U.S. patent application number 14/138345 was filed with the patent office on 2014-04-24 for double-wall pipe, method of manufacturing the same and refrigerant cycle device provided with the same.
This patent application is currently assigned to DENSO AIR SYSTEMS CORPORATION. The applicant listed for this patent is DENSO AIR SYSTEMS CORPORATION, DENSO CORPORATION. Invention is credited to Shun KURATA, Hiroki NAGANAWA, Fumiaki NAKAMURA, Kinji OCHIAI, Hiroki OHARA, Takashi ONO, Takahisa SUZUKI, Yoshiaki TAKANO.
Application Number | 20140109373 14/138345 |
Document ID | / |
Family ID | 36284421 |
Filed Date | 2014-04-24 |
United States Patent
Application |
20140109373 |
Kind Code |
A1 |
NAKAMURA; Fumiaki ; et
al. |
April 24, 2014 |
Double-Wall Pipe, Method Of Manufacturing The Same And Refrigerant
Cycle Device Provided With The Same
Abstract
A double-wall pipe includes an outer pipe, and an inner pipe
disposed inside the outer pipe. An outer wall of the inner pipe has
thereon a ridge portion, which defines a groove portion extending
in a longitudinal direction of the inner pipe. The outer pipe and
the inner pipe are bent to have a straight portion extending
straightly, and a bend portion bent from the straight portion. In
the straight portion, the outer pipe has an inside diameter that is
larger than an outside diameter of an imaginary cylinder defined by
an outer surface of the ridge portion of the inner pipe.
Furthermore, the ridge portion of the inner pipe contacts an inside
surface of the outer pipe to be radially squeezed and held by the
outer pipe, in the bend portion. The double-wall pipe can be
suitably used for a refrigerant cycle device.
Inventors: |
NAKAMURA; Fumiaki;
(Kariya-city, JP) ; TAKANO; Yoshiaki; (Kosai-city,
JP) ; KURATA; Shun; (Kariya-city, JP) ;
SUZUKI; Takahisa; (Nagoya-city, JP) ; ONO;
Takashi; (Okazaki-city, JP) ; NAGANAWA; Hiroki;
(Nishio-city, JP) ; OCHIAI; Kinji; (Kasugai-city,
JP) ; OHARA; Hiroki; (Kariya-city, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DENSO AIR SYSTEMS CORPORATION
DENSO CORPORATION |
Anjo-city
Kariya-city |
|
JP
JP |
|
|
Assignee: |
DENSO AIR SYSTEMS
CORPORATION
Anjo-city
JP
DENSO CORPORATION
Kariya-city
JP
|
Family ID: |
36284421 |
Appl. No.: |
14/138345 |
Filed: |
December 23, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12927924 |
Nov 30, 2010 |
|
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14138345 |
|
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|
11269265 |
Nov 8, 2005 |
7866378 |
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12927924 |
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Current U.S.
Class: |
29/428 |
Current CPC
Class: |
Y10T 29/49428 20150115;
F25B 40/00 20130101; F16L 7/00 20130101; F28F 1/426 20130101; F28F
2210/06 20130101; B23P 17/02 20130101; F28D 7/106 20130101; F28F
1/06 20130101; F16L 9/18 20130101; Y10T 29/49361 20150115; F28F
1/42 20130101; Y10T 29/49826 20150115 |
Class at
Publication: |
29/428 |
International
Class: |
B23P 17/02 20060101
B23P017/02 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 9, 2004 |
JP |
2004-325521 |
Nov 9, 2004 |
JP |
2004-325522 |
Apr 8, 2005 |
JP |
2005-112825 |
May 9, 2005 |
JP |
2005-136390 |
Sep 12, 2005 |
JP |
2005-263967 |
Claims
1. A method of manufacturing a double-wall pipe including an outer
pipe and an inner pipe, the method comprising the steps of: forming
a groove portion extending in a longitudinal direction on an outer
wall of the inner pipe, so as to form thereon a ridge portion
defining the groove portion; inserting the inner pipe into the
outer pipe having an inside diameter greater than an outside
diameter of an imaginary cylinder defined by an outer surface of
the ridge portion of the inner pipe, after the groove portion is
formed; and bending a part of both the inner pipe and the outer
pipe after the inserting step, to form a bend portion in such a
manner that the ridge portion contacts an inside surface of the
outer pipe by radially squeezing and deforming the outer pipe in
the bend portion, thereby the outer pipe squeezes the inner pipe
radially to hold and fix the inner pipe therein in the bend
portion.
2. The method according to claim 1, wherein: in the forming step of
the groove portion, a helical groove of the groove portion
extending helically in the longitudinal direction is formed by
deforming radially inside the outer wall of the inner pipe.
3. The method according to claim 1, wherein: in the forming step of
the groove portion, the groove portion is formed to have a groove
depth in a range of 5% to 15% of an outside diameter of the inner
pipe.
4. The method according to claim 1, wherein: in the forming step of
the groove portion, the groove portion is formed to have a
longitudinal length in a range of 300 mm to 800 mm.
5. The method according to claim 1, wherein the inner pipe is
formed in such a manner that an outside diameter of the outer pipe
is in a range of 1.1 to 1.3 times of an outside diameter of the
inner pipe.
6. The method according to claim 5, wherein the bending step is
performed in such a manner that a minimum outside diameter of the
outer pipe in the bend portion is equal to or larger than 0.85
times of an outside diameter of the outer pipe in the straight
portion.
7. The method according to claim 1, wherein the forming step of the
groove portion is performed such that the outside diameter of an
imaginary cylinder defined by an outer surface of the ridge portion
is in a range of 0.7 to 0.95 times of an inside diameter of the
outer pipe.
8. The method according to claim 1 further comprising: forming a
branch pipe branching out from an end part of the outer pipe.
9. The method according to claim 8, further comprising: connecting
a connection pipe to an end of the inner pipe.
10. The method according to claim 9, further comprising: forming a
holding member for fixedly holding the branch pipe and the
connecting pipe in a predetermined positional relation.
11. The method according to claim 10, wherein the holding member is
fixed to the branch pipe and the connecting pipe by blazing or
fastening.
12. The method according to claim 10, wherein the holding member is
fixedly put on the branch pipe and the connecting pipe.
13. The method according to claim 8, further comprising adjusting
an end position of the branch pipe.
14. The method according to claim 13, wherein a bend portion is
formed in the branch pipe before the end portion of the branch pipe
is adjusted.
