US2247449A

US2247449A - Compressor control

Info

Publication number: US2247449A
Application number: US145587A
Authority: US
Inventors: Charles R Neeson
Original assignee: Chrysler Corp
Current assignee: Old Carco LLC
Priority date: 1937-05-29
Filing date: 1937-05-29
Publication date: 1941-07-01
Anticipated expiration: 1958-07-01

Description

July 1,1941. c. R. NEESON COMPRESSOR CONTROL Filed May'29, 1.937

3 Sheets Sheet 1 INVENTOR E ESQN? A Z TORNEY CHAQES E2.-

c. R. NEESDN COMPRESSOR CONTROL:

Filed May 29,

July 1, 1941.

1937 3 sheets Sheet 2 www.-

42.5"1 7 \vv 1 M.

[NVE1V C H A QLES D.

MW 73:22; W

ATTOR/VEY July 1, 1941. c. R, NEESON COMPRESSOR CONTROL Filed May 29, 1937 3 Sheets-Sheet 3 R V. 8 ay ME n m T W. T QM A i L Q AM H c. y

QQ WQMEkMs R ateniecl July 1, 1941 PATET OFFICE COMPRESSOR. CONTROL ware Application May 29, 1937, Serial No. 145,587

{ Claims.

The present invention relates to refrigerating apparatus for use in the cooling of air, foodstufis, or other substances, but particularly for use in an air conditioning unit for the cooling and conditioning of air. The system derives its greatest utility in maintaining a definite temperature in rooms, enclosures, etc., usually ac- I companied by the extraction of moisture from the loading and unloading means instantaneous and accurate, in combination with a control circuit, subjecting the operation of the compressing machine to conditions of the atmosphere and of the refrigerating systemfof such nature that the reactions of the control system are as fast and as reliable as the reactions of the improved loading and unloading means. The invention is of particular utility in an improved compressing unit comprising a compressor and motor sealed into a casing so as to form an hermetically sealed compressing unit.

The improved compressing unit comprises a motor and compressor assembly in which the rotor of the motor is fastened to a centrally supported main shaft having a crank at the oppo-' site end thereof to which the compressor pistons are attached, the motor and compressor being of such characteristics as to operate efficiently at speeds as high as 1750 R. P. M. Under such conditions rapid control of the unloading means is not only desirable but practically necessary. The main shaft is also connected to an oil pump located in an oil sump at the bottom of the compressing unit for circulating oil,'which oil serves not only to cool the motor, but to operate the loading and unloading means. A feature of the present invention is the provision of satisfactory means whereby a greater quantity of oil than necessary to lubricate the bearings may be circulated about the motor to cool the same, in an oil circulating system having provision for the maintenance of a definite oil pressure in the region of. the unloading means. The oil circulates from the oil sump through an oil cooler, about the motor to cool the same, and then passes into the bearings of the main shaft and other operating parts, the regulating means for the pressure of the oil operating to return excess oil to the oil sump. Another feature of the oil circulating system is the provision of an oversized pump in order that, as the pump parts or bearings wear and become loose, thereby decreasing the total quantity of oil pumped and increasing the quantity of oil passing through the bear ings, the definite oil pressure upon the loading and unloading means may be maintained throughout the life of the compressing unit.

In order to prevent undue strains upon the operating parts and the mounting of the compressing unit, it is desirable to prevent the compressor from compressing refrigerant gas until the motor has attained full speed. This is to relieve strains and shocks on the operating parts and on the mounting and also to permit the use of a smaller, more efficient motor than would otherwise be the case, since the rotor may therefore be utilized as a flywheel to carry the pulsating load after the rotor has come to full speed. The principal object of the pressure relief mechanism located in conjunction with the unloading device is to maintain a constant pressure upon a very sensitive unloading device regardless of the quantity of oil circulated about the motor, provided such quantity is sufllcient for lubrication and cooling.

A further object of the invention is to relieve the compressor of strains which would otherwise result from surges of current such as are occasioned by lightning striking the power lines. A further object of the present invention is to decrease the initial cost and maintenance cost of refrigerating equipment, since a simple, highly efli'cient type of motor may be used if it is not required to start under high torque. Another object is to protect the mounting of a compressing unit from excessive strains and to make possible the use of a form of mounting which prevents the transmission of vibrations to the floors or walls of building in which the refrigerating equipment is placed.

A further object of the invention is to provide means to sense the temperature of air to be conditioned and to control the operation of the compressing unit in accordance therewith. A further object of the invention is to provide means to sense the pressure of the refrigerating gas compressed by the compressor and to control the operation of the compressing unit in accordance with such pressure. A further object of the invention is to provide means to sense the pressure of the gas being returned to the compressing unit after passing through the refrigerating system and to control the operation of the compressing unit in accordance with such pressure. Therefore, a further object of the invention is to provide means whereby three sets of conditions, namely, the temperature of air surrounding the refrigerating coil, the discharge pressure of the gas at the discharge or high-pressure side of the compressing unit, and the back. pressure of the gas at the suction or low-pressure side of the compressing unit, must be satisfactory in order to have the compressing unit operate. It is therefore made possible by the present invention; economically to operate an air-conditioning systemor a refrigerating system since the system will only operate when it is necessary to reduce the temperature of the air, and will only operate under pressure conditions within the refrigerating system itself such that the refrigerating system must be in satisfactory condition. In other words, the present invention provides means comprising a thermostatic cut-out, a high pressure cut-out and a low pressure cut-out, all of which must be satisfied before the compressing unit can operate, thereby preventing loss of life and the destruction of'equipment due to abnormally high pressure within the system, r id also preventing the operation of the compressing unit under such lowsuction pressures as to indicate failure of the thermostatic cut-out or high-pressure cut-out for reasons which should be investigated. A feature of the present invention is the cooperation between the unloading device and the control elements whereby instantaneous operation of the unloading device and instantaneous control of the motor is achieved.

