US2581329A

US2581329A - Compressor control

Info

Publication number: US2581329A
Application number: US792277A
Authority: US
Inventors: Alwin B Newton
Original assignee: Chrysler Corp
Current assignee: Old Carco LLC
Priority date: 1947-12-17
Filing date: 1947-12-17
Publication date: 1952-01-01
Anticipated expiration: 1969-01-01

Description

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Jan. 1, 1952 A. B. NEWTON COMPRESSOR CONTROL 6 Sheets-Sheet 6 Filed Dec. 17, 194'? Patented Jan. 1, 1952 UNITED STATES PATENT OFFICE COMPRESSOR CONTROL Alwin B. Newton, Dayton, Ohio, assignor to Chrysler Corporation, Highland Park, Mich.,' a corporation of Delaware Application December 17, 1947, Serial No. 792,277

Claims.

The present invention relates to the arts of refrigeration and air conditioning, the invention being applicable to a refrigerating system of the compressor-condenser-evaporator type whether the system be used to cool and dehu midify air for air conditioning purposes or to chill a medium surrounding the evaporator, such as air, salt brine, or a liquid such as diethylene glycol, which medium would be used for the purpose of preserving foodstuffs, producing ice, or any other purpose for which refrigerating systerns are of utility.

This application is a continuation in part of my application, Serial No. 625,864, now abandoned.

The present invention is of particular application to a refrigerating system including a compressor of the type disclosed and claimed in the patent to Charles R. Neeson, No. 2,185,473, issued January 2, 1940, the present invention including a device responsive to a condition of air being conditioned or a condition of the medium surrounding the evaporator coil for effecting unloading and loading of the compressor of the refrigerating system in response to the condition.

The present invention involves a change in the construction of Gonzales Patent 2,304,999, December 14, 1942. According to that patent, a control system has a part located in the medium being cooled so as to be responsive to a given condition of the medium for acting on a valve rod for a master valve operating a variable capacity means in a compressor. The valve rod is also connected to a means responsive to suetion pressure of the compressor such as a bellows. The arrangement is such that although the master valve for the variable capacity means is connected both to the condition-responsive part in the medium being cooled and to the suction-pressure-responsive means, the conditionresponsive part always has complete control of the master valve, and the suction-pressure-responsive means has control only in the event that there is failure of control through the conditionresponsive part.

According to the present invention, the control lies with thesuction-pressure-responsive means such as the bellows, and the part responsive to a condition of the medium being cooled acts to modify the control exerted by the suction-pressure-responsive means. The result is that the suction pressure at which the compressor is unloaded is varied for a variation of the aforesaid condition in the medium being cooled.

Also according to the present invention, means responsive to an additional condition such as high suction pressure of the compressor may act to unload the compressor, and this means may be coordinated with the condition-responsive part to vary the control at the same point where the condition-responsive part varies the control. The advantage in a. control dependent upon high suction pressure is that it prevents overloading of the compressor motor. If, for example, the refrigerator is heavily loaded by a high temperature at the outset of the medium being cooled, this is reflected in a high suction pressure. I have discovered that the compressor should be unloaded for a reduction of load on the motor if the heavy loading is to continue for a fairly long time and that this may conveniently be done by unloading in response to a high suction pressure. The result is that the initial cooling period may be somewhat lengthened, but the compressor is not overloaded, and the size of compressor may be determined from normal maximum load after the initial cooling period rather than from the overload that often occurs in the initial cooling period.

The invention will be more fully understood by study of the following specification taken in connection with the accompanying drawings wherein like numerals refer to like parts throughout.

In the drawings,

Fig. 1 discloses an air conditioning system having the present invention applied thereto, the compressor disclosed therein being of the type covered by the aforesaid patent to Neeson.

