US3010289A - Refrigeration system with variable speed compressor - Google Patents

Description

REFRIGERATION SYSTEM WITH VARIABLE SPEED COMPRESSOR Filed April 14, 1959 K mm mm V mw W V- mm 2 E G H .l v. F B bk 6 8 2 3 5 8 gg a 3 6 2 3 4 4 4 5 v m P M 7 5 J ATTOQNEY during pull down.

United States Patent 3,010,289 REFRIGERATION SYSTEM WITH VARIABLE SPEED COMPRESSOR Henry W. Kuklinski, Mattydale, Salina, N.Y., assignor to Carrier Corporation, Syracuse, N.Y., a corporation of Delaware Filed Apr. 14, 1959, Ser. No. 806,288 7 Claims. (Cl. 62-196) This invention relates to controlling the temperature of an enclosed space and more particularly to a system adapted to condition the air in a cargo space of a mobile truck or railway height car.

It is well known in the art that a refrigeration system which is capable of providing both heating and cooling to a refrigerator car is not required to operate at full capacity at all times and that some means for reducing the capacity of the system is desirable. If, for example, the refrigeration system includes a compressor driven by an internal combustion engine a significant decrease in wear of the compressor and engine parts may be achieved by operating the engine at low speed when full refrigeration capacity is not demanded of the system. In addition, by operating a refrigeration system in this manner a substantial saving in fuel consumption may be effected and substantially lower sound levels achieved as well as a reduction in the noxious exhaust fumes produced by the enm'ne which are desirable or necessary features when such a system is operated within a city or depot. Since the use of an evaporator fan is generally necessary to the eflicient operation of an air conditioning system such as might be employed in a railroad refrigeration car, it is desirable to operate the fan at a low speed when the cooling demand of the cargo space is substantially satisfied in order to reduce the power consumed and to produce the least amount of dehydration of the cargo which may include fresh or frozen foods which are generally adversely affected by dehumidi-fication. In order to prevent dehumidification of the cargo in a refrigerator car, it is further desirable that the temperature of the evaporator coil be maintained close to the desired m'r or operating temperature of the area to be conditioned. However, under extreme conditions of temperature and at times when it is necessary to pull down the temperature of the cargo from the ambient temperature to the operating temperature, a high cooling capacity and low evaporator temperature is desirable. At other times it may be desirable to operate the refrigeration system in a manner to supply heat from the coil serving the cargo space in order to maintain the cargo at a desired temperature.

It is also desirable to design a refrigeration system so that it employs standard components of relatively small size and low initial cost and to employ an internal combustion engine operating the refrigeration system which is as small as possible and still provides sufficient power However, when using a relatively small engine for this purpose, it is desirable to provide some type of protection both to prevent high head pressures in the compressor from damaging the components of the system and to prevent high operating loads from stalling the engine.

Accordingly, it is an object of this invention to provide an improved refrigeration system of the type employing an internal combustion engine wherein the speed of the engine, fans and compressor may be decreased in response to decreases in cooling demand of the area to be conditioned.

It is a further object of this invention to provide a refrigeration system which will tend to maintain a relatively uniform temperature and a high level of humidity in the area to be conditioned.

It is a further object of this invention to provide a 3,010,289 Patented Nov. 28, 1961 refrigeration system having 'means to reduce the speed of operation of components of the system under conditions of abnormally high loads or pressures and which may unload the compressor to prevent the engine from stalling.

It is a further object of this invention to provide a refrigeration system employing an internal combustion engine of minimal size for the refrigeration capacity required of the system.

It is a further object of this invention to provide a head pressure control in a refrigeration system which is capable of unloading the compressor and reducing the speed of operation of the engine employed in the system in response to a predetermined condition of high head pressure.

t is a further object of this invention to provide an improved control arrangement for a refrigeration system which will operate the system at varying speeds depending upon the demand made on the system and provide either heating or cooling when necessary.

