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Two-stage screw compressorRelated Patent Categories: Pumps, Motor Driven, Electric Or Magnetic Motor, Rotary Motor And Rotary Nonexpansible Chamber PumpTwo-stage screw compressor description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070003421, Two-stage screw compressor. Brief Patent Description - Full Patent Description - Patent Application Claims
INCORPORATION BY REFERENCE [0001] The present application claims priority from Japanese application JP 2005-190879 filed on Jun. 30, 2005, the content of which is hereby incorporated by reference into this application. BACKGROUND OF THE INVENTION [0002] The present invention relates to a two-stage screw compressor used for a screw refrigerator or the like. [0003] Regarding a noise spectrum generated by a screw compressor, it is known that a fundamental frequency obtained by multiplying the number of teeth of a male rotor by a rotational frequency, and a higher harmonic component of the fundamental frequency constitute a dominant peak. As means of reducing the noise, various measures such as sticking a noise absorbing material to a casing, enhancing sound insulation performance by forming a casing to have a double structure, or enhancing rigidity of a casing by adding a rib thereto have been taken. As a single-stage single screw compressor, there is the one in which a resonance space is provided inside a slide valve so as to communicate with a compression space to reduce the noise, as shown in JP-A-2005-30362. [0004] In the above described prior arts, the measures according to the means such as sticking the noise absorbing material to the casing, forming the casing into the double structure, and adding the rib to the casing show a certain degree of noise reduction effect. However, if adopting the above described means, it is necessary to cover the entire cast casing with the noise absorbing material in the case of sticking the noise absorbing material on the casing, and thus it is often difficult in the case of a screw compressor having a complicated cast shape. Further, in the case of the means according to the double structure of the casing and the rib addition, there are the problems of complication of the cast shape and increase in the cast weight. [0005] In addition, any of the above described prior arts does not take account of increase in noise due to internal resonance in a discharge casing in a two-stage screw compressor, which includes a low pressure stage casing provided with a low pressure stage compression mechanism, the discharge casing provided on a discharge side of the low pressure stage casing, a high pressure stage casing provided with a high pressure stage compression mechanism, and an intermediate stage casing for connecting the discharge casing and the high pressure stage casing and accommodating an electric motor. BRIEF SUMMARY OF THE INVENTION [0006] An object of the present invention is to prevent internal resonance occurring in a discharge casing by means of a simple structure, and thereby realize reduction in noise, in a two-stage screw compressor as described above. [0007] In order to achieve the above-described object, the present invention provides a two-stage screw compressor including: a low pressure stage casing for accommodating a low pressure stage compression mechanism and a bearing member, which low pressure stage casing is provided with a capacity control part constituted by a slide valve, a rod and a piston; a discharge casing provided on a discharge side of the aforesaid low pressure stage casing for accommodating a bearing member supporting the low pressure stage compression mechanism; a high pressure stage casing for accommodating a high pressure stage compression mechanism and a bearing member; and an intermediate stage casing for connecting the aforesaid discharge casing and the aforesaid high pressure stage casing, and accommodating an electric motor, wherein a cavity is formed on a discharge casing side in the slide valve so as to enlarge the capacity of a discharge space formed in the aforesaid discharge casing, so that internal resonance occurring in the discharge casing is prevented. [0008] In this case, by making the length in an axial direction of the cavity formed in the slide valve half or more of the length in an axial direction of the slide valve, it becomes possible to prevent the internal resonance more reliably. [0009] Further, it is more effective to provide a porous material in the cavity formed in the slide valve. As the porous material, it is suitable to use a demister constructed by arranging a plurality of metal wires in a net form. Alternatively, the porous material may be constructed by glass wool. [0010] Another characteristic of the present invention is, in the above described two-stage screw compressor, that the length in an axial direction of a discharge space formed in the aforesaid discharge casing is enlarged by forming the cavity on the discharge casing side in the slide valve so as not to correspond to a wavelength of noise generated by the low pressure stage compression mechanism. In this case, preferably, the wavelength of the noise generated by the low pressure stage compression mechanism