Blow-by passage abnormality diagnosis device

Abstract

To properly determine the presence / absence of abnormality of a blow-by passage.SOLUTION: An abnormality diagnosis device is applied to an engine that is equipped with a blow-by passage 41 connecting a throttle downstream passage 27 in an intake passage 20 and a crank case 5. The abnormality diagnosis device is equipped with a flow rate specifying portion that specifies a flow rate Qb of blow-by gas, and a diagnosing portion that carries out abnormal diagnosis for determining whether abnormality occurs in the blow-by passage 41 or not on the basis of the flow rate Qb of the blow-by gas specified by the flow rate specifying portion. The diagnosing portion carries out abnormal diagnosis of the blow-by passage 41 while a purge valve 54 is opened.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a device for diagnosing an abnormality in a blow-by passage that connects an engine crankcase and an intake passage. [Background technology]

[0002] The following Patent Document 1 discloses that in an engine equipped with a blow-by passage (gas exhaust passage) connecting a portion of an intake passage downstream of a throttle valve (hereinafter referred to as a throttle downstream passage) to a crankcase, an abnormality diagnosis is performed to determine whether or not an abnormality such as a hole has occurred in the blow-by passage. Specifically, in the following Patent Document 1, the amount of gas passing through the blow-by passage (i.e., the flow rate of blow-by gas) estimated from the pressure in the throttle downstream passage and the opening degree of the throttle valve is compared with a predetermined reference flow rate, and if the absolute value of the difference between the two is greater than a predetermined judgment value, it is determined that an abnormality has occurred in the blow-by passage. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2010-96032 A Summary of the Invention [Problem to be solved by the invention]

[0004] Here, the engine of the above-mentioned Patent Document 1 further includes a canister that adsorbs evaporated fuel that has evaporated from a fuel tank, a purge passage that connects the canister with the above-mentioned throttle downstream passage, and a purge valve (control valve) provided in the purge passage. When the purge valve is opened, purge gas (gas containing evaporated fuel) is introduced from the purge passage to the throttle downstream passage.

[0005] However, when the purge valve is open, the purge gas and the blow-by gas are introduced from the purge passage and the blow-by passage, respectively, into the intake passage (passage downstream of the throttle), so the behavior of each gas becomes complicated, and it may be difficult to estimate the flow rate of the blow-by gas with the desired accuracy. As a result, it is not possible to properly determine whether or not there is an abnormality in the blow-by passage, and for example, there is a risk that the blow-by passage may be erroneously determined to be abnormal even when it is normal.

[0006] The present invention has been made in consideration of the above-mentioned circumstances, and has an object to provide an abnormality diagnosis device for a blow-by passage that can appropriately determine the presence or absence of an abnormality in the blow-by passage. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides a method for diagnosing an abnormality in a blow-by passage in an engine that includes a crankcase that defines a crank chamber separated from a combustion chamber via a piston, an intake passage through which intake air introduced into the combustion chamber flows, a throttle valve that is provided in the intake passage so as to be able to open and close, a blow-by passage that connects the crankcase to a throttle downstream passage that is a portion of the intake passage downstream of the throttle valve, and a purge passage that connects a canister that adsorbs evaporated fuel that has evaporated from a fuel tank to the throttle downstream passage. An abnormality diagnosis device comprising: a purge valve provided in the purge passage so as to be able to open and close; a purge control section which controls an opening and closing operation of the purge valve; a flow rate specifying section which specifies a flow rate of blow-by gas which passes through the blow-by passage and is introduced from the crank chamber to the throttle downstream passage; and a diagnosis section which performs an abnormality diagnosis which determines whether or not an abnormality has occurred in the blow-by passage based on the flow rate of the blow-by gas specified by the flow rate specifying section, and the diagnosis section performs an abnormality diagnosis of the blow-by passage in a state in which the purge valve is closed by the purge control section. The purge control unit closes the purge valve when a deceleration fuel cut is executed to stop the fuel supply to the combustion chamber as the engine decelerates, and the diagnosis unit calculates an integrated value of the flow rate of the blow-by gas during the execution of the deceleration fuel cut, and determines that the blow-by passage is abnormal when the calculated integrated value exceeds a predetermined threshold value. This is characterized by the above (Claim 1).

[0008] According to the present invention, the abnormality diagnosis of the blow-by passage based on the flow rate of the blow-by gas is performed in a state where the purge valve is closed, so that the accuracy of the abnormality diagnosis of the blow-by passage can be improved. For example, in a state where the purge valve is open, purge gas (gas containing evaporated fuel released from the canister) is introduced from the purge passage to the throttle downstream passage, and as a result of the purge gas being introduced into the throttle downstream passage in addition to the blow-by gas, the behavior of each gas is likely to become complicated. Therefore, if the flow rate of the blow-by gas is estimated in such a state, the estimation accuracy may be significantly reduced. In contrast, in the present invention, the abnormality diagnosis of the blow-by passage is performed in a state where the purge valve is closed, so that the deterioration of the estimation accuracy due to the above-mentioned circumstances can be avoided. As a result, the flow rate of the blow-by gas can be estimated with high accuracy, and it is possible to appropriately determine whether or not an abnormality occurs in the blow-by passage based on the estimated flow rate of the blow-by gas. Here, when deceleration fuel cut is performed, a strong negative pressure is formed in the throttle downstream passage, so it is assumed that the flow rate of blow-by gas will be significantly different between normal and abnormal blow-by gas. In the present invention, when such deceleration fuel cut is performed, the purge valve is closed and then abnormality diagnosis of the blow-by passage is performed, so that abnormality diagnosis of the blow-by passage can be performed based on the flow rate of blow-by gas that is clearly different between abnormal and normal, and the diagnostic accuracy can be sufficiently improved. Furthermore, in the present invention, an integrated value of the flow rate of the blow-by gas during the execution of the deceleration fuel cut is obtained, and the blow-by passage is judged to be abnormal when the obtained integrated value exceeds a predetermined threshold value, so that the possibility of erroneous judgment of the blow-by passage can be reduced as much as possible. For example, when the flow rate of the blow-by gas itself is compared with the threshold value, if an error in identifying the flow rate of the blow-by gas temporarily increases due to some factor, the blow-by passage may be erroneously judged to be abnormal even though it is normal. In contrast, when the integrated value of the flow rate of the blow-by gas during the deceleration fuel cut is compared with the threshold value as described above, the blow-by passage is judged to be abnormal only when the flow rate of the blow-by gas continuously indicates an abnormal value, so that the possibility of erroneous judgment as described above can be reduced as much as possible.

