Engine diagnostic methods and engine systems

Abstract

To detect catching of deposits between an intake valve and a valve seat even in traveling of a vehicle at a low load.SOLUTION: During traveling of a vehicle, a minimum value af_min (S32) and an average value af_mav (S33) are always calculated from a detection value af from an air flow sensor, and a determination index ind_diag is calculated (S34) on the basis of the calculated minimum value af_min and the calculated average value af_mav. The determination index ind_diag and a determination threshold ind_fail calculated from an operation state of an engine (S35) are compared (S36), and it is determined that deposits are caught when the determination index ind_diag is lower than the determination threshold ind_fail.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to a technique for detecting an abnormal operation of an intake valve in an engine.

Background Art

[0002] In an engine, deposits adhering to an intake passage may peel off and flow toward the combustion chamber, and the deposits may bite between an intake valve and a valve seat. When deposits bite between the intake valve and the valve seat, poor closing of the intake valve occurs, causing compression leakage. When compression leakage occurs, the temperature inside the cylinder does not rise sufficiently during the compression stroke, which may lead to poor ignition in a diesel engine. Therefore, it is necessary to detect poor closing of the intake valve due to the biting of deposits.

[0003] Patent Document 1 discloses a method for detecting poor closing of an intake valve due to the biting of deposits based on crank angular velocity information from a crank angle sensor.

[0004] The technique disclosed in Patent Document 1 detects poor closing of an intake valve due to the biting of deposits based on crank angular velocity information from each crank sensor during deceleration fuel cut of a vehicle. The crank angular velocity information detects poor closing of the intake valve due to the biting of deposits by comparing the ratio (T5 / T7) of each passing time calculated from the passing time T5 of a 30°CA section centered on top dead center of compression and the passing time T7 of a 30°CA section in the subsequent expansion stroke with a threshold value.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The method described in Patent Document 1 is for detection during deceleration fuel cut-off. However, if there is flow in the intake passage, intake valve closure failure due to deposit jamming will occur, so it is necessary to detect intake valve closure failure under any circumstances while the vehicle is running. Therefore, it is conceivable to use the method described in Patent Document 1 even during combustion.

[0007] The detection method during combustion using the technology described in Patent Document 1 is conceivable to be a method that detects intake valve closure failure when the ratio of the passage time (T5 / T7) within the same cycle for each cylinder is significantly lower than the average for all cylinders. However, detection during combustion presents a problem due to slight differences in fuel injection amount between cylinders caused by individual differences in fuel injectors. These slight differences in fuel injection amount result in differences in the torque generated by the engine. Consequently, this causes differences in crank angular velocity during the expansion stroke, so differences in fuel injection amount between cylinders must be taken into account when detecting during combustion.

[0008] Under moderate loads and above, the ratio of the difference in fuel injection amounts between cylinders to the total fuel injection amount from a single fuel injector is small. Therefore, the difference in crank angular velocity is small and does not affect the detection of intake valve closure failure. On the other hand, under low loads, the ratio of the difference in fuel injection amounts between cylinders to the total fuel injection amount from a single fuel injector becomes large. As a result, even if the intake valve closes normally, the difference in crank angular velocity becomes large, making it difficult to detect intake valve closure failure. [Means for solving the problem]

[0009] To address the above problem, the inventor first collected output data from various sensors for a predetermined period prior to the occurrence of an intake valve malfunction in a vehicle. Analysis of this data revealed a phenomenon in which the intake airflow value output by the airflow sensor significantly decreases when an intake valve malfunction occurs. The inventor considered the following regarding this phenomenon: Normally, when the intake valve is properly closed, the data output by the airflow sensor only indicates the amount of air drawn in by the cylinder in the intake stroke. However, when a cylinder with an intake valve malfunction is in the compression stroke, the cylinder with the malfunction generates a blowback of air from inside the cylinder into the intake passage. Therefore, the amount of air blown back from the cylinder with the intake valve malfunction during the compression stroke is approximately equal to the amount of air drawn into another cylinder in the intake stroke at that time, causing a significant decrease in the intake airflow value detected by the airflow sensor. From this consideration, it was found that there is a strong correlation between intake valve malfunction and a significant decrease in intake airflow.

[0010] The first invention based on this finding comprises a cylinder, a piston that reciprocates within the cylinder, an intake passage communicating with the cylinder, and an intake valve that opens and closes the communication between the cylinder and the intake passage by reciprocating. , an exhaust passage communicating with the cylinder, a particulate filter provided downstream of the exhaust passage, an EGR device that recirculates exhaust gas from the exhaust passage upstream of the particulate filter to the intake passage, an intake flow rate detection unit that detects the airflow rate passing through the intake passage, and a controller to which the detection information from the intake flow rate detection unit is input, This is a diagnostic method for an engine equipped with an intake flow detection system. This method detects the intake airflow rate passing through the intake passage. Department , detection of the intake air flow rate Department Detected A valve operation determination step is performed to determine that a malfunction in the intake valve has occurred, provided that a determination index calculated from the intake air flow rate detection value is less than a predetermined determination threshold. The valve operation determination step is not performed when the determination index is less than the predetermined determination threshold at a predetermined rotational speed when the intake valve is functioning normally and there is no malfunction in the intake valve, but is performed when the rotational speed is above the predetermined speed.

[0011] According to the present invention configured in this manner, The aforementioned Intake flow rate detection Department Detected Judgment indicators calculated from but predetermined thresholdThe system diagnoses intake valve closure failure based on the condition that the value is less than a certain threshold. This allows for the diagnosis of intake valve closure failure based on the fact that the amount of air blown back from the cylinder experiencing intake valve closure failure during the compression stroke is approximately equal to the amount of air drawn into another cylinder currently in the intake stroke. Therefore, compared to conventional methods for detecting intake valve closure failure using crank angular velocity information, the diagnostic method of the present invention can perform the diagnosis using only airflow information, and can accurately detect intake valve closure failure even during vehicle operation under low load.

[0012] The aforementioned Intake flow rate detection Department This may be an airflow sensor installed in the intake passage.

[0013] According to this embodiment, by using an airflow sensor as the intake airflow detection unit, the intake airflow can be detected accurately by direct detection.

[0016] In the above embodiment, The aforementioned determination indicator teeth, The aforementioned Intake flow rate detection Department Detected This value is obtained by dividing the average value calculated from multiple intake flow rate detection values, which change in response to changes in piston speed during the intake stroke, by the minimum intake flow rate during the intake stroke calculated by the intake flow rate detection unit. It can be anything.

[0017] According to this embodiment, The aforementioned The average value At the aforementioned minimum value By performing division, deviations from the average value when the intake airflow rate drops significantly can be detected with greater accuracy. This allows for a more precise determination of intake valve closure failures.

