U.S. patent application number 11/827409 was filed with the patent office on 2008-01-17 for exhaust gas heat exchanger.
This patent application is currently assigned to DENSO Corporation. Invention is credited to Takayuki Hayashi, Yuu Oofune.
Application Number | 20080011464 11/827409 |
Document ID | / |
Family ID | 38885132 |
Filed Date | 2008-01-17 |
United States Patent
Application |
20080011464 |
Kind Code |
A1 |
Oofune; Yuu ; et
al. |
January 17, 2008 |
Exhaust gas heat exchanger
Abstract
An exhaust gas heat exchanger has a tube which is made of a
stainless steel and in which exhaust gas flows, and an inner fin
which is made of a stainless steel and arranged in the tube to
improve a heat exchange between the exhaust gas and cooling water.
The cooling water flows at an outer side of the tube. The fin pitch
fp of the inner fin is substantially in the range of 2
mm<fp.ltoreq.12 mm, and the fin height fh of the inner fin is
substantially in the range of 3.5 mm<fh.ltoreq.12 mm.
Inventors: |
Oofune; Yuu; (Anjo-city,
JP) ; Hayashi; Takayuki; (Nagoya-city, JP) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, P.L.C.
P.O. BOX 828
BLOOMFIELD HILLS
MI
48303
US
|
Assignee: |
DENSO Corporation
Kariya-city
JP
|
Family ID: |
38885132 |
Appl. No.: |
11/827409 |
Filed: |
July 11, 2007 |
Current U.S.
Class: |
165/157 ;
165/183 |
Current CPC
Class: |
Y02T 10/12 20130101;
F02M 26/38 20160201; F02B 29/0406 20130101; F28D 21/0003 20130101;
F28F 3/027 20130101; F28D 9/0031 20130101; F28D 7/1684 20130101;
Y02T 10/16 20130101; F02M 26/32 20160201 |
Class at
Publication: |
165/157 ;
165/183 |
International
Class: |
F28F 1/36 20060101
F28F001/36 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 11, 2006 |
JP |
2006-190428 |
Claims
1. An exhaust gas heat exchanger in which exhaust gas generated due
to combustion is heat-exchanged with cooling fluid, comprising: a
tube in which the exhaust gas flows and outside which the cooling
fluid flows; and an inner fin which is arranged in the tube to
improve a heat exchange between the exhaust gas and the cooling
fluid, wherein: the inner fin has a cross section which has a
corrugated shape to include convex portions positioned at crests
and troughs of the corrugated shape, and is constructed of an
offset fin having lanced segments which are partially lanced and
arrayed substantially in a flowing direction of the exhaust gas,
the crests and the troughs being alternately arranged, and the
cross section being substantially perpendicularly to the flowing
direction of the exhaust gas; and a fin pitch fp and a fin height
fh of the inner fin are substantially defined by following formulas
3.5 mm<fh.ltoreq.12 mm, 2 mm<fp.ltoreq.12 mm, wherein the fin
pitch fp is a distance between central lines of the adjacent convex
portions positioned at a side of one of the crest and the trough in
the cross section of the inner fin, and the fin height fh is a
distance between the convex portions which are respectively
positioned at the side of the crest and the side of the trough in
the cross section of the inner fin.
2. An exhaust gas heat exchanger in which exhaust gas generated due
to combustion is heat-exchanged with cooling fluid, comprising: a
tube in which the exhaust gas flows and outside which the cooling
fluid flows; and an inner fin which is arranged in the tube to
improve a heat exchange between the exhaust gas and the cooling
fluid, wherein: the inner fin has a cross section which has a
corrugated shape to include convex portions positioned at crests
and troughs of the corrugated shape, and is constructed of an
offset fin having lanced segments which are partially lanced and
arrayed substantially in a flowing direction of the exhaust gas,
the crests and the troughs being alternately arranged, and the
cross section being substantially perpendicularly to the flowing
direction of the exhaust gas; and an equivalent circle diameter de
is substantially defined by following formulas when 0<L<5 mm,
1.2 mm.ltoreq.de.ltoreq.6.1 mm, when 5 mm.ltoreq.L.ltoreq.15 mm,
1.0 mm.ltoreq.de.ltoreq.4.3 mm, wherein L is a length of the lanced
segment in the flowing direction of the exhaust gas, and the
equivalent circle diameter de is a diameter of an equivalent circle
of a field C which is surrounded by the inner fin and the tube and
positioned between the adjacent convex portions at a side of one of
the crest and the trough in the cross section of the inner fin.
3. The exhaust gas heat exchanger according to claim 2, wherein the
equivalent circle diameter de is substantially defined by following
formulas when 0<L<5 mm, 1.3 mm.ltoreq.de.ltoreq.5.3 mm, when
5 mm<L<15 mm, 1.1 mm.ltoreq.de.ltoreq.4.0 mm.
4. The exhaust gas heat exchanger according to claim 2, wherein the
equivalent circle diameter de is substantially defined by following
formulas when 0<L<5 mm, 1.5 mm.ltoreq.de.ltoreq.4.5 mm, when
5 mm.ltoreq.L.ltoreq.15 mm, 1.3 mm.ltoreq.de.ltoreq.3.5 mm.
5. An exhaust gas heat exchanger in which exhaust gas generated due
to combustion is heat-exchanged with cooling fluid, comprising: a
tube in which the exhaust gas flows and outside which the cooling
fluid flows; and an inner fin which is arranged in the tube to
improve a heat exchange between the exhaust gas and the cooling
fluid, wherein: the inner fin has a cross section which has a
corrugated shape to include convex portions positioned at crests
and troughs of the corrugated shape, and is constructed of an
offset fin having lanced segments which are partially lanced and
arrayed substantially in a flowing direction of the exhaust gas,
the crests and the troughs being alternately arranged, and the
cross section being substantially perpendicularly to the flowing
direction of the exhaust gas; and a length L of the lanced segment
is substantially defined by following formulas when fh<7 mm and
fp.ltoreq.5 mm, 0.5 mm<L.ltoreq.65 mm, when fh<7 mm and
fp>5 mm, 0.5 mm<L.ltoreq.20 mm, when fh.gtoreq.7 mm and
fp.ltoreq.5 mm, 0.5 mm<L.ltoreq.50 mm, when fh.gtoreq.7 mm and
fp>5 mm, 0.5 mm<L.ltoreq.15 mm, wherein the length L is a
dimension in the flowing direction of the exhaust gas, fp is a fin
pitch which is a distance between central lines of the adjacent
convex portions positioned at a side of one of the crest and the
trough in the cross section of the inner fin, and fh is a fin
height which is a distance between the convex portions which are
respectively positioned at the side of the crest and the side of
the trough in the cross section of the inner fin.
