U.S. patent application number 13/119494 was filed with the patent office on 2011-07-21 for sealed compressor.
This patent application is currently assigned to Panasonic Carporation. Invention is credited to Ichiro Morita, Akio Yagi.
Application Number | 20110176942 13/119494 |
Document ID | / |
Family ID | 42128513 |
Filed Date | 2011-07-21 |
United States Patent
Application |
20110176942 |
Kind Code |
A1 |
Yagi; Akio ; et al. |
July 21, 2011 |
SEALED COMPRESSOR
Abstract
A hermetic compressor includes a cylindrical hole (117) forming
a compression space (115) and having a tapered portion (127) so as
to increase its inner diameter from the top dead center to the
bottom dead center of a piston (123). The piston (123) is reversed
in its inclination direction with respect to the axial center of
the cylindrical hole (117) in the initial stage of the compression
stroke. This reduces the contact between the piston (123) and the
cylindrical hole (117) at the time of the reversal, as compared
with the case in which the piston (123) is reversed in its
inclination direction in the middle or later stage of the
compression stroke. As a result, the hermetic compressor is
reliable and has low noise level.
Inventors: |
Yagi; Akio; (Shiga, JP)
; Morita; Ichiro; (Kanagawa, JP) |
Assignee: |
Panasonic Carporation
Kadoma-shi, Osaka
JP
|
Family ID: |
42128513 |
Appl. No.: |
13/119494 |
Filed: |
October 19, 2009 |
PCT Filed: |
October 19, 2009 |
PCT NO: |
PCT/JP2009/005449 |
371 Date: |
March 17, 2011 |
Current U.S.
Class: |
417/410.1 |
Current CPC
Class: |
F04B 39/125 20130101;
F04B 39/126 20130101; F04B 39/023 20130101 |
Class at
Publication: |
417/410.1 |
International
Class: |
F04B 39/12 20060101
F04B039/12 |
Claims
1. A hermetic compressor comprising: an airtight container having
lubricating oil therein; an electric element; and a compression
element, the compression element being driven by the electric
element, and the electric element and the compression element being
housed in the airtight container; the compression element
including: a shaft having a main shaft portion and an eccentric
shaft portion, the main shaft portion being rotatable by the
electric element, and the eccentric shaft portion moving in unison
with the main shaft portion; a cylinder block having a cylindrical
hole and a bearing, the cylindrical hole forming a compression
space, and the bearing supporting the main shaft portion; a piston
reciprocable in the cylindrical hole; and a connection mechanism
for connecting the eccentric shaft portion and the piston, wherein
the cylindrical hole includes a tapered portion so as to increase
an inner diameter thereof from a top dead center to a bottom dead
center of the piston, and the piston is reversed in an inclination
direction thereof with respect to an axial center of the
cylindrical hole in an initial stage of a compression stroke.
2. The hermetic compressor of claim 1, wherein the piston is
reversed in the inclination direction thereof with respect to the
axial center of the cylindrical hole at a moment when the piston
comes into contact with the tapered portion at an edge on a
compression space side thereof.
3. The hermetic compressor of claim 1, wherein the cylindrical hole
includes a straight portion having a uniform inner diameter in an
axial direction, the straight portion being formed in a region
adjacent to the tapered portion and corresponding to an upper end
on the compression space side of the piston when the piston is near
the top dead center position.
4. The hermetic compressor of claim 3, wherein when the straight
portion has an axial length L1, the compression space has a minimum
inner diameter D1, the piston has an outer diameter D2, the
eccentric shaft portion has an eccentricity "e" with respect to the
main shaft portion, a connection center of the connection mechanism
and the piston, and an end face on the compression space side of
the piston have a distance L2 therebetween, the main shaft portion
whose rotation angle is 0 (zero) degrees when the piston is in the
top dead center position has a rotation angle ".theta.", and the
axial center of the compression space and the tapered portion form
an angle ".alpha." therebetween, the angle ".alpha." and a
dimension value ".gamma." satisfy Mathematical Formula 2, the
dimension value ".gamma." being expressed by Mathematical Formula 1
based on the D1, the D2, the L1, the L2, the "e", and the
".theta."; .gamma.={3(D1-D2)/2}/{L1-L2+2e(1-cos .theta.)}
Mathematical Formula 1
0.4.GAMMA..ltoreq.tan(.alpha.).ltoreq.2.0.gamma. where .alpha.>0
Mathematical Formula 2
5. The hermetic compressor of claim 4, wherein when the piston is
in the bottom dead center position, at least a bottom end of the
piston is exposed from the cylindrical hole, and the rotation angle
".theta." of the main shaft portion is in a range of .pi. to 4
.pi./3 (rad).
6. The hermetic compressor of claim 1, wherein the piston is
provided on an outer surface thereof with a concave oil supply
groove, the oil supply groove being communicated with the airtight
container near the bottom dead center of the piston.
7. The hermetic compressor of claim 3, wherein the bearing and the
compression space are arranged in such a manner that a third center
line and a second center line cross each other, the third center
line being parallel to a first center line representing an axial
center of the bearing, and the second center line representing an
axial center of the compression space.
8. The hermetic compressor of claim 7, wherein when the straight
portion has an axial length L1, the compression space has a minimum
inner diameter D1, the piston has an outer diameter D2, the
eccentric shaft portion has eccentricity "e" with respect to the
main shaft portion, a connection center of the connection mechanism
and the piston and an end face on the compression space side of the
piston have a distance L2 therebetween, the main shaft portion
whose rotation angle is zero degrees when the piston is in the top
dead center position has a rotation angle ".theta.", the first
center line and the third center line have a distance "s"
therebetween, and the axial center of the compression space and the
tapered portion form an angle ".alpha." therebetween, the angle
".alpha." and a dimension value ".gamma." satisfy Mathematical
Formula 2, the dimension value ".gamma." being expressed by
Mathematical Formula 3 based on the D1, the D2, the L1, the L2, the
"e", the ".theta.", and the "s"; .gamma.={3(D1-D2)/2}/{L1-L2+2A}
Mathematical Formula 3, wherein A={(e.sup.2(1-cos
.theta.).sup.2-s.sup.2} Mathematical Formula 4
9. The hermetic compressor of claim 8, wherein when the piston is
in the bottom dead center position, at least a bottom end of the
piston is exposed from the cylindrical hole, and the rotation angle
".theta." of the main shaft portion is in the range of .pi. to 4
.pi./3 (rad).
Description
TECHNICAL FIELD
[0001] The present invention relates to a hermetic compressor used
in a refrigeration cycle of a fridge-freezer or the like.
BACKGROUND ART
[0002] One conventional hermetic compressor having a reciprocating
compression mechanism is disclosed on Patent Literature 1. The
hermetic compressor of Patent Literature 1 includes a cylinder, a
piston, and a connecting rod. The cylinder has a cylindrical
compression space on the inner-diameter side. The piston is
cylindrical on the outer-diameter side and reciprocates in the
cylinder. The connecting rod connects the piston to an eccentric
shaft portion of a shaft via a piston pin. The compression
mechanism is driven by the rotation of a rotor of a motor with the
shaft fixed to the axial center of the rotor.
