuel ratio or substantially the stoichiometric air-fuel ratio, and the G / F is operated leaner than the stoichiometric air-fuel ratio. As a result, the engine 1 secures the purification performance of the exhaust gas using the three-way catalyst and aims at the improvement of the fuel consumption performance. When the load of the engine 1 is low, the fuel supply amount is small. When the load on the engine 1 is low, the ECU 10 sets the valve closing timing IVC of the intake valve 21 to a timing on the retard side. The amount of air entering the combustion chamber 17 is limited to correspond to a small fuel supply. Further, since the amount of EGR gas entering the combustion chamber 17 is also limited, combustion stability is ensured.

  When the load on the engine 1 increases, the fuel supply amount increases, and thus the combustion stability increases. The ECU 10 sets the valve closing timing IVC of the intake valve 21 to a timing on the advance side. As the amount of air entering the combustion chamber 17 increases, the amount of EGR gas entering the combustion chamber 17 increases.

  As the load on the engine 1 further increases, the temperature inside the combustion chamber 17 further increases. The amount of the internal EGR gas is reduced and the amount of the external EGR gas is increased so that the temperature in the combustion chamber 17 does not become too high. Therefore, the ECU 10 sets the valve closing timing IVC of the intake valve 21 to the timing on the retard side again.

  When the load on the engine 1 is further increased, the fuel supply amount is increased. The supercharger 44 supercharges the combustion chamber 17 with an amount of air such that the A / F of the air-fuel mixture becomes the stoichiometric air-fuel ratio or substantially the stoichiometric air-fuel ratio for a large fuel supply amount. When the supercharger 44 starts supercharging, the ECU 10 sets the valve closing timing of the intake valve 21 to the timing on the advance side again. Since the amount of air entering the combustion chamber 17 increases and a positive overlap period in which both the intake valve 21 and the exhaust valve 22 are opened is provided, the residual gas in the combustion chamber 17 can be scavenged.

  The control logic of the engine 1 roughly adjusts the SI ratio by adjusting the state quantity in the combustion chamber 17 as described above. The control logic of the engine 1 is also configured to adjust the SI rate and θci by adjusting the fuel injection timing and the ignition timing. By adjusting the injection timing and the ignition timing, for example, it is possible to correct the difference between the cylinders or to finely adjust the self-ignition timing. By performing the adjustment of the SI ratio in two stages, the engine 1 can accurately achieve the target SPCCI combustion corresponding to the operating state.

(Combustion noise suppression control)
Since SPCCI combustion is a combustion mode combining SI combustion and CI combustion, knocking due to SI combustion and knocking due to CI combustion may occur. When knocking caused by SI combustion is referred to as SI knock and knocking caused by CI combustion is referred to as CI knock, SI knock means that unburned gas outside the region where the air-fuel mixture burns in the combustion chamber 17 is abnormal. Auto-ignition (local auto-ignition which is clearly different from normal CI combustion) is a phenomenon of rapid combustion. CI knock is a main component (cylinder block / head) of the engine 1 due to pressure fluctuation due to CI combustion. , Pistons, crank journals, etc.). The SI knock appears as loud noise having a frequency of about 6.3 kHz by causing air column vibration in the combustion chamber 17 due to local self-ignition. On the other hand, the CI knock appears as a loud noise having a frequency of about 1 to 4 kHz (more strictly, a plurality of frequencies included in the range) due to the resonance of the main parts of the engine 1. As described above, the SI knock and the CI knock appear as noise having different frequencies due to different causes.

  The ECU 10 controls SPCCI combustion so that both SI knock and CI knock do not occur. Specifically, the ECU 10 calculates the SI knock index value related to the SI knock and the CI knock index value related to the CI knock by performing Fourier transform on the detection signal of the in-cylinder pressure sensor SW6. The SI knock index value is an in-cylinder pressure spectrum around 6.3 kHz that increases with the occurrence of SI knock, and the CI knock index value is an in-cylinder pressure around 1-4 kHz that increases with the occurrence of CI knock. It is a spectrum.

  Then, the ECU 10 determines a θci limit such that each of the SI knock index value and the CI knock index value does not exceed the allowable limit in accordance with a predetermined map, and determines θci and θci limits determined from the operating state of the engine 1. When the θci limit is the same as θci or on the advance side, θci is set to the target θci, whereas when the θci limit is more retarded than θci, the θci limit is set to the target θci. With this control, SI knock and CI knock are both suppressed.

(Failure diagnosis of in-cylinder pressure sensor)
As described above, the engine 1 that performs SPCCI combustion performs ignition control and combustion noise suppression control using the detection signal of the in-cylinder pressure sensor SW6. In the engine 1, the detection signal of the in-cylinder pressure sensor SW6 is important. If an erroneous detection signal is output due to the failure of the in-cylinder pressure sensor SW6, operation control of the engine 1 may be hindered. Therefore, the engine 1 includes a failure diagnosis device 100 for the in-cylinder pressure sensor SW6.

  FIG. 8 illustrates the configuration of the failure diagnosis device 100 for the in-cylinder pressure sensor SW6. The failure diagnosis device 100 includes a diagnosis unit 111 and an engine control unit 112. The diagnosis unit 111 and the engine control unit 112 are functional blocks configured in the ECU 10. The engine control unit 112 controls the operation of the engine 1. Here, the engine control unit 112 performs fuel cut control of the engine 1. Specifically, the engine control unit 112 stops supplying fuel to the engine 1 through the injector 6 when the deceleration fuel cut condition is satisfied while the vehicle is running. The engine control unit 112 determines that the deceleration fuel cut condition has been satisfied based on the detection signal of the accelerator opening sensor SW12.

  When the supply of fuel is stopped, the engine 1 performs a fuel cut operation. During the fuel cut operation, the ignition plug 25 also does not ignite. The intake electric S-VT 23 sets the valve timing of the intake valve 21 to a preset target valve timing. The target valve timing is a valve timing suitable for returning from the fuel cut. After stopping the supply of fuel to the engine 1, the engine control unit 112 changes the valve timing of the intake valve 21 to the target valve timing through the intake electric S-VT23.

  The diagnosis unit 111 diagnoses a failure of the in-cylinder pressure sensor SW6 when a predetermined condition is satisfied.

