US2221857A - Motor driven compressor - Google Patents

Description

Panarea/nav. 419, 1940 UNITED .STATES PATENT oFFlcE solaims. 4(ci. 23o-1s) This invention relates to motor`driven compressors, and more particularly to improved controlling mechanism for such compressors adapted to regulate the control 'thereof by loading and re-loading, or by stop vand start, as the demand 5 for air makes preferable, and all in accordance with receiver pressure variations.

Some compressors are subjected to widely vary-l ing demands for air, and the nature of the demand may be such that for a considerable portion of the day the compressor is called upon to furnish a rather high percentage of its potential quantity of compressed air. During other portions of the day for substantial periods there may be a much reduced demand for air. During the rst type of period it is advantageous to operate on the load and unload system, because the quantity of current required in starting the .motor and the wear and tear on the starting switch mechanism can be saved. It has been found that if re-loading follows unloading at comparatively short intervals, a definite saving is possible by operating on the load and unload system as compared with the stop and start system. Where, however, the compressor may run loaded for a few minutes and then be shut down for a quarter of an hour, or perhaps longer, a saving will be possible by stopping the motor when the maximum desired pressure is reached and starting it again when the minimum desired pressure is reached, and this is particularly so where it is possible to have a wide range-of pressures between the maximum and minimum. 4Desirably,

when working on the load and unload system, a

comparatively narrower range of pressures will be selected for the purpose of avoiding unnecessary motor stoppage. 4-

It is an object of my invention to provide an improved electrically-driven lcompressor system.

It is another object of my invention to provide o an improved mechanisnifor automatically controlling the operation of a compressor.` A further object of my invention is tov provide an improved controlling mechanism for automatically controlling the operation of a compressor in accordance with the receiver pressure variations, regulating the mode of compressor control in accordance with the nature of the air demand. Still another object of my invention is to provide a controlling mechanism for automatically stopping and starting a motor-driven compressor or for automatically unloading and loading the compressor, dependent upon the nature of the air demand. Yet a further object of my invention'ls to provide an improved controlling mechanlsm for controlling the running of a compressor driving motor and for automatically loading the compressor a predetermined time after the motor has started and for unloading the compressor when the maximum desired receiver pressure has been reached. Still another object of my invention is to provide an improved control- 5 ling mechanism for 'automatically stopping a compressor driving motor a predetermined time after the desired maximum pressure has been reached, and if during such predetermined time the air demand is high, for avoiding the stopping 10 of the motor and resuming a loaded compressor operation. These and other objects will hereinafter more fully appear. I

In the accompanying drawing there is shown forvpurposesof illustration one form which the 15 invention may assume in' practice.

In the drawing- Fig. 1` is a diagrammatic view showing a compressor having an electric driving motor and showing the wiring diagram of the mechanism 20 for controlling said motor and loading and unloading of the compressor.

Fig. 2 is an enlarged detail view, partially in vertical central section, through an electromagnetically controlled pilot device. y 25 Fig. 3 isa cross sectional view taken on the line 3-3 of Fig. 2, showing details of the pilot device.

In Fig. 1 there is shown a compressor C of the so-called angle-compound type` having a low 30 pressure cylinder I and a high pressure cylinder 2 and mounted on a base 3. An electric driving motor t is provided for the compressor and is herein shown as a polyphase motor directly con nected to the compressor crank shaft 5. Fluid 35 compressed by the low pressure cylinder flows through an lntercooler 6 to the high pressure cylinder 2 and, after compression in thev latter, is discharged fromA the compressor through a conduit 'I leading to a receiver 8. 40