[0003] In such hermetic compressors, it is generally necessary to
provide a gap for allowing the inner-diameter side of the cylinder
and the outer-diameter side of the reciprocation piston to slide
with each other. When the gap is large, the high-temperature,
high-pressure refrigerant gas compressed in the compression space
leaks out, having low compression efficiency. When the gap is
small, on the other hand, the sliding loss is large, also having
low compression efficiency.
[0004] To avoid this problem, the hermetic compressor of Patent
Literature 1 has a cylinder which is tapered so as to increase its
inner diameter from the top dead center to the bottom dead center
of the piston.
[0005] This conventional hermetic compressor will be described as
follows with reference to drawings. FIGS. 12A and 12B are
longitudinal sectional views of a compression section of the
hermetic compressor disclosed in Patent Literature 1. FIG. 12A
shows a state in which the piston is in the bottom dead center
position, and FIG. 12B shows a state in which the piston is in the
top dead center position.
[0006] In FIGS. 12A and 12B, the compression section includes
cylinder block 14 having cylindrical hole 16 and piston 23
reciprocable therein, and connecting rod 26 connected to piston 23
via piston pin 25. Connecting rod 26 reciprocates piston 23 between
the bottom dead center shown in FIG. 12A and the top dead center
shown in FIG. 12B by the eccentric movement of an eccentric shaft
portion of a shaft (not shown).
[0007] The compression section also includes an unillustrated valve
plate at an end of cylindrical hole 16 that is opposite (the right
side in the drawing) to connecting rod 26. Piston 23, cylindrical
hole 16, and the valve plate together form compression space
15.
[0008] Cylindrical hole 16 includes tapered portion 17 so as to
increase its inner diameter from Dt to Db (>Dt) from the top
dead center to the bottom dead center of piston 23. Piston 23 has a
uniform outer diameter throughout its length.
[0009] With this structure, the pressure in compression space 15
does not increase very much while the outer surface of piston 23 is
moving from the bottom dead center shown in FIG. 12A toward the top
dead center along tapered portion 17 in the compression stroke to
compress the refrigerant gas. Therefore, even when the gap is
comparatively large, there is almost no leakage of the refrigerant
gas, and piston 23 has low sliding resistance due to the sealing
effect of lubricating oil.
[0010] As the compression stroke proceeds, the pressure of the
refrigerant gas in compression space 15 gradually increases. When
piston 23 comes close to the top dead center position shown in FIG.
12B, the pressure in compression space 15 reaches a predetermined
discharge pressure, making compression space 15 susceptible to
leakage of the refrigerant gas. However, the gap is small on the
top dead center side, thereby obtaining the sealing effect of the
lubricating oil, and hence, reducing the leakage of the refrigerant
gas.
[0011] In the above described conventional structure, however,
piston 23 comes into contact at edge 30 on the compression space 15
side with tapered portion 17 in the compression stroke. As a
result, starting from edge 30, piston 23 is reversed in its
inclination direction with respect to the axial center of
cylindrical hole 16. Then, the region of the outer surface of
piston 23 that did not slide with tapered portion 17 before the
reversal comes into contact with tapered portion 17, possibly
making the sliding too much or causing contact noise when the
contact is severe at the time of the reversal.
[0012] Patent Literature 1: Japanese Patent Unexamined Publication
No. 2002-89450
SUMMARY OF THE INVENTION
[0013] In view of the conventional problems, it is an object of the
present invention to provide a hermetic compressor in which the
piston is reversed in its inclination direction with respect to the
axial center of the cylindrical hole in the initial stage of the
compression stroke. This reduces the contact between the piston and
the tapered portion at the time of the reversal and reduces the
noise, as compared with the case in which the piston is reversed in
its inclination direction in the middle or later stage of the
compression stroke.
[0014] According to the present invention, the hermetic compressor
includes an airtight container having lubricating oil therein; an
electric element; and a compression element, the compression
element being driven by the electric element, and the electric
element and the compression element being housed in the airtight
container. The compression element includes a shaft, a cylinder
block, a piston, and a connection mechanism. The shaft has a main
shaft portion and an eccentric shaft portion, the main shaft
portion being rotatable by the electric element, and the eccentric
shaft portion moving in unison with the main shaft portion. The
cylinder block has a cylindrical hole and a bearing, the
cylindrical hole forming a compression space, and the bearing
supporting the main shaft portion. The piston is reciprocable in
the cylindrical hole. The connection mechanism connects the
eccentric shaft portion and the piston. The cylindrical hole
includes a tapered portion so as to increase an inner diameter
thereof from the top dead center to the bottom dead center of the
piston, and the piston is reversed in the inclination direction
thereof with respect to the axial center of the cylindrical hole in
the initial stage of the compression stroke.
[0015] This structure reduces the sliding resistance, that is, the
sliding loss between the piston and the cylindrical hole. This
structure also reduces the load when the region of the outer
surface of the piston, which did not slide with the tapered portion
at the time of the reversal, comes into contact with the tapered
portion. The load reduction can be achieved because in the initial
stage of the compression stroke, the end face on the compression
space side of the piston is subjected to only a small compressive
load. This reduces the contact between the piston and the tapered
portion, as compared with the case in which the piston is reversed
in its inclination direction in the middle or later stage of the
compression stroke. This results in a reduction in the contact when
the piston is reversed in its inclination direction with respect to
the axial center of the cylindrical hole, thereby achieving noise
reduction.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a longitudinal sectional view of a hermetic
compressor according to a first exemplary embodiment of the present
invention.
[0017] FIG. 2 is a longitudinal sectional view of an essential part
of a compression section of the hermetic compressor according to
the first exemplary embodiment.
[0018] FIG. 3 is a longitudinal sectional view of the essential
part of the compression section, including its design dimensions,
of the hermetic compressor according to the first exemplary
embodiment.
[0019] FIG. 4 is a cross sectional view of the essential part of
the compression section, including its design dimensions, of the
hermetic compressor according to the first exemplary
embodiment.
[0020] FIG. 5A is a schematic diagram showing a behavior of piston
123 in the compression stroke of the hermetic compressor according
to the first exemplary embodiment.
[0021] FIG. 5B is a schematic diagram showing another behavior of
piston 123 in the compression stroke of the hermetic compressor
according to the first exemplary embodiment.
[0022] FIG. 6A is a schematic diagram showing another behavior of
piston 123 in the compression stroke of the hermetic compressor
according to the first exemplary embodiment.
[0023] FIG. 6B is a schematic diagram showing another behavior of
piston 123 in the compression stroke of the hermetic compressor
according to the first exemplary embodiment.
[0024] FIG. 7A is a schematic diagram showing another behavior of
piston 123 in the compression stroke of the hermetic compressor
according to the first exemplary embodiment.
[0025] FIG. 7B is a schematic diagram showing another behavior of
piston 123 in the compression stroke of the hermetic compressor
according to the first exemplary embodiment.
