US2534455A - Refrigerating control apparatus - Google Patents

Description

Dec. 19, 1950 L. B. KOONTZ 2,534,455

REFRIGERATING CONTROL APPARATUS Filed June 8, 1944 I5 Sheets-Sheet 1 Iiiwentor LHNO/VT 3. KOO/V72 attorney Deg. 19, 1950 L. B.IKOONTZ 2,534,455

REFRIGERATING CONTROL APPARATUS Filed June 8, 1944 3 Sheets$heet 2 Gttorneg Dec. 19 1950 Filed June 8, 1944 L. B. KOONTZ REFRIGERATING CONTROL APPARATUS 3 Sheets-Sheet 3 Z'mneutor L/INONT B. IIOONTZ attorney Patented Dec. 19, 190

REFRIGERATIN G CONTROL APPARATUS Lamont B. Koontz, Minneapolis, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application June 8, 1944, Serial No. 539,235

19 Claims. (Ci. 62-4) The present invention relates to improved means for controlling the flow of refrigerant through an evaporator.

The control of flow through a refrigerating evaporator involves difficulties which have not, in the past, been entirely overcome. Normally, an expansion valve is used to control said flow, said valve being operated in response to evaporator pressure, or to refrigerant pressure and temperature at the evaporator outlet. These systems are only partially satisfactory, especially when operated over a wide range of conditions.

In the present invention, applicant gains superior control over his expansion valve by operating same in response to either the temperature or the heat absorbing abilities of the flowing refrigerant at two spaced locations'within or associated with said evaporator. One of the marked characteristics of refrigerant flow through the evaporator is its constantly changing quality, that is, the constantly increasing percentage of the refrigerant which is in the gaseous state. 01 the liquid refrigerant supplied the expansion valve, 9. portion of same evaporates immediately on passingv through'the valve and serves to reduce the temperature of the remaining refrigerant. As the refrigerant then flows through, the evaporator, it absorbs heat from the medium being cooled, absorption of heat resulting in more of the refrigerant being vaporized. So long as some of the refrigerant flowing in the evaporator is liquid, and the evaporator surface is kept wet thereby, the rate of heat transfer is high,.but

when all of the refrigerant is vaporized, the rate of heat transfer is low. The considerable difference in heat transfer rate and heat absorbing ability which exists between gaseous refrigerant and mixtures of gaseous and liquid refrigerant is used in the present system in a manner to be described.

Obviously, maximum evaporator capacity is obtained when a maximum portion of the evaporator surface is wetted by the refrigerant. However, to protect the compressor, it is essential that only gaseous refrigerant leave the evaporator. With the ordinary thermostatic expansion valve, this is insured by permitting the temperature of the refrigerant, before leaving the evaporator, to rise several degrees above its vaporizing temperature, thus "superheating" same. The superheat used may be likened to a factor of safety, for the more superheat used, the more assurance there is that liquid refrigerant will not reach the compressor, althoughthe less eflective the evaporator will be for cooling because of the es amplifying means.

greater portion of same used for heating vaporized refrigerant.

It is thus an object of this invention to provide a control means which responds quickly and accurately to refrigerant conditions within the evaporator and operates to control the flow through said evaporator in a manner to insure full capacity operation of said evaporator and yet insure the passage of only gaseous refrigerant to the compressor.

It is also an object to provide refrigeration control means which is adaptable for use with any conventional refrigerant, and which is of suchvwith other control apparatus. Additionally, the

control circuits provided are such that supplementary control factors may be added to the control system at will, thereby increasing the usefulness and desirability of the present apparatus.

It isan additional object to provide improved and effective means for controlling the flow of refrigerant through an evaporator in response to the percentage of liquid refrigerant flowing past a predetermined location in said evaporator in a manner to maintain said percentage at a maximum value consistent with safe operation of the system.

These and other objects will become apparent upon a study of the following specification and drawings wherein:

Figure 1 shows a schematic embodiment of the present apparatus including spaced temperature responsive resistance means, each of said means including heater means. v

Figure 2 is a cross section of one of the present control devices including a temperature responsive means and heater means, taken on the-line 2- -2 of Figure 1.

Figure 3 is a horizontal section taken on the 7 line 3-3 of Figure 2 of said device.

Figure 4 shows a modified schematic embodiment of the present invention incorporating Figure shows a further modifled schematic embodiment of the present system incorporating fluid filled temperature responsive devices.

As suggested in the objects and as noted in the figures, the present invention includes control means for operating a more or less conventional expansion valve in a conventional compressor type refrigeration system. The control means used responds to conditions of the refrigerant at two spaced locations within, or closely associated with, the evaporator. The refrigerant flow is modified by said control means to maintain the condition differential constant between said spaced locations.

To disclose the present control means, a preferred form of same is disclosed in Figures 1, 2. and 3, this form incorporating heated temperature responsive resistors for the primary control elements. Figure 4 is a modification of the preferred form wherein supplementary heat is not supplied to the thermally sensitive resistors, and Figure 5 shows another modification wherein heat is supplied to fluid filled temperature responsive means which comprise the primary control elements in this modification. A detailed description of the above mentioned forms or modifications of the present invention follows:

Figure 1 In Figure 1, there is schematically shown a quite conventional compressor operated refrigeration system. Compressor I0, driven by an electric motor ll, discharges through pipe l2 into a combined condenser and receiver [3, wherein the compressed refrigerant is condensed and liquified in the usual manner. Condenser I3 supplies liquid refrigerant through pipe I4 and expansion valve l5 to evaporator l6. Expansion valve I5 is a conventional motor operated valve, it being driven by motor 2|, as shown. The outlet of evaporator I6 connects to suction pipe H, which is connected to the inlet of compressor I0. Preferably, a safety trap 38 is included in suction pipe H to positively prevent liquid refrigerant from entering the compressor.

The operation of compressor motor H is controlled by relay l 8, which in turn is controlled by a manual switch I9, controller 20, and float switch 45 of safety trap 38. Relay l8 comprises a coil 44 and two switching means. One switching means, which controls the operation of motor ll, comprises switch arm 40 and fixed contact 4|. Arm 40 moves out of engagement when coil 44 is deenergized. The second switching means, which controls a shunt associated with the control circuit of motor 2|, comprises switch arm 42 and fixed contact 43. Arm 42 breaks engagement with 43 .when coil 44 is energized. Controller 2|! may be of any conventional sort, but preferably it is one responding to suction pressure, head pressure and, if desired, box temperature, such as disclosed in the copending application of Carl G. Kronmiller, Serial No. 371,001, filed December 20, 1940, now Patent No. 2,377,503, is-- sued June 5, 1945. Safety trap 38 comprises a receptacle which is adapted to receive any liquid refrigerant which may flow through pipe I! toward the compressor. If sufiicient liquid accumulates in 38 to raise float 39, the contacts of float switch 45 are opened. Pipe 41 including valve 48 is provided to return any oil that may collect in said trap to the compressor.

With float switch 45 closed and the switching means of controller 20 closed, closing manual motor ll. Motor II will then start and run until it is stopped by opening manual switch l9, by conditions causing opening of the switch means of controller 20, or by the accumulation of liquid refrigerant in safety trap 38 causing opening of float switch 45. Normally, once the compressor is started by manual switch l9, it will be automatically controlled thereafter by controller 20 in a manner which will be made clear upon in spection of the aforementioned copending ap-- plication.

It was previously noted that expansion valve I5 is operated by motor 2|. Motor 2| is a standard modulating motor such as widely used in the control art, and comprises a reversible electric motor driving through a gear train, a balanced armature type relay, and a follow-up resistance also driven by said gear train. For a more complete disclosure of a motor such as 2|, reference is made to Patent 2,028,110, issued to D. G. Taylor. In said patent, and in the present disclosure, it will be noted that the operation of motor 2| depends on its supply of current and also on the conditions of balance of an electrical network. Motor 2| is supplied current by the circuit: line 50, wire 5|, wire 67, motor 2|, wire 68, wire 55, and line 51.

It was previously noted that expansion valve l5 controls the fiow of refrigerant in the present system and that motor 2| controls the operation of said expansion valve. It thus appears that the heart of the control means of the present system is the means controlling the operation of motor 2|.

The control circuit for the system of Figure 1 is seen to comprise an electrical network having a source of current and two branches. Current is supplied by line 51 through wire 10 to the center control terminal of motor 2|, and by line 50 through wire 14 to the left and right control branches. The left control branch comprises wire 1|, attached to the left control terminal of motor 2|, box temperature control device 30, wire [2, temperature responsive resistor 25 of control device 23', and wire 13 which completes the left branch of the control circuit and connects to wire 14. The right control branch comprises wire 11 attached at one end to the right hand control terminal of motor 2|, resistor 22, wire 16, temperature responsive resistor 25 of control device 23, and wire 15 which attaches to wire 14 and completes the right hand control branch of motor 2|. It will be noted that devices 23, 23' and 30 are the control elements, or condition responsive impedance means, in the circuit and, neglecting device 30 for the moment, the division of current flow through the two branches will depend on the relative resistances of resistors 25 and 25'.