15. The method according to claim 1, wherein at least one of the
bend portions is formed in a longitudinal length of 700 mm of the
outer pipe and the inner pipe.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional of U.S. patent application
Ser. No. 12/927,924 filed on Nov. 30, 2010 which is a divisional of
U.S. patent application Ser. No. 11/269,265 filed on Nov. 8, 2005.
This application claims the benefit and priority of Japanese Patent
Applications No. 2004-325522 filed on Nov. 9, 2004, No. 2004-325521
filed on Nov. 9, 2004, No. 2005-112825 filed on Apr. 8, 2005, No.
2005-136390 filed on May 9, 2005, and No. 2005-263967 filed on Sep.
12, 2005. The entire disclosures of each of the above applications
are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a double-wall pipe having
at least a part constructed of an inner pipe defining an inner
passage and an outer pipe enveloping the inner pipe so as to define
an outer passage together with the inner pipe, and a method of
manufacturing a double-wall pipe. The double-wall pipe can be
suitably used for a refrigerant cycle device.
[0004] 2. Description of the Related Art
[0005] A double-wall pipe disclosed in JP-A-2002-318083 includes an
inner pipe, and an outer pipe enveloping the inner pipe so as to
define a passage together with the inner pipe. The double-wall pipe
is capable of performing heat exchange between a first fluid
flowing in the inner pipe and a second fluid flowing through the
passage between the inner pipe and the outer pipe.
[0006] The double-wall pipe is provided in a part thereof with a
core held in the outer pipe, and the inner pipe is extended through
the core. The part provided with the core of the double-wall pipe
is bent by a bending process using a pipe bender to form a bend
portion. The bend portion is formed through the bending process, so
that lines may not be formed in the bend portion, the bend portion
may not be irregularly bent, and the section of the double-wall
pipe may not be flattened.
[0007] Since the inner pipe and the outer pipe are separated by a
space, it is possible that the inner pipe and the outer pipe
vibrate, resonate, strike each other, and generate noise when
external force is applied to the double-wall pipe.
SUMMARY OF THE INVENTION
[0008] In view of the foregoing problem, it is an object of the
present invention to provide a double-wall pipe having a passage
between an outer pipe and an inner pipe inside of the outer part,
which holds and fixes the outer and the inner pipe with a simple
structure.
[0009] It is another object of the present invention to provide a
method of manufacturing a double-wall pipe, and a refrigerant cycle
device using a double-wall pipe.
[0010] According to an aspect of the present invention, in a
double-wall pipe includes an outer pipe and an inner pipe disposed
inside the outer pipe, the inner pipe has thereon a ridge portion
which defines a groove portion extending in a longitudinal
direction of the inner pipe, and the outer pipe and the inner pipe
are bent to have a straight portion extending straightly and a bend
portion bent from the straight portion. Furthermore, the outer pipe
has an inside diameter that is larger than an outside diameter of
an imaginary cylinder defined by an outer surface of the ridge
portion of the inner pipe in the straight portion, and the ridge
portion of the inner pipe contacts an inside surface of the outer
pipe to be radially squeezed and held by the outer pipe in the bend
portion. For example, the groove portion is a helical groove
portion winding around the inner pipe.
[0011] Accordingly, the groove portion forms a passage between the
outer pipe and the inner pipe in the bend portion, and a part of
the outer pipe and a part of the inner pipe can be fixedly held in
the bend portion by a simple structure. Therefore, even when an
external force, such as a vibratory force, is applied to the
double-wall pipe, the outer pipe and the inner pipe can be
prevented from resonation, and generation of noise and breakage of
the double-wall pipe can be prevented.
[0012] When the helical groove is provided on the outer surface of
the inner pipe, the helical groove reduces strains in the bend
portion and facilitates bending the inner pipe. In this case, a
force necessary for bending the double-wall pipe can be effectively
reduced.
[0013] For example, the helical groove portion includes helical
grooves. In this case, even when one of the helical grooves is
destroyed in the bend portion, the rest of the helical grooves can
be used as the passage between the outer pipe and the inner pipe.
Since the helical grooves enlarge the passage, resistance against
the flow of the fluid through the passage can be reduced.
[0014] The groove portion has a groove depth that is in a range of
5% to 15% of an outside diameter of the inner pipe, for example. In
this case, heat exchange between a fluid inside the inner pipe and
a fluid flowing through the passage between the inner pipe and the
outer pipe can be effectively increased while a flow resistance can
be reduced.
[0015] The resistance of the inner pipe against the flow of the
fluid flowing in the inner pipe increases in proportion to the
length of the inner pipe. Further, a temperature difference between
the fluid flowing in the inner pipe and the fluid flowing through
the passage between the outer and the inner pipe decreases as the
length of the groove portion increases. When a longitudinal length
of the groove portion is set in a range of 300 mm to 800 mm, the
heat exchange efficiency can be effectively increased. Furthermore,
the longitudinal length of a helical groove can be set in a range
between 600 mm and 800 mm.
[0016] An outside diameter of the outer pipe can be set in a range
of 1.1 to 1.3 times of an outside diameter of the inner pipe. When
a pipe is bent, a tensile force acts on the outer side of the pipe
and the length of the outer side increases. Therefore, the outside
diameter of the pipe decreases by 10 to 30%. Thus, the inside
diameter of the outer pipe decreases by 10 to 30%. In this case,
the outer pipe and the inner pipe can be surely fixed together.
[0017] Further, a minimum outside diameter of the outer pipe in the
bend portion can be set equal to or larger than 0.85 times of an
outside diameter of the outer pipe in the straight portion. In this
case, the deformation of a round section of the outer pipe into an
elliptic section in the bend portion can be controlled, the
extending deformation of the bend portion by the high-pressure
fluid flowing through the passage inside the outer pipe can be
controlled, the strain of the outer pipe can be limited, and the
outer pipe is prevented from breakage.
[0018] The outside diameter of the imaginary cylinder defined by
the outer surface of the ridge portion of the inner pipe in the
straight portion can be set in a range of 0.7 to 0.95 of the inside
diameter of the outer pipe in the straight portion.
[0019] When the double-wall pipe is bent through an angle of
10.degree. or above, the smallest inside diameter of the outer pipe
in the bend portion is 70% of the original inside diameter or
below. Therefore the outer pipe and the inner pipe can be surely
fixed together in the bend portion and the double-wall pipe is
resistant to vibration when the diameter of a circular imaginary
cylinder defined by the outer surface of the ridge portion is 70%
of the original inside diameter of the outer pipe or above. When
the outer pipe does not have high straightness, it is difficult to
insert the inner pipe into the outer pipe and the productivity of
the double-wall pipe manufacturing line lowers. Therefore, it is
desirable that an outside diameter of an imaginary cylinder defined
by the outer surface of the ridge portion of the inner pipe is 95%
of the inside diameter of the outer pipe or below.
