US2964925A - Compressor controls - Google Patents

Description

Dec. 20, 1960 N. J. JANISSE COMPRESSOR CONTROLS 2 Sheets-Sheet 1 Filed Nov. 12, 1958 CONDENSER.

Final 15 P: EVAPORATOR.

THERMOS'I'A'I COMPRESSOR,

ELE CTBIC MOTOR,

LOAD

q AIR SUPPLY & a

8 ELEC TOR. VALVE.

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INVENTOR Norman J.Jan1'.sse BY @w mw ATTORNEYS United States Patent COMPRESSOR CONTROLS Norman J. Janisse, Grafton, Wis., assignor to Johnson Service Company, Milwaukee, Wis., a corporation of Wisconsin Filed Nov. 12, 1958, Ser. No. 773,248

3 Claims. (Cl. 62-209) This invention relates to means for controlling the operation of a compressor in a refrigeration circuit of the compressor-condenser-evaporator-type. Particularly, it relates to an automatic control means arranged to vary the adjustment of means for varying the rate of flow through the compressor, e.g., a throttling means in the suction connection of the compressor.

The purpose of the control system according to the present invention is to provide a control in which the throttling means is normally controlled by a relay responsive to evaporator temperature but in which the control is transferred from the normally controlling relay to control by a second relay when the current drawn by the compressor motor is excessive, but only when this transfer would cause a reduction in flow rate. It is well known to those skilled in the art that, under various conditions encountered in the normal operation of a refrigeration system, the density of the gases entering the compressor rises, thereby materially increasing the load on the compressor. This increased load is particularly apparent when the refrigeration system is put into operation after it has stood idle for any extended period of time. Under conditions of overload, the compressor motor will draw an excessive current. Unless a motor large enough to operate under any normally encountered overload load is used, it is necessary to provide means to limit the current drawn by the motor. This current limitation may be performed and usually is performed by some type of automatic means effective to vary the load on the compressor. This load-varying means may take a variety of forms. It may be, as has been suggested above, a throttling valve to vary the rate of flow through the compressor. If a reciprocating piston-type of compressor is being used, the control system may be actuated so as to remove the load from one or more of the pistons or to increase the clearance space in the compressor cylinders, or it may be a control which will hold either the suction or the exhaust valves of the compressor open. All of these forms of control are well known in the art, and the present invention is useful regardless of the type of flow-rate-varying control which is used in the compressor. According to the present invention the throttling means, in the compressor suction connection, is provided with a fluid pressure-operated actuator which is operable to shift the throttling means through its adjusting range. This fluid pressure actuator is selectively controlled by either of two fluid pressure-actuated relays. These relays may be of either the Class I type or of the Class II type; the terms Class I and Class II being in every day use in the industry and'designating, respectively, a direct-acting and a reverse-acting relay. Each relay is of a different class. A selector valve mechanism is provided which-has two inlets, one connected to the branch line of one of the relays and the other to the branch line of the other relay.

The selector valve mechanism has a single outlet which is connected with the fluid pressure-operatedactuator. The selector valve mechanism includes a motor connected to shift the selector valve between. two operating posi- 2,984,925 Patented Dec. 20, 1960 tions, namely, a position in which it connects one of its inlets in flow communication with its outlet, and a second position in which it connects the other of its inlets with its outlet. The valve shifting motor includes two opposed working spaces; each working space being connected in flow communication with a ditferent branch line. The valve shifting motor acts in response to the difference between the pressures in the respective branch lines to interconnect its outlet with that branch line whose pressure will cause the actuator to shift the throttling means to produce the lower rate of flow through the compressor.

The first relay is responsive to a temperature produced by the evaporator. The second relay is responsive to the amount by which the current drawn by the electric motor driving the compressor exceeds a predetermined value.

