WO2007040071A1

WO2007040071A1 - Egr system of two stage super-charging engine

Info

Publication number: WO2007040071A1
Application number: PCT/JP2006/318928
Authority: WO
Inventors: Junichiro Nitta
Original assignee: Isuzu Motors Limited
Priority date: 2005-10-06
Filing date: 2006-09-25
Publication date: 2007-04-12
Also published as: JP2007100628A; JP4692202B2

Abstract

An EGR system (10) of a two stage super-charging engine (1) comprising a first EGR passage (11) leading from an exhaust passage (4) between a high pressure stage turbine (6t) and a low pressure stage turbine (5t) to an intake passage (3) between a low pressure stage compressor (5c) and a high pressure stage compressor (6c), a second EGR passage (14) leading from the exhaust passage (4) between an internal combustion engine body (2) and the high pressure stage turbine (6t) to the intake passage (3) between the low pressure stage compressor (5c) and the high pressure stage compressor (6c), a third EGR passage (17) leading from the exhaust passage (4) between the internal combustion engine body (2) and the high pressure stage turbine (6t) to the intake passage (3) between the high pressure stage compressor (6c) and the internal combustion engine body (2), and an EGR controller performing EGR by selecting each EGR passage (11, 14, 17). Consequently, super-charging does not deteriorate even with high EGR rate in the EGR system (10).

Description

Specification

EGR system for two-stage turbocharged engine

Technical field

[0001] The present invention relates to an EGR system for a two-stage supercharged engine including a high-pressure stage turbocharger and a low-pressure stage turbocharger. More specifically, the present invention relates to an EGR system for a two-stage supercharged engine that does not cause deterioration in supercharging even at a high EGR rate.

Background art

[0002] In order to reduce NOx in exhaust gas of an internal combustion engine, EGR is generally performed to recirculate exhaust gas to the intake side.

[0003] In a conventional single-stage turbocharged engine, exhaust energy is recovered by an exhaust turbine in the exhaust path, and the intake compressor in the intake path is driven by this energy, and EGR gas is sent from the upstream side of the exhaust turbine. It circulates downstream of the intake compressor.

[0004] In this conventional supercharged engine EGR system, most of the exhaust gas is circulated from the upstream side of the exhaust turbine through the cooler to the intake side. Therefore, if the EGR rate is increased to operate at a high EGR rate, As a result, the amount of exhaust gas passing through the exhaust turbine decreases and the operating flow rate decreases. As a result, the exhaust energy acting on the turbine is reduced, so that the turbo rotation speed is lowered and the supercharging pressure is lowered. As a result, the operation efficiency of the turbocharger is deteriorated and surging occurs.

[0005] Therefore, when the engine operating conditions are in the low-speed to medium-speed operation region, the supercharging pressure decreases remarkably and the air-fuel ratio (AZF) decreases as the EGR rate increases. Yeah. As a result, when the EGR rate is increased, the air-fuel ratio is decreased, and conversely, when the air-fuel ratio is increased, the EGR rate is decreased. It is difficult to improve the trade-off relationship between air-fuel ratio and EGR rate.

[0006] On the other hand, for exhaust gas regulations that will become stricter in the future, it is essential to achieve both high EGR introduction and high air-fuel ratio. Therefore, more efficient variable capacity turbochargers and two-stage turbocharging systems have been proposed to improve turbocharging characteristics. [0007] Therefore, the two-stage turbocharging system, which has been proposed in the past, has attracted attention mainly by diesel engine manufacturers, and an EGR system in an engine equipped with this two-stage turbocharging system has been studied. An overview of this two-stage turbocharging system is shown in Figs.

[0008] In the engine IX equipped with this two-stage turbocharging system, a low-pressure stage compressor 5c of a low-pressure stage turbocharger 5 and a high-pressure stage compressor 6c of a high-pressure stage turbocharger 6 are provided in order of the upstream side force of the intake passage 3. At the same time, the upstream side force of the exhaust path 4 is also provided with a high-pressure turbine 6t of the high-pressure turbocharger 6 and a low-pressure turbine 5t of the low-pressure turbocharger 5 in this order. In general, the high-pressure turbocharger 6 is smaller than the low-pressure turbocharger 5 and uses a turbocharger to handle the air compressed by the low-pressure compressor 5c.

[0009] The low-pressure stage turbocharger 5 is provided with a low-pressure stage exhaust bypass path 5a for bypassing the low-pressure stage turbine 5t. The low-pressure stage exhaust bypass path 5a is used for controlling the amount of flowing gas. The Westgate valve 5b is installed. The high-pressure stage turbocharger 6 is provided with a high-pressure stage intake bypass path 6a that binos the high-pressure stage compressor 6c in the intake system, and a high-pressure stage exhaust bypass path 6d that bypasses the high-pressure turbine 6t in the exhaust system. A high-pressure stage intake bypass valve 6b and a high-pressure stage exhaust bypass valve 6e for controlling the amount of flowing gas are attached to the bypass paths 6a and 6d, respectively.

