U.S. patent application number 12/880068 was filed with the patent office on 2011-03-17 for regenerative refrigerator.
This patent application is currently assigned to SUMITOMO HEAVY INDUSTRIES, LTD.. Invention is credited to MASAYUKI ISHIZUKA, Kyosuke Nakano, Yuichi Tateishi, Mingyao Xu.
Application Number | 20110061404 12/880068 |
Document ID | / |
Family ID | 43419202 |
Filed Date | 2011-03-17 |
United States Patent
Application |
20110061404 |
Kind Code |
A1 |
ISHIZUKA; MASAYUKI ; et
al. |
March 17, 2011 |
REGENERATIVE REFRIGERATOR
Abstract
A regenerative refrigerator includes a compressor compressing
working fluid; a cylinder fed with the compressed working fluid,
containing a regenerator material, and having an expansion space;
and a rotary valve to switch a first passage and a second passage
formed to cause the working fluid to flow from the compressor to
the expansion space and from the expansion space to the compressor,
respectively. The working fluid expands in the expansion space to
generate cold temperatures in the cylinder. The rotary valve
includes a valve body having a first flat surface; and a valve
plate having a second flat surface and configured to rotate with
the first and second flat surfaces in surface contact. One of the
first and second flat surfaces has an arithmetic average roughness
of 0.1 .mu.m to 0.9 .mu.m. The other one of the first and second
flat surfaces includes resin.
Inventors: |
ISHIZUKA; MASAYUKI;
(Kanagawa, JP) ; Tateishi; Yuichi; (Kanagawa,
JP) ; Xu; Mingyao; (Tokyo, JP) ; Nakano;
Kyosuke; (Tokyo, JP) |
Assignee: |
SUMITOMO HEAVY INDUSTRIES,
LTD.
Tokyo
JP
|
Family ID: |
43419202 |
Appl. No.: |
12/880068 |
Filed: |
September 11, 2010 |
Current U.S.
Class: |
62/6 |
Current CPC
Class: |
Y10T 29/49359 20150115;
F25B 9/14 20130101; F25B 2309/006 20130101 |
Class at
Publication: |
62/6 |
International
Class: |
F25B 9/00 20060101
F25B009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 14, 2009 |
JP |
2009-212348 |
Claims
1. A regenerative refrigerator, comprising: a compressor configured
to compress a working fluid; a cylinder configured to be fed with
the compressed working fluid, the cylinder containing a regenerator
material and having an expansion space provided at one end thereof;
and a rotary valve provided between the compressor and the
cylinder, the rotary valve being configured to switch a first
passage and a second passage, the first passage being formed to
cause the working fluid to flow from the compressor to the
expansion space, the second passage being formed to cause the
working fluid to flow from the expansion space to the compressor,
wherein the working fluid expands in the expansion space to
generate cold temperatures in the cylinder, the rotary valve
includes a valve body having a first flat surface; and a valve
plate having a second flat surface, the valve plate being
configured to rotate with the first flat surface and the second
flat surface in surface contact, and a first one of the first flat
surface and the second flat surface has an arithmetic average
roughness of 0.1 .mu.m to 0.9 .mu.m, and a second one of the first
flat surface and the second flat surface includes a resin.
2. The regenerative refrigerator as claimed in claim 1, wherein the
first one of the first flat surface and the second flat surface
includes a metal-doped carbon film.
3. The regenerative refrigerator as claimed in claim 2, wherein the
first one of the first flat surface and the second flat surface
includes one of an aluminum metal and an aluminum alloy as a base
material.
4. The regenerative refrigerator as claimed in claim 3, wherein the
first one of the first flat surface and the second flat surface is
anodized.
5. The regenerative refrigerator as claimed in claim 2, wherein the
metal-doped carbon film includes at least one selected from the
group consisting of chromium, titanium, tungsten, silicon, and
molybdenum.
6. The regenerative refrigerator as claimed in claim 2, wherein the
first one of the first flat surface and the second flat surface
further includes at least one of a nickel film, a chromium film,
and a chromium nitride film under the metal-doped carbon film.
7. The regenerative refrigerator as claimed in claim 1, wherein the
first one of the first flat surface and the second flat surface
further includes one of an aluminum metal and an aluminum alloy as
a base material.
8. The regenerative refrigerator as claimed in claim 7, wherein the
first one of the first flat surface and the second flat surface is
anodized.
9. The regenerative refrigerator as claimed in claim 1, wherein the
resin includes at least one of polyether sulfone, wholly aromatic
polyester, and polytetrafluoroethylene.
10. The regenerative refrigerator as claimed in claim 1, wherein
the regenerative refrigerator is one of a Gifford-McMahon
refrigerator, a pulse tube refrigerator, and a Solvay refrigerator.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application is based upon and claims the benefit
of priority of Japanese Patent Application No. 2009-212348, filed
on Sep. 14, 2009, the entire contents of which are incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to refrigerators,
and more particularly to a regenerative refrigerator capable of
switching the feeding of working fluid to a cylinder and the
discharging of the working fluid from the cylinder using a rotary
valve.
[0004] In the present invention, the "regenerative refrigerator"
may mean refrigerators in general that generates coldness (cold
temperatures) such as cryogenic temperatures in a cylinder
containing a regenerator material through an adiabatic expansion of
working fluid flowing into the cylinder, such as a Gifford-McMahon
(GM) refrigerator, a pulse tube refrigerator, and a Solvay
refrigerator.
[0005] 2. Description of the Related Art
[0006] Gifford-McMahon (GM) refrigerator has been known as a
refrigerator capable of generating cryogenic temperatures. GM
refrigerator attains a cooling effect based on Gifford-McMahon
refrigeration cycle using a change in the volume of a space caused
by the reciprocation of a displacer inside a cylinder.
[0007] In GM refrigerator, high-pressure working fluid (such as
helium gas) is fed into the cylinder, and is caused to expand
adiabatically inside the cylinder, thereby generating cryogenic
temperatures. This cryogenic working fluid absorbs ambient heat and
performs heat exchange with a regenerator material provided in the
cylinder to be raised to room temperature, and is thereafter
discharged from the cylinder. As a result, cryogenic temperatures
are maintained inside the cylinder, so that an object of cooling
thermally coupled to the cylinder is cooled. The working fluid
discharged from the cylinder is compressed in a compressor into
high-pressure working fluid. Thereafter, this high-pressure working
fluid is re-fed to the cylinder.