6. The exhaust gas heat exchanger according to claim 5, wherein the
length L of the lanced segment is substantially defined by
following formulas when fh<7 mm and fp.ltoreq.5 mm, 0.5
mm<L.ltoreq.25 mm, when fh<7 mm and fp>5 mm, 0.5
mm<L.ltoreq.8 mm, when fh.gtoreq.7 mm and fp.gtoreq.5 mm, 0.5
mm<L.ltoreq.18 mm, when fh.gtoreq.7 mm and fp>5 mm, 0.5
mm<L.ltoreq.6 mm.
7. The exhaust gas heat exchanger according to claim 5, wherein the
length L of the lanced segment is substantially defined by
following formulas when fh<7 mm and fp.ltoreq.5 mm, 0.5
mm<L.ltoreq.7 mm, when fh<7 mm and fp>5 mm, 0.5
mm<L.ltoreq.1 mm, when fh.gtoreq.7 mm and fp.ltoreq.5 mm, 0.5
mm<L.ltoreq.4.5 mm, when fh.gtoreq.7 mm and fp>5 mm, 0.5
mm<L.ltoreq.1.5 mm.
8. An exhaust gas heat exchanger in which exhaust gas generated due
to combustion is heat-exchanged with cooling fluid, comprising: a
tube in which the exhaust gas flows and outside which the cooling
fluid flows; and an inner fin which is arranged in the tube to
improve a heat exchange between the exhaust gas and the cooling
fluid, wherein: the inner fin has a cross section which has a
corrugated shape to include convex portions positioned at crests
and troughs of the corrugated shape, and is constructed of an
offset fin having lanced segments which are partially lanced and
arrayed substantially in a flowing direction of the exhaust gas,
the crests and the troughs being alternately arranged, and the
cross section being substantially perpendicularly to the flowing
direction of the exhaust gas; and a fin pitch fp of the inner fin
and a length L of the lanced segment are substantially defined by
following formulas 2 mm<fp.ltoreq.12 mm, 1.1
mm.ltoreq.X.ltoreq.4.3 mm, wherein
X=de.times.L.sup.0.14/fh.sup.0.18, wherein the fin pitch fp is a
distance between central lines of the adjacent convex portions
positioned at a side of one of the crest and the trough in the
cross section of the inner fin, the length L is a dimension in the
flowing direction of the exhaust gas, fh is a fin height which is a
distance between the convex portions respectively positioned at a
side of the crest and a side of the trough in the cross section of
the inner fin, de is an equivalent circle diameter which is a
diameter of an equivalent circle of a field C, and the field D
which is defined in the cross section of the inner fin is
positioned between the adjacent convex portions of the side of one
of the crest and the trough and surrounded by the inner fin and the
tube, in which the inner fin is arranged.
9. The exhaust gas heat exchanger according to claim 8, wherein the
length L of the lanced segment is substantially defined by a
following formula 1.2 mm.ltoreq.X.ltoreq.3.9 mm, wherein
X=de.times.L.sup.0.14/fh.sup.0.18.
10. The exhaust gas heat exchanger according to claim 8, wherein
the length L of the lanced segment is substantially defined by a
following formula 1.3 mm.ltoreq.X.ltoreq.3.5 mm, wherein
X=de.times.L.sup.0.14/fh.sup.0.08.
11. The exhaust gas heat exchanger according to claim 1, wherein in
a cross section of the inner fin, a ratio of an offset area T to a
area of a field C is substantially in a range from 25% to 40%, the
cross section being substantially perpendicular to the exhaust gas
flowing direction, the field D being positioned between the
adjacent convex portions of the side of one of the crest and the
trough and surrounded by the inner fin and the tube, in which the
inner fin is arranged, the offset area T being an area of a part,
which is defined in the cross section of the inner fin and
surrounded by the two lanced segments which are adjacent to each
other in the exhaust gas flowing direction and offset from each
other in the longitudinal direction of the inner fin.
12. The exhaust gas heat exchanger according to claim 1, wherein
the lanced segments which are adjacent to each other in the flowing
direction of the exhaust gas deviate from each other at an offset
amount s in a longitudinal direction of the inner fin, and the
offset amount s is larger than about 0.5 mm.
13. The exhaust gas heat exchanger according to claim 1, wherein
the tube and the inner fin are arranged at a halfway portion of an
exhaust gas recirculation passage through which the exhaust gas of
an diesel engine having passed a diesel particulate filter is
returned to a suction side of the diesel engine.
14. The exhaust gas heat exchanger according to claim 2, wherein
the tube and the inner fin are arranged at a halfway portion of an
exhaust gas recirculation passage through which the exhaust gas of
an diesel engine having passed a diesel particulate filter is
returned to a suction side of the diesel engine.
15. The exhaust gas heat exchanger according to claim 5, wherein
the tube and the inner fin are arranged at a halfway portion of an
exhaust gas recirculation passage through which the exhaust gas of
an diesel engine having passed a diesel particulate filter is
returned to a suction side of the diesel engine.
16. The exhaust gas heat exchanger according to claim 8, wherein
the tube and the inner fin are arranged at a halfway portion of an
exhaust gas recirculation passage through which the exhaust gas of
an diesel engine having passed a diesel particulate filter is
returned to a suction side of the diesel engine.
17. The exhaust gas heat exchanger according to claim 1, wherein:
each of the tube and the inner fin is made of a stainless steel;
and the cooling fluid is cooling water.
18. The exhaust gas heat exchanger according to claim 2, wherein:
each of the tube and the inner fin is made of a stainless steel;
and the cooling fluid is cooling water.
19. The exhaust gas heat exchanger according to claim 5, wherein:
each of the tube and the inner fin is made of a stainless steel;
and the cooling fluid is cooling water.
20. The exhaust gas heat exchanger according to claim 8, wherein:
each of the tube and the inner fin is made of a stainless steel;
and the cooling fluid is cooling water.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is based on a Japanese Patent Application
No. 2006-190428 filed on Jul. 11, 2006, the disclosure of which is
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to an exhaust gas heat
exchanger. For example, the exhaust gas heat exchanger can be
suitably used for an exhaust gas recirculation cooler (EGR cooler),
which is provided in an exhaust gas recirculation device (EGR) to
cool exhaust gas.
BACKGROUND OF THE INVENTION
[0003] Generally, an exhaust gas recirculation cooler (EGR cooler)
is used in a diesel type engine or the like as an exhaust gas heat
exchanger. For example, with reference to JP-2004-77024A, the
general EGR cooler is arranged at a halfway position of an exhaust
gas recirculation pipe for partially refluxing exhaust gas of the
engine directly to the suction side of the engine.
[0004] In this case, the EGR cooler is provided with multiple tubes
which are stacked and in each of which an inner fin is arranged.
Exhaust gas flowing in the tube is heat-exchanged with cooling
water flowing at the outer side of the tube, so that exhaust gas is
cooled. In this case, the inner fin is constructed of a straight
fin.
