U.S. patent application number 13/498791 was filed with the patent office on 2012-07-19 for hermetic compressor.
This patent application is currently assigned to PANASONIC CORPORATION. Invention is credited to Masanori Kobayashi.
Application Number | 20120183419 13/498791 |
Document ID | / |
Family ID | 43921629 |
Filed Date | 2012-07-19 |
United States Patent
Application |
20120183419 |
Kind Code |
A1 |
Kobayashi; Masanori |
July 19, 2012 |
HERMETIC COMPRESSOR
Abstract
In a hermetic-type compressor, a piston has a sliding face which
slides on an inner wall of the cylindrical hole and is
reciprocatably inserted in the cylindrical hole. A connecting rod
connects an eccentric shaft part and the piston. The cylindrical
hole has a tapered part, whose inside diameter dimension gradually
increases from a top dead center of the piston toward a bottom dead
center, and an end part on the shaft side. A reciprocation
direction of the piston is substantially a horizontal direction. A
recessed part, which is recessed to the inside in a radial
direction of the piston and holds lubricating oil, is provided in
the sliding face of the piston. A part on the lower side in the
vertical direction of the piston which comes into contact with the
end part on the shaft side of the cylindrical hole when the piston
is positioned in the bottom dead center is a part of the sliding
face.
Inventors: |
Kobayashi; Masanori; (Shiga,
JP) |
Assignee: |
PANASONIC CORPORATION
Kadoma-shi, Osaka
JP
|
Family ID: |
43921629 |
Appl. No.: |
13/498791 |
Filed: |
October 27, 2010 |
PCT Filed: |
October 27, 2010 |
PCT NO: |
PCT/JP2010/006337 |
371 Date: |
March 28, 2012 |
Current U.S.
Class: |
417/415 |
Current CPC
Class: |
F04B 39/122 20130101;
F04B 39/023 20130101; F04B 39/0207 20130101 |
Class at
Publication: |
417/415 |
International
Class: |
F04B 35/04 20060101
F04B035/04 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 27, 2009 |
JP |
2009-246173 |
Claims
1. A hermetic-type compressor comprising: a sealed container
storing lubricant oil at its bottom; an electric mechanism disposed
in the sealed container; and a compression mechanism disposed in
the sealed container and driven by the electric mechanism, wherein
the compression mechanism includes: a shaft having a main shaft
part rotated by the electric mechanism and an eccentric shaft part
formed in the main shaft part; a cylinder block having a
cylindrical hole constructing a compression chamber and a bearing
rotatably supporting the main shaft part, in which the cylindrical
hole and the bearing are disposed so that axis of the cylindrical
hole and that of the bearing are orthogonal to each other; a piston
reciprocatably inserted in the cylindrical hole and having a
sliding face which slides on an inner wall of the cylindrical hole;
and a connecting rod connecting the eccentric shaft part and the
piston, the cylindrical hole has a tapered part, whose inside
diameter dimension gradually increases from a top dead center of
the piston toward a bottom dead center, and an end part on the
shaft side, a reciprocation direction of the piston is
substantially a horizontal direction, a recessed part, which is
recessed to an inside in a radial direction of the piston and holds
the lubricating oil, is provided in the sliding face of the piston,
and a part on the lower side in the vertical direction of the
piston, which comes into contact with the end part on the shaft
side of the cylindrical hole when the piston is positioned in the
bottom dead center, is a part of the sliding face.
2. The hermetic-type compressor according to claim 1, wherein the
piston has a piston pin hole in a direction orthogonal to axis of
the piston, the compression mechanism further includes a piston pin
inserted in the piston pin hole, the connecting rod is coupled to
the piston pin so as to be rotatable about the axis of the piston
pin, and the sliding face has an extension part which extends from
an end part on the connecting rod side toward the recessed part
and, when the piston is positioned at the bottom dead center, and
the extension part comes into contact with the end part on the
shaft side of the cylindrical hole.
3. The hermetic-type compressor according to claim 2, wherein the
recessed part is one of a plurality of recessed parts, the
plurality of recessed parts include first and second recessed parts
formed in positions symmetrical with respect to the axis of the
piston extending in the center of the piston pin hole, and the
first and second recessed parts communicate with each other via the
piston pin hole.
4. The hermetic-type compressor according to claim 1, wherein the
recessed part has an annular shape extending in an outer periphery
direction of the piston.
5. The hermetic-type compressor according to claim 4, wherein the
cylindrical hole further includes a straight part provided on the
top dead center side of the piston relative to the tapered part and
an inflection part as a border between the tapered part and the
straight part, and the position of the inflection part and the
position of the recessed part are set so that when the piston is in
a position where lateral pressure load by the piston is maximum,
the inflection part is positioned in a range of width in the axis
direction of the piston in the recessed part.
6. The hermetic-type compressor according to claim 5, wherein depth
of the recessed part is set so that the inflection part is apart
from bottom of the recessed part when the piston is in the position
where lateral pressure load by the piston is maximum and the
inflection part is positioned in the range of width in the axial
direction of the piston in the recessed part.
7. The hermetic-type compressor according to claim 4, wherein the
recessed part is one of a plurality of recessed parts, the
plurality of recessed parts include a first recessed part having an
annular shape and a second recessed part having an annular shape
positioned on the compression chamber side relative to the first
recessed part and extending in the outer periphery direction of the
piston, and space volume of the second recessed part is in a range
from 0.25 mm.sup.3 to 25 mm.sup.3 (inclusive).
8. The hermetic-type compressor according to claim 7, wherein an
interval between the first and second recessed parts is 1 mm or
larger.
9. The hermetic-type compressor according to claim 1, wherein the
cylindrical hole has a straight part provided on the top dead
center side of the piston relative to the tapered part.
10. The hermetic-type compressor according to claim 9, wherein when
the piston is positioned at the bottom dead center, an end face on
the compression chamber side of the piston is positioned in the
tapered part of the cylindrical hole.
11. The hermetic-type compressor according to claim 1, wherein a
notch for exposing a part of the recessed part when the piston is
positioned in the bottom dead center is provided in an upper part
of the end part on the shaft side of the cylindrical hole in the
cylinder block.
12. The hermetic-type compressor according to claim 1, wherein a
sectional shape of a periphery as the border from the sliding face
to the recessed part has an inclination angle of 45.degree. or less
with respect to a surface in the axial direction of the piston or
an equivalent curved shape.
Description
TECHNICAL FIELD
[0001] The present invention relates to a hermetic-type compressor
for use in a refrigeration cycle system such as a refrigerator
freezer.
BACKGROUND ART
[0002] A reciprocation-type hermetic compressor has, as a
compression mechanism, a cylinder forming a cylindrical compression
chamber, a cylindrical piston, and a connecting rod. The piston
reciprocates in the cylinder. By the connecting rod, an eccentric
shaft of a shaft is connected to the piston via a piston pin. The
shaft is fixed to the shaft center of a rotor of a motor, and the
compression mechanism is operated by the rotation of the rotor.
[0003] In such a hermetic-type compressor, a gap is necessary
between the inner peripheral face of the cylinder and a sliding
face of the piston so that the faces slide each other. However,
when the gap is large, a blowby gas as a leaked high-temperature
high-pressure refrigerant gas compressed in the compression chamber
is generated, and the compression efficiency deteriorates. On the
other hand, when the gap is small, a sliding loss increases, and
input-output efficiency deteriorates.