[0008] Usually, GM refrigerator includes a switching valve such as
a rotary valve in order to perform such feeding and discharging of
working fluid to and from the cylinder.
[0009] The rotary valve includes a valve plate, which is a
cylindrical rotator, and a valve body, which is static. When the
flat surface (sliding surface) of the rotating valve plate is
pressed against the flat surface (sliding surface) of the valve
body, a channel for feeding working fluid from the compressor to
the cylinder is formed in response to the relative positions of the
sliding surfaces having a predetermined relationship. Further, a
channel for discharging working fluid is formed in response to the
relative positions of the sliding surfaces having another
predetermined relationship. Accordingly, the rotary valve can cause
the working fluid channels to alternate with each other by causing
a single rotation of the valve plate.
[0010] A combination of metal and resin has been used as a
combination of the materials of the sliding surfaces of the valve
plate and the valve body of the rotary valve.
[0011] Aluminum or its alloy is used as the metal. However, when
aluminum or its alloy, which is relatively low in hardness, is used
for a sliding surface of the rotary valve, the sliding surface is
subjected in advance to surface modification by anodizing, and is
thereafter subjected to polish finishing. Further, in order to
improve the abrasion resistance of the sliding surface, a technique
has been proposed to coat the sliding surface with a thin film of
diamond-like carbon (DLC).
SUMMARY OF THE INVENTION
[0012] According to one aspect of the present invention, a
regenerative refrigerator includes a compressor configured to
compress a working fluid; a cylinder configured to be fed with the
compressed working fluid, the cylinder containing a regenerator
material and having an expansion space provided at one end thereof;
and a rotary valve provided between the compressor and the
cylinder, the rotary valve being configured to switch a first
passage and a second passage, the first passage being formed to
cause the working fluid to flow from the compressor to the
expansion space, the second passage being formed to cause the
working fluid to flow from the expansion space to the compressor,
wherein the working fluid expands in the expansion space to
generate cold temperatures in the cylinder, the rotary valve
includes a valve body having a first flat surface; and a valve
plate having a second flat surface, the valve plate being
configured to rotate with the first flat surface and the second
flat surface in surface contact, and a first one of the first flat
surface and the second flat surface has an arithmetic average
roughness of 0.1 .mu.m to 0.9 .mu.m, and a second one of the first
flat surface and the second flat surface includes a resin.
[0013] The object and advantages of the embodiment will be realized
and attained by means of the elements and combinations particularly
pointed out in the claims.
[0014] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory and not restrictive of the invention as
claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Other objects, features and advantages of the present
invention will become more apparent from the following detailed
description when read in conjunction with the accompanying
drawings, in which:
[0016] FIG. 1 is a schematic cross-sectional view of a
Gifford-McMahon (GM) refrigerator according to an embodiment of the
present invention;
[0017] FIG. 2 is an exploded perspective view of a rotary valve
according to the embodiment of the present invention;
[0018] FIG. 3 is a graph illustrating the relationship between the
arithmetic average roughness of the flat surface of an aluminum
alloy valve plate and the abrasion loss of the flat surface of a
resin valve body according to the embodiment of the present
invention;
[0019] FIG. 4 is a diagram for illustrating maintenance of the
arithmetic average roughness before and after the provision of a
metal-doped carbon film according to the embodiment of the present
invention;
[0020] FIG. 5 is a side view of the valve plate, illustrating
another configuration of the valve plate, according to the
embodiment of the present invention;
[0021] FIG. 6 illustrates the state of an aluminum alloy surface
after anodizing in Example 1 according to the embodiment of the
present invention;
[0022] FIG. 7 illustrates the state of an aluminum alloy surface
after shot peening in Example 2 according to the embodiment of the
present invention;
[0023] FIG. 8 illustrates the state of the aluminum alloy surface
after providing a carbon film containing tungsten in Example 2
according to the embodiment of the present invention;
[0024] FIG. 9 is a graph illustrating a change over time in the
coefficient of friction at the interface between a disk and the
resin ring of Example 1 according to the embodiment of the present
invention;
[0025] FIG. 10 is a graph illustrating a change over time in the
coefficient of friction at the interface between a disk and the
resin ring of Example 2 according to the embodiment of the present
invention; and
[0026] FIG. 11 illustrates the state of an aluminum alloy surface
after shot peening in Example 3 according to the embodiment of the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] As described above, a combination of metal and resin can be
used as a combination of the materials of the sliding surfaces of
the valve plate and the valve body of the rotary valve, and
aluminum or its alloy can be used as the metal. However, the
combination of an aluminum alloy (anodized) and resin as described
above has a problem in that it is desired to perform maintenance or
change parts at relatively short intervals because the sliding
surfaces are likely to be worn by abrasion.
[0028] Further, in the case of coating a sliding surface with DLC,
the degree of abrasion of the coated surface is somewhat
controlled, but the other sliding surface, which is in surface
contact with the coated surface, remains susceptible to wear due to
abrasion. Accordingly, this technique is not a fundamental solution
to the problem.
[0029] According to an aspect of the present invention, a
regenerative refrigerator is provided that includes a rotary valve
stably usable for a long period of time with the wear of its
sliding part due to abrasion being significantly reduced.
[0030] According to an aspect of the present invention, a method of
manufacturing the rotary valve of the regenerative refrigerator is
provided.
[0031] According to an aspect of the present invention, a method of
manufacturing the regenerative refrigerator is provided.
[0032] A description is given below, with reference to the
accompanying drawings, of an embodiment of the present
invention.
[0033] FIG. 1 is a schematic cross-sectional view of a
Gifford-McMahon (GM) refrigerator according to the embodiment of
the present invention.
[0034] Referring to FIG. 1, a GM refrigerator 100 according to this
embodiment includes a gas compressor 101 and a cold head 102. The
cold head 102 includes a housing part 123 and a cylinder part
110.
[0035] The gas compressor 101 draws in working fluid through an
intake port 101a, compresses the working fluid, and discharges the
high-pressure working fluid through a discharge port 101b. Helium
gas is usually used as the working fluid.
