JP2015218697A - EGR device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an EGR device capable of suppressing excessive heat stress from being applied to a heat exchanger of an EGR cooler.SOLUTION: An EGR device 10, which is an EGR device applied to an internal combustion engine executing a combustion stop control, comprises: an EGR cooler 20 including a heat exchanger through which EGR gas passes and a refrigerant passage; and a controller 70 executing a refrigerant-flow-volume reduction control to control a refrigerant-flow-volume reduction mechanism 50 to reduce a flow volume of refrigerant flowing in the refrigerant passage if the combustion stop control is executed, and executing a temperature increase control to control temperature increase mechanisms 50, 60 to increase a temperature of the heat exchanger if the temperature of the heat exchanger is equal to or lower than a threshold value after execution of the refrigerant-flow-volume reduction control.

Description

  The present invention relates to an EGR device.

  2. Description of the Related Art Conventionally, an EGR (Exhaust Gas Recirculation) device is known as a device for recirculating exhaust gas from an internal combustion engine to an intake passage. As this EGR device, for example, Patent Document 1 discloses an EGR device including an EGR cooler that cools EGR gas that is exhaust gas flowing into an intake passage. Patent Document 1 also discloses a technique for stopping combustion in an internal combustion engine by stopping fuel supply to the internal combustion engine when a predetermined stop condition is satisfied.

JP 2006-275031 A

  Although the specific configuration of the EGR cooler is not disclosed in Patent Document 1, for example, as an EGR cooler, heat exchange is performed by taking the heat of the EGR gas transmitted to the heat exchanger and the heat exchanger through which the EGR gas passes. An EGR cooler including a refrigerant passage through which a refrigerant that cools EGR gas passing through the body passes may be used. In an internal combustion engine to which such an EGR cooler is applied, as in Patent Document 1, when combustion is stopped, the passage of high-temperature EGR gas through the heat exchanger of the EGR cooler is suppressed, resulting in heat exchange. The temperature of the body is thought to decrease. In this state, for example, when the EGR cooler is cooled by running wind or the like, the heat exchanger may be excessively cooled. When the combustion of the internal combustion engine is restarted and the passage of the EGR gas to the heat exchanger is restarted in such a state that the heat exchanger is excessively cooled in this way, the temperature of the heat exchanger may rapidly increase. . In this case, an excessive thermal stress may be applied to the heat exchanger.

  An object of this invention is to provide the EGR apparatus which can suppress that an excessive thermal stress is added to the heat exchange body of an EGR cooler.

  An EGR device according to the present invention is an EGR device applied to an internal combustion engine in which combustion stop control for stopping combustion is executed, and a heat exchanger through which EGR gas passes, and the EGR through which the heat exchanger passes. An EGR cooler having a refrigerant passage through which a refrigerant for cooling gas passes, a refrigerant flow reduction mechanism capable of reducing the flow rate of the refrigerant in the refrigerant passage, and the temperature of the heat exchanger can be increased. And when the combustion stop control is executed, the refrigerant flow rate reduction control is performed to control the refrigerant flow rate reduction mechanism so that the flow rate of the refrigerant in the refrigerant passage decreases. A control device that executes temperature rise control for controlling the temperature raising mechanism so that the temperature of the heat exchanger increases when the temperature of the heat exchanger becomes equal to or lower than a threshold value after execution of the control. It has a, and.

  According to the EGR device of the present invention, when the combustion stop control is executed, the flow rate of the refrigerant in the refrigerant passage of the EGR cooler can be reduced by executing the refrigerant flow rate reduction control. Thereby, the temperature decreasing rate of the heat exchanger of the EGR cooler can be slowed down. Furthermore, when the temperature of the heat exchanger becomes equal to or lower than the threshold value after the refrigerant flow rate reduction control is executed, the temperature of the heat exchanger can be raised by executing the temperature increase control. As a result, when the execution of the combustion stop control is finished and the combustion is restarted, the temperature difference between the EGR gas and the heat exchanger can be reduced. Thereby, since the thermal stress added to the heat exchanger of an EGR cooler can be relieved, it can suppress that an excessive thermal stress is added to the heat exchanger of an EGR cooler.

  In the above configuration, the control device acquires a vehicle speed of a vehicle on which the internal combustion engine is mounted when the combustion stop control is executed, and performs threshold value change control for changing the threshold value according to the acquired vehicle speed. Further, it may be executed. The temperature of the EGR gas when the combustion stop control is finished and the combustion is restarted changes according to the vehicle speed when the combustion stop control is executed. Therefore, the magnitude of the thermal stress applied to the heat exchanger when the combustion stop control is finished and the combustion is restarted also changes according to the vehicle speed. In this respect, according to this configuration, since the threshold value is changed according to the vehicle speed when the combustion stop control is executed, it is possible to efficiently suppress application of excessive thermal stress to the heat exchanger. .

  In the above configuration, the control device estimates the temperature of the EGR gas when the combustion stop control is finished and the combustion is restarted based on the acquired vehicle speed in the threshold value changing control. Then, the threshold value may be changed according to the vehicle speed by calculating the threshold value based on a value obtained by subtracting a predetermined value from the estimated temperature of the EGR gas. According to this configuration, the threshold value can be changed according to the vehicle speed when the combustion stop control is executed.

  In the above-described configuration, even when the temperature increase control is executed, the control device has a thermal stress applied to the heat exchanger when the combustion stop control is finished and the combustion is restarted. A vehicle speed region of the vehicle that is larger than an allowable value is calculated when the combustion stop control is executed, and is calculated when the combustion stop control is finished and the combustion is restarted. You may further perform EGR cut control which stops passage of the EGR gas to the heat exchanger in the vehicle speed region. According to this configuration, even when the temperature increase control is executed, the vehicle speed at which the thermal stress applied to the heat exchanger becomes larger than the allowable value when the combustion stop control is finished and the combustion is restarted. In the region, the passage of the EGR gas to the heat exchanger can be stopped. Thereby, it is possible to suppress the application of thermal stress larger than the allowable value to the heat exchanger in such a vehicle speed region.

  The present invention can provide an EGR device capable of suppressing application of excessive thermal stress to the heat exchange body of the EGR cooler.

FIG. 1 is a schematic diagram of an internal combustion engine. FIG. 2A is a schematic cross-sectional view of an EGR cooler. FIG. 2B is a schematic cross-sectional view of the heat exchanger. FIG. 3A is a diagram illustrating an example of a flowchart when the control device according to the first embodiment executes the combustion stop control. FIG. 3B is a diagram illustrating an example of a flowchart when the control device according to the first embodiment performs refrigerant flow rate decrease control and temperature increase control. 4 (a) to 4 (d) show the vehicle speed, the rotational speed, the refrigerant flow rate in the refrigerant passage, and the heat exchanger when the combustion stop control, the refrigerant flow rate decrease control, and the temperature increase control according to the first embodiment are executed. It is a schematic diagram which shows an example of the time change of this temperature. FIG. 5 is a schematic diagram for explaining an EGR device according to a modification of the first embodiment. FIG. 6 is a diagram illustrating an example of a flowchart when the control device according to the modification of the first embodiment executes the refrigerant flow rate decrease control and the temperature increase control. FIG. 7 is a schematic diagram for explaining an image of threshold change control according to the second embodiment. FIG. 8 is a diagram illustrating an example of a flowchart when the control device according to the second embodiment executes threshold value change control, refrigerant flow rate decrease control, and temperature increase control. FIGS. 9A to 9D show the vehicle speed, the rotation speed, and the refrigerant flow rate in the refrigerant passage when the combustion stop control, threshold value change control, refrigerant flow rate decrease control, and temperature rise control according to the second embodiment are executed. It is a schematic diagram which shows an example of the time change of the temperature of a heat exchanger. FIG. 10 is a schematic diagram for explaining an image of control of the control device according to the modification of the second embodiment. FIG. 11 is a diagram illustrating an example of a flowchart when the control device according to the modification of the second embodiment executes threshold value change control, refrigerant flow rate decrease control, and temperature increase control.

  Hereinafter, modes for carrying out the present invention will be described.

  An EGR apparatus 10 according to Embodiment 1 of the present invention will be described. First, the overall configuration of the internal combustion engine 1 to which the EGR device 10 is applied will be described, and then the details of the EGR device 10 will be described. FIG. 1 is a schematic diagram of an internal combustion engine 1. The internal combustion engine 1 is mounted on a vehicle. The type of the internal combustion engine 1 is not particularly limited, and various internal combustion engines such as a diesel engine and a gasoline engine can be used. In this embodiment, a gasoline engine is used as an example of the internal combustion engine 1.