However, depending on the capacity characteristics of the low pressure stage turbine, the low pressure stage exhaust bypass path 5a and the wastegate valve 5b may not be installed. Similarly, depending on the capacity of the high-pressure stage turbocharger, the high-pressure stage intake bypass path 6a and the high-pressure stage exhaust bypass path 6d may not be installed.

[0011] Further, on the intake side, an intercooler (intake air cooler) 7 for cooling the intake air compressed and heated by the low pressure compressor 5c is provided downstream of the low pressure compressor 5c.

In the EGR system 10X shown in FIG. 2, the EGR path 1 IX includes an exhaust path 4 between the engine body 2 on the exhaust side and the high-pressure turbine 6t, and a high-pressure compressor 6c on the intake side. An intake passage 3 between the gin body 2 and the gin body 2 is connected. This EGR path 11X The upstream force is also provided with EGR cooler 13X and EGR valve 12X. The EGR gas Ge is introduced from the exhaust side to the intake side via the EGR path 1 IX via the EGR cooler 13X and the EGR valve 12X in this order. Further, the valves 5b, 6b, 6e, and 12X are opened and closed and the valve opening degree is controlled according to the operating conditions of the engine IX.

[0013] Fig. 2 shows an EGR system in a two-stage supercharged engine provided with a high pressure EGR path for a high-pressure stage turbocharger.

Further, in the EGR system 10Y of FIG. 3, the EGR path 11Y includes an exhaust path 4 between the exhaust-side high-pressure turbine 6t and the low-pressure turbine 5t, an intake-side low-pressure compressor 5c, and a high-pressure compressor. 6c and an intake path 3 upstream of the intercooler 7 is connected. The EGR path 11Y is also provided with an EGR cooler 13Y and an EGR valve 12Y on the upstream side! EGR gas Ge is also introduced into the intake side through the EGR path 11Y through the EGR cooler 13Y and the EGR valve 12Y in this order.

FIG. 3 shows an EGR system in a two-stage supercharged engine provided with a low pressure EGR path for the high-pressure turbocharger 6.

In addition to the above, the following EGR system has been proposed as an EGR system in an engine of a two-stage supercharging system!

[0017] The first is, for example, as described in Japanese Patent Application Laid-Open No. 05-69364, the upstream side force of the high-pressure turbine, between the low-pressure compressor and the high-pressure compressor. It is a system that circulates. This system is the currently known low pressure EGR system.

[0018] The second is a mirror cycle engine equipped with two exhaust turbo-superchargers that are not provided with a bypass valve in series, as described in Japanese Unexamined Patent Publication No. 2000-220480, for example. In this system, an intercooler is installed downstream of each intake compressor, and the EGR gas is circulated between the low-pressure compressor and the high-pressure compressor on the upstream side of the high-pressure turbine. In this system, the EGR gas amount can be adjusted by the EGR valve based on the signal from the knocking sensor, and fuel supply means is provided between the low-pressure compressor and the high-pressure compressor.

[0019] The third is, for example, a two-stage as described in Japanese Patent Application Laid-Open No. 2003-49674. In a ship's internal combustion engine with a turbocharger system consisting of a mechanical supercharger and an exhaust turbocharger, an intercooler is installed downstream of each intake compressor, and both intakes from the upstream side of the exhaust turbine. This system circulates EGR gas between compressors. In this system, the amount of EGR gas is adjusted by the EGR valve and then cooled by the EGR cooler!

[0020] Fourthly, for example, a motor-driven intake compressor having a bypass path is provided on the upstream side of the intake compressor of the turbocharger as described in JP-T-2001-509561. Upstream force of exhaust turbine This is a low pressure EGR system that circulates EGR gas to the upstream side of a motor-driven intake compressor. In this system, after cooling with an EGR cooler, the amount of EGR gas is adjusted with an EGR valve.

[0021] However, even in the EGR system in these two-stage turbocharging system engines, the problem related to the introduction of EGR gas, the problem of the bad trade-off relationship between the EGR rate and the air-fuel ratio, and the intake air cooling are related. There is a problem to do.

[0022] With regard to the introduction of EGR gas, there is a problem that the increase in the EGR rate is limited due to the decrease in the difference between the exhaust pressure and the supercharging pressure due to the improvement of the operation efficiency by the two-stage supercharging system. . In other words, when the operating rate of the supercharger increases due to the two-stage supercharging system, the supercharging pressure increases, so the exhaust pressure decreases with respect to this supercharging pressure. As a result, the differential pressure between the exhaust side pressure and the intake side pressure in the EGR path decreases, or in some cases, the intake side pressure Z exhaust side pressure reverse phenomenon occurs where the intake side pressure becomes larger than the exhaust side pressure. Or Therefore, even if the EGR valve is opened, it becomes difficult to circulate the EGR gas, that is, to introduce the EGR gas into the intake side.

