DISCHARGING VALVE DEVICE FOR A COMPRESSOR

Abstract: A discharging valve device for a compressor discharges gas compressed in a compression chamber outside said chamber against an urging force of a discharging valve (4) to a valve seat (42) and resistance of breaking a film of a lubricating oil deposited at and near a coacting area formed between the valve seat and the discharging valve (4). The discharging valve device comprises a discharging port (l) communicated with the compression chamber, the valve seat (42) being formed at the peripheral portion of said discharging port (l) and having a curvature in cross section, and the discharging valve (4) which is forcibly in contact with a part of said valve seat (42) so as to open and close said discharging port depending on pressure in said compression chamber. The contacting width of the sealing part formed by the contact through an oil film between said discharging valve (4) and said valve seat (42) is smaller than a contac­ ting width of an oil film formed in case of combination of a flat discharging valve with a valve seat having a uniform curvature in cross section.

Description: The present invention relates to a discharging valve device for a compressor comprising the pre-­ characterizing features of claim l (FR-A-l 467 898). Figure l shows a sectional view of an important part of a conventional discharging valve device for a compressor disclosed in Japanese Examined Patent Publication No. l2909/l972. In Figure l, the reference numeral l designates a discharging port formed in a housing wall la; the numeral 2 refers to a valve seat which is formed integrally with the housing wall la at and around the discharge opening of the discharging port l, the shape of the valve seat being like an upper half portion of a doughnut, in other words, in a semicircular shape having a certain curvature in cross section, the numeral 3 denotes a discharging valve fixture and the numeral 4 designates a discharging valve made of a resilient material, which has one end secured to the housing wall la and the other end interposed between the valve seat 2 and the discharging valve fixture 3 thereby to perform opening and closing operations for the discharging port l depending on pressure difference produced in a compression chamber (not shown). In the conventional discharging valve device for a compressor having the construction described above, when gas compressed in a compression chamber (not shown) reaches a predetermined pressure-discharging level, the discharging valve 4 brought in contact with the valve seat 2 formed at the discharging side of the discharging port l communicating with the compression chamber is opened due to discharging pressure to thereby discharge the compressed gas through an air gap formed between the discharging valve 4 and the valve seat 2. Then, reduction in pressure in the compression chamber actuates the discharging valve 4 in its closing direction to bring the discharging valve 4 onto the valve seat 2 thereby to allow again compression in the compression chamber. Thus, compressing and discharging operations are repeatedly carried out. In order to carry out these operations smoothly, it is especially essential to prevent phenomena of reversely flowing of gas at the time of closing of the discharging valve 4 on the valve seat 2 and of delay in opening of discharging valve 4 at the time of opening operation. From the viewpoint of assuring the smooth operations, provisions are made in such a manner that an oil film is formed at the contacting area of the discharging valve 4 to the valve seat 2 to increase gas sealing property; the outer surface of the valve seat 2 is so made as to have a certain curvature in cross section, that is, to form an upper portion of a doughnut-like shape so that a circular contacting area is provided between the discharging valve 4 and the valve seat 2; and the diameter of the circular contacting area of the valve seat 2 is made greater than that of the discharging port l whereby contacting pressure of the discharging valve 4 to the valve seat 2 is increased. The conventional discharging valve described above is, however, disadvantageous in that when the gas compressed in the compression chamber is discharged, a lubricating oil is discharged together with the discharged gas, on account of which the oil film spreads in a strip form over the contacting area between the discharging valve 4 and the valve seat 2 beyond a predetermined contacting width for sealing, with the consequence of increasing resistance of the oil film due to the spread oil film when the discharging valve is to be opened whereby delay is caused in opening operation. This results in increase of input power for the compressor. Further, there is a problem of noise produced when the discharging valve 4 is actuated for opening operation since resistance of the oil film is large. It is the main object of the present invention to overcome the disadvantages inherent in the conventional discharging valve device and to provide a discharging valve device for a compressor, having excellent discharging efficiency. This object is accomplished by the invention of claim l. With a discharging valve according to the invention reverse flow of gas in the opening operation of the discharging valve