  The internal combustion engine 1 includes an EGR device 10, an engine body 3 having a cylinder 2, an intake passage 4 through which intake air introduced into the cylinder 2 passes, and an exhaust passage 5 through which exhaust exhausted from the cylinder 2 passes. And various sensors. The EGR device 10 includes an EGR passage 11, an EGR valve 12 disposed in the EGR passage 11, an EGR cooler 20 disposed in the EGR passage 11, a refrigerant supply passage 40, a refrigerant discharge passage 41, and a flow rate adjustment valve 50. And an electric pump 60 and a control device 70. In the present embodiment, the control device that integrally controls the operation of the engine body 3 of the internal combustion engine 1 also functions as the control device of the EGR device 10. Therefore, the control device 70 according to the present embodiment controls not only the EGR device 10 but also the operation of the engine body 3. However, the configuration of the internal combustion engine 1 is not limited to this. For example, the internal combustion engine 1 may include a control device that controls the EGR device 10 separately from the control device that controls the engine body 3.

  The engine body 3 includes a cylinder block in which the cylinder 2 is formed, a cylinder head disposed on the cylinder block, and a piston disposed in the cylinder 2. The number of cylinders 2 is not particularly limited, but in the present embodiment, it is plural (specifically, four). An engine body refrigerant passage (so-called water jacket) through which a refrigerant for cooling the engine body 3 passes is formed inside the engine body 3. The refrigerant in the engine main body refrigerant passage is circulated in the engine main body refrigerant passage by being pumped by a mechanical refrigerant pressure pump (hereinafter referred to as a mechanical pump) driven by the power of the crankshaft of the internal combustion engine 1. . A so-called mechanical water pump can be used as the mechanical pump. In FIG. 1, the engine main body refrigerant passage and the mechanical pump are not shown.

  In FIG. 1, as an example of various sensors, a crank position sensor 6, a vehicle speed sensor 7, a temperature sensor 8a, and a temperature sensor 8b are illustrated. The crank position sensor 6 detects the position of the crankshaft (crank position) and transmits it to the control device 70. The vehicle speed sensor 7 detects the vehicle speed (vehicle speed) and transmits it to the control device 70. The temperature sensor 8 a detects the temperature of the refrigerant that cools the engine body 3 of the internal combustion engine 1 (hereinafter referred to as engine refrigerant temperature), and transmits the detection result to the control device 70. Specifically, the temperature sensor 8a according to the present embodiment detects the temperature of the refrigerant in the engine body refrigerant passage. The temperature sensor 8 b detects the temperature of a heat exchange element 25 (described later) of the EGR cooler 20 and transmits the detection result to the control device 70.

  The EGR passage 11 of the EGR device 10 is a passage that recirculates a part of the exhaust discharged from the engine body 3 to the intake passage 4. Specifically, the EGR passage 11 communicates between the passage of the intake passage 4 and the passage of the exhaust passage 5. Hereinafter, exhaust passing through the EGR passage 11 (that is, exhaust flowing into the intake passage 4) is referred to as EGR gas. The EGR valve 12 is a valve that adjusts the flow rate of EGR gas in response to an instruction from the control device 70. The EGR valve 12 according to the present embodiment is disposed on the downstream side of the EGR cooler 20 in the EGR passage 11. Note that, as the opening degree of the EGR valve 12 increases, the flow rate of the EGR gas flowing into the intake passage 4 also increases. The EGR cooler 20 is a device that cools EGR gas with a refrigerant. Details of the EGR cooler 20 will be described later.

  The refrigerant supply passage 40 is a refrigerant passage that supplies the refrigerant in the engine main body refrigerant passage to the EGR cooler 20. The refrigerant discharge passage 41 is a refrigerant passage that returns the refrigerant that has passed through the EGR cooler 20 to the engine body refrigerant passage. Thus, in the present embodiment, the refrigerant that cools the engine body 3 is used as the refrigerant for the EGR cooler 20. The flow rate adjustment valve 50 is a valve that adjusts the flow rate of the refrigerant supplied to the EGR cooler 20. The flow rate adjustment valve 50 according to the present embodiment is disposed in the refrigerant supply passage 40. The flow rate adjusting valve 50 operates in response to an instruction from the control device 70. As the opening degree of the flow rate adjusting valve 50 decreases, the flow rate of the refrigerant passing through the refrigerant supply passage 40 decreases, and as a result, the flow rate of the refrigerant supplied to the EGR cooler 20 also decreases. The flow rate adjustment valve 50 according to the present embodiment corresponds to a member having a function as a refrigerant flow rate reduction mechanism capable of reducing the flow rate of the refrigerant in the refrigerant passage 24 described later of the EGR cooler 20.

  The electric pump 60 is an electric refrigerant pressure pump that pumps the refrigerant. The electric pump 60 operates in response to an instruction from the control device 70. The electric pump 60 according to the present embodiment is disposed at a portion upstream of the flow rate adjustment valve 50 of the refrigerant supply passage 40. However, the location of the electric pump 60 is not limited to this. As another example, for example, the electric pump 60 may be disposed in a portion of the refrigerant supply passage 40 on the downstream side of the flow rate adjustment valve 50 or may be disposed in the refrigerant discharge passage 41. The electric pump 60 is normally stopped, and operates when a temperature increase control described later is executed. Further, the electric pump 60 has a structure that allows refrigerant to flow through the electric pump 60 and flow into the EGR cooler 20 even when the electric pump 60 is stopped.

  Since the EGR device 10 includes the electric pump 60 as in the present embodiment, combustion in the internal combustion engine 1 is stopped by execution of combustion stop control, which will be described later, and as a result, rotation of the crankshaft is stopped and the mechanical type is stopped. Even when the operation of the pump is stopped, the refrigerant in the engine body refrigerant passage can be supplied to the EGR cooler 20.

  The control device 70 is an electronic control unit (Electronic Control Unit) including a CPU (Central Processing Unit) 71, a ROM (Read Only Memory) 72, and a RAM (Random Access Memory) 73. The CPU 71 has a function as a control unit that executes control processing of members to be controlled, various arithmetic processing, and the like. The ROM 72 and the RAM 73 have a function as a storage unit that stores information necessary for the operation of the CPU 71. Details of the operation of the control device 70 will be described later.

  Next, details of the EGR cooler 20 will be described. FIG. 2A is a schematic cross-sectional view of the EGR cooler 20. The EGR cooler 20 includes a housing 21, a refrigerant passage 24, and a heat exchanger 25. The housing 21 includes an outer pipe 22 and an inner pipe 23 disposed inside the outer pipe 22. The refrigerant passage 24 is formed between the outer pipe 22 and the inner pipe 23. The heat exchange element 25 is arranged inside the housing 21, specifically, inside the inner pipe 23. In the EGR cooler 20, the EGR gas passes through the heat exchanger 25. 2A is an axis of the housing 21 and the heat exchange element 25 (a line indicating the central axis). In FIG. 2A, the flow direction of the EGR gas is a direction from left to right in a direction along the axis 26 (hereinafter referred to as an axial direction). In FIG. 2A, the internal structure of the heat exchanger 25 is not shown.

  Both ends of the outer pipe 22 in the axial direction are bent inward and connected to the outer peripheral surface of the inner pipe 23. Thereby, a space is provided between the inner periphery of the outer pipe 22 and the outer periphery of the inner pipe 23. The refrigerant passage 24 is formed in this space. Further, the inner pipe 23 according to the present embodiment covers the entire outer peripheral surface of the heat exchange element 25.

  The refrigerant passage 24 according to the present embodiment is provided so as to entirely cover the outer peripheral surface corresponding to the outer peripheral surface of the heat exchange element 25 of the inner pipe 23. Accordingly, the refrigerant in the refrigerant passage 24 indirectly cools the entire outer peripheral surface of the heat exchanger 25 via the inner pipe 23. A refrigerant supply port 27 and a refrigerant discharge port 28 are provided in a portion of the outer pipe 22 that constitutes the wall portion of the refrigerant passage 24. A refrigerant supply passage 40 is connected to the refrigerant supply port 27, and a refrigerant discharge passage 41 is connected to the refrigerant discharge port 28. The refrigerant that has passed through the refrigerant supply passage 40 flows into the refrigerant passage 24 from the refrigerant supply port 27, passes through the refrigerant passage 24, and then flows into the refrigerant discharge passage 41 from the refrigerant discharge port 28.

