US2904973A - Variable displacement rotary compressor - Google Patents

Description

Sept. 22,1959 M. M. KCSFELD 2,904,973

VARIABLE DISPLACEMENT ROTARY COMPRESSOR M Filed Sept. 9. 1957 2 Sheets-Sheet J.

FlG.2 2o 3 INVENTOR. MILTON M. Ken-5L0 HIS ATTORNE Y Sept. 22, 1959 M. M. KOSFELD 2,904,973

VARIABLE DISPLACEMENT ROTARY COMPRESSOR Filed Sept. 9. 1957 2 Sheets-Sheet 2 F'IG.3

INVENTOR. MILTON M. asp-cu:

BY/WKW United States Patent Office 23%,973 Patented Sept. 22, 1959 2,904,973 VARIABLE DISPLACEMENT ROTARY coMrnnsson Milton M. Kosfeld, Louisville, Ky, assignorto General Electric Company, a corporation of New York Application September 9, 1957, Serial No. 682,825 1 Claim. Cl. 62-324) The present invention relates to a rotary gas compressor and more particularly to such a compressor having a displacement which may be selectively changed from a maximum volume to an intermediate volume.

In many instances, gas compressors, of the type used in refrigerating systems, are subjected to such extreme conditions of use that it is desirable to be able to reduce the capacity or volume of displacement of the compressor under certain conditions and to increase the capacity under other conditions. For example, in a compressor used in a heat pump, or in a refrigeration system of the type in which the refrigerant flow may be reversed, and wherein the heat exchangers of the system are subjected to relatively high temperatures during the summer and low temperatures during the winter, it is desirable to operate the compressor at a low volume displacement duced, and, under this condition, the volume displacement of the compressor can be increased to its maximum without overloading the motor. In other words it is desirable .to vary the volume displacement of the corn pressor during the summer and winter such thatthe load on the. compressor during the summer, is approximately equal .to the load on the compressor during the winter. In this manner, themotor which drives the compressor is loaded to capacity during all periods of operation of the compressor and the most efiicient possible operation is obtained for the size of motor necessary to drive the compressor.

Accordingly, it isan objectof the present invention to provide a rotary compressor having an improved arrangement for varying the volume displacement of the compres sor between a maximum and an intermediatevolume.

It is a furtherobject ofthe present inventionto provide a rotary compressor which may be utilized in. a reversible type refrigeration system and which is provided with means for automatically changing the volume displacement of the compressor upon the reversing offlow within the system.

Further objects andadvantages of the invention will become apparent as the following descriptionproceeds and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

In carrying out the objects of the present invention there is provided a rotary compressor having a compres sion chamber with an eccentrically rotatable .rotor therein for compressing :gas within the chamber. A blade, slidably positioned within a slot communicating with the chamber and biased into engagement with the rotor,

divides thechamberinto high and low pressure sides. The compressor contains a gas discharge .port and a gas suction port communicating respectively with the high and low pressure sides of the chamber. An unloader passage, connecting with the chamber at a point intermediate the gas discharge port and the gas: suction port, is provided through which uncompressed gases may be expelled from the chamber during the rotation of the rotor up to the point just beyond the opening to the passage. The unloader passage contains a check valve therein for preventing reverse flow of gas from the passage into the chamber and for permitting flow of gas from the chamber into the passage when the pressure of the chamber is greater than that within the passage. The unloader passage connects at its other end to a means for selectively introducing either discharge pressure or suction pressure into the passage to actuate the check valve into closed or open position respectively. By maintaining the suction pressure within the unloader passage, the check valve permits flow of gas from the chamber into the passage thereby unloading the chamber during a portion of the cycle of the rotor and thereby reducing the volume of displacement of the compressor. Upon introduction of discharge pressure into the passage, the pressure within the passage exceeds that of the chamber and the check valve closes to prevent flow of gas from within the chamber into the passage thereby causing compression of the full or maximum volume displacement of gas within the chamber during each cycle of the rotor.

For abetter understanding of the invention references may be had to the accompanying drawings in which:

Fig. 1 is a cross sectional elevation view of a compressor embodying the present invention;

Fig. 2 is a cross sectional view taken along line 2-2 of Fig. 1;

Fig. 3 is a schematic view showing a valve arrangement for the compressor with suction pressure introduced into the unloader passage;

.Fig. 4 is a view similar to that of Fig. 3 with discharge pressure introduced into the unloader passage;

Fig. 5 is a schematic diagram showing the compressor of the present invention arranged in a reversible refrigerating system; and

Fig. 6 is a similar view of Fig. 5 with the direction of flow of the gas within the system reversed.