These and other objects of my invention which will become apparent by reference to the following description and attached drawings are achieved in the preferred embodiment by providing 'a dual speed internal combustion engine directly driving the compressor of a refrigeration system. The refrigeration system is provided with a hot gas circuit to supply hot gas to the evaporator coil for heating and so as to remove accumulated ice if such should exist when the system is not required to produce refrigeration. A control circuit is provided for the refrigeration system saving a thermostat which controls the throttle of the dual speed engine so that as the temperature of the space to be conditioned approaches the desired operating temperature, the dual speed engine is operated at its lower speed and in addition the compressor may be partially unloaded under these conditions. 'Ihe evaporator and condenser fans employed in the refrigeration system derive their power from an alternator which is driven by the dual speed engine and the fan speed is reduced in proportion to the reduction of engine speed by reason of the lower frequency voltage output of the alternator when the system is operated at partial capacity. A high head pressure safety control reduces the operating speed and unloads the compressor under conditions of high heads experienced by the cornpressor.

In the drawings:

FIGURE '1 is a schematic diagram of a refrigeration system embodying the present invention; and

FIGURE 2 is a schematic diagram of the electrical control circuit of the present invention.

Referring to the drawings and more particularly to FIGURE 1, in the preferred embodiment of my invention I provide a refrigeration system for conditioning the cargo space of a railway refrigeration car or truck which comprises va reciprocating three cylinder compressor '10 discharging into a condenser 11. The condenser 11 discharges liquid refrigerant through line 12 into receiver 13 having a first compartment 14 and a second compartment 15 for the purpose of which will be more fully explained. From receiver 13 liquid refrigerant is conducted to evaporator 22 through liquid line 16 which is interrupted by liquid line solenoid valve 17 actuated by solenoid 18.

Liquid line 16 has an expansion device 19 therein which may be a conventional expansion valve actuated by a diaphragm 20 and a sensing element 21 placed at an suction line 25 conducts the refiigerant back into compressor :10 and the cycle repeated as will be understood by those skilled in the art.

A dual speed internal combustion diesel engine having first and second predetermined operating speeds and a solenoid actuated throttle for selecting the operating speed directly drives compressor 10. Engine 30 has a cooling system and fluid line 31 conducts the warmed cooling fluid from the engine through reevaporator 24 where it is placed in heat exchange relation with refrigerant in the reevaporator and subsequently returned to the engine cooling system through line 32. Unvaporized liquid refrigerant from suction line 23 is placed in heat exchange relation with the cooling system of the engine to assure that all of the refrigerant reaching the compressor through suction line 25 is vaporized regardless of the mode of operation of the system.

The refrigeration circuit of the instant invention is provided with means to defrost accumulated ice which may be formed on the evaporator coil 22 under normal operating conditions and to provide heat to the area to be conditioned when the temperature drops below a predetermined desired operating temperature. The heating defirost system illustrated in the drawing comprises a hot gas line 26 leading directly from the discharge of the compressor cylinders into the second compartment 15 of receiver 13 then through a hot gas defrost and heating solenoid valve 27 actuated by solenoid 28 and from there into evaporator 22 bypassing expansion device 19. When it is desired to defrost evaporator 22 the solenoid 18 actuates liquid line valve 17 and interrupts the refrigeration cycle by preventing flow of refrigerant into evaporator 22. At the same time solenoid 28 opens hot gas valve 27 which permits hot gaseous refrigerant'discharged by compressor to flow through hot gas line 29 directly into the evaporator coil 22. Refrigerant in compartment 14 of receiver 13 is vaporized and floods condenser 11 as explained in Patent No. 2,762,206, issued September 11, 1956 to C. M. Ashley. Initially, the hot gas may be partially condensed in the evaporator and absorbs heat from the evaporator coil melting ice which may have formed on its surface. The partially condensed refrigerant is then conducted through suction line 23 into reevaporator 24 where it is placed in heat exchange relation with the warm cooling fluidof the disel engine and is reevaporated so that it enters compressor 10 through suction line 25 in the vapor state as also explained in the patent referred to above. 7

Internal combustion enganie 30 directly drives compressor 10 through shaft 33. Pulley 34 mounted on shaft 33 drives pulley 36 mounted on shaft 37 of alternator 38 by means of belt 35. Alternator .38 produces an alternating three phase output current or voltage which serves the dual function of supplying power for the operation of condenser A.C. fan motor 40 and evaporator A.C. fan motor 41 and of supplying power to operate the control circuits of the refrigeration system. Fans 40 and 41 are of the alternating current type generally designed for 60 cycle operation.

