JP6415958B2 - EGR system - Google Patents

Description

  The present invention relates to an EGR system.

  Conventionally, an EGR system that recirculates exhaust gas as EGR gas from the exhaust side of the engine to the intake side is known (see, for example, Patent Document 1). In the EGR system described in Patent Document 1, even when the exhaust pressure of the engine is low, the EGR gas is recirculated by pressurizing the EGR gas with an EGR pump disposed on the EGR flow path.

Japanese Patent Laid-Open No. 2001-73884

  In the above EGR system, the exhaust pressure becomes sufficiently high depending on the operating conditions of the engine, and therefore it is conceivable to generate power using the energy of EGR gas. Therefore, in a recent EGR system, an EGR pump / generator is disposed on the EGR flow path, and a pressurizing function for pressurizing EGR gas by rotating the impeller with a motor connected to the impeller (function as an EGR pump) In addition, there is a case where it is desired to realize a power generation function (function as an EGR generator) in which the impeller is rotationally driven with EGR gas to generate electric power with a motor.

  However, normally, the rotation direction of the impeller and the motor when pressurizing the EGR gas is opposite to the rotation direction of the impeller and the motor when generating power by rotating the impeller with the EGR gas. Therefore, when switching between the EGR gas pressurization function and the EGR gas power generation function, it is necessary to stop the rotation of the impeller and the motor once, which may cause a time lag.

  The present invention has been made in view of the above circumstances, and in an EGR system equipped with an EGR pump / generator, an EGR system capable of reducing a time lag when switching between an EGR gas pressurizing function and an EGR gas generating function is provided. The issue is to provide.

  In order to solve the above problems, an EGR system according to the present invention includes an EGR flow path through which EGR gas flows, an impeller disposed in the EGR flow path, and an EGR pump / generator having a motor connected to the impeller, A first flow path that is included in the EGR flow path and guides the EGR gas to the impeller, a second flow path that is included in the EGR flow path separately from the first flow path, and that guides the EGR gas to the impeller, and a first flow path Or a flow path switching unit that selectively circulates EGR gas in any of the second flow paths, and when the EGR gas is circulated through the first flow path and guided to the impeller by the flow path switching unit, the motor When the impeller is driven to rotate in a predetermined rotation direction by the pressure, the EGR gas is pressurized, and when the EGR gas is circulated through the second flow path and guided to the impeller by the flow path switching unit, the impeller is driven by the EGR gas. Is predetermined times By being rotated in the direction, power is generated by a motor.

  In this EGR system, the EGR gas is pressurized by circulating EGR gas through the first flow path and rotating the impeller in a predetermined rotation direction by a motor. Further, the EGR gas is circulated through the second flow path, and the impeller is driven to rotate in the same predetermined rotation direction by the EGR gas, thereby generating electric power by the motor. That is, the EGR gas pressurization function and the EGR gas power generation function can be smoothly switched while rotating the impeller and the motor in the same predetermined rotation direction without stopping the rotation. Therefore, in the EGR system including the EGR pump / generator, the time lag when switching between the EGR gas pressurization function and the EGR gas power generation function can be reduced.

  In the EGR system according to the present invention, either one of the first flow path and the second flow path causes EGR gas to be introduced into the impeller along the axial direction of the impeller, and either the first flow path or the second flow path is used. On the other hand, EGR gas may be introduced into the impeller along the rotation direction of the impeller. With such a configuration, the above-described effects can be suitably realized.

  The EGR system according to the present invention further includes a flow path switching unit and a control unit for controlling the motor, and the control unit performs either EGR control for pump operation control for rotating the motor or power generation operation control for power generation by the motor. This is selectively executed based on the differential pressure between the upstream side and the downstream side of the impeller in the flow path. In the pump operation control, the flow path switching unit is controlled so that the EGR gas flows in the first flow path, and By controlling the motor so that the impeller rotates in a predetermined rotation direction, the EGR gas is pressurized, and in the power generation operation control, the flow path switching unit is controlled so that the EGR gas flows through the second flow path. By doing so, the impeller may be driven to rotate in a predetermined rotation direction with the EGR gas, and power may be generated by the motor. In this case, the pressurization function and the power generation function can be switched based on the differential pressure between the upstream side and the downstream side of the impeller.

