Exhaust gas recirculation system fault diagnosis device

Abstract

To provide a failure diagnosis device of an exhaust emission recirculation system which can diagnose a failure in detail while securing the safety of an engine operation.SOLUTION: A failure diagnosis device for diagnosing the presence or absence of a failure of an EGR system 50 of an engine 2 in a plug-in hybrid vehicle comprises: an EGR temperature sensor 56 for detecting a temperature of an EGR gas; and an EGR failure determination part 60 for determining the presence or absence of the failure of the EGR system 50 on the basis of a change in temperature of the EGR gas when opening and closing an EGR valve 54. The EGR failure determination part 60 determines an open failure of the EGR valve 54 on the basis of the temperature change of the EGR gas by closing the EGR valve 54 at a warmup operation after start of the engine 2 at a transition to a series mode from an EV-mode, and determines a closed failure of the EGR valve 54 on the basis of the temperature change of the EGR gas by opening the EGR valve 54 from a closing operation state after the open failure determination.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a fault diagnosis technique for an exhaust gas recirculation system of an engine. [Background technology]

[0002] Many engines installed in vehicles are equipped with an EGR system (exhaust gas recirculation system) to improve exhaust performance. The EGR system has, for example, an EGR passage (exhaust gas recirculation passage) that recirculates part of the exhaust gas (EGR gas) from the exhaust passage to the intake passage, and is equipped with an EGR valve (exhaust gas recirculation valve) that adjusts the opening area of ​​the EGR passage. The opening area (opening degree) of the EGR valve is controlled by a control unit or the like based on the operating state of the engine.

[0003] Patent Document 1 discloses a technique for determining whether or not there is a malfunction in the EGR system. The malfunction diagnosis device disclosed in Patent Document 1 has a temperature sensor that detects the temperature of the EGR gas, and diagnoses whether or not there is a malfunction such as the EGR valve being stuck based on the change in temperature of the EGR gas accompanying the opening and closing of the EGR valve. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2005-291055 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the failure diagnosis device of Patent Document 1, the EGR valve is forcibly controlled to open and close to a predetermined opening area, and if the temperature of the EGR gas does not change by a predetermined amount, it is determined that the EGR valve is stuck. However, Patent Document 1 does not determine the detailed failure state of the EGR valve, such as whether it is stuck open or stuck closed. Furthermore, engine fault diagnosis is often performed immediately after the engine is started. However, if the EGR valve is forcibly controlled to an open state in order to perform a fault diagnosis immediately after the engine is started, the oxygen concentration in the intake air will be reduced in a cold state, which may impair the stability of engine operation.

[0006] The present invention has been made in consideration of the above problems, and an object of the present invention is to provide a fault diagnosis device for an exhaust gas recirculation system that can perform detailed and rapid fault detection while ensuring stable engine operation in a cold state. [Means for solving the problem]

[0007] In order to achieve the above object, a fault diagnosis device for an exhaust recirculation system of the present invention is a fault diagnosis device for an exhaust recirculation system having an exhaust recirculation passage for directing a portion of exhaust from an exhaust passage of an engine to an intake passage, an exhaust recirculation valve provided in the exhaust recirculation passage and operable to open or close to adjust an opening area of ​​the exhaust recirculation passage, and an exhaust recirculation control unit for controlling the operation of the exhaust recirculation valve based on an operating state of the engine, the device comprising: exhaust recirculation gas temperature detection means for detecting a temperature of exhaust recirculation gas flowing through the exhaust recirculation passage, and a fault determination unit for determining whether or not there is a fault in the exhaust recirculation valve based on a change in the temperature of the exhaust recirculation gas when the exhaust recirculation control unit operates to open or close the exhaust recirculation valve, While the switch remains closed The invention is characterized in that an open failure determination is made for the exhaust recirculation valve based on a temperature change of the exhaust recirculation gas, and a closed failure determination is made for the exhaust recirculation valve based on a temperature change of the exhaust recirculation gas when the exhaust recirculation valve is operated from a closed operating state to an open operating state after the open failure determination is made.