  Specifically, the diagnosis unit 111 diagnoses a failure of the in-cylinder pressure sensor SW6 while the engine 1 continues the steady operation for a predetermined period. For example, the combustion pressure of the air-fuel mixture, the temperature of the wall of the combustion chamber, the specific heat ratio of the air-fuel mixture, and the like are compared while the engine 1 is in the steady operation, for example, when the engine 1 is performing the transient operation. Fluctuation becomes small. If the failure diagnosis of the in-cylinder pressure sensor SW6 is performed when the in-cylinder environment is stable, it is possible to suppress the variation in the output of the in-cylinder pressure sensor SW6 irrelevant to the failure.

  Further, the diagnosis unit 111 diagnoses the failure of the in-cylinder pressure sensor SW6 not only while the engine 1 is continuing the steady operation but also while the engine 1 is performing the fuel cut operation. By doing so, the diagnosis unit 111 can diagnose a failure of the in-cylinder pressure sensor SW6 based on a pressure change in the combustion chamber 17 that is not affected by the combustion of the air-fuel mixture. Further, since the ignition plug 25 does not perform ignition while the engine 1 is performing the fuel cut operation, there is an advantage that the detection signal of the in-cylinder pressure sensor SW6 is not affected by the noise of the ignition plug 25.

−Main configuration of functional blocks−
The diagnosis unit 111 includes, as main components, an operation state determination unit 1111 that determines a steady operation, a fuel cut operation, and the like, and a post-top timing (+ α ° CA) delayed by a specific crank angle with respect to compression top dead center. The estimating unit 1114 for estimating the in-cylinder pressure in the above, the reading unit 1113 for reading the detection signal of the in-cylinder pressure sensor SW6 at the timing after the top, the failure of the in-cylinder pressure sensor SW6 in And a failure determination unit 1112 that determines

  The operating state determination unit 1111 determines that the engine 1 has continued the steady operation for a predetermined period. Here, the operating state determination unit 1111 determines that the engine 1 is performing a steady operation when the operating state of the engine 1 is kept constant or substantially constant. Specifically, the operation state determination unit 1111 supplies the amount of air charged into the combustion chamber 17, the amount of EGR gas contained in the air-fuel mixture in the combustion chamber 17, and the inside of the combustion chamber 17. When at least one of the fuel amount and the fuel amount falls within a predetermined range, it is determined that the engine 1 is operating steadily.

  More specifically, the operating state determination unit 1111 determines the amount of air charged into the combustion chamber 17 and the EGR gas contained in the air-fuel mixture in the combustion chamber 17 based on the detection signals of the sensors SW1 to SW17. And the amount of fuel supplied into the combustion chamber 17 are determined. The operating state determination unit 1111 determines that the engine 1 is operating steadily when it is determined that the change amount of each of these three amounts is equal to or smaller than a predetermined value.

  Then, when the engine 1 continues the steady operation until the set time (several seconds in this configuration example) elapses, the operating state determination unit 1111 reads, “The engine 1 continues the steady operation for a predetermined period. Is determined. The driving state determination unit 1111 is an example of a “first determination unit”.

  When the engine control unit 112 determines that the deceleration fuel cut condition is satisfied, the operating state determination unit 1111 determines that “the engine 1 has started the fuel cut operation”.

  The estimating unit 1114 determines whether or not the driving state determination unit 1111 determines to continue the steady operation, or when the driving state determination unit 1111 determines the fuel cut operation. Estimate the in-cylinder pressure. Hereinafter, the value of the in-cylinder pressure estimated by the estimating unit 1114 is referred to as “post-top predicted value”. The post-top predicted value indicates the value of the in-cylinder pressure that is predicted to reach unless the in-cylinder pressure sensor SW6 has failed.

  The post-top prediction value estimated by the estimation unit 1114 is input to the failure determination unit 1112. The timing after the top is an example of “specific timing”.

  The reading unit 1113 calculates the value of the detection signal of the in-cylinder pressure sensor SW6 at the post-top timing (that is, the post-top signal value) and the pre-top timing at which the compression top dead center is advanced by the same specific crank angle as the post-top timing. The value of the detection signal of the in-cylinder pressure sensor SW6 at (−α ° CA) (that is, the signal value before the top) is read. The timing before the top is an example of the “second specific timing”.

  The specific crank angle is set such that the timing after the top is in the first half of the expansion stroke. Here, the “early period” may be, for example, the first period when the expansion stroke is divided into the first, middle, and second stages. The specific crank angle may be set, for example, around 60 ° CA. By setting the post-top timing to be in the first half of the expansion stroke, the effect of cooling loss can be suppressed. As a result, the accuracy of the failure diagnosis can be improved.

  Further, the specific crank angle may be reset in real time according to the operating state of the engine 1. In this case, the specific crank angle is set not after the intake valve 21 is closed by the intake electric S-VT 23 but after the intake valve 21 is closed. Further, the specific crank angle may be set to be before the ignition timing in each cycle. With this setting, the influence of the valve closing operation of the intake valve 21 and the effect of combustion of the air-fuel mixture can be suppressed. As a result, the accuracy of the failure diagnosis can be improved.

  That is, in order to improve the accuracy of the failure diagnosis of the in-cylinder pressure sensor SW6, the specific crank angle is set such that the timing before top is before the ignition timing, while the timing after top is in the first half of the expansion stroke. It is preferable that such setting be performed after the closing timing IVC of the intake valve 21.

  The pre-top signal value read by the reading unit 1113 is input to the estimation unit 1114. The estimating unit 1114 estimates a post-top predicted value based on the input pre-top signal value. On the other hand, the post-top signal value read by the reading unit 1113 is input to the failure determination unit 1112.

  The failure determination unit 1112 determines a failure of the in-cylinder pressure sensor SW6 based on a decrease in the output of the detection signal of the in-cylinder pressure sensor SW6. As described later, the decrease in the output of the detection signal of the in-cylinder pressure sensor SW6 is caused by an insulation abnormality of the insulating portion 712 of the in-cylinder pressure sensor SW6. The failure determination unit 1112 determines that the in-cylinder pressure sensor SW6 is defective based on a comparison between the after-top predicted value estimated by the estimation unit 1114 and the after-top signal value read by the reading unit 1113. This comparison is made indirectly through a threshold based on the post-top predicted value and a difference based on the post-top signal value.