Engine 30 is of the internal combustion type and in the embodiment described operates at two predetermined speeds. Throttle solenoid 42 adjusts the fuel supply of the engine and determines at which of the twopredetermined speeds the engine will operate. Pulleys 34 and 36 are so constructed as to drive alternator 38 at a speed to produce a 60 cycle A.C. output voltage when engine 30 is operating at the higher of the two predetermined speeds. When engine30 is operated at the lower of its two predetermined speeds alternator 38 will be driven at a lesser speed and consequently the frequency of its output voltage will be reduced in proportion to the change in engine speed. When the speed of engine 30 is'reduced, it has been found that the speed of fans 40 and 41 will correspondingly decrease due to the decreased frequency of the voltage or current supplied to them by alternator 38 without adversely aiiecting the controls;

The control circuit employed with the refrigeration system of the instant invention is shown schematically in FIGURE 2. Electrical conductors 57 and 58 are connected to two of the three electrical output conductors 39 of alternator 38 which supplies power for the control mechanism. Connected bet-ween conductors 57 and 58 are three series legs of the control circuit. The first leg may comprise a first thermostatic switch having a pair of contacts 50 in series with liquid line solenoid 18 previously described. Contacts 50 are shown in FIGURE 2 as being normally closed when the first thermostat calls for full cooling of the area to be conditioned. The thermostat may be located at any convenient place preferably within the compartment or area to be conditioned. Solenoid 18 cooperates with liquid line valve 17, which it controls, to maintain the valve open when solenoid 18 is energized and to close valve 17 when solenoid 18 is deenergized. It will be appreciated that alternatively contacts 50 may be normally open if desired when calling for full refrigeration in which event the solenoid 18 would maintain liquid line valve 17 open when the solenoid was deenergized and closed when the solenoid was energized.

The second leg of the control circuit comprises a second set of contacts 51 which may be'associated with the first thermostatic switch and in a normally open position for full cooling as can be observed from the diagram. Contacts 50 and 51 actually form a single pole double throw switch under such circumstances since one contact of each pair is at all times connected to conductor 57. The other contact of set 51 is connected to a parallel circuit comprising in one leg heating solenoid 28 which, as has been previously described, controls hot gas valve 27 and, in the arrangement shown, maintains valve 27 closed when solenoid 28 is deenergized. The other leg of the parallel circuit referred to may comprise relay solenoid 54 in series, with a first set of contacts 52 of a high pressure switch which will presently be described.

The third leg of the control circuit may comprise relay contacts 55, actuated by relay solenoid 54, in series with a parallel circuit comprising throttle controlsolenoid 42 and suction valve unloading'solenoid 43. The parallel circuit formed by solenoids 42 and 43 is in series with a second parallel circuit formed by a second set of contacts 53 of the high pressure switch referred to above comprising one leg of the circuit anda set of contacts 56 of a second thermostatic switch comprising the other leg; It will be appreciated that the first and second thermostatic switches may be actuated by separate thermostats such as bellows 60 and 61 respectively, or may be actuated -by a single thermostatic element having a plurality of sets of switch contacts adapted to be actuated at different temperatures.

Unloading solenoid 43 serves to actuate the suction valves 62 or two of the three cylinders of compressor 10 and to maintain the two suction valves of these cylinders in open position when it is energized thereby disabling two of the three cylinders of the compressor and unloading it by reducing the amount of work done by the compressor when the suction valves are open. Throttle solenoid 42 in circuit shown will cause engine 30 to operate at the higher of its two speeds when the solenoid is deenergized and will cause the engine to operate at the lower of its two speeds when it is energized.

