EGR system

Abstract

To control the valve-opening of a bypass valve by operating an actuator without forcibly generating intake negative pressure after the complete warmup of an engine, in a constitution for opening / closing-driving the bypass valve of an EGR cooler by the diaphragm-type actuator.SOLUTION: A bypass passage 16 and a bypass valve 17 are arranged at an EGR passage 12, and the bypass valve 17 is opened and closed by an actuator 21. The actuator 21 valve-opens the bypass valve 17 by introducing intake negative pressure into a pressure chamber 23, and valve-closes the bypass valve 17 by introducing atmospheric pressure into the pressure chamber 23. A VSV 28 for switching a state for making a communication path 27 communicating with the pressure chamber 23 communicate with the intake passage 2, and a state for making the communication path communicate with an atmosphere is arranged. When an EGR valve 14 is valve-closed when an engine 1 is operated, an ECU 80 controls the VSV 28, drives the bypass valve 17 so as to be valve-opened by introducing the intake negative pressure which is generated in the intake passage 2 into the pressure chamber 23 via the communication path 27, and stops the drive of the bypass valve in the valve-opened state.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to an EGR system that is applied to a hybrid vehicle that operates the engine intermittently and is provided in the engine. [Background technology]

[0002] A known example of this type of technology is an "engine exhaust gas recirculation device" described in Patent Document 1 below. This device includes an EGR passage that routes a portion of exhaust gas discharged from the engine into an exhaust passage to an intake passage to be recirculated as EGR gas to the engine, and an EGR valve that adjusts the flow rate of the EGR gas flowing through the EGR passage. The EGR valve is configured to be opened and closed by a diaphragm-type actuator. The actuator's casing is divided into a pressure chamber and an atmospheric chamber via a diaphragm. The pressure chamber is provided with a communication passage that communicates with the intake passage. An atmospheric passage branches off from the communication passage, and a switching valve is provided to switch the connection of the communication passage between the atmospheric passage side and the intake passage side. The switching valve switches the pressure state of the communication passage between atmospheric pressure and intake negative pressure, thereby opening and closing the EGR valve. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-170457 Summary of the Invention [Problem to be solved by the invention]

[0004] The EGR valve disclosed in Patent Document 1, which is driven to open and close by a diaphragm-type actuator, can be used as a bypass valve for an EGR cooler in an engine of a hybrid vehicle (hereinafter referred to as "HV") that operates intermittently. This bypass valve is installed in a bypass passage in the EGR passage that bypasses the EGR cooler. In this case, when the engine coolant temperature reaches or exceeds a predetermined temperature, the EGR valve opens simultaneously with restarting the engine from an intermittent stopped state. Therefore, when the EGR valve opens, the intake negative pressure generated in the intake passage is small. Even if the communication passage is connected to the intake passage, sufficient intake negative pressure is not supplied to the pressure chamber, preventing the bypass valve from opening even when necessary. For example, the bypass valve may be opened to warm up the EGR passage, but in this case, the bypass valve cannot be opened, preventing the EGR passage from warming up.

[0005] This disclosed technology has been made in consideration of the above circumstances, and its purpose is to enable valve opening control of the bypass valve by operating the actuator without forcibly generating intake negative pressure after the engine has fully warmed up, in an EGR system provided in an HV engine, in which a bypass valve provided in a bypass passage of an EGR cooler is driven to open and close by a diaphragm-type actuator. [Means for solving the problem]

[0006] In order to achieve the above object, the technology described in claim 1 is applied to a hybrid vehicle in which the engine is operated intermittently, and is an EGR system provided in the engine, the system including an EGR passage that flows a portion of exhaust gas discharged from the engine into an exhaust passage into an intake passage to be recirculated to the engine 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 that bypasses the EGR cooler in the EGR passage, and a bypass valve for opening and closing the bypass passage, the bypass valve being configured to be opened and closed by a diaphragm-type actuator, and the actuator has a casing that is divided into a pressure chamber and an atmospheric chamber via the diaphragm, and the pressure chamber is connected to the bypass valve. The chamber is provided with a communication passage that communicates with the intake passage, the actuator drives the bypass valve to open when intake negative pressure is introduced into the pressure chamber, and drives the bypass valve to close when atmospheric pressure is introduced into the pressure chamber, and the communication passage is provided with an electric switching valve for selectively switching the communication passage between a state in which it is connected to the intake passage and a state in which it is connected to the atmosphere, in this EGR system further comprising EGR control means for controlling the EGR valve, bypass valve, and switching valve, and the EGR control means, when the engine is operating and the EGR valve is closed, controls the switching valve to introduce intake negative pressure generated in the intake passage into the pressure chamber of the actuator via the communication passage, thereby driving the bypass valve to open, and stops it in the open state.

[0007] According to the configuration of the above technology, when the engine is running and the EGR valve is closed, the EGR control means controls the switching valve to introduce the intake negative pressure generated in the intake passage into the pressure chamber of the actuator through the connecting passage, thereby driving the bypass valve to open, and stops the bypass valve in the open state. Therefore, even if the engine intermittently stops after a complete warm-up and the EGR passage needs to be warmed up when the engine is restarted, the bypass valve is already open, so the high-temperature EGR gas flowing through the bypass passage flows into the EGR passage downstream of the EGR cooler.

[0008] In order to achieve the above object, the technology described in claim 2 is the technology described in claim 1, wherein when the engine is stopped intermittently with the bypass valve closed after the engine has fully warmed up, the EGR control means controls the switching valve to introduce the intake negative pressure generated in the intake passage immediately before the engine stopped into the pressure chamber of the actuator via a communication passage, thereby driving the bypass valve to open.

[0009] According to the configuration of the above technology, in addition to the function of the technology described in claim 1, when the engine is stopped intermittently with the bypass valve closed after the engine is fully warmed up, the EGR control means controls the switching valve to introduce the intake negative pressure generated in the intake passage immediately before the engine is stopped into the pressure chamber of the actuator via the communication passage, thereby driving the bypass valve to open. Therefore, even if the EGR passage needs to be warmed up when the engine is restarted after the engine is fully warmed up, the bypass valve has already been opened using the intake negative pressure generated in the intake passage immediately before the engine is stopped, so the high-temperature EGR gas flowing through the bypass passage flows into the EGR passage downstream of the EGR cooler.

[0010] In order to achieve the above object, the technology described in claim 3 is the technology described in claim 1 or 2, wherein when the engine is restarted from an intermittent stop while the bypass valve is stopped in an open state, the EGR control means controls the EGR valve to open with a delay from the restart of the engine.

[0011] According to the configuration of the above technology, in addition to the function of the technology described in claim 1 or 2, when the engine is restarted from an intermittent stop while the bypass valve is stopped in an open state, the EGR control means controls the EGR valve to open with a delay from the restart of the engine. Therefore, even if the intake negative pressure once introduced into the pressure chamber of the actuator leaks when the EGR passage needs to be warmed up when the engine is restarted, the EGR gas does not flow into the intake passage when the engine is restarted, and intake negative pressure is generated in the intake passage, which can be used to drive the bypass valve open.

[0012] In order to achieve the above object, the technology described in claim 4 is the technology described in claim 3, wherein the EGR control means controls the EGR valve to open with a delay after the engine is restarted when the intermittent stop time of the engine exceeds a predetermined time.