More specifically, when the magnitude of the difference between the post-top signal value and the pre-top signal value exceeds a threshold value corresponding to the predicted post-top value, the failure determination unit 1112 determines that the in-cylinder pressure sensor SW6 Is determined to be faulty. The failure determination unit 1112 is an example of a “second determination unit”.
The diagnostic unit 111 further includes a threshold value setting unit 1115. The threshold setting unit 1115 sets a threshold based on the post-top predicted value. The failure determination unit 1112 reads the threshold value set by the threshold value setting unit 1115.

  The failure determination unit 1112 performs notification through the notification unit 57 when determining the failure of the in-cylinder pressure sensor SW6. The user is informed that the in-cylinder pressure sensor SW6 has failed.

-Functional blocks related to the limitation of failure judgment-
Further, as functional blocks related to the limitation of the failure determination, the diagnosis unit 111 includes a limitation unit 1117 that limits the failure determination by the failure determination unit 1112, a delay determination unit 1118 that outputs a signal to the limitation unit 1117, and a valve timing determination. And a unit 1119.

  When the engine 1 continues the steady operation or performs the fuel cut operation, the restriction unit 1117 detects the failure of the in-cylinder pressure sensor SW6 until the valve timing of the intake valve 21 reaches the target valve timing. Limit diagnosis. The in-cylinder pressure sensor SW6 outputs a signal corresponding to a pressure change caused by a change in volume of the combustion chamber 17 or the like. The failure determination unit 1112 makes a failure determination based on a detection signal of the in-cylinder pressure sensor SW6 corresponding to such a pressure change. When the closing timing of the intake valve 21 changes, the timing of starting the compression of the gas in the combustion chamber 17 changes, so that the pressure and the maximum pressure in the combustion chamber 17 during the compression stroke change. As a result, even if the in-cylinder pressure sensor SW6 does not fail, the output of the in-cylinder pressure sensor SW6 varies, and the accuracy of failure diagnosis of the in-cylinder pressure sensor SW6 deteriorates. By limiting the failure diagnosis of the in-cylinder pressure sensor SW6 until the closing timing of the intake valve 21 reaches the target timing, the failure determination unit 1112 allows the in-cylinder pressure sensor SW6 to operate when the intake valve 21 has a specific closing timing. Can be determined. Thereby, the accuracy of the failure diagnosis of the in-cylinder pressure sensor SW6 can be improved.

  The detection signal of the intake cam angle sensor SW13 is input to the valve timing determination unit 1119. When determining that the valve timing of the intake valve 21 has reached the target valve timing based on the detection signal of the intake cam angle sensor SW13, the valve timing determination unit 1119 outputs a signal to the limiting unit 1117.

  During the fuel cut operation, the limit determining unit 1117 determines that the failure determination unit 1112 determines that the in-cylinder pressure sensor SW6 has failed until the set time elapses after the supply of fuel to the engine 1 is stopped. Restrict what you can do. Immediately after the supply of fuel to the engine 1 is stopped, the environment in the combustion chamber 17 is not stable. For example, immediately after the supply of fuel to the engine 1 is stopped, the specific heat ratio of the gas in the combustion chamber 17 may not be constant due to the EGR gas remaining in the EGR passage 52 entering the combustion chamber 17. is there. Immediately after the supply of fuel to the engine 1 is stopped, the temperature of the wall surface inside the combustion chamber 17 may fluctuate greatly. As a result, even if the in-cylinder pressure sensor SW6 does not fail, the output of the in-cylinder pressure sensor SW6 varies, and the accuracy of failure diagnosis of the in-cylinder pressure sensor SW6 decreases.

  Therefore, the limiting unit 1117 limits the failure determining unit 1112 from performing the determination of the failure of the in-cylinder pressure sensor SW6 until the set time elapses after the supply of the fuel to the engine 1 is stopped. By doing so, the diagnosis unit 111 can more accurately diagnose the failure of the in-cylinder pressure sensor SW6 during the fuel cut operation.

  The diagnosis unit 111 includes a delay determination unit 1118. The delay determination unit 1118 counts the number of cycles of the engine 1. The delay determination unit 1118 is a timer for measuring that the set time described above has elapsed. When receiving a signal indicating that the engine 1 has performed the fuel cut operation from the operating state determination unit 1111, the delay determination unit 1118 starts counting the number of cycles. The delay determining unit 1118 outputs a signal to the limiting unit 1117 when determining that the set number of cycles has elapsed since the supply of fuel to the engine 1 was stopped. Note that, instead of counting the number of cycles, the delay determination unit 1118 may measure the time from when the supply of fuel to the engine 1 is stopped.

(Specific configuration related to fault diagnosis)
FIG. 9 illustrates an example of a detection signal output when the in-cylinder pressure sensor SW6 is normal and an example of a detection signal output when the in-cylinder pressure sensor SW6 is out of order. The horizontal axis in FIG. 9 is the crank angle, and 0 is the compression top dead center. The vertical axis in FIG. 9 is the pressure (in-cylinder pressure) in the combustion chamber 17 and is proportional to the detection signal of the in-cylinder pressure sensor SW6.

  As shown in FIG. 9, when the in-cylinder pressure sensor SW6 is normal, the in-cylinder pressure becomes maximum near the compression top dead center, and becomes substantially symmetric about the crank angle at which the pressure becomes maximum. If the in-cylinder pressure sensor SW6 is not out of order (normal), the post-top signal value is slightly lower than the pre-top signal value due to the influence of cooling loss and the like.

  FIG. 10 illustrates a normal pressure difference. The pressure difference shown in FIG. 10 indicates a difference obtained by subtracting the post-top signal value (正常 post-top predicted value) in the normal state from the pre-top signal value.

  As shown in FIG. 10, when the rotation speed of the engine 1 increases, the cooling loss per unit time decreases, and thus the in-cylinder pressure after the compression top dead center increases substantially. As a result, the normal pressure difference is generally small.

  As shown in FIG. 10, when the amount of air (in-cylinder air) charged into the combustion chamber 17 is large, leakage during the compression stroke increases, and the in-cylinder pressure after the compression top dead center substantially decreases. I do. As a result, the normal pressure difference is generally small.

  The tendency shown in FIG. 10 is a tendency when the in-cylinder pressure sensor SW6 is operating normally. On the other hand, the inventors of the present application have earnestly studied and as a result, have obtained new knowledge about the tendency when the in-cylinder pressure sensor SW6 is out of order.

