Refrigerant Compressor Control-relay To Control Two Time Delays

Abstract

An air conditioner refrigerant compressor control having a first time delay means automatically keeping the compressor deenergized for a predetermined period after each stop cycle, a second time delay means operable under certain conditions to keep the compressor energized for at least a predetermined period at initiation of each start cycle, and a single relay means operable to correctly program the two time delay means.

Description

THE DRAWINGS

FIG. 1 is a diagram of a refrigerant compressor control circuit that can be used in practice of the invention.

FIG. 2 is a circuit diagram for a time delay means employable in the FIG. 1 circuit.

FIG. 3 is a circuit diagram of a second time delay means employable in the FIG. 1 circuitry.

FIG. 4 is a fragmentary view through a relay structure that can be used in the FIG. 1 circuitry.

REFRIGERATION SYSTEM--GENERAL OPERATION

This invention relates to the type of air-conditioning system which may include a motor-driven refrigerant compressor, an air-cooled refrigerant condenser located outdoors, and a heat-absorbing refrigerant evaporator located indoors. In operation of such a system the compressor delivers hot refrigerant gas to the condenser at relatively high pressure. The condenser fan moves outdoor air across the condenser fins to thus condense the refrigerant. Condensed refrigerant is then delivered across a flow restrictor (capillary or expansion valve) to the indoor evaporator. A motor-driven fan moves room air across the evaporator fins so that the air gives up heat to the refrigerant; the refrigerant is thus vaporized and subsequently drawn back into the compressor for recycle.

COMPRESSOR FIVE-MINUTE TIME DELAY

In the above type of system the compressor is usually lubricated with lubricant pumped or withdrawn from a small sump; the sump also acts as a refrigerant supply chamber for the compressor. During the first moments of each run cycle all bearing surfaces may not receive an optimum quantity of lubricant. If the run cycle continues for a sufficient time period the lubrication will become adequate to prevent any scoring or premature wear. However if the compressor is caused to operate on very short run and stop cycles there may not be enough continuous run time to provide an adequate lubricating action.

During each run cycle some of the lubricant becomes entrained with the system refrigerant; eventually the lubricant separates out in the sump, given sufficient time. However, with very short run-stop cycles the refrigerant-oil emulsion in the sump does not have sufficient time to break up, and under these circumstances the sump fluid is foamlike in character. This foam has very inadequate lubrication properties.

At the start of each run cycle the motor current is relatively high. If the run-stop cycles are very short the heat incident to each initial current inrush is not fully dissipated, and local hotspots sometimes develop in the windings, thereby shortening motor life.

Because of the above circumstances, and possibly others, it has been a practice to equip air conditioners with control devices which insure a few minutes time delay (usually about 5 minutes) between the end of each run cycle and the beginning of the next run cycle. This lengthens the off periods and indirectly tends to lengthen the run periods because the longer off periods increase the cooling load.

LOW-PRESSURE CUTOUT

Conventional systems usually include a low-pressure cutout switch which responds to pressure conditions in the suction line between the evaporator and compressor. The purpose of this cutout is to prevent the compressor from operating at a suction pressure so low that refrigerant flow path is insufficient to carry excess heat away from the motor windings. This cutout switch unfortunately has a disadvantageous affect at startup under wintertime operation.

During winter periods room cooling may be required even though the outdoor temperature is quite low, for example 40.degree. or less. Under such conditions the condenser may condense refrigerant so effectively that the compressor is unable to maintain a satisfactory hot gas pressure for delivering sufficient refrigerant across the restriction between the high and low sides of the system. As a result the evaporator may be semistarved of refrigerant, especially at startup. At startup the compressor may draw more refrigerant from the evaporator than can be replaced by the condenser, thus causing the suction line pressure to suddenly drop, thereby actuating the low-pressure cutout. The result is a short on-off-on cycling of the compressor which interferes with operation and sometimes necessitates nuisance restarts or maintenance calls.

Because of this circumstance it has become the practice to equip air conditioners with control devices which override the low-pressure cutout during the first moments of each run cycle. Such control devices keep the compressor energized for the initial one or two minutes of the cycle, even though the low-pressure cutout switches to the off position. After the initial two minutes the low-pressure cutout assumes control.

FIG. 1 illustrates by block diagram a control circuit of the present invention. As shown the circuit comprises power lines 10 and 12 for supplying an AC voltage to a compressor relay coil 14. At normal startup the compressor relay coil is energized through a circuit which includes line 16, time delay 18, line 19, the contacts of a controller 20 (which may be a thermostat or relay contacts controlled by a thermostat), line 22, time delay 24, line 26, compressor overload control 28, high-pressure cutout 30 (responsive to excessively high gas pressures in the high side of the refrigerant system), and line 32.