Fig. 2 is a longitudinal section through a compressor having the present invention associated therewith, and showing details of the capacity varying means disclosed in the aforesaid patent to Neeson;

Fig. 3 is a view in elevation of the front cover of the compressor disclosed in Fig. 2, with details of the capacity regulating master valve and the operating mechanism of the present invention attached thereto;

Fig. 4 is an end view of the portion of the apparatus disclosed in Fig. 3;

Fig. 5 is a sectional view taken through the master valve mechanism and the operating mechanism;

Fig. 6 is a sectional view somewhat similar to Fig. 5, of a modified form of apparatus;

Fig. 7 is a plan view of the apparatus of Fig. 6;

Fig. 8 is a diagrammatic view of an electric circuit and associated means for controlling the apparatus of Figs. 6 and 7; and

Fig. 9 is a sectional view similar to Fig. 6 of another modified form of the apparatus.

In Fig. 1 there is disclosed an air conditioning system comprising a refrigerating system of the compressor-condenser-evaporator type of which I the compressor includes a pair of unitary compressors 20 of identical construction fastened to the opposite ends of a double-ended motor 2|.'

The two compressors discharge in to a common condenser 22 from which condensed refrigerant is expanded into an evaporator 23 having connections to the inlets of both compressors. Therefore, for all practical purposes the two compressing units may be considered as a single compressor. The evaporator 23 is located in a duct 24 through which a stream of air is drawn by a blower 25, the air passing over the evaporator being cooled and dehumidified and being then discharged into the space to be served by the action of the blower. It is, of course, readily apparent that the evaporator may be located in a food storage compartment over which air is circulated by a blower means or by gravity, or in a medium of liquid type used for various cooling purposes.

Details of one of the compressing units are disclosed in Fig. 2 wherein it is seen that the compressing unit 20 comprises a crankshaft 30 to which are connected a plurality of connecting rods 3| each operating a piston 32 in a cylinder 33. Gas which is admitted to the suction manifold 34 from the evaporator 23 passes into the interior of the cylinder through the suction valve 35 and is ejected through the discharge valve 36 into the discharge head 3'! which is connected by passage 38 to the common discharge manifold 39 from which the compressed gas passes into the condenser 22. Details of the valve and piston construction may be ascertained from the aforesaid patent to Neeson, as well as the patent to Charles R. Neeson, No. 2,137,965, issued November 22, 1938.

As further explained in the aforesaid Patent No. 2,185,473, the suction manifold 34 is connected through ports 40 with the interior space 4| of the crankcase whereby a flexible, metallic bellows 42 is subjected to the pressure of the expanded refrigerant returned from the evaporator. Movement of the bellows 42, which hasan end piece 42 soldered or welded to a link rod 43, causes reciprocation of the linkrod 43 connected by rocking levers 44 to a master valve member 45. The master valve member 45 (Fig. is provided with a plurality of notches 50 so that a spring pressed ball 5| engaging in the notches permits step-by-step movement of the master valve member. Each step causes one of a plurality of slots 52 to be connected to, or disconnected from, a source of oil pressure through an oil pressure tube 53. Each of the slots 52 is connected to a short tube 54 leading to a cylinder 55 in which is mounted a spring loaded unloader piston 56 connected to unloading mechanism including a yoke 51 adapted to ride on a ramp 58 and to be thereby moved axially as the piston 55 moves the yoke 51 longitudinally. The yoke causes axial movement of a ring 59 having unloader pins 60 mounted thereon, which when moved axially outward cause the suction valve 35 to be held open continuously whereby the cylinder is unloaded or prevented from compressing refrigerant. The position of the variably movable valve part 45, therefore, controls the number of unloader pistons 56 to which oil pressure is applied, and hence controls the number of cylinders in operation. When, as disclosed in Fig. 5, all but one of the slots 52 are connected to tube 53 through the annular space 5| surrounding the reduced portion of valve member 45, all but one of the individual cylinders will be loaded or operating. When valve member 45 is moved inwardly the length of another notch 50, two cylinders will be unloaded since another one of the unloader cylinders 55 will be disconnected from the source of oil pressure. Oil pressure is applied to the unloading mechanism through the master valve from a pressure lubrication pump (not shown), details of which may be ascertained from the aforesaid Neeson Patent No. 2,185,473. As disclosed in the aforesaid patent, the oil pressure pump operates coextensively with operation of motor 2| so that no oil pressure will be supplied to the master valve 26 unless the motor is oper4 ating, and since it takes a short while for the pressure to be built up by the oil pump it is apparent that all cylinders will be unloaded during starting, thereby preventing large starting current inrush. It is also apparent that after oil pressure is available a number of cylinders will be unloaded depending upon the position of the linkrod 43.

