Closed vapor cycle refrigerator

Claim 2

In combination with a closed vapor cycle refrigeration system including in connected closed loop sequence a compressor, a condensor, an expansion valve and an expansion evaporator, improved electronic expansion valve apparatus, characterized in that: (a) a means for sensing the superheat of the expansion evaporator and producing an electrical signal level indicative thereof; (b) a converting means connected to said sensing means and producing from the electrical signal level an on-off modulated signal whose duty cycle is representative of the required flow rate of liquid refrigerant through said valve; and (c) said expansion valve being modulated operated by said converting means from a fully open position to a fully closed position for each cycle of the on-off modulated signal without imparting any substantial pressure shockwaves to the liquid refrigerant on opening and closing of said valve to produce an average refrigerant flow rate therethrough in accordance with the duty cycle of said on-off modulated signal.

Claim 3

An expansion flow control valve for a closed vapor cycle refrigeration system for being operated by an applied control signal, characterized in that: (a) a valve body including, (i) a chamber, an inlet port to the chamber and an outlet port from the chamber, (ii) a valve seat between the inlet port and the outlet port, and (iii) a valve closure operating within said chamber with said valve seat and movable with respect thereto for controlling flow through the inlet port and the outlet port; and (b) a solenoid including, (i) an elongated ferro-magnetic plunger connected for moving said valve closure, (ii) an electromagnetic coil located about said plunger for receiving the control signal, and (iii) a ferro-magnetic housing for said coil, portions of which provide relative magnetic flux to said plunger, (1) a first end of said plunger having a continuous conical surface and said housing having a compatible opposing surface portion thereto, thereby establishing a first magnetic gap therebetween, and (2) a second end of said plunger operating with respect to another portion of said housing in at least some of the movement of said plunger so as to establish magnetic gap therebetween, said plunger movement varying directly with the strength of the magnetic flux established in said first gap and determined by the applied control signal until said plunger movement causes the existence of said second gap, flux therein slowing the plunger movement as the first gap reduces in size and preventing full closure of said first gap.

Claim 4

An expansion flow control valve for a closed vapor cycle refrigeration system for being operated by an applied control signal, characterized in that: (a) a valve body including, (i) a chamber, an inlet port to the chamber and an outlet port from the chamber, (ii) a valve seat between the inlet port and the outlet port, and (iii) a valve closure operating within said chamber with said valve seat and movable with respect thereto for controlling flow through the inlet port and the outlet port; and (b) a solenoid including, (i) an elongated ferro-magnetic plunger connected for moving said valve closure, (ii) an electromagnetic coil located about said plunger for receiving the control signal, and (iii) a ferro-magnetic housing for said coil, portions of which provide relative magnetic flux to said plunger, (1) a first end of said plunger having a continuous conical surface and said housing having a compatible opposing surface portion thereto, thereby establishing a first magnetic gap therebetween, and (2) a second end of said plunger operating with respect to another portion of said housing in at least some of the movement of said plunger so as to establish magnetic gap therebetween, said plunger movement varying directly with the strength of the magnetic flux established in said first gap and determined by the applied control signal until said plunger movement causes the existence of said second gap, flux therein slowing the plunger movement as the first gap reduces in size and preventing full closure of said first gap.

Claim 5

An expansion flow control valve in accordance with claim 2, characterized in that said valve seat and said valve closure open and shut by shear action.

Claim 6

An expansion flow control valve in accordance with claim 2, characterized in that the control signal is a frequency modulated series of pulses, the average flow rate through said valve being determined by the duty cycle represented by said pulses over a period of time.

Claim 7

An expansion flow control valve in accordance with claim 2, characterized in that the control signal is a pulse modulated series of pulses, the average flow rate through said valve being determined by the duty cycle represented by said pulses over a period of time.

Claim 8

An electrically operated expansion valve for controlling refrigerant flow into the evaporator coil of a I closed vapor cycle refrigeration system, characterized in that: (a) valve closure means having a closure for opening and closing fluid flow from the condensor coil of the refrigeration system to said evaporator coil, and (b) electrical control means for alternately operating said valve closure means fully opened and fully closed over a period of time to maintain the fluid in said evaporator coil substantially in its liquid state and so as not to impart a substantial pressure shockwave into said fluid with each opening and closing of said valve.

