Patent Publication Number: US-6341497-B2

Title: Motor reversal switching system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a Division of patent application Ser. No. 09/468,468, filed Dec. 21, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a device for controlling a compressor, and more particularly to an apparatus for controlling a compressor for reversible, dual capacity operation. 
     2. Description of the Related Art 
     Economic advantages are provided in the operation of an air conditioning system if the system is capable of operating efficiently at a lowered volumetric displacement on mild days and at a higher volumetric displacement on hot days. Running the system at a lower capacity reduces the power consumption and increases the life of the system. 
     Typically, multiple compressors or a single dual capacity compressor have been used for this situation. The dual capacity compressor operates two pistons in the forward direction and one piston in the reverse direction. Examples of such a compressor is disclosed in U.S. Pat. No. 4,248,503 and allowed patent application 09/099,013, which are expressly incorporated by reference. A reversible compressor motor is used to run the compressor in the forward or reverse direction. Typically, capacity choice is controlled by a standard mechanical or electronic two stage thermostat. 
     SUMMARY OF THE INVENTION 
     The present invention in one form thereof involves a device for controlling a reversible compressor. The device provides a microprocessor-based control circuit including a pressure switch that differentiates between high and low load conditions and generates a control signal representing such conditions. During high load conditions the motor is controlled to rotate the compressor in the forward direction using dual cylinders and during low load conditions to rotate the compressor in the reverse direction using a single cylinder. The switchover occurs with the compressor at rest and start against equalized pressure, a time delay is introduced to effect this. During the time delay induced off time, a signal is generated to energize a relay to effectuate a switch in the wiring to allow direction reversal. 
     The present invention provides a reversible, dual capacity compressor system. The system comprises a reversible compressor, a pressure sensor coupled to the compressor, and a control assembly electrically coupled to the compressor and the pressure sensor. The reversible compressor operates at a first capacity when the compressor rotates in a first direction and at a second capacity when the compressor rotates in a second direction. The first capacity is greater than the second capacity. The pressure sensor generates a high pressure signal and a low pressure signal, whereby a high pressure signal indicates a high load condition and a low pressure signal indicates a low load condition. The control assembly controls the compressor to rotate in the first direction when receiving the high pressure signal from the pressure sensor and to rotate in the second direction when receiving the low pressure signal from the pressure sensor. 
     An advantage of the present invention is that a single stage thermostat can be used to control life reversible compressor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above mentioned and other features and objects of this invention, and the manner of attaining them, will become more apparent and the invention itself wil be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a block diagram of an air conditioning system with the motor reversal switching system of the present invention; 
     FIGS. 2A and 2B are a schematic diagram thereof; 
     FIG. 3 is a flow chart illustrating the start up routine of the system; and 
     FIG. 4 is a flow chart illustrating the operating routine of the system. 
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates an embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
     DESCRIPTION OF THE PRESENT INVENTION 
     Referring to FIG. 1 there is shown an air conditioning system in accordance with the present invention which includes air conditioning unit  10 , control circuit  20 , AC power source  34 , and thermostat control  36 . Air conditioning unit  10  includes reversible compressor  12 , main contactor  14  for controlling AC power to compressor  12 , reversing relay  16  for controlling direction of rotation of compressor  12 , evaporator fan  18 , and pressure sensor  38  located on suction line  40  or discharge line  42  of compressor  12 . The dotted line connection indicates an alternate connection of the pressure sensor to the compressor. Control circuit board  20  includes DC power supply  22 , oscillator  24 , thermostat rectifier and scaler  26 , microprocessor  28 , contactor control relay  30 , and compressor reversing and fan control relay  32 . 
     Referring now to FIGS. 2A and 2B, DC power supply  22  receives AC power from source  34  through fuse F 1  and converts the AC power to 24 VDC using transformer TX 1  and rectifier bridge  23  comprised of diodes D 5 , D 6 , D 7 , D 8 . The 24 VDC is supplied to relays RY 1 , RY 2 . The 24 VDC is then converted to 5 VDC using RC filter R 3 , C 2  and voltage regulator U 1 . The 5 VDC is supplied to microprocessor  28 . 
     Thermostat rectifier and scaler circuit  26  receives an input of 0 or 28 AC volts from thermostat control  36  and converts that input to a thermostat signal for microprocessor  28  pin  15  using rectifier bridge  27  comprised of diodes D 1 , D 2 , D 3 , D 4  and a scaler comprised of resistors R 1 , R 2  and capacitor C 1 . The thermostat signal is a logic low when the thermostat is on and a logic high when the thermostat is off. 
     Contactor control relay circuit  30  includes diode D 9 , resistor D 9 , capacitors C 7 , C 9 , transistor Q 1 , and relay RY 1 . Circuit  30  is controlled by the output on pin  11  of microprocessor  28 . A logic high on microprocessor  28  pin  11  turns on transistor Q 1  allowing current to flow through the coil of relay RY 1  pulling the connection of COM of NO, which opens main contactor  14 . A logic low on microprocessor  28  pin  11  turns off transistor Q 1  stopping the flow of current through the coil of relay RY 1  and connecting the COM to NC, which the closes main contactor  14 . 
     Compressor reversing and fan control relay circuit  32  includes diode D 10 , resistor R 7 , capacitors C 8 , C 10 , transistor Q 2 , and relay RY 2 . Circuit  32  is controlled by the output on pin  10  of microprocessor  28 . A logic high on microprocessor  28  pin  10  turns on transistor Q 2  allowing current to flow through the coil of relay RY 2  pulling the connection of the pair of COMs to the NOs, which turn evaporator fan  18  to low and switches reversing relay  16  to the position of placing compressor  12  in low capacity or reversed mode. A logic low on microprocessor  28  pin  10  turns off transistor Q 2  stopping the flow of current through the coil of relay RY 2  connecting the pair of COMs to the NCs, which turn evaporator fan  18  to high and switches reversing relay  16  to the position of placing compressor  12  in high capacity or forward mode. 