[0004] Consequently, a hermetic-type compressor using a cylinder
formed so that the inside diameter dimension of a compression
chamber is gradually increased from a side on which a piston is
positioned in a top dead center toward a side on which the piston
is positioned in a bottom dead center has been proposed (refer to,
for example, patent literature 1). FIGS. 16A and 16B are cross
sections of a compression part of a conventional hermetic-type
compressor described in the patent literature 1. FIG. 16A shows a
state where the piston is positioned in the bottom dead center, and
FIG. 16B shows a state where the piston is positioned in the top
dead center.
[0005] Cylinder block 14 includes cylinder 16 having a center axis
in an almost horizontal direction. Piston 23 inserted in an almost
horizontal direction is connected to connecting rod 26 via a piston
pin (not shown), thereby constructing piston assembly 23A. At an
end face (an end face on the right side in the drawing) of cylinder
16 on the side opposite to connecting rod 26, a valve plate (not
shown) is attached. By piston 23, cylinder 16, and the valve plate
constructed as described above, compression chamber 15 is formed.
Piston 23 reciprocates in an almost horizontal direction in
cylinder 16 via connecting rod 26 by eccentric motion of an
eccentric shaft (not shown) of a shaft (not shown).
[0006] The inner face of cylinder 16 is formed so as to have
tapered part 17 whose inner diameter dimension increases from Dt to
Db (>Dt) from a some midpoint on the side where piston 23 is
positioned in the top dead center toward the side where piston 23
is positioned in the bottom dead center. Piston 23 is formed so
that its outer diameter dimension is almost the same in full
length. Consequently, around the top dead center where the pressure
in compression chamber 15 is high, the gap in the sealing part of
piston 23 is reduced, and blow-by gas is prevented. On the other
hand, around the bottom dead center, the gap increases, so that
sliding loss can be reduced.
[0007] However, piston 23 constructed as described above repeats
reciprocating while always slightly vibrating in all directions in
the gap with the inner face of cylinder 16 for the following
reason. At the time of operation, a dynamic compressive load, the
inertia force and gravity of movable members such as piston 23 and
connecting rod 26, and a piston lateral pressure load generated by
converting the rotational motion to the reciprocating motion act on
piston 23. Forces such as sliding resistance of the sliding part
exert influences one another, and act on piston 23 while the
directions and magnitudes of the forces are changing. Such an
action is also a factor of slight vibrations in all directions of
piston in the gap with the inner face of cylinder 16.
[0008] Particularly, in a state where piston 23 is positioned
around the bottom dead center, the gap with tapered part 17 of
cylinder 16 becomes larger than the gap around the top dead center.
Since the center axis of cylinder 16 is disposed in an almost
horizontal direction, by the influence of the gravity of piston
assembly 23A, the bottom dead center side of piston 23 leans more
vertically downward. As a result, connecting rod 26 side of piston
23 leans more vertically downward.
[0009] Due to occurrence of the slight vibration behavior by the
reciprocating motion of piston 23 and pressure applied to piston
23, the sliding part of piston 23 and tapered part 17 of cylinder
16 locally slide each other. There is the possibility that such a
local sliding generates a contact sound and causes abrasion
starting from the contact part.
[0010] The structure that entire piston 23 is disposed in cylinder
16 when piston 23 is in the bottom dead center position relatively
improves stability of the behavior in tapered part 17 of cylinder
16. However, in the structure, the total length of cylinder 16 is
long, and the size of the compression mechanism is inevitably
large. Accordingly, the entire hermetic-type compressor becomes
large. As a result, it is difficult to reduce the weight, and it is
accordingly difficult to save resources.
CITATION LIST
Patent Literature
[0011] PTL 1: Unexamined Japanese Patent Publication No.
2002-89450
SUMMARY OF THE INVENTION
[0012] The present invention relates to a hermetic-type compressor
realizing prevention of noise and improved efficiency and
reliability by avoiding a local contact between a piston and an
inner face of a cylinder (cylindrical hole), simultaneously, by
minimizing sliding area, and preventing generation of noise due to
a contact between the piston and the cylinder and a local contact
causing abrasion.
[0013] A hermetic-type compressor of the present invention has a
sealed container, an electric mechanism, and a compression
mechanism. The sealed container stores lubricant oil at its bottom.
The electric mechanism and the compression mechanism are disposed
in the sealed container. The electric mechanism drives a
compression mechanism. The compression mechanism includes a shaft,
a cylinder block, a piston, and a connecting rod. The shaft has a
main shaft part rotated by the electric mechanism and an eccentric
shaft part formed in the main shaft part. The cylinder block has a
cylindrical hole constructing a compression chamber and a bearing
rotatably supporting the main shaft part. The cylindrical hole and
the bearing are disposed so that axis of the cylindrical hole and
that of the bearing are orthogonal to each other. The piston has a
sliding face which slides on an inner wall of the cylindrical hole
and is reciprocatably inserted in the cylindrical hole. The
connecting rod connects the eccentric shaft part and the piston.
The cylindrical hole has a tapered part, whose inside diameter
dimension gradually increases from a top dead center of the piston
toward a bottom dead center, and an end part on the shaft side. The
reciprocation direction of the piston is substantially a horizontal
direction. A recessed part, which is recessed to an inside in a
radial direction of the piston and holds the lubricating oil, is
provided in the sliding face of the piston. A part on the lower
side in the vertical direction of the piston, which comes into
contact with the end part on the shaft side of the cylindrical hole
when the piston is positioned in the bottom dead center, is a part
of the sliding face.
[0014] With the configuration, by the tapered part in the
cylindrical hole and the recessed part provided in the piston, the
average gap and the sliding area are reduced, and sliding
resistance of the piston can be lessened. Around the bottom dead
center of the piston, the recessed part in the piston does not come
off from the end part on the shaft side of the cylindrical hole.
Consequently, the inclination of the piston does not become
excessive, and a local collision between the periphery of the
recessed part in the piston and the cylinder block can be avoided.
Therefore, occurrence of collision sound is suppressed, and
increase in noise can be prevented. By holding a large amount of
lubricant oil scattered and supplied from the shaft in the recessed
part, the lubricant oil can be amply supplied to the gap between
the inner face of the cylindrical hole and the surface of the
piston. As a result, lubricity and sealing performance between the
cylinder and the piston are improved, so that the compression
efficiency improves. In addition, the total length of the
cylindrical hole is short.
BRIEF DESCRIPTION OF DRAWINGS
[0015] FIG. 1 is a cross section of a main part of a hermetic-type
compressor prior to a first embodiment of the present
invention.
[0016] FIG. 2 is a vertical cross section of a main part of another
hermetic-type compressor prior to the first embodiment of the
present invention.
[0017] FIG. 3 is a top view of the main part of the hermetic-type
compressor shown in FIG. 2.
[0018] FIG. 4 is a cross section showing a state where a piston of
a hermetic-type compressor in the first embodiment of the invention
is positioned at the bottom dead center.
[0019] FIG. 5 is a cross section showing a state where the piston
of the hermetic-type compressor illustrated in FIG. 4 is positioned
at the top dead center.
[0020] FIG. 6 is a bottom view of the piston of the hermetic-type
compressor illustrated in FIG. 4.
[0021] FIG. 7 is a cross section of a compression part showing a
state where the leaned piston of the hermetic-type compressor
illustrated in FIG. 4 is positioned at the bottom dead center.