is based on a meshing frequency of rotors, which meshing frequency is a frequency including a fundamental frequency obtained by multiplying the number of teeth of a male rotor by a rotational frequency, and a higher harmonic component of the fundamental frequency, and it is desirable to enlarge the length in the axial direction of the discharge space formed in the aforesaid discharge casing by forming the cavity on the discharge casing side in the slide valve so as not to correspond to any of the wavelengths based on the above described frequencies. [0011] According to the present invention, in a two-stage screw compressor including a low pressure stage casing provided with a low pressure stage compression mechanism, a discharge casing provided on a discharge side of the low pressure stage casing, a high pressure stage casing provided with a high pressure stage compression mechanism, and intermediate stage casings for connecting the discharge casing and the high pressure stage casing, and accommodating an electric motor, a cavity is formed on a discharge casing side in the slide valve to enlarge the capacity of a discharge space formed in the discharge casing, and thereby internal resonance occurring in the discharge casing is prevented. Therefore, the internal resonance occurring in the discharge casing is prevented with a simple structure and significant noise reduction can be realized. [0012] Hereinafter, an embodiment of the present invention will be described based on the drawings. [0013] Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS [0014] FIG. 1 is a vertical sectional view of a two-stage screw compressor showing one embodiment of the present invention; [0015] FIG. 2 is a vertical sectional view of a main part of a two-stage screw compressor showing another embodiment of the present invention; and [0016] FIG. 3 is a noise spectrum diagram for explaining the effect of the present invention. DETAILED DESCRIPTION OF THE INVENTION [0017] FIG. 1 shows one embodiment of a two-stage screw compressor of the present invention. The screw compressor includes a low pressure stage casing 1 having an inlet opening 26, a discharge casing 2 connected to a discharge side of the low pressure stage casing 1 and having a gas passage 38, a motor cover (intermediate stage casing) 3 which is connected to a downstream side of the discharge casing 2, has a gas passage 39, and accommodates a coil end 8 of an electric motor 7, a motor casing (intermediate stage casing) 4 accommodating the electric motor 7, and a high pressure stage casing 5 having a discharge port 40. These members are connected with bolts or the like to be integrated. [0018] In the low pressure stage casing 1, there are formed a cylindrical bore 31, an inlet port 29 which introduces a refrigerant gas into the cylindrical bore 31, a piston chamber 33 which accommodates a piston 21 for driving a slide valve 23, and the like. In the cylindrical bore 31, a low pressure stage side male rotor 6 which is rotatably supported with roller bearings 11 and 12 and a ball bearing 17, and a low pressure stage side female rotor (not shown) are accommodated so as to mesh with each other. A shaft of the low pressure stage side male rotor 6 is connected to a shaft of the high pressure stage side male rotor 9 by a gear coupling 45. The piston 21 accommodated in the above described piston chamber 33 is connected to the slide valve 23 via a rod 22. [0019] In the discharge casing 2 accommodating the roller bearing 12 and the ball bearing 17 which support the shaft of the low pressure stage side rotor, there is formed a gas passage 38 which allows the cylindrical bore 31 and the above described motor cover 3 to communicate with each other. In the motor cover 3 accommodating a ball bearing 18 which supports a rotary body on the high pressure stage side, there is formed a gas passage 39 which allows the discharge casing 2 and the motor casing 4 to communicate with each other. In the motor casing 4 accommodating the electric motor 7 and a shaft part of the high pressure stage side male rotor 9, there is formed an inlet chamber 28 which introduces the refrigerant gas to the high pressure stage casing 5. In the high pressure stage casing 5, there is formed a cylindrical bore 32, in which the high pressure stage side male rotor 9 which is rotatably supported with roller bearings 13 and 14 and a ball bearing 19, and a high pressure stage side female rotor (not shown) are accommodated so as to mesh with each other. The shaft of the high pressure stage side male rotor 9 is directly connected to the electric motor 7. Continue reading about Two-stage screw compressor... Full patent description for Two-stage screw compressor Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Two-stage screw compressor patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Two-stage screw compressor or other areas of interest. ### Previous Patent Application: Micropump and adhesive-free method for joining two substrates Next Patent Application: Unit for delivering fuel to an internal combustion engine Industry Class: Pumps ### FreshPatents.com Support Thank you for viewing the Two-stage screw compressor patent info. 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