  FIG. 2B is a schematic cross-sectional view of the heat exchange element 25. Specifically, FIG. 2B schematically illustrates a cross section of the heat exchanger 25 cut along a plane having the axis 26 as a normal line. The heat exchanger 25 has a plurality of internal gas passages 29 through which EGR gas passes. The internal gas passage 29 is formed by partitioning the inside of the outer peripheral member 30 constituting the outer periphery of the heat exchanger 25 with a plurality of partition members 31. In this embodiment, the partition members 31 are arranged in a lattice shape. However, the arrangement of the partition members 31 is not limited to such a lattice shape. When the EGR gas flows into the internal gas passage 29 of the heat exchanger 25, the heat of the EGR gas is transmitted to the inner pipe 23 through the partition wall member 31 and the outer peripheral member 30, and then taken away by the refrigerant in the refrigerant passage 24. Is called. Thus, the refrigerant in the refrigerant passage 24 according to the present embodiment cools the EGR gas that passes through the heat exchanger 25. That is, the refrigerant in the refrigerant passage 24 according to the present embodiment cools the EGR gas passing through the heat exchanger 25 by depriving the heat of the EGR gas transmitted to the heat exchanger 25 through which the EGR gas passes.

  As described above, the EGR cooler 20 according to the present embodiment includes the inner pipe 23, but the structure of the EGR cooler 20 is not limited to this. As another example, for example, the EGR cooler 20 does not include the inner pipe 23, that is, the refrigerant in the refrigerant passage 24 is directly on the outer periphery of the heat exchanger 25 (specifically, the outer peripheral surface of the outer peripheral member 30). The structure which contacts may be sufficient. According to this structure, since the refrigerant in the refrigerant passage 24 can directly take away the heat of the EGR gas transmitted to the heat exchanger 25, the cooling efficiency of the EGR gas of the EGR cooler 20 can be improved.

  In addition, although the temperature sensor 8b mentioned above is arrange | positioned at the heat exchange body 25, illustration of the temperature sensor 8b is abbreviate | omitted in Fig.2 (a) and FIG.2 (b). This temperature sensor 8 b detects the temperature of the outer peripheral member 30 or the partition member 31 of the heat exchanger 25. In the present embodiment, the temperature sensor 8b detects the temperature of the outer peripheral member 30 as an example. However, the specific temperature detection part of the temperature sensor 8b is not limited to this as long as the temperature of the heat exchanger 25 can be detected.

  The material of the housing 21 (specifically, the outer pipe 22 and the inner pipe 23) is not particularly limited, but in the present embodiment, metal, specifically, stainless steel is used as an example of the material of the housing 21. In the present embodiment, ceramic is used as an example of the material of the heat exchanger 25. That is, the heat exchange element 25 according to the present embodiment is a ceramic heat exchange element. Specifically, the material of the outer peripheral member 30 and the partition member 31 of the heat exchanger 25 is ceramic. Ceramics have better corrosion resistance against exhaust than metals such as stainless steel.

  Although the specific component of the ceramic which is the material of the heat exchange element 25 is not particularly limited, SiC is preferable. SiC has a good thermal conductivity among ceramics, has particularly good corrosion resistance against exhaust, good workability, and is not expensive, so it is particularly suitable as a material for the heat exchanger 25 of the EGR cooler 20. Because. Therefore, in the present embodiment, as an example of the material of the heat exchange element 25, a ceramic containing SiC in its components is used. As specific examples of the ceramic containing SiC in its components, SiC (that is, a material in which no additive is added in addition to SiC), Si-impregnated SiC, (Si + Al) -impregnated SiC, metal composite SiC, or the like can be used. . In this embodiment, Si-impregnated SiC is used as an example of the material of the heat exchange element 25.

  Next, details of the operation of the control device 70 will be described. The control device 70 according to the present embodiment controls the fuel supply amount of the internal combustion engine 1 in accordance with the accelerator operation of the user (specifically, the driver) of the internal combustion engine 1 during normal operation (hereinafter referred to as this). Is called normal control). Further, the control device 70 executes combustion stop control for stopping combustion in the cylinder 2 of the internal combustion engine 1 when a predetermined stop condition is satisfied. The operation of the control device 70 will be described in detail using a flowchart as follows.

  FIG. 3A is a diagram illustrating an example of a flowchart when the control device 70 executes the combustion stop control. The control device 70 repeatedly executes the flowchart of FIG. 3A at a predetermined period when the internal combustion engine 1 is in operation (from when the start switch for starting the internal combustion engine 1 is turned on until it is turned off). It is assumed that the combustion of the internal combustion engine 1 is not stopped at the start of the flowchart when FIG. 3A is first executed, and the internal combustion engine 1 is normally controlled.

  In step S1, the control unit (CPU 71) of the control device 70 determines whether or not a stop condition is satisfied. In the present embodiment, as an example of the stop condition, a condition that the vehicle speed is a constant value and the rotational speed of the internal combustion engine 1 is a constant value is used. Specifically, in this case, the control unit acquires the vehicle speed based on the detection result of the vehicle speed sensor 7 and acquires the rotation speed of the crankshaft of the internal combustion engine 1 based on the detection result of the crank position sensor 6. The control unit determines whether or not the acquired vehicle speed is a constant value for a predetermined time and the rotational speed is a constant value for a predetermined time. Then, when it is determined that the vehicle speed is a constant value for a predetermined time and the rotational speed is a constant value for a predetermined time, the control unit determines that the stop condition is satisfied (Yes). On the other hand, if the controller determines that the vehicle speed is not constant for a predetermined time, or if the rotational speed is determined not to be constant for a predetermined time, the stop condition is not satisfied. Determine (No).

  When it is determined in step S1 that the stop condition is satisfied, the control unit executes combustion stop control (step S2). The control part which concerns on a present Example performs fuel cut control as an example of combustion stop control. In this fuel cut control, the control unit stops fuel supply by the fuel injection valve that supplies fuel to the internal combustion engine 1. By executing this fuel cut control, the combustion of fuel in the cylinder 2 is stopped. In this embodiment, the clutch is not disengaged in this fuel cut control. That is, when step S2 according to the present embodiment is executed, the internal combustion engine 1 is not burned in the cylinder 2 with the clutch connected, and the crankshaft rotates. By executing step S2, the fuel consumption of the internal combustion engine 1 can be improved. After step S2, the control unit ends the execution of the flowchart.

  If it is not determined in step S1 that the stop condition is satisfied, the control unit executes normal control (step 3). Specifically, when the combustion stop control according to step S2 is executed in the state before step S3 is executed, the control unit ends the execution of the combustion stop control in step S3. As a result, fuel supply to the internal combustion engine 1 is resumed, and combustion in the internal combustion engine 1 is resumed. If the flow rate adjustment valve 50 shown in FIG. 1 is closed or the electric pump 60 is operating in a state before the normal control is executed, the control unit performs the normal control in step S3. At the time of execution, the flow rate adjustment valve 50 is opened (specifically, fully opened in this embodiment), and the operation of the electric pump 60 is also stopped. As a result, when normal control is executed, the refrigerant flows through the engine main body refrigerant passage by being pumped by a mechanical pump, and also passes through the refrigerant supply passage 40 and also to the EGR cooler 20. After step S3, the control unit ends the execution of the flowchart.

  In addition, in step S2 which concerns on a present Example, although the control part is performing fuel cut control for the period until it determines with No by step S1, the specific content of step S2 is not limited to this. Absent. As another example, for example, the control unit may execute intermittent stop control in which fuel cut control is intermittently performed in step S2. Specifically, in this case, the control unit executes the fuel cut control for a predetermined period, then stops the execution of the fuel cut control for a predetermined period (in this case, fuel injection from the fuel injection valve is resumed), and then the fuel Cut control is executed for a predetermined period. The control unit repeatedly executes this cycle until the next time the flowchart of FIG. 3A is executed and it is determined No in step S1. Alternatively, in step S2, the control device 70 may execute coasting control instead of fuel cut control. Specifically, in this case, the control unit stops the combustion in the internal combustion engine 1 and also disconnects the clutch, thereby suppressing the occurrence of engine braking. Thereby, the engine body 3 is in a so-called no-load state.

  In addition to the execution of the control process of FIG. 3A described above, the control device 70 also executes a refrigerant flow rate decrease control and a temperature increase control described below when the combustion stop control according to step S2 is executed. FIG. 3B is a diagram illustrating an example of a flowchart when the control device 70 executes the refrigerant flow rate decrease control and the temperature increase control. The timing when the control unit of the control device 70 first executes the flowchart of FIG. 3B is when step S2 of FIG. 3A is executed after the internal combustion engine 1 is started. That is, when step S2 of FIG. 3A is first executed, the control unit first executes step S10 of the flowchart of FIG. The control unit once executes the flowchart of FIG. 3B, and then repeatedly executes the flowchart of FIG. 3B at a predetermined cycle.

