Fail-safe method and device for exhaust gas recirculation device for internal-combustion engine

Abstract

In an exhaust gas recirculation device for an internal-combustion engine recirculating exhaust gas from an exhaust passage (5) of the internal-combustion engine to an intake passage (3) via an EGR valve (11), it is determined as a primary diagnosis whether or not the EGR valve (11) is operating in accordance with a command. When an abnormality is determined in the primary diagnosis (time t1), energization to the EGR valve (11) is stopped. When a predetermined delay time has elapsed (time t2), as a secondary diagnosis, an actual opening degree (rEGRV) of the EGR valve (11) is detected, and it is determined whether or not the actual opening degree (rEGRV) is in a fully closed position. If the actual opening degree (rEGRV) is not in the fully closed position, an output restriction of the internal-combustion engine is performed. If the actual opening degree (rEGRV) is in the fully closed position, the output restriction is not performed.

Description

Fail-safe method and device for exhaust gas recirculation system of internal combustion engine

[0001] The present invention relates to an exhaust gas recirculation system for an internal combustion engine that recirculates exhaust gas from the exhaust system to the intake system of the internal combustion engine via an exhaust gas recirculation control valve, and more particularly to a fail-safe technique for when an abnormality occurs in the exhaust gas recirculation system.

[0002] Japanese Patent Application Laid-Open No. 2003-144992 discloses that when a self-diagnosis function determines that a valve opening control system of an exhaust gas recirculation device has failed, the exhaust gas recirculation control valve is fully closed.

[0003] Furthermore, Patent Document 2 discloses that when an exhaust gas recirculation control valve is diagnosed as having an open circuit malfunction, the engine output is limited to a small value.

[0004] However, if engine output is uniformly limited when the exhaust gas recirculation control valve fails, as in Patent Document 2, the maximum vehicle speed will decrease, making it impossible for the driver to drive as intended, resulting in a significant decline in vehicle quality.

[0005] On the other hand, even if the exhaust gas recirculation control valve is controlled to be fully closed as in Patent Document 1, there is a possibility that it may not actually transition to being fully closed. In that case, excessive exhaust gas recirculation may cause the combustion in the internal combustion engine to become unstable, leading to a stall.

[0006] JP-A No. 61-081567 JP-A No. 09-025852

[0007] The fail-safe method for an exhaust gas recirculation device of an internal combustion engine according to the present invention is for an internal combustion engine exhaust gas recirculation device that recirculates exhaust gas from the exhaust system of the internal combustion engine to the intake system via an exhaust gas recirculation control valve, and as a primary diagnosis, diagnoses whether the exhaust gas recirculation control valve is operating in accordance with a command, and if an abnormality is diagnosed in this primary diagnosis, fully closes the exhaust gas recirculation control valve, and as a secondary diagnosis, detects the actual opening of the exhaust gas recirculation control valve and diagnoses whether this actual opening is in the fully closed position, and if this actual opening is not in the fully closed position, limits the output of the internal combustion engine.

[0008] If the primary diagnosis reveals an abnormality and the actual opening of the exhaust gas recirculation control valve is actually fully closed, there is no risk of excessive exhaust gas recirculation, so there is no need to limit the output of the internal combustion engine. Therefore, by not limiting the output, it is possible to avoid a deterioration in vehicle quality. On the other hand, if the actual opening is not fully closed, limiting the output can reliably avoid combustion instability and stalling.

[0009] 1 is an explanatory diagram showing the configuration of an exhaust gas recirculation device for an internal combustion engine according to an embodiment; a flowchart showing the processing flow of fail-safe control according to an embodiment; a functional block diagram showing the main parts of an engine controller; a characteristic diagram showing an example of output limitation; a time chart showing an example of the operation of primary diagnosis and secondary diagnosis; a time chart showing another example of operation; a time chart showing yet another example of operation; an explanatory diagram showing another example of the configuration of an exhaust gas recirculation device; an explanatory diagram showing yet another example of the configuration of an exhaust gas recirculation device.

