JP2012057579A - Egr cooler of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an EGR cooler of an internal combustion engine that can suppress an increase in flow passage resistance of an EGR gas and a cooling water and improve the conversion efficiency of thermoelectric elements.SOLUTION: An EGR gas flow passage 21 is formed in a cylinder shape with a square cross section, and thermoelectric elements 23 are provided on four outer surfaces of the EGR gas flow passage 21. The EGR gas flow passage 21 is encircled by a cooling water flow passage 22 that is formed cylindrical along the EGR gas flow passage 21, so as to circulate a cooling water therein. Thus, while the high-temperature end face 23a and low-temperature end face 23b of the thermoelectric elements 23 are ensured enough in areas, an increase in flow passage resistance due to the separation or joint of flow is suppressed and the EGR gas and cooling water are smoothly circulated, thereby permitting efficient heat reception and heat radiation of the thermoelectric elements 23.

Description

  The present invention relates to an EGR cooler provided in an EGR device of an internal combustion engine, and more particularly to an EGR cooler having a function of converting thermal energy of EGR gas into electric energy and recovering it.

2. Description of the Related Art Conventionally, in automobiles or the like that discharge high-temperature exhaust gas, a power generation device that converts the thermal energy of the exhaust gas into electrical energy and recovers it, thereby reducing the amount of power generated by the alternator and reducing the fuel consumption of the internal combustion engine. Proposed. This type of power generation apparatus needs to be provided at any location on the exhaust gas flow path of the internal combustion engine, and is provided, for example, in an EGR cooler.
As is well known, the EGR cooler is a component part of an EGR device that circulates exhaust gas as EGR gas from the exhaust side to the intake side of the internal combustion engine, and plays a role of cooling the EGR gas with cooling water flowing inside. When a power generator is provided in such an EGR cooler, a thermoelectric element is interposed between the EGR gas and the cooling water, and a thermoelectromotive force is generated by the Seebeck effect of the thermoelectric element to generate power ( For example, see Patent Document 1).

  In the technique of Patent Document 1, a three-layer EGR gas flow path and a four-layer cooling water flow path are alternately arranged in the casing of the EGR cooler, and each EGR gas flow path is located between the cooling water flow paths. Each of them is configured with a thermoelectric element interposed. During operation of the internal combustion engine, the high temperature end face of the thermoelectric element receives heat by the EGR gas flowing through the EGR gas flow path, while the low temperature end face of the thermoelectric element dissipates heat by the cooling water flowing through the cooling water flow path. For this reason, a temperature difference arises between the high temperature end face and the low temperature end face of each thermoelectric element, and each thermoelectric element generates a thermoelectromotive force using this temperature difference.

International Publication No. 2007/026432 Pamphlet

However, it has been difficult to say that the EGR cooler described in Patent Document 1 can realize efficient conversion by a thermoelectric element.
In other words, the conversion efficiency of thermoelectric elements from heat energy to electric energy is complicatedly related to the arrangement, number, weight, or flow resistance of EGR gas and cooling water flowing through the EGR cooler. Good conversion efficiency cannot be realized unless these requirements are satisfied in a balanced manner. The EGR cooler of Patent Document 1 has a multilayer structure of the EGR gas flow path and the cooling water flow path, which is used for heat exchange between the high temperature end face and the low temperature end face of each thermoelectric element, in other words, EGR gas and cooling water. This is a result of placing an emphasis on ensuring as wide an area as possible, but on the other hand, the use of a multilayer structure greatly increases the flow resistance of EGR gas and cooling water.

