Abstract:
In order to reduce refrigerant leakage from an automotive air conditioning system, the leakage paths are kept sealed by automatically reducing the output of a variable displacement compressor ( 12 ) after initial operation of the engine for a predetermined number of five minutes, and then only for a predetermined number of ten seconds, that is, so long as there has been an air conditioning on signal by the operator. After the reduction in output for ten seconds, the output of the compressor ( 12 ) is returned to full output for a predetermined number of two air-conditioning minutes, which is then followed by another ten seconds of reduced output.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit of provisional application Ser. No. 60/520,743 filed Nov. 17, 2003. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The subject invention relates to an air conditioning system for a vehicle, frequently referred to as a heating, ventilating and air conditioning (HVAC) system.  
         [0004]     2. Description of the Prior Art  
         [0005]     Such systems typically include a compressor for compressing a refrigerant, a condenser for condensing the refrigerant, an evaporator for evaporating the refrigerant, a discharge fluid line interconnecting the compressor and the condenser, a liquid fluid line interconnecting the evaporator and the condenser, and a suction fluid line interconnecting the evaporator and the compressor. Also, such systems utilize various valve arrangements for controlling flow through the system during operation and during shutdown and/or in response to a leak of refrigerant in the system. In addition, an accumulator/dehydrator is frequently disposed in the suction line for accumulating refrigerant.  
         [0006]     As is known and supported by test data, refrigerant oil reduces refrigerant emissions from components in the compressor. More specifically, polymers and rubber components, such as lip seals and O-rings, exhibit significant reduction in refrigerant permeation and leakage when these components are coated with a film of oil. Such has been recognized in U.S. Pat. No. 3,738,118 to Jacobs.  
         [0007]     In a pressure vessel that contains microscopic leak paths, refrigerant under pressure eventually displaces oil molecules in these leak paths. The pressure vessel develops a leak rate that is substantially higher than the leak rate when such leak paths are blocked with oil.  
         [0008]     Consequently, the absence of refrigerant oil may also result in high rates of refrigerant emission. The phenomenon of “oil migration” can result in the complete absence of oil in the compressor. Should oil migration, which is dependent on thermal cycling, be permitted to continue for several thermal cycles, the compressor may be completely flushed of oil and emit refrigerant at a rate higher than when the compressor components are coated with oil.  
         [0009]     During initial startup of variable compressors, very little oil returns to the rotating lip seal. This is due to the fact that very little suction gas (with oil) enters the crankcase where the rotating seal is located. Therefore, oil return does not occur until the compressor destrokes or cycles allowing the suction gas with oil to flow through the crankcase onto the rotating seal.  
       SUMMARY OF THE INVENTION AND ADVANTAGES  
       [0010]     The subject invention provides an air conditioning system and method of engaging same that is of the type including a compressor for compressing a refrigerant, a condenser for condensing the refrigerant, an evaporator for evaporating the refrigerant, a discharge fluid line interconnecting the compressor and the condenser, a liquid fluid line interconnecting the condenser and the evaporator, and a suction fluid line interconnecting the evaporator and the compressor. The invention includes a controller for performing the steps of sequencing the compressor in response to the engine being in initial operation for a predetermined number of engine minutes and in response to an air conditioning on signal to reduce the output of the compressor for a predetermined number of seconds and to increase the output of the compressor for a predetermined number of air-conditioning minutes.  