[0026] FIG. 8A is a schematic diagram showing another behavior of
piston 123 in the compression stroke of the hermetic compressor
according to the first exemplary embodiment.
[0027] FIG. 8B is a schematic diagram showing another behavior of
piston 123 in the compression stroke of the hermetic compressor
according to the first exemplary embodiment.
[0028] FIG. 9 is a characteristic diagram showing the relationship
between rotation angle and noise obtained from an example of the
design dimensions of the hermetic compressor according to the first
exemplary embodiment.
[0029] FIG. 10 is a longitudinal sectional view of an essential
part of a compression section, including its design dimensions, of
a hermetic compressor according to a second exemplary embodiment of
the present invention.
[0030] FIG. 11 is a cross sectional view of the essential part of
the compression section, including its design dimensions, of the
hermetic compressor according to the second exemplary
embodiment.
[0031] FIG. 12A is a longitudinal sectional view of a compression
section of a conventional hermetic compressor.
[0032] FIG. 12B is another longitudinal sectional view of the
compression section of the conventional hermetic compressor.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0033] Exemplary embodiments of the hermetic compressor of the
present invention will be described as follows. Note that the
present invention is not limited to these exemplary
embodiments.
First Exemplary Embodiment
[0034] FIG. 1 is a longitudinal sectional view of a hermetic
compressor according to a first exemplary embodiment of the present
invention. FIG. 2 is a longitudinal sectional view of an essential
part of a compression section of the hermetic compressor. FIG. 3 is
a longitudinal sectional view of the essential part of the
compression section including its design dimensions. FIG. 4 is a
cross sectional view of the essential part of the compression
section including its design dimensions.
[0035] In FIGS. 1 to 4, the hermetic compressor includes airtight
container 103 having electric element 105 and compression element
107 driven by electric element 105. Electric element 105 includes
stator 105a and rotor 105b. Airtight container 103 has lubricating
oil 101 at its bottom. Compression element 107 includes shaft 113
having main shaft portion 109 and eccentric shaft portion 111,
which is eccentric thereto to move in unison therewith. Main shaft
portion 109 is fixed to the axial center of rotor 105b.
[0036] Compression element 107 also includes bearing 119, which
forms a cantilever bearing by supporting the end on the eccentric
shaft portion 111 side of main shaft portion 109 of shaft 113.
[0037] Compression element 107 also includes balance weight 137
between main shaft portion 109 and eccentric shaft portion 111.
Balance weight 137 is eccentric in the direction opposite to the
eccentric direction of eccentric shaft portion 111 so as to strike
a rotational balance with the eccentric weight attached to main
shaft portion 109. The eccentric weight is the load of eccentric
shaft portion 111 or the pressure load of the refrigerant gas in
compression space 115 which acts on eccentric shaft portion
111.
[0038] Compression element 107 also includes cylinder block 121
having cylindrical hole 117 with a substantially cylindrical shape
and bearing 119, which are arranged in fixed positions relative to
each other. Cylindrical hole 117 has piston 123 reciprocable
therein.
[0039] Compression element 107 also includes connecting rod 125 as
a connection mechanism, whose one end is connected with eccentric
shaft portion 111, and whose other end is connected with piston 123
via piston pin 136. Shaft 113 is provided on its inside and outer
surface with oil supply passage 128. Oil supply passage 128 is
communicated at one end (upper end) thereof with oil supply hole
128a formed in eccentric shaft portion 111. The end of main shaft
portion 109 on the side opposite to eccentric shaft portion 111,
that is, the bottom end of main shaft portion 109 is extended so
that oil supply passage 128 can reach a predetermined depth of
lubricating oil 101.
[0040] Compression element 107 also includes valve plate 139 at an
end of cylindrical hole 117. Cylindrical hole 117 is formed in
cylinder block 121 in such a manner to form compression space 115
together with piston 123 and valve plate 139. As shown in FIG. 3,
cylindrical hole 117 includes tapered portion 127 so as to increase
its inner diameter from D1 to D3 (>D1) from the top dead center
to the bottom dead center of piston 123. Cylindrical hole 117 also
includes straight portion 129 in the position corresponding to the
end on the compression space 115 side of piston 123 when piston 123
is in the top dead center position. Straight portion 129 has a
uniform inner diameter in an axial length L1. Piston 123 has a
uniform outer diameter D2 throughout its length.
[0041] As shown in FIG. 3, cylindrical hole 117 of cylinder block
121 is formed in such a manner that when piston 123 is in the
bottom dead center position, the side opposite to the compression
space 115 side of piston 123 is exposed in airtight container
103.
[0042] Piston 123 is provided on its outer surface 133 on the
compression space 115 side with concave oil supply groove 131 which
is substantially annular (including completely annular).
Cylindrical hole 117 has notch 120 on its peripheral wall so that
oil supply groove 131 is exposed at least partly from cylindrical
hole 117 and is communicated with airtight container 103 when
piston 123 is in the bottom dead center position.
[0043] Piston 123 has the outer diameter D2, and eccentric shaft
portion 111 has an eccentricity "e" with respect to main shaft
portion 109. The center of piston pin 136 and the
compression-space-side end face 134 of piston 123 have a distance
(hereinafter, main sliding surface length) L2 therebetween. The
center of piston pin 136 corresponds to the connection center
between connecting rod 125 and piston 123. Main shaft portion 109,
which has a rotation angle of 0 (zero) degrees when the piston 123
is in the top dead center position, has a rotation angle ".theta.".
The axial center of compression space 115 and tapered portion 127
form an angle ".alpha." therebetween.
[0044] The inner diameter D1 of cylindrical hole 117, the outer
diameter D2 of piston 123, the length L1 of straight portion 129,
the main sliding surface length L2, the eccentricity "e", and the
rotation angle ".theta." are design dimensions to find the
coordinates of the tip position of piston 123 in cylindrical hole
117 when the behaviors of piston 123 in cylindrical hole 117 are
simulated.
[0045] The angle ".alpha." formed by tapered portion 127 when the
above-mentioned design dimensions are selected is set in the range
obtained by multiplying a coefficient in the range of 0.4 to 2.0 by
a value ".gamma.". The value ".gamma." (hereinafter, dimension
value) is obtained by dividing the dimensional numerical value 3/2
of the difference (D1-D2) between the inner diameter D1 of
cylindrical hole 117 and the outer diameter D2 of piston 123 by the
coordinate position {L1-L2+2e(1-cos .theta.)} of the tip on the
top-dead-center side of piston 123 when the top dead center
position is zero.
[0046] The dimensional numerical value 3/2 is a value derived from
the above-mentioned design dimensions (values) to find the
coordinates of the tip position of piston 123 in cylindrical hole
117.
[0047] In other words, according to the present exemplary
embodiment, the angle ".alpha." defines the dimension value
".gamma." expressed by Mathematical Formula 1 based on the
above-mentioned design dimensions: the inner diameter D1 of
cylindrical hole 117, the outer diameter D2 of piston 123, the
length L1 of straight portion 129, the main sliding surface length
L2, the eccentricity "e", and the rotation angle ".theta.". The
angle ".alpha." is defined by Mathematical Formula 2 which is based
on the dimension value ".gamma.".