To improve the response of resistors 25 and 25' to the conditions of the flowing refrigerant, in a manner that will be more fully explained later, heater resistors 26 and 26' are provided for control devices 23 and 23', respectively. These heater resistors are energized and controlled by the following circuit: Line 50, wire 80, resistor 25, wire 8|, resistor 26', wire 82, rheostat 83, wire 84, and line 51. Rheostat 83 controls the heating effects of resistors 26 and 26', and thus the heating of devices 23 and 23'.

By heating devices 23 and 23', resistors 25 and 25' each respond to a temperature which is the resultant of the heating of the respective devices by resistors 25 and 26, and to the cooling of the devices by the flowing refrigerant. This refrigerant.

resultant temperature varies more widely than the temperatures alone of the refrigerant, and thus magnifies the response of 25 and 25'.

It will be noted that device 23' is disposed in a fitting in the outlet passage of the evaporator, although it may be placed in the suction pipe near the evaporator. Device 23 is located at a point in the latter portion of the evaporator at a point wherein the fiowing refrigerant may include but never exceed a predetermined small percentage of liquid refrigerant.

Condition responsive control devices 23 and 23' are similar, hence a description of one should suifice for both. As schematically shown in Figure 1, and more fully shown in Figures 2 and 3, device 23 comprises essentially a temperature responsive resistor 25 and a heater resistor 26 in heat exchange relation therewith. The devices may be used in conjunction with a suitable fitting having a suitably enlarged refrigerant passage therethrough or may be inserted directly into an evaporator passage. Preferably, the passage or fitting which receives the device or devices should have its walls so shaped as to I encourage smooth flow along the surfaces of the temperature responsive elements. Figure 2, taken on line 2-2 of Figure 1, shows a sectional elevation of a preferred form of device 23 and its associated fitting. A plurality of turns of wire having a high temperature coefllcient of resistance (high percentage change in resistance per degree temperature change), such as nickel, are wound on a suitable core 24, said windings being denoted by numeral 25. In heat exchange relation with windings 25, are a few turns of suitable heater resistor wire, shown at 26.

The elements comprising core 24 and windings 25-26 may be inserted in a protective metal cover 23. Preferably, to improve the thermal conductance of the assembled windings and the cover, the windings may be impregnated and the air spaces filled with suitable electrical insulating and impregnating material including resinlike substances. Cover 28 not only serves to protect the windings but may also be used to attach the assembled element to cap portion 21, as shown in Figure 2. Cap portion 2'! acts as a cover or closure for the enlarged and open portion of evaporator 6, or a suitable fitting, and locates the assembled elements including the aforesaid windings in the path of the flowing refrigerant. Cap 21 may be of any suitable substance, including resins, resin-like material, vitreous material, or the like. Wire 29 extending through cap 21 is a lead from winding 25 but obviously any suitable terminal means may be provided in said cap for windings 25 and 26.

Figure 3, taken on line 3-3 of Figure 2, shows a horizontal section of device 23 and its associated fitting. It is noted that the portion of the device located in the refrigerant passage has a substantially streamlined shape. This shape is chosen to insure relatively uniform conditions of heat transfer, it being considered that the various degrees of turbulence in a turbulence flow condition would nonuniformly affect the heat transfer from said device 23 to the flowing It is also desirable that the walls of the passage be suitably modified to encourage smooth and non-turbulent flow.

Although device 23 is shown as including a protective cover portion 28, it is contemplated that the winding element and cap 21 may be molded together as a single unit, the windings being impregnated and protected by the impervi- 6 ous molding material used. The molding material used should, of course, be impervious and resistant to the refrigerants used, resin or resinlike materials having good thermal conductivity and good insulating qualities being preferable. Also, the winding element may be suitably protected by molding material and then attached to the cap portion in any desired manner.

While devices 23 and 23' are shown as extending transversely into fittings associated with an evaporator passage, it is also apparent that these devices may be differently shaped and located. For instance, either of the devices may be located near a bend portion of the evaporator and may comprise elongated elements extending longitudinally of an evaporator passage.

With the control system arranged as described, it is apparent that the system will tend to operate at full capacity. It is sometimes desirable, however, to operate at less than full capacity to minimize short cycling of the compressing equipment. For this purpose, and also to improve the temperature regulation of the cooled medium, box temperature responsive device 30 is provided. Device 30 comprises a fluid chargedtemperature responsive bulb 3| connected by capillary tube 32 to bellows 33. Bellows 33 operates to rotate pivoted arm 34, and thus move arm 36, associated with arm 34, across resistor 31. Spring 35 keeps arm 34 in contact with bellows 33 and may be used for adjustments. With relatively high temperature at bulb 3|, bellows 33 is expanded, arm 36 is at maximum counter-clockwise position, and device 30 adds no resistance to the left hand branch of the control circuit. However, when the temperature at bulb 3| drops to a predetermined low figure, arm 36 is moved across resistor 31 and then adds resistance to said left hand control branch. Added resistance in this branch causes motor 2| to operate valve l5 toward closed position and thus reduces the capacity of the evaporator and prolongs the operating period of the compressor. Obviously, as the primary control of the system is such as to operate same at the maximum safe capacity, then the only feasible supplementary control is that which reduces the capacity of the system.

When the refrigerating system is shut down, motor 2| will tend to drive valve I5 wide open, in a manner which will later appear. This is generally not desirable for there is a tendency for the suction pressure to build up and a possibility that liquid refrigerant may enter the compressor upon again starting. This is usually prer vented by providing a solenoid valve, or the like,

which closes when the system is shut down; however, by providing a shunt between the left hand control branch and a center wire 10, motor 2| can be controlled to close valve i5. The shunt circuit is completed when relay I8 is deenergized, and broken when said relay is energized; hence, it causes motor 2| to close valve I5 whenever the system is shut down.

It is noted that the improved control means for a refrigerating system has been described in a rather specific manner. It should be kept in mind, however, that the present illustrations are given only to clearly disclose the invention. Actually many changes and equivalents are contemplated. While applicant prefers modulating electric motor means to control his expansion valve. it is obvious that other reversible motors be used. Applicant finds electrical heating means more satisfactory, but here again, any equivalent heating means is suitable. Because of the desirably small temperature difference in the refrigerant at the location of devices 23 and 23', applicant prefers to add heat to his control devices toramplify their effect, as noted, but it is apparent that other means may be provided to amplify the efiects of said control devices. Further, by suitable compromises, a measure of control may be effected without any amplifying means. In addition, heat may be added to control devices 23 and 24 and then their controlling effect may be amplified by suitable means for controlling a motor.

To make the present disclosure more clear, the following operation portion of this specification will emphasize the function of the apparatus'just described. Further, to give concrete examples of some of the changes which may be incorporated in the present invention, modifications are described under Figures 4 and 5.

Operation of Figure 1 To make the description of the operation of the present control means more understandable,

certain assumptions may be made. The resistors 25 and 25' may each havea resistance value of 900 ohms at C.; resistor 22 may have a resistance value of 100 ohms, and the follow-up resistor of motor 2| may also have a resistance of 100 ohms. Resistor 64 has sufficient resistance to limit the current flow in the shunt circuit to a safe value. The value of the resistor of control device 30 is not critical, and may depend on the degree of control to be exercised by said device. The current regulating capacity of variable resistor 83 is such that heater resistors 25 and 25' may be suillciently energized to heat devices 23 and 23' about 50 higher than the ambient temperature in the evaporator when no fluid is flowing.

With the system shut down, due to manual switch l9 being opened, it may be assumed that the head pressure and suction pressure are within suitable limits and the switching means of controller 20 is closed. Safety trap 38 is dry and switch 45 is closed. Relay I8 is deenergized; switch blade 40 is out of engagement with contact 4|, and switch blade 42 is in engagement with contact 43.

Heater means 26 and 25' are energized and devices 23 and 23 are equal in temperature and about 50 warmer than the gaseous refrigerant in the evaporator. With equal temperatures of 23 and 23, resistors 25 and 25' have equal resistance values. 'It is now noted that the left hand branch of the control circuit, neglecting device 30, comprises resistor 25', whereas the right hand branch comprises resistor 25 and resistor 22. With resistors 25 and 25' of equal value, the right hand branch has 100 ohms more resistance than the left branch. This unbalance actuates motor 2| in a direction wherein it adds the 100 ohms of its follow up resistance to the left branch and thus balances the network. When the motor moves to add all of its follow-up resistance to the left branch, the valve is driven wide open, and when the motor runs in the opposite direction, the valve is closed. With the system shut down as described, however, the shunt circuit comprising wire 56, contact 43, switch arm 42, wire 53, resistor 64, and wire 65 extends between control wires 10 and H and shunts one of the relay coils of the motor out of the circuit. The other relay coil, being the only one energized, causes the motor to be driven in a direction to close valve I5 regardless of devices 23 and 23.