It is preferred that the thermostat be a Class I instrument. Since the current-responsive relay is of the other class, it will be a Class II instrument. The valve actuator will cause the throttle to close as the pressure it receives falls. In this preferred form, the selector valve will select the lowerbranch line pressure for transmission to the actuator. This embodiment is preferred for the reason that if either branch line is damaged or ruptured, the selector valve will connect that branch line to the actuator, causing the throttling means to assume the position in which the minimum rate of flow through the compressor is established. If the thermostatically con.-. trolled relay is a reverse-acting instrument and the currentresponsive relay is a direct-acting instrument, the selector valve will select the higher branch line pressure for transmission to the actuator, and the actuator would be of the type in which rising pressure will close the throttle valve. The presence of the selector valve mechanism means. that the actuator is never connected simultaneously to the branch lines of both relays. In this way, the control function of each relay is independent of the control function of the other relay. This independent control, by different relays, results in a control system whose operation is unusually stable when contrasted to control sys-- tems in which the two relays were not selectively connected to the actuator but were connected to it simul-'-- ice taneously.

The invention will be described having reference to-the accompanying drawings, in which: a 1 v 4 Fig. 1 is a diagrammatic showing of a refrigerative device equipped with a control system embodying the present invention. 1

' Fig. 2 is a similar diagrammatic showing of an alternate arrangement of the control system.

Fig. 3 is an axial section through the selector valve mechanism. As here shown, the selector valve will transmit the higher of the two pressures supplied thereto.

Fig. 4 is an axial section of the selector valve, but here shown arranged to select the lower of the supplied pres sures.

.Fig. 5 is a sectional view, partly in elevation, showing.

" a piloted relay valve used in the system illustrated in butterfly valve 15, located in the suctionconnection of the compressor 11.- The valve is positioned by' a fluid pressure actuator 16. This actuator 16 receives fluid pressure from a selector valvemechanisrn 17, which selectively connects the actuator 16 with an overload 1 relay 18. or with a thermostatically piloted relay valve The thermostat is shown at 21 and, as shown, is responsive to the temperature of evaporator '13.

The relays 18 and 19 and the thermostat 21 each ress ve ai nder essu f m a air u pl identified b dnni'the d awin may it breach 1in2Is0 taqt w i l t o the e is l e 1 .siit i r the b nch l n 2 1st e y 4. is s nested t9 the other inlet of the selector valve 17. The thermostats bra l 24 i onn cte wi h rela '1 1.9 Pi, t ts operation; The overload relay 18 land thermostat 21 are familiar commercially available tluid pressure relay valves Whose on ant Wel sa Wi in the entral art. While the selector valve 17 and the piloted relay 19 are also commerci 11 m is not so well of these relays is e$lll ajl i nt on 1W di fers 17 a sh w :E ss

is shown in Fig.5. l

' Referring to Fig. 3, the selector valve 17 includes a housing 25' and a cover plate 26, secured together by bolts (n S Q U- Qq fines be ween the dy an sol/er plate 26 is a reversible valve assembly 27. As shown, this valve assembly c rnprises three spaced, annular dia phragms clamped at their peripheries between the body 25, two annular spacers and cover plate 26. The periphcries of the central ppenings in'the diaphragnls are la ed be e n?! fl n e ii t e .mbna emem a 28 l 3a' l at mler s acer an?! 2 nmhe b n des inlet p a es an 1whi ommun at ec iv y, th carna e shamans s2, a d as. Th od ha an e le e 'ss an 34 Web Qi mu satcs de a with 02 s? slumber 35 which 1 in urn; in on t open s mitl ni tibn with ou t Em e Ch m s 35 nd m .i n ate th we a ot r by a of radial P in he tubul r al e m e nd t e no s djacen rrcsi aid- Qone valves 3.6 an 1. w ich are r a e nwar closed pos ive con o ow from inlet passages 29 and 3 1, respectively, to the cornmunicating outlet chambers 35 and 3.5. It will readily be apparent that a dominant pressure in inlet 31 will shift the valve member 28 in a direction to open cone valve 36 and interconnect inlet 31 with the outlet 34. A dominant pressure in inlet connection 29 will unseat valve 37 whereby pressure is admitted to outlet 34 from the inlet 29. v