[0009] Preferably, the flow rate identification unit includes an air flow sensor that detects a throttle passing flow rate, which is the flow rate of intake air passing through the throttle valve, an intake air pressure sensor that detects a throttle downstream pressure, which is the pressure of intake air flowing through the throttle downstream passage, and a calculation unit that estimates the flow rate of the blow-by gas based on the throttle passing flow rate detected by the air flow sensor and the throttle downstream pressure detected by the intake air pressure sensor (Claim 2).

[0010] According to this configuration, the flow rate of blow-by gas can be estimated by an appropriate method that takes into account the balance of gas entering and exiting the throttle downstream passage, and the estimated value can be used to accurately determine whether or not there is an abnormality in the blow-by passage. Effect of the Invention

[0015] As described above, according to the blow-by passage abnormality diagnosis device of the present invention, the presence or absence of an abnormality in the blow-by passage can be appropriately determined. [Brief description of the drawings]

[0016] [Figure 1] 1 is a schematic system diagram showing the overall configuration of an engine to which an abnormality diagnosis device according to an embodiment of the present invention is applied. [Diagram 2] FIG. 2 is a functional block diagram showing a control system of the engine. [Diagram 3] 5 is a flowchart showing a specific procedure for abnormality diagnosis for determining whether or not there is an abnormality in a blow-by passage of the engine. [Figure 4] 4 is a subroutine showing details of the control in step S6 of FIG. 3. [Diagram 5] FIG. 2 is a schematic diagram showing the flow of each gas in an intake passage of the engine. [Figure 6] 5 is a time chart showing an example of time changes of various state quantities accompanying the abnormality diagnosis of the blow-by passage. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] [Overall engine configuration] Fig. 1 is a schematic system diagram showing the overall configuration of an engine to which an abnormality diagnosis device according to one embodiment of the present invention is applied. The engine shown in this diagram is a four-stroke spark-ignition gasoline engine mounted on a vehicle as a power source for running. The engine includes an engine body 1 driven by combustion energy of a fuel containing gasoline, an intake passage 20 through which intake air introduced into the engine body 1 flows, and an exhaust passage 30 through which exhaust gas discharged from the engine body 1 flows.

[0018] The engine body 1 is an in-line multi-cylinder type having a plurality of cylinders 2 (only one of which is shown in FIG. 1) lined up in a direction perpendicular to the paper surface in FIG. 1. The engine body 1 includes a cylinder block 3 that defines the plurality of cylinders 2, a cylinder head 4 attached to the upper side of the cylinder block 3, a crankcase 5 integrally formed on the lower side of the cylinder block 3, and an oil pan 6 attached to the lower side of the crankcase 5. In this embodiment, the side from the cylinder block 3 toward the cylinder head 4 is treated as the top and the opposite is treated as the bottom, but this is for convenience of explanation and is not intended to limit the installation posture of the engine.

[0019] A piston 7 is accommodated in each cylinder 2 of the engine body 1 so as to be able to reciprocate. A combustion chamber C is formed above the piston 7 in each cylinder 2. Each combustion chamber C is a space defined by the lower surface of the cylinder head 4, the side peripheral surface (cylinder liner) of the cylinder 2, and the crown surface of the piston 7.

[0020] A crank chamber K is formed below the piston 7. The crank chamber K is a space that accommodates a crankshaft 15, which is the output shaft of the engine body 1, and is separated from the combustion chamber C via the piston 7. The crankshaft 15 is connected to the piston 7 of each cylinder 2 via a connecting rod 14.

[0021] A water temperature sensor SN1 and a crank angle sensor SN2 are attached to the engine body 1 (cylinder block 3 or crankcase 5). The water temperature sensor SN1 is a sensor that detects the temperature of the cooling water flowing inside the cylinder block 3 and the cylinder head 4, i.e., the engine water temperature. The crank angle sensor SN2 is a sensor that detects the crank angle, which is the rotation angle of the crankshaft 15, and the engine speed, which is the rotation speed of the crankshaft 15.

[0022] Engine oil W is stored in the oil pan 6. The engine oil W is a lubricating oil used for purposes such as lubricating sliding parts of the engine body 1. The engine oil W is pumped up by an oil pump (not shown) and supplied to each part of the engine body 1 via an oil gallery or the like.

[0023] An injector 10, a spark plug 11, an intake valve 12, and an exhaust valve 13 are attached to the cylinder head 4 for each cylinder 2. The injector 10 is an injection valve that injects fuel containing gasoline into the combustion chamber C. The spark plug 11 is a plug that ignites an air-fuel mixture of fuel and air. The intake valve 12 is a valve that opens and closes an intake port 8 that communicates between the intake passage 20 and the combustion chamber C. The exhaust valve 13 is a valve that opens and closes an exhaust port 9 that communicates between the exhaust passage 30 and the combustion chamber C.

[0024] Fuel injected from the injector 10 into the combustion chamber C is mixed with air in the combustion chamber C to form an air-fuel mixture. The air-fuel mixture is ignited by the spark plug 11 and combusts, and the piston 7 reciprocates due to the expansion force caused by the combustion. The reciprocating motion of the piston 7 is transmitted to the crankshaft 15 via a crank mechanism including a connecting rod 14 etc., causing the crankshaft 15 to rotate.

[0025] Fuel is supplied to the injector 10 from a fuel tank 60 provided in the vehicle. Specifically, the injector 10 of each cylinder 2 and the fuel tank 60 are connected to each other via a fuel supply path 61, and fuel stored in the fuel tank 60 is delivered to the injector 10 of each cylinder 2 through the fuel supply path 61. A fuel pump (not shown) that pressure-feeds fuel from the fuel tank 60 to the injector 10 is provided in the fuel supply path 61.

[0026] The cylinder head 4 is equipped with an intake valve train 16 that opens and closes the intake valve 12 of each cylinder 2, and an exhaust valve train 17 that opens and closes the exhaust valve 13 of each cylinder 2. Each valve train 16, 17 includes a camshaft that is interlocked with the crankshaft 15, and opens and closes the intake valve 12 and exhaust valve 13 in conjunction with the rotation of the crankshaft 15.