The second thermostatic switch, referred to above, having contacts 56 is set to operate, in the circuit shown in the drawing, at a temperature a few degrees above the desired operating temperature of the area to be condiwhich as shown in FIGURE 2 actually comprises a single pole double throw switch, is positioned in the refrigeration circuit so actuator 63 senses a predetermined ab normally high head pressure in the cylinders of compressor 10. The high head pressure switch will generally be set to operate at a pressure just below that head pressure which will indicate a load on compressor which may cause malfunctioning of the compressor or require so much power from engine 30 as to put it in danger of stalling.

In the circuit diagram shown in FIGURE 2 all contacts are in the position they will assume when the temperature of the area to be conditioned is sufliciently higher than the desired operating point set by the first thermostat such that the refrigeration system is operating at full capacity but without abnormally high head pressure in the compressor. It will be understood that in FIGURE 2 contacts 51, 53 and 56 are shown as being in a normally open position and contacts 50, 52 and 55 are shown in a normally closed position under those conditions. The particular configuration of open and closed contacts shown in FIGURE 2 is selected merely for convenience of illustration and that other arrmgements of open or closed contacts may be employed to produce the same results by merely selecting valves in the refrigeration circuit which are normally open and closed depending on whether their associated solenoids are energized or deenergized as has been previously explained with reference to contacts 50 and valve 17 actuated by solenoid 18.

In operation engine 30 is started and assuming that the first thermostat calls for full cooling, throttle 42 will be set in a position such that the engine runs at the higher .Of its two speeds. Liquid line valve 17 will be open and hot gas valve 27 will be closed under which circumstances refrigerant will be pumped from compressor 10 through condenser 11 into receiver 13 and from the receiver through expansion valve 19, evaporator 22, reevaporator 24 and back into compressor 10 causing cooling of the location in which the evaporator is placed. Both evaporator 22 and evaporator fan 41 will normally be placed in the cargo compartment of a refrigeration car or other vehicle and cause the same to be pulled down to the desired temperature. When engine 30 is running at full speed, evaporator fan 41 and condenser fan 40 will operate at full speed deriving their power from alternator 38 driven by the engine.

When the temperature of the area to be conditioned drops below the desired operating temperature, the control circuit will cause liquid line valve 17 to be closed and hot gas valve 27 to be opened. Refrigerant is then pumped from compressor 10 through compartment of receiver 13 and directly into evaporator 22 through hot gas line 29. If considerable frost has accumulated on evaporator 22 some of the hot gas from compressor 10 upon heating the cold evaporator may be condensed and flow through suction line 23 into reevaporator 24 where it will be reevaporated and passed through suction line 25 back to the compressor. Reference is made to Patent No. 2,762,206, issued September 11, 1956, to C. M. Ashley for a more complete description of similar defrosting systems and their application in a refrigeration system such as that of the instant invention.

The heating and defrosting operation may be continued until the head pressure in the compressor reaches a point where the high head pressure control switch is actuated. Alternatively, a temperature-responsive switch may be attached to the evaporator housing to sense a rise in temperature above the melting point of ice which would indicate that the evaporator has been defrosted. In the preferred embodiment, the first thermostat having contacts 50, 51 will sense a rise in temperature of the conditioned area and put the system back on refrigeration at the proper time.

The operation of the control circuit shown in FIGURE 2 will now be described. The switches of the control circuit are shown in FIGURE 2 in the position that they would assume when the compartment to be conditioned is at a temperature sufi'iciently above the desired operating temperature to call for full cooling. Under these conditions the contacts 50 of the first thermostat are closed. Liquid line solenoid 18 is energized and therefore liquid line valve 17 is open permitting flow of refrigerant through the evaporator through evaporator 22 in a normal refrigeration cycle. Contacts 51 which as has been previously explained may be associated with first thermostat so as to form a single pole double throw switch are open under conditions calling for full cooling. Heating solenoid 28 is therefore deenergized and keeps hot gas valve 27 closed thereby blocking the entrance of hot refrigerant into evaporator 22. Contacts 52 actuated by the high pressure switch are closed under circumstances Where the compressor head pressures are not excessive. Since contacts 51 are open when the first thermostat calls for cooling, relay 54 is deenergized and contacts 55 associated therewith are closed. Where head pressures in the compressor are not excessive the contacts 53 in the third leg of the control circuit are open and where temperatures are above the desired operating point of the refrigeration system and the operating point of the second thermostat contacts 56 of the second thermostat are likewise open. Under these circumstances both throttle solenoid 42 and unloading solenoid 43 are deenergized so the engine is running at full speed and the compressor is fully loaded.

