US3673811A

US3673811A - Control device for pressure lubricated compressors

Info

Publication number: US3673811A
Application number: US72464A
Authority: US
Inventors: Jay C Adams; Russell E Cook
Original assignee: Ranco Inc
Current assignee: Ranco Inc of Delaware
Priority date: 1970-09-15
Filing date: 1970-09-15
Publication date: 1972-07-04
Anticipated expiration: 1989-07-04

Abstract

Operation of an electric motor driving a refrigerant compressor having forced oil lubrication is controlled by a solenoid operated switch, the solenoid circuit including a thermostatic switch in series with a parallel connected timer switch and oil pressure differential responsive switching means. The timer switch is operated by a relay coil energized by a timing circuit which includes voltage biased switching means having alternate output circuits, one of which includes the relay coil. The switching means is controlled by a capacitor which when charged, causes the timing switching means to change the effective flow of current from one output circuit to the other. In one form of the invention the relay coil is connected in initially energized output circuit of the switching means and is shunted to open the timer switch when the switching means is biased to change energization of the output circuits. The pressure differential responsive switch shunts the timer switch to provide a holding circuit for the solenoid after opening of the timer switch and simultaneously deenergizes the timing circuit. In another form of the invention, the relay coil is connected in the other output circuit and is not energized for a period determined by charging of the capacitor to a given voltage. In this form the pressure responsive switch does not shunt the timer switch and is effective to deenergize the timer circuit in response to normal oil pressures.

Description

United States Patent Adams et a1.

I 1 July 4,1972

I541 CONTROL DEVICE FOR PRESSURE LUBRICATED COMPRESSORS [72] Inventors: Jay C. Adams; Russell E. Cook, both of Columbus, Ohio [73] Assignee: Ranco Incorporated, Columbus, Ohio [22] Filed: Sept. 15, 1970 [21] Appl. No.: 72,464

11/1960 Williams..

8/1962 Olson ..417/13 Primary ExaminerMeyer Perlin AltomeyWatts, Hoffmann, Fisher 8!. Heinke [57] ABSTRACT Operation of an electric motor driving a refrigerant compressor having forced oil lubrication is controlled by a solenoid operated switch, the solenoid circuit including a thermostatic switch in series with a parallel connected timer switch and oil pressure differential responsive switching means. The timer switch is operated by a relay coil energized by a timing circuit which includes voltage biased switching means having alternate output circuits, one of which includes the relay coil. The switching means is controlled by a capacitor which when charged, causes the timing switching means to change the effective flow of current from one output circuit to the other. In one form of the invention the relay coil is connected in initially energized output circuit of the switching means and is shunted to open the timer switch when the switching means is biased to change energization of the output circuits. The pressure differential responsive switch shunts the timer switch to provide a holding circuit for the solenoid after opening of the timer switch and simultaneously deenergizes the timing circuit.

In another form of the invention, the relay coil is connected in the other output circuit and is not energized for a period determined by charging of the capacitor to a given voltage. In this form the pressure responsive switch does not shunt the timer switch and is effective to deenergize the timer circuit in response to normal oil pressures.

14 Claims, 10 Drawing Figures PATENTEDJUL] 1972 3,673.81 1

SHEET 10F 5 v 2 L-2 .7, FL rj I 30 3| 32 I2 ("f I gun 22 27' INVENTORS JAY G. ADA M S RUSSELL E. COOK 9 BY Fl 1 4mm, We 1M G2 'AZTQRNEYS PM'ENTEDJULE I972 3. 673,81 1

SHEET 2 or s INVENTORS JAY C. ADAMS RUSSELL E. COOK ATTORNEYS PATENTEDJULA 1972 SHEEF 3 I)? 5 FIG? INVENTORS JAY C. ADAMS RUSSELL E. COOK BY ATTORNEYS PATENTEmuf4 1972 3 673 81 1 SHEET m 5 39 FIGB INVENTORS JAY C. ADAMS RUSSELL E. 0 00K BY waxy, MW, M'

ATTORNEYS PA'TEMEBJUL' 4 m2 SHEET 5 BF 5 ATTORNEYS CONTROL DEVICE FOR PRESSURE LUBRICATED COMPRESSORS BACKGROUND OF THE INVENTION fails or the control device may be slightly altered and utilized to delay restarting of the compressor after its operation has been interrupted. Safety devices are frequently employed in relatively large capacity refrigerating systems to prevent costly damage to the compressors due to failure of lubrication. Safety control devices heretofore known generally comprise a control circuit for the compressor motor arranged so that the motor energizing circuit is initially closed through a normally closed timer switch. The timer switch may be opened a period after energization of the motor by a thermally responsive element heated by a resistance heater or the like to switch operating temperature. Normally, the heating of the thermal element to its switch operating temperature requires sufficient time for oil circulating pressure to be established in the compressor. The timer switch and its heating element was shunted out of circuit by a second switch operated to close in response to the production of oil pressure and maintain energization of the compressor motor around the opened timed switch.