[0020] A branch pipe can be connected to an outer pipe, and a
connecting pipe can be connected to an end of the inner pipe. In
this case, the branch pipe and the connecting pipe can be fixed
using a holding member to have a predetermined positional relation.
Furthermore, the holding member can be brazed to the branch pipe
and the connecting pipe, or can be fitted to the branch pipe and
the connecting pipe. In addition, the branch pipe can be disposed
to have a deformable portion for adjusting an end position of the
branch pipe. For example, the deformable portion is a bending
portion provided in the branch pipe.
[0021] The double-wall pipe can be suitably used for a refrigerant
cycle device having one or two refrigerant circuits.
[0022] According to another aspect of the present invention, a
method of manufacturing a double-wall pipe includes a step of
forming a groove portion extending in a longitudinal direction on
an outer wall of the inner pipe so as to form thereon a ridge
portion defining the groove portion, a step of inserting the inner
pipe into the outer pipe having an inside diameter greater than an
outside diameter of an imaginary cylinder defined by an outer
surface of the ridge portion of the inner pipe after the groove
portion is formed, and a step of bending a part of both the inner
pipe and the outer pipe after the inserting step, to form a bend
portion in such a manner that the ridge portion contacts an inside
surface of the outer pipe and the outer pipe squeezes the inner
pipe radially to hold and fix the inner pipe therein in the bend
portion. In this case, the double-wall pipe can be easily
formed.
[0023] In the forming step of the groove portion, a helical groove
of the groove portion extending helically in the longitudinal
direction can be formed by deforming radially inside the outer wall
of the inner pipe.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The above and other objects, features and advantages of the
present invention will become more apparent from the following
detailed description of preferred embodiments made with reference
to the accompanying drawings, in which:
[0025] FIG. 1 is a schematic view of an automotive air conditioning
system;
[0026] FIG. 2 is a side view of a double-wall pipe in a preferred
embodiment according to the present invention;
[0027] FIG. 3 is a sectional view of a part III in FIG. 2;
[0028] FIG. 4 is a cross-sectional view taken along the line IV-IV
in FIG. 3;
[0029] FIG. 5 is a sectional view of a part V in FIG. 2;
[0030] FIG. 6 is a cross-sectional view taken along the line VI-VI
in FIG. 5;
[0031] FIG. 7 is a perspective view showing a grooving device for
forming helical grooves on an inner pipe;
[0032] FIG. 8 is a Mollier diagram for explaining a refrigeration
cycle device using the double-wall pipe;
[0033] FIG. 9 is a graph showing the dependence of heat transfer
rate and a pressure loss in a low-pressure pipe relative to the
depth and the pitch of helical grooves;
[0034] FIG. 10 is a graph showing variations of a cooling capacity,
a heat transfer rate and a pressure loss in a low-pressure pipe
relative to a length of helical grooves;
[0035] FIG. 11A is a graph showing the relationship between a
variation of an inside diameter L of an outer pipe and a bending
angle, and FIG. 11B is a graph showing the relationship between a
helical groove pitch and a ratio L(R)/L of an outer diameter L(R)
of an imaginary cylinder connecting outer surfaces of ridges of an
inner pipe to the inside diameter L of the outer pipe;
[0036] FIG. 12 is a graph showing the relationship between a
resonance frequency and a holding pitch;
[0037] FIGS. 13A and 13B are side views showing fixing members,
respectively;
[0038] FIG. 14 is a schematic diagram showing a refrigerant cycle
device using a double-wall pipe, for a dual air conditioning
system; and
[0039] FIG. 15 is a schematic diagram showing a refrigerant cycle
device using two double-wall pipes, for a dual air conditioning
system.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Embodiment
[0040] A double-wall pipe 160 in a first embodiment according to
the present invention is typically used for a refrigerant cycle
device 100A of a vehicle air conditioning system 100. The
double-wall pipe 160 will be described with reference to FIGS. 1 to
5. FIG. 1 is a schematic view of the air conditioning system 100,
FIG. 2 is a view of the double-wall pipe 160, FIG. 3 is a sectional
view of a part III of the double-wall pipe 160 in FIG. 2, FIG. 4 is
a cross-sectional view showing a straight part 163a, FIG. 5 is a
sectional view showing a bend portion 163b in FIG. 2, FIG. 6 is a
cross-sectional view of a bend portion 163b, and FIG. 7 is a
perspective view of a grooving device 200 for forming helical
grooves 162a in an inner pipe 162.
[0041] A vehicle has an engine room 1 holding an engine 10 therein
and a passenger compartment 2 separated from the engine room 1 by a
dash panel 3. The air conditioning system 100 has the refrigerant
cycle device 100A including an expansion valve 131 and an
evaporator 141, and an interior unit 100B. Components of the
refrigerant cycle device 100A excluding the expansion valve 131 and
the evaporator 141 are disposed in a predetermined mounting space
of the engine room 1. The interior unit 100B is arranged in an
instrument panel placed in the passenger compartment 2.
[0042] The interior unit 100B has components including a blower
102, the evaporator 141 and a heater 103 and an air conditioner
case 101 housing the components of the interior unit 100B. The
blower 102 takes in outside air or inside air selectively and sends
air to the evaporator 141 and the heater 103. The evaporator 141 is
a cooling heat exchanger that evaporates a refrigerant used for a
refrigeration cycle to make the evaporating refrigerant absorb
latent heat of vaporization from air so as to cool the air. The
heater 103 uses hot water (e.g., engine-cooling water) for cooling
the engine 10 as heat source to heat air to be blown into the
passenger compartment 2.
[0043] An air mixing door 104 is disposed near the heater 103 in
the air conditioner case 101. The air mixing door 104 is operated
to adjust the mixing ratio between cool air cooled by the
evaporator 141 and hot air heated by the heater 103 so that air
having a desired temperature is sent into the passenger compartment
2.
[0044] The refrigerant cycle device 100A includes a compressor 110,
a condenser 120, the expansion valve 131 and the evaporator 141.
Pipes 150 connect those components of the refrigerant cycle device
100A to form a closed circuit. At least one double-wall pipe 160 of
the present invention can be placed in the pipes 150. The condenser
120 (refrigerant radiator, gas cooler) serves as a high-pressure
heat exchanger for cooling high-pressure high-temperature
refrigerant. The evaporator 141 serves as a low-pressure heat
exchanger and is disposed to cool air passing therethrough. The
expansion valve 131 is a pressure reducer, such as a throttle and
an ejector.
