JP7652006B2 - Fault detection device - Google Patents

Description

The present invention relates to a failure determination device for an EGR system applied to an engine that outputs driving force to cause a generator to generate electricity.

A series-parallel hybrid vehicle equipped with an engine, motor, and generator is known as an example of a device that uses an engine to output driving force for a generator to generate electricity (see Patent Document 1). In this type of hybrid vehicle, different driving sources are used or used together depending on the driving state. For example, when starting or running at low speed, only the motor with high torque at low rotation speeds is used (EV mode). On the other hand, when the battery charge rate is low or during acceleration, the vehicle runs on the driving force of the motor while generating electricity with the generator using the driving force of the engine (series mode). Also, during high-speed running when the engine is efficient, the driving force of the engine is used as the main force, and the driving force of the motor is used as a supplement (parallel mode, ENG mode).

In addition, with regard to determining whether an EGR system applied to an engine such as the one described above has a malfunction, a technique is known for detecting a stuck EGR valve from the change in intake pressure when the EGR valve is opened and closed. For example, it has been proposed to calculate the change in intake pressure when the opening of the EGR valve is changed, and to determine that the EGR valve is stuck if the amount of change is smaller than a threshold value (see Patent Document 2).

JP 2014-088070 A JP 2010-196684 A

To improve the accuracy of fault determination based on changes in intake pressure, it is necessary to recirculate a large amount of EGR gas. Therefore, depending on the operating state of the engine, there is a problem that performing fault determination can easily reduce combustion stability. In particular, in series-parallel hybrid vehicles, changes in the engine's combustion state can cause the amount of power generated by the generator to become unstable, which may have a negative effect on the accuracy of predicting the battery charge level and the accuracy of estimating the cruising range. Note that, not only in hybrid vehicles such as those described above, it is desirable to avoid reducing engine combustion stability as much as possible when determining a fault in the EGR system.

One of the objectives of this invention was devised in light of the above-mentioned problems, and is to provide a failure determination device that can improve the accuracy of failure determination in the EGR system while maintaining engine combustion stability. In addition to this objective, another objective of this invention is to achieve effects that cannot be obtained with conventional technology, which are derived from the configurations shown in the "Mode for carrying out the invention" described below.

The present invention can be realized as the following disclosed aspects or application examples. The disclosed failure determination device solves at least a part of the above-mentioned problems.
The disclosed failure determination device is a failure determination device for an EGR system applied to an engine that outputs driving force to cause a generator to generate electricity , and includes a first determination means for determining a failure of an EGR valve interposed in the exhaust gas recirculation path of the EGR system , and a second determination means for determining, when a failure of the EGR valve is determined by the first determination means, whether the failure state of the EGR valve is an open failure in which the EGR valve does not close in response to a close command, or a closed failure in which the EGR valve does not open in response to an open command.
The judgment condition in the second judgment means for determining that the closed failure has occurred is based on the deviation between the engine torque estimated to be transmitted from the engine to the generator when the EGR system is normal, with the opening of the EGR valve set to a predetermined opening, and the absorption torque which corresponds to the actual value transmitted from the engine to the generator and is converted into electric power by the generator, and the judgment condition in the second judgment means for determining that the open failure has occurred is based on the amount of change in the absorption torque after changing the opening of the EGR valve, relative to the absorption torque before changing the opening of the EGR valve, and the judgment condition for the open failure differs from the judgment condition for the closed failure .

The disclosed failure determination device can improve the accuracy of EGR system failure determination while maintaining engine combustion stability.

1 is a block diagram for explaining a failure determination device as an embodiment; 4 is a graph for explaining the principle of failure determination. 4 is a flowchart (diagnosis flow) relating to failure determination. 11 is a flowchart relating to failure determination (continuation of the diagnosis flow); 11 is a flowchart relating to failure determination (continuation of the diagnosis flow); 6 is a modified example of the flowchart shown in FIG. 5 . 13 is a flowchart (second diagnosis flow) relating to another failure determination. 13 is a flowchart relating to another failure determination (continuation of the second diagnosis flow); 13 is a flowchart relating to another failure determination (continuation of the second diagnosis flow); 10 is a modified example of the flowchart shown in FIG. 9 .

1. Vehicles
The failure determination device 20 as an embodiment is applied to a vehicle 10 shown in Fig. 1. The vehicle 10 is a plug-in hybrid vehicle (hybrid vehicle) that can run using an engine 1 and a motor 3 as drive sources. The engine 1 is an internal combustion engine such as a gasoline engine or a diesel engine, and drives a rotating shaft by combusting a mixture of fuel and air in a combustion chamber. The engine 1 is also capable of outputting a driving force for causing a generator 2 to generate electricity and a driving force for running the vehicle 10.