The aforesaid Neeson Patent No. 2,185,473 discloses that the position of linkrod 43 may be controlled by the degree of compression of the flexible, metallic bellows 42. which compression is efiected by the pressure of the gas in the space 4| connected to the suction side of the refrigerating system through the port 40. The pressure of the gas against bellows 42 operates against a compression spring 65 positioned between the end of the bellows and a disk 65. The disk has wings 66 at opposite sides projecting through slots in a threaded sleeve 61. The sleeve is secured as by soldering or welding to an apertured member 68, to which the bellows 42 is secured. A nut 69 threaded on the sleeve 61 determines the position of the disk 66 and consequently, the compression of the spring 65. The link rod 43 has a reduced outer end on which is threaded a nut 69* serving to guide the rod in the sleeve 61. A look nut-69 retains the nut 69 in position. In the aforesaid patent, it is explained that the compression of the spring 65 controls the unloading pressure of the master valve so that the suction pressure of the refrigerating system may be controlled within reasonable limits. However, it has been found in some instances that the pressure of the gas returning to the compressor is not quite an adequate measure of the conditions in the system that require unloading. Accordingly, I have devised means for controlling the suction pressure at which unloading occurs and for controlling the position of the master valve part 45 directly in response to one or more conditions of the medium being cooled by the evaporator 23 such as temperature, humidity, or pressure.

As seen in Fig. 1, I provide an air pressure control system including an air compressor 10 operated by a motor 10 and discharging into a pressure tank 1|. The motor lll' is controlled by a pressure-responsive device lo which causes the motor to operate when the pressure in the tank 1| falls below a predetermined amount, the device 10* being connected in electric power lines 10. Air is discharged from the tank through a pipe I l in which is located a pressure-reducing valve 11*, into a tank A pipe 12 discharges compressed air from the tank H through pipes l2 and 12 into two pressure regulating valves 13 and 13. Valve 13 includes a pair of fixed

orifices

14 and 14 which maintain a steady discharge of compressed air at a constant pressure depending upon the pressure maintained in tank II by the device 10 and the motor 10. The tank II has a safety blowofi 15. The valve I3 has a space 16 into which orifice 'I4' discharges. The space 16 of valve 13 is connected to pipes 11 and I1 which join in pipe 18, which branches into pipes 18- and 18 leading to housings 19 and 80, respectively, each participating in the control of one of the master valves 25. The pressure exerted in the housings 18' and 88 is controlled by regulating the pressure in pipe 11 which is accomplished by valve 13 and by a second valve 13' interposed in parallel relation with valve I3 and connecting pipes 12 and I1. Valve l3 includes a first chamber 18' operatively connected to pipe 12 and a second chamber 16 operatively connected to pipe 11*. A partition which separates chambers 15' and 18 is provided with an orifice. A plunger 8| cooperates with this orifice to form a variable orifice valve means adapted to vary the amount of air admitted to chamber 18 The plunger 8| is controlled by a diaphragm 82 and return spring 83. The position of the diaphragm 82 and plunger 8| are controlled by pressure in suction line 85 leading from evaporator 23. This pressure is communicated by a line 85 to the diaphragm 82*. It is obvious that as the suction pressure in line 85 increases the diaphragm 82* and plunger 8| are forced downward in Fig. 1 thereby increasing the amount of air admitted to chamber 75' and housings I9 and 80. The valve 13 includes a means for bleeding air to the atmosphere to load the compressor. This means comprises a plunger 8| operated by a bellows 82 and a return spring 83. The position of the plunger 8| is controlled by the pressure in a part 84 connected to the space of which bellows 82 comprises a movable wall. Part 84 contains a fiuid reacting to a condition of the air or fluid medium surrounding it, such as temperature, humidity, pressure etc. As temperature rises, for example, bellows 82 is depressed and the pressure in space 18 drops as a result of increased opening of the valve controlled by plunger 8l. The orifices 14 and I4 provided in valve 13 are required to provide a restriction so that when valve 13 is open a pressure can be built up in pipe I8 even if the valve 13 is open. When valve I3 closes after the compressor has been unloaded the pressure in housings l9 and 88 is relieved through valve I3 when this latter valve is open.

