JP2002004952A - EGR cooler - Google Patents

Abstract

(57) [Problem] To provide an EGR cooler which suppresses the development of a boundary layer due to a decrease in flow velocity on the outlet side of an EGR gas passage in an EGR cooler and improves temperature efficiency. An EG is provided in an EGR passage of an engine.
EGR arranged to allow heat exchange between R gas and cooling medium
In the cooler, the EGR disposed in the EGR cooler 1
The gas passage is constituted by a plurality of pipes 3, and ridges 3c protruding inside each pipe 3 are continuously provided in the circumferential direction, and the height of the ridges 3c is set from the inlet 3a side of the EGR gas to the outlet 3b side. This is a configuration formed by gradually increasing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an EGR cooler for efficiently cooling EGR gas.

[0002]

2. Description of the Related Art NOx in exhaust gas is generated when nitrogen and oxygen in the air-fuel mixture are combined at a high temperature when the air-fuel mixture burns. Therefore, by lowering the combustion temperature, N
Ox can be reduced. As one of the methods for reducing NOx in exhaust gas, exhaust gas recirculation (Exhaust
There is a Gas Recirculation (hereinafter referred to as "EGR") device. In this EGR device, a part of the burned exhaust gas is introduced into the suction side to slow down the combustion to lower the maximum combustion temperature to reduce the generation of NOx.

By the way, exhaust gas (hereinafter referred to as "EGR gas")
As described above, NOx is reduced as described above, but the amount of fresh air is reduced accordingly, resulting in insufficient oxygen and PM (harmful particulate matter) such as smoke and HC. There is a problem of increasing. In order to reduce the PM, it is necessary to reduce the temperature of the EGR gas introduced to the intake side to reduce the volume, and to increase the intake air amount of fresh air accordingly. That is, in order to reduce NOx while suppressing PM in the exhaust gas by the EGR device, it is necessary to lower the temperature of the EGR gas introduced to the intake side.

Therefore, in recent years, EGR coolers have
Techniques for suppressing PM by cooling gas and reducing NOx have been implemented. The EGR cooler includes a plurality of EGR gas passages for passing EGR gas and a cooling medium (cooling water) for cooling the EGR gas in these passages, and communicates an exhaust passage of the engine with an intake passage. The exhaust gas is interposed in an EGR gas passage that introduces a part of the exhaust gas to the intake side, and heat exchange between the EGR gas and the cooling medium is enabled to cool the EGR gas.

However, since the temperature of the EGR gas is significantly different between the inlet side and the outlet side of the EGR cooler, the gas flow rate difference between the inlet side and the outlet side is large (for example, the inlet side gas temperature is about 400 ° C., the outlet side Since the gas temperature is about 100 ° C. and the gas flow rate on the outlet side is about の of the gas flow rate on the inlet side), the cross-sectional area of the conduit is such that the inlet side and the outlet side have the same passage area. In this case, even if the gas flow rate on the inlet side is high, the gas flow rate on the outlet side is low, so that a boundary layer is generated, which tends to be a laminar flow, and the temperature efficiency (cooling efficiency) is reduced.

In order to solve such a problem, for example, there is an EGR gas cooling device disclosed in Japanese Patent Application Laid-Open No. H11-108578. In this EGR gas cooling device, a plurality of EGR gas passages constituting an EGR gas passage are replaced with a normal tube having a smooth inner surface (smooth tube) as a spiral tube provided with a spiral ridge therein. This is to improve the temperature efficiency by shortening the boundary layer of the EGR gas generated inside.

[0007]

However, in the EGR gas cooling device using the spiral tube,
Since the intervals (pitch) of the spiral ridges are formed at equal intervals from the inlet side to the outlet side, it is not possible to sufficiently cope with the development of the boundary layer on the outlet side having a low flow velocity, and the temperature efficiency is not improved. There is a problem that the improvement width is not sufficient.

For this reason, the present invention suppresses the development of the boundary layer due to a decrease in the flow velocity at the exit side of the EGR gas passage in the EGR cooler, thereby improving the temperature efficiency.
It is intended to provide a cooler.

[0009]

In order to achieve the above object, according to the first aspect of the present invention, the EGR gas flowing through the pipeline is cooled by the cooling medium, and the flow velocity gradually decreases.
The turbulent flow of the EGR gas flowing through the pipeline is promoted by the ridge formed so as to protrude inside the pipeline, and the development of the boundary layer is prevented. Since the height of the ridge gradually increases toward the outlet side where the flow velocity is slowed, the turbulence is further promoted and the development of the boundary layer of the EGR gas on the downstream side where the flow velocity is slow is further prevented. Thus, the EGR gas flowing in the pipeline is brought into good contact with the inner surface of the pipeline and cooled, thereby improving the temperature efficiency. EGR gas cooled by the EGR cooler is supplied to the intake side of the engine.