- mediately acting to open valve I5.

Valve I5 is thus closed when the system is shut down. With the shunt circuit causing valve 15 to be closed regardless of the devices 23 and 23', it seems obvious that the temperature affecting bulb 3| has no controlling effect when the system is shut down.

With the condition of the system as Just outlined, closing manual switch It! energizes relay I8 by the circuit: line 50, wire,5l wire 52, wire 58, relay coil 44, wire 59, switch l9, wire 50, float switch 45, wire 45, controller 20, wire 5|, wire 55, wire 56, and line 57. Energizing relay l8 results in switch arm 42 being pulled out of engagement with contact 43, and in switch arm 40 being pulled into engagement with contact 4|. Opening the first named switch means removes the shunt from the control circuit of motor 2|, said motor im- Closing of the second named switch of the relay causes the compressor motor to be energized, the circuit being: line 50, wire 5|, wire 52, contact 4|, arm 40, wire 53, motor II, wire 54, wire 55, wire 55,

and line 51. The compressor I0 is thus started by motor ll.

With the system started, it is noted that the refrigerant flow through evaporator It increases as valve [5 is opened. At the beginning of the operation of the system, and before refrigerant starts to flow through evaporator l5, devices 23 and 23 are at equal temperature and about 50 warmer than the ambient temperature in the said refrigerant evaporator. As was previously noted, when devices 23 and 23' are equal in temperature, valve [5 tends to be driven wide open. The refrigerant flow will thus tend to increase until the control circuit is altered in a manner to limit the valve movement.

Because of the residual heat of the evaporator and the small initial flow of refrigerant, the first refrigerant to circulate past devices 23 and 23' is completely vaporized and therefore has rela-' tively little effect on said devices. Further, because of the comparatively low heat transfer ability of the vaporized refrigerant, the temperatures of the said devices are nearly equal.

As the evaporator picks up its cooling load and the refrigerant flow continues to increase, the temperatures of devices 23 and 23' will drop. However, so long as the flow passing both devices is gaseous, their temperatures will remain quite close together. For the purpose of this illustration, it may be assumed that a maximum flow of gaseous refrigerant will have sufllcient cooling effect on the devices 23 and 23' to reduce the resultant temperature of said devices to about 35 above that of said gaseous refrigerant, instead of the 50 differential when there was no flow.

As the medium being cooled has its temperature reduced, and its heating effect on the evaporator is thus reduced, the liquid, or wetted surface, level of the refrigerant in the evaporator rises and advances toward the outlet. As device 23 is upstream of 23', any change in quality of the refrigerant flow will affect device 23 first. When small amounts of liquid refrigerant come in contact with 23, it not only tends to wet the surface of said device, and thus increase the heat transfer rate, but it also absorbs heat to vaporize same. Small amounts of liquid refrigerant thus have much more effect in carrying away the heat of device 23 than does gaseous refrigerant. A relatively small amount of liquid refrigerant will lower the temperature of 23 to that of said liquid. Assume that a refrigerant flow of 97% quality, that is, a flow wherein 3% of the refrigerant is liquid and 97% is gaseous, will lower the temperature of 23 to the vaporizing temperature of the liquid. It then appears that a change in the quality of the refrigerant flowing across the device 23 varying from 100% gaseous to 97% gaseous and 3% liquid will cause a temperature drop of said device of 35.

The large temperature change at device 23 occasioned by a small amount of liquid refrigerant in the flow at said device causes a proportionately large variation in the ohmage resistance of temperature responsive resistor 23. Temperature of refrigerant having a small portion of same in the liquid state is the vaporizing temperature of said refrigerant and, at constant pressure, this temperature will remain the same until all of the liquid is vaporized. Devices 23 and 23' are so located and adjusted that a refrigerant flow including sufilcient liquid refrigerant at device 23 to lower its temperature to the vaporizing temperature of the refrigerant will gain a small amount, say 5, of superheat by the time it reaches 23'. Should the quality of the flow vary to provide all gaseous refrigerant at vaporizing temperature at device 23, the superheat at 23' will tend to rise, but that rise will be slight, say 2, due to the low-rate of heat transfer to said gas.

It is noted above that a change in refrigerant flow which will cause a small change in the superheat of the outgoing refrigerant, will cause a change of 35 in the temperature of control device 23 relative to 23. There is thus provided a considerably multiplied temperature response which makes possible a highly accurate and responsive control means for regulating a control device. In addition, due to the small rate of change in the temperature coemcient of resistance of the nickel wire used for resistors 23 and 25', the precision of the control remains substantiallyconstant over a wide range of operating temperatures.

With sufllcient liquid refrigerant contacting device 23 to reduce its temperature to that of said liquid, said temperature being about 35 lower than that of device 23', the resistance of resistor 25 becomes about 200 ohms less than that of 25'. If valve l5 was wide open, it was noted that the follow-up resistor of motor 2| was added to the left hand control branch of the control circuit, said follow-up resistor balancing out, resistor 22. If the right hand control branch now has its resistancevaried to 200 ohms less than that of said left hand branch, motor 2| operates to add said follow-up resistance to the right hand branch and removes same from the left hand branch. With resistor 26 having 200 ohms less resistance than 25', it is seen that it requires that both resistor 22 and the follow-up resistor of motor 2|, each of 100 ohms resistance, be added to resistor 23 to balance the circuit. It was previously noted that valve I! was wide open when all the followup resistance was added to the left hand control branch; hence, with the motor having operated to its other extreme to add its follow-up resistance to the right hand branch. the valve is now driven closed.

With the system running, it is now clear that valve i5 is driven toward wide open position when only gaseous refrigerant flows past devices 23 and 23', and the said valve isdriven closed when 3% of the flowing refrigerant at device 23 is liquid. Thus a 200 ohm difference in the resistance value of resistors 23 and 23' is sumcient' to cause motor 2| to operate from one extreme to the other. Obviously, if the flowing refrigerant at device 23 must have 3% of same in the liquid state to decrease the temperature of 23 35 5 below that of 23' and to cause a 200 ohm unbalance in the control circuit, then a smaller quan-- tity or percentage of liquid refrigerant will cause a lesser temperature drop andtherefore cause less unbalance inthe control circuit. Motor 2| will then tend to assume an intermediate position and the flow will be so controlled by valve I6 that the refrigerant flowing past 23 will contain some liquid refrigerant but not more than 3% of same.

Following the present description, it should be kept in mind that the values given are illustratlve only. Further, by changing the amount of heat supplied to devices 23 and 23', device 23 may be made to respond to a larger or smaller percentage of liquid refrigerant. With the present circuit, it is noted that there is a small amount of heat generated in winding 25 and 25' due to the control current flowing through same, but this merely reduces the heat that must be supplied by 26 and 26'. Under some circumstances, however, it may be possible to use large enough a control current to provide the requisite heating effect. Of course, theheat exchange properties of the devices 23 and 23' may also be altered by design and construction changes, and thus become inherently more or less responsive to quality changes of the refrigerant.

S far. in this description of operation, it has been assumed that maximum capacity operation is desired of evaporator l8. However, if the evaporator has a light cooling load, the controller 20, or other such control means may cause frequent but short running cycles of the compressor. To

minimize this short cycling, box temperature responsive device 36 is provided in the left hand control branch of motor 2|. As before noted, device 30 comprises a variable resistor operated by temperature responsive bulb and bellows means. With temperature high at bulb 3|, bellows 33 is expanded and arm 36 is at the minimum resistance portion of resistor 31. The control circuit of motor 2| is thus not afiected by device 30 when temperatures affecting said de- 50 vice are relatively high, or when said device is unsatisfied. However, when device 30 becomes satisfied. bellows 33 is retracted, arm 36 moves across resistor 31, and resistance is added to the left hand control branch of motor 2|. 55 Adding resistance to the left hand branch affects the control circuit in the same manner as lowering the resistance in the right hand branch. Thus motor 2| is caused to move in a direction to add follow-up resistance to the right hand 00 branch, this direction of operation causing closing movement of valve l6, before noted. A partial closing of valve l reduces the evaporator capacity, prolongs the operating period, and thus minimizes short cycling.

when the system is shut. down, as by manual switch l6 or by other means, the immediate result is an increase in suction pressure and a reduced rate of flow through the evaporator. This reduced rate of flow may cause the liquid 79 level to retract or retreat somewhat and thus cause device 23 as well as 23' to be contacted only by gaseous refrigerant. As before noted, when these devices are equal in temperature, valve I6 is driven wide open. Driving valve I3 7 open with the system shut down would cause refrigerant to boil out of condenser and receiver I3 and to distribute itself through the system, evaporator I6 being filled with liquid refrigerant because of its being the coldest part of the system. With the equalized pressures throughout the system, and with the evaporator I full of liquid, starting the compressor might be hazardous.

