JP3948638B2 - EGR gas cooling device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus that cools EGR gas using engine coolant, intercooler refrigerant, car air conditioner refrigerant, cooling air, or the like.
[0002]
[Prior art]
A method in which a part of the exhaust gas is taken out from the exhaust system, returned to the engine intake system, and added to the air-fuel mixture is called EGR (Exhaust Gas Recirculation). EGR suppresses the generation of NOx (nitrogen oxide), reduces pump loss, reduces heat dissipation loss to the coolant due to lowering of combustion gas temperature, and increases specific heat ratio due to changes in working gas amount / composition. Since many effects such as improvement of cycle efficiency can be obtained, it is an effective method for improving the thermal efficiency of the engine.
[0003]
However, if the temperature of the EGR gas increases, the fuel consumption decreases as the intake air temperature rises, and the durability of the EGR valve deteriorates due to its thermal action, leading to premature breakage. It is recognized that it is necessary to In order to avoid such a situation, an apparatus that cools EGR gas with engine coolant or the like is used. As this apparatus, a multi-tube heat exchanger is generally used.
[0004]
As shown in FIGS. 3 and 4, the multitubular heat exchanger used in this case is a trunk pipe provided with a cooling medium inlet 11-1 and a cooling medium outlet 11-2 at both ends. 11, both ends of the heat transfer tube group 12 are fixed to the tube sheet 13 by brazing or welding, while the tube sheet 13 is arranged with its outer peripheral portion fixed to the inner wall of the trunk tube 11 by brazing or welding, An end cap 14 a provided with an EGR gas inlet 14 a-1 is fixed to one end of the barrel 11, and an EGR gas outlet 14 b-1 is provided at the other end. The end cap 14b is fixed, and the fastening flanges 15a and 15b are externally fixed to the outer opening ends of the gas inlet 14a-1 and the outlet 14b-1 of the end caps 14a and 14b. And it has a structure.
[0005]
[Problems to be solved by the invention]
As shown in FIG. 5, the EGR gas inlet 14a-1 and the outlet 14b-1 of the end caps 14a, 14b in the conventional multi-tube heat exchanger used for cooling the EGR gas are all straight tubes as shown in FIG. 14a-2, an inclined portion 14a-3 that rises rapidly, an inclined portion 14b-3 that suddenly falls, and a straight tube portion 14b-2. The fastening flanges 15a and 15b are formed of the straight tube. The structure is fixed to the portions 14a-2 and 14b-2. However, in the case where the EGR gas inlet 14a-1 is the end cap 14a formed of the straight cylinder portion 14a-2, the flow of the EGR gas at the EGR gas inlet portion is shown in FIG. Since the EGR gas that has flowed in at a high speed from the EGR gas inlet 14a-1 is rectified by the straight tube portion, the EGR gas flow is less likely to flow along the inclined portion 14a-3 that rises sharply. As a result, a drift phenomenon occurs in which a large amount flows in the central portion of the tube 13 and a small amount flows in the periphery. As a result, among the heat transfer tube groups 12 fixed to the tube sheet 13, the heat transfer tube group positioned in the central portion As a result of a large amount of gas flowing and a small flow rate of EGR gas flowing in the heat transfer tube group 12 near the inner wall of the trunk tube 11, heat exchange in the heat transfer tube group 12 is performed. The variation occurs, it becomes a cause of lowering the heat exchange performance of the entire heat exchanger, it caused a contraction of flow increase over resistance when flowing into the heat transfer tube group positioned at the center.
[0006]
Further, in the case where the EGR gas outlet 14b-1 is an end cap 14b composed of a straight cylindrical portion 14b-2, the flow of EGR gas at the EGR gas outlet is shown in FIG. Since the outflowed EGR gas immediately hits the inclined portion 14b-3 that suddenly falls, the flow direction is suddenly changed to generate a vortex, and a large flow resistance combined with the contraction in the center portion. As a result, the amount of EGR gas is reduced as an EGR gas cooling device, and a high EGR rate cannot be obtained.
[0007]
The present invention was made to eliminate variations in the amount of heat exchange in the heat transfer tube group due to the EGR gas drifting phenomenon and the contraction phenomenon to the center of the end cap part of the multi-tube heat exchanger described above. The EGR gas that flows in at high speed from the gas inlet of the end cap is improved so that it flows as evenly as possible to the center and the periphery of the heat transfer tube group fixed to the tube sheet, and the EGR that flows out An object of the present invention is to provide an EGR gas cooling device that can reduce the pressure loss of gas and obtain a high EGR rate.