Safety control devices of the type mentioned have several disadvantages. One disadvantage is that the time required to heat the thermal element to its switch operating temperature will not be constant in the event a variation in voltage occurs, thereby affecting the rate of heating of the thermal element. Also, variation in ambient temperature of the thermal element affects the time required for heating the thermal element to its switch opening temperature.

Another disadvantage of the type of oil pressure safety control device mentioned is that should the circuit for heating the thermal element fail for any reason, the timer switch would not be opened. Then, in the event of failure of lubrication pressure, the motor would continue to operate through the timer switch, thereby seriously damaging the compressor.

Another disadvantage found in some prior art oil pressure safety control devices of the type mentioned is that it is necessary to manually reset the timer switch mechanism in the event the switch opens because of failure of lubrication. These reset mechanisms are subjected to corrosion and obstructions of one sort or another which is apt to prevent proper opening of the switch.

It has also been the practice to provide electric motor driven timer devices and control circuits to delay restarting of compressor motors after interruption of current for one reason or another and prevent overloading and locked rotors due to high head pressures. These timer devices are relatively expensive, and are subject to wear and failure.

THE PRESENT INVENTION The present invention relates to an improved control device for controlling the operation of compressors having pressure lubricating systems. One object of the invention is the provision of a control device which includes an electrically operated timer switch which may be connected in one or the other of two alternate energizing circuits of the output of a voltage biased switching means which is responsive to voltage at one plate of a charging condenser to switch current flow from one of the output circuits to the other after a predetermined charging period of the condenser. When the electrically operated timer switch is connected in one of the two energizing circuits, the control device serves as an oil safety control and when the electrically operated timer switch is connected in the other energizing circuit, the control device serves as a time delay control.

Another object of the invention is the provision of a safety control switch mechanism having a timer operated switch in parallel circuit with a switch responsive to the oil pressure in the lubricating system, the timer switch being operated to closed position by energization of a timer circuit for initiating operation of the compressor motor and which switch is opened after a predetermined time, whereby the timer circuit must be in an operative condition for starting of the compressor.

Another object of the invention is the provision of a safety control switching mechanism of the type mentioned in which the timer switch can be reset following a safety shut-down of the compressor merely by interrupting the power supply to the timer circuit whereby restarting of the compressor can be effected remotely from the control mechanism.

Still another object of the invention is the provision of a safety control switching mechanism of the type mentioned which is unaffected in its timing by substantial variations in line voltages supplied to the timer circuit and is unaffected by changes in ambient temperatures.

The invention further contemplates the provision of a safety control switching mechanism of the type mentioned in which the timing period for opening of the timer switch may be accurately regulated over a relatively wide range of time.

A still further object of the invention is the provision of a time delay compressor starting control device in which the delay is controlled by the charging of a condenser, and the circuit for the condenser is discharged when an operating condition of the compressor reaches a normal condition.

Other objects and advantages of the invention will be apparent from the following description of preferred forms of the invention, reference being made to the accompanying drawings wherein:

FIG. 1 is a schematic view of a refrigerating system embodying the invention;

FIG. 2 is a front elevational view of a control device forming a part of the invention;

FIG. 3 is a fragmentary sectional view taken substantially along line 33 of FIG. 2 and on a larger scale;

FIG. 4 is a plan view of a circuit board removed from the control device;

FIG. 5 is an end view taken along line 55 of the circuit board shown in FIG. 4;

FIG. 6 is a view of the reverse side of the circuit board shown in FIG. 4;

FIG. 7 is a wiring diagram of the control device;

FIG. 8 is a sectional view taken substantially along line 8-8 of FIG. 2;

FIG. 9 is a sectional view taken substantially along line 9-9 of FIG. 2; and

FIG. 10 is a wiring diagram of another form of the invention.