  Specifically, it is newly found that when the in-cylinder pressure sensor SW6 fails due to the influence of heat or the like, the post-top signal value greatly increases and decreases as compared with the pre-top signal value. Therefore, if the in-cylinder pressure sensor SW6 fails, the actually detected post-top signal value is relatively largely deviated from the post-top predicted value predicted to reach a normal state. According to the study by the inventors of the present application, it has been found that the signal value after the top decreases when an insulation abnormality occurs in the insulating portion 712. In this case, as a result of the symmetry of the signal value of the in-cylinder pressure sensor SW6 being broken, the difference between the before-top signal value and the after-top predicted value and the after-top signal value increases.

  Therefore, as described above, the diagnosis unit 111 determines that the in-cylinder pressure sensor SW6 is faulty based on the comparison between the post-top predicted value estimated in advance and the post-top signal value read by the reading unit 1113. .

  As long as the engine 1 continues the steady operation, it is possible to suppress the variation in the output irrelevant to the failure of the in-cylinder pressure sensor SW6. Therefore, it is possible to perform the diagnosis at a timing at which the output remarkably increases or decreases at the time of the failure, while suppressing the variation of the output unrelated to the failure. Thereby, a failure related to the insulating unit 712 can be diagnosed more accurately.

  The post-top predicted value is estimated by the estimating unit 1114 as described above. The estimating unit 1114 estimates a post-top prediction value based on the pre-top signal value. The map corresponding to the pressure difference shown in FIG. 10 is stored in the memory 102 of the ECU 10. The estimating unit 1114 reads the pressure difference based on the operating state of the engine 1 based on the map, and estimates the post-top predicted value by subtracting the pressure difference from the pre-top signal value.

  As is apparent from the estimation method, the post-top predicted value matches the post-top signal value when the in-cylinder pressure sensor SW6 is operating normally. Therefore, the difference between the predicted value after the top and the signal value before the top indicates the tendency illustrated in FIG.

  That is, the estimating unit 1114 estimates the post-top predicted value substantially higher when the rotation speed of the engine 1 is higher than when the rotation speed is lower. This means that the effect of cooling loss has been taken into account. The effect of the cooling loss is irrelevant to the failure of the in-cylinder pressure sensor SW6, but may be an error factor in estimating the in-cylinder pressure. In order to perform a failure diagnosis more accurately, it is effective to consider the effect of cooling loss.

  Further, the estimating unit 1114 is configured to estimate the post-top predicted value substantially lower when the amount of air charged into the combustion chamber 17 is large than when the amount is small. This means that leakage from the abutment of the piston ring has been considered. Although this phenomenon has nothing to do with the failure of the in-cylinder pressure sensor SW6, it can be an error factor in estimating the in-cylinder pressure. In order to perform the failure diagnosis more accurately, it is effective to consider the leak from the joint.

  Further, when the air-fuel mixture is combusting in the combustion chamber 17 (when the engine 1 continues the steady operation), the estimating unit 1114 determines that the load of the engine 1 is higher when the load is higher than when the load is lower. Also largely estimates the pressure in the combustion chamber 17.

  When the load of the engine 1 is high, the combustion pressure becomes higher than when it is low. The inventors of the present application have confirmed that when the combustion pressure is high, the value of the signal of the in-cylinder pressure sensor SW6 appears on the low output side as a result of increased engagement between the diaphragm 71 and the piezoelectric element 75. This phenomenon greatly reduces the post-top signal value compared to the pre-top signal value. Although this tendency has nothing to do with the failure of the in-cylinder pressure sensor SW6, it can be an error factor in estimating the in-cylinder pressure. In order to perform the failure diagnosis more accurately, it is effective to consider the influence of the engagement.

  Specifically, when the load on the engine 1 is high, the estimating unit 1114 estimates the post-top predicted value lower than when the load is low. This is advantageous for more accurately diagnosing the failure of the in-cylinder pressure sensor SW6.

  For example, when the air-fuel ratio is constant, the load on the engine 1 increases as the amount of air charged into the combustion chamber 17 increases. Therefore, the pressure difference used for estimating the post-top predicted value has the same tendency as the in-cylinder air amount or a similar tendency as shown in FIG.

  Further, for example, when the amount of the EGR gas is large, the specific heat ratio of the air-fuel mixture, and consequently, the combustion temperature becomes smaller than when the amount is small. In this case, it is considered that the influence of the combustion on the in-cylinder pressure sensor SW6 is relatively small, and the pressure difference in the normal state is small (see FIG. 12). Although this tendency has nothing to do with the failure of the in-cylinder pressure sensor SW6, it can be an error factor in estimating the in-cylinder pressure. Therefore, in order to improve the accuracy of the failure diagnosis, it is effective to consider the amount of the EGR gas.

  Specifically, when the amount of EGR gas contained in the air-fuel mixture is large, the estimating unit 1114 estimates the post-top predicted value higher than when the amount is low. This is advantageous for more accurately diagnosing the failure of the in-cylinder pressure sensor SW6.

  The diagnosis unit 111 sets a threshold value corresponding to the post-top predicted value. Specifically, the threshold value setting unit 1115 sets the threshold value so as to be larger than the difference obtained by subtracting the post-top predicted value from the pre-top signal value (that is, the normal pressure difference). . The threshold value is set to be larger when the post-top predicted value is low than when it is high.

  When such a configuration is adopted, the diagnosis unit 111 sets the threshold value smaller when the engine speed is high than when the engine speed is low, for example. Similarly, the diagnosis unit 111 increases the threshold value when the amount of air charged into the combustion chamber 17 is large, for example, when compared to when the amount is small. This makes it possible to set a threshold value equal to or greater than the pressure difference caused by the cooling loss, or set a threshold value equal to or greater than the spread caused by the leakage loss. Thereby, the accuracy of the failure diagnosis can be improved.

  The failure determination unit 1112 indirectly compares the post-top predicted value with the post-top signal value. Specifically, the failure determination unit 1112 compares the threshold value determined according to the predicted value after the top with the difference between the signal value before the top and the signal value after the top, and determines the magnitude of the difference thus compared. When the threshold value is exceeded, it is determined that the in-cylinder pressure sensor SW6 is out of order. Thus, the failure diagnosis of the in-cylinder pressure sensor SW6 can be performed more accurately.

  Note that the failure determination unit 1112 repeatedly executes the comparison between the difference between the signal value before the top signal and the signal value after the top and the threshold value, and the magnitude of the difference thus compared exceeds the threshold value. May be determined to be faulty when the determination is continuously made a plurality of times.