[0013] According to the configuration of the above technology, in addition to the function of the technology described in claim 3, if the intermittent engine stop time exceeds a predetermined time, the EGR control means controls the EGR valve to open with a delay after the restart of the engine. Therefore, even if the intermittent engine stop time exceeds the predetermined time and the intake negative pressure once introduced into the pressure chamber of the actuator leaks, when the engine is restarted, the EGR gas does not flow into the intake passage, and intake negative pressure is generated in the intake passage, and this intake negative pressure can be used to drive the bypass valve open.

[0014] In order to achieve the above object, the technology described in claim 5 is applied to a hybrid vehicle in which the engine is operated intermittently, and is an EGR system provided in the engine, the system including an EGR passage that flows a part of the exhaust gas discharged from the engine into an exhaust passage into an intake passage to be recirculated to the engine 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 that bypasses the EGR cooler in the EGR passage, and a bypass valve for opening and closing the bypass passage, the bypass valve being configured to be opened and closed by a diaphragm-type actuator, and the actuator has a casing that is formed by a diaphragm. an actuator that drives the bypass valve to open when intake negative pressure is introduced into the pressure chamber and drives the bypass valve to close when atmospheric pressure is introduced into the pressure chamber; and an electrically operated changeover valve that selectively changes the state of the communication passage between communicating with the intake passage and communicating with the atmosphere is provided in the communication passage; the EGR system further comprises EGR control means for controlling the EGR valve, bypass valve, and changeover valve; and the EGR control means controls the EGR valve to open with a delay after the engine restarts when the engine is restarted from an intermittent stop while the bypass valve is stopped in an open state.

[0015] According to the configuration of the above technology, when the engine is restarted from an intermittent stop while the bypass valve is stopped in an open state, the EGR control means controls the EGR valve to open after a delay from the restart of the engine. Therefore, even if the intake negative pressure once introduced into the pressure chamber of the actuator leaks when the EGR passage needs to be warmed up when the engine is restarted, the EGR gas does not flow into the intake passage when the engine is restarted, and intake negative pressure is generated in the intake passage, which can be used to drive the bypass valve open.

[0016] In order to achieve the above object, the technology described in claim 6 is the technology described in claim 5, wherein the EGR control means controls the EGR valve to open with a delay from the bypass valve being driven to open when the intermittent engine stop time exceeds a predetermined time.

[0017] According to the configuration of the above technology, in addition to the function of the technology described in claim 5, if the intermittent stop time of the engine exceeds a predetermined time, the EGR control means controls the EGR valve to open with a delay after the restart of the engine. Therefore, even if the intermittent stop time of the engine exceeds the predetermined time and the intake negative pressure once introduced into the pressure chamber of the actuator leaks, when the engine is restarted, the EGR gas does not flow into the intake passage, and intake negative pressure is generated in the intake passage, and this intake negative pressure can be used to drive the bypass valve open.

[0018] In order to achieve the above object, the technology described in claim 7 is the technology described in any one of claims 1 to 6, wherein the EGR control means switches the communication passage to a state in which it communicates with the atmosphere when the power supply to the switching valve is turned off, thereby driving the bypass valve to close.

[0019] According to the configuration of the above technology, in addition to the function of the technology described in any one of claims 1 to 6, the EGR control means switches the communication passage to a state in which it communicates with the atmosphere and drives the bypass valve to close when the switching valve is de-energized. Therefore, even if the switching valve fails, the switching valve will be in a state in which the communication passage is communicated with the atmosphere, and the bypass valve will be kept in a closed state.

[0020] In order to achieve the above object, the technology described in claim 8 is the technology described in any one of claims 1 to 7, wherein when the engine is started at a low temperature and the EGR valve is in a closed state, the EGR control means controls the switching valve to introduce the intake negative pressure generated in the intake passage into the pressure chamber of the actuator via a communication passage, thereby driving the bypass valve to open.

[0021] According to the configuration of the above technology, in addition to the effect of the technology described in any one of claims 1 to 7, when the engine is started at a low temperature and the EGR valve is in a closed state, it is possible to ensure the intake negative pressure required for the actuator to operate in the intake passage, and it is possible to drive the bypass valve to open. [Effects of the Invention]

[0022] According to the technology described in claim 1, in an EGR system provided in an HV engine, in which a bypass valve provided in a bypass passage of an EGR cooler is driven to open and close by a diaphragm-type actuator, after the engine is fully warmed up, the actuator can be operated by intake negative pressure to control the opening of the bypass valve without forcibly generating intake negative pressure.

[0023] According to the technology recited in claim 2, the same effect as that of the technology recited in claim 1 can be obtained.

[0024] According to the technology described in claim 3, in addition to the effect of the technology described in claim 1 or 2, even if the intake negative pressure once introduced into the pressure chamber of the actuator leaks during intermittent stopping, the actuator can be operated by the intake negative pressure to control the opening of the bypass valve when the engine is restarted after being fully warmed up.

[0025] According to the technology described in claim 4, in addition to the effect of the technology described in claim 3, if it is determined that the intake negative pressure once introduced into the pressure chamber of the actuator during intermittent stopping is leaking, the actuator can be operated with the intake negative pressure to control the opening of the bypass valve when the engine is restarted after being fully warmed up.

[0026] According to the technology described in claim 5, in an EGR system provided in an HV engine, in which a bypass valve provided in a bypass passage of an EGR cooler is driven to open and close by a diaphragm-type actuator, when the engine is restarted after being fully warmed up, the actuator can be operated by intake negative pressure to control the opening of the bypass valve without forcibly generating intake negative pressure.

[0027] According to the technology described in claim 6, in addition to the effect of the technology described in claim 5, regardless of whether or not there is leakage of intake negative pressure from the pressure chamber, the actuator can be operated by intake negative pressure after the engine is fully warmed up, thereby controlling the opening of the bypass valve.

[0028] According to the technology described in claim 7, in addition to the effect of the technology described in any one of claims 1 to 6, when the switching valve fails, it is possible to prevent high-temperature EGR gas from accidentally flowing into the bypass passage, and to suppress melting damage to the EGR passage downstream of the EGR cooler.

[0029] According to the technology described in claim 8, in addition to the effect of the technology described in any one of claims 1 to 7, even during cold start of the engine, the actuator can be operated by the intake negative pressure to control the opening of the bypass valve without forcibly generating the intake negative pressure. [Brief explanation of the drawings]

[0030] [Figure 1] FIG. 1 is a schematic configuration diagram showing an engine system according to a first embodiment. [Figure 2] 3 is a cross-sectional view showing the EGR cooler cut along its longitudinal direction together with the bypass valve opening / closing drive mechanism when the bypass valve is fully closed in the first embodiment; FIG. [Figure 3] 3 is an enlarged cross-sectional view showing a part of the EGR cooler according to the first embodiment, which is a portion surrounded by a dashed-dotted rectangle in FIG. 2. FIG. [Figure 4] 4 is an enlarged cross-sectional view equivalent to FIG. 3 showing a part of the EGR cooler when the bypass valve is fully open in the first embodiment; FIG. [Figure 5] 5A and 5B are schematic views showing an operating state of the opening / closing drive mechanism in the first embodiment. [Figure 6] 5A and 5B are schematic views showing an operating state of the opening / closing drive mechanism in the first embodiment. [Figure 7] 4 is a flowchart showing the contents of bypass valve switching control in the first embodiment. [Figure 8]4 is a flowchart showing the contents of bypass valve switching control in the first embodiment. [Figure 9] 5 is a flowchart showing the contents of bypass valve open request determination control in the first embodiment. [Figure 10] 4 is a valve-opening required water temperature map that is referenced to determine a valve-opening required water temperature according to an intake air temperature in the first embodiment. [Figure 11] 5 is a time chart showing the behavior of various parameters related to bypass valve switching control in the first embodiment. [Figure 12] 10 is a flowchart showing the contents of bypass valve open request determination control according to the second embodiment. [Figure 13] 10 is a valve-opening determination time map that is referenced to determine a valve-opening determination time according to a coolant temperature and an intake air temperature in the second embodiment. [Figure 14] 10 is a flowchart showing the contents of bypass valve open request determination control according to the third embodiment. [Figure 15] 11 is a time correction coefficient map that is referenced to determine a time correction coefficient according to an EGR opening degree according to the third embodiment. [Figure 16] 10 is a flowchart showing the contents of bypass valve open request determination control according to the fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0031] Hereinafter, several embodiments in which this EGR system is embodied in a gasoline engine system mounted on an HV will be described.