The unloading device is an improvement upon the invention set forth in Reissue Patent No. 16,041, issued April 7, 1925, in the name of B. S. Aikman, on an improvement in a Control system for compressors.

The objects and advantages of the invention will be fully apparent from the following description, taken in connection with the accompanying drawings wherein like numerals refer to like parts throughout.

In the drawings:

Figure 1 discloses the essential elements of a preferred form of compressing unit, the figure being taken as a vertical, central section of a compressing unit such as more-fully disclosed in my copending application, Serial No. 145,585, filed concurrently herewith, to which reference may be made for more complete details of the compressing unit and its application to refrigerating machines, the present disclosure being sufficient for an understanding of the present invention;

Figure 2 is a portion of the compressing unit.

broken away from Figure 1 along line A-A;

Figure 3 is an horizontal cross-section through the compressing unit, taken along line 3-3 of Figure 1 and looking in the direction of the arrows, the figure showing the relationship of the unloading device and the pressure relieving device to the remainder of the compressor;

Figure 4 is a view similar .to Figure 3, showing the unloading device in operation;

Figure 5 is a view similar to Figure 3, showing the oil pressure relieving device in operation;

Figure 6 is a cross-section taken along line 6-6 of Figure 3 through the stem of the unloading valve and the mounting therefor;

Figure 7 is a detailed view of the unloading valve piston;

Figure 8 is a detailed view of, the pressure relieving piston; and

Figure 9 is a schematic representation of refrigerating apparatus including the present invention.

The compressing unit is hermetically sealed within a casing I3 comprising a substantially cylindrical shell 40, a top cover (not shown) and an oil sump 42 forming a detachable bottom cover for the casing. The shell is provided with a recess 43 and a ring 44, fitted within the shell, forming a passage for the oil which is thereby caused to circulate about a motor, the stator 45 of which is fitted against ring 44. The oil enters recess 43 through an oil return pipe 29, extending through the shell at the bottom of recess 43, and leaves recess 43 through an opening communicating with bore 49 which extends downward through the shell wall, the opening (not shown) being located at the top of the recess 43 in order that oil will completely surround the stator of the motor and keep it at a desirable, efficient temperature.

The rotor 5| is attached to crankshaft 52 by a key 51 and fastening means (not shown). The rotor is supported by a collar 56 resting upon the upper end of one of a pair of bearings 53 supported in a housing 54 carried by radiating arms 55 integral with the shell. The shaft 52 is provided with an enlarged head 60 bearing against the end of lower bearing 53, the head being provided with an offset crank 62. A sleeve bearing 63 surrounds the crank and is in turn surrounded by the bearing straps of piston rods 64. The bearing 63 and piston rods 66 are maintained on the crank by a cap I0 and extended locking pin 1 I.

The pin II is eccentrically positioned with respect to the axis of shaft 52 and acts as the driver for a pump rotor shaft I2 which is concentric with the axis of shaft 52. The pump rotor shaft is supported in a pump head 13 attached to a pump housing "I4 integral with the oil sump 42. The pump acts to force heated oil from the oil sump through oil discharge pipe 28 and through an oil cooler 21 of any preferred type, which in the present instance is supplied with cooling water passing through a central tube I8. Details of the pump and oil cooler may be obtained from an inspection of my copending application, Serial No. 145,586, filed concurrently herewith. The feature of the pump which is of interest to the present invention is that the pump is preferably capable of supplying more oil to the bearings than can be forced through the bearings. The reason for such an oversized pump is to insure a sufficiency of oil even though the pump parts may wear, and to insure an oil pressure always greater than necessary even though the bearings through which the oil is. forced may become excessively worn and loose.

The oil, after cooling the motor, flows through bore 49 and into a duct leading to an annular space I4I defined by housing 54, shaft 52 and the inner ends of bearings 53. Oil grooves I62, I43, I44 and I45, aid in lubricating the bearing surfaces and permit a certain quantity of oil to return to the oil sump. The oil which emerges from between upper bearing 53 and collar 56 is prevented from striking the stator 50 by a splash ring 82, mounted on arms 55, from which the oil drips into the sump through openings 83 between the arms 55. The oil which emerges from belemmas tWfieil lower bearing 53 and head 60 strikes the inner surface of the casing and also returns to the oil sump. Oil also flows from space I4I into a bore 84 extending longitudinally of the shaft and emerges through openings in bearing 92 and from between the adjacent surfaces of head 60, the bearing straps oiipiston rods 64 and cap I0. Some of this oil strikes the walls of the casing while a portion is thrown into' the pistons to lubricate the same.

The pistons 99 operate in cylindrical liners 90 inserted through discharge heads M as more fully described in my copending application, Serial No. 145,586, filed concurrently herewith. The refrigerating gas enters the compressing unit through a suction inlet 93 leading to a suction manifold 92 surrounding the liners. The gas enters the compression space by way of an annular recess 95 covered by a screen 90 which prevents the passage of foreign matter, such as scale, into the valves and also separates entrained globules of oil which are then free to return to the oil sump by way of opening I I5. The gas enters the compression space through ports 96 and valve 91, and also through auxiliary ports I00, and leaves under compression through discharge valve I05 communicating with the high pressure manifold Id. The valves are more clearly shown in my copending application, Serial No. 145,589, filed concurrently herewith, now Patent No. 2,137,965, issued November 22, 1938, in which the details of the valve seating member I08 and associated parts are described. The open end of each discharge head 9I is closed by a cap II2 against which bears a safety spring holding the valve assembly in position.

The bore i9 communicates with a cross-bore I20 leading to the unloading device and to the oil pressure relieving device as shown in Figures 3, 4 and 5. One end of the cross-bore leads to the unloader valve chamber I23 in boss I2I and the other end leads to the relief valve chamber I24 in boss I22, both bosses being cast with the casing 20. Chamber I 23 contains an unloader piston I25 and chamber I24 contains a pressure re ulating piston I26, the purposes of each of which are subsequently described.