Specifically, the EGR gas is diverted in three directions when flowing into the EGR cooler, and the cooling water is diverted while changing the flow direction in four directions. The EGR gas is diverted from the three directions when flowing out from the EGR cooler. Cooling water merges while changing the flow direction from four directions. During the diversion and merging, the EGR gas and the cooling water generate a large flow resistance, making it difficult to smoothly flow. As a result, as described above, the heat exchange area between the EGR gas and the cooling water is secured. Despite this, the conversion efficiency of thermoelectric elements was not sufficient. In particular, an increase in the flow resistance against EGR gas not only affects the conversion efficiency of the thermoelectric element, but also lowers the EGR function, and consequently deteriorates the performance and exhaust gas characteristics of the internal combustion engine. I had to say that.
The present invention has been made to solve such problems, and the object of the present invention is to suppress an increase in the flow resistance of the EGR gas and the cooling water and avoid the adverse effects caused by this. Another object of the present invention is to provide an EGR cooler for an internal combustion engine that can improve the conversion efficiency of a thermoelectric element.

In order to achieve the above object, the invention of claim 1 is provided in an EGR device of an internal combustion engine that circulates exhaust gas of the internal combustion engine from the exhaust side to the intake side as EGR gas. In an EGR cooler of an internal combustion engine that cools by exchanging heat between, an EGR gas passage that forms a cylinder with a quadrangular cross section and distributes EGR gas inside, and an outer surface of the EGR gas passage each has four high-temperature end faces And a thermoelectric element that generates a thermoelectromotive force by utilizing a temperature difference from the low-temperature end face, and a cylindrical shape along the EGR gas flow path so as to wrap the EGR gas flow path And a cooling water flow path for circulating the cooling water in a space formed between the inside and the low temperature end face of each thermoelectric element.
According to a second aspect of the present invention, in the first aspect, the thermoelectric element is divided into a plurality of portions in the EGR gas flow direction, and the upstream thermoelectric element has a temperature between the high temperature end face and the low temperature end face as compared with the downstream thermoelectric element. The characteristics are set so that high conversion efficiency is exhibited when the difference is larger.

As described above, according to the EGR cooler of the internal combustion engine of the first aspect of the present invention, the EGR gas flow path is formed so as to form a cylinder having a quadrangular cross section, and each of the four outer surfaces of the EGR gas flow path has thermoelectric power. The element was disposed, and the EGR gas flow path was enclosed by a cylindrical cooling water flow path along the EGR gas flow path so that the cooling water was circulated therein.
As described above, the thermoelectric elements are arranged on the four surfaces of the EGR gas flow path, and the cooling water flow path is arranged so as to wrap around the EGR gas flow path. The area of the low temperature end face can be sufficiently secured. Moreover, since the EGR gas and the cooling water are not divided and merged as in the technique of Patent Document 1, the increase in flow resistance can be suppressed, and the heat receiving and heat dissipation to the thermoelectric element can be achieved by smoothly circulating the EGR gas and the cooling water. It is done efficiently. Due to these factors, the conversion efficiency of each thermoelectric element can be greatly improved.

On the other hand, since both the EGR gas flow path and the cooling water flow path have a long cylindrical shape along the flow direction of the EGR gas or the cooling water, the EGR gas flow path is disposed when the cooling water flow path is disposed so as to wrap around the EGR gas flow path. On the other hand, it is not necessary to enlarge the cooling water flow path so much, and the whole EGR cooler can be made compact to improve the mountability to the vehicle. Further, by smoothly circulating the EGR gas, it is possible to perform accurate EGR control, thereby improving the performance and exhaust gas characteristics of the internal combustion engine.
According to the EGR cooler of the internal combustion engine of the second aspect of the invention, in addition to the first aspect, the thermoelectric element is divided into a plurality in the flow direction of the EGR gas, and the upstream thermoelectric element is compared with the downstream thermoelectric element. The characteristics were set so as to exhibit high conversion efficiency when the temperature difference was larger. Although the temperature difference between the EGR gas and the cooling water gradually decreases from the upstream side to the downstream side in the EGR gas flow direction, power generation is always performed by the thermoelectric element having the optimum characteristics with respect to the temperature difference. The conversion efficiency of the entire element can be further improved.

It is a whole lineblock diagram showing an internal-combustion engine provided with an EGR cooler of an embodiment. It is sectional drawing which shows an EGR cooler. It is the III-III sectional view taken on the line of FIG. 2 which similarly shows an EGR cooler. It is sectional drawing corresponding to FIG. 3 which shows the EGR cooler of another example.