  The shut-off valve is further provided on the second flow path, and the shut-off valve prevents the EGR gas that is circulated through the first flow path and led to the impeller from flowing back through the EGR flow path through the second flow path. In addition, the second flow path may be blocked. Thereby, when EGR gas is introduced into the impeller from the first flow path and pressurized, it is possible to prevent the EGR gas from flowing back through the second flow path.

  ADVANTAGE OF THE INVENTION According to this invention, in the EGR system provided with the EGR pump and generator, the time lag at the time of switching the pressurization function of EGR gas and the power generation function by EGR gas can be reduced.

It is a figure showing an engine provided with an EGR system concerning an embodiment. (A) It is a schematic block diagram which shows the EGR system at the time of pump operation control. (B) It is a schematic block diagram which shows the EGR system at the time of electric power generation operation control. (A) It is a schematic plane sectional view for demonstrating operation | movement of the impeller at the time of pump operation control. (B) It is a schematic plane sectional view for demonstrating operation | movement of the impeller at the time of electric power generation operation control. (A) It is a schematic perspective view for demonstrating operation | movement of the impeller at the time of pump operation control. (B) It is a schematic perspective view for demonstrating operation | movement of the impeller at the time of electric power generation operation control. It is a figure which shows an example of an operating condition map.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the following description, the same or equivalent elements will be denoted by the same reference numerals, and redundant description will be omitted.

  FIG. 1 is a diagram illustrating an engine including an EGR system according to an embodiment. FIG. 2 is a schematic configuration diagram showing the EGR system. FIG. 3 is a schematic cross-sectional view for explaining the operation of the impeller. FIG. 4 is a schematic perspective view for explaining the operation of the impeller. As shown in FIGS. 1 to 4, the EGR system 1 according to the present embodiment is mounted on an engine 20 such as a diesel engine in a vehicle, for example, and at least a part of the exhaust gas of the engine 20 is used as EGR gas. Return to the intake side.

  The engine 20 includes one or a plurality of cylinders (six cylinders in the illustrated example). The engine 20 is not limited to a diesel engine, and may be a gasoline engine. The applied vehicle is not limited, and may be, for example, a large vehicle such as a truck, a bus, or a heavy machine, a medium-sized vehicle, a normal passenger car, a small vehicle, or a light vehicle.

  The engine 20 includes a two-stage turbocharging system. Specifically, the engine 20 includes a low-pressure stage turbocharger 21 having a low-pressure stage compressor 22 and a low-pressure stage turbine 23, and a high-pressure stage having a high-pressure stage compressor 25 and a high-pressure stage turbine 26. And a turbocharger 24. On the intake side of the engine 20, the air compressed by the low pressure compressor 22 is cooled by the intercooler 27 and then further compressed by the high pressure compressor 25. The air compressed by the high-pressure compressor 25 is cooled by the aftercooler 28 and is taken into each cylinder of the engine 20 through the intake pipe 29.

  The EGR system 1 is an HPL (High Pressure Loop) system that recirculates high-pressure exhaust gas before passing through the high-pressure turbine 26 of the high-pressure turbocharger 24 to the intake side. A flow path switching unit) 3, an EGR cooler 4, an EGR valve 5, an EGR pump / generator 6, a shut-off valve 9, and a control unit 10.

  The EGR flow path 2 has one end connected to the exhaust pipe 30 and the other end connected to the downstream side of the aftercooler 28 in the intake pipe 29. With such a configuration, the EGR flow path 2 recirculates EGR gas from the exhaust pipe 30 to the intake pipe 29. Further, the EGR flow path 2 includes a first flow path 12 and a second flow path 13 that are branched via the branch portion 11 in the middle thereof. The first flow path 12 and the second flow path 13 are respectively connected to a housing 14 described later on the downstream side.

  The flow path switching valve 3 is disposed in the branching portion 11 and selectively allows the EGR gas flowing through the EGR flow path 2 to flow through either the first flow path 12 or the second flow path 13. When the flow path switching valve 3 selects the first flow path 12, EGR gas flows through the first flow path 12, and when the flow path switching valve 3 selects the second flow path 13, EGR gas Flows through the second flow path 13. As the flow path switching valve 3, for example, a switching valve such as a three-way valve is used.

  The EGR cooler 4 cools the EGR gas and is provided on the EGR flow path 2. In the illustrated example, the EGR channel 2 is provided on the upstream side of the housing 14, but may be provided on the downstream side. The EGR cooler 4 is not particularly limited, and various EGR coolers can be used.