[0022] FIG. 8 is a cross section of a compression part showing a
state where a piston of a hermetic-type compressor in a second
embodiment of the present invention is positioned at the bottom
dead center.
[0023] FIG. 9 is a cross section showing a state where the piston
is positioned at the top dead center, of the compression part
illustrated in FIG. 8.
[0024] FIG. 10 is a vertical cross section of a piston assembly of
the hermetic-type compressor in the second embodiment of the
invention.
[0025] FIG. 11 is a cross section of a top face part of the
compression part showing a state where the piston of the
hermetic-type compressor in the second embodiment of the invention
is in a compression stroke.
[0026] FIG. 12 is a characteristic diagram of the piston lateral
pressure load with respect to crank angle of the hermetic-type
compressor in the second embodiment of the invention.
[0027] FIG. 13 is a characteristic diagram of coefficient of
performance with respect to space volume of a recessed part in the
hermetic-type compressor in the second embodiment of the
invention.
[0028] FIG. 14 is a characteristic diagram of the coefficient of
performance with respect to distance between recessed parts in the
hermetic-type compressor in the second embodiment of the
invention.
[0029] FIG. 15 is a characteristic diagram of the coefficient of
performance with respect to operation frequency of the
hermetic-type compressor in the second embodiment of the
invention.
[0030] FIG. 16A is a vertical cross section of a compression part
showing a state where a piston of a conventional hermetic-type
compressor is positioned in the bottom dead center.
[0031] FIG. 16B is a vertical cross section of the compression part
showing a state where the piston illustrated in FIG. 16A is
positioned in the top dead center.
DESCRIPTION OF EMBODIMENTS
[0032] Hereinafter, exemplary embodiments of the present invention
will be described with reference to the drawings. The present
invention is not limited to the embodiments.
First Exemplary Embodiment
[0033] The inventors of the present invention have proposed another
configuration for compression efficiency improvement and reduction
in sliding loss (Unexamined Japanese Patent Publication No.
2006-169998). FIG. 1 is a cross section of a main part of a
hermetic-type compressor and shows a state where piston 123 is in
the bottom dead center.
[0034] In the surface of piston 123, narrow circular-shaped grooves
141A and 141B and a recessed part 141C which is recessed to an
inside in a radial direction are provided. The inside diameter of
cylindrical-shaped hole 116 is almost constant. At a position
around the bottom dead center, lower end part 123B of piston 123
and recessed part 141C are exposed from cylindrical-shaped hole
116. Grooves 141A and 141B are partially exposed from notch 114A
formed in cylinder block 114. By forming grooves 141A and 141B and
recessed part 141C in the sliding face (outer peripheral face) of
piston 123 in such a manner, when piston 123 reciprocates, the
amount of oil supplied to a sealing part and a sliding part
increases. Consequently, the sealing performance improves, and the
sliding loss can be reduced while improving the compression
efficiency and decreasing the sliding area.
[0035] By combining the configuration of FIG. 1 to the
configuration of FIG. 16A, further improvement in compression
efficiency and reduction in the sliding loss can be expected. FIG.
2 is a vertical cross section of a main part of a hermetic-type
compressor on the assumption of the combination. FIG. 2 shows a
state where the piston is at the bottom dead center. FIG. 3 is a
top view of the main part in a state where the piston of the
hermetic-type compressor shown in FIG. 2 is in the compression
stroke.
[0036] Cylindrical hole 216 has straight part 218 and tapered part
217. In straight part 218, the inside diameter of
cylindrical-shaped hole 216 is almost constant. In tapered part
217, the inside diameter dimension increases from Dt to Db (>Dt)
from a some midpoint on the side where piston 223 is positioned in
the top dead center (the right side in the drawing) toward the side
where piston 23 is positioned in the bottom dead center (the left
side in the drawing). The gap between piston 223 and tapered part
217 is large around the bottom dead center and small around the top
dead center.
[0037] In the surface of piston 223, grooves 241A and 241B and
recessed part 241C which is recessed to the inner side in a radial
direction are formed. In a position around the bottom dead center,
lower end part 223B of piston 223 and recessed part 241C are
exposed from cylindrical-shaped hole 216. Grooves 241A and 241B are
partially exposed from notch 214A formed in cylinder block 214.
[0038] Therefore, the sealing part of piston 223 prevents blowby
gas by reduction in the gap around the top dead center and the
labyrinth seal effect by grooves 241A and 241B. Lubricant oil
scattering around the bottom dead center is held in recessed part
241C, and supplied from recessed part 241C to grooves 241A and 241B
and the sliding part of piston 223. By increasing the oil supply
amount in such a manner, the sealing performance and lubricity can
be improved.
[0039] As a result, by enlargement of the average clearance of the
sliding part of piston 223 and reduction in sliding area, a
hermetic-type compressor with largely reduced sliding loss, high
sealing performance, and high compression efficiency can be
expected. In the configuration, piston 223 is exposed from tapered
part 217 of cylindrical-shaped hole 216 around the bottom dead
center. At this time, piston 223 has a cantilever configuration
that the sliding part of piston 223 inserted in cylindrical-shaped
hole 216 serves as a supporting point, and the deadweight of piston
223, a piston pin (not shown), and connecting rod 226 is supported
by the supporting point. This is because the clearance of a
connection part of connecting rod 226 and an eccentric shaft (not
shown) of the crankshaft and the clearance of a connection part of
a bearing and the crankshaft (which are not shown) are larger than
the gap of the sealing part of piston 223.
[0040] Due to the cantilever configuration, at the bottom dead
center at which piston 223 is exposed most from cylindrical-shaped
hole 216, the bottom dead center side of piston 223 leans
vertically downward in the gap formed by tapered part 217 and
piston 223. This is because, since it is formed to have tapered
part 217 in which the inside diameter dimension of
cylindrical-shaped hole 216 increases from Dt to Db, the gap
between tapered part 217 and piston 223 increases around the bottom
dead center.
[0041] If piston 223 does not have recessed part 241C, long support
length of the sliding part which supports one side of piston 223
can be assured as shown by L1 in FIG. 2. However, when recessed
part 241C is formed, leaning of piston 223 increases only by the
recess amount of recessed part 241C. As a result, support length of
the sliding part which supports one side of piston 223 becomes
shorter as shown by L2 in FIG. 2.
[0042] Therefore, in the configuration shown in FIG. 2, the leaning
of piston 223 becomes excessive. Consequently, when periphery 242
of recessed part 241C enters cylindrical-shape hole 216 in the
compression stroke, there is the possibility that periphery 242
locally collides with end face 216A of cylindrical-shaped hole 216,
and noise increases.
[0043] Next, a configuration solving such a problem will be
described with reference to FIGS. 4 to 7. FIG. 4 is a cross section
showing a state where the piston of the hermetic-type compressor in
the first embodiment of the invention is positioned at the bottom
dead center. FIG. 5 is a cross section showing a state where the
piston of the hermetic-type compressor is positioned at the top
dead center. FIG. 6 is a bottom view of the piston of the
hermetic-type compressor. FIG. 7 is a cross section of a
compression part showing a state where the piston which leans is
positioned at the bottom dead center.
[0044] As shown in FIGS. 4 and 5, the hermetic-type compressor has
sealed container 301, electric mechanism 304, and compression
mechanism 305. Lubricant oil 306 is stored at the bottom of sealed
container 301. Electric mechanism 304 has stator 302 and rotor 303
and is disposed in sealed container 301. Compression mechanism 305
is also disposed in sealed container 301 and driven by electric
mechanism 304.