[0010] An embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

[0011] 1 is an explanatory diagram showing a schematic configuration of an exhaust gas recirculation system according to one embodiment. The internal combustion engine 1 of this embodiment is a spark-ignition internal combustion engine, or so-called gasoline engine, to which an intake passage 3 is connected via an intake manifold 2 and an exhaust passage 5 is connected via an exhaust manifold 4.

[0012] An electronically controlled throttle valve 7, the opening of which is controlled by a control signal from an engine controller 6, is provided in the intake passage 3, and further upstream of this, an air flow meter 8, such as a hot-wire type air flow meter 8, is disposed to measure the amount of intake air.

[0013] An exhaust gas recirculation passage 10 constituting the exhaust gas recirculation device has one end connected to the exhaust passage 5 and the other end connected to the intake passage 3 downstream of the throttle valve 7. A portion of the exhaust gas is recirculated from the exhaust system to the intake system as EGR gas through this exhaust gas recirculation passage 10. An exhaust gas recirculation control valve 11 (hereinafter also referred to as an EGR valve) is provided in the exhaust gas recirculation passage 10 to variably control the amount of recirculated exhaust gas and therefore the exhaust gas recirculation rate (EGR rate). An EGR gas cooler 12 is provided upstream of the EGR valve 11 (i.e., on the exhaust passage 5 side) to cool the EGR gas by, for example, heat exchange with cooling water.

[0014] In one embodiment, the EGR valve 11 is configured to open and close a butterfly valve-type valve element driven by a motor. The spring force of a return spring (not shown) acts on the valve element in the closing direction, and when the motor is not energized, the EGR valve 11 is fully closed due to the action of the return spring. The opening of the EGR valve 11, i.e., the rotation angle of the butterfly valve-type valve element, is detected by a position sensor 13 (hereinafter abbreviated as a POS sensor) built into the EGR valve 11. The rotation of the motor is controlled by the engine controller 6 via a drive circuit (not shown) so that the opening detected by the POS sensor 13 matches the target opening.

[0015] In addition to the detection signals from the POS sensor 13 and air flow meter 8, the engine controller 6 also receives detection signals from a number of sensors, such as a crank angle sensor 15 for detecting engine speed, an accelerator pedal opening sensor 16 for detecting the amount of depression of the accelerator pedal operated by the driver, an air-fuel ratio sensor 17 provided in the exhaust passage 5, a coolant temperature sensor 18, an intake air temperature sensor 19, and a knocking sensor 20. Based on these detection signals, the engine controller 6 controls the output, air-fuel ratio, ignition timing, etc. of the internal combustion engine 1.

[0016] Furthermore, in a predetermined exhaust gas recirculation region, the engine controller 6 controls the opening of the EGR valve 11 to achieve a target EGR rate determined from the load and rotation speed of the internal combustion engine 1. The engine controller 6 also realizes a self-diagnosis function and a fail-safe function of the exhaust gas recirculation device, as will be described later.

[0017] 2 is a flowchart showing the flow of processing related to the self-diagnosis function and fail-safe function of the exhaust gas recirculation device executed by the engine controller 6. The routine shown in this flowchart is repeatedly executed while the internal combustion engine 1 is operating.

[0018] In the first step 1, the engine controller 6 determines whether the difference (absolute value) ΔEGRV between the target opening tEGRV of the EGR valve 11 calculated by the engine controller 6 and the actual opening rEGRV detected by the POS sensor 13 is equal to or greater than a predetermined set value #ΔEGRV. More specifically, the engine controller 6 determines whether the difference ΔEGRV is equal to or greater than the set value #ΔEGRV for a predetermined period (a predetermined time or a predetermined number of cycles). If the result is NO, the process proceeds to step 2, where normal control continues. The set value #ΔEGRV is set to a value greater than the normal difference due to a delay that may occur during the opening control of the EGR valve 11. If the difference ΔEGRV between the target opening tEGRV and the actual opening rEGRV is equal to or greater than the set value #ΔEGRV, this indicates the existence of some abnormality, including a malfunction of the EGR valve 11 itself. In other words, in this embodiment, the determination in step 1 corresponds to a primary diagnosis of whether the EGR valve 11 is operating in accordance with the command. The condition of "continuing for a predetermined period of time" is intended to eliminate erroneous diagnosis due to momentary abnormal values ​​during a transition, and therefore the period is set to be relatively short.