[0018] The second invention, based on the finding that there is a strong correlation between poor closure of the intake valve and a significant decrease in intake airflow, comprises a cylinder and a piston that reciprocates within the cylinder, The aforementioned An intake passage communicating with a cylinder, and an intake valve that opens and closes the communication between the cylinder and the intake passage by reciprocating motion. The engine system comprises: an engine comprising: an intake flow rate detection unit that detects the intake air flow rate that flows into the cylinder when the intake valve is open through the intake passage; an exhaust passage communicating with the cylinder; a particulate filter provided in the exhaust passage downstream of the exhaust passage; and an EGR device that recirculates exhaust gas from the exhaust passage upstream of the particulate filter into the intake passage; and a controller electrically connected to the intake flow rate detection unit and configured to determine that a malfunction of the intake valve has occurred, provided that a determination index calculated from the intake flow rate detection value received from the intake flow rate detection unit is less than a predetermined determination threshold, wherein the controller does not perform the determination when the determination index is less than the predetermined determination threshold in normal operation when there is no malfunction of the intake valve, but performs the determination when the rotational speed is above the predetermined rotational speed.

[0019] According to the second invention, the controller receives from the intake air flow detection unit Judgment index calculated from intake air flow rate detection valueis Below the predetermined threshold On the condition that..., it is determined that there is a malfunction in closing the intake valve. Based on this, it is possible determine a malfunction in closing the intake valve, because the amount of air blown back during the compression stroke from the cylinder in which the malfunction in closing the intake valve has occurred is substantially equal to the amount of air sucked into another cylinder in the intake stroke at that time. Therefore, compared with a conventional determination system for a malfunction in closing the intake valve based on crank angular velocity information, the engine system of the present invention can make a determination only based on air flow rate information, and it is possible to accurately determine a malfunction in closing the intake valve even during vehicle running at a low load.

[0020] In the second invention, the intake air passage may be provided with an air flow sensor in the intake air flow rate detection unit. Established in It may be an air flow sensor.

[0021] According to this aspect, by using an air flow sensor as the intake air flow rate detection unit, the intake air flow rate can be accurately detected by direct detection.

[0024] In the second invention, The aforementioned the controller may be configured to calculate The aforementioned the intake air flow rate detected Department by The determination index is a value obtained by dividing the average value calculated from a plurality of intake flow rate detection values ​​that change in response to changes in piston speed during the intake stroke by the minimum intake flow rate during the intake stroke calculated by the intake flow rate detection unit. the intake air flow rate detection unit. This allows for more accurate detection of significant drops in the values ​​indicated by the airflow sensor.

Advantages of the Invention

[0026] As described above, according to the present invention, it is possible to accurately diagnose a malfunction in closing the intake valve even during vehicle running at a low load.

Brief Description of the Drawings

[0027] [Figure 1] It is a system diagram showing the overall configuration of an engine to which a control device according to an embodiment of the present invention is applied. [Figure 2] It is a cross-sectional view showing details of an intake / exhaust valve and its valve operating mechanism. [Figure 3] It is a plan view schematically showing the structure of a power transmission system between an engine and wheels. [Figure 4]This is a functional block diagram showing the control systems for the engine and automatic transmission. [Figure 5] (a) is the intake airflow detection value af, and (b) is a time chart that is an enlarged view of a portion of (a). [Figure 6] This flowchart shows the control methods used by PMC to diagnose intake valve closure failures. [Figure 7] Figure 6 is a flowchart detailing the control steps in step S3. [Figure 8] (a) is a time chart showing the minimum value af_min, (b) is the average value af_mav, and (c) is a time chart showing the judgment index ind_diag and judgment threshold ind_fail. [Figure 9] Figure 7 is a flowchart showing the details of the engine speed mask in the mask flag of step S31. [Figure 10] Figure 7 is a flowchart showing the details of the intake shutter opening mask in the mask flag of step S31. [Figure 11] Figure 7 is a flowchart showing the details of the startup mask in the mask flag at step S31. [Figure 12] Figure 7 is a flowchart showing the details of the EGR valve opening mask in the mask flag of step S31. [Modes for carrying out the invention]

[0028] Figure 1 is a system diagram showing the overall configuration of an engine to which a control device according to one embodiment of the present invention is applied. The engine 1 shown in this figure is a four-stroke diesel engine mounted on a vehicle as a power source for driving. The engine 1 comprises an engine body 2, an intake passage 30 through which intake air introduced into the engine body 2 flows, an exhaust passage 40 through which exhaust gas discharged from the engine body 2 flows, an EGR device 50 that recirculates a portion of the exhaust gas flowing through the exhaust passage 40 back into the intake passage 30, and a supercharger 60 that supercharges the intake air flowing through the intake passage 30.

[0029] The engine body 2 is a multi-cylinder type having multiple cylinders 2a arranged in a direction perpendicular to the plane of the paper in Figure 1 (see also Figure 3, which will be described later). The engine body 2 comprises a cylinder block 3, a cylinder head 4, and multiple pistons 5. The cylinders 2a are formed by the cylinder block 3 and the cylinder head 4. That is, multiple cylindrical spaces corresponding to multiple cylinders 2a are formed inside the cylinder block 3, and the cylinder head 4 is mounted on the upper surface of the cylinder block 3 so as to close these cylindrical spaces from above. The pistons 5 are housed in each cylinder 2a so as to be able to reciprocate and slide. In this embodiment, the side from the cylinder block 3 toward the cylinder head 4 is treated as the top, and the opposite side as the bottom, but this is for the convenience of explanation and is not intended to limit the mounting position of the engine body 2.

[0030] A combustion chamber C is formed above the piston 5 of each cylinder 2a. Each combustion chamber C is a space defined by the lower surface of the cylinder head 4, the side surface of the cylinder 2a (cylinder liner), and the upper surface (crown surface) of the piston 5. The combustion chamber C receives fuel injected from a fuel injection valve 9, which will be described later. The piston 5 reciprocates vertically in response to the combustion energy of the fuel supplied to the combustion chamber C. Since the engine 1 in this embodiment is a diesel engine, a fuel containing diesel oil is used as the fuel supplied to the combustion chamber C.

[0031] A crankshaft 7, which is the output shaft of the engine body 2, is located at the lower part of the cylinder block 3 (below the piston 5). The crankshaft 7 is connected to the piston 5 of each cylinder 2a via a connecting rod 8 and rotates around its central axis in accordance with the reciprocating motion (up and down motion) of the piston 5.

[0032] The cylinder block 3 is equipped with a crank angle sensor SN1 and a water temperature sensor SN2. The crank angle sensor SN1 is a sensor that detects the crank angle, which is the rotation angle of the crankshaft 7, and the engine speed, which is the rotational speed of the crankshaft 7. The water temperature sensor SN2 is a sensor that detects the temperature of the coolant circulating inside the cylinder block 3 and cylinder head 4, i.e., the engine water temperature.

[0033] The cylinder head 4 is fitted with a fuel injector 9 and a glow plug 10. The fuel injector 9 is an injector that injects fuel into the combustion chamber C of each cylinder 2a. The glow plug 10 is a plug that heats the combustion chamber C of each cylinder 2a. One fuel injector 9 and one glow plug 10 are provided for each cylinder 2a.

[0034] The fuel injector 9 is mounted on the cylinder head 4 so that its tip is exposed to the combustion chamber C. Multiple nozzles (not shown) that serve as fuel outlets are formed at the tip of the fuel injector 9. The fuel injected from each nozzle burns by autoignition in the combustion chamber C, which is heated to a high temperature and pressure by the compression action of the piston 5.

[0035] The glow plug 10 is mounted on the cylinder head 4 such that its tip is exposed to the combustion chamber C. The tip of the glow plug 10 is equipped with a heating element (not shown) that generates heat when an electric current is applied. The heating element heats up to a high temperature in a short time when an electric current is applied, heating the combustion chamber C.