[0032] First Embodiment First, the first embodiment will be described in detail with reference to the drawings.

[0033] [About the engine system] FIG. 1 is a schematic diagram of a gasoline engine system (hereinafter simply referred to as the "engine system") according to this embodiment. This engine system is applied to an HV with an intermittent engine operation. The engine system installed in the HV 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. The intake passage 2 is provided with an air cleaner 9, a throttle device 4, and an intake manifold 5, arranged from the upstream side. The exhaust passage 3 is provided with an exhaust manifold 6 and a catalyst 7, arranged in this order from the upstream side. The catalyst 7 may incorporate, for example, a three-way catalyst to purify exhaust gas. In addition, the engine system is provided with a high-pressure loop-type exhaust gas recirculation (EGR) system 11.

[0034] 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 throttle valve 4a to open and close with a variable opening in response to the driver's accelerator operation. The intake manifold 5 is made primarily of a resin material, and is disposed in the intake passage 2 immediately upstream of the engine 1. It includes one 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. The intake manifold 5 forms part of the intake passage 2.

[0035] 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.

[0036] 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, and the crankshaft (not shown) rotates, thereby generating power for the engine 1. The exhaust manifold 6 constitutes a part of the exhaust passage 3.

[0037] [About the EGR system] 1, an EGR system 11 of this embodiment is provided between an exhaust passage 3 and an intake passage 2. The EGR system 11 includes an EGR passage 12 that flows a portion of the exhaust gas discharged from the engine 1 into the exhaust passage 3 into the intake passage 2 as EGR gas to be recirculated to the engine 1, an EGR cooler 13 that cools the EGR gas flowing through the EGR passage 12, an EGR valve 14 that adjusts the flow rate of the EGR gas flowing through the EGR passage 12, and an EGR gas distributor 15 that distributes the EGR gas flowing through the EGR passage 12 to each branch pipe 5b of the intake manifold 5 so as to distribute the EGR gas flowing through the EGR passage 12 to each cylinder of the engine 1. The flow paths through which the EGR gas flows, including the EGR cooler 13, the EGR valve 14, and the EGR gas distributor 15, also constitute the EGR passage 12. The piping that constitutes the EGR passage 12 upstream of the EGR gas distributor 15 includes an inlet 12a and an outlet 12b. The inlet 12a is connected to the exhaust passage 3 downstream of the catalyst 7, and the outlet 12b is connected to the EGR gas distributor 15. In this embodiment, the EGR gas distributor 15 forms the final stage of the EGR passage 12. In the EGR passage 12, the EGR valve 14 is provided downstream of the EGR cooler 13, and the EGR gas distributor 15 is provided downstream of the EGR valve 14.

[0038] The EGR gas distributor 15 is mainly made of a resin material, has an elongated shape overall, and is disposed so that its longitudinal direction crosses the multiple branch pipes 5b of the intake manifold 5. In this embodiment, the EGR gas distributor 15 includes a gas chamber 15a in which introduced EGR gas collects, and multiple (four) gas distribution passages 15b that distribute the EGR gas from the gas chamber 15a to each branch pipe 5b.

[0039] In this EGR system 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.

[0040] In this embodiment, a bypass passage 16 is integrally provided with the EGR cooler 13. The bypass passage 16 is a passage in the EGR passage 12 that bypasses the EGR cooler 13, and allows a portion of the EGR gas flowing to the EGR cooler 13 to bypass the EGR passage 12. A bypass valve 17 for opening and closing the bypass passage 16 is provided in the bypass passage 16.

[0041] Fig. 2 is a cross-sectional view of the EGR cooler 13 cut along its longitudinal direction when the bypass valve 17 is fully closed, together with the opening / closing drive mechanism 19 of the bypass valve 17. Fig. 3 is an enlarged cross-sectional view of a portion of the EGR cooler 13, which is surrounded by a dashed-dotted rectangle X1 in Fig. 2. Fig. 4 is an enlarged cross-sectional view similar to Fig. 3, showing a portion of the EGR cooler 13 when the bypass valve 17 is fully open.

[0042] As shown in FIG. 2 , the EGR cooler 13 includes a housing 41, a heat exchanger 42 provided within the housing 41, an inlet 43 for introducing EGR gas into the housing 41, and an outlet 44 for discharging the EGR gas from the housing 41. The bypass passage 16 is integrally provided with the housing 41. The heat exchanger 42 includes an inlet 42a through which the EGR gas flows and an outlet 42b through which the EGR gas flows. The bypass passage 16 includes an inlet 16a through which the EGR gas flows and an outlet 16b through which the EGR gas flows. The outlet 16b of the bypass passage 16 is disposed adjacent to the outlet 42b of the heat exchanger 42. The housing 41 also includes an introduction space 45 between the inlet 42a of the heat exchanger 42 and the inlet 43, and an outlet space 46 between the outlet 42b of the heat exchanger 42 and the outlet 44. The bypass passage 16 is adjacent to the heat exchanger 42 via a partition wall 48 .

[0043] As shown in FIG. 2, in this embodiment, the EGR cooler 13 is disposed obliquely when mounted on a vehicle so that EGR gas flows obliquely upward. In this oblique arrangement, the outlet 44 is disposed vertically higher than the inlet 43, and the bypass passage 16 is disposed vertically below the heat exchanger 42. As a result, condensed water generated inside the heat exchanger 42 is discharged from the outlet 42b, flows down into the bypass passage 16, and then flows down toward an upstream portion of the bypass passage 16. The heat exchanger 42 includes a water passage (not shown) through which cooling water for the engine 1 flows, and a gas passage (not shown) disposed within the water passage through which EGR gas flows. Note that, for convenience, the cooling water intake and outlet for the heat exchanger 42 are not shown in FIG. 2, and the heat exchanger 42 and the bypass valve 17 are illustrated in a simplified form.

[0044] 2, in this embodiment, the bypass valve 17 is disposed in the housing 41 in correspondence with the outlet 16b of the bypass passage 16. The bypass valve 17 includes a valve element 61 having a substantially rectangular plate shape and a rotary shaft 62 that rotates the valve element 61. The bypass valve 17 is configured as a swing type in which one side of the valve element 61 is fixed to the rotary shaft 62 and the other side of the valve element 61 opposing the one side swings around the rotary shaft 62. In addition, an arm 63 extending radially from one end of the rotary shaft 62 is provided.