Hereinafter, an embodiment of an EGR cooler of an internal combustion engine embodying the present invention will be described.
FIG. 1 is an overall configuration diagram showing an internal combustion engine including an EGR cooler according to the present embodiment.
The internal combustion engine 1 is configured as an in-line 6-cylinder diesel engine. Each cylinder of the internal combustion engine 1 is provided with a fuel injection valve 2. Each fuel injection valve 2 is supplied with pressurized fuel from a common common rail 3, and is opened at a timing according to the operating state of the engine. Fuel is injected into the cylinder.
An intake manifold 4 is mounted on the intake side of the internal combustion engine 1. An intake passage 5 connected to the intake manifold 4 is opened and closed by an air cleaner 6, a compressor 7 a of a turbocharger 7, an intercooler 8, and an actuator 9 a from the upstream side. An intake throttle valve 9 is provided. An exhaust manifold 10 is mounted on the exhaust side of the internal combustion engine 1, and a turbine 7 b of a turbocharger 7 connected coaxially with the compressor 7 a is connected to the exhaust manifold 10. An exhaust passage 11 is connected to the turbine 7b. The exhaust passage 11 is provided with an exhaust throttle valve 12, an exhaust purification device 13, and a silencer (not shown) that are opened and closed by an actuator 12a from the upstream side.

The exhaust manifold 10 and the intake manifold 4 are connected via an EGR passage 14, and an EGR valve 15 and an EGR cooler 16 that are opened and closed by an actuator 15 a are provided in the EGR passage 14. The EGR cooler 16 is connected to a radiator 18 through a water channel 17, and the cooling water is circulated between the EGR cooler 16 and the radiator 18 by a cooling water pump 19 provided in the water channel 17. In the present embodiment, the radiator 18 is shared with the engine cooling one. However, a radiator dedicated to the EGR cooler may be provided.
During operation of the internal combustion engine 1, the intake air introduced into the intake passage 5 through the air cleaner 6 is pressurized by the compressor 7 a of the turbocharger 7, and then distributed to each cylinder through the intercooler 8, the intake throttle valve 9, and the intake manifold 4. Then, it is introduced into the cylinder in the intake stroke of each cylinder. In the cylinder, fuel is injected from the fuel injection valve 2 at a predetermined timing and ignited and combusted in the vicinity of the compression top dead center. The exhaust gas after combustion rotates the turbine 7b through the exhaust manifold 10, and then the exhaust throttle valve 12, It is discharged to the outside through the exhaust purification device 13 and the silencer.

The intake throttle valve 9, the exhaust throttle valve 12, the actuators 9a, 12a, 15a of the EGR valve 15, the fuel injection valve 2, and the like are connected to an ECU (electronic control unit) not shown, and based on detection information from sensors. The drive is controlled by the ECU. For example, the ECU operates the internal combustion engine 1 by controlling the injection amount and injection timing of the fuel injection valve 2 on the basis of the engine speed and load, and controls the opening of the EGR valve 15 by the actuator 15a to intake air from the exhaust side. The amount of EGR refluxed to the side is adjusted.
Next, the configuration of the EGR cooler 16 will be described in detail.
2 is a cross-sectional view showing the EGR cooler 16, and FIG. 3 is a cross-sectional view taken along the line III-III of FIG.

As a whole, the EGR cooler 16 has a double structure in which the periphery of the EGR gas flow channel 21 through which EGR gas flows is surrounded by a cooling water flow channel 22 through which cooling water flows.
The EGR gas passage 21 is made of a metal plate and has a cylindrical shape with a square cross section. The upstream end 21a of the EGR gas flow path 21 forms a funnel shape and is connected to the exhaust side EGR passage 14, and the downstream end 21b forms a funnel shape and is connected to the intake side EGR passage 14 so that EGR from the exhaust side The gas flows through the EGR gas passage 21 to the intake side.
The EGR gas flow path 21 is partitioned in a mesh shape in the vertical and horizontal directions perpendicular to the gas flow direction, whereby the EGR gas is guided in each of a number of elongated passages partitioned by the mesh in the EGR gas flow path 21. In addition, the mesh cross section is the same everywhere in the distribution direction. As described above, since the EGR gas channel 21 is made of metal having good heat conduction including the mesh portion, the heat of the EGR gas flowing through the center of the EGR gas channel 21 is also from the upstream end 21a to the downstream end 12b. It is efficiently transmitted to the outside of the EGR gas channel 21 in the process of distribution.