  In step S10 of FIG. 3B, the control unit determines whether or not the combustion stop control according to step S2 described above is being executed. As a result of step S2 being executed first, when the flowchart of FIG. 3B is executed first, it is determined Yes in step S10 of FIG. 3B. When it determines with No by step S10, ie, when normal control is performed, a control part complete | finishes execution of a flowchart.

  When it determines with Yes at step S10, ie, when combustion stop control is performed, a control part performs refrigerant | coolant flow volume reduction control (step S20). In the refrigerant flow rate reduction control, the control unit controls the flow rate adjustment valve 50 (refrigerant flow rate reduction mechanism) so that the flow rate of the refrigerant in the refrigerant passage 24 of the EGR cooler 20 is reduced as compared to before execution of the combustion stop control. Specifically, the control unit according to the present embodiment controls the flow rate adjustment valve 50 described with reference to FIG. 1 to be closed so that the flow rate of the refrigerant in the refrigerant passage 24 becomes zero. As a result, the flow rate of the refrigerant in the refrigerant passage 24 decreases compared to before the combustion stop control is executed.

  In addition, the specific content of step S20 is not limited to this. As another example, for example, the control unit may set the flow rate of the refrigerant in the refrigerant passage 24 to a value larger than zero in step S20. Specifically, in this case, the control unit sets the opening degree of the flow rate adjustment valve 50 to a value smaller than the opening degree before the combustion stop control is executed (that is, the opening degree when the normal control is executed). By setting it to a value larger than zero, the refrigerant flow rate in the refrigerant passage 24 is set to a value smaller than that before execution of the combustion stop control (this is also a value larger than zero). Further, as a result of the refrigerant flow rate reduction control being executed, the refrigerant flow rate in the refrigerant passage 24 is decreased from that before the combustion stop control is executed. It decreases compared to the case where the refrigerant decrease control is not executed. Therefore, the refrigerant flow rate reduction control according to the present embodiment, in other words, reduces the refrigerant flow rate in the refrigerant passage 24 as compared with the case where the refrigerant flow rate reduction control is not executed even though the combustion stop control is executed. It can also be called control.

  Here, in the present embodiment, during a predetermined period after the combustion stop control is executed, the rotational speed of the engine body 3 of the internal combustion engine 1 gradually decreases while the combustion is stopped. While this rotational speed is gradually decreasing, exhaust gas may be discharged from the engine body 3, and as a result, EGR gas may also be generated. Therefore, EGR gas may pass through the heat exchanger 25 for a predetermined period after the combustion stop control is executed. However, even if EGR gas is generated during the execution of this combustion stop control, since this EGR gas is at a lower temperature than the EGR gas during normal control, heat exchange is performed by the EGR gas during execution of the refrigerant flow rate reduction control. An excessively high temperature of the body 25 is suppressed.

  After step S20, the control unit determines whether or not the temperature of the heat exchange element 25 is equal to or lower than a threshold value (step S30). As the threshold value, for example, when normal control is executed in a state where the temperature of the heat exchanger 25 becomes the threshold value, and the passage of the high-temperature EGR gas to the heat exchanger 25 is resumed, the heat exchanger 25 It is possible to use a temperature equal to or lower than a temperature at which excessive thermal stress is applied. This threshold value may be obtained in advance by experiments, simulations, etc. and stored in the storage unit (ROM 72), but in the present embodiment, the following is used as the threshold value.

  Specifically, in the present embodiment, the engine refrigerant temperature at the time when the combustion stop control according to Step S2 is executed (in the present embodiment, this is a constant) is used as the threshold value in Step S30. In this case, the control unit acquires the engine refrigerant temperature based on the detection result of the temperature sensor 8a when the combustion stop control according to step S2 is executed, and stores this in the storage unit (for example, the RAM 73). . In step S30, the control unit uses the engine refrigerant temperature stored in the storage unit as a threshold value in step S30. And a control part determines whether the temperature of the heat exchange body 25 acquired based on the detection result of the temperature sensor 8b in step S30 is below the threshold value memorize | stored in the memory | storage part.

  In step S30, the control unit does not acquire the temperature of the heat exchange element 25 based on the detection result of the temperature sensor 8b, but performs heat exchange based on an index (parameter) having a correlation with the temperature of the heat exchange element 25. The temperature of the body 25 may be estimated. The specific type of the index is not particularly limited. As an example, the flow rate of EGR gas immediately before the execution of step S2 in FIG. 3A and the elapsed time after the execution of step S2 are shown. Can be mentioned. As the flow rate of EGR gas immediately before the execution of step S2 increases, the temperature of the heat exchanger 25 at the time of execution of step S30 in FIG. 3B tends to increase, and the process since step S2 has been executed. The shorter the time, the higher the temperature of the heat exchanger 25 at the time of execution of step S30. Therefore, the flow rate and elapsed time of these EGR gases have a correlation with the temperature of the heat exchanger 25.

  Alternatively, the control unit may use the engine refrigerant temperature at the time when step S30 is executed as the threshold value at step S30 instead of setting the engine refrigerant temperature at the time when combustion stop control according to step S2 is executed as the threshold value. . In this case, the control unit obtains the engine refrigerant temperature at the time when step S30 is executed based on the detection result of the temperature sensor 8a at the time when step S30 is executed, and uses the acquired engine refrigerant temperature at step S30. Used as a threshold. Here, the engine refrigerant temperature changes with the elapsed time from the start of execution of step S2 (specifically, gradually decreases). Therefore, according to this configuration, the threshold value can be changed according to the temporal change of the engine refrigerant temperature.

  As described above, the threshold value in step S30 can be set by various methods. However, in the present embodiment, as described above, the engine refrigerant temperature (constant) at the time when the combustion stop control according to step S2 is executed is used as the threshold value.

  When it determines with the temperature of the heat exchange body 25 being below a threshold value in step S30, a control part performs temperature rise control (step S40). In the temperature increase control, the control unit executes a control process for increasing the temperature of the heat exchanger 25. Specifically, the control unit controls the flow rate adjustment valve 50 to open and starts the supply of the refrigerant to the EGR cooler 20 by operating the electric pump 60 (this also ends the execution of the refrigerant flow rate reduction control). To do). By executing Step S40, the supply of the refrigerant to the refrigerant passage 24 of the EGR cooler 20 via the engine body refrigerant passage is resumed (however, in this case, the refrigerant is not a mechanical pump but an electric pump 60). Is pressure-fed to the refrigerant passage 24). Thereby, the temperature of the heat exchange element 25 can be raised as compared with the case where Step S40 is not executed even though Yes is determined in Step S30.

  In addition, the flow regulating valve 50 and the electric pump 60 according to the present embodiment correspond to members having a function as a temperature raising mechanism capable of raising the temperature of the heat exchanger 25. After step S40, the control unit ends the execution of the flowchart.

  On the other hand, when it is not determined in step S30 that the temperature of the heat exchanger 25 is equal to or lower than the threshold value, the control unit ends the execution of the flowchart without executing the temperature increase control. In this case, since the temperature of the heat exchanger 25 is higher than the threshold value, even if the temperature increase control is not executed, the normal control according to step S3 is executed thereafter, and the high temperature EGR gas passes through the heat exchanger 25. It is suppressed that an excessive thermal stress is applied to the heat exchange element 25 when it is restarted.

  The execution end timing of the temperature increase control according to step S40 is not particularly limited, but the control unit according to the present embodiment executes step S3 in FIG. 3A after the execution of the temperature increase control. When this is done, the execution of this temperature rise control is terminated. In addition, as another example of the execution end timing of the temperature increase control, for example, the control unit may end the execution of the temperature increase control after a predetermined time has elapsed after executing the temperature increase control. Alternatively, after executing the temperature increase control, the control unit determines again whether or not the temperature of the heat exchange element 25 has become higher than the threshold value, and determines that the temperature of the heat exchange element 25 has become higher than the threshold value. The execution of the ascent control may be terminated.

4 (a) to 4 (d) show the vehicle speed, the rotational speed, the refrigerant flow rate in the refrigerant passage 24, and heat exchange when the combustion stop control, the refrigerant flow rate decrease control, and the temperature increase control according to this embodiment are executed. 6 is a schematic diagram illustrating an example of a time change in temperature of the body 25. FIG. Specifically, a solid line 100 in FIG. 4A indicates a time change of the vehicle speed (m / s). A solid line 101 in FIG. 4B indicates a change over time in the rotational speed (rpm) of the internal combustion engine 1. A solid line 102 in FIG. 4C indicates a change over time in the refrigerant flow rate (m ³ / s) in the refrigerant passage 24. A solid line 103 in FIG. 4D indicates a change over time of the temperature (° C.) of the heat exchanger 25. A dotted line 104 in FIG. 4D indicates a threshold value (engine coolant temperature in this embodiment). The phantom line 105 in FIG. 4D shows the time change of the temperature of the heat exchanger 25 when Step S40 is not executed even though Yes is determined in Step S30 in FIG. 3B. In FIGS. 4A to 4D, the unit of the horizontal axis (time) is second (s).