[0048] In this case, the rotation angle ".theta." of main shaft
portion 109 is in the range of .pi. to 4 .pi./3 (rad) in the
initial stage of the compression stroke.
.gamma.={3(D1-D2)/2}/{L1-L2+2e(1-cos .theta.)} Mathematical Formula
1
0.4.gamma..ltoreq.tan(.alpha.).ltoreq.2.0.gamma. where .alpha.>0
Mathematical Formula 2
[0049] The coefficients of the dimension value ".gamma." (0.4 and
2.0 in the present exemplary embodiment) are values properly
determined in view of the machining tolerance of tapered portion
127 and the like, and can be set according to the material of
cylinder block 121.
[0050] The following is a description of the operation of the
hermetic compressor structured as above. First, sealing effect and
sliding resistance in tapered portion 127 and straight portion 129
of cylindrical hole 117 will be described as follows.
[0051] Rotor 105b of electric element 10 rotates shaft 113, and the
rotational motion of eccentric shaft portion 111 is transmitted to
piston 123 via connecting rod 125, allowing piston 123 to
reciprocate in cylindrical hole 117. The reciprocation of piston
123 allows refrigerant gas to be suctioned into compression space
115 from an unillustrated cooling system, to be compressed, and to
be discharged into the cooling system.
[0052] By the rotation of shaft 113, oil supply passage 128
performs a pumping action at its bottom end so that lubricating oil
101 at the bottom of airtight container 103 is pumped through oil
supply passage 128 and reaches oil supply hole 128a. Lubricating
oil 101 reached oil supply hole 128a is sprinkled all around
airtight container 103 horizontally from the upper end of shaft 113
so as to be supplied to piston pin 136, piston 123, and other
components, thereby lubricating them.
[0053] The pressure in compression space 115 does not increase very
much while piston 123 is moving from the bottom dead center shown
in FIG. 3 toward the top dead center in the compression stroke to
compress the refrigerant gas. Therefore, even when the gap is
comparatively large between outer surface 133 of piston 123 and
tapered portion 127, there is almost no leakage of the refrigerant
gas, and piston 23 has low sliding resistance due to the sealing
effect of lubricating oil 101.
[0054] As the compression stroke proceeds, the pressure of the
refrigerant gas in compression space 115 gradually increases. When
piston 123 comes close to the top dead center position, the
pressure in compression space 115 suddenly increases. However, the
gap is small between outer surface 133 of piston 123 and tapered
portion 127 on the top-dead-center side, thereby reducing the
leakage of the refrigerant gas. In this case, straight portion 129
reduces the leakage of the refrigerant gas that has increased to
reach the predetermined discharge pressure, as compared with the
case in which straight portion 129 is tapered.
[0055] When piston 123 is in the bottom dead center position, the
connecting rod 125 side of piston 123 is exposed from cylinder
block 121. This allows lubricating oil 101 sprinkled from the upper
end of shaft 113 to be sufficiently supplied to outer surface 133
of piston 123 and to be held there.
[0056] When piston 123 is in the bottom dead center position,
concave substantially annular oil supply groove 131 formed on outer
surface 133 on the compression space 115 side of piston 123 is also
exposed at least partly from cylindrical hole 117 via notch 120.
This allows lubricating oil 101 sprinkled from the upper end of
shaft 113 to be sufficiently supplied to oil supply groove 131 and
to be held therein.
[0057] As a result, a sufficient amount of lubricating oil 101 can
be supplied to the gap between the inner surface of cylindrical
hole 117 of cylinder block 121 and outer surface 133 of piston 123
in the compression stroke.
[0058] Substantially annular oil supply groove 131 can move to the
position facing straight portion 129 of cylindrical hole 117,
making it easy to carry lubricating oil 101 to straight portion 129
in which the sliding resistance becomes the largest.
[0059] As a result, a larger amount of lubricating oil 101 is
supplied to the sliding portion between cylinder block 121 and
piston 123 and is adequately held there. Furthermore, the sliding
resistance when piston 123 comes close to the top dead center
position can be reduced, thereby achieving efficiency
improvement.
[0060] Behaviors of piston 123 in the compression stroke will be
described as follows with reference to FIGS. 5A, 5B to 8A, 8B,
which are schematic diagrams showing the behaviors of piston 123 in
the present exemplary embodiment.
[0061] FIGS. 5A, 5B to 8A, 8B are schematic diagrams showing the
behaviors of piston 123 in the compression stroke. FIGS. 5A to 8A
are schematic diagrams showing a side surface of compression space
115. FIGS. 5B to 8B are schematic diagrams showing a side surface
of shaft 113. FIGS. 5A, 5B to 7A, 7B show the initial stage of the
compression stroke, and FIGS. 8A and 8B show the latter stage of
the compression stroke. FIG. 9 is a characteristic diagram showing
the relationship between rotation angle and noise obtained from an
example of the design dimensions of the hermetic compressor
according to the present exemplary embodiment.
[0062] In the hermetic compressor of the present exemplary
embodiment, bearing 119 forms a cantilever bearing which supports
the end on the eccentric shaft portion 111 side of main shaft
portion 109 of shaft 113. Therefore, shaft 113 is inclined in the
clearance between main shaft portion 109 and bearing 119. It is
known that shaft 113 has intricate behaviors, changing its
direction and inclination angle according to operating and other
conditions.
[0063] This is because shaft 113 is affected by various forces such
as the pressure load in compression space 115 or the inertia force
of piston 123 and connecting rod 125. Therefore, the schematic
diagrams of FIGS. 5B to 8B showing inclinations of shaft 113 are
inferentially drawn by the applicant.
[0064] First, the initial stage of the compression stroke will be
described. It is not known how shaft 113 is inclined in the initial
stage of the compression stroke. As mentioned above, shaft 113 has
intricate inclination behaviors, and hence, piston 123 is
considered to have intricate behaviors.
[0065] In the initial stage of the compression stroke, piston 123
is near the bottom dead center and in the region of tapered portion
127 in cylindrical hole 117. In this case, piston 123 is easily
inclined only by a small force, so that, under normal conditions,
piston 123 is considered to slide along somewhere on the inner wall
surface of tapered portion 127.
[0066] The following description is based on the case in which
piston 123 is inclined nearly in the same manner as shaft 113 and
is slid along an upper region of tapered portion 127 in cylindrical
hole 117.
[0067] Assume that outer surface 133a, which is an upper region of
outer surface 133 of piston 123, moves toward compression space 115
while sliding with the upper region of tapered portion 127 in
cylindrical hole 117. Then, as shown in FIGS. 6A and 6B, edge 135
on the outer surface 133b side of outer surface 133 of piston 123
that does not slide with tapered portion 127 comes into contact
with the region of tapered portion 127 that faces outer surface
133b.
[0068] The inventors have obtained experimental results suggesting
that as shown in FIGS. 7A and 7B, piston 123 is reversed in its
inclination direction with respect to the axial center of
cylindrical hole 117, and consequently, outer surface 133b that did
not slide with tapered portion 127 before that slides with tapered
portion 127.