[0027] The exhaust passage 30 is a tubular member that forms a flow passage for exhaust gas discharged from the combustion chamber C of each cylinder 2. Although details are omitted, the exhaust passage 30 includes, in order from the upstream side, an exhaust manifold including a plurality of branch pipes (arranged in a direction perpendicular to the paper surface of FIG. 1) that branch out corresponding to each cylinder 2, an exhaust collection section where the branch pipes of the exhaust manifold are collected, and a single-tube common exhaust pipe extending downstream from the exhaust collection section. Note that the upstream / downstream of the exhaust passage 30 referred to here refers to the upstream / downstream of the flow direction of exhaust gas flowing through the exhaust passage 30, with the side closer to the engine body 1 being the upstream and the side farther from the engine body 1 being the downstream.

[0028] The intake passage 20 is a tubular member that forms a flow passage of intake air introduced into the combustion chamber C of each cylinder 2, and includes an intake manifold 21, a surge tank 22, and a common intake pipe 23. The intake manifold 21 includes a plurality of branch pipes (arranged in a direction perpendicular to the paper surface of FIG. 1) that branch out corresponding to each cylinder 2, and is connected to the cylinder head 4 so that the downstream end of each branch pipe communicates with the intake port 8 of each cylinder 2. The surge tank 22 is a tank that provides a space for uniformly distributing the intake air to each cylinder 2, and is interposed between the upstream end of each branch pipe in the intake manifold 21 and the common intake pipe 23. The common intake pipe 23 is a single tubular member that extends from the surge tank 22 to the upstream side. Note that the upstream / downstream of the intake passage 20 referred to here refers to the upstream / downstream of the flow direction of the intake air flowing through the intake passage 20, with the side closer to the engine body 1 being downstream and the side farther from the engine body 1 being upstream.

[0029] In the intake passage 20, an air cleaner 24 and a throttle valve 25 are arranged in this order from the upstream side. The air cleaner 24 is a filter that removes foreign matter from the intake air, and is connected to the upstream end of the common intake pipe 23. The throttle valve 25 is an electric butterfly valve that can adjust the flow rate of the intake air flowing through the intake passage 20, and is arranged between the air cleaner 24 and the surge tank 22 in the common intake pipe 23. In the following, the part of the common intake pipe 23 downstream of the throttle valve 25 is referred to as the downstream intake pipe 23a, and the part of the common intake pipe 23 upstream of the throttle valve 25 is referred to as the upstream intake pipe 23b. The combination of the downstream intake pipe 23a and the surge tank 22 is referred to as the throttle downstream passage 27.

[0030] An airflow sensor SN3, an intake air temperature sensor SN4, and a first intake air pressure sensor SN5 are attached to the upstream intake pipe 23b. The airflow sensor SN3 is a sensor that detects the flow rate of intake air flowing through the upstream intake pipe 23b, that is, the flow rate of intake air flowing upstream of the throttle valve 25. The intake air temperature sensor SN4 is a sensor that detects the temperature of intake air flowing through the upstream intake pipe 23b. The first intake air pressure sensor SN5 is a sensor that detects the pressure of intake air in the upstream intake pipe 23b. Note that the pressure of intake air detected by the first intake air pressure sensor SN5 is the pressure of intake air before it is throttled by the throttle valve 25, and therefore can be considered to be substantially the same as atmospheric pressure.

[0031] A second intake pressure sensor SN6 is attached to the surge tank 22. The second intake pressure sensor SN6 is a sensor that detects the pressure of the intake air inside the surge tank 22, in other words, the pressure of the intake air flowing downstream of the throttle valve 25. The second intake pressure sensor SN6 corresponds to the "intake pressure sensor" in this invention.

[0032] The engine of this embodiment further includes a blow-by gas recirculation device 40 and an evaporated fuel treatment device 50. The blow-by gas recirculation device 40 is a device that introduces blow-by gas (gas containing air-fuel mixture and burned gas) that has leaked from the combustion chamber C of each cylinder 2 into the crank chamber K, into the intake passage 20. The evaporated fuel treatment device 50 is a device that introduces evaporated fuel from a fuel tank 60 into the intake passage 20.

[0033] The blow-by gas recirculation device 40 includes a blow-by passage (PCV hose) 41 and a PCV valve 42 provided in the blow-by passage 41.

[0034] The blow-by passage 41 connects the crankcase 5 and the throttle downstream passage 27 (more specifically, the surge tank 22) to each other. That is, the blow-by passage 41 connects the crankcase 5 and the surge tank 22 so as to communicate with the internal space of the crank chamber K and the surge tank 22. Such a blow-by passage 41 functions as a passage for returning the blow-by gas leaked from the combustion chamber C to the crank chamber K into the surge tank 22.

[0035] The PCV valve 42 is attached to the connection between the blow-by passage 41 and the crankcase 5. The PCV valve 42 is a mechanical check valve that opens only when the internal pressure of the surge tank 22 is lower than the pressure of the crank chamber K, and has the function of preventing the backflow of blow-by gas.

[0036] Although not shown, the PCV valve 42 has a valve body, a valve element provided so as to be movable (strokeable) relative to a valve seat in the valve body, and a spring that presses the valve element toward the valve seat side (crank chamber K side). When the pressure difference between the surge tank 22 and the crank chamber K is sufficiently small, the valve element is pressed against the valve seat (closed position) by the spring, thereby stopping the flow of gas through the blow-by passage 41. On the other hand, when the internal pressure of the surge tank 22 decreases (becomes negative pressure) and a significant pressure difference occurs between the surge tank 22 and the crank chamber K, the valve element strokes from the valve seat against the elastic force of the spring. This allows the blow-by passage 41 and the crank chamber K to communicate with each other, allowing the introduction of blow-by gas from the crank chamber K to the surge tank 22. As the negative pressure in the surge tank 22 progresses further, the distance between the valve body and the valve seat increases, but the distance between the valve body and the part of the inner wall of the valve body that faces the valve seat decreases, which narrows the flow passage area of ​​the blow-by gas in the PCV valve 42 and suppresses the flow rate of the blow-by gas. In this way, the flow rate of the blow-by gas does not increase simply proportionally according to the pressure difference between the surge tank 22 and the crank chamber K, but is limited to a certain range. In other words, the PCV valve 42 has a regulating function that limits the flow rate of the blow-by gas to a certain range due to its structure.

[0037] The evaporated fuel treatment device 50 includes a vapor passage 51, a canister 52, a purge passage 53, and a purge valve .

[0038] The vapor passage 51 is a passage for guiding the fuel evaporated from the fuel tank 60 to the canister 52, and is disposed so as to extend from the fuel tank 60 to the engine body 1 side.