[0008] This makes it possible to determine in detail the type of failure in the exhaust gas recirculation system, such as whether the exhaust gas recirculation valve has a closed failure or an open failure. In addition, when the engine is running cold, the exhaust gas recirculation valve is turned on first. Keep it closed Perform open failure judgment thingTherefore, when determining an open valve malfunction, exhaust gas recirculation is suppressed, thereby improving the operating stability of the engine. In addition, by suppressing the rise in exhaust gas recirculation gas temperature during the determination of an open valve malfunction, it is possible to immediately perform a closing valve malfunction determination after completing the determination of an open valve malfunction, and the determination of an open valve malfunction and the determination of a closing valve malfunction can be performed consecutively, thereby completing the malfunction determination in a short time.

[0009] Preferably, after determining an open failure, the failure determination unit performs a closed failure determination of the exhaust recirculation valve based on a temperature change of the exhaust recirculation gas that occurs when the exhaust recirculation control unit opens the exhaust recirculation valve for a predetermined period of time or more due to a request to open the exhaust recirculation valve in conjunction with the operating state of the engine. As a result, after the open failure determination is completed, the exhaust gas recirculation valve opens and closes based on the engine operating state. Therefore, without forcibly opening the exhaust gas recirculation valve when a closed failure determination is made, appropriate exhaust gas recirculation valve operation control based on the engine operating state is quickly initiated, thereby quickly improving the accuracy and responsiveness (drivability) of engine operation control.

[0010] Preferably, the engine is mounted on a vehicle, the vehicle having a storage battery, a generator driven by the engine to generate electricity, and a motor that drives the vehicle using electricity supplied from at least one of the generator and the storage battery, and a driving mode switching control unit that switches between at least a first driving mode in which the engine is stopped and the motor is driven using electricity supplied from the storage battery to drive the vehicle, and a second driving mode in which the engine is operated and the generator is used to generate electricity while the vehicle is running, based on a required output required of the vehicle, and before switching from the first driving mode to the second driving mode while the engine has not been warmed up completely, a warm-up operation is performed on the engine to continue a predetermined low-load operation for a predetermined period of time that is lower than the load of the engine when generating electricity in the second driving mode, and the fault determination unit executes the open circuit fault determination together with the driving of the vehicle by the motor while the warm-up operation is continuing.

[0011] As a result, an open circuit fault determination is performed during engine warm-up operation, which is performed when switching from a first driving mode in which the engine is stopped to a second driving mode in which the engine is operated. This increases the opportunities for determining an exhaust gas recirculation valve fault and enables the engine to be operated in a manner suitable for determining an exhaust gas recirculation valve fault when determining an open circuit fault, enabling fast and accurate fault determination.

[0012] Preferably, even if the required output reaches a value at which the driving mode is switched to the second driving mode before the open circuit fault determination and the closing circuit fault determination are completed during the warm-up operation, the fault determination unit continues the warm-up operation without switching to the second driving mode until the open circuit fault determination and the closing circuit fault determination are completed. This allows the open valve fault determination and the closed valve fault determination to be continuously performed and completed.

[0013] Preferably, the vehicle further includes a power supply unit that supplies power from the storage battery to the outside, and the failure determination unit, during power supply to the outside, performs the closed failure determination by forcibly opening the exhaust recirculation valve after determining an open failure, regardless of a request by the exhaust recirculation control unit for opening / closing control of the exhaust recirculation valve based on the operating state of the engine. As a result, while power is being supplied to the outside, the vehicle is not running and the engine can be operated as desired, so that after the open fault determination, the exhaust gas recirculation valve is forcibly opened to perform the closed fault determination, thereby quickly and reliably completing the closed fault determination.

