EGR system

Abstract

To diagnose the presence or absence of at least one abnormality of a bypass valve and a temperature switch at a low cost by employing one temperature switch.SOLUTION: An EGR system comprises: an EGR passage 12 for making an EGR gas flow; an EGR valve 14 for adjusting a flow rate of the EGR gas; an EGR cooler 13 for cooling the EGR gas; a bypass passage 16 bypassing the EGR cooler 13; a bypass valve 17 for opening and closing the bypass passage 16; a temperature SW 78 arranged at a downstream side rather than a merging part 20 of the EGR gas flowing out of the EGR cooler 13 and the EGR gas flowing out of the bypass passage 16; and an electronic control device (ECU) 80. When an engine 1 is brought into a prescribed operation state, and the EGR valve 14 for making the EGR gas flow to the EGR passage 12 is brought into a valve-opened state, the ECU 80 diagnoses at least one abnormality of the bypass valve 17 and the temperature SW 78 on the basis of the presence or absence of at least an output of an on-signal of the temperature SW 78.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to an EGR system configured to return a portion of the exhaust gas discharged from the engine into the exhaust passage to the intake passage via the EGR passage as EGR gas, and more particularly to an EGR system configured to diagnose abnormalities in the system. [Background technology]

[0002] A known example of this type of technology is an "exhaust gas recirculation device" described in Patent Document 1 (Japanese Patent Laid-Open No. 2003-121094). This device includes an exhaust gas recirculation (EGR) passageway (EGR passageway) connecting the engine's exhaust passageway and intake passageway. The device also includes an EGR control valve (EGR valve) for controlling the EGR flow rate and an EGR cooler for cooling the EGR gas. The device also includes a bypass passageway that bypasses the EGR cooler and a switching control valve (bypass valve) for controlling the flow of EGR gas into the bypass passageway. The device also includes a temperature detection means (temperature sensor) located downstream of the bypass valve, a switching control valve operating means (ECU) for switching the bypass valve at predetermined times, and a diagnostic means (ECU) for diagnosing a cooling abnormality in the EGR cooler. The ECU, which is the diagnostic means, diagnoses a cooling abnormality in the EGR cooler based on the temperature difference between the temperature detected by the temperature sensor before the bypass valve is switched and the temperature detected by the temperature sensor after the bypass valve is switched. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-106633 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the device described in Patent Document 1, the temperature sensor is configured to detect the temperature of the EGR gas flowing through the EGR passage and output a detection signal corresponding to that temperature, which is itself costly. It is also possible to use a temperature switch, which is less expensive than a temperature sensor and outputs a detection signal when it detects only one predetermined temperature or a narrow predetermined range. However, in the above device, in order to diagnose an abnormality in the EGR cooler, two different reference temperatures must be set to determine whether the bypass valve is open or closed. Therefore, even if a temperature switch is used, two reference set temperatures must be detected, which requires two temperature switches, thereby eliminating the benefit of low cost.

[0005] This disclosed technology has been made in consideration of the above circumstances, and its purpose is to provide an EGR system that employs a single temperature switch configured to output a detection signal when only one specified set temperature or a specified narrow range of set temperatures is detected, thereby making it possible to diagnose whether or not there is an abnormality in at least one of the bypass valve and the temperature switch at a lower cost than using a temperature sensor. [Means for solving the problem]

[0006] In order to achieve the above object, the technology described in claim 1 provides an EGR system including an EGR passage for causing a portion of exhaust gas discharged from an engine into an exhaust passage to flow into an intake passage as EGR gas, an EGR valve for adjusting the flow rate of the EGR gas flowing through the EGR passage, an EGR cooler for cooling the EGR gas flowing through the EGR passage, a bypass passage for diverting the EGR gas flowing to the EGR cooler in the EGR passage, and a bypass valve for opening and closing the bypass passage, the EGR system including a temperature switch provided in the EGR passage downstream of a junction of the EGR gas flowing out from the EGR cooler and the EGR gas flowing out from the bypass passage, the temperature switch outputting a detection signal when only one predetermined set temperature or a predetermined narrow range of set temperatures is detected, and when the engine is in a predetermined operating state and the EGR valve is opened to allow the EGR gas to flow into the EGR passage, , differentAn abnormality diagnosis means for diagnosing the presence or absence of abnormalities; The set temperature of the temperature switch is set to a temperature higher than the maximum temperature of the confluence part when the bypass valve is controlled to be closed, and when the flow rate of the EGR gas flowing through the EGR passage is between a predetermined first flow rate value and a predetermined second flow rate value larger than the first flow rate value, if a detection signal from the temperature switch is output, the abnormality diagnosis means diagnoses that the bypass valve is open and abnormal or that the temperature switch is abnormal. The purpose of this is to

[0007] According to the configuration of the above technology, when the engine is in a predetermined operating state and the EGR valve is open to allow EGR gas to flow through the EGR passage, the abnormality diagnosis means diagnoses whether or not there is an abnormality in at least one of the bypass valve and the temperature switch based on whether or not there is an output of a detection signal from at least the temperature switch. Here, the temperature switch is provided downstream of the confluence of the EGR gas flowing out from the EGR cooler and the EGR gas flowing out from the bypass passage, and outputs a detection signal when it detects only one predetermined set temperature or a predetermined narrow range of set temperatures, which is less expensive than a temperature sensor that can detect multiple predetermined temperatures or a predetermined wide range of temperatures. Furthermore, by setting the temperature switch to a temperature higher than the maximum temperature of the junction when the bypass valve is controlled to be closed, the temperature switch can be set to the temperature of the junction when the bypass valve is controlled to be open, thereby reducing the frequency of the temperature switch activation. Furthermore, specifically, when the bypass valve is controlled to be closed and the flow rate of EGR gas flowing through the EGR passage is between a predetermined first flow rate value and a predetermined second flow rate value larger than the first flow rate value, the abnormality diagnosis means diagnoses that the bypass valve is in an open state and that the temperature switch is abnormal if a detection signal from the temperature switch is output. Here, when the bypass valve is controlled to be closed and the flow rate of EGR gas flowing through the EGR passage is between the first flow rate value and the second flow rate value, this is assumed to be when high-temperature EGR gas does not flow through the bypass passage and the temperature of EGR gas downstream of the junction does not reach the temperature switch's set temperature. Therefore, when a detection signal from the temperature switch is output, it is possible to diagnose that the bypass valve is in an open state despite being controlled to be closed, or that the temperature switch is abnormal.

[0010] In order to achieve the above object, claims 2 The technology described in an EGR system including an EGR passage for flowing a portion of exhaust gas discharged from an engine into an exhaust passage into an intake passage as EGR gas, an EGR valve for adjusting the flow rate of the EGR gas flowing through the EGR passage, an EGR cooler for cooling the EGR gas flowing through the EGR passage, a bypass passage for diverting the EGR gas flowing to the EGR cooler in the EGR passage, and a bypass valve for opening and closing the bypass passage; a temperature switch provided in the EGR passage downstream of a junction of the EGR gas flowing out from the EGR cooler and the EGR gas flowing out from the bypass passage, the temperature switch outputting a detection signal when only one predetermined set temperature or a predetermined narrow range of set temperatures is detected; and abnormality diagnosis means for diagnosing the presence or absence of an abnormality when the engine is in a predetermined operating state and the EGR valve is in an open state to allow the EGR gas to flow into the EGR passage, wherein the set temperature of the temperature switch is set to a temperature higher than the maximum temperature of the junction when the bypass valve is controlled to be closed, The abnormality diagnosis means is intended to diagnose that the bypass valve is in a closed state and that the temperature switch is abnormal when the flow rate of EGR gas flowing through the EGR passage is equal to or greater than a predetermined second flow rate value while the bypass valve is being controlled to be open, and when no detection signal is output from the temperature switch.

[0011] According to the configuration of the above technology, The abnormality diagnosis means diagnoses whether or not at least one of the bypass valve and the temperature switch is abnormal based on whether or not a detection signal from the temperature switch is output when the engine is in a predetermined operating state and the EGR valve is open to allow EGR gas to flow through the EGR passage. The temperature switch is located downstream of the confluence of the EGR gas flowing from the EGR cooler and the EGR gas flowing from the bypass passage, and outputs a detection signal when it detects only one predetermined temperature or a narrow predetermined temperature range. This is less expensive than a temperature sensor that can detect multiple predetermined temperatures or a wide predetermined temperature range. Furthermore, by setting the temperature switch to a temperature higher than the maximum temperature at the confluence when the bypass valve is controlled to be closed, the temperature switch can be set to the temperature at the confluence when the bypass valve is controlled to be open, thereby reducing the frequency of the temperature switch activation. Specifically, when the bypass valve is controlled to be open and the flow rate of EGR gas flowing through the EGR passage is equal to or greater than a second flow rate value, and when no detection signal from the temperature switch is output, the abnormality diagnosis means diagnoses that the bypass valve is in a closed state and that the temperature switch is abnormal. Here, when the bypass valve is controlled to be open and the flow rate of EGR gas flowing through the EGR passage is equal to or greater than the second flow rate value, it is assumed that high-temperature EGR gas flows through the bypass passage and the temperature of the EGR gas downstream of the junction reaches the set temperature of the temperature switch. Therefore, when no detection signal from the temperature switch is output, it is possible to diagnose that the bypass valve is in a closed state despite being controlled to be open and that the temperature switch is abnormal.

[0012] In order to achieve the above object, claims 3 The technology described in an EGR system including an EGR passage for flowing a portion of exhaust gas discharged from an engine into an exhaust passage into an intake passage as EGR gas, an EGR valve for adjusting the flow rate of the EGR gas flowing through the EGR passage, an EGR cooler for cooling the EGR gas flowing through the EGR passage, a bypass passage for diverting the EGR gas flowing to the EGR cooler in the EGR passage, and a bypass valve for opening and closing the bypass passage; a temperature switch provided in the EGR passage downstream of a junction of the EGR gas flowing out from the EGR cooler and the EGR gas flowing out from the bypass passage, the temperature switch outputting a detection signal when only one predetermined set temperature or a predetermined narrow range of set temperatures is detected; and abnormality diagnosis means for diagnosing the presence or absence of an abnormality when the engine is in a predetermined operating state and the EGR valve is in an open state to allow the EGR gas to flow into the EGR passage, wherein the set temperature of the temperature switch is set to a temperature higher than the maximum temperature of the junction when the bypass valve is controlled to be closed, The abnormality diagnosis means is intended to diagnose that the bypass valve and the temperature switch are normal when the bypass valve is controlled to be closed and the flow rate of EGR gas flowing through the EGR passage is equal to or greater than a predetermined first flow rate value, by forcibly controlling the bypass valve to be open, and when the temperature switch switches from a state where no detection signal is output to a state where a detection signal is output.

[0013] According to the configuration of the above technology, The abnormality diagnosis means diagnoses whether or not at least one of the bypass valve and the temperature switch is abnormal based on whether or not a detection signal from the temperature switch is output when the engine is in a predetermined operating state and the EGR valve is open to allow EGR gas to flow through the EGR passage. The temperature switch is located downstream of the confluence of the EGR gas flowing from the EGR cooler and the EGR gas flowing from the bypass passage, and outputs a detection signal when it detects only one predetermined temperature or a narrow predetermined temperature range. This is less expensive than a temperature sensor that can detect multiple predetermined temperatures or a wide predetermined temperature range. Furthermore, by setting the temperature switch to a temperature higher than the maximum temperature at the confluence when the bypass valve is controlled to be closed, the temperature switch can be set to the temperature at the confluence when the bypass valve is controlled to be open, thereby reducing the frequency of the temperature switch activation. Specifically, when the flow rate of EGR gas flowing through the EGR passage is equal to or greater than a predetermined first flow rate value while the bypass valve is closed, the abnormality diagnosis means forcibly opens the bypass valve, diagnosing that the bypass valve and the temperature switch are normal when the temperature switch detects a signal that has been switched from a non-existent state to an active state. The case where the flow rate of EGR gas is equal to or greater than the first flow rate value while the bypass valve is closed assumes that high-temperature EGR gas does not flow through the bypass passage and the temperature of the EGR gas downstream of the junction does not reach the set temperature of the temperature switch. Forcibly opening the bypass valve from this state assumes that high-temperature EGR gas flows through the bypass passage and the temperature of the EGR gas downstream of the junction reaches the set temperature of the temperature switch. Therefore, when the temperature switch detects a signal that has been switched from a non-existent state to an active state by forcibly opening the bypass valve, it is possible to diagnose that the bypass valve is normally opened and that the temperature switch is normally operated. [Effects of the Invention]

[0018] Claims 1, 2, 3 According to the technology described in the above, by employing a single temperature switch configured to output a detection signal when only one predetermined set temperature is detected, it is possible to diagnose whether or not there is an abnormality in at least one of the bypass valve and the temperature switch at a lower cost than by employing a temperature sensor. Furthermore, according to the techniques described in claims 1, 2 and 3, the reliability of the temperature switch can be ensured by the reduced frequency of operation of the temperature switch.

