US 3803865 A
A refrigeration control system, useful for air conditioning apparatus, including means for reducing the evaporator pressure for some predetermined time period after the compressor is started. After sufficient time has elapsed to allow the temperature in the cooled space to reach a predetermined "normal" level, the evaporator pressure (and temperature) is increased and maintained slightly above the temperature at which evaporator coil freeze-up can occur.
Claims available in
Description (OCR text may contain errors)
United States Patent 1191 Newton REFRIGERATION CONTROL SYSTEM  Inventor: Alwin B. Newton, York, Pa.
 Assignee: Borg-Warner Corporation, Chicago,
 Filed: June 20, 1972  Appl. No.: 264,649
 US. Cl 62/217, 62/225, 62/227,
62/323  Int. Cl. F25b 41/04  Field of Search 62/2l7, 224, 225, 209
 ReferencesCited UNITED STATES PATENTS 2,ll6,80l 5/1938 Shivers 62/217 2,966,044 l2/l960 Mitchell 62/217 CONTROL INVIRTER 14 1 Apr. 16, 1974 2/1971 Spencer 62/217 9/1972 Newton... 62/217 Primary ExaminerMeyer Perlin Attorney, Agent, or Firm-Donald W. Banner [5 7] ABSTRACT time has elapsed to allow the temperature in the cooled space to reach a predetermined normal" level, the evaporator pressure (and temperature) is increased and maintained slightly above the temperature at which evaporator coil freeze-up can occur.
2 Claims, 1 Drawing Figure PATENTED APR 1 6 1974 INVEHTER CONTROL nnnn 1 REFRIGERATION CONTROL SYSTEM BACKGROUND AND SUMMARY OF Tn INVENTION.
In US. Pat. No. 3,260,064 issued to A. B. Newton on July 12, 1966 there is described an air conditioning system including a compressor, a condenser, an expansion device, and an evaporator, all connected in a closed vapor cycle refrigeration circuit. An important feature described and claimed in the aforementioned patent is the use of me'a'ns'for sensing the superheat of gas leaving the evaporator and means varying the capacity of the compressor operated in response to the amount of superheatto maintain the correct balance between the compressor capacity and the refrigeration load. This system also uses a constant pressure expansion device between the condenser and evaporator to maintain the evaporator pressure at apredetermined' value. In some applications, particularly automotive air conditioning systems, where the temperature of the enclosed vehicle space may reach as high as 180F. if the auto is parked with the air conditioning off, it is desirable to operate the evaporator at a lower temperature (and pressure) to maximize the cooling effect during this period. When the temperature inside the vehicle has been reduced to a normal level say about 75fF. and danger of evaporator coil freeze-up is present, the pressure in the evaporator is then increased and maintained at a constant level for continued operation;
In the present system, a valve is interposed in the suction line between the evaporator and the compressor inlet which is operable to control the flow of refrigerant from the evaporator. At the same time, the pressure in this line is usedto control the setting of a constant pressure expansion device feeding refrigerantto the evaporator. The valve in the suction line is set to produce about a 10 lb. pressure drop when the diaphragm chamber is at atmospheric pressure. A .vacuum is then applied to the diaphragm chamber at a controlled rate which has the effect of opening up the valve and raising the pressure in the suction line downstream from the valve. This pressure is usedas a pneumatic control signal to the constant pressure expansion valve to raise the control point at which the evaporator pressure is controlled. i
Various control means may be utilized to vary the capacity of the compressor. In a preferred embodiment,-
the compressoris driven by an electric motor controlled by an inverter which continuously modulates the speed of the motor in accordance with a control signal derived from the superheat temperature.
BRIEF DESCRIPTION OF THE DRAWING The FIGURE isa schematic diagram of a refrigeration system utilizing the principles of'the present invention. i
DETAILED DESCRIPTION OF THE INVENTION As shown in the FIGURE, the refrigeration system of the present invention includes a compressor 10, a condenser 12, an expansion device 14 and an evaporator 16 all connected to provide a closed circuit refrigerawhich cools the air circulated over it by fan 17. The refrigerant then flows through line 24, commonly referred to as the suction gas line, to the suction connection of compressor 10.
An important feature of the present invention resides in valve 26 which is located in the suction gas line 24 and is designed to produce a pressure drop between the evaporator and compressor when the compressor is first started.
Valve 26 comprises a housing 27, an inlet port 28, an outlet port 29, valve plate 30, and a valve member 31. Thestem 32 of valve member 31 is connected to a movable diaphragm 33 which forms one side of a closed chamber 34 at the upper end of the housing. Spring 35 biases the diaphragm 33 downward to a position tending to close the valve and reduce flow of refrigerant to compressor 10. In practice, the valve is designed to produce about a 10 lb. pressure drop when the valve is in its closed position, either by preventing full closing of valve member 31 or by providing a small bypass, such as an orifice (not shown) through the valve plate 30.