The selector valve shown in Fig. 4 is the same as that.

shown in Fig. 3 except that 'th'e valve assembly 27 has been reversed. With this assembly of the parts, a dominant pressure in the inlet 31 will cause cone valve 37 to be unseated thereby admitting pressure to the outlet 34 from the inlet connection 29S A dominant pressure in inlet connection 29 similarly will connect inlet 31 with the outlet 34. Thus it will be seen that the Fig. 3 arrangement selects the higher inlet pressure for transmission to the outletQwhile the Fig, 4 arrangement causes the lower inlet pressure to be transmitted tothe outlet. Ashas been pointed out, these selector valve mechanisms are commercially available More complete details concerning their construction maybe hadfrom applicants assigne'e and by reference to that assignees Apparatus Bulletin C 120.

The piloted relay 19 shown in Fig. 5 is also a corn: mercially available 'device and is fully'described in applicants assignees Instruction Buletin D 265 A. As shown in Fig. 5, the relay includes a housing having a supply cpnnection 38, an outlet or branch liueconnection 39, and a pilot pressure connection 41. The housing has three diaphragm chambers 42, 43 and 44 therein. Eharnbers 42 and 43 are in constant open communication with each other and with the outlet connection 39. A supply and43. Fluid is admitted through the supply valve front the connection 38, and is vented through exhaust I .iaeaaaas P The supply nd exhau valve 45 is shq n i9 lap position witli b'oth the ,supply and exhaust valves closed. Upward movement of the diaphragm leaves the supply valve closed and opens the exhaust valve. Downward movement of the diaphragm reverses this valving. The diaphragms in chambers 42 and 43 are of equal area. -A lever 48 is pivoted to diaphragm retainer 49 at The Pivot joint :51 is loca ed mid y between diaphragm follower screws 52 and 53 which engage the d p a m 9 h m e 42 a d r specl e y- Lever 48 carries a third diaphragm follower screw 54 which engages the diaphragm of pilot chamber 44. An adjusting springfill' engages-the lever 48, .as shown.

Because of the .egualtareas of the diaphragms in chambers 42 and 43 and the location of pivot 51, the position of lever 48 is indiiierent to the pressure which exists in the outlet connection 39. Thus, it will be apparent that as pressure in ,the pilot chamber 44 increases, the lefthand end of lever .48 will move downward, causing the supply valve to open and admit pressure fluid from the supply connection 38 into the chambers 42 and 43. This pressure fluid, in turn, flows to the outlet connection 39.

As shown in fig. 1, the outlet connection 39 of the piloted relay 19 is connected to branch line 23 and therebyt e n et of the selecto val e -1 cse out et, :i turn. is connected to supply pressure 'fluid to the damper motor 16. Movement oi the d mper ,rnotpr 16, in response to a ation 9? t e Pis n ts p ly o c o l y e t ns an o some 55.- Th s spri 5 is ne ween t e movab e element f m o 16 4 e a m 5.6 Rete r ns a ai o i 5. it will be seen. th t he ar Se s ri idly connected o the lever .48. and n reasi spr n tensi n sen es he arm 6. to are: i cpp s wi o the r ss in ch r 44, r y causing the lever 48 to return to its balanced position in h h the Su pl and al alv a e pp d.- A duction of pressure in the chamber 44 will cause the ever 8 t barn t e h ust a e, the e y entin p es-v sure fluid from the outlet connection 39 which will have the fiecrofr u in the tensi n n th pr 5 w er y the lever .48 is resto'red to its balanced position to again lap the supply and exhaust valves. From this, it will be apparent that the pressure present in the outlet connection 39 Will in accordance with variations of the pressure in the chamber .44. The pilot connection 41 s shaw sti ate wi th b anch i 2 f the thenmostat 21 in Fig. 1 The outlet connection 39 is con: nected branch line 23, while the supply connection 38 connected to the air supply, as shown.