[0045] The compressor 110 is driven by the engine 10 to compress a
low-pressure refrigerant to provide a high-temperature
high-pressure refrigerant in the refrigerant cycle device 100A. A
pulley 111 is attached to the drive shaft of the compressor 110. A
drive belt 12 is extended between the pulley 111 and a crankshaft
pulley 11 to drive the compressor 110 by the engine 10. The pulley
111 is linked to the drive shaft of the compressor 110 by an
electromagnetic clutch (not shown). The electromagnetic clutch
connects the pulley 111 to or disconnects the pulley 111 from the
drive shaft of the compressor 110. The condenser 120 is connected
to a discharge side of the compressor 110. The condenser 120 is a
heat exchanger that cools the refrigerant by outside air to
condense the refrigerant vapor into liquid refrigerant.
[0046] The expansion valve 131 reduces the pressure of the
refrigerant (liquid refrigerant) discharged from the condenser 120
and makes the refrigerant expand. The expansion valve 131 is a
pressure-reducing valve capable of reducing the pressure of the
liquid refrigerant in an isoentropic state. The expansion valve 131
included in the interior unit 100B is placed near the evaporator
141. The expansion valve 131 is a temperature-controlled expansion
valve having a variable orifice and is capable of controlling the
flow of the refrigerant discharged from the evaporator 141 and
flowing into the compressor 110 so that the refrigerant is heated
at a predetermined degree of superheat. The expansion valve 131
controls the expansion of the refrigerant so that the degree of
superheat of the refrigerant in the evaporator 141 is, for example,
5.degree. C. or below, more specifically, in the range of 0.degree.
C. to 3.degree. C. As described above, the evaporator 141 is a
cooling heat exchanger for cooling air to be blown into the
passenger compartment. The discharge side of the evaporator 141 is
connected to the suction side of the compressor 110.
[0047] The double-wall pipe 160 is formed by combining a part of a
high-pressure pipe 151 and a part of a low-pressure pipe 152 in the
pipes 150. The high-pressure pipe 151 extends between the condenser
120 and the expansion valve 131 to carry the high-pressure
refrigerant before being decompressed. The low-pressure pipe 152
extends between the evaporator 141 and the compressor 110 to carry
a low-temperature low-pressure refrigerant after being decompressed
and cooled.
[0048] For example, the double-wall pipe 160 has a length in the
range of 700 to 900 mm. As shown in FIGS. 2 to 6, the double-wall
pipe 160 has a straight part 163a having an outside diameter L0 and
a plurality of bend portions 163b and is extended in the engine
room 1 so that the double-wall pipe 160 may not touch the engine 10
and other equipments and the body of the vehicle.
[0049] The double-wall pipe 160 has an outer pipe 161 and an inner
pipe 162. The inner pipe 162 is inserted into the outer pipe 161.
The outer pipe 161 is, for example, a 22 mm diameter aluminum pipe
having an outside diameter L0 of 22 mm and an inside diameter of
19.6 mm. End parts of the outer pipe 161 are reduced after
connecting the outer pipe 161 and the inner pipe 162, to form
reduced joining parts. The reduced joining parts of the outer pipe
161 are air-tightly welded to the inner pipe 162 having an outside
diameter of 19.1 mm. In this embodiment, the outside diameter of
the inner pipe 162 in the part having the helical grooves 162a
corresponds to the diameter of an imaginary cylinder connecting the
outside surfaces of ridges 162b of the inner pipe 162. After the
helical grooves 162a are formed, the maximum outside diameter of
the inner pipe 162 in the part having the helical grooves 162a
corresponds to the outside diameter of the imaginary cylinder
defined by the outside surfaces of the ridges 162b of the inner
pipe 162. Thus, the outer pipe 161 and the inner pipe 162 define a
passage 160a therebetween. For example, the ratio of the outside
diameter of the outer pipe 161 to the outside diameter of the inner
pipe 162 corresponding to the diameter of the imaginary cylinder
connecting the outside surfaces of the ridges 162b of the inner
pipe 162 is 1.2 (=22/19.1). In this embodiment, the outside
diameter of the outer pipe 161 can be set in a range of 1.1 to 1.3
times of the outside diameter of the inner pipe 162. Further, when
the ratio is set in a range between 1.1 and 1.2, the performance of
the double-wall pipe 160 can be further improved.
[0050] Liquid tubes 164 and 165 (high-pressure refrigerant pipes)
made of aluminum, that is, branch pipes, are connected to end parts
of the outer pipe 161 by brazing so as to communicate with the
passage 160a. The liquid pipe 164 has plural bend portions 164a
(e.g., three) and extends to the condenser 120. A joint 164b is
attached to the free end of the liquid tube 164. The liquid tube
165 has plural bend portions 165a (e.g., three) and extends to the
expansion valve 131. A joint 165b is attached to the free end of
the liquid tube 165. The joint 164b is connected to the condenser
120 and the joint 165b is connected to the expansion valve 131.
Therefore, the high-pressure refrigerant from the condenser 120
flows through the liquid tube 164, the passage 160a and the liquid
tube 165.
[0051] The inner pipe 162 is, for example, a 3/4 in. aluminum pipe
having an outside diameter of 19.1 mm and an inside diameter of
16.7 mm. The outside diameter of the inner pipe 162 is determined
so that the passage 160a has a sectional area large enough to pass
the high-pressure refrigerant, and the outer surface of the inner
pipe 162 is as close to the inner surface of the outer pipe 161 as
possible. Thus, the inner pipe 162 has the largest possible heat
transfer surface area.
[0052] Suction pipes 166 and 167 made of aluminum are also used as
a part of the low-pressure pipes 152. The suction pipes 166 and 167
are connected to the end parts of the inner pipe 162, respectively.
The suction pipe 166 is positioned at the side of the liquid tube
165, and the suction pipe 167 is positioned at the side of the
liquid tube 164, as shown in FIG. 2. Joints 166a and 167a are
attached to the free ends of the suction pipes 166 and 167,
respectively. The joints 166a and 167a are connected to the
evaporator 141 and the compressor 110, respectively. Thus, the
low-pressure refrigerant flows through the suction pipe 166, the
inner pipe 162 and the suction pipe 167.
[0053] Annular grooves 162c (e.g., two) and helical grooves 162a
(e.g., three) are formed on the surface of a part, corresponding to
the passage 160a, of the inner pipe 162. The annular grooves 162c
are provided at positions corresponding to the joint portion
between the liquid tube 164 and the outer pipe 161 and the joint
portion between the liquid tube 165 and the outer pipe 161,
respectively. Each of the annular grooves 162c is a circumferential
groove extending in a circumferential direction at least by a
predetermined angle. The helical grooves 162a communicate with the
annular grooves 162c and extend between the two annular grooves
162c. Ridges 162b are formed on the outer wall surface of the inner
pipe 162. The helical grooves 162a and the ridges 162b are arranged
circumferentially alternately to extend in a pipe longitudinal
direction. The diameter of an imaginary cylinder connecting the
outer surfaces of the ridges 162b is substantially equal to or
slightly smaller than the outside diameter of the inner pipe 162.