The second thermostat as previously described is set to operate at a temperature a few degrees above the desired operating temperature of the compartment to be conditioned. For example, if it is desired to maintain the cargo space of a refrigerator railway car at a temperature of 35 the second thermostat may be set to operate at 37. When the cargo space reaches 37 on pull down contacts 56 of the second thermostat close. Closing contacts 56 actuates both throttle solenoid 42 and unloading solenoid 43 in parallel therewith. Energizing of throttle solenoid 42 actuates the throttle of engine 30 and causes it to reduce its speed to the lower of the two predetermined operating speeds. Energizing of unloading solenoid 43 causes the suction valves of two of the three cylinders in compressor 10 to remain open during their normal operation. This substantially re duces the amount of work which the compressor is called upon to perform and effectively reduces the load on engine 30 when the engine is operated at low speed and therefore consequently reduces the danger that the engine may stall at low speed.

Furthermore, as engine 30 operates at a lower speed the frequency of the output current or voltage of alternator 38 is correspondingly proportionally reduced. The reduction in output voltage frequency of alternator 38 correspondingly reduces the operating speeds of fan motors 40 and 41. The power consumption of an AC. fan motor is proportional to the cube of its speed and a significant reduction in power requirements by the fans is thereby achieved. For example, it has been found that engine 30 may be operated at 1800 r.p.m. on high speed and 1200 rpm. at low speed. If alternator 38 is driven so as to produce a 60 cycle output voltage at the 1800 rpm. speed of engine 30, by dropping the engine speed to 1200 r.p.m. the output frequency of alternator 38 is reduced to 40 cycles and the fan speeds reduced proportionally without affecting the operation of the controls adversely.

The refrigeration system continues to operate at low speed cooling until the temperature of the area to be conditioned is brought down to the desired operating temperature set by the first thermostat. While the refrigeration system is operating at low speed the temperature of evaporator coil 22 is very close to the desired operating temperature and consequently a means of maintaining a high humidity in the refrigerated compartment may be achieved. As is well known in the art, it is generally highly desirable that the cargo space of a refrigerator car be maintained at a relatively high humidity in order to properly preserve foods contained therein. Since evaporator 22 and evaporator fan 41 are generally positioned within the refrigeration compartment and the fan operated to cause circulation of the air within the compartment, the reduction of fan speed circulates a minimum ofair in contact with food in the cargo space and consequently does not cause as much dehumidification of the food as would be experienced if a higher fan speed reaches the desired operating point, the first thermostat which is set to operate at that point opens contacts 50 and closes contacts 51. Opening of contacts 50 deenergizes liquid line solenoid 18 which interrupts the refrigeration circuit by closing liquid line valve 17. At the same time closing contacts 51 energizes heating solenoid 28 which in turn opens hot gas valve 27 admitting hot gas from compressor into evaporator 22 to defrost the evaporator if such is required and to supply heat to the conditioned area until the temperature of the area 7 exceeds the desired operating temperature.

Closing contacts 51 also energizes relay 54 thereby opening contacts 55. When contacts 55 are opened both unloading solenoid 43 and throttle solenoid 42 are deenergized. This reloads the compressor by permitting closure of the suction valves of all cylinders of compressor 10 and causes the engine 30 to go into high speed operation. It will be seen therefore that the defrosting operation is normally done at high speed with a fully loaded compressor and is generally accomplished in a short time interval. 7