TIME DELAY 18

Time delay 18 18 is preferably a solid-state circuit having three terminals 4, 5 and 6. When energizer current begins to flow between terminals 4 and 5 the time delay period (e.g., 5 minutes) starts. During the delay period the circuit between terminals 4 and 6 is interrupted. At the end of the delay period a solid-state AC switch in device 18 is in condition to conduct load current between terminals 4 and 6. Such current flow automatically ceases in response to current interruption in the circuit going through terminals 4 and 5. FIG. 2 illustrates the rudiments of one solid-state circuit that can be used to provide the desired operation.

It will be noted from FIG. 1 that the so-called energizer circuit for delay device 18 includes line 16, terminals 4 and 5, line 35, normally closed contacts 34, and lines 37 and 39. When contacts 34 close the 5 -minute delay period begins; the delay period is halted either by the expiration of 5 minutes or the opening of contacts 34.

TIME DELAY 24

Time delay 24 is preferably a solid-state circuit having three terminals 7, 8 and 9. When energizer current begins to flow between terminals 7 and 8 the 2 -minute delay period begins; during this delay period the load circuit between terminals 7 and 9 is fully conductive. At the end of the 2 -minute delay period an AC switch in device 24 is biased to the nonconducting state, thereby interrupting current flow between terminals 7 and 9 even through energizer current continues to flow between terminals 7 and 8. FIG. 3 illustrates the rudiments of one solid-state circuit that can be used to provide the desired operation.

RELAY OPERATION

The illustrated coil 14 controls two auxiliary sets of contacts 34 and 36 physically arranged so that contacts 36 make before contacts 34 break (FIG. 4 illustrates one way this can be accomplished). Prior to normal startup contacts 34 and 36 are as shown in FIG. 1, coil 14 is deenergized, and delay devices 18 and 24 have both timed out; the load circuit between terminals 4 and 6 is conductive, and the load circuit between terminals 7 and 9 is conductive. Startup is accomplished by closing the contacts in controller 20, as by thermosensitive means (not shown). At startup coil 14 is energized through the aforementioned circuit comprising the series-connected mechanisms 16, 18, 19, 20, 22, 24, 26, 28, 30 and 32. As coil 14 is energized the contacts 36 close to complete a circuit through line 38. A few milliseconds later contacts 34 open to break the energizer circuit for the time delay 18; one purpose in thus breaking the energizer circuit at this time is to interrupt the load current through time delay 18 i.e., through lines 16 and 19). Load current is instead carried by line 38, so that time delay 18 is not subjected to transients caused by lightning, motor surges or other surge conditions. Another purpose in breaking the energizer circuit (at 34) is to halt or prevent the 5-minute delay period; it is intended that switch 34 close at the end of the run cycle to start the 5-minute delay period.

During the initial 2 minutes of the run cycle the current may flow between controller 20 and line 26 through either or both of two separate paths. One path comprises line 22 and time delay 24, and the other path comprises line 23 and low-pressure cutout 25 (responsive to suction line pressures in the refrigerant system). Should the low side of the system be too low the cutout 25 will open the circuit through line 23, and the load current will take the path through time delay 24.

At the end of the initial 2-minute run time the delay device 24 will time out, and low-pressure cutout 25 will assume sole control over the compressor (in conjunction with other safety controls such as the illustrated controls 28 and 30). Normal stop cycle is initiated by opening the contacts in controller 20. This action deenergizes coil 14 which stops the compressor and returns contacts 34 and 36 to their illustrated positions. As contacts 34 close they start a current flow between terminals 4 and 5 which thereby starts the 5-minute delay period. During such delay period the compressor cannot be restarted by coil 14 even though controller 20 closes its contacts to call for cooling. At the end of the 5-minute period the circuit between terminals 4 and 6 becomes conductive so that the controller contacts can thereafter energize the coil 14 in a normal run cycle.

As will be noted from previous remarks, the general purpose of the FIG. 1 circuit is to provide a 2-minute delay period during the initial portion of each run cycle so that the low-pressure cutout 25 is prevented from tripping out the compressor during this 2-minute period. A further purpose of the circuitry is to provide a 5-minute delay at the end of each run cycle so that the compressor cannot be reenergized during the 5-minute period, thus achieving the aforementioned advantages in regard to compressor lubrication and compressor motor life, among others. The circuitry is designed so that a single relay coil 14 can be used to energize the compressor (through contacts not shown) and also to program or control the time delays 18 and 24, as by means of the auxiliary contacts 34 and 36.

It is believed that time delay 18 can take various forms. However for illustration purposes there is shown in FIG. 2 the rudiments of a suitable time delay circuit. As shown, the circuit comprises terminals 4, 5 and 6 numbered to correspond with the same terminals in FIG. 1. The circuit comprises a solid-state AC switch 70 which may for example be a switch marketed by General Electric Company under the trade name Triac. The switch will conduct AC current between terminals 4 and 6 only when a sufficient negative potential is applied to its gate 72.

