Abstract:
A scroll-type refrigeration compressor is disclosed which incorporates an efficient, reliable, low cost modulation system employing a single actuator to effect switching between full and reduced capacity operation. The modulation system of the present invention includes an elongated member movably supported on the non-orbiting scroll which operates to ensure simultaneous opening and closing one or more unloading passages thus avoiding the possibility of even transient pressure imbalances between opposed compression pockets during operation of the compressor. In one embodiment, the elongated member has the opposite ends interconnected by springs and is rotatably movable to effect the intended modulation. In another embodiment, the elongated member is movable generally along a radial line of the non-orbiting scroll member. Further, the modulation system of the present invention provides for reduced capacity at both start up and shut down thus enabling the use of more efficient lower starting torque motors and reducing the potential for noise generating reverse rotation on shut down.

Description:
BACKGROUND AND SUMMARY OF THE INVENTION 
     The present invention relates generally to scroll compressors and more specifically to a capacity modulation system of the delayed suction type for such compressors. 
     Refrigeration and air conditioning systems are commonly operated under a wide range of loading conditions due to changing environmental conditions. In order to effectively and efficiently accomplish the desired cooling under such changing conditions, it is desirable to incorporate means to vary the capacity of the compressors utilized in such systems. 
     A wide variety of systems have been developed in order to accomplish this capacity modulation most of which delay the initial sealing point of the moving fluid pockets defined by scroll members. In one form, such systems commonly employ a pair of vent passages communicating between suction pressure and the outermost pair of moving fluid pockets. Typically these passages open into the moving fluid pockets at a position normally within 360° of the sealing point of the outer ends of the wraps. Some systems employ a separate valve member for each such vent passage which valves are intended to be operated simultaneously so as to ensure a pressure balance between the two fluid pockets. Other systems employ additional passages to place the two vent passages in fluid communication thereby enabling use of a single valve to control capacity modulation. 
     The first type of system mentioned above creates a possibility that the two valves may not operate simultaneously. For example, should one of the two valves fail, a pressure imbalance will be created between the two fluid pockets which will increase the stresses on the Oldham coupling thereby reducing the life of the compressor. Further, such pressure imbalance may result in increasing operating noise to an unacceptable level. Even slight differences in the speed of operation between the two valves can result in objectionable noise generating transient pressure imbalances. 
     While the second type of system mentioned above eliminates the concern over pressure imbalances encountered with the first system, it requires additional costly machining to provide a linking passage across the scroll end plate to interconnect the two vent passages. Further, the addition of this linking passage increases the re-expansion volume of the compressor when it is operated in a full capacity mode thus reducing its efficiency. 
     The present invention, however, overcomes these and other problems by providing a single valving ring operated by a single actuator so as to ensure simultaneous opening and closing of the vent passages thus avoiding any possibility of even transient pressure imbalances in the fluid pockets. The valving ring of the present invention is in the form of a discontinuous generally circularly shaped ring which in one embodiment is rotatably mounted on the non-orbiting scroll member and includes portions operative to open and close, one, two or more vent passages simultaneously. In another embodiment the ring may be moved in a generally radial direction. Actuation of the valving ring is preferably accomplished by means of a solenoid valve although a fluid pressure operated actuator may be used. In both of the embodiments a minimum number of parts are required to accomplish the capacity modulation. Further, the capacity modulation system of the present invention will preferably be designed such that the compressor will be in a reduced capacity mode at both start up and shut down. The reduced capacity starting mode reduces the required starting torque because the compressor is compressing a substantially smaller volume of refrigerant. This reduced starting torque enables use of a lower torque higher efficiency motor. Also, reduced capacity operation at shut down reduces the potential and degree of noise generating reverse rotation of the scrolls thereby enhancing customer satisfaction. Additionally, the system of the present invention is preferably designed such that should the actuating system fail, the compressor will be able to continue operation in a reduced or modulated capacity mode. This is desirable because under normally encountered operating conditions, the compressor will spend most of its running time in the modulated or reduced capacity mode. 
     Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a fragmentary section view of a hermetic scroll compressor incorporating the capacity modulation system of the present invention; 
     FIG. 2 is a section view of the compressor of FIG. 1, the section being taken along the line  2 — 2  thereof; 
     FIGS. 3 and 4 are views of the valving ring and actuator incorporated in the embodiment shown in FIGS. 1 and 2 shown in closed and open positions respectively; 
     FIGS. 5 and 6 are section views each similar to that of FIG. 2 but showing another embodiment of the present invention in open and closed positions respectively; and 
     FIGS. 7 and 8 are views similar to that of FIGS. 3 and 4 but showing the embodiment illustrated in FIGS. 5 and 6. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings and in particular to FIG. 1, there is shown a hermetic scroll-type refrigeration compressor indicated generally at  10  and incorporating a capacity modulation system in accordance with the present invention. 
     Compressor  10  is generally of the type disclosed in U.S. Pat. No. 4,767,293 issued Aug. 30, 1988 and assigned to the same assignee as the present application the disclosure of which is hereby incorporated by reference. Compressor  10  includes an outer shell  12  within which is disposed orbiting and non-orbiting scroll members  14  and  16  each of which include upstanding interleaved spiral wraps  18  and  20  which define moving fluid pockets  22 ,  24  which progressively decrease in size as they move inwardly from the outer periphery of the scroll members  14  and  16 . 
     A main bearing housing  26  is provided which is supported by outer shell  12  and which in turn movably supports orbiting scroll member  14  for relative orbital movement with respect to non-orbiting scroll member  16 . Non-orbiting scroll member  16  is supported by and secured to main bearing housing for limited axial movement with respect thereto in a suitable manner such as disclosed in U.S. Pat. No. 5,407,335 issued Apr. 18, 1995 and assigned to the same assignee as the present application, the disclosure of which is hereby incorporated by reference. 
     A drive shaft  28  is rotatably supported by main bearing housing  26  and includes an eccentric pin  30  at the upper end thereof drivingly connected to orbiting scroll member  14 . A motor rotor  32  is secured to the lower end of drive shaft  28  and cooperates with a stator  34  supported by outer shell  12  to rotatably drive shaft  28 . 
     Outer shell  12  includes a muffler plate  36  which divides the interior thereof into a first lower chamber  38  at substantially suction pressure and an upper chamber  40  at discharge pressure. A suction inlet  42  is provided opening into lower chamber  38  for supplying refrigerant for compression and a discharge outlet  44  is provided from discharge chamber  40  to direct compressed refrigerant to the refrigeration system. 
     As thus far described, scroll compressor  12  is typical of such scroll-type refrigeration compressors. In operation, suction gas directed to lower chamber  38  via suction inlet  42  is drawn into the moving fluid pockets  22  and  24  as orbiting scroll member  14  orbits with respect to non-orbiting scroll member  16 . As the moving fluid pockets  22  and  24  move inwardly, this suction gas is compressed and subsequently discharged into discharge chamber  40  via a center discharge passage  46  in non-orbiting scroll member  16  and discharge opening  48  in muffler plate  36 . Compressed refrigerant is then supplied to the refrigeration system via discharge outlet  44 . 
     In selecting a refrigeration compressor for a particular application, one would normally choose a compressor having sufficient capacity to provide adequate refrigerant flow for the most adverse operating conditions to be anticipated for that application and may select a slightly larger capacity to provide an extra margin of safety. However, such “worst case” adverse conditions are rarely encountered during actual operation and thus this excess capacity of the compressor results in operation of the compressor under lightly loaded conditions for a high percentage of its operating time. Such operation results in reducing overall operating efficiency of the system. Accordingly, in order to improve the overall operating efficiency under generally encountered operating conditions while still enabling the refrigeration compressor to accommodate the “worst case” operating conditions, compressor  10  is provided with a capacity modulation system. 
     The capacity modulation system of the present invention includes a generally circularly shaped valving ring  50  movably mounted on non-orbiting scroll member  16 , an actuating assembly  52  and a control system  54  for controlling operation of the actuating assembly (see FIG.  2 ). 