[0023] The high pressure EGR system for a high-pressure turbine as shown in Fig. 2 is superior in operating flow rate characteristics compared to a conventional supercharger, and is a supercharger in a two-stage supercharging system. When the EGR path is branched upstream, the supercharger pressure decreases because the supercharger operating flow rate decreases as the EGR rate increases. For this reason, operating at a high EGR rate, especially in the low to medium load operating range at low to medium speed rotation, will cause a significant drop in the supercharging pressure, and the relationship between the air-fuel ratio (A / F) and the EGR rate trade-off. There is a problem that it becomes impossible to improve.

[0024] On the other hand, in the low pressure EGR system 10Y for the high-pressure stage turbocharger as shown in FIG. Since the operating flow rate does not decrease, the supercharging pressure does not decrease. Therefore, even when the EGR rate is high, the decrease in air-fuel ratio can be minimized.

However, in the high-load operation region, the operating efficiency of the low-pressure stage turbocharger 5 increases, so that the intermediate exhaust pressure between the high-pressure stage turbine 6t and the low-pressure stage turbine 5t, the low-pressure stage compressor 5c, There is a problem that the intermediate supercharging pressure with the stage compressor 6c is reversed (intermediate supercharging pressure> intermediate exhaust pressure), making it difficult to introduce EGR gas to the intake side.

[0026] Further, the high-pressure compressor 6c in the two-stage turbocharging system is a low-pressure turbocharger.

In order to handle the compressed air that has been supercharged at 5, the capacity can be smaller than that of the low-pressure stage compressor 5c. The high-pressure turbine 6t also handles gas at a higher pressure than the low-pressure turbine 5t. Therefore, even if the gas handled by the high-pressure turbine 6t is the same in mass flow as the low-pressure turbine 5t, the volume is small, so the high-pressure turbine 6t has a smaller capacity than the low-pressure turbine 5t. ,.

[0027] In addition, in order to improve the torque characteristics during low-speed rotation and high-load operation, in order to be able to operate with high supercharging, or at low medium-speed rotation and low-medium load, In order to be able to operate with high supercharging, the capacity of the high-pressure stage turbocharger needs to be extremely small in accordance with these operating conditions.

[0028] However, if the capacity of the high-pressure stage turbocharger is extremely reduced while the force is applied, a large capacity difference is generated between the low-pressure stage turbocharger and the high-pressure stage turbocharger. There is a problem that a problem occurs in the feed characteristics.

Patent Document 1: Japanese Patent Laid-Open No. 05-69364

Patent Document 2: JP 2000-220480 A

Patent Document 3: JP 2003-49674

Patent Document 4: Special Table 2001-509561

Disclosure of the invention

Problems to be solved by the invention

[0029] The present invention has been made to solve the above problems, and an object of the present invention is to provide an EGR system for a two-stage turbocharged engine including a high-pressure stage turbocharger and a low-pressure stage turbocharger. In the system, due to the improvement of the turbocharger operating efficiency, the exhaust gas pressure or the EGR gas outlet pressure force of the exhaust system is lower than the intake manifold pressure or the intake EGR gas inlet pressure, or the low pressure stage compressor and the high pressure High EGR rate operation is possible even under the operating conditions in which the intermediate supercharging pressure with the stage compressor is higher than the intermediate exhaust pressure between the high-pressure turbine and the low-pressure turbine. The objective is to provide an EGR system for a two-stage supercharged engine that can improve the supercharging characteristics in the rotation / high-load operation region.

Means for solving the problem

[0030] An EGR system for a two-stage turbocharged engine to achieve the above-described purpose is provided with a low-pressure stage compressor of a low-pressure stage turbocharger and a high-pressure stage compressor of a high-pressure stage turbocharger in order of the upstream side force of the intake passage. And an EGR system for an internal combustion engine provided with a high-pressure stage turbine of the high-pressure stage turbocharger and a low-pressure stage turbine of the low-pressure stage turbocharger in order from the upstream side of the exhaust path, the high-pressure stage turbine and the low-pressure stage A first EGR path for introducing EGR gas via a first EGR valve from an exhaust path to the turbine to an intake path between the low-pressure stage compressor and the high-pressure stage compressor; an internal combustion engine body; From the exhaust path between the high-pressure stage turbine and the intake path between the low-pressure stage compressor and the high-pressure stage compressor, the EGR gas passes through the second EGR valve. EGR gas is introduced via a third EGR valve from the second EGR path for introducing the engine and the exhaust path between the internal combustion engine body and the high-pressure turbine to the intake path between the high-pressure compressor and the internal combustion engine body And an EGR control device that opens and closes the first EGR valve, the second EGR valve, and the third EGR valve, respectively, and adjusts the valve opening degree.

