JP4962403B2 - Multistage turbocharging system - Google Patents

Description

  The present invention relates to a multistage turbocharger system in which a plurality of turbochargers are connected in series.

In the single turbocharger system, the pressure energy of the exhaust manifold is collected and accumulated in the accumulator tank, and the accumulated gas is supplied as air assist to the turbine upstream side of the turbocharger, improving the response of the turbocharger One is known (Patent Document 1).
JP 2008-002276 A

  On the other hand, in a multistage turbocharger system in which the turbines of a plurality of turbochargers are connected in series and multistage, each turbine inlet pressure takes various values depending on the operation region. If the configuration is simply applied, the pressure in the accumulator tank may not be sufficient for the turbine inlet pressure of the turbocharger to assist, and appropriate assist may not be performed.

  An object of the present invention is to perform more appropriate and effective air assist in a multistage turbocharging system.

  A multi-stage turbocharger system according to the present invention includes a high-pressure turbocharger, a low-pressure turbocharger, a pressure accumulation tank that collects pressure energy from the upstream side of the turbine of the high-pressure turbocharger, and accumulates pressure. It is characterized by comprising a stored gas supply means for supplying the stored gas in the tank to the turbine inlet side of the low-pressure turbocharger.

  The accumulated gas supply means can further supply the accumulated gas to the turbine inlet side of the high-pressure turbocharger, and the accumulated gas is supplied to the high-pressure turbocharger and / or the low-pressure turbocharger according to the operating state. Is supplied to the turbine inlet side of the compressor, and when a supercharging increase request is made, the accumulated gas is preferentially supplied to the turbine inlet side of the high-pressure turbocharger. Thereby, more appropriate air assist can be performed corresponding to the pressure of the accumulated gas.

  The accumulated gas supply means supplies the accumulated gas to the turbine inlet side of the high-pressure turbocharger when the differential pressure between the pressure in the accumulator tank and the turbine inlet pressure of the high-pressure turbocharger is larger than a predetermined value, When the differential pressure is smaller than a predetermined value, the accumulated gas is supplied to the turbine inlet side of the low-pressure turbocharger.

  When the supercharging by the high-pressure turbocharger is stopped in the state where the supercharging is performed by the high-pressure turbocharger and the low-pressure turbocharger, the accumulated gas supply means is connected to the low-pressure turbocharger. Accumulated gas is supplied to the turbine inlet side. Thereby, generation | occurrence | production of a torque level | step difference can be prevented. In particular, when there is a request for increased supercharging such as during acceleration, a more remarkable effect can be obtained.

  The pressure accumulation is performed in an operation region where a part of the exhaust gas supplied to the high-pressure stage turbocharger is bypassed via the high-pressure stage exhaust bypass passage that bypasses the high-pressure stage turbocharger. Thereby, pressure accumulation can be performed without lowering the supercharging efficiency.

  In order to perform accumulating at a higher pressure, it is preferable that accumulating is performed by closing the high pressure exhaust switching valve provided in the high pressure exhaust bypass passage in the operation region.

  As described above, according to the present invention, more appropriate and effective air assist can be performed in a multistage turbocharger system.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of a two-stage turbocharger system that is an example of a multistage turbocharger system according to a first embodiment of the present invention.

  The turbocharger system 10 includes a relatively large-capacity low-pressure turbocharger 11 and a relatively small-capacity high-pressure turbocharger 12. The intake passage 14 guided from the air cleaner 13 is connected to the high-pressure compressor 12C of the high-pressure turbocharger 12 via the low-pressure compressor 11C of the low-pressure turbocharger 11, and is connected to a throttle and intercooler (not shown). To the intake manifold 16 of the internal combustion engine 15. Further, the exhaust passage 17 is connected from the exhaust manifold 18 of the internal combustion engine 14 to the low-pressure turbine 11T of the low-pressure turbocharger 11 via the high-pressure turbine 12T of the high-pressure turbocharger 12 and exhaust catalyst. It communicates with the outside via (not shown) or the like.

