JP4577270B2 - Exhaust gas purification system for internal combustion engine - Google Patents

Description

The present invention relates to an exhaust gas purification system for an internal combustion engine.

As a technique for reducing the amount of nitrogen oxide (hereinafter abbreviated as “NOx”) generated in the combustion process in an internal combustion engine, exhaust gas recirculation (hereinafter referred to as “EGR”) is known. Further, as a technology that enables EGR in a wider operating state of an internal combustion engine, EGR is caused by flowing a part of exhaust flowing in an exhaust passage upstream of a turbocharger turbine into an intake passage downstream of a turbocharger compressor. Is a technology that uses both a high-pressure EGR device that performs EGR and a low-pressure EGR device that performs EGR by causing a portion of the exhaust gas flowing through the exhaust passage downstream of the turbocharger turbine to flow into the intake passage upstream of the turbocharger compressor. It has been developed (for example, see Patent Document 1).
JP 2004-156572 A JP 2000-130964 A JP 2001-303953 A

The EGR device may be provided with an EGR cooler that cools exhaust gas recirculated by the EGR device (hereinafter referred to as “EGR gas”). The EGR cooler cools high-temperature EGR gas by performing heat exchange between a heat medium such as cooling water or air and the EGR gas.

In an EGR device using both a low pressure EGR device and a high pressure EGR device, exhaust gas recirculated by the low pressure EGR device (hereinafter referred to as “low pressure EGR gas”) and exhaust gas recirculated by the high pressure EGR device (hereinafter referred to as “high pressure EGR gas”). When cooling both, it was necessary to provide both a low pressure EGR cooler for cooling the low pressure EGR gas and a high pressure EGR cooler for cooling the high pressure EGR gas.

In the conventional exhaust purification system, the low pressure EGR cooler and the high pressure EGR cooler are mounted on the internal combustion engine as separate devices. That results in the EGR cooler 2 group to the internal combustion engine is mounted, it causes an increase in size and weight of the internal combustion engine, or lose its mountability of the internal combustion engine, or increase the cost of parts is increased There was a fear. Moreover, since it is necessary to provide two cooling water passages, there is a possibility that energy consumed for flowing the cooling water increases, resulting in deterioration of fuel consumption.

The present invention has been made in view of such problems, and in an exhaust purification system that uses both a low pressure EGR device and a high pressure EGR device, the mounting ability of an internal combustion engine is increased, the cost is increased, the fuel consumption is increased, and the like. The main purpose is to provide a technique that enables the low-pressure EGR gas and the high-pressure EGR gas to be cooled while being suppressed.

To achieve the above object, an exhaust gas purification system for an internal combustion engine according to the present invention includes a turbocharger that drives a compressor disposed in an intake passage of the internal combustion engine by a turbine disposed in the exhaust passage of the internal combustion engine; A high pressure EGR passage connecting an exhaust passage upstream of the turbine and an intake passage downstream of the compressor, a low pressure EGR passage connecting an exhaust passage downstream of the turbine and an intake passage upstream of the compressor, and the high pressure Heat exchange is performed between the exhaust flowing through the EGR passage and the exhaust flowing through the low-pressure EGR passage and the heat medium.
And a GR cooler.

In this configuration, both the high pressure EGR gas and the low pressure EGR gas can exchange heat with the heat medium in the EGR cooler. Therefore, both the high pressure EGR gas and the low pressure EGR gas can be cooled.

That is, the EGR cooler according to the present invention has both functions of a high-pressure EGR cooler for cooling the high-pressure EGR gas and a low-pressure EGR cooler for cooling the low-pressure EGR gas.

Therefore, even in an exhaust gas purification system having a high pressure EGR passage and a low pressure EGR passage, it is not necessary to mount two EGR coolers, a high pressure EGR cooler and a low pressure EGR cooler as in the prior art, and one EGR cooler of the present invention is provided. By providing, both the high-pressure EGR gas and the low-pressure EGR gas can be cooled.

As a result, it is possible to suppress an increase in the weight of the exhaust purification system and an increase in the number of parts, and it is possible to suppress a deterioration in mountability to an internal combustion engine and an increase in cost. In addition, when it is necessary to provide a heat medium circulation device that supplies and distributes a heat medium (cooling water) to the EGR cooler, such as a water-cooled EGR cooler, the heat medium circulation device is used for the high-pressure EGR cooler and the low-pressure EGR. Since it is not necessary to provide two systems for the cooler, an increase in energy consumed to circulate the heat medium can be suppressed, and deterioration of fuel consumption can be suppressed.

As such an EGR cooler, one or a plurality of high-pressure EGR cooling passages that are configured so that both ends are connected to the high-pressure EGR passage and become a part of the high-pressure EGR passage, and both ends are connected to the low-pressure EGR passage. One or a plurality of low-pressure EGR cooling passages configured to be a part of the EGR passage, and heat exchange is performed between the exhaust gas flowing through the high-pressure EGR cooling passage and the heat medium, and the low-pressure EGR cooling passage is An EGR cooler in which heat exchange is performed between the flowing exhaust gas and the heat medium can be exemplified.

In this configuration, the high-pressure EGR cooling passage and the low-pressure EGR cooling passage are two independent gas passages of the EGR cooler, and the gas flowing through each gas passage is cooled by exchanging heat with the heat medium. . Therefore, the high-pressure EGR gas flowing through the high-pressure EGR cooling passage and the low-pressure EGR gas flowing through the low-pressure EGR cooling passage are independently cooled by exchanging heat with the heat medium. Thereby, the high pressure EGR gas and the low pressure EGR gas can be simultaneously cooled in parallel.

By the way, in an exhaust purification system having a high-pressure EGR passage and a low-pressure EGR passage, it is common that EGR is performed by switching between the high-pressure EGR passage and the low-pressure EGR passage according to the operating state of the internal combustion engine. There are also cases where EGR is performed using both the high pressure EGR passage and the low pressure EGR passage in the operation state. According to the above configuration, the high pressure EGR gas and the low pressure EGR gas can be cooled in parallel. Therefore, the present invention can also be applied to an exhaust purification system that performs EGR using both the high pressure EGR passage and the low pressure EGR passage.

Note that the high pressure EGR cooling passage and the low pressure EGR cooling passage may be constituted by a plurality of passages. Taking the high-pressure EGR cooling passage as an example, for example, a heat medium such as liquid or gas flows around the high-pressure EGR cooling passage, and exhaust and heat flowing through the high-pressure EGR cooling passage by heat conduction through the partition walls of the high-pressure EGR cooling passage. Heat exchange with the medium takes place. By configuring the high-pressure EGR cooling passage with a plurality of passages, the surface area of the partition wall of the high-pressure EGR cooling passage that is in contact with the heat medium is increased, so heat exchange is performed more efficiently between the high-pressure EGR gas and the heat medium. Thus, the high-pressure EGR gas can be cooled more reliably.