A portion of a refrigerating system which may embody both forms of the invention is shown at 10. The refrigerating system is a conventional electric motor driven compressor-condenser-expander type, and because the details of such systems are familiar to those skilled in the art a detailed showing and explanation is unnecessary for an understanding of the invention. The refrigerating system may be for a food storage compartment or for an air cooling system for a room or buildings, for example. The condenser and evaporator are not shown, but it will be understood that the evaporator is utilized for cooling air circulated in the space to be cooled. Suffice to say, the compressor C is driven by an electric motor 1 1, the operation of which is controlled by a suitable control switch 12, shown as a thermostatic switch, so as to maintain a predetermined range of refrigerating temperatures. The thermostatic switch 12 is located to respond to the temperature of the air, or other medium, to be cooled by the refrigerating system. The compressor C includes a lubricating oil pump P which is normally operative to force lubricant to the moving parts of the compressor requiring lubrication.

A control device 13 is provided for shutting down the compressor motor in response to a failure of the pump to circulate lubricant at a given pressure differential between the pump discharge and the compressor crankcase, thereby preventing damage to the compressor from lack of lubrication. The control device 13 permits short periods of operation of the compressor without the pumping of lubrication in the compressor at the required pressure differential, particularly during initial g by the switch 34 so as to maintain the circuit of solenoid 17 start up where several seconds of operation is required to establish the lubricant circulating pressure. Should the required lubrication pressure fail to develop within a given time or fail during operation of the compressor the control 13 will cause the compressor motor to be deenergized, all of which is described in detail hereinafter.

Referring to FIG. 1, two power lines L1,L2 supply a suitable electric current for the motor 11. The current supply may be V l v. A.C. for example. One side of the motor 1 1 is connected to L1 through a conventional solenoid operated contactor switch 15 and the other side of the motor isconnected to line L2 by a wire 16. The switch 15 includes a solenoid 17 which is operative to close the switch and complete the compressor motor circuit when energized, and when deenergized the switch opens.

The circuit for the solenoid 17 includes line Ll, thermostatic switch 12, a normally closed reset switch 20, conductor 21 to one side of the solenoid, conductor 22 to a tenninal 23 of the control device 13, a time switch 24 in the circuitry of the control device 13, terminal 26 and conductor 27 to line L2.

The thermostatic switch 12 may be of any suitable well known construction, and it is shown comprising an expansible bellows 30 which is filled with a suitable fluid to cause expansion and contraction of the bellows in accordance with increases and decreases in temperature. The expansion and contraction of the bellows 30 operates a movable contact to close the switch at a given upper temperature limit and to open the switch in response to a decrease from the temperature limit.

The reset switch includes a contact assembly 31 which is continuously urged by a spring 32 to close on a pair of fixed contacts. The switch may be opened by depressing a plunger 33.

Aswitch 34, comprising a component of the circuitry of the control device 13, is arranged to form an energizing circuit for the solenoid l7 and is connected with

terminals

23,26 in parallel with the time switch 24. The switch 34 is a double throw type and is operated in response to pressure differential between the interior of the crankcase of the compressor C and the discharge of the lubricant pump. When the oil pressure differential is relatively low, the switch opens the circuit parallel to t the switch 24. When an oil pressure differential is present which is indicative of proper lubrication of the compressor, the parallel circuit around the time switch 24 is closed lwhenthe time switch 24 opens.

In general, when the thermostat l2 closes after an appreciable. shut down period of the compressor, the solenoid 17 is energized to close thecompressor motor circuit. The initial energization circuit for the solenoid 17 includes the time c switch 24, as the switch 34 will be open with respect to the solenoid circuit. After a predetermined period of compressor operation, the time switch 24 opens. If the pressure differential switch 34 has operated in response to establishment of normal lubrication pressures the solenoid circuit is thereby maintained around switch 24 and the solenoid remains energized; otherwise the solenoid 17 is deenergized in response to opening of the timer switch 24 and the motor is stopped before damage occurs due to lack of lubrication in the compressor.

The

switches

24,34 and a timer circuit 35 for operating the switch 24 are carried on a frame 36 comprising the control device 13. In the form shown, the device 13 includes a base or frame 36 and a housing 37 attached to the frame. The

switches

24,34 and the'circuitry 35 are mounted on a circuit board 38 and are enclosed by the housing 37 and the frame. The frame 36 comprises a channel-shape sheet metal member having a main wall 39 and

opposed side flanges

40,41. Fastening means, not shown, are provided for attaching the frame to a suitable support. The housing 37 is formed of molded insulation and includes a box-like chamber having an open side. The open side of the housing is closed by the circuit board 38, and the housing is attached to the main wall of the frame 36 by two rivets 42 with the circuit board facing the wall.