An intake-closure` type unloading valve 9 is arranged in the inlet I9 of the low presure cylinder, and is actuated through a stem' II connected to a piston I2 of a servomotor I3. When fluid is admitted to the motor I3 to force down the piston 45 l2 and so move the valve 9 to closed position, the admission of air or other fluid to the low pressure cylinder I is completely cut on, and the compressor is thereby unloaded. Fluid for actuating the piston I2 is delivered thereto through 50 a pipe I4 under the control of a magnetvalve generally designated I5, the magnet valve being connected to the receiver tank 8 by a pipe I6. 'I'he pipe I6 is connected to a lower chamber I1 in the magnet valve, andthe magnet valve also 55 has an upper chamber I8, which is connected to atmosphere by a vent port I9. The upper and lower chambers open into a central chamber 29 through alined passages numbered 2| and 22 5 respectively. The pipe I4 opens into this central A chamber. Valves 23 and 24 seating towards the central chamber control the flow of iluid through passages 2| and 22, and are continuously urged toward closed position by springs 25 and 26. A lever arm 21 is pivoted at one end 28 within the central chamber 20 and is suitably connected at its other end to a plunger 29 projecting within a solenoid 39. The stem portions of the valves 23 and 24 engage upper and lower portions of th lever respectively. When the solenoid 3|! is energized the lever arm 21 is swung upwardly about its pivot 28, and the valve 23 is' lifted to open the passage 2| between the central chamber and the upper chamber I8. The servomotor 20 I3 is then vented through pipe I4, central chamber 20, passage 2|, upper chamber I 8'and vent I9. When the servomotor is vented the piston I2 is moved to its upper position by any suitable means, herein represented by a spring I2, thus 25 opening the valve 9 and loading the compresor. When the solenoid 30 is deenergized, the weight of the plunger 29 moves the lever arm 21 to its lower position, opening the valve 24 and allowing the spring 25 to close the Valve 23. The pipe I4 30 is thenconnected to the receiver tank 8 through pipe I6, chamber I1, passage 22, and chamber 28, and pressure fluid is conducted tothe servomotor I3 to act upon the piston I2 and close the valve 9, thereby unloading the compressor. Suitable high pressure cylinder venting means,

herein generally designated H, and of any suitable type, suchA for example as is shown in the W. E. Hughes Patent No. 1,786,114, granted Dec. 23, 1930, is controlled also by the magnet valve I5, having presure supplied thereto and vented therefrom through a passage I4a connected with the passage I4.

My improved controlling mechanism is designed, among other purposes, to energize the solenoid 30 after the motor 4 has been started and brought up to speed, to deenergize the solenoid 38 when a predetermined maximum pressure in the receiver -tank has been reached, and to reenergize it while the motor 4 continuesto operate if the demand for air is above aA predetermined rate. My improved mechanism is furthermore designed to start and stop the motor in accordance with receiver pressure variations and t'o determine whether the motor shall be stopped or the compressor reloaded instead, de#

pending upon the demand.for pressure fluid.

I-ha-ve herein, as a part of my improved controlling system, provided a pair of pressure switches 3| and 32. The pressure switch 3| 'is 00 designed to close when receiver pressure drops to, say 80 pounds, and to be opened when any desired higher pressure below the desired maximum pressure, which we will assume to be 100 pounds, is reached. It may be assumed to open, forl the purpose of illustration, at 85 pounds. Pressure switch 32 closes when receiver pressure falls. say, to 98 pounds and opens when receiver pressure rises to 1GO pounds, in the illustrative embodiment oi' the invention disclosed herein. The motor is adapted to have its leads 35, 31 and 3S connected by a main line contactor switch 39 to the power lines 33, 34, 35. A solenoid 40 is provided for closing the main line contactor switch 39, and is adapted to do this when energized. A time relay 4| controls the solenoid circuit and operates to close the same a prede termined time after the coil 42 of the relay 4| is energized. Current to energize the coil 42 is sup-v plied by a control circuit including a manually operated switch 43, which is closable to establish 5 a connection with the main line Wire 35, a conductor 44, the switch element 3| of the pressure switch 3|, a conductor 45, time relay coil 42, and conductors 46 and 41, the latter connected to the main line wire 34. If the pressure acting on l0 the pressure switch 3| be below 85 pounds and the manually operated switch 43 be closed, current will flow through the circuit described to energize the time relay coil 42; and after a predetermined time the relay 4| will complete, 15 through the solenoid 40, a circuit which includes the manually operated switch 43,` the conductor 44, the pressure switch element 3|', a conductor 48, a conductor 49, the switch element 32' of the pressure switch 32, a conductor 50, time relay 4I, 20 a conductor 5I, solenoid 4I), and a conductor 52 leading to main line wire 34. The main line contactorY switch 39 will then be closed by the energizedsolenoid 49 and the motor 4 will be started. A circuit through the solenoid 30 of the 25' magnet valve I5 is controlled by a time relay 53 which may be of any standard type and is adjusted to operate after the main line contactor switch 39 has been closed and the motor 4 has been brought up to full speed. As will shortly 30 appear, the coils of the relays 4| and 53 are energized at the sime time. However, time relay 53 is of the type which opens immediately when dee'nergized, but closes only after the desired time delaywhen energized, while relay 4I is of the 35 type which closes immediately when energized, but does not open until after a predetermined delay. With the receiver tank pressure below vpounds and the manually operated switch 43 closed, a circuit .through the coil 5.4 of the time 0 relay 53 exists which includes the manually operated switch 43, connected to line wire 35, the conductor 44, pressure switch element ,3|', conductors 45 and 48, conductor 49, pressure switch element 32', a conductor 55, time relay coil 54, a 5 conductor 56 and the conductor 41 leading to the main line wire 34. After the elapse of the time period required for the closing of the time relay 53, a circuit `is established through the manually operated switch 43, conductor 44, pres- 50 sure switch element 3|', conductors 45 and 48, conductor 51, the solenoid 30, a conductor 58, the time relay 53, and the conductors 56 and 41 back to the main line wire 34, and the magnet valve I5 is operated to vent the servomotor I3 and 55 load the compressor.