Claim 9

An electrically operated expansion valve for controlling refrigerant flow into the evaporator coil of a I closed vapor cycle refrigeration system, characterized in that: (a) valve closure means having a closure for opening and closing fluid flow from the condensor coil of the refrigeration system to said evaporator coil, and (b) electrical control means for alternately operating said valve closure means fully opened and fully closed over a period of time to maintain the fluid in said evaporator coil substantially in its liquid state and so as not to impart a substantial pressure shockwave into said fluid with each opening and closing of said valve.

Claim 10

An electrically operated expansion valve in accordance with claim 6, characterized in that said valve closure means is a shear acting closure mechanism.

Claim 11

An electrically operated expansion valve in accordance with claim 6, characterized in that said valve closure means includes magnetic means for operating said closure in linear fashion through at least a substantial range of closure movement.

Claim 12

A solenoid actuated expansion valve for use in a refrigeration system having in a closed loop connection a compressor having an inlet and an outlet end, a condenser connected to the outlet end of said compressor and responsive to a high pressure gaseous phase recirculating refrigerant for condensing the refrigerant from its gaseous to its liquid phase, an evaporator having an inlet and an outlet end and connected to said condenser and to the inlet end of said compressor, an expansion valve having an inlet and an outlet end and connected between the outlet end of said condenser and the inlet end of said evaporator, said condenser delivering high pressure liquid refrigerant to the inlet end of said expansion valve, said refrigerant expanding as it flows through said expansion valve, said valve including an on-off modulator responsive to the instantaneous superheat of said refrigerant in said evaporator for generating a variable duty cycle on-off modulated solenoid control signal, said solenoid control signal alternately energizing and deenergizing said solenoid for each cycle of said control signal to cycle said valve from a first flow rate position to a second flow rate position thereby to obtain an average flow rate of refrigerant through the valve which results in a desired superheat for the refrigerant.

Claim 13

A solenoid actuated expansion valve for use in a refrigeration system having in a closed loop connection a compressor having an inlet and an outlet end, a condenser connected to the outlet end of said compressor and responsive to a high pressure gaseous phase recirculating refrigerant for condensing the refrigerant from its gaseous to its liquid phase, an evaporator having an inlet and an outlet end and connected to said condenser and to the inlet end of said compressor, an expansion valve having an inlet and an outlet end and connected between the outlet end of said condenser and the inlet end of said evaporator, said condenser delivering high pressure liquid refrigerant to the inlet end of said expansion valve, said refrigerant expanding as it flows through said expansion valve, said valve including an on-off modulator responsive to the instantaneous superheat of said refrigerant in said evaporator for generating a variable duty cycle on-off modulated solenoid control signal, said solenoid control signal alternately energizing and deenergizing said solenoid for each cycle of said control signal to cycle said valve from a first flow rate position to a second flow rate position thereby to obtain an average flow rate of refrigerant through the valve which results in a desired superheat for the refrigerant.

Claim 14

The valve of claim 9 characterized in that said first flow rate position results in a fully open maximum flow rate therethrough, and said second flow rate position results in a fully closed zero flow rate therethrough, said average flow rate being determined by the duty cycle of said solenoid control signal.

Claim 15

The valve of claim 10 characterized in that said valve further includes a closure rate control means controlling the rate of change in flow rate positions of said valve between said first and said second flow rate positions, and vice versa, thereby to minimize any pressure shock waves in said refrigerant on opening or closing of said valve.

Claim 16

The valve of claim 10 characterized in that said valve further includes a closure rate control means for controlling the rate of change in flow rate positions of said valve between said fully open and said fully closed positions, and vice versa, thereby to minimize any pressure shock waves in said liquid refrigerant on opening or closing of said valve.

Claim 17

The valve of claims 11 or 12 further including a low ambient start-up means responsive to the presence of liquid refrigerant at the inlet end of said expansion valve for overriding normal operations of said valve and maintaining said expansion valve open for refrigerant flow therethrough when liquid refrigerant is not present, said low ambient start-up means returning control for normal operations of said valve when liquid refrigerant is present.

Claim 18

The valve of claim 13 characterized in that said low ambient start-up means comprises: (a) a first temperature sensor coupled proximal to the inlet end of said expansion valve, said first sensor generating a voltage representative of the temperature of the liquid refrigerant from said condensor; (b) a second temperature sensor coupled proximal to the outlet end of said expansion valve, said second means generating a voltage representative of the temperature of the expanding liquid refrigerant into the inlet end of said evaporator; (c) a comparator circuit responsive to the voltages from said first and second temperature sensors for generating a low ambient start signal when the temperature differential between said first and second sensors is less than a temperature threshold ; and (d) a clamping means responsive to the low ambient start signal for overriding normal control of said expansion valve and maintaining said expansion valve open for refrigerant flow therethrough until the temperature differential between said first and second sensors is greater than the temperature threshold indicating expansion of liquid refrigerant through said valve.