The switch 34 is a snap acting double throw type which is well known in the art. The switch includes a movable contact 43, (see FIG. 7) which is adapted to engage one or the other of fixed

contacts

44 and 45. The contact 43 is caused to be shifted by suitable snap mechanism not shown, operated by swinging movement ofan actuator arm 46. The contacts and snap mechanism of the switch 34 are enclosed in a casing attached to the board as and inside the housing. The actuator arm 46 extends from the casing and housing and is engaged by an actuating lever of an oil pressure responsive mechanism described more fully hereinafter. When a normal oil pressure differential is established between the discharge of the pump P and the interior of the compressor crankcase, the arm 46 is moved to cause contact 43 to engage contact 45. This switching movement establishes a holding circuit for the solenoid 17 around the timer switch 24. When the oil pressure differential is below a safe value, contact 43 engages contact 44.

Referring more particularly to FIG. 7 of the drawings, the timer switch 24 comprises a relay type switch operated by a solenoid coil 47. When the coil 47 is energized the switch is closed and when the coil is deenergized the switch opens. Relay switches of the type described are commercially available. The energization of coil 47 is controlled by the timer circuit described hereinafter.

The circuit board 38 has four

flat terminal members

23, 26,48,49 attached thereto and these members project through slots in the housing 37 and provide terminal connections with the power supply and the solenoid l7.

The relay coil 47 and the timer circuit are energized by a power supply circuit which includes line Ll, thermostatic switch 12, switch 20, a conductor 50, terminal 49, resistor R1, diode D1, resistor R2, a normally closed reset switch 51 and junction 52. As an alternative source of power a 220v. A.C. supply could be connected with conductor which in turn would be connected to the terminal 48 instead of terminal 49.. For such an eventuality a suitable resistor R is interposed between the terminal 48 and diode D1. In either case, the diode D1 provides a pulsating DC. current which is smoothed and maintained at a given voltage by a voltage regulator comprised of a capacitor C1 and a zenor diode D2.

The energizing circuit for the relay coil 47 includes junction 52, resistor R3, transistor Q1, coil 47, junction 53,

contacts

43,44 of switch 34, terminal 26 and conductor 27. The base of the transistor Q1 controlled by a timer circuit is comprised of junction 52, a field effect transistor (FET) Q2, junction 54, a potentiometer R4 and junction 53. The base of the FET O2 is connected with a junction of a charging circuit for a condenser C2, which charging circuit includes junction 52, resistor R5, condenser C2, and the potentiometer R4.

When a potential is initially applied to the junction 52, the voltages at

junctions

54,55 are relatively low due to the charging capacity of C2 and as a result, O1 is turned on to supply an operating current flow to the relay coil 47 which closes switch 24. When C2 has been charged to a given level, the voltage at junction 55 turns on Q2 which causes an increase in voltage at junction 55, thus turning off Q1 and effectively deenergizing coil 47. The length of time required for charging C2 to the level mentioned depends upon the setting of the potentiometer R4. Preferably, the values of the capacitor C2, and resistors R4,R5 are such that the charging time may range from 10 to 240 seconds, depending upon the setting of the potentiometer R4. The resistance of the potentiometer R4 can be varied by rotating a shaft 56. The shaft projects through an opening in the board 38 and is slotted to receive a screwdriver for rotation. The adjustment is made prior to assembly of the board 38 into the housing 37.

The transistor Q] is latched off by a transistor Q3 having its base connected with the emitter of 01 through a resistor R6 and its collector connected with the collector of Q1. The emitter of O3 is connected with junction 53 through a resistor R7.

When the current supply for the coil 47 and the timer circuit is interrupted, the condenser C2 will immediately discharge through FET O2 to a substantial degree and thereby is immediately reset for a succeeding timer cycle. The current interruption may result in opening of the thermostatic switch 12 or by opening of the

contacts

43,44 of the oil pressure switch 34.

It will be seen that when the thermostatic switch 12 closes to establish operation of the compressor, if the oil pressure responsive switch 34 does not establish a holding circuit for the solenoid 17 through

contacts

43,45 the timer switch 24 will open when the coil 47 is deenergized and the circuit for the solenoid 17 will then open and cause a shut down of the compressor. If the switch 34 is operated to move contact 43 to contact 45 by the time the timer switch 24 opens, the solenoid 17 continues energized through these contacts and the motor circuit remains closed for a normal operating cycle as dictated by the thermostat 12.

