CA1186030A - Variable load motor efficiency correlating arrangement - Google Patents

Abstract

ABSTRACT

Method and apparatus for optimizing the effi-ciency of a hermetic unit having an induction motor permanently coupled to a compressor wherein the com-pressor capacitor is varied in accordance with require-ments of the system being served by the hermetic unit and the extent of running or main winding of the motor which is energized during operation of the unit is changed in accordance with the compressor capacity variations to thereby operate the motor near maximum efficiency despite variations in the demand of the system. When the motor is a single phase induction motor it may be provided with a tapped main winding so that changes in the extent of that winding which is energized may be accomplished by connecting a selected pair of taps to line voltage. Typically, the efficiency is optimized by loading the motor to near maximum torque for the extent of winding which is energized.

Description

l~B60.~

,VARIABLE LOAD MOTOR EFFICIEMC~
CoRRELATI~ G

The present invention relates yenerally to the efficlent operation of induc~.~on motors which are 5 ~ubjected tv varia~le load~ and more particularly to a method and apparatus ~or operatlng a hermetic unit as might be found in a re~rigeration system at near maximum efficiency despite variation~ in load or systcm demand.
The en~ancem~nt o~ machin~ efficiency i~ oE
continuing concern in a wlde vaxiety o disciplines.
~or exam.ple, in the induction motor art, new and improved stator designs and winding confi~uxations are continually being davised with only a small per-centage improvement in e~ficiency ~eing meritorious.
~he improvement in ~he efficiency of motor-compressor hermetic units as may be used in refrigeration system~, such as air condltioners, common refrigerators, heat pumps and the like is a continuing goal.
A wide variety of arran~ements for modulating or cont~olliny the output o~ such hermetic units are known and include the conventional thermostat arranye-m~t for energi~ing or ~e-energizing the com~ressor motor, as well as a num~er of schemes for reclucing the compre~sox capacity either by varying the sp~ed of op~ration of ~he compressor or in the case o~ multi-cyllnd~r piston type compressors by disabling one or more of the cylinders by blockage o~ the suction inlet thereto or a ~ypas~ arrangem2nt from th~ outlat 3~
thereof back to the suction inle-t. One partic~larly slgnificant cylinder unloading mechanisms for refrig-eration compressors is illustrated in applicart's ~T,S, Patent No 4r326~839/ issued April 271 1982r ~'nerein a fluid actuating valving arrangement selectively blocks off the suction inlet to successive cylinders to succes-sively decrease the capacity oE the compressor, for example in response to thermostat indicated system demand.
In such compressor unloading mechanisms it is also known to control the unloading in accordance with discharge pressure or suction pressure.

In the induction motor art, it ls also known to provide multiple main or running winding sections to be interconnected in differént ways for 2irferent purposes. For example, two main winding sections may be series connected to operate a given induction motor as a consequent pole machine at a slower speed while -those two main winding sections are connected in parallel with that parallel combination connected in series with a so-called extended main winding section Eor operation as an induction motor with half the previous number of poles so as to operate at a higher speed. Extended main windings which are energized at certain times but not at others even though the normal main winding coils are energized are not unique to IJ.S. Patent No. ~r326r839.

Among the several objects of the present inven-tion may be noted the provision of a system for matching the quantity of main winding which is energized with the load driven by an induction motor to improve o~erall efficiency particularly when the load is of a varying na-ture; the provision of an arrangement to optimize the efficiency of a hermetic unit kh/~

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such as a refrigeration unit which i5 subjecte~ to varying load; the coordination o~ compressor un-loading with motor operation so as to improve the e~fici~nt operation of a motor-compressor unit;
5 the provision of an improved he~natic motor-compxessor unit for a reErigeration system with only a nominal increase in cost and complexity; and tlle provision of a system for sel~ct~ng a pair of main winding taps for connection -~o line voltage so that the load on a motor ls n~ar maximum tor~ue for the extent of wind-lng of that motor which is energized. These as well as other o~jects and advantageous features will be in part pointed out hereinafter.
In yeneral, the ef~iciency of a hermetic unit having an induction ~otor permane~tly connected in driving relation ~o a compressor i5 optimized by ~arylng the compressor capacity in accordance with the requirements of the sys~em served by the henmetic unit and changing the extent of main winding of the motor which is energized ~uring unit o~eration in accordance with the compressor capacitor variations so as to o~erate the motor n ar maximum eficiency despite s~stem demanfl variations. The motor may be a single phase induction motor with a tapped main winding w:ith select~d pairs o main winding taps connected to line voltage so that the load on the motor is near the maximum torque of the motor for the extent o~ winding which is energized.
Also, in general, the e~ficiency of an induction motor which is subjected to a variable load is opti-mized by sensing change~ in the loaa on the motor and increaslng the extent of running windinq to be energized when the ~ensed load decreases while de-crea~ing the extent of running winding to be ~nergized 6~