Claim 19

The valve of claims 11 or 12 further including a flood detector means responsive to the outlet-to-inlet temperature differential across said evaporator coil for throttling down the flow rate through said expansion valve when the temperature differential is less than a temperature threshold, said flood detector means generating a throttling control signal representative of a lower heat load condition on said evaporator coil to said valve as long as the temperature differential is less than said temperature threshold, said valve resuming normal operation from the throttled-down condition when said temperature differential is greater than said temperature threshold.

Claim 20

The valve of claims 11 or 12 further including a low refrigerant detection means responsive to the percent on time of said valve for generating a low refrigerant alarm signal when the percent on time of the valve exceeds a threshhold value for a period of time.

Claim 21

In a refrigeration system having in a closed loop connection a compressor having an inlet and an outlet end, a condensor connected to the outlet end of said compressor and responsive to a high pressure gaseous phase recirculating refrigerant for condensing the refrigerant from its gaseous to its liquid phase, an evaporator having an inlet and an outlet end and connected to said condensor and to the inlet end of said compressor, an expansion valve having an inlet and an outlet end and connected between the outlet end of said condensor and the inlet end of said evaporator, said condensor delivering high pressure liquid refrigerant to the inlet end of said expansion valve, said refrigerant expanding as it flows through said expansion valve, and a controller circuit responsive to the superheat of the refrigerant in said evaporator for controlling the flow of refrigerant through said expansion valve, a low ambient start-up means responsive to the presence of liquid refrigerant at the inlet end of said expansion valve for overriding normal operations of said valve and maintaining said expansion valve open for refrigerant flow therethrough when liquid refrigerant is not present, said low ambient start-up means returning control for normal operations of said valve when liquid refrigerant is present.

Claim 22

In a refrigeration system having in a closed loop connection a compressor having an inlet and an outlet end, a condensor connected to the outlet end of said compressor and responsive to a high pressure gaseous phase recirculating refrigerant for condensing the refrigerant from its gaseous to its liquid phase, an evaporator having an inlet and an outlet end and connected to said condensor and to the inlet end of said compressor, an expansion valve having an inlet and an outlet end and connected between the outlet end of said condensor and the inlet end of said evaporator, said condensor delivering high pressure liquid refrigerant to the inlet end of said expansion valve, said refrigerant expanding as it flows through said expansion valve, and a controller circuit responsive to the superheat of the refrigerant in said evaporator for controlling the flow of refrigerant through said expansion valve, a low ambient start-up means responsive to the presence of liquid refrigerant at the inlet end of said expansion valve for overriding normal operations of said valve and maintaining said expansion valve open for refrigerant flow therethrough when liquid refrigerant is not present, said low ambient start-up means returning control for normal operations of said valve when liquid refrigerant is present.

Claim 23

In a refrigeration system characterized in thatis has in a closed loop connection a compressor having an inlet and an outlet end, a condensor connected to the outlet end of said compressor and responsive to a high pressure gaseous phase recirculating refrigerant for condensing the refrigerant from its gaseous to its liquid phase, an evaporator having an inlet and an outlet end and connected to said condensor and to the inlet end of said compressor, an expansion valve having an inlet and an outlet end and connected between the outlet end of said condensor and the inlet end of said evaporator, said condensor delivering high pressure liquid refrigerant to the inlet end of said expansion valve, said refrigerant expanding as it flows through said expansion valve, and a controller circuit responsive to the superheat of the refrigerant in said evaporator for controlling the flow of refrigerant through said expansion valve, a flood detector means responsive to the outlet-to-inlet temperature differential across said evaporator coil for throttling down the flow rate through said expansion valve when the temperature differential is less than a temperature threshold, said flood detector means generating a throttling control signal representative of a lower heat load condition on said evaporator coil to said controller circuit as long as the temperature differential is less than said temperature threshold, said controller resuming normal operation from the throttled-down condition when said temperature differential is greater than said temperature threshold.