  In the intake passage 14, the inlet side and the outlet side of the high-pressure compressor 12 </ b> C are communicated by an intake bypass passage 19, and an intake switching valve 20 is provided in the intake bypass passage 19. On the other hand, in the exhaust passage 17, the inlet side and the outlet side of the high-pressure stage turbine 12 </ b> T are communicated by a high-pressure stage exhaust bypass passage 21, and the high-pressure stage exhaust bypass passage 21 is provided with a high-pressure stage exhaust switching valve 22. The exhaust passage 17 on the inlet side of the low-pressure turbine 11T is connected to the exhaust passage 17 on the outlet side of the low-pressure turbine 11T by the low-pressure exhaust bypass passage 23. A valve 24 is provided.

  Further, in the present embodiment, the upstream side of the high-pressure turbine 12 </ b> T of the exhaust passage 17 and the pressure accumulation tank 25 are communicated by the pressure accumulation passage 26, and the first valve 27 is provided in the pressure accumulation passage 26. In FIG. 1, the pressure accumulation passage 26 is connected to the exhaust passage 17. However, a configuration in which the pressure accumulation passage 26 is directly connected to the exhaust manifold 18 without the pressure accumulation passage 26 may be employed. Further, the pressure accumulation tank 25 is communicated with the inlet side of the low pressure stage turbine 11T of the exhaust passage 17 via the low pressure stage air assist passage 28, and the second valve 29 is disposed in the low pressure stage air assist passage 28.

  Note that the ECU 30 controls the opening and closing of the intake air switching valve 20, the high pressure exhaust switching valve 22, the low pressure exhaust switching valve 24, the first valve 27, and the second valve 29. In the present embodiment, an aero flow meter S1 is provided upstream of the low-pressure compressor 11C in the intake passage 14, a throttle opening sensor S2 is provided in a throttle valve (not shown), and an intake manifold pressure sensor S3 is provided in the intake manifold 16. However, a pressure sensor S4 is provided in the pressure accumulation tank 25, and each sensor signal is input to the ECU 30.

  Next, with reference to the flowchart of FIG. 2, the air assist control process using the pressure accumulation gas in the pressure accumulation tank 25 in the first embodiment will be described. Note that the air assist control process shown in FIG. 2 is repeatedly executed by the ECU 30 at a predetermined timing. The pressure accumulation in the pressure accumulation tank 25 via the pressure accumulation passage 26 is separately performed by a conventionally known method.

  In step S100, it is determined whether or not a request for increasing supercharging, such as a rapid acceleration request determination based on, for example, a change in throttle opening, has occurred. If it is determined that there is no supercharging increase request, this process ends. If it is determined that there is a supercharging increase request, in step S102, the pressure in the pressure accumulation tank 25 (tank pressure) P0 is set. It is determined whether or not the differential pressure ΔP1 (= P0−P1) of the inlet pressure P1 of the high-pressure turbine 12T is greater than a predetermined value.

  When ΔP1> predetermined value, the tank internal pressure P0 has a value sufficient to assist the high-pressure turbine 12T. Therefore, in step S104, the first valve 27 is opened and the second valve 29 is closed (or closed). Maintained). As a result, the accumulated gas is supplied to the inlet side of the high-pressure turbine 12T via the accumulator passage 26 to assist the high-pressure turbine 12T, and this air assist control process is completed.

  On the other hand, when it is determined in step S102 that the differential pressure ΔP1 is not greater than the predetermined value, the tank internal pressure P0 is not a value sufficient to assist the high-pressure turbine 12T. Therefore, in step S106, the stored gas in the pressure storage tank 26 Is not usable for assisting the low-pressure turbine 11T. That is, in step S106, it is determined whether or not the differential pressure ΔP2 (= P0−P2) between the tank internal pressure P0 and the inlet pressure P2 of the low-pressure turbine 12T is greater than a predetermined value.

  When ΔP2> predetermined value, the tank internal pressure P0 has a value sufficient to assist the low-pressure turbine 11T. Therefore, in step S108, the second valve 29 is opened and the first valve 27 is closed (or closed). Maintained). As a result, the accumulated gas is supplied to the inlet side of the low-pressure stage turbine 11T via the low-pressure stage air assist passage 28 to assist the low-pressure stage turbine 11T, and this air assist control process ends.

  When it is determined in step S106 that ΔP2> predetermined value is not satisfied, the tank pressure P0 is not a value sufficient to assist either the high-pressure turbine 12T or the low-pressure turbine 11T. Therefore, the first and first pressures are determined in step S110. The two valves 27 and 29 are closed (or maintained in the closed state), and the air assist control process ends.