when the sensad load increases. The sensing may be accomplished by monitoring maln winding current vaxiation~, monitoring ambierlt temperature or detec-ting changes in ~ompressor capacity.
$ Still further in yeneral and in one ~orm of the invention, a hermetic motor compressor unit includes an induction motor with a run winding including a plurality o.~ s~ri~s connected optionally energized winding ~ection~ and a common winding sec~ion connected in series th~rewlth along with an arrangement for supplyin~ l~ne volta~e to the common winding section and selectively to optlonally engaged winding sections as determined by demands on the system. The compres~or may be selectively partially disableable having as many discxete partially disable~ states as there are optionally energized run winding sections with an increase in system demand corresponding to a decrease in t~a number o~ optional winding sections which are energized while a ~ecrease in system demand increases ~he number of optional winding sections to be energizea.
Fig. 1 schamatically illustrates a control arrange-ment or a r~frigeration ~yst~m with a portion o.~
a hermetic unit having an unloadable compxessor illus-trated in detail;
X5 Fig~ 2 graphically illustrates motor ef~iciency as a fu~ction o~ deliv~red tor~ue for three exemplar~
main winding configurations;
Fig. 3 is a schematic diagram for a system similar to Fig. 1 matching compressor unloading and maln winding selection, and Fig. 4 is a schematic diagram of another arrangement ~or matching main wlnding selection to a var:iable load.

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Corresponding reEerence characters indicate corresponcllng parts tnrou~hout the several views of the dra-;in~.

The exemplifications set out herein illustrate a preferred embodiment of the invention in one form thereof and such exemplifications are not to be construed as lirniting the scope of the disclosure or the scope oE
the invention in any manner.

In fig. 1, a portion of a hermetic unit 11 having an induction motor 13 permanently connec-ted in driving relation to a multi-cylinder compressor 15 is connected in a refrigeration ci.rcuit 17 and influenced by a control circuit 19. The hermetic unit 11 is illustrated in grea-ter detail in the aforementioned U.S. 2atent No 4,326,~33g. Briefly/ that hermetic unit 11 may incluae crankshaft 21 generally coupling -the induction motor 13 and compressor 15 with crankshaft 21 having a plurality of connecting rods, such as 23 and 25, respectively connected to pistons, such as 27, reciprocable in respective radially distributed cylinders, such as 29. Such a cylinder may include an inlet valve 31 and exhaust valve 33 so that refrigerant is pumped from suction line 35 through the induction motor to cool that motor upwardly through suction passage 37 past valve 39 when in its open position, illustrated in dotted lines, and through inlet valve 31 when piston 27 moves downwardly, as illustrated. Upward movement of -the piston 27 closes valve 31, opens valve 33 and forces refrigerant out of the compressor by way of line 41. The unloading o,~ cylinder 25 is accomplise~ by moving valve 39 from the dotted to the solid position due to hydraulic pressure in line 44. This pressure in line 43 is from a hydraulic source by way of the pilot valve ~5 under control of thermostat 47. When thermostat ~7 kh~

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indicates an increased system demand, the ac-tua-ting coil 49 actuates valve 45, so that the El!lid pressure from the fluid source on line 51 passes through valve 45 to line 43, forcing piston 53 toward the left, as viewed, openin~ valve 39, and activating ~ylinder 29.
Additional cylinder unloading, as by similar unloader arrangement 55, may be sequentially controlled by t~e thermostat 47, with the total number of c-~linders and the number of cylinders which may be sequentially loaded and unloaded being a mere design consideration. Com-pressor 11 is illustrated in Fig. 1 as being coupled in a refrigeration circuit 17 which includes conventional evaporator coils 57, an expansion valve 59, and a condensor 61. The system as thus far des_ribed is either conventional or as illustrated in the afore-mentionæd U.S. Patent No. 4,326,839.