Claim 24

In a refrigeration system characterized in thatis has in a closed loop connection a compressor having an inlet and an outlet end, a condensor connected to the outlet end of said compressor and responsive to a high pressure gaseous phase recirculating refrigerant for condensing the refrigerant from its gaseous to its liquid phase, an evaporator having an inlet and an outlet end and connected to said condensor and to the inlet end of said compressor, an expansion valve having an inlet and an outlet end and connected between the outlet end of said condensor and the inlet end of said evaporator, said condensor delivering high pressure liquid refrigerant to the inlet end of said expansion valve, said refrigerant expanding as it flows through said expansion valve, and a controller circuit responsive to the superheat of the refrigerant in said evaporator for controlling the flow of refrigerant through said expansion valve, a flood detector means responsive to the outlet-to-inlet temperature differential across said evaporator coil for throttling down the flow rate through said expansion valve when the temperature differential is less than a temperature threshold, said flood detector means generating a throttling control signal representative of a lower heat load condition on said evaporator coil to said controller circuit as long as the temperature differential is less than said temperature threshold, said controller resuming normal operation from the throttled-down condition when said temperature differential is greater than said temperature threshold.

Claim 25

The valve of claim 18 characterized in that said flood detector means comprises: (a) a first temperature sensor responsive to the temperature of the refrigerant at the inlet end of said evaporator; (b) a second temperature sensor responsive to the temperature of the refrigerant at the outlet end of said evaporator; and (c) a first comparator means responsive to said first and second temperature sensors for generating a flood condition signal when the temperature differential between said first and second sensors is less than said temperature threshold, said flood condition control signal representing a reduced heat load demand condition on said evaporator and which is applied to said controller means to effect throttling down of the flow of liquid refrigerant through said expansion valve, said comparator means returning normal control of said expansion valve over to said controller means when said temperature differential between said first and second sensors is greater than said temperature threshold.

Claim 26

The valve of claims 18 or 19 further including a second comparator means responsive to the absolute temperature of said liquid refrigerant at said inlet end of said evaporator and to a maximum operating refrigerant temperature signal for outputting to said controller means a maximum operating temperature control signal to throttle down the flow of refrigerant through said expansion valve when the temperature of said liquid refrigerant at the inlet end of said evaporator coil is greater than the maximum operating refrigerant temperature, said comparator means returning normal control of said expansion valve over to said controller means when said evaporator inlet temperature is less than the maximum refrigerant temperature.

Claim 27

In a refrigeration system characterized in that it has in a closed loop connection a compressor having an inlet and an outlet end, a condensor connected to the outlet end of said compressor and responsive to a high pressure gaseous phase recirculating refrigerant for condensing the refrigerant from its gaseous to its liquid phase, an evaporator having an inlet and an outlet end and connected to said condensor and to the inlet end of said compressor, a solenoid actuated expansion valve having an inlet and an outlet end and connected between the outlet end of said condensor and the inlet end of said evaporator, said condensor delivering high pressure liquid refrigerant to the inlet end of said solenoid actuated expansion valve, said refrigerant expanding as it flows through said solenoid actuated expansion valve, and a controller circuit responsive to the superheat of the refrigerant in said evaporator for controlling the flow of refrigerant through said solenoid actuated expansion valve, said controller circuit including an on-off modulator for generating an on-off modulated solenoid control signal whose duty cycle varies as a function of the superheat, a low refrigerant detection means responsive to the duty cycle of the on-off modulated solenoid control signal for generating a low refrigerant alarm signal when the duty cycle of the solenoid control signal exceeds an upper threshhold value for a period of time.

Claim 28

In a refrigeration system characterized in that it has in a closed loop connection a compressor having an inlet and an outlet end, a condensor connected to the outlet end of said compressor and responsive to a high pressure gaseous phase recirculating refrigerant for condensing the refrigerant from its gaseous to its liquid phase, an evaporator having an inlet and an outlet end and connected to said condensor and to the inlet end of said compressor, a solenoid actuated expansion valve having an inlet and an outlet end and connected between the outlet end of said condensor and the inlet end of said evaporator, said condensor delivering high pressure liquid refrigerant to the inlet end of said solenoid actuated expansion valve, said refrigerant expanding as it flows through said solenoid actuated expansion valve, and a controller circuit responsive to the superheat of the refrigerant in said evaporator for controlling the flow of refrigerant through said solenoid actuated expansion valve, said controller circuit including an on-off modulator for generating an on-off modulated solenoid control signal whose duty cycle varies as a function of the superheat, a low refrigerant detection means responsive to the duty cycle of the on-off modulated solenoid control signal for generating a low refrigerant alarm signal when the duty cycle of the solenoid control signal exceeds an upper threshhold value for a period of time.

