JP2006348873A - Egr cooler - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an EGR cooler having improved collecting efficiency while preventing the deposition of unburnt components without the need for special facilities. <P>SOLUTION: The EGR cooler 26 cools part of exhaust gas from an internal combustion engine 100 and recirculates it as EGR gas into intake air I for cooling operation in an EGR device. It comprises a solvent coat T coating a wall face S of a passage 38 for the EGR gas G. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an EGR cooler used in an EGR device for an internal combustion engine.

The EGR device is a device that cools a part of the exhaust gas from the internal combustion engine to an appropriate temperature and recirculates it to the intake system, and the EGR cooler is a heat exchanger for performing the above cooling. The recirculated exhaust gas (EGR gas) is a burned gas, and most of it is an inert gas (H ₂ O, N ₂ , CO _2, etc.). Since the maximum combustion temperature is lowered by the heat capacity of the active gas, NOx is reduced.

  However, the EGR gas contains a small amount of unburned fuel, which is condensed and liquefied in the EGR cooler and adheres as a continuous liquid film to the wall of the EGR gas passage of the EGR cooler. Adheres and accumulates. As a result, the passage wall surface, which is a heat transfer surface with the EGR gas, is covered with the adhesion / deposition layer, and the cooling performance of the EGR cooler is deteriorated. At the same time, similar adhesion / deposition occurs on the EGR valve at the inlet of the intake system on the downstream side of the EGR cooler, causing malfunction of the valve.

  As a countermeasure, Patent Document 1 proposes that plasma is generated by discharge in exhaust gas to oxidatively decompose unburned components. However, this requires a large-scale plasma generator and lacks practicality.

  Patent Document 2 proposes oxidizing and removing the soot adhering in the EGR cooler. However, this method is also disadvantageous in practice because it requires special incidental equipment.

JP 2004-340048 A JP 2003-336549 A

  An object of the present invention is to provide an EGR cooler that eliminates the above-mentioned drawbacks of the prior art and prevents the adhesion of unburned components and improves the recovery efficiency without requiring special equipment.

In order to achieve the above object, an EGR cooler according to the present invention is an EGR cooler that performs the above cooling in an EGR device that cools a part of exhaust gas of an internal combustion engine and recirculates it as EGR gas to the intake side.
An oil repellent film is coated on the wall surface of the EGR gas passage.

  Since the oil repellent coating is coated on the wall surface of the EGR gas passage, the oil component condensed and liquefied by contact with the wall surface becomes droplets without spreading in the form of a liquid film, and immediately falls from the wall surface by gravity and leaves. Therefore, the wall surface is not always covered with a liquid film as in the prior art, and is always exposed, and the effective action is maintained as a heat transfer surface for EGR gas. In this way, the mechanism of unburned components in EGR gas → droplet generation → falling / leaving is stably maintained on the wall surface of the EGR gas passage, so that no adhesion or deposition of liquid film or soot occurs, and the EGR cooler The cooling performance is maintained well.

  Moreover, since the liquefied high temperature oil component is isolate | separated from EGR gas, the fall of EGR gas temperature is accelerated | stimulated.

  In the EGR cooler of the present invention, it is desirable to provide oil collecting means including unburned fuel downstream from the passage coated with the oil repellent coating.

  Thereby, it is possible to easily prevent the oil component in which the unburned component has been liquefied from returning to the intake system.

In one exemplary embodiment of the EGR cooler of the present invention,
An EGR gas inlet connected to the tip of the intake passage branched from the exhaust passage upstream of the turbocharger,
The EGR gas outlet connected to the start end of the supply flow path that guides the cooled EGR gas separated from the unburned fuel-containing oil, and the unburned fuel-containing oil collected by the collecting means to the turbo An oil passage for joining the exhaust passage downstream of the charger;
It has.

  The upstream side of the turbocharger that is the EGR gas intake part to the EGR cooler has a higher gas pressure than the downstream side of the turbocharger that is the part that collects oil liquefied by the EGR cooler. Thus, the collected oil can be supplied to the DPNR downstream of the turbocharger as part of the rich spike additive fuel.

  An embodiment of the EGR cooler of the present invention will be described with reference to FIGS. 1 and 2.

  FIG. 1 schematically shows a system in which an EGR system including an EGR cooler of the present invention and a DPNR catalyst are combined with a common rail direct injection diesel engine, and FIG. 2 shows a preferred embodiment of the EGR cooler of the present invention. Indicates.