Fig. 1 also includes the actuating coil 63 of a control relay for inserting or deleting additional main winding turns in the induction motor circuit.
Where multiple cylinders are sequentially loaded and unloaded, a further control relay actuating coil 65 may similarly be included. As an alternative to these control relays, a pressure sensitive relaA7 Z~ may be inserted in the suction line 35 to measure pressure therein and provide winding selected control signals, if desired. Outlet line 41 could be similarly pressure monitoxed, as could the current to the induction motor 13, with the selection of parameters or combinations of parameters used to determine motor load ~otor load being nearly endless. The reason for moritoring motor ~h/ ~-load will become more ap~arent in conjunction with the description of Fig. 2.
Fig. 2 illustrates tne manner in which motor e~ficiency varies as a ~unction of outPut torque as abscissa or three different main or running winding configurations o~ the same induction motor. If the common portion only of the main winding is eneryized, ef~iciency varies wikh torque as illustrated ~n curve 69, with maximum eeficiency occurring at the tor~ue indlcated at 71, which torque is near maximum torque ~or the common winding portion. I additional main winding -turns are connected in sexies w.ith the common ~ortion, the e~ficiency var.ies as a function o:~ torque, as depicted by curve 73, with maximum torque occurr~ng at 750 The introduction of st~ll further main winding turns gi~es ef~iciency cu.rve 77 with maximum e~ficiency occu:rring at a still further reduced torque ~alue 7~. Ref2rrlng jointly to Figs. 2 and 3, the curve 69 would correspond to operation with only the common ~0 main winding portion 81 energized, whlle curv* 73 would correspond to the series combination of main windirit~ sections 81 and 83, and curve 77 would corres~
pond to the series combination of common main winding portlon 81 along with the series combinatlon of ex-tended ma~n winding portions 83 and 85.
In Flg. 3, the induction motor circuitry lnclud~sa conventional main or runnlng winding 81~ an auxiliary or start wind~ng 87, a voltage actuated starting swl~ch 89, which senses -the voltage across start winding ~7, and when that ~oltat3e becomes su~flcient~y hig~, .int.~icatin~ that the motox is runnin~ at a sueficient speecl, opens th~ switch 91, disabling the start winding and allowinq the motor to continus to run, energized onl~ by the main winding 81, Also conventiorlal in ~¢~3~

the motor circuitry is a starting capacltor 93 and running capacitor 95, as well as an internal pro-tective device 97 which i5 a thermally resPonsive device which flmctions to dis~ble the motor in the e~ent o~ excessive winding temperature or exces ive current through either the main or start w~nding~.
Such internal protection devices as 97 are co~mercially avallable rom Texas Instrument Company. Line voltage îs applied between *erminals 99 and 101 to complete the conventlorlal aspects of the induction motor cireuit of Fi~. 3.
The induction motor stator may be pro~ided with additional windings, such as the extended maln winding section ~3 and extended main windlng section 85, so ~hat with relay contacts 103 closed, the motor operates, utili~ing only the common main winding portion 81, ~hila if contacts 103 are open, and contacts 105 clo~ed, ~he motor 0~2rates utilizing the series combînation of common main winding portion 81 and extended main ~0 winding section B3. Sim.ilarly, closure of contaets 107 with contacts 103 and 105 open, oPerates tha motor with all three main winding ~ectlons in series and sub~ected to line voltageO
The cixeuit of ~ig. 3 i5 depicted as being sensi-~ive to suction line ~res3ure employing the pressuresensor 67 o~ Fig. 1. It will be understood that therm-05 tat 47 typically would not be employed .in this par-tlcular embodlment, however, a multistage thermostat or othar device ~or sensing a change in demand or load may be employed for control purposes. As the 3~

g air conditioning or refrigeration load decreases, pressure sensiti~e swi tch contacts 67a close, and thereafter as that load continues to decrease, pres-~ure sensitive switch contacts ~7b would closeO ~s the load increases, o~ course, this sequence of switch actuations would reverse. Under full o~ nearly full load condition~, switches 67a and 67b are normally open with relay coils 63 and 65 de-engeriæed. These two coils actuate a pair of normally closed switch contacts 109 and 111 so that the pressure sen~itive switches open, relay coil 113 i~ normally energi2ed.
The contacts corresponding to relay 113 are contacts 103, so that under these circumstances only the common portion 81 of the main winding is energized wi~h this condition corresponding to ef~iciency curv~ 69 of Fig. 2~ Closure of con~acts 67a energizes relay coil 65, openi~g contacts 111 and therefore o~ening con-tacts ~0~. R~lay coil 65 also functions to close contacts 105 so that two winding sections axe con~
nected in series to ~he line terminals 99 and 101, with this last situation corr~sponding to efficiency curve 73 o~ Fig. 2. A further decrease in th2 load on the refrigerating system results in the closure of con-tacts 67b, energizin~ relay coil 63, whose normall~ closed con~acts 115 open, disabling relay 65. Relay coil 63 actuates the contacts 107 so that all ~hree winding sections are connected in series, ~ielding the e~ficiency curve 77 o~ Fig~ 20 Relay coil 63 also controls normally open contacts 121 and 122 while relay coil 65 controls normally open contacts 120. ~en relay coil 65 is energize~ due to s~itch 67a closing, the closure of contacts 1~0 energ:iæes relay coil 117 which in which in turn actua-tes the pilot valve 119 of Fig. 1, to disable one cylinder o~ the compressor. Further load reduction and t.he closure o contacts 67b energizes relay coil 63 and, dtle to the closure of contacts 122, also energiæes relay coil 49, actuatin~ pilot valve 45 of Fig. 1 to disable a second compr~sso.r cylinder at the same time that contacts 107 close and contacts 115 open~
Aaditional latchin~ circuitry to hold the relay coils 117 clo~ed under these circumstances so both of the unloaded compxessor cylind~r~ remain unloaded is pro-lS vided due to khe closure o.~ contacts 121 and 122 and the opening o contacts 120 when coil 63 is energized.
On the other hand, an increase in load, opening contacts 67b, while contacts 67a remain closed, will re.sult in only one cylinclar being unloaded due to the actuation