[0069] The inventors have another supposition as follows. Edge 135
on the outer surface 133b side of piston 123 that does not slide
with tapered portion 127 comes into contact with tapered portion
127. At this moment, shaft 113 is inclined largely toward the side
opposite to the compression space 115 side, making piston 123
reversed in its inclination direction with respect to the axial
center of cylindrical hole 117.
[0070] At any rate, when the compression stroke proceeds to the
middle or later stage and the refrigerant gas pressure in
compression space 115 is increased, the compressive load of the
refrigerant gas applied to eccentric shaft portion 111 of shaft 113
is supported only by main shaft portion 109 of the cantilever
bearing. As a result, as shown in FIGS. 8A and 8B, shaft 113 is
inclined in the clearance between main shaft portion 109 and
bearing 119. Although it keeps changing its direction, shaft 113 is
inclined on the side opposite to the compression space 115
side.
[0071] As a result, the inclination of piston 123 is adjusted in
such a manner that its axial center substantially coincides with
the axial center of straight portion 129 in cylindrical hole 117,
and then piston 123 further moves toward the compression space 115
side. Thus, compression is performed in such a manner as to reduce
the leakage of the refrigerant gas that has increased to reach the
predetermined discharge pressure, as compared with the case in
which straight portion 129 is tapered.
[0072] In the above-described case, in the initial stage of the
compression stroke, piston 123 is inclined nearly in the same
manner as shaft 113 and is slid along the upper region of tapered
portion 127 in cylindrical hole 117. Even when piston 123 and shaft
113 are inclined differently, however, at least piston 123 is
considered to be inclined along some region of tapered portion 127.
As a result, it is likely that piston 123 is reversed in its
inclination direction, and consequently, the region of outer
surface 133 that did not slide with tapered portion 127 before that
slides with tapered portion 127.
[0073] Those are the inference-based description of the behaviors
of piston 123. The inventors have performed experiments changing
the design dimensions of tapered portion 127, while watching the
behaviors of piston 123 shown in FIGS. 5A, 5B to 8A, 8B. The
experimental results indicate that noise is smaller when tapered
portion 127 is designed by making a timing range suggestive of edge
135 of piston 123 coming into contact with tapered portion 127 as
the initial stage of the compression stroke than by making the
timing range as the middle or later stage of the compression
stroke. The timing range is hereinafter referred to as a rotation
angle .theta.1.
[0074] The reason is considered as follows. In the middle or later
stage of the compression stroke in which compression space 115 has
a high gas pressure and a large compressive load, shaft 113 or
piston 123 is reversed in its inclination direction at high speed.
This causes outer surface 133 of piston 123 to come into contact
and to collide with tapered portion 127 severely.
[0075] From these results and inferences, piston 123 should be
designed to be reversed in its inclination direction with respect
to the axial center of cylindrical hole 117 in the initial stage of
the compression stroke. This reduces the contact between piston 123
and cylindrical hole 117 at the time of the reversal, as compared
with the case in which piston 123 is reversed in its inclination
direction in the middle or later stage of the compression stroke.
As a result, noise reduction can be achieved.
[0076] In order to allow piston 123 to be reversed in its
inclination direction with respect to the axial center of
cylindrical hole 117 in the initial stage of the compression
stroke, tapered portion 127 and compression element 107 can be
designed to meet the following requirements. When outer surface
133a of piston 123 is moved toward compression space 115 along
tapered portion 127, edge 135 of outer surface 133b of piston 123
that does not slide with tapered portion 127 comes into contact
with the region of tapered portion 127 with which outer surface 133
does not slide.
[0077] It is also possible that piston 123 is reversed in its
inclination direction without edge 135 of piston 123 coming into
contact with tapered portion 127. Even in such a case, noise
reduction is expected to be achieved in the initial stage of the
compression stroke.
[0078] Therefore, according to the present exemplary embodiment, as
part of the design to make edge 135 of piston 123 come into contact
with tapered portion 127 in the initial stage of the compression
stroke, straight portion 129 is formed in cylindrical hole 117 as
follows. Straight portion 129 is formed in a region which is
adjacent to tapered portion 127 and corresponds to the upper end on
the compression space 115 side of piston 123. Straight portion 129
is uniform in the inner diameter direction.
[0079] As described above, straight portion 129 designed as above
can reduce the leakage of the refrigerant gas that has increased to
reach the predetermined discharge pressure, as compared with the
case in which straight portion 129 is tapered.
[0080] More specifically, edge 135 of piston 123 comes into contact
with tapered portion 127 at the timing at which the difference
between the outer diameter D2 of piston 123 and the minimum inner
diameter of compression space 115 (the inner diameter D1 of
straight portion 129 in the present exemplary embodiment) is
reduced. This means that edge 135 of piston 123 comes into
geometric contact with the region of tapered portion 127 that is in
the vicinity of straight portion 129.
[0081] Thus, providing straight portion 129 advances the timing at
which edge 135 of piston 123 comes into contact with tapered
portion 127 as early as the initial stage of the compression
stroke.
[0082] Increasing the axial length of straight portion 129 can more
advance the timing at which edge 135 of piston 123 comes into
contact with tapered portion 127. This reduces, however, the axial
length of tapered portion 127 by just that much, decreasing the
effect of reducing the sliding resistance in tapered portion
127.
[0083] Therefore, it is necessary to balance two opposing actions.
One action is to reduce the refrigerant gas leakage in compression
space 115 by providing straight portion 129, and also to make the
timing at which edge 135 of piston 123 comes into contact with
tapered portion 127 in the initial stage of the compression stroke.
The other action is to ensure the axial length of tapered portion
127 by reducing the axial length of straight portion 129, thereby
reducing the sliding resistance in tapered portion 127.
[0084] The inventors have examined the angle ".alpha." formed by
the axial center of compression space 115 and tapered portion 127,
and other design dimensions of compression element 107, while
watching the timing at which edge 135 of piston 123 comes into
contact with tapered portion 127 in the initial stage of the
compression stroke.
[0085] As a result, it has turned out that the angle ".alpha." of
tapered portion 127 and the design dimensions of compression
element 107 can be determined so that the dimension value ".gamma."
and the angle ".alpha." of tapered portion 127 satisfy Mathematical
Formula 2. As described above, the dimension value ".gamma." is
expressed by the Mathematical Formula 1 when the design dimensions
of compression element 107 are used as parameters, and the rotation
angle ".theta." of main shaft portion 109 is set in the range of
.pi. to 4 .pi./3 (rad) in the initial stage of the compression
stroke.
[0086] Properly designing the design values such as the axial
length of straight portion 129 and the angle ".alpha." of tapered
portion 127 in the range of the design dimensions can provide a
hermetic compressor having higher performance.