One of the features of the invention is the fact that unless the relay coil 47 is initially energized when the thermostat 12 calls for operation of the compressor, the compressor would not operate. Thus, in the event the coil circuit is not energized due to failure of one portion or another of the timer circuit, the compressor will not operate. Hence, the danger of loss of protection against lubrication failure is greatly minimized.

Another feature of the invention is the fact that the system can be restarted, after it has shut down due to lack of oil pressure, merely by opening and reclosing the power supply to the circuit 35 for example. Assuming that the thermostat 12 closes to initiate operation of the compressor and there is a failure of lubrication pressure, the switch 34 will not close the holding circuit to the solenoid 17 and the switch 24 will open the solenoid circuit after the time period. The timer circuit, however will continue to be energized from L1 through the thermostat 12, switch 20, and through

contacts

44,43 of the switch 34 to line L2. If the power supply to the timer circuit is interrupted, the capacitor C2 immediately substantially discharges through the field effect transistor Q2 and upon re-establishment of the power the relay coil 47 will be energized and close switch 24 for another time period. In the form of the invention shown, the timing circuit can be restarted in the manner just described by depressing plunger 33 of the reset switch 20, or it may be interrupted by depressing the plunger 57 of the normally closed switch 51. The switch 51 is located in the housing 37 and is described more fully hereinafter.

it frequently occurs that the control device 13 and the compressor C will be located in a relatively inaccessible area so that it may be inconvenient for an operator to go to the control device for restarting by opening of the switch 51. To avoid such inconvenience switch may be located at any suitable point along the power supply lines, and may be positioned quite remote from the control device 13.

The switch 51 is mounted on the circuit board 38 and it includes a leaf spring type contact arm 61. One end of the arm 61 is secured to a conductor connected with the resistor R2 and the other end yieldingly engages a contact 62 connected with one side of the timer circuit. The contact arm 61 may be deflected by depression of the plunger 57 which extends through an opening in a wall of the housing 37. The plunger 57 is guided in axial movement by the walls of a recessed opening 63 in the forward wall of the housing 37, as best seen in FIG. 3, and a coiled spring 64 which surrounds the portion of the plunger in the recess. The spring 64 urges the plunger 57 outwardly and causes a flange 65 secured to the plunger to abut the inner end of the recessed portion of the housing wall. A knob 66 is attached to the outer end of the plunger to provide a finger pad for depressing the plunger. When the knob 66 is depressed against the outside of the housing 37, the inner end of the plunger engages the contact 61 and deflects it to break the electrical circuit therethrough.

The oil pressure differential responsive mechanism for operating the switch 34 comprises, in general, an actuator lever 70 pivoted to the frame and arranged to engage and shift the actuator arm 53. The lever 70 is moved about its pivot by a piston 71 which reciprocates in a cylinder 72.

The piston 71 is comprised of a permanent magnet, the flux of which cooperates with the flux of magnets carried on the operating lever to cause the lever to move according to movements of the piston. Opposite ends of the cylinder 72 are connected with the interior of the compressor crankcase and the discharge side of the oil pump P. The piston is spring biased towards one end of the cylinder 72 and responds to a differential in pressure in opposite ends of the cylinder to move against the spring and operate the actuator lever 70.

Referring to the construction details of the pressure differential mechanism which are best seen in FIG. 8, the cylinder 72 comprises a tubular member of non-magnetic

material having fittings

74 and 75 suitably secured in opposite ends. The inner end portion of the fitting 74 has a neck 76 which projects well into the cylinder. The neck 76 forms a support for a coil spring 77 which urges the piston 71 towards the fitting 75. The inner end of the neck forms a stop to limit the travel of the piston to the left, as viewed in FIG. 8. The outer end 80 of the fitting 74 is threaded to receive a coupling 81 by which the fitting is connected with a tube 82 leading to the crankcase of the compressor C. The fitting 74 has an axial bore 83 which forms a fluid path from the interior of the cylinder to the tube 82.

The fitting 75 has a stub portion 84 which extends into the cylinder 72 and the end thereof forms a seat against which the piston is urged by the spring 77. The outer end of the fitting 75 is threaded to receive a coupling 85 by which the fitting is connected with a tube 86 leading to the discharge side of the pump P. The fitting 75 has an axial bore 87 which connects the tube 86 with the interior of the cylinder 72.

