Abstract:
An accumulator for the air conditioning system of a motor vehicle. The accumulator includes a housing defining an accumulator chamber for receiving a fluid and permitting the fluid to separate into a gas state portion and a liquid state portion. A conduit, which defines a passageway for carrying fluid along a flowpath, extends through the housing and across the accumulator chamber such as to permit heat transfer between the accumulator chamber and the passageway. When utilized in the air conditioning system, the accumulator is preferably located upstream of the evaporator.

Description:
BACKGROUND  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates generally to an air conditioning system for a motor vehicle. More specifically, the invention relates to an accumulator of such a system having an improved efficiency.  
         [0003]     2. Related Technology  
         [0004]     Currently-used air conditioning systems experience efficiency losses, a generally poor response time, and a potential risk of compressor damage. Generally, efficiency losses occur when a working fluid fails to completely undergo a phase change during one of the various stages of the air conditioning cycle, as will be discussed below in more detail. Response time refers to the delay between the time that an air conditioner operator turns on the system and the time that the system effectively cools the air flowing into the vehicle passenger compartment. The response time may be undesirably lowered by various factors or system configurations, as will also be discussed in more detail below. Also, compressor damage may occur if the working fluid fails to undergo the desired phase changes at the desired times.  
         [0005]     Air conditioning systems known in the art typically include a plurality of components connected to each other in series to circulate a working fluid, such as refrigerant. One such air conditioning system  100 , which is shown in  FIG. 1 , includes a compressor  102 , a condenser  104 , an expansion device  106 , an evaporator  108 , and an accumulator  110 , all connected in series via various conduits.  
         [0006]     During operation of the system  100 , the compressor  102  receives and compresses a refrigerant. Due to the natural uncompressible properties of liquids, the refrigerant received by the compressor  102  is preferably in a substantially gaseous state. In fact, the compressor  102  may be inadvertently damaged or destroyed if a substantial amount of liquid is permitted to enter the compressor  102 . The compressor  102  is typically a pump driven by a belt that is connected to the engine of the motor vehicle. Therefore, the moving components of the compressor  102  often require a form of lubrication during operation. A lubricant, such as oil, is therefore typically mixed with the working fluid to properly lubricate the working components. The refrigerant exits the compressor  102  as a relatively high-pressure gas  114 .  
         [0007]     From the compressor  102 , the high temperature, high pressure gas  114  flows through the first conduit  112  and into the condenser  104 , where it becomes cooled through a heat exchange process with a secondary fluid, such as air flowing across the exterior of the condenser  104 . After being condensed, at least partially, the high pressure liquid refrigerant  118  flows along a second conduit  116  to the expansion device  106 , which regulates the amount of refrigerant that is permitted to flow therethrough. The expansion device  106  lowers the pressure of the refrigerant and allows a liquid/gas mixture of refrigerant  122  to flow into the evaporator  108  via a third conduit  120 .  
         [0008]     In the evaporator  108 , the low pressure, low temperature liquid/gas mixture flows into a plurality of parallel heat transfer tubes (not shown). Ambient air, or air from the passenger compartment to be recirculated, flows across the heat transfer tubes and the relatively cool refrigerant  122  absorbs heat from the relatively warm air and is evaporated. The air is then passed into the passenger compartment of the vehicle. Thus the temperature of the air entering the passenger compartment is controlled by the compressor and/or the expansion valve. However, the liquid/gas mixture of refrigerant  122  may be unevenly distributed among the heat transfer tubes, thereby causing the air to be unevenly cooled and the refrigerant  122  to be unevenly evaporated. Therefore, a liquid/gas mixture of refrigerant  126  will exit the evaporator  108  via the fourth conduit  124 . While the refrigerant  126  is typically mostly in a gaseous state, a relatively small amount of liquid state refrigerant is mixed therein.  
         [0009]     From the evaporator  108 , the refrigerant  126  flows into the accumulator  110  where it is separated into liquid and gas states. More specifically, the accumulator  110  is a reservoir that causes the refrigerant to separate into a gas portion  126   a , located in the top of the accumulator  110 , and a liquid portion  126   b , located in the bottom of the accumulator  110 . A fifth conduit  128 , which leads to the compressor  102 , includes an end  130  located in the top portion of the accumulator  110  such that only the gas portion  126   a  of the refrigerant is able to flow therein. As discussed above, a lubricant is preferably delivered to the compressor  102  from the accumulator  110 . Therefore, the fifth conduit  128  also includes a U-shaped portion  132  extending into the liquid portion  126   b  and having an oil bleed hole (not shown) that draws oil therein from the liquid portion  126   b . Along with the oil, a relatively small amount of the liquid portion  126   b  of refrigerant is drawn through the oil bleed hole. This liquid portion  126   b  is therefore evaporated in the compressor  102 , rather than in the evaporator  108 , reducing the overall efficiency of the air conditioning system  100 .  
