WO2025023012A1 - Failure detection device for exhaust gas recirculation device - Google Patents

Abstract

This failure detection device for an exhaust gas recirculation device comprises: a failure type estimation unit (31) for estimating the type of failure that has occurred in an exhaust gas recirculation device (20); and a determination unit (32) for determining the presence or absence of a failure according to an intake pressure change when the opening degree of an exhaust gas recirculation valve (22) is switched during a fuel cut operation. The determination unit (32) determines the presence or absence of a failure by changing a valve opening degree set for the exhaust gas recirculation valve (22) according to the type of failure estimated by the failure type estimation unit (31) during failure diagnosis.

Description

Fault detection device for exhaust gas recirculation system

This invention relates to a fault detection device for an exhaust gas recirculation system.

　Generally, an exhaust gas recirculation system is provided between the exhaust passage and the intake passage of an engine, which introduces a portion of the exhaust gas into the intake air as exhaust gas recirculation gas. The exhaust gas recirculation system is equipped with an exhaust gas recirculation passage that connects the exhaust passage and the intake passage, and an exhaust gas recirculation valve provided in the exhaust gas recirculation passage. Depending on the pressure state in the intake passage caused by the opening and closing of the exhaust gas recirculation valve and the opening and closing of the throttle valve, an appropriate amount of exhaust gas recirculation gas is introduced into the intake air. Introducing the exhaust gas recirculation gas into the intake air lowers the combustion temperature in the combustion chamber, and this temperature drop suppresses nitrogen oxides and improves fuel efficiency, and also suppresses knocking.

However, exhaust gas recirculation systems can develop abnormalities (failures) over time. Examples of these include the exhaust gas recirculation valve sticking, foreign matter getting caught in the exhaust gas recirculation valve, or foreign matter clogging the exhaust gas recirculation passage.

If the malfunction is due to the exhaust recirculation valve being stuck open or a foreign object getting caught in it, preventing it from closing from a certain opening, then excessive exhaust recirculation gas will be introduced into the intake, which can result in unstable combustion. Also, if the malfunction is due to the exhaust recirculation valve being stuck closed or a foreign object getting stuck in the exhaust recirculation passage, which causes the exhaust recirculation gas flow rate to be less than it should be (the desired value), then too little exhaust recirculation gas will be introduced, which can result in an increase in the combustion temperature depending on the operating conditions.

To detect such failures, for example, there is a failure detection device described in Patent Document 1. In this failure detection device, as a failure diagnosis operation, if the difference between the intake pressure (P1) when a predetermined time has elapsed with the exhaust gas recirculation valve fully closed during fuel cut and the intake pressure (P2) when a predetermined time has elapsed thereafter with the exhaust gas recirculation valve open becomes equal to or exceeds a predetermined value, it is determined that there is a failure in the exhaust gas recirculation device.

JP 2022-128831 A

In conventional fault detection devices, the valve opening of the exhaust gas recirculation valve when fault detection is performed is always set to a constant value. This creates a problem in that the accuracy of fault determination varies depending on the type of fault. For example, in the case of a fault that causes the flow rate of exhaust gas recirculation gas to increase above the normal flow rate, if the valve opening set at the time of fault detection is large (larger than the engagement opening), the intake differential pressure (P2-P1) may exceed a predetermined value even though a fault has occurred, and the fault may not be determined to be a fault.

The objective of this invention is to improve the accuracy of fault determination for exhaust gas recirculation systems and to provide a substantive fault determination that corresponds to the type of fault.

In order to solve the above problems, the present invention provides a fault detection device for an exhaust gas recirculation system that includes an exhaust gas recirculation passage that communicates between the exhaust passage and the intake passage of an engine, and an exhaust gas recirculation valve provided in the exhaust gas recirculation passage. The fault detection device includes a fault type estimation unit that estimates the type of fault that has occurred in the exhaust gas recirculation system, and a determination unit that determines the presence or absence of a fault from a change in intake pressure when the opening of the exhaust gas recirculation valve is switched during fuel cut operation, and the determination unit determines the presence or absence of a fault by changing the valve opening set for the exhaust gas recirculation valve according to the type of fault estimated by the fault type estimation unit when diagnosing the presence or absence of a fault (Configuration 1).