The generator 2 is a generator that generates electricity using the driving force of the engine 1. The motor 3 is an electric motor/generator that has both the function of driving the drive wheels with the power of the battery 4 and the function of charging the battery 4 with regenerative power generated by using the inertial rotation of the drive wheels. The engine 1, generator 2, and motor 3 are connected via a transaxle 5. The transaxle 5 contains, for example, a speed change gear and a clutch device. The operating states of the engine 1, generator 2, and motor 3 are selected according to the driving state of the vehicle 10 and the operation of the driver, or are used in combination.

The engine 1 and generator 2 are connected to the motor 3 and drive wheels via a clutch. The vehicle 10 can select a series mode in which the engine 1 and generator 2 are disconnected from the motor 3 and drive wheels (the clutch is disengaged) and the vehicle runs. The EV mode is achieved by stopping the engine 1 and generator 2 with the clutch disengaged. Also, by engaging the clutch, the parallel mode or ENG mode can be achieved.

The power generated by the generator 2 and the motor 3 is charged into the battery 4. The battery 4 is a secondary battery such as a lithium-ion secondary battery or a nickel-metal hydride battery, and can be charged by an external charging facility (external charging). A converter 11 that converts power between DC and AC is connected to the battery 4. The converter 11 has a function of converting AC power supplied from the charging port 12 during external charging into DC to charge the battery 4, and a function of converting DC power stored in the battery 4 into AC to supply to the in-vehicle outlet 13. The in-vehicle outlet 13 can output, for example, 100 [V] AC power at a frequency of 50 to 60 [Hz]. This allows the battery 4 to be charged using power supplied from a household outlet, and allows general home appliances to be connected to the in-vehicle outlet 13 for use.

The engine 1 is applied with an EGR system 6. The EGR system 6 is a system that recirculates a portion of the exhaust gas discharged from the cylinders of the engine 1 to the intake system. By applying the EGR system 6 to the engine 1, it is possible to reduce the oxygen concentration and combustion temperature in the cylinders, thereby improving fuel efficiency and exhaust gas performance. The EGR system 6 of this embodiment has an EGR valve 7 that is interposed in an exhaust recirculation passage (EGR passage) that connects the exhaust system and the intake system. By changing the opening degree of the EGR valve 7, it is possible to adjust the flow rate (EGR amount) of exhaust gas (EGR gas) introduced from the exhaust system to the intake system.

[2. Failure determination device]
The failure determination device 20 is a computer (ECU, Electronic Control Unit) having at least the function of determining a failure of the EGR valve 7. The failure determination device 20 has built-in a processor (central processing unit), a memory (main memory), a storage device, an interface device, and the like, all of which are communicatively connected to each other via an internal bus. The contents of the determination and control performed by the failure determination device 20 are recorded and saved in the memory as firmware or an application program. When a program is executed, the contents of the program are expanded in the memory space and executed by the processor.

As shown in FIG. 1, the failure determination device 20 of this embodiment is connected to the engine 1, generator 2, motor 3, battery 4, EGR valve 7, engine speed sensor 14, airflow sensor 15, generator speed sensor 16, and current sensor 17. The failure determination device 20 determines a failure of the EGR valve 7 based on information transmitted from these various devices. The engine speed sensor 14 is a sensor that detects the engine speed (the number of revolutions per unit time, the rotation speed of the engine 1), and the airflow sensor 15 is a sensor that detects the intake amount of the engine 1. The generator speed sensor 16 is a sensor that detects the generator speed (the number of revolutions per unit time, the rotation speed of the generator 2), and the current sensor 17 is a sensor that detects the generated current of the generator 2.

The failure determination device 20 determines a failure based on two principles.
The first principle is that by increasing the EGR amount without fixing the throttle opening, the specific heat ratio in the cylinder changes, and the combustion torque generated by the engine 1 increases. As shown in FIG. 2, the increase rate of the engine torque increases as the EGR rate increases (as the EGR amount increases). Therefore, by observing the change in the absorption torque of the generator 2 when a command is issued to change the opening of the EGR valve 7, the actual fluctuation of the EGR rate can be estimated, and the presence or absence of a failure (close failure or open failure) of the EGR valve 7 can be determined. Note that the open failure means a failure in which the EGR valve 7 does not close in response to a close command, and the close failure means a failure in which the EGR valve 7 does not open in response to an open command. The open failure includes, for example, a failure in which the valve does not close beyond a predetermined opening due to sticking, and a failure in which the valve remains open. Similarly, the close failure includes, for example, a failure in which the valve does not open beyond a predetermined opening due to sticking, and a failure in which the valve remains closed.