In FIG. 4 (a) ~ FIG 4 (d), the time t ₁ together with the combustion stop control is time executed in the step S2 of FIG. 3 (a), coolant flow reduction control is executed according to the step S20 It is also time. Time t ₄ is the time at which the normal control according to the step S3 ends the execution of the combustion stop control is executed. As shown by the solid line 100 in FIG. 4 (a), the vehicle speed, until the time t ₁ before the combustion stop control is performed is constant, and starts to decrease at time t _1. Then, the vehicle speed, the execution of the combustion stop control is started to increase at time t ₄ when finished. In this embodiment, the vehicle speed is not zero. Therefore, during execution of the combustion stop control, specifically, the housing 21 of the EGR cooler 20 is cooled by the traveling air. As indicated by the solid line 101 in FIG. 4B, the rotational speed of the internal combustion engine 1 starts decreasing at time t ₁ and becomes zero at time t ₂ . Thereafter, the rotational speed is started to increase at time t _4.

Figure 4 As shown by the solid line 102 of the (c), but the refrigerant flow rate of the refrigerant passage 24 until the time t ₁ before has a constant value, that the refrigerant flow rate reduction control in time t ₁ is performed, the refrigerant The refrigerant flow rate in the passage 24 is zero. As shown by the solid line 103 in FIG. 4 (d), that the combustion stop control at time t ₁ is executed, the temperature of the heat exchanger 25 is started to decrease. In addition, as shown by the solid line 103, according to this embodiment, not only the combustion stop control at time t ₁ is performed, since even coolant flow reduction control is executed, the heat exchanger at the time t ₁ after the lapse of The temperature of 25 is gradually decreasing. When this is a result of coolant flow reduction control is executed at time t _1, when the combustion stop control is despite coolant flow reduction control execution is not executed at time t ₁ (i.e., normal control after combustion stop control This means that the temperature decrease rate of the heat exchanger 25 has become lower than when the refrigerant having the same flow rate is supplied to the EGR cooler 20.

Thereafter, the temperature of the heat exchanger 25 at time t _3, is equal to or less than a threshold value indicated by the dotted line 104. As a result, the temperature rise control in the step S40 is executed, as shown in solid line 102 (solid line 102 of the time _{t 3} or later) in FIG. 4 (c), the refrigerant flow rate of the refrigerant passage 24 is rapidly increased, the time t It is in the state before ₁ . As a result, as shown in FIG. 4 (d), the temperature shown in phantom line 105 at a temperature and time _{t 3} of the heat exchanger 25 (i.e., even though the step S40 is determined as Yes is not performed in step S30 The temperature of the heat exchanger 25 in this case). Specifically the temperature of the heat exchanger 25 shown in solid line 103 in FIG. 4 (d), has a threshold near at time t ₃ or later. After that, the normal control ends the execution of the combustion stop control at time t ₄ is executed, the temperature of the heat exchanger 25 shown in solid line 103 in FIG. 4 (d) has started to rise.

  As explained above, according to the EGR device 10 according to the present embodiment, when the combustion stop control is executed, the refrigerant flow rate reduction control according to step S20 is executed, so that the combustion stop control is executed. Furthermore, the flow rate of the refrigerant in the refrigerant passage 24 of the EGR cooler 20 can be reduced. Thereby, as demonstrated in FIG.4 (d), the temperature fall rate of the heat exchanger 25 of the EGR cooler 20 can be made slow.

Further, according to the EGR device 10, when the temperature of the heat exchanger 25 becomes equal to or lower than the threshold value after the refrigerant flow rate reduction control is performed, the temperature of the heat exchanger 25 is decreased by executing the temperature increase control according to step S40. Can be raised. Specifically, as described in FIG. 4D, the temperature (solid line 103) of the heat exchange element 25 according to the present embodiment is higher than the temperature of the heat exchange element indicated by the virtual line 105. As a result, when the execution of the combustion stop control is finished and the combustion is restarted (time t _{4 in} FIG. 4D), the temperature difference between the EGR gas and the heat exchanger 25 can be reduced. Thereby, the thermal stress applied to the heat exchanger 25 can be relaxed. As a result, application of excessive thermal stress to the heat exchanger 25 can be suppressed. Thus, since it can suppress that an excessive thermal stress is added to the heat exchanger 25, it can suppress that a crack occurs in the heat exchanger 25.

  In this embodiment, the heat exchange element 25 is made of ceramic, but the material of the heat exchange element 25 is not limited to this, and may be a metal such as stainless steel. However, the case where the heat exchanger 25 is made of ceramic is preferable in that the corrosion resistance against exhaust gas can be improved compared to the case where the heat exchanger 25 is made of metal. Moreover, when the case where the heat exchanger 25 is made of ceramic and the housing 21 is made of metal as in this embodiment and the case where both the heat exchanger 25 and the housing 21 are made of metal are compared, the former ( In this embodiment, the difference between the thermal expansion coefficient of the heat exchanger 25 and the thermal expansion coefficient of the housing 21 is large. Therefore, the former tends to increase the thermal stress applied to the heat exchanger 25 when the heat exchanger 25 becomes hot. Therefore, when the heat exchange element 25 is made of ceramic and the housing 21 is made of metal, the problem of the present application (problem that excessive heat stress is applied to the heat exchange element 25) is particularly likely to occur. Therefore, the refrigerant flow rate decrease control and the temperature increase control according to the present embodiment are particularly effective when executed in the EGR cooler 20 in which the heat exchanger 25 is made of ceramic and the housing 21 is made of metal.

(Modification)
FIG. 5 is a schematic diagram for explaining an EGR device 10 according to a modification of the first embodiment. The EGR device 10 according to the present modification is different from the EGR device 10 shown in FIG. Although this will be described later, since the electric pump 60 is not controlled in the temperature rise control in the present modification, the EGR device 10 according to the present modification may not include the electric pump 60 illustrated in FIG. The energization device 80 is a device that allows current to flow through the heat exchanger 25. Specifically, the energization device 80 includes an electrode 81a, an electrode 81b, and an electricity supply device 82 that is electrically connected to the electrode 81a and the electrode 81b.

  The electrode 81a is connected to the upstream end in the flow direction of the EGR gas of the outer peripheral member 30 of the heat exchange element 25. The electrode 81b is connected to the downstream end in the flow direction of the EGR gas of the outer peripheral member 30 of the heat exchange element 25. The electricity supply device 82 supplies electricity to the heat exchanger 25 by receiving electricity from the control device 70 and supplying electricity to the electrodes 81a and 81b. Since the heat exchanging body 25 according to the present modification is a ceramic heat exchanging body (specifically, a heat exchanging body made of SiC), an electric current flows through the heat exchanging body 25 by the electric supply from the electric supply device 82. In this case, the heat exchanger 25 generates heat. Thereby, the temperature of the heat exchanger 25 rises. That is, the energization device 80 according to the present modification has a function as a temperature raising mechanism that can raise the temperature of the heat exchange element 25. The specific configuration of the electricity supply device 82 is not particularly limited as long as it can supply electricity to the heat exchanger 25 upon receiving an instruction from the control device 70, and a known electricity supply device may be used. Can be used. Therefore, further detailed description of the electricity supply device 82 is omitted.

  FIG. 6 is a diagram illustrating an example of a flowchart when the control device 70 according to the present modification performs the refrigerant flow rate decrease control and the temperature increase control. The flowchart of FIG. 6 differs from the flowchart of FIG. 3B in that step S40a is provided instead of step S40. The control part of the control apparatus 70 performs energization control in the temperature rise control which concerns on step S40a. In this energization control, the control unit specifically controls the electricity supply device 82 of the electricity supply device 80 so that electricity is supplied to the heat exchanger 25. Thereby, the heat exchanger 25 generates heat and the temperature of the heat exchanger 25 rises. In addition, the control part which concerns on this modification does not control the flow regulating valve 50 to open in step S40a. Therefore, the control unit controls the flow rate adjustment valve 50 to be open when step S3 of FIG. 3A is executed (this completes the execution of the refrigerant flow rate reduction control). However, the configuration of step S40a is not limited to this. For example, the control unit may control the flow rate adjustment valve 50 to be opened in step S40a.

