WO1996006316A1

WO1996006316A1 - Self-adjusting superheat valve

Info

Publication number: WO1996006316A1
Application number: PCT/US1994/010255
Authority: WO
Inventors: Richard H. Alsenz
Original assignee: Alsenz Richard H
Priority date: 1994-08-25
Filing date: 1994-08-25
Publication date: 1996-02-29
Also published as: EP0777843A1; EP0777843A4; CA2197572A1; AU7954994A

Abstract

The present invention discloses an automatic self-adjusting thermally powered expansion valve (22) for controlling the flow of refrigerant to an evaporator (18) of a refrigeration system (10). The valve (22) includes a generally cylindrical interior valve chamber (84) with an inlet port (90) and an outlet port (92) providing a passage for the flow of refrigerant through the valve (22). The flow of refrigerant through the valve (22) is regulated by valve element (98), which moves longitudinally within chamber (84). The valve element (98) includes one or more grooves (100) along the circumference thereof to provide a passage for the refrigerant. The number and size of grooves (100) which align with inlet port (90) and outlet port (92) determine the flow rate of the refrigerant through valve (22). The longitudinal position of the valve element (98) is controlled by force generators (102, 106, 108) and probes (74, 78). The force generators (102, 106) preferably comprise bellows, while force generator (108) comprises a compression spring. As a result, the position of the valve element (98) depends on the fluid pressure in and the size and configuration of, bellows (102, 106), and the spring constant of compression spring (103). As the temperature at probes (74, 78) increase, so too does the pressure in conduits (76, 80) and bellows (102, 106). Fluid pressure within the evaporator coil (20) is communicated through the valve element (98) by passages (112, 114) so that the movement of valve element (98) is not hindered by a fluid pressure differential in the chamber.

Description

Self-Adiusting Superheat Valve Technical Field

The present invention relates to techniques for configuring valves to control the flow of fluid therethrough in response to selected parameters, and particularly to methods and apparatus for automatically controlling fluid flow with an automatic, self-adjusting valve which responds to system changes. The present invention finds particular application to closed loop vapor cycle refrigeration systems, and more particularly to apparatus and methods for automatically adjusting the refrigerant flow in such a refrigeration system for variations in the refrigeration system design and changes in the operating and ambient conditions. The term "refrigeration system" as used herein refers to any such system to lower temperature, and includes air conditioning systems as well as systems to cool relatively confined spaces, such as systems typically called refrigerators and freezers, for example. Background Art

Mechanical expansion valves frequently are used in refrigeration systems to meter the liquid refrigerant flow into an evaporator coil. A type of mechanical expansion valve commonly used contains a body having an inlet port and an outlet port and a movable valve, or closure, element placed within the body for opening and closing the valve orifice. A compression spring is placed at one end of the valve element to apply a force to it in a first direction. A second force generator, such as a fluid-filled bellows or diaphragm, is placed against the other end of the closure element to provide a force against it representative of a system parameter, such as the outlet temperature of the evaporator coil, in a second direction that is opposite to the direction of the force provided by the compressed spring. The second force generator is coupled in fluid communication with a thermal probe, with the second force generator, the probe and the communication conduit therebetween being filled with an appropriate fluid. The probe typically is attached thermally to the evaporator coil outlet. As the temperature of the probe changes, the pressure in the probe, and thus in the second force generator, changes, causing the bellows or diaphragm, for example, to expand or to contract, thereby providing a force at the closure device that is representative of the temperature of the region where the probe is located, such as at the evaporator coil outlet. Examples of various valves may be found in U.S. Patent Nos. 5.026,022, 5,065,595, and 5,148,684.

Such expansion valves, however, do not have a single set point and, therefore, must be adjusted in response to a change in the operating conditions of the refrigeration system. Such adjustments can be both time-consuming and may necessitate disassembling the system to obtain access to the valve. In addition, if the valve is not adjusted, operating problems and/or power inefficiencies in the refrigeration system operation will typically be the end result. Because, as a practical matter, valves cannot be adjusted continuously in response to every change affecting the operation of the refrigeration system, refrigeration systems have inherent power inefficiencies. Thermomechanical expansion valves which permit remote adjustments to the valve stem have been developed to alleviate the necessity of disassembling the system for adjustment. These devices, however, are susceptible to undesirable leakage and require continued readjustment.

Other attempts have been made to solve some of the aforementioned problems and to increase the power efficiencies of these systems by making the inlet and outlet ports balanced, thus making the opening of the vale orifice independent of the pressure drop across the orifice. The problem with these mechanisms is that they fail to compensate for variable flow through the orifice. The flow through an orifice varies as the square root of the pressure drops across the orifice.

Disclosure of Invention

The present invention provides a method and apparatus for controlling the flow of refrigerant fluid in a refrigeration system, which is responsive to parameters of the system. More particularly, the present invention provides method and apparatus for controlling the flow of refrigerant in a refrigeration system by providing an automatic continuously self-adjusting thermally powered expansion valve. In a refrigeration system wherein air is cooled by passing externally by an evaporator of the system, a probe senses the temperature of the air flowing past the evaporator and applies a quantity of fluid pressure that is representative of the temperature of the air to configure the valve to control the flow of refrigerant to the evaporator. The configuring of the valve controls the flow of refrigerant to maintain the temperature at the outlet end of the evaporator lower than the temperature of the air external to the evaporator and higher than the temperature within the evaporator decreases; the flow of refrigerant decreases when the difference between the temperature at the outlet end of the evaporator and the temperature within the evaporator decreases, or the difference between the temperature of the air external to the evaporator and the temperature within the evaporator increases.