A holding circuit is established when the -main line contactor switch 39 closes, to holdthe main line switch closed even after the receiver pressure has increased to such a value as to cause the 60 pressure switch 3| to open. This holding circuit includes a switch element 59 which is connected to and operates with the main line switch 39. The switch element 59 Ais connectible through a conductor 68 and the manually operated switch 43 to 05 the main line wire 35. A contact of the switch 59 is connected through a conductor 6|, conductor 55, conductor 50, time relay 4|, conductor 5I, solenoid 40 and conductor 52 to the line wire 34, thereby forming, on closure of switch ele- 10 ment 59, the holding circuit for the main line' switch 39. Another holding circuit is -set up at 'the same time to maintain the time relay 4I closed. This circuit extends from the main line wire 35, through the manually operated switch 16 assise? 43, conductor 50, switch 59, conductors 5|, 55, pressure switch element 32', conductorv 49, conductor 48, conductor 45, time relay coi142, conductor 46 and conductor 41 back to the main line wire 34. Still another holding circuit is established through the ytime relay coil 54 to hold the time relay 53 closed for a time after the pressure switch 3| opens, and this circuit includes the manually operated switch 43, conductor 60, switchelement 59, conductor 6|, time relay coil 54, and conductors 56 and 41, the latter leading back to the main line Wire 34. The solenoid is maintained energized after the pressure switch 3| opens by current flowing from the main line? 35 through the manually operated switch 4 3,

conductor 60, switch element 59, conductors 5| and 55, pressure switch element 32', conductors 49 .and 51, solenoid 3l), conductor 58, time relay 53. conductor 56, and conductor 4`| leading to the main line wire 34. A manually operated switch 62, shunting the pressure switch 3|, is provided to start the motor 4 when the receiver pressure is above that at which the pressure switch 3| Will remain closed.

In the operation of my improved control, asA` energized by current iiowing between lines 35 and 34 through the switch 43, conductor 44, pressure switch element 3|', and conductor 45, coil 42, and conductors 46 and 41. Relay 4| immediately closes the circuit including switch 43, conductor 44, switchelement 3|', conductors 48 and. 49, switch element 32', conductor 50, relay 4|, conductor 5|, coil 40 and conductor 52,l closing the main line switch and starting the motor 4. At the same time that coil 42 is supplied with current, current also'ows through the conductors 48 and 49, pressure switch v,element 32', conductor 55, time relay coil 54 and conductors 56 and 41. The time relay 53, however, being, as above explained, of the delayed closing type,