[0036] The cylinder part 110 has a two-stage structure of a
first-stage cylinder 110a and a second-stage cylinder 110b. The
second-stage cylinder 110b is smaller in diameter than the
first-stage cylinder 110a. Displacers 103a and 103b are inserted in
the cylinders 110a and 110b, respectively, so as to be
reciprocatable in the cylinders 110a and 110b in their axial
directions. The displacers 103a and 103b are interconnected.
Further, the displacers 103a and 103b have their respective gas
passages formed inside, which gas passages are filled with
regenerator materials 104 and 105, respectively.
[0037] A first-stage expansion chamber 111 is formed at one end of
the first-stage cylinder 110a on the second-stage cylinder 110b
side. Further, an upper chamber 113 is formed at the other end of
the first-stage cylinder 110a. A second-stage expansion chamber 112
is formed at an end of the second-stage cylinder 110b on the side
opposite from the first-stage cylinder 110a side.
[0038] The upper chamber 113 communicates with the first-stage
expansion chamber 111 via a gas passage L1 provided at the upper
end of the displacer 103a, the gas passage filled with the
regenerator material 104 inside the displacer 103a, and a gas
passage L2 provided at the lower end of the displacer 103a. On the
other hand, the first-stage expansion chamber 111 communicates with
the second-stage expansion chamber 112 via a gas passage L3
provided at the upper end of the displacer 103b, the gas passage
filled with the regenerator material 105 inside the displacer 103b,
and a gas passage L4 provided at the lower end of the displacer
103b.
[0039] A first-stage cooling stage 106 formed of a thermally
conductive material is attached to the exterior cylindrical surface
(peripheral surface) of the first-stage cylinder 110a at a position
corresponding to the first-stage expansion chamber 111. Further, a
second-stage cooling stage 107 formed of a thermally conductive
material is attached to the exterior cylindrical surface
(peripheral surface) of the second-stage cylinder 110b at a
position corresponding to the second-stage expansion chamber
112.
[0040] A sealing mechanism 150 is provided on the exterior
cylindrical surface (peripheral surface) of the first-stage
displacer 103a near its end on the upper chamber 113 side. The
sealing mechanism 150 seals the clearance between the exterior
cylindrical surface of the displacer 103a and the interior
cylindrical surface of the first-stage cylinder 110a.
[0041] A Scotch yoke 122 is connected to the first-stage displacer
103a. The Scotch yoke 122 extends outward (upward in FIG. 1) from
the first-stage cylinder 110a. The Scotch yoke 122 is supported by
sleeve bearings 117a and 117b fixed to a housing 124 so as to be
movable in the axial directions of the displacers 103a and 103b.
The airtightness of a sliding part is maintained at the sleeve
bearing 117b, so that the space inside the housing 124 and the
upper chamber 113 are separated. A motor 115 is housed in the
housing 124. The rotation of the motor 115 is transmitted to the
displacer 103a via a crank 114 and the Scotch yoke 122. Thereby,
the displacers 103a and 103b are reciprocated.
[0042] In the working fluid channel, a rotary valve 155 is provided
between the intake port 101a and the discharge port 101b of the gas
compressor 101 and the upper chamber 113. The rotary valve 155
switches the working fluid channel (from one to another) so as to
introduce the working fluid discharged from the discharge port 101b
of the gas compressor 101 into the upper chamber 113 or introduce
the working fluid inside the upper chamber 113 to the intake port
101a of the gas compressor 101.
[0043] The rotary valve 155 includes a valve body 161 and a valve
plate 171. The valve plate 171 is rotatably supported by a rolling
bearing 116 in the housing 124. An eccentric pin 114a of the crank
114, which drives the Scotch yoke 122, revolves around an axis of
rotation, so that the valve plate 171 rotates. The valve body 161
is pressed against the valve plate 171 by a coil spring 120.
However, the valve body 161 is locked by a pin 119 so as not to
rotate.
[0044] FIG. 2 is an exploded perspective view of the rotary valve
155.
[0045] The cylindrical valve body 161 includes a flat surface 165a.
Further, a gas passage 165b is formed in the cylindrical valve body
161. The gas passage 165b penetrates through the valve body 161
along the center axis of the valve body 161. One end of the gas
passage 165b is open at the flat surface 165a. The other end of the
gas passage 165b is connected to the discharge port 101b of the gas
compressor 101 illustrated in FIG. 1.
[0046] Further, a groove 165c is formed along an arc (of a circle)
having a center at the center axis of the valve body 161 at the
flat surface 165a of the valve body 161. An end part 165d of the
groove 165c is connected to one end of an L-shaped gas passage 165e
framed inside the valve body 161. Further, the other end of the gas
passage 165e has an opening at the exterior cylindrical surface
(peripheral surface) of the valve body 161. The gas passage 165e
communicates with the upper chamber 113 via this opening and a gas
passage 121 illustrated in FIG. 1.
[0047] On the other hand, the valve plate 171 has a flat surface
175a that is in surface contact with the flat surface 165a of the
valve body 161. A groove 175d is formed at the flat surface 175a.
The groove 175d extends along a radial direction of the flat
surface 175a from the center of the flat surface 175a. Accordingly,
when the valve plate 171 rotates so that the peripheral-side end
part of the groove 175d overlaps (in part) with the groove 165c of
the flat surface 165a of the valve body 161, the gas passage 165b
and the gas passage 165e communicate with each other via the groove
175d.
[0048] Further, a gas passage 175b is formed in the valve plate 171
to extend from the flat surface 175a along the directions of the
axis of rotation of the valve plate 171 so as to penetrate through
the valve plate 171 in its axial directions. One end of the gas
passage 175b is open at the flat surface 175a. The gas passage 175b
is open in the flat surface 175a at substantially the same radial
position as the groove 165c is open in the flat surface 165a of the
valve body 161. The other end of the gas passage 175b is connected
to the intake port 101a of the gas compressor 101 via a hollow
inside the housing 124 as illustrated in FIG. 1. Accordingly, when
the valve plate 171 rotates so that the opening of the gas passage
175b at the flat surface 175a overlaps (in part) with the groove
165c of the valve body 161, the gas passage 165e and the gas
passage 175b communicate with each other. As a result, the upper
chamber 113 communicates with the intake port 101a of the gas
compressor 101 via the gas passage 121, the gas passage 165e, and
the gas passage 175b.