[0005] In addition to the straight fin or a wave fin, the inner fin
can be also constructed of an offset fin which is generally used in
an inter cooler or the like to have a different use from the EGR
cooler, for example, with reference to JP-3766914.
[0006] The offset fin is susceptible to being clogged, although
having a higher heat-exchanging capacity than the straight fin.
Because there is lot of coal in exhaust gas flowing through the EGR
cooler so that the offset fin is susceptible to be clogged, it is
difficult to use the offset fin as the inner fin of the EGR
cooler.
[0007] Moreover, because the cooling method, the required
performance, the specifications environment and the like of the EGR
cooler are different from those of the inter cooler, specifications
(such as fin pitch fp, fin height fh, segment length L and the
like) of the offset fin used in the inter cooler can not be
directly (without being changed) used in the EGR cooler.
[0008] For example, the cooling method of the inter cooler is
different from that of the EGR cooler. That is, the inter cooler is
generally an air cooling type, while the EGR cooler is generally a
water cooling type. Thus, the contribution degree of the inner fin
to the heat exchanging capacity in the inter cooler is different
from that in the EGR cooler.
[0009] Moreover, the temperature (e.g., 170.degree. C.) of the
cooling object gas of the inter cooler is different from that
(e.g., 400.degree. C.) of the EGR cooler.
[0010] Moreover, the inter cooler is made of a different material
from that of the EGR cooler. The inter cooler is generally made of
aluminum. On the other hand, the EGR cooler is to be made of a
stainless steel to maintain a corrosion resistance, because the EGR
cooler is exposed to a corrosion environment due to
high-temperature oxidation and condensation water.
[0011] The specifications of the offset fin are set in such a
manner that the heat exchanging capacity (related to cooling
method, temperature of cooling object gas, material of inner fin
and the like) of the EGR cooler has a maximum value. However, in
the case where the specifications of the offset fin for the inter
cooler is simply used as the specifications of the offset fin for
the EGR cooler, the heat exchanging capacity of the EGR cooler will
be lowered.
[0012] Moreover, in an exhaust gas recirculation device where the
EGR cooler is used, in order to maintain the flow amount in the
case of the high load, it is necessary for the pressure loss in the
EGR cooler to be small. However, for example, in the case where the
specifications (fin pitch fp=2 mm) of the offset fin are defined as
disclosed in JP-3766914, the pressure loss in the tube will become
excessively large.
[0013] The above described disadvantages will occur in not only the
EGR cooler but also other sort of exhaust gas heat exchanger which
is a water-cooling type and made of the stainless steel.
SUMMARY OF THE INVENTION
[0014] In view of the above-described disadvantages, it is an
object of the present invention to provide an exhaust gas heat
exchanger having an improved performance in the case where an
offset fin is used as an inner fin.
[0015] According to a first aspect of the present invention, an
exhaust gas heat exchanger in which exhaust gas generated due to
combustion is heat-exchanged with cooling fluid includes a tube in
which the exhaust gas flows and outside which the cooling fluid
flows, and an inner fin which is arranged in the tube to improve a
heat exchange between the exhaust gas and the cooling fluid. The
inner fin has a cross section which has a corrugated shape to
include convex portions positioned at crests and troughs of the
corrugated shape, and is constructed of an offset fin having lanced
segments which are partially lanced and arrayed substantially in a
flowing direction of the exhaust gas. The crests and the troughs
are alternately arranged, and the cross section is substantially
perpendicularly to the flowing direction of the exhaust gas. A fin
pitch fp and a fin height fh of the inner fin (32) are defined by
3.5 mm<fh.ltoreq.12 mm, and 2 mm<fp.ltoreq.12 mm, wherein the
fin pitch fp is a distance between central lines of the adjacent
convex portions positioned at a side of one of the crest and the
trough in the cross section of the inner fin, and the fin height fh
is a distance between the convex portions which are respectively
positioned at the side of the crest and the side of the trough in
the cross section of the inner fin.
[0016] Thus, the pressure loss of the exhaust gas flowing in the
tube and the hydraulic resistance of the cooling fluid (such as
cooling water) can be restricted. Therefore, the tube can be
restricted from being clogged, and can be provided with a higher
heat-radiating capacity.
[0017] According to a second aspect of the present invention, an
exhaust gas heat exchanger in which exhaust gas generated due to
combustion is heat-exchanged with cooling fluid is provided with a
tube in which the exhaust gas flows and outside which the cooling
fluid flows, and an inner fin which is arranged in the tube to
improve a heat exchange between the exhaust gas and the cooling
fluid. The inner fin has a cross section which has a corrugated
shape to include convex portions positioned at crests and troughs
of the corrugated shape, and is constructed of an offset fin having
lanced segments which are partially lanced and arrayed
substantially in a flowing direction of the exhaust gas. The crests
and the troughs are alternately arranged, and the cross section is
substantially perpendicularly to the flowing direction of the
exhaust gas. An equivalent circle diameter de is defined by
following formulas
when 0<L<5 mm, 1.2 mm.ltoreq.de.ltoreq.6.1 mm,
when 5 mm.ltoreq.L.ltoreq.15 mm, 1.0 mm.ltoreq.de.ltoreq.4.3
mm,
[0018] wherein L is a length of the lanced segment in the flowing
direction of the exhaust gas, and the equivalent circle diameter de
is a diameter of an equivalent circle of a field C which is
surrounded by the inner fin and the tube and positioned between the
adjacent convex portions at a side of one of the crest and the
trough of the corrugated shape in the cross section of the inner
fin.
[0019] Thus, the gas density which is a factor considering both the
cooling capacity and the pressure loss will be larger than or equal
to 93%, so that the exhaust gas heat exchanger has an improved
performance can be provided.
[0020] According to a third aspect of the present invention, an
exhaust gas heat exchanger in which exhaust gas generated due to
combustion is heat-exchanged with cooling fluid is provided with a
tube in which the exhaust gas flows and outside which the cooling
fluid flows, and an inner fin which is arranged in the tube to
improve a heat exchange between the exhaust gas and the cooling
fluid. The inner fin has a cross section which has a corrugated
shape to include convex portions positioned at crests and troughs
of the corrugated shape, and is constructed of an offset fin having
lanced segments which are partially lanced and arrayed
substantially in a flowing direction of the exhaust gas. The crests
and the troughs are alternately arranged, and the cross section is
substantially perpendicularly to the flowing direction of the
exhaust gas. A length L of the lanced segment is defined by
following formulas
when fh<7 mm and fp.ltoreq.5 mm, 0.5 mm<L.ltoreq.65 mm,
when fh<7 mm and fp>5 mm, 0.5 mm<L.ltoreq.20 mm,
when fh.gtoreq.7 mm and fp.ltoreq.5 mm, 0.5 mm<L.ltoreq.50
mm,
[0021] when fh.gtoreq.7 mm and fp>5 mm, 0.5 mm<L.ltoreq.15
mm,
[0022] wherein the length L is a dimension in the flowing direction
of the exhaust gas, fp is a fin pitch which is a distance between
central lines of the adjacent convex portions positioned at a side
of one of the crest and the trough in the cross section of the
inner fin, and fh is a fin height which is a distance between the
convex portions which are respectively positioned at the side of
the crest and the side of the trough in the cross section of the
inner fin.