circuit which it controls until after the motor 4 has had time to be started and bring the compressor upto a safe speed. After the motor 4 has attained a suitable speed, however, the timere- Vlay 53 brings about energization of the solenoid 30 through a circuit including the conductors 51 and 59, as previously described, and the solenoid 30 in turn operates the magnet valve I5 to cause loading of the compressor. When the receiver pressure builds up and the pressure switch 3| opens, the motor 4 will continue to drive the compressor loaded and the latter will remain loaded because thevswitch 59 closed at the same timey the main line switch closed and established a circuit through the manually. operated switch 43, conductor 60, switch 59, conductors 5|, 55, 59, time relay 4|, wire 5|, solenoid 49 and wire 52, to hold the main line switch closed while time relay 4| remains closed, and concurrently established circuits through the time lrelay coils 42 and 54 to hold the time relays 4| and 53 closed, thereby, until the switch 32 ope respectively holding the lcircuit closed for energizing the solenoid 49 (which in turn, as, just explained, holds'the line switch 39 closed to operate the motor 44) and holding the circuit tor energizing the solenoid l3|) energized to keep the compressor loaded; When'the receiver pressure reaches the -heavy the receiver pressure may drop sufllciently,

tor 4 is started;

does not close the will be further evident that the improved auto- 51, solenoid 30, conductor 59. time relay 53, and

conductors 55 and v41, and the compressor is unloaded. At the same time the circuit through the time relay coil 42 is broken, but the'time relay 4I remains closed for a predetermined period, as above explained, and the solenoid 40 accordingly continues to be energized, thereby holding the line` switch 39 cled to supply current to the motor 4, and the compressor operatesunloaded for a selected period. If the demand for air is e.'g., to 98 pounds, to allow the pressure switch 3l to close before the time relay'4l operates to open the line switch holding circuit. When this happens the circuit through the solenoid 30 is again closed to operate the magnet valve I5 and load the compressor, and the circuit through the time relay coil 42 is re-completed to hold the time relay 4| closed and to maintain the solenoid 40 energized. If the demand for air is light, however, and the time relay 4| opens before the receiver pressure drops to 98 pounds, the circuit through 'the solenoid 40 will be broken, and the line switch 39 and switch'=59 Willopen. The circuit through the time relay coil 54 is also broken then, and the time relay 53 opens. The solenoid 30 40 will now not be energized again automatically to' close the line switch 39 until the receiver .pres-` sure drops to the lower setting of pressure switcn 3|', say 80 pounds, at which time the pressure switch 3| will close to establish circuits again t-hrough the time relay coils 42 and 54 and bring about motor starting and compressor loading.

If it is desired to start the compressor before the receiver pressure drops to pounds, the hand switch 62 may be held closed until the molthen the switch 62 may be opened again and, due to the holding circuits de scribed, the motor 4 will continue to drive the compressor loaded until the receiver pressure reaches 100 pounds again. l

clearly apparent that I have provided an improved 'controlling mechanism for starting a compressor when the receiver pressure falls to the minimum limit, and for'continuing the compressor in operation on `the unload and re-load system as, longv as the demand for air is high. It

matic controlling mechanism is operative without operator intervention to change the system of compressor control to stop-and start operation when the air demand becomes less. When the air .demand again increases, the structure de scribed will again automatically return to the load and unload system oi' regulation. It will be evident that the controlling system is simple and has no parts which should be likely. to be a source- 70 of trouble in operation. l

, while there 1s described andmustrated in this application one form which the invention may assumein practice, it will be understood that this form oi' the same is shown for purposes of mustrauon and that the invention 'my be moai- 1I 45 I t will of course be understood that the various i pressure limits herein described may be varied in What I claim as new and desire to secure by Letters Patent is:

`1. In 'a compressor system, in combination, a compressor, unloading means therefor, a driving motor for said compressor, a control switch for said driving motor, and compressor discharge pressure responsive devices for controlling the operation of said control switch and said unloading means, one of said pressure responsive devices operative to close at one compressor discharge pressure and to open at a higher discharge pressure, and another of said pressure responsive devices operative to close at a` discharge pressure above that at which said rst mentioned pressure responsive device opens and to open at a still higher discharge pressure.

