JPH10185489A - Egr gas cooler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance corrosion resistance of EGR gas circulation system components of an EGR gas cooler where an end cap is provided with EGR gas flow-in port and flow-out port and cooling medium flow-in port and flow-out port are secured to the outer circumferential surface of a duct by providing a thermal insulation means on the outer circumferential surface on the flow-in side and/or flow-out side of EGR gas flow. SOLUTION: The EGR gas cooler comprises a group of heating tubes 12 arranged in a duct while being bonded thereto and a thermal insulation means comprising sleeves 15a, 15b is provided on the outer circumferential surface on the EGR gas flow-in side and/or flow-out side of the heating tube 12. The thermal insulation means is disposed tightly to the outer circumferential surface of the heating tube 12 or spaced apart therefrom in the radial direction. High temperature EGR gas flowing into the heating tube 12 prevents bubbles from adhering to the outer surface of the heating tube 12 to cause lowering of heat-exchange rate and to prevent generation of mist or droplet on the EGR gas flow-out side. Consequently, the inner circumferential surface of the heating tube 12 and the components of EGR gas piping system are protected against corrosion due to adhesion of a corrosive substance resulting in smooth operation of an engine.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for cooling an EGR gas by a cooling medium such as a cooling liquid for an engine, a refrigerant for an intercooler, a refrigerant for a car air conditioner, or a cooling air. Is a liquid such as an engine coolant, it is possible to prevent the generation of bubbles due to boiling on the outer surface of the heat transfer tube on the inlet side due to a high temperature and high flow rate of EGR gas exceeding the cooling capacity. EGR that is prevented from deteriorating in performance and increases the heat exchange rate, and that is excessively cooled in the heat transfer tube by a cooling medium.
The present invention relates to an EGR gas cooling device that prevents the formation of corrosive substances due to the condensation of moisture in a gas, thereby improving the durability of components of an EGR gas circulation system and smoothing the operation of an engine. It is.

[0002]

2. Description of the Related Art A method of extracting a part of exhaust gas from an exhaust system, returning the exhaust gas to an intake system of an engine, and adding the exhaust gas to an air-fuel mixture is based on an EGR (Exhaust Gas Recircucu).
ration: exhaust gas recirculation). EGR is NO
x (nitrogen oxide) generation suppression, pump loss reduction, heat radiation loss to cooling fluid due to combustion gas temperature decrease, increase in specific heat ratio due to changes in working gas amount and composition, and cycle efficiency accompanying this Therefore, it is considered to be an effective method for purifying the exhaust gas of the engine and improving the thermal efficiency as well as many other effects.

[0003] However, when the temperature of the EGR gas increases, the durability of the EGR valve and the like deteriorates due to a decrease in fuel efficiency due to a rise in the intake air temperature and its thermal action, which may lead to early breakage or to prevent such a problem. It is known that the EGR valve itself needs to have a water cooling structure. In order to avoid such a situation, a device that cools the EGR gas by using an engine coolant or the like is used. As this device, a multi-tube heat exchanger is mainly used. In some cases, these heat exchangers may be used in combination with a tube heat exchanger or a multi-tube heat exchanger.

The present applicant has proposed Japanese Patent Application No. 7-267691 as an EGR gas cooling device using a multi-tube heat exchanger. In this apparatus, as shown in FIG. 7, a plurality of heat transfer tubes 12 are fixedly arranged on tube sheets 3a and 3b fixed to the inner wall of the body tube 11 at both ends of the body tube 11. EGR gas inlet 14a and EG
This is a multi-tube EGR gas cooling device provided with an R gas outlet 14b, and further provided with a cooling medium inlet 6a in the body tube 11 itself.
And a cooling medium outlet 6b.
The branch pipes 7a and 7b are joined directly to the cooling medium outlet 6b by brazing or welding. Reference numeral 10 denotes a baffle plate provided as needed, which is provided to increase the heat exchange efficiency by meandering the cooling medium flowing into the body tube 11 to increase the contact time with the heat transfer tube 12. In FIG. 7, solid arrows indicate the flow of the cooling medium, and dotted arrows indicate the flow of the EGR gas. It should be noted that the flow of the cooling medium may be in the opposite direction to the solid arrow.