[0019] If the determination in step 1 is YES, that is, if an abnormality is diagnosed in the primary diagnosis, the process proceeds from step 1 to step 3, and the power supply to the EGR valve 11 is cut off. In this embodiment in which the EGR valve 11 is equipped with a return spring, turning off the power supply to the EGR valve 11 corresponds to the process of fully closing the EGR valve 11 when an abnormality is diagnosed in the primary diagnosis.

[0020] Next, the process proceeds to step 4, where a secondary diagnosis is made to determine whether the EGR valve 11 is fully closed. Specifically, it is determined whether the actual opening rEGRV detected by the POS sensor 13 is equal to or less than a predetermined first threshold value #EGRV1, which corresponds substantially to the fully closed position (rEGRV=0). This determination is actually made when a predetermined delay time has elapsed since the EGR valve 11 was de-energized. That is, even if the EGR valve 11 was de-energized in step 3, it takes some time for the valve disc to return to the fully closed position due to the spring force of the return spring. Therefore, the delay time is set taking this required time into consideration.

[0021] If the determination in step 4 is YES, the process proceeds to step 5, and fail-safe operations including output limitation, which will be described later, are not performed. In other words, since the EGR valve 11 is actually fully closed, there is no concern about combustion instability due to excessive exhaust gas recirculation, and therefore normal operation is permitted even if the primary diagnosis indicates that there is some abnormality in the exhaust gas recirculation device.

[0022] If the determination in step 4 is NO, this means that the EGR valve 11 is not actually fully closed even though it should be. Therefore, the output of the internal combustion engine 1 is limited to avoid stalling due to excessive exhaust gas recirculation. Here, in this embodiment, the output limit is prepared in two different levels, and one of the output limits is selected depending on the actual opening degree rEGRV of the EGR valve 11.

[0023] Specifically, if the determination in step 4 is NO, the process proceeds from step 4 to step 6, where it is determined whether the actual opening rEGRV detected by the POS sensor 13 is equal to or less than a predetermined second threshold #EGRV2. The second threshold #EGRV2 is set to an appropriate opening greater than the first threshold #EGRV1. If the determination in step 6 is YES, the process proceeds to step 7, where a first output restriction with a relatively small degree of restriction is implemented. If the determination in step 6 is NO, the process proceeds to step 8, where a second output restriction with a relatively large degree of restriction is implemented. By limiting the output of the internal combustion engine 1 in this manner, combustion instability and stalling can be avoided even if exhaust gas is recirculated through the EGR valve 11 that is not fully closed. Furthermore, if the actual opening rEGRV is smaller than the second threshold #EGRV2 even when the EGR valve 11 is not fully closed, the amount of exhaust gas recirculated into the intake system is relatively small, so stalling can be avoided by the first output restriction with a small degree of restriction.

[0024] Although not shown in the flowchart, a fault diagnosis to determine whether there is an abnormality in the POS sensor 13 is performed by another routine not shown, and the secondary diagnosis (step 4) using the detection value (rEGRV) of the POS sensor 13 is performed on the condition that there is no abnormality in the POS sensor 13.

[0025] In one preferred example, if the POS sensor 13 is diagnosed as abnormal, the secondary diagnosis is not performed in response to the abnormality diagnosed in the primary diagnosis, and no output restriction is imposed on the internal combustion engine 1. That is, after the power supply to the EGR valve 11 is turned off in step 3 of Fig. 2, the process proceeds to step 5. This is done in consideration of the fact that the reliability of the primary diagnosis is low due to an abnormality in the POS sensor 13, and is intended to avoid a deterioration in driving performance due to an erroneous diagnosis.

[0026] In another example, if the POS sensor 13 is diagnosed as abnormal, the secondary diagnosis is not performed in response to the abnormality diagnosis in the primary diagnosis, and the output of the internal combustion engine 1 (for example, the second output limit or the first output limit) is uniformly limited. That is, after the power supply to the EGR valve 11 is turned off in step 3 of Fig. 3, the process proceeds to step 8 or step 7. This prioritizes reliably avoiding a stall even if it results in a deterioration in driving performance.