         [0010]     After exiting the accumulator  110 , the gas phase refrigerant  134  flows into the compressor  102 , where the above-described cycle begins again.  
         [0011]     When the air conditioning system  100  shown in  FIG. 1  is first turned on, after being off for an extended period of time, the refrigerant is typically primarily contained within the accumulator  110 . Thus, the refrigerant must flow through most of the above-described cycle (from the accumulator  110  to the compressor  102 , to the condenser  104 , and to the expansion device  106 ) before reaching the evaporator  108 . The current design therefore has an undesirable response time between the time that the air conditioning system  100  is turned on and the time that the vehicle passenger compartment becomes cooled.  
         [0012]     It is therefore desirous to provide an accumulator having improved efficiency, an improved response time, and has a reduced risk of compressor damage.  
       SUMMARY  
       [0013]     In overcoming the limitations and drawbacks of the prior art, the present invention provides an improved air conditioning system. The system includes an accumulator defining an accumulator chamber for receiving a fluid and permitting the fluid to separate into a gas state portion and a liquid state portion. A conduit, which defines a passageway for carrying fluid, extends through the housing and across the accumulator chamber such as to permit heat transfer between the accumulator chamber and the fluid in the conduit. To further promote the heat transfer, the conduit may extend in a serpentine path through the accumulator.  
         [0014]     The conduit additionally defines a vapor bleed hole that permits fluid exchange between the conduit and the accumulator chamber. More specifically, the vapor bleed hole is positioned so as to be located in a top portion of the accumulator chamber so that the gas phase portion in the accumulator is permitted to flow through the vapor bleed hole into the conduit.  
         [0015]     With the present air conditioning system, the evaporator is positioned downstream from the accumulator such that refrigerant flows from the accumulator to the evaporator; thereby reducing the response time of the air conditioning system.  
         [0016]     Because the fluid flowing through the conduit is at a pressure that is less than that of the fluid in the accumulator chamber, the fluid in the conduit is superheated by the fluid in the accumulator chamber, thereby further improving the efficiency of the system.  
         [0017]     Further objects, features and advantages of this invention will become readily apparent to persons skilled in the art after a review of the following description, with reference to the drawings and claims that are appended to and form a part of this specification. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]      FIG. 1  is a schematic representation of a prior art air conditioning system;  
         [0019]      FIG. 2  is a schematic representation of an air conditioning system embodying the principles of the present invention; and  
         [0020]      FIG. 3  is an enlarged schematic representation of the accumulator shown in  FIG. 2 . 
     
    
     DETAILED DESCRIPTION  
       [0021]     Referring now to  FIG. 2 , shown therein is an air conditioning system  10  embodying the principles of the present invention and including a compressor  12 , a condenser  14 , an expansion device  16 , an accumulator  18 , and an evaporator  20  connected in series with each other via a plurality of conduits. More specifically, the respective components  12 ,  14 ,  16 ,  18 , and  20  are all fluidly connected in a closed-loop system for circulating a working fluid, typically a refrigerant, such as R-134, but any suitable fluid may be used.  
         [0022]     During operation of the system  10 , the compressor  12  receives and compresses a refrigerant that is in a substantially gaseous state. The compressor  12  indudes a pump (not shown) that is driven by a belt connected to the engine of the motor vehicle. To minimize friction between the moving parts of the compressor  12 , a lubricant, such as oil, is typically mixed with the working fluid. The refrigerant exits the compressor  12  via a first conduit  22  as a relatively high-pressure gas  24 .  
         [0023]     From the compressor  12 , the high temperature, high pressure gas  24  flows into the condenser  14  and is cooled into a high-pressure liquid through a heat exchange process with a secondary fluid. More specifically, in the condenser  14  shown in  FIG. 2 , the refrigerant  24  enters a first header  26 , flows across a plurality of heat exchange tubes  28  that are exposed to the secondary fluid, flows into a second header  30 , and flows out of the condenser  14 . The secondary fluid is typically air that flows across the heat exchange tubes  28  and absorbs heat from the high temperature, high pressure gas  24 . The air, having been heated, is then discharged from the motor vehicle into the ambient air. The refrigerant, having been cooled to a liquid-phase refrigerant  32 , flows along a second conduit  34  to the expansion device  16 .  
         [0024]     The expansion device  16  regulates the amount of refrigerant that is permitted to flow therethrough and substantially lowers the pressure of the refrigerant. The expansion device  16  shown in  FIG. 2  is an orifice tube device having a fixed opening that restricts the fluid flow therethrough. However, any commonly known or suitable expansion device may be used. The refrigerant flows from the expansion device  16  via a third conduit  36  as a low pressure, low temperature liquid/gas mixture  38 .  