[0023] Therefore, the gas density can be larger than or equal to
97%. Thus, the exhaust gas heat exchanger has the further improved
performance can be provided.
[0024] According to a fourth aspect of the present invention, an
exhaust gas heat exchanger in which exhaust gas generated due to
combustion is heat-exchanged with cooling fluid is provided with a
tube in which the exhaust gas flows and outside which the cooling
fluid flows, and an inner fin which is arranged in the tube to
improve a heat exchange between the exhaust gas and the cooling
fluid. The inner fin has a cross section which has a corrugated
shape to include convex portions positioned at crests and troughs
of the corrugated shape, and is constructed of an offset fin having
lanced segments which are partially lanced and arrayed
substantially in a flowing direction of the exhaust gas. The crests
and the troughs are alternately arranged, and the cross section is
substantially perpendicularly to the flowing direction of the
exhaust gas. A fin pitch fp and a length L of the lanced segment
are substantially defined by following formulas
2 mm<X.ltoreq.12 mm
1.1 mm.ltoreq.X.ltoreq.4.3 mm, wherein
X=de.times.L.sup.0.14/fh.sup.0.18
[0025] wherein the length L is a dimension in the flowing direction
of the exhaust gas, fh is a fin height which is a distance between
the convex portions respectively positioned at a side of the crest
and a side of the trough in the cross section of the inner fin, de
is an equivalent circle diameter which is a diameter of an
equivalent circle of a field C surrounded by the inner fin and the
tube and positioned between the adjacent convex portions of the
side of one of the crest and the trough in the cross section of the
inner fin, and the fin pitch fp is a distance between central lines
of the adjacent convex portions positioned at a side of one of the
crest and the trough in the cross section of the inner fin.
[0026] Thus, the gas density can be larger than or equal to 93%, so
that the exhaust gas heat exchanger has an improved performance can
be provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] Other objects, features and advantages of the present
invention will become more apparent from the following detailed
description made with reference to the accompanying drawings, in
which:
[0028] FIG. 1 is a schematic view showing an exhaust gas
recirculation device where an exhaust gas heat exchanger is used
according to a first embodiment of the present disclosure;
[0029] FIG. 2 is a schematic side view showing an EGR cooler as the
exhaust gas heat exchanger according to the first embodiment;
[0030] FIG. 3 is a schematic sectional view taken along the line
III-III in FIG. 2;
[0031] FIG. 4 is a schematic sectional view taken along the line
IV-IV in FIG. 3;
[0032] FIG. 5 is a schematic perspective view showing the EGR
cooler according to the first embodiment;
[0033] FIG. 6 is a schematic sectional view of an inner fin of the
EGR cooler which is taken along a direction substantially
perpendicular to an exhaust gas flowing direction according to the
first embodiment;
[0034] FIG. 7 is a graph showing a relation between a fin height of
an offset fin and a pressure loss ratio according to the first
embodiment;
[0035] FIG. 8 is a graph showing a relation between the fin height
and a hydraulic resistance according to the first embodiment;
[0036] FIG. 9 is a schematic sectional view showing an inner fin of
an EGR cooler which is taken along a direction substantially
perpendicular to an exhaust gas flowing direction according to a
second embodiment of the present disclosure;
[0037] FIG. 10 is a graph showing a relation between an equivalent
circle diameter of an offset fin and an EGR gas density ratio
according to the second embodiment;
[0038] FIG. 11 is a graph showing a relation between a segment
length of an offset fin and an EGR gas density ratio according to a
third embodiment of the present disclosure;
[0039] FIG. 12 is a graph showing a relation between an EGR gas
density ratio and a function using an equivalent circle diameter, a
segment length and a fin height according to a fourth embodiment of
the present disclosure;
[0040] FIG. 13A is a graph showing a variation of a PM advantage
sedimentation thickness at the offset fin with respect to time, and
FIG. 13B is a schematic view showing a sedimentation of PM at the
offset fin; and
[0041] FIG. 14 is a graph showing a relation between a heat
radiating performance of the EGR cooler and a fin pitch of the
offset fin.
DETAILED DESCRIPTION OF THE EXAMPLED EMBODIMENTS
First Embodiment
[0042] An exhaust gas heat exchanger according to a first
embodiment of the present invention will be described with
reference to FIGS. 1-8. The exhaust gas heat exchanger can be
suitably used as an exhaust gas recirculation cooler 10 (EGR
cooler), for example.
[0043] As shown in FIG. 1, the EGR cooler 10 can be provided for an
exhaust gas recirculation device. The exhaust gas recirculation
device has, for example, an air cleaner 3, a variable tube actuator
4, an inter cooler 5 and an intake manifold 6 which are arranged at
a halfway portion of an air suction passage 2 of an engine 1.
[0044] The tube actuator 4 and a DPF 8 (diesel particulate filter)
are arranged at a half portion of an exhaust passage 7 of the
engine 1. A first exhaust gas recirculation pipe 9 is connected
with a downstream side of exhaust gas of the DPF 8 and an upstream
side of suction air of the tube actuator 4. The EGR cooler 10 and
an exhaust gas recirculation valve 11 (EGR valve) are arranged at a
halfway portion of the first exhaust gas recirculation pipe 9,
which is a pipe for refluxing a part of exhaust gas having passed
the DPF 8 to the suction side of the engine.
[0045] The exhaust gas recirculation device further has a second
exhaust gas recirculation pipe 12 and an exhaust gas recirculation
valve 13 (EGR valve) which is arranged at a halfway portion of the
second exhaust gas recirculation pipe 12. A part of exhaust gas of
the engine is refluxed through the second exhaust gas recirculation
pipe 12 directly to the suction side of the engine, immediately
before passing the DPF 8. The pressure of exhaust gas flowing
through the first exhaust gas recirculation pipe 9 can be lower
than that of exhaust gas flowing through the second exhaust gas
recirculation pipe 12. In this case, the exhaust gas recirculation
can be operated even when the engine 1 has a high load.
[0046] In this case, when exhaust gas generated due to combustion
in the engine 1 is recycled to the engine 1, the EGR cooler 10
cools exhaust gas by coolant of the engine 1, which is cooling
liquid (for example, cooling water) in this embodiment. As shown in
FIGS. 2-4, the EGR cooler 10 has multiple tubes 21, multiple inner
fins 22, water side tanks 23 and gas side tanks 24, which can be
made of a stainless steel and integrated with each other by
brazing, welding or the like.