The second principle is that by increasing the EGR amount with the throttle opening fixed, the proportion of fresh air in the intake air decreases, and the combustion torque generated by the engine 1 decreases. In other words, when a command is issued to change the opening of the EGR valve 7 with the throttle opening fixed, the actual fluctuation in combustion torque can be estimated by observing the change in the absorption torque of the generator 2, and the presence or absence of a malfunction of the EGR valve 7 (closed malfunction or open malfunction) can be determined.

The failure determination device 20 is provided with a first calculation means 21, a second calculation means 22, and a determination means 23. The first calculation means 21 calculates the engine torque A transmitted from the engine 1 to the generator 2 when the generator 2 generates electricity using the driving force of the engine 1. The engine torque A is calculated based on, for example, the engine speed and the intake amount. Note that the method of calculating the engine torque A is not limited to this. For example, it may be calculated based on the vehicle speed, the accelerator opening, etc., or it may be calculated taking into account the fuel injection amount and the air-fuel ratio.

The second calculation means 22 calculates the absorption torque B that is converted into electric power by the generator 2 (i.e., recovered as charging power for the battery 4) when the generator 2 is generating electricity with the driving force of the engine 1. The absorption torque B is calculated, for example, based on the generator rotation speed and the generated current. Note that the calculation method for the absorption torque B is not limited to this. For example, it may be calculated based on the current value and voltage value charged from the generator 2 to the battery 4, or it may be calculated taking into account the generator temperature and the battery temperature.

The determination means 23 performs a failure determination of the EGR valve 7 by comparing at least the engine torque A and the absorption torque B. The determination means 23 is provided with an initial determination means 24, a first determination means 25, and a second determination means 26. The initial determination means 24 determines whether or not there is a possibility that the EGR valve 7 interposed in the exhaust gas recirculation path of the EGR system 6 is malfunctioning. When the possibility of a malfunction of the EGR valve 7 is recognized, the first determination means 25 closely examines the possibility and determines whether or not there is a malfunction of the EGR valve 7. In addition, when the first determination means 25 determines that the EGR valve 7 is malfunctioning (has malfunctioned), the second determination means 26 determines whether the malfunction state is an open malfunction or a closed malfunction.

In the initial determination means 24, for example, based on a deviation C which is a value obtained by subtracting the engine torque A from the absorption torque B, the following failure determination is performed.
Judgment 1: When the absolute value of the deviation C is equal to or greater than a predetermined deviation _C0 ,
It is determined that the EGR valve 7 may be malfunctioning.
Judgment 2: If the absolute value of the deviation C is less than the predetermined deviation _C0 ,
It is determined that the EGR valve 7 is not malfunctioning (normal).

These failure determinations are performed at least when the engine 1 is driving the generator 2 (for example, in the series mode, the parallel mode, or the ENG mode). Preferably, the failure determinations are performed when the engine 1 is started while the vehicle 10 is receiving external power feeding.
The external power supply means power supply to a home appliance connected to the in-vehicle outlet 13. For example, a hot plate may be connected to the in-vehicle outlet 13 of the vehicle 10 parked at a campsite, and the hot plate may be used with power from the battery 4. In this case, when the charge level of the battery 4 decreases, the engine 1 is operated, power generation by the generator 2 is started, and a failure determination is performed.

When the initial determination means 24 determines that there is a possibility of a malfunction in the EGR valve 7, the first determination means 25 performs a malfunction determination based on the deviation C, for example, as follows.
Judgment 3: When the absolute value of the deviation C is equal to or greater than the predetermined deviation _C0 in the fully closed state,
It is determined that there is a high possibility that the EGR valve 7 has an open valve malfunction.
Judgment 4: When the absolute value of the deviation C is less than the predetermined deviation _C0 in the fully closed state,
It is determined that there is a high possibility that the EGR valve 7 has a closed malfunction.

These fault judgments are preferably made with the ignition timing of the engine 1 retarded compared to when the initial judgment means 24 judged the fault. For example, the ignition timing of the engine 1 is controlled based on an ignition timing map used when the EGR system 6 is not in operation (EGR off). In general, the ignition timing of the engine 1 when the EGR system 6 is in operation is controlled to be more advanced compared to when the EGR system 6 is not in operation. Therefore, by setting the ignition timing of the engine 1 with reference to the ignition timing map used when the EGR system 6 is not in operation, the ignition timing of the engine 1 is given a retarded tendency.