[0045] Concretely, compression mechanism 305 has shaft 310,
cylinder block 314, piston 423, and connecting rod 326. Shaft 310
has main shaft part 311 rotated by electric mechanism 304 and
eccentric shaft part 312 formed eccentrically at one end of main
shaft part 311. Main shaft part 311 is fixed to the shaft center of
rotor 303.
[0046] Oil support path 313 is provided on the inside and the
peripheral face of shaft 310, and one end of oil support path 313
extends in the axial direction in eccentric shaft part 312. Oil
support path 313 is communicated with an oil support path (not
shown) which is open at the upper end of eccentric shaft part 312.
A branch oil path (not shown) which is branched from oil supply
path 313 in a radius direction and is open is provided in a some
midpoint of eccentric shaft part 312. The lower end of main shaft
part 311 extends so that the other end of oil supply path 313 is
dipped in predetermined depth in lubricant oil 306.
[0047] Cylinder block 314 has an almost cylindrical shaped
cylindrical hole 316 constructing compression chamber 315 and
bearing 320 rotatably supporting main shaft part 311. Cylindrical
hole 316 and bearing 320 are disposed so as to be fixed in
predetermined positions. Cylindrical hole 316 and bearing 320 are
disposed so that their axes are orthogonal to each other. Bearing
320 serves as a cantilever bearing by axially supporting the end on
the side of eccentric shaft part 312 in main shaft part 311 of
shaft 310. In cylinder block 314, notch 319 is formed in an upper
wall on which lubricant oil 306 falls, in the peripheral wall of
cylindrical hole 316.
[0048] Piston 423 is reciprocatably inserted in cylindrical hole
316 and has sliding face 423C which slides on the inner wall of
cylindrical hole 316 as shown in FIG. 6. The reciprocation
direction of piston 423 is substantially the horizontal direction.
By connecting rod 326, eccentric shaft part 312 and piston 423 are
connected to each other. Specifically, one end of connecting rod
326 is coupled to eccentric shaft part 312, and the other end is
coupled to piston 423 via piston pin 425 inserted in piston pin
hole 423 as shown in FIG. 6. Connecting rod 326 and piston 423
construct piston assembly 440.
[0049] In piston 423, piston pin hole 423A is formed in a direction
orthogonal to the axis of piston 423. Compression mechanism 305 has
piston pin 425 inserted in piston pin hole 423A. Connecting rod 326
is coupled to piston pin 425 so as to be rotatable about the axis
of piston pin 425.
[0050] Next, cylindrical hole 316 and piston 423 will be described
in detail with reference to FIGS. 6 and 7. As shown in FIG. 7, the
dimension in the axial direction of cylindrical hole 316 is set so
that, when piston 423 is positioned in the bottom dead center, the
end on connecting rod 326 side of piston 423 protrudes from end
face 316A on the side of shaft 310 of cylindrical hole 316.
[0051] The inner face of cylindrical hole 316 is constructed by, as
shown in FIG. 7, straight part 318 in which the inside diameter
dimension is constant in the axial direction only in an interval of
predetermined length L from the top dead center side and tapered
part 317 whose inside diameter dimension increases from Dt to Db
(>Dt) toward the bottom dead center. That is, cylindrical hole
316 has tapered part 317 whose inside diameter dimension gradually
increases in a direction in which piston 423 moves from the top
dead center to the bottom dead center. Cylindrical hole 316 has end
face 316A as the end on the side of shaft 310.
[0052] The border between straight part 318 and tapered part 317 is
the start point of tapered part 317, and is inflection part 317A at
which the change rate of taper angle is large.
[0053] As shown in FIGS. 6 and 7, the outside diameter of piston
423 is the same in full length. That is, piston 423 does not have a
tapered shape. In the outer peripheral face (sliding face 423C) of
piston 423, a plurality of recessed parts 441A, 441B, 4411C, and
4412C are provided. Recessed parts 441A and 441B close to
compression chamber 315 are formed in an annular shape extending in
the entire outer periphery of piston 423. The space volume of each
of recessed parts 441A and 441B is 6 mm.sup.3 and the interval
between them is set to 2 mm.
[0054] Recessed parts 4411C and 4412C furthest from compression
chamber 315 do not have an annular shape. Recessed parts 4411C and
4412C are formed to, mainly, reduce the area of contact with
cylindrical hole 316 of piston 423 and hold lubricant oil 306. When
recessed parts 4411C and 4412C hold lubricant oil 306, the sliding
face with cylindrical hole 316 of piston 423 can be made lubricant.
Therefore, when it is necessary to further reduce the weight of
piston 423, recessed parts 4411C and 4412C may be formed deeper or
wider.
[0055] In FIG. 6, recessed part 4412C is shown representatively.
Recessed part 4411C has a similar shape. The outline of recessed
part 4412C extends so that its width is gradually decreased from
the part parallel to recessed parts 441A and 441B toward end 423B
side on connecting rod 326 side, and the terminating end extends
oppositely toward compression chamber 315 side.
[0056] As shown in FIG. 6, recessed parts 4411C and 4412C are
formed symmetrically with respect to axis X as the center of piston
pin hole 423A, and their terminating end extends to piston pin hole
423A. Therefore, recessed parts 4411C and 4412C are provided so as
to surround piston pin hole 423A, and extension part 423D which
extends to the inside of recessed parts 4411C and 4412C is formed
in end part 423B. Extension part 423D serves as a part of end part
423B of piston 423. Recessed parts 4411C and 4412C are formed so as
to be recessed to the inside in a radial direction of piston 423
and hold lubricant oil 306.
[0057] The volume of space formed by the inner face (straight part
318) of cylindrical hole 316 of recessed parts 4411C and 4412C is
set to 6 mm.sup.3 or larger. Since recessed parts 4411C and 4412C
do not face straight part 318, an imaginary state is assumed. An
interval of 1.5 mm (interval including the dimension of periphery
442 which will be described later) is provided for recessed part
441B using the deepest point of recessed parts 4411C and 4412C as a
base point. The volume of recessed parts 4411C and 4412C can be set
arbitrarily as described above.
[0058] Recessed parts 4411C and 4412C are provided so as to
surround piston pin hole 423A and are therefore communicated with
piston pin hole 423A. Specifically, recessed parts 4411C and 4412C
are first and second recessed parts formed in positions symmetrical
with respect to axis X of piston 423 passing through the center of
piston pin hole 423A. Recessed parts 4411C and 4412C communicate
with each other via piston pin hole 423A.
[0059] Further, a section corner of periphery 442 of recessed parts
4411C and 4412C is formed in an inclined face of about
30.degree..
[0060] Recessed parts 4411C and 4412C are provided in positions
symmetrical with respect to axis X as a center in the surface of
piston 423. In this case, it is unnecessary to provide recessed
part 4411C with extension part 423D. However, by employing the same
shape, it becomes unnecessary to recognize the side in the vertical
direction of piston 423 at the time of assembly, and workability
improves.
[0061] In the configuration, piston 423 serves as a component of
piston assembly 440 by making piston pin 425 inserted in piston pin
hole 423A penetrate connecting rod 326, and is assembled as
compression mechanism 305. In this case, extension part 423D is
disposed so as to be the bottom face as shown in FIG. 7.