Assuming contacts 34 are closed to apply an AC voltage across terminals 4 and 5, the capacitance 74 will slowly charge on the half-cycles while terminal 4 is positive; charging will be through the resistance 76. Resistances 76, 77 and 79 are so chosen that initially the emitter potential of transistor 80 is greater than the base potential, thereby producing a reverse bias which holds the transistor off. As the capacitance 74 becomes fully charged the base potential for transistor 80 increases so that the transistor is fired on, thereby producing a collector-emitter current through a circuit which includes resistance 81 and line 82.

The collector-emitter current flow through transistor 80 lowers the positive potential at junction 83, thereby permitting the second transistor 82 to fire through a circuit that includes resistance 84, the emitter-collector of the transistor, and resistance 86. This action makes the gate 72 more negative so that switch 70 fires to permit load current to flow between terminals 4 and 6. The resistances and capacitance may be chosen to obtain a 5-minute delay time between initial triggering voltage across terminals 4 and 5 (closing of contacts 34 at the end of the run cycle) and conduction across terminals 4 and 6 (start of the next run cycle).

Time delay 24 can be similar in general character to time delay 18; therefore similar numerals are used where applicable. Delay 24 differs from delay 18 in that the load circuit is on during the delay period, not off. When a voltage is initially applied across terminals 7 and 8 (as when the controller 20 contacts close) a trigger voltage is applied to the gate 72 of AC switch 70 through a circuit which includes line 71, and resistance 73. Current flow on alternate half-cycles takes a path that includes line 71, resistance 73, diode 75, resistance 77, and line 79. This flow lowers the potential at junction 81, (see FIG. 3, thereby causing the gate to become more positive for thus firing the AC switch to the conducting mode.

During the initial 2-minute period capacitance 74 slowly charges, after which the transistors 80 and 82 are fired on, as by the action previously outlined in connection with FIG. 2. As transistor 82 fires its collector becomes more positive, thereby raising the positive potential at junction 85. This causes the gate 72 to go more positive, thereby biasing the switch 70 into the nonconducting mode.

FIG. 4 illustrates a portion of a relay coil 14 which includes winding 100, core 101 and flux-conducting frame 102 having a pivotal plate-type armature 104 hingedly mounted on pivot 106 for upward movement against a stop 108 (struck out of the frame) under the urging of a tension spring 110. Energization of the coil causes armature 104 to swing downwardly so that its attached arm 112 moves the spring leaf contact elements 34 and 36 downwardly. Suitable length slots 116 and 118 are formed in arm 112 so that leaf 36 engages the subjacent leaf 36' before leaf 34 leaves the superjacent leaf 34' . This make-before-break action is advantageous in that it eliminates a time race problem that can occur when the relay is used in the FIG. 1 circuit.

RELAY ACTION

Assuming the contacts 36 and 34 are in the FIG. 1 conditions, the energization of coil 14 causes contacts 36 to close and contacts 34 to open. As noted above, contacts 36 should be closed before contacts 34 start to open. If contacts 34 were allowed to open before contacts 36 closed the load circuit through terminals 4 and 6 might open before contacts 36 could take over as the holding contacts; in that event the relay coil 14 might be prematurely deenergized. With the make-before-break action shown in FIG. 4 this situation is prevented.

Claims

I claim:

1. An air conditioner refrigerant compressor control comprising a controller for initiating the compressor start and stop actions on a substantially nondelayed basis; first time delay means keeping the compressor deenergized for a predetermined period after each stop action; a compressor cutout responsive to low side conditions in the refrigerant system; second time delay means keeping the compressor energized for a predetermined period after each start action irrespective of the condition of the compressor cutout; and a single relay means controlled by the start and stop actions for electrically programming both time delay means.

2. The control of claim 1 wherein the compressor cutout and second time delay means are in electrical parallelism with one another and in series circuit connection with the controller.

3. The control of claim 1 wherein the relay means comprises a set of normally closed contacts effective to energize the first time delay means at each compressor stop action.

4. The control of claim 1 wherein the relay means comprises a set of normally open contacts arranged in electrical parallelism with the first time delay means; said first time delay means and the normally open contacts forming alternate energizer connections for the compressor during the startup period.

5. The control of claim 1 wherein the controller is series-connected with the first and second time delay means so that an open circuit at the controller deenergizes the compressor irrespective of the condition of the time delay means.

6. The control of claim 1 wherein the first time delay means comprises a solid-state device operable to provide an open load circuit when initially provided with an input energizer signal by the relay means.

7. The control of claim 1 wherein the second time delay means comprises a solid-state device operable to provide a closed load circuit when initially provided with an input energizer signal by the relay means.