     Microprocessor  28  controls air conditioning unit  10  inputs from thermostat rectifier and scaler  26  and pressure sensor  38 . Oscillator  24  comprises capacitors C 3 , C 4 , resistor R 4 , and crystal X 1  and supplies a 1 MHz clock to microprocessor  28 . Pressure sensor  38  supplies a pressure sensor signal to pin  14  of microprocessor  28 . A high pressure signal indicates a high load condition and a low pressure signal indicates a low load condition. Microprocessor  28  uses the start up routine in FIG. 3 to initialize air conditioning unit  10  and the operating routine in FIG. 4 to run air conditioning unit  10 . 
     The routines in FIGS. 3 and 4 show the control of the operating mode of the compressor. The compressor is operated in the high capacity mode when the thermostat has been off for more than a predetermined period of time, such as two hours for example, or the compressor last ran for more a predetermined period of time, such asthan twenty minutes and the compressor was last run in a high capacity mode. The two hours of off time represent a sufficient period of time for the temperature in the room to have risen significantly. The twenty minutes of run time represent a substantial amount of time to lower the temperature in the room. The compressor is operated in the low capacity mode when the thermostat has been off for less than two hours and the compressor last ran for less than twenty minutes or the compressor last ran for more than twenty minutes and the last checked pressure state was low or the compressor was last run in low capacity mode. The low capacity mode allows the compressor to operate more economically when the load requirements are low by reducing power consumption and improving the life of the compressor. The evaporator fan is also operated at low speed with the compressor in low capacity mode and at high speed with the compressor in high capacity mode. Different periods of time may be set into the microprocessor, if desired. 
     Referring now to FIG. 3, the start up routine begins by checking the state of the thermostat signal on pin  15  of microprocessor  28 . If the thermostat signal is a logic high, then the start up routine continues to monitor the thermostat signal. If the thermostat signal is a logic low, then the time since last run is calculated. 
     If the time since last run is greater than two hours, then microprocessor  28  pin  10  is set to a logic low placing compressor  12  in high capacity or forward mode and fan  18  to high. After a wait of two seconds, microprocessor  28  pin  11  is set to a logic low closing main contactor  14  and supplying power to compressor  12 . The start up routine then passes control to the operating routine. 
     If the time since last run is less than two hours, then the last run time is calculated. If the last run time is greater than twenty minutes, then the low pressure trigger is checked. If the low pressure signal trigger is a logic low, then microprocessor  28  pin  11  is set to a logic low closing main contactor  14  and supplying power to compressor  12 . The start up routine then passes control to the operating routine. Compressor  12  and fan  18  remain in their last running state. 
     If the low pressure signal trigger is a logic high, then microprocessor  28  pin  11  is set to a logic high operating main contactor  14  and removing power from compressor  12 . After a wait of ten seconds, microprocessor  28  pin  10  is set to a logic high placing compressor  12  in low capacity or reverse mode and fan  18  to low. After a wait of two seconds, microprocessor  28  pin  11  is set to a logic low closing main contactor  14  and supplying power to compressor  12 . The start up routine then passes control to the operating routine. 
     If the last run time is less than twenty minutes, then microprocessor  28  pin  11  is set to a logic high opening main contactor  14  and removing power from compressor  12 . After a wait of ten seconds, microprocessor  28  pin  10  is set to a logic high placing compressor  12  in low capacity or reverse mode and fan  18  to low. After a wait of two seconds, microprocessor  28  pin  11  is set to a logic low closing main contactor  14  and supplying power to compressor  12 . The start up routine then passes control to the operating routine. 
     Referring now to FIG. 4, the operating routine begins by checking the state of the thermostat signal. If the thermostat signal is a logic high, then microprocessor  28  pin  11  is set to a logic high opening main contactor  14  removing power from compressor  12 , and the operating routine returns control to the start up routing. If the thermostat signal is a logic low, then the pressure sensor on pin  14  of microprocessor  28  is checked. 
     If the pressure sensor signal is a logic high indicating high pressure and microprocessor  28  pin  10  is a logic low indicating compressor  12  in high capacity or forward mode, the operating routine returns to its beginning and checks the thermostat signal. 
     If the pressure sensor signal is a logic high indicating high pressure and microprocessor  28  pin  10  is a logic high indicating compressor  12  in low capacity or reverse mode, then microprocessor  28  pin  11  is set to a logic high opening main contactor  14  and removing power from compressor  12 . After a wait of sixty seconds, microprocessor  28  pin  10  is set to a logic low placing compressor  12  in high capacity or forward mode and fan  18  to high. After a wait of ten seconds, microprocessor  28  pin  11  is set to a logic low closing main contactor  14  and supplying power to compressor  12 . The operating routine then returns to its beginning and checks the thermostat signal. 
     If the pressure sensor signal is a logic low indicating low pressure and microprocessor  28  pin  10  is a logic high indicating compressor  12  in low capacity or reverse mode, the operating routine returns to its beginning and checks the thermostat signal. 
     If the pressure sensor signal is a logic low indicating low pressure and microprocessor  28  pin  10  is a logic low indicating compressor  12  in high capacity or forward mode, then the low signal trigger is set to a logic high for placing compressor  12  in low capacity or reverse mode during the next start up. 
     While this invention has been described as having an exemplary design, the present invention may be modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosures as come within known or customary practice in the art to which this invention pertains. For example, the present invention has been described herein with certain time values. Those skilled in the art will recognize, however, that other time values may be used, typically dependent in large part upon the particular application and assign goals, without departing from the scope of the present invention.