  The EGR valve 5 allows or stops the recirculation of the EGR gas to the intake pipe 29 by opening and closing. Although it does not specifically limit as the EGR valve 5, For example, a butterfly valve etc. are applicable. In the illustrated example, the EGR valve 5 is provided on the downstream side of the housing 14 in the EGR flow path 2, but may be provided on the upstream side of the housing 14.

  The EGR pump / generator 6 includes a motor 7 and an impeller 8. The EGR pump / generator 6 is a pressurizing function as an EGR pump that pressurizes the EGR gas by driving the impeller 8 by the motor 7, and an EGR generator that generates power by the motor 7 by driving the impeller 8 by the EGR gas. And both power generation functions.

  The motor 7 is supplied with power from a storage battery (not shown) or the like and rotationally drives the impeller 8. Further, the motor 7 generates electric power by being rotationally driven by the impeller 8. The motor 7 is not particularly limited, and various motors can be used. The rotation shaft 7 a of the motor 7 extends through the wall of the housing 14 into the housing 14 and is connected to the impeller 8.

  The impeller 8 is fixed to the end of the rotary shaft 7a so that the axis L thereof is coaxial with the rotary shaft 7a of the motor 7. The impeller 8 includes a plurality of blades 18 extending radially from the top 8a side to the side 8b side as viewed in the axis L. The impeller 8 is a radial impeller, for example, and is formed in an umbrella-shaped outer shape in which a cross section including the axis L is substantially trapezoidal. Note that a mixed flow impeller or the like may be applied as the radial impeller. The impeller 8 is disposed in the EGR flow path 2. Specifically, the impeller 8 has a minute gap G between the housing 14 provided on the EGR flow path 2 and the inner wall surface 14 a of the housing 14. Are stored.

  The housing 14 stores the impeller 8 disposed in the EGR flow path 2. The housing 14 includes a first inlet 15 to which the first channel 12 is connected, a second inlet 16 to which the second channel 13 is connected, and an outlet to which the intake pipe 29 side of the EGR channel 2 is connected. 17.

  The first inflow port 15 causes EGR gas flowing through the first flow path 12 to flow into the top 8 a side of the impeller 8 in the housing 14. The second inlet 16 allows the EGR gas flowing through the second flow path 13 to flow into the housing 14 so as to strike the side 8b side of the impeller 8 along the rotation direction A1. The outlet 17 allows the EGR gas flowing out from the side 8 b side of the impeller 8 to flow out of the housing 14.

  In the illustrated example, the first inlet 15 is opened toward the top 8 a of the impeller 8. The second inlet 16 is opened in a direction along the tangential direction of the outer periphery of the impeller 8. The outlet 17 is opened in a direction along the tangential direction of the outer periphery of the impeller 8. In addition, the outlet 17 is provided at a position away from the second inlet 16 along the rotational direction A1 and not opposed thereto.

  As shown in FIGS. 3A and 4A, when the impeller 8 is rotationally driven by the motor 7, the EGR gas introduced into the housing 14 through the first inlet 15 Inhale and pressurize from 8a and discharge from side 8b. On the other hand, as shown in FIGS. 3B and 4B, the impeller 8 is not driven to rotate by the motor 7, and the EGR gas introduced into the housing 14 through the second inlet 16. Is rotated in the rotational direction A1. At this time, the EGR gas travels around the outer periphery of the side portion 8 b of the impeller 8 so as to circulate along the rotation direction A 1 of the impeller 8 while hitting the blade 18, and then to the outside of the housing 14 through the outlet 17. leak.

  In the case where the impeller 8 is not rotationally driven by the motor 7, even if the EGR gas is guided to the top 8 a of the impeller 8 through the first inflow port 15, any of the rotational direction A1 and the reverse rotational direction can be obtained. Does not rotate in any direction.

  The shut-off valve 9 is provided in the second flow path 13. The shut-off valve 9 prevents EGR gas from flowing back through the EGR flow path 2. Specifically, the shutoff valve 9 is closed by the control unit 10 when EGR gas flows through the first flow path 12, and the EGR gas passes through the EGR flow path 2 from the housing 14 via the second flow path 13. Suppresses backflow. The shut-off valve 9 is not particularly limited, and various shut-off valves 9 can be used. For example, a check valve may be used as the shut-off valve 9. In this case, since it is not necessary to control the opening / closing of the shut-off valve 9, the control and structure are simplified, and the opening / closing of the shut-off valve 9 is simplified. The backflow of EGR gas due to the delay can be suppressed.