To avoid the troubles associated with leaving valve I5 open when the system is shut down, motor 2I is controlled by the previously mentioned shunt circuit to drive valve I5 closed upon system shut-down. When the relay circuit is deenergized to cause said shut-down, arm 42 engage contact 43 and one of the relay coils of motor 2| is shunted out of the control circuit by the following circuit: wire 10, wire 68, contact 43, arm 42, wire 63, resistor 54, wire 55, and wire 1I. It is thus seen that the relay coil of the left hand branch is shunted out, hence the relay coil of the right hand branch is the only one energized and, acting in the same manner as though there is lower resistance in the right hand branch, it causes said motor to drive valve I5 completely closed.

In brief review, it is noted that a refrigeration system may be controlled by operating the expansion valve with a modulating motor, said modulating motor being controlled by devices responsive to the heat exchange properties of the refrigerant at two spaced locations associated with the outlet portion of the evaporator. By using temperature responsive resistors at said locations, and using said resistors directly in the control circuit of said motor, the resulting system is made desirably simple. Heat is added to the control devices so that the actual temperatures to which said resistors respond are the resultant temperatures due to said heating and to cooling by refrigerant. Because these resultant temperatures vary widely with small changes in liquid content of the refrigerant, the present control apparatus is many times more responsive to changes in the refrigerant flow than are the known control systems of the prior art. Temperature responsive resistors, which interpret these changes in resultant temperature in terms of electrical resistance, have relatively stable and dependable characteristics, hence the apparatus may be used without adjustment or change over a wide range of temperature. Further, it is shown that, by simple modifications of the apparatus, other control factors, such as box temperature, may be considered. It has been previously mentioned'that the present examples are to be considered illustrative only and not in a limiting sense. Various substitutions and alterations are obviously feasible in the present apparatus, such as device 30 being humidity instead of temperature responsive. Motor 2I may have a separate follow-up means, or in some instances, may be a reversible motor floating between end positions. The effect of changing refrigerant conditions is shown to be amplified by the addition of heat to the control devices, but it appears that the response to the description of the apparatus of Figure 4, which follows.

Figure 4 The system and apparatus shown in Figure 4 will be noted as a modification of Figures 13, and wherein temperature responsive resistors are used to detect refrigerant temperatures at spaced locations. However, this modification differs from Figure 1 by providing a different electrical network circuit incorporating the resistors, and by magnifying the controlling signal potentials from said network by clamp-needle amplifying means. The comparison of this modification with Figure 1 will become more clear as the description proceeds.

The basic refrigeration system used herein is the same as that of Figure l, and like parts have been given the same numerals. It is noted that compressor I0, driven by motor II, discharges through pipe I2 into condenser and receiver I3. Receiver and condenser I3 discharges liquid refrigerant through pipe I4 to an expansion valve I5 which controls flow through evaporator I6. Suction means I1 extends between the outlet of evaporator I6 and the inlet of compressor I0.

The operation of the compressor may be controlled by controller 20, which responds to high pressure, suction pressure, and possibly box temperature, as before, and a manual switch I9. The circuit controlling motor II is: line 50, wire 5I, manual switch I9, wire 52, controller 20, wire 53, wire 54, motor II, wire 55, and line 51.

Obviously, any suitable means of controlling the of the control devices may be amplified by other 7 means. In addition, other means than temperature responsive resistors may be used to respond to the resultant temperatures as herein described.

These and other changes and modifications are believed within the scope of the present invention. To more fully consider possible modifications of the present apparatus, reference is made operation of motor I I may be used.

In this apparatus, as before, novelty is believed to lie in the means controlling the expansion valve, the valve itself being conventional. The reciprocable stem of the expansion valve I 5 carries a rack IOI which is reciprocated by pinion I02. Rack I 0| carries a slider I25 which coacts with follow-up resistor I23 in a manner to be described. Pinion I02 is driven through a gear train by a reversible motor I03, said motor I03 being controlled and operated by current supplied through a sensitive clamp-needle type relay I04. The motor I03 has a pair of field windings I83 and I88 and its direction of operation depends on which, if any, of the windings is energized by said relay. Relay means I04, as herein used, is preferably of the sort shown in Gille et a1. Patent 2,331,183, issued October 5, 1943. "Upon reference to said patent, it will be noted that the sensitive element of this relay means comprises a galvanometer which responds to the unbalance of the present electrical network.

Essentially, and as schematically shown in Figure 4, relay I04 includes control input terminals I13 and I14 which are connected to and energize galvanometer I80. Relay I04 also includes control output terminals I11, I18, and I10, and power input terminals I15 and I16. Galvanometer I actuates switch arm I which is connected to power input terminal I16 and which may engage eitherof contacts I92 or I03, connected to output terminals I11 and I19, respectively. Power input terminal I15 is connected directly to control output terminal I18. Power is supplied to relay I04 by wire I84 from line 50 to terminal I16, and by wire I85 from line 51 to terminal I15.

Box temperature responsive device I3I includes a fluid charged ,bulb I32 connected by a capillary tube I33 to bellows I34. Bellows I34 causes motion of pivoted arm I35 which sweeps over accuse resistor I06. In an unsatisfied condition, bellows I34 of device I3I is expanded and arm I36 is at a position of minimum resistance on resistor I36. Upon reaching a predetermined low temperature at bulb I32, bellows I34 is retracted and arm I36 slides along resistor I36.

Temperature responsive devices I42 and I60 may be generally similar to devices 23 and 24 of Figure 1, with the heaters omitted. Resistors I43 and I46 of devices I42 and I60, respectively, are preferably of wire having a high and relatively unchanging coeflicient of resistance, such as nickel. If desired, the devices 23 and 23' of Figure 1 may be used, heating windings 26 and 26' not being used. However, because the heat exchange between said devices I42 and I50 and the flowing refrigerant is of less consequence than in the preceding example, the shape of these devices is not as critical as in said preceding example. These devices may be incorporated in suitable fittings, or inserted directly into evaporator passages, as shown.

These control devices are associated together in the electrical network herein used which is seen to be a modified bridge circuit and is generally designated by the numeral I I0. The source of current for. the control network comprises battery I I I, one terminalof said battery connecting through wire II2 to input terminal H3, and the other terminal of the battery connecting through wire H4 to input terminal II 6. The upper left hand branch of network IIO includes, in series, wire II6, resistance II1, wire II8, and output terminal H9. The upper right hand branch of said network includes, in series, wire I20, fixed resistance I2I, wire I22, terminal I23, the portion of resistor I24 between terminal I23 and slider I26, and slider I25, said slider I26 being connected to the other network output terminal I26 by wire I21.

The lower left branch of network I I0 includes, in series from terminal II6, wire I30, box temperature responsive device I3I, wire I, temperature responsive resistor I43of device I42, wire I44, balancing resistor I46, and output terminal II9.

The lower right hand branch of said network includes, in series from terminal II6, wire I48, temperature responsive resistor I46 of device I60, wire I5I, terminal I62, the portion of resistor I24 lying between terminal I62 and slider I26, and slider I25, said slider I26 being connected by wire I21 to the output terminal I26 of said network. Network output terminal H6 is connected by wire I6I to terminal I13, and terminal I26 connects by wire I02 to terminal I14. Thus an unbalance in network H0 is communicated to galvanometer I30 of relay I04, which controls the operation of motor I03 in a manner previously related.

Because this system, as just outlined and as will be more fully explained later, will inherently drive motor I03 to close valve I5 upon stopping the operation of compressor I0, thermal time delay relay means I60 is used to condition the control circuit in such manner that valve I6 will assume an open position during times of non-operation. Solenoid valve I10, connected in parallel with heater I6I by wires HI and I12, is used to stop refrigerant flow to valve I6 when the system is not operating, for reasons which will appear.