[0014] Preferably, the vehicle includes a charging rate detection unit that detects the charging rate of the storage battery, and the driving mode switching control unit selects the second driving mode when at least the charging rate is equal to or lower than a first predetermined value, and the warm-up operation is started when the charging rate falls to or lower than a second predetermined value that is higher than the first predetermined value. This makes it possible to start the open circuit fault determination before the charging rate of the rechargeable battery drops due to the vehicle being driven in the first driving mode, causing the mode to switch to the second driving mode, for example. Effect of the Invention

[0015] According to the exhaust gas recirculation system fault diagnosis device of the present invention, it is possible to determine in detail the fault mode of the exhaust gas recirculation valve, such as whether the exhaust gas recirculation valve has a closed fault or an open fault. This can be used as information when making repairs, and by controlling the operation of the engine according to the fault mode, it is possible to continue stable engine operation. In addition, when the engine is operating in a cold state, an open circuit fault determination is performed first based on a command to close the exhaust gas recirculation valve, and then a closed circuit fault determination is performed based on an opening command, so that when an open circuit fault determination is performed, the exhaust gas recirculation valve is closed, which makes it possible to suppress the inflow of exhaust gas recirculation gas into the intake air and suppress engine misfires, thereby improving the stability of engine operation and making it possible to perform the open circuit fault determination and the closed circuit fault determination in succession and complete them in a short time. This makes it possible to suppress the forced operation time of the exhaust gas recirculation valve when determining an open circuit fault and when determining a closed circuit fault, thereby improving drivability in engine operation control. [Brief description of the drawings]

[0016] [Figure 1] 1 is a schematic configuration diagram of a driving system of a vehicle according to an embodiment of the present invention; [Diagram 2] 1 is a configuration diagram of a fault diagnosis device for an intake and exhaust system and an EGR system of an engine according to an embodiment of the present invention. [Diagram 3] 4 is a flowchart showing a procedure of EGR failure determination control in the EGR system failure diagnosis device. [Figure 4] 4 is an example of a time chart showing the operation of the EGR valve and the transition of the EGR temperature, etc., in EGR failure determination control when an EGR opening failure occurs. [Diagram 5] 4 is an example of a time chart showing the operation of the EGR valve and the transition of the EGR temperature, etc., during EGR failure determination control when an EGR closing failure occurs. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram of a plug-in hybrid vehicle (hereinafter, referred to as a vehicle 1) according to one embodiment of the present invention. As shown in FIG. 1, a vehicle 1 equipped with the EGR system fault diagnosis device of this embodiment is a four-wheel drive vehicle that can run by driving front wheels 3 with the output of an engine 2, and is equipped with an electric front motor 4 (motor) that drives the front wheels 3 and an electric rear motor 6 (motor) that drives the rear wheels 5.

[0018] The engine 2 is capable of driving a drive shaft 8 of the front wheels 3 via a reduction gear 7, and is also capable of driving a motor generator 9 (electric generator) via the reduction gear 7 to generate electricity. The front motor 4 is driven by high-voltage power supplied from an on-board battery 11 (storage battery) and a motor generator 9 mounted on the vehicle 1 via a front inverter 10, and drives a drive shaft 8 of the front wheels 3 via a reduction gear 7. The reduction gear 7 has a built-in clutch 7a that can switch between connecting and disconnecting the transmission of power between the output shaft of the engine 2 and the drive shaft 8 of the front wheels 3.

[0019] The rear motor 6 is driven by high-voltage power supplied from the on-board battery 11 and the motor generator 9 via a rear inverter 12 , and drives a drive shaft 14 of the rear wheels 5 via a reduction gear 13 . The electric power generated by the motor generator 9 can charge an in-vehicle battery 11 via a front inverter 10, and can also supply electric power to the front motor 4 and the rear motor 6.

[0020] The vehicle-mounted battery 11 is composed of secondary batteries such as lithium-ion batteries, and has a battery module (not shown) that is composed of multiple battery cells. The vehicle-mounted battery 11 also has a monitoring unit 11a (charging rate detection unit) that monitors the state of the battery module, such as the voltage, charging rate, and temperature, and estimates (detects) the charging rate of the entire vehicle-mounted battery 11.