[0049] Next, a description is given of a method of cooling an
object of cooling using this GM refrigerator 100.
[0050] When the GM refrigerator 100 is in operation, the flat
surface 165a of the valve body 161 and the flat surface 175a of the
valve plate 171 of the rotary valve 155 are in surface contact, and
the rotating flat surface 175a of the valve plate 171 is pressed
against the flat surface 165a of the valve body 161.
[0051] Then, the working fluid is fed into the upper chamber 113
from the gas compressor 101 when the gas passage 165b and the gas
passage 165e communicate with each other via the groove 175d. On
the other hand, when the gas passage 165e and the gas passage 175b
communicate with each other, the working fluid inside the upper
chamber 113 is collected into the gas compressor 101. Accordingly,
by rotating the valve plate 171, it is possible to repeatedly
introduce working fluid into the upper chamber 113 and collect the
working fluid from the upper chamber 113.
[0052] Here, referring again to FIG. 1, when the motor 115 is
driven during the operation of the GM refrigerator 100, the crank
114 rotates to vertically reciprocate the Scotch yoke 122. As a
result, not only the first-stage displacer 103a connected to the
Scotch yoke 122 but also the second-stage displacer 103b vertically
reciprocates.
[0053] When the displacers 103a and 103b move to the upper chamber
113 side, the volume of the upper chamber 113 is reduced, while the
volumes of the first-stage expansion chamber 111 and the
second-stage expansion chamber 112 increase. On the other hand,
when the displacers 103a and 103b move to the opposite side, the
increase and the decrease in volume are reversed. In particular,
when the volumes of the first-stage expansion chamber 111 and the
second-stage expansion chamber 112 increase, the working fluid
expands adiabatically to generate cold temperatures inside the
first-stage expansion chamber 111 and the second-stage expansion
chamber 112. Further, the working fluid moves through the gas
passages L1 through L4 with changes in the volumes of the upper
chamber 113, the first-stage expansion chamber 111, and the
second-stage expansion chamber 112. During this, heat exchange is
performed between the low-temperature working fluid and the
regenerator materials 104 and 105.
[0054] The repetition of the introduction and collection of working
fluid and the reciprocation of the displacers 103a and 103b as
described above synchronize with the rotation of the crank 114.
Accordingly, by suitably adjusting the phase of the repetition of
the introduction and collection of working fluid and the phase of
the reciprocation of the displacers 103a and 103b, it is possible
to continuously generate cold temperatures inside the first-stage
expansion chamber 111 and the second-stage expansion chamber 112.
Further, this makes it possible to cool an object of cooling (not
graphically illustrated) attached to the first-stage cooling stage
106 and the second-stage cooling stage 107.
[0055] A combination of resin and non-magnetic metal can be used as
a material combination for the flat surface 165a of the valve body
161 and the flat surface 175a of the valve plate 171 of the rotary
valve 155. Non-magnetic metal can be used because use of magnetic
metal may cause the rotary valve 155 to adversely affect the
operations of the GM refrigerator 100 and an object of cooling
connected to the GM refrigerator 100. (In particular, the object of
cooling is often a device or an apparatus using magnetic
properties, such as a superconducting device.
[0056] Aluminum or its alloy is employed as non-magnetic material,
and tetrafluoroethylene (for example, BEAREE FL 3000, manufactured
by NTN Corporation) is employed as resin. In general, aluminum and
its alloys are relatively low in hardness. Therefore, when aluminum
or its alloy is used for a sliding surface of a rotary valve (the
flat surface 165a or 175a in this case), this sliding surface is
subjected in advance to surface modification by anodizing. The
anodized sliding surface is thereafter subjected to polish
finishing, so that a smooth flat surface is finally obtained.
Conventionally, the arithmetic average roughness Ra of the sliding
surface finally obtained by this method is less than 0.1 .mu.m.
[0057] In addition, in order to improve the abrasion resistance of
flat surfaces, a technique has been proposed to coat a metal-side
flat surface with a thin film of diamond-like carbon (DLC).
[0058] However, according to the above-described combination of
resin and an aluminum alloy (anodized), there is a problem in that
the flat surfaces of the valve body and the valve plate are
degraded and worn in a relatively short period of time because of
mutual abrasion. This may lead to the problem of a shortened useful
service life of not only the rotary valve but also the entire GM
refrigerator. Further, there may be a problem in that it is
necessary to maintain the rotary valve or replace its components at
relatively short intervals.
[0059] Further, for example, in the case of coating an
aluminum-alloy-side flat surface with DLC, the degree of abrasion
of the coated flat surface is somewhat reduced. However, the other
flat surface (for example, the flat surface 165a in FIG. 2) in
contact with this flat surface (for example, the flat surface 175a
in FIG. 2) still remains susceptible to degradation due to
abrasion. Accordingly, this technique is not a fundamental solution
to the problem.
[0060] On the other hand, according to this embodiment, the
arithmetic average roughness Ra of one flat surface (for example,
the flat surface 175a of the valve plate 171) may be in the range
of 0.1 .mu.m to 0.9 .mu.m, and a metal-doped carbon film may be
provided at this flat surface.
[0061] A description is given below of the (technical) idea and one
or more effects of this feature. In the following, a description is
given of one or more effects of the above-described feature by
taking the case of the flat surface 175a of the valve plate 171
having the above-described configuration (that is, an arithmetic
average roughness Ra of 0.1 .mu.m to 0.9 .mu.m and a metal-doped
carbon film provided at the flat surface 175a) as an example.
[0062] (a) According to this embodiment, the arithmetic average
surface roughness Ra (hereinafter referred to simply as "surface
roughness Ra") of the flat surface 175a of the valve plate 171 is
in the range of 0.1 .mu.m to 0.9 .mu.m.