[0005] However, this Japanese Patent Application No. Hei 7-267691
The EGR gas cooling device proposed in the above-mentioned publication has an extremely high temperature EGR gas flowing into a tube constituting a heat transfer tube group, and is cooled by heat exchange with a cooling medium through the tube. Was recirculated to the intake system of the engine.

The EGR gas is extremely high in temperature as described above. However, when the cooling medium is a liquid, especially when the engine is rotating at a high speed and under a high load, the EGR gas cooling device has an EGR gas inflow side. A high temperature and high flow rate of EGR gas exceeding the cooling capacity of the heat transfer tube flows into the heat transfer tube, and this heat is transferred to the outer surface of the heat transfer tube on the inflow side of the EGR gas, and the outer surface also becomes extremely hot, so that it comes into contact with the outer surface Since the coolant partially boiled to form bubbles, which grow to form a layer of bubbles widely on the outer surface of the heat transfer tube, an effective heat transfer area (coolant and outer surface of the heat transfer tube) The area of the heat transfer effect) due to the contact with the EGR gas, and the heat exchange rate is reduced, so that the temperature at the outlet side of the EGR gas is greatly increased.

On the other hand, EGR recirculated from the exhaust system of the engine to the intake system of the engine via the EGR gas cooling device
The gas contains a sulfurous acid gas and a nitrous acid gas which are compositions of the exhaust gas. When the EGR gas is excessively cooled by the cooling medium, moisture in the EGR gas is condensed to generate mist and small droplets. As a result, the EGR gas that has been excessively cooled by the EGR gas cooling device becomes mist or small droplets due to condensation of moisture in the gas, and the sulfurous acid gas or nitrous acid gas in the EGR gas is converted into the mist or small droplets. As a result, sulfuric acid and nitrous acid are produced, and these are oxidized to produce sulfuric acid, nitric acid, or a strong acid as a mixed acid obtained by mixing them. The strong acid composed of sulfurous acid and nitrous acid generated in this way corrodes the inner peripheral surfaces of heat transfer tubes and EGR piping, as well as engine parts such as cylinders, piston rings, and intake valves, and also causes engine operation. The result is a lack of smoothness.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conflicting difficulties by slightly changing the components.
The high temperature and high flow rate of EGR gas that exceeds the cooling capacity flowing into the gas cooling device prevents the generation and growth of bubbles due to boiling on the outer surface of the heat transfer tube, and the cooling of the EGR gas flowing into the EGR gas cooling device. This prevents the water in the gas from condensing in the heat transfer tube due to excessive cooling by the medium to generate corrosive substances, thereby improving the durability of the components of the EGR gas circulation system against corrosion and improving the engine performance. It is an object of the present invention to provide an EGR gas cooling device whose operation is smooth.

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a heat transfer tube group fixedly arranged inside a body tube, and an end cap fixed to at least one end of the body tube.
In an EGR gas cooling apparatus having a GR gas inlet and an outlet, and further having an inlet and an outlet for a cooling medium fixed to an outer peripheral surface near an end of the body tube, the EGR gas of the heat transfer tube flows in Insulating means is provided on the outer peripheral surface on the side and / or on the outflow side, and the insulating means comprises at least one sleeve, and is in close contact with the outer peripheral surface of the heat transfer tube, or has a radial gap. Is characterized by an EGR gas cooling device arranged in a position.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to an EGR gas cooling device as shown in FIG.
A group of heat transfer tubes 12 is fixedly arranged inside, and an end cap 14 fixed to at least one end of the body tube 11 is provided with an EGR gas inlet 14a and an outlet 14b. E having a cooling medium inlet 6a and an outlet 6b such as an engine coolant fixed to the outer peripheral surface.
In the GR gas cooling device, at least one heat-insulating means including at least one sleeve 15 is provided on the outer surface of the heat transfer tube 12 on the side where the EGR gas flows in or out, or on both sides thereof. They are closely attached to the surface or are arranged at intervals in the radial direction.