2. In a compressor system, in combination, a compressor, unloading means therefor, a driving motor for said compressor, a control switch for said driving motor, compressor discharge pressure responsive devices for controlling the operation of said control switch and vsaid unloading means, one of said pressure responsive4 devices operative to effect closure of said control switch and start said motor, and means operative with said control switch for making the second pressure responsive device effective to maintain said control switch closed.l after said rst pressure responsive device opens.

3. In a compressor system, in combination, a

compressor, unloading means therefor, a driving motor for said compressor, a control switch for said driving motor, compressor discharge pressure responsive devices for controlling the operation of said control switch and said unloading means, means operative immediately after operation 'of one of said pressure responsive devices for eifecting closure of said control switch and starting said motor, and a switch operative with .said control switch for completing a circuit through a second pressureresponsive device and said second mentioned means to maintain said control switch closed after said first pressure responsive device opens.

4. In a compressor system, in combination, a compressor, unloading means therefor, a driving motor for said compressor, a control switch for said driving motor, compressor discharge pressure responsive devices for controlling the operation of said control switch and said unloading means, means operative on operation of one of said pressure responsive devices for effecting closure of said control switch and starting said motor, means operative a predetermined time after closure of the control switch for effecting loading operation of said unloading means, and a switch operative with said control switch for completing separate circuits through the second pressure responsive device and through said second and third mentioned means for maintaining said control switch closed and said compressor loaded after said rst pressure responsive device opens.

5. In combination, a compressor, an electric driving motor therefor, an electrically operated starting switch for said motor, unloading means for said compressor having electrical control means operative on energization to effect compressor loading, a time delay relay for controlling said starting switch and operative on current supply thereto to effect immediate cunent supply to eiect closure of said switch and upon interruption of current supply thereto to 'interrupt operating current supply to said switch only after alpredetermined time delay, 'a time delay relay for controlling the control means for said unloading means operative only after a predetermined delay following current supply thereto to supply current to eifect loading and operative immediately upon interruption of current supply thereto to discontinue current supply to said control means and effect unloading, and controlling means for said time delay relays including ressure responsive devices operative at pre eterminedlimits of receiver pressure to control circuits supplying current to said time delay relays.

6. Apparatus for controlling a prime mover operated compressor comprising a compressor discharge pressure responsive device arranged to control the loading and unloading of said compressor and .the running and stopping of the prime mover, said pressure responsive device including a switch operable at an upper limit to eiect unloading of said compressor and stopping of said prime mover after -a predetermined time or operative at a lower limit to close and reload said compressor and effect continued running of said prime mover if the lower limit is reached before the end ofthe predetermined time, means operative ing of said switch to preclude restarting thereof by closure of said switch, and means operative only on a further predetermined drop in pressure to effect restarting.

7. Apparatus for controlling a prime mover operated compressor comprising, in combination, unloading means for said compressor having electrical control means operative on `energization to eifect compressor loading and on deenergization compressor unloading, time delay means having electrical control means operative. on energization to effect operation of said compressor and a predetermined time after deenergzation a stopping of the compressor, pressure responsive means arranged to simultaneouslyrdeenergize the electrical control means for said unloading means and said time delay means when the compressor discharge pressure reaches a predetermined value and to reenergize said electrical control means if the compressor discharge pressure dropsto a predetermined lower value before said compressor is stopped, and means including a pressure responsive device operative at a predetermined pressure below the lower operating pressure of said pressure responsive means for reenergizing the electrical control means of said time delay means if said compressor is stopped.

8. In a compressor system, in combination, a. compressor, unloading means therefor, a driving motor for said compressor, a control switch for said driving motor, and compressor discharge pressure responsive devices for controlling the operation of said control switch and said un loading means, one of said pressure responsive devices operative to close at one compressor vdischarge pressure and to open at a higher discharge pressure, another of said pressure responsive devices operative to close at a discharge pressure above that at which said rst mentioned pressure responsive device closes and to open at a discharge pressure higher than that at which said rstvmentioned pressure responsive device opens. i

JESS M. BARTHOLOMEW.

if said prime mover stops due to open-`

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