[0047] As shown in FIGS. 3 and 4, the tube 21 defines therein an
exhaust passage 21a in which exhaust gas flows. Cooling water flows
at the outer side of the tube 21, and exhaust gas is heat-exchanged
with cooling water through the tube 21.
[0048] Specifically, as shown in FIG. 3, the tube 21 having a long
side 21c and a short side 21d is provided with a flat-shaped cross
section when being viewed from the exhaust gas flowing direction.
The multiple tubes 21 are stacked in a stacking direction (for
example, up-down-direction in FIG. 3) which is perpendicular to the
longitudinal direction (i.e., extension direction of long side 21c)
of the tube 21. Moreover, as shown in FIGS. 3 and 4, the outer wall
surfaces of the tubes 21 which are adjacent to each other defines
therebetween a cooling water passage 21b through which cooling
water flows between the adjacent tubes 21.
[0049] Cooling water having flowed into the EGR cooler 10 is
distributed and supplied for the tubes 21 by the one water side
tank 23. Cooling water having flowed through the cooling water
passage 21b between the tubes 21 are collected and retrieved by the
other water side tank 23. The water side tanks 23 are arranged
around the tubes 21 which are stacked, in the vicinity of the two
ends (of exhaust gas flowing direction) of the tube 21. Each of the
water side tanks 23 is provided with a cooling water port 23a (as
cooling water outlet or inlet).
[0050] The gas side tanks 24 are respectively arranged at the two
ends (of exhaust gas flowing direction) of the tube 21. The gas
side tanks 24 are connected with the first exhaust gas
recirculation pipe 9. Exhaust gas is distributed and supplied for
the tubes 21, by the one gas side tank 24. The exhaust gas having
been heat-exchanged is colleted and retrieved from the tubes 21, by
the other gas side tank 24.
[0051] The inner fins 22 are respectively arranged in the tubes 21,
to improve the heat exchange between exhaust gas and cooling water.
The inner fin 22 can be fixed to the inner wall surface of the tube
21.
[0052] With reference to FIGS. 5 and 6, the inner fin 22, being
constructed of the offset fin, has a cross section (taken along a
direction which is substantially perpendicular to exhaust gas
flowing direction), which has a corrugated shape extending in the
longitudinal direction of the tube 21. That is, this cross section
of the inner fin 22 has convex portions 31 which are respectively
arranged at crest positions and trough positions of the corrugated
shape which are alternately arranged. The convex portion 31 of the
inner fin 22 is arranged to contact the inner wall surface of the
tube 21.
[0053] The inner fin 22 (offset fin) is partially lanced (cut and
raised) to have multiple lanced segments 32. The lanced segments 32
are arrayed in the exhaust gas flowing direction, in such a manner
that the adjacent lanced segments 32 offset from each other in the
longitudinal direction of the tube 21 (i.e., longitudinal direction
of inner fin 22). In this case, the inner fin 22 can be provided
with multiple rows (substantially in exhaust gas flowing direction)
of the lanced segments 32.
[0054] As shown in FIG. 3, by providing the inner fin 22 in the
tube 21, the interior of the tube 21 is divided into multiple
passages which are substantially parallel to each other with
respect to the longitudinal direction (extension direction of long
side 21a) of the tube 21.
[0055] That is, as shown in FIG. 5, the wall portions 33 of the
lanced segments 32 which define therein the passage are arranged
staggeringly in the longitudinal direction of the inner fin 22. In
this case, as shown in FIG. 6, it is desirable for an offset amount
s to be substantially equal to a half of the passage height u, so
that the heat transfer coefficient can become high and the gas
resistance can become small. The offset amount s and the passage
height u are dimensions in the longitudinal direction of the
longitudinal direction of fin 22. In this case, the lanced segments
32 which are adjacent to each other in the flowing direction of the
exhaust gas deviate from each other at the offset amount s in the
longitudinal direction (which is substantially perpendicular to
flowing direction of exhaust gas) of the fin 22.
[0056] The inner fin 22 can be shaped in such a manner that the
convex portion 31 includes a linear portion or does not include a
linear portion in the cross section (taken along a direction
substantially perpendicular to exhaust gas flowing direction) of
the inner fin 22.
[0057] In this case, with reference to FIG. 6 which is a cross
section (substantially perpendicular to exhaust gas flowing
direction) of the inner fin 22, it is desirable for the ratio of an
offset area T to the area of a field C (which is dotted to be
indicated) in this cross section of the inner fin 22 is
substantially in a range from 25% to 40%, considering that the
pressure loss will increase when the ratio of the offset area to
the area of the field C is smaller than 25%.
[0058] The dotted field C in this cross section of the inner fin 22
is positioned between the convex portions 31 which are arranged at
the crest positions (or trough positions) and adjacent to each
other in the longitudinal direction of inner fin 22, and surrounded
by the inner fin 22 and the tube 21. That is, the dotted field C is
positioned between the wall portions 33 (facing each other) of the
two lanced segments 32 which are adjacent to each other in the
longitudinal direction of the inner fin 22, and surrounded by the
inner fin 22 and the tube 21. The offset area T is an area of a
part, which is defined in this cross section and surrounded by the
wall portions 33 of the two lanced segments 32 which are adjacent
to each other in the exhaust gas flowing direction and offset from
each other in the longitudinal direction of inner fin 22.
[0059] The inner fin 22 can be manufactured by a flat plate which
is bent to have a corrugated shape by pressing and further lanced
by pressing to form the segment 32.
[0060] The lancing of the segment 32 can be performed in such a
manner that slits are beforehand formed before the corrugated shape
is provided and thereafter the raising is performed. Thus, the
inner fin 22 has the cross section with the corrugated shape is
formed. Alternatively, the lancing of segment 32 can be also
performed in such a manner that the two surfaces of the flat plate
are pressed by a press machine so that the cutting and raising are
simultaneously performed. Moreover, the inner fin 22 can be also
manufactured by rolling, or by a combination of rolling and
pressing.
[0061] The performance of the EGR cooler 10 is related to the
specifications of the inner fin 22 such as a fin pitch fp, a fin
height fh and the like. The fin pitch fp is a distance between
central lines of the two convex portions 31 (which adjacent to each
other) of one of a crest side and a trough side, in the corrugated
cross section (taken along substantially perpendicular to exhaust
gas flowing direction) of the inner fin 22. The fin height fh is a
distance between the tops of the two convex portions 31 which are
respectively positioned at the crest side and the trough side in
this corrugated cross section.
[0062] The optimum specifications of the inner fin 22 are
investigated in this embodiment. In this case, experiments are
performed for the EGR coolers 10 which are respectively provided
with the various fin pitches fp and fin heights fh, to evaluate the
pressure loss of the exhaust gas flowing in the tube 21, the
hydraulic resistance of cooling water flowing at the outer side of
the tube 21, the clogged degree of the tube 21, and the heat
radiating performance of the each EGR cooler 10 when exhaust gas
and cooling water flow under a predetermined condition. Thus, the
optimum specifications of the inner fin 22 can be determined. The
predetermined condition is set in such a manner that the
temperature Tg1 at the exhaust gas inlet is equal to 400.degree.
