Spherical casing and elastic support for a hermetic motor compressor

A hermetic motor compressor includes a generally spherical casing having a generally spherical side wall and a first downwardly curved bottom wall, an integrated structure accommodated in said casing and having a compression section and a drive section integrally formed with each other, and a plurality of supporting units for elastically supporting the integrated structure. A plurality of legs are secured to the first downwardly curved bottom wall, and each of them is of the same shape as the downwardly curved bottom wall.

TECHNICAL FIELD
 The present invention relates generally to a hermetic motor compressor for
 use in a refrigerator or the like and, in particular but not exclusively,
 to a hermetic motor compressor capable of reducing noise emission.
 BACKGROUND ART
 Recently, hermetic motor compressors (hereinafter referred to simply as
 compressors) with reduced vibration and reduced noise emission are
 demanded. Because conventional refrigerants have a tendency to cause ozone
 layer damage or global warming, the use of hydrocarbon refrigerants having
 an ozone damaging coefficient of zero and a global warming coefficient of
 zero is commenced to protect global environment.
 FIG. 6 depicts a conventional compressor as disclosed in Japanese Patent
 Publication (examined) No. 1-47632, which includes a hermetically sealed
 casing 1 and an integrated structure 4 accommodated in the casing 1. The
 integrated structure 4 is made up of a compression section 2 and a drive
 section 3 integrally formed with each other. The compression section 2
 includes a cylinder 5, a piston 6 reciprocally mounted in the cylinder 5,
 a crankshaft 7 connected to a rotor 3a of the drive section 3 for rotation
 together therewith, and a connecting rod 8 for connecting the piston 6 to
 the crankshaft 7 to convert rotation of the crankshaft to a reciprocating
 motion of the piston 6.
 The casing 1 has a generally flat bottom wall 1a and a generally
 cylindrical side wall1b unitarily formed with each other. A gas inlet tube
 10 is welded to the side wall 1b, while a plurality of legs 11 are welded
 or secured to the bottom wall 1a. The integrated structure 4 is supported
 by a stay 12 welded to the inner surface of the side wall 1b, while the
 drive section 3 is electrically connected to a power source (not shown)
 via a hermetic terminal 13 hermetically welded to the side wall 1b.
 In the above-described construction, because the bottom wall 1a is
 generally flat, the plurality of legs 11 can be welded thereto with good
 workability. Also, because the side wall1b is generally cylindrical and
 not spherical, the stay 12 can be welded thereto with good workability.
 The casing 1 is, however, low in rigidity due to the generally flat shape
 of the bottom wall 1a and the generally cylindrical shape of the side wall
 1b. Because of this, the casing 1 oscillates slightly and generates noise,
 or sound produced during operation of the integrated structure 4
 accommodated therein leaks through the generally flat or cylindrical
 portion, thus increasing the noise.
 Particularly, in applications where a hydrocarbon refrigerant such as, for
 example, isobutane is used for a compression refrigerant, the
 concentration of circulating refrigerant is reduced during cyclic
 operation of the compressor at the same condensation and evaporation
 temperatures as in the operation with the use of a conventional
 refrigerant (for example, CFCR12, HFCR134a or the like) including fluorine
 or chlorine. Accordingly, enlargement of the internal volume of the
 cylinder 5 is required, which in turn causes an increase in unbalanced
 mass, thus increasing vibration and generating noise.
 The present invention has been developed to overcome the above-described
 disadvantages.
 It is accordingly an objective of the present invention to provide a
 hermetic motor compressor capable of reducing vibration and noise emission
 even if the unbalanced mass is increased which has been hitherto caused by
 enlargement of the internal volume of the cylinder.
 DISCLOSURE OF THE INVENTION
 In accomplishing the above and other objectives, the hermetic motor
 compressor according to the present invention includes a generally
 spherical casing having a generally spherical side wall and a first
 downwardly curved bottom wall, an integrated structure accommodated in the
 casing and having a compression section and a drive section integrally
 formed with each other, a plurality of supporting units for elastically
 supporting the integrated structure, and a plurality of legs secured to
 the first downwardly curved bottom wall and having the same shape as the
 downwardly curved bottom wall.
 This construction is particularly useful when a hydrocarbon refrigerant is
 used. The reason for this is that the use of the hydrocarbon refrigerant
 requires enlargement of the internal volume of a cylinder, which in turn
 causes an increase in unbalanced mass, thus increasing noise. The noise
 can be considerably reduced by forming the casing into a generally
 spherical shape having no flat or cylindrical portions, because the
 generally spherical casing has a high rigidity. In addition, the legs
 secured to the bottom wall rigidify the casing and reduce noise.
 The casing preferably has a second downwardly curved bottom wall having a
 radius of curvature different from that of the first downwardly curved
 bottom wall. The two downwardly curved bottom walls having different radii
 of curvature further rigidify the casing, thus reducing noise.
 Advantageously, each of the plurality of supporting units includes a stay
 of substantially the same shape as the side wall. This stay increases the
 rigidity of the casing, thus reducing noise.
 The stay preferably has a protruding portion integrally formed therewith, a
 ring-shaped elastic member through which the protruding portion extends,
 and a stopper mounted on the ring-shaped elastic member, with the
 protruding portion inserted into the stopper.
 Because the ring-shaped elastic member acts as a cushioning member,
 vibration caused by the compression section and increased with the
 increase in unbalanced mass is not easily transmitted to the stay via the
 stopper, thus reducing noise during operation of the compressor.