[0027] FIG. 4 is a characteristic diagram showing example characteristics of the first output limit and the second output limit, with the torque and rotational speed of the internal combustion engine 1 as parameters. In the diagram, line WOT indicates the full-throttle characteristic when no output limit is applied. Line LIM1 indicates the characteristic of the first output limit, and line LIM2 indicates the characteristic of the second output limit. Under the output limit, even if the driver increases the accelerator pedal depression, the respective characteristic lines cannot be exceeded. The output limit is realized, for example, by limiting the opening of the throttle valve 7. Under the second output limit (LIM2), the output is significantly limited to avoid stalling, but under the first output limit (LIM1), a relatively large output can be obtained, allowing, for example, normal driving.

[0028] FIG. 3 is a functional block diagram showing the functions of the main parts of the engine controller 6 related to the above-described diagnosis and fail-safe. As shown in the figure, the engine controller 6 includes a primary diagnosis unit 21, a secondary diagnosis unit 22, a POS sensor diagnosis unit 23, an EGR valve drive permission command unit 24, and a fail-safe command unit 25. The primary diagnosis unit 21 receives the target opening tEGRV and the actual opening rEGRV as inputs and performs the above-described primary diagnosis based on the difference ΔEGRV between the two. The EGR valve drive permission command unit 24 commands permission or prohibition of drive of the EGR valve 11 and outputs an EGR valve drive stop command when an abnormality signal is input from the primary diagnosis unit 21. The POS sensor diagnosis unit 23 diagnoses whether or not there is an abnormality in the POS sensor 13. When the secondary diagnostic unit 22 receives an abnormality signal from the primary diagnostic unit 21, it performs a secondary diagnosis to determine whether the actual opening rEGRV is in the fully closed position, provided that the POS sensor 13 is not abnormal. If the secondary diagnosis determines that the actual opening rEGRV is not in the fully closed position, it outputs a signal to that effect to the fail-safe command unit 25. The fail-safe command unit 25 outputs a fail-safe command based on this input.

[0029] The fail-safe command includes the first and second output limits described above, as well as a combustion limit for improving stall resistance, such as increasing the idle speed above normal. Furthermore, if a variable device such as a variable valve timing mechanism is included, control is executed in response to the fail-safe command to fix the variable device to a default position.

[0030] Next, the operation of each part relating to the diagnosis and fail-safe of the exhaust gas recirculation system will be described with reference to the time charts of FIGS.

[0031] 5 shows an example in which an abnormality is determined by the primary diagnosis while the vehicle is running with the internal combustion engine 1, and the secondary diagnosis determines that the EGR valve 11 is in the fully closed position. From top to bottom, the diagram shows (a) the result of the primary diagnosis, (b) whether or not the EGR valve 11 is energized, (c) the timer, (d) the actual opening rEGRV, (e) whether or not an output limit is applied, (f) whether or not a combustion limit is applied, (g) whether or not the device is fixed, and (h) whether or not a warning light (so-called MIL) is illuminated.

[0032] At time t1, the primary diagnosis outputs a diagnosis result indicating an abnormality, and power to the EGR valve 11 is turned off. At the same time, a timer is started. At time t2, when the timer reaches a predetermined value (the delay time described above), a secondary diagnosis is performed to determine whether the actual opening rEGRV is equal to or less than a first threshold value #EGRV1, which substantially corresponds to the fully closed position. In the example of FIG. 5 , the actual opening rEGRV is equal to or less than the first threshold value #EGRV1, and the fully closed position is determined. Therefore, no output limitation, no combustion limitation, and no device fixation of the variable valve timing mechanism or the like is performed.

[0033] The warning light shown in column (h) is not illuminated at this stage. At time t3, the next trip of the vehicle begins. During this next trip, the warning light is illuminated when an abnormality is diagnosed in the primary diagnosis (time t4).