Here, since the inside of the EGR gas flow path 21 is partitioned in a mesh shape, the EGR gas is divided into each elongated passage at the upstream end of the EGR gas flow path 21, and after flowing through each passage, joins at the downstream end. However, since the flow direction of the EGR gas does not change in these branching and merging, it does not become a factor that increases the channel resistance. However, the configuration of the EGR gas flow channel 21 is not limited to this, and may be a single wide passage without partitioning the inside into a mesh shape, for example.
Thermoelectric elements 23 are respectively disposed on the four outer surfaces of the EGR gas flow path 21. These thermoelectric elements 23 have a function of generating a thermoelectromotive force by the Seebeck effect using a temperature difference between the high temperature end surface 23a that is one side surface and the low temperature end surface 23b that is the other side surface, and the high temperature end surface 23a side. Is disposed in close contact with the outside of the EGR gas channel 21.

For each surface of the EGR gas flow path 21, three thermoelectric elements 23 are arranged in a line along the flow direction of the EGR gas (a total of 12 sheets), and each surface of the EGR gas flow path 21 is formed by these thermoelectric elements 23. Almost the whole is covered. Here, the three thermoelectric elements 23 for each surface have different characteristics depending on the flow direction of the EGR gas, and the thermoelectric element 23 on the most upstream side of each surface (the right side in FIG. 2) has a high temperature end surface 23a and a low temperature end surface. When the temperature difference from 23b is large, high conversion efficiency is exhibited, and the middle-stream side thermoelectric element 23 exhibits high conversion efficiency when the temperature difference between the high temperature end surface 23a and the low temperature end surface 23b is medium, The downstream thermoelectric element 23 (left side in FIG. 2) is set to exhibit high conversion efficiency when the temperature difference between the high temperature end surface 23a and the low temperature end surface 23b is small.
However, the setting of each thermoelectric element 23 is not limited to this. For example, the thermoelectric elements 23 having the same characteristics may be used, or divided into two or four without being divided into three, You may use the big thermoelectric element 23 (a total of 4 sheets).

A partition wall 24 having a square cross section made of a metal plate material is disposed around the EGR gas flow path 21, and the inner surface of the partition wall 24 is in close contact with the low temperature end surface 23 b of each thermoelectric element 23. . The upstream and downstream sides of the partition wall 24 are bent toward the inner peripheral side, that is, the EGR gas flow path 21 side, thereby sealing each thermoelectric element 23 inside. The entire EGR gas flow path 21 including the partition wall 24 is encased by a cooling water flow path 22 having a square cross section made of a metal plate, and the upstream end and the downstream end of the cooling water flow path 22 are lid bodies 22a. , 22b.
As a result, as shown in FIG. 3, a liquid-tight space having a quadrangular cross section is formed in the cooling water channel 22, more specifically, between the entire outside of the partition wall 24 and the entire inside of the cooling water channel 22. The cooling water is stored in this space. The water channel 17 described above is connected to one side of the upstream end and one side of the downstream end of the cooling water channel 22, and the internal cooling water circulates between the radiator 18 through these water channels 17. ing.
The partition wall 24 is not always necessary and may be omitted. In this case, the low temperature end face 23 b of each thermoelectric element 23 is directly exposed to the cooling water in the cooling water flow path 22.