[0031] An EGR cooler can be provided for each EGR path, and a common EGR cooler can be used for the first EGR path and the second EGR path. Also, these EGR coolers are usually installed upstream of the EGR valve to protect the EGR valve from high-temperature exhaust gas (EGR gas). However, an EGR cooler may be provided downstream of the EGR valve.

[0032] In the EGR system, when the intermediate supercharging pressure between the low-pressure stage compressor and the high-pressure stage compressor becomes larger than the intermediate exhaust pressure between the high-pressure stage turbine and the low-pressure stage turbine, Solves the problem that it becomes difficult to introduce EGR gas to the intake side. Even in such a case, the internal combustion engine can be operated at a high EGR rate, and the supercharging characteristic in the medium speed rotation / high load operation region is improved.

[0033] That is, in addition to the first EGR path which is the high pressure stage low pressure EGR path, the EGR path is also branched between the internal combustion engine main body and the high pressure stage turbine, and the EGR gas is introduced upstream of the high pressure stage compressor. The second EGR route and the third EGR route, which is the high-pressure high pressure EGR route to be introduced downstream, will be installed. Each EGR path has a first EGR valve, a second EGR valve, and a third EGR valve. With this configuration, the EGR path is selected according to the operating conditions of the internal combustion engine to control the EGR gas flow.

[0034] Thereby, it is possible to operate at a high EGR rate under optimum conditions over the entire operating conditions of the internal combustion engine. For example, depending on the operating conditions, in the first EGR path, which is the high pressure stage low pressure EGR path, the supercharging pressure on the intake side is higher than the exhaust pressure on the exhaust side, making it difficult to introduce EGR gas to the intake side. Even in this case, the EGR gas can be easily introduced to the intake side by using the second EGR path or the third EGR path.

[0035] Then, in the EGR system for the two-stage supercharged engine, the EGR is performed by selecting the first to third EGR paths depending on which operating region the operating condition of the internal combustion engine is in.

[0036] In the EGR system of the internal combustion engine, when the EGR control device performs EGR, the operation condition of the internal combustion engine is a low speed rotation or medium speed rotation operation region and a low load or medium load operation region. Or an intermediate exhaust pressure, which is an exhaust pressure between the high-pressure turbine and the low-pressure turbine, in the low-speed rotation operation region and the high-load operation region. When the intermediate boost pressure is higher than the intermediate boost pressure with the high-pressure compressor, the first EGR valve and the second EGR valve are controlled to open and close, and the third EGR valve is closed. When the intermediate exhaust pressure is equal to or lower than the intermediate supercharging pressure, the second EGR valve and the third EGR valve are opened and closed and the valve opening is controlled, and the first EGR valve is closed. Configured to perform second EGR control.

[0037] As a result, operating conditions at high EGR rate under low and medium speed rotation and low and medium load operating conditions. However, since the decrease in working gas flow to the high-pressure stage turbocharger can be minimized, the decrease in supercharging pressure when the EGR rate increases can be minimized.

[0038] In the normal high pressure EGR system under low and medium speed rotation and high load operating conditions, the operating pressure at the high EGR rate greatly reduces the supercharging air operating flow rate. Shifting to the surge line side, the efficiency drops significantly. Under such operating conditions, the first EGR path with the first EGR valve is used, or the second EGR path with the second EGR valve is used. This increases the operating flow rate of the high-pressure compressor and improves the operating efficiency. As a result, an increase in the supercharging pressure and a corresponding increase in the EGR rate can reduce the exhaust pressure.

[0039] In the EGR system of the internal combustion engine, when the EGR control device performs EGR, and the operation condition of the internal combustion engine is in a medium speed rotation operation region and a high load operation region, The second EGR valve and the third EGR valve are opened / closed and the opening degree of the valve is controlled, and the third EGR control for closing the first EGR valve is performed.

[0040] In this medium speed rotation 'high load operation region, a high EGR rate is generally not required, and the supercharger operating flow rate at this time is sufficiently secured. Therefore, in this operating condition, the third EGR path with the third EGR valve is used. As a result, the conventional high-pressure stage high pressure EGR can be implemented, and the operating flow rate of the high-pressure stage turbocharger can be suppressed.

[0041] In the EGR system of the internal combustion engine, when the EGR control device performs EGR, and the operation condition of the internal combustion engine is in a high-speed rotation operation region, the third EGR valve is opened and closed and the valve It is configured to perform fourth EGR control that controls the opening and closes the first EGR valve and the second EGR valve.