The cylinder 72 is supported by the flanges of the frame 36. The flanges have aligned openings which receive the central portions of the

fittings

74,75, as shown. The fitting 75 has a collar 90 which abuts the frame flange 41 about the edge of the opening receiving the fitting. The fitting 74 has a threaded portion on which a nut 9.1 is threaded and which engages the portion of the frame flange 40 about the opening through which the fitting extends.

It will be seen that when the compressor is operating normally, the oil discharge from the pump P will enter the bore 87 and overcome the force of the spring 77 and move the piston to the neck 76. The piston 71 has a relatively loose fit with the cylinder walls and oil passes thereabout. Furthermore, the

conduits

82,86 are of appreciable diameter so that the change in oil pressure difi'erential is quickly reflected by movement of the piston. This movement of the pistonswings the lever 70 clockwise about its pivot, as viewed in FIG. 2, and shifts the arm 46 to actuate the switch 34. When the oil pressure is low or the pressure differential between the crankcase and pump discharge is too low to circulate the lubricating oil and maintain the piston on the neck 76 the spring 77 moves the piston to the stub 84. This shifts the lever 70 counterclockwise about its pivot. The arm 46 is normally biased to follow counterclockwise movement of the lever 70 to operate the switch 34 to break the circuit to solenoid 17. It will be appreciated that the tension of the spring 77 determines the differential in pressure at which the piston is operated.

The lever 70 has a U-shaped portion which includes a yoke and two legs 101,102. The legs are pivoted on a pivot pin 103, one end of which is attached to the main wall of the frame 36 in an opening therethrough. The legs 100,101 straddle the cylinder 72 and carry a pair of

magnets

104 and 105. The magnets 104,105 are preferably of a ceramic type and are arranged with north and south poles of the magnetic piston 71. This causes the magnets 104,105 to follow the piston and swing the lever 70 about the pivot pin 103. The yoke 100 of the lever 70 has a turned lug portion 106 having an opening into which an adjusting screw 107 is threaded. One end of the screw 107 is positioned to engage the actuating arm 46 of the switch 34. The arm 46 is inherently biased to retain engagement with the screw 107. By turning the screw 107 one direction or the other, the pressure differential at which the piston 71 operates the switch 34 can be more or less varied.

SUMMARY OF OPERATION When the thermostatic switch 12 closes in response to a demand for refrigeration the circuit for the compressor motor is closed by energization of the solenoid 47 and closure of switch 24 as described. After the compressor has operated for a given number of seconds, determined by the setting of the potentiometer R7, switch 24 is opened by the shunting of the relay solenoid 47 by the timer circuit. If, during the predetermined period of operation a normal pressure differential is developed between the outlet of pump P and the interior of the compressor crankcase, switch 34 is shifted to establish the contactor circuit through the

contacts

43,45. This operation of the double throw switch 34 interrupts the current supply to the timer circuit and that circuit is reset by the discharge of the capacitor C2. When the thermostatic switch 12 is satisfied, the circuit for the solenoid 17 is opened and the compressor motor is stopped. Should lubrication pressure fail during operation of the refrigerating system switch 34 shifts contact 43 from contact 45 tocontact 44. Uponthe closing'of the contact 43 on contact 44 the timer circuit and the circuit for solenoid 47 are reenergized, causing switch 24 to be reclosed. The switch 24 is maintained closed for the time period described after which the switch is reopened. If normal lubrication pressure has been re-established, the compressor will be maintained in operation through

contacts

43,45 of the switch 34. On the other hand, if oil pressure has not been re-established the timer circuit will function to prevent effective energization of the solenoid 47 for the switch 24.

After repairs or adjustments have been made to restore normal oil pressure in the compressor, the compressor motor can be restarted merely by momentarily interrupting the power to the timer circuit. This may be effected by momentarily opening either of the switches or 51, whichever is most convenient. This action causes immediate discharge of the capacitor C2 as described, and upon re-establishment of current the timing cycle is initiated. The timer circuitry disclosed is exceptionally accurate in timing irrespective of wide variations in ambient temperatures and in line voltage variations. The pressure differential responsive switch actuating mechanism disclosed is particularly suitable in that the piston 71 acts rapidly in response to changes in pressure differentials. Furthermore, because the piston normally rests against the stop formed by the inner end of the'neck 76 of the fitting 74 there isno movement of the piston and its associated parts during normal operation of the refrigerating system although fluctuations in pressure differential will occur.

ln certain relatively larger refrigeration and air conditioning systems, oil pressures must develop relatively rapidly. In such cases the control device can be set to shut down the motor in a sufficiently short time to also protect overheating of the motor due to a locked rotor.