As seen in Fig. 5, tube 18 is connected to a ring 85 forming part of the casing 88. The rest of the casing is composed of a fitting 81 threaded on the ring 85, a seal 88 between the fitting and the ring, and a dome member 88 with a generally hemi-spherical end joined to the fitting as by soldering or-welding. The ring 86 has an inwardly extending fiange 80 by which the casing 80 is attached to an end part 8| of the compressor with the aid of screws 82. The screws also attach the apertured member 68 to the end part 9|. The pressure of the air or gas in tube 18 is transmitted through the casing 88 and acts against the inner side of the bellows 42 so as to tend to expand it. The change of pressure exerted by the air pump through the tube 18 by way of valve 13 acting in response to change in condition of the medium being cooled and by way of valve I3 acting in response to high suction pressure in line 85 is preferably so selected as to add or subtract from the efiect of spring 65 without rendering its effect negligible so that control of the master valve 45 through the bellows 42 is retained by the suction pressure of the compressor, the change in air pressure merely acting against the inner side of the bellows to modify.

the control of the master valve.

The operation of the present invention is as .follows: The compressor forces hot refrigerant gas into the condenser where the refrigerant is liquefied ,at the condensing pressure. The refrigerant is expanded in the evaporator 23 and extracts heat from the air or other surrounding medium. The expanded refrigerant is returned to the compressor and through the suction manitold 34 into the cylinders where it is again compressed. The suction pressure, which refiects the load on the evaporator, exerts pressure on the bellows 42 which tends variably to control the position of the unloader valve part 45. However, this control of the unloader valve part 45 is modified by the part 84 responsive to a condition such as temperature, pressure, humidity, etc., in the duct 24 and by a high suction pressure on the line 85, since the air or gas pressures in the housings 19 and 88 and the inner side of bellows 42 are determined by the part 84 and the return line 85. As the air pressure varies, there is inward or outward movement of the valve part 45 in steps controlled by the ball 5| riding in the notches 50. The movement of the master valve part 45 controls the connecting or disconnect-' lng of one or more of the unloader cylinder spaces 55 and the source of fiuid pressure through

tubes

53 and 54. When pressure is applied to a cylinder space 55 the piston 58 therein is moved inward and causes the yoke 51 to ride down on ramp 58, thus dropping the pins 88 from the suction valve 35 and allo 'g the cylinder to compress gas. Disconnection of the cylinder space 55 from the source of fiuid pressure causes the cylinder to become unloaded. In this manner the number of cylinders in operation varies so that the capacity of the compressor varies directly in response to the temperature produced by the evaporator.

The valve l3 acts to modify the control of the master valve 45 only when the suction pressure in the return line is very high. A high suction pressure is due to a heavy load on the refrigerating system, which may, for example, occur when a food locker or building cooled by the system is first being cooled. The load required to bring the temperature down to the desired value is many times heavier than that required to maintain the desired value oftemperature. It is economically desirable to select a refrigerator system for the low rating required for maintenance of a certain temperature instead of one of a high rating required for lowering to the certain temperature. Yet the system should not be overloaded. According to my invention, I prevent such overloading by making the compressor unloader responsive to a high suction pressure. This is accomplished by adjustment of the valve 13 which acts to adjust the pressure exerted on the inside of the bellows 42.. When a certain high suction pressure is reached in the return line 85 such as would indicate overloading of the system, the plunger 8| changes the amount of opening of the variable orifice valve in the valve 13. This change in opening is reflected in an increased pressure in the chamber 18*, which is communicated to the interior of the bellows 42.