In the above configuration, the EGR cooler has a heat medium that exchanges heat with the exhaust flowing through the high-pressure EGR cooling passage (hereinafter referred to as “heat medium for high-pressure EGR cooling”) and a heat medium that exchanges heat with the exhaust flowing through the low-pressure EGR cooling passage (hereinafter referred to as “heat medium”). The heat that separates the high-pressure EGR cooling heat medium and the low-pressure EGR cooling heat medium so that heat exchange with each other is possible, although they are not physically mixed. You may have a medium separation means.

For example, in the case of a water-cooled EGR cooler, a cooling water circulation passage through which cooling water that exchanges heat with the exhaust flowing through the high pressure EGR cooling passage circulates, and a cooling water circulation passage through which the cooling water that exchanges heat with the exhaust flowing through the low pressure EGR cooling passage circulates As two independent cooling water passages, and in the EGR cooler, the two cooling water circulation passages are integrated so as to contact each other via a partition wall having thermal conductivity, thereby separating the heat medium. Means can be configured.

In this case, it is possible to independently control the two coolant circulation paths. For example, the flow rate of the cooling water in each cooling water circulation passage can be adjusted according to the cooling request of the high pressure EGR gas or the low pressure EGR gas. Thereby, it becomes possible to cool the high pressure EGR gas and the low pressure EGR gas efficiently. For example, when a large amount of low-pressure EGR gas is recirculated, the low-pressure EGR gas can be cooled more efficiently by increasing the flow rate of the low-pressure EGR cooling water.

In addition, since heat exchange can be performed between the heat medium for cooling the high pressure EGR and the heat medium for cooling the low pressure EGR, heat exchanged with the EGR gas, which has a high cooling requirement, has caused the heat to reach a high temperature. Heat exchange is performed between the medium and the EGR gas having a low cooling requirement to perform heat exchange with a relatively low-temperature heat medium, and the temperature of the high-temperature heat medium can be reduced. Thereby, it becomes possible to cool more reliably the EGR gas with a high cooling request.

The EGR cooler has one or a plurality of EGR cooling passages capable of exchanging heat between the exhaust gas flowing through the EGR cooler and the heat medium, and the flow state of the high-pressure EGR gas and the low-pressure EGR gas in the EGR cooler (1 ) Both ends of the EGR cooling passage are connected to the high pressure EGR passage to constitute a part of the high pressure EGR passage, heat exchange is possible between the high pressure EGR gas and the heat medium, and the flow of the low pressure EGR gas is blocked. (1) Both ends of the EGR cooling passage are connected to the low-pressure EGR passage to form a part of the low-pressure EGR passage, and heat exchange is possible between the low-pressure EGR gas and the heat medium. There may be provided switching means for switching to any one of the second state in which the flow of EGR gas is blocked.

In this configuration, the EGR cooling passage is one gas passage of the EGR cooler, and the gas flowing through the gas passage is cooled by exchanging heat with the heat medium. This one-system EGR cooling passage is connected to either the high-pressure EGR passage or the low-pressure EGR passage by the switching means to constitute a part thereof.

When the EGR cooling passage is connected to the high pressure EGR passage, the high pressure EGR gas is cooled by the high pressure EGR gas flowing through the EGR cooling passage and exchanging heat with the heat medium. On the other hand, when the EGR cooling passage is connected to the low pressure EGR passage, the low pressure EGR gas is cooled by the heat exchange between the low pressure EGR gas and the heat medium through the EGR cooling passage.

In this configuration, the EGR cooler is sufficient if it has the ability to cool the exhaust gas flowing through the EGR cooling passage of one system, so the size of the EGR cooler can be reduced. For example, in the case of a water-cooled EGR cooler, the flow path of the cooling water EGR cooler, which is a heat medium, is large enough to circulate an amount of cooling water that can sufficiently cool the exhaust flowing through one EGR cooling passage. Since this is sufficient, the size of the cooling water flow path can be reduced.

As described above, the high pressure EGR passage and the low pressure EGR passage are switched according to the operating state of the internal combustion engine. Therefore, when the operation state of the internal combustion engine is an operation state in which EGR is performed using the high-pressure EGR passage (hereinafter referred to as “high-pressure EGR operation state”), the state of the exhaust gas flow in the EGR cooler is the first state. When the operation state of the internal combustion engine is an operation state in which EGR is performed using the low pressure EGR passage (hereinafter referred to as “low pressure EGR operation state”), the state of the exhaust gas flow in the EGR cooler is changed to the second state. You may make it switch to a state. Thereby, also in the exhaust gas purification system provided with the high-pressure EGR passage and the low-pressure EGR passage, the high-pressure EGR gas and the low-pressure EGR gas can be cooled by the EGR cooler having the above-described configuration having only one EGR cooling passage.

In the present invention, the EGR cooler has two EGR gas cooling passages, a high pressure EGR cooling passage and a low pressure EGR cooling passage, and further upstream of the high pressure EGR passage and the low pressure EGR cooling passage. First connection means for connecting the low pressure EGR passage, and second connection means for connecting the high pressure EGR passage downstream of the high pressure EGR cooling passage and the low pressure EGR passage downstream of the low pressure EGR cooling passage, and EGR The flow state of the high pressure EGR gas and the low pressure EGR gas in the cooler is as follows. (1) The high pressure EGR gas flows through both the high pressure EGR cooling passage and the low pressure EGR cooling passage, and heat exchange is possible between the high pressure EGR gas and the heat medium. In addition, the first state where the flow of the low-pressure EGR gas is interrupted, and (2) the low-pressure EGR in both the high-pressure EGR cooling passage and the low-pressure EGR cooling passage And a second state where the flow of the high-pressure EGR gas is interrupted, and (3) both ends of the high-pressure EGR cooling passage become high-pressure EGR passages. Are connected to form a part of the high-pressure EGR passage, heat exchange is possible between the high-pressure EGR gas and the heat medium, and both ends of the low-pressure EGR cooling passage are connected to the low-pressure EGR passage to A third state in which heat exchange is possible between the low-pressure EGR gas and the heat medium, and the gas flow in the high-pressure EGR cooling passage and the gas flow in the low-pressure EGR cooling passage are independent of each other; Switching means for switching to any of these states may be provided.

In this configuration, the high-pressure EGR cooling passage and the low-pressure EGR cooling passage are two independent gas passages of the EGR cooler, and the gas flowing through each gas passage is cooled by exchanging heat with the heat medium. .

Further, the high pressure EGR passage and the low pressure EGR passage are connected upstream of the two gas passages by the first connecting means, and the high pressure EGR passage is connected downstream of the two gas passages by the second connecting means. The low pressure EGR passage is connected.