[0021] The front inverter 10 has a function of controlling the output of the front motor 4 based on a control signal from a hybrid control unit 20 (a driving mode switching control unit), and also has a function of controlling the output of the motor generator 9 based on a control signal from the hybrid control unit 20. The rear inverter 12 has a function of controlling the output of the rear motor 6 based on a control signal from the hybrid control unit 20 .

[0022] The vehicle 1 is equipped with an engine control unit 22 that controls the operation of the engine 2, and a charger 23 that charges the on-board battery 11 from an external power source. Further, within the passenger compartment of the vehicle 1, an external outlet 24 (power supply unit) is provided for supplying electric power from the on-board battery 11 to the outside. The hybrid control unit 20 is a comprehensive control device for controlling the running of the vehicle 1, and is configured to include input / output devices, storage devices (ROM, RAM, non-volatile RAM, etc.), a central processing unit (CPU), a timer, etc. The engine control unit 22 is also configured to include input / output devices, storage devices (ROM, RAM, non-volatile RAM, etc.), a central processing unit (CPU), a timer, etc.

[0023] The input side of the hybrid control unit 20 is connected to a monitoring unit 11a of the on-board battery 11, the front inverter 10, the rear inverter 12, the engine control unit 22, an accelerator opening sensor 40 that detects the amount of accelerator operation, and a vehicle speed sensor 41 that detects the traveling speed of the vehicle 1, and detection, activation and operation information from these devices is input.

[0024] On the other hand, to the output side of the hybrid control unit 20, the front inverter 10, the rear inverter 12, the reduction gear 7 (clutch 7a), and the engine control unit 22 are connected. The hybrid control unit 20 then calculates the required driving torque required to drive the vehicle 1 based on the various detection amounts and various operation information from the accelerator opening sensor 40, vehicle speed sensor 41, etc., and sends control signals to the engine control unit 22, the front inverter 10, the rear inverter 12, and the reduction gear 7 to switch the driving mode (EV mode: electric vehicle mode), series mode, parallel mode), and control the output of the engine 2, the front motor 4, the rear motor 6, and the output of the motor generator 9.

[0025] In the EV mode, the engine 2 is stopped, and the front motor 4 and the rear motor 6 are driven by electric power supplied from the vehicle battery 11 to cause the vehicle 1 to travel. In the series mode, the clutch 7a of the reduction gear 7 is disengaged and the motor generator 9 is operated by the engine 2. The front motor 4 and the rear motor 6 are then driven by the electric power generated by the motor generator 9 and the electric power supplied from the vehicle battery 11 to drive the vehicle. Also, in the series mode, the rotation speed of the engine 2 is set to a predetermined rotation speed, and surplus electric power is supplied to the vehicle battery 11 to charge it.

[0026] In the parallel mode, the clutch 7a of the reduction gear 7 is connected, and power is mechanically transmitted from the engine 2 via the reduction gear 7 to drive the front wheels 3. In addition, the front motor 4 and the rear motor 6 are driven by electric power generated by operating the motor generator 9 by the engine 2 and electric power supplied from the on-board battery 11 to cause the vehicle to travel. The hybrid control unit 20 sets the driving mode to the parallel mode in an area where the engine 2 is efficient, such as a high-speed area. In areas other than the parallel mode, i.e., in the medium-low speed area, the hybrid control unit 20 switches between the EV mode and the series mode based on the driving torque of the vehicle 1 and the charging rate SOC of the on-board battery 11.

[0027] The EV mode corresponds to the first driving mode in the present invention, and the series mode and parallel mode correspond to the second driving mode in the present invention. FIG. 2 is a configuration diagram of a failure diagnosis device for the intake and exhaust system of the engine 2 and the EGR system 50 (exhaust gas recirculation system). 2, the engine 2 is equipped with an EGR system 50. The EGR system 50 includes an EGR passage 53 (exhaust gas recirculation passage) that connects an intake passage 51 and an exhaust passage 52 of the engine 2, an EGR valve 54 (exhaust gas recirculation valve) that adjusts the opening area of ​​the EGR passage 53, and an EGR control unit 55 (exhaust gas recirculation control unit) that controls the opening degree of the EGR valve 54 (the opening area of ​​the EGR passage 53).