Relay I00 comprises a bimetal strip I66 carrying a contact which engages a stationary contact when strip I66 is cool. when strip I66 is warmed by heater I6I, said strip warps and breaks the circuit through the contacts. The heater is so designed relative to strip I66 so as to require energization for a predetermined time before its heat is sufficient to warp said strip. Heater I6I is energized by the circuit: line 60, wire 6|, manual switch I6, wire 62, controller 20, wire 63, wire I64, heater I6I, wire I63, wire I62 and line 61. Heater I6I is thus energized in parallel with motor II. The contacts of relay I control a shunt comprising wires I and I 96, connected to wires I H and I44 respectively. This shunt short circuits resistor I43, thus the resistance of the lower right hand branch of the net work is high compared to the lower left branch. This unbalance, as before described, causes valve I6 to be opened. I

It should be noted in a description of the present system that many of the present devices are illustrative only and may be of different sort without essentially altering the system. For instance, I3I may just as well be a humidity responsive apparatus, or the like, and device I60 may be any suitable sort of time delay relay. Further, other conventional amplifying means suitable for controlling the operation of a reversible motor in responseto the unbalance of a network circuit may be used, such as an electronic amplifier. In addition, certain rearrangements in the control network are considered feasible and within the bounds of this invention.

The relation and function of the apparatus in the present system will be more fully explained in the following operation schedule.

Operation of Figure 4 With the parts in the positions shown, the

system is in normal operation and compressor I0 is being operated by motor II. Motor II is energized by the circuit above described and solenoid valve I10 and heater I6I of relay I60 are also energized in parallel with motor II, as previously set forth.

Valve I6 is shown as being about half open and, as device I3I is in an unsatisfied condition, control over motor I03, which operates valve I5, is being exercised only by temperature responsive devices I42 and I60. It is noted that temperature responsive device I42 is located far enough upstream in the evaporator so that it may always be in contact with liquid refrigerant and thus be at the temperature of the liquid refrigerant. Device I60 is located near the outlet of the evaporator, and it is intended that all refrigerant passing same must have a predetermined number of degrees superheat. Assuming that the refrigerant passing device I50 should have at-least 4 of superheat, and not over 8 of superheat, neglecting the effect of the box temperature responsive device, then it is seen that a change in relative temperature between device I42 and device I50 of 4 should sufficiently unbalance said network IIII to cause valve [I6 to assume either of its extreme positions. For instance, when the superheat falls to 4, valve I5 should be driven to its closed position to insure against liquid refrigerant leaving the evaporator. When the superheat rises to 8, valve I6 is fully open to permit full capacity operation of evaporator I6.

With the system in operating equilibrium, and the refrigerant flowing past temperature responsive device I60 having about 6 of superheat, device I42 is at the vaporizing temperature of the refrigerant, and network H0 is balanced in the following manner: the ratio of the resistance of the upper left hand branch of the network to that of the lower left hand branch of the network is the same as the ratio of the resistance of the upper right hand branch to that of the lower right hand branch of said network. With the network balanced as described, there is no output current at terminals H9 and I26, galvanometer I80 of relay I04 is not energized, and the system continues to operate as before.

Should the number of degrees of superheat of the refrigerant pass in device I50 rise above 6, the resistance of temperature responsive resistor I49 is increased and unbalances network IIO. This causes current to flow from network output terminals H9 and I26 to control input terminals I13 and I 14 of relay device I04 through wires I8I and I82, respectively. The flow of current to said input terminal energizes galvanometer I80 and causes same to deflect to the right. When galvanometer switch arm I85 engages contact I 93, winding I83 of motor I03 is energized. Motor I 03 then rotates pinion I 02 in a direction to open valve I5. The energizing circuit for said winding is: power input terminal I16, galvanometer arm I85, contact I93, control terminal I19, wire I86, winding I83, wire I81, control terminal I18 and power input terminal I15. Of course, it should be noted that the circuit within relay means I04 is only schematic and may not represent the actual circuit within same.

It is noted, however, that as valve I5 is opened, slider I 25 is raised along resistor I 24 and thus decreases the amount of resistor I24 which is in the network branch which contains temperature responsive resistor I49. The decrease in resistance of the upper portion of resistor I24 tends to offset the increase in resistance of I49 due to the added superheat. Further, the resistance of the lower portion of I24 is increased, thereby increasing the resistance of the upper right-hand branch of the network. Thus the network is brought back into balance at a more widely open position of valve I5. The more widely opened valve may supply suilicient refrigerant to decrease the number of degrees superheat at device I50 to the previous six degrees. but if the superheat continues to rise, the network becomes unbalanced again, and again rebalances at a more widely open position of the valve. When the superheat rises to 8, the valve will be fully opened. as before noted.

Should the number of degrees of superheat at device I50 diminish below a previous level and under 8", network H0 is unbalanced in the opposite direction. The current flow at output terminals H9 and I26 is in reverse direction and galvanometer arm I85 deflects to the left and engages contact I92, thus energizing winding I08 01' motor I03 in a manner previously described. This causes a reverse operation of motor I03 and a closing motion oi said valve. As the valve is operated, slider I25 moves over resistor I24 to rebalance the network. Should the superheat continue to diminish, the valve will be further operated to reduce the flow, and when the superheat diminishes to 4, the valve will be completely closed.

In the above discussion, box temperature responsive device I3I has been ignored. So long as the temperature affecting bulb I32 is relatively high, and bellows I34 is expanded, arm I35 is at a position of minimum resistance on resistor I36 and the device has no effect on the network. However, as the temperature of the cooled medium is reduced, and bellows I 24 is retracted thereby, arm I35 moves along resistor I36 and adds resistance to the lower left branch of the network. Added resistance in the lower left branch has the same effect on the network as less resistance in the lower right-hand branch and thus causes a closing of the valve and requiring a higher number of degrees of superheat at device I50 to rebalance the network. The reduction of capacity caused by device I3I tends to minimize short cycling and also permits closer temperature control even though the compressor be started and stopped in response to box temperature. When the evaporator is stopped with an evaporator full of liquid, appreciable cooling of a medium can take place after the compressor has stopped. This is minimized by increasing the number of degrees of superheat as the medium cooling becomes satisfied.

Just as device I3I can cause the control system to maintain various degrees of superheat, so can variable resistor I45 vary the degrees of superheat to be maintained. Variable resistor I45, in the lower left branch of the network H0, is used to adjust the network to maintain a desired superheat.

Assume now that the system is shut down due to controller 20, or the opening of manual switch I9. Upon stopping the system, it is noted that the circuit supplying current to heater I6I and solenoid valve I10 is deenergized. Solenoid valve I10 immediately closes and prevents further flow of refrigerant to the evaporator. The time delay relay cools and closes its contacts. Closing the contacts of relay I60 causes resistor I43 to be shorted out of the network circuit by wires I and I96, which connect to wires MI and I44, respectively. Whatever the position of valve I5 when the compressor was stopped, the closing of solenoid valve I 10 stops all further refrigerant flow to the evaporator, and because of the lack of flow through evaporator I6, devices I42 and I 50 assume equal temperature. This equal temperature due to shut down has the same effect on the network circuit as lowering the superheat to zero, therefore the circuit would normally control the operation of motor I03 to drive valve I5 closed.

There is no harm in valve I5 being closed when the system is shut down but, with the valve closed, the refrigerant flow cannot be established again on starting the compressor. However. by shunting resistor I43 out of the network I I0. as above described, motor I03 is caused to operate in a manner to open valve I5. Thus, when the solenoid valve is opened, refrigerant flow may be established. Control devices I42 and I50 then come within the influence of said flow before the thermal time delay relay opens its contacts and removes the shunt. As was previously noted, when the resistance of the lower right-hand branch of the control network is relatively high, the valve is opened. In this case, the resistance of the lower right-hand branch has been made relatively high by lowering that of the lower left-hand branch. The period of time required to open the contact of time delay relay I60 is so chosen as to permit a suflicient refrigerant flow to be established so that devices I42 and I50 can take over the control of valve I5 in the intended manner.

In review, the expansion valve of the present refrigerating system is operated by a reversible electric motor. The motor is controlled to operate for a period of time and in a direction determined by an electrical network associated with sensitive relay means. The network comprises spaced temperature responsive resistor means located so that one is kept at the vaporizing temperature of the refrigerant, whereas the other responds to the superheated outlet gas temperature. A rise in temperature at the outlet relative to the vaporizing temperature, unbalances the network to cause the valve to be opened. whereas a decrease in the outlet temperature, relative to the vaporizing temperature, causes said valve to be closed. Supplementarycontrol factors may be considered in the network by varying the resistance of a branch of the network. Further, to insure the valve being opened at the start of operation of the system, a portion of the network is modified by a shunt controlled by a time delay relay, the relay being energized by the circuit controlling the compressor operation.

It is noted that certain modifications are obviously within the scope of the present invention. For instance, relay I may be of any suitable sort, or may be more in the nature of amplifying means, such as an electronic amplifier. The time delay relay may be of any suitable sort. In addition, the particular part of the network modified by the action of said time delay relay device is subject to certain changes. The box temperature responsive device 3| may or may not be used and it, too, may modify the network in a manner other than shown, if desired. These and other changes will be readily apparent to those skilled in this art.