Therefore, when the first connecting means and the second connecting means are in a conductive state and the flow of the low pressure EGR gas is interrupted, both the high pressure EGR cooling passage and the low pressure EGR cooling passage communicate with the high pressure EGR passage. The high pressure EGR gas flows through the high pressure EGR cooling passage and the low pressure EGR cooling passage. Thereby, heat exchange is performed between the high-pressure EGR gas and the heat medium, and the high-pressure EGR gas is cooled (first state).

Further, when the first connection means and the second connection means are in a conductive state and the flow of the high pressure EGR gas is interrupted, both the high pressure EGR cooling passage and the low pressure EGR cooling passage communicate with the low pressure EGR passage. The low pressure EGR gas flows through the high pressure EGR cooling passage and the low pressure EGR cooling passage. Thereby, heat exchange is performed between the low-pressure EGR gas and the heat medium, and the low-pressure EGR gas is cooled (second state).

On the other hand, when the first connecting means and the second connecting means are in a non-conductive state, the high pressure EGR cooling passage communicates with the high pressure EGR passage, and the low pressure EGR cooling passage communicates with the low pressure EGR passage. The high-pressure EGR gas flowing through the passage and the low-pressure EGR gas flowing through the low-pressure EGR cooling passage are independently cooled by exchanging heat with the heat medium. Thereby, the high pressure EGR gas and the low pressure EGR gas are simultaneously cooled in parallel (third state).

When the flow state of the high pressure EGR gas and the low pressure EGR gas is switched to the first state (or the second state), the high pressure EGR gas (or the low pressure EGR gas) is the high pressure EGR cooling passage and the low pressure EGR. Since heat exchange is performed with the heat medium through the two EGR cooling passages of the cooling passage, the high-pressure EGR gas (or low-pressure EGR gas) is more efficiently cooled.

Further, when the high-pressure EGR gas and the low-pressure EGR gas are switched to the third state, the high-pressure EGR gas and the low-pressure EGR gas can be simultaneously cooled in parallel. In addition, the present invention can be suitably applied to an exhaust purification system that performs EGR using a low pressure EGR passage.

According to the present invention, in an exhaust purification system using both a low pressure EGR device and a high pressure EGR device, low pressure EGR gas and high pressure EGR gas are cooled while suppressing deterioration in mountability of the internal combustion engine, increase in cost, increase in fuel consumption, and the like. It becomes possible.

The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which the present invention is applied. An internal combustion engine 1 shown in FIG. 1 is a diesel engine having four cylinders 2. The internal combustion engine 1 is provided with a fuel injection valve 3 for injecting fuel directly into the combustion chamber of the cylinder 2 for each cylinder.

An intake manifold 8 is connected to the internal combustion engine 1, and each branch pipe of the intake manifold 8 communicates with a combustion chamber of each cylinder 2 through an intake port. An intake passage 9 is connected to the intake manifold 8. An intercooler 13 for cooling the gas flowing through the intake passage 9 is provided in the middle of the intake passage 9. A compressor housing 6 of a turbocharger 10 that operates using exhaust energy as a drive source is provided upstream of the intercooler 13.

An exhaust manifold 18 is connected to the internal combustion engine 1, and each branch pipe of the exhaust manifold 18 communicates with the combustion chamber of each cylinder 2 through an exhaust port. A turbine housing 7 of the turbocharger 10 is connected to the exhaust manifold 18. An exhaust passage 19 is connected to the turbine housing 7. An exhaust purification device 32 is provided in the exhaust passage 19. The exhaust passage 19 is open to the atmosphere downstream of the exhaust purification device 32. The exhaust purification device 32 includes a particulate filter that collects PM in the exhaust, an oxidation catalyst disposed upstream of the particulate filter, and a NOx catalyst that stores and reduces NOx in the exhaust. . The configuration of the exhaust purification device 32 is not limited to this.

The exhaust manifold 18 and the intake manifold 8 communicate with each other via a high pressure EGR passage 15. The high-pressure EGR passage 15 is provided with a high-pressure EGR valve 21 that can change the flow path cross-sectional area of the high-pressure EGR passage 15. The high pressure EGR valve 21 is connected to the ECU 22 via electrical wiring, and the amount of exhaust gas flowing through the high pressure EGR passage 15 (hereinafter, “high pressure” is controlled by controlling the valve opening degree based on a control signal from the ECU 22. "EGR gas amount") is adjusted.

A location downstream of the exhaust gas purification device 32 in the exhaust passage 19 and a location upstream of the compressor housing 6 in the intake passage 9 communicate with each other via a low pressure EGR passage 23. The low pressure EGR passage 23 is provided with a low pressure EGR valve 5 that can change the flow path cross-sectional area of the low pressure EGR passage 23. The low pressure EGR valve 5 is connected to the ECU 22 via electrical wiring, and the amount of exhaust gas flowing through the low pressure EGR passage 23 (hereinafter referred to as “low pressure”) is controlled by controlling the valve opening based on a control signal from the ECU 22. "EGR gas amount") is adjusted.

An EGR cooler 14 is provided in the middle of the high pressure EGR passage 15 and the low pressure EGR passage 23, and both the high pressure EGR gas and the low pressure EGR gas are cooled in the EGR cooler 14. Details of the EGR cooler 14 will be described later.

The accelerator pedal 31 in the driver seat is provided with an accelerator opening sensor 24 that detects the accelerator opening. The internal combustion engine 1 is provided with a crank position sensor 25 that detects the number of rotations of a crankshaft (not shown). The accelerator opening sensor 24 and the crank position sensor 25 are each connected to the ECU 22 via electrical wiring, and the detection values of each sensor are input to the ECU 22. The value detected by the accelerator opening sensor 24 is used as a parameter representing the engine load in various controls performed by the ECU 22. The value detected by the crank position sensor 25 is used as a parameter representing the engine speed in various controls performed by the ECU 22.

The internal combustion engine 1 is provided with an ECU 22 that is an electronic control computer that controls the internal combustion engine 1. The ECU 22 includes a ROM, a RAM, a CPU, an input port, an output port, and the like (not shown), and controls the fuel injection amount and opens the high-pressure EGR valve 21 and the low-pressure EGR valve 5 in accordance with the operation state of the internal combustion engine 1 or a request from the driver. Perform degree control.

When the high-pressure EGR valve 21 is opened, the high-pressure EGR passage 15 becomes conductive, and a part of the exhaust gas flowing through the exhaust manifold 18 flows into the intake manifold 8 via the high-pressure EGR passage 15 to burn the internal combustion engine 1. Recirculate to room.