C., the exhaust gas flow amount is equal to 30 g/s, the exhaust gas
inlet pressure Pg1 is equal to 50 kPa, the temperature Tw1 at the
cooling water inlet is equal to 80.degree. C. and the flow amount
of cooling water is equal to 10 L/min.
[0063] FIG. 7 shows the relation between the fin pitch height fh
and a pressure loss ratio (.DELTA.Pg ratio). The pressure loss is a
difference between the exhaust gas pressure Pg1 at the exhaust gas
inlet of the water side tank 14 and the exhaust gas pressure Pg2 at
the exhaust gas outlet of the water side tank 14. The pressure loss
ratio (.DELTA.Pg ratio) is a ratio (percentage) when the maximum
value of the pressure loss at the various conditions is set as
100.
[0064] In this case, the offset fin 22 is provided with the plate
thickness of about 0.2 mm, the fin pitch fp of about 5 mm or 7 mm,
the length L (which is dimension in exhaust gas flowing direction
and named segment length L later) of the lanced segment 32 of about
1 mm or 5 mm, and the curvature radius R (of convex portion 31) of
about 0.2 mm.
[0065] The curves A-C shown in FIG. 7, indicating the relation
between .DELTA.Pg and fh, are obtained in such a manner that the
build of the EGR cooler 10 has a fixed value (that is, size of
water side tank 23 and that of gas side tank 24 are fixed) and the
fin pitch fp and the segment length L are provided with different
values.
[0066] The curve A is obtained in such a manner that the fin pitch
fp is equal to about 5 mm and the segment length L is equal to
about 1 mm. The curve B is obtained in such a manner that the fin
pitch fp is equal to about 5 mm and the segment length L is equal
to about 5 mm. The curve B is obtained in such a manner that the
fin pitch fp is equal to about 7 mm and the segment length L is
equal to about 5 mm.
[0067] With reference to the curve A shown in FIG. 7, the ascent
variation ratio of the pressure loss when the fin height fh is
smaller than or equal to 3.5 mm is larger that when the fin height
fh is larger than 3.5 mm. There are inflection points at the curves
A-C when the fin height fh is equal to about 3.5 mm. That is, the
ascent variation ratio of the pressure loss has different values at
the two sides of the in height fh of 3.5 mm.
[0068] Thus, in the case where the built of the cooler has the
fixed value and the fin pitch fp and the segment length L are
substantially equal to each other, the pressure loss when fh is
smaller than or equal to 3.5 mm is relatively large and the
pressure loss when fh is larger than 3.5 mm is relatively small.
Therefore, it is desirable for the fin height fh to be larger than
3.5 mm.
[0069] FIG. 8 shows the relation between the fin height fh and a
hydraulic resistance .DELTA.Pw which is a difference between a
water pressure at the cooling water inlet 23a of the water side
tank 23 and the cooling water outlet 23a thereof. The relation
shown in FIG. 8 is obtained with the inner fin 22 being provided
with a same condition as that of FIG. 7.
[0070] As shown in FIG. 8, when the fin height fh becomes large and
the build of the EGR cooler 10 has a fixed value, the hydraulic
resistance .DELTA.Pw tends to increase. Thus, a water pump having a
high performance becomes necessary to maintain the flowing amount
of cooling water (in order to maintain cooling performance) when
the hydraulic resistance .DELTA.Pw becomes lager than or equal to 3
kPa. For example, the hydraulic resistance .DELTA.Pw is
substantially equal to 3.2 kPa in the case where the fin height fh
is set as 12 mm. Thus, the cost will become high. Therefore, it is
desirable for the fin height fh to be smaller than or equal to 10
mm.
[0071] Furthermore, when the fin pitch fp becomes small, the offset
amount s will become small. In the case where the fin plate
thickness t is smaller than or equal to about 0.2 mm, the offset
amount s will become excessively small when the fin pitch fp is
smaller than or equal to about 2 mm. Thus, the inner fin 22 will be
susceptible to being clogged by coal in exhaust gas. Therefore, it
is desirable for the fin pitch fp to be larger than 2 mm.
[0072] The offset amount s can be set to be larger than 0.5 mm,
considering that the advantage sedimentation thickness of the PM
(particulate matter) at the surface of the single lanced segment 32
is about 0.25 mm when about 8 hours has elapsed, as shown in FIGS.
13A and 13B. Thus, the clogging can be restricted.
[0073] Moreover, the heat-radiating capacity of the inner fin 22
can be heightened, by shortening the segment length L. In this
case, the relation between the fin pitch fp and the heat-radiating
capacity of the inner fin 22 in the case where the segment length L
is provided with a minimum value is investigated. As a result, when
the fin pitch fp is larger than about 16 mm, it is difficult for
the EGR cooler 10 to be provided with the necessary heat-radiating
capacity. Accordingly, it is desirable for the fin pitch fp to be
smaller than or equal to about 16 mm. Moreover, it is desirable
that the fin pitch fp is smaller than or equal to 12 mm, which is
an approximate maximum fin pitch for satisfying the performance
required by the exhaust gas regulation, as shown in FIG. 14. In
FIG. 14, Q represents the heat radiating amount of the EGR cooler
10, and V represents the capacity of the core (which contributes to
heat-exchanging and includes exhaust gas passage and cooling water
passage) of the EGR cooler 10. In this case, the relation between
Q/V and fp (fin pitch) is determined with respectively setting the
fin height fh as 12 mm (fh12) and 3.6 mm (fh3.6) and setting the
segment length L as 1 mm (L1) and 10 mm (L10).
[0074] According to the above-described investigations, it is
desirable for the fin pitch fp and the fin height fh to be in the
range defined by the following formula (I).
3.5 mm<fh.ltoreq.12 mm
2 mm<fp.ltoreq.12 mm (1)
[0075] Thus, the pressure loss of exhaust gas flowing in the tube
21 and the hydraulic resistance .DELTA.Pw of cooling water flowing
at the outer side of the tube 21 can be restricted, so that the
tube 21 can be restricted from being clogged and the heat radiating
capacity can be improved.
Second Embodiment
[0076] According to a second embodiment of the present invention,
the optimum specifications of the inner fin 22 are determined
according to different criterions and parameters from those of the
above-described first embodiment.
[0077] In the second embodiment, the optimum specifications of the
inner fin 22 are determined based on the relation between an
equivalent circle diameter de and an EGR gas density ratio
.rho..
[0078] In this case, as shown in FIG. 6, the equivalent circle
diameter de means a diameter of an equivalent circle into which the
field C in the cross section (substantially perpendicular to
exhaust gas flowing direction) of the inner fin 22 is converted.