Two temperature sensing probes may be used, with one probe sensing the temperature at the outlet end of the evaporator and the other probe sensing the temperature of the air external to the evaporator. Forces that are representative of the sensed temperatures and of the pressure in the evaporator are generated to control the configuration of the valve. T e flow of refrigerant to the evaporator is thus increased when the temperature of the air external to the evaporator decreases, or the temperature at the outlet end of the evaporator increases, or the pressure in the evaporator decreases. Likewise, the flow of refrigerant is decreased when the temperature of the air external to the evaporator increases, or the temperature at the outlet end of the evaporator decreases, or the pressure in the evaporator increases. Two force generators, operable by application of fluid pressure thereto, are provided to operate in generally opposite directions to configure the valve. Each of the two probes is in fluid pressure communication with one of the force generators so that one force generator generates force representative of the temperature sensed by one of the probes and the other force generator generates force representative of the temperature sensed by the oώer probe. The force generators apply force in generally opposite directions to a valve element whose position in a valve body determines the flow passage area for flow of refrigerant through the valve. Fluid pressure is communicated to the valve element from within the evaporator as well so that forces representative of the two sensed temperatures and of the pressure within the evaporator configure the valve. A spring provides a force to tend to close the valve to provide a response of the valve to change in the difference between the temperature at the outlet end of the evaporator and the temperature within the evaporator that is at least partially proportional.

One of the force generators may generate force greater than the force generated by the other force generator in response to the same quantity of fluid pressure applied to each of the force generators. In a particular embodiment, the two force generators may comprise bellows such that the operable area of one bellows for generating force for configuring the valve is larger than the operable area of the other bellows.

A self-adjusting thermally powered valve according to the present invention may comprise a sliding valve element within a chamber in a valve body, intermediate in inlet port and an outlet port, with the position of the valve element determining the fluid flow through the valve, and multiple force generators applying ratiometric forces representative of system parameters to move the valve element accordingly.

The present invention provides method and apparatus for controlling the flow of refrigerant in a refrigeration system by the generation of forces representative of parameters of the refrigeration system, including the temperature of the air flow by the evaporator of the system, for example, wherein the forces are so produced ratiometrically, that is, proportional to the difference in the operative areas of the two force generators of the valve of the invention for producing force to configure the valve. The valve of the present invention features balanced inlet and outlet ports so that he movement of the valve element is not hindered by flow of fluid through the valve. Further, the valve is not responsive to liquid line pressure upstream of the valve. A compression spring operates to provide a proportional response of the valve element to changes in the temperature of the superheat of the refrigeration system.

A valve according to the present invention is self-adjusting, that is, the valve adjusts automatically in response to changes in the parameters of the system employing the valve such as the air being cooled by a refrigeration system; the valve is thermally powered, that is, the configuration of the valve is determined and changed by forces that are generated by heat changes and according to differences in temperatures; and the valve is mechanically self-adjusted, that is. the thermal powering of the valve configuration changes is effected utilizing fluid pressure applied to the valve components. Brief Description of Drawings

Fig. 1 is a schematic illustration of a closed loop vapor cycle refrigeration system utilizing a self-adjusting thermally powered expansion valve according to the present invention; Fig. 2 is an enlarged, schematic, cross-sectional view of an expansion valve according to the present invention utilized in the system illustrated in Fig. 1; and Fig. 3 is a graph of a response curve of the expansion valve shown in Fig. 2.

Best Mode for Carrying Out the Invention

A closed loop vapor cycle refrigeration system 10 is shown generally in Fig. 1. The refrigeration system 10 preferably includes a compressor 12 for compressing a low pressure gas refrigerant, a condenser 14 for condensing the compressed gas refrigerant to a liquid, a receiver 16 for receiving and storing the liquid refrigerant, and an evaporator system 18 including an evaporator coil 20 for evaporating the liquid refrigerant to the low pressure gas. The evaporator system 18 further includes a self-adjusting thermally powered mechanical expansion valve 22 coupled to the evaporator coil 20 for controlling the flow of refrigerant to the evaporator coil. The refrigeration system 10 also features a microcontroller circuit 24 for controlling the operation of the system in response to various system parameters in accordance with programmed instructions.

Various sensors, identified below, provide information about selected system parameters of the refrigeration system 10 to the control circuit 24.

The compressor 12 preferably receives the low pressure gas refrigerant from the evaporator coil 20 by way of a suction line 26 and compresses the low pressure gas to a high pressure and high temperature gas refrigerant. The high pressure gas refrigerant is conducted by way of a line

28 to the condenser 14. A fan 30 at the condenser 14 causes air to flow across the condenser 14. as indicated by the arrow 32, thereby condensing the compressed gas refrigerant to a liquid. The fan 30 may be of any appropriate type, including a fixed or variable speed type. The air 32 flowing across the condenser 14 removes thermal energy of condensation from the refrigerant in the condenser and causes the refrigerant to condense to liquid. The liquid refrigerant from the condenser 14 discharges by way of a liquid return line 34 to the receiver or reservoir 16 where the liquid is stored as indicated at 36. A conduit 38 conveys the liquid refrigerant from the reservoir 16 to the inlet side of the expansion valve 22. The valve 22 is located between the reservoir 16 and the inlet end 40 of the evaporator coil 20 for controlling the flow of refrigerant from the reservoir to the evaporator coil. In progressing along the evaporator coil 20 the refrigerant fluid absorbs thermal energy of evaporation from air in contact with the coil, and evaporates to the gaseous state for egress through the outlet end 42 of the coil and return to the compressor 12 along the refrigerant tube 26. The flow path of refrigerant around the refrigeration system 10 is thus a closed loop, or circuit. Ambient air flows into the evaporator system 18 and over the evaporator coil 20 as indicated by the arrows 44. The ambient air that is cooled by removal of thermal energy to evaporate the refrigerant in the evaporator coil 20 is discharged from the area of the coil 20 as indicated by the arrows 46. The cooling of the ambient air flow 44 and 46 establishes the useful refrigeration effect. The ambient air may be circulated so that the flow 44 into the evaporator system is return air that is to be cooled again after absorbing thermal energy in cooling a load at some other location.