Refer again to Fig. 1. Relay 18 is a pneumatic relay of the type shown on the Otto Patent 1,500,260 assigned to applicantls assignee. The lid which controls the bleed port is connected to be shifted progressively by a solenoid which is energized by the current flow through the sec.- ondary circuit of a transformer 57 whose primary wind,- ing is connected in series with the compressor motor Th pr s re in he branc i n 2 of this re ay remains constant so long as motor current is below a prescribed amount; When this current is exceeded, the relay ii checked-i s. will in eas ts r nc n pressure. it it rcversmacting, as it will he in the illustrated preferred crnbodi ent, the branch line pres ure w ll e cd,.. ..c l-

In a typical installation, the supply pressure would be on the order of 20 pounds per square inch. The branch line pressure trout the relay is would vary between 13 d 8 s.i. The pressure in the branch line 24 15 p.s. a a luwer limit of .i p.s.i. The pilot relay 19, under the control of the pressure in branch line 4, might between .8 and 13 p.s.i. The fluid pressure actuator 16 would be designed to be moved between its extreme positions by pressures in the8 to 13 p.s.i. range.- v In the normal operation of'the system, overload cur- 1' woul ny betw en an upper limit o rents would be encountered only under conditions of abnormally high cooling loads. When abnormally high cooling loads are encountered, the thermostat 21 will increase its branch line pressure, causing pilot relay 19 to increase its branch line pressure and cause the valve 15 to assume its maximum flow position. If the thermostat 21 is direct-acting, the pressure in branch line 23 would be 13 p.s.i. This pressure, formerly the lower one received by selector valve 17, is still not greater than the 13 p.s.i. normally present in branch line 22, and the selector valve will transmit this pressure. This abnormally high cooling load is likely to cause an excessive current to be drawn by the motor. This excessive current will cause a reduction of pressure in branch line 22, thus immediately causing the selector valve 17 to shift over and transmit this pressure to the actuator 16. A reduction of pressure in actuator 16 will permit valve 15 to move toward closed position. This will, in turn, reduce the tension in spring 55 whereby the supply valve of the relay 19 will open because the pressure in diaphragm chamber 44 will not have changed. This will charge the branch line 23 with air at 20 psi. In this way, the selector valve is prevented from shifting back until the pressure in the thermostats branch line is reduced, which is an indication that the system has restored a proper temperature at the evaporator and need not continue to operate at full capacity.

When the overload relay restores its branch line pressure to full value, the valve 15 will again be in maximum open position, restoring the tension of spring 55 and causing the pilot relay 19 to lap. Any reduction of the pressure in the thermostats branch line will vent pressure from the branch line of relay 19. When this pressure falls below the pressure in branch line 22, the selector valve 17 will resume normal position and the relay 19 will again be in control to establish the proper setting of valve 15.

The advantage of this system is that once the overload relay 18 responds to an overload current, it remains in command until the refrigeration apparatu can meet the cooling demand without producing an overload current. Thus the system operates at maximum safe capacity to overcome the abnormal cooling load.

In some installations the stability, afiorded by locating the piloted relay 19 in the position shown in Fig. 1. can be sacrificed in order to permit use of the control system to control the operation of more than one actuator, such as 16. This alternate form of control system is shown in Fig. 2. The reference numerals applied to the components of this system are the same as the reference numerals applied to the same components in the Fig. 1 system, except that they are followed by the designation prime.

As shown in Fig. 2, the refrigeration system comprises a compressor 11, a condenser 12', an evaporator 13', a throttling valve 15', and a fluid pressure actuator 16' connected to vary the position of the valve 15'. The compressor is driven by an electric motor 14. The control system comprises an air supply (indicated by legend), an overload relay 18', a selector valve 17, a thermostat 21', and a piloted relay 19.