  The control unit 10 is configured by a computer including, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). The control unit 10 is electrically connected to the flow path switching valve 3, the motor 7, and the cutoff valve 9, and controls switching of the flow path switching valve 3, rotational driving of the motor 7, and opening / closing of the cutoff valve 9. .

  The control unit 10 performs either of the pump operation control for rotationally driving the motor 7 or the power generation operation control for generating electric power by the motor 7 based on the differential pressure between the upstream side and the downstream side of the impeller 8 in the EGR flow path 2. Run selectively. Since the differential pressure has a correlation with the engine speed and the engine load, the control unit 10 of the present embodiment performs either the pump operation control or the power generation operation control based on the engine speed and the engine load. select. Specifically, the control unit 10 selects either pump operation control or power generation operation control using an operation condition map described later based on the engine speed and the engine load.

  In the pump operation control, the control unit 10 controls the flow path switching valve 3 so that the EGR gas flows through the first flow path 12, and the motor 7 so that the impeller 8 is rotationally driven in a predetermined rotational direction A1. Control and pressurize the EGR gas. On the other hand, in the power generation operation control, the control unit 10 controls the flow path switching valve 3 so that the EGR gas flows through the second flow path 13, and the impeller 8 rotates in the same rotation direction A1 as the EGR gas. The motor 7 is driven to rotate in the direction A <b> 1 to generate power.

  FIG. 5 is a diagram illustrating an example of an operation condition map. In the operating condition map shown in FIG. 5, the horizontal axis indicates the engine speed, and the vertical axis indicates the engine load. This operating condition map includes regions R1 and R2 set so as to be partitioned by boundary lines B1 and B2. The state of the engine speed and the engine load in the region R1 corresponds to a state in which the EGR gas pressure (intake pressure) on the downstream side of the impeller 8 is higher than the EGR gas pressure (exhaust pressure) on the upstream side. When the engine speed and the engine load of the engine 20 fall within the range of the region R1, the pump operation control is selected and executed by the control unit 10. The state of the engine speed and the engine load in the region R2 corresponds to a state in which the EGR gas pressure (intake pressure) on the downstream side of the impeller 8 is lower than the upstream EGR gas pressure (exhaust pressure). When the engine speed and engine load of the engine 20 fall within the range of the region R2, the power generation operation control is selected and executed by the control unit 10.

  In the operating condition map here, the region R1 tends to spread toward the high load side of the engine load, and the region R2 tends to spread toward the low load side of the engine load. Further, the region R2 tends to expand to the high engine load side (upper side in FIG. 5) on the high engine speed side (right side in FIG. 5) compared to the low engine speed side. The boundary line B1 is defined based on, for example, the idling speed of the engine 20. The boundary line B2 is defined based on the engine transient performance, exhaust gas pulsation, and the like, in addition to the differential pressure between the intake pressure and the exhaust pressure of the engine 20. For example, the operating condition map may be set based on an actual measurement value, or may be set based on a calculated value.

  Next, the operation of the EGR system 1 will be described.

  First, the control unit 10 acquires engine speed and engine load data from various sensors (not shown). Based on the data, the operation condition map described above is used to determine whether the engine 20 is in the region R1 or the region R2, and whether to perform pump operation control or power generation operation control is selected.

  When performing pump operation control, the control part 10 controls the flow-path switching valve 3 so that EGR gas may distribute | circulate through the 1st flow path 12 (refer Fig.2 (a)). As a result, as shown in FIGS. 3A and 4A, the EGR gas flowing through the EGR flow path 2 flows to the first flow path 12 side at the branch portion 11, and in the axial direction A <b> 2 of the impeller 8. Along the first inlet 15 and into the housing 14. As a result, the EGR gas flows into the vicinity of the top 8 a of the impeller 8.

  At the same time, the control unit 10 rotationally drives the motor 7 and rotationally drives the impeller 8. Further, the control unit 10 closes the shut-off valve 9. As a result, the EGR gas flows from the top 8 a side to the side 8 b side in the impeller 8 and is pressurized, and flows out of the housing 14 through the outlet 17. As described above, the EGR pump / generator 6 exhibits a pressurizing function as an EGR pump. In this way, by making the EGR pump / generator 6 function as an EGR pump, it is possible to perform EGR even when the exhaust pressure is lower than the intake pressure, and increase in fuel consumption due to an increase in pumping loss. Can be suppressed.