[0019] In particular, according to the technology described in claim 1, More specifically, the bypass valve can be diagnosed as having an opening abnormality or a temperature switch abnormality. Furthermore, according to the technology described in claim 2, it is possible to diagnose that the bypass valve, more specifically, is abnormally closed, or that the temperature switch is abnormal. Furthermore, according to the technology described in claim 3, it is possible to simultaneously diagnose that both the bypass valve and the temperature switch are normal. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 is a schematic configuration diagram showing an engine system according to a first embodiment. [Figure 2] 4 is a flowchart showing the contents of abnormality diagnosis control for a bypass valve, etc. according to the first embodiment. [Figure 3] 4 is a flowchart showing the contents of abnormality diagnosis control for a bypass valve, etc. according to the first embodiment. [Figure 4] 4 is a flowchart showing the contents of abnormality diagnosis control for a bypass valve, etc. according to the first embodiment. [Figure 5] 4 is a flowchart showing the contents of abnormality diagnosis control for a bypass valve, etc. according to the first embodiment. [Figure 6] 5 is a time chart showing the behavior of various parameters under abnormality diagnosis control for the bypass valve, etc., in a case where both the bypass valve and the temperature SW are determined to be normal, according to the first embodiment. [Figure 7] 5 is a time chart showing the behavior of various parameters under abnormality diagnosis control for the bypass valve, etc., in the first embodiment, in which the bypass valve is determined to be abnormally open and the temperature SW is determined to be normal. [Figure 8] 5 is a time chart showing the behavior of various parameters under abnormality diagnosis control for the bypass valve, etc., in the first embodiment, in which the bypass valve is determined to be abnormally closed and the temperature SW is determined to be normal. [Figure 9] 5 is a time chart showing the behavior of various parameters under abnormality diagnosis control for the bypass valve, etc., in the first embodiment, when the bypass valve is determined to have a possible valve closing abnormality and the temperature SW is determined to be abnormal. [Figure 10] 10 is a flowchart showing the contents of abnormality diagnosis control for a bypass valve, etc. according to a second embodiment. [Figure 11] 10 is a flowchart showing the contents of abnormality diagnosis control for a bypass valve, etc. according to a second embodiment. [Figure 12]10 is a flowchart showing the contents of abnormality diagnosis control for a bypass valve, etc. according to a second embodiment. [Figure 13] 10 is a time chart showing the behavior of various parameters under abnormality diagnosis control for the bypass valve, etc., in a case where both the bypass valve and the temperature SW are determined to be normal, according to the second embodiment. [Figure 14] 10 is a time chart showing the behavior of various parameters under abnormality diagnosis control for the bypass valve, etc., in a case where the bypass valve is determined to be abnormally open and the temperature SW is determined to be normal, according to the second embodiment. [Figure 15] 10 is a time chart showing the behavior of various parameters due to abnormality diagnosis control of the bypass valve, etc., in the second embodiment, in which the bypass valve and temperature SW are both determined to be normal when the bypass valve is forcibly opened in a high water temperature range. [Figure 16] FIG. 10 is a time chart showing the behavior of various parameters due to abnormality diagnosis control of the bypass valve, etc., in the second embodiment, in which the bypass valve is determined to be abnormally closed and the temperature SW is determined to be abnormal when the bypass valve is forcibly opened in a high water temperature range. [Figure 17] 10 is a flowchart showing the contents of abnormality diagnosis control for a bypass valve, etc. according to a third embodiment. [Figure 18] 10 is a flowchart showing the contents of abnormality diagnosis control for a bypass valve, etc. according to a third embodiment. [Figure 19] 10 is a flowchart showing the contents of abnormality diagnosis control for a bypass valve, etc. according to a third embodiment. [Figure 20] 10 is a time chart showing the behavior of various parameters under abnormality diagnosis control for the bypass valve, etc., in a case where both the bypass valve and the temperature SW are determined to be normal, according to the third embodiment. [Figure 21] 10 is a time chart showing the behavior of various parameters under abnormality diagnosis control for the bypass valve, etc., in a case where the bypass valve is determined to be abnormally open and the temperature SW is determined to be normal, etc., according to the third embodiment. [Figure 22] 10 is a time chart showing the behavior of various parameters under abnormality diagnosis control for the bypass valve, etc., in the third embodiment, in which the bypass valve is determined to be abnormally closed or the temperature SW is determined to be abnormal. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, several embodiments in which the EGR system is embodied in a gasoline engine system will be described.

[0026] First Embodiment First, the first embodiment will be described in detail with reference to the drawings.

[0027] [About the engine system] FIG. 1 is a schematic diagram showing a gasoline engine system (hereinafter simply referred to as "engine system") according to this embodiment. The engine system mounted on an automobile includes an engine 1 having multiple cylinders. The engine 1 is a four-cylinder, four-stroke reciprocating engine, and includes well-known components such as pistons and a crankshaft. The engine 1 is provided with an intake passage 2 for introducing intake air into each cylinder, and an exhaust passage 3 for discharging exhaust gas from each cylinder of the engine 1. An air cleaner 9, a throttle device 4, and an intake manifold 5 are provided in the intake passage 2, arranged in this order from the upstream side. In addition, the engine system is provided with a high-pressure loop type exhaust gas recirculation device (EGR device) 11.

[0028] The throttle device 4 is disposed in the intake passage 2 upstream of the intake manifold 5, and adjusts the amount of intake air flowing through the intake passage 2 by driving a butterfly-type throttle valve 4a to open and close to a variable degree in response to accelerator operation by the driver. The intake manifold 5 is primarily made of a resin material and is disposed in the intake passage 2 immediately upstream of the engine 1. It includes a surge tank 5a into which intake air is introduced, and multiple (four) branch pipes 5b branching off from the surge tank 5a to distribute the intake air introduced into the surge tank 5a to each cylinder of the engine 1. An exhaust manifold 6 and a catalyst 7 are provided in the exhaust passage 3, in this order from the upstream side. The catalyst 7 may contain, for example, a three-way catalyst to purify the exhaust gas.

[0029] The engine 1 is provided with a fuel injection device (not shown) for injecting fuel into each cylinder. The fuel injection device is configured to inject fuel supplied from a fuel supply device (not shown) into each cylinder of the engine 1. In each cylinder, a combustible mixture is formed by the fuel injected from the fuel injection device and the intake air introduced from the intake manifold 5.

[0030] The engine 1 is provided with an ignition device (not shown) corresponding to each cylinder. The ignition device is configured to ignite a combustible air-fuel mixture in each cylinder. The combustible air-fuel mixture in each cylinder explodes and burns when ignited by the ignition device, and the exhaust gas after combustion is discharged from each cylinder to the outside via an exhaust manifold 6 and a catalyst 7. At this time, the pistons (not shown) in each cylinder move up and down, causing the crankshaft (not shown) to rotate, thereby generating power for the engine 1.

[0031] [About the EGR system] The EGR system of this embodiment includes a high-pressure loop type EGR device 11. The EGR device 11 includes an exhaust gas recirculation passage (EGR passage) 12 for causing a portion of the exhaust gas discharged from each cylinder of the engine 1 into the exhaust passage 3 to flow into the intake passage 2 as exhaust gas recirculation gas (EGR gas), an exhaust gas recirculation cooler (EGR cooler) 13 for cooling the EGR gas flowing through the EGR passage 12, an exhaust gas recirculation valve (EGR valve) 14 provided downstream of the EGR cooler 13 for adjusting the flow rate of the EGR gas flowing through the EGR passage 12, and a plastic exhaust gas recirculation gas distributor (EGR gas distributor) 15 for distributing the EGR gas flowing through the EGR passage 12 to each branch pipe 5b of the intake manifold 5 in order to distribute the EGR gas flowing through the EGR passage 12 to each cylinder of the engine 1. The EGR gas distributor 15 is provided in the EGR passage 12 downstream of the EGR cooler 13 and the EGR valve 14. The EGR passage 12 includes an inlet 12a and an outlet 12b. An inlet 12a of the EGR passage 12 is connected to the exhaust passage 3 downstream of the catalyst 7, and an outlet 12b of the passage 12 is connected to an EGR gas distributor 15. In this embodiment, the EGR gas distributor 15 constitutes the final stage of the EGR passage 12. In the EGR passage 12, an EGR valve 14 is provided downstream of the EGR cooler 13 and adjacent to the EGR cooler 13. The EGR valve 14 is configured to drive a valve body using a step motor as a drive source. Engine cooling water flows through the EGR cooler 13. The EGR cooler 13 is configured to exchange heat between the EGR gas and the engine cooling water in order to cool the EGR gas flowing through the EGR passage 12. Here, detailed descriptions of the EGR valve 14 and the EGR cooler 13 will be omitted.

[0032] In this EGR device 11, when the EGR valve 14 opens, a portion of the exhaust gas flowing through the exhaust passage 3 flows through the EGR passage 12 as EGR gas, and is distributed to each branch pipe 5b of the intake manifold 5 via the EGR cooler 13, the EGR valve 14, and the EGR gas distributor 15, and is further distributed and recirculated to each cylinder of the engine 1.

[0033] In this embodiment, the EGR cooler 13 is provided with a bypass passage 16. The bypass passage 16 is a passage in the EGR passage 12 for diverting a portion of the EGR gas flowing to the EGR cooler 13. The bypass passage 16 is provided with a bypass valve 17 for opening and closing the bypass passage 16.

[0034] The EGR gas distributor 15 is mainly made of a resin material, has a horizontally elongated shape as a whole, and is disposed so as to cross the multiple branch pipes 5b of the intake manifold 5 in its longitudinal direction (left-right direction in Fig. 1) as shown in Fig. 1. In this embodiment, the EGR gas distributor 15 includes one gas chamber 15a in which EGR gas introduced from the outlet 12b of the EGR passage 12 collects, and multiple (four) gas distribution passages 15b branching from the gas chamber 15a and distributing the EGR gas from the gas chamber 15a to each branch pipe 5b.

[0035] [About bypass valves] In this embodiment, the bypass valve 17 is attached to the housing of the EGR cooler 13 and is configured to open and close the bypass passage 16 that is integrated with the housing. In this embodiment, the bypass valve 17 is configured to open and close a valve body using a step motor as a drive source. Here, a detailed description of the configuration of the bypass valve 17 will be omitted.

[0036] In this embodiment, the bypass valve 17 is controlled to be open at low temperatures to open the bypass passage 16, and is controlled to be closed at high temperatures to shut off the bypass passage 16. That is, in this embodiment, when the temperature of the cooling water of the engine 1 is low, the bypass valve 17 is controlled to be open, so that part of the EGR gas flowing from the exhaust passage 3 to the EGR passage 12 flows into the bypass passage 16, and the remaining EGR gas flows into the EGR cooler 13, and these EGR gases are joined at a joining point 20 in the EGR passage 12 downstream of the EGR cooler 13. The EGR gas joined at the joining point 20 further flows to the EGR gas distributor 15 and is distributed to each cylinder of the engine 1 via the intake manifold 5. On the other hand, when the temperature of the cooling water is high, the bypass valve 17 is controlled to close, and all of the EGR gas flowing from the exhaust passage 3 to the EGR passage 12 flows to the EGR cooler 13 to be cooled, and then flows further to the EGR valve 14 and the EGR gas distributor 15, and is distributed and recirculated to each cylinder of the engine 1 via the intake manifold 5.

[0037] [Electrical configuration of the engine system] Next, an example of the electrical configuration of an engine system will be described. In FIG. 1, various sensors 69-79 provided in this engine system constitute an operating condition detection means for detecting the operating conditions of the automobile and engine 1. A vehicle speed sensor 69 provided in the automobile detects the automobile speed SPD and outputs an electrical signal corresponding to the detected value. An ignition switch (IG switch) 70 provided in the driver's seat is turned on or off by the driver to start or stop the engine 1, and outputs an electrical signal corresponding to the operation. A water temperature sensor 71 provided in the engine 1 detects the temperature (coolant temperature) THW of the coolant flowing inside the engine 1 and outputs an electrical signal corresponding to the detected value. A rotation speed sensor 72 provided in the engine 1 detects the rotation angle (crank angle) of the crankshaft of the engine 1, detects changes in the crank angle (crank angular velocity) as the rotation speed (engine rotation speed) NE of the engine 1, and outputs an electrical signal corresponding to the detected value. An air flow meter 73 provided near the air cleaner 9 detects the amount of intake air Ga flowing through the air cleaner 9 and outputs an electrical signal corresponding to the detected value. An intake pressure sensor 74 provided in the surge tank 5a detects the intake pressure PM in the intake passage 2 (surge tank 5a) downstream of the throttle device 4 and outputs an electrical signal corresponding to the detected value. A throttle sensor 75 provided in the throttle device 4 detects the opening (throttle opening) TA of the throttle valve 4a and outputs an electrical signal corresponding to the detected value. An oxygen sensor 76 provided in the exhaust passage 3 upstream of the catalyst 7 detects the oxygen concentration Ox in the exhaust and outputs an electrical signal corresponding to the detected value. An intake air temperature sensor 77 provided at the inlet of the air cleaner 9 detects the temperature (intake air temperature) THA of the outside air taken into the air cleaner 9 and outputs an electrical signal corresponding to the detected value. A temperature switch (hereinafter referred to as "temperature SW") 78 is provided in the EGR passage 12 downstream of the confluence 20 (the piping upstream of the EGR gas distributor 15), which outputs an "on signal" as a detection signal when only one predetermined set temperature or a predetermined narrow range of set temperatures is detected.The temperature switch 78 is a detection means that outputs an ON signal when it detects only one predetermined set temperature or only a narrow range of predetermined set temperatures, and is therefore less expensive than a temperature sensor configured to detect multiple predetermined set temperatures or a wide range of predetermined set temperatures. In this embodiment, the set temperature of the temperature switch 78 is set to "110°C," and the temperature switch 78 is configured to output an ON signal when it detects "110°C," which is the temperature of the inner wall of the piping of the EGR passage 12. This set temperature of "110°C" is set to a temperature higher than the maximum temperature of the junction 20 when the bypass valve 17 is in a closed state. An accelerator sensor 79 attached to the accelerator pedal 10 at the driver's seat detects the amount of depression of the accelerator pedal 10 by the driver as the accelerator opening ACC and outputs an electrical signal corresponding to the detected value.

[0038] This engine system further includes an electronic control unit (ECU) 80 that controls the system. The ECU 80 is connected to various sensors 69-79. In addition to the EGR valve 14, an injector (not shown) and an ignition coil (not shown) are also connected to the ECU 80. The ECU 80 corresponds to an example of an "abnormality diagnosis means" in the disclosed technology. As is well known, the ECU 80 includes a central processing unit (CPU), various memories, an external input circuit, an external output circuit, and the like. Predetermined control programs relating to various controls are stored in the memory. The CPU is configured to execute fuel injection control, ignition timing control, EGR control, and bypass valve abnormality diagnosis control based on the predetermined control programs, in response to detection signals from the various sensors 69-79 input via the input circuits.