[0028] The EGR control unit 55 is provided in the engine control unit 22. The EGR control unit 55 controls the opening degree of the EGR valve 54 based on the operating state of the engine 2, for example, a required load based on an accelerator operation amount, an engine rotation speed, and the like. Further, an EGR temperature sensor 56 (exhaust gas recirculation temperature detection means) that detects the temperature of EGR gas (exhaust gas recirculation gas) is provided in the EGR passage 53. The EGR temperature sensor 56 is provided on the intake passage 51 side of the EGR valve 54, and detects the temperature of the EGR gas, which is part of the exhaust gas that flows from the exhaust passage 52 through the EGR passage 53, passes through the EGR valve 54, and flows into the intake passage 51.

[0029] Furthermore, the engine control unit 22 of this embodiment is provided with an EGR malfunction determination section 60 (malfunction determination section) that diagnoses malfunctions in the EGR system 50, specifically, that determines malfunctions in the EGR valve . The EGR failure determination unit 60 controls the operation of the EGR valve 54, and performs EGR failure determination control based on the temperature of the EGR gas (EGR temperature) detected by the EGR temperature sensor 56. The EGR control unit 55 (exhaust gas recirculation control unit), the EGR temperature sensor 56, and the EGR failure determination unit 60 correspond to the failure diagnosis device for the exhaust gas recirculation system of the present invention.

[0030] Next, the EGR failure determination control will be described with reference to Figs. Fig. 3 is a flowchart showing the procedure of EGR failure determination control executed by the EGR failure determination unit 60. Fig. 4 is an example of a time chart showing the operation of the EGR valve and the transition of the EGR temperature, etc., in the EGR failure determination control when an EGR opening failure occurs. Fig. 5 is an example of a time chart showing the operation of the EGR valve and the transition of the EGR temperature, etc., in the EGR failure determination control when an EGR closing failure occurs.

[0031] In Fig. 4, the solid line indicates when the EGR is normal or when there is an EGR closing failure, and the dashed line indicates when there is an EGR opening failure. In Fig. 5, the solid line indicates when the EGR is normal, and the dashed line indicates when there is an EGR closing failure. The EGR failure determination control is started during pre-operation (warm-up operation: corresponding to a predetermined cold operation of the present invention) immediately after engine start. When the vehicle 1 is powered on and the engine 2 transitions from the EV mode to the series mode or the parallel mode, the engine 2 is started immediately before the transition and the pre-operation is executed. The pre-operation is performed by operating the engine 2 at low revolutions and low load, for example, to warm up the engine 2 and stabilize the engine operation. The pre-operation is performed at a load (a predetermined low load) smaller than the load of the engine 2 in the series mode and is completed when, for example, the exhaust temperature increases to a predetermined temperature or higher, after which the engine is operated according to the required load set by the hybrid control unit 20.

[0032] As shown in Fig. 3, first, in step S10, the EGR valve 54 is controlled to be fully closed (EGR cut). In Figs. 4 and 5, EGR cut is performed immediately after the engine starts. Also, when the EGR valve 54 starts to be fully closed, the EGR temperature is input from the EGR temperature sensor 56 and stored in a storage device or the like of the engine control unit 22. Then, the process proceeds to step S20.

[0033] In step S20, when the time elapsed from the start of the full-close operation control of the EGR valve 54 in step S10 (the time elapsed after starting) reaches a predetermined failure judgment time ta (for example, about 100 seconds), the EGR temperature is input from the EGR temperature sensor 56, and the EGR temperature change amount (EGR temperature change amount for open circuit failure judgment) which is the difference from the EGR temperature at the start of the full-close operation control of the EGR valve 54 (at the start) stored in the storage device is calculated. Then, it is determined whether or not this EGR temperature change amount is equal to or greater than a predetermined open circuit failure judgment value a. The open circuit failure judgment value a may be set to a value near and higher than the upper limit value of the EGR gas temperature change amount when, for example, a pre-operation is performed for the failure judgment time ta with the EGR valve 54 in a fully closed state from the start of the engine 2. As shown by the dashed line in FIG. 4, if the EGR temperature change amount is equal to or greater than the open circuit failure judgment value a, the process proceeds to step S30. As shown by the solid line in FIG. 4, if the EGR temperature change amount is less than the open circuit failure judgment value a, the process proceeds to step S40.