Referring to Figs. 1 and '2, there is shown a hermetic compressor 1 including a hermetic casing 2 in Which is disposed a refrigerant compressor unit 3 having an annular chamber or compression chamber 4 defined within a cylinder or housing 6. Disposed for rotation within the chamber 4 is a rotor 7 which is rotatably driven Within the chamber by a. motor 8. In the illustrated embodiment of the invention, the rotor '7 is rotated around the chamber 4 by an eccentric portion 9 which is an integral portion of the shaft 11 extending from the motor '8. A hearing 12, which with its supporting frame 13 defines the upper end wall .of the annular chamber 4-, supports the shaft 11 for rotation by the motor 8.

As better seen in Fig. 2, a radial slot 14 which communicates with the chamber 4, is provided in the cylinder or housing 6. Positioned slidably in the radial slot 14 is a blade 16 which is biased into engagement with the rotor 7 thereby dividing the chamber 4 into high and low pressure sides 4a and 4b. Upon rotation of the rotor 7, the blade 16 follows the rotor and reciprocates back and forth within the slot 14. In the present modification of the invention, the blade 16 is biased into contact with the rotor 7 by means of a spring 17 which is positioned within the slot 14 behind the blade.

Connecting with .the low pressure side 4!: of the chamber 4 is an inlet or suction port 18 through which suction gases may .be drawn into the chamber. .On. the other side of the blade 16, or on the high pressure side 4a of the compression chamber 4, is an outlet or discharge port O I? through which the compressed gases are discharged from the compression chamber. It is normal practice in rotary compressors, in order to obtain the maximum possible displacement, to position the suction and discharge ports as closely as possible to the oposite sides of the blade 16. A suitable valve 21 is provided in the discharge passage for assuring proper compression of the gases issuing through the discharge port 19 and for V preventing reverse flow of discharge gases back into the compression chamber 4. During the operation of this type of compressor in a refrigerating system, the suction port 18 is connected to the suction line 23 leading from the evaporator of the system and the discharge port 19 expels the compressed gases from the chamber into the discharge cavity 20 and hence into the high pressure passage and the high pressure line 22 which leads to the condenser of the system. It is sometimes desirable, in order to cool the motor with the compressed gases, to discharge gases from the compressor into the hermetic casing prior to expelling them into the high pressure line 22. When this is the case, the volume within the hermetic casing becomes filled with high pressure discharge gas and forms a part of the passage leading to the high pressure line 22. However, the operation of the compressor is the same regardless of whether the high pressure line connects directly with the compressor or with the hermetic casing.

The operation of the compressor as thus far described, may best be seen by referring to Fig. 2, wherein the rotor has just completely uncovered the suction port 18 and suction gases are being drawn into the low pressure side 4b of the chamber 4. As the eccentric 9 and shaft 11 rotate counterclockwise, the rotor is moved around the chamber in a counterclockwise eccentric movement and increases the volume of the suction or low pressure side 41) of the chamber while it decreases the volume of the high pressure side 4a of the chamber. As the rotor rotates in this direction the gases within the high pressure side 4a of the chamber are forced in the direction of the discharge port 19 and are compressed within the decreasing volume bounded by the blade 16, the rotor 7 and the wall of the compression chamber 4. As is evident from Fig. 2, the maximum volume displacement of this type of compressor occurs at a time during the rotation of the rotor when the periphery of the rotor 7 progresses just beyond the opening to the suction port 18. That is, all the volume of gas within the high pressure side 4:; of the chamber 4 just after the rotor 7 has passed the point 18a of the suction port will be compressed or displaced by the rotor during the remaining portion of its cycle. As will hereinafter be described, the present invention provides a simple and improved means whereby, in a compressor of the above type, the displacement of the compressor may be decreased from the above described maximum volume to some intermediate volume.

For the purpose of obtaining a decreased displacement from the compressor there is provided, in accordance with this invention, a means for unloading a portion of the gas drawn into the compression chamber 4 during the first part of the compression cycle. More specifically there is provided a bypass conduit or unloading passage 24 which includes an unloader port 24a leading into the compression chamber 4 at a point intermediate the suction port 18 and the discharge port 19 of the chamber. A check valve 26 (better seen in Fig. l) is positioned within the unloader passage 24 for preventing the reverse flow of gases from the passage 24 into the chamber 4 and for permitting the flow of gas from within the chamber into the passage at such times when the pressure within the chamber 4 exceeds the pressure within the unloader passage 24.

