JP2015048758A - Exhaust pressure reduction mechanism of internal combustion engine and exhaust pressure reduction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an internal combustion engine which prevents an increase of a pumping loss by suppressing a rise of the pressure of an exhaust gas of the internal combustion engine, and can further improve the fuel economy of the internal combustion engine, related to the internal combustion engine having a supercharge system and a low-pressure EGR system.SOLUTION: In an internal combustion engine 1 which comprises a turbo-type supercharger system, and a low-pressure EGR passage 14 for connecting an exhaust passage 13 at a downstream side of a turbine 15a of the turbo-type supercharger system, and an intake passage 12 at an upstream side of a compressor 15b of the turbo-type supercharger system, an exhaust pump 20 is arranged at the exhaust passage 13 at a downstream side rather than the turbine 15a, and at a downstream side rather than a branch point of the low-pressure EGR passage 14, and an EGR pump 21 is arranged at the low-pressure EGR passage 14.

Description

  In an internal combustion engine having a low pressure EGR system and a supercharging system, the present invention prevents an increase in pumping loss by suppressing an increase in the pressure of exhaust gas in the exhaust passage, and further improves the fuel efficiency of the internal combustion engine. The present invention relates to an internal combustion engine capable of performing the same and an exhaust pressure reduction method thereof.

  Generally, in a diesel vehicle equipped with a diesel engine, exhaust gas discharged from an internal combustion engine contains NOx, PM, and the like. Therefore, from the viewpoint of preventing air pollution, an exhaust purification treatment device (NOx selective reduction type) is provided in the exhaust passage. A catalyst, a DPF, etc.) are provided, and before exhaust gas is released to the atmosphere, this exhaust purification processing device purifies NOx, PM, etc. in the exhaust gas to less than the legal regulation value.

  In particular, since the amount of NOx generated in the internal combustion engine decreases as the combustion temperature in the cylinder decreases, an EGR system that recirculates part of the exhaust gas from the exhaust passage to the intake passage through the EGR passage is used in diesel vehicles. Is generally provided. By mounting this EGR system on a vehicle, the oxygen concentration in the intake air to the internal combustion engine can be reduced, so that the combustion temperature of the internal combustion engine can be lowered and the temperature of the exhaust gas can be lowered.

  On the other hand, a turbocharging system that achieves high output and low fuel consumption of an internal combustion engine by increasing the intake pressure and intake air amount to the internal combustion engine using the energy of exhaust gas discharged from the internal combustion engine is also a diesel vehicle. Is generally provided.

  The EGR system is classified into two types, a high pressure EGR system and a low pressure EGR system, depending on the positional relationship between the turbine and compressor constituting the supercharging system and the EGR passage. As shown in FIG. 3, in the engine 1X having the low pressure EGR system and the supercharging system, the low pressure EGR passage 14 is provided by connecting an intake passage 12 upstream of the compressor 15b and an exhaust passage 13 downstream of the turbine 15a. The low pressure EGR passage 14 is provided with an EGR cooler 17 and an EGR valve 18 in order from the upstream side.

  In this low pressure EGR system, exhaust energy is consumed by the turbine 15a in order to introduce the exhaust gas into the low pressure EGR passage 14 from the downstream side of the turbine 15a, and the pressure of the exhaust gas is low. In this case, for example, an EGR pump of an internal combustion engine that pumps EGR gas into the intake passage by an EGR pump provided in the low pressure EGR passage may occur. An apparatus has been proposed (see, for example, Patent Document 1).

  On the other hand, during high load operation of the internal combustion engine, in order to produce a high output, a large amount of intake air is required to burn a large amount of fuel, and a large amount of exhaust gas is discharged, resulting in a high exhaust gas temperature. The exhaust pumping loss increases as the pressure of the exhaust gas at the outlet of the internal combustion engine increases. For this reason, there is a problem in that improvement in fuel consumption of the internal combustion engine is limited.

JP 2010-236381 A

  The present invention has been made in view of the above, and an object of the present invention is to suppress an increase in the pressure of exhaust gas at the outlet of an internal combustion engine for an internal combustion engine equipped with a turbocharging system and a low pressure EGR system. Thus, an object of the present invention is to provide an internal combustion engine and an exhaust pressure reduction method for the internal combustion engine that can prevent an increase in pumping loss and further improve the fuel consumption of the internal combustion engine.