As in configuration 1, by changing the exhaust gas recirculation valve opening when a fault is detected depending on the type of fault, the accuracy of the fault detection can be improved.

In an embodiment having configuration 1, the fault type estimation unit estimates a first fault in which the flow rate of exhaust recirculation gas increases from the original flow rate when the difference between the intake amount upstream and downstream of the connection of the intake passage with the exhaust recirculation passage is equal to or greater than a first threshold value with the exhaust recirculation valve closed, and the determination unit can adopt a configuration in which, when the first fault is estimated, the valve opening set for the exhaust recirculation valve is set smaller than when the first fault is not estimated (configuration 2).

In this configuration 2, when a first fault (i.e., a fault in which the exhaust recirculation gas flow rate increases from the intended flow rate due to a foreign object getting caught in the exhaust recirculation valve, etc.) is suspected, the opening of the exhaust recirculation valve during fault diagnosis is made smaller than when other faults (i.e., a fault in which the exhaust recirculation gas flow rate decreases from the intended flow rate, etc.) are suspected. This improves the accuracy of fault determination in the case of a fault in which the exhaust recirculation gas flow rate increases from the intended flow rate.

In an embodiment having configuration 2, the failure type estimation unit can be configured to estimate a first failure when a state in which the difference between the intake air amount upstream of the connection part of the intake passage with the exhaust gas recirculation passage and the intake air amount downstream of the connection part is equal to or greater than a first threshold value and the engine rotation fluctuation is equal to or greater than a second threshold value is measured a predetermined number of times (configuration 3). This configuration 3 allows the first failure to be estimated more accurately.

In an embodiment having configuration 2, the failure type estimation unit can be configured to estimate a second failure in which the flow rate of exhaust recirculation gas is reduced from the original flow rate when the difference between the intake amount upstream and downstream of the connection of the intake passage with the exhaust recirculation passage is less than a third threshold value with the exhaust recirculation valve open, and the determination unit can be configured to set the exhaust recirculation valve opening degree set at the time of failure determination to be larger when the second failure is estimated compared to when a failure other than the second failure is estimated (Configuration 4). This configuration 4 can also be adopted in the embodiment of configuration 1 that does not have configuration 2.

In this configuration 4, if a second fault (i.e., a fault in which the exhaust recirculation gas flow rate is reduced from the intended flow rate due to clogging of the exhaust recirculation passage by foreign matter, etc.) is suspected, the opening of the exhaust recirculation valve during fault diagnosis is made larger than when other faults (i.e., a fault in which the exhaust recirculation gas flow rate is increased from the intended flow rate, etc.) are suspected. As a result, in the case of a fault in which the exhaust recirculation gas flow rate is reduced from the intended flow rate, a fault determination is made less easily than in the case of other fault types, and a diagnosis is made according to the urgency of the fault.

In an embodiment having configuration 4, the failure type estimation unit can be configured to estimate a second failure when a state in which the difference between the intake amount upstream and downstream of the connection of the intake passage with the exhaust gas recirculation passage is less than a third threshold and the engine rotation fluctuation is equal to or greater than a fourth threshold is measured a predetermined number of times (configuration 5). This allows the second failure to be estimated more accurately.

In an embodiment having configuration 4, if the fault type estimation unit estimates both the first fault and the second fault, the determination unit can adopt a configuration in which the opening of the exhaust gas recirculation valve that is set at the time of fault determination is reduced (configuration 6). This configuration 6 aims to prioritize the first fault determination in anticipation of a safety hazard when there is concern about both the first fault and the second fault. In other words, the first fault is prioritized over the second fault as the fault type estimated by the fault type estimation unit.