[0039] In this embodiment, the ECU 80 controls the EGR valve 14 (its step motor) in EGR control according to the operating state of the engine 1. Specifically, the ECU 80 controls the EGR valve 14 to be fully closed when the engine 1 is stopped, idling, or decelerating, and calculates a target EGR opening according to the operating state at other times and controls the EGR valve 14 to the target EGR opening. When the EGR valve 14 is opened at this time, exhaust gas is discharged from the engine 1 into the exhaust passage 3, and a portion of the exhaust gas flows as EGR gas through the EGR passage 12, the EGR cooler 13, the EGR valve 14, the EGR gas distributor 15, etc. into the intake passage 2 (intake manifold 5), where it is distributed and recirculated to each cylinder of the engine 1. In this embodiment, when the engine 1 is started, the ECU 80 opens the EGR valve 14 and starts EGR when the coolant temperature THW detected by the water temperature sensor 71 becomes "40°C" or higher and the EGR operation conditions are met.

[0040] [About abnormality diagnosis control of bypass valves, etc.] In this embodiment, in order to diagnose abnormalities in the bypass valve 17 and the temperature SW 78 depending on the EGR operation state when the engine 1 is started and after the engine is started, the following abnormality diagnosis control for the bypass valve, etc. is executed.

[0041] 2 to 5 are flowcharts showing the contents of the bypass valve abnormality diagnosis control of this embodiment. In this bypass valve abnormality diagnosis control, in order to diagnose abnormalities in the bypass valve 17 and the temperature SW 78, one temperature SW 78 is employed that is configured to detect a set temperature (110°C) within a temperature range (for example, "120°C or less") when the bypass valve 17 is closed, and to output an ON signal as a detection signal.

[0042] When the process proceeds to this routine, the ECU 80 determines whether the IG is on, i.e., whether the IG switch 70 has been turned on, in step 100. If the result of this determination is positive, the ECU 80 proceeds to step 110, and if the result of this determination is negative, the ECU 80 proceeds to step 320.

[0043] In step 110, the ECU 80 determines whether the temperature SW state flag XigonTSoff at the start of the engine is "0." When this flag XigonTSoff is "0," it indicates that the initial state has not been confirmed, and when it is "1," it indicates that the initial state has been confirmed. If the result of this determination is positive, the ECU 80 proceeds to step 120, and if the result of this determination is negative, the ECU 80 jumps to step 150.

[0044] In step 120, the ECU 80 acquires the engine speed NE, engine load KL, and coolant temperature THW based on the detected values ​​of the water temperature sensor 71, the rotation speed sensor 72, and the throttle sensor 75, and also acquires the flow rate (EGR flow rate) GF of EGR gas flowing through the EGR passage 12. For example, by referring to a predetermined EGR flow rate map, the ECU 80 can determine the EGR flow rate GF according to the control command value (opening degree of the EGR valve 14) for the step motor of the EGR valve 14 and the intake air amount Ga or intake pressure PM detected at that time. In addition, the ECU 80 acquires the state (on state or off state) of the temperature SW 78.

[0045] Next, in step 130, the ECU 80 determines whether the temperature switch 78 is off. If the result of this determination is positive, the ECU 80 proceeds to step 140, and if the result of this determination is negative, the ECU 80 proceeds to step 240.

[0046] In step 140, the ECU 80 sets the temperature sensor state flag XigonTSoff at the beginning of startup to "1."

[0047] Moving on from step 110 or step 140, in step 150, the ECU 80 determines the opening and closing of the bypass valve 17 according to the coolant temperature THW, and the abnormality judgment EGR flow rate value FJGF (first flow rate value A1 and second flow rate value B1 (>A1)) of the temperature SW78.

[0048] Next, in step 160, the ECU 80 determines whether the coolant temperature THW is equal to or higher than 40° C. If the result of this determination is positive, the ECU 80 determines that EGR has started and proceeds to step 170. If the result of this determination is negative, the ECU 80 determines that EGR has not started and proceeds to step 290.

[0049] In step 170, the ECU 80 determines that EGR at low temperature is to be started and controls the bypass valve 17 to open.

[0050] Next, in step 180, the ECU 80 determines whether the coolant temperature THW is less than 80° C. If the result of this determination is positive, the ECU 80 proceeds to step 190, and if the result of this determination is negative, the ECU 80 proceeds to step 420.

[0051] In step 190, the ECU 80 determines whether the temperature SW abnormality determination flag XTSng is "0." When this flag XTSng is "0," it indicates that the temperature SW 78 has not yet been determined to be abnormal, and when it is "1," it indicates that the temperature SW 78 has already been determined to be abnormal. If the result of this determination is positive, the ECU 80 proceeds to step 200, and if the result of this determination is negative, the ECU 80 returns to step 100.

[0052] In step 200, the ECU 80 determines whether the EGR flow rate GF is equal to or greater than a predetermined first flow rate value A1. If the result of this determination is positive, the ECU 80 proceeds to step 210, and if the result of this determination is negative, the ECU 80 returns to step 100.

[0053] In step 210, the ECU 80 determines whether the temperature switch 78 is on. If the result of this determination is positive, the ECU 80 proceeds to step 220, and if the result of this determination is negative, the ECU 80 proceeds to step 300.

[0054] In step 220, the ECU 80 determines that the temperature SW 78 is normal, and sets the temperature SW normality determination flag XTSok to 1. When this flag XTSok is 0, it indicates that the normality of the temperature SW 78 has not been determined, and when it is 1, it indicates that the normality of the temperature SW 78 has been determined.

[0055] Next, in step 230, the ECU 80 determines that the bypass valve 17 is open, and sets a bypass valve open determination flag XBOP to "1." When this flag XBOP is "0," it indicates that it has not yet been determined whether the bypass valve 17 is open, and when it is "1," it indicates that it has already been determined that the bypass valve 17 is open. The ECU 80 then returns the process to step 100.

[0056] On the other hand, in step 240 after step 130, the ECU 80 determines whether the coolant temperature THW is equal to or higher than 40° C. If the result of this determination is positive, the ECU 80 proceeds to step 250, and if the result of this determination is negative, the ECU 80 proceeds to step 260.

[0057] In step 250, the ECU 80 determines whether or not an EGR cut time f1, which indicates the duration of EGR cut, has elapsed. If the result of this determination is positive, the ECU 80 proceeds to step 260, and if the result of this determination is negative, the ECU 80 returns to step 100. The EGR cut time f1 corresponds to an example of the "predetermined time" in the disclosed technology.

[0058] In step 260, which follows step 240 or step 250, the ECU 80 determines whether the temperature switch 78 is on. If the result of this determination is positive, the ECU 80 proceeds to step 270, and if the result of this determination is negative, the ECU 80 proceeds to step 280.

[0059] In step 270, the ECU 80 determines that the temperature switch 78 is abnormal, sets the temperature switch abnormality determination flag XTSng to "1", and then ends the abnormality detection.

[0060] On the other hand, in step 280, the ECU 80 determines that the temperature switch 78 is normal, sets the temperature switch normality determination flag XTSok to “1”, and proceeds to step 140.

[0061] On the other hand, in step 290 following step 160, the ECU 80 controls the bypass valve 17 to close, and returns the process to step 100.

[0062] On the other hand, in step 300 after step 210, the ECU 80 determines whether or not a first predetermined time a1 serving as a reference has elapsed. If the result of this determination is positive, the ECU 80 proceeds to step 310, and if the result of this determination is negative, the ECU 80 returns to step 210.

[0063] In step 310, the ECU 80 determines that the temperature SW 78 is temporarily abnormal and sets the temperature SW temporary abnormality flag XTSTng to "1." Also, the ECU 80 determines that the bypass valve 17 is temporarily abnormal in the closed state (closed valve temporary abnormality), sets the bypass valve closed valve temporary abnormality flag XBCSTng to "1," and returns the process to step 100. The temperature SW temporary abnormality flag XTSTng indicates that the temperature SW 78 is temporarily not abnormal when it is "0," and indicates that the temperature SW 78 is temporarily abnormal when it is "1." Furthermore, the bypass valve closed valve temporary abnormality flag XBCSTng indicates that the bypass valve 17 is temporarily not abnormal when it is "0," and indicates that the bypass valve 17 is temporarily abnormal when it is "1." In step 310, the ECU 80 cannot determine which of the bypass valve 17 and the temperature SW 78 is abnormal, but determines that one of them is abnormal and therefore temporarily abnormal.

[0064] On the other hand, in step 320 following step 100, the ECU 80 sets the temperature SW state flag XigonTSoff at the beginning of startup to "0".

[0065] Next, in step 330, the ECU 80 sets the temperature SW temporary abnormality flag XTSTng to "0."

[0066] Next, in step 340, the ECU 80 sets the temperature SW abnormality determination flag XTSng to "0."

[0067] Next, in step 350, the ECU 80 sets the temperature SW normality determination flag XTSok to "0."

[0068] Next, in step 360, the ECU 80 sets the bypass valve closed temporary abnormality flag XBCSTng to "0."

[0069] Next, in step 370, the ECU 80 sets the bypass valve closing abnormality flag XBCSng to "0." The bypass valve closing abnormality flag XBCSng indicates that the bypass valve 17 is in a closed state and not abnormal when it is "0," and indicates that the bypass valve 17 is in a closed state and abnormal (valve closing abnormality) when it is "1."

[0070] Next, in step 380, the ECU 80 sets the bypass valve opening abnormality flag XBOPng to "0." When the bypass valve opening abnormality flag XBOPng is "0," it indicates that the bypass valve 17 is in an open state and not abnormal, and when the flag is "1," it indicates that the bypass valve 17 is in an open state and abnormal (valve opening abnormality).

[0071] Next, in step 390, the ECU 80 sets the bypass valve close determination flag XBCS to "0." When the bypass valve close determination flag XBCS is "0," it indicates that it has not yet been determined whether the bypass valve 17 is closed, and when the flag is "1," it indicates that it has been determined that the bypass valve 17 is closed.

[0072] Next, in step 400, the ECU 80 sets the bypass valve open determination flag XBOP to "0".

[0073] Next, in step 410, the ECU 80 sets the bypass valve normality determination flag XBok to "0." When the bypass valve normality determination flag XBok is "0," it indicates that the normality of the bypass valve 17 has not yet been determined, and when the flag is "1," it indicates that the normality of the bypass valve 17 has already been determined. Thereafter, the ECU 80 ends the processing.

[0074] On the other hand, moving from step 180 to step 420, the ECU 80 controls the bypass valve 17 to close it.

[0075] Next, in step 430, the ECU 80 waits for the passage of a fourth predetermined time c1, which serves as a reference, and then proceeds to step 440.

[0076] In step 440, the ECU 80 determines whether the bypass valve open determination flag XBOP is 1. If the result of this determination is positive, the ECU 80 proceeds to step 450, and if the result of this determination is negative, the ECU 80 proceeds to step 510.

[0077] In step 450, the ECU 80 determines whether the EGR flow rate GF is less than a predetermined second flow rate value B1. If the result of this determination is positive, the ECU 80 proceeds to step 460, and if the result of this determination is negative, the ECU 80 returns to step 100.

[0078] In step 460, the ECU 80 determines whether the temperature switch 78 is off. If the result of this determination is positive, the ECU 80 proceeds to step 470, and if the result of this determination is negative, the ECU 80 proceeds to step 490.

[0079] In step 470, the ECU 80 determines that the bypass valve 17 is closed, and sets the bypass valve closed determination flag XBCS to "1."

[0080] Next, in step 480, the ECU 80 determines that the bypass valve 17 is normal, sets the bypass valve normality determination flag XBok to "1", and ends the abnormality detection.

[0081] On the other hand, in step 490, which follows step 460, the ECU 80 determines whether a second predetermined time b1 (>a1) serving as a reference has elapsed. If the result of this determination is positive, the ECU 80 proceeds to step 500, and if the result of this determination is negative, the ECU 80 returns to step 460.

[0082] In step 500, the ECU 80 determines that the bypass valve 17 has an opening abnormality, sets the bypass valve opening abnormality flag XBOPng to "1", and ends the abnormality detection.

[0083] On the other hand, in step 510 after step 440, the ECU 80 determines whether the EGR flow rate GF is equal to or greater than the second flow rate value B1. If the result of this determination is positive, the ECU 80 proceeds to step 520, and if the result of this determination is negative, the ECU 80 proceeds to step 570.

[0084] In step 520, the ECU 80 determines whether the temperature switch 78 is on. If the result of this determination is positive, the ECU 80 proceeds to step 530, and if the result of this determination is negative, the ECU 80 proceeds to step 550.

[0085] Next, in step 530, the ECU 80 determines that the temperature switch 78 is normal, and sets the temperature switch normality determination flag XTSok to "1."

[0086] Next, in step 540, the ECU 80 determines that the bypass valve 17 is abnormally closed, and sets the bypass valve abnormally closed flag XBCSng to 1. Thereafter, the ECU 80 ends the abnormality detection.

[0087] On the other hand, in step 550, which follows step 520, the ECU 80 determines whether a third predetermined time b2 (>b1) has elapsed. If the result of this determination is positive, the ECU 80 proceeds to step 560, and if the result of this determination is negative, the ECU 80 returns to step 520.

[0088] In step 560, the ECU 80 determines that the temperature switch 78 is abnormal and sets the temperature switch abnormality determination flag XTSng to 1, and also determines that the bypass valve 17 is abnormally closed and sets the bypass valve abnormality closing flag XBCSng to 1. After that, the ECU 80 ends the abnormality detection.

[0089] On the other hand, in step 570, which follows step 510, the ECU 80 determines whether the EGR flow rate GF is equal to or greater than the first flow rate value A1. If the result of this determination is positive, the ECU 80 proceeds to step 580, and if the result of this determination is negative, the ECU 80 returns to step 100.

[0090] In step 580, the ECU 80 performs a forced valve opening control on the bypass valve 17 (forced valve opening control).