  In order to achieve the above object, an internal combustion engine of the present invention comprises a turbocharging system, an exhaust passage downstream of a turbine of the turbocharging system, and an intake air upstream of a compressor of the turbocharging system. In the internal combustion engine having a low pressure EGR passage connecting the passage, an exhaust pump is provided in the exhaust passage downstream of the turbine and downstream of the branch point of the low pressure EGR passage, and the low pressure EGR passage is provided in the internal combustion engine. An EGR pump is provided.

  According to this configuration, by providing an exhaust pump in the exhaust passage and assisting exhaust gas exhaust by driving the exhaust pump, the pressure of the exhaust gas in the exhaust passage not only downstream of the turbine but also upstream of the turbine is reduced. Therefore, the increase in pressure can be suppressed, so that the exhaust pumping loss can be reduced and the fuel consumption of the engine can be improved. Further, since the differential pressure across the turbine can be increased, the driving force of the turbine and the compressor can be increased to assist supercharging, and the increase in the indicated mean effective pressure (IMEP) can be achieved by this high supercharging. Therefore, the fuel consumption of the internal combustion engine can be further improved.

  Further, during EGR, the EGR gas flow rate can be adjusted by the EGR pump provided in the low pressure EGR passage, and the exhaust gas can be assisted by driving the EGR pump, not only downstream of the turbine but also upstream of the turbine. It is possible to suppress the pressure increase by lowering the pressure of the exhaust gas in the exhaust passage.

  In the above internal combustion engine, an exhaust heat recovery device is provided in the exhaust passage between the branch point of the low pressure EGR passage and the exhaust pump, or in the low pressure EGR passage, and the exhaust heat recovery device is provided with exhaust gas. When configured to drive at least one of the exhaust pump or the EGR pump with electric power generated using exhaust heat, the following effects can be obtained.

  When the exhaust heat recovery device is provided in the exhaust passage, the thermal energy of the exhaust gas before flowing into the exhaust pump can be recovered, and the exhaust gas temperature can be lowered to reduce the volumetric flow rate of the exhaust gas. The exhaust pump can be downsized. Further, since the exhaust gas pressure can be further reduced by cooling the exhaust gas, an increase in exhaust pumping loss can be further prevented.

  In addition, when the exhaust heat recovery device is provided in the low pressure EGR passage, the temperature of the EGR gas can be reduced by recovering the thermal energy of the EGR gas, so the load on the EGR cooler and the EGR pump can be reduced. The EGR cooler and EGR pump can be downsized. Moreover, by reducing the temperature of the EGR gas, the EGR rate can be further increased, and NOx generation can be suppressed.

  Further, in the internal combustion engine, an exhaust pressure control means for controlling driving of the exhaust pump and the EGR pump based on a flow rate of EGR gas passing through the low pressure EGR passage and a pressure of exhaust gas in the exhaust passage. By ensuring the flow rate of EGR gas, it is possible to prevent the increase in exhaust pumping loss by suppressing the increase in exhaust gas pressure in the exhaust passage while ensuring the exhaust gas purification performance with reduced NOx. Can do.

  In addition, the exhaust pressure reduction method for an internal combustion engine of the present invention for achieving the above object includes a turbocharging system, an exhaust passage downstream of a turbine of the turbocharging system, and the turbocharging system. In an exhaust pressure reduction method for an internal combustion engine having a low-pressure EGR passage that connects an intake passage upstream of a compressor of the compressor, the exhaust passage is downstream of the turbine and downstream of the branch point of the low-pressure EGR passage. In this method, the exhaust pump provided is driven and the EGR pump provided in the low-pressure EGR passage is driven.

  In the exhaust pressure reduction method for an internal combustion engine, the exhaust heat recovery device provided in the exhaust passage between the turbine and the exhaust pump or the low pressure EGR passage may generate power using exhaust heat of the exhaust gas. At least one of the exhaust pump and the EGR pump is driven with the generated electric power.

  In the exhaust pressure reduction method for an internal combustion engine, the driving of the exhaust pump and the EGR pump is controlled based on the flow rate of the EGR gas passing through the low pressure EGR passage and the pressure of the exhaust gas in the exhaust passage. To do.

  According to these methods, the same effects as those of the internal combustion engine can be obtained.