If during the heating or cooling cycle of the refrigeration system excessively high head pressures are experienced by compressor 10, the high pressure will actuate the high head pressure switch thereby opening contacts 52 and closing contacts 53. Opening contacts 52 deenergizes relay 54 which closes contacts 55. Closing contacts 5S enengizes throttle solenoid 42 and unloading solenoid 43 thereby unloading compressor 10 and reducing the speed of engine 30 regardless of the position of contacts 56, i.e. the second thermostat. It will be appreciated that if high head pressures occur while the refrigeration system of the instant invention is operating, either on the heating or ,the cooling cycle, above the predetermined maximum safe operating head pressure set by the head pressure control switch, the system will instantly go into low speed, unloaded operation providing reduced capacity heating or cooling. This in turn will prevent engine 30 from stalling and will prevent damage to the components of the refrigeration system. After the excessively high head pressure is reduced below the predetermined pressure, the head pressure switch will again close contacts 52 and open contacts 53 putting the system back into high speed operation assuming that the thermostats do not call for low speed operation.

When the temperature of the area to be conditioned rises on account of the hot gas flowing through evaporator 22 to a point above the desired opera-ting temperature of the area to be conditioned, contacts 50 of the first thermostat will close while contacts 51 will open. This places the refrigeration system on low speed cooling again until such time as either the temperature in the area'to be conditioned rises causing contacts 56 of the second thermostat to open, which puts the refrigeration system into high speed cooling, or until the temperature of the area to be conditioned drops causing contacts 50 to open and contacts 51 to close, putting the system on high speed heating.

It will be noted that in the system described engine 30 is always operating as is compressor 10 and that the system is always either heating or cooling the conditioned area. If, however, it is desired to provide a dead hand between heating and cooling the same may be achieved by disassociating contacts 51 from the first thermostat and associating them with a third thermostat or a third set of switch contacts which are actuated at a temperature slightly below the desired operating temperature.

By means of the system described I am enabled to pro vide a refrigeration system suitable for use in a railway refrigeration car or other transportation cooling system which employs standard alternating current components throughout and which is simple in operation and effective for the purposes desired. By providing a dual speed diesel engine in the system and a compressor which is unloaded and operated at low speed under high loads, I am enabled to employ an engine which may be sized for the anticipated normal cooling load imposed on the system. This results in cost economies because the engine need not be large enough to supply all of the power that would be required if the compressor were fully loaded and operating at high speed during severe operating conditions as might be experienced upon initial pull down of the cargo space. Further, low speed operation of the engine enables quiet and economical operation of the refrigeration system when maximum cooling capacity is not required. The overall power consumption of the refrigeration system on low speed operation is further reduced by operating the fans at low speed due to the change in alternator voltage frequency while at the same time I have found that the alternator voltage and frequency is sufficient to operate standard electric and thermostatic controls. If, for any reason, the first thermostatic switch should fail to operate, the engine and compressor are protected by the high head pressure switch from damage. In addition, low speed operation is desirable both from the standpoint of control of noxious exhaust fumes and reduction of noise should the refrigeration car he required to stand in a building or at a depot. Likewise, it has previously been noted that by operating the evaporator fans at reduced speed and the evaporator coil at a temperature close to the desired operating temperature of the cargo space a relatively high humidity is maintained which is desirable in the preservation of many foods.

While I have shown and described the preferred form of my invention it will be appreciated that the same may be otherwise embodied within the scope of the following claims.

I claim 1. In a refrigeration system having a compressor, a variable speed internal combustion engine adapted to drive the compressor, an evaporator located in heat exchange relation with air being conditioned, a condenser and an expansion device connected to form a refrigeration system, said engine having two predetermined speeds of operation, speed control means associated with said engine to control its speed of operation, a thermostatically actuated control circuit for sensing the temperature of an area to be conditioned, said speed control means being regulated by said thermostatically actuated control circuit, an alternator adapted to be dn'ven by said engine at a speed proportional'to the speed of the engine and thereby adapted to provide an alternating electrical current output of a frequency proportional to the speed' of operation of the engine, a fan having an A.C. motor associated with said refrigeration system, said fan motor being electrically connected to and deriving its power from said alternator thereby having an operating speed proportional to the frequency of the electrical output of said alternator, so

that the speed of said fan and the capacity of said refrigeration system are changed in response to changes in the temperature of the area to be regulated.

