Hermetic motor-driven compressor
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a hermetic motor-driven compressor for use in a refrigerator, an air-conditioner or the like, and more particularly to a low noise, hermetic motor-driven compressor. 
     2. Description of the Prior Art 
     In recent years, there has been an increased demand for a low noise, hermetic motor-driven compressor (hereinafter referred to, for brevity, as &#34;compressor&#34;). 
     A conventional compressor disclosed in Japanese Patent Laid-open Publication No. 52-130013 includes, as shown in FIGS. 4 through 6, a closed container 1 in which a compressor element 2 and a motor element 3 are disposed as a single combined motor-and-compressor assembly 4. The compressor element 2 is composed of a cylinder 5, a piston 6 reciprocating within the cylinder 5, a crankshaft 7 rotatable in unison with a rotor 3a of the motor element 3, and a connecting rod 8 for translating a rotary motion of the crankshaft 7 into a reciprocating motion of the piston 6. 
     A tube 9 is welded at its one end to the closed container 1. Numeral 10 is a so-called hermetic terminal hermetically welded to the closed container 1 for supplying electricity to the motor element 3. The closed container 1 has flat bottom wall portions 1a and 1b to which a flat leg 11 is welded. The combined motor-and-compressor assembly 4 is resiliently supported by four snubbers 12 each having a suspension spring 13 acting between the corresponding snubber 12 an the combined motor-and-compressor assembly 4. The snubbers 12 are welded to the flat bottom wall portions 1a and 1b of the closed container 1. 
     Since the leg 11 and the snubbers 12 are attached by welding to the flat bottom wall portions 1a and 1b of the closed container 1, as described above, the welding work can be performed easily and efficiently. 
     However, since the stiffness of flat bottom wall portions 1a and 1b is relatively low, the closed container 1 tends to vibrate and thereby produce a noise. At the same time, an operation noise of the combined motor-and-compressor assembly 4 is likely to leak out from the flat bottom wall portions 1a and 1b. Thus, the conventional compressor generates relatively large operation noises and hence cannot meet a severe noise level which is required for modern compressors. 
      SUMMARY OF THE INVENTION 
     With the foregoing drawbacks of the prior art in view, it is an object of the present invention to provide a low noise, hermetic motor-driven compressor which is capable of operating silently and hence is able to meet a severe noise level which is required for modern compressors. 
     A hermetic motor-driven compressor comprises a closed container having a spherical wall portion, a compressor and a motor coupled together to form a combined motor-and-compressor assembly, and suspension means, disposed in the closed container, for resiliently supporting the combined motor-and-compressor assembly within the closed container. The suspension means includes a plurality of suspension springs, and a plurality of pairs of first and second snubbers corresponding in number to the number of the suspension springs and retaining opposite ends of the respective suspension springs. The first snubbers are secured to the combined motor-and-compressor assembly. At least one plate-like snubber stay has opposite end portions to which the second snubbers are attached, and a spherical central portion complementary in contour to the shape of the spherical wall portion of the closed container and welded to the spherical wall portion. 
     Preferably, the snubber stay has a plurality of embossed projections on the spherical central portion. The embossed projections are snugly received in a plurality of recesses, respectively, formed in the spherical wall portion as a result of formation of embossed projections on the spherical wall portion. 
     Since the wall portion of the enclosed container which supports the combined motor-and-compressor assembly via the suspension is spherical other than flat and hence has a greater stiffness than the flat wall portion, the container is unlikely to vibrate in resonance with the combined motor-and-compressor assembly. In addition, the spherical wall portion is reinforced by the snubber stay, so that the operation noise of the motor-and-compressor assembly cannot leak out from the closed container. The snubber stay is preferably made of a resilient material such as spring steel. The resilient snubber stay gives a damping effect which is added up with a damping effect attained by the suspension springs. With this combined damping effect, the vibration of the combined motor-and-compressor assembly is considerably reduced and thus the hermetic compressor operates silently. 