[0042] In this high-speed rotation operation region, the intake flow rate of the internal combustion engine increases. However, if the 1st EGR path and the 2nd EGR path are used, the load on the turbine and compressor of the high-pressure turbocharger becomes larger and the exhaust pressure tends to increase compared to the case where the 3rd EGR path is used. Show. Therefore, by introducing EGR gas to the intake side using the 3rd EGR path, the intake flow rate (operating flow rate) for the high-pressure stage compressor is suppressed and the operating flow rate for the high-pressure turbine is also suppressed. Can be avoided. [0043] Therefore, since the change in the supercharger operating flow rate for the high-pressure turbocharger caused by the change in the operating condition of the internal combustion engine can be suppressed to the minimum, the capacity of the high-pressure turbocharger can be increased. Can do. As a result, the operating range of the high-pressure turbocharger can be expanded, and the supercharging characteristics can be greatly improved over the entire operating conditions of the internal combustion engine.

[0044] In the above EGR system for an internal combustion engine, the intercooler is further downstream of the low-pressure stage compressor and more than both the connection portion of the first EGR path and the connection portion of the second EGR path. It is configured to be provided in the upstream intake path.

[0045] According to this configuration, since the intercooler is provided in the intermediate supercharging pressure section between the low-pressure compressor and the high-pressure compressor, the exhaust gas for EGR does not pass through the intercooler! Therefore, the occurrence of corrosion and clogging in the intercooler can be prevented.

[0046] Further, since cooling is performed by the intake air intercooler that has exited the low-pressure compressor, EGR can be performed while suppressing an increase in intake air temperature to a minimum. In particular, the intake air temperature at the inlet of the high-pressure compressor can be significantly reduced even in the medium-speed rotation / high-load operation region where the engine intake temperature is expected to rise to about 50 ° C to 80 ° C in the conventional technology. wear.

[0047] Therefore, the operating efficiency of the high-pressure compressor is significantly improved. As a result, high supercharging is possible, and the mass intake amount can be significantly increased. Also, since the intake air temperature at the inlet of the high-pressure stage compressor can be lowered, the aluminum alloy material used in the prior art can be used as the material of the compressor blade. Therefore, it is not necessary to use expensive titanium materials for high temperature measures.

[0048] According to the EGR system of the present invention, even when the intake air temperature rises in the low-speed to medium-speed rotation operation region, the low pressure is applied to the high-pressure turbocharger when the first EGR path is used. Therefore, the operation efficiency of the supercharger is improved, and the supercharging pressure is significantly increased over the conventional EGR system. Therefore, the trade-off relationship between the EGR rate and air-fuel ratio is improved by improving the supercharging pressure. Since the improvement effect of this trade-off relationship exceeds the bad intake efficiency associated with the rise in intake air temperature, it is possible to operate at a higher air-fuel ratio and higher EGR rate than the conventional EGR system. The invention's effect

[0049] According to the EGR system for a two-stage turbocharged engine according to the present invention, the EGR system for a two-stage turbocharged engine equipped with a high-pressure turbocharger and a low-pressure turbocharger! However, EGR gas is sucked not only from the downstream side of the high-pressure stage turbine but also from the upstream side of the high-pressure stage turbine without deteriorating supercharging. It can be circulated downstream of the stage compressor.

[0050] Therefore, since the change in the supercharger operating flow rate for the high-pressure turbocharger caused by the change in the operating condition of the internal combustion engine can be suppressed to the minimum, the capacity of the high-pressure turbocharger can be increased. Can do. As a result, the operating range of the high-pressure turbocharger can be expanded, and the supercharging characteristics can be greatly improved over the entire operating conditions of the internal combustion engine.

Brief Description of Drawings

FIG. 1 is a diagram showing a configuration of an EGR system of a two-stage supercharged engine according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of the configuration of a high-pressure stage pressure / pressure EGR system.

FIG. 3 is a diagram showing an example of the configuration of a high pressure stage low pressure EGR system.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an EGR system for a two-stage turbocharged engine according to an embodiment of the present invention will be described with reference to the drawings.

As shown in FIG. 1, the EGR system 10 is applied to an engine (internal combustion engine) 1 of a two-stage supercharging system. In this engine 1, a low-pressure stage compressor 5 c of a low-pressure stage turbocharger 5, an intercooler 7, and a high-pressure stage compressor 6 c of a high-pressure stage turbocharger 6 are provided in order from the upstream side of the intake path 3. At the same time, a high-pressure turbine 6 t of the high-pressure turbocharger 6 and a low-pressure turbine 5 t of the low-pressure turbocharger 5 are provided in this order from the upstream side of the exhaust path 4.

[0054] Further, the low-pressure stage turbocharger 5 is provided with a low-pressure stage exhaust bypass path 5a for bypassing the low-pressure stage turbine 5t. A wastegate valve 5b for controlling the amount of gas flowing is attached to the low-pressure stage exhaust bypass path 5a. [0055] Further, the high pressure turbocharger 6 is provided with a high pressure stage intake bypass path 6a for bypassing the high pressure stage compressor 6c in the intake system. A high-pressure stage intake bypass valve 6b for controlling the amount of flowing gas is attached to the high-pressure stage intake bypass path 6a. Further, in the exhaust system, a high-pressure stage exhaust bypass path 6d for bypassing the high-pressure stage turbine 6t is provided. A high-pressure stage exhaust bypass valve 6e for controlling the amount of flowing gas is attached to the high-pressure stage exhaust bypass path 6d.