[0062] As shown in FIG. 7, in a state where piston 423 is
positioned at the bottom dead center, extension part 423D faces
(comes into contact with) the corner of end face 316A of
cylindrical hole 316. The dimensional relations between piston 423
and end face 316A on the side of connecting rod 326 in cylindrical
hole 316 are set to achieve such a state. Specifically, when piston
423 is positioned at the bottom dead center, the lower part in the
vertical direction of piston 423 which comes into contact with end
face 316A as an end on the side of shaft 310 of cylindrical hole
316 is extension part 423D as a part of sliding face 423C.
[0063] The operation of the hermetic-type compressor constructed as
mentioned above will now be described. By applying current to
electric mechanism 304, rotor 303 of electric mechanism 304 rotates
shaft 310, rotary motion of eccentric shaft part 312 is converted
to reciprocating motion via connecting rod 326 and the
reciprocating motion is transmitted to piston 423. Consequently,
piston 423 inserted in cylindrical hole 316 (compression chamber
315) of cylinder block 314 reciprocates in cylindrical hole 316. By
the reciprocating motion of piston 423, refrigerant gas from a
cooling system (not shown) is taken into compression chamber 315
and compressed. After that the gas is discharged again to the
cooling system.
[0064] The lower end part of oil supply path 313 functions as a
pump using centrifugal force by rotation of shaft 310. By the
pumping action, lubricant oil 306 at the bottom of sealed container
301 passes through oil supply path 313, is pumped up, and jets and
scatters to respective directions from the oil supply path and the
branched oil path provided for eccentric shaft part 312.
[0065] Lubricant oil 306 jetted from the oil supply path collides
with the ceiling face of sealing container 301 and scatters to
mainly cool compression mechanism 305 and make the sliding part
lubricant. Lubricant oil 306 from the branched oil path flies
almost horizontally in all circumferences in sealed container 301,
is supplied mainly to piston pin 325, piston 423, and the like, and
makes the sliding part lubricant.
[0066] In the reciprocating motion of piston 323, in the beginning
of a compression stroke (around the bottom dead center), blowby gas
is hardly generated, and sliding resistance of piston 423 is small.
Just before piston 423 reaches a position around the top dead
center, the pressure in compression chamber 315 further increases.
Since the gap between sliding face 423C of piston 423 and tapered
part 317 becomes small at the top dead center side, occurrence of
blowby gas can be reduced.
[0067] In other words, in a state where piston 423 is positioned in
the bottom dead center, lubricant oil 306 is supplied amply from
notch 319 formed in the upper wall of cylindrical hole 316 to
recessed parts 4411C and 4412C formed in sliding face 423C of
piston 423 and is held. A part of lubricant oil 306 is supplied to
recessed parts 441A and 441B and held. Consequently, also when
piston 423 moves to straight part 318 where the gap is narrow, a
larger amount of lubricant oil is supplied to the sliding part
formed by piston 423 and straight part 318. Therefore, the
lubricant oil makes the sliding part lubricant and sealed. As a
result, occurrence of gas leakage is prevented, and the volumetric
efficiency can be improved.
[0068] Further, preferably, cylindrical hole 316 has straight part
318 provided on the top dead center side of piston 423 relative to
tapered part 317. With the configuration, the sealed part of piston
423 around the top dead center where the pressure increases most in
the compression stroke can be formed in straight part 318 whose
inside diameter dimension is constant in the axial direction. In
the sealed part, the distance in the axial direction of the minimum
gap between piston 423 and cylindrical hole 316 is long, so that
action of preventing occurrence of gas leakage accompanying
increase in pressure of the refrigerant gas is large. When piston
423 is positioned in tapered part 317 around the bottom dead
center, the gap in the radius direction is wide, so that the
sliding loss is small. As a result, higher efficiency can be
achieved.
[0069] In a state where piston 423 is positioned at the bottom dead
center, the end part on the side of connecting rod 326 of piston
423 is exposed from the end part on the side of shaft 310 of
cylindrical hole 316. Consequently, a large amount of lubricant oil
306 scattered and supplied is adhered to the surface of exposed
piston 423 and can be supplied to the sliding part and the sealed
part as piston 423 reciprocates. As a result, sliding loss is
reduced, and higher efficiency can be achieved together with the
above-described prevention of occurrence of gas leakage.
[0070] By making periphery 442 of recessed parts 4411C and 4412C an
inclined face, the wedge film effect of lubricant oil 306 is
obtained, and an oil film can be reliably formed in the gap between
piston 423 and cylindrical hole 316.
[0071] When piston 423 is positioned at the bottom dead center, the
bottom dead center side of piston 423 leans downward in the
vertical direction in the gap between cylindrical hole 316 and
piston 423. However, extension part 423D is in contact with the
corner of end face 316A of cylindrical hole 316. Consequently,
piston assembly 440 leans due to its own weight, so that periphery
442 is deviated vertically downward from cylindrical hole 316 and
does not collide with the lower corner of end face 316A. Therefore,
occurrence of collision noise is suppressed, and reduction in noise
can be achieved. Connecting rod 326 is coupled to piston pin 425 so
as to be rotatable about the axis of piston pin 425. Consequently,
piston 423 does not rotate about the axis, and extension part 423D
reliably comes into contact with the corner of end face 316A.
[0072] Since recessed parts 4411C and 4412C communicate with piston
pin hole 423A, a circulation path is formed by lubricant oil 306
scattered and supplied around the bottom dead center of piston 423,
and piston 423 is cooled by lubricant oil 306. By the cooling, the
temperature of piston 423 decreases. Accordingly, temperature rise
in compression chamber 315 is suppressed, and deterioration in the
volume efficiency caused by heat reception is prevented.
[0073] Further, in the case of driving an inverter at operation
frequency equal to or less than power-supply frequency, by the
synergetic effect of maintenance of oil retentivity by the
capillary action of recessed parts 441A and 441B, formation of
eddying flow by the labyrinth effect, formation of decelerating
flow accompanying passage in recessed parts 441A, 441B, 4411C, and
4412C of leakage flow of the refrigerant gas, and the like, leakage
of refrigerant can be suppressed.
[0074] As a result, particularly, the refrigeration capacity and
efficiency at the time of operating the hermetic-type compressor in
a low operation frequency range equal to or less than the
power-supply frequency can be increased. The effect will be
described specifically in a second exemplary embodiment.
Second Exemplary Embodiment
[0075] FIG. 8 is an enlarged cross section of a compression part
showing a state where a piston of a hermetic-type compressor in a
second embodiment of the present invention is positioned at the
bottom dead center. FIG. 9 is an enlarged cross section of the
compression part, showing a state where the piston is positioned at
the top dead center. FIG. 10 is a vertical cross section of a
piston assembly of the hermetic-type compressor in the second
embodiment. FIG. 11 is a top view of the compression part, showing
a state where the piston of the hermetic-type compressor in the
second embodiment is in a compression stroke. FIG. 12 is a
characteristic diagram of the piston lateral pressure load with
respect to crank angle of the hermetic-type compressor in the
second embodiment.
[0076] In the embodiment, a general configuration of a compressor
will be described mainly with respect to parts different from the
first embodiment by quoting the description (including the
reference numerals) of the first embodiment and FIGS. 4 and 5.
[0077] The part different from the first embodiment is the
configuration of recessed parts formed in a piston, and the other
configuration is similar to the first embodiment. Therefore, the
piston having the different configuration will be mainly
described.