[0063] Conventionally, it has been considered preferable to reduce
the surface roughness Ra of a metal-side flat surface as much as
possible. This is because an increase in the surface roughness Ra
of the metal-side flat surface increases the risk of the
counterpart resin flat surface in surface contact with the
metal-side flat surface being worn by projecting portions of the
metal-side flat surface. Further, the metal-side flat surface
itself is worn by abrasion while wearing down the counterpart resin
flat surface. This is why an anodized flat surface of the
conventional valve plate is ultimately subjected to polish
finishing and smoothed. Conventionally, the surface roughness Ra of
the finished metal-side flat surface is controlled to less than
0.10 .mu.m.
[0064] On the other hand, according to this embodiment, which
employs a technical idea opposite to the conventional one, the
surface roughness Ra of the flat surface 175a of the valve plate
171 is more than or equal to 0.1 .mu.m. This is based on the
experimental result, which has been obtained for the first time by
the inventors of the present invention, that the abrasion loss of
the flat surface 165a of the counterpart valve body 161 increases
as the surface roughness Ra of the flat surface 175a of the valve
plate 171 decreases where the surface roughness Ra of the flat
surface 175a is less than 0.1 .mu.m.
[0065] FIG. 3 is a graph illustrating the relationship between the
surface roughness Ra of the flat surface 175a of the valve plate
171 and the abrasion loss of the flat surface 165a of the valve
body 161, measured by the inventors of the present invention. The
flat surface 175a used in this experiment (measurement) is formed
of an aluminum alloy subjected to polish finishing after anodizing.
Further, the flat surface 165a is formed of three kinds of
material, which are polyether sulfone (PES), wholly aromatic
polyester (WADE), and polytetrafluoroethylene (PTFE). The
rotational speed of the valve plate 171 is 135 rpm, and the
experiment time is 167 hours.
[0066] This graph shows that in the range where the surface
roughness Ra is less than 0.1 .mu.m, the abrasion loss of the flat
surface 165a of the valve body 161 increases as the surface
roughness Ra decreases. One reason for this behavior is believed to
be that if the flat surface 175a is excessively smooth, adhesion is
likely to occur between the flat sliding surfaces 165a and 175a,
thus resulting in poor slidability (increased friction) between
them. Further, another possible reason is that excessive smoothness
of the flat surface 175a causes its edge-like (sharply pointed)
projecting portions to be relatively emphasized so that these
projecting portions are likely to cause sharp "scratch damage" to
the opposed flat surface 165a.
[0067] On the other hand, as is clear from FIG. 3, the abrasion
loss of the flat surface 165a of the valve body 161 hardly changes
even with an increase in the surface roughness Ra of the flat
surface 175a where the surface roughness Ra of the flat surface
175a is more than or equal to 0.1 .mu.m. This is believed to be
because there is more slidability between the flat surfaces 165a
and 175a (that is, the flat surfaces 165a and 175a slide relative
to each other more smoothly) in the case of a surface roughness Ra
of more than or equal to 0.1 .mu.m than in the case of a surface
roughness Ra of less than 0.1 .mu.m. Further, it is also considered
to be another reason that edge-like projecting portions are
relatively inconspicuous on the flat surface 175a to make it less
likely to cause sharp "scratch damage" to the opposed flat surface
165a so that there is not much increase in the abrasion loss of the
flat surface 165a.
[0068] This result shows that on the contrary, the conventional
technique, which performs surface adjustment in a direction to
reduce the surface roughness Ra as much as possible (for example,
Ra<0.1 .mu.m) in order to control abrasion loss, is highly
likely to increase the abrasion loss of the flat surface 165a of
the valve body 161.
[0069] On the other hand, with the surface roughness Ra of the flat
surface 175a of the valve plate 171 being more than or equal to 0.1
.mu.m, it is possible to reduce the abrasion loss of the flat
surface 165a of the valve body 161 compared with the conventional
case.
[0070] According to this embodiment, the upper limit of the surface
roughness Ra of the flat surface 175a of the valve plate 171 is 0.9
.mu.m. This is because the abrasion loss of the flat surface 165a
of the valve body 161 starts to increase again if the surface
roughness Ra of the flat surface 175a of the valve plate 171
exceeds 0.9 .mu.m, as is clear from FIG. 3. One reason for this
behavior is believed to be that if the surface roughness Ra of the
flat surface 175a increases to exceed 0.9 .mu.m, the damage to the
flat surface 165a caused by projecting portions of the flat surface
175a becomes more conspicuous as has been expected.
[0071] For the foregoing reasons, the surface roughness Ra of the
flat surface 175a on the metal side is adjusted to the range of 0.1
.mu.m to 0.9 .mu.m according to this embodiment.
[0072] A surface having such a surface roughness range may be
obtained easily by application of, for example, shot peening with
ceramic particles in the range of 10 .mu.m to 200 .mu.m in particle
size.
[0073] (b) According to this embodiment, a "metal-doped carbon
film" may be provided at the flat surface 175a of the valve plate
171.
[0074] In this embodiment, the "metal-doped carbon film" means a
film in general that has a metal dispersed or disposed in a carbon
film employed as a matrix. The metal may be dispersed as particles
or disposed in layers in the carbon matrix.
[0075] The metal-doped carbon film serves to improve the abrasion
resistance of a surface on which the metal-doped carbon film is
provided. Accordingly, by providing a metal-doped carbon film at
the flat surface 175a of the valve plate 171, the abrasion of the
flat surface 175a is prevented. The inventors of the present
invention have found that there is little change in the surface
roughness Ra before and after the provision of the metal-doped
carbon film unless the metal-doped carbon film is extremely
thick.
[0076] FIG. 4 is a diagram for illustrating this maintenance of the
surface roughness Ra before and after the provision of the
metal-doped carbon film. In FIG. 4, (a) illustrates the valve plate
171 before provision of a metal-doped carbon film 172 on a flat
surface 175a', and (b) illustrates the valve plate 171 having the
metal-doped carbon film 172 formed on the flat surface 175a' of (a)
of FIG. 4. If the surface roughness Ra of the flat surface 175a' is
controlled to 0.1 .mu.m to 0.9 .mu.m before the provision of the
metal-doped carbon film 172, this surface roughness Ra is
maintained in the flat surface 175a after the provision of the
metal-doped carbon film 172.