[0034] In this way, as a secondary diagnosis, it is determined whether the actual opening rEGRV is in the fully closed position, and if it is fully closed, no fail-safe operation such as output restriction is performed, allowing the driver to continue driving as intended and avoiding a decline in vehicle quality.

[0035] 6 shows an example in which an abnormality is determined in the primary diagnosis while the vehicle is running using the internal combustion engine 1, and in the secondary diagnosis at time t2, the actual opening rEGRV is determined to be equal to or less than the second threshold value #EGRV2, although it is not in the fully closed position. In other words, this corresponds to a state in which the EGR valve 11 is open at a relatively small opening due to the valve body of the EGR valve 11 sticking, foreign matter getting caught, an abnormality in the control system, or the like.

[0036] In this case, according to the results of the secondary diagnosis at time t2, a first output limitation with a small degree of limitation is implemented as shown in (e), and further, a combustion limitation as shown in (f) and a device fixation as shown in (g) are also implemented. This makes it possible to maintain sufficient driving performance while avoiding stalls due to exhaust gas recirculation.

[0037] 7 shows an example in which an abnormality is determined in the primary diagnosis while the vehicle is running using the internal combustion engine 1, and the actual opening rEGRV is determined to be greater than the second threshold value #EGRV2 in the secondary diagnosis at time t2. In other words, this corresponds to a state in which the EGR valve 11 is open at a relatively large opening due to the valve body of the EGR valve 11 sticking, foreign matter getting caught in it, an abnormality in the control system, or the like.

[0038] In this case, according to the results of the secondary diagnosis at time t2, a second output limitation with a greater degree of limitation is implemented as shown in (e), and further, combustion limitation as shown in (f) and device fixation as shown in (g) are also implemented. This limits vehicle acceleration and high-speed driving, but ensures that stalls due to exhaust gas recirculation can be avoided.

[0039] 8 is an explanatory diagram showing an example of the configuration of an exhaust gas recirculation system in a supercharged internal combustion engine. As shown in the figure, a supercharger 31, such as a compressor of a turbocharger, is disposed upstream of the throttle valve 7 in the intake passage 3, and the tip of the exhaust gas recirculation passage 10 is connected to the intake passage 3 at a position upstream of the supercharger 31. A differential pressure sensor 32 is also provided to detect the pressure difference between above and below the EGR valve 11 in the exhaust gas recirculation passage 10. The target opening of the EGR valve 11 is set taking into account the pressure difference detected by the differential pressure sensor 32.

[0040] 9 shows another example of the configuration of an exhaust gas recirculation system for a turbocharged internal combustion engine. In this example, a negative pressure generating valve 33 for generating the negative pressure required for exhaust gas recirculation is added between the air flow meter 8 and the turbocharger 31 in the intake passage 3. The end of the exhaust gas recirculation passage 10 is connected to the intake passage 3 between the negative pressure generating valve 33 and the turbocharger 31.

[0041] The self-diagnosis and fail-safe control of the exhaust gas recirculation system described above can be similarly applied to the exhaust gas recirculation system in these internal combustion engines with a supercharger.

[0042] Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment and can be modified in various ways. For example, the type of exhaust gas recirculation control valve is not limited to the butterfly valve type described above. The present invention can also be applied to known exhaust gas recirculation control valves, such as step motor type EGR valves. Furthermore, the present invention may be applied to an exhaust gas recirculation control valve that does not have a return spring. In the case of an exhaust gas recirculation control valve that does not have a return spring, if an abnormality is diagnosed in the primary diagnosis, a fully closed position is commanded as the target opening of the exhaust gas recirculation control valve. The delay time until the start of the secondary diagnosis described above is set taking into account the time required for the valve to be fully closed by control.

[0043] Furthermore, the primary diagnosis method is not limited to the method described in the above embodiment in which the difference between the target opening and the actual opening is compared with a predetermined value, but may be any method that can diagnose an abnormality in the exhaust gas recirculation device.

[0044] Furthermore, the present invention is not limited to application to gasoline engines, but can also be applied to exhaust gas recirculation systems for diesel engines.