In an embodiment having configuration 4, the determination unit can adopt a configuration in which it notifies the occupant of the occurrence of a malfunction only when the first malfunction is determined (configuration 7). This configuration 7 aims to prevent unnecessary notifications to the occupant by making it relatively more difficult to determine a malfunction in the case of a malfunction that reduces the flow rate of exhaust recirculation gas, since the amount of harmful components in the exhaust gas does not worsen.

This invention makes it possible to improve the accuracy of fault determination in the exhaust gas recirculation system and to realize a substantive fault determination according to the type of fault.

1 is a schematic diagram showing an embodiment of the present invention, illustrating the configuration of an engine equipped with an exhaust gas recirculation system and a failure detection device thereof. FIG. 4 is a graph showing an example of control according to the present invention. FIG. 4 is a graph showing an example of control according to the present invention. FIG. 4 is a graph showing an example of control according to the present invention. FIG. 4 is a graph showing an example of control according to the present invention. FIG. 4 is a graph for explaining the control of the present invention. FIG. 4 is a graph for explaining the control of the present invention. FIG. 4 is a graph for explaining the control of the present invention. 3 is a flowchart showing the control of the present invention.

An embodiment of the present invention will be described with reference to the drawings. Figure 1 is a schematic diagram showing the configuration of an engine 1 equipped with an exhaust gas recirculation system and its failure detection device according to the present invention.

Engine 1 is a four-cylinder engine for automobiles. As shown in FIG. 1, it has four cylinders (combustion chambers) 2 with pistons housed in them arranged in parallel, an intake passage 4 connected to an intake port that feeds air into each cylinder 2, an exhaust passage 5 connected to an exhaust port through which exhaust gas in each cylinder 2 is discharged, and an injection device 10 that supplies fuel to each cylinder 2. Note that FIG. 1 shows only the components and means directly related to this invention, and other components are omitted. Also, the drawing shows an example with four cylinders 2, but the number of cylinders 2 is free, and the arrangement of the cylinders is not limited to in-line. Also, although the injection device 10 is assumed to inject fuel directly into each cylinder 2, it may be assumed to inject fuel into the intake port.

A throttle valve 3 that adjusts the flow area is provided in the upstream portion of the intake passage 4, making it possible to adjust the amount of intake air. In addition, various sensors (not shown) such as an air-fuel ratio sensor that detects the air-fuel ratio in the exhaust passage 5 are provided in the exhaust passage 5. Furthermore, in the exhaust passage 5, an exhaust purification device 13 equipped with a catalyst or the like that removes harmful substances in the exhaust is provided downstream, and further downstream of that, a muffler 15 or the like is provided.

Between the intake passage 4 and the exhaust passage 5, there is provided an exhaust gas recirculation system 20, which includes an exhaust gas recirculation passage 21 that connects the intake passage 4 and the exhaust passage 5, and an exhaust gas recirculation valve 22 that opens and closes the exhaust gas recirculation passage 21. The exhaust gas recirculation passage 21 is connected to the intake passage 4 downstream of the throttle valve 3. Depending on the pressure state in the intake passage 4 caused by the opening and closing of the exhaust gas recirculation valve 22 and the opening and closing of the throttle valve 3, a portion of the exhaust gas is introduced into the intake air as exhaust gas recirculation.

Each of the devices necessary for the operation of the engine, including the throttle valve 3, the injector 10, and the exhaust gas recirculation valve 22, is controlled by an electronic control unit (ECU) 30 provided in the vehicle on which the engine 1 is mounted. Information from various sensors is also transmitted to the ECU 30.

The electronic control unit 30 controls the throttle valve 3 to adjust the amount of intake air in the intake passage 4 and the amount of fuel injected from the injector 10 into the cylinder 2 through feedback control, thereby controlling the air-fuel ratio in the cylinder 2. The exhaust from each cylinder 2 is discharged into the exhaust passage 5, purified by the exhaust purification device 13, and then discharged through the muffler 15. The electronic control unit 30 also controls the opening and closing of the exhaust recirculation valve 22 and the pressure state in the intake passage 4 according to the driving conditions, and adjusts the amount of exhaust recirculation gas introduced into the intake air. The amount of exhaust recirculation gas introduced into the intake air may be adjusted through feedback control that brings the actual exhaust recirculation gas rate closer to the target exhaust recirculation gas rate.