  The inlet pressures P1 and P2 of the high-pressure turbine 12T and the low-pressure turbine 11T are, for example, as shown in FIG. 3, referring to a map created based on experimental values, for example, the engine speed and the intake manifold pressure. It is requested from. That is, in FIG. 3, the curve group LG is an isoline of the pressures P1 and P2.

  Next, a specific example of the air assist control processing operation in the first embodiment will be described with reference to FIG. FIG. 4 is a graph showing temporal changes in the inlet pressures P1, P2 and the tank internal pressure P0 of the high-pressure turbine 12T and the low-pressure turbine 11T. The horizontal axis corresponds to time, and the vertical axis corresponds to pressure. .

  For example, before the air assist is executed, the tank internal pressure P0 is maintained at a value sufficiently higher than the inlet pressures P1 and P2 of the high-pressure stage and low-pressure stage turbines 12T and 11T by the pressure accumulation process performed so far. When acceleration is started at time t0, for example, the processing after step S102 described with reference to FIG. 2 is started, and air assist is executed.

  Since the tank internal pressure P0 is sufficiently high at the beginning of execution of air assist, the accumulated gas is supplied to the high-pressure turbine T12. As a result, the accumulated gas accumulated in the accumulator tank 25 is consumed, the tank pressure P0 gradually decreases, and the inlet pressures P1 and P2 of both turbines increase. At time t1 (> t0), when the pressure difference ΔP1 between the tank pressure P0 and the inlet pressure P1 of the high-pressure turbine T12 becomes equal to or lower than a predetermined value, the supply of the accumulated gas is switched from the high-pressure turbine T12 to the low-pressure turbine T11. .

  When the accumulated gas is further consumed and the differential pressure ΔP2 between the tank pressure P0 and the inlet pressure P2 of the low-pressure turbine T11 becomes equal to or lower than a predetermined value at the time t2 (> t1), the supply of the accumulated gas is stopped and the tank pressure P0 becomes a constant value until the next pressure accumulation is started. That is, in the section A of FIG. 4, air assist to the high pressure stage turbine T12 is executed, and in section B, air assist to the low pressure stage turbine T11 is executed.

  As described above, according to the first embodiment, in the multi-stage turbocharger system, pressure energy is collected and accumulated from the upstream side of the high-pressure stage turbine. When the pressure is no longer sufficient to assist, the accumulated gas can be supplied to the low-pressure turbine to assist the low-pressure turbine, so that the accumulated energy can be effectively utilized in accordance with the operating state.

  That is, in the multi-stage turbocharging system, the exhaust manifold pressure at the same air amount is higher than that in the single-stage type, so the minimum tank pressure that can be used for assisting the high-pressure turbine is higher than that in the single-stage type. For this reason, if the accumulated pressure and the supply of the accumulated gas are performed at the same position as in the air assist of the single-stage turbocharging system, the accumulated energy cannot be effectively used. However, in this embodiment, since the accumulated gas can be supplied to the low-pressure turbine, the accumulated energy can be used effectively.

  Next, a second embodiment of the present invention will be described with reference to FIG. 1 and FIG. The configuration of the second embodiment is substantially the same as the configuration of the first embodiment, and the difference from the first embodiment is only the air assist control processing operation. Therefore, only the configuration related to the air assist control processing operation of the second embodiment will be described. In the second embodiment, when switching from a mode using two turbochargers (two turbo mode) to a mode using only one turbocharger (single turbo mode), the low-pressure stage turbine Air assist is performed on 11T to prevent torque step.

  FIG. 5 is a flowchart of the air assist control process of the second embodiment, which is repeatedly executed by the ECU 30 at a predetermined timing.

  In step S200, it is determined whether or not the current operating point is in the two-turbo region (two-turbo mode). If it is determined that the two turbo regions are not present, the air assist control process is immediately terminated. On the other hand, when it is determined that the operating point is in the two turbo region, in step S202, there is a supercharging increase request such as an acceleration request, and the current operating point is a switching region from the two turbo mode to the single turbo mode. It is determined whether or not there is.

  When there is no supercharging increase request or the current operating point is not in the switching region from the two-turbo mode to the one-turbo mode, the air assist control process ends. On the other hand, when there is a supercharging increase request and the current operating point is in the switching region from the two turbo mode to the single turbo mode, the target supercharging pressure is calculated in step S204, and the low pressure stage is determined in step S206. The second valve 29 provided in the air assist passage 28 is opened, and air assist to the low pressure turbine 11T is executed.

