Air conditioning system

Abstract

Air conditioning system ( 10 ), in particular an air conditioning system having carbon dioxide as refrigerant, particularly for use in a motor vehicle. The air conditioning system ( 10 ) comprises a compressor ( 12 ), a gas cooler ( 14 ), an expansion valve ( 16 ) and an evaporator ( 18 ) arranged in series and forming a closed circuit for the refrigerant. The compressor ( 12 ) has a compressor capacity control element and the air conditioning system ( 10 ) further comprises a controller ( 42 ) for controlling the compressor capacity control element and the expansion valve ( 16 ) so as to regulate an expansion valve inlet pressure. The controller ( 42 ) regulates the expansion valve inlet pressure by controlling the compressor capacity control element so as to align evaporator air off temperature with a set point; by monitoring expansion valve inlet temperature; by determining a required expansion valve inlet pressure corresponding to the monitored expansion valve inlet temperature by means of a control algorithm; and by adjusting the expansion valve ( 16 ) and the compressor capacity control element together along an iso-capacity curve to the required expansion valve inlet pressure.

1 . Air conditioning system, in particular air conditioning system having carbon dioxide as refrigerant, particularly for use in a motor vehicle, 
 said air conditioning system comprising a compressor, a gas cooler, an expansion valve and an evaporator arranged in series and forming a closed circuit for said refrigerant;    said compressor having a compressor capacity control element and said air conditioning system further comprising a controller for controlling said compressor capacity control element and said expansion valve so as to regulate an expansion valve inlet pressure;    said controller regulating said expansion valve inlet pressure by 
 controlling said compressor capacity control element so as to align evaporator air off temperature with a set point;  
 monitoring expansion valve inlet temperature;  
 determining a required expansion valve inlet pressure corresponding to said monitored expansion valve inlet temperature by means of a control algorithm; and  
 adjusting said expansion valve and said compressor capacity control element together along an iso-capacity curve to said required expansion valve inlet pressure.  
   
   
   
       2 . System according to  claim 1 , wherein said control algorithm comprises one or more control parameters chosen from the list comprising: 
 front end air flow;    gas cooler air inlet temperature;    evaporator air flow;    evaporator air inlet temperature;    evaporator air inlet humidity;    compressor speed; and    set point.    
   
   
       3 . System according to  claim 2 , wherein said control parameters are set, estimated or measured.  
   
   
       4 . System according to  claim 2  or  3 , wherein said front end air flow is estimated as a function of vehicle speed and fan speed.  
   
   
       5 . System according to any of  claims 2  to  4 , wherein said gas cooler air inlet temperature is estimated as a function of vehicle speed and ambient temperature.  
   
   
       6 . System according to any of  claims 2  to  5 , wherein said evaporator air flow is estimated as a function of blower speed, air temperature door setting, air distribution mode and air recirculation mode.  
   
   
       7 . System according to any of  claims 2  to  6 , wherein said evaporator air inlet temperature is estimated as a function of cabin temperature, ambient temperature and air recirculation mode.  
   
   
       8 . System according to any of  claims 1  to  7 , wherein said compressor is a variable stroke compressor and said compressor capacity control element is a compressor control valve.  
   
   
       9 . System according to any of  claims 1  to  7 , wherein said compressor is a variable speed compressor and said compressor capacity control element is a variable speed electric drive.  
   
   
       10 . System according to any of  claims 1  to  9 , wherein an internal heat exchanger is arranged between said gas cooler and said expansion valve.