The electronic control unit 30 also has a function (device) for detecting a malfunction of the exhaust gas recirculation device 20. Specifically, the electronic control unit 30 has a malfunction type estimation unit 31 for estimating the type of malfunction that has occurred in the exhaust gas recirculation device 20, and a determination unit 32 for determining the presence or absence of a malfunction from a change in the intake amount when the opening degree of the exhaust gas recirculation valve 22 is switched during fuel cut operation. The information on the change in the intake amount here includes information on the change in the intake pressure and the change in the charging efficiency in the intake passage 4. For example, as shown in FIG. 1, the intake amount in the intake passage 4 can be grasped from information from an intake amount sensor 7 provided in the intake passage 4 upstream of the throttle valve 3 and downstream of the air cleaner 6, and a pressure sensor 8 provided in the intake manifold. Note that the sensors for grasping the intake amount in the intake passage 4 are not limited to the intake amount sensor 7 and the pressure sensor 8, and the positions and the number of sensors are not limited to those described above.

The fault type estimation unit 31 estimates a first fault in which the exhaust recirculation gas flow rate increases from the original flow rate when the difference between the intake air volume upstream of the connection of the intake passage 4 with the exhaust recirculation passage 21 (information obtained by the intake air volume sensor 7) and the intake air volume downstream of the connection of the intake passage 4 with the exhaust recirculation passage 21 (information obtained by the pressure sensor 8) is equal to or greater than a preset first threshold value with the exhaust recirculation valve 22 closed. The fault type estimation unit 31 also estimates a second fault in which the exhaust recirculation gas flow rate decreases from the original flow rate when the difference between the intake air volume upstream of the connection of the intake passage 4 with the exhaust recirculation passage 21 and the intake air volume downstream of the connection of the intake passage 4 with the exhaust recirculation passage 21 with the exhaust recirculation valve 22 open is less than a preset third threshold value.

In other words, the fault type estimation unit 31 acquires information on the difference in the intake volume before and after the exhaust recirculation gas is mixed in the intake passage 4 in both a state where an exhaust recirculation gas introduction control command is being issued (when the exhaust recirculation valve 22 is commanded to be open) and a state where the command is not being issued (when the exhaust recirculation valve 22 is commanded to be fully closed), and estimates the type of fault that has occurred in the exhaust gas recirculation device 20. If the difference is large (greater than or equal to the first threshold value), a first fault is assumed, and if the difference is small (less than the third threshold value), a second fault is assumed.

Here, when inferring that a first failure has occurred in the exhaust gas recirculation device 20, if the difference between the intake air volume upstream and downstream of the connection point of the intake passage 4 with the exhaust gas recirculation passage 21 is equal to or greater than a first threshold value, and in addition, the rotation fluctuation of the engine 1 is measured a predetermined number of times to be equal to or greater than a preset second threshold value, then the first failure can be inferred more accurately.

Specifically, when the fault type estimation unit 31 estimates a first fault in the exhaust gas recirculation device 20, the fault diagnosis is first performed with the diagnosis start condition being that the air-fuel ratio is stable near the stoichiometric (theoretical air-fuel ratio) during stoichiometric feedback control in an idling state after warm-up is complete (hot idling). Then, the fault diagnosis estimates that a first fault has occurred in the exhaust gas recirculation device 20 if the following requirements (a) "Ec (charging efficiency) deviation judgment" and (b) "combustion failure judgment" are simultaneously satisfied when a command to fully close the exhaust gas recirculation valve 22 is issued continuously for a predetermined period (e.g., 5 seconds).
(a) Ec deviation amount = MAPS calculated Ec - AFS calculated Ec > first threshold (b) Combustion index ΔNe < second threshold