In the preferred embodiment, appropriate sensors are positioned throughout the refrigeration system 10 to generate electrical signals representative of the temperature or fluid pressure at respective locations. The electrical signals are conveyed to the control circuit 24 for processing and utilization by the control circuit in the operation of the system 10. For example, a temperature sensor 48 is placed in the liquid flow conduit 28 to obtain a signal that is representative of the temperature of the liquid entering the condenser 14. A temperature sensor 50 and a pressure sensor

52 may be positioned along the liquid return line 34 to the reservoir 16 to provide electrical signals representative of the temperature and pressure, respectively, of the refrigerant in that return line.

A temperature sensor 54 is placed in the evaporator system 18 in the path of the return air flow 44 to provide an electrical signal representative of the of the temperature of the return air. A temperature sensor 56 is positioned in the path of the discharge air flow 46 from the evaporator system 18 to provide a signal representative of the temperature of the air leaving the evaporator coil 20. Temperature sensors 58 and 60 are positioned at the inlet end 40 of the evaporator coil 20 and at the outlet end 42 of the coil to provide signals representative of the temperature of the refrigerant entering and leaving the evaporator coil, respectively. Additionally, pressure sensors

62 and 64 are connected to the inlet end 40 and the outlet end 42 of the evaporator coil 20 to provide signals that are representative of the pressure of the refrigerant at the coil inlet and outlet ends, respectively.

Additional temperature sensors, such as 66 and 68, may be located in the compressor 12 to determine the temperature of the compressor crankcase and the temperature of the oil in the compressor, respectively.

The microcontroller circuit 24 includes a microprocessor, appropriate analog-to-digital converters and comparators, for example, and switching circuitry. The control circuit 24 is operatively coupled to the temperature sensors 48, 50, 54, 56, 58, 60, 66 and 68, the pressure sensors 52, 62 and 64, the compressor 12 and the fan 30 by appropriate conductors (not shown). Outgoing arrows as parts of the sensor symbols and inward arrows 70 at the controller circuit 24 indicate that the sensors are operatively coupled to and provide relevant information signals to the controller. Similarly, outgoing arrows 72 at the microcontroller 24 and inward arrows as parts of the symbols of system components, such as the compressor 12 and the fan 30, indicated that the microcontroller circuit is operatively connected to these components by appropriate conductors (not shown) for controlling their operation by appropriate operation command and control signals. During operation of the system 10, the control circuit 24 continually receives information from the various sensors of the system and, in response thereto, controls the operation of various system components, such as the compressor 12 and the fan 30, in accordance with instructions provided to or stored in the circuit 24.

The configuration of the expansion valve 22 is automatically and continuously adjusted directly with the use of two thermal sensing probes operatively connected to the valve itself. A first probe 74 is connected to a first end of the expansion valve 22 by a conduit 76, and a second probe 78 is connected to the opposite, second end of the valve by a conduit 80. The first probe 74 is thermally connected to the outlet end 42 of the evaporator coil 20, which is connected to the suction line 26 to the compressor 12. The second probe 78 is place in a suitable location in the refrigeration system 10 such as in the path of the return air 44 to the evaporator system 18 as illustrated, or in the refrigeration area (not shown) being cooled by the cooled air flow 46 discharged from the evaporator system 18, or in the path of the discharge air flow 46, for example. The construction and operation of the valve 22 and the operation of the probes 74 and 78 will now be discussed with reference to Fig. 2.

The expansion valve 22 preferably includes a generally elongate body 82 having a generally cylindrical inner chamber 84, a first (or upper) end 86, a second (or lower) end 88, an inlet port 90 to the chamber transverse to the cylindrical axis of the body 82, and an outlet port 92 leading from the chamber substantially on the opposite side of the body 82 from the inlet port 90 and at least approximately longitudinally aligned with the inlet port. A tubular inlet coupling 94 extends transversely from the cylindrical axis of the body 82 at the inlet port 90, and a tubular outlet coupling 96 extends transversely from the body at the outlet port 92. When the valve 22 is installed in a refrigeration system 10 as in Fig. 1 , the conduit 38 from the reservoir 16 is connected to the inlet coupling 94 so that liquid refrigerant may be communicated to the inlet port 90 of the valve

22, and the valve outlet coupling 96 is joined to the inlet end 40 of the evaporator coil 20 so that refrigerant allowed to pass through the valve 22 to its outlet port 92 may flow into the evaporator coil.