[0039] The canister 52 is a collector that collects the evaporated fuel supplied through the vapor passage 51, and is connected to the end of the vapor passage 51 opposite to the fuel tank 60. The canister 52 has an adsorbent material such as activated carbon built in, and has the function of temporarily storing the evaporated fuel by adsorbing the evaporated fuel to the adsorbent.

[0040] The purge passage 53 connects the canister 52 and the throttle downstream passage 27 (more specifically, the downstream intake pipe 23a) to each other. That is, the purge passage 53 connects the canister 52 and the downstream intake pipe 23a so that the internal space of the canister 52 containing the adsorbent communicates with the internal space of the downstream intake pipe 23a. Such a purge passage 53 functions as a passage for introducing gas containing evaporated fuel released from the canister 52 (hereinafter, this will be referred to as purge gas) into the downstream intake pipe 23a.

[0041] The purge valve 54 is an electrically operated control valve that adjusts the flow rate of the purge gas introduced from the purge passage 53 to the downstream intake pipe 23a, and is provided in the middle of the purge passage 53 so as to be openable and closable. In this embodiment, in order to utilize the evaporated fuel collected in the canister 52 as efficiently as possible, the purge valve 54 is basically opened during engine operation, and the purge gas is supplied through the purge passage 53. However, as an exception, the purge valve 54 is closed under operating conditions in which fuel injection by the injector 10 is stopped (when deceleration fuel cut is performed, which will be described later). This is to prevent the purge gas containing the evaporated fuel from being supplied to the combustion chamber C during combustion stop (in other words, the evaporated fuel from being released wastefully).

[0042] [Control system] 2 is a functional block diagram showing the engine control system. The ECU 100 shown in the figure is a control device for controlling the engine in an integrated manner, and is composed of a microcomputer including a processor (CPU) for performing various arithmetic operations, memories such as ROM and RAM, and various input / output buses.

[0043] Information detected by various sensors provided in the engine is input to the ECU 100. For example, the ECU 100 is electrically connected to the water temperature sensor SN1, the crank angle sensor SN2, the air flow sensor SN3, the intake air temperature sensor SN4, the first intake pressure sensor SN5, and the second intake pressure sensor SN6. Information detected by the sensors SN1 to SN6, that is, information such as the engine water temperature, the crank angle, the engine speed, the intake air flow rate, the intake air temperature, and the intake air pressure, is sequentially input to the ECU 100.

[0044] In addition, detection information from various sensors provided in the vehicle is also input to the ECU 100. For example, the vehicle is provided with an accelerator sensor SN7 that detects the opening degree of an accelerator pedal operated by the driver, i.e., the accelerator opening degree, and detection information (accelerator opening degree) from the accelerator sensor SN7 is also sequentially input to the ECU 100.

[0045] The ECU 100 controls each part of the engine while executing various calculations and judgments based on the input information from the above-mentioned sensors SN1 to SN7. For example, the ECU 100 is electrically connected to the injector 10, the spark plug 11, the throttle valve 25, and the purge valve 54, and outputs control signals to these devices based on the results of the above-mentioned calculations.

[0046] Specifically, the ECU 100 includes, as its functional elements, a calculation unit 101, a combustion control unit 102, and a diagnosis unit 103. The combustion control unit 102 corresponds to the "purge control unit" according to the present invention.

[0047] The combustion control unit 102 is a control module that controls the combustion of the air-fuel mixture in each cylinder 2. For example, the combustion control unit 102 controls the combustion of the air-fuel mixture in each cylinder 2 using the injector 10, the spark plug 11, the throttle valve 25, etc., so as to obtain an appropriate output torque according to conditions such as the accelerator opening degree.

[0048] The diagnosis unit 103 is a control module that performs abnormality diagnosis of the blow-by passage 41. Although details will be described later, the diagnosis unit 103 judges whether or not there is an abnormality in the blow-by passage 41 based on an estimated value of the flow rate of the blow-by gas. For example, if an abnormality occurs such as a hole being opened in the blow-by passage 41 or a connection of the blow-by passage 41 being released (a connection between one end of the blow-by passage 41 and the surge tank 22, or a connection between the other end of the blow-by passage 41 and the crankcase 5), the accuracy of estimating the flow rate of the blow-by gas is significantly deteriorated, and an abnormal value of the flow rate is calculated. If such a situation is confirmed, the diagnosis unit 103 judges that an abnormality has occurred in the blow-by passage 41.

[0049] The calculation unit 101 is a control module that obtains, by calculation, various data and the like required for the combustion control unit 102 and the diagnosis unit 103 to execute control.

[0050] [Abnormality diagnosis] Next, a specific procedure for diagnosing the abnormality of the blow-by passage 41 will be described with reference to the flowchart shown in FIG.

[0051] When the flow of FIG. 3 starts, the diagnosis unit 103 of the ECU 100 reads information required for diagnosing an abnormality in the blow-by passage 41 from each of the sensors SN1 to SN7 (step S1).

[0052] Next, the diagnosis unit 103 determines whether or not a diagnosis permission condition is satisfied (step S2). The diagnosis permission condition is a condition that permits an abnormality diagnosis of the blow-by passage 41. In this embodiment, the diagnosis unit 103 determines that the diagnosis permission condition is satisfied when both of the following requirements (i) and (ii) are satisfied. (i) The engine speed is equal to or lower than a predetermined first engine speed N1 (see FIG. 6). (ii) Atmospheric pressure is equal to or greater than a predetermined reference pressure.

[0053] That is, the diagnosis unit 103 applies the engine speed detected by the crank angle sensor SN2 and the atmospheric pressure (the pressure of the intake air upstream of the throttle valve 25) detected by the first intake pressure sensor SN5 to the above requirements (i) and (ii). If it is confirmed that both the above requirements (i) and (ii) are satisfied, it is determined that the diagnosis permission condition is satisfied. On the other hand, if it is confirmed that even one of the above requirements (i) and (ii) is not satisfied, it is determined that the diagnosis permission condition is not satisfied.

[0054] Here, the first rotation speed N1 in the above requirement (i) and the reference pressure in the above requirement (ii) are determined from the viewpoint of ensuring the estimation accuracy when estimating the flow rate of blow-by gas in step S6 described later. That is, it is known that the estimation accuracy of the flow rate of blow-by gas significantly decreases when the engine rotation speed is excessively high or the atmospheric pressure is excessively low (in other words, when the altitude is high). Therefore, the above requirements (i) and (ii) are set in order to avoid performing an abnormality diagnosis of the blow-by passage 41 based on such an estimated value with low accuracy. The reference pressure in the above requirement (ii) can be set to a value equivalent to the atmospheric pressure at a high altitude, for example, about 2,000 meters above sea level.