In the Ec deviation judgment, the difference between the intake air amount upstream and downstream of the connection point of the intake passage 4 with the exhaust gas recirculation passage 21 is obtained. The MAPS calculated Ec is the charging efficiency calculated based on the information of the pressure sensor 8. The AFS calculated Ec is the charging efficiency calculated based on the information of the intake air amount sensor 7 (see FIG. 3A). The Ec deviation is the difference between the MAPS calculated Ec and the AFS calculated Ec (see FIG. 3B). As shown in FIG. 3A and FIG. 3B, the larger the opening of the exhaust gas recirculation valve 22 is and the larger the amount of exhaust gas recirculation gas is, the larger the Ec deviation becomes. In other words, if the Ec deviation is larger than the first threshold value, it can be estimated that the exhaust gas recirculation valve 22 is wide open despite the command to fully close the exhaust gas recirculation valve 22. Here, the combustion index ΔNe is the variation in the rotation speed of the engine 1 and corresponds to the rotation fluctuation of the engine 1 (see FIG. 3C). When the combustion state of the engine 1 deteriorates, the rotation speed of the engine 1 drops significantly (the rotation fluctuation increases), and the combustion index ΔNe falls below the second threshold. In this embodiment, as shown in FIG. 3C, the number of times that the combustion index ΔNe falls below the second threshold is also counted, and when the number of times that the combustion index ΔNe falls below the second threshold exceeds a predetermined number of times, it is determined that the requirement for "determining poor combustion" in (b) is met. The greater the opening of the exhaust gas recirculation valve 22 and the greater the amount of exhaust gas recirculation gas, the worse the combustion state of the engine 1 becomes, and the greater the rotation speed of the engine 1 drops. In other words, when the combustion index ΔNe falls below the second threshold (the rotation speed of the engine 1 drops significantly), it can be estimated that the exhaust gas recirculation valve 22 is wide open despite the issuance of a command to fully close the exhaust gas recirculation valve 22. There are various methods for calculating the combustion index ΔNe, and for example, the rotation fluctuation may be calculated from the output of a rotation speed sensor that acquires the rotation speed of the engine 1.

Furthermore, when inferring that a second failure has occurred in the exhaust gas recirculation device 20, if the difference between the intake air volume upstream and downstream of the connection of the intake passage 4 with the exhaust gas recirculation passage 21 is less than the third threshold value, and in addition, the second failure is inferred when the rotation fluctuation of the engine 1 is measured a predetermined number of times to be equal to or greater than a preset fourth threshold value, then the second failure can be inferred more accurately. Here, the third threshold value may be the same value as the first threshold value. Also, the fourth threshold value may be the same value as the second threshold value.

Specifically, when the fault type estimation unit 31 estimates the second fault of the exhaust gas recirculation device 20, the fault diagnosis is performed with the diagnosis start condition being that the air-fuel ratio is stable near stoichiometric during stoichiometric feedback control at hot idle. Then, the fault diagnosis estimates that the second fault has occurred in the exhaust gas recirculation device 20 if both of the following conditions (c) "Ec (charging efficiency) deviation judgment" and (d) "combustion failure judgment" are not satisfied when a command is issued to open the exhaust gas recirculation valve 22 for a predetermined period (e.g., 5 seconds).
(c) Ec deviation amount = MAPS calculated Ec - AFS calculated Ec > third threshold (d) Combustion index ΔNe < fourth threshold

In other words, if neither of requirements (c) nor (d) is met, a specified amount of exhaust gas recirculation gas should be introduced, but since there is no deviation in Ec and no fluctuation in engine 1 rotation speed, it is presumed that sufficient exhaust gas recirculation gas is not being introduced, causing a second failure.

Note that the method of estimating a fault by the fault type estimation unit 31 is not limited to the above example. For example, a method of estimating whether the fault in the exhaust gas recirculation device 20 is a first fault or a second fault based only on the fluctuation information of the intake volume (intake manifold pressure) obtained by the pressure sensor 8, although this would result in a slightly lower diagnostic accuracy, is also conceivable.