 The casing is generally of two-piece construction having two halves welded
 together. In this case, it is preferred that the side wall has a radius of
 curvature smaller than 100% of a radius of curvature of an opening of one
 of the two halves, while the first downwardly curved bottom wall has a
 radius of curvature smaller than 120% of the radius of curvature of the
 opening. It is also preferred that the second downwardly curved bottom
 wall has a radius of curvature smaller than 35% of the radius of curvature
 of the opening. The above limitations in radius of curvature are
 particularly effective in increasing the rigidity of the casing to reduce
 noise.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 This application is based on application No. 9-130774 filed May 21, 1997 in
 Japan, the content of which is incorporated hereinto by reference.
 Referring now to the drawings, there is shown in FIG. 1 a hermetic motor
 compressor according to the present invention. As shown therein, the
 compressor includes a hermetically sealed generally spherical casing 21
 and an integrated structure 24 accommodated in the casing 21. The
 integrated structure 24 is made up of a compression section 22 and a drive
 section 23 integrally formed with each other. As is the case with the
 conventional compressor shown in FIG. 6, the compression section 22
 includes a cylinder, a piston reciprocally mounted in the cylinder, a
 crankshaft connected to a rotor of the drive section for rotation together
 therewith, and a connecting rod for connecting the piston to the
 crankshaft. The casing 21 has a downwardly curved central bottom wall 21a
 and a downwardly curved annular bottom wall 21b formed externally of the
 central bottom wall 21a so as to be continuous thereto. The central bottom
 wall 21a and the annular bottom wall 21b have different radii of
 curvature. As illustrated, each of the central bottom wall 21a and the
 annular bottom wall 21b protrudes downwardly and a junction between the
 central bottom wall 21a and annular bottom wall 21b is constituted by an
 upwardly protruding portion protruding upwardly beyond downwardly
 protruding portions of the central bottom wall 21a and the annular bottom
 wall 21b.
 The casing 21 has a plurality of legs 26 welded or secured to the annular
 bottom wall 21b and, hence, a portion of each of the plurality of legs 26
 is of substantially the same shape as the annular bottom wall 21b.
 Although in the illustrated embodiment the plurality of legs 26 are welded
 to the annular bottom wall 21b, they may be welded to the central bottom
 wall 21a, as shown in FIG. 3.
 As shown in FIG. 2, the integrated structure 24 is elastically supported by
 a plurality of supporting units 25 each having a stay 27 welded to a
 generally spherical side wall 21c of the casing 21. To this end, the stay
 27 is formed into substantially the same spherical shape as the side wall
 21c of the casing 21.
 If the casing 21 has generally flat portions, sound of 2-3 kHz generated
 within the integrated structure 24 resonates at such flat portions, thus
 amplifying the sound. On the other hand, if the casing 21 does not have
 any flat portions but has a spherical shape, the vibration frequency is in
 the neighborhood of 4 kHz that differs from the frequency of 2-3kHz
 referred to above, resulting in a quiet compressor.
 According to modal analysis tests made so far by the inventors of the
 present invention, the casing 21 had the highest rigidity when the casing
 21 has the following radii of curvature:
 Radius of curvature R2 of the side wall 21c as measured in the vertical
 direction: smaller than 100% of an inlet radius of curvature R1;
 Radius of curvature r1 of the central bottom wall 21a: smaller than 120% of
 the inlet radius of curvature R1; and
 Radius of curvature r2 of the annular bottom wall 21b: smaller than 35% of
 the inlet radius of curvature R1.
 It is to be noted that the casing 21 is of two-piece construction having
 upper and lower halves welded together and that the inlet radius of
 curvature R1 referred to above is the radius of curvature of an opening of
 the lower half.
 As discussed above, the rigidity of the casing 21 can be increased and
 noise emission can be considerably reduced by forming the casing 21 into a
 generally spherical shape in place of a generally flat or cylindrical
 shape.
 Noise tests of the compressor revealed that the noise level of the
 compressor according to the present invention was 53 dB(A), whereas that
 of the conventional compressor was 60 dB(A).
 It is to be noted that a plurality of laterally outwardly protruding
 projections having a radius of curvature different from those of the
 central bottom wall 21a and the annular bottom wall 21b may be formed with
 the annular bottom wall 21b or the side wall 21c to further rigidify the
 casing 21.
 A compressor as shown in FIG. 4 includes an integrated structure made up of
 a compression section 34 and a drive section 35, and a plurality of
 supporting units for elastically supporting the integrated structure.
 As shown in FIG. 5, each of the supporting units includes a stay 29 welded
 to the generally spherical side wall 21c of the casing and having an
 upwardly protruding portion 32 integrally formed therewith. The stay 29 is
 of substantially the same shape as the generally spherical side wall 21c.
 A ring-shaped elastic member 31 is mounted on the stay 29, and the
 upwardly protruding portion 32 extends through the ring-shaped elastic
 member 31. The upwardly protruding portion 32 is also inserted in a hole
 30a defined in a snubber or stopper 30 so that the snubber 30 may be
 fixedly mounted on the upper surface 31a of the ring-shaped elastic member
 31.
 A suspension spring 28 is interposed between the compression section 34 and
 each supporting unit to elastically support the integrated structure. The
 suspension spring 28 has one end engaged with the snubber 30 and the other
 end engaged with a snubber or stopper 33 that is formed with the
 compression section 34.
 In the above-described construction, the ring-shaped elastic member 31 acts
 as a cushioning member for absorbing vibration transmitted from the
 compression section 34 via the suspension spring 28 and for preventing
 such vibration from being transmitted to the stay 29 via the upwardly
 protruding portion 32.
 Although the present invention has been fully described by way of examples
 with reference to the accompanying drawings, it is to be noted here that
 various changes and modifications will be apparent to those skilled in the
 art. Therefore, unless such changes and modifications otherwise depart
 from the spirit and scope of the present invention, they should be
 construed as being included therein.