The annular grooves 162c and the helical grooves 162a enlarge the
passage 160a between the inner pipe 162 and the outer pipe 161.
[0054] The grooved depth of the helical grooves 162a, that is, half
the difference between the diameter of an imaginary cylinder
connecting the outer surfaces of the ridges 162b and the diameter
of an imaginary cylinder connecting the bottom surfaces of the
helical grooves 162a, is in the range of 5 to 15% of the outside
diameter of the inner pipe 162, that is, the diameter of the
imaginary cylinder connecting the outer surfaces of the ridges
162b, based on the performance of the double-wall pipe 160. The
length of the helical grooves 162a along a pipe longitudinal
direction is set in a range between 300 and 800 mm. The length of
the helical grooves 162a corresponds to the length of a part, in
which the helical grooves 162a are formed, of the inner pipe
162.
[0055] The annular grooves 162c and the helical groove 162a of the
inner pipe 162 can be formed by a grooving tool 200 shown in FIG. 7
by way of example. The grooving tool 200 has an annular block 210,
three balls 220 and three bolts 230 for determining and adjusting
the positions of the balls 220. The annular block 210 is provided
with a center hole 210a in which the inner pipe 162 is inserted,
and three internally threaded radial bores. The balls 220 are
disposed into the bores and the bolts 230 are screwed into the
radial bores. The bolts 230 are turned to adjust the radial
positions of the balls 220 so that the balls 220 protrude from the
inner ends of the radial bores by a predetermined distance. The
three sets, each of which has the ball 220 and the bolt 230, form
the three helical grooves 162a. The inner pipe 162 is inserted into
the center hole 210a, the longitudinal end parts of the inner pipe
162 are fixedly held by holding devices (not shown), and then the
bolts 230 are turned to press the balls 220 to the surface of the
inner pipe 162 by a predetermined depth corresponding to the depth
of the helical grooves 162a.
[0056] Then, the annular block 210 holding the balls 220 and the
bolts 230 is turned, so as to form the annular grooves 162c.
Subsequently, the annular block 210 is rotated and is moved along
the longitudinal axis of the inner pipe 162, so as to form the
helical grooves 162a. The moving speed of the annular block 210 is
adjusted so that the helical grooves 162a are formed at desired
pitches. After the helical grooves 162a have been formed, the
annular block 210 is kept rotating while the longitudinal movement
of the annular block 210 is stopped, so as to form the other
annular groove 162c.
[0057] Referring to FIGS. 5 and 6, in the bend portion 163b of the
double-wall pipe 160 in the first embodiment, the ridges 162b are
in contact with the inside surface of the outer pipe 161 and the
outer pipe 161 squeezes the inner pipe 162, thereby holding the
inner pipe fixedly in the outer pipe 161. A desired part of the
double-wall pipe 160 is bent to form the bend portion 163b, after
inserting the inner pipe 162 provided with the annular grooves 162c
and the helical grooves 162a into the outer pipe 161. In this case,
a part, corresponding to the bend portion 163b, of the outer pipe
161 is deformed and the round cross section of the same part of the
outer pipe 161 changes into an elliptic cross section before the
inner pipe 162 is deformed. Consequently, the outer pipe 161 comes
into contact with the ridges 162b and squeezes the inner pipe 162
radially so as to hold the inner pipe 162 fixedly in the outer pipe
161.
[0058] As shown in FIG. 5, the bend portion 163b is formed such
that inner side of the part, corresponding to the bend portion
163b, of the outer pipe 161 is curved in a circular shape having a
radius R1 of curvature. The bend portion 163b may contain an angle
of about 90.degree.. As shown in FIG. 6, the part, corresponding to
the bend portion 163b, of the outer pipe 161 is deformed so that
the round cross section thereof is changed into an elliptic cross
section. A part, corresponding to a middle part of the bend portion
163b, of the outer pipe 161 has a major axis of a length L2 greater
than the original outside diameter L0, and a minor axis of a length
L1 shorter than the length L2. When the outer pipe 161 is deformed,
the ridges 162b defining the helical grooves 162a of the inner pipe
162 come into contact with the inside surface of the outer pipe
161. Thus, the outer pipe 161 squeezes the inner pipe 162 radially
to hold the inner pipe 162 fixedly therein.
[0059] The outside diameter of the inner pipe 162, that is, the
diameter of an imaginary cylinder connecting the outer surfaces of
the ridges 162b, is in the range of 0.7 to 0.95 or 0.8 to 0.95
times of the original inside diameter of the outer pipe 161 to
enable the outer pipe 161 to hold the inner pipe 162 fixedly
therein.
[0060] At least one bend portion 163b in which the inner pipe 162
is held fixedly by the outer pipe 161 can be formed in a length of
700 mm of the double-wall pipe 160 to improve the vibration
resistance of the double-wall pipe 160. The double-wall pipe 160 in
the first embodiment is provided with the two bend portions 163b in
a length of 700 mm.
[0061] The double-wall pipe 160 has the straight part 163a and the
bend portions 163b. In the straight part 163a, the diameter of an
imaginary cylinder connecting the outer surfaces of the ridges 162b
of the inner pipe 162 is smaller than the inside diameter of the
outer pipe 161 as shown in FIG. 4. In the straight part 163a, the
outside surface is separated from or in partial contact with the
inside surface of the outer pipe 162. Consequently, the inner pipe
162 is able to move slightly in radial directions or able to
vibrate in the straight part 163a.
[0062] As shown in FIG. 3, the inner pipe 162 provided with the
helical grooves 162a and the ridges 162b has a wavy wall having a
pleated shape resembling a bellows. The wavy wall is deformed in
the bend portion 163b as shown in FIG. 5. The respective widths of
parts, on the inner side of the bend portion 163b, of the helical
grooves 162a and the ridges 162b are decreased and the wavy wall is
contracted. The respective widths of parts, on the outer side of
the bend portion 163b, of the helical grooves 162a and the ridges
162b are increased and the wavy wall is stretched. Thus, the inner
pipe 162 can be deformed inside the outer pipe 161 without inducing
excessively high stresses in the part thereof corresponding to the
bend portion 163b.