When it is determined that the EGR valve 7 is highly likely to have an open valve malfunction, the second determination means 26 executes a malfunction determination for the EGR valve 7 based on the amount of change in the absorption torque B caused by changing the EGR opening degree stepwise. At this time, the throttle opening degree is held at a constant value and the intake amount of the engine 1 is controlled to be constant. Here, the absorption torque before changing the EGR opening degree is designated as _B1 , and the absorption torque after changing the EGR opening degree is designated as _B2 . The second determination means 26 executes the following malfunction determination based on the amount of change D obtained by subtracting _B1 from _B2 .
Decision 5: If the absolute value of the change amount D is less than the predetermined change amount _D0 ,
It is determined that the EGR valve 7 has an open valve malfunction.
Judgment 6: If the absolute value of the change amount D is equal to or greater than the predetermined change amount _D0 ,
It is determined that the previous judgment was an incorrect judgment (no malfunction).

On the other hand, when it is determined that the EGR valve 7 is highly likely to have a closed valve malfunction, the second determination means 26 outputs an instruction to open the EGR valve 7 to a predetermined opening degree. After that, the second determination means 26 recalculates the deviation C, and performs the following malfunction determination.
Judgment 7: If the absolute value of the deviation C is equal to or greater than the predetermined deviation _C0 ,
It is determined that the EGR valve 7 has a closed malfunction.
Decision 8: If the absolute value of the deviation C is less than the predetermined deviation _C0 ,
It is determined that the previous judgment was an incorrect judgment (no malfunction).

As described above, the conditions for determining an open fault in the second determination means 26 (conditions for determinations 5 and 6) are different from the conditions for determining a close fault in the second determination means 26 (conditions for determinations 7 and 8). By using different determination conditions in this way, the accuracy of determining an open fault and a close fault is improved.

3. Flowchart
3 to 5 are flowcharts (diagnosis flows) relating to the failure determination performed by the failure determination device 20. These flows can be repeatedly executed at a predetermined calculation cycle within the failure determination device 20. The operating state (operating point) of the engine 1 for executing these flows is not important, and failure determination can be made independent of the engine speed or the magnitude of the load.

In step A1, it is determined whether the engine 1 has started while the vehicle 10 is receiving external power supply. In addition, in step A2, it is determined whether the engine 1 is driving the generator 2 (for example, in series mode with the clutch disengaged). If either condition is met, the process proceeds to step A3, and if neither condition is met, the process ends (returns). In step A3, the first calculation means 21 calculates the engine torque A, and the second calculation means 22 calculates the absorption torque B. In the following step A4, the determination means 23 calculates the deviation C obtained by subtracting the engine torque A from the absorption torque B.

In step A5, the initial determination means 24 compares the absolute value |C| of the deviation C with a preset predetermined deviation _C0 . If |C|< _C0 , the process proceeds to step A6, where it is determined that there is no malfunction in the EGR valve 7 (EGR system 6), and this flow ends. On the other hand, if |C|≧ _C0 , it is determined that there is a possibility of some malfunction, and the process proceeds to step A7, where the malfunction determination by the first determination means 25 continues.

In step A7, the ignition timing map for setting the ignition timing of the engine 1 is fixed to the map for when EGR is off (when the EGR valve 7 is fully closed). In the following step A8, the EGR opening is set to 0% (fully closed), and a control command for this is sent from the failure determination device 20 to the EGR valve 7. After that, in step A9, the first calculation means 21 calculates the engine torque A, and the second calculation means 22 calculates the absorption torque B. In the following step A10, the determination means 23 calculates the deviation C by subtracting the engine torque A from the absorption torque B.

In step A11, the first determination means 25 compares the absolute value |C| of the deviation C with a predetermined deviation _C0 . If |C|< _C0 , it is determined that there is a high possibility that the EGR valve 7 has a closed malfunction, and the process proceeds to step A12 shown in Fig. 4. On the other hand, if |C| ≥ _C0 , it is determined that there is a high possibility that the EGR valve 7 has an open malfunction, and the process proceeds to step A18 shown in Fig. 5.

Steps A12 to A17 shown in FIG. 4 are a flow for examining the EGR valve 7 for a closed failure. In step A12, the EGR opening is set to a predetermined K% (open), and a control command is sent from the failure determination device 20 to the EGR valve 7. The opening set here may be 100% (fully open), or may be an opening less than 100%. Then, in step A13, the first calculation means 21 calculates the engine torque A, and the second calculation means 22 calculates the absorption torque B. In the following step A14, the determination means 23 calculates the deviation C by subtracting the engine torque A from the absorption torque B.