The unloader piston I25 closely fits chamber I23 and is of lesser overall length than the chamber so as to be free to move against the spring 200 which constantly urges the piston toward the position shown in Figure 3. One end of the piston is recessed to form a shoulder defining an annular space which is always in communication with cross-bore I20. The piston is held against the force of the springby a plunger guiding member 20I which closes the outer end of the chamber I23. The spring is held within a central cavity in the piston, which cavity communicates with the cross-bore I20 by means of a small, leak-opening 202 drilled through the end of the piston, oil thereby being returned to the interior of the casing through an opening 209 connecting the interior of the casing and chamber I23. The piston is provided with a plurality of circumferential surface grooves 200 which serve not only to prevent material leakage of oil around the piston, but are also spaced apart at a distance less than the length of travel of the piston so as to collect any grit from the cylinder walls and thereby prevent excessive wear and scoring. A constant fiow of a definite amount of oil, under a constant pressure as will presently appear, is therefore permitted to flow through leak opening 202.

The chamber I 23 is closed by the plunger guiding member 201 which is seated in an enlarged cavity 205, the outer end of which is closed by a cap 206. The guiding member is held against its seat by a spring 201 interposed between a flange on the member and a socket in the cap. The spring holds the member in position under all circumstances, its purpose being firmly to seat the member to seal the chamber I23, it being thereby possible to drill cavity 205, chamber I23, and opening 203 from the outer surface of the casing with the aid of asimple set of locating fixtures. The member 20I is placed in its permanent position after spring 200 and piston I25 are assembled from the outer end of the cavity 205, the inner surface of member 20I forming an abutment against which the raised central portion of the piston strikes as it is urged forward by spring 200. A plunger 208 is guided by member 20I and is held in the position shown in Fig. 3 by the central portion of piston I25 when the compressor is idle. The opposite end of plunger 208 bears against the stem of a valve 209, the stem being triangular in shape and freely slidable within a guiding bore 2I0 in the cap 206. The sides of the triangular stem define .small passageways through which gas may escape when the valve 209 is raised from its seat, as shown in Fig. 3. A spring 2 bears against the head of the valve, the spring being compressed between the valve and a pipe fitting 2I2 threaded into the cap, the pipe fitting leading to a by-pass pipe 2| 3. When the piston I25 is forced away from member 20I as shown in Fig. 4, the spring 2II causes the valve to close as shown, the valve stem causing the plunger 208 to extend into chamber I23. If the oil pressure in passage I20 should decrease below the diflerence between the normal strength of spring 2 and the normal strength of spring 200, the piston will again move to the position shown in Fig. 3, causing the plunger to unseat valve 209. The spring 2II has much less strength than spring 200, the difference in strength of the two springs being slightly less than the force exerted by the oil pump when sufiicient oil is being passed through the unit to lubricate the bearings. If the pump should fail, or one of the passageways should become blocked, or the motor should stop, the oil pressure would drop and permit valve 209 to open, thereby unloading the compressor.

Cavity 205 communicates with the interior of the casing by way of an opening 2I5 drilled through the casing wall alongside of chamber I23. Pipe 2I3 leads from cap 206 to one end of the discharge manifold I4 which is in communication with all of the cylinders of the compressor and with the refrigerating apparatus, As long as valve 209 is open, gas compressed by the pistons will tend to follow the path of least resistance and, instead of going through the condenser, expansion valvr and evaporator, will return to the interior of the casing by way of pipe 2I3 and valve 209 and thence into the suction manifold 92 by way of openings M5, 83 and II5. Opening II5 may be supplemented by grooves 2I6 (Fig. 1) in the sides of the cylinder liners through which gas may be drawn from the interior of the casing in case the opening II5 should be blocked by oil dripping from the interior of the suction manifold. The gas therefore, travels through a short, open circuit from and into the interior of the casing as long as, valve 209 is open. Valve 209 will stay open until the oil pressure is sufficient to retract the piston I25, whereupon valve 209 will close and the gas will be forced through its refrigerating cycle.

In order to assure proper operation of the unloading device and proper lubrication of the bearings, the pump encased in housing 14 is preferably made larger than necessary. This permits erating gas and oil within the casing. The bearings aretherefore designed to permit a fairly small quantity of oil to escape, which quantity would not be sufilcient properly to cool the motor to its efilcient working temperature.

Also, as the bearings wear from long use, the quantity of I 7 oil which will escape therefrom as previously de scribed, will naturally increase. If the pump were designed originally to create a certain pressure due to the flow of a certain amount of oil through the bearings, this pressure would drop as the bearings wear, thereby upsetting the balance of the unloading valve assembly. In order, therefore, to permit the use of a greater variable flow of cooling oil and at the same time maintain a definite oil pressure, the pressure relieving device shown in Figs. 3 and 5 is utilized. The device comprises a pressure regulating piston I28 located in relief valve chamber I24. The piston is normally maintained inthe position shown in Fig. 3 by a spring 220 held against the piston by a plug 22I-threaded into the boss I22 and closing the chamber I24. The chamber I24 communicates with an opening 222 in the wall of the casing into which is threaded a pipe connection 223 leading to an oil relief pipe 224. When the oil pressure increases to a point beyond the strength of spring 220, the piston I26 will be retracted, as shown in Fig.5, thereby uncovering the opening 222 and permitting oil to flow through pipe 224 into the oil sump through an opening 225 in the lower end of the casing. The piston I26 is formed with a valve head 221 of less width than the diameter of theopening 222 and comprises a reduced portion 228 immediately beyond the valve head. The reduced portion 228 communlcates with the closed end of chamber I2t through an opening 229 and connecting bore 230 in the body of the piston, the reduced portion 228 being always in communication with the opening 222 so as to prevent oil which may creep past the piston from looking the piston in the position shown in Fig. 3.