[0055] If the above step S2 is judged as YES and it is confirmed that the diagnosis permission condition is satisfied, the combustion control unit 102 of the ECU 100 judges whether or not the deceleration fuel cut condition is satisfied (step S3). The deceleration fuel cut condition is a condition under which the execution of deceleration fuel cut, which stops fuel injection by the injector 10 when the vehicle is decelerating, is permitted for the purpose of reducing fuel consumption. In this embodiment, the combustion control unit 102 judges that the deceleration fuel cut condition is satisfied when all of the following requirements (iii) to (v) are satisfied. (iii) The accelerator opening is substantially zero (i.e., the accelerator pedal is not depressed). (iv) The engine speed is equal to or higher than a predetermined second speed N2 (see FIG. 6). (v) The engine water temperature is above a predetermined reference temperature.

[0056] That is, the combustion control unit 102 applies the accelerator opening detected by the accelerator sensor SN7, the engine speed detected by the crank angle sensor SN2, and the engine water temperature detected by the water temperature sensor SN1 to the above requirements (iii) to (v). If it is confirmed that all of the above requirements (iii) to (v) are satisfied, it is determined that the deceleration fuel cut condition is satisfied. On the other hand, if it is confirmed that any one of the above requirements (iii) to (v) is not satisfied, it is determined that the deceleration fuel cut condition is not satisfied. Note that the second rotation speed N2 in the requirement (iv) is a rotation speed slightly higher than the idling rotation speed and sufficiently lower than the first rotation speed N1 (i.e., the upper limit rotation speed at which abnormality diagnosis is permitted) used in the requirement (i) regarding the above-mentioned diagnosis permission condition.

[0057] When the result of the determination in step S3 is NO and it is confirmed that the deceleration fuel cut condition is not satisfied, the combustion control unit 102 executes normal combustion control to burn the fuel injected from the injector 10 in the combustion chamber C of each cylinder 2 (step S15). Specifically, the combustion control unit 102 calculates the required torque of the engine based on information such as the accelerator opening degree detected by the accelerator sensor SN7, and controls the amount of fuel injected by the injector 10, the ignition timing of the spark plug 11, the opening degree of the throttle valve 25, and the like so that combustion accompanied by heat generation commensurate with the calculated required torque is performed in the combustion chamber C of each cylinder 2. In addition, the combustion control unit 102 opens the purge valve 54 and introduces purge gas containing evaporated fuel into the intake passage 20 (throttle downstream passage 27) through the purge passage 53. At this time, the opening degree of the purge valve 54 is adjusted so that the concentration of the fuel (air-fuel ratio of the mixture) consisting of the evaporated fuel in the purge gas and the fuel injected from the injector 10 becomes a desired value in the combustion chamber C of each cylinder 2.

[0058] On the other hand, if the determination in step S3 is YES and it is confirmed that the deceleration fuel cut condition is satisfied, the combustion control unit 102 executes deceleration fuel cut (step S4). That is, the combustion control unit 102 controls the injector 10 so that fuel injection into the combustion chamber C of each cylinder 2 is stopped, and the combustion of the air-fuel mixture in each combustion chamber C is stopped.

[0059] Next, the combustion control unit 102 closes the purge valve 54 (step S5). That is, the combustion control unit 102 reduces the opening degree of the purge valve 54 to an opening degree equivalent to a fully closed state, thereby blocking the purge passage 53, so that the introduction of the purge gas containing evaporated fuel into the intake passage 20 is stopped.

[0060] Next, the calculation unit 101 of the ECU 100 calculates the blow-by gas flow rate Qb (step S6). The blow-by gas flow rate Qb calculated here is the flow rate of blow-by gas introduced from the crank chamber K to the surge tank 22 through the blow-by passage 41, as shown in Fig. 5. This blow-by gas flow rate Qb is calculated (estimated) based on the intake flow rate Qth detected by the air flow sensor SN3 and the intake pressure Ps detected by the second intake pressure sensor SN6.

[0061] Here, the intake air flow rate Qth detected by the air flow sensor SN3 upstream of the throttle valve 25 is equivalent to the intake air flow rate passing through the throttle valve 25. Therefore, hereinafter, the flow rate detected by the air flow sensor SN3 is referred to as the throttle passing flow rate Qth. Also, the intake air pressure Ps detected by the second intake air pressure sensor SN6 provided in the surge tank 22 (throttle downstream passage 27) is equivalent to the pressure of the intake air flowing downstream of the throttle valve 25. Therefore, hereinafter, the pressure detected by the second intake air pressure sensor SN6 is referred to as the throttle downstream pressure Ps. In the above step S6, the calculation unit 101 calculates the blow-by gas flow rate Qb from the throttle passing flow rate Qth and the throttle downstream pressure Ps. Specifically, the calculation unit 101 calculates the blow-by gas flow rate Qb according to a subroutine shown in FIG. 4.

[0062] When the subroutine of FIG. 4 starts, the calculation unit 101 acquires the throttle passing flow rate Qth detected by the air flow sensor SN3 (step S21).

[0063] Next, the calculation unit 101 calculates the throttle downstream flow rate Qs shown in FIG. 5 based on the throttle downstream pressure Ps detected by the second intake pressure sensor SN6 and the intake air temperature detected by the intake air temperature sensor SN4 (step S22). The throttle downstream flow rate Qs calculated here is the flow rate of the intake air passing through the surge tank 22. This throttle downstream flow rate Qs can be calculated from the throttle downstream pressure Ps and the intake air temperature using a gas state equation. That is, the calculation unit 101 calculates the mass of the intake air in the surge tank 22 from the throttle downstream pressure Ps and the intake air temperature using a predetermined calculation formula utilizing the state equation, and calculates the throttle downstream flow rate Qs based on the change in the calculated mass over time.

[0064] Next, the calculation unit 101 calculates the cylinder flow rate Qcy, which is the flow rate of intake air sucked into the combustion chamber C of each cylinder 2 (step S23). Specifically, the calculation unit 101 calculates the cylinder flow rate Qcy based on the throttle passing flow rate Qth detected by the air flow sensor SN3 and the charging efficiency of each cylinder 2 estimated from the valve timing of the intake valve 12, the engine speed, etc. For example, the mass of intake air introduced into the combustion chamber C of each cylinder 2 increases as the most recent throttle passing flow rate Qth (more specifically, the throttle passing flow rate Qth at a time preceding by a predetermined delay time determined from the moving distance from the position of the air flow sensor SN3 to the combustion chamber C of each cylinder 2) increases, and increases as the charging efficiency, which is the ratio of the intake air suction amount to the maximum volume of each cylinder 2, increases. The calculation unit 101 calculates the cylinder flow rate Qcy from the detected value of the throttle passing flow rate Qth and the estimated value of the charging efficiency using a predetermined calculation formula utilizing such characteristics.