     As best seen with reference to FIGS. 2 through 4, valving ring  50  comprises an elongated strip member  56  formed into a generally circular shape with the opposite ends  58  and  60  thereof being positioned in spaced generally opposed relationship. One or more springs  62  is provided having opposite ends connected to respective ends  58  and  60  of strip  56  and operates to draw them toward each other. Preferably ring  50  will be formed from a relatively thin metal and formed to a generally circular shape having a radius slightly less than the radius of non-orbiting scroll member. A pair of openings  64 ,  66  are provided in ring  50  positioned intermediate the ends thereof and in generally diametrically opposed relationship to each other. 
     As previously mentioned, valving ring  50  is designed to be movably mounted on non-orbiting scroll member  16 . In order to accommodate valving ring  50 , non-orbiting scroll member  16  includes a radially outwardly facing cylindrical sidewall portion  68  thereon having an annular groove  70  formed therein adjacent the upper end thereof. 
     Groove  70  is sized to movably accommodate ring  50  when it is assembled thereto having a relatively shallow radial depth approximately equal to or slightly greater than the thickness of ring  50  and an axial width just slightly greater than ring  50 . Ring  50  may be easily assembled to non-orbiting scroll member  16  by merely spreading the ends apart slightly to enlarge the diameter thereof and slipping it axially into position within groove  70 . Once in position, springs  62  will operate to bias ends  58  and  60  toward each other thereby retaining ring  50  properly seated within groove  70 . Alternatively, ring  50  may be fabricated in a circular shape from a material having a suitable resilient shape retaining capability so as to enable it to be expanded for assembly yet still be sufficiently resistant to such radial expansion once assembled as to eliminate the need for springs  62 . Of course this resistance to radial expansion must be sufficient as to enable ring  50  to maintain a seal over the capacity modulating vent passages described below when in a position for full capacity operation. 
     Non-orbiting scroll member  16  also includes a pair of generally diametrically opposed radially extending passages  72  and  74  opening into the inner surface of groove  70  and extending generally radially inwardly through the end plate of non-orbiting scroll member  16 . An axially extending passage  76  places the inner end of passage  72  in fluid communication with moving fluid pocket  24  while a second axially extending passage  78  places the inner end of passage  74  in fluid communication with moving fluid pocket  22 . Preferably, passages  76  and  78  will be oval in shape so as to maximize the size of the opening thereof without having a width greater than the width of the wrap of the orbiting scroll member  14 . Passage  76  is positioned adjacent an inner sidewall surface of scroll wrap  20  and passage  78  is positioned adjacent an outer sidewall surface of wrap  20 . Alternatively passages  76  and  78  may be round if desired however the diameter thereof should be such that the opening does not extend to the radially inner side of the wrap  18  of the orbiting scroll member  14  as it passes thereover. 
     Actuating assembly  52  includes a solenoid  80  having a cylindrical housing  82  sealingly secured to outer shell  12  and extending generally radially outwardly therefrom which defines a cylinder within which elongated piston  86  is axially movably disposed. An actuating coil assembly  88  is provided on the outwardly projecting portion of cylindrical housing  82  and serves to create a magnetic field when actuated drawing piston axially into cylinder housing  82 . A generally Z-shaped actuating rod  90  has one end rotatably secured to the outer end of piston  86  with the other end being rotatably secured to the outer surface of valving ring  50  in a suitable manner such as by strap  92 . As shown in FIGS. 3 and 4, actuating rod is secured to valving ring  50  at a location circumferentially displaced from the axis of piston  86  such that as piston  86  is drawn axially into cylinder  82 , actuating rod  90  will rotate with respect thereto with the end secured to valving ring moving circumferentially toward the line of movement of piston  86  and thus effecting circumferential movement of ring  50 . 