         [0011]     Accordingly, the limiting of refrigerant emissions is enhanced with a variable compressor air conditioning system in one of two ways. The first option would to be to destroke the compressor allowing the oil and suction gas to flow through the crankcase and onto the rotating seal. The second methodology would be to cycle the compressor off for a short period of time to allow the refrigerant to surge into the crankcase coating the seal with oil and refrigerant. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:  
         [0013]      FIG. 1  is a schematic view of an air conditioning system employing the subject invention;  
         [0014]      FIG. 2  is a schematic view of a compressor for implementing the subject invention;  
         [0015]      FIG. 3  is a bar graph of refrigerant leakage over time  
         [0016]      FIG. 4  is a chart of the operation of an pneumatically controlled variable displacement compressor operated in accordance with the subject invention; and  
         [0017]      FIG. 5  is a chart of the operation of an electronically controlled variable displacement compressor operated in accordance with the subject invention; 
     
    
     DESCRIPTION OF THE INVENTION  
       [0018]     As alluded to above, the subject invention relates to an air conditioning system for a vehicle that comprises a compressor  12  for compressing a refrigerant, a condenser  14  for condensing the refrigerant, and an evaporator  16  for evaporating the refrigerant. Of course, a discharge fluid line  18  interconnects the compressor  12  and the condenser  14 , while a liquid fluid line  20  interconnects the condenser  14  and the evaporator  16 , and a suction fluid line  22  interconnects the evaporator  16  and the compressor  12  (it being appreciated that  FIG. 1  is not proportional as it is schematic).  
         [0019]     As is well known in the art, an accumulator/dehydrator (A/D)  24  is disposed in the suction fluid line  22  for accumulating refrigerant.  
         [0020]     In addition, various valves  26 ,  28  and  32  are included for controlling the flow of refrigerant through the system. A thermal expansion device  30  is also disposed in the liquid fluid line  20  between the condenser  14  and the evaporator  16 . The expansion device is normally an orifice tube but generally could be replaced by any expansion device such as a capillary tube, TXV, etc. Of course, with the TXV, the A/D would be replaced by a receiver/dryer (R/D) that would be in the fluid line  20  between the condenser  14  and the expansion device  30 .  
         [0021]     This may be accomplished in an electronic variable stroke, i.e., variable displacement, compressor  12  as illustrated in  FIG. 3 . An example of a compressor that could be used to implement the subject invention is described in U.S. Pat. No. 6,247,900 granted Jun. 19, 2001 to Archibald et al. Such a compressor  12  is well known in the art and includes an electric motor  34  for rotating a swash plate  36  to various angles to vary the stroke of a plurality of pistons  38 . Various valves  40  control the flow into and out of the chambers surrounding the pistons  38  via the suction  22  and discharge  18  fluid lines, i.e., by varying the displacement. An electronic control valve  42  controls the angular position of the swash plate  36  to establish the length of stroke of the pistons  38  and, therefore, the displacement. The compressor may be controlled by pneumatic controller instead of an electronic controller.  
         [0022]     The system includes a controller  44  for disengaging the compressor  12  in response to an engine being in initial operation and air conditioning on signal and for a predetermined length of time. In other words, the controller  44  sequences the compressor  12  in response to the engine being in initial operation for a predetermined number of engine minutes and in response to an air conditioning on signal to reduce the output of the compressor  12  for a predetermined number of seconds and to increase the output of the compressor  12  for a predetermined number of air-conditioning minutes.  
         [0023]     The controller  44  includes a timer  46  for establishing the predetermined number of engine and air-conditioning minutes as five and the predetermined number of seconds as ten for air conditioning off or reduced output and the predetermined number of air-conditioning minutes as two and for providing a second predetermined number of seconds as ten following the two minutes of air-conditioning. This illustrated in  FIGS. 4 and 5 . In the embodiment of  FIG. 4 , the controller  44  is pneumatic and the output of the compressor  12  is reduced to zero whereas the embodiment of  FIG. 5  illustrates an electronic controller  44  and engages the compressor  12  at a fifty percent duty cycle during the predetermined number of seconds of reduced output. The compressor  12  varies its displacement by being a variable stoke compressor  12  and the controller  44  is electronic and engages the compressor  12  at fifty percent of full stoke during the predetermined number of seconds of reduced output. In case of the electronically-controlled duty cycle, the shape of the curve in  FIG. 5  can be changed to be a smoother curve than the square one shown such that the duty cycle is varied gradually. In both cases illustrated in  FIGS. 4 and 5 , the controller  44  operates by disengaging the compressor or reducing output  12  for a second predetermined number of ten seconds at the end of the predetermined number of two air-conditioning minutes.  