[0036] The glow plug 10 operates when the engine 1 is cold to heat the combustion chamber C. Specifically, the glow plug 10 operates when the engine water temperature at startup, that is, the temperature detected by the water temperature sensor SN2 when the engine 1 is started, is below a predetermined first temperature. After the engine 1 has finished starting, the operation of the glow plug 10 (heating of the combustion chamber C) continues until the engine water temperature reaches a second temperature, which is higher than the first temperature.

[0037] The cylinder head 4 has intake ports 11 and exhaust ports 12. The intake ports 11 connect the combustion chamber C of each cylinder 2a to the intake passage 30. The exhaust ports 12 connect the combustion chamber C of each cylinder 2a to the exhaust passage 40. Each intake port 11 of each cylinder 2a is provided with an intake valve 13, and each exhaust port 12 of each cylinder 2a is provided with an exhaust valve 14.

[0038] The cylinder head 4 is equipped with an intake valve mechanism 15 and an exhaust valve mechanism 16. The intake valve mechanism 15 is a mechanism that drives the intake valves 13 of each cylinder 2a to open and close in conjunction with the rotation of the crankshaft 7. The exhaust valve mechanism 16 is a mechanism that drives the exhaust valves 14 of each cylinder 2a to open and close in conjunction with the rotation of the crankshaft 7. The intake valves 13 periodically open and close the opening on the combustion chamber C side of the intake port 11 in response to the drive of the intake valve mechanism 15. The exhaust valves 14 periodically open and close the opening on the combustion chamber C side of the exhaust port 12 in response to the drive of the exhaust valve mechanism 16.

[0039] An alternator 18 is connected to the crankshaft 7 via a transmission member such as a belt. The alternator 18 is a generator that obtains driving force from the crankshaft 7 and generates electricity, and is a type of auxiliary equipment of the engine 1. The alternator 18 has a built-in regulator circuit (not shown) for adjusting the amount of electricity generated. The regulator circuit can adjust the amount of electricity generated according to conditions such as the vehicle's electrical load and battery level.

[0040] The intake passage 30 is a tubular member for introducing intake air into the combustion chamber C of each cylinder 2a. The intake passage 30 has an intake manifold 30a and a surge tank 30b in the downstream portion closer to the engine body 2. The surge tank 30b is a tank that provides an expanded space to equalize the amount of intake air introduced into each cylinder 2a. The intake manifold 30a includes a plurality of branch pipes connecting the surge tank 30b to the intake port 11 of each cylinder 2a. The portion of the intake passage 30 upstream of the surge tank 30b is formed as a single pipe.

[0041] Upstream of the surge tank 30b in the intake passage 30, an air cleaner 31, an intercooler 32, and an intake shutter valve 33 are provided. The air cleaner 31 is a filter that removes foreign matter from the intake air. The intercooler 32 is a heat exchanger that cools the intake air compressed by the supercharger 60. The intake shutter valve 33 is an electrically operated butterfly valve that is openable and closable in the intake passage 30 to restrict the flow rate of the intake air. The air cleaner 31, intercooler 32, and intake shutter valve 33 are arranged in this order from the upstream side, furthest from the engine body 2.

[0042] An airflow sensor SN3 and an intake pressure sensor SN4 are installed in the intake passage 30. The airflow sensor SN3 is a sensor that detects the flow rate of intake air introduced into the engine body 2 and is located in the intake passage 30 downstream of the air cleaner 31. The intake pressure sensor SN4 is a sensor that detects the pressure of intake air introduced into the engine body 2 and is located in the surge tank 30b.

[0043] The exhaust passage 40 is a tubular member for discharging exhaust gas discharged from the combustion chamber C of each cylinder 2a to the outside. The exhaust passage 40 has an exhaust manifold 40a in the upstream portion closer to the engine body 2. Although detailed illustrations are omitted, the exhaust manifold 40a includes a plurality of branch pipes communicating with the exhaust ports 12 of each cylinder 2a, and an exhaust manifold where these branch pipes converge. The portion of the exhaust passage 40 downstream of the exhaust manifold 40a (exhaust manifold) is formed as a single pipe.

[0044] A catalytic converter 41 is provided in the exhaust passage 40 downstream of the exhaust manifold 40a. The catalytic converter 41 incorporates an oxidation catalyst 41a that oxidizes and neutralizes CO and HC in the exhaust gas, and a DPF (diesel particulate filter) 41b that collects particulate matter contained in the exhaust gas.

[0045] The supercharger 60 is a so-called two-stage type supercharger, comprising a first supercharger 61 and a second supercharger 62 arranged in series.

[0046] The first supercharger 61 is a turbocharger that includes a first compressor 61a located in the intake passage 30 and a first turbine 61b coaxially connected to the first compressor 61a and located in the exhaust passage 40. The first compressor 61a is located in the intake passage 30 between the air cleaner 31 and the intercooler 32. The first turbine 61b is located in the exhaust passage 40 upstream of the catalytic converter 41.

[0047] Similarly, the second supercharger 62 is a turbocharger that includes a second compressor 62a located in the intake passage 30 and a second turbine 62b coaxially connected to the second compressor 62a and located in the exhaust passage 40. The second compressor 62a is located in the intake passage 30 downstream of the first compressor 61a, that is, in the portion between the first compressor 61a and the intercooler 32. The second turbine 62b is located in the exhaust passage 40 upstream of the first turbine 61b.

[0048] The first turbocharger 61 is a larger turbocharger than the second turbocharger 62. That is, the first compressor 61a and the first turbine 61b are formed to be larger in size than the second compressor 62a and the second turbine 62b.

[0049] An intake bypass passage 63 is connected to the intake passage 30. The intake bypass passage 63 is a passage for bypassing the second compressor 62a. An electrically operated bypass valve 63a is provided in the intake bypass passage 63 so as to be openable and closable.

[0050] The exhaust passage 40 is connected to a first exhaust bypass passage 64 and a second exhaust bypass passage 65. The first exhaust bypass passage 64 is a passage for bypassing the first turbine 61b, and the second exhaust bypass passage 65 is a passage for bypassing the second turbine 62b. An electrically operated wastegate valve 64a is provided in the first exhaust bypass passage 64 so as to be openable and closable. An electrically operated regulator valve 65a is provided in the second exhaust bypass passage 65 so as to be openable and closable.

[0051] When supercharging is performed by the first supercharger 61, the wastegate valve 64a is closed. As a result, exhaust gas discharged from the engine body 2 is introduced into the first turbine 61b, and the first turbine 61b is rotated by the exhaust gas. The first compressor 61a rotates in conjunction with the first turbine 61b, thereby pressurizing and sending intake air downstream. In other words, supercharging is achieved by the first supercharger 61, which compresses the intake air in the intake passage 30 and sends it to the engine body 2.

[0052] When supercharging is performed by the second supercharger 62, the regulator valve 65a and the bypass valve 63a are closed. As a result, exhaust gas discharged from the engine body 2 is introduced into the second turbine 62b, and the second turbine 62b is rotated by the exhaust gas. The second compressor 62a rotates in conjunction with the second turbine 62b, thereby pressurizing and sending intake air downstream. In other words, supercharging that compresses the intake air in the intake passage 30 and sends it to the engine body 2 is achieved by the second supercharger 62.