     As shown in FIG. 2, when solenoid coil  88  is de-energized, valving ring  50  will be in a position in which openings  64  and  66  are in alignment with respective passages  72  and  74  thereby venting compression chambers  22  and  24  to the interior of shell  12 . When solenoid coil assembly  88  is energized, piston  86  will be drawn into cylinder housing  82  thereby effecting rotary movement of valving ring  50  with respect to non-orbiting scroll member  16  and moving openings  64  and  66  out of alignment with respective passages  72  and  74 . In this position, valving ring  50  will prevent suction gas from respective compression chambers  22  and  24  being vented to the interior of the shell so that the compressor will then operate at substantially full capacity. 
     In order to return valving ring  50  to a position in which passages  64  and  66  are vented to the interior of the shell when solenoid coil  88  is de-energized, a spring  94  is provided having one end secured to a post  96  upstanding from main bearing housing  26  and the other end secured to the end of actuating rod  90  that is secured to valving ring. Thus when solenoid coil  88  is de-energized, spring  94  will operate to rotate valving ring in the opposite circumferential direction to move openings  64  and  66  back into aligned relationship with respective passages  72  and  74  as well as to move piston  86  axially outwardly from cylinder housing  82 . 
     Control system  54  operates to control actuation of actuating assembly  52  and includes a control module  98  and one or more sensors  100 . Control module  98  is connected to solenoid coil  88  via line  102  and operates to selectively energize solenoid coil  88  in response to system operating conditions as sensed by sensors  100  and transmitted thereto via line  104 . Preferably, control module  98  will operate to ensure that solenoid coil  88  is de-energized both just prior to shut down of compressor  10  as well as at start up. 
     When valving ring  50  is in the position shown in FIG. 2, moving fluid pockets  22  and  24  will remain in fluid communication with lower chamber  38  at suction pressure via passages  72 ,  76  and  74 ,  78  after the initial sealing of the flank surfaces of the scroll wraps at the outer end thereof until such time as the moving fluid pockets have moved inwardly to a point at which they are no longer in fluid communication with passages  76  and  78 . Thus, when valving ring  50  is in a position such that fluid passages  72  and  74  are in open communication with the suction gas chamber  38 , the effective working length of scroll wraps  18  and  20  is reduced as is the compression ratio and hence the capacity of the compressor. It should be noted that the degree of modulation or reduction in compressor capacity may be selected within a given range based upon the positioning of passages  76  and  78 . These passages will preferably be located so that they are in communication with the respective suction pockets at any point up to 360° inwardly from the point at which the trailing flank surfaces move into sealing engagement. If they are located further inwardly than this, compression of the fluid in the pockets will have begun and hence venting thereof will result in lost work and a reduction in efficiency. 
     It should also be noted that by ensuring passages  72  and  74  are in open communication with suction pressure at start up, the required starting torque for the compressor is substantially reduced. This enables the use of a more efficient lower starting torque motor, thus further contributing to overall system efficiency. 
     In any event, so long as system conditions as received by control module  98  indicate, compressor  10  will continue to operate in this reduced capacity mode. However, should system conditions dictate that additional capacity is required such as may be indicated by a signal from sensor  100  to controller  98 , controller  98  will actuate solenoid valve  80  causing valving ring  50  to rotate in a clockwise direction as shown in FIG. 2 so as to substantially simultaneously close off passages  72  and  74  thereby avoiding the possibility of pressure imbalances between fluid pockets  22  and  24 . With valving ring  50  in this position, it overlies and closes off passages  72  and  74  respectively thus preventing further venting of the suction fluid pockets therethrough and increasing the capacity of compressor  10  to its full rated capacity. So long as system operating conditions require, solenoid valve will be maintained in its energized position thereby maintaining compressor  10  at its full rated capacity. It should be noted that because the solenoid valve is selected to be in a normal position to reduce the capacity of the compressor, failure of either the solenoid valve or control module will not prevent continued operation of the compressor. 
     It should be noted that if desired the actuating solenoid valve assembly may be replaced by a pressure actuated piston assembly. In such an embodiment, it is contemplated that a solenoid valve would be incorporated to control flow of pressurized fluid to and venting from the actuating piston/cylinder. It is also contemplated that the discharge fluid would be utilized as the pressurized fluid to actuate the piston cylinder assembly in such an embodiment. 