  Also in the EGR device 10 according to this modification, the refrigerant flow rate reduction control according to step S20 and the temperature increase control according to step S40a are executed. And the temperature difference can be reduced. Thereby, since the thermal stress applied to the heat exchange body 25 can be relieved, it can suppress that an excessive thermal stress is added to the heat exchange body 25. FIG. Further, according to the EGR device 10 according to this modification, even if the engine refrigerant temperature is low, the temperature of the heat exchanger 25 can be reliably increased by the temperature increase control according to step S40a. it can.

  Note that the EGR device 10 may include a heater (for example, an electric heater) for heating the heat exchanger 25 instead of including the energization device 80 as in the present modification. Specifically, for example, when the heat exchanging body 25 is made of metal instead of ceramic, it is not easy to raise the temperature of the heat exchanging body 25 by the energization device 80. In such a case, a heater may be disposed on the heat exchanger 25, and the temperature of the heat exchanger 25 may be increased by the heater in the temperature increase control. That is, in this case, the heater corresponds to a member having a function as a temperature raising mechanism capable of raising the temperature of the heat exchange element 25. Specifically, in this case, in step S40a, the control unit controls the heater to generate heat, thereby increasing the temperature of the heat exchanger 25 with the generated heater. Even in this case, it is possible to suppress application of excessive thermal stress to the heat exchanger 25.

  Next, the EGR device 10 according to the second embodiment of the present invention will be described. The hardware configuration of the internal combustion engine 1 to which the EGR device 10 according to the present embodiment is applied is the same as that of FIG. The hardware configuration of the EGR cooler 20 of the EGR device 10 is the same as that shown in FIGS. 2 (a) and 2 (b). Therefore, also in this embodiment, FIG. 1 is used as a schematic diagram of the internal combustion engine 1, and FIGS. 2A and 2B are used as schematic diagrams of the EGR cooler 20. The EGR device 10 according to the present embodiment is different from the first embodiment in the control content of the control device 70. Specifically, the control device 70 according to the present embodiment performs threshold value change control for changing the threshold value used in determining whether or not to execute the temperature increase control according to the vehicle speed when the combustion stop control is executed. Furthermore, it differs from the control apparatus 70 of Example 1 in the point to perform. The other configuration of the EGR apparatus 10 according to the present embodiment is the same as that of the second embodiment, and thus the description thereof is omitted.

  Before describing the details of the threshold change control according to the present embodiment, an image of this threshold change control will be described. FIG. 7 is a schematic diagram for explaining an image of threshold change control. The vertical axis in FIG. 7 indicates the temperature, and the horizontal axis indicates the vehicle speed when the execution of the combustion stop control is completed and the combustion is restarted (hereinafter referred to as the time when the combustion is restarted). For reference, in FIG. 7, the engine refrigerant temperature obtained based on the detection result of the temperature sensor 8 a when the combustion stop control is executed is indicated by a dotted line 108. The dotted line 108 is referred to when comparing FIG. 7 with FIG. 10 described later (this will be described in a modification of the second embodiment).

A solid line 106 in FIG. 7 indicates the temperature of the EGR gas (referred to as EGR gas temperature) when combustion is resumed. As can be seen from the fact that the solid line 106 has an upwardly convex curve shape, the EGR gas temperature at the time of resuming combustion is the highest when the vehicle speed is a predetermined value (V _x ). EGR gas temperature in the case at the time of specifically, combustion resumed, the vehicle speed becomes low enough slower than a predetermined value (V _x) the following areas, and the low temperature as the vehicle speed becomes faster at higher region than the predetermined value (V _x) It has become.

  A solid line 107 in FIG. 7 is a value obtained by subtracting a predetermined value (ΔT) from the solid line 106. The solid line 107 indicates the temperature (allowable temperature) allowed for the heat exchanger 25 when combustion is resumed. That is, when the temperature of the heat exchanger 25 is equal to or higher than the solid line 107 when combustion is resumed, the difference between the EGR gas temperature (solid line 106) and the temperature of the heat exchanger 25 is equal to or less than a predetermined value (ΔT). It becomes. In this case, as a result of the thermal stress applied to the heat exchange element 25 being less than the allowable value, no cracks are generated in the heat exchange element 25. On the contrary, when the temperature of the heat exchanger 25 becomes lower than the solid line 107 in the case of restarting combustion, the difference between the EGR gas temperature and the temperature of the heat exchanger 25 becomes larger than a predetermined value (ΔT). In this case, as a result of the thermal stress applied to the heat exchanger 25 exceeding the allowable value, the heat exchanger 25 may crack.

  Therefore, the control unit according to the present embodiment estimates the EGR gas temperature corresponding to the solid line 107 based on the vehicle speed when the combustion stop control is executed in the threshold change control. And a control part calculates a threshold value (threshold value used by determination whether temperature rise control is performed) based on this estimated EGR gas temperature. In this way, the control unit changes this threshold according to the vehicle speed when the combustion stop control is executed. Details of the threshold value change control will be described in the flowchart of FIG.

  FIG. 8 is a diagram illustrating an example of a flowchart when the control device 70 according to the present embodiment executes threshold value change control, refrigerant flow rate decrease control, and temperature increase control. The flowchart in FIG. 8 differs from the flowchart shown in FIG. 3B in that step S11, step S12, and step S13 are further provided, and that step S30a is provided instead of step S30. Steps S11 to S13 correspond to the threshold value change control described above.

  The control unit of the control device 70 according to the present embodiment executes Step S11 when it is determined as Yes in Step S10, that is, when the combustion stop control is executed. In step S11, the control unit acquires the vehicle speed when the combustion stop control is executed (that is, while the combustion stop control is executed). Specifically, in step S11, the control unit acquires the vehicle speed when the combustion stop control is executed by acquiring the vehicle speed at the time of execution of step S11 based on the detection result of the vehicle speed sensor 7. The vehicle speed acquisition method by the control unit is not limited to the method based on the detection result of the vehicle speed sensor 7. For example, the control unit may calculate the vehicle speed based on the rotational speed of the engine body 3 in step S11.

  After step S11, the control unit estimates the EGR gas temperature in the case of resuming combustion based on the vehicle speed acquired in step S11 (step S12). Here, the temperature of the EGR gas at the time of resuming combustion changes according to the vehicle speed when the combustion stop control is executed. Therefore, the control unit according to the present embodiment estimates the EGR gas temperature when the combustion is restarted based on the vehicle speed when the combustion stop control is executed.

Specifically, the control unit estimates the EGR gas temperature when the combustion is restarted by extracting it from the map. When a map defining the vehicle speed when the combustion stop control is executed (hereinafter referred to as the vehicle speed during the combustion stop control) and the EGR gas temperature when the combustion is restarted is visualized, a solid line in FIG. The EGR gas temperature 106 has the same shape as that shown in FIG. 7 by changing the horizontal axis of FIG. 7 to the vehicle speed during execution of the combustion stop control. In other words, the solid line 106 shown in the figure, in which the vehicle speed on the horizontal axis is changed to the vehicle speed during execution of the combustion stop control, indicates that the vehicle speed is low in the region where the vehicle speed during the execution of the combustion stop control is equal to or less than a predetermined value (V _x ). As the vehicle speed becomes higher, the temperature of the EGR gas becomes lower, and in a region where the vehicle speed during execution of the combustion stop control is higher than a predetermined value (V _x ), the temperature of the EGR gas becomes lower as the vehicle speed becomes higher. This map is obtained in advance by experiments, simulations, etc., and is stored in the storage unit (ROM 72) of the control device 70.

The control unit executes step S12 by extracting the EGR gas temperature corresponding to the vehicle speed acquired in step S11 from this map, and acquiring the extracted EGR gas temperature as the EGR gas temperature in step S12. And this one example, in the map was changed to the vehicle speed in the combustion stop control executing the horizontal axis in FIG. 7, for example, when the vehicle speed acquired in step S11 is V _x, the control unit, in step S12, the V _The EGR gas temperature (value of the solid line 106) corresponding to _x is acquired. However, the specific method for calculating the EGR gas temperature by the control unit is not limited to this. As another example, in step S12, the control unit performs EGR based on, for example, a predetermined arithmetic expression (an arithmetic expression for calculating the EGR gas temperature when combustion is restarted based on the vehicle speed during execution of combustion stop control). The gas temperature may be calculated.