Figs. 6 and 7 show a modified form of apparatus in which the modifying effect of a condition such as temperature, pressure, or humidity in the cooling duct 24 and a high suction pressure in the return line 85 is applied by electrical means to the valve rod 43. The reduced threaded end of the valve rod 43 is slidably guided in a sleeve 93 in which is threaded an adjustable bolt 94 providing a limit to the movement of the valve primary coil rod 43 to the left. The sleeve 93 is suitably mounted in a cage 96, which is threaded upon the sleeve 61. The cage 96 may be adjusted by rotation along the sleeve 61 and a jam nut 91 prevents such rotation. A sleeve 98 is slidably mounted upon the sleeve 93 and within the threaded sleeve 01 and engages one end of a coil 'by means of a nut and bolt I03 to an arm I04 actuated by an electric motor I05, the arm having its center of angular movement at I06. The motor I05 is bolted to a bracket I09 supported on the end part 9| of the compressor by screws 92.

As seen in Fig. 8, the motor I05 is controlled by windings I08 and I09, one being adapted to rotate the motor in one direction, and the other, in the opposite direction. Associated with the windings I08 and I09 are contact points IIO and I I I, spaced as shown above and below a movable switch member II2 pivoted at H3. The switch member has legs H4 and H5, which extend respectively through coils H5 and H1. The coil I I6 is connected in a line I I9 at one end of which is connected a resistance H9 and at the other of which is connected a resistance I20. The coil I I1 is connected in a, line I2 I, at one end of which is connected the resistance I20 and at the other a movable arm I22 controlled by a pressure-responsive element I23. The arm I22 contacts a resistance I24 connected by a line I25 to the resistance H9. The resistance H9 is contacted by a movable arm I26 controlled by an element I21 responsive to a condition such as temperature, pressure, or humidity, the element being conventionally represented as a bellows. The arm I26 is connected in a line I28, connected to a secondary coil I29 of a transformer having a I30. High voltage is impressed across the primary coil I30, and a low voltage is taken from the secondary coil I29. A line I3I leads from a junction point I32 with the line I28 to the motor windings I08 and I09, which are shown to be connected in parallel with one another. The motor I05 controls an arm I33 connected by a link with an arm I35 contacting the coil I20 and connected by a line I36 with the secondary coil I29. The switch member II2 is connected to the line I36.

When, as viewed in Fig. 8, the portions of the resistances H9 and I20 to the left of the arms I26 and I35 equal the effective portion of resistance I24 and the portions of the resistances H9 and I20 to the right of the arms I26 and I35, the secondary current is divided equally between line III! and lines I2I and I25. Thus the same pull is exerted by the coils II6 and H1 upon the legs H4 and H5 of the switch II2 and the left end of the switch is maintained as shown in Fig. 8, out of contact with the points H and III. However, if more current flows through the coil II1 than through the coil II6, a greater pull will be exerted upon the leg II than upon the leg H4, and the left end of the switch moves up into contact with point IIO, causing current to fiow in the coil I08. This makes the motor I05 rotate in a clockwise direction as viewed in Fig. 8. If a greater current flows in the coil IIB, the switch I I2 contacts the point I I I, causing current flow in the coil I09 and rotation of the motor I05 in a clockwise direction in Fig. 8. Rotation of the motor causes angular movement of the arm I04 and movement of the sleeve 98 to the left or right. The sleeve 98 acts through the spring 99 against the plate 42 of the bellows 42'. This adjusts the valve rod 43 and changes the suction pressure at which the compressor unloads.