[0053] The EGR system 50 comprises an EGR passage 51, an EGR cooler 52, and an EGR valve 53. The EGR passage 51 is a passage for recirculating exhaust gas from the exhaust passage 40 to the intake passage 30, and connects the exhaust passage 40 and the intake passage 30 to each other. Specifically, the EGR passage 51 connects the portion of the exhaust passage 40 upstream of the second turbine 62b and the portion of the intake passage 30 between the intake shutter valve 33 and the surge tank 30b. The EGR cooler 52 is a heat exchanger that cools the exhaust gas, i.e., EGR gas, that is recirculated to the intake passage 30 through the EGR passage 51. The EGR valve 53 is an electrically operated valve provided in the EGR passage 51 to adjust the recirculation rate of the exhaust gas, i.e., the amount of EGR. The EGR valve 53 is located downstream of the EGR cooler 52 (closer to the intake passage 30) in the EGR passage 51.

[0054] Figure 2 is a cross-sectional view showing details of the intake and exhaust valves 13, 14 and their valve trains 15, 16 of the engine body 2. As shown in this figure, the intake valve 13 has a stem portion 13a and a head portion 13b. The stem portion 13a is a vertically elongated cylindrical member and is supported by the cylinder head 4 so as to be slidable in the axial direction (vertical direction). The head portion 13b is a disc-shaped member capable of blocking the opening of the intake port 11 on the combustion chamber C side and is formed to widen in diameter from the lower end of the stem portion 13a.

[0055] Similarly, the exhaust valve 14 has a stem portion 14a and a head portion 14b. The stem portion 14a is a vertically elongated cylindrical member that is supported by the cylinder head 4 so as to be slidable in the axial direction (vertical direction). The head portion 14b is a disc-shaped member that can close the opening of the combustion chamber C of the exhaust port 12, and is formed to widen in diameter from the lower end of the stem portion 14a.

[0056] Valve seats 11a and 12a are attached to the cylinder head 4. Valve seat 11a is a ring-shaped member attached to the opening of the intake port 11 on the combustion chamber C side, and it is in close contact with the periphery of the umbrella portion 13b of the intake valve 13 when the valve is closed. Valve seat 12a is a ring-shaped member attached to the opening of the exhaust port 12 on the combustion chamber C side, and it is in close contact with the periphery of the umbrella portion 14b of the exhaust valve 14 when the valve is closed.

[0057] The intake valve mechanism 15 comprises a camshaft 21, a swing arm 23, and a valve spring 25. The camshaft 21 is a rotatable shaft linked to the crankshaft 7 via a transmission member such as a timing chain. Specifically, the camshaft 21 includes a shaft portion 21a extending in the direction of the cylinder arrangement 2a (the direction perpendicular to the plane of the paper in Figure 2), and a plurality of cam portions 21b provided on the shaft portion 21a at positions corresponding to the intake valves 13 of each cylinder 2a. The swing arm 23 is pivotably supported below the cam portions 21b of each cylinder 2a. The valve spring 25 is attached to the cylinder head 4 in a state that biases the intake valves 13 in the closing direction (upward). The intake valves 13 periodically open when they receive a downward pressing force transmitted from the cam portions 21b via the swing arm 23 as the camshaft 21 rotates. On the other hand, when the pressing force is not applied, the intake valve 13 is maintained in a closed state, with the umbrella portion 13b tightly pressed against the valve seat 11a, due to the upward biasing force of the valve spring 25.

[0058] Similarly, the exhaust valve train mechanism 16 comprises a camshaft 22, a swing arm 24, and a valve spring 26. The camshaft 22 is a rotatable shaft linked to the crankshaft 7 via the transmission member. Specifically, the camshaft 22 includes a shaft portion 22a extending in the direction of the alignment of the cylinders 2a (the direction perpendicular to the plane of the paper in Figure 2), and a plurality of cam portions 22b provided on the shaft portion 22a at positions corresponding to the exhaust valves 14 of each cylinder 2a. The swing arm 24 is pivotably supported below the cam portions 22b of each cylinder 2a. The valve spring 26 is attached to the cylinder head 4 in a state that biases the exhaust valves 14 in the closing direction (upward). The exhaust valves 14 periodically open in response to a downward pressing force transmitted from the cam portions 22b via the swing arm 24 as the camshaft 22 rotates. On the other hand, when the pressing force is not applied, the exhaust valve 14 is maintained in a closed state, with the umbrella portion 14b tightly pressed against the valve seat 12a, due to the upward biasing force of the valve spring 26.

[0059] Here, deposits (foreign matter) may adhere to the valve seat portion of the intake valve 13. For example, deposits adhering to the inner wall of the intake passage 30 may detach for some reason and flow downstream, becoming lodged between the umbrella portion 13b of the intake valve 13 and the valve seat 11a. Such deposit adhesion (lodging) to the valve seat portion can cause the intake valve 13 to fail to close properly, leading to compression leakage, a phenomenon in which compressed air leaks from the combustion chamber C through the intake port 11a during the compression stroke. When compression leakage occurs, ignition failure is more likely to occur, where the fuel-air mixture injected into the combustion chamber C does not burn properly (or misfires).

[0060] Figure 3 is a schematic plan view showing the structure of the power transmission system that transmits the output of the engine 1 described above to the vehicle's wheels W1. The vehicle in this example is a front-engine, rear-wheel-drive (FR) vehicle. Therefore, in Figure 3, the wheels W1 are the rear wheels, and the engine body 2 is located in the engine compartment at the front of the vehicle. Although Figure 3 illustrates an inline four-cylinder engine body 2 with four cylinders 2a arranged in a row, the number and arrangement of the cylinders 2a can be changed as appropriate.

[0061] As shown in Figure 3, the vehicle's power transmission system in this embodiment includes an automatic transmission 101 connected to the engine body 2, a propeller shaft 102 extending rearward from the automatic transmission 101, a differential 103 connected to the rear end of the propeller shaft 102, and a pair of drive shafts 104 extending left and right from the differential 103. Wheels W1 are attached to the vehicle width end of each drive shaft 104. The output rotation of the engine body 2 is shifted by the automatic transmission 101 and then input to the differential 103 via the propeller shaft 102. The rotation input to the differential 103 is transmitted to each wheel W1 via the left and right drive shafts 104.

[0062] The automatic transmission 101 includes a torque converter 110 and a transmission body 120. The torque converter 110 is a fluid clutch that transmits the output rotation of the engine body 2, i.e., the rotation of the crankshaft 7, to the transmission body 120 via a working fluid (ATF). The transmission body 120 is a device that transmits the rotation input from the torque converter 110 to the wheels W1 while changing the speed.

[0063] The torque converter 110 incorporates a pump impeller 111 that rotates integrally with the crankshaft 7 of the engine body 2, a turbine runner 112 positioned opposite the pump impeller 111, and a stator 113 positioned between the pump impeller 111 and the turbine runner 112. The rotation of the pump impeller 111 is transmitted to the turbine runner 112 via the working fluid within the torque converter 110. The rotation of the turbine runner 112 is input to the transmission body 120 via the turbine shaft 114.