  According to the internal combustion engine and the exhaust pressure reduction method of the present invention, since the exhaust pump is provided in the exhaust passage, the exhaust gas is assisted by driving the exhaust pump, so that not only the downstream of the turbine but also the turbine Since the pressure of the exhaust gas in the upstream exhaust passage can be reduced to suppress the increase in the exhaust pressure, the exhaust pumping loss can be reduced and the fuel consumption of the engine can be improved. Further, since the differential pressure across the turbine can be increased, the driving force of the turbine and the compressor can be increased to assist supercharging, and the increase in the indicated mean effective pressure (IMEP) can be achieved by this high supercharging. Therefore, the fuel consumption of the internal combustion engine can be further improved.

  Furthermore, since the EGR pump is provided in the low pressure EGR passage, during EGR, the EGR gas flow rate can be adjusted by the EGR pump, and exhaust gas can be assisted by driving the EGR pump, and only downstream of the turbine. Instead, the pressure increase can be suppressed by reducing the pressure of the exhaust gas in the exhaust passage upstream of the turbine.

It is a figure showing composition of an internal-combustion engine of an embodiment concerning the present invention. It is a figure which shows the flow of control of the exhaust pressure reduction method of the internal combustion engine of embodiment which concerns on this invention. It is a figure which shows the structure of the internal combustion engine which concerns on a prior art.

  Hereinafter, an internal combustion engine and an exhaust pressure reduction method thereof according to an embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, an engine (internal combustion engine) 1 according to an embodiment of the present invention includes an engine body 10, an intake passage 12, an exhaust passage 13, and a low pressure ECR passage 14.

  The intake passage 12 is connected to an intake manifold 11a, and a compressor 15b and an intercooler 16 of a turbocharger (turbo supercharger) 15 are provided in order from the upstream side. The exhaust passage 13 is connected to the exhaust manifold 11b, and a turbine 15a of the turbocharger 15 is provided. The low pressure EGR passage 14 is provided by connecting an intake passage 12 upstream of the compressor 15b and an exhaust passage 13 downstream of the turbine 15a, and an EGR cooler 17 and an EGR valve 18 are provided in this order from the upstream side.

  Fresh air A introduced from the atmosphere is sent to the intake manifold 11a via the compressor 15b and the intercooler 16 together with the exhaust gas Ge flowing into the intake passage 12 from the low pressure EGR passage 14 as necessary. The engine 1 generates power by being mixed and compressed with the fuel injected into the cylinder (cylinder) and burning the fuel. Then, the exhaust gas G generated by the combustion in the engine 1 flows out to the exhaust passage 13 and partly flows as the EGR gas Ge to the low-pressure EGR passage 14 via the turbine 15a, and the remaining exhaust gas (G -Ge) is purified by an exhaust gas purification apparatus (not shown) and then released to the atmosphere via a muffler.

  On the other hand, in the turbocharger 15, when the turbine 15a is rotationally driven using the energy of the exhaust gas G, the compressor 15b directly connected to the turbine 15a is driven to compress the intake air A + Ge. Therefore, by using the turbocharger 15, the intake pressure can be increased and the intake amount can be increased, so that the power generated in the engine 1 can be increased. However, on the other hand, the exhaust pressure of the exhaust gas G discharged from the engine 1 increases.

ここで、Ｌ：仕事[ｋｗ]、η：効率[−]、ｃｐ：定圧比熱[ｋＪ／ｋｇＫ]、Ｔ１：入口温度[Ｋ]、ｍ：ガス質量流量[ｋｇ／ｓ]、ＰＲ：圧力比[−]、ＥＲ：膨張比[−]、κ：比熱比[−]、添字のｃ：コンプレッサ、添字のｔ：タービンである。 Further, the expansion ratio of the turbine 15a and the pressure ratio of the compressor 15b are expressed by the following equations.

Here, L: work [kw], η: efficiency [−], cp: constant pressure specific heat [kJ / kgK], T1: inlet temperature [K], m: gas mass flow rate [kg / s], PR: pressure ratio [−], ER: expansion ratio [−], κ: specific heat ratio [−], subscript c: compressor, subscript t: turbine.

  The above formula shows that the expansion ratio ER of the turbine 15a increases as the pressure ratio PR of the compressor 15b increases.

  In the present invention, in the engine 1, an exhaust pump 20 is provided in the exhaust passage 13 downstream from the turbine 15 a and downstream from the branch point with the low-pressure EGR passage 14, and the EGR pump 21 is provided in the low-pressure EGR passage 14. Provide.