With certain types of controls it may happen that the compressor motor will cycle under certain operating conditions, which is to say that until a safety switch or other means of opening the motor circuit is operated the motor may start and stop in very rapid sequence. The same condition may occur if a demonstrator rapidly connests and disconnects the motor to and from the source of power. Another circumstance which must be guarded against .is the condition created by a powerful surge of voltage such as caused by a bolt of lightning striking the power lines, this condition being familiarly referred to as a locked motor, meaning that the rotor is locked against rotation by conflicting surges of current.

Under any of these conditions the motor might burn out If forced to resume normal operation against the compression of the gas in the discharge chamber, which should be about to 1'75 pounds, if the refrigerant is dichlorodifluoromethane (CClaFz), or higher under certain conditions. Since the motor should be as small as possible and, in order to be eflicient, should not be designed to have a high starting torque, the unloader valve should be immediately brought into operation at the instant the rotor stops, In order to assure this happening the leak opening 202 is provided. The constant stream of oil which flows through the opening 202 is accounted for in designing springs 200, 2 and 220 so that when the motor is operating at normal speed with a constant quantity of oil flowing through opening 202 and an increasing quantity of oil flowing through the bearings, the piston I25 will be in th position shown in Fig. 4 thereby closing valve 2&3, and the piston I26 may be held in the position shown in Fig. 5 or slowly moving from opened to closed positionas the pressure created by the oil pump mayyary, If themotor should stop, however, the piston I25 could notact rapidly enough to protect the unit were it not that the opening 202 permits the escape within areasonably short space of time of any oil tending to hold the piston in retracted position, in spite of the fact that the piston I26 thereupon moves so as to decrease the available space for the oil to occupy.

Figur 9 discloses the electrical circuits, the course taken by'the refrigerating medium and the paths of the oil and water. The diagram illustrates the basic wiring required for a singlephase, or two-phase, or three-phase compressor motor, as indicated by the four power lines 240, MI, 242, and 243, the specific example being for a three-phase motor. If a single-phase compressor motor is employed, only wires 240 and 242 would be necessary; a three-phase compressor motor requires wires 240, MI and 242;

and a two-phase compressor motor requires use or all four wires. The power lines maybe disconnected by a manually operated safety switch 244 which must be closed in order to'have the automatic control circuit operate the control switch 245 also interposed across the power lines. The current in the power lines may be supplied at 110, 220, 440 or any common commercial voltage, the compressor motor (of which the stator is indicated at 50 and the rotor at 5|), being correspondingly selected. The control circuit is connected to the power lines by

wires

246 and 247 leading to the primary of a transformer 248,

which reduces the voltage to that desired for a standard fan motor 249. By connecting wires 248 and 201 to power lines 240'and 242, respectlvely, and passing the current obtained through the transformer, it is possible to use a standard fan motor in an air conditioning system in which the compressor is driven by a motor chosen to meet local power characteristics The fan motor may thus always be a single-phase, -volt motor since the fan motor of an air conditioning unit is usually of this character, The compressor motor however, may be a motor of from one to possibly several hundred horsepower and may require direct line voltage. The transformer 248 is therefore preferably selected to maintain the voltage between the wires 250 and 25I, leading to the fan motor 249, at 110 volts.

In order .to control the compressor motor, a number of automatic controls may be utilized to operate the switch 245. Such controls usually operate more satisfactorily at much lower voltage than that required to drive a motor and therefore further reduction of the Voltage is desirable. To obtain this lower voltage, such as 24 volts,

wires

252 and 253 are connected to wires 256 and 26!, respectively. A switch 254 in wire 25! is interposed between transformer 248 and wire 253, the switch controlling the operation of the fan motor 249. A switch 255 is placed in wire 253 to control the flow of current to the primary of a step-down transformer 256, by which 24-volt current is induced in

wires

251 and 258 leading to the control elements. Switches 254 and 255 are schematically shown as being controlled by a single button 259, to be closed in sequence rather than simultaneously. The switch 254 closes before switch 255 in order to insure the starting of fan motor 249 before current flows through the control elements, and the stopping of fan motor 246 only after current ceases flowing through the control elements.

Wire 251 leads to a wire 266 through three .switches, 26!, 262 and 263, placed in series. Wire 266 leads to a wire 264 through a magnetic switch 265. Wire 264 leads to a wire 266 which leads back to wire 266 through switches 261, 268 and 269; placed in series. Wire 264 is also connected to a wire 216 having an induction coil 21! therein and which leads to a circuit breaker 212 placed opposite line 242 between the switch 245 and stator 56. Circuit breaker 212 is controlled by a thermostatic element 213 placed opposite a noninductive resistance coil 214 in line 242. Circuit breaker 212 connects wire 216 to a wire 215 which also leads to one contact of a circuit breaker 216 controlled by a thermostatic element 211 placed opposite a non-inductive resistance coil 218 in line 266. Circuit breaker 216 bridges the gap between wire 215 and the wire 258 which goes back to the secondary of transformer 256.

Switches 26! and 261 are connected together and are operated by a push-rod connected to a bellows 286., Switches 262 and 268 are connected together and operated by a push-rod and bellows 28!. Switches 263 and 269 are connected together and operated by a push-rod and bellows 282. The switches 26!, 261, 262, and 268 wil close upon expansion of their respective bellows while the switches 263 and 268 will close upon contraction of the bellows 282.