[0056] When the operating condition of the engine is in the high-speed rotation operation region, the high-pressure stage intake bypass valve 6b is opened, and the intake air is caused to flow to the high-pressure stage intake bypass path 6a to bin the high-pressure stage compressor 6c. . In this case, supercharging is performed only with the low-pressure compressor 5c.

[0057] On the other hand, when the operating condition of the engine is in the low-speed to medium-speed rotation operation region, the high-pressure stage intake bypass valve 6b is closed and the intake air is flowed to the high-pressure stage compressor 6c. Supercharge in stages.

[0058] In the above configuration, a sequential two-stage supercharging system using a high-pressure stage turbocharger 6 having a relatively small capacity characteristic will be described. In this sequential two-stage supercharging system, the high-pressure stage turbocharger 6 is small, so that a good supercharging characteristic can be obtained in the low and medium speed range. However, since the high-pressure turbocharger 6 is small, the exhaust pressure rapidly increases in the high-speed rotation range. For this reason, the high-pressure turbocharger 6 needs to be binos, and has the above-described configuration.

However, the present invention can be applied to a series type two-stage supercharging system other than the sequential two-stage supercharging system. In this series type two-stage turbocharging system, the turbocharger (supercharger), which has a large capacity compared to the sequential type, is set to a high-pressure stage, and supercharging is performed without switching control in the high-speed rotation range. Actually, the high-pressure turbine 6t is used for the supercharging pressure control, the high-pressure stage exhaust noisle path 6d and the high-pressure stage exhaust bino-relevant 6e are used for the supercharging pressure control, or the wastegate type is set for the high-pressure stage turbine 6t. To do. With this configuration, at least the high-pressure stage intake bypass path 6a in the intake-side high-pressure stage compressor 6c is not necessary.

[0060] With respect to the EGR system 1, the first EGR valve 12 and the first EGR cooler 13 are provided. 1EGR path 11 is provided by connecting exhaust path 4 between high-pressure turbine 6t and low-pressure turbine 5t and intake path 3 between intercooler 7 and high-pressure compressor 6c. This first EGR path 11 passes through the first EGR valve 12 from the exhaust path 4 between the high pressure turbine 6t and the low pressure turbine 5t to the intake path 3 between the low pressure compressor 5c and the high pressure compressor 6c. EGR gas Ge 1 is introduced.

[0061] Further, the second EGR path 14 including the second EGR valve 15 and the second EGR cooler 16 is connected to the exhaust path 4 between the engine body 2 and the high pressure turbine 6t, the intercooler 7 and the high pressure compressor 6c. Connected to the intake path 3 between the two. By this second EGR path 14, the exhaust path 4 between the engine body (internal combustion engine body) 2 and the high-pressure turbine 6t leads to the intake path 3 between the low-pressure compressor 5c and the high-pressure compressor 6c. 2 EGR gas Ge2 is introduced via EGR valve 15.

[0062] Further, the second EGR path 17 including the third EGR valve 18 and the third EGR cooler 19 is connected to the exhaust path 4 between the engine body 2 and the high-pressure turbine 6t, the high-pressure compressor 6c, and the engine body 2. And an intake path 3 between them. By this third EGR path 17, the exhaust path 4 between the engine main body 2 and the high-pressure turbine 6t goes to the intake path 3 between the high-pressure compressor 6c and the engine body 2 via the third EGR valve 18. EGR gas Ge3 is introduced.

[0063] With these configurations, the intercooler 7 is located downstream of the low-pressure compressor 5c and upstream of both the connecting portion 11a of the first EGR path 11 and the connecting portion 14a of the second EGR path 14. It was established in 3. In addition, the EGR valves 12, 15, 18 are arranged downstream of the EGR coolers 13, 16, 19, respectively, and the exhaust gas Gel, Ge2, Ge3 are cooled by the EGR coolers 13, 16, 19, respectively. Leave and let it flow through EGR valves 12, 15 and 18.

[0064] Next, the EGR control will be described. This EGR control is performed by an EGR control device incorporated in an engine control device called ECU that controls the engine. This EGR control device selects the first to third EGR controls that selectively use the first to third EGR paths 11, 14, and 17 according to the operating conditions of the engine 1, and selects the optimal EGR for each operating condition. I do.

[0065] The first purpose of this EGR control is not to generate a gas flow (reverse flow) to the intake side force exhaust side, and there are various methods for this control. [0066] For example, a method based on open control using a control map, or detection that detects the pressure, temperature, or flow rate of each gas in each flow path of each gas such as intake gas, exhaust gas, and EGR gas There is a method of arranging means and controlling the opening and closing of each valve and the valve opening degree based on the information of the detecting means.