  In the diesel engine 100 shown in FIG. 1, after the inflow air I taken in via the inflow air amount sensor 10 shown at the left end of the figure passes through the intercooler 12 and the intake control valve 14 as shown by the arrow, the fuel line 16 Is mixed with the fuel from the fuel and injected into each combustion chamber 18, and the generated exhaust E is discharged through the turbocharger 20 and the DPNR 22.

  A part of the exhaust gas is branched upstream of the turbocharger 20 and flows as EGR gas G from the EGR gas inlet 24 to the EGR cooler 26, and after cooling, flows out from the EGR gas outlet 28, and the upper EGR valve 30. To the intake air I.

  The unburned fuel-containing oil component separated and collected from the EGR gas G in the EGR cooler 26 passes downstream of the turbocharger 20 via an oil passage 32 branched from before the EGR gas outlet 28 of the EGR cooler 26. Merge into the exhaust stream.

  From the additive injector 34, rich spike additive fuel for the DPNR 22 is injected into the exhaust, and unburned fuel joined into the exhaust through the oil passage 32 is added thereto.

  In the above description, the EGR gas G is taken in from the exhaust upstream of the turbocharger 20 and the unburned fuel (light oil) is supplied to the exhaust downstream of the turbocharger 20 because the high gas pressure upstream of the turbocharger 20 is taken over. This is because the supply of light oil can be promoted by utilizing the pressure difference between the relatively high pressure EGR cooler 26 and the low gas pressure of the exhaust gas downstream of the turbocharger 20.

  The EGR cooler 26 according to a preferred embodiment of the present invention shown in the longitudinal cross-sectional view of FIG. 2A is composed of a tube 36 as a whole, and the EGR gas G flows from the right end inlet 24 and flows to the left end. It flows out from the outlet 28. A large number of EGR gas passages 38 are arranged in parallel inside the tube body 36, and each passage 38 is water cooled by a water cooling jacket 40. The EGR gas passage 38 is formed by a pipe member 38P.

  As a feature of the present invention, the oil repellent coating T is coated on the wall surface S of the EGR gas passage 38 as shown in the partially enlarged sectional view of FIG. For convenience of illustration, the oil-repellent coating T is drawn extremely thick, but since it is actually thinner than the thickness of the outline in the figure, it does not hinder heat transfer between the passage wall surface S and the EGR gas G.

  When the EGR gas G flowing into the EGR cooler 26 from the inlet 24 passes through the passage 38, it is cooled by the water-cooled wall surface S as the heat transfer surface, and the light oil component that is unburned fuel in the EGR gas G is liquefied by condensation. And deposited on the passage wall surface S. Since the oil repellent coating T is coated on the passage wall surface S according to the present invention, the deposited oil liquid does not spread as an oil film on the wall surface S but becomes oil droplets, and immediately slides off from the wall surface S due to gravity. Therefore, the passage wall surface S as the heat transfer surface is always kept in an exposed state without being covered with the oil film, and the high cooling performance of the EGR cooler 26 is always ensured.

  Further, as an additional cooling effect, the oil liquid having an overwhelmingly large heat capacity as compared with the gas is efficiently separated at a high temperature and with a large amount of heat, thereby promoting the cooling of the EGR gas G.

  Further, since the passage wall surface S does not get wet with the oil solution, soot does not adhere and accumulate, and the deterioration of the wall surface S due to this does not occur.

  The oil droplets that have slid down from the wall surface S of the EGR gas passage 38 are collected in the oil pit 42 downstream of the passage 38, flow into the oil passage 32, and are guided to the downstream exhaust of the turbocharger 20.

  As described above, the EGR cooler 26 is inclined with respect to the horizontal plane H by an appropriate angle θ in order to facilitate the sliding of the oil droplets and the progress to the pit 42.

  A plurality of perforated plates 44 having a large number of through holes are arranged on the upstream side and immediately downstream side of the oil pit 42 with respect to the traveling direction of the EGR gas G so as to block the progress of the EGR gas G. Thus, oil collecting means such as unburned fuel is constituted. This is to prevent the oil droplets deposited in the passage 38 from splashing and riding on the flow of the EGR gas G to advance to the intake system, and to collect efficiently.

  It is desirable that the surface of the porous plate 44 is also coated with an oil repellent coating. As a result, the droplets of the oil trapped on the porous plate 44 do not spread as an oil film on the surface of the porous plate 44 but are immediately slid to the pits 42 as oil droplets, thereby increasing the recovery efficiency. Further, if the oil film adheres to the surface of the perforated plate 44, there is a possibility that the EGR gas G flows again and proceeds to the intake system.

  Adjacent perforated plates 44 are preferably produced and / or arranged so that the positions of the holes P are shifted from each other. This prevents the oil droplets from passing through the oil collecting means composed of a plurality of perforated plates 44 and increases the fuel recovery efficiency.