[0010] According to the second aspect of the present invention, the EG flowing in the pipeline is provided.
The turbulent flow of the R gas is protruded by the ridge formed so as to protrude inside the pipe, so that the boundary layer is prevented from developing. The arrangement interval (pitch) of the ridges gradually narrows toward the outlet side where the flow velocity is slowed, so that turbulence is further promoted and the development of the boundary layer of the EGR gas on the downstream side where the flow velocity is slow is further prevented. You.

According to the third aspect of the present invention, the EG flowing in the pipeline is provided.
The R gas flows so as to be entangled by the plurality of projections formed to protrude inside the pipeline, turbulence is promoted, and the development of the boundary layer is prevented. The number of the protrusions gradually increases toward the outlet side where the flow velocity is slowed, so that the turbulence is further promoted and the development of the boundary layer of the EGR gas on the downstream side where the flow velocity is slow is further prevented.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be illustratively described in detail below with reference to the drawings. (Embodiment 1) FIG. 1 is a sectional view of an EGR cooler according to the present invention, and FIG. 2 is a sectional view taken along the line II-II of FIG.

As shown in FIGS. 1 and 2, an EGR cooler 1 includes a cylindrical case 2, a plurality of conduits 3 as EGR gas passages housed in the case 2, and a case 2.
And supporting plates 4 and 5 for supporting each pipe 3 and baffle plates 6 and 7. One end 2a of the case 2 serves as an inlet for EGR gas (hereinafter referred to as “inlet 2a”), and the other end 2b serves as an outlet for EGR gas (hereinafter referred to as “outlet 2b”). Both ends of each conduit 3 are respectively provided with holes 4a, 5a formed in support plates 4, 5, respectively.
a, and the outer peripheral portions of the support plates 4 and 5 are fixed to the inner peripheral surface of the case 2 in a liquid-tight manner. An EGR gas chamber 11 is formed between the EGR gas inlet 2a and the support plate 4, and an EGR gas chamber 12 is formed between the support plate 5 and the EGR gas outlet 2b.
Are open to these gas chambers 11 and 12.

The baffle plates 6 and 7 each have a substantially semicircular shape, are arranged at substantially equal intervals between the support plates 4 and 5, and the arc-shaped outer peripheral portion is liquid-tightly fixed to the inner peripheral surface of the case 2. Have been. The baffle plate 6 on one side includes a plurality of conduits 3.
And the other half baffle plate 7 inserts each of the conduits 3 on the other half of the plurality of conduits 3 into the respective holes 7a. It is supported by being inserted in a liquid-tight manner.

A cooling water inlet 8 serving as a cooling medium is provided on one side of the outer peripheral surface of the case 2 so as to open between the support plate 5 and the baffle plate 7, and a cooling water outlet 9 is provided on the other side of the outer peripheral surface. Is provided between the support plate 4 and the baffle plate 6 so as to open. Then, the cooling water flowing from the cooling water inlet 8 flows from the space between the support plate 5 and the baffle plate 7 to the baffle plates 7 and 6 as shown by arrows.
And flows out from the outlet 9 through the space between the baffle plate 6 and the support plate 4 to cool the outer peripheral surface of each pipe 3.

As shown in FIG. 3, the pipe 3 has a ridge 3c protruding inward from an EGR gas inlet 3a.
It is formed continuously at a predetermined interval (pitch) in a spiral shape in the circumferential direction up to the outlet 3b of the R gas, and the protrusion height is gradually increased from the inlet 3a to the outlet 3b, that is, formed so as to gradually increase. Have been. This EGR cooler 1
EGR passage (not shown) of the engine
The gas inlet 2a is connected to the exhaust gas passage side (upstream side) of the engine, and the EGR gas outlet 2b is connected to the intake passage side (downstream side) of the engine. Further, a cooling water inlet 8 and a cooling water outlet 9 are respectively interposed and connected to the cooling water passage.

The operation will be described below. Part of the exhaust gas discharged into the exhaust gas passage of the engine is introduced into the gas chamber 11 of the EGR cooler 2 through the EGR gas passage. The high-temperature, high-speed EGR gas introduced into the gas chamber 11 is distributed to each pipe 3, flows through these pipes 3, and reaches the gas chamber 12. On the other hand, the cooling water that has flowed into the case 2 from the cooling water inlet 8 flows as shown by the arrows and cools the EGR gas flowing through each pipe 3. The cooling water flows from the outlet 3b side of the EGR gas toward the inlet 3a side of the outer circumference of each pipe 3 so that the EGR gas flowing in the pipe 3 can be cooled well.