The field C is positioned between the convex portions 31 which are
arranged at the crest positions (or trough positions) and adjacent
to each other, and surrounded by the inner fin 22 and the tube 21.
The equivalent circle diameter de can be calculated by the
following formula (2).
de=4.times.S/W (2)
[0079] S represents an area (which corresponds to the cross section
area of the circle and is calculated by .PI.D.sup.2/4 wherein the
circle diameter is represented by D) of the cross section of the
exhaust gas passage. W represents a length of a wetted perimeter
corresponding to a circumference calculated by .PI.D wherein the
circle diameter is represented by D. The length W is a length (that
is, length of the part where the inner wall surface contacts
exhaust gas) of the inner wall surface of the single gas passage
defined by the inner fin 22 and the tube 21.
[0080] Next, the calculation of the equivalent circle diameter de
will be described. FIG. 9 is a schematic sectional view of the
inner fin 22 which is taken long the direction perpendicular to the
exhaust gas flowing direction.
[0081] As shown in FIG. 9, the half of the wetted perimeter length
W/2 (corresponding to right half of the dotted field C shown in
FIG. 6, for example) is indicated by five parts w1-w5. The half of
the wetted perimeter length W/2, which is a sum of w1-w5 (that is,
W/2=w1+w2+w3+w4+w5), can be calculated based on the fin pitch fp,
the fin height fh, the plate thickness t and the curvature radius R
of the bent portion of the inner fin 22 according to the following
formulas (3)-(7) when the linear length of the part w3 is larger
than or equal to zero.
w1=fp/2-(fp/2-(2R+t))/2 (3)
w2= (R+t)/2 (4)
w3=fh-2(R+t) (5)
w4=.PI.R/2 (6)
w5=(fp/2-(2R+t))/2 (7)
[0082] The half of the cross section area S/2 of the gas passage
(corresponding to right half of the dotted field C shown in FIG. 6,
for example) is indicated by four parts a-d. The half of the cross
section area S/2, which is a sum of a-d (that is, S/2=a+b+c+d), can
be calculated based on the fin pitch fp, the fin height fh, the
plate thickness t and the curvature radius R of the bent portion
according to the following formulas (8)-(11).
a=(fh-t)(fp/2-(2R+t))/2 (8)
b=(fh-(R+t))R (9)
c=.PI.R2/4 (10)
d=(R+t)2-.PI.(R+t)2/4 (11)
[0083] Therefore, the equivalent circle diameter de can be
determined according to the fin pitch fp, the fin height fh, the
plate thickness t and the curvature radius R of the bent
portion.
[0084] On the other hand, the EGR gas density .rho. (having a unit
of kg/m.sup.3, for example) is a factor considering both the
cooling capacity of the EGR cooler 10 and the pressure loss, and
can be calculated according to the following formula (12). The
filling factor of the EGR gas will become high when the EGR gas
density .rho. becomes large. Thus, the EGR rate can be
increased.
.rho.=Pg2/(RTg2) (12)
[0085] Pg2 represents an absolute pressure (Pa) of the gas outlet.
R represents a gas constant 287.05 J/kgK. Tg2 represents a
temperature (K) of the gas outlet.
[0086] FIG. 10 shows a relation between the equivalent circle
diameter de and the EGR gas density ratio (.rho. ratio), which is a
ratio when the maximum value of the EGR gas density .rho. is set as
100%. The relations shown in FIG. 10 are obtained with the gas
inlet temperature Tg1 of about 400.degree. C., the gas flowing
amount of about 30 g/s, the gas inlet pressure Pg1 of about 50 kPa,
the cooing water inlet temperature Tw1 of about 80.degree. C., the
cooling water flowing amount of about 10 L/min, the fin plate
thickness t of about 0.2 mm, the fin height fh of about 9 mm and
the curvature radius of about 0.2 mm.
[0087] The curve D shown in FIG. 10 is measured when the segment
length L is equal to about 1 mm, and the curve E shown in FIG. 10
is measured when the segment length L is equal to about 5 mm. When
the segment length L is in the range of about 0<L<5, the
relation between the equivalent circle diameter de and the EGR gas
density ratio can be indicated by a curve similar to the curve D.
When the segment length L is in the range of about
5.ltoreq.L.ltoreq.15, the relation can be indicated by a curve
similar to the curve E.
[0088] With reference to the curve D in FIG. 10, in the case of
about 0<L<5, the .rho. ratio can become larger than or equal
to about 93% by setting the equivalent circle diameter de in the
range of about 1.2.ltoreq.de.ltoreq.6.1, the .rho. ratio can become
larger than or equal to about 95% by setting the equivalent circle
diameter de in the range of about 1.3.ltoreq.de.ltoreq.5.3, and the
.rho. ratio can become larger than or equal to about 97% by setting
the equivalent circle diameter de in the range of about
1.5.ltoreq.de.ltoreq.4.5.
[0089] With reference to the curve E in FIG. 10, in the case of
about 5.ltoreq.L.ltoreq.15, the .rho. ratio can become larger than
or equal to about 93% by setting the equivalent circle diameter de
in the range of about 1.0.ltoreq.de.ltoreq.4.3, the .rho. ratio can
become larger than or equal to about 95% by setting the equivalent
circle diameter de in the range of about 1.1.ltoreq.de.ltoreq.4.0,
and the .rho. ratio can become larger than or equal to about 97% by
setting the equivalent circle diameter de in the range of about
1.3.ltoreq.de.ltoreq.3.5.
[0090] In this case, the segment length L and the equivalent circle
diameter de and the like are provided with the unit of mm.
[0091] The relation shown in FIG. 10 is measured when the plate
thickness t and the curvature radius R of the fin are equal to 0.2
mm. This relation can be indicated by curves similar to the curves
D and E, even when the plate thickness t and the curvature radius R
are changed in the range which can be embodied. For example, this
relation can be indicated by curves similar to the curves D and E'
when the plate thickness t and the curvature radius R are
respectively changed in the range from 0.1 mm to 0.2 mm.
[0092] About the construction of the EGR cooler 10, what has not
described in the second embodiment is the same as the first
embodiment.
Third Embodiment
[0093] According to a third embodiment of the present invention,
the optimum specifications of the inner fin 22 are determined
according to different criterions and parameters from those of the
above-described embodiments.
[0094] In the third embodiment, the optimum specifications of the
inner fin 22 are determined based on the relation between the
segment length L and the EGR gas density ratio (.rho. ratio).
[0095] FIG. 11 shows the relation between the segment length L and
the EGR gas density ratio (.rho. ratio), which is a ratio when the
maximum value of the EGR gas density .rho. is set as 100%. The
relation shown in FIG. 11 is obtained with the same condition as
that of FIG. 10, excepting the fin height fh and the segment length
L.