In order to appreciate the invention, the refrigerating apparatus and the compressor are indicated schematically as shown at the right of Fig. 9. Bellows 286 is shown as being connected by a pipe 283 to a sealed container 284 holding an expansible fluid and placed in the air stream of the conditioner 22 between the dust filter or screen 23 and the evaporator coil 286, by means of which the temperature of the air drawn into the conditioner by the fan associated with fan motor 249 may be made to actuate the switches 26! and 261. Bellows 28! is shown as be n connected to the suction pipe 24 by a tube 281, while bellows 282 is shown as being connected-to the discharge manifold !4 by a tube 268. Upon expansion of bellows 286, due to a rise in tem erature of the air entering the condit oner 22, switches 26'! and 26! will close in the order named against the force of a spring 296: upon contraction of bellows 28!, due to a lowered pressure of the gas in suction pipe 24, switches 268 and 262 will open in the order named against the tension of a spring 29!; and upon expansion of bellows 282, due to the increasing pressure of the gas in discharge manifold I4, switches 269 and 263 will open in the order named against the force of a spring 292. Bellows 286 is designed to open its switches 26! and 261 lithe temperature of the air entering the conditioner drops below a desirable minimum of, for example, 72 F.; bellows 28! is designed to open its switches 262 and 268 if the suction pressure in pipe 24 drops below a desirable,minimum of, for example, 25pounds; and bellows 282 is designed to open its switches 263 and 269 if the discharge pressure in manifold l4 rises above a desirable maximum of, for example, 200 pounds. Switches 26! and 261 therefore constitute a low temperature cut-out; switches 262 and 268, a low pressure cut-out;

and switches 263 and 269 a high pressure cutout.

Since the switches are in series, all the conditions of pressure and temperaturemust be such that all the switches are closed before the compressor can operate. If it is assumed that the compressor has been idle for some time, the pressure in pipe 24 and in manifold M will be equal due to the return of compressed gas through the unloader valve 269. If the fan switch 254 is now closed, causing air at, for example, 96 F. to be drawn over the thermostatic element 284, switches 26! and 261 will be soon closed and, since switches 262, 263, 268 and 269 would already be closed because the pressure in pipe 24 is not excessively low nor the pressure in manifold I4 excessively high, wire 251 will be connected to wire 266. When the control circuit switch 255 is likewise closed the primary of the transformer 256 may be excited and a current induced in the secondary of transformer 256. No current will be induced in the secondary of transformer 256 however, unless switch 255 is closed; and current will only flow as long as the air surrounding element 284 is at a higher temperature than the desirable minimum. If all the switches are closed, current will flow through wire 251, switches 26!, 262, 263 to the junction of wire 266, from the junction of wire 266 through switches 269, 268, and 261 to wire 266, through inductance coil 21! to wire 216, across circuit-breaker 212 to wire 215, and across circuit-breaker 216 to wire 258, which completes the circuit to the transformer 256. This results in energizing coil 21!, which moves the magnetic switch 265 to bridge the contacts at the ends of wires 266 and 264 and to close switch 245, thereby causing the compressor motor to become connected to the power lines. Current will now fiow from wire 251 through switches 26!, 262. and 263, wire 266, across magnetic switch 265 to wire 264, which is connected to wire 258 through the coil 21!, and the circuit breakers 212 and 216.

If one or more of the pressure and temperature conditions under which the compressor motor can operate is now upset so that one of the bellows begins to contract or expand as the case may be, the corresponding switch 261, 268, o 269 will break before the corresponding switch 26!. 262, or 263 will break as previously explained. In such case the first circuit to lose current of the two circuits leading to coil 21! will be the one including wire 266, current, however, continuing to flow through coil 21! by way of wires 266 and 264. The compressor motor will continue to operate since the magnetic switch 265 and switch 245 are held in operative position by the energized coil 21!. If the degree of unscttlement of the condition causing the bellows to operate is very slight, the opened switch may again close, re-establishlng the flow of current through wire 266. Similarly, if the condition is at the point of passing from satisfactory to unsatisfactory, the vibrations of the compressor, motors, fan, or adjacent machinery, might cause the switches to vibrate. Were it not for the continued energizing of coil 21'! this would result in a series of rapidly interrupted periods of operation of the compressor, causing undue strains on various moving parts. However, if the condition which is unsettled continues to progress toward the unsatisfactory state, the corresponding switch 26!, 262, or 263 will also open, thereby breaking line 251 which leads to both of the parallel circuits to the coil 21!, causing switch 245 to open and the compressor to come to a complete stop. Under such circumstances the compressor cannot again start until all of the switches 26!, 262, 263, 261, 268, and 269 are concurrently closed.

Switch 26! is preferably designed to operate at a predetermined temperature, such as 72, while switch 26! operates at a predetermined temperature of 72 plus one or two degrees. Switch 262 is preferably designed to operate at a predetermined suction pressure, such as 25 pounds, while switch 268 operates at a predetermined suction pressure of 25 pounds plus several pounds. Switch 263 is preferably designed to operate at a predetermined discharge pressure, such as 200 pounds, while switch 269 operates at a predetermined discharge pressure of 200 pounds minus several pounds. Therefore, when the compressor is inactive and the suction and discharge pressures have balanced through the compressor so as to cause the pressure in the discharge and suction pipes to be equalized at some pressure, such as 75 pounds, all of the switches 26!, 262, 269, and 2168 are closed and the compressor will begin to operatewhen the temperature rises to 72, causing switch 26! to close, and then to 72 plus, causing switch 26'! toclose. Now if the temperature lowers slightly below 72 plus, switch 261i opens but the compressor continues to operate because of the parallel holding circuit through wire 260, holding switch 265, and wire 264. Similarly, if the suction pressure lowers to 25 pounds plus, switch 268 will open but the compressor will continue to operate through the holding circuit. Similarly, if the dischar e pressure rises to 200 pounds minus, switch 269 will open but the compressor will continue to operate because of the holding circuit. However, if the temperature continues to drop to 72, switch 26! will open and the compressor will stop since neither circuit leading to the coil 21! will be complete: or if the suction pressure continues to drop to 25 pounds, switch 262 will open, thus stopping the compressor; or, if the discharge pressure rises to 200 pounds, switch 263 will open, thus stopping the compressor.