[0091] Next, in step 590, the ECU 80 determines whether the temperature switch 78 is on. If the result of this determination is positive, the ECU 80 proceeds to step 600, and if the result of this determination is negative, the ECU 80 proceeds to step 690.

[0092] In step 600, the ECU 80 determines that the bypass valve 17 is open, and sets the bypass valve open determination flag XBOP to "1."

[0093] Next, in step 610, the ECU 80 determines that the temperature switch 78 is normal, and sets the temperature switch normality determination flag XTSok to "1."

[0094] Next, in step 620, the ECU 80 performs a control to forcibly close the bypass valve 17 (forced valve closing control).

[0095] Next, in step 630, the ECU 80 waits for the passage of a fourth predetermined time c1, which serves as a reference, and then proceeds to step 640.

[0096] In step 640, the ECU 80 determines whether the EGR flow rate GF is equal to or greater than the first flow rate value A1. If the result of this determination is positive, the ECU 80 proceeds to step 650, and if the result of this determination is negative, the ECU 80 proceeds to step 710.

[0097] In step 650, the ECU 80 waits for the first predetermined time a1 to elapse, and then proceeds to step 660.

[0098] In step 660, the ECU 80 determines whether the temperature switch 78 is on. If the result of this determination is positive, the ECU 80 proceeds to step 670, and if the result of this determination is negative, the ECU 80 proceeds to step 720.

[0099] In step 670, the ECU 80 determines that the bypass valve 17 is abnormally opening, and sets the bypass valve abnormally opening flag XBOPng to "1."

[0100] Next, in step 680, the ECU 80 determines that the temperature switch 78 is in an abnormal state (ON abnormality), sets the temperature switch abnormality determination flag XTSng to "1", and then ends the abnormality detection.

[0101] On the other hand, in step 690, moving from step 590, the ECU 80 determines whether or not the first predetermined time a1 has elapsed. If the result of this determination is positive, the ECU 80 proceeds to step 700, and if the result of this determination is negative, the ECU 80 returns to step 590.

[0102] In step 700, the ECU 80 determines that the temperature switch 78 is abnormal (off abnormality) and sets the temperature switch abnormality determination flag XTSng to 1, and also determines that the bypass valve 17 is closed abnormally and sets the bypass valve closed abnormality flag XBCSng to 1. After that, the ECU 80 ends the abnormality detection.

[0103] On the other hand, in step 710 after step 640, the ECU 80 determines whether the temperature switch 78 is off. If the result of this determination is positive, the ECU 80 proceeds to step 720, and if the result of this determination is negative, the ECU 80 proceeds to step 740.

[0104] In step 720, the ECU 80 determines that the bypass valve 17 is closed, and sets the bypass valve closed determination flag XBCS to "1."

[0105] Next, in step 730, the ECU 80 determines that the bypass valve 17 is normal, and sets the bypass valve normality determination flag XBok to 1. Thereafter, the ECU 80 ends the abnormality detection.

[0106] On the other hand, in step 740 after step 710, the ECU 80 determines whether or not the first predetermined time a1 has elapsed. If the result of this determination is positive, the ECU 80 proceeds to step 750, and if the result of this determination is negative, the ECU 80 returns to step 710.

[0107] In step 750, the ECU 80 determines that the bypass valve 17 is abnormally opening, and sets the bypass valve abnormally opening flag XBOPng to "1."

[0108] Next, in step 760, the ECU 80 determines that the temperature switch 78 is abnormally turned on, sets the temperature switch abnormality determination flag XTSng to "1", and then ends the abnormality detection.

[0109] According to the bypass valve abnormality diagnosis control, when the engine 1 is in a predetermined operating state and the EGR valve 14 is in an open state to allow EGR gas to flow into the EGR passage 12, the ECU 80 diagnoses whether or not there is an abnormality in at least one of the bypass valve 17 and the temperature SW 78 based on whether or not an on signal (detection signal) is output from at least the temperature SW 78.

[0110] Specifically, when the bypass valve 17 is controlled to be closed (step 420), if the EGR flow rate GF flowing through the EGR passage 12 is less than the second flow rate value B1 (the determination in step 450 is YES), and if an ON signal is output from the temperature SW78 (the determination in step 460 is NO), the ECU 80 diagnoses that the bypass valve 17 is in an open state and abnormal (valve opening abnormality) (step 500).

[0111] Specifically, when the bypass valve 17 is controlled to be closed (step 420), if the EGR flow rate GF flowing through the EGR passage 12 is equal to or greater than the first flow rate value A1 (the determination in step 570 is YES), the ECU 80 forcibly controls the bypass valve 17 to be open (step 580), and when an ON signal is output from the temperature SW 78 (the determination in step 590 is YES), the ECU 80 determines (diagnoses) that the bypass valve 17 and the temperature SW 78 are normal (step 610).

[0112] Specifically, after the engine 1 is cold started and before EGR gas starts to flow through the EGR passage 12 or after a predetermined time has passed since EGR gas stopped flowing through the EGR passage 12 (the judgment in step 250 is YES), when an ON signal is output from the temperature SW78 (the judgment in step 260 is YES), the ECU 80 determines (diagnoses) that the temperature SW78 is abnormal (step 270).

[0113] According to the bypass valve abnormality diagnosis control, the ECU 80 detects an opening abnormality and a closing abnormality of the bypass valve 17 as follows. That is, the abnormality detection range is the range in which the EGR flow rate GF is a first flow rate value A1 to a second flow rate value B1. Here, in the low water temperature range of the cooling water temperature THW (for example, 40 to 80°C), if the temperature SW 78 is off in the range in which the EGR flow rate GF is equal to or higher than the first flow rate value A1 (the EGR gas flowing through the confluence portion 20 is "less than 110°C"), the ECU 80 determines that the bypass valve 17 has a closing abnormality. On the other hand, in a high water temperature range of the coolant temperature THW (for example, 80°C or higher + c1 delay), if the temperature SW 78 is turned on (the EGR gas flowing through the confluence 20 is "110°C or higher") in a range where the EGR flow rate GF changes from the first flow rate value A1 to the second flow rate value B1, the ECU 80 determines that the bypass valve 17 is abnormally open. Here, the abnormality detection range (the range of the EGR flow rate GF) can be changed based on the coolant temperature THW. By correcting the coolant temperature THW, abnormality detection can be performed even in a low water temperature range. In addition, after the bypass valve 17 is switched from open to closed, abnormality detection is delayed. Furthermore, if the coolant temperature THW becomes "100°C or higher," the determination of the bypass valve 17's abnormal opening may be stopped.

[0114] According to the bypass valve abnormality diagnosis control, the ECU 80 detects an abnormality in the temperature SW 78 during normal vehicle driving as follows. It is essential that the temperature SW 78 be set to a temperature at which the temperature SW 78 can operate even when the bypass valve 17 is in an abnormally closed state. In this embodiment, when the maximum temperature of the EGR gas flowing out of the EGR cooler 13 is set to 120°C or less, the temperature SW 78 is set to 110°C. After the engine 1 starts in the low water temperature range, if the temperature SW 78 is turned on (the EGR gas flowing through the confluence 20 is 110°C or higher), the ECU 80 determines that the temperature SW 78 is abnormal. Furthermore, after the engine 1 starts in the high water temperature range, if the temperature SW 78 turns on (the EGR gas flowing through the junction 20 becomes "110°C or higher") and continues to be on for the EGR cut time f1 or longer (the EGR gas flowing through the junction 20 continues to be "110°C or higher"), the ECU 80 determines that the temperature SW 78 is abnormal. If the temperature SW 78 switches off (the EGR gas flowing through the junction 20 becomes "less than 110°C"), the ECU 80 determines that the temperature SW 78 is normal. Here, if the temperature SW 78 does not turn on when the EGR flow rate GF becomes equal to or greater than the second flow rate value B1 in the high water temperature range, the ECU 80 determines that the temperature SW 78 is abnormal. If the temperature SW 78 turns on when the EGR flow rate GF is around the second flow rate value B1, the ECU 80 determines that the temperature SW 78 is normal.

[0115] According to the bypass valve abnormality diagnosis control described above, when the detection condition is not satisfied in the low water temperature range, the ECU 80 detects an abnormality under the condition that the EGR gas temperature is "less than 110°C" in the low EGR flow rate range after the engine is fully warmed up and the bypass valve 17 is closed, as follows: That is, when the bypass valve 17 is in the valve closing control condition, the temperature SW 78 is turned off (the EGR gas flowing through the junction 20 is "less than 110°C"), and if the temperature SW 78 is turned on by forcibly controlling the bypass valve 17 to be open (the EGR gas flowing through the junction 20 is "110°C or higher"), the ECU 80 determines that the bypass valve 17 is normal. On the other hand, if the temperature SW 78 remains off even when the bypass valve 17 is forcibly controlled to be open (the EGR gas flowing through the junction 20 remains "less than 110°C"), the ECU 80 determines that the bypass valve 17 has a valve closing abnormality and a temperature SW abnormality. Furthermore, if the bypass valve 17 is forcibly closed and the temperature SW 78 remains on (the EGR gas flowing through the confluence 20 continues to be "110°C or higher"), the ECU 80 determines that the bypass valve 17 is abnormally open.

[0116] [About the behavior of various parameters due to abnormality diagnosis control of bypass valves, etc.] The behavior of various parameters due to the bypass valve and other abnormality diagnosis control is shown in time charts in Figures 6 to 9. Figure 6 shows a case where both the bypass valve 17 and the temperature SW 78 are determined to be normal. In Figure 6, (A) shows changes in the vehicle speed (SPD) and engine speed (NE), (B) shows changes in the EGR flow rate (GF), (C) shows the establishment of conditions for the opening and closing control of the bypass valve 17, (D) shows changes in the abnormality detection allowance flag (XBPGF), (E) shows changes in the on / off state of the temperature SW 78 at 110°C, (F) shows changes in the temperature SW normality determination flag (XTSok) and the temperature SW abnormality determination flag (XTSng), (G) shows changes in the bypass valve open determination flag (XBOP) and the bypass valve closed determination flag (XBCS), (H) shows changes in the bypass valve abnormality closing flag (XBCSng) and the bypass valve abnormality opening flag (XBOPng), (I) shows changes in the bypass valve normality determination flag (XBok), and (J) shows changes in temperatures (coolant temperature (THW) and EGR gas temperature (THG). The abnormality detection tolerance flag XBPGF (D) indicates whether the EGR flow rate GF is in a state that allows for abnormality detection of the bypass valve 17 and temperature SW78, with "1" indicating an allowable state and "0" indicating an unallowable state.

[0117] 6, at time t1, the engine 1 starts to start, and the engine speed NE (A) rises. From time t2, as the engine speed NE (A) begins to increase or decrease, the vehicle speed SPD also increases or decreases accordingly. Then, just before time t3, when the coolant temperature THW (J) exceeds 40°C, EGR is started, the EGR flow rate GF (B) rises, and the open control condition for the bypass valve 17 (C) is satisfied. Thereafter, the EGR flow rate GF (B) increases or decreases in accordance with the increase or decrease in the engine speed NE, but as the coolant temperature THW (J) exceeds 80°C just after time t8, the close control condition for the bypass valve 17 (C) is satisfied. Here, when the EGR gas temperature THG of (J) exceeds "110°C" immediately after time t6, the temperature SW78 of (E) starts to turn on (output an ON signal), and when the EGR gas temperature THG of (J) falls below "110°C" just before time t9, the temperature SW78 of (E) turns off (stops outputting an ON signal). Also, when the EGR gas temperature THG of (J) exceeds "110°C" and falls below "110°C" around time t12, the temperature SW78 of (E) turns on and then off.

[0118] Here, just before time t7, the bypass valve 17 (C) is under valve opening control, the EGR flow rate GF (B) is equal to or greater than the first flow rate value A1, and at time t7 when the first predetermined time a1 has elapsed, the EGR gas temperature THG (J) exceeds 110°C, the temperature SW 78 (E) is on, the EGR flow rate GF is in a state that allows for detection of abnormalities in the bypass valve 17 and the temperature SW 78, and the abnormality detection allowance flag XBPGF (D) becomes "1." At this time, it is determined that the temperature SW 78 is normal, and the temperature SW normality determination flag XTSok (F) becomes "1." Also, at time t7, the bypass valve open determination flag XBOP (G) becomes "1", the bypass valve closed determination flag XBCS becomes "0", and further, the bypass valve closed abnormality flag XBCSng and the bypass valve open abnormality flag XBOPng (H) each become "0", and it is determined that the bypass valve 17 is in an open state and normal.

[0119] Also, just before time t10, the bypass valve 17 (C) is under valve closing control, the EGR flow rate GF (B) is less than the second flow rate value B1, the fourth predetermined time c1 has elapsed during the bypass valve closing control, the abnormality detection allowance flag XBPGF (D) is set to "1", and the temperature SW78 (E) is turned off. At this time, the bypass valve closing determination flag XBCS (G) is set to "1", so it is determined that the bypass valve 17 is normal in the closed state. Since it has already been determined that the bypass valve 17 is normal in the open state at time t7, the bypass valve 17 is normal in both the open state and the closed state, so the bypass valve normality determination flag XBok (I) is set to "1", and it is determined that the bypass valve 17 is normal.

[0120] Figure 7 shows a case where the bypass valve 17 is determined to be abnormally open and the temperature SW 78 is determined to be normal. In Figure 7, parameters (A) to (J) are the same as those in Figure 6. In Figure 7, the behavior of parameters (E), (G), (H), and (J) differs from that in Figure 6.

[0121] Regarding Figure 7, differences from Figure 6 will be mainly described. The normality determination of the temperature SW 78 is the same as in Figure 6. In Figure 7, immediately before time t10, the bypass valve 17 (C) is under valve closing control, the EGR flow rate GF (B) is less than the second flow rate value B1, and when the second predetermined time b1 has elapsed since then, the abnormality detection allowance flag XBPGF (D) becomes "1." Therefore, the EGR gas temperature THG (J) exceeds "110°C" and the temperature SW 78 (E) is turned on. Therefore, the bypass valve closing determination flag XBCS (G) remains "0" and the bypass valve open abnormality flag XBOPng (H) becomes "1," and it is determined that the bypass valve 17 is in an open state and abnormal.