[0045] [About the opening and closing mechanism] As shown in FIGS. 1 and 2, the EGR system 11 of this embodiment includes an opening / closing drive mechanism 19 that rotates a rotary shaft 62 of the bypass valve 17 to open and close the valve element 61. FIGS. 5 and 6 are schematic diagrams illustrating the operation of the opening / closing drive mechanism 19. As shown in FIGS. 1, 2, 5, and 6, the opening / closing drive mechanism 19 includes a diaphragm-type actuator 21 that opens and closes the bypass valve 17. The actuator 21 has a casing 21a, which is divided by a diaphragm 22 into a pressure chamber 23 and an atmospheric chamber 24. A spring 25 is provided in the pressure chamber 23 to bias the diaphragm 22 toward the atmospheric chamber 24. A base end of a rod 26 that protrudes from the atmospheric chamber 24 is fixed to the diaphragm 22. As shown in FIG. 2, the tip of the rod 26 is connected to an arm 63 to rotate the rotary shaft 62. A communication passage 27 that communicates with the surge tank 5a (which also serves as the intake passage 2) is provided in the pressure chamber 23. The atmosphere chamber 24 communicates with the atmosphere via an atmosphere port 21b.

[0046] In this opening / closing drive mechanism 19, the actuator 21 drives the bypass valve 17 to open when intake negative pressure is introduced into the pressure chamber 23, and drives the bypass valve 17 to close when atmospheric pressure is introduced into the pressure chamber 23. An electric vacuum switching valve (VSV) 28 is provided in the communication passage 27 to selectively switch the communication passage 27 between a state in which the communication passage 27 is connected to the surge tank 5a and a state in which the communication passage 27 is connected to the atmosphere. The VSV 28 corresponds to an example of a "switching valve" in the technology disclosed herein. As shown in FIGS. 2, 5, and 6, the VSV 28 has a first port 28a, a second port 28b, and a third port 28c. The first port 28a is connected to the communication passage 27 extending from the pressure chamber 23. The second port 28b is connected to an air filter 29 communicating with the atmosphere. The third port 28c is connected to the communication passage 27 extending from the surge tank 5a. A check valve 30 is provided in the communication passage 27 extending from the surge tank 5a. The check valve 30 is configured to block airflow from the surge tank 5a toward the third port 28c and to allow airflow from the third port 28c toward the surge tank 5a.

[0047] In this embodiment, the VSV 28 is a normally-open valve, and is configured such that when not energized (power-off), the first port 28a communicates with the second port 28b, connecting the communication passage 27 extending from the pressure chamber 23 to the atmosphere, and when energized (on), the first port 28a communicates with the third port 28c, connecting the communication passage 27 extending from the pressure chamber 23 to the surge tank 5a. That is, when the VSV 28 is turned off, atmospheric pressure acting on the air filter 29 is introduced into the pressure chamber 23 of the actuator 21 through the communication passage 27, as shown in FIG. 5. At this time, the diaphragm 22 is displaced toward the atmospheric chamber 24, causing almost the entire rod 26 to protrude from the casing 21a, and the bypass valve 17 is fully closed, as shown in FIGS. 2 and 3. On the other hand, when the VSV 28 is turned on, the intake pressure acting on the communication passage 27 from the surge tank 5a is introduced into the pressure chamber 23 of the actuator 21, as shown in Fig. 6. At this time, the diaphragm 22 is displaced toward the pressure chamber 23 against the biasing force of the spring 25, and a part of the rod 26 is immersed in the casing 21a, causing the bypass valve 17 to change from a fully closed state to a fully open state as shown in Fig. 4.

[0048] [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 71 to 77 provided in this engine system constitute an operating condition detection means for detecting the operating condition of the engine 1. 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 and detects changes in the crank angle (crank angular velocity) as the rotation speed (engine 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 between the exhaust manifold 6 and 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.

[0049] This engine system further includes an electronic control unit (ECU) 80 that controls the system. The various sensors 71-77 are connected to the ECU 80. The ECU 80 is also connected to an injector (not shown) and an ignition coil (not shown) in addition to the EGR valve 14 and VSV 28. In this embodiment, the ECU 80 corresponds to an example of a control means in the disclosed technology. As is well known, the ECU 80 includes a central processing unit (CPU), various memories, external input circuits, external output circuits, and the like. Predetermined control programs relating to various controls are stored in the memory. The CPU executes fuel injection control, ignition timing control, EGR control, and the like based on the predetermined control programs, in response to detection signals from the various sensors 71-77 input via the input circuits.

[0050] In this embodiment, the ECU 80 controls the EGR valve 14 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. During other operating conditions, the ECU 80 calculates a target EGR opening according to the operating state and controls the EGR valve 14 to the target EGR opening. When the EGR valve 14 is opened, exhaust gas is discharged from the engine 1 into the exhaust passage 3. 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, and the like into the intake passage 2 (intake manifold 5), where it is distributed and recirculated to each cylinder of the engine 1. Additionally, the ECU 80 executes bypass valve switching control in connection with the EGR control to switch the bypass valve 17 between open and closed states according to the HV driving mode.

[0051] [Bypass valve switching control] Next, the bypass valve switching control of this embodiment will be described. Figures 7 and 8 are flowcharts showing the contents of the bypass valve switching control. When the process proceeds to this routine, the ECU 80 determines in step 100 whether the ignition (IG) is on, i.e., whether the ignition device is on. 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 190.

[0052] In step 190, the ECU 80 controls the VSV 28 to turn off in order to close the bypass valve 17, and sets the VSV on flag XVON, which indicates that the VSV 28 has been turned on, to "0." After that, the ECU 80 returns the process to step 100.

[0053] In step 110, the ECU 80 acquires the coolant temperature THW, engine speed NE, throttle opening TA, and intake pressure PM, as well as the EGR opening / closing operation, i.e., the open or closed state of the EGR valve 14, based on the detected values ​​of the water temperature sensor 71, engine speed sensor 72, throttle sensor 75, and intake pressure sensor 74.

[0054] Next, in step 120, the ECU 80 determines whether the HV is in running mode (1) based on the various parameters THW, NE, TA, and PM that have been acquired and the EGR opening and closing operation. Running mode (1) refers to a state in which the engine 1 is started at a low water temperature, is idling, and is in an EGR cut state (EGR valve closed). In running mode (1), a high intake negative pressure is generated in the intake passage 2 due to EGR cut. If the result of this determination is positive, the ECU 80 proceeds to step 150, and if the result of this determination is negative, the ECU 80 proceeds to step 130.

[0055] In step 130, the ECU 80 determines whether the HV is in driving mode (2) based on the various parameters THW, NE, TA, and PM that have been acquired and the EGR opening / closing operation. Driving mode (2) refers to a state in which the engine 1 is started at a low water temperature and the EGR is on (EGR valve open). In this driving mode (2), the high intake negative pressure generated in the previous driving mode (1) has already been introduced into the pressure chamber 23 of the actuator 21. If the result of this determination is positive, the ECU 80 proceeds to step 150, and if the result of this determination is negative, the ECU 80 proceeds to step 140.

[0056] In step 140, the ECU 80 determines whether the HV is in running mode (3) based on the various parameters THW, NE, TA, and PM and the EGR opening / closing operation. Running mode (3) refers to a state in which the engine 1 has restarted and is idling. Even in running mode (3), a high intake negative pressure is generated by cutting the EGR. If the result of this determination is positive, the ECU 80 proceeds to step 150, and if the result of this determination is negative, the ECU 80 proceeds to step 200.