Here, in this embodiment, as indicated by an arrow in FIG. 2, the flow direction of the cooling water in the cooling water passage 22 is made to coincide with the flow direction of the EGR gas in the EGR gas passage 21 (from the right side). left). For this reason, the temperature difference between the EGR gas and the cooling water is greatest on the upstream side of the EGR gas flow path 21, and the temperature difference is reduced on the downstream side. However, the flow directions of EGR gas and cooling water are not limited to this, and they may be circulated in opposite directions.
Although not shown, each thermoelectric element 23 is connected to a battery mounted on the vehicle via a voltage regulator, and the electric power generated by the Seebeck effect is charged to the battery as described later, or the generated electric power from the alternator is combined with the generated electric power of the vehicle. It is supplied to each electric load.

In this embodiment, the passage cross-sectional area of the EGR gas passage 21 is set to be substantially the same as that of a general EGR cooler, and the length thereof is also set to be substantially the same as that of a general EGR cooler. The outer dimensions of the EGR gas passage 21 are substantially the same as the outer dimensions of a general EGR cooler. Moreover, although the thermoelectric element 23 is arrange | positioned on the outer side of this EGR gas flow path 21, since each thermoelectric element 23 is closely_contact | adhered to 4 surfaces, an occupation space is hardly required.
Furthermore, as shown in FIG. 2, both the EGR gas channel 21 and the cooling water channel 22 have a long cylindrical shape along the flow direction so that the EGR gas and the cooling water flow in parallel with each other. For this reason, when the cooling water flow path 22 is arranged so as to wrap the EGR gas flow path 21, it is not necessary to enlarge the cooling water flow path 22 with respect to the EGR gas flow path 21, and as a result, the outside of the entire EGR cooler 16 is removed. The size is almost the same as a general EGR cooler and is compact.

Next, the operation of the EGR cooler 16 of the internal combustion engine of the present embodiment configured as described above will be described.
The exhaust gas of the internal combustion engine 1 is circulated as EGR gas from the exhaust manifold 10 to the intake manifold 4 via the EGR passage 14 according to the opening degree of the EGR valve 15, and circulates in the EGR gas passage 21 of the EGR cooler 16 at that time. To do. Further, the cooling water in the cooling water flow path 22 is circulated between the radiator 18 and the water path 17. For this reason, the high temperature end surface 23a of each thermoelectric element 23 arranged on the four surfaces of the EGR gas flow path 21 receives heat from the high temperature EGR gas, the low temperature end surface 23b dissipates heat to the low temperature cooling water, and each thermoelectric element 23 has a temperature. A thermoelectromotive force is generated using the difference. As a result, the heat of the EGR gas is radiated to the cooling water side through the thermoelectric element 23, and the cooled EGR gas is circulated to the intake side of the internal combustion engine 1.

And in this embodiment, since the thermoelectric element 23 is arrange | positioned on 4 surfaces of the EGR gas flow path 21, and the cooling water flow path 22 is arrange | positioned so that this EGR gas flow path 21 may be wrapped, the high temperature end surface with respect to EGR gas As for the area 23a, the area of the low-temperature end face 23b with respect to the cooling water can be sufficiently secured, and a wide area can be used for heat exchange between the EGR gas and the cooling water.
Further, as described above, the passage cross-sectional area of the EGR gas passage 21 is sufficiently ensured without being inferior to that of a general EGR cooler, and at the upstream end or the downstream end as in the technique of Patent Document 1. Therefore, the flow resistance does not increase due to the merge of the EGR gas. Therefore, the EGR gas smoothly flows from the upstream side to the downstream side in the EGR gas flow path 21, and heat reception from the EGR gas to each thermoelectric element 23 is performed efficiently.

The same applies to the cooling water flow path 22, and the flow resistance does not increase because the cooling water flows through the cooling water flow path 22 without being divided or joined. Therefore, the cooling water smoothly flows from the upstream side to the downstream side in the cooling water flow path 22, and heat radiation from each thermoelectric element 23 to the cooling water is efficiently performed.
As a result, each thermoelectric element 23 arranged on the four surfaces of the EGR gas flow path 21 greatly contributes to reducing fuel consumption by converting heat energy into electric energy with high efficiency and effectively using the generated electric power in the vehicle. can do.