Any change from the position of equilibrium of Fig. 8 in which the switch II2 causes no current to flow either in the coil I08 or in the coil I09 is brought about by a change in position of the arm I25 or the arm I22 due to a change in the condition to which the element I21 or I23 is respon sive. Let it be assumed that the element I21 corresponds to the part 84 and valve 13 of Fig. l, or in other words, that the element I21 is responsive to a condition of the medium being cooled in the duct 24, such as temperature, humidity, or pressure. Assume that the condition in question is temperature and that the element I21 will expand with increase in temperature and contrast with decrease in temperature. Assume further that there is an increase in temperature. The resultant expansion of the element I21 will shift the arm I26 in a counterclockwise direction, causing less of the resistance II9 to be to the left of the arm I25 and more of the resistance to be to the right. This causes a greater current to flow in the coil II6 than in the coil H1 and the switch II2 moves down to the point III causing current to flow in the coil I09. This causes the motor I05 to rotate in a counterclockwise direction as viewed in Fig. 8. The arms I33 and I35 are shifted counterclockwise, and the portion of the resistance I20 to the right of arm I35 decreases, and the portion to the left increases. Thus compensation is provided for the decrease in the portion of resistance II9 to the left of arm I26 due to counterclockwise shifting of arm I26, and when the portions of the resistances I I9 and I20 to the left of the arms I26 and, I35 again equals the effective portion of resistance I24 and the portions of resistances H9 and I20 to the right of arms I26 and I 35, the current becomes the same in both coils II6 and H1, causing the switch II2 to move out of contact with point III to the position of Fig. 8. Current no longer flows in the coil I09 and rotation of the motor I05 and shifting of the arms I33 and I35 stop.

The above described counterclockwise rotation of the motor I05 as viewed in Fig. 8, due for example to an increase in temperature in the duct 24 causes the arm I04 to shift clockwise as viewed in Fig. 6. This shifts the sleeve 99 to the left reducing the force applied through the spring 99 to the plate 42. The bellows 42 is thus permitted to collapse somewhat, moving the valve rod 43 to the left and causing an increase in the amount of loading of the compressor.

From the above it can readily be pictured what a reduction in the temperature of the medium being cooled in the duct 24 will do to the apparatus of Figs. 6 and '1.

Consider that the element I23 corresponds in function to the valve 13 and is subject to a suction pressure in the return line so as to act in response to a high suction pressure indicative of overloading of the system. Assume that the element I23 is so connected with the return line 85 that this undesirable high suction pressure will collapse the element I23 to the point where the arm I22 reduces the effective portion of the resistance I24. This increases the current in coil II1, causing switch II2 to move up into contact with point II 0. Current now flows in coil I08, causing clockwise rotation of motor I05 as viewed 9 in Fig. 8. This causes clockwise shifting of arms I33 and I35 and an increase in the portion of the resistance to the right of arm I35. When the arm I35 has shifted sufliciently in a clockwise direction, the various resistances are so balanced as to cause the same flow of current in coils H6 and H1, and the switch II2 returns to the neutral position of Fig. 8, and the motor I05 is stopped. In the meantime, the arm I04 has shifted in a counterclockwise direction, moving the sleeve 98 to the right and causing it to act through the spring 99 to urge the plate 42 of the bellows 42 to the right. This moves the valve rod 43 to the right and thereby increases the amount of the unloading of the compressor.

The apparatus of Figs. 6 and 7 provides for modification of the control of unloading of a compressor determined by suction pressure through electrical means that are responsive to two different conditions occurring simultaneously, for example, a condition of a medium being cooled such as temperature, pressure, or humidity and another condition such as high suction pressure in the return line of the compressor.

The apparatus of Fig. 9 is also electrically controlled in the manner illustrated in Fig. 8, but differs from that of Figs. 6 and 7 in certain respects. A disk I31 engages the left end of the valve rod 43. One end of a coil spring I38 engages the disk I31, and the other end is engaged by a sleeve I39. The sleeve and spring are mounted within the threaded sleeve 31. The sleeve is pivotally connected to and between the spaced ends of strips IOI forming the link I02, which is pivotally connected by nut and bolt I03 to the arm I04, actuated by the electric motor I05. The motor may be controlled by a means like that of Fig. 8. The motor may act through rotation in a certain direction to produce a counterclockwise shifting of arm I04, which brings about movement to the right of sleeve I39. The sleeve urges the spring I38 against the disk I31, causing the valve rod 43 and bellows disk 42 to be urged to the right. This action increases the unloading of the compressor.