Claim 29

A solenoid actuated flow control valve characterized in that it has a movable orifice opening element responsive to the solenoid control signal, and a control means for generating a flow rate control signal representative of a desired average orifice opening size, said valve having hysteresis errors represented by positional errors in said orifice opening element in response to the flow rate control signal, said valve including a means responsive to said flow rate control signal for generating the solenoid control signal which represents the flow rate control signal superimposed with an oscillatory hysteresis control signal, said orifice opening element being moved from a first flow rate position to a second flow rate position in response to the oscillatory portion of said solenoid control signal thereby to obtain, free of hysteresis errors, the desired orifice opening size in response to the flow rate control portion of the solenoid control signal.

Claim 30

A solenoid actuated flow control valve characterized in that it has a movable orifice opening element responsive to the solenoid control signal, and a control means for generating a flow rate control signal representative of a desired average orifice opening size, said valve having hysteresis errors represented by positional errors in said orifice opening element in response to the flow rate control signal, said valve including a means responsive to said flow rate control signal for generating the solenoid control signal which represents the flow rate control signal superimposed with an oscillatory hysteresis control signal, said orifice opening element being moved from a first flow rate position to a second flow rate position in response to the oscillatory portion of said solenoid control signal thereby to obtain, free of hysteresis errors, the desired orifice opening size in response to the flow rate control portion of the solenoid control signal.

Claim 31

The flow control valve of claim 22 characterized in that said oscillatory hysteresis control signal is sinusoidal with a frequency within the response range of said solenoid and orifice opening element assembly thereby to produce the desired oscillatory movement about the desired orifice opening size as determined by said flow rate control signal.

Claim 32

The flow control valve of claim 22 characterized in that said valve is used in a fluid flow system, said valve further including a communications means for transmitting coded information to various parts of said system using the fluid as the communication transmission medium, said communications means superimposing a communications signal coded with the information onto said flow rate control signal where the communications signal is within the response range of said orifice opening element, and where the communications signal generates pressure variations in said fluid for transmission therethrough said system including a sensor positioned on said system for detecting said transmitted communications pressure variations.

Claim 33

In a refrigeration system characterized in that it has in a closed loop connection a compressor having an inlet and an outlet end, a condensor connected to the outlet end of said compressor and responsive to a high pressure gaseous phase recirculating refrigerant for condensing the refrigerant from its gaseous to its liquid phase, an evaporator having an inlet and an outlet end and connected to said condensor and to the inlet end of said compressor, an expansion valve having an inlet and an outlet end and connected between the outlet end of said condensor and the inlet end of said evaporator, said condensor delivering high pressure liquid refrigerant to the inlet end of said expansion valve, said refrigerant expanding as it flows through said expansion valve, and a controller circuit responsive to the superheat of the refrigerant in said evaporator for controlling the flow of refrigerant through said expansion valve, said valve including an on-off modulator responsive to the instantaneous superheat of said refrigerant in said evaporator for generating a variable duty cycle on-off modulated solenoid control signal, said solenoid control signal alternately energizing and deenergizing said solenoid for each cycle of said control signal to cycle said valve from a first flow rate position to a second flow rate position thereby to obtain an average flow rate of refrigerant through the valve which results in a desired superheat for the refrigerant, said refrigeration system further including a communications means for transmitting coded information to various parts of said system using the fluid as the communication transmission medium, said communications means superimposing a communications signal coded with the information onto said flow rate control signal where the communications signal is within the response range of said orifice opening element, and where the communications signal generates pressure variations in said fluid for transmission therethrough, said system including a sensor positioned on said system for detecting said transmitted communications pressure variations.