[0122] Figure 8 shows a case where the bypass valve 17 is determined to be abnormally closed and the temperature SW 78 is determined to be normal. In Figure 8, parameters (A) to (J) are the same as those in Figures 6 and 7. In Figure 8, the newly added (K) indicates a change in the temperature SW temporary abnormality flag XTSTng, and (L) indicates a change in the bypass valve temporary abnormality flag XBCSTng. In Figure 8, the behavior of parameters (A) and (B) is particularly different from that in Figures 6 and 7 after time t11, with the values ​​becoming higher.

[0123] 8, immediately before time t7, the bypass valve 17 (C) is under valve open control, the EGR flow rate GF (B) is equal to or greater than the first flow rate value A1 and less than the second flow rate value B1, and at time t7, when a first predetermined time a1 has elapsed, the abnormality detection allowance flag XBPGF (D) becomes "1." At this time, the EGR gas temperature THG (J) is less than "110°C," and the temperature SW 78 (E) is turned off. Therefore, it is determined that the temperature SW 78 is temporarily abnormal, the temperature SW temporary abnormality flag XTSTng (K) becomes "1," the bypass valve 17 is determined to be temporarily abnormal in a closed state, and the bypass valve closed temporary abnormality flag XBCSTng (L) becomes "1."

[0124] On the other hand, at time t12, the bypass valve 17 (C) is under valve closing control, the EGR flow rate GF (B) is equal to or greater than the second flow rate value B1, the EGR gas temperature THG (J) is greater than "110°C", and the temperature SW 78 (E) is on, so the temperature SW normality determination flag XTSok (F) becomes "1", the bypass valve closing abnormality flag XBCSng (H) becomes "1", and the bypass valve normality determination flag XBok (I) remains at "0", and it is determined that the bypass valve 17 is closing abnormally.

[0125] Fig. 9 shows a case where the bypass valve 17 is determined to have a possible valve closing abnormality and the temperature SW 78 is determined to be abnormal. In Fig. 9, the parameters (A) to (L) are the same as those in Fig. 8. In Fig. 9, only the behavior of the parameters (D) to (F) and (H) differs from that in Fig. 8.

[0126] In Figure 9, at time t7, as in Figure 8, the EGR gas temperature THG at (J) is less than "110°C", and the temperature SW78 at (E) is off, so the temperature SW78 is determined to be temporarily abnormal, the temperature SW temporary abnormality flag XTSTng at (K) becomes "1", the bypass valve 17 is determined to be in a closed state and is temporarily abnormal, and the bypass valve closed temporary abnormality flag XBCSTng at (L) becomes "1".

[0127] 9, at time t12, the bypass valve 17 (C) is under valve closing control, the EGR flow rate GF (B) becomes equal to or greater than the second flow rate value B1, and at time t13 when a third predetermined time b2 has elapsed, the EGR gas temperature THG (J) exceeds 110°C, but the temperature SW 78 (E) remains off and the temperature SW abnormality determination flag XTSng (F) becomes 1, so it is determined that the temperature SW 78 is abnormal. Also, at time t13, the bypass valve closing abnormality flag XBCSng (H) becomes 1, the bypass valve closing temporary abnormality flag XBCSTng (L) becomes 1, and the bypass valve normality determination flag XBok (I) remains 0, so it is determined that the bypass valve 17 may be closing abnormally.

[0128] [About the EGR system's function and effects] As described above, according to the configuration of the EGR system in this embodiment, when the bypass valve 17 is normally open, a portion of the EGR gas flowing from the exhaust passage 3 to the EGR passage 12 flows into the bypass passage 16, and the remainder flows into the EGR cooler 13. These two flows merge at the junction 20 and flow into the intake manifold 5 (intake passage 2) via the downstream EGR passage 12 (including the EGR gas distributor 15), and are then recirculated to the engine 1. Therefore, even if high-temperature EGR gas flows from the exhaust passage 3 to the EGR passage 12, a portion of the EGR gas flows through the bypass passage 16, and the remaining EGR gas flows through the EGR cooler 13 and undergoes heat exchange, decreasing its temperature before merging with the EGR gas that flowed through the bypass passage 16 at the junction 20. This reduces the temperature of the EGR gas after the junction 20. Therefore, the EGR gas, whose temperature has been reduced to an appropriate level, flows into the intake manifold 5 via the downstream EGR gas distributor 15 and the like. On the other hand, when the bypass valve 17 is normally closed, almost all of the EGR gas flowing from the exhaust passage 3 to the EGR passage 12 flows through the EGR cooler 13 and undergoes heat exchange, and after being cooled to an appropriate temperature, flows into the intake manifold 5 via the downstream EGR gas distributor 15, etc.

[0129] According to the configuration of this embodiment, when the engine 1 is in a predetermined operating state and the EGR valve 14 is open to allow EGR gas to flow through the EGR passage 12, the ECU 80 diagnoses whether or not at least one of the bypass valve 17 and the temperature SW 78 is abnormal based on whether or not at least the temperature SW 78 outputs an ON signal (detection signal). The temperature SW 78 is located downstream of the confluence 20 of the EGR gas flowing from the EGR cooler 13 and the EGR gas flowing from the bypass passage 16, and outputs an ON signal (detection signal) when it detects only a single predetermined temperature, "110°C." This is less costly than a temperature sensor that can detect multiple predetermined temperatures or a wide range of predetermined temperatures. Therefore, by employing a single temperature SW 78 configured to output an ON signal (detection signal) when it detects only a single predetermined temperature, "110°C," it is possible to diagnose whether or not at least one of the bypass valve 17 and the temperature SW 78 is abnormal at a lower cost than using a temperature sensor.

[0130] According to the configuration of this embodiment, specifically, when the EGR flow rate GF flowing through the EGR passage 12 is less than the second flow rate value B1 while the bypass valve 17 is being controlled to be closed, the ECU 80 diagnoses the bypass valve 17 as being abnormal (valve opening abnormality) in the open state if the temperature switch 78 outputs an ON signal. Here, the case where the EGR flow rate GF flowing through the EGR passage 12 is less than the second flow rate value B1 while the bypass valve 17 is being controlled to be closed is assumed to be a case where high-temperature EGR gas does not flow through the bypass passage 16 and the EGR gas temperature THG downstream of the junction 20 does not reach the set temperature of 110°C of the temperature switch 78. Therefore, the output of the ON signal (detection signal) of the temperature switch 78 makes it possible to diagnose the bypass valve 17 as being abnormal (valve opening abnormality) despite being controlled to be closed. Therefore, the bypass valve 17, more specifically, the bypass valve 17, or more specifically, the temperature switch 78, can be diagnosed as being abnormal.

[0131] According to the configuration of this embodiment, more specifically, when the ECU 80 controls the bypass valve 17 to be closed, the ECU 80 forcibly opens the bypass valve 17, and when the EGR flow rate GF flowing through the EGR passage 12 is equal to or greater than a predetermined first flow rate value A1, the ECU 80 diagnoses the bypass valve 17 and the temperature SW 78 as normal when the temperature SW 78 switches from an on-signal output state to an on-signal output state. Here, the case where the EGR flow rate GF is equal to or less than the twelfth flow rate value AB1 while the bypass valve 17 is closed is assumed to be a case where high-temperature EGR gas does not flow through the bypass passage 16 and the EGR gas temperature THG downstream of the junction 20 does not reach the set temperature of the temperature SW 78, which is 110°C. Furthermore, the case where the bypass valve 17 is forcibly opened from that state and the EGR flow rate GF is equal to or greater than the first flow rate value A1 is assumed to be a case where high-temperature EGR gas flows through the bypass passage 16 and the EGR gas temperature THG downstream of the junction 20 reaches 110°C. Therefore, by forcibly controlling the opening of the bypass valve 17, the temperature SW 78 switches from an ON signal output state to an ON signal output state, and it becomes possible to diagnose that the bypass valve 17 is normally opened and that the temperature SW 78 is operating normally. Therefore, it is possible to simultaneously diagnose that both the bypass valve 17 and the temperature SW 78 are normal.

[0132] According to the configuration of this embodiment, more specifically, the ECU 80 diagnoses that the temperature SW 78 is abnormal when an ON signal is output for the temperature SW 78 after a cold start of the engine 1 and before EGR gas flows through the EGR passage 12 or after a predetermined time has elapsed since EGR gas stopped flowing through the EGR passage 12. Here, "before EGR gas flows through the EGR passage 12 or after a predetermined time has elapsed since EGR gas stopped flowing through the EGR passage 12" refers to a case where EGR gas is not flowing through the EGR passage 12 and it is clear that no ON signal is output for the temperature SW 78. Therefore, the output of an ON signal for the temperature SW 78 makes it possible to diagnose that the temperature SW 78 is clearly abnormal. This makes it possible to reliably diagnose whether or not the temperature SW 78 is abnormal.

[0133] According to the configuration of this embodiment, the ECU 80 sets the set temperature of the temperature SW 78 to "110°C," which is higher than the maximum temperature of the junction 20 when the bypass valve 17 is controlled to be closed. This makes it possible to set the set temperature of the temperature SW 78 to the temperature of the junction 20 when the bypass valve 17 is controlled to be open, thereby reducing the activation frequency of the temperature SW 78. Therefore, the reliability of the temperature SW 78 can be ensured by the amount of the reduction in the activation frequency of the temperature SW 78.

[0134] In this embodiment, since it is possible to diagnose whether or not there is an abnormality in at least one of the bypass valve 17 and the temperature switch 78 as described above, the ECU 80 can control the EGR valve 14, i.e., control the execution of EGR, in accordance with the diagnosis result. Therefore, it is possible to prevent high-temperature EGR gas from unnecessarily flowing into the downstream EGR passage 12 (including the EGR gas distributor 15). Therefore, even if the bypass valve 17 provided in the bypass passage 16 fails, it is possible to suppress the generation of condensed water in the EGR passage 12 (including the EGR gas distributor 15) downstream of the EGR cooler 13 and the bypass passage 16 and the melting damage of the EGR passage 12 (including the EGR gas distributor 15).

[0135] According to the configuration of this embodiment, the ECU 80 diagnoses an abnormality in the bypass valve 17 based on the coolant temperature THW detected by the water temperature sensor 71 after the engine 1 is started and on whether or not the temperature SW 78 outputs an ON signal. Here, the temperature SW 78 is normally used to control the engine 1. Therefore, there is no need to provide a special detection means other than the temperature SW 78 to diagnose an abnormality in the bypass valve 17. Therefore, since there is no need to provide a special detection means, the configuration of the EGR system can be simplified and the product cost can be reduced.

[0136] Second Embodiment Next, the second embodiment will be described in detail with reference to the drawings. In the following description, the same components as those in the first embodiment will be denoted by the same reference numerals and will not be described again, and differences will be mainly described.

[0137] This embodiment differs from the first embodiment in the content of the bypass valve abnormality diagnosis control executed by the ECU 80.

[0138] [About abnormality diagnosis control of bypass valves, etc.] The contents of the bypass valve abnormality diagnosis control of this embodiment are shown in the form of flowcharts in Figures 10 to 12. In the flowcharts shown in Figures 10 to 12, steps indicated with the same reference numerals as in the flowcharts of Figures 2 to 5 indicate the same processing contents as in the flowcharts of Figures 2 to 5, and steps indicated with different reference numerals indicate different processing contents.

[0139] According to the bypass valve abnormality diagnosis control of the first embodiment, abnormality diagnosis is possible even in the low water temperature range. However, the tradeoff is that the temperature SW 78 operates more frequently, which raises concerns about the reliability (durability) of the temperature SW 78. Therefore, in the bypass valve abnormality diagnosis control of this embodiment, abnormality diagnosis is performed for the opening and closing of the bypass valve 17 using a single temperature SW 78 that is configured to output an ON signal (detection signal) at a temperature (130°C) or higher (e.g., 120°C or higher) at which the bypass valve 17 is in the open state. That is, in this embodiment, the set temperature is set to 130°C, and the temperature SW 78 is configured to output an ON signal when it detects a temperature equal to or higher than 130°C. This set temperature, 130°C, is set to a temperature higher than the maximum temperature of the confluence section 20 when the bypass valve 17 is in the closed state.

[0140] During the processing of this routine, the ECU 80 proceeds from step 110, step 140, or step 270 to step 155, where it determines the EGR flow rate FJGF (third flow rate value A2 and fourth flow rate value B2 (>A2)) for determining whether the bypass valve 17 is open or closed according to the coolant temperature THW and for determining an abnormality of the temperature SW 78. In this embodiment, the third flow rate value A2 is set to a value greater than the first flow rate value A1 of the first embodiment, and the fourth flow rate value B2 is set to a value greater than the second flow rate value B1 of the first embodiment.

[0141] During the processing of this routine, the ECU 80 proceeds from step 190 to step 205, where it determines whether the EGR flow rate GF is equal to or greater than the fourth flow rate value B2. If the result of this determination is positive, the ECU 80 proceeds to step 800, and if the result of this determination is negative, the ECU 80 returns the processing to step 100.

[0142] In step 800, the ECU 80 determines whether the first predetermined time a1 has elapsed. If the result of this determination is positive, the ECU 80 proceeds to step 210, and if the result of this determination is negative, the ECU 80 returns to step 205.

[0143] In step 210, the ECU 80 determines whether the temperature switch 78 is on. If the result of this determination is positive, the ECU 80 proceeds to step 220. However, if the result of this determination is negative, the ECU 80 proceeds to step 310 instead of step 300.

[0144] During the processing of this routine, the ECU 80 proceeds from step 440 to step 455, where it determines whether the EGR flow rate GF is less than the fourth flow rate value B2. If the result of this determination is positive, the ECU 80 proceeds to step 810 instead of step 460, and if the result of this determination is negative, it returns the processing to step 100.