When the low pressure EGR valve 5 is opened, the low pressure EGR passage 23 becomes conductive, and a part of the exhaust gas flowing out from the exhaust purification device 32 flows into the intake passage 9 via the low pressure EGR passage 23. The low pressure EGR gas flowing into the intake passage 9 is recirculated to the combustion chamber of the internal combustion engine 1 via the compressor housing 6 and the intake manifold 8.

By recirculating a part of the exhaust gas to the combustion chamber of the internal combustion engine 1 via the low pressure EGR passage 23 and / or the high pressure EGR passage 15, the combustion temperature in the combustion chamber decreases, and the amount of NOx generated in the combustion process Decreases.

Exhaust gas recirculation (hereinafter referred to as “low pressure EGR”) performed via the low pressure EGR passage 23 and exhaust gas recirculation performed via the high pressure EGR passage 15 (hereinafter referred to as “high pressure EGR”) can be suitably performed. The conditions of the operating state of such an internal combustion engine are obtained in advance through experiments or the like. In this embodiment, the exhaust gas is recirculated by switching the low pressure EGR and the high pressure EGR according to the operating state of the internal combustion engine or using them together.

FIG. 2 is a diagram showing a switching pattern between the low pressure EGR and the high pressure EGR determined for each region of the operating state of the internal combustion engine 1. 2 represents the engine speed of the internal combustion engine 1, and the vertical axis represents the engine load of the internal combustion engine 1.

In FIG. 2, a region HPL is a region where the operating state of the internal combustion engine 1 is a low load and low rotation, and high pressure EGR is performed here. The operating state of the internal combustion engine 1 belonging to the region HPL is hereinafter referred to as “high pressure EG”.
It is called “R operation state”.

A region LPL + HPL in FIG. 2 is a region where the operating state of the internal combustion engine 1 is a medium-load / medium-speed rotation, and here, the high pressure EGR and the low pressure EGR are used together. Hereinafter, the operating state of the internal combustion engine 1 belonging to the region LPL + HPL is referred to as “mixed EGR operating state”.

A region LPL in FIG. 2 is a region where the operating state of the internal combustion engine 1 is a high load and high rotation speed, and here, low pressure EGR is performed. The operation state of the internal combustion engine 1 belonging to the region LPL is hereinafter referred to as “low pressure EGR operation state”.

As described above, EGR can be performed in a wide range of operation by switching between high-pressure EGR and low-pressure EGR or using EGR in combination.

By the way, since the temperature of the air-fuel mixture flowing into the combustion chamber decreases when the temperature of the EGR gas decreases, the combustion temperature of the air-fuel mixture in the combustion chamber further decreases. Thereby, the reduction effect of NOx generation amount by EGR can be further enhanced. In addition, when EGR is performed, the intake gas temperature may increase due to the mixture of the intake air and the high-temperature exhaust gas, and the intake charging efficiency may decrease. However, by reducing the EGR gas temperature, the intake charging efficiency may be reduced. Reduction can be suppressed. In addition, by reducing the temperature of the EGR gas, it is possible to suppress the temperature of the gas passing through the equipment such as the EGR valve and the turbocharger compressor from becoming excessively high, and problems such as heat damage occur in the operation of these equipment. Can be suppressed.

Therefore, in general, an exhaust gas purification system including an EGR device is provided with an EGR cooler that cools EGR gas. In the case of an exhaust purification system having a high-pressure EGR passage and a low-pressure EGR passage, two EGR coolers are provided: a high-pressure EGR cooler for cooling high-pressure EGR gas and a low-pressure EGR cooler for cooling low-pressure EGR gas. It is common.

However, if the internal combustion engine is equipped with two EGR coolers, the size and weight of the exhaust gas purification system may increase and the mounting on the vehicle may deteriorate, or the number of parts may increase and the manufacturing cost may increase. There was sex. In addition, when the EGR cooler is a water-cooled type cooler that uses cooling water as a heat medium, two cooling water circulation systems that supply and circulate cooling water to the EGR cooler are required. There is a possibility that the energy consumed will increase and fuel consumption will deteriorate.

On the other hand, in the case of the present embodiment, the high-pressure EGR gas cooling function and the low-pressure EGR gas cooling function that were conventionally realized by two EGR coolers are provided by one EGR cooler 14. Hereinafter, the EGR cooler 14 of the present embodiment will be described in detail with reference to the drawings.

(Reference Example 1)
FIG. 3 is a conceptual diagram showing a schematic configuration of the EGR cooler 14 in Reference Example 1 . The inside of the region drawn with a broken line in FIG. 3 represents the internal configuration of the EGR cooler 14 conceptually shown using a square figure in FIG.

The EGR cooler 14 of Reference Example 1 is a water-cooled type, and cooling water as a heat medium is flowed around the EGR gas flow passage so that heat can be exchanged between the EGR gas and the cooling water to cool the EGR gas. To do.

Specifically, the EGR cooler 14 includes a core 16 through which cooling water flows, a cooling water inflow path 4 that is connected to the core 16 and allows cooling water to flow into the core 16, and flows out of the cooling water from the core 16 that is connected to the core 16. And a cooling water outflow passage 42 to be caused. The cooling water inflow path 4 and the cooling water outflow path 42 are connected to a cooling water tank or the like (not shown) and constitute a cooling water circulation system.

In FIG. 1, components corresponding to the cooling water circulation system, the cooling water inflow passage 4, and the cooling water outflow passage 42 are not shown. The cooling water circulation system may be a part of the cooling system of the internal combustion engine 1 or may be provided exclusively for the EGR cooler 14.

A plurality of EGR gas cooling pipes through which the EGR gas flows pass through the core 16, and heat exchange is performed between the EGR gas flowing through the EGR gas cooling pipe and the cooling water flowing through the core 16. In FIG. 3, four pipes are shown for simplicity, but the number of pipes is not limited to this.

In FIG. 3, two of the four pipes are connected to the high pressure EGR passage 15 at both ends, constitute a part of the high pressure EGR passage 15, and the high pressure EGR gas flows. Hereinafter, these two pipes are referred to as a high-pressure EGR cooling pipe 11. When the high-pressure EGR gas flows through the high-pressure EGR cooling pipe 11, heat exchange is performed between the high-pressure EGR gas and the cooling water flowing in the core 16, thereby cooling the high-pressure EGR gas.

The remaining two of the four pipes in FIG. 3 are connected to the low-pressure EGR passage 23 at both ends thereof, constitute a part of the low-pressure EGR passage 23, and low-pressure EGR gas flows. Hereinafter, these two pipes are referred to as a low pressure EGR cooling pipe 12. When the low-pressure EGR gas flows through the low-pressure EGR cooling pipe 12, heat exchange is performed between the low-pressure EGR gas and the cooling water flowing in the core 16, thereby cooling the low-pressure EGR gas.