[0064] A lock-up clutch 115 is provided inside the torque converter 110. The lock-up clutch 115 is a clutch that connects and disconnects the crankshaft 7 of the engine body 2 and the turbine runner 112. When the crankshaft 7 and the turbine runner 112 are connected by engaging the lock-up clutch 115, a state is obtained in which the crankshaft 7 and the turbine shaft 114 (input shaft of the transmission body 120) are mechanically connected without the use of fluid, and the rotation of the crankshaft 7 is transmitted directly to the wheel W1. In other words, the lock-up clutch 115 is a clutch that directly connects the output shaft (crankshaft 7) of the engine 1 and the wheel W1.

[0065] Engaging the lock-up clutch 115 improves power transmission efficiency. However, engaging the lock-up clutch 115 when the engine speed or vehicle speed is low makes it easier for vibrations from the engine 1 to be transmitted to the vehicle. For this reason, the lock-up clutch 115 is engaged under predetermined conditions, except when the engine speed or vehicle speed is low, and is released (unengaged) when the engine speed or vehicle speed is low.

[0066] The transmission body 120 incorporates a multi-stage transmission mechanism 121 capable of achieving multiple gear stages with different reduction ratios. The transmission mechanism 121 includes a gear mechanism 122 composed of multiple planetary gear sets, multiple friction fastening elements (not shown) including clutches and brakes that are fastened or released to switch the power transmission path by the gear mechanism 122, and a hydraulic control valve 123 (Figure 4) consisting of a solenoid valve or the like that controls the hydraulic pressure supplied to each friction fastening element to switch between fastening and releasing. By fastening or releasing the appropriate friction fastening elements, the hydraulic control valve 123 achieves the desired gear stage in the transmission mechanism 121 according to the vehicle speed, etc. The output rotation of the torque converter 110, i.e., the rotation of the turbine shaft 114, is transmitted to the propeller shaft 102 (and thus to the wheels W1) after being shifted at a reduction ratio corresponding to the gear stage of the transmission mechanism 121.

[0067] Figure 4 is a functional block diagram showing the control system of the engine 1 and automatic transmission 101 described above. The PCM70 shown in this figure is a microprocessor for comprehensively controlling the engine 1 and automatic transmission 101, and is composed of a well-known CPU, ROM, RAM, etc. The PCM70 corresponds to the "controller" in this invention.

[0068] The PCM70 receives detection information from various sensors. For example, the PCM70 is electrically connected to the crank angle sensor SN1, water temperature sensor SN2, airflow sensor SN3, and intake pressure sensor SN4 mentioned above. The PCM70 receives sequential information detected by each of these sensors (i.e., information such as crank angle, engine speed, engine water temperature, intake airflow rate, and intake pressure).

[0069] The vehicle is also equipped with an accelerator sensor SN5 and a vehicle speed sensor SN6. The accelerator sensor SN5 is a sensor that detects the degree to which the accelerator pedal is opened, i.e., the accelerator opening, operated by the driver operating the vehicle. The vehicle speed sensor SN6 is a sensor that detects the vehicle's speed, i.e., the vehicle speed. The detection information from these accelerator sensor SN5 and vehicle speed sensor SN6 is also input to the PCM70 sequentially.

[0070] The PCM70 controls the engine 1 and the automatic transmission 101 based on the input information from each of the sensors SN1 to SN6. Specifically, the PCM70 is electrically connected to the fuel injector 9, glow plug 10, alternator 18, intake shutter valve 33, EGR valve 53, bypass valve 63a, wastegate valve 64a, and regulator valve 65a, as well as to the lock-up clutch 115 and hydraulic control valve 123 of the automatic transmission 101. The PCM70 outputs control signals to these devices that are generated based on the input information from each of the sensors SN1 to SN6.

[0071] Next, we will explain the mechanism by which the airflow sensor SN3 detects intake valve closure failure. Figure 5(a) shows the change in intake airflow rate in a 4-cylinder engine. Specifically, it shows the change in intake airflow rate detected value af read from the airflow sensor SN3 over time. Figure 5(b) shows an enlarged view of the period from T1 to T2 in Figure 5(a). Around the time T11, only the intake valve of cylinder C1, which is in the intake stroke among the four cylinders, is open. The intake flow rate detection value af_11 at time T11 is the maximum value during the intake stroke of cylinder C1 between time T1 and time T12. This is because time T11 corresponds to 90 CA (Crank Angle) ATDC (After Top Dead Center), when the downward speed of the piston 5 of cylinder C1 is at its maximum and the intake flow rate at the intake port is at its maximum. In this way, the intake flow rate detection value af changes in response to the change in piston speed during the intake stroke.

[0072] After timing T11, the intake airflow detection value af decreases, reaching its minimum at timing T12, and then begins to rise. From the perspective of piston motion, at timing T12, cylinder C1 reaches intake bottom dead center and the piston stops, while cylinder C2, which enters the next intake stroke, is at intake top dead center and its piston is also stopped. After timing T12, the piston of cylinder C2 begins to descend. Since the piston is stationary at timing T12, the intake airflow to cylinder C1 is almost zero, but the intake airflow is maintained by inertia on the upstream side of the intake passage where the airflow sensor SN3 is located, and a certain intake airflow detection value af_12 is detected.

[0073] At time T12, cylinder C2 enters the intake stroke, and at time T13, the piston descent speed reaches its maximum of 90 CA ATDC. Then, from time T13 to time T14, the intake airflow detection value a decreases, and at time T14, the piston of cylinder C2 reaches the intake bottom dead center. At time T14, the piston of cylinder C2 is stationary, so the intake airflow to cylinder C2 is almost zero. However, the intake airflow is maintained by inertia on the upstream side of the intake passage where the airflow sensor SN3 is located, and a certain intake airflow detection value af_14 is detected. Thus, in the normal state before time T22, when intake valve closure failure occurs, the minimum value of the intake airflow detection value a does not decrease significantly.

[0074] Next, we will explain the intake airflow detection value af around time T22, when a failure to close the intake valve occurs in cylinder C1. Around time T21, only the intake valve of cylinder C1, which is in the intake stroke, is open among the four cylinders. Cylinder C1 corresponds to 90 CA ATDC, where the piston descent speed is maximum, at time T21, one cycle after time T11. During the intake stroke of cylinder C1, including time T21, deposits get trapped between the intake valve and valve seat of cylinder C1. However, since the intake valve is open, there is no significant difference when comparing the intake airflow detection value af_21 at time T21 with the intake airflow detection value af_11 at time T11 of cylinder C1 one cycle earlier. The next time, T22, corresponds to the intake bottom dead center of the piston of cylinder C1, one cycle after time T12. When the engine reaches timing T22, that is, when the piston of cylinder C1 reaches the intake bottom dead center, the intake valve of cylinder C1 moves in the closing direction, causing deposits that have accumulated between the intake valve and the valve seat during the intake stroke to become lodged. However, since this does not affect the intake action, there is no significant difference when comparing the intake flow rate detected value af_22 at timing T22 with the intake flow rate detected value af_12 at the previous cycle's timing T12.