  According to this configuration, by providing the exhaust pump 20 in the exhaust passage 13 and assisting the discharge of the exhaust gas G by driving the exhaust pump 20, not only the downstream of the turbine 15a but also the exhaust passage 13 upstream of the turbine 15a. Since the increase in the pressure of the exhaust gas G can be suppressed by reducing the pressure of the exhaust gas G, the exhaust pumping loss can be reduced and the fuel consumption of the engine 1 can be improved. Further, since the differential pressure across the turbine 15a can be increased, the driving force of the turbine 15a and the compressor 15b can be increased to assist supercharging, and the increase in the indicated mean effective pressure (IMEP) can be achieved by this high supercharging. Therefore, the fuel consumption of the engine 1 can be further improved.

  Further, at the time of EGR, the flow rate of the EGR gas Ge can be adjusted by the EGR pump 21 provided in the low pressure EGR passage 14, and the exhaust gas G can be assisted by driving the EGR pump 21, and only downstream of the turbine 15a. Instead, the pressure increase can be suppressed by lowering the pressure of the exhaust gas G in the exhaust passage 13 upstream of the turbine 15a.

  Further, as shown in FIG. 1, in the engine 1, an exhaust heat recovery device 30 a that generates power using the heat of exhaust gas is provided in the exhaust passage 13 between the branch point of the low-pressure EGR passage 14 and the exhaust pump 20, Another exhaust heat recovery device 30 b is provided in the low pressure EGR passage 14, and electric power recovered from the exhaust heat of the exhaust gas G by the exhaust heat recovery devices 30 a and 30 b is generated at least by the exhaust pump 20 or the EGR pump 21. One drive source is configured. That is, at least one of the exhaust pump 20 or the EGR pump 21 is driven by the power generated by the exhaust heat recovery devices 30a and 30b using the exhaust heat of the exhaust gas G. Although either one of the exhaust heat recovery devices 30a and 30b is effective, it is more preferable to provide both.

  These exhaust heat recovery devices 30a and 30b can be configured by a system using a thermoacoustic engine or a Rankine cycle, for example. A thermoacoustic engine uses a thermoacoustic phenomenon in which the oscillating fluid in a narrow channel with a temperature gradient performs a thermodynamic process of compression, expansion, heating, and cooling. Energy conversion can be performed, and this sound wave can be converted into electric power by using a linear generator.

  Rankine cycle is an ideal thermodynamic cycle consisting of four processes: constant pressure specific heat, isentropic expansion (adiabatic expansion), constant pressure exhaust heat, isentropic compression (adiabatic compression), and can be condensed like a steam engine. It is used as an ideal standard for heat engines using various working fluids.

  However, in the present invention, it is only necessary to recover exhaust heat of the exhaust gas G and be a drive source of the exhaust pump 20, and it is not particularly limited to a system using a thermoacoustic engine or a Rankine cycle.

  When the exhaust heat recovery device 30a is provided in the exhaust passage 13, the thermal energy of the exhaust gas G before flowing into the exhaust pump 20 is recovered, the temperature of the exhaust gas G is lowered, and the volume flow rate of the exhaust gas G is increased. Since it can reduce, the exhaust pump 20 can be reduced in size. Moreover, since the pressure of the exhaust gas G can be further reduced by cooling the exhaust gas G, an increase in exhaust pumping loss can be further prevented.

  Further, when the exhaust heat recovery device 30b is provided in the low-pressure EGR passage 14, the temperature of the EGR gas Ge can be lowered by recovering the thermal energy of the EGR gas Ge, so that the EGR cooler 17 and the EGR pump 21 The EGR cooler 17 and the EGR pump 21 can be reduced in size. Moreover, by lowering the temperature of the EGR gas Ge, the EGR rate can be further increased and NOx generation can be suppressed.

  As shown in FIG. 1, the exhaust pump 20 and the EGR pump 21 are driven in the engine 1 based on the flow rate of the EGR gas Ge passing through the low pressure EGR passage 14 and the pressure of the exhaust gas G in the exhaust passage 13. Exhaust pressure control means 41 is provided for controlling the above. The exhaust pressure control means 41 is usually configured to be incorporated in a control device 40 of the overall system that performs overall control of the engine 1 and overall control of a vehicle on which the engine 1 is mounted.

  According to this configuration, by ensuring the flow rate of the EGR gas Ge, the increase in the exhaust gas pumping loss can be suppressed by suppressing the increase in the pressure of the exhaust gas G in the exhaust passage 13 while ensuring the exhaust gas purification performance with reduced NOx. Can be prevented.