[0087] Experimental results of an example of the design dimensions
are shown in FIG. 9. In FIG. 9, solid line 91 represents a noise
level in the case of using the design dimensions of the present
invention. Dotted line 92 represents a noise level in the case of
using conventional design dimensions. Solid line 93 represents the
range of rotation angle .theta.1 in the case of using the design
dimensions of the present invention. Dotted line 94 represents the
range of rotation angle .theta.1 in the case of using the
conventional design dimensions. The experimental results have been
obtained by measuring noise values under the following conditions:
the inner diameter D1 of cylindrical hole 117 is about 22.01 mm,
the outer diameter D2 of piston 123 is about 22 mm (D1>D2), the
main sliding surface length L2 is about 13 mm, the eccentricity "e"
is 10 mm, and the length L1 of straight portion 129, which is one
of the design dimensions, is about 4 mm, about 8 mm, or about 10 mm
(the rotation angle ".theta." is about 190 degrees, about 210
degrees, or about 225 degrees). The angle ".alpha." obtained in
this experiment is in the range of 0.03 to 0.05 degrees. It goes
without saying that this range includes some tolerance.
[0088] These results indicate that an improvement in noise
characteristics can be expected under the following conditions. The
design dimensions of cylindrical hole 117, piston 123, and other
components are set, and the timing at which edge 135 of piston 123
comes into contact with tapered portion 127 is set to between about
180 degrees (the initial stage of the compression stroke) at which
compression is started and about 240 degrees in the middle stage of
the compression stroke.
[0089] In other words, as shown in FIG. 9, the design dimensions in
the conventional design are determined to be used over a wide range
including the middle stage of the compression stroke, and
therefore, the design dimensions include those having high noise
levels. In the present exemplary embodiment, on the other hand, the
dimension value ".gamma." is defined by Mathematical Formula 1
above, and the timing at which edge 135 of piston 123 comes into
contact with tapered portion 127 is set in the range of .pi. to 4
.pi./3 (rad). As a result, design can be implemented in a
reasonable manner to improve noise characteristics, thereby
simplifying the design.
[0090] According to the compressor designed as defined in
Mathematical Formulas 1 and 2, when piston 123 is reversed in its
inclination direction with respect to the axial center of
cylindrical hole 117, outer surface 133b that did not slide with
tapered portion 127 before that slides with tapered portion 127. In
this case, even when the axial length of outer surface 133 of
piston 123 that comes into contact with tapered portion 127 is
short, outer surface 133 can be supplied with a sufficient amount
of lubricating oil 101 sprinkled all around airtight container 103
horizontally from the upper end of shaft 113.
[0091] As a result, lubricating oil 101 sufficiently supplied to
outer surface 133 of piston 123 reduces the contact between outer
surface 133 of piston 123 and tapered portion 127, thereby
achieving efficiency improvement and noise reduction.
[0092] In addition, piston 123 is provided on its outer surface
with concave oil supply groove 131, and cylindrical hole 117 has
notch 120 on its peripheral wall so that oil supply groove 131 can
be communicated with airtight container 103 near the bottom dead
center of piston 123.
[0093] With this structure, lubricating oil 101 sprinkled all
around airtight container 103 from the upper end of oil supply hole
128a formed at eccentric shaft portion 111 of shaft 113 can be held
in oil supply groove 131 and sufficiently supplied to tapered
portion 127 and straight portion 129 of cylindrical hole 117. As a
result, the sealing effect of lubricating oil 101 is achieved,
which prevents the refrigerant gas leakage. In addition,
lubricating oil 101 sufficiently supplied to outer surface 133 of
piston 123 reduces the contact between outer surface 133 of piston
123 and tapered portion 127, thereby achieving efficiency
improvement and noise reduction.
[0094] According to the present exemplary embodiment, eccentric
shaft portion 111 and piston 123 are connected using connecting rod
125 as a connection mechanism, but the same effect can be obtained
by using a connection mechanism having a movable portion such as a
ball joint.
Second Exemplary Embodiment
[0095] A present exemplary embodiment has the same structure as the
first exemplary embodiment except that bearing 119 and compression
space 115 are arranged differently. Therefore, the following
description of the present exemplary embodiment will be mainly
focused on the difference.
[0096] FIG. 10 is a longitudinal sectional view of an essential
part of a compression section, including its design dimensions, of
a hermetic compressor according to the present exemplary
embodiment. FIG. 11 is a cross sectional view of the essential part
of the compression section, including its design dimensions, of the
hermetic compressor.
[0097] As shown in FIGS. 10 and 11, in the present exemplary
embodiment, bearing 119 and compression space 115 are arranged in
such a manner that third center line 142 and second center line 143
cross each other. Third center line 142 is parallel with first
center line 141 representing the axial center of bearing 119.
Second center line 143 represents the axial center of compression
space 115. In FIG. 11, each of first and third center lines 141 and
142 is illustrated as a dot because FIG. 11 is a cross sectional
view.
[0098] In the present exemplary embodiment, second center line 143
and offset line 144, which passes through first center line 141 and
is parallel with second center line 143 have a distance
(hereinafter, offset distance) "s" therebetween. Thus, bearing 119
is arranged offset with respect to compression space 115. The first
exemplary embodiment does not have this offset.
[0099] In the present exemplary embodiment shown in FIG. 10, shaft
113 rotates clockwise when viewed from above in FIG. 1. Therefore,
the offset arrangement of bearing 119 and compression space 115
plays a role in reducing the sliding loss between cylinder block
121 and piston 123. The offset distance "s" is one of the design
dimensions in the present exemplary embodiment, additional to the
design dimensions of the first exemplary embodiment. More
specifically, the offset distance "s" is designed in the range of 1
to 4 mm, and is designed to be 2 mm in a hermetic compressor for a
refrigerator.
[0100] In the present exemplary embodiment, too, the angle
".alpha." formed by the axial center of compression space 115 and
tapered portion 127 is defined by Mathematical Formula 2 described
in the first exemplary embodiment.
[0101] More specifically, the angle ".alpha." is set based on the
following design dimensions: the inner diameter D1 of cylindrical
hole 117, the outer diameter D2 of piston 123, the length L1 of
straight portion 129, the main sliding surface length L2, the
eccentricity "e", and the rotation angle ".theta." of main shaft
portion 109, which are defined in the first exemplary embodiment,
and also offset distance "s".
[0102] Further more specifically, the angle "a" is set in the range
obtained by multiplying a coefficient in the range of 0.4 to 2.0 by
the dimension value ".gamma.". The dimension value ".gamma." is
obtained by dividing the dimensional numerical value 3/2 of the
difference (D1-D2) between the inner diameter D1 of cylindrical
hole 117 and the outer diameter D2 of piston 123 by the coordinate
position {L1-L2+2A} of the tip on the top-dead-center side of
piston 123 when the top dead center position of piston 123 is 0
(zero).
[0103] The "A" is an assignment expression used to simplify the
calculation formula because the offset arrangement of bearing 119
and compression space 115 makes it necessary to correct the
coordinate position of the tip of the piston.
[0104] More specifically, as shown in Mathematical Formula 4, the
offset distance "s" is taken into consideration in addition to the
eccentricity "e".