2. A control circuit for a refrigeration system having a compressor driven by a dual speed internal combustion engine, an evaporator, an expansion device and a condenser connected to form a refrigeration system, comprising a first thermostatic switch having a pair of contacts, the thermostatic element of which is adapted to sense the temperature in an area to be conditioned and to actuate said first thermostatic switch at the desired operating temperature of said area, the contacts of said first thermostatic switch being in series with a relay solenoid, a high pressure switch adapted to sense abnormally high head pressures in the compressor of said refrigeration system and to be actuated thereby at a predetermined pressure, said high pressure switch having a pair of contacts in series with said first thermostatic switch and said relay solenoid to form a leg of said control circuit, saidcontrol circuit further comprising another leg connected in parallel with said first described leg and comprising a series connected circuit comprising a pair of contacts associated with said relay solenoid and connected in series with solenoid means for reducing the power demand on said internal combustion engine connected in series with a pair of sets of parallel connected switch contacts, one of said sets of contacts being actuated by said high pressure switch and the other being actuated by the thermostatic element of a second thermostatic switch adapted to sense the temperature of said area to be conditioned and to be actuated at a temperature a predetermined few degrees above the desired operating temperature of said area, and means to supply electrical current to the junctions of the two legs of said control circuit connected in parallel.

3. A control circuit for a refrigeration system having a compressor, an evaporator, a condenser, an expansion device and a dual speed internal combustion engine to drive the compressor wherein said engine has a predetermined high speed and a predetermined low speed operating condition, a throttle solenoid and a throttle adapted to be actuated by said throttle solenoid to control the Speed of operation of said engine, said control circuit comprising a thermostatic switch in series with said throttle solenoid, the thermostatic element of said switch being adapted to sense the temperature of an area to be conditioned, said thermostatic switch and said solenoid throttle being adapted to co-act to change the speed of said engine in response to the cooling demand of the area to be conditioned, another thermostatic switch the thermostatic element of which is adapted to sense the temperature of the area to be conditioned, a solenoid valve in said refrigeration system adapted to interrupt the refrigeration cycle, the solenoid of said valve being in series with said other thermostatic switch and cooperating therewith to interrupt the refrigeration cycle when said other thermostatic switch is satisfied, the first named switch being adapted to be actuated at a predetermined temperature above the desired operating temperature and said other thermostatic switch being adapted to be actuated at said operating temperature, and an unloading solenoid also in series with said first named thermostatic switch adapted to unload a cylinder of said compressor when the temperature of the area to be controlled is lower than said predetermined temperature above the operating temperature.

4. A control circuit for a refrigeration system having a compressor, an evaporator, a condenser, an expansion device and a dual speed internal combustion engine to drive the compressor wherein said engine has a predetermined high speed and a predetermined low speed operating condition, a throttle solenoid and a throttle adapted to be actuated by said throttle solenoid to control the speed of operation of said engine, said control circuit comprising a thermostatic switch in series with said throttle solenoid, the thermostatic element of said switch being adapted to sense the temperature of an area to be conditioned, said thermostatic switch and said solenoid throttle being adapted to co-act to change the speed of said engine in response to the cooling demand of the area to be conditioned, another thermostatic switch the thermostatic element of which is adapted to sense the temperature of the area to be conditioned, a solenoid valve in said re.- friger-ation system adapted to interrupt the refrigeration cycle, the solenoid of said valve being in series with said other thermostatic switch and cooperating therewith to interrupt the refrigeration cycle when said other thermostatic svu'tch is satisfied, the first named switch being adapted to be actuated at a predetermined temperature above the desired operating temperature and said other thermostatic switch being adapted to be actuated at said operating temperature, and means to reduce the speed of said engine to the lower of the two predetermined speeds when the engine is operating at the higher of said predetermined speeds, comprising a compressor head pressure responsive switch associated with said compressor and adapted to actuate said throttle solenoid at a predetermined maximum head pressure in said compressor to reduce the compressor speed and thereby prevent stalling of said engine.