[0096] The curve F in FIG. 11 is calculated when fh<7 and
fp.ltoreq.5, for example, when fh is equal to 4.6 and fp is equal
to 4.5. Thus, when the segment length L is in the range of
0.5<L.ltoreq.65, the EGR gas density ratio (.rho. ratio) can be
larger than or equal to about 95%. When the segment length L is in
the range of 0.5<L.ltoreq.25, the .rho. ratio can be larger than
or equal to about 97%. When the segment length L is set in the
range of 0.5<L.ltoreq.7, the .rho. ratio can be larger than or
equal to about 99%.
[0097] The curve G in FIG. 11 is calculated when fh<7 and
fp>5, for example, when fh is equal to about 4.6 and fp is equal
to about 5.5. Thus, when the segment length L is in the range of
0.5<L.ltoreq.20, the EGR gas density ratio (.rho. ratio) can be
larger than or equal to about 95%. When the segment length L is in
the range of 0.5<L.ltoreq.8, the .rho. ratio can be larger than
or equal to about 97%. When the segment length L is in the range of
0.5<L.ltoreq.1, the .rho. ratio can be larger than or equal to
about 99%.
[0098] The curve H in FIG. 11 is calculated when fh.gtoreq.7 and
fp.ltoreq.5, for example, when fh is equal to about 9 and fp is
equal to about 4.5. Thus, when the segment length L is in the range
of 0.5<L.ltoreq.50, the EGR gas density ratio (.rho. ratio) can
be larger than or equal to about 95%. When the segment length L is
in the range of 0.5<L.ltoreq.15, the .rho. ratio can be larger
than or equal to about 97%. When the segment length L is set in the
range of 0.5<L.ltoreq.4.5, the .rho. ratio can be larger than or
equal to about 99%.
[0099] The curve I in FIG. 11 is calculated when fh.gtoreq.7 and
fp>5, for example, when fh is equal to about 9 and fp is equal
to about 5.5. Thus, when the segment length L is in the range of
0.5<L.ltoreq.15, the EGR gas density ratio (.rho. ratio) can be
larger than or equal to about 95%. When the segment length L is in
the range of 0.5<L.ltoreq.6, the .rho. ratio can be larger than
or equal to about 97%. When the segment length L is in the range of
0.5<L.ltoreq.1.5, the .rho. ratio can be larger than or equal to
about 99%.
[0100] In this case, the fin pitch fp, the fin height fh, the
segment length L and the like are provided with the unit of mm. The
relation shown in FIG. 11 is obtained when the plate thickness t
and the curvature radius R of the inner fin 22 are equal to about
0.2 mm. This relation can be indicated by curves similar to the
curves F-I, even when the plate thickness t and the curvature
radius R are changed in the range which can be embodied. For
example, this relation can be indicated by curves similar to the
curves F-I when the plate thickness t and the curvature radius R
are respectively changed in the range from 0.1 mm to 0.2 mm.
[0101] About the construction of the EGR cooler 10, what has not
described in the third embodiment is the same as the first
embodiment.
Fourth Embodiment
[0102] According to a fourth embodiment of the present invention,
the optimum specifications of the inner fin 22 are determined
according to different criterions and parameters from those of the
above-described embodiments.
[0103] In the fourth embodiment, the optimum specifications of the
inner fin 22 are determined based on the relation between the EGR
gas density ratio (.rho. ratio) and a function X using the
equivalent circle diameter de, the segment length L and the fin
height fh.
[0104] FIG. 12 shows the relation between the EGR gas density ratio
(.rho. ratio) and the function X which can be indicated by the
following formula (13).
X=de.times.L.sup.0.14/fh.sup.0.18 (13)
[0105] Moreover, FIG. 12 shows the calculation result a of the EGR
gas density ratio (.rho. ratio) in the case where the fin pitch fp,
the fin height fh and the segment length L are respectively
provided with various values.
[0106] The curves in FIG. 10 are obtained in the case where the fin
pitch fp has an arbitrary value while the segment length L and the
fin height fh are provided with a fixed value.
[0107] Specifically, the fin pitch fp is provided with a value in
the substantial range from 1.5 mm to 14 mm, while the fin height fh
is substantially equal to one of 3.6 mm, 4.6 mm, 5.6 mm, 7 mm, 9 mm
and 12 mm and the segment length L is substantially equal to one of
1 mm and 10 mm. Other measurement conditions of FIG. 12 are same as
those of FIGS. 10 and 11.
[0108] As shown in FIG. 12, the curves indicating the relation
between the EGR gas density ratio (.rho. ratio) and the function X
show a similar tendency under different conditions. Thus, when the
segment length L and the equivalent circle diameter de are set so
that the function X has a value in the substantial range of
1.1.ltoreq.X.ltoreq.4.3, the EGR gas density ratio (.rho. ratio)
can be larger than or equal to about 93%. When the segment length L
and the equivalent circle diameter de are set so that the function
X has a value in the substantial range of 1.2.ltoreq.X.ltoreq.3.9,
the .rho. ratio can be larger than or equal to about 95%.
[0109] The segment length L and the equivalent circle diameter de
can be set so that the function X has a value in the substantial
range of 1.3.ltoreq.X.ltoreq.3.5. Thus, the .rho. ratio can be
larger than or equal to about 97%. Furthermore, the size of the
core of the exhaust gas heat exchanger can be reduced.
[0110] In this case, the function X and the like is provided with
the unit of mm. The relations shown in FIG. 12 are obtained when
the plate thickness t and the curvature radius R of the fin are
equal to about 0.2 mm. This relation can be indicated similarly to
what is shown in FIG. 12, even when the plate thickness t and the
curvature radius R are changed in the range which can be embodied.
For example, this relation can be indicated similarly when the
plate thickness t and the curvature radius R are respectively
changed in the range from 0.1 mm to 0.2 mm.
[0111] About the construction of the EGR cooler 10, what has not
described in the fourth embodiment is the same as the first
embodiment.
Other Embodiment
[0112] Although the present invention has been fully described in
connection with the preferred embodiments thereof with reference to
the accompanying drawings, it is to be noted that various changes
and modifications will become apparent to those skilled in the
art.
[0113] The exhaust gas heat exchanger according to the present
invention can be also suitably used as an EGR cooler which is
arranged at a halfway portion of the second exhaust gas
recirculation pipe 12 through which a part of the exhaust gas of
the engine 1 is returned directly to the suction side of the engine
1 before flowing through the DPF 8.
[0114] Moreover, the present invention can be also suitably used
for the other exhaust gas heat exchanger made of a stainless steel
or the like, other than the EGR cooler. The present invention can
be suitably used for the exhaust gas heat exchanger through which
cooling water is heat-exchanged with exhaust gas discharged to the
ambient air to be heated.
[0115] Such changes and modifications are to be understood as being
in the scope of the present invention as defined by the appended
claims.
* * * * *