GB2068522A

GB2068522A - Temperature-sensitive control system

Info

Publication number: GB2068522A
Application number: GB8040113A
Authority: GB
Original assignee: Borg Warner Corp
Current assignee: Borg Warner Corp
Priority date: 1980-01-14
Filing date: 1980-12-15
Publication date: 1981-08-12
Also published as: FR2473649A1; IT1135006B; JPS56102659A; AU6508880A; IT8119096A0; ZA807992B; DE3047368A1

Abstract

A temperature-sensitive control system for use in an air conditioning apparatus comprising an automatic expansion valve (20) and a control device (28). The automatic expansion valve is connected between the condenser (14) and the evaporator (24) to maintain a relatively constant pressure in the evaporator. The control device includes a compressor crankcase bypass valve (28) which is responsive to the temperature of the refrigerant at the outlet of the evaporator for controlling the capacity of the compressor e.g. of the wobble plate type. The control device further includes a thermal-sensitive bulb (50) mounted on the outlet of the evaporator for sensing the temperature thereof. <IMAGE>

Description

SPECIFICATION Temperature-sensitive control system Field of the Invention This invention relates generally to compressors and more particularly, it relates to a temperaturesensitive control system for use with variable displacement compressors. The invention has particular applications in variable displacement compressors of the wobble plate type used in automotive air conditioning systems and/or refrigeration systems.

Description of the Prior Art In U.S. Patent No. 3,959,983 issued to R. W.

Roberts et al on June 1, 1976, and assigned to the same assignee as this invention, there is disclosed a controlled, variable displacement, wobble plate compressor which includes a capacity control system having a main control valve. The control valve comprises a valve member for controlling the flow of gas from the crankcase of the compressor to the suction gas line. The valve member is controlled in response to the pressure sensed in the suction line by means of a diaphragm which is biased in the opposite direction with a spring.

In the present invention, there is provided a temperature-sensitive control system which includes an automatic expansion valve and a compressor crankcase bypass valve for controlling the capacity of the compressor at partial loads so as to reduce losses.

Accordingly, it is a general object of the present invention to provide an improved capacity control system for use with variable displacement compressors.

It is an object of the present invention to provide a temperature-sensitive control system for use in air conditioning apparatus which includes an automatic expansion valve and a compressor crankcase bypass valve for controlling the capacity of the compressor at partial loads.

It is another object of the present invention to provide a temperature-sensitive control system which includes a compressor crankcase bypass valve having a housing and a diaphragm disposed within the housing so as to be responsive to the temperature of the refrigerant at the outlet of the evaporator.

It is still another object of the present invention to provide a temperature-sensitive control system which includes a compressor crankcase bypass valve and a thermal-sensitive bulb mounted on the outlet of the evaporator for sensing the temperature thereof to control the operation of the valve.

In accordance with these aims and objectives, there is provided in accordance with the instant invention a temperature-sensitive control system for use in an air conditioning apparatus of the type including a variable displacement compressor, a condenser, an evaporator, and conduit means for connecfing the compressor, condenser and evaporator to form a closed system for refrigerant fluid flow. The temperature-sensitive control system includes an automatic expansion valve and a control device. The automatic expansion valve is connected between the condenser and the evaporator to maintain a relative constant pressure in the evaporator. The control device consisting of a compressor crankcase bypass valve responds to the temperature of the refrigerant at the outlet of the evaporator for controlling the capacity of the compressor.

These and other objects and advantages of the present invention will become more fully apparent from the detailed description when read in conjunction with the accompanying drawing in which there is shown a schematic diagram of the temperature-sensitive control system constructed in accordance with the present invention.

Referring now with particuiarity to the single sheet of drawing, there is shown a temperaturesensitive control system for a variable displacement compressor in a refrigeration system designated generally by reference number 10. The refrigeration system 10 includes a variable displacement compressor 12, preferably of the wobble plate type, which compresses the refrigerant vapor and delivers it to a condenser 14 via line 1 6. The refrigerant is condensed to a liquid form in the condenser and is passed through line 18 to an automatic expansion valve 20. After the refrigerant passes the expansion valve, it flows via a line 22 to an evaporator 24 which cools the air or other fluid which is passed over the surfaces of the evaporator. The refrigerant then is returned through a suction line 26 to the inlet side of the compressor 12.

The automatic expansion valve 20 is of a pressure-responsive type for maintaining a relative constant pressure in the evaporator 24. The constant pressure regulating valve 20 can be of any conventional type similar to that illustrated and described in U.S. Patent No. 3,688,516 issued to A. B. Newton on September 5, 1972.

This type of valve senses a drop in pressure to open for permitting more refrigerant to flow and will close upon an increase in pressure. This valve is also provided with means for adjusting the control point to permit various pressure settings for the evaporator.