With this configuration, the high temperature EGR gas flowing into the heat transfer tube 12 causes the coolant to partially boil on the outer surface of the heat transfer tube 12 to form bubbles, and the bubbles grow to grow into the heat transfer tube 12. It is possible to prevent the heat exchange rate from being reduced by adhering to the outer surface, and also to prevent the moisture in the EGR gas from condensing on the outflow side of the EGR gas to form mist and small droplets. The purpose of the present invention is to prevent the corrosion deterioration phenomenon of the components due to the corrosive substance generated from adhering to the inner peripheral surface of the heat transfer tube and the piping system through which the EGR gas passes, and to smoothly operate the engine.

Next, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a partially enlarged sectional view of a main part of an embodiment of an EGR gas cooling device of the present invention, and FIG. FIG. 4 is a partially enlarged half-sectional view showing an example, in which (a) is a view showing a first modification;
(B) is a diagram showing a second modification, FIG. 3 is a partially enlarged half-section showing another embodiment of the present invention, FIG. 4 is a partially enlarged half-section showing a modification of FIG. 3, and FIG. FIG. 6 is a partially enlarged sectional view showing still another embodiment of the present invention, and FIG. 6 is a partially enlarged sectional view showing still another embodiment of the present invention.

The present invention can be applied not only to the EGR gas cooling device shown in FIG. 7 but also to an EGR gas cooling device using a known multi-tube heat exchanger as shown in Japanese Utility Model Publication No. 57-309. However, the EGR gas cooling device shown in FIG. 7 will be described as an example. The EGR gas cooling device according to one embodiment of the present invention is formed by burring outward so as to have a rising portion formed by curved surface processing inward near both ends of the body tube 11, and a cooling medium inlet such as an engine coolant. 6a and the same outlet 6b, and the cooling medium inlet 6a and the same outlet 6b
The branch pipe 7a for supplying a cooling medium such as an engine coolant and the branch pipe 7b for discharging the metal are directly joined to each other by welding so that they do not protrude into the body tube 11. Since the rising portion formed by the above-mentioned curved surface processing is provided inside the cooling medium inlet 6a and the cooling outlet 6b, the flow of the cooling medium such as the engine coolant or the cooling wind smoothly bends so as not to cause resistance. Can be.

Each of the heat transfer tubes 12 is brazed at both ends to tube sheets 3a and 3b to form a group of heat transfer tubes 12, and the tube sheets 3a and 3b are brazed at both ends of the inner circumference of the body tube 11. It is fixedly arranged inside the fuselage. EGR
The end caps 14 having the gas inlet 14a and the EGR gas outlet 14b are fixed to the outer periphery of the body tube 11 near both ends by brazing or welding. FIG.
6 to 6, solid arrows indicate the flow of the cooling medium,
The dotted arrows indicate the flow of the EGR gas.
Although the thermal stress increases to reduce the condensation on the R gas outflow side, the direction may be opposite to the solid arrow.

In the EGR gas cooling apparatus thus constructed, in the present invention, the heat transfer tube 12 is provided on the outer peripheral surface of the EGR gas inflow side and / or the EGR gas outflow side with a radial distance 13 from the outer peripheral surface. Sleeve 1 as shown in FIG.
5a and 15b are fixed by brazing or welding.

In the embodiment shown in FIG. 1, the free ends of the sleeves 15a and 15b fixed by brazing or welding are formed by caulking or inwardly projecting thick portions, and as shown in FIG. When the portion or the thick portion is brazed to the outer peripheral surface of the heat transfer tube 12 using a vacuum furnace, a gap (gap) 13 formed between the inner peripheral surface of the sleeves 15a and 15b and the outer peripheral surface of the heat transfer tube 12 is formed. The space (gap) 13 can be made into a vacuum adiabatic gap by brazing with a vacuum furnace at the time of brazing. Further, as shown in FIG. 2B, the second sleeves 16a and 16b can be provided inside the caulked portion or the thick portion. 2B, the interface between the outer peripheral surface of the heat transfer tube 12 and the sleeves 15a and 15b, and the sleeves 15a and 15b and the second sleeve 16a,
16b provides a heat shielding effect, and the second
When the sleeves 16a and 16b are made of a heat insulating material such as ceramic, the heat insulating effect can be further improved. 2 (a) and 2 (b) show the configuration on the inflow side of the EGR gas. However, since this configuration can be used as it is on the outflow side, it is shown in parentheses.