Based on the result of the fault estimation by the fault type estimation unit 31, the determination unit 32 performs fault diagnosis by changing the valve opening set for the exhaust recirculation valve 22 according to the type of fault estimated. By changing the opening of the exhaust recirculation valve 22 during fault diagnosis according to the type of fault, the accuracy of fault determination can be improved.

Here, the judgment unit 32 judges that the system is normal if the difference ΔP = P' - P between the intake manifold pressure (P) when the exhaust gas recirculation valve 22 is instructed to be fully closed, i.e., the output value of the pressure sensor 8, and the intake manifold pressure (P') when the exhaust gas recirculation valve 22 is instructed to be open, is equal to or greater than a predetermined value, and judges that the system is faulty if the difference ΔP = P' - P is less than the predetermined value.

Specifically, when the first fault is estimated, the determination unit 32 sets the opening of the exhaust recirculation valve 22 set during fault diagnosis, i.e., the opening of the exhaust recirculation valve 22 when acquiring the intake manifold pressure (P'), to a smaller value compared to when the first fault is not estimated. The opening (basic opening) of the exhaust recirculation valve 22 when acquiring the intake manifold pressure (P') is determined based on a map including the relationship between the engine speed and the opening of the exhaust recirculation valve 22. In the event of a first fault, a correction is made to reduce the opening of the exhaust recirculation valve 22 relative to the engine speed on the map as a reduction correction of the basic opening. FIG. 2A shows an example in which the basic opening is reduced (an example in which the basic opening is smaller than the trapped opening) when a foreign object is caught in the exhaust recirculation valve 22 (a fault that does not result in a fully closed state) as the first fault, and FIG. 2B shows an example in which the basic opening is increased (an example in which the basic opening is larger than the trapped opening) when a foreign object is caught in the exhaust recirculation valve 22 as the first fault.

In FIG. 2A, when a foreign object is caught (dashed line), the difference ΔP=P'-P between the intake manifold pressure (P) when the valve is fully closed and the intake manifold pressure (P') when the valve is open is extremely small (almost zero), so a malfunction can be determined. On the other hand, in FIG. 2B, even when a foreign object is caught (dashed line), the difference ΔP=P'-P is equal to or greater than a predetermined value, so a malfunction cannot be determined. In this way, when a foreign object is caught, the smaller the basic opening, the easier it is to determine that a malfunction has occurred. Note that when the exhaust gas recirculation valve 22 is stuck open, no matter what the basic opening is set to, the difference ΔP=P'-P between the intake manifold pressure P when the exhaust gas recirculation valve 22 is in the fully closed state and the intake manifold pressure P' when the exhaust gas recirculation valve 22 is in the open state is extremely small (almost zero), so a malfunction can be determined with high accuracy regardless of the basic opening.

In addition, when a second fault is estimated, the determination unit 32 sets the opening of the exhaust recirculation valve 22 set at the time of fault diagnosis to be larger than when a second fault is not estimated. That is, when a second fault occurs, a correction is made to increase the opening of the exhaust recirculation valve 22 relative to the engine speed on the map as an increase correction of the basic opening. FIG. 2C shows an example in which the basic opening is reduced (an example in which exhaust recirculation gas does not flow even at the basic opening) when the exhaust recirculation passage 21 is clogged with foreign matter as the second fault (a fault in which foreign matter impedes the passage of exhaust recirculation gas), and FIG. 2D shows an example in which the basic opening is increased (an example in which exhaust recirculation gas flows at the basic opening) when the exhaust recirculation passage 21 is clogged with foreign matter as the second fault. In FIG. 2C, when a foreign matter is clogged (dashed line), the difference ΔP=P'-P described above becomes extremely small (almost zero), so it is determined to be a fault. On the other hand, in Figure 2D, even when there is a foreign object clogging (dashed line), the difference ΔP = P' - P is equal to or greater than the specified value, and it is not determined to be a malfunction.