[0145] In step 810, the ECU 80 determines whether the second predetermined time b1 has elapsed. If the result of this determination is positive, the ECU 80 proceeds to step 460, and if the result of this determination is negative, the ECU 80 returns to step 455.

[0146] In step 460, the ECU 80 determines whether the temperature switch 78 is off. If the result of this determination is positive, the ECU 80 proceeds to step 470. However, if the result of this determination is negative, the ECU 80 proceeds to step 500 instead of step 490.

[0147] During the processing of this routine, the ECU 80 proceeds from step 440 to step 820, where it determines whether the EGR flow rate GF is equal to or greater than the third flow rate value A2. If the result of this determination is positive, the ECU 80 proceeds to step 830, and if the result of this determination is negative, the ECU 80 returns to step 100.

[0148] In step 830, the ECU 80 performs a forced valve opening control on the bypass valve 17 (forced valve opening control).

[0149] Next, in step 840, the ECU 80 waits until a fifth predetermined time d1 has elapsed, and then proceeds to step 850.

[0150] In step 850, the ECU 80 determines whether the temperature switch 78 is on. If the result of this determination is positive, the ECU 80 proceeds to step 860, and if the result of this determination is negative, the ECU 80 proceeds to step 900.

[0151] In step 860, the ECU 80 determines that the bypass valve 17 is open, and sets the bypass valve open determination flag XBOP to "1."

[0152] Next, in step 870, the ECU 80 determines that the temperature SW is normal, and sets the temperature SW normality determination flag XTSok to "1."

[0153] Next, in step 880, the ECU 80 determines that the bypass valve 17 is normal, and sets the bypass valve normality determination flag XBok to "1."

[0154] Next, in step 890, the ECU 80 performs a forced valve closing control on the bypass valve 17, and ends the abnormality detection.

[0155] On the other hand, moving from step 850 to step 900, the ECU 80 determines that the temperature SW 78 is abnormal and sets the temperature SW abnormality determination flag XTSng to "1", and also determines that the bypass valve 17 is abnormally closed and sets the bypass valve abnormality flag XBCSng to "1", and then proceeds to step 890.

[0156] Specifically, when the bypass valve 17 is being controlled to open (step 170), if the EGR flow rate GF flowing through the EGR passage 12 is equal to or greater than the fourth flow rate value B2 (the determination in step 205 is YES), and if there is no ON signal output from the temperature SW78 (the determination in step 210 is NO), the ECU 80 determines (diagnoses) that the bypass valve 17 is in a closed state and is provisionally abnormal (abnormal) and that the temperature SW78 is provisionally abnormal (abnormal) (step 310).

[0157] According to the above-described bypass valve abnormality diagnosis control, when the ECU 80 is controlling the bypass valve 17 to be closed (step 420), if the EGR flow rate GF flowing through the EGR passage 12 becomes equal to or greater than the third flow rate value A2 (determination of YES in step 820), the ECU 80 forcibly controls the bypass valve 17 to be open (step 830), and when the state in which the temperature SW 78 has no on signal output (determination of YES in step 130 and determination of NO in step 210) changes to a state in which the on signal is output (determination of YES in step 850), the ECU 80 determines (diagnoses) that the bypass valve 17 and the temperature SW 78 are normal (steps 870 and 880).

[0158] According to the bypass valve abnormality diagnosis control, the ECU 80 detects an open valve abnormality and a closed valve abnormality of the bypass valve 17 as follows. That is, the abnormality detection range is the range in which the EGR flow rate GF is equal to or greater than the third flow rate value A2. Here, in the low water temperature range (for example, 40 to 80°C), if the temperature SW 78 is ON (the EGR gas flowing through the confluence 20 is "130°C or higher") in the range in which the EGR flow rate GF is equal to or greater than the fourth flow rate value B2, the ECU 80 determines that the bypass valve 17 is in an open state (not in a closed valve abnormality). On the other hand, if the temperature SW 78 is OFF (the EGR gas flowing through the confluence 20 is "less than 130°C"), the ECU 80 determines that the bypass valve 17 is in a temporary closed valve abnormality. On the other hand, in the high water temperature range and after a delay in forcibly opening the bypass valve 17, if the temperature SW 78 is turned on (the EGR gas flowing through the confluence 20 is "130°C or higher"), the ECU 80 determines that both the bypass valve 17 and the temperature SW 78 are normal. If the temperature SW 78 is turned off (the EGR gas flowing through the confluence 20 is "less than 130°C"), the ECU 80 determines that the bypass valve 17 is abnormally closed or that the temperature SW 78 is abnormal.

[0159] According to the bypass valve abnormality diagnosis control, the ECU 80 detects an abnormality in the temperature SW 78 during normal vehicle driving as follows. The set temperature of the temperature SW 78 must be set to a temperature at which the temperature SW 78 is inactivated (not turned on) when the bypass valve 17 is in a closed valve abnormality state, but is activated (turned on) when the bypass valve 17 is in an open valve state. In this embodiment, when the maximum temperature of the EGR gas flowing out of the EGR cooler 13 is set to "120°C or higher," the set temperature of the temperature SW 78 is set to "130°C." After the engine 1 starts in the low water temperature range, if the temperature SW 78 is turned on (the EGR gas flowing through the confluence 20 is "130°C or higher"), the ECU 80 determines that the temperature SW 78 is abnormal. Furthermore, if the temperature SW 78 is turned on (the EGR gas flowing through the junction 20 is "130°C or higher") after the engine 1 starts in the high water temperature range and the temperature SW 78 remains on for the EGR cut time f1 or longer (the EGR gas flowing through the junction 20 remains "130°C or higher"), the ECU 80 determines that the temperature SW 78 is abnormal. If the temperature SW 78 is switched off (the EGR gas flowing through the junction 20 is "less than 130°C"), the ECU 80 determines that the temperature SW 78 is normal. Here, if the EGR flow rate GF is equal to or greater than the fourth flow rate value B2 after the engine 1 starts in the low water temperature range and the temperature SW 78 is turned on or the temperature SW 78 is turned off with the bypass valve 17 closed, the ECU 80 determines that the temperature SW 78 is normal. After the engine 1 starts in the low water temperature range, the temperature SW 78 turns off, and then the temperature SW 78 continues to be off while the EGR flow rate GF is equal to or greater than the fourth flow rate value B2. If the bypass valve 17 is forcibly opened while the EGR flow rate GF is equal to or greater than the third flow rate value A2 in the high water temperature range and the temperature SW 78 does not turn on after a fifth predetermined time d1, the ECU 80 determines that the temperature SW 78 is abnormal or that the bypass valve 17 is abnormally closed. If the temperature SW 78 turns on, the ECU 80 determines that the temperature SW 78 and the bypass valve 17 are normal.

[0160] According to the bypass valve abnormality diagnosis control described above, when the detection condition is not met (when the EGR flow rate GF is less than the third flow rate value A2) in the low water temperature range and the high water temperature range, the ECU 80 may continue to control the bypass valve 17 to be open, and may detect an abnormality after a fifth predetermined time d1 has elapsed in a state in which the EGR flow rate GF is equal to or greater than the third flow rate value A2. Here, when the temperature SW 78 changes from the OFF state to the ON state, the ECU 80 determines that the temperature SW 78 and the bypass valve 17 are normal. On the other hand, when the temperature SW 78 remains in the OFF state, the ECU 80 determines that the temperature SW 78 is abnormal or that the bypass valve 17 has a closed valve abnormality.

[0161] According to the configuration of this embodiment, when the temperature SW 78 and the bypass valve 17 are normal, the temperature SW 78 is activated only once or twice per trip of the vehicle, improving the durability of the temperature SW 78, compared to the bypass valve abnormality diagnosis control of the first embodiment. However, when the bypass valve 17 experiences an opening abnormality, the temperature SW 78 is activated and deactivated repeatedly, which increases the frequency of activation of the temperature SW 78.

[0162] [About the behavior of various parameters due to abnormality diagnosis control of bypass valves, etc.] The behavior of various parameters due to the bypass valve and other abnormality diagnostic control is shown in time charts in Figures 13 to 16. Figure 13 shows a case where both the bypass valve 17 and the temperature SW 78 are determined to be normal. In Figure 13, parameters (A) to (J) are the same as those in Figure 6, but (E) shows the on / off change of the temperature SW 78 at 130°C. In Figure 13, the behavior of parameters other than (D), (E), (G), (I), and (J) is the same as that in Figure 6.

[0163] 13, immediately before time t7, the bypass valve 17 (C) is under valve opening control, the EGR flow rate GF (B) is equal to or greater than the fourth flow rate value B2, and at time t7 when the first predetermined time a1 has elapsed, the EGR flow rate GF is in a state that allows for detection of abnormalities in the bypass valve 17 and the temperature SW 78, and the abnormality detection allowance flag XBPGF (D) becomes "1." At this time, the EGR gas temperature THG (J) exceeds "130°C," the temperature SW 78 (E) is on, and it is determined that the temperature SW 78 is normal, so the temperature SW normality determination flag XTSok (F) becomes "1," and the temperature SW abnormality determination flag XTSng becomes "0." Also, at time t7, the bypass valve open determination flag XBOP (G) becomes "1", the bypass valve closed determination flag XBCS becomes "0", and further, the bypass valve closed abnormality flag XBCSng and the bypass valve open abnormality flag XBOPng (H) each become "0", and it is determined that the bypass valve 17 is in an open state and normal.

[0164] Also, immediately after time t12, the bypass valve 17 (C) is under valve closing control, the EGR flow rate GF (B) is less than the fourth flow rate value B2, and at time t13, when the second predetermined time b1 has elapsed, the abnormality detection allowance flag XBPGF (D) becomes "1." At this time, the temperature SW78 (E) is off, and the bypass valve closing determination flag XBCS (G) becomes "1," so it is determined that the bypass valve 17 is in a closed state and normal. Since it has already been determined that the bypass valve 17 is in an open state and normal at time t7, the bypass valve 17 is normal in both the open state and the closed state, and the bypass valve normality determination flag XBok (I) becomes "1," so it is determined that the bypass valve 17 is normal.

[0165] Figure 14 shows a case where the bypass valve 17 is determined to be abnormally open and the temperature SW 78 is determined to be normal. In Figure 14, parameters (A) to (J) are the same as those in Figure 7. In Figure 14, the behavior of parameters other than (D), (E), (H), (I), and (J) is the same as that in Figure 7.

[0166] Regarding Figure 14, differences from Figure 13 will be mainly described. The normality determination of the temperature SW 78 is the same as in Figure 13. In Figure 14, immediately before time t13, the bypass valve 17 (C) is under valve closing control, and the EGR flow rate GF (B) is less than the fourth flow rate value B2. At time t13, when the second predetermined time b1 has elapsed, the abnormality detection allowance flag XBPGF (D) becomes "1." Then, the EGR gas temperature THG (J) exceeds "130°C," and the temperature SW 78 (E) is turned on. At time t13, the bypass valve open determination flag XBOP (G) becomes "1," the bypass valve close determination flag XBCS becomes "0," and the bypass valve abnormal opening flag XBOPng (H) becomes "1." Therefore, it is determined that the bypass valve 17 is abnormally opening.

[0167] Figure 15 shows a case where the bypass valve 17 is temporarily determined to be closed and the temperature SW 78 is temporarily determined to be abnormal in the low water temperature range, and both the bypass valve 17 and the temperature SW 78 are determined to be normal when the bypass valve 17 is forcibly controlled to be open in the high water temperature range. In Figure 15, parameters (A) to (L) are the same as those in Figure 8. In Figure 15, the behavior of parameters other than (A) to (J) is the same as that in Figure 8.

[0168] 15, immediately before time t7, the bypass valve 17 (C) is under valve open control, the EGR flow rate GF (B) is equal to or greater than the fourth flow rate value B2, and at time t7 when the first predetermined time a1 has elapsed, the abnormality detection allowance flag XBPGF (D) becomes "1." At this time, the EGR gas temperature THG (J) is less than "130°C," the temperature SW 78 (E) is turned off, the temperature SW 78 is determined to be temporarily abnormal, the temperature SW temporary abnormality flag XTSTng (K) becomes "1," the bypass valve 17 is determined to be temporarily abnormal in a closed state, and the bypass valve closed temporary abnormality flag XBCSTng (L) becomes "1."

[0169] On the other hand, just before time t12, the bypass valve 17 (C) is under valve closing control, the EGR flow rate GF (B) is less than the third flow rate value A2, the EGR gas temperature THG (J) is less than "130°C", the temperature SW 78 (E) is off, the temperature SW normality determination flag XTSok (F) is "0", but the temperature SW temporary abnormality flag XTSTng (K) is "1". In addition, the bypass valve closed determination flag XBCS and the bypass valve open determination flag XBOP (G) are both "0", and the bypass valve closed abnormality flag XBCSng and the bypass valve open abnormality flag XBOPng (H) are both "0", but the bypass valve closed temporary abnormality flag XBCSTng (L) is "1".

[0170] Thereafter, at time t12, the EGR flow rate GF (B) becomes equal to or greater than the third flow rate value A2 (step 820 in FIG. 12), the bypass valve 17 (C) is forcibly opened, and at time t14 after the fifth predetermined time d1 has elapsed, the EGR flow rate GF (B) remains equal to or greater than the third flow rate value A2, and the abnormality detection allowance flag XBPGF (D) becomes "1." At this time, the EGR gas temperature THG (J) becomes equal to or greater than "130°C," the temperature SW 78 (E) turns on, the temperature SW normality determination flag XTSok (F) becomes "1," and the temperature SW abnormality determination flag XTSng remains at "0," so it is determined that the temperature SW 78 is normal. Furthermore, at time t14, the bypass valve open determination flag XBOP (G) becomes "1", the bypass valve closed determination flag XBCS remains "0", and the bypass valve closed abnormality flag XBCSng and the bypass valve open abnormality flag XBOPng (H) both become "0", so the bypass valve normality determination flag XBok (I) becomes "1", and it is determined that the bypass valve 17 is normal. Thereafter, the bypass valve 17 is subjected to forcible valve closing control (step 890 in FIG. 12).