[0034] In step S30, it is determined that an EGR open failure has occurred, that is, the EGR valve 54 is stuck in the open position, and then this routine is terminated. In step S40, the EGR valve 54 is controlled to open (EGR introduction). When the EGR valve 54 opening control starts, the EGR temperature is input from the EGR temperature sensor 56 and stored in a storage device or the like of the engine control unit 22. Then, the process proceeds to step S50.

[0035] In step S50, when the time elapsed from the start of the EGR valve 54 opening operation in step S40 (the time elapsed after the introduction of EGR) reaches a predetermined failure judgment time tb (for example, about 100 seconds), the EGR temperature is input from the EGR temperature sensor 56, and it is determined whether the EGR temperature change amount (EGR temperature change amount for closing failure judgment), which is the difference from the EGR temperature at the start of the opening operation control of the EGR valve 54 stored in the storage device, is equal to or less than a predetermined closing failure judgment value b. The closing failure judgment value b may be set to a value near and lower than the lower limit value of the temperature change amount of the EGR gas when the pre-operation is performed with the EGR valve 54 open for the failure judgment time tb. As shown by the solid line in FIG. 5, if the EGR temperature change amount is equal to or less than the closing failure judgment value b, the process proceeds to step S60. As shown by the dashed line in FIG. 5, if the EGR temperature change amount is greater than the closing failure judgment value b, the process proceeds to step S70.

[0036] In step S60, it is determined that an EGR closed failure has occurred, that is, the EGR valve 54 is stuck in the closed position, and then this routine is terminated. In step S70, it is determined that the EGR valve 54 is in a normal state, and then this routine ends. As described above, in this embodiment, by performing EGR failure determination control to determine whether or not the EGR valve 54 has a failure based on the temperature change of the EGR gas when the EGR valve 54 is opened and closed, more specifically, by performing EGR open failure determination (open failure determination) and EGR closed failure determination (close failure determination), it is possible to determine not only whether or not the EGR valve 54 has a failure, but also whether or not it has a closed failure and whether or not it has an open failure.

[0037] This allows the malfunction mode of the EGR valve 54 to be determined in detail, and can be effectively used as malfunction information when repairing the engine. Alternatively, even if the operation of the engine 2 continues, the operation of the engine 2 can be controlled in response to this malfunction. For example, in the case of an open valve malfunction, there is a possibility that a large amount of EGR gas constantly flows into the intake passage 51 of the engine 2, so that the idle speed of the engine 2 can be increased in a cold idle state such as immediately after starting to stabilize the engine operation.

[0038] In addition, the EGR failure determination control in this embodiment is started during cold operation such as immediately after the engine is started, and first, an EGR open failure determination is performed, and then an EGR close failure determination is performed. In this EGR open failure determination, the EGR cut is performed, so that the EGR valve 54 is closed, and the inflow of exhaust gas recirculated gas into the intake air can be suppressed, and misfires of the engine 2 can be suppressed and the stability of engine operation can be improved. In addition, when it is determined that the EGR valve 54 is not in an open failure state in the EGR open failure determination, the temperature change amount of the EGR gas is equal to or less than the failure determination time ta at that time, and the temperature of the EGR gas is in a low temperature state. Therefore, when it is determined that the EGR valve 54 is not in an open failure state, the EGR close failure determination can be performed immediately after it is determined that the EGR valve 54 is not in an open failure state. This shortens the time required for the EGR failure determination control including the EGR open failure determination and the close failure determination, i.e., the time for forcibly operating the EGR valve 54 to full close and open, and the EGR opening degree can be controlled based on the operating state of the engine 2 such as the required output earlier, thereby improving the accuracy of the engine operation control.

