Air-Conditioning Assembly

Abstract

The invention relates to a motor vehicle air-conditioning assembly provided with a supercritical fluid refrigerant circuit and comprising a pressure relief member ( 12 ) defining a cross-section of fluid flow. The assembly comprises an electronic control device ( 401 ) for interacting with the fluid refrigerant circuit. The electronic control device includes a computing function using an estimation of the cross-section of flow of the pressure relief member, the density coefficient of the fluid refrigerant, and the pressure of the fluid refrigerant at the inlet of the pressure relief member for calculating an estimation of the mass flow rate of the fluid refrigerant in the pressure relief member ( 12 ).

1 . A motor vehicle air conditioning unit, provided with a supercritical refrigerant circuit ( 10 ) comprising a compressor ( 14 ), a gas cooler ( 11 ), an expander ( 12 ), defining a refrigerant flow area, and an evaporator ( 13 ), the assembly further including an electronic control device designed to interact with the refrigerant circuit, 
 characterized in that the electronic control device includes a calculating function using an estimate of the flow area of the expander, the density (ρ) of the refrigerant and the pressure (P 20 ) of the refrigerant at the inlet of the expander in order to calculate an estimate of the refrigerant mass flow rate (m exp ) at the expander.    
   
   
       2 . The air conditioning unit as claimed in  claim 1 , characterized in that the flow area of the expander is estimated from the value of the refrigerant pressure (P 20 ) at the inlet of the expander.  
   
   
       3 . The air conditioning unit as claimed in  claim 2 , characterized in that the electronic control device is capable of reacting to the fact that the value of the refrigerant pressure P 20  at the inlet of the expander is: 
 less than or equal to a first pressure value P 1 , a first constant S 1  being assigned to the flow area S of the expander;    less than or equal to a second pressure value P 2  greater than the first pressure value P 1 , by solving the following equation in order to calculate an estimate of the flow area S of the expander:        S=S 1+( S 2 −S 1)×( P   20   −P 1)/( P 2 −P 1),    where S 2  is a second constant;    less than or equal to a third pressure value P 3     less than or equal to a third pressure value P 3  and greater than the second pressure value P 2 , solving the following equation in order to calculate an estimate of the flow area S of the expander:        S=S 2+( S 3 −S 2)×( P   20   −P 2)/( P 3 −P 2),    where S 3  is a third constant; and    greater than or equal to the third pressure value P 3 , a fourth constant S 4  being assigned to the flow area of the expander.    
   
   
       4 . The air conditioning unit as claimed in  claim 3 , characterized in that the first pressure value P 1  is approximately equal to 80 bar, the second pressure value P 2  is approximately equal to 110 bar and the third pressure value P 3  is approximately equal to 135 bar and in that the first constant S 1  is approximately equal to 0.07 mm 2 , the second constant S 2  is approximately equal to 0.5 mm 2 , the third constant S 3  is approximately equal to 0.78 mm 2  and the fourth constant S 4  is approximately equal to 3.14 mm 2 .  
   
   
       5 . The air conditioning unit as claimed in one of the preceding claims, characterized in that the calculating function is specific to calculating the density (ρ) of the refrigerant from the refrigerant temperature (T 30 ) at the inlet of the expander and from the refrigerant pressure (P 20 ) at the inlet of the expander.  
   
   
       6 . The air conditioning unit as claimed in  claim 5 , characterized in that it includes a probe ( 30 ) placed at the inlet of the expander ( 12 ) for measuring the refrigerant temperature (T 30 ) at the inlet of the expander.  
   
   
       7 . The air conditioning unit as claimed in one of the preceding claims, characterized in that it includes a sensor ( 20 ) placed at the inlet of the expander ( 12 ) for measuring the refrigerant pressure (P 20 ) at the inlet of the expander.  
   
   
       8 . The air conditioning unit as claimed in one of the preceding claims, characterized in that the electronic control device further includes a power estimation function capable of estimating the power absorbed by the compressor from: 
 the refrigerant mass flow rate (m exp ) provided by the calculating function;    the work (ΔHise) of the compressor; and    the rotation speed (N) of the compressor.    
   
   
       9 . The air conditioning unit as claimed in  claim 8 , characterized in that the electronic control device is capable of estimating the work (ΔHise) of the compressor from the refrigerant pressure (P 20 ) at the inlet of the expander, from the refrigerant pressure (P 35 ) at the inlet of the compressor and from a refrigerant temperature (T comp ) relative to the compressor.  
   
   
       10 . The air conditioning unit as claimed in  claim 9 , characterized in that the refrigerant pressure (P 35 ) at the inlet of the compressor is estimated from a pressure (P 50 ) at the inlet or at the outlet of the evaporator ( 13 ) combined with the refrigerant mass flow rate (m exp ).  
   
   
       11 . The air conditioning unit as claimed in  claim 10 , characterized in that the pressure (P 50 ) at the inlet or at the outlet of the evaporator ( 13 ) is determined from the refrigerant temperature (T 50 ) at the inlet or at the outlet of the evaporator ( 13 ), said temperature being either measured by a probe or estimated from: 
 a temperature (T 40 ) relative to the evaporator ( 13 );    the efficiency (η evap ) of the evaporator ( 13 ); and    the temperature (T 60 ) of the air to be cooled.    
   
   
       12 . The air conditioning unit as claimed in one of  claims 9  to  11 , characterized in that the refrigerant temperature relative to the compressor ( 10 ) is the refrigerant temperature (T 35 ) at the inlet of the compressor.  
   
   
       13 . The air conditioning unit as claimed in  claim 12 , characterized in that it includes a probe ( 35 ) placed at the inlet of the compressor ( 14 ) for measuring the refrigerant temperature (T 35 ) at the inlet of the compressor.  
   
   
       14 . The air conditioning unit as claimed in one of  claims 9  to  11 , characterized in that the refrigerant temperature relative to the compressor ( 14 ) is the refrigerant temperature (T 36 ) at the outlet of the compressor.  
   
   
       15 . The air conditioning unit as claimed in  claim 14 , characterized in that it includes a probe ( 36 ) placed at the outlet of the compressor ( 14 ) for measuring the refrigerant temperature (T 36 ) at the outlet of the compressor.