Oil return algorithm for capacity modulated compressor

Abstract

A control for a compressor motor is programmed to operate the motor at at least one low capacity and at least one higher capacity. The control is operable to estimate an amount of oil which will have migrated from said compressor shell, at least when the compressor is operating at the lower capacity rate. The motor control moves the compressor motor from the lower capacity to at least one higher capacity once the estimated quantity of oil exceeds a predetermined limit. The capacity may be related to space.

1 . A compressor comprising:
 a compressor pump unit, and said compressor pump unit and said motor being housed within a shell, said shell having a sump for maintaining a quantity of lubricant;   a control for said compressor, said control being programmed to operate at at least one low capacity and at least one higher capacity, and said control also being operable to estimate an amount of oil which will have migrated from said compressor shell at least when said compressor is operating at said at least one lower capacity, and said motor control being operable to move said compressor motor from the at least one lower capacity to the at least one higher capacity once the estimated quantity of oil exceeds a predetermined limit.   
   
   
       2 . The compressor as set forth in  claim 1 , wherein said at least one lower capacity and said at least one higher capacity are achieved by varying the speed of the motor. 
   
   
       3 . The compressor as set forth in  claim 1 , wherein said estimate of the amount of oil is based upon pressures in the system. 
   
   
       4 . The compressor as set forth in  claim 3 , wherein the amount of oil estimate is based upon the pressures at both a condenser and an evaporator that are connected to said compressor. 
   
   
       5 . The compressor as set forth in  claim 3 , wherein the amount of oil estimate is based upon the estimated saturated temperature at both a condenser and an evaporator that are connected to said compressor 
   
   
       6 . The compressor as set forth in  claim 1 , wherein said estimate of the amount of oil is based upon temperature measurements. 
   
   
       7 . The compressor as set forth in  claim 1 , wherein a multiplier factor which includes a Capacity ratio quantity multiplied by an oil loss rate calculated from the pressures or estimate of saturated temperatures at said condenser and said evaporator. 
   
   
       8 . A refrigerant system comprising:
 a condenser, an evaporator, an expansion device and a compressor;   the compressor having a motor for driving a compressor pump unit, and said compressor pump unit and motor being housed within a shell, said shell having a sump for maintaining a quantity of lubricant, a control for said motor, said control being programmed to operate at at least one low capacity and at least one higher capacity, and said control also being operable to estimate an amount of oil which will have migrated from said compressor shell at least when said compressor is operating at said at least one lower capacity, and said motor control being operable to move said compressor motor from the at least one lower capacity to the at least one higher capacity once the estimated quantity of oil exceeds a predetermined limit.   
   
   
       9 . The refrigerant system as set forth in  claim 8 , wherein said estimate of the amount of oil lost is based upon pressures in the system. 
   
   
       10 . The refrigerant system as set forth in  claim 8 , wherein the amount of oil estimate is based upon the pressures at both the condenser and the evaporator. 
   
   
       11 . The refrigerant system as set forth in  claim 8 , wherein a multiplier factor which includes an RPM quantity is multiplied by an oil loss rate calculated from the pressures at said condenser and said evaporator. 
   
   
       12 . The refrigerant system as set forth in  claim 8 , wherein said at least one lower capacity and said at least one higher capacity are achieved by varying the speed of the motor. 
   
   
       13 . A method of operating a compressor comprising the steps of:
 (a) operating a motor for a compressor at at least one low capacity and at least one higher capacity;   (b) estimating an amount of oil which will have migrated from a compressor shell at least when said compressor is operating at said at least one lower capacity rate; and   (c) moving said motor from the at least one lower capacity to the at least one higher capacity once the estimated quantity of oil exceeds a predetermined limit.   
   
   
       14 . The method as set forth in  claim 13 , wherein said estimate of the amount of oil lost is based upon pressures in the system. 
   
   
       15 . The method as set forth in  claim 14 , wherein the amount of oil estimate is based upon the pressures at both a condenser and an evaporator that are connected to said compressor. 
   
   
       16 . The method as set forth in  claim 13 , wherein a multiplier factor which includes an RPM quantity is multiplied by an oil loss rate calculated from the pressures at said condenser and said evaporator. 
   
   
       17 . The method as set forth in  claim 13 , wherein said at least one lower capacity and said at least one higher capacity are achieved by varying the speed of the motor 
   
   
       18 . The method as set forth in  claim 13 , wherein said estimate of the amount of oil is based upon temperature measurements.