In step A15, the second judgment means 26 compares the absolute value |C| of the deviation C with a predetermined deviation _C0 . If |C|< _C0 , the process proceeds to step A16, where the previous judgment (the judgment in step A11) is cancelled as being an erroneous judgment (i.e., there is no malfunction), and the flow ends. On the other hand, if |C|≧ _C0 , the process proceeds to step A17, where it is judged that the EGR valve 7 has a closed malfunction, and the flow ends.

Steps A18 to A25 shown in FIG. 5 are a flow for closely examining an open failure of the EGR valve 7. In step A18, the value of the absorption torque B at this time point is substituted for _B1 . In step A19, the throttle opening is fixed (kept at a constant value) and the intake amount of the engine 1 is controlled to be constant. In step A20, similar to step A12, the EGR opening is set to a predetermined K% (open), and a control command for this is issued from the failure determination device 20 to the EGR valve 7. The opening set here may be 100% (fully open) or may be an opening smaller than 100%. In addition, it does not have to be the same as the indicated value in step A12.

In step A21, the second calculation means 22 calculates the absorption torque B, and substitutes the value for _B2 . In the following step A22, the determination means 23 calculates the amount of change D of the absorption torque B ( _B2 minus _B1 ). In step A23, the second determination means 26 compares the absolute value |D| of the amount of change D with a predetermined amount of change _D0 . Here, if |D|< _D0 , the process proceeds to step A24, where it is determined that the EGR valve 7 has an open malfunction, and this flow ends. On the other hand, if |D|≧ _D0 , the process proceeds to step A25, where the previous determination (the determination in step A11) is cancelled as being an erroneous determination (i.e., there is no malfunction), and this flow ends.

(B) Flowchart of Fig. 6 The flowchart shown in Fig. 6 is a modified example (adding steps A26 to A28) of the flowchart shown in Fig. 5. In this flowchart, the presence or absence of an opening malfunction is determined based on the amount of change D in the absorption torque B when the EGR opening is increased in a stepwise manner, and the opening degree of the opening malfunction is also determined.

The EGR opening set in step A20 in FIG. 6 is not at least 100%, but is, for example, 10%. Thereafter, if |D|< _D0 in step A23, the process proceeds to step A24, where it is determined that the EGR valve 7 has an open malfunction at an opening of 10%. That is, the opening at the time when the condition in step A23 is satisfied (when |D|< _D0 ) is determined to be the opening malfunction. On the other hand, if |D|≧ _D0 , the process proceeds to step A26, where it is determined whether the EGR opening is fully open (100%). This condition is initially not satisfied, and the process proceeds to step A27.

In step A27, the value of the absorption torque B at this point is substituted for _B1 . In the following step A28, the EGR opening is set even larger, for example to 20%. Thereafter, in step A21, the value of the absorption torque B is substituted for _B2 , in step A22, the amount of change D of the absorption torque B is calculated, and in step A23, the absolute value |D| is compared with a predetermined amount of change _D0 . Here, if |D|< _D0 , the process proceeds to step A24, where it is determined that the EGR valve 7 has an opening malfunction at an opening of 20%.

On the other hand, if |D|≧ _D0 , the EGR opening is gradually increased until it reaches full opening (100%), and the determination in step A23 is repeated. If the condition in step A23 is not satisfied even though the EGR opening is full opening (100%), the previous determination (the determination in step A11) is cancelled in step A25 as being an erroneous determination (i.e., there is no malfunction), and this flow ends.

7 to 9 are flowcharts (second diagnosis flow) relating to another fault determination. This flow can be repeatedly executed at a predetermined calculation cycle inside the fault determination device 20. The fault determination in this flow is performed with the throttle opening of the engine 1 fixed, and the operating state (operating point) of the engine 1 is limited.

In step B1, it is determined whether the engine 1 has started while the vehicle 10 is receiving external power. In step B2, it is determined whether the engine 1 is driving the generator 2. If either of the conditions is met, the process proceeds to step B3. If neither of the conditions is met, the process ends. In step B3, it is determined whether the EGR rate is greater than 0% (i.e., the EGR system 6 is in operation). If the EGR system 6 is in operation, the process proceeds to step B4, where the EGR opening is set to 0% (fully closed), and a control command is sent from the failure determination device 20 to the EGR valve 7, after which the process proceeds to step B5. If the EGR system 6 is not in operation, the process proceeds directly to step B5.