Rotation of the motor I05 in the opposite direction causes clockwise shifting of arm I04 and movement to the left by link I0! and the sleeve I39. The compression of the spring I30 is decreased, and the valve rod 43 moves to the left under the action of the bellows 42. The unloading of the compressor is thus decreased. The compression spring 65 acting between the bellows disk 42 and the disk 60 positioned by the nut 69 threaded on the sleeve 61 resists collapse of the bellows 42 by the compressor suction pressure.

I claim:

1. Unloading mechanism for a variable capacity compressor adapted to be connected to a cooling system and having a plurality of compressing cylinders, each of a number of which may be selectively rendered inoperative in order to vary the capacity of the compressor, comprising a plurality of individual cylinder unloading means each operatively associated with a single cylinder, fluid pressure creating means for operating said individual cylinder unloading means, means for selectively connecting said fluid pressure creating means to said individual cylinder unloading means comprising a master valve including a valve rod adapted to be selectively positioned at a plurality of positions, and means for selecting the position of said valve rod comprising a spring biased to move said valve rod in a first direction, a bellows subjected on one side to the suction pressure of said compressor and operating against said spring for returning said valve rod in the opposite direction to a plurality of successive positions when the suction pressure rises successively above a number of predetermined pressures, means for supplying pressure fluid against the other side of the collapsible bellows as to tend to expand the same for moving said valve rod in said first direction against the force exerted on the bellows by the aforesaid suction pressure, and means for controlling the extent of movement of said valve rod caused by the action of pressure fluid against the said other side of the bellows, said controlling means comprising a device for regulating the pressure exerted by the pressure fluid and means responsive to the temperature of the medium subjected to the action of the cooling system and responsive to the suction pressure of the compressor for variably controlling the setting of the device.

2. Unloading mechanism for a variable capacity compressor adapted to be connected to a cooling system and having a plurality of compressing cylinders, each of a number of which may be selectively rendered inoperative in order to vary the capacity of the compressor, comprising a plurality of individual cylinder unloading means each operatively associated with a single cylinder, fluid pressure creating means for operating said individual cylinder unloading means, means for selectively connecting said fluid pressure creating means to said individual cylinder unloading means comprising a master valve including a valve rod adapted to move in a first direction to effect the fluid connection and cylinder loading and to move in a second direction to interrupt the fluid connections and unload the compressor cylinders and to be selectively positioned at a plurality of positions each of which correspond to the loading of a selected number of said cylinders, and means for selecting the position of said valve rod comprising a bellows operatively connected to said valve rod, means for supplying pressure fluid against one side of the bellows so as to tend to move said valve rod in said second direction to unload compressor cylinders, and means for controlling the extent of movement of said valve rod caused by the action of the pressure fluid on said bellows comprising a device .for regulating the pressure exerted by the pressure fluid and means responsive to high compressor suction pressure and low temperature of the medium subjected to the action of the cooling system for providing increased fluid pressures to move said valve rod in said second direction to eiTect unloading of said compressor cylinders.

3. A cooling system comprising a compressorcondenser-evaporator system of refrigeration, the compressor of which comprises a plurality of cylinders and means to vary the number of cylinders compressing refrigerant comprising individual cylinder unloading means associated with each of a number of said cylinders, fluid pressure means for operating said individual cylinder unloading means including a master valve having a valve rod capable of being moved to a number of control positions to vary the number of said individual cylinder unloading means operatively connected to said fluid pressure means, and means for selecting the control position of the rod, said means comprising an expansiblecollapsible device subjected at one side to the suction pressure of the compressor, means for subjecting the other side of the expansible-collapsible device to pressure fluid, and control means operative to regulate the pressure of said last mentioned fluid in response to variations in both compressor suction pressure and evaporator temperature.

4. In a refrigerating system of the compressorcondenser evaporator type, capacity varying means associated with the compressor for altering the amount of refrigerant compressed, said capacity-varying means including a master valve capable of being moved to a number of control positions, an expansible-collapsible device conn cted with the master valve and subjected over a' flrst pressure area to the suction pressure of the compressor to move the master valve, means for supplying pressure fluid to oppose said suction pressure on a second and substantially equal pressure area associated with said master valve, and means responsive to the temperature of the medium being cooled by the evaporator of the system and to compressor suction pressure for varying the pressure of the pressure fluid.