[0171] Figure 16 shows a case where the bypass valve 17 is temporarily closed and the temperature SW 78 is temporarily determined to be abnormal in the low water temperature range, and when the bypass valve 17 is forcibly opened in the high water temperature range, the bypass valve 17 is temporarily closed and the temperature SW 78 is determined to be abnormal. In Figure 16, parameters (A) to (L) are the same as those in Figure 15. In Figure 16, only the behavior of parameters (E), (F), and (H) differs from that in Figure 15.

[0172] 16, at time t12, the EGR flow rate GF (B) becomes equal to or greater than the third flow rate value A2 (step 820 in FIG. 12), the bypass valve 17 (C) is forcibly opened, and at time t14 after the fifth predetermined time d1 has elapsed, the EGR flow rate GF (B) remains equal to or greater than the third flow rate value A2, and the abnormality detection allowance flag XBPGF (D) becomes "1." At this time, the EGR gas temperature THG (J) becomes less than "130°C," and the temperature SW 78 (E) remains off. Therefore, the temperature SW normality determination flag XTSok (F) becomes "0," and the temperature SW abnormality determination flag XTSng (F) becomes "1," and it is determined that the temperature SW 78 is abnormal. Furthermore, at time t14, the bypass valve open determination flag XBOP (G) becomes "0", the bypass valve closed determination flag XBCS becomes "1", the bypass valve abnormal closed flag XBCSng (H) becomes "1", and the bypass valve abnormal open flag XBOPng becomes "0", so the bypass valve normal determination flag XBok (I) becomes "0", and it is determined that the bypass valve 17 is abnormally closed. Thereafter, the bypass valve 17 is subjected to forcible valve closing control (step 890 in FIG. 12).

[0173] [About the EGR system's function and effects] As described above, according to the configuration of the EGR system in this embodiment, the set temperature of the temperature SW78 is "130°C", which is different from the set temperature of "110°C" in the first embodiment, but basically the same action and effect as in the first embodiment can be obtained.

[0174] According to the configuration of this embodiment, more specifically, when the EGR flow rate GF flowing through the EGR passage 12 is equal to or greater than the fourth flow rate value B2 while the bypass valve 17 is being controlled to be open, the ECU 80 diagnoses that the bypass valve 17 is in a closed state and abnormal (valve closure abnormality) and that the temperature SW 78 is abnormal if the ON signal for the temperature SW 78 is not output. Here, when the EGR flow rate GF flowing through the EGR passage 12 is equal to or greater than the fourth flow rate value B2 while the bypass valve 17 is being controlled to be open, it is assumed that high-temperature EGR gas flows through the bypass passage 16 and the EGR gas temperature THG downstream of the junction 20 reaches 130°C, which is the set temperature for the temperature SW 78. Therefore, it is possible to diagnose that the bypass valve 17 is in a closed state despite being controlled to be open, and that the temperature SW 78 is abnormal, based on the absence of an ON signal for the temperature SW 78. Therefore, the bypass valve 17 can be more specifically diagnosed as having a valve closure abnormality and that the temperature SW 78 is abnormal.

[0175] In addition, according to the configuration of this embodiment, when the EGR flow rate GF flowing through the EGR passage 12 is equal to or greater than a predetermined third flow rate value A2 while the bypass valve 17 is being closed, the ECU 80 forcibly opens the bypass valve 17, and when the temperature SW 78 switches from an ON signal output state to an ON signal output state, the ECU 80 diagnoses that the bypass valve 17 and the temperature SW 78 are normal. Here, the case where the EGR flow rate GF is equal to or greater than the third flow rate value A2 while the bypass valve 17 is being closed is assumed to be a case where high-temperature EGR gas does not flow through the bypass passage 16 and the EGR gas temperature THG downstream of the junction 20 does not reach 130°C, which is the set temperature of the temperature SW 78. Furthermore, the case where the bypass valve 17 is forcibly opened from that state is assumed to be a case where high-temperature EGR gas flows through the bypass passage 16 and the EGR gas temperature THG downstream of the junction 20 reaches 130°C. Therefore, by forcibly controlling the opening of the bypass valve 17, the temperature SW 78 switches from an ON signal output state to an ON signal output state, and it becomes possible to diagnose that the bypass valve 17 is normally opened and that the temperature SW 78 is operating normally. Therefore, it is possible to simultaneously diagnose that both the bypass valve 17 and the temperature SW 78 are normal.

[0176] Third Embodiment Next, a third embodiment will be described in detail with reference to the drawings. This embodiment differs from the previous embodiments in the content of the bypass valve abnormality diagnosis control executed by the ECU 80. In particular, this embodiment differs from the previous embodiments in that abnormality diagnosis is performed based on the estimated temperature of EGR gas.

[0177] [About abnormality diagnosis control of bypass valves, etc.] 17 to 19 are flowcharts showing the contents of the bypass valve abnormality diagnosis control of this embodiment. In this embodiment, as in the second embodiment, the set temperature is set to "130°C", and the temperature SW 78 is configured to output an ON signal when it detects a temperature of "130°C" or higher.

[0178] When the process proceeds to this routine, the ECU 80 determines whether the IG is on, i.e., whether the IG switch 70 has been turned on, in step 1000. If the result of this determination is positive, the ECU 80 proceeds to step 1010, and if the result of this determination is negative, the ECU 80 proceeds to step 1360.

[0179] In step 1010, the ECU 80 acquires the engine speed NE, engine load KL, coolant temperature THW, intake air temperature THA, and vehicle speed SPD based on the detected values ​​of the vehicle speed sensor 69, water temperature sensor 71, rotation speed sensor 72, and intake air temperature sensor 77, and also acquires the EGR flow rate GF. For example, by referring to a predetermined EGR flow rate map, the ECU 80 can determine the EGR flow rate GF according to the control command value for the step motor of the EGR valve 14 (opening degree of the EGR valve 14) and the intake air amount Ga or intake air pressure PM detected at that time. In addition, the ECU 80 acquires the open / closed state of the bypass valve 17.

[0180] Next, in step 1020, the ECU 80 calculates an estimated EGR gas temperature ETegr when the bypass valve 17 is normal, based on the engine speed NE, engine load KL, coolant temperature THW, intake air temperature THA, vehicle speed SPD, etc. The ECU 80 can calculate the estimated EGR gas temperature ETegr according to the various parameters NE, KL, THW, THA, and SPD, for example, by referring to a predetermined estimated EGR gas temperature map.

[0181] Next, in step 1030, the ECU 80 captures the state of the temperature SW 78.

[0182] Next, in step 1040, the ECU 80 determines whether the estimated EGR gas temperature ETegr is equal to or higher than 120° C. If the result of this determination is positive, the ECU 80 proceeds to step 1050, and if the result of this determination is negative, the ECU 80 proceeds to step 1140.

[0183] In step 1050, the ECU 80 sets the 120° C. or lower flag XLT120, which indicates that the estimated EGR gas temperature ETegr is 120° C. or lower, to "0."

[0184] Next, in step 1060, the ECU 80 determines whether the temperature switch 78 is off. If the result of this determination is positive, the ECU 80 proceeds to step 1070, and if the result of this determination is negative, the ECU 80 proceeds to step 1120.

[0185] In step 1070, the ECU 80 determines whether the bypass valve open determination flag XBOP is 0. If the result of this determination is positive, the ECU 80 determines that the bypass valve 17 is not open and proceeds to step 1080. If the result of this determination is negative, the ECU 80 determines that the bypass valve 17 is open and ends the abnormality detection.

[0186] In step 1080, the ECU 80 determines whether the estimated EGR gas temperature ETegr is equal to or higher than 140° C. If the result of this determination is positive, the ECU 80 proceeds to step 1090, and if the result of this determination is negative, the ECU 80 proceeds to step 1210.

[0187] In step 1090, the ECU 80 determines whether the 140° C. or higher flag XMT140, which indicates that the estimated EGR gas temperature ETegr is 140° C. or higher, is “0.” If the result of this determination is positive, the ECU 80 proceeds to step 1100, and if the result of this determination is negative, the ECU 80 returns to step 1000.

[0188] In step 1100, the ECU 80 sets the 140° C. or higher flag XMT140 to "1."

[0189] Next, in step 1110, the ECU 80 determines whether the temperature switch 78 is on. If the result of this determination is positive, the ECU 80 proceeds to step 1120, and if the result of this determination is negative, the ECU 80 proceeds to step 1350.

[0190] In step 1120, the ECU 80 determines that the temperature switch 78 is normal, and sets the temperature switch normality determination flag XTSok to "1."

[0191] Next, in step 1130, the ECU 80 determines that the bypass valve 17 is open, sets the bypass valve open determination flag XBOP to "1", and then returns the process to step 1000.

[0192] On the other hand, moving from step 1040 to step 1140, the ECU 80 sets the 120° C. or lower flag XLT120 to "1".

[0193] Next, in step 1150, the ECU 80 determines whether the temperature switch 78 is off. If the result of this determination is positive, the ECU 80 proceeds to step 1160, and if the result of this determination is negative, the ECU 80 proceeds to step 1180.

[0194] In step 1160, the ECU 80 determines whether the bypass valve open determination flag XBOP is 0. If the result of this determination is positive, the ECU 80 proceeds to step 1170, and if the result of this determination is negative, the ECU 80 ends the abnormality detection.

[0195] In step 1170, the ECU 80 determines whether the coolant temperature THW is less than 80° C. If the result of this determination is positive, the ECU 80 returns the process to step 1000, and if the result of this determination is negative, the ECU 80 proceeds to step 1260.

[0196] At step 1180, which follows step 1150, the ECU 80 determines whether the bypass valve open determination flag XBOP is 0. If the determination result is positive, the ECU 80 proceeds to step 1190, and if the determination result is negative, the ECU 80 proceeds to step 1200.

[0197] Then, in step 1190, the ECU 80 determines that the temperature switch 78 is abnormal, sets the temperature switch abnormality determination flag XTSng to "1", and then ends the abnormality detection.

[0198] In step 1200, the ECU 80 determines that the bypass valve 17 is in an open state and is abnormal, sets the bypass valve open abnormality flag XBOPng to "1", and then ends the abnormality detection.

[0199] On the other hand, in step 1210 following step 1080, the ECU 80 sets the 140° C. or higher flag XMT140 to "0."

[0200] Next, in step 1220, the ECU 80 determines whether the bypass valve open determination flag XBOP is 1. If the result of this determination is positive, the ECU 80 determines that the bypass valve 17 is open and proceeds to step 1230. If the result of this determination is negative, the ECU 80 determines that the bypass valve 17 is not open and proceeds to step 1260.

[0201] In step 1230, the ECU 80 determines whether the temperature switch 78 is off. If the result of this determination is positive, the ECU 80 proceeds to step 1240, and if the result of this determination is negative, the ECU 80 returns to step 1000.

[0202] On the other hand, at step 1240 following step 1070, step 1160 or step 1230, the ECU 80 determines that the bypass valve 17 is in a closed state, and sets the bypass valve closed determination flag XBCS to "1".

[0203] Next, in step 1250, the ECU 80 determines that the bypass valve 17 is normal, sets the bypass valve normality determination flag XBok to "1", and then ends the abnormality detection.

[0204] On the other hand, moving from step 1110 to step 1350, the ECU 80 determines that the temperature SW 78 is abnormal, sets the temperature SW temporary abnormality flag XTSTng to "1", and sets the temperature SW abnormality determination flag XTSng to "1", and also determines that the bypass valve 17 is closed abnormally, sets the bypass valve closed temporary abnormality flag XBCSTng to "1", and sets the bypass valve closed abnormality flag XBCSng to "1". Then, the ECU 80 ends the abnormality detection.

[0205] Furthermore, at step 1260, which is the next step following step 1170 or step 1220, the ECU 80 forcibly controls the bypass valve 17 to open.

[0206] Next, in step 1270, the ECU 80 determines whether the estimated EGR gas temperature ETegr is equal to or higher than 120° C. If the result of this determination is positive, the ECU 80 proceeds to step 1280, and if the result of this determination is negative, the ECU 80 returns to step 1000.

[0207] In step 1280, the ECU 80 determines whether the temperature switch 78 is off. If the result of this determination is positive, the ECU 80 proceeds to step 1290, and if the result of this determination is negative, the ECU 80 proceeds to step 1310.

[0208] In step 1290, the ECU 80 determines whether the estimated EGR gas temperature ETegr is equal to or higher than 140° C. If the result of this determination is positive, the ECU 80 proceeds to step 1300, and if the result of this determination is negative, the ECU 80 returns to step 1000.

[0209] In step 1300, the ECU 80 determines whether the temperature switch 78 is on. If the result of this determination is positive, the ECU 80 proceeds to step 1310, and if the result of this determination is negative, the ECU 80 proceeds to step 1340.

[0210] At step 1310, which follows step 1280 or step 1300, the ECU 80 determines that the temperature switch 78 is normal, and sets the temperature switch normality determination flag XTSok to "1."

[0211] Next, in step 1320, the ECU 80 determines that the bypass valve 17 is in an open state, and sets the bypass valve open determination flag XBOP to "1."

[0212] Next, in step 1330, the ECU 80 controls the bypass valve 17 to close, and then returns the process to step 1000.

[0213] Furthermore, moving from step 1300 to step 1340, the ECU 80 determines that the temperature SW 78 is abnormal, sets the temperature SW temporary abnormality flag XTSTng to "1", and sets the temperature SW abnormality determination flag XTSng to "1", and determines that the bypass valve 17 is closed abnormally, sets the bypass valve closed temporary abnormality flag XBCSTng to "1", and sets the bypass valve closed abnormality flag XBCSng to "1". Thereafter, the ECU 80 ends the abnormality detection.