[0008]
In order to solve the above problems, the present invention has a heat transfer tube group fixedly arranged on a tube sheet fixed in the vicinity of both ends of the inner wall of the trunk tube, and end caps are fixed to the outside of both ends of the trunk tube. In addition, the end cap is provided with an EGR gas inlet and outlet, and a multi-tube having a fastening flange externally fixed to the outer opening ends of the gas inlet and outlet of the end cap. In the EGR gas cooling device of the type, the end cap mounting hole of the fastening flange is composed of a straight hole part and a tapered hole part that extends toward the tube sheet side, and the inclination angle of the tapered hole part with respect to the tube axis is 20 to The EGR gas cooling device is characterized in that it has an angle of 60 degrees and the axial width of the tapered hole portion is 40 to 85% of the thickness of the fastening flange. It is preferable that the inclination angle with respect to the tube axis of the tapered portion of the 25 to 40 degrees.
[0009]
That is, according to the present invention, the difference in flow velocity between the central flow and the peripheral flow of EGR gas flowing at high speed from the gas inlet of the end cap is reduced as much as possible, and the EGR gas flowing out of the heat transfer tube group is made possible. As a result, the flow of EGR gas flowing in at high speed from the gas inlet of the end cap is as smooth as possible in the space region formed by the end cap and the tube sheet. The end cap mounting hole of the fastening flange is composed of a straight hole and a taper hole that smoothly spreads to the tube sheet side so that it spreads out and smoothly flows out to the gas outlet of the end cap with less resistance. Is. That is, the hole of the fastening flange is composed of the straight hole portion and the tapered hole portion that smoothly spreads toward the tube sheet side, so that the flow of the EGR gas that has flowed into the space region can be easily spread and the EGR that has flowed out. This is to facilitate the smooth discharge of gas.
[0010]
In the present invention, the inclination angle of the tapered hole portion with respect to the tube axis is limited to 20 to 60 degrees, preferably 25 to 40 degrees. If the angle is less than 20 degrees, the inclination becomes close to a straight hole and the EGR gas cooling device has a dimension in the axial direction. This is because an increase in the smoothness of the flow of the EGR gas is hardly obtained when the angle is increased and the inclination angle exceeds 60 degrees. In consideration of both the size of the EGR gas cooling device and the smooth spreading effect of the EGR gas flow, the inclination angle is preferably 25 to 40 degrees. Moreover, the axial width of the tapered hole portion is limited to 40 to 85% of the thickness of the fastening flange. If the thickness is less than 40%, the straight hole portion becomes long and the effect of spreading the EGR gas flow is small. The reason why it is less than 85% is that the angle accuracy of the fastening flange with respect to the shaft core of the EGR gas cooling device is ensured and the strength balance is taken into consideration.
[0011]
As described above, the end cap mounting hole of the fastening flange is configured by the straight hole portion and the tapered hole portion that extends toward the tube sheet side, and the inclination angle of the tapered hole portion with respect to the tube axis is set to 20 to 60 degrees. The axial width of the tapered hole portion is 40 to 85% of the thickness of the fastening flange, and the tapered hole portion of the fastening flange is formed in a shape along the outer peripheral surface of the tapered portion of the end cap, The EGR gas flow in the space region formed by the end cap and the tube sheet spreads as smoothly as possible to the outside, reducing the difference in flow velocity between the central flow and the peripheral flow, and the central portion fixed to the tube sheet In addition, it is possible to reduce variations in the amount of heat exchange between the heat transfer tube groups in the peripheral portion, and it is possible to obtain a high EGR rate by reducing pressure loss due to flow resistance.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a partially broken plan view showing a structural example of a multi-tube EGR gas cooling device according to the present invention, and FIG. 2 is an enlarged central portion showing an EGR gas inlet side and an EGR gas outlet side of the same device 1 is a body tube, 2 is a heat transfer tube group, 3 is a tube sheet, 4a and 4b are end caps, 4a-1 is an EGR gas inlet, and 4b-1 is an EGR gas flow. The outlets 5a and 5b are fastening flanges.
[0013]
That is, the multi-tube EGR gas cooling device according to the present invention includes both end portions of the heat transfer tube group 2 inside the trunk tube 1 provided with the cooling medium inlet port 1-1 and the cooling medium outlet port 1-2 at both ends. Is fixed to the tube sheet 3 by brazing or welding, while the tube sheet 3 is arranged with its outer periphery fixed to the inner wall of the barrel tube 1 by brazing or welding, and at one end of the barrel tube 1 An end cap 4a provided with an EGR gas inlet 4a-1 is fixed, and an end cap 4b provided with an EGR gas outlet 4b-1 is fixed to the other end. And fastening flanges 5a and 5b are externally fitted and fixed to the outer opening ends of the gas inlet 4a-1 and the outlet 4b-1 of the end caps 4a and 4b, respectively. Flanges 5a and 5b Each is composed of a tapered hole part 5a-2,5b-2 extending end cap mounting hole in the straight hole portion 5a-1,5b-1 and the tube sheet 3 side. The tapered hole portions 5a-2 and 5b-2 of the fastening flanges 5a and 5b are shaped along the outer peripheral surface of the tapered portions 4a-3 and 4b-3 spreading toward the tube sheet 3 side of the end caps 4a and 4b. Is formed. The fastening flanges 5a and 5b are fixed to the outer peripheral surfaces of the gas inlet 4a-1 and the gas outlet 4b-1 of the end caps 4a and 4b by brazing or welding, respectively.