As shown, the air supply is connected to supply air to the thermostatic relay 21' and the overload relay 18'. The branch lines 24' and 22 are connected to the inlets of the selector valve 17'. The outlet 58 of the selector valve is connected to supply air to the pilot connection of the relay 19'. The supply connection 38' of the relay 19' receives air from the air supply and, in accordance with the variation of pressure in the outlet 58, pilots the admission of air to the fluid pressure actuator 16 through the branch line 23'. The outlet connection 58 has a second branch 59, as shown, which may be connected to the piloted relay of other fluid actuators whose operation are to be controlled. This arrangement is resorted to because the flow capacity Q of the thermostats 21 and 21' is small ';compared' to that of the relays 19 and 19 and it is ,desirable, in order to assure quick response of the controlled actua tor, to provide a piloted relay which is directly associated with each fluid pressure actuator.

While the embodiment shown in Fig. 2 is not quite as stable under overload conditions as is the Fig. l embodiment, its operation is satisfactory. It should be particularly noted that in each embodiment the actuator 16 or 16' is selectively and independently controlled by the corresponding thermostat or overload relay, depending on the current drawn by the motor.

What is claimed is:

1. In a compressor-condenser-evaporator refrigerative circuit unit of the type including an electric motor to drive the compressor and throttling means adjustable to vary the rate of refrigerant flow through the compressor, the combination of control means to adjust the throttling means comprising in combination a fluid pressure-operated actuator connected with the throttling means to adjust it; a selector valve mechanism having two inlet connections and an outlet connection, said outlet connection connected to the actuator; a first fluid pressureoperated relay responsive to a temperature produced by the evaporator and having its branch line connected to supply fluid to one of the inlets of the selector valve mechanism; a second fluid pressure-operated relay responsive to the amount by which the current drawn by the electric motor exceeds a predetermined value, the second relay being of a class different from the class of said first relay and having its branch line connected to supply fluid to the other inlet of the selector valve mechanism; fluid pressure motor means to shift the selector valve mechanism and having two opposed working spaces, each space being in constant free flow communication with a different one of said branch lines, the motor means serving in response to a difference between the branch line pressure to interconnect the outlet with that inlet which will cause the actuator to adjust the throttling means to produce the lower rate of refrigerant flow.

2. The combination defined in claim 1 in which said first fluid pressure-operated relay is a direct-acting relay.

3. In a compressor-condenser-evaporator refrigerative circuit unit of the type including an electric motor connected to drive the compressor and means adjustable to vary the rate of refrigerant flow through the compressor, the combination of control means to adjust the flow-ratevarying means comprising in combination a fluid pressureoperated actuator connected with the flow-rate-varying means to adjust it; a selector valve mechanism having two inlet connections and an outlet connection, said outlet connection connected in flow communication with the actuator; a first direct-acting fluid pressure-operated relay having a supply connection, an exhaust connection and a branch line and including a supply and exhaust valve, a valve operator, a pressure motor connected to said operator and urging said valve toward supply position, and spring means connected between the movable element of said actuator and the operator and urging said supply and exhaust valve toward exhaust position,- said relay having its branch line connected to one inlet of said selector valve; a direct-acting fluid pressure-operated thermostatic relay, responsive to evaporator temperature and having a branch line connected to supply fluid to said pressure motor; a reverse-acting fluid pressure-operated relay responsive to the amount by which the current drawn by the electric motor exceeds a predetermined value and having a branch line connected to supply fluid to the other inlet of the selector valve mechanism; fluid pressure motor means to shift said selector valve mechanism and having two opposed working spaces, one space being in constant free flow communication with the branch line of said reverse-acting relay, and the other being in constant flow communication with the branch 7 fine "of said first rlay whereby the pressure diiferential between branch lines controls, the connection of the branch line's beingso chosen that the slector'v'alve mechanism transmits the lower branch line pressure to its outlet.

References Cited in the file of this patent UNITED STATES PATENTS Ross June 3,1958-

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