The temperature-sensitive control system embodying the present invention includes a compressor crankcase bypass valve 28 having a housing 30 and a pressure-responsive means such as an actuating diaphragm 32 arranged within the housing 30 to form separate chambers 34 and 36.

A tapered-shape valve member 38 is connected to one end of a valve stem 40 which is fixedly attached at its opposite end to the diaphragm 32.

a coil spring 42 is disposed in a chamber 44 against a top portion of the valve member 38 and expands to exert a force for urging the valve member downwardly. The valve member 38 is positioned above an orifice or opening 46 formed by internal flange surfaces 48. The orifice 46 can be progressively opened by upward movement of the valve member 38 away from the flange surfaces 48.

For sensing the suction line refrigeration temperature, temperature-responsive means such as a thermal-sensitive, refrigerant-filled bulb 50 is mounted on the outlet of the evaporator 24 which responds to evaporator-outlet refrigerant temperature. The bulb 50 is in fluid communication with the chamber 34 of the housing 30 via a capillary tube 52. The chamber 36 is in fluid communication with the crankcase pressure of the compressor via passage 54. The chamber 44 is in fluid communication with the suction line inlet 26 of the compressor 12 via passage 56.It can be thus seen that the vertical movement of the stem 40 and the valve member 38 controls the amount of blow-by gas from the crankcase of the compressor to the suction inlet 26 which raises or lowers the crankcase pressure in response to the evaporator-refrigerant temperature, thereby resulting in an increase or decrease in the piston stroke and the compressor displacement. For detailed discussion of the operation of the wobble plate mechanism due to variations in the crankcase pressure, reference is made to U.S. Patent No. 3,861,829 issued to R. W. Roberts and R. D. Salie on January 21, 1 975, which is entitled "Variable Capacity Wobble Plate Compressor".

When the compressor 12 is being operated at a relatively low capacity, the valve member 38 closes the orifice 46 since the combination of the suction pressure in the passage 56 and the expansion force of the spring 42 is much greater than the pressure on the underneath side of the diaphragm 34 caused by the refrigerant gas in the bulb 50. As a consequence of the closed position of the valve member 38, there is an increased pressure in the crankcase of the compressor 12 causing a corresponding minimum piston stroke and thus minimum displacement of the compressor. As the refrigerant load is increased, there is an increase in the evaporator-outlet refrigerant temperature which expands the refrigerant gas in the bulb 50 to create higher pressures on the underneath side of the diaphragm 34.This will cause the position of the valve stem 40 to move upwardly, thereby to progressively open the orifice 46. In turn, the crankcase pressure will be reduced allowing the compressor displacement to increase and to lower the suction pressure in the passage 56. In response to the drop in suction pressure, the automatic expansion valve will open so as to supply more refrigerant to the increasing load.

As the demands of the refrigerant load are achieved, the temperature of the evaporator-outlet refrigerant will decrease so as to cause progressively the closing of the orifice 46 so as to increase the pressure in the crankcase and thus reducing the stroke of the compressor 1 2. In addition, the automatic expansion valve 20 will close due to the increase in the suction pressure, thereby reducing the refrigerant flow.

From the foregoing detailed discussion, it can be thus seen that the present invention provides a new and improved temperature-sensitive control system which includes an automatic expansion valve and a compressor crankcase bypass valve for controlling the capacity of the cdmpressor at partial loads so as to reduce losses. Further, the temperature-senstive control system includes a thermal-sensitive bulb mounted on the outlet of the evaporator for sensing the temperature thereof.

While there has been illustrated and described what is at present to be a preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made and equivalents may be substituted for elements thereof without departing from the true scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the inventions without departing from the central scope thereof. Therefore, it is intended that this invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

1. In an air conditioning apparatus of the type including a variable displacement compressor, a condenser, an evaporator, and conduit means for connecting the compressor, condenser and evaporator to form a closed system for refrigerant fluid flow, the improvement comprising temperature-sensitive control system which includes: an automatic expansion valve connected between said condenser and said evaporator to maintain a relatively constant pressure in the said evaporator; and control means responsive to the temperature of the refrigerant at the outlet of the evaporator for controlling the capacity of said compressor.

2. In an air conditioning apparatus as claimed in Claim 1, wherein said control means includes a compressor crankcase bypass valve having a housing and pressure-responsive means disposed, within said housing.

3. In an air conditioning apparatus as claimed in Claim 1, wherein said control means includes as temperature-sensitive bulb mounted on the outlet of said evaporator for sensing the temperature thereof.

4. In an air conditioning apparatus as claimed in Claim 2, wherein said pressure-responsive means comprises a diaphragm.

5. In an air conditioning apparatus as claimed in Claim 2, wherein said bypass valve further includes an orifice which is progressively opened so as to reduce the crankcase pressure in said compressor and thus increasing the compressor displacement.

6. Air conditioning apparatus constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.