As described above, in the EGR cooler 14 of Reference Example 1 , both the high-pressure EGR gas and the low-pressure EGR gas can be cooled by one cooling water circulation system and one core 16. Therefore, since the high pressure EGR gas and the low pressure EGR gas can be cooled by providing one EGR cooler 14, an increase in the size, weight, number of parts, etc. of the exhaust purification system can be suppressed. In addition, since it is not necessary to provide two cooling water circulation systems, an increase in energy consumed for circulating the cooling water can be suppressed, and hence deterioration of fuel consumption can be suppressed.

In the reference example 1, a high-pressure EGR cooling pipe 11 is high pressure EGR cooling passage, the low pressure EGR cooling pipe 12 is low pressure EGR cooling passage.

(Reference Example 2)
Next, a configuration of the EGR 14 different from the reference example 1 will be described. In the following, detailed description of components equivalent to those in Reference Example 1 is omitted, and the same names and symbols are used.

FIG. 4 is a conceptual diagram showing a schematic configuration of the EGR cooler 14 of Reference Example 2 .

The EGR cooler 14 has a high-pressure EGR core 27 that cools the high-pressure EGR gas that flows through the high-pressure EGR cooling pipe 11, and a low-pressure EGR core 20 that cools the low-pressure EGR gas that flows through the low-pressure EGR cooling pipe 12.

The high-pressure EGR core 27 is connected to a high-pressure EGR cooling water inflow passage 26 through which cooling water flows into the high-pressure EGR core 27 and a high-pressure EGR cooling water outflow passage 43 through which cooling water in the high-pressure EGR core 27 flows out. The high-pressure EGR cooling water inflow passage 26 and the high-pressure EGR cooling water outflow passage 43 are connected to a cooling water tank (not shown) and constitute a cooling water circulation system.

The low pressure EGR core 20 is connected to a low pressure EGR cooling water inflow passage 17 through which cooling water flows into the low pressure EGR core 20 and a low pressure EGR cooling water outflow passage 44 through which cooling water in the low pressure EGR core 20 flows out. The low-pressure EGR cooling water inflow passage 17 and the low-pressure EGR cooling water outflow passage 44 are connected to a cooling water tank (not shown) and constitute a cooling water circulation system.

The high pressure EGR core 27 and the low pressure EGR core 20 are partitioned by a partition wall 40, and cooling water in the high pressure EGR core 27 (hereinafter referred to as “high pressure EGR cooling water”) and cooling water in the low pressure EGR core 20 (hereinafter referred to as “low pressure”). It is physically separated from “EGR cooling water”. The partition wall 40 does not mix the high-pressure EGR cooling water and the low-pressure EGR cooling water, but the partition wall 40 of Reference Example 2 uses a member having high thermal conductivity, and the high-pressure EGR cooling water and the low-pressure EGR cooling water. It is possible to exchange heat with each other.

For example, by installing the EGR cooler 14 so that the vertical direction in FIG. 4 is substantially parallel to the vertical direction, the high temperature portion of the low pressure EGR cooling water rises in the direction of the partition wall 40 and the high pressure EGR cooling. The low temperature portion of the water descends toward the partition 40. Thus, the low pressure EGR cooling water having a high temperature is cooled by heat exchange via the partition wall 40, and the high pressure EGR cooling water having a low temperature is warmed.

Thereby, the low-pressure EGR gas cooling performance of the low-pressure EGR core 20 can be improved. Generally, since over to EGR in a large amount of exhaust is performed low-pressure EGR passage 23 is recycled, although the low-pressure EGR cooler sometimes higher cooling performance than the high-pressure EGR cooler is required, the EGR cooler 14 of Reference Example 2 According to this, the low-pressure EGR gas can be cooled more effectively.

Note that the high-pressure EGR core 27 may be installed vertically below the low-pressure EGR core 20 when there is a high cooling request for the high-pressure EGR gas.

In Reference Example 2 , the cooling water circulation system that supplies the cooling water to the high-pressure EGR core 27 and the cooling water circulation system that supplies the cooling water to the low-pressure EGR core 20 can be controlled independently. Therefore, the high-pressure EGR gas and the low-pressure EGR gas The amount of cooling water supplied to the high-pressure EGR core 27 and the amount of cooling water supplied to the low-pressure EGR core 20 can be adjusted according to the cooling request.

Thereby, the high pressure EGR gas and the low pressure EGR gas can be cooled more efficiently.

As a method for independently controlling the cooling water supplied to the high pressure EGR core 27 and the cooling water supplied to the low pressure EGR core 20, for example, a flow control valve is provided in the middle of the high pressure EGR cooling water inflow passage 26 or the high pressure EGR cooling water outflow passage 43. And a flow rate control valve provided in the middle of the low pressure EGR cooling water inflow passage 17 or the low pressure EGR cooling water outflow passage 44, and the opening degree of these flow control valves can be controlled.

In the EGR cooler 14 of the reference example 2 , since the high pressure EGR core 27 and the low pressure EGR core 20 are integrally configured, an increase in the size, weight, and number of parts of the exhaust purification system can be suppressed, and the mountability is deteriorated. And increase in cost can be suppressed.

(Reference Example 3)
Next, a configuration of the EGR cooler 14 different from the above reference example will be described. In the following, detailed description of components equivalent to those in the reference example is omitted, and the same names and symbols are used.

FIG. 5 is a conceptual diagram showing a schematic configuration of the EGR cooler 14 of Reference Example 3 .

The EGR cooler 14 includes a core 16 through which cooling water flows, a cooling water inflow passage 4 that is connected to the core 16 and allows cooling water to flow into the core 16, and a cooling water flow that is connected to the core 16 and causes cooling water in the core 16 to flow out. And an exit path 42. The cooling water inflow path 4 and the cooling water outflow path 42 are connected to a cooling water tank (not shown) and constitute a cooling water circulation system.

An EGR cooling pipe 29 passes through the core 16, and heat exchange is performed between the EGR gas flowing through the EGR cooling pipe 29 and the cooling water flowing through the core 16. In FIG. 5, two EGR cooling passages are illustrated for simplicity, but the number of EGR cooling passages is not limited to this.

Both ends of the EGR cooling pipe 29 are connected to the shared passage 28 and constitute a part of the shared passage 28. Both ends of the shared passage 28 are connected to the high pressure EGR passage 15 and the low pressure EGR passage 23. The gas flowing through the EGR cooling pipe 29 is cooled by exchanging heat with the cooling water flowing through the core 16.