In this modification, as in the preferred extem is illustrative only and is subject to wide variation.

ample, control means are disclosed which regulate the action of a motor operated expansion valve in response to the temperature differential between spaced devices associated with the re-. frigerant fiow through the evaporator. As both devices respond to temperature, their responses to changing conditions are uniform and equally rapid. The temperature responsive resistors used have a relatively stable temperature coeflicient of resistance and thereby make the control system accurate and efficient over a wide range of operating conditions. It is noted that. due to the improved control means described, the present systems are quickly responsive, accurate and dependable at any operating condition within a wide range. These characteristics make possible another advantage; namely, the control of the system to a relatively small number degrees of superheat, thus increasing the efiectiveness of the system for its intended purpose. These and other advantages are believed inherent in greater or lesser degree to both of the examples given. Another modification incorporating many of the advantages recited and having other advantages peculiar to itself will be found described under Figure 5, which follows:

Figure 5 The system of Figurej is quite similar to that of Figure 1, but differs therefrom in using fluid temperature responsive means for controlling the operation of the expansion valve rather than electrical means as in Figure l. The basic While the expansion valve used at present is shown to be different from that of the other figures, it may be the same as valve l5 and have its fiuid motor as a separate unit. However, itis quite conventional to combine a fluid motor with an expansion valve and this has been done in this instance. Expansion valve 2| 5, which controls the refrigerant flow from pipe I to evaporator IO, comprises movable valve member 2l6 which is connected to flexible diaphragm 2l'i. Diaphragm 2| I separates the motor portion of said valve 2|! i'nto compartments M8 and M9. Obviously, differences in pressure between chambers 2|! and 2| 9 will tend to cause movement of said diaphragm 2H and associated valve member Ill. Valve member 2|6 and diaphragm 2|! are constantly urged upwardly, or toward a closed position, by spring 220. is connected to suction pipe ll of the refrigeratlng system by tube Hi and pipe 222, whereas chamber 2" is connected to a closed receptacle.

225 by tube 228. In the structure recited, valve member 2i! is urged toward closed position by spring 220 and by pressure in chamber 2I9, corresponding to suction pressure, and is urged toward open position by the pressure existing in chamber 2", corresponding to that in receptacle 225.

Receptacle 22! is a closed vessel having an upper connection to tube 228, as before noted, another upper connection through restrictor means 221 to pipe 222, and a third connection to tube 228 which connects to the outlet of pilot valve 280. The inlet of valve 230 is supplied with liquid refrigerant through tube 23] which is also connected to liquid refrigerant line H. Tube 2" includes solenoid valve 2H), previously mentioned. Valve 22!! comprises movable member 232 which controls flow from tube 23I to tube 222.

It will now be noted that the position of valve member 232 will determine the position of expansion valve member 2. The pressure in chamber 2|! always corresponds to suction pressure. The pressure in chamber 2! corresponds to that in receptacle 225, which depends on the comparative rates of flow into and out of said receptacle. The fiow out is through restrictor 221, and flow in is through valve 230. If the flow through valve 220 is stopped, pressure in 225 will be reduced to-suction pressure, and thus the pressure in chambers 2| 8 and H9 will be the same. Valve member 2 I6 is then closed by spring 220. With pilot valve 230 open, the pressure in 22! will exceed the suction pressure by an Chamber 2 I 9' the flow through restrictor 221 is at varying pressures and, without receptacle 225, both liquid and as may flow through same. Receptacle 225 is provided to insure that only gaseous refrigerant will flow through the restrictor 221, thus keeping its flow characteristics uniform. If the ambient temperature at the location of said receptacle is not high enough to insure the vaporization of any liquid that may be collected in same, the receptacle may be placed in heat exchange relation to a liquid line, the compressor cooling system, or the like. Further, rather than a separate re ceptacle, 225 may comprise an outer chamber associated with pilot valve 230, said outer chamber thus being in heat exchange relation to the inner liquid chamber of said valve.

Valve member 232 of ilot valve 23!) is operated by a pivoted lever 234, which is connected by link 235 to pivoted lever 236 of differential controller 240. Controller 24!] comprises oppositely arranged bellows 241 and 25! operating against pivoted lever 23; in such manner that the position of said lever is a resultant of the forces of the opposing bellows. Bellows 241 and 25! are driven by fluid pressure transmitted through capillary tubes 246 and 250, associated with devices 242 and 244, respectively.

Devices 242 and 244 are similar and a description of one is pertinent to the other. Device 242 comprises a fluid charged bulb 245 connected to tube 246, and arranged longitudinally in a passage of evaporator !6. A heater element 255 is arranged in heat exchange relation with said bulb for a purpose which will be explained.

Device 244 is arranged in the outlet passage of evaporator !6, although it may be in the suction pipe near said evaporator. Device 242 is positioned at a point beyond which the refrigerant flow should never contain more than a predetermined small quantity of liquid refrigerant. As in the first example, the present control devices and the surrounding refrigerant passages should preferably be shaped to minimize turbulence in the refrigerant flow.

Heaters 255 and 256 of devices 242 and 244 are energized as follows: line 50, wire 210, rheostat 258, wire 21!, heater element 256, wire 212, heater element 255, wire 213, and line 51.

As is well known, the pressure exerted by a bulb-bellows arrangement is dependent on the temperature affecting the bulb. Thus the pressures exerted by bellows 241 and 25! are dependent on the temperatures of bulbs 245 and 249, respectively. Relatively high temperature at bulb 249 will be seen to cause bellows 25! to force lever 236 counterclockwise, thus closing pilot valve 230 and resulting in closing of expansion valve 2!5. Likewise, relatively high temperature of bulb 245 will result in expansion valve 2!5 being opened.

In addition to bellows 241 and 25! acting on lever 236, a bellows 260, connected by capillary tube 26! to box temperature responsive bulb 262, is provided. Bellows 26D coacts with lever 236 through an arm 263 having an angularly disposed pivot portion 264 bearing against the righthand side of said lever. Pivot portion 264 and lever 236 is spaced far enough away from bellows 260 that expansion of said bellows will have no effect on said lever. However, contraction of bellows 260 will cause pivot portion 264 to bear against and to move lever 236 counterclockwise. Thus a predetermined low temperature of bulb 262 will result in the expansion valve 2!5 being adjusted toward closed position.

Although fluid operation of the expansion valve is illustrated, it is apparent that lever 236 might be used to operate a control potentiometer, or like means, associated with an electric motor for operating expansion valve 2l5. This and other modifications of the present apparatus are believed obvious when considering the present invention as a whole.

To more fully disclose the function and cooperation of the various parts of the present control means, a fuller description of theoperation of the system of Figure 5 follows:

Operation of Figure 5 With the parts in the position shown, the system is at rest, motor is not operating, solenoid valve 2 I0 is closed, expansion valve 2 !5 is closed, and pilot valve 230 is opened. As previously noted, control devices 242 and 244 include temperature responsive bulb means 245 and 249, respectively. When refrigerant is flowing through the system, these bulbs respond to the resultant temperatures due to the effect of refrigerant flowing past same and the heat being added by their heaters. But no refrigerant is flowing, there is nothing to cause a temperature differential to exist between them and their effect on their respective bellows are equivalent.

It may be assumed that sufficient current is supplied to heater elements 255 and 256 so that bulbs 245 and 249 will be about 50 warmer than the ambient temperature in said evaporator when there is no flow through same.

Controller 240 and pilot valve 230 are initially adjusted so that a condition of zero temperature differential between devices 242 and 244 will result in said valve 230 being wide open. As before noted, valve 230 controls refrigerant flow from tube 23! to tube 228, but, as solenoid valve 2!!) in tube 23! is closed, there is no flow through said pilot valve. In consequence, the pressure existing in receptacle 225 is due to the communication of said receptacle through restrictor 221 and pipe 222 with suction means !1. However, the pressure in chamber 2!!) of valve 2!5 is also due to that existing in suction means I1. As the pressures existing in chambers 2!8 and 2!9 are equal and opposite, valve member 2!6 is then driven closed by spring 220.

To place the system in operation, manual switch !9 may be closed and, if the switches in controller 20 are closed, relay coil 244 is energized by the circuit: transformer secondary 206, wire 58, solenoid valve 2!0, wire 59, controller 20, wire 60, relay coil 44, wire 6!, switch !9, wire 62, and said transformer secondary 206. Energization of relay coil 44 pulls switch arm 40 into engagement with contact 4! and starts motor I! by the circuit: line 5!], wire 5!, wire 52, contact 4!, arm 40, wire 53, motor !I, wire 54, wire 55, and line 51. Compressor I0 is now operating and compressing refrigerant which is liquified in condenser l3.