  For example, as a result of the engagement of the components constituting the in-cylinder pressure sensor SW6 changing during the compression stroke, the pressure in the combustion chamber 17 may decrease after the compression top dead center. Such a pressure drop is only a temporary phenomenon, but may cause erroneous diagnosis of the in-cylinder pressure sensor SW.

  On the other hand, if the in-cylinder pressure sensor SW6 has actually failed, the pressure in the combustion chamber 17 will continuously change. Therefore, the determination by the failure determination unit 1112 is repeatedly performed as described above. This is advantageous in performing more accurate failure diagnosis of the in-cylinder pressure sensor SW6.

(Procedure for failure diagnosis of in-cylinder pressure sensor)
FIG. 13A and FIG. 13B are flowcharts illustrating a procedure of failure diagnosis of the in-cylinder pressure sensor SW6, which is executed by the failure diagnosis device 100. In step S1 after the start, the failure diagnosis device 100 reads detection signals of the sensors SW1 to SW17.

  In the following step S2, the operation state determination unit 1111 determines whether or not the engine 1 has continued the steady operation for a predetermined time based on the detection signals of the sensors SW1 to SW17. Specifically, the operation state determination unit 1111 supplies the amount of air charged into the combustion chamber 17, the amount of EGR gas contained in the air-fuel mixture in the combustion chamber 17, and the amount supplied to the combustion chamber 17. It is determined that the engine 1 is operating steadily when it is determined that all of the changes with respect to the amount of the fuel are below a predetermined value. For example, the amount of fuel supplied into the combustion chamber 17 may be determined based on a detection signal of the accelerator opening sensor SW12.

  If it is determined in step S2 that the steady operation is continuing, the process proceeds to step S12. If it is determined that the steady operation has not been continued, the process proceeds to step S3. In the former case, the process proceeds to the process (steps S13 to S24) of performing a failure diagnosis of the in-cylinder pressure sensor SW6 after performing the determination regarding the valve closing timing of the intake valve 21 (step S12). In the latter case, a process of performing the failure diagnosis (steps S10 to S11) after performing the determination (steps S3 to S9) of whether or not to execute the fuel cut operation and then performing the process related to the limitation of the failure diagnosis. The process proceeds to (Steps S13 to S24).

  Specifically, in step S12, the valve timing determination unit 1119 of the diagnosis unit 111 determines whether the valve closing timing of the intake valve 21 has reached the target timing or has almost reached the target timing. While the determination in step S12 is NO, the process repeats step S12. While the process repeats step S12, the limiting unit 1117 limits the execution of the failure diagnosis by the failure determination unit 1112. If the determination in step S12 is YES, the process proceeds to step S13.

  On the other hand, in step S3, the operation state determination unit 1111 determines whether the deceleration fuel cut condition is satisfied. Specifically, the operating state determination unit 1111 determines whether the accelerator opening has become zero based on the detection signal of the accelerator opening sensor SW12. When the accelerator opening becomes zero and the deceleration fuel cut condition is satisfied, the process proceeds to step S4. When the deceleration fuel cut condition is not satisfied, the process returns.

  In step S4, the operating state determination unit 1111 determines whether the engine water temperature exceeds a predetermined value based on the detection signal of the water temperature sensor SW10. If the engine water temperature exceeds a predetermined value, a fuel cut is executed. If the engine water temperature does not exceed the predetermined value, the fuel cut is not performed. If the determination in step S4 is YES, the process moves to step S5. When the determination in step S4 is NO, the process returns.

  In step S5, the operating state determination unit 1111 determines whether the opening of the EGR valve 54 has become zero or almost zero. The EGR valve 54 closes during the combustion cut. When the determination in step S5 is YES, the process proceeds to step S6, and when the determination in step S5 is NO, the process returns.

  In step S6, the engine control unit 112 stops supplying fuel to the engine 1 through the injector 6 (that is, cuts fuel). In the following step S7, the engine control unit 112 changes the valve timing of the intake valve 21 to the target valve timing set during the fuel cut operation via the intake electric S-VT23.

  In step S8, the operation state determination unit 1111 determines whether a condition for stopping the deceleration fuel cut has been satisfied. For example, when the engine speed is too low, the engine control unit 112 stops the fuel cut. When the accelerator opening exceeds zero, the fuel cut is stopped. If the determination in step S8 is YES, the process proceeds to step S9, and the engine control unit 112 stops the deceleration fuel cut. If the determination in step S8 is NO, the process proceeds to step S10.

  In step S10, the valve timing determination unit 1119 of the diagnosis unit 111 determines whether the closing timing of the intake valve 21 has reached the target timing or has almost reached the target timing. While the determination in step S10 is NO, the process repeats step S10. While the process repeats step S10, the limiting unit 1117 limits the execution of the failure diagnosis by the failure determination unit 1112. If the determination in step S10 is YES, the process proceeds to step S11.

  In step S11, the delay determination unit 1118 of the diagnosis unit 111 determines whether a delay cycle has elapsed since the start of the fuel cut. Here, the upper diagram 141 of FIG. 14 shows the relationship between the engine speed and the delay cycle. The delay cycle is constant regardless of the level of the engine speed. By passing the predetermined number of cycles, at least one gas exchange can be performed for each combustion chamber 17, and the environment in each combustion chamber 17 is stabilized.

  Note that, as described above, the delay determination unit 1118 may measure time instead of counting the number of cycles of the engine 1. The lower diagram 142 of FIG. 14 illustrates the relationship between the engine speed and the delay time. The higher the engine speed, the shorter the delay time. This is because the higher the engine speed, the shorter the time required for one cycle.

  Returning to the flow of FIG. 13A, when the determination in step S11 is NO, the process repeats step S11. The limiting unit 1117 limits the execution of the failure diagnosis by the failure determination unit 1112. If the determination in step S10 is YES, the process proceeds to step S13.

  The restriction unit 1117 determines whether the closing timing of the intake valve 21 has reached the target timing and that the delay cycle (or delay time) has elapsed since the start of the fuel cut until the two conditions are satisfied. Limit the failure diagnosis of the in-cylinder pressure sensor SW6. Accordingly, the failure determination unit 1112 can perform the failure diagnosis of the in-cylinder pressure sensor SW6 when the inside of the combustion chamber 17 is in the same state, and thus the accuracy of the failure diagnosis can be improved.