In step B5, the throttle opening is fixed (kept at a constant value) and the intake amount of the engine 1 is controlled to be constant. In step B6, the ignition timing map for setting the ignition timing of the engine 1 is fixed to the map for EGR off (when the EGR valve 7 is fully closed). In the following step B7, the second calculation means 22 calculates the absorption torque B, and the value is substituted for _B3 . In step B8, the EGR opening is set to a predetermined _K1 % (open), and a control command for this is issued from the failure determination device 20 to the EGR valve 7. The opening _K1 set here is larger than 0% (fully closed) and smaller than 100% (fully open).

In step B9, the second calculation means 22 calculates the absorption torque B again, and substitutes the value for _B4 . In step B10, the determination means 23 calculates the amount of change D of the absorption torque B ( _B4 minus _B3 ). In step B11, the first determination means 25 compares the absolute value |D| of the amount of change D with a predetermined amount of change _D0 . Here, if |D|< _D0 , it is determined that there is a high possibility that the EGR valve 7 has a closed malfunction, and the process proceeds to step B12 shown in FIG. 8. On the other hand, if |D|≧ _D0 , it is determined that there is a high possibility that the EGR valve 7 has an open malfunction, and the process proceeds to step B18 shown in FIG. 9.

Steps B12 to B17 shown in FIG. 8 are a flow for examining the EGR valve 7 for a closed failure. In step B12, the EGR opening is set to 0% (fully closed), and a control command is sent from the failure determination device 20 to the EGR valve 7. Then, in step B13, the first calculation means 21 calculates the engine torque A, and the second calculation means 22 calculates the absorption torque B. In the following step B14, the determination means 23 calculates the deviation C by subtracting the engine torque A from the absorption torque B.

In step B15, the second judgment means 26 compares the absolute value |C| of the deviation C with a predetermined deviation _C0 . If |C|< _C0 (i.e., the engine torque A and the absorption torque B are approximately equal), the process proceeds to step B16, where it is judged that the EGR valve 7 has a closed malfunction, and this flow ends. On the other hand, if |C|≧ _C0 , the process proceeds to step B17, where the previous judgment (the judgment in step B11) is cancelled as it was an erroneous judgment (i.e., there is no malfunction), and this flow ends.

Steps B18 to B23 shown in Fig. 9 are a flow for closely examining an open failure of the EGR valve 7. In step B18, the EGR opening is set to a predetermined _K2 % (open), and a control command for this is issued from the failure determination device 20 to the EGR valve 7. The opening _K2 set here is, for example, larger than the opening K1 set in step _B8 . In step B19, the second calculation means 22 calculates the absorption torque B, and this value is substituted for _B5 . In the following step B20, the determination means 23 calculates the change amount E of the absorption torque B ( _B5 minus _B4 ).

In step B21, the second determination means 26 compares the absolute value |E| of the amount of change E with a predetermined amount of change _E0 . If |E|< _E0 , the process proceeds to step B22, where it is determined that the EGR valve 7 has an open malfunction, and this flow ends. On the other hand, if |E|≧ _E0 , the process proceeds to step B23, where the previous determination (the determination in step B11) is cancelled as being an erroneous determination (i.e., there is no malfunction), and this flow ends.

(D) Flowchart of Fig. 10 The flowchart shown in Fig. 10 is a modified example (adding steps B24 to B26) of the flowchart shown in Fig. 9. In this flowchart, the presence or absence of an opening malfunction is determined based on the amount of change E of the absorption torque B when the EGR opening is increased in a stepwise manner, and the opening degree of the opening malfunction is also determined.

The EGR opening set in step B18 in Fig. 10 is set to an opening degree (e.g., 30%) that is greater than the opening degree _K1 set in step B8 and is at least not 100%. After that, if |E| < _E0 in step B21, the process proceeds to step B22, where it is determined that the EGR valve 7 has an open malfunction at an opening degree of 30%. In other words, the opening degree at the time when the condition in step B21 is established (when |E| < _E0 ) is determined to be the opening degree causing the open malfunction.

On the other hand, if |E|≧ _E0 in step B21, the process proceeds to step B24, where it is determined whether the EGR opening is fully open (100%). This condition is not satisfied initially, and the process proceeds to step B25. In step B25, the value of the absorption torque B at this point is substituted for _B4 . In the following step B26, the EGR opening is set even larger (for example, to 40%). Thereafter, in step B19, the value of the absorption torque B is substituted for _B5 , and in step B20, the amount of change E of the absorption torque B is calculated, and in step B21, the absolute value |E| is compared with a predetermined amount of change _E0 .