The EGR gas flowing through the pipe 3 is cooled by the cooling water and its flow velocity gradually decreases, so that the flow velocity at the outlet 3b side is about half of the flow velocity at the inlet 3a side. Line 3
The turbulent flow of the EGR gas flowing inside is promoted by the ridges 3c formed to protrude inside the pipeline 3, and the development of the boundary layer is prevented. Moreover, the ridges 3c gradually increase toward the outlet 3b side where the flow velocity is slowed, so that the turbulence is further promoted and the development of the boundary layer of the EGR gas on the downstream side where the flow velocity is slow is further prevented. Thereby, the EGR gas flowing in the pipeline 3 is cooled in good contact with the inner surface of the pipeline 3, and the temperature efficiency (cooling efficiency) is improved. Each pipeline 3
The EGR gas cooled by the gas is supplied to the gas chamber 1 through the outlet 3b.
2 and is further supplied from an EGR gas outlet 2b to an intake passage of the engine.

Since the EGR gas is cooled well by the EGR cooler 1, the volume introduced to the intake side of the engine is reduced, and the amount of fresh air taken into the engine is increased. As a result, a large amount of low temperature EGR
It is possible to appropriately control the gas, and it is possible to further suppress NOx while suppressing an increase in PM. In the above embodiment, the ridge 3c protruding inside the pipe 3 is used.
Is described as a case where the spiral is continuously formed in the circumferential direction from the inlet 3a to the outlet 3b of the EGR gas. However, the present invention is not limited to this.
The protrusions may be formed at predetermined intervals from the inlet 3a to the outlet 3b, and the height of each ridge may be gradually increased (increased) from the inlet 3a to the outlet 3b. (Embodiment 2) FIG. 4 shows a second embodiment of the EGR gas pipeline. In the figure, an EGR gas pipeline 15 has a ridge 15c protruding inward from an EGR gas inlet 15a to an outlet 1a.
The spiral is continuously formed in the circumferential direction up to 5b, and the interval (pitch) is formed so as to be gradually narrowed (gradually reduced) from the inlet 15a to the outlet 15b. As a result, the EGR due to the decrease in the flow velocity at the outlet 15b side
The development of the boundary layer of gas is prevented, and the temperature efficiency is improved.

In the above-described embodiment, the case where the ridge 15c protruding inside the conduit 3 is formed in a spiral shape continuously in the circumferential direction from the inlet 15a to the outlet 15b of the EGR gas has been described. The present invention is not limited to this, and is formed in an annular shape that is continuous in the circumferential direction, and the interval is formed so as to be gradually narrowed from the inlet 15a to the outlet 15b, and the height of each ridge is gradually increased from the inlet 15a to the outlet 15b. May be formed to be higher. (Embodiment 3) FIG. 5 shows a third embodiment of the EGR gas pipeline. In the figure, the EGR gas pipeline 16 is formed such that its inner diameter is gradually reduced (gradually reduced) from the inlet 16a side to the outlet 16b side, and a ridge 16c protruding inward is formed.
It is formed spirally at predetermined intervals continuously in the circumferential direction from the inlet 16a to the outlet 16b. As described above, by reducing the diameter of the pipe on the downstream side where the flow velocity decreases, the development of the boundary layer can be further prevented.

In the above-described embodiment, the interval between the protrusions 16c is formed at a constant interval. However, the present invention is not limited to this. The interval (pitch) from the inlet 16a to the outlet 16b as in the second embodiment. It may be formed so as to be gradually narrowed (gradually reduced). (Embodiment 4) FIG. 6 shows a fourth embodiment of the EGR gas pipeline. In the figure, the gas pipeline 17 is provided with a plurality of inwardly projecting projections 17c, and the number of the projections 17c is E.
The GR gas is formed so as to gradually increase (increase gradually) from the inlet 17a to the outlet 17b of the GR gas. These projections 17c act to engulf the EGR gas flowing in the pipeline 17 to the back side, whereby the development of the boundary layer of the EGR gas due to the decrease in the flow rate at the outlet 17b side is favorably prevented, and the temperature efficiency is reduced. Improvement is achieved.