  The process after step S13 shown in the flow of FIG. 13B is common to the case where the engine 1 continues the steady operation and the case where the delay cycle has elapsed since the start of the fuel cut.

  Specifically, in step S13, the diagnosis unit 111 sets the specific crank angle based on the closing timing of the intake valve 21 and the ignition timing of the ignition plug 25. In this configuration example, the diagnosis unit 111 sets the specific crank angle such that the post-top timing is the first half of the expansion stroke and the pre-top timing is before the ignition timing.

  Subsequently, in step S14, the reading unit 1113 of the diagnosis unit 111 reads the detection signal of the in-cylinder pressure sensor SW6. Specifically, the reading unit 1113 sets the pre-top timing based on the specific crank angle set in step S13, and reads the pre-top signal value corresponding to the setting.

  Subsequently, in step S15, the estimating unit 1114 of the diagnosis unit 111 determines, based on the pre-top signal value, a post-top signal value (post-top predicted value) that is predicted to be realized if the in-cylinder pressure sensor SW6 has not failed. ). Then, in step S16 subsequent to step S15, threshold setting section 1115 of diagnosis section 111 sets a threshold value corresponding to the post-top predicted value.

  Then, in step S17, the reading unit 1113 of the diagnosis unit 111 reads the detection signal of the in-cylinder pressure sensor SW6 again. Specifically, the reading unit 1113 sets the post-top timing based on the specific crank angle set in step S13, and reads a post-top signal value corresponding to the setting.

  Then, in step S18, the failure determination unit 1112 of the diagnosis unit 111 compares the post-top predicted value with the post-top signal value. Specifically, the failure determination unit 1112 compares a threshold value set based on the predicted value after the top with a difference obtained by subtracting the signal value after the top from the signal value before the top.

  In step S19, the failure determination unit 1112 determines whether the difference between the before-top signal value and the after-top signal value exceeds a threshold based on the after-top prediction value. If the threshold value is exceeded, it is considered that the in-cylinder pressure sensor SW6 has failed, and the process proceeds to step S20. In step S20, the failure determination unit 1112 counts up the failure determination counter by one. If the threshold value is not exceeded, it is considered that the in-cylinder pressure sensor SW6 has not failed, and the process proceeds to step S21. In step S21, the failure determination unit 1112 sets the failure determination counter to zero.

  Thereafter, in step S22, the failure determination unit 1112 determines whether the failure determination counter has exceeded a predetermined value. The predetermined value may be, for example, about 3 to 5. If the determination in step S22 is NO, the process returns. If the determination in step S22 is YES, the process proceeds to step S23. That is, when the failure determination unit 1112 determines the failure of the in-cylinder pressure sensor SW6 several times continuously, the failure determination unit 1112 diagnoses that the in-cylinder pressure sensor SW6 has failed in step S23. By diagnosing the failure of the in-cylinder pressure sensor SW6 based on a plurality of determinations, erroneous diagnosis can be suppressed.

  In step S24 following step S23, the failure determination unit 1112 performs notification through the notification unit 57. The user is informed that the in-cylinder pressure sensor SW6 has failed. As a result, replacement of the failed in-cylinder pressure sensor SW6 is performed.

(Time chart)
FIGS. 15 and 16 are time charts exemplifying the change of each parameter when the failure diagnosis device 100 for the in-cylinder pressure sensor SW6 performs the failure diagnosis of the in-cylinder pressure sensor SW6 according to the flowcharts of FIGS. 13A and 13B. The horizontal axis in FIGS. 15 and 16 indicates the passage of time.

  Here, FIG. 15 is a time chart when the failure diagnosis is performed while the engine 1 continues the steady operation, and FIG. 16 is a time chart when the failure diagnosis is performed during the fuel cut operation. .

-Diagnosis of failure when steady operation is continued-
First, it is assumed that the accelerator pedal opening is gradually reduced by returning the accelerator pedal opening which the driver has depressed while the vehicle is running, and the accelerator opening becomes substantially constant at time t1 (see waveform 151). . Thus, the amount of fuel supplied into the combustion chamber 17 becomes substantially constant. As a result, it is determined that the change amount of the fuel becomes equal to or less than a predetermined value.

  Further, the opening of the EGR valve 54 gradually decreases with the accelerator opening, and the opening of the EGR valve 54 becomes substantially constant at time t1 (see waveform 152). As a result, the amount of EGR gas contained in the air-fuel mixture formed in the combustion chamber 17 also becomes substantially constant. As a result, it is determined that the change amount of the EGR gas becomes equal to or less than a predetermined value.

  Although not shown in FIG. 15, in the time chart illustrated here, the amount of air charged into the combustion chamber 17 is also substantially constant at time t1. As a result, it is determined that the amount of change in the air charged into the combustion chamber 17 also becomes less than or equal to the predetermined value at the time t1.

  In response to these determinations, the ECU 10 determines that the engine 1 is performing a steady operation. The steady operation flag indicating that the engine 1 is operating in a steady state changes from 0 to 1 at time t1, as shown by a waveform 153. When the steady operation flag becomes 1, the operation state determination unit 1111 counts the elapsed time since the steady operation flag changed from 0 to 1 (see the waveform 155). For this count, the time may be measured directly, or the wear may be indirectly performed via the number of cycles.

  At this time, the closing timing of the intake valve 21 is changed to a target timing suitable for steady operation. The time until the valve closing timing of the intake valve 21 reaches the target timing changes according to the phase difference between the valve closing timing before the change and the target timing.

  As shown in the waveform 155, the operation state determination unit 1111 determines that the engine 1 has continued the steady operation for a predetermined set time at the time t2. Thereafter, at time t3, the operating state determination unit 1111 determines that the valve timing of the intake valve 21 has reached the target timing. As described above, when both the condition that the steady operation is continued and the condition that the valve timing of the intake valve 21 becomes the target valve timing are satisfied, the failure diagnosis execution flag becomes, as shown in the waveform 156, It changes from 0 to 1 at time t3.

  In response to the failure diagnosis execution flag being set to 1, the failure determination unit 1112 starts to determine the failure of the in-cylinder pressure sensor SW6. Then, at time t4, when the driver depresses the accelerator pedal and the engine 1 shifts from the steady operation to the transient operation, the steady operation flag changes from 1 to 0. At the same time, the failure diagnosis execution flag changes from 1 to 0 in order to stop the failure diagnosis of the in-cylinder pressure sensor SW6. The elapsed time count is also reset.