[0063] In the double-wall pipe 160 of the first embodiment, the
outer pipe 161 has a circular cross section and the inner pipe 162
provided with the helical grooves 162 has the shape of a bellows.
Thus, the outer pipe 161 and the inner pipe 162 have different
shapes, respectively. When the double-wall pipe 160 formed by
inserting the inner pipe 162 into the outer pipe 161 is bent, the
outer pipe 161 and the inner pipe 162 are bent simultaneously.
Since the outer pipe 161 and the inner pipe 162 have different
shapes, respectively, the outer pipe 161 and the inner pipe 162 are
strained and deformed differently. The difference between the outer
pipe 161 and the inner pipe 162 in strain and deformation
facilitates bringing the inside surface of the outer pipe 162 and
the ridges 162b of the inner pipe 162 into contact with each
other.
[0064] The inner pipe 162 is separated from the inside surface of
the outer pipe 161 or is in contact with one side of the inside
surface of the outer pipe 161 in the straight part 163a. The inner
pipe 162 is in contact with a plurality of parts of the inside
surface of the outer pipe 162 with respect to circumferential
directions in the bend portion 163b. Preferably, the inner pipe 162
is in contact with a plurality of parts of the inside surface of
the outer pipe 162 in the bend portion 163b so that the inner pipe
162 is unable to move radially relative to the outer pipe 161. For
example, the inner pipe 162 may be in contact with at least
diametrically opposite two parts or three or more circumferentially
spaced parts.
[0065] The operation and functional effect of the double-wall pipe
160 thus constructed will be described in connection with a Mollier
diagram shown in FIG. 8.
[0066] When a passenger in a passenger compartment desires to
operate the air conditioning system 100 for a cooling operation,
the electromagnetic clutch is engaged to drive the compressor 110
by the engine 10. Then, the compressor 110 sucks in the refrigerant
discharged from the evaporator 141, compresses the refrigerant and
discharges the high-temperature high-pressure refrigerant into the
condenser 120. The condenser 120 cools the high-temperature
high-pressure refrigerant into a liquid refrigerant state with a
substantially totally liquid phase. The liquid refrigerant from the
condenser 120 flows into the expansion valve 131 through the liquid
tube 164 connected to the double-wall pipe 160, and through the
passage 160a of the double-wall pipe 160. The expansion valve 131
reduces the pressure of the liquid refrigerant and allows the
liquid refrigerant to expand. The evaporator 141 evaporates the
liquid refrigerant into a substantially saturated gas refrigerant
having a degree of superheat in the range of 0.degree. C. to
3.degree. C. The refrigerant evaporated by the evaporator 141
absorbs heat from air flowing through the evaporator 141 to cool
the air to be blown into the passenger compartment. The saturated
gas refrigerant evaporated by the evaporator 141, that is, the
low-temperature low-pressure refrigerant, flows through the suction
pipe 165, the inner pipe 162 and the suction pipe 167 into the
compressor 110.
[0067] Heat is transferred from the high-temperature high-pressure
refrigerant flowing through the double-wall pipe 160 to the
low-temperature low-pressure refrigerant flowing through
double-wall pipe 160. Consequently, in the double-wall pipe 160,
the high-temperature high-pressure refrigerant is cooled and the
low-temperature low-pressure refrigerant is heated. The liquid
refrigerant discharged from the condenser 120 is sub-cooled and the
temperature thereof drops while the liquid refrigerant is flowing
through the double-wall pipe 160. The saturated gaseous refrigerant
discharged from the evaporator 141 is superheated into a gaseous
refrigerant having a degree of superheat. Since the inner pipe 162
in which the low-pressure refrigerant flows is covered with the
outer pipe 161, the low-pressure refrigerant is scarcely heated by
heat radiated by the engine 10 and hence the reduction of the
cooling performance of the refrigerant cycle device 100A can be
prevented.
[0068] In the bend portions 163b of the double-wall pipe 160 in the
first embodiment, the ridges 162b of the inner pipe 162 are in
contact with the inside surface of the outer pipe 161 and the inner
pipe 162 is partially squeezed and held in place by the outer pipe
161. Thus, the helical grooves 162a secures the passage between the
outer pipe 161 and the inner pipe 162, and the inner pipe 162 can
be held fixedly in the outer pipe 161 by a simple structure. Since
the inner pipe 162 can be surely fixedly held in the outer pipe
161, the vibration and resonation of the outer pipe 161 and the
inner pipe 162 can be prevented, the outer pipe 161 and the inner
pipe 162 are prevented from striking against each other, noise will
not be generated, and a breakage of the outer pipe 161 and the
inner pipe 162 can be prevented.
[0069] The inner pipe 162 provided with the helical grooves 162a is
easily bendable and can be bent without being greatly strained and
without collapsing the passage 160a between the outer pipe 161 and
the inner pipe 162. Since the inner pipe 162 can be bent without
being greatly strained, the double-wall pipe 160 can be bent by a
low working force.
[0070] The inner pipe 162 is provided with the plurality of helical
grooves 162a. Therefore, even when one of the helical grooves 162a
is obstructed, the rest of the helical grooves 162a can form the
passage 160a between the outer pipe 161 and the inner pipe 162.
Since the plurality of helical grooves 162a enlarges the passage
160a, resistance against the flow of the refrigerant through the
passage 160a can be reduced.
[0071] Heat can be efficiently transferred from the high-pressure
refrigerant flowing through the passage 160a to the low-pressure
refrigerant inside the inner pipe 162 without increasing the
resistance against the flow of the low-pressure refrigerant in the
inner pipe 162 when the depth of the helical grooves 162a is
between 5 and 15% of the outside diameter of the inner pipe
162.
[0072] The capability of the double-wall pipe 160 to transfer heat
at a high transfer rate enables the double-wall pipe 160 to serve
as an internal heat exchanger and contributes to the improvement of
the efficiency of the refrigerant cycle device 100A. The low
pressure loss in the double-wall pipe 160 improves the cooling
capacity of the refrigerant cycle device 100A. Referring to FIG. 9,
the helical grooves 162a makes the low-pressure refrigerant to flow
in swirling streams in the inner pipe 162 to promote heat transfer
from the high-pressure refrigerant flowing through the passage 160a
to the low-pressure refrigerant flowing through the inner pipe 162
when the depth of the helical grooves 162a is not less than 5% of
the outside diameter of the inner pipe 162. However, the pressure
loss in the low-pressure pipe increases with the increase of the
depth of the helical grooves 162a to obstruct the improvement of
the cooling capacity. A pressure loss of 6 kPa in the low-pressure
pip reduces the cooling capacity by 1%. The upper limit of the
depth of the helical grooves 162a that causes a pressure loss
increase of 6 kPa relative to a pressure loss caused by an
equivalent inner pipe not provided with any grooves is 15% of the
outside diameter of the inner pipe 162. The depth of the helical
grooves 162a equal to 15% of the outside diameter of the inner pipe
162 is a critical depth. When the helical grooves 162a are formed
in a depth exceeding 15% of the outside diameter of the inner pipe
162, flaking occurs in the surface of the inner pipe 162.