If the motor stopped due to an excess of pressure in discharge manifold !4 only, it would start as soon as sufflcient gas had returned to the suction or low-pressure side through the unloading valve 209 to reduce the pressure in discharge manifold !4 below the pressure at which switch 269 opens (200 pounds minus several pounds in the above example), In case, on the other hand. the compressor stopped due to a lowering of pressure in suction pipe 24 it would only start again when sufficient gas had returned from the high-pressure side to bring th pressure in pipe 24 above the pressure at which switch 268 opens (25 pounds plus several pounds in the above example), subject to manual operation of a safety latch 298, as subsequently explained, If the compressor stopped only because the temperature of the air passing over bulb 284, adjacent the evaporator 286 dropped below the set temperature, the compressor would start only when the air temperature rose sufficiently to close switches 26! and 261. In any case the compressor would only start when all of the switches 26!, 262, 263, 261, 268 and 269 had made contact, thereby preventing a series of false starts, which might otherwise occur, particularly if adjoining machinery caused vibrations to be transmitted to the switch-board.

The foregoing operations occur under conditions such as the following: The outside air fluctuates in temperature and it is desirable only to operate the conditioner when the air is too warm for comfort. Bellows 280 operates against a return mechanism exemplified by spring 290 so that switches 26! and 261 are always free to open or close in accordance with the demand created by the temperature of the air. Bellows 282 on the other hand is influenced by the pressure of the gas compressed by the compressor. The gas is compressed to a certain desirable pressure, which raises its temperature. The cooling water flowing through the condenser l6 removes heat from the compressed gas and thereby causes the gas to liquefy at the compression pressure. The expansion valve 295 is preferably of the type having an adjustable orifice, the extent of opening of the orifice being controlled by pressure transmitted to the valve through a tube 296 connected to a closed container 29'! holding an expandible fluid, which container is placed in heattransmitting relationship with the suction pipe 24. As the outside air fluctuates in temperature, the amount of liquid to be evaporated in the evaporator coil 286 must fluctuate in order to maintain conditioned air at the desired temperature. If the temperature of the air entering conditioner 22 rises, the rate of heat transmission from the air to the refrigerating medium inside of coil 286 also rises, which rise, sensed by the fluid in container 291, results in the continuous increase in size of the orifice in expansion valve 295, thereby permitting an increasing amount of liquefied refrigerant to be evaporated in the coil 286 in order to carry the increasing load. The reverse of the foregoing is likewise true, so that as the temperature of the air entering conditioner 22 drops, the orifice in expansion valve 295 is reduced to permit a lesser quantity of refrigerant to be evaporated in the coil 286. Since the compressor is designed to operate at a constant speed, its displacement at this speed is'sufflcient to compress all of the gaseous refrigerant passing through pipe 24 and this rate of flow is the result of full load operation of the evaporating coil 286. If for any reason, the pressure in pipe I4 becomes excessive, as would be the case when valve 295 closes, bellows 282 expands and opens switches 263 and 269, thereby stopping the compressor. If the flow of refrigerant through the valve 295 is equivalent to a fraction of the flow representing full load, then the compressor will operate until the pressure in pipe !4 and condenser !6 rises to the amount sufficient to cause bellows 262 to open switches 263 and 269; but after a lapse of time during which refrigerant continues passing through valve 295, the pressure in condenser i6 and manifold M will be sufficiently reduced so that bellows 282 will contract. thus permitting the closing of switches 263 and 269 by which the compressor is thrown back into operation. Conditions may arise under which more gas will be forced into the condenser I6 than the condenser is designed t o hold, in which case the bellows 282 would expand to open switches 2G3 and 269, thereby stopping the compressor. The pressures in the refrigerant system on opposite sides of expansion valve 295 would balance as previously described and switches 263 and 269 would be closed due to the force of spring 292, thereby re-starting the compressor. However, if the high pressure in condenser I6 is caused by the closing of valve 295 due to a drop in temperature of the outside air low enough to result in opening switches MI and 261, the compressor still could not operate,

Bellows 28I will open switches 262 and 268 if the pressure in suction pipe 24 drops below a minimum, which would probably be due to the substantial or complete closing of the orifice in valve 295. This may be normal due to a sharp drop in temperature of the air entering conditioner 22, but the thermostatic cut-out 284 is preferably designed to break the motor circuit long before the expansion valve 295 becomes completely closed so that under normal conditions the low-pressure cut-out is unnecessary. However, conditions may arise such as a break in one of the pipes, or failure of bellows 280, or failure of the fan motor 249, etc., under which conditions the thermostatic control element 284 might call for operation of the compressor motor when the compressor should not operate. One such condition would be created by the complete blocking of air inlet 23, with the fan in operation exhausting the air from the interior of the conditioning unit 22. This condition may result in damage to the coils, due to the building up of frost and ice, or to other parts. Therefore, the bellows 28I is preferably designed to operate automatically in one direction only, since the reasons for its existence are abnormal. Whenever the bellows-28l opefates to open switches 262 and 263, something is wrong to which attention should be given, and for this reason a safety latch 298 actuated by a spring 299 is preferably provided to prevent bellows 28I from again closing the switches 262 and 268 after the compressor stops due to low suction pressure.

The circuit breakers 212 and 216 are placed in series with the coil 21I, each circuit breaker being normally held in contact-making position by its associated thermostatic element 213 and 211 respectively, as long as the current through the power lines leading to the compressor motor remains normal. However, if an abnormal surge of current passes through the power lines, or if the motor becomes overloaded, the resistance coils 212 and 218 will create heat suflicient to expand the associated thermostatic elements far enough to break the control circuit. The circuit breakers are preferably of the type requiring manual resetting in order to prevent reoperation of the compressor until the wiring has been inspected. If the motor is a 2-phase or 3-phase motor, the circuit breakers 212 and 216 are required; whereas, if it is a single-phase motor, circuit breaker 216 only would be required.