[0075] The next timing T23 corresponds to the 90 CA ATDC of the piston of cylinder C2, one cycle after timing T13. When cylinder C2 is in the intake stroke, including timing T23, cylinder C1, which experienced a failure to close the intake valve at timing T22, is in the compression stroke. During the compression stroke of cylinder C1, the compressed air in the cylinder is blown back into the intake passage 30 due to the failure to close the intake valve. This blowback reduces the intake airflow rate. Therefore, the intake airflow rate detection value af_23 at timing T23 is smaller than the intake airflow rate detection value af_13 at timing T13, when the intake valve of cylinder C1 is functioning normally.

[0076] The next timing point T24 corresponds to the intake bottom dead center of the piston of cylinder C2, one cycle after timing point T14. At timing point T24, the airflow sensor SN3 on the upstream side of the intake passage detects the intake airflow value a due to inertial force. However, during the intake stroke of cylinder C2, including timing point T23, the inertial force of the air decreases due to blowback from cylinder C1 into the intake passage 30. Therefore, the intake airflow value af_24 decreases significantly compared to the intake airflow value af_14 from one cycle earlier. By detecting a significant decrease in the intake airflow value af, such as af_24, using the airflow sensor SN3, it is possible to determine whether there is a malfunction in the intake valve closing.

[0077] Next, the control of engine 2 performed by the PCM70 shown in Figure 4 will be described. As shown in Figure 6, the overall control of engine 2 repeatedly performed by the PCM70 consists of the following steps: step S1 for reading sensor information, step S2 for performing normal engine control, step S3 for diagnosing intake valve closure failure, step S4 for determining whether the abnormal flag f_fail is set, and step S5 for performing engine control corresponding to the intake valve closure failure. The signals read in step S1 include the crank angle sensor SN1, water temperature sensor SN2, airflow sensor SN3, intake pressure sensor SN4, accelerator sensor SN5, vehicle speed sensor SN6, etc. In this embodiment, there is nothing particularly noteworthy about the normal engine control in step S2, so a detailed explanation will be omitted. The diagnosis of intake valve closure failure in the next step S3 will be described later based on Figures 7 to 12. In the next step S4, it is determined whether or not the abnormal flag f_fail is set. If the error flag f_fail is not set (NO in step S4), the process from step S1 is repeated. If the error flag f_fail is set (YES in step S4), the process proceeds to step S5.

[0078] In step S5, it is determined whether the glow plug 10 is inactive or not. If the glow plug 10 is active (NO in step S5), the process proceeds to step S7. If the glow plug 10 is not active (YES in step S5), the process proceeds to step S6. In the next step S6, the glow plug 10 is activated, and the process proceeds to step S7. That is, the PCM 70 energizes the heating element of the glow plug 10 to raise the temperature of the heating element. This heats the combustion chamber C and improves the ignition of the air-fuel mixture. The glow plug 10 to be activated in step S6 is at least the glow plug 10 of the cylinder 2a where deposit adhesion was confirmed in the determination in step S3. However, depending on the engine, it may not be possible to switch the glow plug 10 on / off for each cylinder 2a due to the control configuration. In such cases, the PCM 70 activates the glow plugs 10 of all cylinders 2a in step S6.

[0079] In the next step, S7, it is determined whether the alternator 18 is operating or not. That is, the PCM 70 checks the power generation status by the alternator 18 and determines that the alternator 18 is operating if it is generating more than a predetermined amount of power. If the alternator 18 is not operating (NO in step S7), the process from step S1 is repeated. If the alternator 18 is operating (YES in step S7), the process proceeds to step S8. In the next step, S8, the operation of the alternator 18 is stopped. That is, the PCM 70 controls the regulator circuit in the alternator 18 so that power generation by the alternator 18 stops (the amount of power generated becomes virtually zero). As a result, the reverse torque acting from the alternator 18 on the crankshaft 7 decreases, and the rotational resistance (external load) of the crankshaft 7 is reduced.

[0080] Next, we will explain the intake valve closure failure diagnosis S3 shown in Figure 7. First, in step S31 of Figure 7, it is determined whether or not one of the mask flags f_mask_1 to f_mask_9, f_mask_n, which will be described in detail later, is set. If any of the mask flags is set (YES in step S31), the intake valve closure failure diagnosis S3, which will be described later based on steps S32 to S43, is not performed, and step S31 is executed repeatedly. If none of the mask flags are set (NO in step S31), the process proceeds to step S32. In the next step S32, the minimum value af_min is calculated for every 180 CA from 108 CA BTDC (Before Top Dead Center) to 108 CA BTDC of the next cylinder, based on the intake airflow detection value af from the airflow sensor SN3 acquired in step S1. Figure 8(a) is a graph of the minimum value af_min calculated based on the intake airflow detection value af. This minimum value af_min is calculated based on the intake airflow detection value af shown in Figure 5(a), which is read from the airflow sensor SN3 in step S1.

[0081] The process proceeds to step S33, where the average value af_mav of the intake airflow detection value a is calculated every 16 msec. The average value af_mav is calculated by applying a low-pass filter to the intake airflow detection value a. Figure 8(b) is a graph of the average value af_mav calculated based on the intake airflow detection value a. This average value af_mav is calculated based on the intake airflow detection value a shown in Figure 5(a), which was read from the airflow sensor SN3 in step S1.

[0082] The process proceeds to step S34, where the judgment index ind_diag is calculated by dividing the minimum value af_min calculated in step S32 by the average value af_mav calculated in step S33. In the next step S35, the judgment threshold ind_fail is calculated based on the engine operating state, such as engine load and engine speed. Note that the judgment threshold ind_fail may be a constant value regardless of the engine operating state. Figure 8(c) is a graph of the judgment threshold ind_fail and the judgment index ind_diag calculated based on the minimum value af_min and the average value af_mav. This judgment index ind_diag is calculated based on the minimum value af_min in Figure 8(a) and the average value af_mav in Figure 8(b), which were calculated in step S32.

[0083] The process proceeds to step S36, where the judgment index ind_diag calculated in step S34 and the judgment threshold ind_fail calculated in step S35 are compared. If the judgment index ind_diag is smaller than the judgment threshold ind_fail (YES in step S36), it is determined that there is a failure to close the intake valve, and the process proceeds to step S37. In the next step, S37, it is determined whether or not the abnormal flag f_fail is set. If the abnormal flag f_fail is not set (NO in step S37), the process proceeds to step S38. Otherwise (YES in step S37), the intake valve failure diagnosis S3 shown in Figure 6 from step S31 is repeated again. In the next step, S38, the abnormal flag f_fail is set, and the intake valve failure diagnosis S3 shown in Figure 6 from step S31 is repeated again. If, in step S36, the judgment index ind_diag is greater than or equal to the judgment threshold ind_fail (i.e., NO in step S36), it is determined that there is no intake valve closure failure, and the process proceeds to step S39.

[0084] In the next step, S39, it is determined whether the error flag f_fail is set. If the error flag is not set (NO in step S39), the intake valve closure failure diagnosis S3 in Figure 6, starting from step S31, is repeated. Otherwise (YES in step S39), the process proceeds to step S40. In the next step, S40, it is determined whether the count value count_0 is higher than the threshold C0. If the count value count_0 is lower than the threshold C0 (NO in step S40), the process proceeds to step S41. In the next step, S41, the count of the count value count_0 is increased by 1. If the count value count_0 is higher than the threshold C0 (YES in step S40), the process proceeds to step S42. In the next step, S42, the count of the count value count_0 is reset to 0. Then, the process proceeds to step S43, and the error flag f_fail is reset.