In the above embodiment, the heights of the projections 17c are the same. However, the height is not limited to this, and the height of the projections 17c is gradually increased toward the outlet side. Is also good. Further, a ridge similar to that of the first to third embodiments may be provided inside the conduit 17. Further, the ridge may be formed in a spiral shape that is continuous in the circumferential direction from the inlet 17a to the outlet 17b, and may be formed so that its height gradually increases from the inlet 3a to the outlet 3b. Alternatively, the ridges may be arranged so as to be gradually narrowed from the inlet 17a to the outlet 17b. Further, the ridges are formed in a continuous annular shape in the circumferential direction, and the interval is gradually narrowed from the inlet 17a to the outlet 17b. May be arranged. (Embodiment 5) FIG. 7 shows a fifth embodiment of the EGR gas pipeline. In the figure, a pipe 18 has a ridge 18 projecting inward.
c is formed spirally at a predetermined pitch continuously in the circumferential direction from the inlet 18a to the outlet 18b, and is formed so that the protrusion height gradually increases from the inlet 18a to the outlet 18b. The fin 1 is located in the pipe 18.
9 are inserted over the entire length. The fins 19 are formed by spirally twisting a strip-shaped thin plate, and are formed such that the pitch gradually narrows from the inlet 18a to the outlet 18b of the conduit 18. Thus, the EGR gas flows along the fins 19 and is turbulent by the ridges 18c, thereby preventing the boundary layer from developing due to a decrease in the flow velocity at the outlet 18b side, thereby improving the temperature efficiency.

FIG. 8 is a graph showing an example in which the performance of the EGR cooler is compared, showing the EGR gas flow rate and the amount of heat exchanged with the cooling medium (cooling water). In the figure, the solid line I is EGR
The characteristics of a conventional EGR cooler using a normal pipe (smooth pipe) as a plurality of gas pipes in the cooler, and the solid line II shows the characteristics of a conventional EGR cooler using a spiral pipe as a gas pipe. The solid line III shows the characteristics of the EGR cooler to which the pipeline shown in the first embodiment of the present invention is applied, and the solid line IV shows
13 shows the characteristics of an EGR cooler to which the pipeline shown in the fifth embodiment is applied. As is clear from FIG. 8, the EGR cooler of the present invention can improve the temperature efficiency as compared with the EGR cooler of the conventional structure.

[0024]

As described above, according to the present invention, a plurality of Es in an EGR cooler interposed in an EGR passage of an engine and arranged to exchange heat between an EGR gas and a cooling medium are provided.
The development of the boundary layer due to the decrease in the flow velocity of the EGR gas flowing through the GR gas passage at the outlet side can be prevented, the temperature efficiency by the cooling medium can be improved, and the large amount of low-temperature EGR gas can be appropriately controlled. And suppresses an increase in harmful particulate matter (PM) contained in exhaust gas,
x can be further suppressed.

[Brief description of the drawings]

FIG. 1 is a sectional view of an EGR cooler according to the present invention.

FIG. 2 is a cross-sectional view of the EGR cooler shown in FIG. 1, taken along the line II-II.

FIG. 3 is a sectional view of Example 1 of the EGR gas passage shown in FIG.

FIG. 4 is a sectional view of a second embodiment of the EGR gas passage shown in FIG. 1;

FIG. 5 is a sectional view of a third embodiment of the EGR gas passage shown in FIG. 1;

FIG. 6 is a cross-sectional view of Embodiment 4 of the EGR gas passage shown in FIG.

FIG. 7 is a sectional view of Example 5 of the EGR gas passage shown in FIG. 1;

FIG. 8 is a graph showing an example comparing the performance of a conventional EGR cooler and the performance of an EGR cooler of the present invention.

[Explanation of symbols]

 1 EGR cooler 2 Case 3, 15, 16, 17, 18 Pipe line (EGR gas passage) 4, 5 Support plate 6, 7 Baffle plate 19 Fin

Claims (3)

[Claims] 1. An EG mounted in an EGR passage of an engine.
EGR arranged to allow heat exchange between R gas and cooling medium
In the cooler, an EGR gas passage provided in the EGR cooler is constituted by a plurality of pipes, and ridges protruding inside each of the pipes are continuously provided in a circumferential direction, and a height of the ridges is increased. Characterized by being gradually increased from the inlet side to the outlet side of the EGR gas. 2. An engine control device, which is interposed in an EGR passage of an engine,
EGR arranged to allow heat exchange between R gas and cooling medium
In the cooler, an EGR gas passage provided in the EGR cooler is constituted by a plurality of pipes, and ridges protruding inside each of the pipes are continuously provided in a circumferential direction, and an arrangement interval of the ridges is provided. Is gradually reduced from the inlet side to the outlet side of the EGR gas. 3. An EG mounted in an EGR passage of an engine.
EGR arranged to allow heat exchange between R gas and cooling medium
In the cooler, an EGR gas passage provided in the EGR cooler is constituted by a plurality of pipes, and a plurality of projections projecting inside each of the pipes is provided, and the number of the projections is increased from the inlet side of the EGR gas. An EGR cooler characterized by being formed so as to gradually increase toward an outlet side.