5. In a refrigerating system of the compressor-condenser-evapora'tor type, capacity-varying means associated with the compressor for altering the amount of refrigerant compressed, means responsive to increased suction pressure of the compressor for exerting control over the capacity-varying means tending to increase the compressor capacity, means responsive to a high temperature of the medium being cooled by the system for adjusting the control in a direction tending to. increase the compressor capacity and means responsive to compressor suction pressures above a predetermined value tending to decrease the compressor capacity.

6. Inc. refrigerating system of the compressor-condenser-evaporator type, capacity-varying means associated with the compressor for altering the amount of refrigerant compressed, means responsive to suction pressure of the compressor for exerting control over the capacity-varying means, means responsive to the temperature of the medium being cooled by the system for ad- Justing the control exerted by the means responsive to suction pressure, and means responsive to a high suction pressure indicating overloading of the compressor for modifying the control exerted by the capacity-varying means in such a way as to reduce the amount of refrigerant compressed.

'7. In a refrigerating system of the compressor-condenser-evaporator type, capacity-varying means associated with the compressor for altering the amount of refrigerant compressed, a pressure-movable device associated with the capacityvarying means so as to cause the same to decrease the amount of refrigerant compressed when subjected to pressure from one direction, means response to a low temperature of the medium being cooled by the system for applying pressure in the said one direction over a, predetermined area to the pressure-movable device and means responsive to an overloaded compressor condition for applying pressure in the said one direction over an equal area to the pressure-movable device.

8. In a refrigerating system of the compressor-condenser-evaporator type, capacity-varying means associated with the compressor for altering the amount of refrigerant compressed, an expansible-collapsible device subjected on its outer side to suction pressure of the compressor and associated with the capacity-varying means so as to cause control thereover to be exerted by suction pressure, a first spring engaging the inner side of the expansible-collapsible device, means 12 engaging the first spring for causing it to exert a predetermined force against the expansiblecollapsible device, a second spring acting against the expansible-collapsible device, and means re- I sponsive to the temperature of the medium being cooled by the system and a high suction pressure indicative of overloading of the compressor engaging the second spring for causing it to exert a variable force against the expansible-collapsible device in opposition to the force exerted on the device by the suction pressure for modifying the control exerted by the suction pressure.

9. In a refrigerating system of the compressor-condenser-evaporator type, capacity-varying means associated with the compressor for alter ing the amount of refrigerant compressed, an expansible-collapsible device subjected on its outer side to suction pressure of the compressor, a rod extending through and fixed to an end of the expansible-collapsible device, means associating the end of the rod outward of the expansib1e collapsible device with the capacity-varying means for causing the suction pressure to act through the device and therod for exerting control over the capacity-varying means, a first spring engaging the inner side of the said end of the device, means engaging the first spring for causing it to exert a predetermined force against the device in opposition to the force exerted thereon by the suction ressure, a second spring acting against the ot r end of the rod, and means responsive to the temperature of the medium being cooled by the system and a high suction pressure indicative of overloading of the compressor for acting against the second spring to cause it to act with a variable force through the rod against the device in opposition to the force of the suction pressure acting thereagainst for modifying the control exerted on the capacity-varying means by the suction pressure.

10. In a refrigerating system of the compressor-condenser-evaporator type, capacity-varying means associated with the compressor for altering the amount of refrigerant compressed, means responsive to suction pressure for exerting a control over the capacity-varying means, an electric motor for modifying the control exerted by the means responsive to suction pressure over the capacity-varying means, parallel lines connected with a power source and having resistance, means responsive to disturbance of a predetermined relation of the resistances in the parallel lines for operating the motor, means responsive to the temperature of the medium being cooled by the systern for varying the relation of the resistances in the parallel lines, means responsive to high suction pressures indicative of overloading of the compressor for varying the relation of the resistances in the parallel lines, and means driven by the motor for restoring the predetermined relation of the resistances in the parallel lines to stop the motor.

ALWIN B. NEWTON.

(1o REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number