[0065] Next, the calculation unit 101 calculates the flow rate of the blow-by gas introduced into the surge tank 22 through the blow-by passage 41, that is, the blow-by gas flow rate Qb (step S24). Specifically, the calculation unit 101 calculates the blow-by gas flow rate Qb using the following formula (1) based on the throttle passing flow rate Qth acquired in the above step S21, the throttle downstream flow rate Qs calculated in the above step S22, and the cylinder flow rate Qcy calculated in the above step S23.

[0066] Qb = Qs - Qth + Qcy (1) Here, the mass of intake air in the surge tank 22 increases as the throttle passage flow rate Qth and the blow-by gas flow rate Qb, which are the flow rates of gas flowing into the surge tank 22, increase, and decreases as the cylinder flow rate Qcy, which is the flow rate of gas flowing out from the surge tank 22, increases. Therefore, the mass flow rate of intake air in the surge tank 22, that is, the throttle downstream flow rate Qs, can be obtained using an equation (Qs=Qth+Qb-Qcy) in which the throttle passage flow rate Qth and the blow-by gas flow rate Qb are positive elements and the cylinder flow rate Qcy is a negative element. By modifying this equation and rearranging the terms so that Qb and Qs are interchangeable, the above equation (1) can be obtained. In other words, in the above step S24, the calculation unit 101 estimates the blow-by gas flow rate Qb based on the balance between the gas flowing into the surge tank 22 and the gas flowing out from the surge tank 22. The combination of the air flow sensor SN3, the second intake pressure sensor SN6, and the calculation unit 101 utilized for estimating the blow-by gas flow rate Qb corresponds to the "flow rate determination unit" in the present invention.

[0067] As already explained, the blow-by gas flow rate Qb is calculated (estimated) when the purge valve 54 is closed in conjunction with the execution of the deceleration fuel cut (see FIG. 3). Therefore, when calculating the blow-by gas flow rate Qb, it is not necessary to take into account the flow rate of the purge gas flowing into the surge tank 22 through the purge passage 53. This is why the above formula (1) does not include a term representing the flow rate of the purge gas.

[0068] Returning to FIG. 3, the rest of the control will be explained. After calculating the blow-by gas flow rate Qb as described above, the calculation unit 101 judges whether or not the deceleration fuel cut has continued for a predetermined specified time (step S7). That is, the deceleration fuel cut in step S4 is continued while the judgment in step S3 is YES (while the deceleration fuel cut condition is satisfied). The calculation unit 101 measures the time during which the deceleration fuel cut has continued in this manner, and judges whether or not the measured time has reached the specified time.

[0069] When the determination in step S7 is YES and it is confirmed that the deceleration fuel cut has continued for the specified time, the diagnosis unit 103 calculates an integrated value Zb by integrating the blow-by gas flow rate Qb. That is, the diagnosis unit 103 calculates the integrated value Zb of the blow-by gas flow rate by integrating the blow-by gas flow rate Qb repeatedly calculated by the routine of Fig. 4 during the specified time (step S8).

[0070] Next, the diagnosis unit 103 determines whether or not the integrated value Zb of the blow-by gas flow rate calculated in the above step S8 is greater than a predetermined threshold value X (step S9).

[0071] When the result of the determination in step S9 is YES and it is confirmed that the integrated value Zb of the blow-by gas flow rate is larger than the threshold value X, the diagnosis unit 103 determines that an abnormality has occurred in the blow-by passage 41 (step S10), and displays a predetermined display on a display unit inside the vehicle to notify the driver or the like of the abnormality (step S11). For example, the diagnosis unit 103 performs control such as turning on a warning light provided on the meter panel of the vehicle.

[0072] On the other hand, if the result of the above step S9 is NO and it is confirmed that the integrated value Zb of the blow-by gas flow rate is equal to or less than the threshold value X, the diagnosis unit 103 determines that the blow-by passage 41 is normal (step S12). In this case, the diagnosis unit 103 resets the integrated value Zb of the blow-by gas flow rate to zero (step S13) without performing any particular display control to notify of an abnormality.

[0073] FIG. 6 is a time chart showing an example of changes over time in various state quantities accompanying an abnormality diagnosis of the blow-by passage 41 shown in FIGS. 3 and 4, where chart (a) shows the change over time in the accelerator opening degree, chart (b) shows the change over time in the engine speed, chart (c) shows the change over time in the amount of fuel injected from the injector 10, chart (d) shows the change over time in the throttle downstream pressure Ps or the throttle opening degree (the opening degree of the throttle valve 25), chart (e) shows the change over time in the opening degree of the purge valve 54, chart (f) shows the change over time in the blow-by gas flow rate Qb, and chart (g) shows the change over time in the integrated value Zb of the blow-by gas flow rate.

[0074] In Fig. 6, the time when the accelerator opening degree decreases to zero is set as t1. At this time t1, the engine speed is lower than a first speed N1, which is the upper limit speed at which an abnormality diagnosis is permitted, and higher than a second speed N2, which is the lower limit speed at which deceleration fuel cut is permitted. Since the engine speed is higher than the second speed N2, deceleration fuel cut is permitted, and at a time t2, which is slightly later than time t1, deceleration fuel cut is started (chart (c)). That is, the amount of fuel injected from the injector 10 is reduced to zero.

[0075] As the deceleration fuel cut starts at time t2, the opening of the throttle valve 25 is reduced and the throttle downstream pressure Ps drops (chart (d)). That is, as the opening of the throttle valve 25 is reduced, the pressure difference before and after the throttle valve 25 increases, and the throttle downstream pressure Ps, which is the pressure in the surge tank 22 downstream of the throttle valve 25, drops. As a result, the throttle downstream pressure Ps changes to a stronger negative pressure.

[0076] Furthermore, with the start of deceleration fuel cut at time t2, the purge valve 54 is closed and its opening is reduced to zero (chart (e)). This stops the introduction of purge gas into the intake passage 20 through the purge passage 53.