-Failure diagnosis during combustion cut operation-
First, it is assumed that the driver gradually releases the accelerator pedal by stepping on the accelerator pedal while the vehicle is running, and the accelerator opening becomes zero at time t1 (see waveform 161). The opening of the EGR valve 54 gradually decreases with the accelerator opening, and the opening of the EGR valve 54 also becomes zero at time t1 (see waveform 162). Although not shown in FIG. 16, the water temperature of the engine 1 exceeds a predetermined value, and deceleration fuel cut can be performed. The F / C flag changes from zero to 1 at time t1, as shown by the waveform 163. When the F / C flag becomes 1, the engine control unit 112 stops supplying the fuel. Therefore, after time t1, the engine 1 performs the fuel cut operation.

  The valve closing timing of the intake valve 21 is changed to a preset target timing. The time until the valve closing timing of the intake valve 21 reaches the target timing changes according to the phase difference between the valve closing timing before the change and the target timing. When the phase difference is large, as shown by the solid line in the waveform 164, the time until the valve closing timing of the intake valve 21 reaches the target timing is long. When the phase difference is small, the time until the closing timing of the intake valve 21 reaches the target timing is short, as indicated by the dashed line in the waveform 154.

  As shown by the waveform 165, when the fuel cut starts, the delay determination unit 1118 starts counting cycles. The delay cycle may be, for example, 7 to 9 cycles. In the example of FIG. 16, the delay cycle elapses at time t2.

  Here, the delay cycle is set to be between the longest time (t3-t1) until the closing timing of the intake valve 21 reaches the target timing and the shortest time (t3'-t1). . The failure diagnosis of the in-cylinder pressure sensor SW6 is performed while the engine 1 is performing the fuel cut operation. When the engine 1 ends the fuel cut operation, the failure diagnosis of the in-cylinder pressure sensor SW6 cannot be performed. In order to increase the frequency of the failure diagnosis of the in-cylinder pressure sensor SW6, it is preferable to perform the failure diagnosis promptly after stopping the supply of the fuel to the engine 1. To increase the frequency of diagnosis, it is advantageous to have as few delay cycles as possible. By making the elapsed time of the delay cycle shorter than the longest change time at which the valve timing of the intake valve 21 becomes the target timing, it is advantageous in improving the frequency of failure diagnosis.

  On the other hand, by making the elapsed time of the delay cycle longer than the shortest change time at which the valve timing of the intake valve 21 becomes the target timing, the state in the combustion chamber 17 is stabilized, so that the accuracy of the failure diagnosis is improved. It is advantageous in raising. By adjusting the delay cycle (or delay time), it is possible to improve the accuracy of the failure diagnosis and the frequency of the failure diagnosis at the same time.

  In the example shown in FIG. 16, at time t3, both conditions that the delay cycle elapses and that the valve timing of the intake valve 21 becomes the target valve timing are satisfied. The execution flag of the failure diagnosis changes from zero to 1 at time t3, as indicated by the waveform 166, and the failure determination unit 1112 performs the failure determination of the in-cylinder pressure sensor SW6.

  In the example shown in FIG. 16, when the valve timing of the intake valve 21 reaches the target timing earlier (time t3 '), the failure diagnosis execution flag indicates the time as indicated by the one-dot chain line in the waveform 166. It changes from zero to one at t2.

  Then, at time t4, when the driver depresses the accelerator pedal and the accelerator opening becomes larger than zero, the F / C flag becomes zero to stop the fuel cut. At the same time, the failure diagnosis of the in-cylinder pressure sensor SW6 is also stopped, and the failure diagnosis execution flag becomes zero.

<< Other embodiments >>
-Modification of diagnostic method-
In the above embodiment, the failure determination unit 1112 is configured to indirectly compare the post-top predicted value and the post-top signal value, but the present invention is not limited to this configuration. For example, the post-top predicted value and the post-top signal value may be directly compared. Specifically, the failure determination unit 1112 may make the determination using the difference between the predicted value after the top and the detected value after the top instead of the difference between the signal value before the top and the signal value after the top. In this case, the failure determination unit 1112 determines that the in-cylinder pressure sensor SW6 is defective when the difference between the predicted value after top and the signal value after top exceeds a predetermined threshold value. Will do.

-Flow modification-
FIG. 17 shows a modification of the flow relating to the failure diagnosis of the in-cylinder pressure sensor. Steps S20 to S26 in FIG. 17 are configured by replacing steps S20 to S24 in FIG. 13B.

  First, in step S19, when the failure determination unit 1112 determines that the difference between the pre-top signal value and the post-top signal value exceeds a threshold based on the post-top prediction value, the process proceeds to step S20. On the other hand, if it is determined that the difference is equal to or smaller than the threshold, the process proceeds to step S21.

  When the process proceeds to step S20, it is considered that the in-cylinder pressure sensor SW6 has failed, so the failure determination unit 1112 counts up the failure determination counter by one and counts down the normality determination counter by one. On the other hand, in step S21, since it is considered that the in-cylinder pressure sensor SW6 has not failed, the failure determination unit 1112 counts down the failure determination counter by one and counts up the normality determination counter by one.

  In subsequent step S22, failure determination unit 1112 determines whether the failure determination counter has exceeded a predetermined value. If the determination in step S22 is YES, the process proceeds to step S23. That is, since the frequency at which it is determined that the in-cylinder pressure sensor SW6 has failed is higher than the frequency at which it is determined that the in-cylinder pressure sensor SW6 has not failed, the failure determination unit 1112 determines that the in-cylinder pressure sensor SW6 has failed. The failure determination unit 1112 performs a notification through the notification unit 57 in the subsequent step S24.

  On the other hand, if the determination in step S22 is NO, the process proceeds to step S25. In step S25, the failure determination unit 1112 determines whether the normality determination counter has exceeded a predetermined value. If the determination in step S25 is YES, the process proceeds to step S26. Since the frequency at which it is determined that the in-cylinder pressure sensor SW6 has not failed is higher than the frequency at which it is determined that the in-cylinder pressure sensor SW6 has failed, the failure determination unit 1112 determines that the in-cylinder pressure sensor SW6 has failed. If not, it is diagnosed and the failure determination counter is set to zero. The failure determination unit 1112 also sets the normality determination counter to zero. On the other hand, if the determination in step S25 is NO, the process returns.