A structured valve element or closure device 98, such as a piston, preferably is located in the valve chamber 84 for longitudinal movement along the cylindrical axis of the chamber. The valve element 98 is generally cylindrical, and fits within the chamber 84 with the outer surface of the valve element in sliding, sealing engagement with the interior surface of the body 82 defining, in part, the chamber 84. The valve element 98 divides the chamber 84 into two regions on opposite sides of the valve element. The cylindrical surface of the valve element 98 is broken by one or more (three are shown) grooves or circular passages 100. The longitudinal position of the valve element 98 relative to the valve body 82 determines the position of each groove 100 relative to the inlet port 90 and the outlet port 92. Each groove 100 provides a fluid flow passage around the interior of the chamber 84 between the inner surface of the body 82 and the valve element 98 so that a groove aligned with both the inlet port 90 and the outlet port 92 establishes a flow path for fluid through the valve 22. When no grooves 100 are aligned with both ports 90 and 92 at the same time, the valve element 98 provides a seal across the inlet port 90, and the valve is closed.

When multiple grooves 100 are provided in the valve element 98, the grooves may be of different cross-sectional areas, or two or more such grooves may have the same cross-sectional area. Multiple grooves 100 in the valve element 98 may also be positioned at various spacings along the valve element, or the grooves may be evenly spaced. As illustrated in Fig. 2, the valve inlet port 90 preferably is smaller than the outlet port 92. For a given number, size and spacing distribution of grooves 100 in the valve element 98, some or all of the grooves may be aligned with the outlet port 92, while at the same time a smaller number, or even none, of the grooves are aligned with the inlet port 90. Any groove 100, or any portion of a groove cross section, that is aligned with the inlet port 90 will also be aligned with the outlet port 92 in the port configuration illustrated. A groove 100 aligned only with the outlet port 92 and not the inlet port 90 does not break the seal between the valve element 98 and the inner surface of the body 82, and does not provide a passage for fluid through the valve 22.

The greater the groove cross-sectional area that is aligned with the inlet port 90, provided by one or more grooves 100, the greater is the flow passage cross-sectional area for fluid flow through the inlet port 90 and, therefore, through the valve 22. The inlet port 90 may be considered the orifice of the valve 22, whose opening is controlled by the position of the valve element 98 relative to the valve body 82. The flow rate of refrigerant through the valve 22 to the evaporator coil 20 thus is determined by the position of the valve element 98 within the valve body 82, so that moving die valve element along the chamber 84 causes the flow rate through the valve to vary. The number, size and spacing of the grooves 100 may be selected to achieve different degrees of sensitivity of the valve control as well as different amounts of flow rate change for given valve configuration changes.

The use of a sliding piston, or spool, valve element in a cylindrical valve body chamber to control the fluid communication between the valve inlet and the valve outlet, as disclosed herein. provides balanced valve ports. The movement of d e sliding valve element is not opposed by die flow of fluid against die valve element such as would be die case for a plunger-type valve element, for example; also, die valve configuration using die sliding element is not responsive to d e fluid line pressure upstream of die valve inlet port. The operation of the valve 22, diat is, die positioning of die valve element 98 widiin die valve chamber 84, is controlled by a combination of forces acting at die opposite, longitudinal ends 86, 88 of die valve element 98. A large diameter bellows 102 preferably is located widiin die valve chamber 84 between die first end 86 of die valve 22 and die near end of die valve element 98. The conduit 76 is sealed to die valve body 82 and is in fluid communication with die interior of die large bellows 102. The opposite end 104 of die large bellows 102 contacts die near end of die valve element 98. The bellows 102, die conduit 76 and die diermal probe 74 are fluid-filled so that an increase in pressure of die fluid due to its heating with a temperature rise at die probe 74 is communicated to die bellows 102, which then tends to expand against die valve element 98. The force applied to die valve element 98 by the bellows 102 is given by die product of die pressure of die fluid in die bellows and die cross-sectional area A, of die bellows end 104 contacting the end of die valve element 98.

A small diameter bellows 106, diat is, a bellows having an end 108 with a cross-sectional contact area A₂ diat is smaller than die area A,, preferably is placed widiin die valve chamber 84 between die second end 88 of die valve body 82 and die opposite end of die valve element 98 from diat which is in contact widi die large bellows 102. The fluid conduit 80 is sealed to die valve body

82 and is in fluid communication with die interior of die small bellows 106. The small bellows 106, die conduit 80 and die diermal probe 78 are fluid-filled so diat an increase in pressure of die fluid due its heating with a temperature rise at die probe 78 is communicated to die interior of die bellows, which then tends to expand against die valve element 98. The force exerted by die small bellows 106 on die valve element 98 is given by die product of die pressure in die bellows and die area A₂ of die bellows end 108 contacting d e valve element.

The probes 74, 78 may comprise, for example, diermal bulbs. The fluid in die probes 74 and 78, die conduits 76 and 78, and the two bellows 102 and 106 preferably comprises an appropriate fluid, such as a refrigerant, to respond to temperature changes in the temperature ranges to which die probes are exposed to effect corresponding pressure changes at die respective bellows to contribute to control of die valve 22.

A compression spring 110 preferably circumscribes die small bellows 106 widiin die valve chamber 84 and is generally compressed between die second end 88 of die valve body 82 and die near end of die valve element 98. The spring 110 dius exerts a force on die valve element 98 diat is determined by die amount of compression of die spring and die spring constant. It will be appreciated d at die spring 110 and die small bellows 106 may both apply forces on die valve element 98 in die upward direction as viewed in Fig. 2, and die large bellows may apply a force on die valve element in die opposite, or downward, direction, widi each force tending to move the valve element in die direction of die applied force. The valve element 98 is broken by a longitudinal passage 112 extending die entire length of die element and providing a fluid pressure communication conduit across die valve element. The two bellows 102 and 106 are not sealed to die ends of the valve element 98. Thus, the region widiin die valve body chamber 84 above die valve element 98, as viewed in Fig. 2, and outside die large bellows 102 is in fluid pressure communication, along d e passage 112, with the region widiin die chamber 84 below die valve element 98 and outside die small bellows 106. Longitudinal movement of die valve element 98 widiin die chamber 84, dierefore, is not hindered or opposed by a fluid pressure differential in die chamber, across die valve element and outside the two bellows.