  On the other hand, when the power generation operation control is executed, the control unit 10 controls the flow path switching valve 3 so that the EGR gas flows through the second flow path 13 (see FIG. 2B). As a result, as shown in FIGS. 3B and 4B, the EGR gas flowing through the EGR flow path 2 stops flowing to the first flow path 12 side in the branch portion 11 and the second It flows to the flow path 13 side and flows into the housing 14 from the second inlet 16 of the housing 14. Thereby, the EGR gas flows into the vicinity of the side portion 8b of the impeller 8.

  In addition, the control unit 10 stops power supply to the motor 7. As a result, the motor 7 does not apply a rotational driving force to the impeller 8, but the EGR gas rotates in the rotational direction while striking the blade 18 along the rotational direction A1 of the impeller 8 with respect to the side 8b side of the impeller 8. It proceeds so as to circulate around A <b> 1 and flows out of the housing 14 through the outlet 17. Thereby, the impeller 8 is rotationally driven in the rotational direction A1 by the EGR gas, and the motor 7 is rotationally driven. As a result, the motor 7 generates electric power. As described above, the EGR pump / generator 6 exhibits a power generation function as an EGR generator. As described above, by causing the EGR pump / generator 6 to function as an EGR generator, the engine 20 can obtain a fuel consumption reduction effect.

  Here, as shown in FIG. 3 and FIG. 4, the flow path for the EGR gas to flow into the impeller 8 and the EGR gas when the EGR pump / generator 6 functions as an EGR pump and when it functions as an EGR generator. However, the path | route which flows along the top part 8a or the side part 8b of the impeller 8 differs. With such a configuration, the EGR pump / generator 6 can rotate in the same predetermined rotation direction A1 when the EGR gas is pressurized by the impeller 8 and when the impeller 8 is rotationally driven by the EGR gas.

  Therefore, when the control unit 10 switches from pump operation control to power generation operation control, the EGR gas without stopping the rotation of the EGR pump / generator 6 from the state in which the motor 7 rotates the impeller 8 in the predetermined rotation direction A1 can be obtained. Thus, the impeller can be switched to a state where it is rotationally driven in the same predetermined rotational direction A1. This makes it possible to switch between the EGR gas pressurization function and the EGR gas power generation function finely and smoothly. Moreover, the time lag at the time of switching the pressurization function of EGR gas and the power generation function by EGR gas can be reduced.

  Similarly, when the control unit 10 switches from power generation operation control to pump operation control, the motor 7 without stopping the rotation of the EGR pump / generator 6 from the state in which the impeller 8 is rotationally driven by the EGR gas in the predetermined rotation direction A1. Can be switched to a state in which the impeller 8 is rotationally driven in the same predetermined rotational direction A1. This makes it possible to switch between the EGR gas pressurization function and the EGR gas power generation function finely and smoothly. Moreover, the time lag at the time of switching the pressurization function of EGR gas and the power generation function by EGR gas can be reduced.

  As described above, according to the EGR system 1 according to the present embodiment, the EGR gas pressurization function and the EGR gas power generation function while the impeller 8 and the motor 7 are rotated in the same predetermined rotation direction A1 without stopping the rotation. Can be switched smoothly. Therefore, in the EGR system 1 including the EGR pump / generator 6, the time lag when switching between the EGR gas pressurizing function and the EGR gas generating function can be reduced, and the responsiveness related to the switching can be improved. It becomes possible.

  In the present embodiment, one of the first flow path 12 and the second flow path 13 introduces EGR gas into the impeller 8 along the axial direction A2 of the impeller 8, and the first flow path 12 or the second flow path. Any one of 13 introduces EGR gas into the impeller 8 along the rotation direction A1 of the impeller 8. With such a configuration, the above-described effects can be suitably realized.

  In the present embodiment, the engine operating condition corresponds to either the region R1 corresponding to the state where the intake pressure is higher than the exhaust pressure or the region R2 corresponding to the state where the intake pressure is lower than the exhaust pressure with reference to the operating condition map. Whether to perform pump operation control or power generation operation control is selected. That is, based on the differential pressure between the upstream side and the downstream side of the impeller 8 in the EGR flow path 2, the EGR gas pressurizing function and the EGR gas generating function can be switched. Further, as described above, since the operation condition map is further set based on the engine transient performance and the exhaust gas pulsation, etc., the pump operation control and the power generation operation control are not limited to the differential pressure but also the engine transient performance. In addition, it is possible to perform switching at a suitable timing in consideration of exhaust gas pulsation and the like.