[0039] In the above embodiment, the EGR valve 54 is opened in step S40 in order to perform an EGR closed failure determination after performing an EGR open failure determination. However, it is preferable to perform an EGR closed failure determination based on the EGR temperature change amount in step S50 when the EGR control unit 55 opens the EGR valve 54 based on the operating state of the engine 2 without forcibly opening the valve. This makes it possible to determine an EGR closed failure when the EGR valve 54 is opened for the failure determination time tb or more in conjunction with the operating state of the engine 2. Therefore, after performing an EGR open failure determination immediately after starting the engine, the EGR valve 54 is not forcibly opened, and the opening degree is appropriately controlled based on the operating state of the engine, so that the accuracy and responsiveness (drivability) of the engine operation control can be quickly ensured.

[0040] In addition, the vehicle 1 of this embodiment is a plug-in hybrid vehicle and can be in an EV mode or a series mode, so that it can be driven regardless of the engine operation. For example, when switching from the EV mode to the series mode, in the pre-operation immediately after the engine is started, the EGR open failure determination is executed, so that it is possible to secure many opportunities to determine the failure of the EGR valve 54, not only when the engine is started after the vehicle power is turned on. In addition, when switching from the EV mode to the series mode, the engine can be operated in a manner suitable for determining the failure of the EGR valve 54, so that it is possible to perform a quick and accurate failure determination.

[0041] In addition, the transition from the EV mode to the series mode is determined based not only on the required output but also on the SOC of the vehicle battery 11. For example, when the SOC of the vehicle battery 11 becomes equal to or lower than a first predetermined value in the EV mode, the mode is switched to the series mode, but the warm-up operation is set to start when the SOC falls to or lower than a second predetermined value that is slightly higher than the first predetermined value. As a result, the warm-up operation is started before the SOC of the vehicle battery 11 falls to or lower than the first predetermined value, so that the EGR failure determination is performed before the SOC of the vehicle battery 11 is switched to the series mode, and the SOC of the vehicle battery 11 can be prevented from falling below the first predetermined value.

[0042] During execution of the EGR failure determination control, if the required output increases due to accelerator operation or the like, the engine 2 escapes from pre-operation and operates based on the required output, and then the required output falls below the EV driving torque, the engine operation should be continued without switching to the EV mode, and the EGR failure determination control should be completed before switching to the EV mode. This allows the EGR failure determination to be continued and completed.

[0043] However, the vehicle 1 of this embodiment is a plug-in hybrid vehicle, and is capable of supplying power from a large-capacity on-board battery 11 to the outside via an external outlet 24. Then, when power is being fed to the outside, an EGR closed failure determination may be performed after the EGR open failure determination is performed, regardless of the operation control of the engine 2. During power feeding to the outside, the vehicle is in a stopped state, and even if the engine 2 is operating to generate power, it is in steady operation with a constant output, so that high accuracy in engine operation control is not required. This allows the EGR failure determination control to be completed quickly and reliably.

[0044] Although the description of the present invention is now completed, the present invention is not limited to the above embodiment. For example, in the above embodiment, the EGR failure determination unit 60 is provided in the engine control unit 22, but it may be provided in the hybrid control unit 20, or may be provided in the vehicle 1 independently. In addition, for example, the vehicle 1 in the above embodiment is a PHEV vehicle, but the present invention can also be applied to an engine of an HEV vehicle. The present invention can also be applied to an engine of a gasoline engine vehicle or a diesel engine vehicle. The present invention can also be applied to an engine equipped with an EGR system other than a vehicle. [Explanation of symbols]

[0045] 1 vehicle 2 Engine 4 Front motor (motor) 6 Rear motor (motor) 9 Motor generator (generator) 11 Vehicle batteries (storage batteries) 11a Monitoring unit (charging rate detection unit) 20 Hybrid control unit (driving mode switching control unit) 22 Engine control unit 24 External outlet (power supply unit) 50 EGR system (exhaust gas recirculation system) 53 EGR passage (exhaust gas recirculation passage) 54 EGR valve (exhaust gas recirculation valve) 55 EGR control section (exhaust gas recirculation control section) 56 EGR temperature sensor (exhaust gas recirculation temperature detection means) 60 EGR failure determination section (failure determination section)

