JP7743348B2 - EGR system - Google Patents

Description

The technology disclosed in this specification is applied to hybrid vehicles that operate the engine intermittently, and relates to an EGR system installed in the engine.

An example of this type of technology is the "engine exhaust gas recirculation device" described in Patent Document 1 below. This device includes an EGR passage that flows a portion of the exhaust gas discharged from the engine into the exhaust passage into the intake passage to be recirculated as EGR gas back to the engine, and an EGR valve that adjusts the flow rate of 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 vacuum, thereby opening and closing the EGR valve.

JP 2013-170457 A

The configuration described in Patent Document 1, in which the EGR valve is opened and closed by a diaphragm-type actuator, can be envisioned as a bypass valve for an EGR cooler installed in an engine of a hybrid vehicle (hereinafter referred to as "HV") that operates the engine 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 engine is restarted from a stopped state of intermittent operation and the EGR valve is simultaneously opened. Therefore, when the EGR valve opens, the intake vacuum generated in the intake passage is small. Even if the communication passage is connected to the intake passage, sufficient intake vacuum is not supplied to the pressure chamber, preventing the bypass valve from opening even when it needs to be opened. 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.

This disclosed technology was developed in light of the above circumstances, and its purpose is to provide an EGR system for an HV engine that uses a diaphragm-type actuator to drive the opening and closing of a bypass valve installed in the bypass passage of the EGR cooler, and that enables the actuator to operate and control the opening of the bypass valve without forcibly generating intake negative pressure after the engine has fully warmed up.

In order to achieve the above object, the technology described in claim 1 is applied to a hybrid vehicle with an intermittent engine operation, and is an EGR system provided in the engine, comprising: an EGR passage that flows a portion of exhaust gas discharged from the engine into the 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 having a casing that is divided into a pressure chamber and an atmospheric chamber via the diaphragm, The chamber is provided with a communication passage that communicates with the intake passage, and the actuator opens the bypass valve when intake negative pressure is introduced into the pressure chamber and closes the bypass valve when atmospheric pressure is introduced into the pressure chamber. The communication passage is provided with an electric switching valve that selectively switches the communication passage between communicating with the intake passage and communicating with the atmosphere. The EGR system further includes EGR control means for controlling the EGR valve, bypass valve, and switching valve, and when the engine is operating and the EGR valve is closed, the EGR control means 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 opening the bypass valve and stopping it in the open state.

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 vacuum generated in the intake passage into the pressure chamber of the actuator via the connecting passage, thereby driving the bypass valve to open, and then stops the bypass valve in the open state. Therefore, even if the engine intermittently stops after a full 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 will flow into the EGR passage downstream of the EGR cooler.

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 the communication passage, thereby driving the bypass valve to open.

According to the configuration of the above technology, in addition to the effect of the technology described in claim 1, 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 open the bypass valve by introducing the intake vacuum generated in the intake passage immediately before the engine stopped into the pressure chamber of the actuator via the connecting passage. Therefore, even if the EGR passage needs to be warmed up when the engine is restarted after the engine has fully warmed up and the bypass valve has already been opened using the intake vacuum generated in the intake passage immediately before the engine stopped, the high-temperature EGR gas flowing through the bypass passage will flow into the EGR passage downstream of the EGR cooler.

To achieve the above object, the technology described in claim 3 is the technology described in claim 1 or 2, in which the EGR control means controls the EGR valve to open after a delay from the restart of the engine when the engine is restarted from an intermittent stop while the bypass valve is stopped in an open state.

According to the configuration of the above technology, in addition to the effects 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 after the engine restart. Therefore, even if the intake vacuum that was once introduced into the actuator pressure chamber leaks when the EGR passage needs to be warmed up when the engine is restarted, EGR gas does not flow into the intake passage when the engine is restarted, and intake vacuum is generated in the intake passage, which can be used to drive the bypass valve open.

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 if the engine's intermittent stop time exceeds a predetermined time.

According to the configuration of the above technology, in addition to the effect 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 engine is restarted. Therefore, even if the intermittent engine stop time exceeds the predetermined time and the intake vacuum once introduced into the actuator pressure chamber leaks, EGR gas does not flow into the intake passage when the engine is restarted, and intake vacuum is generated in the intake passage, which can be used to drive the bypass valve open.