[0057] In step 150, which follows step 120, step 130, or step 140, the ECU 80 determines whether or not there is a request to open the bypass valve 17. This request is issued by the ECU 80 when it determines that the EGR passage 12 needs to be warmed up. The control for determining this request will be described later. If the result of this determination is positive, the ECU 80 proceeds to step 160, and if the result of this determination is negative, the ECU 80 proceeds to step 170.

[0058] In step 160, the ECU 80 controls the VSV 28 to turn on in order to open the bypass valve 17, and sets a VSV-on flag XVON, which indicates that the VSV 28 has been turned on, to "1."

[0059] In step 170, the ECU 80 controls the VSV 28 to turn off in order to close the bypass valve 17, and sets the VSV on flag XVON to "0."

[0060] In step 180, which follows from step 160 or step 170, the ECU 80 determines whether there is a request for intermittent engine stop. This request for intermittent engine stop is issued by the HV control controller in consideration of the drive of the HV motor. If the result of this determination is negative, the ECU 80 returns the process to step 100, and if the result of this determination is positive, the ECU 80 proceeds to step 250.

[0061] On the other hand, in step 200, moving from step 140, the ECU 80 determines whether the HV is in running mode (4) based on the various parameters THW, NE, TA, and PM that have been acquired and the EGR opening and closing operation. Running mode (4) refers to a state in which the engine 1 has restarted and the EGR is on (the EGR valve is open). In running mode (4), a low intake negative pressure is generated due to the EGR being on. 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 proceeds to step 260.

[0062] In step 210, the ECU 80 determines whether the VSV-on flag XVON is 1. 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 240.

[0063] In step 220, it is determined whether or not there is a request to close the bypass valve 17. This request to close the valve is a request that the ECU 80 determines when there is no need to warm up the EGR passage 12. The control for determining this request to close the valve will be described later together with the control for determining a request to open the valve. If the result of this determination is positive, the ECU 80 proceeds to step 230, and if the result of this determination is negative, the ECU 80 proceeds to step 240.

[0064] In step 230, the ECU 80 controls the VSV 28 to turn off in order to close the bypass valve 17, and sets the VSV on flag XVON to "0."

[0065] In step 240, which follows from step 210, step 220, or step 230, the ECU 80 determines whether or not there is an intermittent stop request for the engine 1. 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 returns the process to step 100.

[0066] At step 250, which follows step 180 or step 240, the ECU 80 controls the VSV 28 to turn on in order to open the bypass valve 17, and sets the VSV on flag XVON to "1."

[0067] In step 260, moving from step 200 or step 250, the ECU 80 intermittently stops the engine 1. In this case, the driving mode (5) is entered. In this driving mode (5), when the engine 1 is intermittently stopped, the high intake negative pressure generated in the intake passage 2 by closing the throttle device 4 and cutting the EGR (closing the EGR valve) can be introduced into the pressure chamber 23 of the actuator 21. If the time period during which the engine 1 is intermittently stopped (cuts the EGR) is long, the introduction of EGR gas into the intake passage 2 can be delayed when the engine 1 is restarted, thereby generating the intake negative pressure.

[0068] Next, in step 270, the ECU 80 determines whether or not there is a request to restart the engine 1. This restart request is issued by the HV control controller in consideration of the HV motor drive. If the result of this determination is positive, the ECU 80 proceeds to step 280, and if the result of this determination is negative, the ECU 80 returns to step 100.

[0069] In step 280, the ECU 80 acquires the intermittent stop time TIstp of the engine 1. This intermittent stop time TIstp is the time counted by the ECU 80 from the last time the engine 1 was intermittently stopped.

[0070] Next, in step 290, the ECU 80 determines whether the intermittent stop time TIstp has exceeded a predetermined time A1. This predetermined time A1 is a time that assumes that a small amount of air leaks from the VSV 28 will cause the intake negative pressure to be lost from the pressure chamber 23 of the actuator 21. If the result of this determination is positive, the ECU 80 determines that a large amount of intake negative pressure has been lost from the pressure chamber 23, and proceeds to step 300. If the result of this determination is negative, the ECU 80 determines that a small amount of intake negative pressure has been lost from the pressure chamber 23, and proceeds to step 310.

[0071] Next, in step 300, the ECU 80 restarts the engine 1 and executes delayed EGR control, and then returns the process to step 100. That is, in steps 290 to 300, if the intermittent stop time TIstp is long, the ECU 80 determines that a large amount of intake negative pressure has been released from the pressure chamber 23 of the actuator 21, and delays the start of EGR after the engine 1 is restarted. In this case, the intake negative pressure is generated in the intake passage 2 by the amount of the delay in the start of EGR and the delay in the introduction of EGR gas into the EGR passage 12, and this intake negative pressure is used to operate the actuator 21, making it possible to open the bypass valve 17.

[0072] On the other hand, in step 310, moving from step 290, the ECU 80 restarts the engine 1 and executes normal EGR control, and then returns the process to step 100. That is, in step 310, moving from step 290, if the intermittent stop time TIstp is not long, the ECU 80 determines that no loss of intake negative pressure has occurred from the pressure chamber 23 of the actuator 21, and starts EGR as usual after the engine 1 is restarted.

[0073] According to the bypass valve switching control described above, when the engine 1 is operating and the EGR valve 14 is closed (if YES in step 120 and YES in step 140), the ECU 80 controls the VSV 28 to introduce the intake negative pressure generated in the surge tank 5a (intake passage 2) into the pressure chamber 23 of the actuator 21 via the communicating passage 27 to drive the bypass valve 17 to open (if YES in step 150, processing of step 160; if YES in step 180, processing of step 250), and stops the engine in the open state. Here, particularly when the engine 1 intermittently stops with the bypass valve 17 closed after the engine 1 has fully warmed up, the ECU 80 controls the VSV 28 to introduce the intake negative pressure generated in the intake passage 2 immediately before the engine 1 was stopped into the pressure chamber 23 of the actuator 21 via the communicating passage 27 to drive the bypass valve 17 to open.

[0074] According to the bypass valve switching control described above, when the engine 1 is restarted from an intermittent stop while the bypass valve 17 is stopped in an open state (YES in step 270), the ECU 80 controls the VSV 28 to introduce the intake negative pressure generated in the surge tank 5a (intake passage 2) into the pressure chamber 23 of the actuator 21, thereby intermittently stopping the engine 1 while maintaining the bypass valve 17 in an open state (processing of steps 250 and 260), so there is no need to control the opening of the bypass valve 17 when the engine 1 is restarted. If the ECU 80 determines that the intake negative pressure once introduced into the pressure chamber 23 of the actuator 21 during the intermittent stop is leaking, it controls the EGR valve 14 to open (processing of step 300) with a delay after the engine 1 is restarted. Furthermore, when restarting the engine 1, if the intermittent stop time TIstp of the engine 1 exceeds a predetermined time A1 (if step 290 is YES), the ECU 80 controls the EGR valve 14 to open (process step 300) with a delay from the restart of the engine 1. In other words, if the time from the intermittent stop of the engine 1 to the restart (intermittent stop time TIstep) exceeds the predetermined time A1, there is a concern that pressure loss may have occurred, so the opening of the EGR valve 14 is delayed to generate intake negative pressure.

[0075] According to the bypass valve switching control described above, when the VSV 28 is de-energized, the ECU 80 switches the communication passage 27 to a state in which it communicates with the atmosphere, and drives the bypass valve 17 to close (steps 170, 190, 230).