  In step S208, switching control from the two turbo mode to the single turbo mode (steps S208 to S216) is started, and the high-pressure stage exhaust switching valve 22 is fully opened. In step S210, it is determined whether or not the low-pressure stage compressor outlet pressure is equal to or higher than the high-pressure stage compressor outlet pressure, and this determination is repeated until the low-pressure stage compressor outlet pressure becomes equal to or higher than the high-pressure stage compressor outlet pressure.

  When the low-pressure stage compressor outlet pressure becomes equal to or higher than the high-pressure stage compressor outlet pressure, the intake air switching valve 20 is fully opened in step S212. In step S214, it is determined whether or not the current boost pressure is equal to or higher than the target boost pressure, and this determination is repeated until the boost pressure is equal to or higher than the target boost pressure. If it is determined in step S214 that the current supercharging pressure is equal to or higher than the target supercharging pressure, the second valve 29 is closed in step S216, and the air assist control process ends.

  As described above, in the second embodiment, in the multi-stage turbocharging system, pressure energy is collected and accumulated from the upstream side of the high-pressure turbine, and there is a request for increasing supercharging, and from the two-turbo mode to the one-turbo mode. By switching to the low pressure turbine, the stored gas is supplied and air assist is performed to prevent the occurrence of torque steps when switching from the two-turbo mode to the single-turbo mode. Air assistance.

  Next, a third embodiment of the present invention will be described with reference to FIGS. The configuration of the third embodiment is substantially the same as the configuration of the second embodiment, and the only difference from the second embodiment is the pressure accumulation processing operation. Therefore, in the following description, only the configuration related to the pressure accumulation processing operation of the third embodiment will be described.

  Since the third embodiment performs pressure accumulation in a specific region (exhaust gas switching valve slightly open region) in the two-turbo mode, first, referring to FIGS. 6 and 7, a general two-stage turbocharging system is generally used. The operation mode will be described. FIG. 6 is a map showing operation modes of the low-pressure turbocharger 11 and the high-pressure turbocharger 12, where the horizontal axis corresponds to the engine speed and the vertical axis corresponds to the load torque.

  In the two-stage turbocharging system, the engine speed is relatively low, the two-turbo mode in which the low-pressure stage and high-pressure stage turbochargers 11 and 12 are operated together, and the engine speed is relatively high. A single turbo mode in which the high-pressure stage exhaust switching valve 22 is fully opened and only the low-pressure stage turbocharger 11 is operated.

  In the two-turbo mode, the high-pressure stage exhaust switching valve 22 is fully closed and the low-pressure stage turbocharger 11 and the high-pressure stage turbocharger 12 are both fully operated, and the high-pressure stage exhaust switching valve 22. Is partially opened and the low-pressure turbocharger 11 is fully operated, but the high-pressure turbocharger 12 is divided into the exhaust switching valve fine opening mode operated using only part of the exhaust. It is done. That is, the exhaust gas switching valve slight opening mode is a mode as a transition section connecting between the full operation mode and the single turbo mode. In each mode, the low-pressure stage exhaust switching valve 24 is basically maintained in a fully closed state.

  In FIG. 6, the full operation region corresponding to the full operation mode is indicated by D1, the exhaust changeover valve slight open region corresponding to the exhaust changeover valve slight open mode is indicated by D2, and the single turbo region corresponding to the single turbo mode is indicated by D3. It is. Further, the boundary line L1 is a boundary line between the two turbo mode (corresponding to the full operation region D1 and the exhaust switching valve slight opening region D2) and the one turbo mode (corresponding to the one turbo region D3). Further, the boundary line L2 is a boundary line between the full operation region D1 and the exhaust valve slight opening region D2 in the two turbo mode.

  FIG. 7 is a graph showing a change in the opening degree of the high-pressure stage exhaust switching valve 22 when the operating state changes from the full operation mode to the single turbo mode along the arrow M shown in FIG. Indicates the engine speed, and the vertical axis corresponds to the opening of the high-pressure exhaust switch 22.