[0067] Whether or not the operating condition of the engine 1 is within the operating range is determined based on the detected engine speed and engine load with reference to map data for control prepared in advance. To do. Further, a supercharging intermediate supercharging pressure that is a supercharging pressure between the low pressure stage compressor 5c and the high pressure stage compressor 6c, and an intermediate exhaust pressure that is an exhaust pressure between the high pressure stage turbine 6t and the low pressure stage turbine 5t The pressure detection means such as the first pressure gauge 9a that detects the intermediate supercharging pressure of the intercooler 7 and the second pressure gauge 9b that detects the intermediate exhaust pressure of the 6t high-pressure turbine 6t It is determined based on the intermediate exhaust pressure and the intermediate supercharging pressure detected by. These are merely examples of various control methods, and other control methods may be used.

[0068] In the first EGR control, when EGR is performed, the operating condition force of the engine 1 is in the low-speed or medium-speed rotation operation region and in the low-load or medium-load operation region, or in the low-speed rotation operation region and high. This is performed when the engine is in the load operating range and the intermediate exhaust pressure is greater than the intermediate boost pressure.

[0069] In the first EGR control, the first EGR valve 12 is mainly used, and the second EGR valve 15 is used as an auxiliary, and the first EGR valve 12 and the second EGR valve 15 are opened and closed and the valve opening degree is controlled. At the same time, the third EGR valve 18 is closed.

More specifically, the opening degree of the first EGR valve 12 is prioritized over the opening degree of the second EGR valve 15. In other words, if the first EGR valve 12 alone can introduce a predetermined amount of EGR gas, only the first EGR valve 12 adjusts the valve opening and introduces EGR gas, and at the same time the second EGR valve 15 is fully closed. To do. If a predetermined amount of EGR gas cannot be introduced even when the first EGR valve 12 is fully open, the first EGR valve 12 is left in the fully open state or close to the fully open state, and the second EGR valve 15 Adjust the valve opening and adjust the opening of the second EGR valve 15 so that a predetermined amount of EGR gas can be introduced.

[0071] Further, in the second EGR control, when performing EGR, when the operating condition force of the engine 1 is in the low speed rotation or medium speed rotation operation region and in the low load or medium load operation region, or In the case of the low-speed rotation operation region and the high-load operation region, it is further performed when the intermediate exhaust pressure is equal to or lower than the intermediate boost pressure.

In the second EGR control, the second EGR valve 15 is mainly used, and the third EGR valve 18 is used as an auxiliary, and the second EGR valve 15 and the third EGR valve 18 are opened and closed and the valve opening degree is controlled. At the same time, the first EGR valve 12 is closed.

[0073] The third EGR control is performed when the EGR is performed and the operating condition force of the engine 1 is in the medium speed rotation operation region and the high load operation region. In the second EGR control, the second EGR valve 15 and the third EGR valve 18 are opened and closed and the valve opening degree is controlled. At the same time, the first EGR valve 12 is closed.

[0074] The fourth EGR control is performed when the EGR is performed and the operating condition force of the engine 1 is in the high-speed rotation operation region. In the fourth EGR control, the third EGR valve 18 is opened and closed and the valve opening degree is controlled, and the first EGR valve 12 and the second EGR valve 15 are closed.

[0075] The first and second EGR controls described above minimize the decrease in the working gas flow rate for the high-pressure stage turbocharger 6 even under the low E / G speed and low E / R operation conditions. As a result, it is possible to minimize the decrease in supercharging pressure when the EGR rate increases.

[0076] Also, under low-medium speed rotation and high-load operating conditions, operating conditions with a high EGR rate significantly reduce the supercharged air flow rate, so the compressor operating point moves to the surge line side and efficiency increases. Is significantly reduced. Under such operating conditions, using the first EGR path 11 or using the second EGR path 14 increases the operating flow rate of the high-pressure compressor 6c and improves the operating efficiency. As a result, an increase in the supercharging pressure and a corresponding increase in the EGR rate can reduce the exhaust pressure.

[0077] In the third EGR control, in the medium speed rotation / high load operation region, generally, a high EGR rate is not required, and the third EGR path is operated under the operating conditions in which the turbocharger operating flow is sufficiently secured. Use 17. By this third EGR control, the conventional high-pressure stage high pressure EGR can be implemented, and the operating flow rate of the high-pressure stage turbocharger 6 can be suppressed.

[0078] In the fourth EGR control, when the first E GR path 11 and the second EGR path 14 are used in the high-speed rotation operation region where the intake flow rate of the engine 1 increases, it is compared with the case where the third EGR path 17 is used. As a result, the load on the turbine 6t and the compressor 6c of the high-pressure turbocharger 6 increases and the exhaust pressure tends to increase. Therefore, this problem is avoided by introducing the EGR gas Ge3 to the intake side using the third EGR path 17.