[0076] Furthermore, according to the bypass valve switching control described above, when the engine 1 is started at a low temperature (if step 120 is YES) and the EGR valve 14 is in a closed state (if step 150 is YES), the ECU 80 controls the VSV 28 to introduce the intake negative pressure generated in the intake passage 2 into the pressure chamber 23 of the actuator 21 via the connecting passage 27, thereby driving the bypass valve 17 to open.

[0077] [Bypass valve opening request determination control] Next, the bypass valve open request determination control will be explained. The bypass valve open request determination control is shown in a flowchart in FIG.

[0078] When the process proceeds to this routine, the ECU 80 acquires the coolant temperature THW, the engine speed NE, and the intake air temperature THA based on the detected values ​​of the water temperature sensor 71, the speed sensor 72, and the intake air temperature sensor 77 in step 400.

[0079] Next, in step 410, the ECU 80 determines whether the engine speed NE has exceeded 500 rpm. If the result of this determination is positive, the ECU 80 determines that the engine 1 is running and proceeds to step 420. If the result of this determination is negative, the ECU 80 determines that the engine 1 is stopped and proceeds to step 450.

[0080] In step 420, the ECU 80 calculates the valve-opening required water temperature THWBO according to the intake air temperature THA. The ECU 80 can determine the valve-opening required water temperature THWBO according to the intake air temperature THA by, for example, referring to a predetermined valve-opening required water temperature map shown in FIG.

[0081] Next, in step 430, the ECU 80 determines whether the valve-opening required water temperature THWBO is higher than the cooling water temperature THW. If the result of this determination is positive, the ECU 80 proceeds to step 440, and if the result of this determination is negative, the ECU 80 proceeds to step 450.

[0082] Then, in step 440, the ECU 80 determines that the EGR passage 12 needs to be warmed up, and after determining that a bypass valve opening request is made, returns the process to step 400.

[0083] On the other hand, in step 450, the ECU 80 determines that the EGR passage 12 does not need to be warmed up, and after determining that the bypass valve is to be closed, returns the process to step 400.

[0084] According to the bypass valve open request determination control described above, the ECU 80 determines whether the bypass valve is required to be opened or closed depending on the intake air temperature THA, i.e., the outside air temperature, while the engine 1 is running.

[0085] [About the EGR system's function and effects] According to the configuration of the EGR system of this embodiment described above, particularly the configuration of the opening / closing drive mechanism 19, the pressure in the surge tank 5a (intake passage 2) downstream of the throttle device 4 varies depending on the operating state of the engine 1, ranging from intake negative pressure to atmospheric pressure. Here, by turning off the VSV 28, the first port 28a and the second port 28b are connected to each other, and atmospheric pressure introduced into the connecting passage 27 via the air filter 29 is introduced into the pressure chamber 23 of the actuator 21. As shown in FIG. 5, the diaphragm 22 is displaced toward the atmospheric chamber 24, and the actuator 21 is in a predetermined operating state, i.e., the rod 26 protrudes from the casing 21a. This drives the bypass valve 17 to a fully closed position. On the other hand, by turning on the VSV 28, the first port 28a and the third port 28c are connected to each other, and atmospheric pressure no longer acts on the connecting passage 27. At this time, if the surge tank 5a (intake passage 2) is under negative intake pressure, that negative intake pressure is introduced into the pressure chamber 23 via the check valve 30 and the communication passage 27, and as shown in Figure 6, the diaphragm 22 is displaced toward the pressure chamber 23 against the biasing force of the spring 25, causing the actuator 21 to assume an operating state opposite to the above-mentioned predetermined operating state, i.e., a state in which a portion of the rod 26 is immersed in the casing 21a. This causes the bypass valve 17 to be driven to fully open. At this time, by keeping the VSV 28 on, atmospheric pressure does not act on the pressure chamber 23, and the check valve 30 prevents the release of negative intake pressure from the pressure chamber 23 to the surge tank 5a (intake passage 2). This keeps the negative intake pressure in the pressure chamber 23 at its largest, and keeps the bypass valve 17 fully open.

[0086] Here, when the engine 1 is operating with the bypass valve 17 closed after the engine 1 has fully warmed up and the EGR valve 14 is closed, the ECU 80 controls the VSV 28 to introduce the intake negative pressure generated in the surge tank 5a (intake passage 2) into the pressure chamber 23 of the actuator 21 via the communicating passage 27, thereby driving the bypass valve 17 to open, and stops the bypass valve 17 in the open state. Therefore, even if the EGR passage 12 needs to be warmed up when the engine 1 is subsequently restarted after being stopped intermittently after the engine 1 has fully warmed up, the bypass valve 17 is already open, so the high-temperature EGR gas flowing through the bypass passage 16 flows into the EGR passage 12 (EGR gas distributor 15) downstream of the EGR cooler 13. Therefore, in an EGR system provided in an HV engine 1, in which a bypass valve 17 provided in a bypass passage 16 of an EGR cooler 13 is driven to open and close by a diaphragm-type actuator 21, when the engine 1 is restarted after being fully warmed up, the actuator 21 can be operated by the intake negative pressure to control the opening of the bypass valve 17 without forcibly generating an intake negative pressure (for example, without controlling the throttle device 4).

[0087] That is, in this embodiment, the ECU 80 (C1) controls the bypass valve 17 to be open when the engine 1 is stopped intermittently, and stops the engine in the open state, and (C2) when the engine 1 is restarted, the bypass valve 17 is opened to allow high-temperature EGR gas to flow through the bypass passage 16, thereby warming up the EGR passage 12 downstream of the EGR cooler 13. Then, (C3) when the warm-up of the EGR passage 12 is completed, the ECU 80 controls the bypass valve 17 to be closed. By repeating the above processes (C1) to (C3) in accordance with the intermittent operation of the engine 1, the ECU 80 controls the bypass valve 17 to be open after the engine 1 is completely warmed up, without forcibly generating an intake negative pressure in the intake passage 2.

[0088] Furthermore, according to the configuration of this embodiment, when the engine 1 is restarted from an intermittent stop while the bypass valve 17 is in an open state, the ECU 80 controls the VSV 28 to introduce the intake negative pressure generated in the surge tank 5a (intake passage 2) into the pressure chamber 23 of the actuator 21, thereby intermittently stopping the engine 1 while maintaining the bypass valve 17 in an open state. This eliminates the need to control the opening of the bypass valve 17 when restarting the engine 1. If the ECU 80 determines that the intake negative pressure once introduced into the pressure chamber 23 of the actuator 21 during the intermittent stop is leaking, it controls the EGR valve 14 to open with a delay after the engine 1 is restarted. FIG. 11 shows the behavior of various parameters related to this control using a time chart. In FIG. 11, (a) shows changes in the engine speed NE, (b) shows changes in the intake pressure PM, and (c) shows changes in the EGR opening TEGR. 11 , if the engine 1 is restarted between times t1 and t4 after an intermittent stop, if normal EGR control is executed after the engine 1 starts restarting at time t1, the EGR valve 14 starts opening at time t2, as shown by the solid line in (c). Therefore, at time t3, as shown by the solid line in (b), no appropriate intake negative pressure is generated, and the intake negative pressure cannot be introduced into the pressure chamber 23 of the actuator 21. In contrast, in this embodiment, as shown by the dashed line in (c), the EGR valve 14 starts opening at time t3, which is later than time t2. Therefore, as shown by the dashed line in (b), appropriate intake negative pressure is generated at time t3, and the intake negative pressure can be introduced into the pressure chamber 23 of the actuator 21. Therefore, even if the EGR passage 12 needs to be warmed up when the engine 1 is restarted after the engine 1 has stopped intermittently after being fully warmed up, the bypass valve 17 remains open before the EGR valve 14 opens, and so valve opening control is not necessary. Even if the intake negative pressure once introduced into the pressure chamber 23 of the actuator 21 leaks, the EGR gas does not flow into the intake passage 2 by delaying the opening of the EGR valve 14 when the engine 1 is restarted, and intake negative pressure is generated in the intake passage 2, which can be used to drive the bypass valve 17 to open.In this sense, in an EGR system provided in an HV engine 1, in which the bypass valve 17 provided in the bypass passage 16 of the EGR cooler 13 is driven to open and close by a diaphragm-type actuator 21, when the engine 1 is restarted after being fully warmed up, the actuator 21 can be operated by the intake negative pressure to control the opening of the bypass valve 17 without forcibly generating intake negative pressure (for example, without controlling the throttle device 4).