A conduit 114 connects the interior of the valve outlet coupling 96 widi die valve body chamber 84 above die valve element 98. Widi die valve 22 incorporated in a refrigeration system such as at 10 in Fig. 1, die fluid pressure downstream of die valve element 98, particularly downstream of die inlet port 90, and widiin die evaporator coil 20 is thus communicated along die outlet coupling 96 and die conduit 114 to die upper region of die valve chamber 84 above die valve element 98 and, by way of die valve element passage 112, to die valve chamber region below d e valve element 98. The evaporator coil pressure is dius equalized across die valve element 98.

However, die forces applied to die two bellows 102 and 106 due to die evaporator coil pressure are dependent on die surface area of die respective bellows, as discussed below.

The fluid pressure widiin die evaporator coil 20 may be communicated across the valve element 98 and to die two bellows 102 and 106 by odier structures. For example, a second conduit (not shown) may be provided between die oudet coupling 96 and die valve body chamber 84 below die valve element 98 radier dian utilizing a passage 112 dirough the valve element. Then, fluid pressure from die evaporator coil 20 is communicated directly to bodi sides of die valve element 98. Alternatively, die passage 112 may be positioned away from die central axis of the valve element 98 so as to communicate widi each of die grooves 100, and no external conduits such as 114, for example, are utilized to connect die outlet coupling 96 widi die valve chamber 84 on eidier side of die valve element 98. In such case, fluid pressure from die evaporator coil 20 is communicated dirough die outlet port 92 to any of die grooves 100 aligned widi die outlet port and along the longitudinal passage dirough die valve element 98 to both sides of die valve element.

Referring now to Figures 1 and 2, during operation of die refrigeration system 10. the liquid refrigerant 36 is conveyed to d e valve 22 by die tube 38. and passes dirough die valve inlet port 90 into die body chamber 84, along one or more groove passages 100 of die valve element 98, and out dirough die oudet port 92 to die evaporator coil 20. The refrigerant begins to change state upon traversing die oudet port 92 and die outlet tubular connector 96, and enters the evaporator coil 20 as a liquid and vapor mixture. The pressure of die refrigerant itself exerts force diat affects die tendency of die valve element 98 to be moved along die valve body 82 to alter die flow rate dirough die valve 22. Disregarding friction as a factor for purposes of simplicity and clarity, mere are generally five forces which interact in determining die configuration of die valve 22 to control die flow of refrigerant to die evaporator coil 20. The net effect on die valve element 98, diat is, die determination of die position of die valve element relative to die valve body 82 and. therefore, die position of die passageway grooves 100 of die valve element 98 relative to die inlet port 90, is due to die sum of die longitudinal forces applied to die valve element 98 and to die bellows 102 and 106. These forces, dierefore, determine die flow rate of refrigerant dirough the valve 22.

The pressure of die fluid in die first probe 74, which preferably is representative of die coil outlet temperature, diat is, die temperature of die refrigerant exiting die evaporator coil 20, generates a downward (as viewed in Fig. 2) force F_co dirough die large bellows 102 acting on die upper end of die valve element 98. The force F_co increases as die coil outlet temperature increases to expand die fluid in die probe 74, and such force decreases as die coil outlet temperature decreases. The force F_co is given by F_eo = P_co(A,) (1) where P_co is die pressure in die probe 74, which is representative of die outlet coil temperature, and A,, as mentioned above, represents die cross-sectional area of bellows 102.

The pressure of die refrigerant in die evaporator coil 20, communicated to die chamber 84 above die valve element 98 as discussed above, generates an upward (as viewed in Fig. 2) force. F_cu acting at die contact of die large bellows 102 widi die valve element 98, is given by

F_cu = P_C(A,) (2) where P_c is die fluid pressure in die coil. Similarly, die fluid pressure P_c in die evaporator coil 20. communicated to die chamber 84 below die valve element 98 as discussed above, generates a downward force F_cd on die small bellows 106 at its contact widi die valve element 98 given by F_cd = P_C(A₂). (3)

It will be appreciated diat die net force applied by die fluid pressure P_c of die refrigerant in the valve 22, tending to affect die valve element 98, is given by die product P_C(A, - A₂) and acts on die large bellows 102, tending to allow die valve element 98 to be moved upwardly (as viewed in Fig. 2) against die large bellows 102. The fluid pressure in die second probe 78, which preferably is representative of die temperature of die return air flow 44 as illustrated, and which increases or decreases as diat temperature rises or falls, respectively, generates an upward force on die small bellows 106 contacting die valve element 98, as viewed in Fig. 2, given by F_r = P_r(A₂) (4) where P_r is die fluid pressure in die second diermal probe. The compression spring 1 10 generates an upward force F_f on die bottom end of die valve element 98, as viewed in Fig. 2, diat is proportional to die spring displacement, or compression, from die zero compression state, X, and is given by F, = K(X) (5) where K is die spring constant of die spring 1 10. It will be appreciated diat Equation (5) applies only in die range of compression of die spring 110 where die force generated is proportional to die degree of compression. In some applications of die valve 22, a force-generating device featuring a non-linear response may be desired; in other applications, it may be desirable to use no spring to apply a force to die valve element. A spring 110 exhibiting the response of Equation (5) will be considered for purposes of illustration.