Fig. 9 also illustrates the oil circuit diagrammatically as follows: The pump 15 is indicated assume motor, and then passes Into bore 49.

I reducing valve I26 is indicated as by-passing oil through oil relief pipe 224 to the oil sump 42. Piston I and plunger 208 are shown as controlling the unloader valve 209 which permits gas to pass from the discharge manifold I4 by way bf pipe 2 I3 into the suction side of the compressor by way of opening 2I5. The leak opening 202 and oil return opening 203 are also indicated in the diagram.

as a constant delivery pump, taking oil from the A feature which is of importance to efficient operation is also indicated, comprising the branch 300 of tube 288, which branch leads to a throttle valve 30I controlling the flow of water from pipe I1, through the condenser I6, into the pipe I8, and through the oil cooler 21. The amount of water used by the system may therefore be controlled by the demand upon the system since throttle valve 30! is designed to close the water pipe as soon'as the pressures in the system balance due to opening of unloading valve 209, and to regulate the flow of water in accordance with the demand therefor when the compressor is in operation, which demand isproportional to the pressure in the discharge manifold I4. In other words, as the temperature increases, more gas is compressed and more water is required not only to condense the gas in the candenser, but to cool the oil in the oil cooler.

In sulmnarizing it is apparent that the refrigerating system may be designed to operate under many conditions such as the following:

The compressed gas may be under a pressure of from to pounds, it being apparent that the higher the temperature of the air entering conditioner 22, the more gas should be compressed in order to satisfy the demand as sensed by the thermostatic element 291 controlling the expansion valve 295. Likewise, the pressure of the gas in the suction side of the system may be from 30 pounds to 50 pounds, depending upon the temperature of the air entering the conditioner 22, since as the temperature varies, thereby causing a variance in the size of the orifice in the expansion valve 295, the amount and pressure of the gas admitted to the suction side will also vary. The high-pressure cu -out is designed however, to prevent the operation of the compressing unit after the pressure of the high pressure gas passes a definite limit, such as pounds, in order to prevent the failure of com pressor parts if the expansion valve 295 should become jammed in the closed position. The low pressure cut-out is designed to operate in case.

the pressure of the gas in the suction side drops below a definite limit, such as 25 pounds, due to failure of the expansion valve to open, or other reasons, such as the placing of an obstruction over the'air inlet to an air conditioning unit. The thermostatic cut-out is designed to operate if the temperature of the air being drawn through an air conditioning unit, or the temperature maintained within a refrigerating cabinet, dr ps below a predetermined minimum temp erat re. The construction of each control device-is such that the system will automatically start to operate if the gas in the discharge side drops in pressure to a safe degree, or if the temperature on the air s 1 1rrounding the evaporator coil rises,

The low-pressure cut-out, however, is designed not to permit reoperation unless the latch 296 is manually released. As soon as the compressing unit stops the unloader valve opens, thereby lowering the pressure in the discharge side, and it is permissible for the compressor to commence operation as soon as the unloader valve balances the system if the motor stopped solely due to the operation of the high-pressure cut-out, since such operation is due to conditions indicating that the compressor is operating satisfactorily and that the reason for the increased pressure lies in the condenser, evaporator or other parts of the refrigerating mechanism. It is undesirable however, for the compressor to re-commence,

operation if the motor stopped solely due to operation of the low-pressure cut-out, since action of the low-pressure cut-out indicates that some 7 condition exists in the system which should be remedied before permitting the compressor 'to operate. Also, it is permissible to have the compressor commence reoperation if the motor stopped solely due to a drop in temperature of the air entering the conditioner and surrounding the evaporator coil, since a drop in temperature is normal and tobe expected. However, if the low temperature cut-out operates because of some failure in the system, it is apparent that either the low-pressure cut-out or the high-pressure cut-out, or perhaps both, will have operated at the same time, and subsequent reclosing of the switches controlled by the low temperature cut-out cannot result in the starting of the compressor motor until the other controls are satisfled. 1

It is apparent that means are provided to prevent the operation of the compressing unit in spite of all three of the controls being satisfied, if the reason for stopping has been an abnormal surge of current, or overloading, or short-circuiting of the stator windings, such as to cause the non-inductive resistance coils to become overheated. Under such conditions the entire control circuit would be broken, thereby preventing the reoperation of the compressing unit. until such time as the circuit breakers had been manually re-set after inspection of the apparatus.

It is apparent that the control elements are so designed as to operate a holding circuit including switches 26l, 262 and 263, wire 260, magnetic switch 265, and wires 264 and 210) for the inductance coil 21 l, which holding circuit prevents discontinuance of operation unless a condition is clearly unsatisfactory; and a starting circuit (including switches 26!, 262, 263, 269, 268 and 261, and wires 266 and 210) for the inductance coil 21 I, which starting circuit must be closed in order I to start operation, and which closes only when all conditions are clearly satisfactory. However, it is also apparent that the starting circuit includes a portion which is in parallel with a portion of the holding circuit, the said portion of the starting circuit including switches 269, 268, 261 and wire 266, and the said portion of the holding circuit including wire 260, magnetic switch 265 and wire 264,50 that the parallel portion of the starting circuit may be broken without effecting the operation of the unit until and unless one or more of the conditions progresses toward the unsatisfactory state to such an extent that the holding circuit will also be broken,

It is to be appreciated that the control circuit shown herein is diagrammatically set forth and that details of the switches, bellows and valves need not be disclosed for proper understanding enemas of the invention, such details being well known and forming no part of my'invention. It is also apparent that various modifications in arrangement and detail will be apparent to those skilled in the art, all such as come within the scope of the following claims being considered as a form of my invention.