.Valve 26 is operated in response'to the pressure (vacuum) in diaphragm chamber 34. A suitable force of vacuum may be provided from the suction manifold 40 of the vehicle engine 42 through pneumatic control line 44. .Upon engine start-up, the induction-will create a high vacuum in the suction manifold which will be transmitted through line 44 to chamber 34. The rate at which the vacuum is applied is controlled by an orifice 46 in the line.'Accordingly, the time period that it. takes for the vacuum chamber 34 to reach its maximum value is determined by the size of the orifice so that any desired time period can be designed into the system. Normally, this would be about five minutes to allow a sufficient amount of time for the interior of the automobile to be cooled down to a comfortable level.
In accordance with the teaching in US. Pat. No. 3,260,064, there is provided a means for varying the capacity of the compressor in response to the amount of superheat present in the suction gas leaving the evaporator. Various means may be utilized such as unloading the compressor and/or using hot gas bypassing but, in the present invention, a more convenient and effective mechanism may taken the form of an inverter 50 controlling the speed of the electric motor 52 driving the compressor. A control'unit 54, such as described in co-pending application Ser. No. 264,686 filed June 20, l972-by Thomas C. Jednacz et al. entitled Inverter Control System filed concurrently with the present application may be used to control inverter 50. Such unit senses the temperature difference across evaporator coil 16 (absolute superheat) and is effective 'to vary compressor motor speed to maintain the superheat at a constant value. In the use of such a system, the compressor capacity is matched to the load at all times to maintain effective use of the evaporator coil and provide the most efiicient manner of operation.
The expansion device, i.e. valve 16 is of a constant pressure type, but may be adjusted within limits to vary the. control point and corresponding evaporator pressure (and temperature). Valve 14 comprises housing 56, an inlet port 57, an outlet port 58, valve plate 59 and valve member 60. In a construction similar to valve 26, valve member 60 has a stem 61 secured to a movable diaphragm 62 forming a chamber 63. The compression on springs 64 and 65 determine the setting of the valve member, while the respective pressures in the diaphragm chamber 63 and chamber 66 (underneath the diaphragm) furnish the control forces operating the valve. The diaphragm chamber 63 is equalized via control line 68 to the suction gas line 24 at a position downstream from valve 26; and chamber 66 is always at about the same pressure as the evaporator.
OPERATION Prior to starting the engine and compressor motor the pressure in chamber 34 of valve 26 is atmospheric and the valve itself is closed, at least to the extent necessary to produce about a lb. pressure drop. The control point of valve 14 is determined by the adjustment of opposed springs 64, 65.
When the engine 42 and compressor motor 52 are started, the pressure in suction gas line 24 will drop rapidly because the closed" valve 26 will partially starve the compressor. This low pressure is transmitted through control (equalizing) line 68 to chamber 63 causing an increased bias tending to close the valve and reduce the pressure (and temperature) of the evaporator. As operation of the engine continues, an increased vacuum is gradually applied through line 44 to chamber 34 of valve 26, such action being determined by the size of orifice 46. As the vacuum in chamber 34 increases, the valve begins to open, reducing the pressure drop and increasing the pressure in suction line 24. This pressure is transmitted to chamber 63 and gradually raises the control point of valve 14, increasing evaporator pressure (and temperature). Once the system has stabilized, with full vacuum in chamber 34, the system will be solely under the control of valve 14 and superheat sensing unit 54. A constant pressure (about 30 lb.) is maintained in the evaporator by valve 14 and a constant superheat is maintained by unit 54 which controls compressor speed (and capacity).
While this invention has been described in connection with a certain specific embodiment thereof, it is to be understood that this is by way of illustration and not by way of limitation; and the scope of the appended claims should be construed as broadly as the prior art will permit.
What is claimed is:
l. A refrigerant control system for an air conditioning system of the type including a compressor (10), a condenser (12), a constant pressure expansion device (14) and an evaporator (16) connected to provide a closed, vapor cycle refrigerant circuit, said control system comprising: valve means (26) in said circuit operatively disposed between said evaporator and said compressor, said valve means being normally at least partially closed to produce a substantial pressure drop between said evaporator and said compressor, valve operating means (44, 46, 33) associated with said valve means for gradually opening said valve means over a predetermined time period, said valve operating means including a vacuum source, a diaphragm actuating said valve means, means interconnecting said vacuum source to said diaphragm, and an orifice in said lastnamed means for applying vacuum to said diaphragm at a controlled rate; means (68) for deriving a control signal as a function of the pressure between said valve means and said compressor; and means (63) for varying the control point of said constant pressure expansion device in response to said control signal.
2. A system as defined in claim 1 including a conduit for transmitting refrigerant pressure downstream of said valve means to said constant pressure expansion device; and an actuator for said expansion device responsive to said downstream refrigerant pressure for varying the evaporator pressure.