     The above and other objects, features and advantages of the present invention will become more apparent from the following description when making reference to the detailed description and the accompanying sheets of drawings in which a preferred structural embodiment incorporating the principles of the present invention is shown by way of illustrative example. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic longitudinal cross-sectional view of a compressor according to the present invention; 
     FIG. 2 is a diagrammatical plan view showing an internal structure of a closed container of the compressor; 
     FIG. 3 is an enlarged cross-sectional view of a bottom portion of the compressor shown in FIG. 1; 
     FIG. 4 is a schematic longitudinal cross-sectional view of a conventional compressor; 
     FIG. 5 is a diagrammatical plan view showing the an internal structure of a closed container of the conventional compressor; and 
     FIG. 6 is a cross-sectional view taken along VI--VI of FIG. 5. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As shown in FIGS. 1 through 3, a hermetic motor-driven compressor according to the present invention includes a closed container 20 having a spherical bottom wall portion 20a, a compressor element 21 and a motor element 22 coupled together to jointly form a combined motor-and-compressor assembly 23, and a suspension means or mechanism 24 disposed in the closed container 20 for resiliently supporting the combined motor-and-compressor assembly 23 within the closed container 20. The combined motor-and-compressor assembly 23 is structurally and functionally the same as one 4 of the conventional compressor described above with reference to FIGS. 4-6, and a further description thereof can be omitted. 
     The suspension mechanism 24 includes a plurality of suspension springs 25 (four in the illustrated embodiment) in the form of compression coil springs, a plurality of pairs of upper and lower frustoconical snubbers 26 corresponding in number to the number of the suspension springs 25 and retaining opposite ends of the respective suspension spring 25, and a pair of elongate plate-like snubber stays 27 each holding thereon two lower snubbers 26 at opposite ends thereof. The upper snubbers 26 are attached to the motor element 22 of the combined motor-and-compressor assembly 23. 
     Each of the snubber stays 27 includes a downwardly convex, spherical central portion 27a substantially complementary in contour to the shape of the spherical bottom wall portion 20a of the closed container 20, and upwardly offset, inverted L-shaped opposite end portions 27b on which the two snubbers 26 are fixedly mounted. The spherical central portion 27a is welded to the spherical bottom wall portion 20a to attach the snubber stay 27 to the closed container 20. The spherical central portion 27a has two projections 28 formed by embossing and spaced from one another in the longitudinal direction of the snubber stay 27. The projections 28 are snugly received in two recesses 29 formed in the spherical bottom wall portion 20a as a result of formation of two embossed projections 29a. The projections 29a on the spherical bottom wall portion 20a project outwardly (downwardly in FIGS. 1 and 3) from a plane of a leg 30 welded to the spherical bottom wall portion 20a of the closed container 20 so that the projections 29a are engageable with a floor FL (FIG. 3) to prevent the hermetic motor-driven compressor from becoming wobbly or unstable when the hermetic motor-driven compressor is disposed on the floor FL. 
     The snubber stays 27 are preferably made of a resilient material such as spring steel. With the suspension mechanism 24 thus constructed, vibrations generated during operation of the combined motor-and-compressor assembly 23 can be dampened or absorbed in two stages, that is, first by the suspension springs 25 and subsequently by the resilient snubber stays 27. Thus, a considerable reduction in the noise level can be attained. 
     When the hermetic motor-driven compressor of the type concerned is operating, the combined motor-and-compressor assembly generates an operation noise having frequencies in the rage of between 2 and 3 kHz. In the case of the conventional compressor whose container 1 has flat bottom wall portions 1a and 1b, as shown in FIG. 4, the flat bottom wall portions 1a and 1b is resonant with the operation noise of the frequencies specified above. Thus, the operation noise of the compressor as a whole is greatly amplified. On the other hand, in the case of the hermetic motor-driven compressor of this invention, the closed container 20 has a resonance frequency around 4 kHz and hence is not resonant with the operation noise of the combined motor-and-compressor assembly 23 even if the suspension mechanism 24 is directly attached to the spherical bottom wall portion 20a. This is because the closed container 20 including a spherical bottom wall portion 20a has a greater stiffness than the conventional closed container 1 having flat bottom wall portions 1a and 1b. In addition, the spherical bottom wall portion 20a of the container 20 is reinforced by the spherical central portions 27a of the snubber stays 27. Furthermore, the operation noise of the combined motor-and-compressor assembly 23 is considerably reduced by the combined damping effect of the suspension springs 25 and the resilient stays 27. Thus, the operation noise of the hermetic motor-driven compressor of this invention is considerably reduced to such an extent that a severe noise level needed for modern compressors is satisfied. 
     Obviously, various minor changes and modifications of the present invention are possible in the light of the above teaching. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.