         [0024]     Accordingly, when the vehicle operator turns the ignition on and starts the engine, and engages the air conditioning system, the timer  46  sets the predetermined number of five engine and air conditioning minutes, and so long as the operator initiates, or causes to be initiated, an air conditioning turn on signal during the five minutes, the controller  44  will operate turn off of reduce output to the compressor  12  for the predetermined number of ten seconds or destroke the compressor. The timer  46  will set another period of ten seconds at the end of the predetermined number of two air-conditioning minutes, after which the compressor will be continuously operated so long as the air conditioner is turned on.  
         [0025]     Accordingly, the invention provides a method of disengaging such an air conditioning system including the step of sequencing the compressor  12  in response to the engine being in initial operation for a predetermined number of engine minutes and in response to an air conditioning on signal to reduce the output of the compressor  12  for a predetermined number of seconds and to increase the output of the compressor  12  for a predetermined number of air-conditioning minutes. The methodology establishes the predetermined number of engine and air conditioning minutes as five, and the predetermined number of seconds as ten and the predetermined number of air-conditioning minutes as two and establishing a second predetermined number of seconds as ten following the two minutes of air-conditioning minutes.  
         [0026]     The method is further defined as electronically engaging the compressor  12  at a fifty percent duty cycle during the predetermined number of seconds of reduced output. More specifically, since the compressor  12  is a variable stoke compressor  12 , the method is further defined as electronically engaging the compressor  12  at fifty percent of full stoke during the predetermined number of seconds of reduced output. Finally, the method is further defined as establishing a second predetermined number of ten seconds of reduced output of the compressor  12  at the end of the predetermined number of air-conditioning minutes.  
         [0027]     The only other induced a/c system operation different from subject operation is referenced in U.S. Pat. No. 3,738,118 granted Jun. 12, 1973 to Jacobs et al. Such a system utilized turning the air conditioning system on every engine start cycle. This is almost the reverse of the subject invention. In those situations, the system is turned on, where this invention turns off the variable compressor to allow the oil to return to the rotating lip seal section.  
         [0028]     In the normal operation of variable displacement compressors, oil is required to return to the compressor lip seal region in one of two ways. The first would to be to destroke the compressor allowing the oil and suction gas to flow through the crankcase and onto the rotating seal. The second would be to cycle the compressor off for a short period of time to allow the refrigerant to surge into the crankcase coating the seal with oil and refrigerant as illustrated. The effects of destroking the variable stroke compressor can be shown in the graph of  FIG. 3 . The compressor emission is near zero after the compressor destrokes and allows oil to return to the lip seal. The near zero emission continues even after the compressor returns to full stroke. Variable displacement compressors (induced a/c operation); 
        1) Confirm engine has been on of 5 minutes and confirm that a/c request was present in the preceding 5 minutes.     2) Disengage a/c compressor for 10 seconds. Rengage for 2 minutes. Disengage a/c compressor for 10 seconds again. Rengage. For electronically controlled compressors, set constant duty cycle of 50 percent during the 2.10 second runs. Note that for the case of the electronically-controlled duty cycle, the shape of the curve can be changed to be a smoother curve than the one shown so that the duty cycle is varied gradually.        
 
         [0031]     Obviously, many modifications and variations of the present invention are possible in light of the above teachings. The invention may be practiced otherwise than as specifically described within the scope of the appended claims.  
                                         ELEMENT LIST            Element Symbol   Element Name               12   compressor       14   condenser       16   evaporator       18   discharge fluid line       20   liquid fluid line       22   suction fluid line       24   accumulator/dehydrator       26   check valve       28   first solenoid-operated valve       30   second solenoid-operated valve       32   thermal expansion device