[0077] Examples of the metal material contained in the metal-doped
carbon film of this embodiment, which may be the metal-doped carbon
film illustrated in (b) of FIG. 4, include chromium (Cr), titanium
(Ti), tungsten (W), silicon (Si), molybdenum (Mo), and combinations
of two or more of these materials. The carbon film (matrix portion)
may be DLC.
[0078] The thickness of the metal-doped carbon film 172 is not
limited in particular, and may be, for example, in the range of 1
.mu.m to 15 .mu.m. If the thickness of the metal-doped carbon film
172 is extremely large, the surface roughness Ra of the flat
surface 175a illustrated in (b) of FIG. 4 (that is, the
ultimately-obtained surface roughness Ra) may be out of the range
of 0.1 .mu.m to 0.9 .mu.m even if the surface roughness Ra of the
flat surface 175a' illustrated in (a) of FIG. 4 is controlled in
advance to the 0.1 .mu.m to 0.9 .mu.m range before the provision of
the metal-doped carbon film 172. In this case, after the provision
of the metal-doped carbon film 172, the flat surface 175a is
finished so as to have a surface roughness Ra in the range of 0.1
.mu.m to 0.9 .mu.m.
[0079] The metal-doped carbon film 172 may be provided directly on
the base material (such as an aluminum alloy or an anodized
surface) forming the flat surface 175a' of the valve plate 171 as
illustrated in FIG. 4. Alternatively, the metal-doped carbon film
172 may be provided on an intermediate layer 173 provided on the
base material (the flat surface 175a') as illustrated in FIG. 5.
The interposition of the intermediate layer 173 between the base
material and the metal-doped carbon film 172 increases the adhesion
of the metal-doped carbon film 172. Examples of the intermediate
layer 173 include a nickel (Ni) plating layer and a chromium (Cr)
plating layer. Alternatively, a chromium nitride (CrN) layer may be
provided on the surface of the base material (the flat surface
175a') by a technique such as chemical vapor deposition (CVD), and
be employed as the intermediate layer 173. The thickness of the
intermediate layer 173 may be, for example, in the range of 1 .mu.m
to 15 .mu.m.
[0080] On the other hand, the resin forming the flat surface 165a
of the valve body 161, which is in surface contact with the flat
surface 175a of the valve plate 171 having the metal-doped carbon
film 172 provided at the flat surface 175a, is preferably formed of
engineering plastics.
[0081] The resin may include at least one material selected from
the group consisting of polyimide, polyether ether ketone,
polyamide-imide, polyether ether sulfone, and phenolic resin. The
resin may also be a mixture of polyamide-imide and
polytetrafluoroethylene (PTFE). Alternatively, the resin may
contain polyether sulfone (PES), wholly aromatic polyester (WAPE),
and/or polytetrafluoroethylene (PTFE). In particular, in the case
of using a resin including PES, WAPE, and PTFE (hereinafter
referred to as "three-kind-mixture resin") for the flat surface
165a, a coefficient of friction is significantly reduced between
the flat surface 165a and the flat surface 175a including the
metal-doped carbon film 172. Accordingly, the "three-kind-mixture
resin" is particularly preferable.
[0082] According to this embodiment, because of the above-described
two effects of (a) and (b), abrasion due to sliding is reduced in
each of the flat surface 165a and the flat surface 175a.
Accordingly, it is possible to use the rotary valve 155 according
to this embodiment with stability for a long period of time and to
reduce the number of times components are replaced and the
frequency of maintenance. Further, use of this rotary valve 155
makes it possible to provide the GM refrigerator 100 (FIG. 1),
whose characteristics are stable for a long period of time.
[0083] A description is given above of the case where the flat
surface 175a of the valve plate 171 is on the metal side and the
flat surface 165a of the valve body 161 is on the resin side.
However, the application of metal and resin may be reversed. That
is, the flat surface 175a of the valve plate 171 is on the resin
side and the flat surface 165a of the valve body 161 is on the
metal side.
[0084] Further, a description is given above of configurations and
effects according to this embodiment, taking the GM refrigerator
100 as an example of the apparatus to which the rotary valve 155
according to this embodiment is applied. However, the rotary valve
155 of this embodiment may also be applied to other apparatuses
having the same cooling mechanism as the GM refrigerator, such as a
single-stage or multi-stage pulse tube refrigerator and a Solvay
refrigerator.
[0085] The inventors of the present invention have further advanced
research and development to find that the abrasion loss of the flat
surfaces of the valve plate and the valve body of a rotary valve
may be significantly reduced without providing a metal-doped carbon
film on the metal-side flat surface, that is, the abrasion loss may
be significantly reduced compared with the conventional case only
by causing the arithmetic average roughness Ra of the metal-side
flat surface to be controlled to the above-described range.
Therefore, according to this embodiment, for example, there may be
further provided a regenerative refrigerator including: a
compressor configured to compress a working fluid; a cylinder
configured to be fed with the compressed working fluid, the
cylinder containing a regenerator material and having an expansion
space provided at one end thereof; and a rotary valve provided
between the compressor and the cylinder, the rotary valve being
configured to switch a first passage and a second passage, the
first passage being formed to cause the working fluid to flow from
the compressor to the expansion space, the second passage being
formed to cause the working fluid to flow from the expansion space
to the compressor, wherein the working fluid expands in the
expansion space to generate cold temperatures in the cylinder, the
rotary valve includes a valve body having a first flat surface; and
a valve plate having a second flat surface, the valve plate being
configured to rotate with the first flat surface and the second
flat surface in surface contact, and a first one of the first flat
surface and the second flat surface has an arithmetic average
roughness of 0.1 .mu.m to 0.9 .mu.m, and a second one of the first
flat surface and the second flat surface includes a resin.
[0086] In this case, the first one of the first flat surface and
the second flat surface may be, for example, the flat surface 175a'
illustrated in (a) of FIG. 4, and the flat surface 175a illustrated
in FIG. 2 may be replaced with the flat surface 175a'. Further, the
flat surface 175a' may include one of an aluminum metal and an
aluminum alloy as a base material.
[0087] Here, it is preferable that the surface (the flat surface
175a') of the aluminum metal or the aluminum alloy be anodized. The
thickness of the anodized layer may be, for example, approximately
5 .mu.m to approximately 100 .mu.m (for example, 20 .mu.m, 50
.mu.m, etc.).