As may be best seen in Figs. 3 and 4, one end of the unloader passage 24 is connected to a means for selectively introducing suction pressure or discharge pressure the operation of the check valve and, thereby, the volume displacement of the compressor. More specifically, the passage 24 connects with a valve 27 which in one position, illustrated schematically in Fig. 4, connects the passage with the discharge gases and in a second position, illustrated schematically in Fig. 3, connects the passage with suction gases. In the operation of the compressor, when the valve 27 is positioned such that suction pressure is introduced to the unloader passage 24, gases within the chamber will be discharged through the passage 24 as the rotor rotates counterclockwise within the chamber until the rotor, during its rotation within the chamber, seals off to the port 24a of the unloader passage. As the chamber 4a is reduced in size and the port 24a to the unloader passage 24 is sealed by the periphery of the rotor 7, compression of the gases within the chamber 4 takes place only for the remaining portion of the rotors movement around the chamber. In other words, the volume of gas compressed or displaced is only that amount remaining within the chamber when the rotor has progressed to a point where it just seals off the opening to the port 24a to the unloader passage 24. It is contemplated that the compressor will be operated on this low capacity or low volume displacement when the suction pressure of the gases entering the compression chamber 4 is relatively high, thus reducing the load on the motor 8.

In order to operate the compressor at full volume displacement, the valve 27 is moved to the position shown in Fig. 4 and discharge pressure is introduced into the unloader passage 24. The check valve 26 is then forced into the closed position by the pressure within the passage 24. When discharge pressure is ported into the passage 24, the gas within the high side 4a of the chamber is compressed for the entire rotation of the rotor within the chamber. Thus referring to Fig. 2, as the rotor rotates counterclockwise, there is no flow of the gas from within the chamber through the bypass passage 24 since the pressure in the high side 4a of the chamber never equals or exceeds the pressure within the unloader passage 24 until just prior to full compression within the chamber 4a, and this happens only after the rotor has effectively sealed off the port 24a to the unloader passage 24.

It should be noted that the volume of displacement of the compressor, when operating at this intermediate level, depends on the particular location of the opening to the port 24a of the unloader passage with respect to the discharge port 18. For optimum efiiciency the location of the port 24a of the unloader passage should be determined so that the load on the motor when operating at this intermediate capacity, under conditions of high suction pressure, is approximately equal to the load on the motor during maximum displacement, under conditions of relatively low suction pressure. The precise location of the opening to the unloader passage depends on many factors, such as the type of gas used and the expected temperature conditions under which the compressor will be operated.

The valve 27 may be any of a number of well known valves now on the market for porting one or the other of two separate lines into a third line. It may also be automatically or manually operable depending upon the requirements of the apparatus in which the compressor will be assembled. In most cases it would be desirable to have the valve move automatically to operate the compressor at its intermediate displacement level according to predetermined pressure being attained in the discharge line. For example, the valve could be operated by a suitable electrical solenoid which is energized into one position or the other by a pressure responsive means, such as a switch operating bellows tapped into the discharge line.

Referring now to Figs. 5 and 6 there is shown a reversible type refrigerating system which effectively utilizes the compressor of the present invention. The system comprises a pair of heat exchangers 28 and 29 which are connected by a pair of refrigerant carrying lines or tubes 31 and 32 to a reversing valve 33 which, in turn, is connected to the high pressure or discharge tube 22 and the low pressure or suction tube 23 leading from the compressor 1. It is contemplated that, in such a system, flow between the heat exchangers will be through an expansion means, such as a capillary, in which expansion of the refrigerant gases takes place in either direction. This is normally the type of refrigerating system used in a heat pump wherein each of the heat exchangers is utilized either as a condenser or as an evaporator, depending upon the particular conditioning requirements desired. For the purpose of explanation, we will assume that in Fig. 5 the heat exchanger 28 is operating as a condenser and heat exchanger 29 is operating as an evaporator. Thus, compressed refrigerant discharging from the compressor flows through the discharge line 22 and through the reversing valve 33 into the line 31 to the heat exchanger 28 operating as a condenser. The refrigerant then flows to the heat exchanger 29 through any suitable expansion means and is returned to the compressor via the reversing valve 33 and the suction line 23. By connecting the unloader passage 24 to the line 32 or low pressure line, the compressor will operate on its reduced or intermediate capacity when the gases are flowing in this direction since suction pressure will be ported into the unloader passage 24 and the check valve 26 will be free to open and permit flow of gas from within the chamber 4 into the passage. This would be the desirable operation for the compressor during the summer time when the suction gases from the evaporator 29 are relatively high and it is necessary, to prevent overloading of the compressor motor, to compress only a small volume of the gas.