Claims

1. An exhaust gas recirculation system includes an exhaust gas recirculation passage that guides a portion of exhaust gas from an exhaust passage of an engine to an intake passage, an exhaust gas recirculation valve that is provided in the exhaust gas recirculation passage and opens or closes to adjust an opening area of ​​the exhaust gas recirculation passage, and an exhaust gas recirculation control unit that controls the operation of the exhaust gas recirculation valve based on an operating state of the engine, an exhaust gas recirculation temperature detection unit that detects a temperature of the exhaust gas recirculation gas flowing through the exhaust gas recirculation passage; and a failure determination unit that determines whether or not the exhaust gas recirculation valve has a failure based on a change in the temperature of the exhaust gas recirculation gas when the exhaust gas recirculation control unit opens and closes the exhaust gas recirculation valve, The fault diagnosis device for an exhaust gas recirculation system, characterized in that the fault judgment unit judges an open fault of the exhaust gas recirculation valve based on a temperature change of the exhaust gas recirculation gas while the exhaust gas recirculation valve is maintained in a closed state during a specified cold operation of the engine, and judges a closed fault of the exhaust gas recirculation valve based on the temperature change of the exhaust gas recirculation gas when the exhaust gas recirculation valve is operated from a closed operating state to an open state after the open fault judgment.

2. 2. The fault diagnosis device for an exhaust gas recirculation system according to claim 1, wherein the fault determination unit determines a closed fault of the exhaust gas recirculation valve based on a temperature change of the exhaust gas recirculation gas that occurs when the exhaust gas recirculation control unit opens the exhaust gas recirculation valve for a predetermined period or more due to a request to open the exhaust gas recirculation valve in conjunction with an operating state of the engine after determining an open fault.

3. The engine is mounted on a vehicle, the vehicle having a storage battery, a generator driven by the engine to generate electricity, and a motor that drives the vehicle to travel using electric power supplied from at least one of the generator and the storage battery, and a travel mode switching control unit that switches between a first travel mode in which the engine is stopped and the motor is driven using electric power supplied from the storage battery to travel, and a second travel mode in which the engine is operated and the generator is used to generate electricity while the vehicle travels, based on at least a required output required of the vehicle, before switching from the first traveling mode to the second traveling mode in a state where warming up of the engine has not been completed, a warm-up operation is performed on the engine for a predetermined period of time, the predetermined low-load operation being lower than the load of the engine when generating electricity in the second traveling mode; 3. The exhaust gas recirculation system fault diagnosis device according to claim 1, wherein the fault determination unit executes the open circuit fault determination while the motor is driving the vehicle while the warm-up operation is continuing.

4. 4. The exhaust gas recirculation system fault diagnosis device according to claim 3, wherein the fault determination unit continues the warm-up operation without switching to the second driving mode until the open circuit fault determination and the closing circuit fault determination are completed, even if the required output reaches a value at which the second driving mode is switched to before the open circuit fault determination and the closing circuit fault determination are completed during the warm-up operation.

5. The vehicle further includes a power supply unit that supplies power from the storage battery to an outside, 5. The exhaust gas recirculation system fault diagnosis device according to claim 3 or 4, characterized in that, during power supply to the outside, the fault determination unit forcibly opens the exhaust gas recirculation valve after determining an open fault, regardless of a request by the exhaust gas recirculation control unit for opening and closing control of the exhaust gas recirculation valve based on the operating state of the engine, to determine the closed fault.

6. A charging rate detection unit for detecting a charging rate of the storage battery, The driving mode switching control unit selects the second driving mode at least when the charging rate is equal to or lower than a first predetermined value, 6. The exhaust gas recirculation system fault diagnosis device according to claim 3, wherein the warm-up operation is started when the charging rate falls to or below a second predetermined value that is higher than the first predetermined value.

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