[0085] The mask flags f_mask_1 to f_mask9 in step S31 of Figure 7 will be explained in order below. First, the engine speed mask will be explained using Figure 9. In step S51, it is determined whether the engine speed NE obtained from the crank angle sensor SN1 in step S1 is between 700 rpm and 2000 rpm. Note that when the engine speed NE is less than 700 rpm, even if there is no intake valve closure failure, the intake airflow detection value af at top dead center and bottom dead center during the intake stroke, i.e., the minimum value af_min, will be small. As a result, the value of the judgment index ind_diag, which is calculated by dividing the minimum value af_min by the average value af_mav in step S34 of Figure 7, will be small. Therefore, even under normal circumstances, there is a high possibility that the judgment index ind_diag will fall below the judgment threshold ind_fail in step S36, making it difficult to detect intake valve closure failure. On the other hand, when the engine speed NE is higher than 2000 rpm, the motion speed of the piston 5 increases. Therefore, if the intake valve fails to close properly, the flow velocity of the air flowing back from inside the cylinder through the gap between the intake valve and the valve seat into the intake passage 30 during the compression stroke increases, increasing the throttling effect of the gap and restricting the flow rate. As a result, a significant decrease in the intake flow rate detection value af becomes less likely, making it difficult to detect the intake valve failure.

[0086] If the engine speed NE is less than 700 rpm or higher than 2000 rpm (NO in step S51), the process proceeds to step S52. In the next step S52, the mask flag f_mask_1 is set. If the engine speed NE is 700 rpm or more and 2000 rpm or less (YES in step S51), the process proceeds to step S53. In the next step S53, it is determined whether or not the mask flag f_mask_1 is set. If the mask flag f_mask_1 is set (YES in step S53), the process proceeds to step S54. Otherwise (NO in step S53), the process proceeds to step S56.

[0087] In step S54, it is determined whether the count value count_1 is higher than the threshold C1. To obtain the intake airflow detection value a when the engine is running continuously within the range of engine speed NE being between 700 rpm and 2000 rpm, it is necessary to delay the measurement for a predetermined period (until the count value count_1 becomes higher than the threshold C1).

[0088] If the count value count_1 is lower than the threshold C1 (step S54 is NO), the process proceeds to step S55. In the next step S55, the count of count_1 is incremented by 1. If the count value count_1 is higher than the threshold C1 (step S54 is YES), the process proceeds to step S56. In the next step S56, the count value count_1 is reset to 0. Then, the process proceeds to step S57, where the mask flag f_mask_1 is reset.

[0089] Next, in Figure 10, intake shutter This shows the opening mask. In step S61, from the information read in step S1, the intake shutter It is determined whether the opening degree TVO is less than the threshold TVO_1. Inspiration shutter If the opening degree TVO is less than the threshold TVO_1 (YES in step S61), the process proceeds to step S62. In the next step S62, the mask flag f_mask_2 is set. Intake shutter The smaller the opening of the TVO, the higher the flow velocity. Since the flow velocity does not exceed a certain value, the intake... shutter When the opening degree TVO falls below a predetermined value, the airflow rate decreases. Therefore, even if there is a closure failure in the intake valve located downstream of the intake passage, the influence of the airflow sensor N3 upstream of the intake passage is reduced, and the fluctuation in the intake flow rate detection value af becomes smaller. As a result, it becomes difficult to detect the closure failure of the intake valve.

[0090] Meanwhile, intake shutterIf the opening degree TVO is greater than the threshold TVO_1 (NO in step S61), the process proceeds to step S63. In the next step, S63, it is determined whether the mask flag f_mask_2 is set or not. If the mask flag f_mask_2 is set (YES in step S63), the process proceeds to step S64. Otherwise (NO in step S63), the process proceeds to step S66.

[0091] In step S64, it is determined whether the count value count_2 is higher than the threshold C2. If the count value count_2 is lower than the threshold C2 (the result in step S64 is NO), the process proceeds to step S65. In the next step, S65, the count of the count value count_2 is incremented by 1. If the count value count_2 is higher than the threshold C2 (the result in step S64 is YES), the process proceeds to step S66. In the next step, S66, the count of the count value count_2 is reset to 0. Then, the process proceeds to step S67, where the mask flag f_mask_2 is reset.

[0092] Next, Figure 11 shows the starting mask. In step S71, it is determined whether the engine speed NE obtained from the crank angle sensor SN1 in step S1 is less than 700 rpm. During engine startup, the engine speed changes significantly, causing the intake airflow detection value a to fluctuate greatly. Therefore, it becomes difficult to detect intake valve closure failure.

[0093] If the engine speed NE is less than 700 rpm (YES in step S71), the process proceeds to step S72. In the next step S72, the mask flag f_mask_3 is set. If the engine speed NE is 700 rpm or greater (NO in step S71), the process proceeds to step S73. In the next step S73, it is determined whether the mask flag f_mask_3 is set or not. If the mask flag f_mask_3 is set (YES in step S71), the process proceeds to step S74. If the mask flag f_mask_3 is not set (NO in step S71), the process proceeds to step S76.

[0094] In step S74, it is determined whether the count value count_3 is higher than the threshold C3. If the count value count_3 is lower than the threshold C3 (the result in step S74 is NO), the process proceeds to step S75. In the next step, S75, the count of the count value count_3 is increased by 1. If the count value count_3 is higher than the threshold C3 (the result in step S74 is YES), the process proceeds to step S76. In the next step, S76, the count of the count value count_3 is set to 0. Then, the process proceeds to step S77, where the mask flag f_mask_3 is reset.

[0095] Next, Figure 12 shows the EGR valve opening mask. In step S81, a threshold R3 is set based on the fuel injection amount ΔQ obtained in step S1. The threshold R3 decreases as the fuel injection amount ΔQ increases. Then, the process proceeds to step S82, where it is determined whether the EGR valve opening OP_EGR_A is smaller than the threshold R3 determined in step S81. If the EGR valve opening OP_EGR_A is large, the flow rate on the upstream side of the intake passage (near the airflow sensor SN3) and the flow rate on the downstream side of the intake passage (near the intake valve) will no longer match. Therefore, it becomes difficult to detect a failure to close the intake valve. If the EGR valve opening OP_EGR_A is greater than the threshold R3 (step S82 is NO), the process proceeds to step S83. In the next step S83, the mask flag f_mask_4 is set. If the EGR valve opening OP_EGR_A is less than the threshold R3 (YES in step S82), the process proceeds to step S84. In the next step, S84, the mask flag f_mask_4 is reset.

[0096] Next, let's discuss the sensor malfunction mask. The sensor malfunction mask is set when a malfunction is detected in the airflow sensor SN3, and the mask flag f_mask_5 is set.

[0097] Next, let's discuss the playback mask. During playback mode, Intake shutter valve The opening of valve 33 can change abruptly, potentially causing a large fluctuation in the intake airflow detection value af. Furthermore, the combustion of fuel in the cylinder due to post-injection generates torque, causing fluctuations in rotational speed, which can also significantly alter the intake airflow detection value af, making it difficult to detect intake valve closure failure. Therefore, If playback mode is active, the mask flag f_mask_6 is set.