  Further, an exhaust pressure reduction method for an internal combustion engine using the engine 1 described above will be described with reference to an example of a control flow shown in FIG. The control flow of FIG. 2 is started from the advanced control flow when the engine 1 is started. When the exhaust pump 20 and the EGR pump valve 21 are controlled, the control flow returns to the advanced control flow. Called from the advanced control flow, it is shown as being repeatedly performed during operation of the engine 1. Then, as the engine 1 is stopped, the control flow is returned by an interrupt to return to the advanced control flow, and is shown as a control flow that ends when the advanced control flow ends.

  When the control flow of FIG. 2 is called from an advanced control flow and started, an engine speed Ne and a fuel flow rate q are input in step S11. Thereafter, the process proceeds to step S12. In step S12, the target value of the flow rate of the EGR gas Ge passing through the low pressure EGR passage 14 while referring to the preset target value calculation map data M1 based on the input engine speed Ne and the fuel flow rate q. The target value of the pressure of the exhaust gas G passing through the exhaust passage 13 (hereinafter referred to as “target exhaust pressure Pegrm”) is calculated (hereinafter referred to as “target EGR gas flow rate Qegrm”). The target value calculation map data M1 is set in advance by experiments or the like. It is incorporated in the control device 40.

  Here, the target EGR gas flow rate Qegrm and the target exhaust pressure Pegrm are calculated using the target value calculation map data M1 created based on the experimental values, but the engine rotation is calculated based on a control model constructed by a theoretical formula. The target NeGR gas flow rate Qegrm and the target exhaust pressure Pegrm may be calculated by inputting the number Ne and the fuel flow rate q.

  After the calculation in step S12, the process proceeds to step S13. In step S13, the actual value of the flow rate of the EGR gas Ge passing through the low pressure EGR passage 14 (hereinafter referred to as “actual EGR gas flow rate Qegra”) and the actual value of the pressure of the exhaust gas G passing through the exhaust passage 13 (hereinafter referred to as “real EGR gas flow rate Qegra”). , “Actual exhaust pressure Pegra”) is detected by a sensor or the like, and these detected values are input.

  In the next step S14, a preset control amount value is calculated based on the target EGR gas flow rate Qegrm and target exhaust pressure Pegrm calculated in step S12 and the actual EGR gas flow rate Qegra and actual exhaust pressure Pegra detected in step S13. With reference to the map data M2, the exhaust pump 20 and the EGR pump 21 that are necessary to set the actual EGR gas flow rate Qegra and the actual exhaust pressure Pegra, which are actual values, to the target EGR gas flow rate Qegrm and the target exhaust pressure Pegrm that are target values. The control amount is calculated.

  For example, the control amount α of the exhaust pump 20 necessary for setting the actual EGR gas flow rate Qegra to the target EGR gas flow rate Qegrm and the control amount β of the EGR pump 21 required for setting the actual exhaust pressure Pegra to the target exhaust pressure Pegrm. Is calculated. The control amount value calculation map data M2 is set in advance by experiments or the like and incorporated in the control device 40. Here, the control amounts α and β for the actual EGR gas flow rate Qegra and the actual exhaust pressure Pegra are calculated using the control amount value calculation map data M2 created based on the experimental values. The control amounts α and β may be calculated based on the constructed control model.

  In the next step S15, the exhaust pump 20 is driven and controlled by the amount corresponding to the control amount α calculated in step S14 (corresponding to “EGR control” in FIG. 2), and the amount corresponding to the control amount β calculated in step S14. The EGR pump 21 is driven and controlled (corresponding to “exhaust pressure control” in FIG. 2). After completion, the process returns to step S11, and the above-described steps S11 to S15 are repeated until the end of the advanced control flow accompanying the stop of the engine 1.

  Thus, the driving of the exhaust pump 20 and the driving of the EGR pump 21 are controlled based on the actual EGR gas flow rate Qegra of the EGR gas Ge passing through the low pressure EGR passage 11 and the actual exhaust pressure Pegra of the exhaust gas in the exhaust passage 13. Then, the exhaust pump 30 provided in the exhaust passage 13 downstream of the turbine 15a and downstream of the branch point of the low-pressure EGR passage 17 is driven, and the exhaust passage 13 downstream of the confluence of the low-pressure EGR passage 14 is driven. The valve opening degree of the provided EGR pump 21 can be controlled.

