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Screw compressorScrew compressor description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20080038127, Screw compressor. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001]The present invention relates to a screw compressor, and in particular, relates to a screw compressor suitable for a screw chiller. [0002]As a screw compressor used for a conventional refrigerating apparatus, there is the one disclosed in JP-A-59-211790. A scroll wrap compressor of JP-A-59-211790 operates to vary a ratio of volume by performing an unload control with a capacity control valve (slide valve) in the capacity control range of 100% to 75% of a refrigerating capacity. Further, in the capacity control range of 75% to 37.5% of the refrigerating capacity, the scroll wrap compressor increases the rotational speed of the screw compressor by 1.5 times by an inverter, and by using the capacity control valve in the range of 50% to 25% of the refrigerating capacity, can operate to vary the ratio of volume. Such operation can provide efficiency better than when operated under a 100% load. [0003]Further, as another conventional screw compressor, there is the one disclosed in JP-A-2004-137934. The screw compressor of JP-A-2004-137934 concurrently uses a rotating speed control by means of an inverter and a compression ratio control for varying the ratio of volume by changing the end of the compression stroke by means of a variable VI valve at the time of adjusting the capacity so that the optimum compressor efficiency is attained depending on the operating condition of the screw compressor. [0004]Because the screw compressor in JP-A-59-211790 adopts an operating method in which the rotational speed is increased to a constant rotational speed and a capacity control valve is used in the range of 50% to 25%, there is a problem that a highly improved performance cannot be expected because of the increase in mechanical loss due to the increased speed and a bypass imposed by the capacity control valve. [0005]In the screw compressors in JP-A-59-211790 and JP-A-2004-137934, no disclosure has been made regarding the effective use of the screw compressors as one for a screw chiller. That is, a compressor for the screw chiller is often operated at a refrigerating capacity ratio lower than the 100% rated refrigerating capacity ratio, that is, in the vicinity of 80% of the rated ratio, whereas, the screw compressors in JP-A-59-211790 and JP-A-2004-137934 are controlled such that the maximum efficient point is attained at rated operation, and therefore, effective operation has not been provided as the compressor for the screw chiller. [0006]An object of the present invention is to obtain a screw compressor capable of operation performing an effective operation for a screw chiller. SUMMARY OF THE INVENTION [0007]To achieve the above described object, a screw compressor for a screw chiller according to the present invention comprises a pair of screw rotors, a casing housing the screw rotors, a capacity control valve for varying a ratio of volume, a motor for driving the screw rotors, and an inverter for varying rotational speed of the motor, wherein the screw compressor is controlled using rotational speed control means by the inverter and mechanical capacity control means by the capacity control valve either independently or combined together according to a load, and wherein the maximum efficient point in a capacity control performed solely by the inverter is set to a rotational speed side lower than rated operation point, and in an area where the rotational speed is higher than the maximum efficient point, the inverter solely takes control from a rated rotational speed to a high rotational speed side. [0008]Specific preferable configuration examples according to the present invention are as follows. [0009](1) When an operation in the rotational speed range at or below the maximum efficient point is demanded, the rotational speed control means by the inverter and the mechanical capacity control means by the capacity control valve are used concurrently according to the capacities, thereby operating such that an efficiency becomes the maximum. [0010](2) The capacity control valve varies a compression starting position provided in the casing. [0011](3) The maximum efficient point is set around 80% of the rated refrigerating capacity when the capacity control is performed independently by the inverter. [0012](4) The position of the capacity control valve is controlled based on the rotational speed of the motor according to a suction pressure, a discharge pressure, and the load of the pair of screw rotors. [0013](5) When an anomaly occurs on the inverter, so that the continuous operation of the motor by the inverter is made impossible, the motor is directly connected to a commercial power in an emergency manner, thereby the capacity controlled operation is continued by the capacity control valve same as before. [0014]According to the present invention, a screw compressor capable of performing an effective operation as a screw chiller can be obtained. [0015]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 DRAWINGS [0016]FIG. 1 is a sectional view of a screw compressor showing one embodiment of the present invention; [0017]FIG. 2 is an operation explanatory view of a capacity control valve in FIG. 1; and [0018]FIG. 3 is a view showing a characteristic curve of compressor efficiency relative to refrigerating capacity ratio in the screw compressor of FIG. 1. DETAILED DESCRIPTION OF THE INVENTION [0019]Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 1 to 3. FIG. 1 is a sectional view of a screw compressor showing an embodiment of the present invention, FIG. 2 is an operation explanatory view of a capacity control valve in FIG. 1, and FIG. 3 is a view showing a characteristic curve of compressor efficiency relative to refrigerating capacity ratio in the screw compressor of FIG. 1. [0020]A screw compressor 50 is constituted by a screw compressor for a screw chiller comprising a compressor portion 17, a motor portion 18 and a control device 23. Refrigerant gas to be compressed flows to the compressor portion 17 through the motor portion 18, and after being compressed by the compressor portion 17, is discharged outside the compressor. While the screw compressor 50 performing a capacity control operates in such a manner that the rotational speed and the position of a capacity control valve are changed so that pressure becomes constant, the control pressure is set to an arbitrary pressure. Continue reading about Screw compressor... Full patent description for Screw compressor Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this 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 Screw compressor or other areas of interest. ### Previous Patent Application: Assembly for transporting fluids Next Patent Application: Micropump for peristaltic pumping of a liquid medium Industry Class: Pumps ### FreshPatents.com Support Thank you for viewing the Screw compressor patent info. IP-related news and info Results in 0.42754 seconds Other interesting Feshpatents.com categories: Software: Finance , AI , Databases , Development , Document , Navigation , Error 174 |
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