Lubricant return schemes for use in refrigerant cycle

Abstract

A control algorithm is developed which takes corrective action in the event that system conditions indicate there may be an inadequate flow of lubricant in the system. In particular, if a discharge pressure is below a predetermined amount or if the suction modulation valve is throttled, there is a possibility of inadequate lubricant flow. The system control then turns off the condenser fan, and if that first step is not sufficient, may also turn on an evaporator heater and then control a suction modulation valve. A fail safe control loop also takes effect if the condition sensor appears to have failed.

1 . A method of monitoring operation of a refrigerant cycle comprising the steps of: 
 (a) monitoring for a condition indicative of an inadequate flow of lubricant; and    (b) taking preventative actions should said monitoring of step (a) indicate that an inadequate flow of lubricant exists, said preventative action providing lubricant flow.    
   
   
       2 . The method as set for in  claim 1 , wherein said monitoring includes the step of monitoring a discharge pressure downstream of a compressor.  
   
   
       3 . The method as set forth in  claim 1 , wherein the preventative steps including turning off a condenser fan associated with a condenser heat exchanger.  
   
   
       4 . The method as set forth in  claim 3 , wherein once the condenser fan has been turned off, the condition continues to be monitored, and the condenser fan is maintained off until the condition has changed to indicate that the refrigerant cycle is moving to a condition where it is less likely that there will be an inadequate flow of lubricant.  
   
   
       5 . (canceled)  
   
   
       6 . The method as set forth in  claim 5 , wherein once the heater has been turned on, the condition continues to be monitored, and the heater maintained on until the condition is changed to indicate that the refrigerant cycle is moving to a condition where it is less likely that there will be an inadequate flow of lubricant.  
   
   
       7 - 10 . (canceled)  
   
   
       11 . The method as set forth in  claim 1 , wherein three or less preventative actions are taken in serial order, with said preventative actions including turning off a condenser fan, turning on a heater associated with an evaporator, and controlling the opening in a suction modulation valve.  
   
   
       12 . (canceled)  
   
   
       13 . The method as set forth in  claim 11 , wherein the control of said suction modulation valve is taken as the first corrective action.  
   
   
       14 . A refrigerant cycle comprising: 
 a compressor delivering a refrigerant to a condenser, said condenser having a fan for blowing air over said condenser, said refrigerant being delivered from said condenser to a downstream expansion device, and said refrigerant being delivered from said expansion device to an evaporator, refrigerant being delivered from said evaporator through a modulating valve back to the compressor; and    a control for controlling said refrigerant cycle, said control monitoring a condition within said refrigerant cycle, and determining whether conditions are indicative of a an inadequate flow of lubricant, said control taking a corrective action to provide lubricant flow if said conditions are indicative of an inadequate flow of lubricant.    
   
   
       15 . The refrigerant cycle as set for in  claim 14 , wherein said monitoring includes the step of monitoring a discharge pressure downstream of the compressor.  
   
   
       16 . The refrigerant cycle as set forth in  claim 15 , wherein the preventative steps including turning off a condenser fan associated with a condenser heat exchanger.  
   
   
       17 . The refrigerant cycle as set forth in  claim 16 , wherein once the condenser fan has been turned off, the condition continues to be monitored, and the condenser fan is maintained off until the condition has changed to indicate that the refrigerant cycle is moving to a condition where it is less likely that there will be an inadequate flow of lubricant.  
   
   
       18 - 26 . (canceled)  
   
   
       27 . The method as set forth in  claim 1 , wherein a compressor associated with the refrigerant cycle continues to be driven while the step (b) occurs.  
   
   
       28 . The refrigerant cycle as set forth in  claim 14 , wherein said compressor continues to be driven while the corrective action is taking place.