[0105] The dimensional numerical value 3/2 is a value derived from
the design dimensions (values) to find the coordinates of the tip
position of piston 123 in cylindrical hole 117 in the same manner
as in the first exemplary embodiment.
[0106] In other words, according to the present exemplary
embodiment, because bearing 119 is arranged offset with respect to
compression space 115, the angle ".alpha." is defined by
Mathematical Formula 2 shown in the first exemplary embodiment,
which is based on the dimension value ".gamma." expressed by
Mathematical Formula 3.
.gamma.={3(D1-D2)/2}/{L1-L2+2A} Mathematical Formula 3
A= {(e.sup.2(1-cos .theta.).sup.2-s.sup.2} Mathematical Formula
4
[0107] As described above, according to the present exemplary
embodiment, bearing 119 is arranged offset with respect to
compression space 115. This makes it possible to reduce the sliding
loss between cylinder block 121 and piston 123 in addition to the
effect of the first exemplary embodiment.
[0108] As described hereinbefore, the hermetic compressor of the
present invention includes an airtight container having lubricating
oil therein; an electric element; and a compression element, the
compression element being driven by the electric element, and the
electric element and the compression element being housed in the
airtight container. The compression element includes a shaft, a
cylinder block, a piston, and a connection mechanism. The shaft has
a main shaft portion and an eccentric shaft portion, the main shaft
portion being rotatable by the electric element, and the eccentric
shaft portion moving in unison with the main shaft portion. The
cylinder block has a cylindrical hole and a bearing, the
cylindrical hole forming a compression space, and the bearing
supporting the main shaft portion. The piston is reciprocable in
the cylindrical hole. The connection mechanism connects the
eccentric shaft portion and the piston. The cylindrical hole
includes a tapered portion so as to increase an inner diameter
thereof from the top dead center to the bottom dead center of the
piston, and the piston is reversed in the inclination direction
thereof with respect to the axial center of the cylindrical hole in
the initial stage of the compression stroke.
[0109] This structure reduces the sliding resistance, that is, the
sliding loss between the piston and the cylindrical hole. This
structure also reduces the load when the region of the outer
surface of the piston that did not slide with the tapered portion
before the reversal comes into contact with the tapered portion.
The load reduction can be achieved because in the initial stage of
the compression stroke, the end face on the compression space side
of the piston is subjected to only a small compressive load. This
reduces the contact between the piston and the tapered portion at
the time of the reversal, as compared with the case in which the
piston is reversed in its inclination direction in the middle or
later stage of the compression stroke. This results in a reduction
in the contact when the piston is reversed in its inclination
direction with respect to the axial center of the cylindrical hole,
thereby achieving sliding loss reduction, and hence, achieving
efficiency improvement and noise reduction.
[0110] According to the present invention, the piston is revered in
its inclination direction with respect to the axial center of the
cylindrical hole at the moment when the edge on the compression
space side of the piston comes into contact with the tapered
portion.
[0111] With this structure, when the edge on the compression space
side of the piston comes into contact with the tapered portion,
this contact is likely to cause the piston to be reversed in its
inclination direction with respect to the axial center of the
cylindrical hole. Even in such a case, however, it is possible to
reduce the contact between the outer surface of the piston and the
tapered portion when the piston is reversed in its inclination
direction with respect to the axial center of the cylindrical hole,
and hence, to achieve efficiency improvement and noise
reduction.
[0112] According to the present invention, the cylindrical hole
includes the straight portion designed as follows. The straight
portion has a uniform inner diameter in the axial direction, and is
formed in the region which is adjacent to the tapered portion and
corresponds to the upper end on the compression space side of the
piston when the piston is near the top dead center position.
[0113] This structure advances the timing at which the piston is
reversed in its inclination direction with respect to the axial
center of the cylindrical hole as early as the initial stage of the
compression stroke, much earlier than the middle or later stage. In
the initial stage of the compression stroke, the end face on the
compression space of the piston is subjected to only a small
compressive load. Therefore, this structure also reduces the load
when the region of the outer surface of the piston that did not
slide with the tapered portion before the reversal comes into
contact with the tapered portion. This reduces the contact between
the outer surface of the piston and the tapered portion when the
piston is reversed in its inclination direction with respect to the
axial center of the cylindrical hole, thereby achieving efficiency
improvement and noise reduction. When the outer surface of piston
123 is moving toward the top dead center in the compression stroke,
there is almost no leakage of refrigerant gas, and piston has low
sliding resistance. As the compression stroke proceeds, and the
piston comes close to the top dead center position, the refrigerant
gas leakage due to an increased pressure to compress the
refrigerant gas can be reduced as compared with the case in which
the tapered portion is formed along the entire length of the
cylindrical hole, thereby obtaining high freezing capacity.
[0114] According to the present invention, assume that the axial
length of the straight portion is L1, the minimum inner diameter of
the compression space is D1, the outer diameter of the piston is
D2, the eccentricity of the eccentric shaft portion with respect to
the main shaft portion is "e", the distance from the connection
center of the connection mechanism and the piston to the
compression-space-side end face of the piston is L2, the rotation
angle of the main shaft portion whose rotation angle is 0 (zero)
degrees when the piston is in the top dead center position is
".theta.", and the angle formed by the axial center of the
compression space and the tapered portion is ".alpha.". In this
case, the angle ".alpha." defines the dimension value ".gamma."
expressed by Mathematical Formula 1 based on the design dimensions:
the inner diameter D1 of the cylindrical hole, the outer diameter
D2 of the piston, the length L1 of the straight portion, the main
sliding surface length L2, the eccentricity "e", and the rotation
angle ".theta.". The angle ".alpha." is defined by Mathematical
Formula 2 which is based on the dimension value ".gamma.".
[0115] With this structure, the design dimensions of the hermetic
compressor that are involved in the behaviors of the piston can be
determined in such a manner as to reduce the contact between the
outer surface of the piston and the tapered portion when the piston
is reversed in its inclination direction with respect to the axial
center of the cylindrical hole. As a result, this reduces the
contact between the outer surface of the piston and the tapered
portion when the piston is reversed in its inclination direction,
as compared with the case in which the piston is reversed in its
inclination direction in the middle or later stage of the
compression stroke.
[0116] As an example of a specific design, the angle ".alpha."
formed by the axial center of the compression space and the tapered
portion can be determined by setting the rotation angle ".theta."
of the main shaft portion with respect to which the piston is
reversed in its inclination direction, and also by setting the
following design values: the inner diameter D1 of the cylindrical
hole, the outer diameter D2 of the piston, the length L1 of the
straight portion, the main sliding surface length L2, and the
eccentricity "e".
[0117] According to the present invention, when the piston is in
the bottom dead center position, at least the bottom end of the
piston is exposed from the cylindrical hole, and the rotation angle
".theta." of the main shaft portion is in the range of .pi. to 4
.pi./3 (rad).