[0077] The decrease (negative pressure) of the throttle downstream pressure Ps at time t2 increases the pressure difference between the crank chamber K and the surge tank 22, but the effect of this increase in pressure difference on the blow-by gas flow rate Qb differs depending on whether the blow-by passage 41 is normal or abnormal. In the chart (f), the blow-by gas flow rate Qb when the blow-by passage 41 is normal is indicated by a solid line, and the blow-by gas flow rate Qb when the blow-by passage 41 is abnormal is indicated by a dashed line. According to the waveform of the solid line, when the blow-by passage 41 is normal, even if the throttle downstream pressure Ps becomes significantly negative (the pressure difference with the crank chamber K increases) at time t2, the blow-by gas flow rate Qb does not change significantly. This is due to the regulating function of the PCV valve 42 already explained. On the other hand, when the blow-by passage 41 is abnormal, as shown by the waveform of the broken line, the throttle downstream pressure Ps becomes significantly negative at time t2, and the blow-by gas flow rate Qb increases significantly.

[0078] For example, if an abnormality occurs in which a hole is opened in the blow-by passage 41, the gas flowing from the blow-by passage 41 into the intake passage 20 is a mixture of the original blow-by gas drawn into the blow-by passage 41 from the crank chamber K and the outside air flowing in through the hole in the blow-by passage 41. In this case, the amount of outside air flowing in through the hole in the blow-by passage 41 increases as the throttle downstream pressure Ps becomes negative, and this causes the blow-by gas flow rate Qb to increase significantly in appearance. Also, if an abnormality occurs in which the connection between one end of the blow-by passage 41 and the surge tank 22 is released, the surge tank 22 is essentially open to the atmosphere, and outside air is freely introduced into the surge tank 22 from the connection port of the blow-by passage 41 in the surge tank 22. In this case, the original blow-by gas (blow-by gas drawn from the crank chamber K) is not introduced into the intake passage 20, but the amount of outside air introduced into the surge tank 22 from the connection port increases in response to the throttle downstream pressure Ps becoming negative, so that the blow-by gas flow rate Qb also increases significantly in appearance. This is also true when an abnormality occurs in which the connection between the other end of the blow-by passage 41 and the crankcase 5 is released. This is why the blow-by gas flow rate Qb when the blow-by passage 41 is abnormal is significantly larger than when it is normal, after time t2 when the throttle downstream pressure Ps becomes significantly negative.

[0079] The difference between the blow-by gas flow rate Qb in the abnormal and normal states described above also causes a difference in the integrated value Zb (chart (g)) obtained by integrating the blow-by gas flow rate Qb. That is, the integration of the blow-by gas flow rate Qb starts from time t2 when the deceleration fuel cut starts, and the integrated value Zb obtained by the integration increases steadily from time t2 onwards. However, since the blow-by gas flow rate Qb is significantly larger when the blow-by passage 41 is abnormal than when it is normal, the rate of increase of the integrated value Zb is significantly larger when it is abnormal than when it is normal.

[0080] Time t3 in FIG. 6 is the time when the elapsed time from the start time t2 of the deceleration fuel cut reaches the specified time in the above step S7 (FIG. 3). At this time t3, the integrated value Zb of the blow-by gas flow rate in the abnormal state is larger than the threshold value X (above step S9), and the integrated value Zb of the blow-by gas flow rate in the normal state is smaller than the threshold value X. In other words, if the blow-by passage 41 is abnormal, the integrated value Zb exceeds the threshold value X before time t3, and if the blow-by passage 41 is normal, the integrated value Zb remains below the threshold value X even at time t3. As a result, at time t3, the abnormal blow-by passage 41 is judged to be abnormal, and the normal blow-by passage 41 is judged to be normal. If the blow-by passage 41 is judged to be normal, the integrated value Zb is reset to zero at the judgment time t3.

[0081] At time t4, which is slightly delayed from time t3, the engine speed drops to the second speed N2 (chart (b)). This stops the deceleration fuel cut and restarts fuel injection by the injector 10 (chart (c)). With the restart of fuel injection, the opening of the throttle valve 25 is increased (chart (d)), and the purge valve 54, which was closed, is opened again (chart (e)).

[0082] [Effects] As described above, in this embodiment, during execution of the deceleration fuel cut in which fuel injection by the injector 10 is stopped, the blow-by gas flow rate Qb, which is the flow rate of the blow-by gas introduced into the throttle downstream passage 27 through the blow-by passage 41, is estimated by calculation, and it is determined whether or not an abnormality has occurred in the blow-by passage 41 based on the estimated blow-by gas flow rate Qb. Such a configuration has the advantage that the presence or absence of an abnormality in the blow-by passage 41 can be appropriately determined.

[0083] During execution of the deceleration fuel cut, the introduction of purge gas (gas containing evaporated fuel) from the purge passage 53 to the throttle downstream passage 27 is stopped by closing the purge valve 54. Therefore, if the blow-by gas flow rate Qb is estimated during the deceleration fuel cut as described above, it is possible to avoid estimating the blow-by gas flow rate Qb in a state in which both the blow-by gas and the purge gas are introduced into the throttle downstream passage 27 (in other words, a state in which the behavior of each gas is likely to become complicated). This ensures good estimation accuracy of the blow-by gas flow rate Qb, so that it is possible to appropriately determine whether or not an abnormality has occurred in the blow-by passage 41 based on the estimated blow-by gas flow rate Qb.

[0084] Specifically, in the above embodiment, an integrated value Zb is obtained by accumulating the estimated blow-by gas flow rate Qb during the deceleration fuel cut, and the blow-by passage 41 is determined to be abnormal if the obtained integrated value Zb is greater than the threshold value X. In this way, when the integrated value Zb of the blow-by gas flow rate is used as an index for determining the abnormality of the blow-by passage 41, it is possible to reduce as much as possible the possibility of erroneously determining that the blow-by passage 41 is abnormal even though it is normal. For example, the blow-by gas flow rate Qb calculated (estimated) sequentially during the deceleration fuel cut may be calculated as an abnormally large value temporarily due to some factor that increases the error at the time of calculation. In this case, if the blow-by gas flow rate Qb itself is compared with the threshold value, there is a possibility that the normal blow-by passage 41 may be erroneously determined to be abnormal when the above-mentioned temporary error increase occurs. In contrast, when the integrated value Zb of the blow-by gas flow rate Qb during the deceleration fuel cut is compared with the threshold value X as described above, the blow-by passage 41 is judged to be abnormal only when the blow-by gas flow rate Qb continuously indicates an abnormal value, so that the possibility of the above-mentioned erroneous judgment occurring can be reduced as much as possible.