  Further, the shut-off valve 9 provided on the second flow path 13 is further provided, and the shut-off valve 9 blocks the second flow path 13 when the EGR gas is circulated through the first flow path 12. Thereby, when EGR gas is introduced into the impeller 8 from the first flow path 12 and pressurized, it is possible to prevent the EGR gas from flowing back through the second flow path 13.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments. The present invention can be modified without departing from the scope described in the claims or applied to other embodiments. May be.

  For example, in the above embodiment, the EGR system 1 is of the HPL system, but an LPL (Low Pressure Loop) system that recirculates the low-pressure exhaust gas after passing through the low-pressure turbine 23 of the low-pressure turbocharger 21 to the intake side. It may be a thing.

  In the above embodiment, the first flow path 12 introduces EGR gas into the impeller 8 along the axial direction A2, and the second flow path 13 introduces EGR gas into the impeller 8 along the rotation direction A1, but EGR The flow path configuration for introducing the gas into the impeller 8 is not particularly limited. For example, the second channel may be introduced along the axial direction of the impeller, and the first channel may be introduced along the rotation direction of the impeller. In short, the first flow path only needs to introduce EGR gas into the impeller when the EGR gas pressurizing function is exhibited, and the second flow path is EGR when the EGR gas generates a power generation function. What is necessary is just to introduce gas into the impeller.

  In the above embodiment, the operation condition map shown in FIG. 5 is used as one aspect of selectively executing the pump operation control or the power generation operation control based on the differential pressure between the upstream side and the downstream side of the impeller in the EGR flow path. Either pump operation control or power generation operation control is selected, but a different operation condition map may be used. For example, an operating condition map based on the exhaust pressure, intake pressure, etc. of the engine 20 in addition to the engine speed and the engine load may be used. In this case, for example, the pump operation control and the power generation operation control can be switched at a more suitable timing according to the vehicle type or the like.

  DESCRIPTION OF SYMBOLS 1 ... EGR system, 2 ... EGR flow path, 3 ... Flow path switching valve (flow path switching part), 6 ... EGR pump and generator, 7 ... Motor, 8 ... Impeller, 12 ... 1st flow path, 13 ... 2nd Flow path.

Claims (3)

An EGR channel through which EGR gas flows;
An EGR pump / generator having an impeller disposed in the EGR flow path and a motor coupled to the impeller;
A first flow path that is included in the EGR flow path and guides the EGR gas to the impeller;
A second flow path that is included in the EGR flow path separately from the first flow path and guides the EGR gas to the impeller;
A flow path switching unit that selectively circulates the EGR gas in either the first flow path or the second flow path,
The impeller is a radial impeller,
The first flow path causes the EGR gas to be introduced into the impeller along the axial direction of the impeller,
The second flow path causes the EGR gas to be introduced into the impeller along the rotation direction of the impeller,
When the EGR gas is circulated through the first flow path and guided to the impeller by the flow path switching unit, the EGR gas is pressurized by being driven to rotate in a predetermined rotation direction by the motor. And
When the EGR gas is circulated through the second flow path and guided to the impeller by the flow path switching unit, the impeller is rotationally driven in the predetermined rotation direction by the EGR gas, so that the motor An EGR system that generates electricity. A controller for controlling the flow path switching unit and the motor;
The controller is
One of pump operation control for rotationally driving the motor or power generation operation control for generating electric power with the motor is selectively executed based on the differential pressure between the upstream side and the downstream side of the impeller in the EGR flow path,
In the pump operation control, the flow path switching unit is controlled so that the EGR gas flows through the first flow path, and the motor is controlled so that the impeller is rotationally driven in the predetermined rotation direction. To pressurize the EGR gas,
In the power generation operation control, by controlling the flow path switching unit so that the EGR gas flows in the second flow path, the impeller is rotationally driven in the predetermined rotation direction by the EGR gas, and the motor The EGR system according to claim 1 , wherein the EGR system generates electric power. A shut-off valve provided on the second flow path;
The shut-off valve shuts off the second flow path so that the EGR gas that is circulated through the first flow path and guided to the impeller does not flow back through the EGR flow path via the second flow path. The EGR system according to claim 1 or 2 .

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