[0098] Next, we will explain the clutch opening mask. When the clutch pedal is pressed and the clutch opening exceeds a predetermined value, the engine speed changes abruptly, causing large fluctuations in the intake airflow detection value af, making it difficult to detect a malfunction in the intake valve closing. Therefore, when the clutch opening exceeds a predetermined value, the mask flag f_mask_7 is set.

[0099] Next, let's discuss the oxygen concentration deviation mask. If the actual oxygen concentration inside the cylinder does not match the target oxygen concentration, combustion will become unstable. This can cause fluctuations in torque, which in turn can change the engine speed and potentially lead to large fluctuations in the intake airflow detection value af. Therefore, the mask flag f_mask_8 is set.

[0100] Next, we will explain the mask for sudden EGR valve changes. When the EGR valve opening degree OP_EGR_A changes suddenly, if there is a deviation of more than a predetermined value between the actual value and the target value of the opening degree, the flow rate on the upstream side of the intake passage (near the airflow sensor SN3) and the flow rate on the downstream side of the intake passage (near the intake valve) will no longer match. Therefore, it becomes difficult to detect a malfunction in the intake valve closing. For this reason, if there is a deviation of more than a predetermined value between the actual value and the target value of the EGR valve opening degree OP_EGR_A, the mask flag f_mask_9 is set.

[0101] As described above, in this embodiment, a determination index ind_diag and determination threshold ind_fail are determined from the minimum value af_min and average value af_mav of the intake airflow detection value a of the airflow sensor SN3 to determine whether a failure to close the intake valve has occurred. If it is determined that a failure to close the intake valve has occurred, control (S6) is performed to activate the glow plug 10 and heat the combustion chamber C, and control (S8) is performed to stop power generation by the alternator 18.

[0102] In this embodiment, the intake valve closure failure diagnosis (S3) shown in Figure 7 is performed only when the mask flag f_mask_n is not set, i.e., when a stable intake airflow detection value af can be read during operation. Furthermore, the intake valve closure failure diagnosis (S3) is always performed when normal engine control (S2) is being carried out, and the intake valve closure failure is determined by the intake airflow detection value af read by the PCM70 from the airflow sensor SN3 shown in Figure 4. This makes it possible to diagnose intake valve closure failures even when the vehicle is running at low load.

[0103] Specifically, in step S36 of Figure 7, a diagnosis of intake valve closure failure is performed based on the judgment index ind_diag and judgment threshold ind_fail shown in Figure 8(c). As mentioned above, the judgment index ind_diag is obtained by dividing the minimum value af_min (Figure 8(a)) of the intake flow rate detected by the airflow sensor SN3 shown in Figure 5 (Figure 5) by the average value af_mav (Figure 8(b)).

[0104] Prior to T23 shown in Figure 5(b), the minimum value af_min and the average value af_mav are calculated from the intake airflow detection value af from the airflow sensor SN3. Based on the calculated minimum value af_min and average value af_mav, the judgment index ind_diag is calculated. Prior to T23, since the judgment index ind_diag exceeds the judgment threshold ind_fail, it is determined that there is no intake valve closure failure and the abnormal flag f_fail is not set.

[0105] In the stages from T23 onward, as shown in Figure 5(b), the minimum value af_min and the average value af_mav are calculated from the intake airflow detection value af from the airflow sensor SN3. Based on the calculated minimum value af_min and average value af_mav, the judgment index ind_diag is calculated. At T24, since the judgment index ind_diag is below the judgment threshold ind_fail, it is determined that there is a failure to close the intake valve, and the abnormal flag f_fail is set.

[0106] When the abnormal flag f_fail is set, engine control to address the failure to close, such as the operation of the glow plug 10 as shown in steps S5 to S8 of Figure 6, is executed. [Explanation of Symbols]

[0107] 1: Engine C: Combustion chamber 7: Crankshaft (output shaft) 9: Fuel Injector 10: Glow plug 11: Intake port 12: Exhaust port 13: Intake valve 14: Exhaust valve 18: Alternator (generator; auxiliary equipment) 30: Intake passage 40: Exhaust passage 50:EGR passage 53: EGR valve 70: PCM (Controller, Compression Leak Detection Unit) SN3: Airflow sensor (intake airflow detection unit, compression leak detection unit) 101: Automatic transmission 115: Lock-up clutch

Claims

1. A method for diagnosing an engine comprising: a cylinder; a piston that reciprocates within the cylinder; an intake passage communicating with the cylinder; an intake valve that opens and closes the communication between the cylinder and the intake passage by reciprocating; an exhaust passage communicating with the cylinder; a particulate filter provided downstream of the exhaust passage; an EGR device that recirculates exhaust gas from the exhaust passage upstream of the particulate filter into the intake passage; an intake flow rate detection unit that detects the airflow rate through the intake passage; and a controller to which the detection information from the intake flow rate detection unit is input, wherein The controller includes a valve operation determination step in which it determines that a malfunction of the intake valve has occurred, provided that the determination index calculated from the intake flow rate detection unit detected by the intake flow rate detection unit is less than a predetermined determination threshold, An engine diagnostic method comprising: when the intake valve is functioning normally and there is no failure to close, the valve operation determination step is not performed when the determination index is below a predetermined rotational speed that is below a predetermined determination threshold; and the valve operation determination step is performed when the rotational speed is above the predetermined speed.

2. The intake air flow rate detection unit is characterized by being an airflow sensor provided in the intake passage. The method for diagnosing an engine according to claim 1.

3. The aforementioned judgment indicators are, The method for diagnosing an engine according to claim 1 or claim 2, wherein the average value calculated from a plurality of intake flow detection values ​​that change in response to changes in piston speed during the intake stroke detected by the intake flow detection unit is divided by the minimum intake flow value during the intake stroke calculated by the intake flow detection unit.

4. An engine comprising: a cylinder; a piston that reciprocates within the cylinder; an intake passage communicating with the cylinder; an intake valve that opens and closes the communication between the cylinder and the intake passage by reciprocating; an intake flow rate detection unit that detects the intake air flow rate that flows through the intake passage into the cylinder when the intake valve is open; an exhaust passage communicating with the cylinder; a particulate filter provided in the exhaust passage downstream of the exhaust passage; and an EGR device that recirculates exhaust gas from the exhaust passage upstream of the particulate filter into the intake passage. The system includes a controller electrically connected to the intake airflow detection unit, configured to determine that a malfunction of the intake valve has occurred, provided that a determination index calculated from the intake airflow detection value received from the intake airflow detection unit is less than a predetermined determination threshold, The controller is characterized in that, when there is no failure to close the intake valve, the determination is not made when the rotational speed is below a predetermined rotational speed at which the determination index falls below a predetermined determination threshold, and the determination is made when the rotational speed is above the predetermined rotational speed.

5. The intake air flow rate detection unit is an airflow sensor located upstream of the intake passage. The engine system according to claim 4.

6. The controller further The system is configured to use as a determination index a value obtained by dividing the average value calculated from a plurality of detected values ​​that change in response to the change in piston speed during the intake stroke, received from the intake flow rate detection unit, by the minimum value of the intake flow rate detected during the intake stroke, received from the intake flow rate detection unit. The engine system according to claim 4 or claim 5.

Images