[0085] Here, when an abnormality such as a hole being opened in the blow-by passage 41 or the connection of the blow-by passage 41 is caused, particularly during deceleration fuel cut, a large amount of gas including outside air is introduced into the throttle downstream passage 27 from the connection port of the throttle downstream passage 27 (surge tank 22) with the blow-by passage 41, so that the blow-by gas flow rate Qb appears to increase significantly, and the calculated value (estimated value) of the blow-by gas flow rate Qb becomes abnormally large. In contrast, in this embodiment, when the integrated value Zb obtained by integrating the blow-by gas flow rate Qb during deceleration fuel cut is greater than the threshold value X, the blow-by passage 41 is determined to be abnormal, so that when an abnormality such as the above-mentioned hole being opened or the connection being cut is caused, it can be accurately determined.

[0086] If the above-mentioned abnormality occurs in the blow-by passage 41, it is inevitable that the air-fuel ratio of the mixture formed in the combustion chamber C of each cylinder 2 will deviate significantly from the target value during normal operation except for deceleration fuel cut. Such deviation in the air-fuel ratio, for example, deteriorates the emission performance (exhaust purification performance) of the engine, so it is necessary to avoid leaving the blow-by passage 41 in an abnormal state. In contrast, in this embodiment, the presence or absence of an abnormality in the blow-by passage 41 is determined with high accuracy by the above-mentioned method, so it is possible to avoid leaving the blow-by passage 41 in an abnormal state. This is effective in guaranteeing the emission performance.

[0087] In addition, in this embodiment, the blow-by gas flow rate Qb is estimated by calculation based on the throttle passing flow rate Qth detected by the air flow sensor SN3 upstream of the throttle valve 25 and the throttle downstream flow rate Qs calculated from the detection value (throttle downstream pressure Ps) by the second intake pressure sensor SN6 provided in the surge tank 22, etc., so that the blow-by gas flow rate Qb can be estimated by an appropriate method taking into account the balance of gas entering and leaving the throttle downstream passage 27 (surge tank 22), and the presence or absence of an abnormality in the blow-by passage 41 can be accurately determined using the estimated value.

[0088] [Variations] In the above embodiment, the blow-by gas flow rate Qb is estimated by calculation from the detection values ​​of the air flow sensor SN3 and the second intake pressure sensor SN6. However, for example, a sensor capable of directly detecting the flow rate of gas flowing into the surge tank 22 from the connection port with the blow-by passage 41 may be added, and the blow-by gas flow rate Qb may be determined using the additional sensor.

[0089] In the above embodiment, the blow-by gas flow rate Qb is specified during the execution of the deceleration fuel cut in which the fuel injection by the injector 10 is stopped as the vehicle decelerates, and the abnormality diagnosis of the blow-by passage 41 is performed based on the specified blow-by gas flow rate Qb, but the abnormality diagnosis of the blow-by passage 41 only needs to be performed when at least the purge valve 54 is closed (when the introduction of purge gas from the purge passage 53 to the throttle downstream passage 27 is stopped), and the abnormality diagnosis can also be performed at other times besides when the deceleration fuel cut is being performed. For example, during idling operation of the engine, the abnormality diagnosis of the blow-by passage 41 may be performed with the purge valve 54 closed.

[0090] In the above embodiment, the integrated value Zb of the blow-by gas flow rate Qb determined during the deceleration fuel cut is calculated, and the blow-by passage 41 is determined to be abnormal if the calculated integrated value Zb is greater than the threshold value X. However, it is not necessary to use the integrated value Zb of the blow-by gas flow rate as an index for abnormality diagnosis. For example, the blow-by gas flow rate Qb may be determined multiple times during the period in which the purge valve 54 is closed, and the average value of the determined blow-by gas flow rate Qb may be compared with a predetermined threshold value to perform abnormality diagnosis of the blow-by passage 41.

[0091] In the above embodiment, the crankcase 5 and the cylinder block 3 are integrated in the engine body 1, but the crankcase 5 and the cylinder block 3 may be separate bodies. [Explanation of symbols]

[0092] 5 Crankcase 7 Piston 20 Intake passage 25 Throttle valve 27 Throttle downstream passage 41 Blow-by passage 52 Canister 53 Purge Passage 54 Purge valve 101 Arithmetic section 102 Combustion control unit (purge control unit) 103 Diagnostic Department C. Combustion chamber K Crankcase SN3 Airflow Sensor SN6 2nd intake pressure sensor (intake pressure sensor)

Claims

1. An abnormality diagnosis device for diagnosing an abnormality in a blow-by passage in an engine including: a crankcase defining a crank chamber separated from a combustion chamber via a piston; an intake passage through which intake air introduced into the combustion chamber flows; a throttle valve provided in the intake passage so as to be able to open and close; a blow-by passage connecting the crankcase to a throttle downstream passage, which is a portion of the intake passage downstream of the throttle valve; and a purge passage connecting a canister that adsorbs evaporated fuel from a fuel tank to the throttle downstream passage, a purge valve provided in the purge passage so as to be capable of opening and closing; A purge control unit that controls an opening and closing operation of the purge valve; a flow rate specifying unit that specifies a flow rate of blow-by gas that passes through the blow-by passage and is introduced from the crank chamber into the throttle downstream passage; a diagnosis unit that performs an abnormality diagnosis to determine whether or not an abnormality has occurred in the blow-by passage based on the flow rate of the blow-by gas specified by the flow rate specification unit, the diagnosis unit performs an abnormality diagnosis on the blow-by passage in a state in which the purge valve is closed by the purge control unit, the purge control unit closes the purge valve when a deceleration fuel cut is performed to stop the fuel supply to the combustion chamber due to deceleration, The diagnosis unit calculates an integrated value of the flow rate of the blow-by gas while the deceleration fuel cut is being performed, and determines that the blow-by passage is abnormal if the calculated integrated value exceeds a predetermined threshold value.

2. 2. The blow-by passage abnormality diagnosis device according to claim 1, the flow rate specifying unit comprises an air flow sensor that detects a throttle passing flow rate which is the flow rate of intake air passing through the throttle valve, an intake pressure sensor that detects a throttle downstream pressure which is the pressure of intake air flowing through the throttle downstream passage, and a calculation unit that estimates the flow rate of blow-by gas based on the throttle passing flow rate detected by the air flow sensor and the throttle downstream pressure detected by the intake pressure sensor.

Images