  As described above, by diagnosing the failure of the in-cylinder pressure sensor SW6 using the two types of counters, the normality determination counter and the failure determination counter, the failure diagnosis device 100 can suppress erroneous diagnosis.

  Instead of this configuration, the operating state determination unit 1111 determines the amount of air charged into the combustion chamber 17, the amount of EGR gas contained in the air-fuel mixture in the combustion chamber 17, The amount of change in the amount of supplied fuel per unit time may be determined. In this case, when it is determined that all of these three changes are equal to or less than the predetermined value, it can be determined that the engine 1 is operating normally.

  Note that the technology disclosed herein is not limited to being applied to the engine 1 configured as described above. The engine 1 can adopt various configurations.

1 engine 100 failure diagnosis device 111 diagnosis unit 1111 operating state determination unit (first determination unit)
1112 Failure determination unit (second determination unit)
1113 Reading unit 1114 Estimating unit 17 Combustion chamber 25 Spark plug (ignition unit)
71 diaphragm 75 piezoelectric element SW1 air flow sensor (detection unit)
SW2 First intake air temperature sensor (detection unit)
SW3 1st pressure sensor (detection part)
SW4 Second intake air temperature sensor (detection unit)
SW5 Intake pressure sensor (detection unit)
SW6 In-cylinder pressure sensor (detection unit)
SW7 Exhaust gas temperature sensor (detection part)
SW8 linear _{O 2} sensor (detecting unit)
SW9 lambda _{O 2} sensor (detecting unit)
SW10 Water temperature sensor (detection unit)
SW11 Crank angle sensor (detection unit)
SW12 accelerator opening sensor (detection unit)
SW13 Intake cam angle sensor (detection unit)
SW14 Exhaust cam angle sensor (detection unit)
SW15 EGR differential pressure sensor (detection unit)
SW16 Fuel pressure sensor (detection unit)
SW17 Third intake air temperature sensor (detection unit)

Claims (9)

An in-cylinder pressure sensor that is disposed facing a combustion chamber of an engine mounted on an automobile and outputs a signal corresponding to a pressure in the combustion chamber;
A diagnostic unit that receives a signal of the in-cylinder pressure sensor and diagnoses a failure of the in-cylinder pressure sensor based on a signal of the in-cylinder pressure sensor,
The diagnostic unit includes:
A first determination unit that determines that the engine has continued a steady operation for a predetermined period;
Estimating the pressure in the combustion chamber at a specific timing delayed by a specific crank angle with respect to the compression top dead center based on the operating state of the engine when the first determination unit determines the continuation of the steady operation. An estimator to perform
A reading unit that reads a signal of the in-cylinder pressure sensor at the specific timing,
A second determining unit that determines that the in-cylinder pressure sensor is faulty based on a comparison between the pressure estimated by the estimating unit and a value of a signal read by the reading unit. Diagnostic device for an in-cylinder pressure sensor. The failure diagnosis device for an in-cylinder pressure sensor according to claim 1,
The reading unit reads a signal of the in-cylinder pressure sensor at a second specific timing advanced by the specific crank angle with respect to the compression top dead center,
The in-cylinder pressure sensor failure diagnostic device, wherein the estimating unit estimates the pressure in the combustion chamber at the specific timing based on a signal value of the in-cylinder pressure sensor at the second specific timing. The failure diagnosis device for an in-cylinder pressure sensor according to claim 1 or 2,
The estimating unit is configured to determine a pressure in the combustion chamber at the specific timing based on at least one of an amount of air charged into the combustion chamber and an amount of EGR gas included in an air-fuel mixture in the combustion chamber. A failure diagnosis device for a cylinder pressure sensor. The failure diagnosis device for an in-cylinder pressure sensor according to any one of claims 1 to 3,
The in-cylinder pressure sensor failure diagnosis device, wherein the estimating unit estimates the pressure in the combustion chamber at the specific timing higher when the engine speed is high than when the engine speed is low. The failure diagnosis device for an in-cylinder pressure sensor according to any one of claims 1 to 4,
The in-cylinder pressure sensor failure diagnostic device, wherein the estimating unit estimates the pressure in the combustion chamber at the specific timing lower when the amount of air charged into the combustion chamber is large than when the amount of air charged into the combustion chamber is small. The failure diagnosis device for an in-cylinder pressure sensor according to any one of claims 1 to 5,
The engine is configured as a reciprocating engine,
The in-cylinder pressure sensor,
A diaphragm disposed facing the combustion chamber,
The diaphragm is deformed by bending, and a piezoelectric element that outputs a current according to the amount of deformation,
The in-cylinder pressure sensor failure diagnostic device, wherein the estimating unit estimates the pressure in the combustion chamber to be lower when the load on the engine is high than when the load is low. The failure diagnosis device for an in-cylinder pressure sensor according to any one of claims 1 to 6,
The failure diagnosis device for an in-cylinder pressure sensor, wherein the diagnosis unit sets the specific crank angle such that the specific timing is in a first half of an expansion stroke. The failure diagnosis device for an in-cylinder pressure sensor according to any one of claims 1 to 7,
The first determination unit is configured to determine an amount of air charged into the combustion chamber, an amount of EGR gas contained in an air-fuel mixture in the combustion chamber, and an amount of fuel supplied into the combustion chamber. Wherein at least one of the two is within a predetermined range, it is determined that the engine is operating in a steady state. The failure diagnosis device for an in-cylinder pressure sensor according to any one of claims 1 to 8,
A signal of a detection unit including at least the in-cylinder pressure sensor is input, and an engine control unit that operates the engine based on the signal of the detection unit,
An ignition unit disposed facing the combustion chamber and igniting an air-fuel mixture in the combustion chamber in response to an ignition signal of the engine control unit,
The air-fuel mixture in the combustion chamber, after a part of the air-fuel mixture starts combustion with flame propagation by the forced ignition of the ignition unit, the remaining unburned air-fuel mixture burns by self-ignition,
The engine control unit outputs the ignition signal to the ignition unit before the target timing so that the unburned mixture self-ignites at the target timing,
The in-cylinder pressure sensor failure diagnosis device, wherein the engine control unit estimates a timing at which the unburned air-fuel mixture self-ignites based on a signal from the in-cylinder pressure sensor.

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