Further, as shown in FIG. 3, the sleeves 15a and 15b are press-fitted on the outer peripheral surface of the heat transfer tube 12 and fixed so as to be in close contact therewith, or as shown in FIG. Between the second sleeves 16a, 16b
May be interposed and polymerized to form a sleeve composed of multiple layers (two layers in the illustrated embodiment). When a multi-layered sleeve is provided as shown in FIG. 4, the interface between the outer peripheral surface of the heat transfer tube 12 and the sleeves 15a and 15b and the sleeves 15a and 15b and the second sleeve are provided in the same manner as in the embodiment of FIG. The interface with the sleeves 16a and 16b can exhibit a heat blocking effect, and the heat blocking effect can be further improved if each layer of the sleeve is made of a material having a different heat transfer coefficient. FIG. 4 shows the configuration on the inflow side of the EGR gas. However, since this configuration can be used as it is on the outflow side, it is shown in parentheses.

Next, if necessary, the contact portion is fixed by brazing or the like, and as shown in FIG.
b) an inwardly directed annular groove or a plurality of recesses 1 in the circumferential direction.
5 a ′ and 15 b ′ are provided to form a bellows shape, and the inner tops of the concave grooves or recesses 15 a ′ and 15 b ′ are in contact with the outer peripheral surface of the heat transfer tube 12 to form a spacer, so that the outer peripheral surface of the heat transfer tube 12 Sleeve 1 at intervals 13 in the direction
5a, 15b may be fixed, or if necessary, the contact portion may be fixed by brazing or the like, and the gap 13 formed by this brazing acts as an adiabatic gap. Further, when brazing is performed by a vacuum furnace at the time of brazing, the gap (gap) 13 can be made a vacuum adiabatic gap.

Further, when a plurality of baffle plates 10 are provided as required as shown in FIG. 6, the baffle plate on the side closer to the EGR gas inlet 14a and / or the EGR gas outlet 14b is provided. And tubesheet 3
a and 15b, the end faces of the sleeves 15a and 15b are fixed to the baffle plate 11 and the tube sheets 3a and 3b.
It is also possible to maintain a gap 13 in the radial direction between the inner peripheral surfaces of the heat transfer tubes 12 and the inner peripheral surfaces of the heat transfer tubes 12 and 15 a to form an adiabatic gap. If the end faces of the sleeves 15a and 15b are fixed to the baffle plate 11 and the tube sheets 3a and 3b by brazing using a vacuum furnace, the gap (gap) 13 is set to a vacuum insulating gap as in the above-described embodiment. It can also be formed as

In the present invention, whether the sleeve as the heat insulating means is provided on the EGR gas inflow side, the EGR gas outflow side or on both sides, and the length of the sleeve are determined by the displacement, the maximum torque, and the maximum rotation. Engine performance such as number, engine coolant, intercooler refrigerant,
The type and cooling capacity of a cooling medium such as a refrigerant for a car air conditioner or cooling air, the temperature, flow rate, flow velocity, composition, EG
The size and the like of the R gas cooling device are comprehensively examined in advance and determined appropriately.

In the above-described embodiment, the sleeves 15a and 15b having the same configuration are provided on the outer peripheral surfaces of the heat transfer tube 12 on the EGR gas inflow side and the EGR gas outflow side. It is also possible to arrange differently configured sleeves on the gas outlet side. For example, the sleeve shown in FIG. 1 may be provided on the outer peripheral surface on the inflow side of the EGR gas, and the sleeve shown in FIG. 3 may be provided on the outer peripheral surface on the outflow side of the EGR gas. It is possible.

As described above, the sleeve 1 is provided on the outer peripheral surface of the heat transfer tube 12 on the EGR gas inflow side and / or the EGR gas outflow side.
5a, 15b and, if necessary, the second sleeves 16a, 16
When the cooling medium is liquid, the temperature of the outer surface of the heat transfer tube on the EGR gas inflow side is reduced even if a high temperature and high flow rate EGR gas exceeding the cooling capacity flows in by providing the heat insulating means by providing b. To prevent the generation of air bubbles due to boiling, and to prevent the generation of air bubbles even if they occur, thereby preventing the air bubbles from widely covering the outer surface of the heat transfer tube. Effectively contributes to heat transfer, prevents a decrease in the heat exchange rate, lowers the temperature of the EGR gas outlet,
On the other hand, the temperature of the EGR gas flowing through the heat transfer tube is excessively cooled by the cooling medium and becomes equal to or lower than the dew point temperature.
This also prevents the moisture in the GR gas from dewing to form corrosive substances.