This allows diagnosis according to the urgency of the failure. In other words, whether a first or second failure is suspected, it is easier to determine that there is a failure by reducing the basic opening, but in the case of a second failure in which the flow rate of exhaust recirculation gas is reduced, the urgency of the failure is low because this alone does not worsen the exhaust gas, and the requirements for failure determination are deliberately set high by increasing the basic opening.

In contrast, the first failure causes the exhaust recirculation gas flow rate to increase above the normal flow rate, which can lead to unstable combustion and deterioration of exhaust gas. For this reason, when a first failure is suspected, a correction is made to reduce the basic opening, making it easier to determine whether a failure has occurred.

The determination unit 32 notifies the occupant of the occurrence of a malfunction only when it is determined that a first malfunction has occurred, and does not notify the occupant when it is determined that a second malfunction has occurred. This prevents unnecessary notifications from being given to the occupant.

Fault diagnosis is performed while the engine 1 is being cut off from fuel (while the vehicle is decelerating), but with the above method, the opening of the exhaust gas recirculation valve 22 is reduced during fault diagnosis, which increases the rotational resistance of the engine 1 and ensures a sense of deceleration of the vehicle that accompanies fuel cut.

FIG. 4 is a flow chart relating to this control. Control begins in step S1, and the counter is reset (Nm = 0) in step S2. In step S3, it is determined whether fault diagnosis is possible. The conditions for determining that fault diagnosis is possible are that the engine 1 is in a fuel cut and that the filling efficiency and rotation speed of the engine 1 are within a predetermined range. If fault diagnosis is possible, the process proceeds to step S4, and if not, step S3 is repeatedly applied.

In step S4, the exhaust gas recirculation valve 22 is instructed to be fully closed, and the process proceeds to step S5, where the intake manifold pressure (P) is measured. The intake manifold pressure (P) is obtained by the pressure sensor 8 when the exhaust gas recirculation valve 22 is instructed to be fully closed. Then, in step S6, it is determined whether a first or second failure has already been estimated in the previous stage of this control, and whether a first or second failure has occurred.

If either the first or second fault has already been estimated at the stage of moving to step S6, the process moves to step S8 to correct the opening of the exhaust recirculation valve 22 at the time of fault diagnosis (exhaust recirculation valve fault opening). As described above, the correction of the opening is a decrease correction in the case of the first fault, and an increase correction in the case of the second fault. Here, if the fault type estimation unit 31 estimates both the first fault and the second fault, the judgment unit 32 reduces the opening of the exhaust recirculation valve 22 set at the time of fault judgment. In other words, when there is a concern about both the first fault and the second fault, the judgment unit 32 prioritizes making it easier to judge the first fault in anticipation of a safe flank. If it is estimated at the stage of moving to step S6 that neither the first fault nor the second fault has occurred, the process moves to step S7 to perform fault diagnosis at the normal opening (normal diagnosis opening). Note that even if neither the first fault nor the second fault has been estimated, the process moves to step S7 to perform fault diagnosis at the normal opening.

Then, the process proceeds to step S9, where the intake manifold pressure (P') is measured. Then, in step S10, the difference between the intake manifold pressure (P) and the intake manifold pressure (P'), ΔP = P' - P, is calculated.

If in step S11 the difference ΔP = P'-P is equal to or greater than a predetermined value, the process proceeds to step S15 and the counter value is maintained at the current value. In the following step S16, it is determined that the exhaust gas recirculation device 20 is normal, and control is terminated in step S17. Also, in step S11, if the difference ΔP = P'-P is less than the predetermined value, the process proceeds to step S12 and the counter value is incremented by one (Nm = Nm + 1). Then, steps S3 to S12 are repeated, and if the counter value becomes 3 (Nm = 3) in step S13, it is determined that a failure determination has been performed three times, and a failure (first failure or second failure) is determined to have occurred in the following step S14, and control is terminated in step S17. The counter value for determining that a failure has occurred is not limited to 3, and may be any appropriate value.