[0073] The refrigerant cycle device 100A has a proper cooling
capacity when the longitudinal length of the helical grooves 162a
is in the range of 300 to 800 mm, more preferably, in the range of
600 to 800 mm. As shown in FIG. 10, pressure loss in the
low-pressure refrigerant flowing in the inner pipe 162 increases in
proportion to the length of the helical grooves 162a, and the
temperature difference between the low-pressure refrigerant flowing
in the inner pipe 162 and the high-pressure refrigerant flowing
through the passage 160a decreases as the length of the helical
grooves 162a decreases. Consequently, the rate of heat transfer
from the high-pressure refrigerant to the low-pressure refrigerant
saturates when the length of the helical grooves 162a is increased
to a length between 600 and 800 mm. The length of the helical
grooves 162a corresponds to the length of the part, in which the
helical grooves 162a are formed, of the inner pipe 162.
[0074] The outer pipe 161 and the inner pipe 162 can be surely
fixed together in the bend portions 163b when the outside diameter
of the outer pipe 161 is in the range of 1.1 to 1.3 times of the
outside diameter of the inner pipe 162. FIG. 11A is a graph showing
the relationship between a variation rate of an inside diameter L
of an outer pipe and a bending angle, and FIG. 11B is a graph
showing the relationship between a helical groove pitch and a ratio
L(R)/L of an outer diameter L(R) of an imaginary cylinder
connecting outer surfaces of ridges of an inner pipe to the inside
diameter L of the outer pipe. Generally, a tensile force acts on
the outer side of a pipe and the outer side of the pipe is
stretched when the pipe is bent. Consequently, the outside diameter
of the pipe decreases by 10 to 30% of the original outside diameter
of the pipe. A maximum reduction of 30% occurs when a bending angle
of a bend portion is 10.degree.. In this embodiment, by bending,
the inside diameter of the outer pipe 161 decreases by 10 to 30% of
the original inside diameter of the pipe. Thus, the outer pipe 161
and the inner pipe 162 can be surely fixed together when the
bending angle is not smaller than 10.degree..
[0075] When the diameter L(R) of the imaginary cylinder connecting
the outer surfaces of the ridges 162b of the inner pipe 162 is in
the range of 0.7 to 0.95 or 0.8 to 0.95 times of the original
inside diameter L of the outer pipe 161, the outer pipe 161 and the
inner pipe 162 can be surely fixed together in the bend portion
163b and the double-wall pipe 160 has satisfactory vibration
resistance when the bending angle is 10.degree. or above as shown
in FIG. 11B. The diameter L(R) of the imaginary cylinder connecting
the outer surfaces of the ridges 162b decreases with the decrease
of the pitch of the helical grooves 162a. Therefore, it is
desirable that the pitch of the helical grooves 162a is 12 mm or
above to ensure that the diameter L(R) of the imaginary cylinder
connecting the outer surfaces of the ridges 162b is equal to or
greater than 0.7 times of the original inside diameter L of the
outer pipe 161. When the outer pipe 161 does not have high
straightness, it is difficult to insert the inner pipe 162 into the
outer pipe 161 and the productivity of the double-wall pipe
manufacturing line lowers. Therefore, it is desirable that the
diameter L(R) of the imaginary cylinder connecting the outer
surfaces of the ridges 162b is equal to or smaller than 95% of the
inside diameter of the outer pipe 161.
[0076] Resonating of the double-wall pipe 160 with the vibration of
the vehicle can be prevented by forming at least one bend portion
163b in a length of 700 mm of the double-wall pipe 160. As shown in
FIG. 12, resonance frequency decreases with the increase of the
length of the bend portion 163b in which the outer pipe 161 and the
inner pipe 162 are fixed together. The length between the bend
portions 163b will be called a holding pitch. Suppose that the
frequency of the vibration of the body of the vehicle is 50 Hz.
Then, the holding pitch for a 3/4 in. pipe carrying the refrigerant
and resonating with vibrations of 100 Hz is 700 mm. In this case,
the double-wall pipe 160 can be prevented from resonating with the
vibration of the vehicle by forming the bend portions 163b in the
double-wall pipe 160 at pitches of 700 mm, and generation of noise,
abrasion of the outer pipe 161 and the inner pipe 162 and
production of particles due to the striking of the outer pipe 161
and the inner pipe 162 against each other can be prevented.
[0077] The respective positions of the free ends of the liquid
tubes 164 and 165 can be properly adjusted by properly forming the
bend portions 164a and 165a in the liquid tubes 164 and 165,
respectively. The bend portions 164a and 165a are formed between
the fixed ends blazed to the outer pipe 162 and the free ends of
the liquid tubes 164 and 165a, that is, branch pipes. The liquid
tubes 164 and 165 are formed in excess lengths, respectively, to
provide the liquid tubes 164 and 165 with bending allowances for
the positional adjustment of the free ends thereof. When the bend
portions 164a and 165a are formed in the liquid tubes 164 and 165
to adjust the positions of the free ends of the liquid tubes 164
and 165, stresses are induced in the bend portions 164a and 165a to
suppress the induction of stresses in the blazed ends. Thus, the
positions of the free ends of the liquid tubes 164 and 165 can be
easily adjusted, and the liquid tubes 164 and 165 can be connected
easily to the condenser 120 and the expansion valve 131,
respectively, which facilitates assembling work.
[0078] As mentioned above in connection with FIG. 7, the three
balls 220 of the grooving tool 200 are pressed against the outer
surface of the inner pipe 162 and the annular block 210 holding the
balls 220 is rotated to form the three helical grooves 162a.
Formation of the three helical grooves 162a with the three balls
220 pressed against the surface of the inner pipe 162 improves the
straightness of the inner pipe 162. Consequently, the inner pipe
162 can be smoothly inserted into the outer pipe 161 even when the
difference between the outside diameter of the inner pipe 162 and
the inside diameter of the outer pipe 161 is small. Fixing force
for fixing the outer pipe 161 and the inner pipe 162 in the bend
portion 163b is higher and the vibration resistance of the
double-wall pipe 160 is higher when the gap between the outer pipe
161 and the inner pipe 162 is narrower.