[0089] Furthermore, according to the configuration of this embodiment, if the intermittent stop time TIstp of the engine 1 exceeds the predetermined time A1, the ECU 80 controls the opening of the EGR valve 14 with a delay from the time of restarting the engine. Therefore, even if the intermittent stop time TIstp of the engine 1 exceeds the predetermined time A1 and the intake negative pressure once introduced into the pressure chamber 23 of the actuator 21 leaks, EGR gas does not flow into the intake passage 2 when the bypass valve 17 opens, and instead, intake negative pressure is generated in the intake passage 2. This intake negative pressure can be used to drive the bypass valve 17 to open. Therefore, if it is determined that the intake negative pressure once introduced into the pressure chamber 23 of the actuator 21 during the intermittent stop is leaking, the actuator 21 can be operated by the intake negative pressure to control the opening of the bypass valve 17 when the engine 1 is restarted after being fully warmed up.

[0090] Furthermore, according to the configuration of this embodiment, when the VSV 28 is de-energized, the ECU 80 switches the communication passage 27 to a state in which it communicates with the atmosphere and drives the bypass valve 17 to close. Therefore, even if the VSV 28 fails, the VSV 28 maintains the communication passage 27 in a state in which it communicates with the atmosphere, and the bypass valve 17 is kept closed. Therefore, when the VSV 28 fails, it is possible to prevent high-temperature EGR gas from accidentally flowing into the bypass passage 16, and to suppress melting damage to the EGR passage 12 downstream of the EGR cooler 13.

[0091] In addition, according to the configuration of this embodiment, when the engine 1 is started at a low temperature and the EGR valve 14 is in a closed state, it is possible to ensure the intake negative pressure required for the actuator 21 to operate in the intake passage 2, thereby enabling the bypass valve 17 to be driven to open. Therefore, even during a low temperature start of the engine 1, the actuator 21 can be operated by the intake negative pressure to control the opening of the bypass valve 17 without forcibly generating the intake negative pressure.

[0092] 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 the following description will focus on the differences.

[0093] [Bypass valve opening request determination control] This embodiment differs from the first embodiment in the content of the bypass valve open request determination control, which is shown in a flowchart in Fig. 12.

[0094] When the process proceeds to this routine, in step 500, the ECU 80 acquires the coolant temperature THW, the engine speed NE, and the intake air temperature THA based on the detected values ​​of the water temperature sensor 71, the engine speed sensor 72, and the intake air temperature sensor 77. The ECU 80 also acquires a command value for controlling the opening of the EGR valve 14 as the EGR opening degree TEGR.

[0095] Next, in step 510, the ECU 80 determines whether the engine speed NE has exceeded, for example, 500 rpm. If the result of this determination is positive, the ECU 80 determines that the engine 1 is running and proceeds to step 520. If the result of this determination is negative, the ECU 80 determines that the engine 1 is stopped and proceeds to step 610.

[0096] On the other hand, in step 520, the ECU 80 determines whether the EGR opening TEGR is equal to or greater than a predetermined value B1. 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 540.

[0097] In step 530, the ECU 80 calculates the cumulative time TMEON(i) when the EGR opening TEGR is equal to or greater than a predetermined value B1. In this case, the ECU 80 calculates the current cumulative time TMEON(i) by adding a predetermined cumulative value α to the previous cumulative time TMEON(i-1).

[0098] On the other hand, in step 540, the ECU 80 subtracts the accumulated time TMEON(i) when the EGR opening TEGR is less than a predetermined value B1. In this case, the ECU 80 calculates the current accumulated time TMEON(i) by subtracting a predetermined subtraction value β from the previous accumulated time TMEON(i-1).

[0099] At step 550 following step 530 or step 540, the ECU 80 directly replaces the cumulative time TMEON(i) with the bypass valve open time TBON.

[0100] Next, in step 560, the ECU 80 determines whether the bypass valve open time TBON is equal to or greater than 0. 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 proceeds to step 570.

[0101] In step 570, the ECU 80 sets the bypass valve open time TBON to “0” and proceeds to step 580.

[0102] In step 580, which follows step 560 or step 570, the ECU 80 calculates the valve opening determination time FTBON according to the coolant temperature THW and the intake air temperature THA. The ECU 80 can determine the valve opening determination time FTBON according to the coolant temperature THW and the intake air temperature THA by, for example, referring to a valve opening determination time map such as that shown in FIG.

[0103] Next, in step 590, the ECU 80 determines whether the valve opening determination time FTBON is greater than the bypass valve opening time TBON. 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 610.

[0104] Then, in step 600, the ECU 80 determines that the EGR passage needs to be warmed up, and therefore, a bypass valve opening request is made, and the process returns to step 500.

[0105] On the other hand, in step 610 following step 510 or step 590, the ECU 80 determines that the bypass valve needs to be closed because the EGR passage 12 does not need to be warmed up, and returns the process to step 500.

[0106] According to the above-described bypass valve open request determination control, the ECU 80 determines whether the bypass valve is required to be open or closed based on the cumulative time TMEON(i) that the EGR valve 14 is open at an EGR opening TEGR that is equal to or greater than the predetermined value B1.

[0107] Third Embodiment Next, a third embodiment will be described in detail with reference to the drawings.

[0108] [Bypass valve opening request determination control] This embodiment differs from the second embodiment in the content of the bypass valve open request determination control. Figure 14 shows a flowchart of the content of the bypass valve open request determination control of this embodiment. The flowchart of Figure 14 differs from the flowchart of Figure 12 in that steps 700 and 710 are provided instead of steps 520 to 540.

[0109] That is, in the flowchart of Fig. 14, if the determination result in step 510 is positive, the ECU 80 calculates a time correction coefficient Kα corresponding to the EGR opening TEGR in step 700. The ECU 80 can determine the time correction coefficient Kα corresponding to the EGR opening TEGR by referring to a time correction coefficient map as shown in Fig. 15, for example. In Fig. 15, "β" corresponds to the subtraction value in step 540 of Fig. 12.

[0110] Next, in step 710, the ECU 80 calculates the cumulative time TMEON(i) corresponding to the EGR opening TEGR. In this case, the ECU 80 calculates the current cumulative time TMEON(i) by adding the time correction coefficient Kα to the previous cumulative time TMEON(i-1). Thereafter, the ECU 80 executes the process from step 550 onwards.