and delay in opening operation of the discharging valve are prevented. A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: Figure l is a sectional view partly omitted of an essential portion of a conventional discharging valve device for a compressor; Figure 2 a vertically cross-sectional view showing a compressor in which the discharging valve device according to the present invention is installed; Figure 3 is an enlarged perspective view of a first embodiment of the discharging valve device of the present invention; Figure 4 is a cross sectional view of an essential part of the first embodiment of the discharging valve device of the present invention; Figure 5 is a perspective view of the discharging valve of the first embodiment; Figures 6 to 9 are perspective views showing the valve seat of a second to fifth embodiments of the present invention; Figure l0 is a diagram showing noise characteristic of the first, third and fifth embodiments of the present invention which are respectively shown in Figures 4,5,7 and 9 ; Figure ll is a diagram showing noise characteristic of the second and fourth embodiments of the present invention which are respectively shown in Figures 6 and 8 ; Figure l2 is a diagram for the purpose of illustrating strength of an oil film obtained by each embodiment of the present invention. First of all, description will be made as to a compressor in which the discharging valve device of the present invention is installed with reference to Figure 2. A sealing container ll holds therein an electric motor comprising a stator l2 and a rotor l3, a crankshaft l4 driven by the motor, a cylinder l5, a piston l6 and vanes (not shown) for defining a compression chamber to form a high pressure chamber and a low pressure chamber so as to perform compressing operations. There are placed, at both ends of the cylinder, side housings 47, l7 which form the compression chamber and serve as bearings for the crankshaft l4. A refrigerant is introduced to the compression chamber through an intake pipe (not shown) and is compressed by means of the piston l6 eccentrically rotated by the crankshaft l4 driven by the motor, the cylinder l5 and vanes (not shown). When pressure in the compression chamber becomes higher than an inner pressure in the sealing container ll, the discharging valve 4 is opened to discharge the gas in the compression chamber into a discharging muffler 20 from the discharging port formed in the side housing l7a. A discharging valve fixture l9 is provided to restrict the movement of a discharging valve l8. The refrigerant gas subjected to reduction in noise in the discharging muffler is discharged into the sealing container ll and is fed to a heat exchanger through a discharging pipe. Thus, refrigeration cycle is repeated. Figure 3 is an enlarged perspective view showing general construction of the discharging valve device of the present invention, the detail of the construction being described below, in which a discharging port is formed in the side housing 47 and each end of the discharging valve 4 and the discharging valve fixture l9 is secured to the side housing 47 by a screw. Figure 4 is a sectional view of the discharging valve device of an embodiment of the present invention and Figure 5 is a perspective view of a valve seat used in this embodiment wherein the reference numeral l designates a discharging port formed in a housing 47, the numeral 42 designates a valve seat having a uniform radius of curvature in view of the cross section, which is formed integrally with the housing 47 at the peripheral portion of the discharging port l, the numeral l9 designates a discharging valve fixture, the numeral 4 designates a discharing valve having a flat surface which is similar to the valve as in Figure l and the numeral 45 designates a slit formed in the valve seat 42 so as to cross a circumference having the same center as the discharging port l. The operation of this embodiment of the present invention is described in the following. Resistance taking place when the discharging valve is about to open is primarily determined by the width of the oil film for contact sealing and the thickness of the oil film at the contacting area formed between the discharging valve 4 and the valve seat 42. The slit 45 in the valve seat 42 crosses a circumference having the same center as the discharging port l to reduce the width of the oil film for contact sealing to thereby control the content of oil film deposited. Consequently, the resistance of the oil film is reduced at the opening operation of the discharging valve 4 to prevent delay in the opening operation. A smooth opening operation of the discharging valve 4 suppresses noise produced to a lower level. Further, since a single slit 45 is formed in the valve seat 42, the direction to open the discharging valve 4 in the initiation of the opening operation is fixed whereby fluctuation of acoustic property can be small. It is, however, noted that the valve seat 42 having a deeper slit 45 is not desirable for the purpose of increasing gas-sealing property when the discharging valve 4 is closed. Figures 6 and 7 respectively show the second and third embodiments of the present invention in which a plurality of slits 45 are formed in the valve seat 42 in a radial form with