In order to achieve the above object, the technology described in claim 5 is applied to a hybrid vehicle with an intermittent engine operation, and is an EGR system provided in the engine, comprising: an EGR passage that flows a portion of exhaust gas discharged from the engine into the 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 having a casing that is diaphragm-type. The EGR system is configured so that the bypass valve is divided into a pressure chamber and an atmospheric chamber via a valve, the pressure chamber having a communication passage that communicates with the intake passage, the actuator opening the bypass valve when intake negative pressure is introduced into the pressure chamber and closing the bypass valve when atmospheric pressure is introduced into the pressure chamber, and the communication passage has an electrically operated switching valve that selectively switches the communication passage between communicating with the intake passage and communicating with the atmosphere.The system further includes EGR control means for controlling the EGR valve, bypass valve, and switching valve, and the EGR control means controls the EGR valve to open after a delay from the restart of the engine when the engine is restarted from an intermittent stop while the bypass valve is stopped in the open state.

According to the configuration of the above technology, when the engine restarts 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 after the engine restart. Therefore, even if the intake vacuum that was once introduced into the actuator's pressure chamber leaks when the EGR passage needs to be warmed up when the engine restarts, EGR gas does not flow into the intake passage when the engine restarts, and intake vacuum is generated in the intake passage, which can be used to drive the bypass valve open.

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 engine's intermittent stop time exceeds a predetermined time.

According to the configuration of the above technology, in addition to the effect of the technology described in claim 5, 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 engine is restarted. Therefore, even if the intermittent engine stop time exceeds the predetermined time and the intake vacuum once introduced into the actuator pressure chamber leaks, EGR gas does not flow into the intake passage when the engine is restarted, and intake vacuum is generated in the intake passage, which can be used to drive the bypass valve open.

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

According to the configuration of the above technology, in addition to the effects of the technology described in any one of claims 1 to 6, the EGR control means switches the communication passage to a state that connects the communication passage to 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 remains in a state that connects the communication passage to the atmosphere, and the bypass valve remains closed.

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 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.

With the configuration of the above technology, in addition to the effects 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 closed, it is possible to ensure the intake negative pressure required to operate the actuator in the intake passage, making it possible to drive the bypass valve open.

According to the technology described in claim 1, in an EGR system installed in an HV engine, in which a bypass valve installed in the bypass passage of the EGR cooler is driven to open and close by a diaphragm-type actuator, after the engine has 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.

The technology described in claim 2 can achieve the same effect as the technology described in claim 1.

The technology described in claim 3, in addition to the effects of the technology described in claim 1 or 2, makes it possible to operate the actuator with intake negative pressure and control the opening of the bypass valve when the engine is restarted after being fully warmed up, even if the intake negative pressure once introduced into the actuator's pressure chamber leaks during an intermittent stop.

In addition to the effect of the technology described in claim 3, the technology described in claim 4 makes it possible to operate the actuator with intake negative pressure and control the opening of the bypass valve when the engine is restarted after being fully warmed up, if it is determined that the intake negative pressure once introduced into the actuator's pressure chamber during intermittent stopping is leaking.

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.

The technology described in claim 6 achieves the same effect as the technology described in claim 5, but it also makes it possible to operate the actuator with intake negative pressure after the engine has fully warmed up, thereby controlling the opening of the bypass valve, regardless of whether or not there is leakage of intake negative pressure from the pressure chamber.

The technology described in claim 7, in addition to the effects of the technology described in any one of claims 1 to 6, can prevent high-temperature EGR gas from accidentally flowing into the bypass passage when the switching valve fails, thereby suppressing melting damage to the EGR passage downstream of the EGR cooler.

The technology described in claim 8 achieves the effects of any of the technologies described in claims 1 to 7, and also makes it possible to control the opening of the bypass valve by operating the actuator with intake negative pressure without forcibly generating intake negative pressure, even during cold engine start-up.

1 is a schematic configuration diagram showing an engine system according to a first embodiment; 4 is a cross-sectional view showing the EGR cooler cut along its longitudinal direction when the bypass valve is fully closed, together with the opening/closing drive mechanism of the bypass valve in the first embodiment; FIG. 3 is an enlarged cross-sectional view showing a part of the EGR cooler according to the first embodiment, the part being surrounded by a dashed-dotted rectangle in FIG. 2 . FIG. 4 is an enlarged cross-sectional view equivalent to FIG. 3 showing a part of the EGR cooler when the bypass valve is fully opened in the first embodiment; 5A and 5B are schematic diagrams illustrating an operating state of the opening/closing drive mechanism in the first embodiment. 5A and 5B are schematic diagrams illustrating an operating state of the opening/closing drive mechanism in the first embodiment. 4 is a flowchart showing the contents of bypass valve switching control in the first embodiment. 4 is a flowchart showing the contents of bypass valve switching control in the first embodiment. 5 is a flowchart showing the contents of bypass valve open request determination control in the first embodiment. 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; 4 is a time chart showing the behavior of various parameters related to bypass valve switching control in the first embodiment. 10 is a flowchart showing the contents of bypass valve open request determination control according to the second embodiment; 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; 10 is a flowchart showing the contents of bypass valve open request determination control according to the third embodiment; 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. 10 is a flowchart showing the contents of bypass valve open request determination control according to the fourth embodiment;