[0111] According to the bypass valve open request determination control described above, the ECU 80 determines the bypass valve open request and the bypass valve close request based on the accumulated time TMEON(i) during which the EGR valve 14 is open with the EGR opening TEGR equal to or greater than the predetermined value B1, as in the second embodiment. However, this embodiment differs from the second embodiment in that the accumulated time TMEON(i) is corrected by a time correction coefficient Kα according to the EGR opening TEGR.

[0112] <Fourth embodiment> Next, a fourth embodiment will be described in detail with reference to the drawings.

[0113] [Bypass valve opening request determination control] This embodiment differs from the previous embodiments in the content of the bypass valve open request determination control. Fig. 16 is a flowchart showing the content of the bypass valve open request determination control of this embodiment. In this embodiment, the bypass valve open request determination is made based on the EGR gas temperature THeGr in the EGR passage 12. Therefore, the engine system can be provided with a gas temperature sensor 78 for detecting the EGR gas temperature THeGr in the EGR passage 12 downstream of the EGR valve 14, for example, as shown by the two-dot chain line in Fig. 1.

[0114] When the process proceeds to the routine of the flowchart of FIG. 16, in step 800, the ECU 80 acquires the EGR gas temperature THegr based on the value detected by the gas temperature sensor 78.

[0115] Next, in step 810, the ECU 80 determines whether the EGR gas temperature THegr is less than 130° C. If the result of this determination is positive, the ECU 80 proceeds to step 820, and if the result of this determination is negative, the ECU 80 proceeds to step 830.

[0116] Then, in step 820, since the EGR gas temperature THegr is low, ie, less than "130°C", it is determined that a bypass valve opening request is made, and the process returns to step 800.

[0117] On the other hand, in step 830, since the EGR gas temperature THegr is high, at "130°C" or higher, it is determined that a bypass valve closing request is required, and the process returns to step 800.

[0118] According to the bypass valve open request determination control described above, the ECU 80 determines whether the bypass valve is required to be opened or closed based on the EGR gas temperature THegr detected by the gas temperature sensor 78 .

[0119] <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.

[0120] (1) In the above-described embodiments, the switching valve of the disclosed technology is configured by the VSV 28, which is a three-way valve. However, the switching valve may also be configured by two on-off valves.

[0121] (2) In each of the above embodiments, when the engine 1 intermittently stops after the engine 1 has fully warmed up, the VSV 28 is controlled to introduce the intake negative pressure generated in the intake passage 2 immediately before the engine 1 is stopped into the pressure chamber 23 of the actuator 21 via the communicating passage 27, thereby driving the bypass valve 17 to open. However, it is also possible to control the VSV to introduce the intake negative pressure generated in the intake passage 2 into the pressure chamber of the actuator via the communicating passage when the engine is intermittently stopped, not after the engine has fully warmed up or not immediately before the engine is stopped, thereby driving the bypass valve to open.

[0122] (3) This disclosed technology is directed to controlling the opening and closing of the bypass valve 17, but it can be implemented as long as it uses a diaphragm-type actuator and controls the valve using intake negative pressure. [Industrial Applicability]

[0123] The disclosed technology can be applied to the engine of a hybrid vehicle that operates the engine intermittently. [Explanation of symbols]

[0124] 1 engine 2 Intake passage 3 Exhaust passage 5 Intake manifold (intake passage) 11 EGR system 12 EGR passage 13 EGR cooler 14 EGR valve 15 EGR gas distributor (EGR passage) 16 Bypass Passage 17 Bypass valve 21 Actuator 21a casing 22 diaphragm 23 Pressure Chamber 24 Atmospheric Chamber 27 Communication path 28 VSV (switching valve) 80 ECU (EGR control means)

Claims

1. An EGR system applied to a hybrid vehicle that operates an engine intermittently and provided in the engine, an EGR passage that allows a portion of exhaust gas discharged from the engine into an exhaust passage to flow into an intake passage so as to be recirculated to the engine 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 in the EGR passage that bypasses the EGR cooler; a bypass valve for opening and closing the bypass passage; Equipped with the bypass valve is configured to be opened and closed by a diaphragm-type actuator; The actuator has a casing that is divided into a pressure chamber and an atmospheric chamber via a diaphragm, and the pressure chamber is provided with a communication passage that communicates with the intake passage, the actuator drives the bypass valve to open when intake negative pressure is introduced into the pressure chamber, and drives the bypass valve to close when atmospheric pressure is introduced into the pressure chamber; The communication passage is provided with an electrically operated switching valve for selectively switching the communication passage between a state in which the communication passage is connected to the intake passage and a state in which the communication passage is connected to the atmosphere. In the EGR system configured as above, an EGR control means for controlling the EGR valve, the bypass valve, and the switching valve; When the engine is operating and the EGR valve is closed, the EGR control means controls the switching valve to introduce the intake negative pressure generated in the intake passage into the pressure chamber of the actuator via the communication passage, thereby driving the bypass valve to open and stopping the bypass valve in the open state. An EGR system characterized by:

2. 2. The EGR system according to claim 1, When the engine is intermittently stopped with the bypass valve closed after the engine is fully warmed up, the EGR control means controls the switching valve to introduce the intake negative pressure generated in the intake passage immediately before the engine is stopped into the pressure chamber of the actuator via the communication passage, thereby driving the bypass valve to open. An EGR system characterized by:

3. 3. The EGR system according to claim 1, When the engine is restarted from an intermittent stop while the bypass valve is stopped in an open state, the EGR control means controls the EGR valve to open with a delay from the restart of the engine. An EGR system characterized by:

4. 4. The EGR system according to claim 3, The EGR control means controls the EGR valve to open with a delay after the engine is restarted when the engine has been intermittently stopped for a predetermined period of time. An EGR system characterized by:

5. An EGR system applied to a hybrid vehicle that operates an engine intermittently and provided in the engine, an EGR passage that allows a portion of exhaust gas discharged from the engine into an exhaust passage to flow into an intake passage so as to be recirculated to the engine 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 in the EGR passage that bypasses the EGR cooler; a bypass valve for opening and closing the bypass passage; Equipped with the bypass valve is configured to be opened and closed by a diaphragm-type actuator; The actuator has a casing that is divided into a pressure chamber and an atmospheric chamber via a diaphragm, and the pressure chamber is provided with a communication passage that communicates with the intake passage, the actuator drives the bypass valve to open when intake negative pressure is introduced into the pressure chamber, and drives the bypass valve to close when atmospheric pressure is introduced into the pressure chamber; The communication passage is provided with an electrically operated switching valve for selectively switching the communication passage between a state in which the communication passage is connected to the intake passage and a state in which the communication passage is connected to the atmosphere. In the EGR system configured as above, an EGR control means for controlling the EGR valve, the bypass valve, and the switching valve; When the engine is restarted from an intermittent stop while the bypass valve is stopped in an open state, the EGR control means controls the EGR valve to open with a delay from the restart of the engine. An EGR system characterized by:

6. 6. The EGR system according to claim 5, The EGR control means controls the EGR valve to open with a delay after the engine is restarted when the engine has been intermittently stopped for a predetermined period of time. An EGR system characterized by:

7. 7. The EGR system according to claim 1, The EGR control means switches the communication passage to a state in which the communication passage is communicated with the atmosphere when the switching valve is de-energized, and drives the bypass valve to close. An EGR system characterized by:

8. 8. The EGR system according to claim 1, When the engine is started at a low temperature and the EGR valve is closed, the EGR control means controls the switching valve to introduce the intake negative pressure generated in the intake passage into the pressure chamber of the actuator via the communication passage, thereby driving the bypass valve to open. An EGR system characterized by:

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