SECOND FORM OF INVENTION By slight alteration of circuitry, the control device 13 can be utilized to provide a time delay between shut down of the compressor motor I1 and restarting. This is desirable to permit more or less equalization of pressures in the refrigerating system before restarting the compressor.

Referring to FIG. 10, the control device 13 is shown altered to provide time delay in restarting the compressor motor. Like parts of the device have the same reference characters as the parts shown and described relative to FIG. 7.

It will be appreciated that the relay coil 47-and the resistor R7 are connected in alternate output circuits of the switching means comprised of the transistors 01,03. In FIG. 10, the relay coil 47 is connected in the output circuit comprising: the emitter of Q3 and the resistor R7 connected with the emitter of Q]. Thus, when the thermostat 12 calls for refrigeration, the timer circuit is energized and the initial output circuit is through resistor R7 rather than coil 47. Consequently, the contactor coil 17 is not energized until capacitor C2 becomes the control circuitry is altered to eliminate the effectiveness of contact 45 so that when contact 43 shifts from contact 44 to contact 45, the timer circuit is broken and the capacitor C2 discharges; however,

contacts

43,45 are ineffective to shunt switch 24. When the oil pressure differential falls, due to termination of operation of the compressor, the timer circuit is re-energized by closure of

contacts

43,44.

In either form of the invention, should there be a malfunction in the timer circuit which destroys the current supply through the circuit, the switch 24 cannot close. Thus, the refrigerating system will not operate without the protection of the timer circuit.

We claim: I

1. In a refrigerating system having a refrigerant compressor including a lubrication pump for circulating lubricant in said compressor and a motor for driving said compressor, control circuitry for said motor including a condition responsive switching means and electrically powered means including energizing circuitry controlled by said condition responsive switch and operative to energize said motor when said electrically powered means is energized, second and third switching means in said energizing circuitry, said second switching means having first and second alternate switching positions, said third switching means normally open and including electrically energized means to close said third switching means and cooperate with said condition responsive switch to complete said energizing circuit, electrically responsive timer means to deenergize said electrically energized means a period after energization of said electrically energized means, said electrically responsive timer means having an energizing circuit including said first alternative switching position of said second switching means, said second switching means being operative in its second alternative switching position to deenergize said timer means and complete a shunt circuit around said third switching means, and means responsive to lubrication oil pressure conditions in said pump and compressor for shifting said second switching means from said first alternate position to said second alternate position.

2. A refrigerating system as defined in claim 1 in which said electrically powered means and said electrically energized means each comprises a solenoid.

' 3. A refrigerating system as defined in claim 1 in which said timer means is automatically reset in response to interruption of its energizing circuit whereby conditions are established for initiating a time period upon reenergization thereof.

4. A refrigerating system as defined in claim 3 in which said electrically responsive timer means-includes a transistor controlling energization of said electrically energized means, a biasing circuit for said transistor including a capacitor and resistor regulating the charging rate of said capacitor, and means to discharge said capacitor when said electrically responsive timer is deenergized.

5. A refrigerating system as defined in claim 3 including normally closed manually operated switching means for selectively interrupting the energizing circuit of said timer means.

6. In a refrigerating system comprising a refrigerant compressor including a lubricating system having a lubricant pump and a motor for driving said compressor, a control system for said motor including condition responsive means to initiate and terminate operation of said compressor, timer means operative to terminate operation of said compressor after a limited period following initiation of operation of said compressor means forming a cylinder, a piston movable in said cylinder, means urging said piston towards one end of said cylinder, means connecting said one end of said cylinder with the discharge of said lubricant pump, means connecting the other end of said cylinder with the intake of said pump, and means operated by movement of said piston to a predetermined position away from said one end of said cylinder for rendering said timer means ineffective to terminate operation of said compressor.

7. In a control system for apparatus requiring maintenance of a fluid pressure differential during operation thereof, electrically powered means operative to effect and maintain operation of said apparatus when said means is energized, an energizing circuit for said electrically powered means, switch means to control energization of said circuit, said circuit including timer means to provide an effective energizing current to said electrically powered means when said circuit is initially energized by closure of said switch means and after a period of energization to render said circuit ineffective to energize said electrically powered means, and means responsive to the presence of said fluid pressure differential for maintaining operation of said apparatus irrespective of the ineffective condition of said electrically powered means.