Below, we will explain several embodiments in which this EGR system is implemented in a gasoline engine system installed in an HV.

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

[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 including 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, from its upstream side. The exhaust passage 3 is provided with an exhaust manifold 6 and a catalyst 7, from its upstream side, in this order. 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.

The throttle device 4 is located 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 opening and closing a butterfly-type throttle valve 4a to a variable degree in response to the driver's accelerator operation. The intake manifold 5 is primarily made of resin and is located 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. The intake manifold 5 forms part of the intake passage 2.

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 engine 1. In each cylinder, a combustible mixture is formed by the fuel injected from the fuel injection device and the intake air introduced through the intake manifold 5.

Engine 1 is provided with an ignition device (not shown) corresponding to each cylinder. The ignition device is configured to ignite a combustible mixture in each cylinder. The combustible 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 exhaust manifold 6 and catalyst 7. At this time, pistons (not shown) in each cylinder move up and down, causing the crankshaft (not shown) to rotate, generating power for engine 1. The exhaust manifold 6 forms part of the exhaust passage 3.

[About the EGR system]
1, the EGR system 11 of this embodiment is provided between the exhaust passage 3 and the intake passage 2. The EGR passage 12 is configured to allow a portion of the exhaust gas discharged from the engine 1 into the exhaust passage 3 to flow into the intake passage 2 as EGR gas for recirculation to the engine 1. The EGR passage 12 includes an EGR cooler 13 for cooling the EGR gas flowing through the EGR passage 12, an EGR valve 14 for adjusting the flow rate of the EGR gas flowing through the EGR passage 12, and an 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 so as to distribute the EGR gas 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 constitutes 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.

The EGR gas distributor 15 is primarily made of a resin material and has an overall horizontally elongated shape. It is positioned 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 where the 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.

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, EGR valve 14, and EGR gas distributor 15, and is further distributed and recirculated to each cylinder of the engine 1.

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 it. A bypass valve 17 is provided in the bypass passage 16 to open and close the passage 16.

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

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 introduction port 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.

As shown in FIG. 2, in this embodiment, the EGR cooler 13 is disposed obliquely when installed in a vehicle so that EGR gas flows obliquely upward. In this oblique position, the outlet 44 is positioned vertically higher than the inlet 43, and the bypass passage 16 is positioned vertically below the heat exchanger 42. This allows condensed water generated inside the heat exchanger 42 to be discharged from the outlet 42b, flow down into the bypass passage 16, and then flow toward the upstream portion of the bypass passage 16. The heat exchanger 42 includes a water passage (not shown) through which engine 1 cooling water 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 bypass valve 17 are shown in simplified form.

As shown in FIG. 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 facing the first side swings around the rotary shaft 62. In addition, an arm 63 extending radially from one end of the rotary shaft 62 is provided.

[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 21 a, 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. The pressure chamber 23 is provided with a communication passage 27 that communicates with the surge tank 5a (which also serves as the intake passage 2). The atmospheric chamber 24 communicates with the atmosphere via an atmospheric port 21b.

In this opening/closing drive mechanism 19, the actuator 21 opens the bypass valve 17 when intake negative pressure is introduced into the pressure chamber 23, and closes the bypass valve 17 when atmospheric pressure is introduced into the pressure chamber 23. An electrically operated 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 this disclosed technology. As shown in Figures 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 connected to 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. This 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.

In this embodiment, the VSV 28 is a normally-open valve. When de-energized (power-off), the first port 28a is connected to the second port 28b, connecting the communication passage 27 extending from the pressure chamber 23 to the atmosphere. When energized (on), the first port 28a is connected to 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 de-energized, as shown in FIG. 5, atmospheric pressure acting on the air filter 29 is introduced into the pressure chamber 23 of the actuator 21 through the communication passage 27. 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, fully closing the bypass valve 17 as shown in FIGS. 2 and 3. Meanwhile, 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 part of the rod 26 is retracted into 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.