As before stated, however, valve 2l5 was closed hence no refrigerant flow from condenser and receiver !3 can immediately take place through valve 2!5. However, the opening of valve 2!!) permits high pressure refrigerant to flow through tube 23! and open pilot valve 230 into receptacle 225 thereby raising the pressure within said receptacle. At the same time, operation of the compressor has started to reduce the suction pressure in I1; hence with the lowering of the pressure in chamber 2!!! and an increasing of the pressure in chamber 218, the force of spring 220 ward open position. Refrigerant flow through said va'lve2i5' into evaporator" is thus graduallystarted. {While itmay appear that the head ressure ofathe system would tend to rise and open a switch of controller 26, due to valve 2l5 being closed, it is noted that the head pressure is dependent on the condenser temperature, the condenser, not having been used for some time, shouldbe sufficiently low in temperature to keep said head pressure from rising. It is of course, assumed that the condenser and receiver II have adequate capacity to hold the liquifled refrigerant of the system.

With a flow of refrigerant now established in evaporator, I6 and with pilot valve 230 wide open, valve 215 is drivento a wide open position hence evaporator l6 tends to be loaded to'its maximum capacity. 80 long as gaseous refrigerant only is flowing past bulbs 245 and 249, they drop but little in temperature due to the relatively low heat transfer abilities of the gaseous refrigerant, it being noted that heaters 255 and 256 are energized by the circuit previously related. As bulbs 245 and 249 are equally heated, and as they are both being swept across by gaseous refrigerant,

their temperature drop is relatively small and rather uniform because the temperature of the gaseous refrigerant is changed relatively slowly as it passes through the evaporator. There is thus little temperature difl'erential to cause the operation of controller 246, therefore pilot valve 2" remains open until liquid refrigerant comes in contact with bulb 245.

When liquid refrigerant begins to contact bulb 245, it removes heat from said bulb at a much higher rate than the gaseous refrigerant due to its better heat conductive properties and its ability to absorb heat to change its state. A comparatively small amount of liquid refrigerant contacting bulb 245 is sufficient to cause a marked lowering of temperature of said bulb. As a. lower temperature of a fluid-charged bulb causes a reduction in pressure of the fluid in said bulb, bellows 241 is contracted and arm 236 of controller 246 is moved counterclockwise by the higher pressure of bellows 25l, thereby actuating valve member 232 of pilot valve 230 toward closed position.

When pilot valve 230 was open, the pressure existing in receptacle 225 was high due to high pressure refrigerant being supplied through tube 23l, valve 230, and tube 228 at a higher rate than it could flow from said receptacle through restrictor 221 to the suction line. However, as valve 230 is moved toward closed position, the pressure in receptacle 225 is lowered and, as said pressure is the resultant of the inward flow through the pilot valve and the outward flow through the restrictor, the more nearly valve 230 approaches closed position, the more nearly the pressure existing in chamber 225 approaches that of suction means ll. As before noted, since chamber .2l9 always exists at suction pressure, then as chamber 2 l 8 approaches suction pressure, spring 220 is able to urge valve member 2i6 toward closed position, thus reducing the flow to the evaporator and permitting a larger portionof the refrigerant to vaporize before reaching bulb 245.

By adjusting the amount'of heat furnished said bulb, the percentage of liquid required in the refrigerant flow passing bulb 245 to reduce the temperature of the bulb to the vaporizing temperature of the refrigerant may be varied.

2", is urged 1'0- As was previously stated, sufficient heat maybe added to raise the temperature of the bulb about 50 above the ambient temperature in the evaporator when there is no circulation. Then, assume that with gaseous refrigerant only flowing, the temperature may be reduced about 15 at each of said bulbs. When a suillcient quantity of liquid refrigerant contacts bulb 245, its temperature may drop to that of the liquid refrigerant. When the temperature of bulb 245 drops to liquid temperature, and with bulb 249 reduced only about 15, there results a diflerential of about 35 for actuating controller 240. The ability to obtain a temperature differential of 35 from a variation in refrigerant quality at the location of device 242 from gaseous to, for instance, 97% gaseous'and 3% liquid, makes this a highly sensitive control means.

Obviously device 242 may be located at such a position that liquid refrigerant will always contact same, and control may be affected by device 244 on a basis of superheat, as in the example of Figure 4, but note that to control on the basis of superheat, 35 of superheat must be obtained to give the same temperature difference to actuate device 240. Thirty-five degrees of superheat is normally considered excessive for maximum operation of a system and would not be acceptable in most installations. By controlling on the basis of heat-dissipating characteristics of the flowing refrigerant, the precision and speed of response on the present apparatus makes it possible to more fully utilize the evaporator than is feasible with conventional control systems. Thus a change in refrigerant quality in device 242 from 100% to 97% is sufllcient to operate expansion valve 2l5 from'fully open to closed position. When the refrigerant contacting bulb 245 contains 3% liquid, for instance, the bulb temperature is lowered to that of the liquid, bellows 241 is retracted and bellows 25l is able to push lever 236 to its counterclockwise limit. As before described, this closes pilot valve 230 and causes expansion valve 2l5 to close. As before noted, when'no liquid refrigerant is contacting bulb 245, its temperature rises to approximately that of bulb 249. When 'both bulbs are at equal temperature, the expansion valve is drivenopen.

As in the previous instances, the present system is intended to operate the evaporator at maximum capacity but, at times, it is desired to reduce the capacity of the evaporator to minimize short cycling, or for improved temperature regulation. Upon a reduction in temperature at bulb 262, the pressure imposed on bellows 260 is diminished and portion 264 of link 263 is pulled against arm 236 and serves to rotate same counterclockwise. This urges pilot valve 230 toward closed position and tends to close Valve 2l5, thereby reducing the capacity of the system and lengthening the period of operation of the system.

valve 2|0 immediately closes. With the supply of high pressure refrigerant to receptacle 225 thus cut off, the pressures in said receptacle and chamber 2l9 are quickly equalized. This permits spring 220 to close valve member 2i6; hence, expansion valve 2 I 5 is closed during periods of nonoperation of the'system.

In each of the examples herein given, means are provided to control an expansion valve in response to temperatures at spaced locations in the refrigerant circuit. This results in uniform control conditions and makes feasible higher load- Upon shut down of the system, the solenoid ings of an evaporator than was previously con sidered safe. Due to the use of temperature responsive resistors for control elements, the operating characteristics of the system remain quite uniform over widely varying conditions of operation. Then, by supplying heat to temperature responsive means so that said means responds to the temperature resulting from said heat and the cooling effects of the flowing refrigerants, it is possible to gain a large response from small quality differences in refrigerant fiow. Thus, the novel devices and systems disclosed in this application are believed to improve the art of refrigeration.

It is to be noted that many substitutions and equivalents have been mentioned in the present disclosure, but these cannot represent all the modifications that will be obvious to one skilled in the art upon study of this specification and drawing. Therefore, it is intended that the examples given be considered as illustrative only and that the scope of the invention be determined only by the appended claims.

I claim as my invention:

1. In a refrigerating system, in combination, a condensing unit having a liquid refrigerant supply means and a gaseous refrigerant receiving means, an expansion valve, an evaporator, said valve being connected to said supply means for controlling refrigerant flow to said evaporator, reversible motor means for actuating said valve between open and closed positions, and a normally balanced electrical network circuit means for controlling the operation of said motor means, said circuit means comprising a plurality of spaced electrical temperature responsive impedance means, one of same being located within and near the exit of the evaporator and another of said impedance means being located within the evaporator and upstream of said one electrical impedance means.

2. In a refrigerating system, in combination, a condensing unit comprising a compressor, a motor driving said compressor, an expansion valve, an evaporator, said unit supplying liquid refrigerant through said expansion valve to said evaporator, the outlet of said evaporator being connected to the inlet of said compressor, reversible motor means operatively connected to said valve for actuating same, electrical network circuit means having a plurality of branches controlling the operation of said motor, said circuit means comprising first and second resistance means each having a relatively high temperature coefiicient of resistance and located in the path of the flowing refrigerant of the system, said first resistance means being located at a point past which only gaseous refrigerant should flow, said second resistance means being located upstream of said first means at a point wherein the flowing refrigerant should include a small portion of liquid, said first resistance means being in one branch of said network circuit and said second resistance means being in another branch of said circuit, means responsive to the'temperature of the medium being cooled for varying the impedance in one of said branches, means supplying predetermined and relatively uniform amount of heat to each of said resistance means, and means simultaneously actuated with stopping of the compressor motor for short circuiting one of the branches of said circuit to cause said reversible motor to drive said valve closed when the compressor is stopped.

3. Refrigerating apparatus comprising, in

combination, an evaporator, said evaporator having a passage through which refrigerant may be circulated, and a temperature responsive device located within said passage in a position to be contacted by refrigerant flowing through said passage, said device including heater means arranged to be continuously and uniformly heated when said apparatus is being used.