  After step S12, the control unit calculates a threshold based on the EGR gas temperature estimated in step S12 (step S13). Specifically, the control unit calculates a value obtained by subtracting a predetermined value (ΔT) from the EGR gas temperature estimated in step S12. Then, the control unit calculates a threshold value based on the calculated value. Specifically, the control unit according to the present embodiment employs the calculated value itself (a value obtained by subtracting a predetermined value (ΔT) from the EGR gas temperature estimated in step S12) as a threshold value. Note that the threshold value obtained in this way has the same shape as that shown in FIG. 7 by changing the solid line 107 in FIG. 7 to the vehicle speed in which the horizontal axis in FIG. That is, in the diagram in which the horizontal axis in FIG. 7 is replaced with the vehicle speed during execution of the combustion stop control, the solid line 107 indicates the threshold curve calculated in step S13 according to the present embodiment.

  In the present embodiment, the predetermined value (ΔT) used in the calculation of step S13 is an EGR gas temperature at which the thermal stress applied to the heat exchanger 25 is less than or equal to an allowable value when combustion is resumed. A value corresponding to the difference from the temperature of the heat exchanger 25 is used. The predetermined value (ΔT) is obtained in advance by experiments, simulations, etc., and is stored in the storage unit (ROM 72). After step S13, the control unit executes step S20, and then executes step S30a.

  In step S30a, the control unit determines whether or not the temperature of the heat exchange element 25 is equal to or less than the threshold value calculated in step S13. When it determines with Yes by step S30a, a control part performs step S40, and when it determines with No by step S30a, a control part complete | finishes execution of a flowchart.

  As described above, the control unit according to the present embodiment acquires the vehicle speed during execution of the combustion stop control (the vehicle speed acquired in step S11) in the threshold change control, and performs combustion based on the acquired vehicle speed. A value obtained by estimating the EGR gas temperature at the time of resumption (when the combustion stop control is finished and the combustion is resumed) (step S12) and subtracting a predetermined value (ΔT) from the estimated EGR gas temperature The threshold value is calculated based on (Step S13). The threshold value calculated in this way has a different value depending on the vehicle speed during execution of the combustion stop control. That is, according to this configuration, the threshold value can be changed according to the vehicle speed during execution of the combustion stop control. And the control part uses the threshold value changed in this way in step S30a which is a determination process of whether to perform temperature rise control.

  According to the EGR device 10 according to the present embodiment, in addition to the operational effects of the EGR device 10 according to the first embodiment, the following operational effects can be achieved. First, as described above, the temperature of the EGR gas at the time of resuming combustion changes according to the vehicle speed during execution of the combustion stop control. Therefore, the magnitude of the thermal stress applied to the heat exchanger 25 when the combustion is restarted also changes according to the vehicle speed. In this regard, according to the EGR device 10 according to the present embodiment, the threshold value is changed according to the vehicle speed by executing the threshold value change control according to Steps S11 to S13 described above, and as a result, according to Step S40. The execution start timing of the temperature rise control is changed according to the vehicle speed. Thereby, it can suppress efficiently that an excessive thermal stress is added to the heat exchange body 25. FIG. As a result, the energy required for temperature rise control can be saved, and the fuel efficiency of the internal combustion engine 1 can be improved.

In order to facilitate understanding of the operation and effect of the EGR device 10 according to the present embodiment described above, this operation and effect will be specifically described again with reference to the drawings as follows. FIG. 9A to FIG. 9D are schematic views for explaining the operational effects of the EGR device 10 according to the present embodiment. Specifically, FIGS. 9A to 9D show vehicle speed, rotation speed, and refrigerant when combustion stop control, threshold value change control, refrigerant flow rate decrease control, and temperature rise control according to this embodiment are executed. An example of the time change of the refrigerant | coolant flow rate of the channel | path 24 and the temperature of the heat exchange body 25 is typically shown. 9A to 9D correspond to FIGS. 4A to 4D described above, respectively. 9A to 9D, a solid line 100 to a solid line 103, a dotted line 104, and a virtual line 105 represent the same contents as those in FIGS. 4A to 4D, respectively. 9A to 9D, time t ₁ , time t ₂ , time t ₃ and time t ₄ represent the same contents as in FIGS. 4A to 4D, respectively. ing. The dotted line 104 (threshold value) in FIG. 9D has a constant value at a time before time t _2, but this value (temperature) is higher than the value of the dotted line 104 in FIG. It is a value.

The dotted line 104 (threshold) in FIG. 9 (d) results threshold change control is executed, at time t ₂ later it is assumed that the threshold value according to the decrease of the vehicle speed is calculated so as to reduce It is drawn. Specifically, in this embodiment, although the vehicle speed indicated by a solid line 100 in FIG. 9 (a) starts decreasing from time t _1, the dotted line 104 in FIG. 9 (d) the result of the operation of step S13 , it is depicted as threshold value is computed to start decreasing at time t ₂ later.

As shown by a dotted line 104 in FIG. 9 (d), the result of the threshold is decreased at time _{t 2} later, the temperature of the heat exchanger 25 indicated by the solid line 103 in FIG. 9 (d) equal to or less than the threshold value at time _{t 3} ing. Thereby, a result of the temperature rise control at time _{t 3} is started, as shown by the solid line 102 of FIG. 9 (c), has skyrocketed refrigerant flow rate of the refrigerant passage 24 of the EGR cooler 20 at time _{t 3.}

Here, it is assumed that the time t _x shown in FIG. 9D is that the threshold value indicated by the dotted line 104 does not decrease according to the vehicle speed after the time t ₂ (that is, a constant state). (The threshold value thus assumed is referred to as a virtual threshold value), and represents the time during which the temperature of the heat exchange element 25 indicated by the solid line 103 is equal to or lower than the virtual threshold value. Thus, when the threshold value is not changed according to the vehicle speed, the temperature increase control is executed at this time t _x . Imaginary line 109 shown in FIG. 9 (c) shows the refrigerant flow rate of the refrigerant passage 24 in a case where if the temperature increase control is executed at time t _x. If this that the virtual line 109 is shown, which does not change by temporarily according to threshold vehicle speed, the coolant flow rate of the refrigerant passage 24 is time t _{x (which} is the time is before the t ₃₎ has skyrocketed in.

As can be seen from the above figures, by changing the threshold according to the vehicle speed when the combustion stop control is executed as in the present embodiment, the execution start timing of the temperature rise control can be delayed as a result. (Specifically, it is possible to slow the time t ₃ than the execution start timing of the temperature rise control time t _x). As a result, it is possible to save energy necessary for executing the temperature rise control (in the present embodiment, energy required particularly for the rotation of the electric pump 60). Thereby, fuel consumption can be improved.

  Note that the control device 70 of the EGR apparatus 10 according to the present embodiment executes the temperature increase control according to the modification of the first embodiment (step S40a in FIG. 6) instead of the temperature increase control according to the step S40 in FIG. May be. Even in this case, according to the present embodiment, the energy required for executing the temperature rise control (particularly the energy required for the operation of the energizing device 80) can be saved, so that the fuel consumption can be improved.

  Further, in the threshold change control, the control unit 70 of the control device 70 according to the present embodiment estimates the EGR gas temperature at the time of resuming combustion based on the vehicle speed during execution of the combustion stop control, and sets the estimated EGR gas temperature Although the threshold value is calculated based on this, the threshold value calculation method is not limited to this. For example, in the threshold change control, the control unit may calculate the threshold directly from the vehicle speed during execution of the combustion stop control (that is, calculate the threshold directly from the vehicle speed without estimating the EGR gas temperature). Good). Specifically, in this case, the storage unit of the control device 70 stores in advance a map that associates and defines the vehicle speed and the threshold value during execution of the combustion stop control. The control unit may calculate a threshold value directly from the vehicle speed by extracting a threshold value corresponding to the vehicle speed during execution of the combustion stop control from this map. Alternatively, a predetermined arithmetic expression for calculating a threshold value from the vehicle speed during execution of the combustion stop control is stored in advance in the storage unit of the control device 70. The control unit may calculate the threshold value directly from the vehicle speed by calculating the threshold value from the vehicle speed during execution of the combustion stop control using this calculation formula.

(Modification)
An EGR device 10 according to a modification of the second embodiment will be described. In the EGR device 10 according to this modification, the control content of the control device 70 is different from the control content of the second embodiment described above. Specifically, the control device 70 according to the present modified example generates heat even when the temperature rise control is executed, when the combustion is restarted (when the execution of the combustion stop control is completed and the combustion is restarted). A vehicle speed region in which the thermal stress applied to the exchanger 25 is greater than an allowable value is calculated when the combustion stop control is executed. Then, the control device 70 further executes EGR cut control for stopping the passage of the EGR gas to the heat exchanger 25 in the calculated vehicle speed region when the combustion is resumed. In the point which performs such control, the control apparatus 70 which concerns on this modification differs from the control apparatus 70 of Example 2 mentioned above.