[0078] As illustrated in FIGS. 8 and 9, the outside diameter of
piston 323 is constant in full length. In the surface of piston
323, three recessed parts 341A, 341B, and 341C are provided at
predetermined intervals. Each of recessed parts 341A, 341B, and
341C is formed in an annular shape in the entire circumference in
the surface of piston 323.
[0079] The volume of space formed by each of recessed part 341A
formed in a position closest to compression chamber 315 and
recessed part 341B in the second closest position and the inner
face (straight part 318) of cylindrical hole 316 is set to 6
mm.sup.3. The interval between recessed parts 341A and 341B is set
to 2 mm.
[0080] The volume of space formed by recessed part 341C in a third
position and the inner face (straight part 318) of cylindrical hole
316 is set to 6 mm.sup.3 or larger. However, since recessed part
341C does not face straight part 318, an imaginary state is
assumed. Between recessed parts 341C and 341B, the interval of 1.5
mm (interval including the dimension of periphery 342 which will be
described later) is provided using the deepest point of recessed
part 341C as a base point. A part of recessed part 341C is
communicated with piston pin hole 323A. Recessed part 341C is
formed for purposes similar to those of recessed parts 4411C and
44112C in the first embodiment. Therefore, the volume of recessed
part 341C can be arbitrarily set.
[0081] As shown in FIG. 8, end part 323B on the side opposite to
the compression chamber (on the side of connecting rod 326) of
piston 323 positioned at the bottom dead center is exposed only by
length A from end face 316A on the shaft side of cylinder block
314. Piston 323 is formed in such dimensions. In other words, the
dimension in the axial direction of cylindrical hole 316 is set so
that, when piston 323 is positioned at the bottom dead center, the
corner of end face 316A of cylindrical hole 316 comes into contact
with end part 323B. End part 323B is the outer peripheral face
between the end on the side of connecting rod 326 in piston 323 and
recessed part 341C having the annular shape.
[0082] Further, in cylinder block 314, notch 319 is provided in the
upper wall on which lubricant oil 306 falls in the peripheral wall
of cylindrical hole 316 in a manner similar to the first
embodiment. By notch 319, at least recessed part 341C is exposed in
a state where piston 323 is positioned at the bottom dead center.
In other words, recessed part 341C is defined as a part of recesses
in the configuration having the plurality of recesses 341A, 341B,
and 341C.
[0083] As shown in FIG. 8, recessed part 341C is formed so that, in
a state where piston 323 reaches the position of the bottom dead
center, all of recessed part 341C is positioned on the side of the
top dead center only by length B from end face 316A of cylindrical
hole 316. End face 323C on the side of compression chamber 315 of
piston 323 is positioned on the side of tapered part 317 only by
distance of length C. Further, as shown in FIG. 10, periphery 342
of recessed part 341C has a shape inclined at almost 30.degree. in
cross section.
[0084] FIG. 11 shows disposition of piston 323 when the crank angle
is 320 degrees in the compression stroke. As shown in FIG. 12, the
crank angle of 320 degrees is the angle at which the lateral
pressure load of piston 320 becomes the maximum. The maximum
lateral pressure load acts on the lateral pressure load sliding
part on the side face in the horizontal direction of cylindrical
hole 316. At this time, inflection part 317A between straight part
318 and tapered part 317 is positioned in the range of the width of
recessed part 341C in piston 323. In FIG. 11, to clearly show that
inflection part 317A is positioned in the range of the width of
recessed part 341C, the clearance between piston 323 and straight
part 318 of cylindrical hole 316 is illustrated largely.
[0085] The operation of the hermetic-type compressor constructed as
mentioned above will now be described. By applying current to
electric mechanism 304, rotor 303 of electric mechanism 304 rotates
shaft 310, rotary motion of eccentric shaft part 312 is converted
to reciprocating motion via connecting rod 326, and the
reciprocating motion is transmitted to piston 323. By the motion,
piston 323 reciprocates in cylindrical hole 316.
[0086] Piston 323 shifts from the bottom dead center position shown
in FIG. 8 to the compression stroke of compressing the refrigerant
gas. In a compression initial state during the shift to the top
dead center side shown in FIG. 9, rise of pressure in compression
chamber 315 is small. Consequently, even if the clearance between
tapered part 317 formed in cylindrical hole 316 and the sliding
face (peripheral face) of piston 323 is relatively large, blowby
gas is hardly generated by the sealing effect of the lubricant oil.
Since the clearance is large, sliding resistance of piston 323 is
also small.
[0087] When the compression stroke progresses and the crank angle
becomes 320 degrees, piston 323 is in the position shown in FIG.
11. At this time, the lateral pressure load of piston 323 becomes
the maximum value as shown in FIG. 12.
[0088] In the configuration shown in FIG. 3 described in the first
embodiment, when the lateral pressure load becomes the maximum, the
surface pressure of a sliding part in the side face of piston 223
locally rises and inflection part 217A as the start point of
tapered part 217 easily slides on the sliding part. As a result, a
lubricant state deteriorates, and there is the possibility such
that sliding sound increases.
[0089] In the second embodiment, however, inflection part 317A
having high change rate of the taper angle as the start point of
tapered part 317 is positioned in the range of the width of
recessed part 341C in piston 323. In addition, since the depth of
recessed part 341C is assured, inflection part 317A is apart from
the bottom of recessed part 341C in a state where inflection part
317A faces recessed part 341C. Therefore, even when the lateral
pressure load increases, the lubricant state does not decrease in
inflection part 317A in which an oil film is not easily formed,
inflection part 317A does not locally slide, and no sliding sound
is generated.
[0090] When the compression stroke further progresses, the pressure
of the refrigerant gas in compression chamber 315 gradually
increases. Just before piston 323 reaches a position near the top
dead center shown in FIG. 9, the pressure in compression chamber
315 further rises. On the top dead center side, the gap between the
sliding face of piston 323 and tapered part 317 becomes small, so
that generation of blowby gas can be reduced. At this time,
straight part 318 formed in cylindrical hole 316 reduces leakage of
the refrigerant gas increased to predetermined discharge pressure
more than tapered part 317.
[0091] In the state where piston 323 is positioned at the bottom
dead center, the side of connecting rod 326 of piston 323 is
exposed from cylinder block 314. Lubricant oil 306 scattered from
the upper end of shaft 310 is amply supplied from notch 319 formed
in the upper wall of cylindrical hole 316 to recessed part 341C
formed in the sliding face of piston 323 and is held. A part of
lubricant oil 306 is supplied to recessed parts 341A and 341B.
Consequently, the lubricant oil supplied to the gap between the
inner peripheral face of cylindrical hole 316 of cylinder block 314
and the sliding face of piston 323 becomes large in the compression
stroke.
[0092] During movement of piston 323 to the top dead center, all of
piston 323 is positioned in cylindrical hole 316. Due to this,
escape of lubricant oil 306 held in recessed parts 341A, 341B, and
341C from cylindrical hole 316 is suppressed. In addition,
lubricant oil 306 is easily carried to straight part 318 in which
sliding resistance is highest.
[0093] Further, end face 323C on the side of the compression
chamber of piston 323 is positioned on the side of tapered part 317
only by distance of length C in FIG. 8 at the bottom dead center.