[0014]
Further, the axial width _{W 1} of the tapered hole 5a-2,5b-2 extending into the tube sheet 3 side, formed in a range of 40% to 85% of the thickness W of the fastening flanges 5a, 5b, and The inclination angle θ with respect to the tube axis is in the range of 20 to 60 degrees, preferably 25 to 40 degrees.
[0015]
That is, the multi-tube EGR gas cooling device according to the present invention is provided in the EGR gas inlet 4a-1 or the end cap 4b provided in the end cap 4a fixed to the end of the trunk tube 1. The length of the straight holes 5a-1, 5b-1 formed at the EGR gas outlet 4b-1 is short, and the paper parts 4a-3, 4b-3 of the end cap 4a or 4b are tapered holes. Therefore, the EGR gas flowing in from the EGR gas inlet 4a-1 is caused by the end cap 4a and the tube sheet 3 along the 5a-2 or 5b-2 side. In the space region to be formed, the tube sheet is formed by forming a large amount of the peripheral flow y that smoothly flows outward along the inner surface of the tapered portion 4a-3 of the end cap 4a. The difference in flow velocity from the central flow x flowing toward the central portion of the tube is reduced, and EGR gas flows into the heat transfer tube group 2 at the central portion and the peripheral portion fixed to the tube sheet 3 as evenly as possible. In the central and peripheral heat transfer tubes, almost the same flow velocity can be obtained, and therefore almost the same heat transfer coefficient (kcal / m ² hr ° C) can be obtained, and the heat exchange performance due to the EGR gas drift phenomenon Can be easily prevented, and the occurrence of contraction at the inflow portion to the heat transfer tube group located at the center can be prevented, and the occurrence of large pressure loss due to this contraction can be prevented. it can.
Further, the EGR gas exiting the heat transfer tube group 2 also abuts against the inner surface of the tapered portion 4b-3 of the end cap 4b on the EGR gas outlet side, and the flow direction is suddenly changed to generate vortices. Without flowing smoothly along the inner surface, the central flow x and the peripheral flow y flow out from the outlet 4b-1 at substantially the same flow velocity. Therefore, the EGR gas exiting the heat transfer tube group can be used at a high EGR rate without causing a large pressure loss.
[0016]
【The invention's effect】
As described above, according to the EGR gas cooling device of the present invention, the flow of EGR gas in the space region formed by the end cap and the tube sheet can be smoothly spread outward as much as possible. The difference in flow velocity between the central flow and the peripheral flow of the EGR gas flowing in from the inlet is reduced, and the EGR gas flows into the central and peripheral heat transfer tube groups fixed to the tube sheet as evenly as possible. The EGR gas that exits the heat tube group flows out at the same flow rate in the center flow and the peripheral flow, so that the flow rate in the heat transfer tube can be made uniform and the heat transfer coefficient can be made uniform. There is an excellent effect of reducing the variation of.
[Brief description of the drawings]
FIG. 1 is a partially broken plan view showing an example of the structure of a multi-tube EGR gas cooling device according to the present invention.
FIG. 2 is a cross-sectional view in which an EGR gas inlet side and an EGR gas outlet side of the above apparatus are enlarged and shown in a central portion.
FIG. 3 is a partially cutaway plan view showing an example of a conventional multi-tube EGR gas cooling device that is a subject of the present invention.
4 is a view taken in the direction of arrows AA in FIG. 3;
FIG. 5 is a cross-sectional view of the EGR gas inlet side and the EGR gas outlet side of the conventional EGR gas cooling apparatus as shown in FIG.
[Explanation of symbols]
1 trunk tube 2 heat transfer tube group 3 tube sheet 4a, 4b end cap 4a-1 EGR gas inlet 4b-1 EGR gas outlet 5a, 5b fastening flange 5a-1, 5b-1 straight hole 5a- 2, 5b-2 Taper hole x Center flow y Peripheral flow W Fastening flange thickness W ₁ Taper hole width in the axial direction

Claims (2)

A heat transfer tube group is fixedly arranged on tube sheets fixed near both ends of the inner wall of the trunk tube, and end caps are fixed to the outer sides of both ends of the trunk tube, and EGR gas is attached to the end caps. In the multi-tube EGR gas cooling apparatus having a structure in which an inflow port and an outflow port are provided, and a fastening flange is fitted and fixed to an outer opening end of the gas inflow port and the outflow port of the end cap. The flange end cap mounting hole is composed of a straight hole portion and a taper hole portion extending toward the tube sheet side, and the inclination angle of the taper hole portion with respect to the tube axis is set to 20 to 60 degrees. An EGR gas cooling device, wherein the axial width is 40 to 85% of the thickness of the fastening flange. The EGR gas cooling device according to claim 1, wherein an inclination angle of the tapered portion of the end cap mounting hole with respect to the tube axis is set to 25 degrees to 40 degrees.

Images