  FIG. 3 shows an example of a preferred embodiment of the porous plate 44. 3A is a plan view, and FIG. 3B is a cross-sectional view taken along line II-II in FIG.

  The desirable perforated plate 44 shown in FIG. 3 is burred as indicated by B around the through hole P. The oil droplet Q trapped in the perforated plate 44 is blocked by the burring B when it slides down on the plate surface of the perforated plate 44 and bypasses the periphery of the through hole P, so that it does not fall into the through hole P. As a result, the oil splash once trapped in the perforated plate 44 is prevented from traveling again to the intake system through the through hole P, and the recovery efficiency is increased.

  FIG. 4 shows a longitudinal cross-sectional view of an EGR cooler according to another preferred embodiment of the present invention. The parts corresponding to those in the embodiment of FIG.

  The EGR cooler 26 ′ shown in FIG. 4 is provided with water cooling fins 46 on the upstream side and downstream side of the passage 38, with the position of the oil pit 42 interposed therebetween. Different from the EGR cooler 26 of FIG. Regarding other configurations, the embodiment of FIG. 4 and the embodiment of FIG. 2 are common. The water cooling fins 46 are internally water cooled by a water cooling jacket 48. The two water-cooled fins 46 extend in the direction opposite to the traveling direction of the EGR gas G to form a zigzag gas path. As a result, the flow of the EGR gas G collides with the fins 46 and is cooled, and the residual unburnt fuel that has not deposited in the passage 38 is condensed here and deposited as an oil liquid, and falls into the oil pit 42.

  Also in this case, it is desirable that the surface of the fin 46 is covered with an oil repellent coating. Thereby, the oil liquid deposited on the surface of the fin 46 does not spread as an oil film but forms oil droplets and immediately slides down. As a result, the residual oil is prevented from proceeding to the intake system, and the recovery efficiency is increased.

  FIG. 5 shows an example of a preferred embodiment of the water cooling fin 46. Of the two water-cooled fins 46A and 46B, the downstream water-cooled fin 46B has a folded back 50 formed at the extending tip, making it difficult for oil droplets Q deposited from the EGR gas G to be taken away by the gas flow. It is. This further prevents the residual oil from proceeding to the intake system and increases the recovery efficiency.

  ADVANTAGE OF THE INVENTION According to this invention, the EGR cooler which prevented adhesion of an unburned component and improved collection | recovery efficiency is provided, without requiring special equipment.

FIG. 1 is a layout diagram showing a typical configuration example of a diesel engine equipped with an EGR cooler of the present invention. FIG. 2 is (1) a sectional view and (2) a partially enlarged sectional view showing an example of an EGR cooler according to a preferred embodiment of the present invention. 3 is a (1) plan view and (2) a cross-sectional view showing a preferred embodiment of a porous plate as an oil collecting means in the EGR cooler of FIG. FIG. 4 is a cross-sectional view illustrating an example of an EGR cooler according to another preferred embodiment of the present invention. FIG. 5 is a cross-sectional view showing a preferred embodiment of water-cooled fins as oil collecting means in the EGR cooler of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Diesel engine I Inflow air, intake air G EGR gas S Wall surface of EGR gas passage T Oil-repellent coating 10 Inflow air amount sensor 12 Intercooler 14 Intake control valve 16 Fuel line 18 Combustion chamber 20 Turbocharger 22 DPNR
24 EGR gas inlet 26 EGR cooler 28 EGR gas outlet 30 EGR valve 32 Oil passage 34 Additive injector 36 Tubing body 38 EGR gas passage 38P Pipe member 40 Water cooling jacket 42 Oil pit 44 Perforated plate 46, 46A, 46B Water cooling fin 48 Water cooling jacket 50 folded

Claims (3)

In an EGR cooler that performs the above cooling in an EGR device that cools a part of the exhaust gas of the internal combustion engine and recirculates it as EGR gas to the intake side.
An EGR cooler characterized in that an oil repellent film is coated on the wall surface of the EGR gas passage.   2. The EGR cooler according to claim 1, wherein means for collecting oil containing unburned fuel is provided downstream of the passage coated with the oil repellent coating. In claim 2,
An EGR gas inlet connected to the tip of the intake passage branched from the exhaust passage upstream of the turbocharger,
The EGR gas outlet connected to the start end of the supply flow path that guides the cooled EGR gas separated from the unburned fuel-containing oil, and the unburned fuel-containing oil collected by the collecting means to the turbo An oil passage for joining the exhaust passage downstream of the charger;
An EGR cooler characterized by comprising:

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