5. In combination: a refrigeration system comprising a compressor having a plurality of cylinders, a condenser, an expansion device, and an evaporator connected to form a refrigeration circuit; an engine operatively connected to drive said compressor, said engine having at least a first operating speed and a second operating speed, said first operating speed being greater than said second operating speed, and speed control means associated with said engine to reduce the speed thereof from said first operating speed to said second operating speed; refriger ant pressure sensing means to sense a refrigerant pressure condition of said refrigeration system which is indicative of a heavy load being imposed on said engine; compressor unloading means for unloading a cylinder of said compressor; and means to actuate said speed control means to reduce said engine speed from said first operating speed to said second operating speed and said compressor unloading means from a loaded condition to an unloaded condition of said compressor in response to said refrigerant pressure condition being sensed by said sensing means to thereby reduce the power demand on said engine when said sensing means senses a refrigerant pressure condition indicative of a heavy load being imposed on the engine.

6. In combination: a refrigeration system comprising a compressor having a plurality of cylinders, a condenser, an expansion device, and an evaporator connected to form a refrigeration circuit; an engine operatively connected to drive said compressor, said engine having at least a first operating speed and a second operating speed, said first operating speed being greater than said second operating speed, and speed control means associated with said engine to reduce the speed thereof from said first operating speed to said second operating speed; a fan associated with said refrigeration system, an alternating current fan motor connected to drive said fan, and an alternator driven by said engine at a speed proportional to the speed of said engine and electrically connected to said fan motor to supply current thereto of a frequency proportional to the speed of said engine so as to drive said fan at a speed proportional to the speed of said engine; refrigerant pressure sensing means to sense a refrigerant pressure condition of said refrigeration system which is indicative of a heavy load being imposed on said engine; compressor unloading means for unloading a cylinder of said compressor; and means to actuate said speed control means to reduce said engine speed from said first op erating speed to said second operating speed and said compressor unloading means from a loaded condition to an unloaded condition of said compressor in response to said refrigerant pressure condition being sensed by said sensing means to thereby reduce the power demand on said engine when said sensing means senses a refrigerant pressure condition indicative of a heavy load being imposed on the engine, said reduction in engine speed also serving to reduce the speed of said fan and fan motor thereby further reducing the power demand on said engine.

7. In a refrigeration system, a compressor, a dual speed internal combustion engine adapted to drive said compressor, said engine having first and second predetermined operating speeds, said first speed being higher than said second speed, pressure sensing means to sense a predetermined pressure condition in said refrigeration system, an evaporator, a condenser, and an expansion device connected with the compressor to form a refrigeration circuit, a fan having an AC. motor associated with said refrigeration system said AC. motor being adapted to drive said fan at a speed proportional to the frequency of the current supplied to it, an alternator adapted to be driven by said engine at a speed proportional to the speed of said engine, said alternator providing an alternating current electrical output having a frequency proportional to the driving speed thereof, said fan motor being electrically connected to and adapted to be driven by the electrical output of said alternator, said pressure sensing means 12 being operatively associated with said engine to reduce its speed from the predetermined first operating speed to the predetermined second operating speed to thereby reduce the speed of said compressor upon sensing said pressure condition, said system serving to reduce the load imposed on said engine by said alternator when the engine is operating at the reduced speed condition by reducing the speed of said fan motor proportionally to the reduction in speed of said engine.

References Cited in the file of this patent UNITED STATES PATENTS 2,134,107 Dempsey Oct. 25, 1938 2,286,316 Snook June 16, 1942 2,400,665 Thomas May 21, 1946 2,462,514 Lehane et al. Feb. 22, 1949 2,498,861 Newton Feb. 28, 1950 2,734,346 Dickieson Feb. 14, 1956 2,786,334 Wolf Mar. 26, 1957 2,887,853 Talmey May 26, 1959 UNITED STATES PATENT. OFFICE CERTIFICATE OF CORRECTION Patent No,\ 3,01%289 November 28 1961 Henry We Kuklinski It is hereby certified that. error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2 line 30,, for "saving" read having} column 3, line 45 for -"enganie" read engine =-q Signed and sealed this 17th day of April 1962o (SEAL) Attestz' ESTON G. JOHNSON DAVID L. LADD' Attesting Officer Commissioner of Patents

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