A high pressure EGR passage 15 upstream of the shared passage 28 is provided with a second valve 33 for opening and closing the high pressure EGR passage 15, and a low pressure EGR passage 23 upstream of the shared passage 28 is provided with a fourth valve for opening and closing the low pressure EGR passage 23. A valve 35 is provided. Further, a first valve 30 for opening and closing the high pressure EGR passage 15 is provided in the high pressure EGR passage 15 downstream of the shared passage 28, and the low pressure EGR passage 23 is opened and closed in the low pressure EGR passage 23 downstream of the shared passage 28. A third valve 34 is provided.

The first valve 30, the second valve 33, the third valve 34, and the fourth valve 35 are each connected to the ECU 22 through electrical wiring, and are opened and closed by the ECU 22.

Specifically, when the operating state of the internal combustion engine 1 is the high pressure EGR operating state, the first valve 30 and the second valve 33 are opened and the third valve 34 and the fourth valve 35 are closed. . As a result, the high pressure EGR passage 15 and the common passage 28 are brought into conduction, and the common passage 28 and the EGR cooling pipe 29 constitute a part of the high pressure EGR passage 15. The high pressure EGR gas flows through the EGR cooling pipe 29, and the high pressure EGR gas is cooled in the core 16.

On the other hand, when the operation state of the internal combustion engine 1 is the low pressure EGR operation state, the first valve 30 and the second valve 33 are closed and the third valve 34 and the fourth valve 35 are opened. As a result, the low pressure EGR passage 23 and the common passage 28 are brought into conduction, and the common passage 28 and the EGR cooling pipe 29 constitute a part of the low pressure EGR passage 23. The low pressure EGR gas flows through the EGR cooling pipe 29, and the low pressure EGR gas is cooled in the core 16.

In the case of Reference Example 3 , the region LPL + HPL in FIG. 2 is divided into an HPL region and an LPL region, and the high pressure EGR / low pressure is changed so that the operating state of the internal combustion engine 1 belongs to either the HPL region or the LPL region. An EGR switching map is used.

FIG. 6 is a diagram illustrating a gas flow in the EGR cooler 14 when the operation state of the internal combustion engine 1 is the low pressure EGR operation state. The flow of the high pressure EGR gas is blocked by closing the first valve 30 and the second valve 33, and only the low pressure EGR gas flows through the common passage 28 and the EGR cooling pipe 29.

Since the EGR cooler 14 of the reference example 3 is sufficient if it has a performance capable of cooling only one of the high pressure EGR gas and the low pressure EGR gas, compared with the case of the reference example 1 and the reference example 2. Furthermore, the size of the EGR cooler 14 can be reduced. As a result, an increase in the size and weight of the exhaust purification system can be more reliably suppressed, and deterioration in mountability can be suppressed.

In the reference example 3 , at the branching portion of the common passage 28 to the high pressure EGR passage 15 and the low pressure EGR passage 23, the first switching position where the common passage 28 and the high pressure EGR passage 15 communicate with each other, the common passage 28 and the low pressure EGR A path switching valve that can be switched to any one of the second switching position for communicating the path 23 is provided, and the gas cooled by the EGR cooler 14 is switched to the high-pressure EGR gas or the low-pressure EGR gas by switching the path switching valve. You may do it. In this case, since the number of valves provided in the EGR cooler 14 is two, the number of parts can be reduced.

Reference Example 3, EGR cooling pipe 29 is E GR cooling passages.

In addition, the first valve 30 and the second valve 33 are opened, the third valve 34 and the fourth valve 35 are closed, the high-pressure EGR gas flows into the common passage 28 and the EGR cooling pipe 29, and the low-pressure EGR gas state flow is interrupted is in the first state.

Further, the first valve 30 and the second valve 33 are closed and the third valve 34 and the fourth valve 35 are opened. The low pressure EGR gas flows into the common passage 28 and the EGR cooling pipe 29, and the high pressure EGR gas state flow is interrupted in the second state.

The first valve 30, second valve 23, third valve 34, the fourth valve 35, and ECU22 for controlling these valves is SWITCHING means.

(Example)
Next, the configuration of the EGR cooler 14 according to the embodiment of the present invention will be described. In the following, detailed description of components equivalent to those in the reference example is omitted, and the same names and symbols are used.

FIG. 7 is a diagram showing a schematic configuration of the EGR cooler 14 of the present embodiment.

The EGR cooler 14 of the present embodiment has an upstream configuration in which the high pressure EGR passage 15 upstream of the high pressure EGR cooling pipe 11 and the low pressure EGR passage 23 upstream of the low pressure EGR cooling pipe 12 communicate with each other in the configuration of the EGR cooler 14 of Reference Example 1. The side communication passage 39 is further provided with a downstream communication passage 38 that connects the high pressure EGR passage 15 downstream of the high pressure EGR cooling pipe 11 and the low pressure EGR passage 23 downstream of the low pressure EGR cooling pipe 12. .

Then, a sixth valve 37 provided in the upstream communication passage 39 for opening and closing the upstream communication passage 39 and a high pressure EGR passage 15 provided upstream of the connection point of the upstream communication passage 39 are provided for opening and closing the high pressure EGR passage 15. A second valve 33 that is provided in the low pressure EGR passage 23 upstream from the connection point of the upstream communication passage 39 and a fourth valve 35 that opens and closes the low pressure EGR passage 23, and a downstream communication passage 38 provided in the downstream side. A fifth valve 36 that opens and closes the communication passage 38; a first valve 30 that is provided in the high-pressure EGR passage 15 downstream from the connection point of the downstream communication passage 38; and that opens and closes the high-pressure EGR passage 15; And a third valve 34 that is provided in the low pressure EGR passage 23 downstream from the connection location and opens and closes the low pressure EGR passage 23.

The first valve 30, the second valve 33, the third valve 34, the fourth valve 35, the fifth valve 36, and the sixth valve 37 are each connected to the ECU 22 through electric wiring, and are opened and closed by the ECU 22.

Specifically, when the operating state of the internal combustion engine 1 is a high pressure EGR operating state, the first valve 30 and the second valve 33 are opened, and the third valve 34 and the fourth valve 35 are closed, Further, the sixth valve 37 and the fifth valve 36 are opened. As a result, the high-pressure EGR cooling pipe 11 and the upstream communication path 3
9. The low pressure EGR cooling pipe 12 and the downstream communication passage 38 are in a conductive state, and the high pressure EGR cooling pipe 11, the low pressure EGR cooling pipe 12, the upstream communication passage 39, and the downstream communication passage 38 are part of the high pressure EGR passage 15. Constitute. The high pressure EGR gas flows through the high pressure EGR cooling pipe 11 and the low pressure EGR cooling pipe 12, and the high pressure EGR gas is cooled in the core 16.