[0118] With this structure, the bottom end of the piston is exposed
from the cylindrical hole when the piston is returned to the bottom
dead center position. This allows a large amount of lubricating oil
to be supplied and held, thereby reducing the sliding loss between
the piston and the cylindrical hole, and hence, achieving
efficiency improvement. Furthermore, when the piston is reversed in
its inclination direction, the region of the outer surface of the
piston that did not slide with the tapered portion before the
reversal comes into contact with the tapered portion. In this case,
even when the axial length of the outer surface of the piston that
comes into contact with the tapered portion is short, a sufficient
amount of lubricating oil is supplied. As a result, the lubricating
oil can reduce the contact between the outer surface of the piston
and the tapered portion, thereby achieving efficiency improvement
and noise reduction.
[0119] According to the present invention, the piston is provided
on its outer surface with the concave oil supply groove, which is
communicated with the airtight container near the bottom dead
center of the piston.
[0120] With this structure, a sufficient amount of lubricating oil
is supplied to the cylindrical hole so as to achieve the sealing
effect of the lubricating oil, thereby reducing the refrigerant gas
leakage. Furthermore, the lubricating oil lubricates the sliding
portion, thereby achieving a hermetic compressor having high
freezing capacity and reliability. In addition, when the piston is
reversed in its inclination direction, the region of the outer
surface of the piston that did not slide with the tapered portion
before the reversal comes into contact with the tapered portion. In
this case, even when the axial length of the outer surface of the
piston that comes into contact with the tapered portion is short,
the outer surface is supplied with a sufficient amount of
lubricating oil. As s result, the lubricating oil reduces the
contact between the outer surface of the piston and the tapered
portion, and ensures the sealing between the outer surface of the
piston and the tapered portion, thereby achieving efficiency
improvement and noise reduction.
[0121] According to the present invention, the bearing and the
compression space are arranged in such a manner that the third
center line and the second center line cross each other. The third
center line is parallel with the first center line representing the
axial center of the bearing. The second center line represents the
axial center of the compression space.
[0122] This structure reduces the sliding resistance, that is, the
sliding loss between the piston and the cylindrical hole. This
structure also reduces the load when the region of the outer
surface of the piston that did not slide with the tapered portion
before the reversal comes into contact with the tapered portion.
The load reduction can be achieved because in the initial stage of
the compression stroke, the end face on the compression space of
the piston is subjected to only a small compressive load. This
reduces the contact between the piston and the tapered portion at
the time of the reversal, as compared with the case in which the
piston is reversed in its inclination direction in the middle or
later stage of the compression stroke. In other words, this reduces
the contact when the piston is reversed in its inclination
direction with respect to the axial center of the cylindrical hole,
thereby achieving efficiency improvement and noise reduction.
Furthermore, the offset arrangement of the bearing and the
compression space reduces the sliding loss between the cylinder
block and the piston.
[0123] According to the present invention, assume that the axial
length of the straight portion is L1, the minimum inner diameter of
the compression space is D1, the outer diameter of the piston is
D2, the eccentricity of the eccentric shaft portion with respect to
the main shaft portion is "e", the distance from the connection
center of the connection mechanism and the piston to the
compression-space-side end face of the piston is L2, the rotation
angle of the main shaft portion whose rotation angle is 0 (zero)
degrees when the piston is in the top dead center position is
".theta.", the offset distance (the distance between the first and
third center lines) is "s", and the angle formed by the axial
center of the compression space and the tapered portion is
".alpha.". In this case, the angle ".alpha." is defined by
Mathematical Formula 2 which is based on the dimension value
".gamma." expressed by Mathematical Formula 3 based on the design
dimensions: the inner diameter D1 of the cylindrical hole, the
outer diameter D2 of the piston, the length L1 of the straight
portion, the main sliding surface length L2, the eccentricity "e",
the rotation angle ".theta.", and the offset distance "s".
[0124] With this structure, even when the bearing and the
compression space are arranged offset with respect to each other,
the design dimensions of the hermetic compressor that are involved
in the behaviors of the piston can be determined in such a manner
as to reduce the contact between the outer surface of the piston
and the tapered portion when the piston is reversed in its
inclination direction with respect to the axial center of the
cylindrical hole. As a result, it becomes possible to specifically
design a hermetic compressor which reduces the contact between the
outer surface of the piston and the tapered portion when the piston
is reversed in its inclination direction, as compared with the case
in which the piston is reversed in its inclination direction in the
middle or later stage of the compression stroke. As an example of a
specific design, the angle ".alpha." formed by the axial center of
the compression space and the tapered portion can be determined by
setting the rotation angle ".theta." of the main shaft portion with
respect to which the piston is reversed in its inclination
direction, and also by setting the following design values: the
inner diameter D1 of the cylindrical hole, the outer diameter D2 of
the piston, the length L1 of the straight portion, the main sliding
surface length (the distance from the center of the piston pin to
the compression-space-side end face of the piston) L2, the
eccentricity "e", and the offset distance "s".
[0125] According to the present invention, when the piston is in
the bottom dead center position, at least the bottom end of the
piston is exposed from the cylindrical hole, and the rotation angle
"0" of the main shaft portion is in the range of .pi. to 4 .pi./3
(rad).
[0126] With this structure, even when the bearing and the
compression space are arranged offset with respect to each other,
the bottom end of the piston is exposed from the cylindrical hole
when the piston is returned to the bottom dead center position.
This allows a large amount of lubricating oil to be supplied and
held, thereby reducing the sliding loss between the piston and the
cylindrical hole, and hence, achieving efficiency improvement.
Furthermore, when the piston is reversed in its inclination
direction, the region of the outer surface of the piston that did
not slide with the tapered portion before the reversal comes into
contact with the tapered portion. In this case, even when the axial
length of the outer surface of the piston that comes into the
tapered portion is short, a sufficient amount of lubricating oil is
supplied. As a result, the lubricating oil can reduce the contact
between the outer surface of the piston and the tapered portion,
thereby achieving efficiency improvement and noise reduction.
INDUSTRIAL APPLICABILITY
[0127] Thus, the hermetic compressor of the present invention,
which has low sliding loss of the piston, low input, high
efficiency, and low collision impact with low noise, is applicable
to any device having a refrigeration cycle such as domestic
refrigerators, dehumidifiers, showcases, and vending machines.
REFERENCE MARKS IN THE DRAWINGS
[0128] 101 lubricating oil [0129] 103 airtight container [0130] 105
electric element [0131] 105a stator [0132] 105b rotor [0133] 107
compression element [0134] 109 main shaft portion [0135] 111
eccentric shaft portion [0136] 113 shaft [0137] 115 compression
space [0138] 117 cylindrical hole [0139] 119 bearing [0140] 120
notch [0141] 121 cylinder block [0142] 123 piston [0143] 125
connecting rod [0144] 127 tapered portion [0145] 128 oil supply
passage [0146] 128a oil supply hole [0147] 129 straight portion
[0148] 131 oil supply groove [0149] 133, 133a, 133b outer surface
[0150] 134 compression-space-side end face [0151] 135 edge [0152]
136 piston pin [0153] 137 balance weight [0154] 139 valve plate
[0155] 141 first center line [0156] 142 third center line [0157]
143 second center line [0158] 144 offset line
* * * * *