[0079] Therefore, according to the above-described EGR system 10 for the two-stage turbocharged engine, the change in the supercharger operating flow rate for the high-pressure turbocharger 6 caused by the change in the operating condition of the engine 1 is minimized. As a result, the capacity of the high-pressure turbocharger 6 can be increased. As a result, the operating range of the high-pressure stage turbocharger 6 can be expanded, and the supercharging characteristics can be greatly improved over the entire operating conditions of the engine 1.

[0080] Further, according to the EGR system 10 of the above-described two-stage turbocharged engine, the intake air that has exited the low-pressure stage compressor 5c is cooled by the intercooler 7. Therefore, in the conventional technology, the intake air temperature at the inlet of the high-pressure stage compressor 6c is greatly reduced even in the medium speed rotation / high load operation region where the intake air temperature of the engine 1 is considered to rise to about 50 ° C to 80 ° C. You can.

[0081] Therefore, the operating efficiency of the high-pressure compressor 6c is remarkably improved. As a result, high supercharging becomes possible, and the mass intake air amount can be greatly increased. In addition, the aluminum alloy material used in the prior art can be used for the material of the compressor wing of the high-pressure compressor 6c. Therefore, it is not necessary to use an expensive titanium material for high temperature countermeasures.

[0082] Since the force is also introduced downstream of the EGR gas power intercooler 7, the exhaust gas does not pass through the intercooler 7. Therefore, the occurrence of corrosion and clogging in the intercooler 7 can be prevented.

Industrial applicability

[0083] The EGR system of the internal combustion engine of the present invention having the above-described excellent effects can be used very effectively for many internal combustion engines such as an internal combustion engine mounted on an automobile.

Claims

The scope of the claims

[1] A low-pressure stage compressor of a low-pressure stage turbocharger and a high-pressure stage compressor of a high-pressure stage turbocharger are provided in order on the upstream side of the intake path, and the high-pressure stage turbine of the high-pressure stage turbocharger and An EGR system for an internal combustion engine provided with a low-pressure stage turbine of a low-pressure stage turbocharger,

E from the exhaust path between the high-pressure stage turbine and the low-pressure stage turbine to the intake path between the low-pressure stage compressor and the high-pressure stage compressor via the first EGR valve

1st EGR route to introduce GR gas,

A second EGR that introduces EGR gas via a second EGR valve from the exhaust path between the internal combustion engine body and the high-pressure turbine to the intake path between the low-pressure compressor and the high-pressure compressor Route,

A third EGR path for introducing EGR gas via a third EGR valve from an exhaust path between the internal combustion engine body and the high-pressure turbine to an intake path between the high-pressure stage compressor and the internal combustion engine body; ,

An EGR system for a two-stage supercharged engine, comprising: an EGR control device that opens and closes the first EGR valve, the second EGR valve, and the third EGR valve, respectively, and adjusts the valve opening.

[2] When the EGR control device performs EGR,

Operating condition force of the internal combustion engine When in the low-speed or medium-speed rotation operation region and in the low-load or medium-load operation region, or when in the low-speed rotation operation region and in the high-load operation region

When an intermediate exhaust pressure that is an exhaust pressure between the high-pressure stage turbine and the low-pressure stage turbine is greater than an intermediate supercharging pressure that is a supercharging pressure between the low-pressure stage compressor and the high-pressure stage compressor, The first EGR valve and the second EGR valve are opened and closed and the opening degree of the valve is controlled, and the first EGR control is performed to close the third EGR valve.

When the intermediate exhaust pressure is equal to or lower than the intermediate supercharging pressure, the second EGR valve and the third EGR valve are opened / closed and the opening degree of the valve is controlled, and the second EGR control for closing the first EGR valve is performed. The EGR system for a two-stage supercharged engine according to claim 1, wherein:

[3] When the EGR control device performs EGR,

When the operating condition of the internal combustion engine is in the medium speed rotation operation region and the high load operation region, the second EGR valve and the third EGR valve are opened and closed and the valve opening degree is controlled, and the first E GR valve is closed. 2. The EGR system for a two-stage turbocharged engine according to claim 1, wherein the third EGR control for setting the state is performed.

[4] When the EGR control device performs EGR,

When the operating condition of the internal combustion engine is in the high-speed rotation operation region, the fourth EGR control is performed to open and close the third EGR valve and control the valve opening degree, and to close the first EGR valve and the second EGR valve. The EGR system for a two-stage turbocharged engine according to claim 1, wherein the EGR system is used.

[5] The intercooler is provided downstream of the low-pressure compressor and in an intake path upstream of both the connection part of the first EGR path and the connection part of the second EGR path. The EGR system for a two-stage turbocharged engine according to any one of claims 1 to 4.