Consequently, when piston 323 moves from the bottom dead center to
the top dead center in the compression stroke, a part of lubricant
oil 306 adhered to the surface of piston 323 moves to the top dead
center side, and a part of lubricant oil 306 adhered to the surface
of cylindrical hole 316 is also taken and supplied to the gap
between piston 323 and cylindrical hole 316 as piston 323
moves.
[0094] In the state shown in FIG. 8, the end face on the side of
compression chamber 315 of piston 323 is positioned in tapered part
317. Consequently, the gap between piston 323 and cylindrical hole
316 is larger than that in the case where piston 323 is positioned
in straight part 318. The amount of lubricant oil 306 held in the
space of the gap is accordingly larger.
[0095] Therefore, also when piston 323 moves to straight part 318
in which the gap is narrow, a larger amount of lubricant oil is
supplied to the sliding part formed by piston 323 and straight part
318, and the sliding part can be made lubricant and sealed. As a
result, occurrence of gas leakage is prevented, and volume
efficiency can be improved. The configuration can be applied also
to the first embodiment.
[0096] Since recessed part 341C is provided in the annular shape in
the sliding face of piston 323, for example, by widening the width
of recessed part 341C in the axial direction of piston 323, the
area of recessed part 341C can be maximized.
[0097] With the configuration as described above, the sliding area
between cylindrical hole 316 (compression chamber 315) and piston
323 is reduced maximally, and sliding resistance can be decreased.
In addition, lubricant oil 306 can be supplied uniformly and stably
to the lubricant part and the sealing part in the entire
circumference of piston 323. Consequently, poor lubrication and
deterioration in sealing performance caused by nonuniform and
unstable oil supply can be prevented.
[0098] Further, periphery 342 of recessed part 341C is constructed
as a face inclined from the surface in the axial direction of
piston 323 by about 30.degree. in a sectional shape. Consequently,
when piston 323 reciprocates, lubricant oil 306 held in recessed
part 341C gains force in recessed part 341C. Along the inclination
of periphery 342 of recessed part 341C, lubricant oil 306 is pulled
in the gap between piston 323 and cylindrical hole 316, enters the
gap, and acts so as to correct the inclination of piston 323. In
such a manner, a so-called wedge film effect is produced in the gap
between piston 323 and cylindrical hole 316.
[0099] As a result, by the wedge film effect of lubricant oil 306,
the inclination of piston 323 is corrected so as to be reduced, and
the gap with cylindrical hole 316 in the entire circumference of
piston 323 is made uniform. Therefore, lubricating oil 306 is
carried more easily to the sliding part and the sealing part around
the top dead center in which the gap is particularly formed narrow,
and the frequency of inevitable local metal contact can be
reduced.
[0100] The angle of periphery 342 of recessed part 341C is not
limited to about 30.degree.. The angle may be any angle at which
the wedge film effect such that, as described above, when piston
323 reciprocates, lubricant oil 306 held in recessed part 341C is
pulled in the gap between piston 323 and cylindrical hole 316 is
easily produced. That is, it is sufficient to the angle properly in
accordance with the reciprocation speed of piston 323 and the like.
In the embodiment, the angle with respect to the surface in the
axial direction of piston 323, of periphery 342 is preferably in
the range of 25.degree. to 35.degree.. However, in a sectional
shape having an inclination angle of 45.degree. or less or an
equivalent curved shape, the angle may be any angle at which
lubricant oil 306 held in recessed part 341C is pulled in the gap
between piston 323 and cylindrical hole 316.
[0101] As a result, a larger amount of lubricant oil 306 can be
supplied to the gap between cylindrical block 314 and piston 323,
lubricant oil 306 is excellently held, and sealing performance can
be improved. Further, with ample supply of lubricant oil 306, the
sliding resistance of piston 323 can be reduced, so that the
compression efficiency is improved, an input is reduced, and higher
efficiency can be achieved. The configuration may be applied to
recessed parts 4411C and 4412C of the first embodiment.
[0102] Piston assembly 340 has a cantilever configuration that the
deadweight of piston assembly 340 is supported only by the sliding
part of piston 323 inserted in cylindrical hole 316. Consequently,
around the bottom dead center at which piston 323 is exposed from
cylindrical hole 316 most, the bottom dead center side of piston
323 leans downward in the vertical direction in the gap between
piston 323 and cylindrical hole 316.
[0103] However, periphery 342 on the connecting rod side of
recessed part 341C is positioned on the top dead center side
relative to end face 316A of cylindrical hole 316. End part 323B of
piston 323 and the corner of end face 316A of cylindrical hole 316
are in contact with each other. Consequently, periphery 342 of
recessed part 341C is not deviated vertically downward from
cylindrical hole 316 and does not collide with the lower corner of
end face 316A. Therefore, occurrence of collision noise is
suppressed, and reduction in noise can be achieved.
[0104] A part of recessed part 341C is communicated with piston pin
hole 323A. That is, preferably, the upper and lower sides of
recessed part 341C communicate with each other via piston pin hole
323A. With the configuration, a circulating path that lubricant oil
306 scattered and supplied to the upper part of piston 323 around
the bottom dead center passes through circular shaped recessed part
341C and is ejected downward via the end face of piston pin hole
323A is formed. Piston 323 heated by high-temperature,
high-pressure refrigerant gas is cooled by
relatively-low-temperature lubricant oil 306 passing through the
circulating path. By the cooling, the temperature of piston 323
decreases. Accordingly, temperature rise in compression chamber 315
is suppressed, and deterioration in the volume efficiency caused by
heat reception can be prevented.
[0105] Further, in the case of driving an inverter at operation
frequency equal to or less than power-supply frequency,
particularly, in a low-speed operation of 30 r/sec or less, the
reciprocating motion speed of piston 323 becomes slow and, in
addition, the supply amount of lubricant oil 306 supplied by the
pumping action of shaft 310 decreases. Consequently, the amount of
lubricating oil 306 sprayed from eccentric shaft part 312 into
hermetic container 301 decreases.
[0106] However, around the bottom dead center, at least recessed
part 341C is exposed from cylindrical hole 316. Consequently,
lubricant oil 306 is reserved mainly in recessed part 341C and
supplied to the sealing part. The oil retentivity is maintained by
the capillary action of recessed parts 341A and 341B, and eddying
flow by the labyrinth effect is formed. Further, after leakage flow
of the refrigerant gas passes through recessed parts 341A, 341B,
and 341C, decelerating flow by contraction flow is formed. By the
synergetic effect of formation of eddying flow by the labyrinth
effect, formation of decelerating flow by contraction flow, and the
like, leakage of refrigerant can be suppressed. As a result,
particularly, the refrigeration capacity and efficiency at the time
of operating the hermetic-type compressor in a low operation
frequency range equal to or less than the power-supply frequency
can be increased.
[0107] Hereinafter, a result of conducting a confirmatory
experiment of coefficient of performance (C.O.P.) of the
hermetic-type compressor in the embodiment will be described with
reference to FIGS. 13 to 15. The coefficient of performance is the
ratio of refrigeration capacity to an applied input and is
generally used as an index indicating the efficiency of a
compressor. In tests, R600a (isobutane) was used as the
refrigerant. The operation frequency was 27 r/sec, and operation
conditions close to operation conditions in a refrigerator were
evaporation temperature of -30.degree. C. and condensation
temperature of 40.degree. C.