[0088] The flat metal surface having an arithmetic average
roughness Ra in such a range may be formed easily with shot peening
as described above. For example, by performing shot peening on an
anodized aluminum metal or aluminum alloy, using ceramic particles
of approximately 1 .mu.m to approximately 200 .mu.m in average
particle size as a medium, it is possible to form a surface having
an arithmetic average roughness Ra in the range of 0.1 .mu.m to 0.9
.mu.m with ease.
[0089] Examples of the material of the ceramic particles as a
medium include alumina, silica (including sand or glass containing
silica as a principal component), and zirconia.
EXAMPLES
[0090] A description is given below of examples according to this
embodiment.
[0091] According to this embodiment, the arithmetic average
roughness Ra in each example was calculated (determined) as
follows. First, five samples manufactured by the same method were
prepared. At or near the center of one of the samples, the surface
roughness was measured once in each of a direction substantially
parallel to the direction of surface polishing (or an arbitrarily
determined first direction if the direction of surface polishing is
unknown) and a direction substantially perpendicular to the
direction of surface polishing (or a second direction substantially
perpendicular to the first direction if the direction of surface
polishing is unknown), and the average of the measurements was
determined (referred to as "Value 1"). The same measurement was
performed at two points in the peripheral portion of the disk
(sample), and an average was determined in each measurement so that
Value 2 and Value 3 were obtained. Values 1 through 3 were
averaged, and Data A was determined. This operation was performed
with respect to the five samples, so that Data A through E were
obtained (determined). Finally, these five values (Data A through
E) were averaged, and the (calculated) average was determined as
the arithmetic average roughness Ra of the sample surfaces, which
may be collectively referred to as the objective surface, of the
example.
Example 1
[0092] Aluminum alloy disks (50 mm in diameter and 7 mm in
thickness) were prepared, and were anodized by a common method. By
anodizing, the hardness of the aluminum alloy disks increased from
pre-anodizing 150 Hv to approximately 500 Hv. Next, these treated
(anodized) surfaces were subjected to mechanical polishing. The
arithmetic average roughness Ra of the surfaces was measured to be
approximately 0.08 .mu.m.
[0093] FIG. 6 illustrates electron microscope photographs of a
polished surface. In FIG. 4, (a) is a photograph of low
magnification (200-fold magnification), and (b) is a photograph of
high magnification (3000-fold magnification). FIG. 6 shows that
while the processed surface is relatively smooth, sharply-pointed
"edge-like" projecting portions are formed linearly along the same
direction partly on the surface.
Example 2
[0094] The same as in Example 1, aluminum alloy disks (50 mm in
diameter and 7 mm in thickness) were anodized, and thereafter,
their surfaces were further subjected to shot peening using alumina
particles of 30 .mu.m to 50 .mu.m in particle size. The arithmetic
average roughness Ra of the processed surfaces was measured to be
approximately 0.79 .mu.m (a value determined by the above-described
method).
[0095] FIG. 7 illustrates electron microscope photographs of an
obtained surface. In FIG. 7, (a) is a photograph of low
magnification (200-fold magnification), and (b) is a photograph of
high magnification (3000-fold magnification). FIG. 7 shows that the
processed surface is uneven with numerous relatively-large
projecting and depressed portions. However, such sharply-pointed
"edge-like" projecting portions as in FIG. 6 were not observed, and
it is shown that projecting portions have a relatively round
form.
[0096] Next, a Ni plating film was provided on the surfaces of the
aluminum alloy disks subjected to shot peening by electroless
plating. The Ni plating film was approximately 10 .mu.m in
thickness. Thereafter, a carbon film containing tungsten was
further provided on the surfaces. A common physical vapor
deposition (PVD) technique was employed to deposit the carbon film
containing tungsten. The film was formed by sputtering, causing
argon ions to collide with two targets of carbon and tungsten. The
carbon film containing tungsten was approximately 2 .mu.m in
thickness.
[0097] FIG. 8 illustrates electron microscope photographs of an
obtained surface after the provision of the carbon film containing
tungsten. In FIG. 8, (a) is a photograph of low magnification
(200-fold magnification), and (b) is a photograph of high
magnification (3000-fold magnification). FIG. 8 shows that while
the surface still includes large unevenness, "edge-like" projecting
portions as in Example 1 are not formed on the surface. It has been
found from the comparison of the photographs of FIG. 7 and FIG. 8
that projecting portions of the surface tend to be further rounded
with the provision of the carbon film containing tungsten.
[0098] The arithmetic average roughness Ra of the surfaces was
measured to be approximately 0.8 .mu.m (the average of five
measurements), which is substantially the same as the value after
shot peening.
[0099] [Evaluation Test 1]
[0100] An abrasion test (ring-on-disk test) was conducted using the
aluminum alloy disks of Examples 1 and 2 and a resin ring. A resin
formed of the three materials of polyether sulfone (PES), wholly
aromatic polyester (WAPE), and polytetrafluoroethylene (PTFE) was
used for the resin ring. The resin ring was 37 mm in diameter and 6
mm in thickness.
[0101] In the test, the rotating resin ring was pressed against a
stationary aluminum alloy disk, and a change over time in the
coefficient of friction at their contact surface was monitored. The
pressing pressure was 0.25 MPa, and the rotational speed of the
resin ring was 180 rpm. No lubricant was used in order to simulate
an actual environment. The test was conducted in a helium gas
atmosphere. The test time was 168 hours. After the measurement, the
abrasion loss of the aluminum alloy disk and the resin ring was
measured.
[0102] FIG. 9 and FIG. 10 illustrate the measurement results of the
change over time in the coefficient of friction in Example 1 and
Example 2, respectively.
[0103] The result of FIG. 9 shows that the friction of coefficient
at the interface between the aluminum alloy disk and the resin ring
varies greatly between 0.18 and 0.30 in the case of using the
aluminum alloy disks of Example 1. Such a variation in the
coefficient of friction is not preferable for the rotary valve.
This is because the occurrence of such a variation in the
coefficient of friction between the flat surfaces of the valve
plate and the valve body of the rotary valve may cause a variation
in the load of a motor that rotates the valve plate of the rotary
valve, thus shortening the useful service life of the motor.
