Patent Publication Number: US-2007119197-A1

Title: Device for storing cold for an evaporator

Description:
The invention relates to a device for controlling the temperature of an air stream, in particular for the air conditioning of the passenger cell of a vehicle, comprising a first closed loop containing an evaporator capable of being traversed by the air stream and in which a first heat exchanging fluid may circulate so as to give up cold to the air stream in the evaporator.  
      In the particular case of air conditioning of a motor vehicle, a refrigerating fluid passes through the evaporator in order to cool the air stream and to produce refrigerated air which is sent into the vehicle passenger cell.  
      In a conventional air conditioning circuit, the refrigerating fluid passes in this order through: a compressor, a condenser, a pressure reducing valve and an evaporator before returning to the compressor. In the evaporator, the refrigerating fluid passes from a liquid phase or liquid/vapour phase to a vapour phase by taking heat from the air stream which is thus cooled. A circuit of this type is conventionally passed through by a refrigerating fluid formed of a fluorocarbon such as that known as R 134 A.  
      Air conditioning circuits are also known which are passed through by a refrigerating fluid operating according to a supercritical cycle, such as CO 2  for example.  
      One disadvantage of the known evaporators is that their capacity to cool the air stream depends on functioning of the compressor. In other words, the air stream is no longer cooled as soon as the compressor is stationary.  
      Now, in most motor vehicles, the compressor is driven via the engine and is therefore put out of operation as soon as the engine is stationary.  
      Within the scope of anti-pollution standards, it is conceived to create motor vehicles which ensure stopping of the internal combustion engine when the vehicle is stationary, then restarting of the engine when necessary, by virtue of a generator-starter motor. Thus when a vehicle of this type is stationary, since the internal combustion engine is stopped, the air conditioning is also stopped. Stopping of the internal combustion engine results in stopping of the compressor, leading to a feeling of discomfort for the passenger(s) of the vehicle.  
      The object of the invention is in particular to overcome these disadvantages by proposing means of storing cold (thus giving up heat) when the engine of the vehicle is running and to give this cold back to the passenger cell when the engine is stationary.  
      The invention aims in particular at a device of the type defined in the introduction and provides that it comprises a second closed loop in which a second heat exchanging fluid may circulate so as to receive cold from the first heat exchanging fluid in the evaporator and pass the same back to the air stream in the evaporator according to the refrigeration power produced by the first loop and the processing needs of the air stream.  
      Optional, additional or alternative features of the invention are given below: 
          The second closed loop contains an electric pump for the circulation of the second heat exchanging fluid.     The second closed loop contains means of storing cold when the refrigeration power produced by the first loop exceeds the processing needs and in order to give back cold when this power is insufficient.        

      An electric valve is interposed between the pump and the storage means in order to promote the conservation of cold therein. 
    
    
      The features and advantages of the invention are explained in more detail in the description below with reference to the attached drawing in which the only FIGURE is a circuit diagram of a device according to the invention for the air conditioning of the passenger cell of a motor vehicle. 
    
    
      The device shown comprises in a conventional manner a refrigerating fluid loop BF in which the fluid passes successively through a compressor BF 1 , a condenser BF 2 , a reservoir or “bottle” BF 3 , a pressure reducing valve BF 4  and an evaporator BF 5  before returning to the compressor. An air stream shown by the arrow F passes through the evaporator BF 5  in order to be cooled before being introduced into the passenger cell of the vehicle.  
      According to the invention, the evaporator BF 5  also forms part of a loop BS which further contains an electric circulation pump BS 1  and a fluid storage reservoir BS 2 . The loop BS contains a heat exchanging fluid which is capable of exchanging heat with the refrigerating fluid and with the air stream F in the evaporator BF 5 .  
      During the initial period of operation of the device, the pump BS 1  is stationary and the fluid does not circulate in the loop BS. Only the small quantity of this fluid contained in the evaporator BF 5  is cooled by the refrigerating fluid, allowing rapid bringing to temperature of the evaporator. As soon as the temperature desired for the evaporator or for the air stream F is reached, the pump BS 1  is set in action, so that the cooled fluid circulates in the loop BS, leading to storage of cold in the reservoir BS 2 . In the case where the engine is stopped, and hence the compressor BF 1  also, circulation of the fluid in the loop BS continues under the action of the pump BS 1 , and this fluid takes over from the refrigerating fluid in order to cool the air stream F by taking cold from the reservoir BS 2 .  
      Advantageously, an electric valve BS 3  interposed between the pump BS 1  and the reservoir BS 2  makes it possible to isolate the same when the pump is stationary, thus promoting the conservation of cold, to be given back later.  
      The total quantity of heat exchanging fluid in the loop BS depends on the heat energy (cold) sought to be transferred to the air stream to be sent to the passenger cell.