     Another embodiment of a modulation system in accordance with the present invention is illustrated and will be described with reference to FIGS. 5 through 8. As this embodiment is very similar to the embodiment shown in FIGS. 1 through 4 except for the valving ring and a portion of the actuating mechanism as noted below, corresponding portions will be indicated by the same reference numbers used in FIGS. 1 through 4 primed. 
     In this embodiment valving ring  106  is fabricated from a suitable resilient shape retaining material such as spring steel and has a generally circular shape extending circumferentially somewhat greater than 180° . The opposite ends  108  and  110  of valving ring  106  are spaced apart approximately 90° and flare slightly radially outwardly. Preferably, valving ring  106  will have an unstressed diameter slightly less than that of the diameter of groove  70 ′ provided in non-orbiting scroll  16 ′ within which it is seated. 
     Actuating mechanism  112  is similar to actuating mechanism  80  in that it utilizes a solenoid actuated plunger to effect movement of valving ring  106 . However, a rocker arm  114  is pivotably supported on main bearing housing  26 ′ by means of a suitable pivot pin  116 . Rocker arm  114  includes a first arm  118  extending outwardly from pivot pin  116 , the outer end of which is pivotably connected to the outwardly projecting end of plunger  86 ′. A second arm  120  extending outwardly from pivot pin  116  in generally the opposite direction from arm  118  is adapted to pivotably receive one end of an actuating rod  122 . The other end of actuating rod  122  is fixedly secured to the outer periphery of valving ring  106  via strap  124  such as by welding. Preferably, valving ring  106  will be positioned relative to non-orbiting scroll member  16 ′ such that the midpoint thereof is substantially centered with respect to diametrically opposed vent passages  72 ′ and  74 ′ and actuating rod will be secured thereto at this midpoint location. 
     In operation, when solenoid coil  80 ′ is de-energized valving ring will be in a position as shown in FIG. 5 in which the midpoint portion thereof is positioned in radially spaced relationship to non-orbiting scroll member  16 ′ with the opposite ends thereof being positioned within groove  70 ′. When in this position, vent passages  72 ′ and  74 ′ will both be in open communication with chamber  38  which is at suction gas pressure as valving ring will be radially outwardly spaced therefrom as shown in the drawings. Thus, the compressor will operate at a reduced capacity. 
     Should conditions indicate that increased capacity is required, solenoid valve  80 ′ will be energized by the control module in response to signals from system load sensors. Energization of solenoid valve  80 ′ will result in plunger being drawn radially outwardly with respect to compressor  10 ′ thereby causing rocker arm  114  to pivot about pin  116  in a clockwise direction to a position as shown in FIG.  6 . This pivoting motion of rocker arm  114  will in turn move valving ring  106  radially inwardly with respect to non-orbiting scroll member  16 ′ such that it is fully seated within groove  70 ′. In this position valve ring  106  will be in overlying relationship to respective vent passages  72 ′ and  74 ′ and will operate to prevent venting of suction gas therethrough. Thus, the compressor will operate at substantially full capacity until such time as the sensors indicate it can be returned to reduced capacity. 
     It should be noted that because the opposite ends of valving ring  106  extend more than 90° in opposite directions from the radial line of movement of actuating rod  122 , the radially inwardly directed biasing force exerted by opposite end portions  108  and  110  on the radially outwardly facing curved surface of groove  70  will operate to assist solenoid coil  80 ′ in moving valving ring  106  into a closed position. Further, the slight radially outward flare provided on end portions  108  and  110  ensures that the radially inner edges at the opposite terminal ends of valving ring  106  will not dig into the groove  70  and thereby resist movement into a closed non-venting position. While the circumferential extent of valving ring  106  is not critical, it should be sufficient to ensure that it will expand radially enough to uncover passages  72 ′ and  74 ′ so that the compression pockets may be vented to the low pressure chamber of the compressor. 
     While it will be apparent that the preferred embodiments of the invention disclosed are well calculated to provide the advantages and features above stated, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope or fair meaning of the subjoined claims.