2~ of coils 65 and 117 and deactuat~on o~ coils 63 and 49 ~ince when coil 63 is deactuatea, cont~cts 121 and 12~ open, while contacts 120 are closed under the control of coil 65 so that coil 117 remains energized.
~he winding arrangement, protective device and starting switch of Fig. 4 are as in the previously descxibed circuit, however, Fig. 4 illustrates the use o two swltching deYices 121 and 123. These devices may be pressure sensitive to qucti.on or out let pressure somewhat as px~vlou~ly decribed or may 3q D

he responsive to a motor wincling current sensor 125,since motor current will increase with load. In either e~ent, at hi~h load, sa~ hi~h suctlon ~ressure, ~he compressor will run with coil winding ~1 ener-gized, whereas if the suction pressur~ decrea~essufficiently to actuate the switch 121, windings 81 and 83 will be connected in series and if that pressure d~creases even .~urther (or the winding cur-rent decrea~es further) switch 123 will be actuated so that all three winding sections are connec~ed to lina ~oltage. Thus, actuation of switch 121 moves motor operatlon Prom curve 69 o~ Fig. 2 to curve 73 o~ Fig. 2, while actuation of switch 123 moves the motor operation from curve 73 to curve 77 o Fig~
2 so that as, for example, the load decreases, the motor tends to be o~erated close to its peak effic-iency at all time. In one embodiment, for example, at the torque identiied as 79 of Fi~. 2, the motor operated at around 38% efficiency with all three windings e~ergized in series whereas that same motor employing only winding 81 would operate around 83 to 84~ eficiency~
From the foregoing it is now apparent that a ~o~el scheme for optimizing the efficiency o~ an in-duction motor in, for example, a hermetic environmenthas b~en disclosed meeting the ob~ects an~ advantageous features set out hereinbefore as well as others and that modi~ications as to th~ precise con~igurations, shapes and details may be made hy those having ordinary

3~ 5kill in the art without departing from the spirit of the invention.

Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. The method of optimizing the efficiency of a hermetic compressor having an induction motor perman-ently connected in driving relation to a multiple cylinder compressor, the motor having a selectable length running winding, comprising:
selectively varying the capacity of the com-pressor by selectively unloading one or more but less than all of the cylinders, and reducing the output torque of the motor to substantially match the selected capacity of the compressor by increasing the length of running winding of the motor.

2. The method of claim 1 wherein the induction motor is a single phase motor having a tapped running winding, the step of changing including connecting a selected pair of running winding taps to line voltage.

3. The method of claim 1 wherein the step of varying includes sensing an ambient temperature.

4. The method of claim 3 wherein the step of varying includes the step of selectively disabling certain ones of the cylinders as the sensed temperature decreases.

5. The method of claim 3 wherein the induction motor is a single phase motor having a tapped running winding including a common portion and a plurality of series connected extended portions connected in series with the common portion with the number of disableable cylinders being the same as the number of extended running winding portions.

6. A hermetic motor-compressor unit for a refrigeration system comprising means determining system demand, an induction motor having a run winding including a plurality of series connected optionally energized winding sections and a common winding section connected in series therewith, means for supplying line voltage to the common winding section and selectively to optionally energized winding sections as determined by the system demand determining means, means for selectively partially mechanically unloading the compressor capacity in discrete steps, there being as many discrete partially unloaded states of the compressor as there are optionally energized run winding sections, and control means responsive to said means determining system demand for controlling said means for supplying line voltage and means for unloading to operate together to one of decrease and increase the number of energized winding sections as the compressor is one of loaded and unloaded, respectively, in discrete steps.

7. The motor-compressor unit of claim 6 wherein the means for determining comprises an ambient temperature responsive thermostat.

8. A motor-compressor unit of claim 6 wherein the means for selectively partially unloading is responsive to the system demand determining means.

9. The motor-compressor unit of claim 6 wherein the means determining system demand comprises a pressure responsive switch in the refrigeration system suction line.

10. The motor-compressor unit of claim 6 wherein the means determining system demand comprises means responsive to run winding current.