  Note that the EGR control and the exhaust pressure control in step S15 are performed independently and in parallel, and when the control converges, it is simpler to adopt this independent control. However, if the control does not converge in the independent control, the cooperative control of the EGR control and the exhaust pressure control is performed.

  According to the internal combustion engine 1 and its exhaust pressure reduction method, the exhaust passage 13 is provided with the exhaust pump 20, and the low pressure EGR passage 14 is provided with the EHR pump 21, and the exhaust pump 20 is driven to assist the exhaust gas G discharge. As a result, not only the downstream of the turbine 15a but also the pressure of the exhaust gas G in the exhaust passage 13 upstream of the turbine 15a can be reduced to suppress an increase in the exhaust pressure. 1 fuel efficiency can be improved. Further, since the differential pressure across the turbine 15a can be increased, the driving force of the turbine 15a and the compressor 15b can be increased to assist supercharging, and the increase in the indicated mean effective pressure can be achieved by this increase in supercharging. Therefore, the fuel consumption of the engine 1 can be further improved.

  Further, since the EGR pump 21 is provided in the low-pressure EGR passage 14, during EGR, the flow rate of the EGR gas Ge can be adjusted by the EGR pump 21, and the exhaust gas G can be assisted by driving the EGR pump 21. In addition, not only the downstream of the turbine 15a but also the pressure of the exhaust gas G in the exhaust passage 12 upstream of the turbine 15a can be reduced to suppress an increase in pressure.

1, 1X engine (internal combustion engine)
10, 10X Engine body 11a Intake manifold 11b Exhaust manifold 12 Intake passage 13 Exhaust passage 14 Low pressure EGR passage 15 Turbocharger (turbo supercharger)
15a Turbine 15b Compressor 16 Intercooler 17 EGR cooler 18 EGR valve 20 Exhaust pump 21 EGR pumps 30a, 30b Exhaust heat recovery device 40 Control device 41 Exhaust pressure adjusting means A Fresh air G Exhaust gas Ge EGR gas Ne Engine speed Pegrm Target exhaust pressure Pegra Actual exhaust pressure q Fuel flow rate Qegrm Target EGR gas flow rate Qegra Actual EGR gas flow rate α Exhaust pump control amount β EGR pump control amount

Claims (6)

In an internal combustion engine comprising a turbocharger system, and a low pressure EGR passage that connects an exhaust passage downstream of a turbine of the turbocharger system and an intake passage upstream of a compressor of the turbocharger system,
An exhaust pump is provided in the exhaust passage downstream of the turbine and downstream of the branch point of the low pressure EGR passage,
An internal combustion engine comprising an EGR pump provided in the low-pressure EGR passage.   An exhaust heat recovery device is provided in the exhaust passage between the branch point of the low pressure EGR passage and the exhaust pump or in the low pressure EGR passage, and the exhaust heat recovery device uses the exhaust heat of the exhaust gas to generate power. The internal combustion engine according to claim 1, wherein at least one of the exhaust pump and the EGR pump is driven by the generated electric power.   An exhaust pressure control means is provided for controlling the driving of the exhaust pump and the EGR pump based on the flow rate of EGR gas passing through the low pressure EGR passage and the pressure of the exhaust gas in the exhaust passage. The internal combustion engine according to claim 1 or 2. Exhaust gas from an internal combustion engine having a turbocharger system, and a low pressure EGR passage that connects an exhaust passage downstream of the turbine of the turbocharger system and an intake passage upstream of a compressor of the turbocharger system In the pressure reduction method,
Driving an exhaust pump provided in the exhaust passage downstream of the turbine and downstream of a branch point of the low-pressure EGR passage;
An exhaust pressure reduction method for an internal combustion engine, wherein an EGR pump provided in the low pressure EGR passage is driven.   The exhaust heat recovery device provided in the exhaust passage between the turbine and the exhaust pump or the low-pressure EGR passage generates power using exhaust heat of exhaust gas, and at least the exhaust pump or the EGR pump 5. The exhaust pressure reduction method for an internal combustion engine according to claim 4, wherein one of them is driven.   6. The drive of the exhaust pump and the EGR pump is controlled based on the flow rate of EGR gas passing through the low pressure EGR passage and the pressure of exhaust gas in the exhaust passage. The exhaust pressure reduction method of the internal combustion engine.

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