Claim 34

In a refrigeration system characterized in that it has in a closed loop connection a compressor having an inlet and an outlet end, a condensor connected to the outlet end of said compressor and responsive to a high pressure gaseous phase recirculating refrigerant for condensing the refrigerant from its gaseous to its liquid phase, an evaporator having an inlet and an outlet end and connected to said condensor and to the inlet end of said compressor, an expansion valve having an inlet and an outlet end and connected between the outlet end of said condensor and the inlet end of said evaporator, said condensor delivering high pressure liquid refrigerant to the inlet end of said expansion valve, said refrigerant expanding as it flows through said expansion valve, and a controller circuit responsive to the superheat of the refrigerant in said evaporator for controlling the flow of refrigerant through said expansion valve, said valve including an on-off modulator responsive to the instantaneous superheat of said refrigerant in said evaporator for generating a variable duty cycle on-off modulated solenoid control signal, said solenoid control signal alternately energizing and deenergizing said solenoid for each cycle of said control signal to cycle said valve from a first flow rate position to a second flow rate position thereby to obtain an average flow rate of refrigerant through the valve which results in a desired superheat for the refrigerant, said refrigeration system further including a communications means for transmitting coded information to various parts of said system using the fluid as the communication transmission medium, said communications means superimposing a communications signal coded with the information onto said flow rate control signal where the communications signal is within the response range of said orifice opening element, and where the communications signal generates pressure variations in said fluid for transmission therethrough, said system including a sensor positioned on said system for detecting said transmitted communications pressure variations.

Claim 35

A solenoid actuated flow control valve characterized in that it has a movable orifice opening element responsive to a solenoid control signal for obtaining an orifice opening size, said valve having hysteresis errors in the position of said orifice opening element in response to said solenoid control signal, said valve including a means for generating a solenoid control signal having an oscillator component whose frequency is within the response range for movement of said orifice opening element thereby eliminating said positional hysteresis errors in obtaining a desired orifice opening size.

Claim 36

A solenoid actuated flow control valve characterized in that it has a movable orifice opening element responsive to a solenoid control signal for obtaining an orifice opening size, said valve having hysteresis errors in the position of said orifice opening element in response to said solenoid control signal, said valve including a means for generating a solenoid control signal having an oscillator component whose frequency is within the response range for movement of said orifice opening element thereby eliminating said positional hysteresis errors in obtaining a desired orifice opening size.

Claim 37

The valve of claim 26 characterized in that said means for oscillating said element includes a means for generating an on-off modulated control signal whose duty cycle represents a desired average flow rate through the valve, said oscillating means responsive to the on-off control signal moving said orifice opening element alternately from a fully closed position to a fully open position for each cycle of said on-off signal.

Claim 38

The valve of claim 26 characterized in that the amplitude of said oscillatory component of said solenoid control signal is representative of the magnitude of the positional hysteresis error and causes no positional movement of said orifice opening element.

Claim 39

A solenoid actuated expansion valve for use in a refrigeration system having in a closed loop connection a compressor having an inlet and an outlet end, a condenser connected to the outlet end of said compressor and responsive to a high pressure gaseous phase recirculating refrigerant for condensing the refrigerant from its gaseous to its liquid phase, an evaporator having an inlet and an outlet end and connected to said condenser and to the inlet end of said compressor, an expansion valve having an inlet and an outlet end and connected between the oulet end of said condenser and the inlet end of said evaporator, said condenser delivering high pressure liquid refrigerant to the inlet end of said expansion valve, said refrigerant expanding as it flows through said expansion valve, said expansion valve having a movable orifice opening element responsive to a solenoid control signal for obtaining an orifice opening size, said valve having hysteresis errors in the position of said orifice opening element in response to said solenoid control signal, said valve including a means for generating a solenoid control signal having an oscillatory component whose frequency is within the response range for movement of said orifice opening element, thereby eliminating said positional hysteresis errors in obtaining a desired orifice opening size.

Claim 40

A solenoid actuated expansion valve for use in a refrigeration system having in a closed loop connection a compressor having an inlet and an outlet end, a condenser connected to the outlet end of said compressor and responsive to a high pressure gaseous phase recirculating refrigerant for condensing the refrigerant from its gaseous to its liquid phase, an evaporator having an inlet and an outlet end and connected to said condenser and to the inlet end of said compressor, an expansion valve having an inlet and an outlet end and connected between the oulet end of said condenser and the inlet end of said evaporator, said condenser delivering high pressure liquid refrigerant to the inlet end of said expansion valve, said refrigerant expanding as it flows through said expansion valve, said expansion valve having a movable orifice opening element responsive to a solenoid control signal for obtaining an orifice opening size, said valve having hysteresis errors in the position of said orifice opening element in response to said solenoid control signal, said valve including a means for generating a solenoid control signal having an oscillatory component whose frequency is within the response range for movement of said orifice opening element, thereby eliminating said positional hysteresis errors in obtaining a desired orifice opening size.

Claim 41

The valve of claim 26 characterized in that the amplitude of said oscillatory component of said solenoid control signal is representative of the magnitude of the positional hysteresis error and causes no positional movement of said orifice opening element.