[0108] FIG. 13 is a characteristic diagram of coefficient of
performance with respect to space volume of recessed parts 341A and
341B. FIG. 14 is a characteristic diagram of the coefficient of
performance with respect to distances among neighboring recessed
parts 341A, 341B, and 341C. FIG. 15 is a characteristic diagram of
the coefficient of performance with respect to operation frequency
of the compressor.
[0109] In FIG. 13, the vertical axis denotes the coefficient of
performance of the compressor, and the horizontal axis denotes the
sum of volume of space surrounded by the section of recessed parts
341A and 341B and the extension face of the outside diameter of
piston 323.
[0110] The test result shown in FIG. 13 is a result of conducting
the test using the recessed parts on the side of compression
chamber 315 as a plurality of recessed parts 341A and 341B having
small sectional area. However, the invention is not limited to a
plurality of recessed parts. One recessed part formed in a volume
with which the result shown in FIG. 13 is obtained may be
employed.
[0111] As obvious from FIG. 13, it is preferable to set the space
volume of recessed parts 341A and 341B in a range T of 0.25
mm.sup.3 to 25 mm.sup.3 (inclusive). By such setting, the
coefficient of performance higher than that in the case where the
space volume is smaller than 0.25 mm.sup.3 and that in the case
where the space volume is larger than 25 mm.sup.3 can be
obtained.
[0112] Referring now to FIG. 14, the influence of distance S
between neighboring recessed parts 341A, 341B, and 341C will be
described. In FIG. 14, the vertical axis denotes the coefficient of
performance of the compressor, and the horizontal axis denotes
distance S between neighboring recessed parts 341A, 341B, and
341C.
[0113] As shown in FIG. 14, by setting the distance between
neighboring recessed parts 341A, 341B, and 341C to 1 mm or larger,
the coefficient of performance (C.O.P) increases. It is assumed
that, by setting distance S between neighboring recessed parts
341A, 341B, and 341C to 1 mm or larger, the gap between the surface
of piston 323 and cylindrical hole 316 becomes a reducer.
Consequently, the flow rate of a mixed fluid of the refrigerant gas
and lubricant oil 306 increases so that the pressure of the mixed
fluid is reduced. As a result, the leakage amount from the gap
between piston 323 and cylindrical hole 316 further decreases.
Therefore, by further reducing the amount of leakage to the side
opposite to the compression chamber, reduction in the volumetric
efficiency is prevented, and the efficiency of the compressor can
be increased.
[0114] In the embodiment, recessed parts 341A, 341B, and 341C are
formed by setting the distance between neighboring recessed parts
341A, 341B, and 341C to 1 mm or larger. Consequently, in addition
to the above-described effects, even in the case where oil in any
one of recessed parts 341A, 341B, and 341C becomes discontinuous
and the sealing performance deteriorates, the sealing performance
can be maintained by the other recessed parts.
[0115] Next, with reference to FIG. 15, the characteristics of the
coefficient of performance when the compressor of the embodiment is
assembled in a refrigeration cycle and the operation frequency of
the compressor is changed under predetermined operation load
conditions (certain conditions) will be described. The vertical
axis indicates the coefficient of performance of the compressor,
and the horizontal axis indicates the operation frequency at which
the piston is driven. For comparison, as a conventional technique,
a result of the case where the operation frequency is set in the
range of about 20 r/sec to about 45 r/sec in a state where a
compressor having specifications (cylinder volume: 10 ml and
capability at the time of operation of 27 r/sec: 74 W) equivalent
to those of the embodiment is assembled in a similar refrigeration
cycle is shown. In the conventional compressor, the cylindrical
hole does not have a tapered part, and recessed part 341C is not
formed in the piston.
[0116] As obvious from FIG. 15, in the case of low operation
frequency at which the effect of reducing power consumption is
large in a cooling system such as a refrigerator, the coefficient
of performance is largely improved as compared with that in the
conventional compressor. It is therefore understood that the
sealing performance of piston 323 and cylindrical hole 316 improves
dramatically, and the leakage amount can be reduced.
[0117] Generally, in a low-speed rotation range, refrigeration
capacity is small and the ratio of loss of leakage from the gap
between piston 323 and cylindrical hole 316 to the refrigeration
capacity becomes high, so that the efficiency of the compressor
deteriorates. However, in the embodiment, by the stable sealing by
lubricant oil 306 and the labyrinth effect, the amount of leakage
from the gap between piston 323 and cylindrical hole 316 can be
reduced. Consequently, extreme deterioration in the efficiency of
the compressor accompanying deterioration in volume efficiency can
be prevented, and power consumption of the cooling system can be
largely reduced.
[0118] As described above, in the hermetic-type compressor
according to the embodiment, a local contact between piston 323 and
cylindrical hole 316 is avoided and, simultaneously, the sliding
area is minimized and the sliding loss can be minimized. Moreover,
lubricant oil 306 contributing to the performance of sealing
between piston 323 and cylindrical hole 316 is stably supplied to
the gap between piston 323 and cylindrical hole 316 and can be
reliably assured between piston 323 and cylindrical hole 316.
[0119] As a result, a metal contact causing abrasion and noise is
prevented, reliability is improved and, moreover, occurrence of
noise can be reduced. Further, by assurance of the sealing
performance accompanying assurance of stability of lubricant oil
306, the volumetric efficiency is increased and, as a result, the
efficiency of the compressor can be improved. Therefore, higher
efficiency and reliability and prevention of occurrence of noise
can be simultaneously achieved, and partly contradictory challenges
can be solved.
[0120] As described above, according to the first and second
embodiments, the full length of cylindrical hole 316 is shortened
and the hermetic-type compressor is downsized and, moreover,
occurrence of contact noise is prevented, and occurrence of
abrasion can be reduced. Consequently, higher efficiency, lower
noise, and higher reliability of the hermetic-type compressor can
be simultaneously achieved.
INDUSTRIAL APPLICABILITY
[0121] According to the present invention, the compression
efficiency of the hermetic-type compressor is increased, and sound
of collision between the piston and the cylindrical hole can be
suppressed. The hermetic-type compressor can be widely applied as a
hermetic-type compressor for use in a machine using a refrigeration
cycle such as an air conditioner or an automatic vending
machine.
REFERENCE MARKS IN THE DRAWINGS
[0122] 114, 214, 314 cylinder blocks
[0123] 114A, 214A, 319 notches
[0124] 116, 216, 316 cylindrical holes
[0125] 123, 223, 323, 423 pistons
[0126] 123B, 223B lower end parts
[0127] 226, 326 connecting rods
[0128] 141A, 141B, 241A, 241B grooves
[0129] 141C, 241C, 341A, 341B, 341C, 441A, 441B, 4411C, 4412C
recessed parts
[0130] 216A, 316A, 323C end faces
[0131] 217, 317 tapered parts
[0132] 217A, 317A inflection parts
[0133] 218, 318 straight parts
[0134] 242, 342, 442 peripheries
[0135] 301 sealed container
[0136] 302 stator
[0137] 303 rotor
[0138] 304 electric mechanism
[0139] 305 compression mechanism
[0140] 306 lubricant oil
[0141] 310 shaft
[0142] 311 main shaft part
[0143] 312 eccentric shaft part
[0144] 313 oil supply path
[0145] 315 compression chamber
[0146] 320 bearing
[0147] 323A, 423A piston pin holes
[0148] 323B end part
[0149] 340, 440 piston assemblies
[0150] 325, 425 piston pins
[0151] 423B end part
[0152] 423C sliding face
[0153] 423D extension part
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