[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 through 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 engine speed (engine speed) NE 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 degree (throttle opening degree) TA of the throttle valve 4a and outputs an electric 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 electric 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 electric signal corresponding to the detected value.

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

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, EGR cooler 13, EGR valve 14, 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. Additionally, the ECU 80 executes bypass valve switching control in connection with EGR control to switch the bypass valve 17 between open and closed states according to the HV driving mode.

[Bypass valve switching control]
Next, the bypass valve switching control of this embodiment will be described. The bypass valve switching control is shown in a flowchart in Figures 7 and 8. 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.

In step 190, the ECU 80 turns off the VSV 28 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." The ECU 80 then returns the process to step 100.

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.

Next, in step 120, 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 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 intake passage 2 due to EGR cut. If the result of this determination is positive, ECU 80 proceeds to step 150; if the result of this determination is negative, ECU 80 proceeds to step 130.

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 and closing operation. Driving mode (2) refers to a state in which the engine 1 starts at a low water temperature and the EGR is on (EGR valve open). In this driving mode (2), the high intake vacuum 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; if the result of this determination is negative, the ECU 80 proceeds to step 140.

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

In step 150, which follows from step 120, step 130, or step 140, the ECU 80 determines whether there is a request to open the bypass valve 17. This valve open request is issued when the ECU 80 determines that the EGR passage 12 needs to be warmed up. The control for determining this valve open 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.

In step 160, 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, which indicates that the VSV 28 has been turned on, to "1."

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."

In step 180, moving from step 160 or step 170, the ECU 80 determines whether there is a request for intermittent engine 1 stop. This intermittent stop request is issued by the HV control controller in consideration of the HV motor drive. 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.

Meanwhile, moving from step 140 to step 200, 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 (EGR valve open). In this running mode (4), a low intake vacuum 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.

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; if the result of this determination is negative, the ECU 80 proceeds to step 240.

In step 220, it is determined whether there is a request to close the bypass valve 17. This request to close 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 will be described later, along 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.

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."

In step 240, which follows from step 210, step 220, or step 230, the ECU 80 determines whether there is a request for intermittent stopping of 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 to step 100.

In step 250, moving from 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."

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 engine 1 is intermittently stopped (EGR cut) for a long period of time, the introduction of EGR gas into the intake passage 2 can be delayed to generate intake negative pressure when the engine 1 is restarted.

Next, in step 270, the ECU 80 determines whether 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; if the result of this determination is negative, the ECU 80 returns to step 100.

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 most recent time the engine 1 was intermittently stopped.

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 the time during which intake negative pressure is assumed to be lost from the pressure chamber 23 of the actuator 21 due to a small amount of air leakage from the VSV 28. If the result of this determination is positive, the ECU 80 proceeds to step 300, assuming that a large amount of intake negative pressure has been lost from the pressure chamber 23. If the result of this determination is negative, the ECU 80 proceeds to step 310, assuming that a small amount of intake negative pressure has been lost from the pressure chamber 23.

Next, in step 300, the ECU 80 restarts the engine 1 and executes delayed EGR control, before returning 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 vacuum has been lost 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 vacuum is generated in the intake passage 2 by the amount of the delay in EGR start and the introduction of EGR gas into the EGR passage 12. This intake vacuum is then used to operate the actuator 21, thereby opening the bypass valve 17.

On the other hand, in step 310, moving from step 290, the ECU 80 restarts the engine 1 and performs normal EGR control, before returning 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 intake negative pressure has been lost from the pressure chamber 23 of the actuator 21, and starts EGR as normal after the engine 1 is restarted.

According to the bypass valve switching control described above, when the engine 1 is operating and the EGR valve 14 is closed (steps 120 and 140 are YES), 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 connecting passage 27, thereby driving the bypass valve 17 open (step 160 is executed if step 150 is YES; step 250 is executed if step 180 is YES), and the bypass valve 17 is stopped in this open state. Here, particularly when the engine 1 is stopped intermittently 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 via the connecting passage 27 into the pressure chamber 23 of the actuator 21, thereby driving the bypass valve 17 open.

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 vacuum 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 in steps 250 and 260). Therefore, opening control of the bypass valve 17 is not necessary when the engine 1 is restarted. If the ECU 80 determines that the intake vacuum 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 in 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 the 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.

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 is connected to the atmosphere, thereby driving the bypass valve 17 to close (steps 170, 190, 230).