Further, a variation in the load of the motor may be a factor of
impairment of the operational stability of the refrigerator as a
whole, such as a cooling characteristic.
[0104] On the other hand, FIG. 10 shows that in the case of using
the aluminum alloy disks of Example 2, a variation over time is
relatively small with the coefficient of friction at the interface
being controlled to 0.20 to 0.25.
[0105] These indicate that by preparing the flat surface of the
rotary valve on the metal side by the method illustrated in Example
2, it is possible to further stabilize the friction between the
metal-side flat surface and the resin-side flat surface and thereby
to improve the operational stability of the refrigerator as a
whole.
[0106] Table 1 below shows the results of measurement of the
abrasion loss generated in the case of using the aluminum alloy
disks of Example 1 and Example 2.
TABLE-US-00001 TABLE 1 Variation Abrasion Loss (mg) Range of Metal
Disk Resin Ring Coefficient Example Side Side of Friction Example 1
0.2 46.4 0.18-0.30 Example 2 0.2 30.1 0.20-0.25
[0107] In the case of Example 1, the abrasion loss of the aluminum
alloy disk is 0.2 mg, while the abrasion loss of the resin ring is
high at 46.4 mg. On the other hand, in the case of Example 2, the
abrasion loss of the aluminum alloy disk is 0.2 mg, which is the
same as in Example 1, while the abrasion loss of the resin ring is
30.1 mg, which is reduced by approximately 35% compared with
Example 1.
[0108] Thus, it has been confirmed that according to this
embodiment, the abrasion of a metal flat surface is controlled and
the abrasion of a resin flat surface in surface contact with the
metal flat surface also is significantly reduced.
Example 3
[0109] The same as in Example 1, aluminum alloy disks (50 mm in
diameter and 7 mm in thickness) were anodized, and thereafter,
their surfaces were further subjected to shot peening using alumina
particles of 30 .mu.m to 50 .mu.m in particle size. The arithmetic
average roughness Ra of the processed surfaces was measured to be
approximately 0.2 .mu.m (a value determined by the above-described
method).
[0110] FIG. 11 illustrates electron microscope photographs of an
obtained surface. In FIG. 11, (a) is a photograph of low
magnification (200-fold magnification), and (b) is a photograph of
high magnification (3000-fold magnification).
[0111] [Evaluation Test 2]
[0112] The above-described abrasion test (ring-on-disk test) was
conducted using the aluminum alloy disks of Examples 1 and 3 and a
resin ring. A resin formed of the three materials of polyether
sulfone (PES), wholly aromatic polyester (WAPE), and
polytetrafluoroethylene (PTFE) was used for the resin ring. The
resin ring was 37 mm in diameter and 9 mm in thickness.
[0113] The rotating resin ring was pressed against a stationary
aluminum alloy disk, and the abrasion of the aluminum alloy disk
and the resin ring was measured after passage of a predetermined
period of time. The pressing pressure was 0.25 MPa, and the
rotational speed of the resin ring was 135 rpm. No lubricant was
used in order to simulate an actual environment. The test was
conducted in a helium gas atmosphere. The test time was 146
hours.
[0114] Table 2 below shows the results of measurement of the
abrasion loss generated in the case of using the aluminum alloy
disks of Example 1 and Example 3.
TABLE-US-00002 TABLE 3 Abrasion Loss (mg) Example Metal Disk Side
Resin Ring Side Example 1 1.0 20.5 Example 3 N.D. 14.5
[0115] In the case of Example 1, the abrasion loss of the aluminum
alloy disk is small at approximately 1 mg, while the abrasion loss
of the resin ring is relatively high at 20.5 mg. On the other hand,
in the case of Example 3, the abrasion loss of the aluminum alloy
disk is less than or equal to a detection limit and is not
detected. Further, the abrasion loss of the resin ring is 14.5 mg,
which is reduced by approximately 30% compared with Example 1.
[0116] The present invention may be applied to rotary valves in GM
refrigerators, pulse tube refrigerators, and Solvay
refrigerators.
[0117] According to one aspect of the present invention, a method
of manufacturing a rotary valve for a regenerative refrigerator,
the rotary valve including a valve body having a first flat surface
and a valve plate having a second flat surface, the valve plate
being configured to rotate with the first flat surface and the
second flat surface in surface contact, includes one of (a) forming
the valve body of one of an aluminum metal and an aluminum alloy
and forming the valve plate of a resin and (b) forming the valve
body of the resin and forming the valve plate of one of the
aluminum metal and the aluminum alloy; (b) anodizing a surface of
the one of the aluminum metal and the aluminum alloy; and (c)
performing shot peening on the anodized surface so that the
anodized surface has an arithmetic average roughness of 0.1 .mu.m
to 0.9 .mu.m.
[0118] According to one aspect of the present invention, a method
of manufacturing a regenerative refrigerator, the regenerative
refrigerator including a compressor configured to compress a
working fluid; a cylinder configured to be fed with the compressed
working fluid, the cylinder containing a regenerator material and
having an expansion space provided at one end thereof; and a rotary
valve provided between the compressor and the cylinder, the rotary
valve being configured to switch a first passage and a second
passage, the first passage being formed to cause the working fluid
to flow from the compressor to the expansion space, the second
passage being formed to cause the working fluid to flow from the
expansion space to the compressor, wherein the working fluid
expands in the expansion space to generate cold temperatures in the
cylinder, and the rotary valve includes a valve body having a first
flat surface; and a valve plate having a second flat surface, the
valve plate being configured to rotate with the first flat surface
and the second flat surface in surface contact, includes
manufacturing the rotary valve by the method as set forth
above.
[0119] All examples and conditional language recited herein are
intended for pedagogical purposes to aid the reader in
understanding the invention and the concepts contributed by the
inventors to furthering the art, and are to be construed as being
without limitation to such specifically recited examples and
conditions, nor does the organization of such examples in the
specification relate to a showing of the superiority or inferiority
of the invention. Although the embodiment of the present inventions
has been described in detail, it should be understood that various
changes, substitutions, and alterations could be made hereto
without departing from the spirit and scope of the invention.
* * * * *