On the other hand, when the operation state of the internal combustion engine 1 is the low pressure EGR operation state, the first valve 30 and the second valve 33 are closed, the third valve 34 and the fourth valve 35 are opened, and further, The sixth valve 37 and the fifth valve 36 are opened. As a result, the low-pressure EGR passage 23, the high-pressure EGR cooling pipe 11, the upstream communication passage 39, the low-pressure EGR cooling pipe 12, and the downstream communication passage 38 become conductive, and the high-pressure EGR cooling pipe 11, the low-pressure EGR cooling pipe 12, and the upstream communication The passage 39 and the downstream communication passage 38 constitute a part of the low pressure EGR passage 23. Low pressure EGR gas flows through the high pressure EGR cooling pipe 11 and the low pressure EGR cooling pipe 12, and the low pressure EGR gas is cooled in the core 16.

When the operation state of the internal combustion engine 1 is the mixed EGR operation state, the first valve 30, the second valve 33, the third valve 34, and the fourth valve 35 are opened, and the fifth valve 36 and the sixth valve The valve 37 is closed. As a result, the high pressure EGR passage 15 and the high pressure EGR cooling pipe 11 become conductive, and the high pressure EGR cooling pipe 11 constitutes a part of the high pressure EGR passage 15. The high pressure EGR gas flows through the high pressure EGR cooling pipe 11, and the high pressure EGR gas is cooled in the core 16. Further, the low pressure EGR passage 23 and the low pressure EGR cooling pipe 12 are in a conductive state, and the low pressure EGR cooling pipe 12 constitutes a part of the low pressure EGR passage 23. Low pressure EGR gas flows through the low pressure EGR cooling pipe 12, and the low pressure EGR gas is cooled in the core 16.

FIG. 8 is a diagram illustrating a gas flow in the EGR cooler 14 when the operation state of the internal combustion engine 1 is the high-pressure EGR operation state. The flow of the low pressure EGR gas is shut off by closing the fourth valve 35 and the third valve 34, and the upstream communication passage 39, the downstream communication passage 38, the high pressure EGR cooling pipe 11, and the low pressure EGR cooling pipe 12 High pressure EGR gas is flowing.

FIG. 9 is a diagram illustrating a gas flow in the EGR cooler 14 when the operation state of the internal combustion engine 1 is the mixed EGR operation state. The fifth valve 36 and the sixth valve 37 are closed, and the flow of the high pressure EGR gas and the low pressure EGR gas in the EGR cooler 14 is the same as in the case of the reference example 1.

In the EGR cooler 14 of the present embodiment, when the operation state of the internal combustion engine 1 is the low pressure EGR operation state or the high pressure EGR operation state, the EGR gas is both in the high pressure EGR cooling pipe 11 and the low pressure EGR cooling pipe 12. for flowing, in the case of the configuration in which an EGR cooling pipe of reference example 1 and the same size as the core 16 and the same number, it is possible to obtain a higher cooling performance compared to example 1.

Alternatively, even or reducing the number of EGR cooling pipe or to reduce the core 16 as compared with Example 1, it is possible to obtain the same cooling performance and an EGR cooler 14 of Reference Example 1, the EGR cooler 14 The size can be made more compact. For example, it can be made the same size as the EGR cooler 14 of the reference example 3. In the case of the present embodiment, the high-pressure EGR gas and the low-pressure EGR gas can be simultaneously cooled in parallel, so that it is not necessary to change the high-pressure EGR / low-pressure EGR switching map as in Reference Example 3. Therefore, EGR more suitable for the operating state of the internal combustion engine 1 can be performed.

When the high pressure EGR passage 15 and the low pressure EGR passage 23 are adjacent to each other in the vicinity of the connection portion of the upstream communication passage 39 or in the vicinity of the connection portion of the downstream communication passage 38, the upstream communication passage 39 or the downstream communication passage. 38 may simply be an opening opened in a partition wall between the high pressure EGR passage 15 and the low pressure EGR passage 23. In that case, the fifth valve 36 and the sixth valve 37 are valves that open and close the opening.

In the present embodiment, the upstream communication path 39 and the sixth valve correspond to the first connection means in the present invention, and the downstream communication path 38 and the fifth valve 36 correspond to the second connection means in the present invention. .

Further, the first valve 30 and the second valve 33 are opened, the third valve 34 and the fourth valve 35 are closed, the sixth valve 37 and the fifth valve 36 are opened, and the high pressure EGR passage 15 is opened. The high pressure EGR cooling pipe 11, the upstream communication passage 39, the low pressure EGR cooling pipe 12, and the downstream communication passage 38 are in a conductive state, and the flow of the low pressure EGR gas is cut off, which corresponds to the first state in the present invention. To do.

The first valve 30 and the second valve 33 are closed, the third valve 34 and the fourth valve 35 are opened, the sixth valve 37 and the fifth valve 36 are opened, and the low-pressure EGR passage 23 is opened. The high-pressure EGR cooling pipe 11, the upstream communication passage 39, the low-pressure EGR cooling pipe 12, and the downstream communication passage 38 are in a conductive state, and the flow of the high-pressure EGR gas is interrupted, which corresponds to the second state in the present invention. To do.

Further, the first valve 30, the second valve 33, the third valve 34, and the fourth valve 35 are opened, the fifth valve 36 and the sixth valve 37 are closed, and the high pressure EGR passage 15 and the high pressure EGR cooling pipe 11 are closed. Is in a conductive state, the low pressure EGR passage 23 and the low pressure EGR cooling pipe 12 are in a conductive state, and the state where the gas flow in the upstream side communication passage 39 and the downstream side communication passage 38 is blocked is the third state in the present invention. Corresponds to the state.

The first valve 30, the second valve 23, the third valve 34, the fourth valve 35, the fifth valve 36, the sixth valve 37, and the ECU 22 that controls these valves correspond to the switching means in the present invention.

Each drawing referred to in the above-described reference example or embodiment is a conceptual diagram, and the size and scale of each illustrated component need not be as illustrated. For example, in FIG. 3, the numbers and thicknesses of the high-pressure EGR cooling pipes 11 and the low-pressure EGR cooling pipes 12 are drawn equally, but they may be different from each other. Moreover, although the magnitude | size of the high voltage | pressure EGR core 27 and the low voltage | pressure EGR core 20 is drawn equally in FIG. 4, these may also differ. The same applies to other drawings.

The embodiment described above is an example for explaining the present invention, and various modifications can be made to the above-described embodiment without departing from the gist of the present invention. For example, in the above description, an embodiment in which the present invention is applied to a water-cooled EGR cooler has been described. However, in the present invention, the heat medium of the EGR cooler is not limited to cooling water. A liquid or gas can be used as the heat medium. As the liquid heat medium, for example, cooling water of an internal combustion engine may be used, or a cooling liquid circulation system dedicated to the EGR cooler may be provided. For example, outside air can be used as the gaseous heat medium.