[0214] On the other hand, in steps 1360 to 1440 following step 1000, the ECU 80 executes the same processes as steps 330 to 410 in FIG. 2, and then ends the subsequent processes.

[0215] In the bypass valve abnormality diagnosis control, the ECU 80 executes this control assuming that the accuracy of the estimated EGR gas temperature ETegr is, for example, ±5°C and the tolerance of the temperature SW 78 is, for example, ±5°C. Here, the estimated EGR gas temperature ETegr at which the temperature SW 78 operates (turns on / off) is between 120°C and 140°C. Therefore, if the estimated EGR gas temperature ETegr is 120°C or lower and the temperature SW 78 is turned on, the ECU 80 determines that the temperature SW 78 is abnormal. On the other hand, if the estimated EGR gas temperature ETegr is 140°C or higher and the temperature SW 78 is turned off, the ECU 80 determines that the bypass valve 17 is abnormally closed. Furthermore, if the temperature SW 78 switches from off to on when the estimated EGR gas temperature ETegr is between 120°C and 140°C, the ECU 80 determines that the temperature SW 78 is normal and that the bypass valve 17 is in an open state. Furthermore, when the temperature switch 78 is switched from on to off, the ECU 80 determines that the bypass valve 17 is normal.

[0216] [About the behavior of various parameters due to abnormality diagnosis control of bypass valves, etc.] The behavior of various parameters under the bypass valve abnormality diagnosis control is shown in time charts in FIGS. 20 to 22. FIG. 20 illustrates a case where both the bypass valve 17 and the temperature SW 78 are determined to be normal. In FIG. 20, parameters (A) to (C) and (E) to (I) are the same as those in FIG. 6, except that (E) indicates the on / off change of the 130°C temperature SW 78, and (J) indicates the changes in the coolant temperature THW and the estimated EGR gas temperature ETegr. Here, it is assumed that the estimated EGR gas temperature ETegr matches the actual EGR gas temperature THG. (M) indicates the change in the 120°C or lower flag XLT120, and (N) indicates the change in the 140°C or higher flag XMT140. In FIG. 20, the behavior of parameters other than (A), (C), and (H) differs from that in FIG. 6.

[0217] Here, at time t6, the bypass valve 17 (C) is being controlled to be open, the EGR flow rate GF (B) is beginning to increase, and the estimated EGR gas temperature ETegr (J) is below 120°C, so the 120°C or lower flag XLT120 (M) is set to "1." Thereafter, at time t7, when the estimated EGR gas temperature ETegr (J) exceeds 120°C, the 120°C or lower flag XLT120 (M) is set to "0." At time t8, when the estimated EGR gas temperature ETegr (J) exceeds 130°C, the temperature SW78 (E) is turned on. Thereafter, at time t9, when the estimated EGR gas temperature ETegr (J) exceeds 140°C, the 140°C or higher flag XMT140 (N) is set to "1." At this time, the temperature SW 78 is determined to be normal, and the temperature SW normality determination flag XTSok (F) is set to "1." The bypass valve 17 is determined to be open, and the bypass valve open-valve determination flag XBOP (G) is set to "1." Thereafter, at time t12, the bypass valve 17 (C) is under valve closing control, the temperature SW 78 (E) is turned off, and the estimated EGR gas temperature ETegr (J) is equal to or lower than "120°C." Therefore, the 120°C or lower flag XLT120 (M) is set to "1," the bypass valve closed-valve determination flag XBCS (G) is set to "1," and the bypass valve normality determination flag XBok (I) is set to "1," and it is determined that the bypass valve 17 is normal. That is, both the bypass valve 17 and the temperature SW 78 are determined to be normal.

[0218] FIG. 21 shows a case where the bypass valve 17 is determined to be abnormally open and the temperature SW 78 is determined to be normal. In FIG. 21, the various parameters are the same as those in FIG. 20. In FIG. 21, the behavior of parameters other than (A) to (C), (F), and (M) differs from that in FIG. 20. In (J), the estimated EGR gas temperature ETegr (assumed under normal conditions) is shown by a solid line, and the actual EGR gas temperature THG (under abnormal conditions) is shown by a bold line (the same applies to FIG. 22). The actual EGR gas temperature THG does not have to be detected by a sensor or the like.

[0219] In Figure 21, the behavior of each parameter from time t6 to time t10 is the same as that in Figure 20, so when the estimated EGR gas temperature ETegr (J) exceeds "140°C" at time t9, the 140°C or higher flag XMT140 (N) becomes "1", the temperature SW78 is determined to be normal, and the temperature SW normal determination flag XTSok (F) becomes "1". 21, at time t12, the bypass valve 17 (C) is under valve closing control, the estimated EGR gas temperature ETegr (assumed under normal conditions) (J) is below "120°C", and the below-120°C flag XLT120 (M) is set to "1". However, the temperature SW78 (E) is not turned off (abnormal condition in which the actual EGR gas temperature THG exceeds "130°C"), and the bypass valve open determination flag XBOP (G) is set to "1". Therefore, the bypass valve open abnormality flag XBOPng (H) is set to "1", and the bypass valve close abnormality flag XBCSng is set to "0". Therefore, the bypass valve normality determination flag XBok (I) is set to "0", and it is determined that the bypass valve 17 is abnormally open. That is, the bypass valve 17 is determined to be abnormally open, and the temperature SW78 is determined to be normal.

[0220] Figure 22 shows a case where the bypass valve 17 is determined to be closed abnormally or the temperature SW 78 is determined to be abnormal. In Figure 22, parameters other than (K) and (L) are the same as those in Figures 20 and 21. In Figure 22, the behavior of parameters other than (A) to (C), (I), (M), and (N) differs from that in Figure 20.

[0221] In FIG. 22, at time t9, the bypass valve 17 (C) is under valve opening control, the estimated EGR gas temperature ETegr (assumed under normal conditions) (J) is 140°C or higher, the 120°C or lower flag XLT120 (M) is set to "0," and the 140°C or higher flag XMT140 (N) is set to "1." However, since the temperature SW 78 (E) remains off (step 1350 in FIG. 17), it is determined that the temperature SW 78 is temporarily abnormal and abnormal, and the temperature SW normality determination flag XTSok (F) is set to "0," and the temperature SW abnormality determination flag XTSng is set to "1." Furthermore, the temperature SW temporary abnormality determination flag XTSTng (K) is set to "1." Furthermore, the bypass valve closed abnormality flag XBCSng (H) is set to "1," and the bypass valve closed temporary abnormality flag XBCSTng (L) is set to "1." Also, the bypass valve closed determination flag XBCS of (G) becomes "1", and the bypass valve open determination flag XBOP becomes "0". Then, the bypass valve normality determination flag XBok becomes "0", and it is determined that the bypass valve 17 is abnormal. That is, it is determined that the bypass valve 17 is abnormally closed or that the temperature SW 78 is abnormal.

[0222] [About the EGR system's function and effects] As described above, the configuration of the EGR system in this embodiment differs from the previous embodiments in that abnormality diagnosis of the bypass valve 17 and the temperature SW78 is performed based on the estimated EGR gas temperature ETegr when the bypass valve 17 is normal, which is calculated based on the engine speed NE, engine load KL, coolant temperature THW, intake air temperature THA, vehicle speed SPD, etc., in that abnormality diagnosis of the bypass valve 17 and the temperature SW78 is performed based on the on / off operation of the temperature SW78.

[0223] <Another embodiment> The disclosed technology is not limited to the above-described embodiments, and can be implemented by appropriately modifying part of the configuration within the scope of the disclosed technology.

[0224] (1) In each of the above embodiments, the set temperature of the temperature SW78 is set to a single predetermined temperature, "110°C" or "130°C." However, this set temperature can also be set to a predetermined narrow range of temperatures that allows for error, for example, "105°C to 115°C" or "125°C to 135°C."

[0225] (2) In each of the above embodiments, the temperature SW 78 is provided in the EGR 12 (piping upstream of the EGR gas distributor 15) downstream of the confluence 20 of the EGR gas flowing out from the EGR cooler 13 and the EGR gas flowing out from the bypass passage 16, but the temperature SW can also be provided in the EGR gas distributor.

[0226] (3) In each of the above embodiments, the temperature of the inner wall of the piping of the EGR passage 12 is detected by the temperature SW 78, but it is also possible to configure the temperature of the EGR gas flowing through the EGR passage 12 (including the EGR gas distributor 15) to be detected by the temperature SW.

[0227] (4) In each of the above embodiments, the ECU 80 is configured to refer to a predetermined EGR flow rate map to determine the EGR flow rate GF according to the control command value (opening of the EGR valve 14) for the step motor of the EGR valve 14 and the intake air amount Ga or intake air pressure PM detected at that time. Alternatively, a sensor for detecting the EGR flow rate may be provided in the EGR passage, and the EGR flow rate may be determined from the value detected by the sensor.

[0228] (5) In the first embodiment, when the ECU 80 is controlling the bypass valve 17 to close, if the EGR flow rate GF flowing through the EGR passage 12 is a flow rate value between the first flow rate value A1 and the larger second flow rate value B1, and if an ON signal is output from the temperature SW 78, the ECU 80 diagnoses that the bypass valve 17 is abnormally open. However, under the same conditions, the ECU 80 can also diagnose that the temperature SW 78 is abnormal. [Industrial Applicability]

[0229] The disclosed technology can be applied to EGR devices for gasoline engines and diesel engines mounted on vehicles. [Explanation of symbols]

[0230] 1 engine 2 Intake passage 3 Exhaust passage 12 EGR passage 13 EGR cooler 14 EGR valve 15 EGR gas distributor (EGR passage) 16 Bypass Passage 17 Bypass valve 20 Junction 78 Temperature SW (temperature switch) 80 ECU (abnormality diagnosis means) GF EGR flow rate A1 First flow rate value B1 Second flow rate value A2 Third flow rate value (corresponding to the first flow rate value) B2 Fourth flow rate value (corresponding to the second flow rate value) f1 EGR cut time (predetermined time)

Claims

1. an EGR passage for allowing a portion of exhaust gas discharged from the engine into the exhaust passage to flow into the intake passage as EGR gas; an EGR valve for adjusting the flow rate of the EGR gas flowing through the EGR passage; an EGR cooler for cooling the EGR gas flowing through the EGR passage; a bypass passage for bypassing the EGR gas flowing to the EGR cooler in the EGR passage; and a bypass valve for opening and closing the bypass passage, a temperature switch that is provided in the EGR passage downstream of a confluence of the EGR gas flowing out from the EGR cooler and the EGR gas flowing out from the bypass passage, the temperature switch outputting a detection signal when detecting only one predetermined set temperature or a predetermined narrow range of set temperatures; an abnormality diagnosis means for diagnosing the presence or absence of an abnormality when the engine is in a predetermined operating state and the EGR valve is in an open state to allow the EGR gas to flow through the EGR passage, The set temperature of the temperature switch is set to a temperature higher than a maximum temperature of the confluence portion when the bypass valve is controlled to be closed, The abnormality diagnosis means diagnoses that the bypass valve is open and abnormal or that the temperature switch is abnormal when the flow rate of the EGR gas flowing through the EGR passage is between a predetermined first flow rate value and a predetermined second flow rate value that is larger than the first flow rate value and when the detection signal is output from the temperature switch while the bypass valve is controlled to be closed. An EGR system characterized by:

2. an EGR passage for allowing a portion of exhaust gas discharged from the engine into the exhaust passage to flow into the intake passage as EGR gas; an EGR valve for adjusting the flow rate of the EGR gas flowing through the EGR passage; an EGR cooler for cooling the EGR gas flowing through the EGR passage; a bypass passage for bypassing the EGR gas flowing to the EGR cooler in the EGR passage; and a bypass valve for opening and closing the bypass passage, a temperature switch that is provided in the EGR passage downstream of a confluence of the EGR gas flowing out from the EGR cooler and the EGR gas flowing out from the bypass passage, the temperature switch outputting a detection signal when detecting only one predetermined set temperature or a predetermined narrow range of set temperatures; an abnormality diagnosis means for diagnosing the presence or absence of an abnormality when the engine is in a predetermined operating state and the EGR valve is in an open state to allow the EGR gas to flow through the EGR passage, The set temperature of the temperature switch is set to a temperature higher than a maximum temperature of the confluence portion when the bypass valve is controlled to be closed, When the flow rate of the EGR gas flowing through the EGR passage is equal to or greater than a predetermined second flow rate value while the bypass valve is being controlled to be open, and when the temperature switch does not output the detection signal, the abnormality diagnosis means diagnoses that the bypass valve is in a closed state and that the temperature switch is abnormal. An EGR system characterized by:

3. an EGR passage for allowing a portion of exhaust gas discharged from the engine into the exhaust passage to flow into the intake passage as EGR gas; an EGR valve for adjusting the flow rate of the EGR gas flowing through the EGR passage; an EGR cooler for cooling the EGR gas flowing through the EGR passage; a bypass passage for bypassing the EGR gas flowing to the EGR cooler in the EGR passage; and a bypass valve for opening and closing the bypass passage, a temperature switch that is provided in the EGR passage downstream of a confluence of the EGR gas flowing out from the EGR cooler and the EGR gas flowing out from the bypass passage, the temperature switch outputting a detection signal when detecting only one predetermined set temperature or a predetermined narrow range of set temperatures; an abnormality diagnosis means for diagnosing the presence or absence of an abnormality when the engine is in a predetermined operating state and the EGR valve is in an open state to allow the EGR gas to flow through the EGR passage, The set temperature of the temperature switch is set to a temperature higher than a maximum temperature of the confluence portion when the bypass valve is controlled to be closed, When the flow rate of the EGR gas flowing through the EGR passage is equal to or greater than a predetermined first flow rate value while the bypass valve is being controlled to be closed, the abnormality diagnosis means forcibly controls the bypass valve to be open, and when the detection signal output of the temperature switch is switched from a non-existent state to a present state, the abnormality diagnosis means diagnoses that the bypass valve and the temperature switch are normal. An EGR system characterized by:

Images