  Before describing details of the control according to the above-described modification, an image of this control will be described. FIG. 10 is a schematic diagram for explaining an image of control of the control device 70 according to the present modification. FIG. 10 corresponds to FIG. 7 described above. The vertical axis in FIG. 10 indicates the temperature, and the horizontal axis indicates the vehicle speed when combustion is resumed. A solid line 106 in FIG. 10 indicates the EGR gas temperature in the case of resuming combustion, as in FIG. The dotted line 108a in FIG. 10 shows the engine refrigerant temperature obtained based on the detection result of the temperature sensor 8a when the combustion stop control is executed, as in the dotted line 108 in FIG. The dotted line 108a has a lower temperature than the dotted line 108 in FIG. 7 (the value on the vertical axis is lower). That is, FIG. 10 is drawn assuming that the engine refrigerant temperature is lower than that in FIG. A specific example of the temperature of the dotted line 108a in FIG.

A solid line 110 in FIG. 10 indicates the temperature of the heat exchanger 25 when combustion is resumed. As indicated by the solid line 110, the temperature of the heat exchanger 25 is not equal to or higher than the engine refrigerant temperature indicated by the dotted line 108a. As described above, since the dotted line 108a in FIG. 10 is lower in temperature than the dotted line 108 in FIG. 7, the maximum temperature of the heat exchanger 25 shown in FIG. 10 is higher than the maximum temperature of the heat exchanger 25 shown in FIG. The temperature is low. Therefore, in the case of Figure 10, the difference is a predetermined value between the temperature of a heat exchange element 25 shown in EGR gas temperature and the solid line 110 shown in a solid line 106 (△ T) in the vehicle speed range (10 to greater than, _{V a} or V vehicle speed range below _b ) has occurred.

In the region where the vehicle speed is V _a or more and V _b or less, the difference between the temperature of the EGR gas and the temperature of the heat exchange element 25 is larger than a predetermined value (ΔT), so that the thermal stress applied to the heat exchange element 25 is an allowable value. Will be bigger than. That is, this vehicle speed region (region of V _a or more and V _b or less) is a case where temperature increase control (specifically, temperature increase control for supplying the refrigerant to the refrigerant passage 24 of the EGR cooler 20 by the electric pump 60) is executed. Even if it exists, it is a vehicle speed area | region where the thermal stress added to the heat exchange body 25 becomes larger than an allowable value in the case of restarting combustion. As a result, cracks may occur in the heat exchanger 25 in this vehicle speed region.

Therefore, the control device 70 of the EGR device 10 according to the present modification executes EGR cut control in this vehicle speed region (region of V _a or more and V _b or less). Specifically, the control unit stops the flow of the EGR gas in the EGR passage 11 by controlling the EGR valve 12 to be closed in this vehicle speed region. Thereby, the control unit stops the passage of the EGR gas to the heat exchanger 25. Thereby, in this vehicle speed area | region, it is suppressed that the thermal stress added to the heat exchange body 25 becomes larger than an allowable value.

FIG. 11 is a diagram illustrating an example of a flowchart when the control device 70 according to the present modification executes threshold value change control, refrigerant flow rate decrease control, and temperature increase control. The flowchart of FIG. 11 is different from the flowchart of FIG. 8 in that step S14 is further provided. The control unit of the control device 70 according to the present modification executes step S14 after step S13. Even in the case where the temperature rise control is executed in step S14, the control unit performs a vehicle speed region (V _a or more V _a or more) such that the thermal stress applied to the heat exchanger 25 becomes larger than the allowable value when combustion is resumed. _b or less area) is calculated. Specifically, the control unit uses the vehicle speed region for the EGR gas temperature estimated in step S12, the engine refrigerant temperature at the time when the combustion stop control is executed, and the predetermined threshold value used in calculating the threshold value in step S13. And based on the value. The specific calculation process in step S14 will be described as follows with reference to FIG.

  First, when the horizontal axis in FIG. 10 is changed to the vehicle speed during execution of the combustion stop control, the solid line 106 in FIG. 10 indicates the EGR gas estimated in step S12, as described in step S12 in FIG. Corresponds to temperature. Further, the engine refrigerant temperature at the time when the combustion stop control according to step S2 is executed is considered to be substantially the same as the engine refrigerant temperature shown by the dotted line 108a in FIG. Therefore, the dotted line 108a in FIG. 10 is used as the engine refrigerant temperature at the time when the combustion stop control is executed. Further, the predetermined value used in the threshold value calculation in step S13 corresponds to ΔT when the horizontal axis in FIG. 10 is replaced with the vehicle speed during execution of the combustion stop control.

  In step S14, the control unit according to this modification example replaces the horizontal axis in FIG. 10 with the vehicle speed during execution of the combustion stop control as described above, and the EGR gas temperature estimated in step S12 (the solid line 106 described above). The value obtained by subtracting the engine refrigerant temperature (the above-mentioned dotted line 108a) at the time when the combustion stop control according to step S2 is executed from the predetermined value (ΔT described above) used when calculating the threshold value according to step S13. The vehicle speed region that also increases is calculated. And a control part acquires the vehicle speed area | region calculated in this way as a vehicle speed area | region of step S14. After step S14, the control unit executes step S20.

Then, after executing the flowchart of FIG. 11, the control unit according to the present modification ends the execution of the combustion stop control and executes the normal control according to step S3 of FIG. When is restarted, EGR cut control is executed in the vehicle speed region (region of V _a or more and V _b or less) calculated in step S14 of FIG. If the vehicle speed region calculated in step S14 of FIG. 11 is zero (that is, when there is no vehicle speed region), the control unit does not execute EGR cut control when combustion is resumed.

According to the EGR device 10 according to the present modification, in addition to the operational effects of the second embodiment described above, the following operational effects can be achieved. Specifically, according to the EGR device 10, since the EGR cut control described above is executed, even when the temperature rise control is executed, the thermal stress applied to the heat exchanger 25 when the combustion is resumed is In the vehicle speed region (region of V _a or more and V _b or less) that is larger than the allowable value, the passage of the EGR gas to the heat exchanger 25 can be stopped. Thereby, in such a vehicle speed region, it is possible to suppress the heat exchanger 25 from being applied with a thermal stress larger than the allowable value. Thereby, generation | occurrence | production of the crack to the heat exchange body 25 can be suppressed effectively.

  Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 4 Intake passage 10 EGR apparatus 12 EGR valve 20 EGR cooler 24 Refrigerant passage 25 Heat exchanger 50 Flow control valve 60 Electric pump 70 Control apparatus 71 CPU
80 Energizer

Claims (4)

An EGR device applied to an internal combustion engine in which combustion stop control for stopping combustion is executed,
An EGR cooler having a heat exchanger through which EGR gas passes, and a refrigerant passage through which a refrigerant for cooling the EGR gas passing through the heat exchanger passes;
A refrigerant flow rate reduction mechanism capable of reducing the flow rate of the refrigerant in the refrigerant passage;
A temperature raising mechanism capable of raising the temperature of the heat exchanger;
When the combustion stop control is executed, a refrigerant flow rate reduction control is performed to control the refrigerant flow rate reduction mechanism so that the flow rate of the refrigerant in the refrigerant passage decreases, and after the execution of the refrigerant flow rate reduction control, An EGR device comprising: a control device that executes temperature rise control for controlling the temperature raising mechanism so that the temperature of the heat exchange body rises when the temperature of the heat exchange body becomes a threshold value or less.   The control device further executes threshold change control for acquiring a vehicle speed of a vehicle on which the internal combustion engine is mounted when the combustion stop control is executed, and changing the threshold according to the acquired vehicle speed. Item 1. An EGR device according to Item 1.   In the threshold change control, the control device estimates and estimates the temperature of the EGR gas when the combustion stop control is finished and the combustion is restarted based on the acquired vehicle speed. The EGR device according to claim 2, wherein the threshold value is changed according to the vehicle speed by calculating the threshold value based on a value obtained by subtracting a predetermined value from the temperature of the EGR gas.   Even when the temperature increase control is executed, the control device has a thermal stress applied to the heat exchanger larger than an allowable value when the combustion stop control is finished and the combustion is restarted. The vehicle speed region of the vehicle is calculated when the combustion stop control is executed, and when the combustion stop control is finished and the combustion is restarted, the calculated vehicle speed region is The EGR device according to claim 3, further executing EGR cut control for stopping passage of the EGR gas to the heat exchanger.

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