It is a figure which shows schematic structure of the internal combustion engine and its intake-exhaust system in the Example of this invention. It is a figure which shows the switching map of the high voltage | pressure EGR and low voltage | pressure EGR in the Example of this invention. It is a figure which shows schematic structure of the EGR cooler in the reference example 1. It is a figure which shows schematic structure of the EGR cooler in the reference example 2. It is a figure which shows schematic structure of the EGR cooler in the reference example 3. It is a figure which shows the flow of the gas in an EGR cooler when the operation state of an internal combustion engine is a low pressure EGR operation state in Reference Example 3. It is a diagram showing a schematic configuration of an EGR cooler in Example of the present invention. When the operation state of Oite internal combustion engine to an embodiment of the present invention is a high-pressure EGR operation state is a diagram showing a gas flow in the EGR cooler. When it is operating condition is mixed EGR operation state of Oite internal combustion engine to an embodiment of the present invention, is a diagram showing a gas flow in the EGR cooler.

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Cylinder 3 Fuel injection valve 4 Cooling water inflow path 5 Low pressure EGR valve 6 Compressor housing 7 Turbine 8 Intake manifold 9 Intake passage 10 Turbocharger 11 High pressure EGR cooling pipe 12 Low pressure EGR cooling pipe 13 Intercooler 14 EGR cooler 15 High pressure EGR passage 16 Core 17 Low pressure EGR cooling water inflow passage 18 Exhaust manifold 19 Exhaust passage 20 Low pressure EGR core 21 High pressure EGR valve 22 ECU
23 Low pressure EGR passage 24 Accelerator opening sensor 25 Crank position sensor 26 High pressure EGR cooling water inflow passage 27 High pressure EGR core 28 Shared passage 29 EGR cooling pipe 30 First valve 31 Accelerator pedal 32 Exhaust gas purification device 33 Second valve 34 Third valve 35 4th valve 36 5th valve 37 6th valve 38 Downstream side communication path 39 Upstream side communication path 40 Partition 42 Cooling water outflow path

Claims (3)

A turbocharger for driving a compressor disposed in an intake passage of the internal combustion engine by a turbine disposed in an exhaust passage of the internal combustion engine;
A high pressure EGR passage connecting an exhaust passage upstream of the turbine and an intake passage downstream of the compressor;
A low pressure EGR passage connecting an exhaust passage downstream of the turbine and an intake passage upstream of the compressor;
An EGR cooler in which heat is exchanged between the exhaust flowing through the high-pressure EGR passage and the exhaust flowing through the low-pressure EGR passage and a heat medium;
With
The EGR cooler is
One or a plurality of high-pressure EGR cooling passages whose both ends are connected to the high-pressure EGR passage and constitute a part of the high-pressure EGR passage;
One or a plurality of low-pressure EGR cooling passages whose both ends are connected to the low-pressure EGR passage and constitute a part of the low-pressure EGR passage;
Have
The high-pressure EGR cooling passage is capable of exchanging heat between the exhaust flowing through the high-pressure EGR cooling passage and the heat medium,
The low-pressure EGR cooling passage is capable of exchanging heat between the exhaust flowing therein and the heat medium,
A first connecting means for connecting the high pressure EGR passage upstream from the high pressure EGR cooling passage and the low pressure EGR passage upstream from the low pressure EGR cooling passage;
A second connecting means for connecting the high pressure EGR passage downstream from the high pressure EGR cooling passage and the low pressure EGR passage downstream from the low pressure EGR cooling passage;
Have
The state of the exhaust flow in the EGR cooler is
The high-pressure EGR passage, the high-pressure EGR cooling passage, the low-pressure EGR cooling passage, the first connection means, and the second connection means are communicated, and the exhaust gas flowing through the high-pressure EGR passage, the heat medium, A first state in which heat exchange is performed between the two and the flow of exhaust gas in the low pressure EGR passage is interrupted,
The low-pressure EGR passage, the high-pressure EGR cooling passage, the low-pressure EGR cooling passage, the first connection means, and the second connection means are communicated, and the exhaust gas flowing through the low-pressure EGR passage, the heat medium, A second state in which heat exchange is performed between the two and the flow of the exhaust gas in the high-pressure EGR passage is interrupted,
The high pressure EGR passage and the high pressure EGR cooling passage are communicated, heat exchange is performed between the exhaust gas flowing through the high pressure EGR passage and the heat medium, and the low pressure EGR passage and the low pressure EGR cooling passage are A third state in which heat exchange is performed between the exhaust gas that is communicated and flows through the low-pressure EGR passage and the heat medium, and the flow of exhaust gas in the first connection means and the second connection means is blocked;
An exhaust purification system for an internal combustion engine comprising switching means for switching to any one of the states.   In claim 1
  The first connection means is an upstream communication path that connects the high pressure EGR path upstream from the high pressure EGR cooling path and the low pressure EGR path upstream from the low pressure EGR cooling path,
  The second connection means is a downstream side communication path that connects the high pressure EGR path downstream from the high pressure EGR cooling path and the low pressure EGR path downstream from the low pressure EGR cooling path,
  The EGR cooler is
    A first valve that is provided in the high-pressure EGR passage downstream from the connection point of the downstream communication passage and opens and closes the high-pressure EGR passage;
    A sixth valve provided in the upstream communication path and opening and closing the upstream communication path;
    A second valve that is provided in the high-pressure EGR passage upstream from the connection point of the upstream communication passage and opens and closes the high-pressure EGR passage;
    A fourth valve that is provided in the low-pressure EGR passage upstream from the connection point of the upstream communication passage and opens and closes the low-pressure EGR passage;
    A fifth valve provided in the downstream communication path for opening and closing the upstream communication path;
    A third valve that is provided in the low-pressure EGR passage downstream from the connection point of the downstream communication passage and opens and closes the low-pressure EGR passage;
With
  The switching means is
    Switching to the first state by opening the first valve and the second valve, closing the third valve and the fourth valve, and opening the fifth valve and the sixth valve;
    Switching to the second state by closing the first valve and the second valve, opening the third valve and the fourth valve, and opening the fifth valve and the sixth valve;
    An exhaust gas purification system for an internal combustion engine that switches to the third state by opening the first valve, the second valve, the third valve, and the fourth valve, and closing the fifth valve and the sixth valve.   In claim 1 or 2,
  The switching means is
    When the operating state of the internal combustion engine is in a predetermined low load low rotation region, switching to the first state,
    When the operating state of the internal combustion engine is in a predetermined medium load / medium rotation region, switching to the third state,
    An exhaust purification system for an internal combustion engine that switches to the second state when the operating state of the internal combustion engine is in a predetermined high-load high-rotation region.

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