[0079] When the pressure tightness of the outer pipe 161 in the
bend portion 163b is important, it is preferable that the minimum
outside diameter of the outer pipe 161 in the bend portion 163b is
0.85 times of the original outside diameter L0 of the outer pipe
161 or greater. When the outer pipe 161 is bent to form the bend
portion 163b such that the minimum outside diameter of the outer
pipe 161 is 85% of the original outside diameter of the outer pipe
161 or below, the outer pipe 161 in the bend portion 163b has an
elliptic section. When the outer pipe 161 is bent and has an
elliptic section, the bending angle in which the outer pipe 161 is
bent tends to decrease when the high-pressure refrigerant flows
through the passage 160a between the outer pipe 161 and the inner
pipe 162. Consequently, a force not lower than 600 .mu.s that
causes the fatigue fracture of aluminum pipes acts on the outer
side of the curved outer pipe 161 and cracks may be developed in
the outer side of the outer pipe 161. Therefore, the outer pipe 161
has sufficient pressure tightness when the minimum outside diameter
of the outer pipe 161 in the bend portion 163b is 0.85 times of the
original outside diameter L0 of the outer pipe 161 or above.
Second Embodiment
[0080] A double-wall pipe 160 in a second embodiment according to
the present invention will be described with reference to FIGS. 13A
and 13B. The double-wall pipe 160 in the second embodiment includes
a holding member 168. The holding member 168 fixedly holds end
parts of a liquid tube 165 and a suction tube 166 in a
predetermined positional relation.
[0081] As shown in FIG. 13A, the holding member 168, similarly to
the liquid tube 165 and the suction tube 166, is made of aluminum.
The holding member 168 is fastened to the liquid tube 165 and the
suction tube 166 by brazing or staking.
[0082] The end parts of the liquid tube 164 and the suction tube
166 fixedly held by the holding member 168 are unmovable relative
to each other. Consequently, the liquid tube 164 and the suction
tube 166 can be easily connected to the expansion valve 131 and the
evaporator 141, respectively.
[0083] As shown in FIG. 13B, a holding member 168A made of a resin
may be used. The holding member 168A can be fixedly put on the
liquid tube 165 and the suction tube 166 to hold the liquid tube
165 and the suction tube 166. The holding member 168A made of a
resin can be formed in a low cost. In the second embodiment, the
other parts can be made similarly to those of the above-described
first embodiment.
Third Embodiment
[0084] FIG. 14 shows a double-wall pipe 160 in a third embodiment
according to the present invention. The double-wall pipe 160 in the
third embodiment can be used for a refrigerant cycle device 100A of
a dual air conditioning system provided with an evaporator for a
rear area in a passenger compartment of a vehicle.
[0085] The refrigerant cycle device 100A includes a first circuit
including a first expansion valve 131 and a first evaporator 141
(first low-pressure heat exchanger), and a second circuit including
a second expansion valve 132 and a second evaporator 142 (second
low-pressure heat exchanger). The first circuit and the second
circuit are connected in parallel by using a bypass passage 153
through which refrigerant flows while bypassing the first
evaporator 141 and the first expansion valve 131. The bypass
passage 153 is connected to the first circuit at a branching point
A and a joining point B, so as to form the second circuit. A
condenser 120 includes a condensing unit 121, a gas-liquid
separator 122 and a super-cooling unit 123.
[0086] The double-wall pipe 160 has an outer pipe 161 extending
between the condenser 120 and the branching point A of the bypass
passage 153, and an inner pipe 162 extending between the joining
point B of the bypass passage 153 and a compressor 110.
[0087] The high-pressure refrigerant super-cooled through heat
exchange in the double-wall pipe 160 flows through the first
evaporator 141 and the second evaporator 142. Thus, the cooling
function in both the evaporators 141 and 142 can be obtained.
[0088] Another double-wall pipe 160A may be used in combination
with the double-wall pipe 160 as shown in FIG. 15. The outer pipe
161 of the double-wall pipe 160A extends between the branching
point A of the bypass passage 153 and the second expansion valve
132 and the inner pipe 162 of the double-wall pipe 160A extends
between the second evaporator 142 and the joining point B of the
bypass passage 153.
[0089] The high-pressure refrigerant super-cooled through heat
exchange in the double-wall pipe 160A flows through the second
evaporator 142. Thus, the cooling performance of the second
evaporator 142 can be improved. In the third embodiment, the
structures of the double-wall pipe 160, 160A can be formed similar
to those of the above-described first embodiment.
Other Embodiments
[0090] Although the present invention has been described in
connection with some 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.
[0091] For example, the inner pipe 162 may be provided with any
suitable number (e.g., one or plural) of helical grooves instead of
the three helical grooves 162a. Further, the inner pipe 162 may be
provided with longitudinal, straight grooves instead of the helical
grooves.
[0092] The liquid tubes 164 and 165 may be straight tubes, provided
that the liquid tubes 164 and 165 can be properly connected to the
relevant devices.
[0093] Pipes made of a material other than aluminum, such as steel
or copper, may be used instead of the pipes 161 and 162 made of
aluminum.
[0094] Although the double-wall pipe 160 of the invention has been
described as used to the refrigerant cycle device 100A of the
automotive air conditioning system 100, the present invention is
not limited thereto in its practical application. The double-wall
pipe 160 may be suitably used for domestic air conditioners. When
the double-wall pipe 160 is used for the domestic air conditioner,
the temperature of the atmosphere around the outer pipe 161 is
lower than that of air in the engine room 1. Therefore, the
low-pressure refrigerant can be set to pass through the passage
160a and the high-pressure refrigerant can be set to pass through
the inside passage of the inner pipe 162 when the heat transferring
condition between the high-pressure refrigerant and the
low-pressure refrigerant permits.
[0095] The refrigerant that flows through the double-wall pipe 160
is not limited to the refrigerant employed in the refrigerant cycle
device 100A, a refrigerant having physical properties different
from those of the refrigerant employed in the refrigerant cycle
device 100A may be used. For example, refrigerant flowing in
different directions, refrigerants respectively having different
temperatures or refrigerants respectively having different
pressures may be used in combination. Furthermore, different fluids
other than the refrigerant of the refrigerant cycle device 100A can
be used in the double-wall pipe.
[0096] While the invention has been described with reference to
preferred embodiments thereof, it is to be understood that the
invention is not limited to the preferred embodiments and
constructions. The invention is intended to cover various
modification and equivalent arrangements. In addition, while the
various elements of the preferred embodiments are shown in various
combinations and configurations, which are preferred, other
combinations and configuration, including more, less or only a
single element, are also within the spirit and scope of the
invention.
* * * * *