  The arrow M indicates that the operating point transitions from the full operating region D1 to the single turbo region D3 through the exhaust switching valve slightly opened region D2. In the full operation region D1, the opening degree of the high-pressure stage exhaust switching valve 22 is fully opened. When the engine speed is increased and reaches the rotational speed Ne1, the operating point crosses the boundary line L2, enters the exhaust valve slightly open region D2, and further moves toward the single turbo region D3. At this time, the high-pressure stage exhaust switching valve 22 is gradually closed, and the opening degree becomes small.

  When the engine speed reaches Ne2 and the operating point exceeds the boundary line L1, the operating point enters the single turbo region D3. Therefore, the operating mode is switched to the single turbo mode, and the high-pressure stage exhaust switching valve 22 is fully open. It is said. A switching region for switching from the two turbo mode to the single turbo mode is set in the vicinity of the boundary line L1 along the boundary line.

  Next, the pressure accumulation processing operation of the second embodiment will be described with reference to the flowchart of FIG. This pressure accumulation process is repeatedly executed in the ECU 30 at a predetermined timing. Note that the pressure accumulation processing operation of the third embodiment is performed in the exhaust switching valve slightly open region. This is because, in order to perform pressure accumulation when the high-pressure stage exhaust switching valve 22 is fully closed, the variable pressure of the turbine is used. This is because the vane needs to be closed to reduce the supercharging efficiency.

  In step S300, it is determined whether or not the current operating point is in the exhaust gas switching valve slightly open region D2. When it is determined that it is not in the exhaust switching valve slightly open region D2, this process is immediately terminated. When it is determined that it is in the exhaust switching valve slightly open region D2, the tank internal pressure P0 is higher than a predetermined value in step S301. It is determined whether or not.

  In step S301, when the tank internal pressure P0 of the pressure storage tank 25 is higher than a predetermined value, the main pressure storage process is terminated. When the tank internal pressure P0 is equal to or lower than the predetermined value, in step S302, the high pressure stage exhaust gas switching is performed. Valve 22 is closed. In step S304, it is determined whether or not the current operating point is in a switching region where the two-turbo mode is switched to the one-turbo mode. That is, it is determined whether or not there is an operating point in a predetermined switching region set in the vicinity of the boundary line L1 in FIG.

  If it is determined that it is the switching region, it is necessary to switch to the single turbo mode, so whether or not the first valve 27 (see FIG. 1) provided in the pressure accumulation passage 26 is closed in step S306. If it is closed, the pressure accumulating process is terminated as it is, and the switching process to the single turbo mode is executed as conventionally known. If it is determined that the valve is not closed, the first valve 27 is closed in step S308, and the pressure accumulation process ends.

  On the other hand, if it is determined in step S304 that the current operating point is not in the switching region for switching from the 2-turbo mode to the 1-turbo mode, it is determined in step S310 whether the exhaust manifold pressure has increased. The If the exhaust manifold pressure has increased, in step S312, the first valve 27 is opened to accumulate pressure in the accumulator tank 25, the process returns to step S304, and the same process is repeated thereafter. When the exhaust manifold pressure has not increased, the first valve 27 is closed in step S314, and the process returns to step S304. That is, steps S304 and S310 to S314 are repeated until the switching area is entered, and only when the exhaust manifold pressure increases, the first valve 27 is opened and a higher pressure is accumulated. The exhaust manifold pressure is obtained from the engine speed and the intake manifold pressure by the same method as the inlet pressure P1 of the high-pressure turbine 12T shown in FIG. 3, for example.

  As described above, according to the third embodiment of the present invention, the same effect as in the second embodiment can be obtained, and the pressure accumulation processing operation is executed in the exhaust switching valve slightly open region, so that the supercharging efficiency can be improved. It becomes possible to accumulate high pressure without reducing it.

  In the first embodiment, the pressure accumulation passage is also used as an air assist passage for supplying pressure accumulation gas to the high pressure turbine. However, the pressure accumulation passage and the air assist passage to the high pressure turbine may be provided separately.

  In the present embodiment, a two-stage turbocharging system has been described as an example. However, the present invention can also be applied to a configuration having two or more stages.