In die equilibrium state, die sum of all die forces tending to move die valve element 98 upwardly equals die sum of all die forces tending to move die valve element downwardly. Considering die forces of Equations (1) dirough (5), die equilibrium equation may be given as F_co + F_cd = F_eu + F_r + F,. (6)

Substituting for die forces from Equations (1) dirough (5) yields die equilibrium equation

P_co(A,) + P_C(A₂) = P_C(A,) + P_r(A₂) + F_s, (7) or

A,(P_co - P_c) = A₂(P_r - P_e) + F_t. (8) If die ratio A₂/A- of the surface area of die small bellows end 108 to die large bellows end 104 is set equal to R, then

R = (Pco - Pc)/(P_r " Pc) - F_s/(A,)(P_r - P_c). (9)

If no compression spring 110 is present, dien F, is zero, and if die same fluid is used in the two diermal probes 74 and 78 diat is used as die refrigerant, die temperature and pressure of the fluid for all remaining terms are proportional, and die temperatures may be substituted for the corresponding pressure values to yield

R = (T_co - T_c) _r - T_c) = T,/T₂ (10) where T_co is die evaporator coil oudet temperature, T_c is die temperature of fluid widiin die coil and T_r is die return air temperature. The ratio of die surface areas of die bellows R, therefore, is die ratio of die difference T- between die coil outlet temperature T_co and die coil temperature T_c, which temperature difference is also known as die superheat temperature of die system 10, to die difference T₂ between die return air temperature T_r and die coil temperature T_c. The relationship of Equation (10) provides a single set point for die expansion valve 22 which is independent of fluctuations in odier system parameters, including die suction pressure in die suction line 26. Generally, die valve 22 is configured so diat downward movement of die valve element 98 is required to increase fluid flow dirough die valve. Thus, die valve element 98 is in die off, or closed, configuration when it is positioned in die chamber 84 toward die large bellows 102. Then die grooves 100 are all displaced toward die first end 86 of die valve body 82, and none of die grooves are aligned widi die inlet port 90. It will be appreciated d at die coil fluid pressure acting on die two bellows 102 and 106 is die same for both bellows; however, since die bellows end areas

104 and 108 are different, die total force due to die fluid pressure in die evaporator coil 20 is greater on die large bellows 102 than on die small bellows 106 by die factor of die ratio of their respective surface areas A-/A-, = 1/R = G. The valve 22 is, dierefore, responsive, in part, to the fluid pressure in die evaporator coil 20. Similarly, in die event diat die fluid pressures in die probes 74 and 78 are equal, die larger bellows 102 would apply a force on die valve element 98 diat is greater man die force die smaller bellows 106 would apply on die valve element by die same factor G = A,/A₂. Widi some portion of die total cross-sectional area of die groove flow passages 100 aligned widi die inlet port, 90 refrigerant passes dirough die valve 22 to die coil 20. In practice, die return air temperature T_r will be higher dian die coil temperature T_c as will die coil outlet temperature T_co. Also, die coil outlet temperature T_co will be lower dian die return air temperature

T_r so diat T, is smaller dian T₂.

During normal operation of die refrigeration system 10 die valve 22 adjusts according to Equation (10) so that die valve element 98 is moved to increase die cross-sectional area of die grooves intersecting die inlet port 90, and refrigerant flow dirough die valve increases when (a) die return air temperature decreases, (b) die coil outlet temperature increases, or (c) die pressure in die coil 20 decreases. Conversely, die valve 22 adjusts so diat die valve element 98 is moved to decrease d e cross-sectional area of die grooves 100 intersecting die inlet port 90, and refrigerant flow dirough die valve decreases when (a) die return air temperature increases, (b) the coil outlet temperature decreases, or (c) die pressure in die coil 20 increases. For example, if die return air temperature T_r decreases, F_r decreases, T_r - T_c decreases, and die force imbalance on die valve element 22 moves die valve element downwardly toward die second end 88 of die valve body 82 to align more groove flow passage cross-sectional area widi die inlet port 90, diereby allowing a greater flow rate of refrigerant into die evaporator coil 20.

More particularly, Equation 10 makes clear diat die valve element 98 is moved to increase die flow passage area for fluid dirough die valve 22 if die difference between die coil outlet temperature and die temperature of refrigerant in die coil 20 increases or die difference between die return air temperature and die temperature widiin die coil decreases, and die valve element moves to decrease die flow passage area dirough die valve if die difference between die coil outlet temperature and die temperature widiin die coil decreases or die difference between die return air temperature and die temperature widiin die coil increases.