Furthermore, according to the bypass valve switching control described above, when the engine 1 is cold-started (if step 120 is YES) and the EGR valve 14 is closed (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 communication passage 27, thereby driving the bypass valve 17 to open.

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

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

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.

In step 420, the ECU 80 calculates the valve-opening required water temperature THWBO corresponding to the intake air temperature THA. The ECU 80 can determine the valve-opening required water temperature THWBO corresponding to the intake air temperature THA, for example, by referring to a predetermined valve-opening required water temperature map shown in Figure 10.

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

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

On the other hand, in step 450, the ECU 80 determines that there is no need to warm up the EGR passage 12, determines that there is a request to close the bypass valve, and then returns the process to step 400.

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

[About the EGR system's function and effects]
According to the configuration of the EGR system of this embodiment, 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. Turning off the VSV 28 connects the first port 28a and the second port 28b, and atmospheric pressure, introduced into the communication 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 enters 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, turning on the VSV 28 connects the first port 28a and the third port 28c, and atmospheric pressure is no longer applied to the communication 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. As shown in FIG. 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-described predetermined operating state, i.e., a state in which a portion of the rod 26 is immersed in the casing 21a. This drives the bypass valve 17 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, maintaining the bypass valve 17 fully open.

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 connecting passage 27, thereby driving the bypass valve 17 to open, and then stops the engine in that open state. Therefore, even if the engine 1 intermittently stops after fully warming up and the EGR passage 12 needs to be warmed up when the engine 1 is subsequently restarted, 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 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).

In other words, 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 this open state, and (C2) when the engine 1 is restarted, the open bypass valve 17 allows high-temperature EGR gas to flow through the bypass passage 16 to warm up the EGR passage 12 downstream of the EGR cooler 13. Then, (C3) once warm-up of the EGR passage 12 is complete, 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 complete warm-up, without forcibly generating intake negative pressure in the intake passage 2.

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 vacuum generated in the surge tank 5a (intake passage 2) into the pressure chamber 23 of the actuator 21, thereby maintaining the bypass valve 17 in an open state and intermittently stopping the engine 1. This eliminates the need to control the opening of the bypass valve 17 when the engine 1 is restarted. If the ECU 80 determines that the intake vacuum 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. Figure 11 shows the behavior of various parameters related to this control using a time chart. In Figure 11, (a) shows changes in engine speed NE, (b) shows changes in intake pressure PM, and (c) shows changes in EGR opening TEGR. 11 , if the engine 1 is restarted between times t1 and t4 after an intermittent stop, and 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), and therefore, as shown by the solid line in (b), no appropriate intake negative pressure is generated at time t3, and it is not possible to introduce the intake negative pressure 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, and therefore, an appropriate intake negative pressure is generated at time t3, as shown by the dashed line in (b), and it becomes possible to introduce the intake negative pressure 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 being stopped intermittently after being fully warmed up, there is no need to control the opening of the bypass valve 17 because the bypass valve 17 remains open before the EGR valve 14 opens. Even if the intake vacuum once introduced into the pressure chamber 23 of the actuator 21 leaks, delaying the opening of the EGR valve 14 when the engine 1 is restarted prevents EGR gas from flowing into the intake passage 2, generating intake vacuum in the intake passage 2, which can be used to drive the bypass valve 17 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).

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 engine restart. Therefore, even if the intermittent stop time TIstp of the engine 1 exceeds the predetermined time A1 and the intake vacuum 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 intake vacuum is generated in the intake passage 2. This intake vacuum can be used to drive the bypass valve 17 open. Therefore, if it is determined that the intake vacuum 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 vacuum to control the opening of the bypass valve 17 when the engine 1 is restarted after being fully warmed up.

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 is connected to 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 is connected to the atmosphere, and the bypass valve 17 is kept closed. Therefore, in the event of a failure of the VSV 28, 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.

In addition, with the configuration of this embodiment, when the engine 1 is started in a cold temperature and the EGR valve 14 is closed, it is possible to ensure the intake negative pressure required to operate the actuator 21 in the intake passage 2, making it possible to drive the bypass valve 17 open. Therefore, even during a cold 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 intake negative pressure.

Second Embodiment
Next, a 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 are denoted by the same reference numerals and will not be described again. The following description will focus on the differences.

[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 .

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

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.

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; if the result of this determination is negative, the ECU 80 proceeds to step 540.

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).

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

In step 550, which follows step 530 or step 540, the ECU 80 simply replaces the cumulative time TMEON(i) with the bypass valve open time TBON.