1 is a block diagram illustrating a configuration of a two-stage turbocharging system that is a first embodiment of the present invention. FIG. It is a flowchart of the air assist control process of 1st Embodiment. FIG. 3 is an isoline diagram of inlet pressures P1 and P2 of a high-pressure turbine and a low-pressure turbine with respect to engine speed and intake manifold pressure. It is a graph which shows the time change of inlet pressure P1, P2 and tank internal pressure P0 of a high pressure stage turbine and a low pressure stage turbine. It is a flowchart of the air assist control process of 2nd Embodiment. It is a map which shows the operation mode of the low pressure stage turbocharger with respect to engine speed and load torque, and a high pressure stage turbocharger. It is a graph which shows the opening degree state of a high pressure stage exhaust gas switching valve when an operation state changes along the arrow M shown by FIG. It is a flowchart of the pressure accumulation process in 3rd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Two-stage turbocharger system 11 Low pressure stage turbocharger 12 High pressure stage turbocharger 11C Low pressure stage compressor 11T Low pressure stage turbine 12C High pressure stage compressor 12T High pressure stage turbine 17 Exhaust passage 21 High pressure stage exhaust bypass passage 22 High pressure stage Exhaust gas switching valve 25 Accumulation tank 26 Accumulation passage 27 First valve 28 Low pressure stage air assist passage 29 Second valve 30 ECU
S4 Pressure sensor

Claims (7)

A high-pressure stage turbocharger, a low-pressure stage turbocharger, a pressure accumulation tank that collects and accumulates pressure energy from a turbine upstream side of the high-pressure stage turbocharger, and a pressure accumulation gas in the pressure accumulation tank Pressure- accumulated gas supply means that can be supplied to the turbine inlet side of the turbocharger and the turbine inlet side of the high-pressure stage turbocharger, and the accumulated gas is supplied to the high-pressure stage turbocharger according to the operating state. And / or a multi-stage turbocharger system for supplying the low-pressure turbocharger to the turbine inlet side, wherein the accumulated gas supply means supplies the accumulated gas to the high-pressure turbocharger when a supercharge increase request is made. A multi-stage turbocharging system characterized in that it is preferentially supplied to the turbine inlet side of the engine. When the pressure difference between the pressure in the pressure accumulating tank and the turbine inlet pressure of the high pressure turbocharger is greater than a predetermined value, the accumulated gas supply means is configured to store the pressure on the turbine inlet side of the high pressure turbocharger. gas supply, multistage turbocharging system of claim 1 wherein the differential pressure, characterized by supplying the accumulator gas turbine inlet side of the low-pressure stage turbocharger when less than the predetermined value. In the state where supercharging is performed by the high-pressure stage turbocharger and the low-pressure stage turbocharger, when the supercharging by the high-pressure stage turbocharger is stopped, the accumulated gas supply means is the low-pressure stage The multistage turbocharger system according to claim 1 or 2 , wherein the accumulated gas is supplied to a turbine inlet side of the turbocharger. The pressure accumulation is performed in an operation region in which a part of the exhaust gas supplied to the high-pressure stage turbocharger is bypassed via a high-pressure stage exhaust bypass passage that bypasses the high-pressure stage turbocharger. The multistage turbocharging system according to any one of claims 1 to 3 . The multi-stage turbocharging system according to claim 4 , wherein the pressure accumulation is performed by closing a high-pressure stage exhaust switching valve provided in the high-pressure stage exhaust bypass passage in the operation region. A high-pressure stage turbocharger, a low-pressure stage turbocharger, a pressure accumulation tank that collects and accumulates pressure energy from a turbine upstream side of the high-pressure stage turbocharger, and a pressure accumulation gas in the pressure accumulation tank Accumulating gas supply means for supplying to the turbine inlet side of the turbocharger,
In the state where supercharging is performed by the turbocharger and the low-pressure turbocharger, when the supercharging by the high-pressure turbocharger is stopped, the accumulated gas supply means performs the low-pressure turbocharger. A multistage turbocharger system, wherein the accumulated gas is supplied to a turbine inlet side of a machine. A high-pressure stage turbocharger, a low-pressure stage turbocharger, a pressure accumulation tank that collects and accumulates pressure energy from a turbine upstream side of the high-pressure stage turbocharger, and a pressure accumulation gas in the pressure accumulation tank Accumulating gas supply means for supplying to the turbine inlet side of the turbocharger, and the accumulated pressure is supplied to the high-pressure stage turbocharger via a high-pressure stage exhaust bypass passage that bypasses the high-pressure stage turbocharger. A multi-stage turbocharging system characterized in that it is performed in an operating region where a part of the exhaust to be bypassed is bypassed.

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