In the above embodiment, the configuration of the present invention is described using an engine 1 without a turbocharger as an example, but the present invention may also be applied to an engine 1 with a turbocharger. In addition, the engine 1 may be equipped with either a high-pressure exhaust gas recirculation device that has an exhaust gas recirculation passage 21 connecting the downstream side of the turbocharger compressor and the upstream side of the turbine, and handles relatively high-pressure exhaust gas recirculation, or a low-pressure exhaust gas recirculation device that has an exhaust gas recirculation passage 21 connecting the upstream side of the turbocharger compressor and the downstream side of the turbine, and handles relatively low-pressure exhaust gas, or both, as the exhaust gas recirculation device 20. In addition, the engine 1 to which the present invention can be applied may be a gasoline engine, a diesel engine, etc.

1 Engine 2 Combustion chamber (cylinder)
3 throttle valve 4 intake passage 5 exhaust passage 6 air cleaner 7 intake pressure sensor 8 pressure sensor 10 injection device (in-cylinder injection device)
13 exhaust gas purification device 20 exhaust gas recirculation device 21 exhaust gas recirculation passage 22 exhaust gas recirculation valve 30 electronic control unit 31 fault type estimation section 32 determination section

Claims (7)

An exhaust gas recirculation system failure detection device including an exhaust gas recirculation passage communicating between an exhaust passage and an intake passage of an engine, and an exhaust gas recirculation valve provided in the exhaust gas recirculation passage,
a failure type estimation unit that estimates a type of failure that has occurred in the exhaust gas recirculation device; and a determination unit that determines the presence or absence of a failure from a change in intake pressure when an opening degree of the exhaust gas recirculation valve is switched during a fuel cut operation,
The determination unit determines the presence or absence of a malfunction by changing a valve opening degree set in the exhaust gas recirculation valve in accordance with the type of malfunction estimated by the malfunction type estimation unit during malfunction diagnosis. the fault type estimation unit estimates a first fault in which a flow rate of exhaust recirculation gas increases from an original flow rate when a difference between an intake amount on an upstream side of a connection portion of the intake passage with the exhaust recirculation passage and an intake amount on a downstream side of the connection portion is equal to or larger than a first threshold value with the exhaust recirculation valve closed,
2. The fault detection device for an exhaust gas recirculation device according to claim 1, wherein when the first fault is estimated, the judgment unit sets a valve opening degree set for the exhaust gas recirculation valve to be smaller than when the first fault is not estimated. The fault detection device for an exhaust gas recirculation system according to claim 2, wherein the fault type estimation unit estimates a first fault when a state in which the difference between the intake air volume upstream of the connection of the intake passage with the exhaust gas recirculation passage and the intake air volume downstream of the connection is equal to or greater than a first threshold value and the engine rotation fluctuation is equal to or greater than a second threshold value is measured a predetermined number of times. the fault type estimation unit estimates a second fault in which a flow rate of exhaust recirculation gas is reduced from an original flow rate when a difference between an intake air amount upstream of a connection portion of the intake passage with the exhaust recirculation passage and an intake air amount downstream of the connection portion is less than a third threshold value with the exhaust recirculation valve open;
4. The fault detection device for an exhaust gas recirculation device according to claim 2 or 3, wherein when the second fault is estimated, the judgment unit sets the opening degree of the exhaust gas recirculation valve, which is set during fault diagnosis, to a larger value compared to when a fault other than the second fault is estimated. The fault detection device for an exhaust gas recirculation system according to claim 4, wherein the fault type estimation unit estimates a second fault when a state in which the difference between the intake amount upstream and downstream of the connection of the intake passage with the exhaust gas recirculation passage is less than a third threshold value and the engine rotation fluctuation is equal to or greater than a fourth threshold value is measured a predetermined number of times. The fault detection device for an exhaust gas recirculation system according to claim 4 or 5, wherein, when the fault type estimation unit estimates both the first fault and the second fault, the determination unit reduces the opening of the exhaust gas recirculation valve that is set during fault diagnosis. The exhaust gas recirculation system failure detection device according to any one of claims 4 to 6, wherein the determination unit notifies an occupant of the occurrence of a failure only when the first failure is determined.

Images