The combination of die two bellows 102 and 106 having contact surfaces 104 and 108. respectively, widi die ends of die. valve element 98 diat are of different size areas results in die production of ratiometric forces controlling, at least in part, die configuration of die valve 22. and enables die valve to have a single, self-adjusting set point for control of die flow of refrigerant dirough die valve to die evaporator coil 20. Thus, forces due to selected temperatures and to the evaporator coil pressure are generated to configure die valve in die same ratio as die ratio of die bellows' ends, as may be appreciated by reference to Equations (7) and (10), for example. Forces generated proportional to temperature differences, such as die superheat T, which is die difference between T_co and T_c, configure die valve 22 to control die flow of refrigerant dierethrough. Fig. 3 shows die response curve of die self-adjusting expansion valve 22 of Fig. 2. The opening of die valve orifice, diat is, die total cross-sectional area of die grooves 100 aligned with die inlet port 90, taken as a percentage of die maximum possible opening, or 100%, diat is, die alignment of die maximum cross-sectional area of die grooves widi die inlet port diat is possible, is plotted along die ordinate as a function of die temperature difference T, between the coil outlet temperature T_co and die coil temperature T_c, plotted along die abscissa. The range of T- dirough which die valve 22 will self-adjust to different percentages of die maximum opening of die valve orifice is between die values A and B of T- as indicated in Fig. 3. For all values of T, less dian die value A, die force F, of die spring 110 acting on die valve element 98 is large enough compared to the force acting in opposition to die spring force diat die valve orifice is maintained closed and no refrigerant flows dirough die valve. As die coil outlet temperature T_co rises the force

F_co increases to gradually overcome die spring force. The inlet port 90 begins to open at die point A where T, is equal to RC ^), and continues to open in linear relation to T, as indicated by the line C. At T| equal to the value B die valve element is positioned so mat die valve orifice is open 100%, and for all values of T- greater dian die value B die valve orifice stays completely open for maximum refrigerant flow rate to die evaporator coil. The value of T, equal to B is less dian die value of T_r as die graph of Fig. 3 illustrates.

The slope of die line C depends on die spring constant. The values of A and B at which die valve orifice is fully closed and fully open, respectively, may be altered by changing die geometry of die valve. The length of die valve element 98, for example, and die position of die groove passages 100 along die length of die valve element determine how far die valve element must move to open or close die orifice. Varying die pattern of die groove passages, by changing die number of grooves, dieir positions along die valve element, and dieir cross-sectional areas, for example, can vary die shape of die line C from a straight line as shown to a selected curve.

A significant advantage of die valve according to die present invention is diat die range of operation of die valve in which die valve orifice opening is variable, such as die range of values of Ti from A to B as illustrated in Fig. 3, is selectable by selection of die relative sizes of the bellows surface areas. A) and A₂. During operation of die refrigeration system 10 die coil outlet temperature T_co is always higher dian die coil temperature T_c and lower than die return air temperature T_r. As noted above wid reference to Equation 10, die valve orifice opening adjusts according to Equation 10 in response to changes in T_r, T_co and die pressure in die coil, which is related to T_c. It will be appreciated diat T_c is a measure of die temperature of die refrigerant entering die evaporator coil 20, and T_r is a measure of die amount of cooling of die load being provided by die refrigeration system 10. It is suggested diat die value of R = A₂/A, be chosen so diat T_co is set at 0.6(T₂), diat is, 0.6 of die difference between T_r and T_c for optimal control of die refrigerant flow dirough die valve. A further advantage of die above-described expansion valve is diat die valve is integral, or self-contained, and self-adjusts without external electrical control signals, for example. Additionally, existing refrigeration systems can easily be modified to incorporate die present invention.

The foregoing disclosure and description of die invention is illustrative and explanatory thereof, and various changes in die mediod steps as well as die details of die apparatus may be made widiin die scope of die appended claims widiout departing from die spirit of die invention.

Claims

1. An automatic, continuously self-adjusting diermally powered expansion valve for controlling die flow of refrigerant fluid in a refrigeration system.

2. A valve as in claim 1 , wherein said refrigeration system includes an evaporator and said valve comprises an expansion valve for die evaporator.

3. A valve as defined in Claim 2 further comprising a probe for sensing the temperature external to die evaporator and providing a fluid pressure diat is representative of die sensed temperature to configure die valve for controlling die flow of refrigerant fluid to the evaporator.

4. A valve as defined in Claim 1 further comprising: a valve body having a chamber dierein, an inlet port and an outlet port for passage of fluid dirough die body, and a valve element widiin die chamber to intermediate to die inlet port and die oudet port such diat die position of die valve element relative to die inlet port determines die flow passage area for die flow of fluid dirough die valve.

5. A valve as in claim 4, further comprising: a first force generator, operable by application of fluid pressure diereto for applying force tending to move die valve element in a first direction to open die flow passage area for die flow of fluid dirough die valve; and a second force generator, operable by application of fluid pressure diereto for applying force tending to move die valve element in a second direction to close die flow passage area for die flow of fluid dirough die valve.

6. A valve as in claim 5, further comprising: a first probe, in fluid pressure communication widi die first force generator, diat senses die temperature at a first location relative to die refrigeration system and applies fluid pressure to die first force generator diat is representative of die temperature sensed at die first location; and a second probe, in fluid pressure communication widi die second force generator, diat senses die temperature at a second location relative to the refrigeration system and applies fluid pressure to die second force generator diat is representative of die temperature sensed at die second location.

7. A valve as in claim 6, further comprising: at least one fluid pressure communication passage allowing fluid pressure from die evaporate to equalize on bodi sides of said valve element.

8. A valve as defined in Claim 7 wherein: die valve element is a sliding valve element generally dividing die chamber into two regions on opposite sides of die valve element; die first force generator operatively connects to die valve element on one side diereof; die second force generator operatively connects to die valve element die opposite side diereof; and die at least one fluid pressure communication passage communicates fluid pressure from downstream of die valve to die two regions of die chamber.

9. A valve as defined in Claim 8 wherein die at least one fluid pressure communication passage to allow fluid pressure to communicate from downstream of the valve to die two regions of die chamber comprises a fluid pressure communication passage dirough the valve element and connecting die two regions of die chamber.