Here, if |E|< _E0 , the process proceeds to step B22, where it is determined that the EGR valve 7 has an open malfunction at 40% opening. On the other hand, if |E|≧ _E0 , the EGR opening is gradually opened until it becomes fully open (100%), and the determination in step B21 is repeated. If the condition in step B21 is not satisfied even though the EGR opening is fully open (100%), the previous determination (the determination in step B11) is deemed to have been an erroneous determination (i.e., there is no malfunction) in step B23, and the determination is cancelled, and this flow ends.

[4. Effects]
(1) In the failure determination device 20 according to the above embodiment, the failure state of the EGR valve 7 is determined in multiple stages. The failure determination device 20 includes a first determination means 25 for determining a failure of the EGR valve 7, and a second determination means 26 for determining whether the failure state is an open failure or a closed failure when the first determination means 25 determines a failure of the EGR valve 7. In addition, the determination condition for an open failure in the second determination means 26 is different from the determination condition for a closed failure in the second determination means 26. With this configuration, the conditions suitable for determining an open failure and the conditions suitable for determining a closed failure can be set individually, and the failure of the EGR valve 7 can be determined with high accuracy. In addition, since the failure determination accuracy is increased, there is no need to recirculate a large amount of EGR gas. Therefore, the failure determination accuracy of the EGR system 6 can be improved while maintaining the combustion stability of the engine 1.

(2) The first determination means 25 determines whether or not there is a malfunction in the EGR valve 7 while instructing the EGR valve 7 to be fully closed. With this configuration, it is possible to accurately determine whether or not there is a malfunction in the EGR valve 7, and it is possible to improve the accuracy of determining a malfunction in the EGR system 6.
(3) The first determination means 25 can determine whether or not there is a malfunction in the EGR valve 7 in a state in which the ignition timing of the engine 1 is retarded, compared to when the first determination means 25 has not determined whether or not there is a malfunction in the EGR valve 7. With this configuration, it is possible to accurately determine whether or not there is a malfunction in the EGR valve 7, and it is possible to improve the accuracy of malfunction determination for the EGR system 6.

(4) If the "state in which the ignition timing of the engine 1 is retarded" is set to the "state in which the ignition timing is set to the same value as that set when the EGR system 6 is not in operation," an appropriate retard tendency can be imparted to the ignition timing by using an existing ignition timing map. This makes it possible to determine with high accuracy whether or not the EGR valve 7 is malfunctioning, thereby improving the accuracy of malfunction determination for the EGR system 6.

(5) The second determination means 26 instructs the EGR valve 7 to open the EGR opening in stages, calculates the absorption torque B for each EGR opening, and performs a failure determination for the EGR valve 7 based on the change amounts D and E. With this configuration, it is possible to accurately determine whether or not the EGR valve 7 has an open failure, and to reduce false detections. Therefore, it is possible to improve the accuracy of failure determination for the EGR system 6.

(6) When determining whether the EGR valve 7 has an open-state malfunction, the second determination means 26 described above can execute control to gradually open the EGR opening, with the final opening being fully open, until an open-state malfunction of the EGR valve 7 is detected. With this configuration, an open-state malfunction can be reliably detected somewhere along the way until the EGR opening is fully open. Therefore, the accuracy of malfunction determination of the EGR system 6 can be improved.

(7) When determining whether the EGR valve 7 has an open-circuit malfunction, the second determination means 26 determines that the EGR valve 7 has an open-circuit malfunction if the absolute values of the amounts of change D, E of the absorption torque B before and after a change in the EGR opening degree become less than predetermined amounts of change _D0 , _E0 . With this configuration, it is possible to accurately determine whether the EGR valve 7 has an open-circuit malfunction, and it is possible to improve the accuracy of determining a malfunction in the EGR system 6.

(8) When determining whether the EGR valve 7 has an open failure, the second determination means 26 can determine the degree of opening of the EGR valve 7 at which the open failure has occurred. In this way, by determining the degree of opening at which the EGR valve 7 has an open failure, the accuracy of determining a failure in the EGR system 6 can be improved. In addition, since the amount of EGR gas recirculated and the combustion torque can be accurately estimated, the controllability of the engine 1 and the generator 2 can be improved.

(9) The engine 1 and generator 2 are mounted on a hybrid vehicle 10 that is connected to the motor 3 and drive wheels via a clutch. The hybrid vehicle 10 can select a series mode in which the engine 1 and generator 2 can be disconnected from the motor 3 and drive wheels to run, and fault diagnosis can be performed during the series mode. In other words, fault diagnosis can be performed while driving the drive wheels with the motor 3 without transmitting the driving force of the engine 1 to the drive wheels. Therefore, fault diagnosis can be performed without adversely affecting drivability even if the operating conditions of the engine 1 are changed for fault diagnosis.