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; if the result of this determination is negative, the ECU 80 proceeds to step 570.

In step 570, the ECU 80 sets the bypass valve open time TBON to "0" and proceeds to step 580.

In step 580, which follows step 560 or step 570, the ECU 80 calculates the valve opening judgment time FTBON according to the coolant temperature THW and the intake air temperature THA. The ECU 80 can determine the valve opening judgment time FTBON according to the coolant temperature THW and the intake air temperature THA, for example, by referring to a valve opening judgment time map such as that shown in Figure 13.

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; if the result of this determination is negative, the ECU 80 proceeds to step 610.

Then, in step 600, the ECU 80 determines that the EGR passage needs to be warmed up, so it requests that the bypass valve be opened, and returns the process to step 500.

On the other hand, in step 610, which follows from step 510 or step 590, the ECU 80 determines that there is no need to warm up the EGR passage 12, and therefore requests that the bypass valve be closed, and returns the process to step 500.

According to the bypass valve open request determination control described above, 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 with an EGR opening TEGR equal to or greater than the predetermined value B1.

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

[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 is a flowchart showing 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.

That is, in the flowchart of FIG. 14, if the determination result in step 510 is positive, the ECU 80 calculates the 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, for example, referring to a time correction coefficient map such as that shown in FIG. 15. In FIG. 15, "β" corresponds to the subtraction value in step 540 of FIG. 12.

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). The ECU 80 then executes the processing from step 550 onwards.

According to the bypass valve open request determination control described above, the ECU 80, like the second embodiment, determines whether to request the bypass valve to be opened or closed based on the cumulative time TMEON(i) that the EGR valve 14 is open with an EGR opening TEGR equal to or greater than the predetermined value B1. However, this embodiment differs from the second embodiment in that the cumulative time TMEON(i) is corrected by a time correction coefficient Kα that corresponds to the EGR opening TEGR.

Fourth Embodiment
Next, a fourth embodiment will be described in detail with reference to the drawings.

[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.

When processing transitions to the routine of the flowchart in Figure 16, in step 800, the ECU 80 acquires the EGR gas temperature THEgr based on the detection value of the gas temperature sensor 78.

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; if the result of this determination is negative, the ECU 80 proceeds to step 830.

Then, in step 820, since the EGR gas temperature THEgr is low, at less than 130°C, it is determined that a bypass valve opening request is required, and processing returns to step 800.

On the other hand, in step 830, since the EGR gas temperature THEgr is high, at or above 130°C, it is determined that a bypass valve closure request is required, and processing returns to step 800.

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

<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.

(1) In the above embodiments, the switching valve of this disclosed technology is configured as a VSV 28 consisting of a three-way valve, but the switching valve can also be configured as two on-off valves.

(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 communication passage 27, thereby driving the bypass valve 17 open. In contrast, even if the engine is not fully warmed up or not immediately before the engine is stopped, the VSV can also be controlled to introduce the intake negative pressure generated in the intake passage 2 into the pressure chamber of the actuator via the communication passage, thereby driving the bypass valve open.

(3) This disclosed technology controls the opening and closing of the bypass valve 17, but it can be implemented using a diaphragm actuator and control by intake negative pressure.

This disclosed technology can be applied to hybrid vehicle engines that operate intermittently.

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 passage 28 VSV (switching valve)
80 ECU (EGR control means)

Claims (8)

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,
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;
In an EGR system configured such that 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,
an EGR control means for controlling the EGR valve, the bypass valve, and the switching valve;
The EGR system is characterized in that, 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 connecting passage, thereby driving the bypass valve to open and stopping it in the open state. 2. The EGR system according to claim 1,
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 the connecting passage, thereby driving the bypass valve to open. 3. The EGR system according to claim 1,
The EGR system is characterized in that, 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. 4. The EGR system according to claim 3,
The EGR system is characterized in that, when 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. 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,
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;
In an EGR system configured such that 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,
an EGR control means for controlling the EGR valve, the bypass valve, and the switching valve;
The EGR system is characterized in that, 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. 6. The EGR system according to claim 5,
The EGR system is characterized in that, when 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. 7. The EGR system according to claim 1,
The EGR system is characterized in that, when the switching valve is de-energized, the EGR control means switches the communication passage to a state in which it communicates with the atmosphere, thereby driving the bypass valve to close. 8. The EGR system according to claim 1,
The EGR system is characterized in that, 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 connecting passage, thereby driving the bypass valve to open.