4. Refrigerating control means comprising, in combination, a temperature responsive device suitable for insertion into a conduit carrying flowing refrigerant, said device being shaped in a manner to cause a minimum of turbulence of fluid flow, attachment means for securing said device in a refrigerant passage, heater means disposed within said device and in intimate thermal relation therewith, connection means for said device extending through said attachment means, and connection means for said heater means also extending through said attachment means.

5. Refrigerating means, comprising, in combination, an evaporator, said evaporator having a passage through same for circulation of refrigerant, and a plurality of control devices located within said passage in a manner to be contacted by said circulating refrigerant, one of said devices being located near the outlet of said evaporator and another of said devices being located a predetermined distance from said one device in a direction toward the inlet of said evaporator, said devices each including electrical resistance means having a relatively high temperature coefficient of resistance, at least said device toward said inlet including a heater means.

6. In a refrigerating system having an expansion device and an evaporator, motor operated means for controlling a flow of refrigerant through said expansion device and evaporator, and a plurality of temperature responsive devices operatively connected to said motor to reversibly control its operation, said temperature responsive devices being spaced apart and located in the path of the refrigerant, said temperature responsive devices including means for heating them several degrees above an ambient of circulating gaseous refrigerant.

7. In a refrigerating system, a source of liquid refrigerant under pressure, an expansion valve, an evaporator, said valve being connected to said source and said evaporator for controlling refrigerant flow through said evaporator, reversible motor means operatively connected to said valve for opening and closing same, electrical network circuit means, said circuit means including electrical resistance means having an appreciable temperature coefficient of resistance associated with said evaporator at spaced points, one of said points being near the outlet and the other of said points being upstream of said one point, means for adding substantially uniform quantities of heat to each of said resistance means, and amplifying means responsive to the unbalance of said network circuit means, said amplifying means controlling said motor means in a manner to maintain a predetermined state of balance of said network circuit means.

8. In a refrigerating system, a source of liquid refrigerant under pressure, an expansion valve, an evaporator, said valve being connected to said source and said evaporator and arranged to regulate a flow of refrigerant through said evaporator, reversible motor means for operating said valve between minimum and maximum flow positions, and a, control circuit means for said motor, said circuit means including a plurality of temperature responsive elements located at spaced points in the path of flow of said refrigerant, means for adding predetermined quantities of heat to each of said elements so that said elements may respond to the heat exchange properties of said re- ;frigerant at said elements, said control circuit being connected and adJusted to cause stable refrigerant flow conditions when the heat exchange characteristics of refrigerant at one of said elements differs from that at another of said elements, a change in said characteristics at said one of said elements which is not reflected in a like change at said other element causing opera? tion of said motor to restore the previous relation of characteristics between said points.

9. In a flow control system, in combination, a valve, reversible motor means for actuating said valve, and control means for said motor comprising a plurality of devices each including temperature responsive means and heater means, the temperature responsive means of each of said devices normally responding to the resultant temperature due to said heater and the influence of the medium, such as a flowing fluid, surrounding said device, said devices being connected in controlling relation to said motor in such manner that a change in resultant temperature of one device relative to another causes operation of said motor and valve to permit a change in flow of a sort to restore the previous relation of resultant temperatures.

10. In a refrigerating system comprising a I source of liquid refrigerant under high pressure,

a supply of gaseous refrigerant under low pressure, an expansion valve, an evaporator, said ex-.

pansion valve being connected to said source and said evaporator and controlling refrigerant flow through said evaporator, the outlet of said evaporator providing said supp y of gaseous refrigerant; control means for said system including a reversible motormeans for actuating said valve, a plurality of control devices each comprising temperature responsive means and heater means, said devices being locatedin the path of the circulating refrigerant. one of said devices being located in a portion of the system beyond which no liquid refrigerant should pass, the other of said devices being located upstream of said one device in a location where it will be contacted by liquid refrigerant, said temperature responsive means responding to resulting device temperatures due to the heating effect of the heater means and the cooling efiect of refrigerant contacting same, and control circuit means including power amplifying means controlling said motor in response to said plurality of control devices, said devices exercising control over said amplifying means and said amplifying means controlling said motor.

11. In a refrigerating system, in combination, a condensing unit having an outlet supplying liquid refrigerant under pressure, said unit including suction means receiving gaseous refrigerant under lower pressure, an expansion valve, an evaporator, said expansion valve being connected to said outlet and to said evaporator chambers, conduit means connecting the other of said chambers to said, suction means, and conduit means including a restriction connecting the upper portion of said receptacle to said suction means, said expansion valve being actuated in response to the relative rates of flow through said pilot valve and said restriction.

12. In a refrigerating control apparatus, a pair of devices arranged to be inserted in a stream of flowing refrigerant, one of said devices being upstream of the other, each of said devices-including temperature responsive means and heater means, said temperature responsive means responding to the resultant temperature of said devices due to the influence of said refrigerant and said heaters, reversible motor means for actuating an expansion valve for controlling the rate of flow of said stream, and means controlling the operation of said motor in response to said temperature responsive means.

13. In a control apparatus responsive to changes in heat absorbing ability of a flowing fluid of changing quality, a movable member, a control device operable by said member, a pair of opposed force exerting bellows coacting with said member in such manner that said member is moved in response to the resultant of the forces exerted by said :bellows, a pair of fluid-charged bulb means each connected by tube means to its respective bellows, and heater means in heat exchange relation with at least one of said bulbs, said heater means being arranged for continuous and uniform energization, said bulb means being disposable at spaced locations in the path of said flowing fluid.

14. Refrigerating control means comprising, in combination, an electrical resistor means having an appreciable temperature coeflicient of resistance, an electrical heater means in heat exchange relation with said resistor, means consolidating said resistor and heater in' a unitary element adapted to be inserted into a conduit carrying refrigerant, said consolidating means being suitable to protect said resistor and heater means from said refrigerant =but providing a good thermal path between said resistor, heater means and said refrigerant, said resistor means being adapted to respond, when said heater is energized, to the temperature of said element resulting from the effects of said heater and said refrigerant.

15. -In a control apparatus responsive to changes in heat absorbing ability of a flowing fluid of changing quality, a movable member, a control device operable by said member, a pair of opposed force exerting bellows coacting with said member in such manner that said member is moved in response to the resultant of the forces exerted by said bellows, a pair of fluid-charged bulb means each connected by tube means to its respective bellows. heater means in heat exchange relation with at least one of said bulbs, said heater means being arranged for continuous and uniform energization, said bulb means being disposable at spaced locations in the path of said flowing fluid, and additional force exerting condition responsive means arranged to move said member in one direction in response to changes in said condition.

16. In a refrigerating control means, in combination, a conduit having a refrigerant passage therethrough, and a temperature responsive device including heater means disposed in said passage, said device having a streamlined shape, said passage surrounding said device being shaped to cooperate with the streamlined shape of said device to maintain smooth flow conditions under varying rates of fluid flow.

1'7. A refrigerating control device comprising, in combination, an electrical resistor having an appreciable temperature coefficient of resistance, an electric heater element closely associated with said resistor, a container of streamlined shape receiving said resistor and said element, means consolidating said resistor, element and container in a manner to provide good heat transfer characteristics for said assembly, and a cover in sealing relation over said container through which extends leads to said resistor and said element.

18. In a refrigerating system, in combination, a condensing unit having a liquid refrigerant supply means and a gaseous refrigerant receiving means, an evapora r connected to said supply means and to said receiving means, a valve for controlling the flow of refrigerant through said supply means, motor means for actuating said valve between open and closed positions, an electrical network circuit for controlling the operation of said motor means, said circuit including a plurality of spaced temperature responsive electrical impedance devices, one of said impedance devices being located in a manner to contact refrigerant near the exit of the evaporator and another of said impedance devices being located upstream of said one impedance device in a manner to contact the refrigerant at said upstream location, and means for continuously and uniformly heating one of said impedance devices by a predetermined amount.

19. In a refrigerating system including a compressor, a condenser, an adjustable expansion valve and an evaporator, said expansion valve being arranged to control refrigerant flow from said condenser to said evaporator, suction means connecting the outlet of said evaporator to the inlet of said compressor, condition responsive control means for adjusting the expansion valve in a manner to maintain maximum quantities of liquid refrigerant in said evaporator, motor means for operating said compressor, safety trap means including a float operated switch con nected to said suction means, and electric circuit means for controlling the operation of said motor means, said circuit means including said float operated switch whereby the presence of liquid refrigerant in said safety trap means will cause said float operated switch to open its contacts and stop the motor means, thus protecting the compressor from damage.

LAMONT B. KOONTZ.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS

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