8. A control system for apparatus as defined in claim 7 further characterized by said electrically powered means comprising a solenoid, said timer means comprising a field efi'ect transistor, a transistor having its base connected with the emitter of said field effect transistor, and an RC circuit including a condenser connected with the base of said field effect transistor.

9. A control system for apparatus as defined in claim 7 further characterized by the means responsive to the pressure of said fluid differential being operative to interrupt the circuit to said timer means substantially simultaneously with maintaining operation of said apparatus.

10. In a motor driven mechanism having lubricated moving parts and including a lubrication pump for circulating lubricant, control circuitry for said motor including a condition responsive switching means and electrically powered means including energizing circuitry controlled by said condition responsive switch and operative to energize said motor when said electrically powered means is energized, second and third switching means in said energizing circuitry, said second switching means having first and second alternate switching positions, said third switching means normally open and including electrically energized means to close said third switching means and cooperate with said condition responsive switch to complete said energizing circuit electrically responsive timer means to deenergize said electrically energized means a period after energization of said electrically energized means, said electrically responsive timer means having an energizing circuit including said first alternative switching position of said second switching means, said second switching means being operative in its second alternative switching position to deenergize said timer means and complete a shunt circuit around said third switching means, and means responsive to lubrication oil pressure conditions in said pump and mechanism for shifting said second switching means from said first alternate position to said second alternate position.

11. A motor driven mechanism as defined in claim 10 in which said electrically powered means and said electrically energized means each comprises a solenoid.

12. In a refrigerating system having a refrigerant compressor including a lubrication pump for circulating lubricant in said compressor, and a motor for driving said compressor, control circuitry for said motor including a control switching means and electrically powered means including energizing circuitry controlled by said control switching means and operative to energize said motor when said electrically powered means is energized, second and third switching means in said energinng circuitry, said second switching means having first and second alternate switching positions, said third switching means normally open and including electrically energized means to close said third switching means to thereby cooperate with said condition responsive switch to complete said energizing circuit, electrically responsive timer means having alternative parallel circuits, one of which parallel circuits includes said electrically energized means, said timer means comprising switching means operative in response to energization of said timer means for a period to change the flow of current from one of said parallel circuits to the other parallel circuit and thereby control the energization of said electrically energized means, an energizing circuit for said electrically responsive timer means including said first alternative switching position of said second switching means, and means responsive to lubrication oil pressure conditions in said pump and compressor for shifting said second switching means from said first alternative position to said second alternative position.

13. A refrigerating system as defined in claim 12 further characterized by said second switching means being operative in its second alternative switching position to deenergize said timer means and complete a shunt circuit around said third switching means.

14. A refrigerating system as defined in claim 12 further characterized by said electrically energized means being connected in said other parallel circuit of said electrically energized timer means.

Claims

3. A refrigerating system as defined in claim 1 in which said timer means is automatically reset in response to interruption of its energizing circuit whereby conditions are established for initiating a time period upon reenergization thereof.

4. A refrigerating system as defined in claim 3 in which said electrically responsive timer means includes a transistor controlling energization of said electrically energized means, a biasing circuit for said transistor including a capacitor and resistor regulating the charging rate of said capacitor, and means to discharge said capacitor when said electrically responsive timer is deenergized.

8. A control system for apparatus as defined in claim 7 further characterized by said electrically powered means comprising a solenoid, said timer means comprising a field effect transistor, a transistor having its base connected with the emitter of said field effect transistor, and an RC circuit including a condenser connected with the base of said field effect transistor.

12. In a refrigerating system having a refrigerant compressor including a lubrication pump for circulating lubricant in said compressor, and a motor for driving said compressor, control circuitry for said motor including a control switching means and electrically powered means including energizing circuitry controlled by said control switching means and operative to energize said motor when said electrically powered means is energized, second and third switching means in said energizing circuitry, said second switching means having first and second alternate switching positions, said third switching means normally open and including electrically energized means to close said third switching means to thereby cooperate with said condition responsive switch to complete said energizing circuit, electrically responsive timer means having alternative parallel circuits, one of which parallel circuits includes said electrically energized means, said timer means comprising switching means operative in response to energization of said timer means for a period to change the flow of current From one of said parallel circuits to the other parallel circuit and thereby control the energization of said electrically energized means, an energizing circuit for said electrically responsive timer means including said first alternative switching position of said second switching means, and means responsive to lubrication oil pressure conditions in said pump and compressor for shifting said second switching means from said first alternative position to said second alternative position.