[5. Other]
The above embodiment is merely illustrative, and is not intended to exclude various modifications or application of techniques not specified in the embodiment. Each configuration of the embodiment can be modified in various ways without departing from the spirit of the embodiment. Furthermore, each configuration of the embodiment can be selected or combined as necessary.

In the above embodiment, the failure determination device 20 applied to a plug-in hybrid vehicle is exemplified, but the application of this invention is not limited to this type of vehicle 10. If an EGR system 6 is applied to at least the engine 1 that outputs driving force to cause the generator 2 to generate electricity, control similar to that of the above embodiment can be applied. Specifically, this invention can be applied to ships, plants, power generation facilities, etc. in which the generator 2 can be driven by the engine 1 to which the EGR system 6 is applied. Even in these applications, the accuracy of failure determination of the EGR system 6 can be improved while maintaining the combustion stability of the engine 1 by making the determination condition for an open failure in the second determination means 26 different from the determination condition for a closed failure.

1 Engine
2 Generator
3 Motor
4 Battery
5 Transaxle
6 EGR system
7 EGR valve
10 Vehicles (plug-in hybrid vehicles, hybrid vehicles)
11 Converter
12 Charging port
13 In-car power outlet
14 Engine speed sensor
15 Airflow sensor
16 Generator RPM Sensor
17 Current Sensor
20 Fault determination device
21 First calculation means
22 Second calculation means
23 Determination means
24 Initial determination means
25 First determination means
26 Second determination means
A Engine torque
B Absorption torque
C Deviation
C₀Prescribed deviation
D Amount of change
D₀Predetermined change amount
E Amount of change
E₀Predetermined change amount

Claims (9)

A failure determination device for an EGR system applied to an engine that outputs a driving force for causing a generator to generate electricity, comprising:
a first determination means for determining a failure of an EGR valve disposed in an exhaust gas recirculation passage of the EGR system;
and a second determination means for determining, when the first determination means determines that the EGR valve has a malfunction, whether the malfunction state of the EGR valve is an open malfunction in which the EGR valve does not close in response to a close command or a close malfunction in which the EGR valve does not open in response to an open command,
A failure determination device characterized in that the determination condition in the second determination means for determining that the closed failure has occurred is based on the deviation between the engine torque estimated to be transmitted from the engine to the generator when the EGR system is normal, with the opening of the EGR valve set to a predetermined opening, and the absorption torque equivalent to the actual value transmitted from the engine to the generator and converted into electric power by the generator, and the determination condition in the second determination means for determining that the open failure has occurred is based on the amount of change in the absorption torque after changing the opening of the EGR valve, relative to the absorption torque before changing the opening of the EGR valve, and the determination condition for the open failure is different from the determination condition for the closed failure . 2. The failure determination device according to claim 1, wherein the first determination means determines the failure while instructing the EGR valve to be fully closed. 3. The failure determination device according to claim 1, wherein the first determination means determines a failure of the EGR valve in a state in which the ignition timing of the engine is retarded compared to a state in which the first determination means has not determined a failure of the EGR valve. 4. The failure determination device according to claim 3, wherein the state in which the ignition timing of the engine is retarded is the same as the ignition timing that is set when the EGR system is not in operation. The failure determination device according to any one of claims 1 to 4, characterized in that the second determination means instructs the EGR valve to open the EGR valve in a stepwise manner, calculates an absorption torque converted into electric power by the generator when the generator generates power using the driving force of the engine for each EGR opening, and determines the presence or absence of the open circuit failure based on an amount of change in the absorption torque. 6. The failure determination device according to claim 5, wherein the second determination means, when making the failure determination according to claim 5, gradually opens the EGR opening degree from a final opening degree of a fully opened state until an open failure of the EGR valve is detected. 7. The failure determination device according to claim 5, wherein the second determination means, when performing the failure determination according to claim 5, confirms a determination that the EGR valve has an open failure when an absolute value of an amount of change in the absorption torque before and after a change in the EGR opening degree becomes less than a predetermined amount of change. The failure determination device according to any one of claims 5 to 7, wherein the second determination means determines at what opening degree the EGR valve has an open failure, when performing the failure determination according to claim 5. the engine and the generator are mounted on a hybrid vehicle connected to a motor and drive wheels via a clutch,
the hybrid vehicle is capable of selecting a series mode in which the engine and the generator are separated from the motor and the drive wheels;
9. The failure determination device according to claim 1, wherein the first determination means and the second determination means perform the determination during the series mode.

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