In particular, in the present embodiment, since the characteristics of the thermoelectric element 23 are different depending on the position of the EGR gas passage 21 in the flow direction, more efficient conversion can be realized.
That is, the EGR gas that has flowed into the upstream side of the EGR gas flow channel 21 and the cooling water that has flowed into the cooling water flow channel 22 are exchanged in the downstream of the flow channels 21 and 22 while exchanging heat with the thermoelectric element 23 interposed therebetween. The temperature difference gradually decreases. On the other hand, the upstream thermoelectric element 23 has characteristics suitable for a large temperature difference (high temperature difference and high efficiency), and the midstream thermoelectric element 23 has characteristics suitable for an intermediate temperature difference, The thermoelectric element 23 has characteristics suitable for a small temperature difference. For this reason, power is always generated by the thermoelectric element 23 having the optimum characteristics with respect to the temperature difference that gradually decreases from the upstream side toward the downstream side, and the thermal energy of the EGR gas can be converted into electrical energy without waste. Thus, the conversion efficiency of the entire thermoelectric element 23 can be further improved.

On the other hand, since the flow resistance of the EGR gas and the cooling water does not increase, it is not necessary to enlarge the cross-sectional areas of the EGR gas passage 21 and the cooling water passage 22 more than necessary. As a result, the entire EGR cooler 16 is compact as described above. The mounting of the EGR cooler 16 on the vehicle can be improved.
Further, since the increase in flow resistance against the EGR gas becomes a factor that limits the EGR ring flow rate, accurate EGR control according to the opening degree of the EGR valve 15 becomes difficult, and the EGR function is lowered. It leads to deterioration of performance and exhaust gas characteristics. In the present embodiment, appropriate EGR control can always be realized by reducing the flow path resistance of the EGR gas, and these problems can be prevented in advance.

This is the end of the description of the embodiment, but the aspect of the present invention is not limited to this embodiment. For example, in the said embodiment, although it actualized as an EGR cooler of the diesel engine 1, the classification of an internal combustion engine is not limited to this, For example, you may apply to a gasoline engine.
Further, the structure of the EGR cooler 16 is not limited to the above embodiment, and can be variously changed. For example, in the above embodiment, the cooling water flow path 22 is formed so as to form a complete annular cross section that wraps the entire outside of the EGR gas flow path 21 as shown in FIG. 3, but the cooling water flow path 22 may be configured as shown in FIG. Good. In this other example, four cooling water flow paths 22 are formed so as to correspond to the thermoelectric elements 23 arranged on the outer four surfaces of the EGR gas flow path 21, respectively. Even in this case, since the contact area between the low-temperature end face 23b of each thermoelectric element 23 and the cooling water is not different from that in FIG. 3, the same effects as those in the above embodiment can be obtained.

1 Internal combustion engine 16 EGR cooler 21 EGR gas flow path 22 Cooling water flow path 23 Thermoelectric element 23a High-temperature end face 23b Low-temperature end face

Claims (2)

EGR of an internal combustion engine that is provided in an EGR device of an internal combustion engine that circulates exhaust gas of the internal combustion engine as EGR gas from the exhaust side to the intake side, and that circulates the EGR gas inside and exchanges heat with cooling water for cooling. In the cooler
An EGR gas flow path in which the EGR gas is circulated in a cylindrical shape having a rectangular cross section;
Thermoelectric elements that are arranged so that the high temperature end faces are in close contact with the four outer surfaces of the EGR gas flow path, and generate a thermoelectromotive force using a temperature difference between the low temperature end faces;
It is arranged so as to wrap around the EGR gas flow path in a cylindrical shape along the EGR gas flow path, and the cooling water is circulated in a space formed between the inside and the low temperature end face of each thermoelectric element An EGR cooler for an internal combustion engine, comprising: a cooling water flow path.   The thermoelectric element is divided into a plurality in the flow direction of the EGR gas, and the upstream thermoelectric element has a higher conversion when the temperature difference between the high temperature end surface and the low temperature end surface is larger than the upstream thermoelectric element. 2. An EGR cooler for an internal combustion engine according to claim 1, wherein the characteristics are set so as to exhibit efficiency.

Images