Claims

1. In an exhaust gas recirculation system for an internal combustion engine that recirculates exhaust gas from the exhaust system to the intake system via an exhaust gas recirculation control valve, As a primary diagnostic step, we will check whether the exhaust gas return control valve is operating according to the command. If an abnormality is detected in this initial diagnosis, the exhaust gas return control valve will be fully closed for the secondary diagnosis. As a secondary diagnosis, the actual opening degree of the exhaust gas return control valve is detected, and a diagnosis is made as to whether or not this actual opening degree is in the fully closed position. If the actual opening is not at the fully closed position, the output of the internal combustion engine will be limited; if the actual opening is at the fully closed position, the output of the internal combustion engine will not be limited. Fail-safe methods for exhaust gas recirculation systems in internal combustion engines.

2. In the secondary diagnosis, if the actual opening is not at the fully closed position, it is further determined whether the actual opening is below a predetermined threshold. If it is below the threshold, a first output limit with a relatively small degree of restriction is applied. If it is greater than the threshold, a second output limit with a relatively greater degree of restriction is applied. A fail-safe method for an exhaust gas recirculation device of an internal combustion engine according to claim 1.

3. The above primary diagnosis is made when the difference between the commanded target opening and the actual opening remains above a predetermined value for a predetermined period of time or longer. A fail-safe method for an exhaust gas recirculation device of an internal combustion engine according to claim 1.

4. The above secondary diagnosis will not be performed until an abnormality is diagnosed in the above primary diagnosis. A fail-safe method for an exhaust gas recirculation device of an internal combustion engine according to claim 1.

5. The above secondary diagnosis is performed after a predetermined time has elapsed time since the exhaust gas return control valve was fully closed. A fail-safe method for an exhaust gas recirculation device of an internal combustion engine according to claim 1.

6. The exhaust gas return control valve has a return spring that biases the valve in the fully closed direction. When an abnormality is diagnosed during the initial diagnosis, the exhaust gas return control valve is completely closed by cutting off the power supply to that valve. The above predetermined time is set considering the time required for the return spring to fully close. A fail-safe method for an exhaust gas recirculation device of an internal combustion engine according to claim 5.

7. When an abnormality is diagnosed during the initial diagnosis, the exhaust recirculation control valve is commanded to the fully closed position to be completely closed. The above predetermined time is set taking into consideration the time required for the control of the exhaust gas return control valve. A fail-safe method for an exhaust gas recirculation device of an internal combustion engine according to claim 5.

8. Perform a fault diagnosis on the sensor that detects the actual opening degree mentioned above. The above secondary diagnosis is performed on the condition that there is no abnormality in the sensor. A fail-safe method for an exhaust gas recirculation device of an internal combustion engine according to claim 1.

9. Perform a fault diagnosis on the sensor that detects the actual opening degree mentioned above. If the sensor is found to be abnormal, the secondary diagnosis will not be performed, and the output of the internal combustion engine will not be limited, as determined by the primary diagnosis. A fail-safe method for an exhaust gas recirculation device of an internal combustion engine according to claim 1.

10. Perform a fault diagnosis on the sensor that detects the actual opening degree mentioned above. If an abnormality is detected in the sensor, the output of the internal combustion engine will be limited without performing the secondary diagnosis, as determined by the primary diagnosis. A fail-safe method for an exhaust gas recirculation device of an internal combustion engine according to claim 1.

11. Internal combustion engines and This internal combustion engine has an exhaust gas recirculation device that recirculates exhaust gas from the exhaust system to the intake system via an exhaust gas recirculation control valve, A sensor for detecting the actual opening degree of the exhaust gas return control valve, Controller and Equipped with, The above controller is A primary diagnostic unit that diagnoses whether the exhaust gas return control valve is operating in accordance with the command, When the primary diagnostic unit diagnoses an abnormality, the exhaust gas return control valve is fully closed for secondary diagnosis, and the secondary diagnostic unit diagnoses whether the actual opening degree is in the fully closed position while the valve is fully closed. A fail-safe command unit that limits the output of the internal combustion engine if the actual opening is not in the fully closed position, and does not limit the output of the internal combustion engine if the actual opening is in the fully closed position. Having, A fail-safe device for the exhaust gas recirculation system of an internal combustion engine.