respect to the discharging port and Figures 8 and 9 respectively show the fourth and fifth embodiments of the present invention in which a plurality of slits 45 are formed in the valve seat 42 in a radial form so as to be alternately arranged at the inner part and outer part with respect to the top portion of the valve seat. Description will be made as to how noise property is improved by the embodiments of the present invention. Figures l0 and ll are respectively graphs showing comparison of noise property B obtained by the embodiments with noise property A of the conventional discharging valve device. It is understood from Figure 10 that the first, third and fifth embodiments corresponding respectively to Figures 4,5,7 and 9 in which a single or plurality of slits 45 are eccentrically arranged, improve both noise level and the fluctuation in comparison with those A of the conventional device. Figure ll shows performance of the second and fourth embodiments corresponding respectively to Figures 6 and 8 in which plurality of slits are uniformly arranged. It is understood from Figure ll that the embodiments as in Figures 6 and 8 do not improve noise level in comparison with those A of the conventional device. As described above, the embodiments of the present invention are provided with a single or plurality of slits which are formed in the valve seat 42 so as to cross a circumference having the same center as the discharging port whereby delay in the opening operation of the discharging valve 4 is improved. Further, since the opening operation of the discharging valve 4 is made smooth, noise produced at the opening operation is reduced. In addition, provision of the slits eccentrically arranged renders the direction to open the discharging valve 4 to be uniform and the fluctuation of noise at the opening operation of the discharging valve to be suppressed. Description will be made as to the strength of the layer of a lubricating oil formed between the discharging valve and the valve seat, which is the important point of the present invention, with reference to Figure l2. This Figure schematically shows the shape of the oil film formed by the contact of the discharging valve 5l to the valve seat 50 by means of the surface tension of the lubricating oil. Now, easiness of opening the discharging valve will be examined. Easiness of opening α is expressed by the equation (l). Easiness of opening: α= .... (l) wherein ΣF is surface tension of oil and ΣP is pressure difference between an inner pressure Pc and an outer pressure Pd. The surface tension of oil ΣF and pressure difference ΣP are respectively expressed by the euqations (2), (3). ΣF = 2 π ra.F .... (2) ΣP = πr².Δ P = π r².(Pd-Pc) .... (3) wherein a is an average width of oil film and r is an average radius of oil film. The equation (4) is obtained by substituting the equations (2), (3) into the equation (l) and by rearranging it. Accordingly, the equation 4 represents that the easiness of opening α of the discharging valve is proportional to a/r. In the case of Figure l2, the conditions of a₅<a₁ and r₅ = r₁ are established and accordingly, is established with the consequence of α₅<α₁. For the shown embodiments, easiness of opening is obtainable without any condition in comparison with the known discharging valve. Further, for sealing property, it is possible to practice the present invention by suitably selecting the dimensions of each part as far as refrigeration property is not impaired.

Claims: 1. A discharging valve device for a compressor which discharges gas compressed in a compression chamber out of said chamber through a discharging port (l) communicating with the compression chamber against an urging force of a discharging valve (4; 51) biassed towards a valve seat (42; 50) formed around the peripheral portion of said discharging port and having a radius of curvature in cross section so as to open and close said discharging port depending on pressure in said compression chamber, characterized in that a curved portion of said valve seat forms part of a contacting area which is disposed between the valve seat (42; 50) and the discharging valve (4; 51), that a lubricating oil film is deposited at and near said contacting area, that the width of said contacting area is made smaller than the contacting width of an oil film formed in case of a flat discharging valve cooperating with a valve seat having a uniform curvature in cross section, and that at least one slit (45) is formed in said valve seat (42). 2. The discharging valve device according to Claim l, characterized in that in the surface of said valve seat (42) a plurality of slits (45) extending radially to said discharging port is formed. 3. The discharging valve device according to Claim 2, characterized in that said slits (45) are arranged in said valve seat in an asymmetrical manner. 4. The discharging valve device according to Claim 2 or 3, characterized in that slits (45) are alternately arranged at the inside and outside with respect to the top portion of said valve seat (42).

Inventors: HIRAHARA, TAKUHO, ISHIJIMA, KOJI, IWABUCHI,OSAMA, KAWAGUCHI, SUSUMU, NAKANE, KAZUHIRO, SANO, FUMIAKI
Applicants: MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1984
Main classification: F04B39
IPC codes: F16K15, F04B39