[0023]

As described above, the EG according to the present invention is used.
Since the R gas cooling device is provided with heat insulating means on at least one outer peripheral surface of the heat transfer tube on the side where the EGR gas flows in or on the side where the EGR gas flows out, when the cooling medium is a liquid,
Even when high temperature and high flow rate EGR gas exceeding the cooling capacity of the EGR gas inflow side of the EGR gas cooling device flows in, the temperature of the outer surface of the heat transfer tube on the EGR gas inflow side is reduced to generate bubbles due to boiling. In addition, even if bubbles are generated, the growth is prevented, and the bubbles do not widely cover the outer surface of the heat transfer tube, so that the entire outer surface of the heat transfer tube effectively contributes to heat transfer, and heat exchange. The temperature of the EGR gas outlet is reduced by preventing the rate of decrease, and the moisture in the EGR gas flowing into the EGR gas cooling device is excessively cooled by the cooling medium and condensed, thereby generating mist and droplets. In order to prevent this, sulfurous acid gas, nitrous acid gas and the like are dissolved in the mist and droplets to generate sulfurous acid, nitrous acid, and the like, which are further oxidized to form a strong acid such as sulfuric acid, nitric acid, or a mixed acid obtained by mixing them. Without corrosive substances, such as occurs, the inner peripheral surface and E of the heat transfer tube of the resulting EGR gas cooling device
Corrosion deterioration caused by the adhesion of corrosive substances to the inner peripheral surfaces of various parts constituting the piping system through which the GR gas passes is greatly suppressed, and the operation of the engine is also smoothed.

Further, in the present invention, when the sleeve is brazed to the outer peripheral surface of the heat transfer tube, an adiabatic space can be formed between the inner peripheral surface of the sleeve and the outer peripheral surface of the heat transfer tube, and a vacuum furnace may be used. When attached, the gap (gap) between the inner peripheral surface of the sleeve and the outer peripheral surface of the heat transfer tube can be a vacuum insulation gap.

[Brief description of the drawings]

FIG. 1 is a partially enlarged sectional view of a main part of an embodiment of an EGR gas cooling device of the present invention.

FIG. 2 is a partially enlarged half-sectional view showing a modification of FIG. 1;
Is a diagram showing a first modification, and (b) is a diagram showing a second modification.

FIG. 3 is a partially enlarged half cutaway view showing another embodiment of the present invention.

FIG. 4 is a partially enlarged half cutaway view showing a modification of FIG. 3;

FIG. 5 is a partially enlarged half cutaway view showing still another embodiment of the present invention.

FIG. 6 is a partially enlarged sectional view showing still another embodiment of the present invention.

FIG. 7 is a cross-sectional view of an EGR gas cooling device proposed by the present applicant.

[Explanation of symbols]

 3a, 3b Tube sheet 6a Cooling medium inlet 6b Same outlet 7a Cooling medium supply branch 7b Same discharge branch 10 Baffle plate 11 Body tube 12 Heat transfer tube 13 Interval 14a EGR gas inlet 14b Same outlet 15a, 15b Sleeve 15a ', 15b' Groove or recess 16a, 16b Second sleeve

Claims (2)

[Claims] A heat transfer tube group is fixedly arranged inside a body tube, and an end cap fixed to at least one end of the body tube has an E cap.
In an EGR gas cooling apparatus having a GR gas inlet and an outlet, and further having an inlet and an outlet for a cooling medium fixed to an outer peripheral surface near an end of the body tube, the EGR gas of the heat transfer tube flows in An EGR gas cooling device, wherein a heat insulating means is provided on an outer peripheral surface on a side and / or an outflow side. 2. The EGR according to claim 1, wherein said heat insulating means comprises at least one sleeve, and is provided in close contact with an outer peripheral surface of said heat transfer tube or is arranged at a radial interval. Gas cooling device.