Lclaim:

1. In a refrigerating system including a com pressing unit comprising a motor, a compressor connected to said motor, a pump operating in unison with said motor, a circulatory system through which a lubricating medium is forced by said pump to cool said motor and lubricate said compressor, pressure relief mechanism in said circulatory system for maintaining the pressure created by said pump at a constant value and unloading means controlled by the pressure of said lubricating. medium to unload said'compressor when the motor stops and to load said compressor when the motor attains full speed, the combination with said compressing unit of a main switch for connecting said motor to a source of power and means for operating said main switch to start or stop said motor, said means including a control circuit for said main switch comprising a control switch, a maintaining switch and means to place said maintaining switch in parallel with said control switch when said main switch is closed whereby to form a holding circuit for said main switch.

2. In a refrigerating system including a compressing unit comprising a motor, a compressor connected to said motor, a pump operating in unison with said motor, a circulatory system through which a lubricating medium is forced by said pump to cool said motor and lubricate said compressor, pressure relief mechanism in said circulatory system for maintaining the pressure created by said pump at a constant value, and unloading means controlled by the pressure of said lubricating medium to unload said compressor when the motor stops and to load said compressor when the motor attains full speed, the combination with said compressing unit of a main switch for connecting said motor to a source of power and means for operating said main switch to start or stop said motor, said means including a control circuit for said main switch comprising a first portion in series with a second portion of said circuit and a third portion in parallel with said second portion when said main switch is closed whereby said third portion becomes a part of a holding circuit for said main switch excluding said second portion, and a a bridge controlled by said main switch for placing said third portion in parallel with said second portion when said main switch is closed,

3. In a refrigerating system having high-pressure and low-pressure sides and a compressor discharging a refrigerating medium to said highpressure side and drawing said medium from said low-pressure side, a fluid pressure system for circulating a lubricating-medium through said compressor when said compressor is in operation, and means controlled by said fluid pressure system to load the compressor when the compressor is in operation and to unload the compressor by directly connecting the high-pressure and lowpressure sides as soon as the compressor ceases operating, a control circuit for said compressor comprising switches and controls to open one of said switches if the pressure in the high-pressure side rises above a predetermined maximum and another of said switches if the temperature at the region of the low-pressure side falls below a predetermined minimum, means to reclose the switch affected by said pressure if said pressure falls below said predetermined maximum as a result of the operation of said unloading means, and means to reclose the switch afiected by said temperature if said temperature returns to a point above said predetermined minimum, said switches being in series whereby reoperation of the compressor is prevented if the high pressure is due to low temperature at the region of said low-pressure side.

4. In a refrigerating system having high-pressure and low-pressure sides and a'compressor discharging a refrigerating medium to said highpressure side and drawing said medium from said low-pressure side, a control circuit for said compressor comprising switches in series and controls to open one of said switches ii the pressure in the high-pressure side rises above a predetermined maximum, another of said switches if the temperature at the region of the low-pressure side falls below a predetermined minimum temperature, and a third switch if the pressure in the low-pressure side falls below a predetermined minimum pressure, means to reclose said firstmentioned and second-mentioned switches if the pressure in the high-pressure side falls below said predetermined maximum and the temperature at the region of the low-pressure side rises above said predetermined minimum, and means to latch said third switch in open position whereby to prevent reoperation of the compressor if the pressure in said low-pressure side once falls below said predetermined minimum.

5. In a refrigerating system having high-pressure and low-pressure sides and a compressor discharging a refrigerating medium to said highpressure side and drawing said medium from said low-pressure side, a control circuit for said compressor comprising a device responsive to the pressure in the low-pressure side of the system and a switch connected thereto to beheld thereby in circuit-closing position when the pressure in the low-pressure side is above a predetermined minimum and moved thereby to circuit-breaking position if the pressure in the low-pressure side falls below said predetermined minimum, and means to latch said switch in circuit-breaking position when moved to such position whereby to prevent reoperation of said compressor after bein stopped by the action of said device.

6. In a refrigerating system having high-pressure and low-pressure sides and a compressor discharging a refrigerating medium to said highpressure side and drawing said medium from said low-pressure side, a fluid circulating system for circulating a lubricating and cooling medium through said compressor comprising a pump operating in unison with said compressor, said pump having greater capacity than necessary to lubricate said compressor whereby to assure a copious flow of lubricating medium for cooling purposes, an unloading device controlled by the pressure of said fluid circulating system to unload the compressor by directly connecting the highpressure and low-pressure sides when the compressor stops and to load the compressor when the compressor is in operation, a pressure relief mechanism for by-passing the excess lubricatingmedium around said unloading device, a control circuit for said compressor comprising switches and controls to open one of said switches if the pressure in the high-pressure side rises above a predetermined maximum, another of said switches if the temperature at the region of the low-pressure side falls below a predetermined temperature, and a third switch if the pressure in the low-pressure side falls below a predetermined minimum, means to reclose said first-mentioned switch if the pressure in the high-pressure side falls below said predetermined maximum as a result of the operation of said unloading device, means to reclose said second-mentioned switch if the temperature at the region of the low-pressure side rises above said predetermined minimum, and means to latch the third-mentioned switch in open position, said switches being in series whereby said compressor will cease operation if the pressure in the high-pressure side rises V i above said predetermined maximum, or if the temperature at the region of the low-pressure side falls below said predetermined minimum, and will recommence operation if the pressure in the high-pressure side drops below said predetermined maximum and the temperature at the region of the low-pressure side rises above said predetermined minimum, but cannot recommence operation once said latching'means has latched the third-mentioned switch in open position due to the pressure in the low-pressure side passing below said predetermined minimum,

CHARLES R. NEESON.