10. A valve as defined in Claim 6 wherein die first and second force generators comprise first and second bellows, respectively, and die operable area of die first bellows for generating forces to configure die valve is larger than die operable area of die second bellows for generating forces to configure die valve.

11. A valve as defined in Claim 6 further comprising a spring widiin die chamber to apply a force tending to move die valve element in die second direction.

12. A valve as defined in Claim 6 wherein die refrigeration system includes an evaporator and air is cooled by passing externally by die evaporator, and wherein die first location is at die outlet end of die evaporator and die second location is in die flow of air external to die evaporator.

13. A valve as defined in Claim 6 wherein die first force generator produces force in response to a quantity of fluid pressure applied diereto diat is greater dian force produced by the second force generator in response to die same quantity of fluid pressure applied diereto.

14. A closed loop refrigeration system, comprising: a compressor for compressing a refrigerant; a condenser for condensing die refrigerant coupled to said compressor via a line; an evaporator for evaporating die refrigerant coupled to said condenser via a conduit and to said compressor by a suction line; wherein said evaporator includes an evaporator coil and an automatic continuously self- adjusting diermally powered expansion valve for controlling die flow of refrigerant into the evaporator coil.

15. A mediod of controlling die flow of refrigerant to an evaporator of a refrigeration system, wherein air is cooled by passing externally by die evaporator, comprising providing an automatic continuously self-adjusting diermally powered expansion valve to control die flow of refrigerant to die evaporator.

16. A mediod as defined in Claim 16 further comprising maintaining die temperature at die oudet end of d e evaporator lower dian die temperature of die air external to die evaporator and higher dian the temperature widiin die evaporator.

17. A mediod as defined in Claim 16 further comprising sensing die temperature of die air external to die evaporator and applying a quantity of fluid pressure diat is representative of die sensed temperature to configure die valve.

18. A mediod as defined in Claim 16 further comprising: increasing refrigerant flow when die temperature of die air external to die evaporator decreases, or die temperature at die outlet end of the evaporator increases, or die pressure in the evaporator decreases; and decreasing refrigerant flow when die temperature of the air external to the evaporator increases, or die temperature at the outlet end of die evaporator decreases, or the pressure in the evaporator increases.

19. A mediod as defined in Claim 16 further comprising: increasing refrigerant flow when die difference between die temperature at die outlet end of die evaporator and die temperature widiin die evaporator increases, or die difference between die temperature of die air external to die evaporator and die temperature widiin die evaporator decreases; and decreasing refrigerant flow when die difference between die temperature at the outlet end of die evaporator and die temperature widiin die evaporator decreases, or die difference between die temperature of die air external to die evaporator and die temperature widiin die evaporator increases.

20. A mediod as defined in Claim 16 further comprising: providing a first probe diat senses die temperature at die outlet end of die evaporator: providing a second probe diat senses die temperature of die air external to the evaporator: and generating forces to configure die valve diat are representative of die sensed temperatures and of d e pressure in die evaporator, diereby: increasing refrigerant flow when die temperature of die air external to die evaporator decreases, or die temperature at die outlet end of die evaporator increases, or die pressure in the evaporator decreases; and decreasing refrigerant flow when die temperature of die air external to die evaporator increases, or die temperature at die oudet end of die evaporator decreases, or die pressure in die evaporator increases.

21. A mediod as defined in Claim 16 further comprising: providing d e valve including a first force generator, operable by application of fluid pressure diereto, and a second force generator, operable by application of fluid pressure diereto, operating generally in opposite senses to configure die valve; providing a first probe to sense die temperature at die oudet end of die evaporator and apply a quantity of fluid pressure to die first force generator diat is representative of the sensed temperature; providing a second probe to sense die temperature of die air external to die evaporator and apply a quantity of fluid pressure to die second force generator diat is representative of the sensed temperature; and applying fluid pressure, communicated from die evaporator, to die first and second force generators.

22. A mediod as defined in Claim 22 further comprising using the first force generator to provide a force representative of die temperature at die outlet end of die evaporator to tend to open die valve, using die second force generator to provide a force representative of the temperature of die air external to die evaporator to tend to close die valve, and applying forces, diat are representative of die pressure in die evaporator, in opposition to die forces generated by die first and second force generators, diereby utilizing forces diat are representative of die sensed temperatures and of die pressure in die evaporator to configure die valve.

23. A mediod as defined in Claim 22 further comprising providing die valve wherein die first force generator produces force in response to a quantity of fluid pressure applied thereto diat is greater dian force produced by die second force generator in response to die same quantity of fluid pressure applied diereto.

24. A mediod as defined in Claim 22 further comprising providing die valve having an inlet port communicating widi an outlet port and a sliding valve element dierebetween whose position relative to die inlet port determines die configuration of die valve and the flow of refrigerant, and wherein die first and second force generators apply forces to die valve element in opposite senses.

25. A mediod as defined in Claim 22 further comprising providing die first and second force generators as first and second bellows, respectively, operating on opposite sides of a valve element whose position determines the configuration of the valve and die flow of refrigerant, and wherein die operable area of die first bellows for generating force to configure the valve is larger dian die operable area of die second bellows for generating force to configure die valve.

26. A mediod as defined in Claim 22 further comprising providing a spring to apply force to tend to close die valve, diereby making the response of die valve to change in die difference between die temperature at die outlet end of the evaporator and die temperature within die evaporator at least partially proportional.