However, in the winter when the heat pump is operated to obtain heat from the heat exchanger 29 for heating an enclosure, it is necessary to reverse the flow of gases within the system and operate the heat exchanger 29 as a condenser. In this case the reversing valve 33 is placed in the position shown schematically in Fig. 6 and the flow of refrigerant is from the discharge line 22 of the compressor through the reversing valve 33 to the line 32 and thence to the heat exchanger 29. From there the refrigerant flows to the heat exchanger 28 which is now operating as the evaporator and is returned to the compressor 1, through the line 31 via the reversing valve 33 and the suction line 23. During this operation when discharge gases are flowing through the line 32, discharge pressure will exist in the unloader passage 24 and the pressure therein will force the check valve 26 to close and prevent the flow of gases into the unloader passage from within the chamber 4. Thus, when the refrigerating system is reversed for operation on the heating cycle, under temperature conditions when the discharge gases from the evaporator are at a relatively low pressure, this type of an arrangement very conveniently converts the compressor operation from its reduced or intermediate capacity to its maximum capacity.

Another advantage of a compressor unloader arrangement such as this is that, when the compressor is first started and there is no or very little difierence in the pressures between the high and low pressure lines of the sys term, the compressor will always discharge gas into the unloader passage 24 until the pressure within the discharge line 22 builds up to the point where the pressure ported into the unloader passage 24 becomes greater than that within the compression chamber 4. Thus, even though the unloader line 24 is connected to the high pressure line 22, as in Fig. 4, or line 32 as in Fig. 6, the compressor will operate at reduced capacity or reduced volume displacement until the discharge pressure builds up. In other words, whenever the compressor begins to operate, if the pressure of the gas within the bypass passage 24 is less than that within the chamber, as will always be the case when the compressor starts after a suspended time of non-operation, the gases will always flow into the discharge passage 24 during the first portion of the compression cycle, until suflicient discharge pressure has built up to close the check valve 26. In this manner the present invention provides a means for reducing the load on the motor 3 during the starting of the compressor 1, thereby reducing the starting torque and current necessary to start the motor.

By the present invention there has been provided a rotary gas compressor having an improved arrangement whereby the volume of displacement of the compressor may be selectively changed from a maximum volume to an intermediate volume and vice versa. Moreover, the compressor of the present invention is particularly well adapted to operate in those systems utilizing reversible refrigerant flow to obtain heating in the winter or cooling in the summer and, when connected properly in such a system, the compressor automatically provides for maximum volume displacement under conditions of low compressor load and intermediate volume displacement under conditions of high compressor load.

While in accordance with the Patent Statutes there has been described what at present is considered to be the preferred embodiment of the invention, it. will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, the aim of the appended claims to cover all equivalent variations that fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

In a refrigeration system having first and second refrigerant tubes; the combination comprising a rotary refrigerant compressor and a reversing valve for reversing the direction of flow of refrigerant from said compressor through said first and second refrigerant tubes,

" said compressor including a cylinder having a chamber and a radial slot communicating with said chamber, a rotor eccentrically rotatable within said chamber, a motor having a shaft thereon for driving said rotor within said chamber, a blade slidably positioned within said radial slot, means biasing said blade against said rotor for following said rotor thereby to divide said chamber into high and low pressure sides, a suction port connecting with said low pressure side of said chamber, a discharge port conecting with said high pressure side of said chamber, a bypass conduit connecting at one end with said chamber at a point intermediate said suction port and said discharge port and connecting at the other end with one of said refrigerant tubes of said refrigerating system, a check valve in said bypass conduit for preventing reverse flow of gas from said bypass conduit into said chamber and for permitting flow of gas from said chamber into said bypass conduit when the gas pressure within said chamber is greater than the gas pressure within said bypass conduit, said reversing valve having low pressure and high pressure conduits leading respectively to said suction port and said outlet port of said compressor, said reversing valve operating to selectively channel high pressure refrigerant gas into one or the other of said refrigerant tubes while receiving low pressure gas from the remaining tube so that the displacement of said compressor is a maximum when gas at discharge pressure is flowing through said refrigerant tube connecting With said bypass conduit and an intermediate volume displacement when gas at suction pressure is flowing through said refrigerant tube connecting with said bypass conduit.

References Cited in the file of this patent UNITED STATES PATENTS 2,006,584 DePuy July 2, 1935 2,123,123 Small et al. July 5, 1938 2,328,824 McCormack et al. Sept. 7, 1943 2,342,174 Wolfert Feb. 22, 1944 2,619,326 McLenegan Nov. 25', 1952 2,794,323 Rataiczak et al. June 4, 1957

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