         [0025]     The low pressure, low temperature liquid/gas mixture  38  then enters the accumulator  18  via an inlet  40  and separates into a gas phase portion  42  and a liquid phase portion  44  within an accumulator chamber  46  defined by the accumulator housing  47 . More specifically, the accumulator chamber  46  acts as a reservoir for the refrigerant such that the different densities of the respective portions  42 ,  44  cause the refrigerant to separate. Obviously, the liquid phase portion  44  settles in the bottom portion of the accumulator  18  and the gas phase portion  42  rises to the top portion of the accumulator.  
         [0026]     The accumulator chamber  46  also acts as a reservoir for the oil that is used to lubricate the compressor  12 . In the design shown in  FIG. 2 , the oil and the liquid refrigerant are in a single-phase solution where the oil partides are evenly-distributed among the liquid phase portion  44  of the refrigerant. This type of homogeneous mixture is especially beneficial for delivering an even supply of oil to the compressor  12 . However, other suitable configurations for lubricant delivery may be used.  
         [0027]     The liquid phase portion  44  flows through an outlet  48  of the accumulator chamber  46  and into a fourth conduit  50  that leads to the evaporator  20  to undergo heat exchange with a secondary fluid that will subsequently be provided to the passenger compartment of the motor vehicle. More specifically, in the evaporator  120  the liquid phase portion  44  of the refrigerant flows through a first header  56 , into a plurality of heat exchange tubes  58 , through a second header  60 , and into a fifth conduit  54 . While the liquid phase portion  44  of the refrigerant flows through the heat exchange tubes  58 , ambient air flows across the heat transfer tubes and subsequently into the passenger compartment of the motor vehicle. Therefore, the relatively cool refrigerant absorbs heat from the relatively warm ambient air, thereby cooling the air and the passenger compartment if desired.  
         [0028]     Because the refrigerant entering the evaporator  20  is typically a single phase fluid, the refrigerant is evenly distributed among the heat exchange tubes and the air is evenly cooled. Therefore, the undesirable temperature gradients that are described above with respect to evaporators currently used in the art are minimized or eliminated.  
         [0029]     Furthermore, during the initial start-up of the air conditioning system  10 , the refrigerant flows along a relatively short path from the fluid reservoir (the accumulator  18 ) to the heat exchange portion (the evaporator  20 ). Therefore, the air conditioner system  10  shown in  FIG. 2  is able to begin cooling the air entering the passenger compartment relatively quickly during system start-up.  
         [0030]     Due to the natural properties of fluids, the liquid phase portion  44  of the refrigerant is able to absorb heat during evaporation without increasing in temperature. In other words, the heat energy absorbed by the refrigerant causes evaporation rather than a temperature increase. Therefore, an output flow  62  of refrigerant that exits the evaporator  108  does not have a significantly higher temperature than the liquid phase portion  44  that enters the evaporator  20 . More specifically, a pressure drop in the refrigerant as it flows through the evaporator  20  causes the output flow  62  to have a lower temperature than the liquid phase portion  44  that enters the evaporator  20 , despite the heat that the refrigerant absorbs from the air.  
         [0031]     The output flow  62  is mostly in a gas state when flowing away from the evaporator  20 . However, to ensure that the refrigerant is superheated, and to “pre-cool” the refrigerant located in the accumulator chamber  46 , the fifth conduit  54  extends through the accumulator chamber  46 . More specifically, the fifth conduit  54  extends through the housing  47  passing through both the liquid phase portion  44  and the gas phase portion  42 . In the conduit  54 , the output flow  62  is kept separated from the refrigerant within the accumulator chamber  46 , but heat exchange is permitted to occur between the respective fluids  62 ,  44 . To further promote the heat exchange, the fifth conduit  54  includes a serpentine portion  70  that coils through or extends back and forth across the accumulator chamber  46 .  
         [0032]     As mentioned above, the output flow  62  has a lower pressure, and thus any liquid present will have a lower temperature than the liquid phase portion  44  of the refrigerant. Due to its lower pressure, the output flow  62  has a lower saturation temperature than the liquid portion  44  in the accumulator chamber  46 . Therefore, when the temperature of the output flow  62  is raised by heat exchange with the liquid portion  44  in the accumulator chamber  46 , the output flow  62  becomes superheated. Therefore, the refrigerant flowing along the passageway  68  is substantially superheated. Additionally, the liquid phase portion  44  in the accumulator  118  is cooled by the output flow  62  before reaching the evaporator  120  and is therefore able to more-effectively cool the air flowing across the evaporator  20 .  
         [0033]     After the output flow  62  flows through the serpentine portion  70  of the fifth conduit  54 , it flows past the vapor bleed hole  52 . Because the output flow  62  is at a lower pressure than the gas phase portion  42  of the refrigerant located in the accumulator  18 , the output flow  62  is substantially prevented from flowing out of the vapor bleed hole  52 . Likewise, due to the pressure differential, the gas phase portion  42  flows through the vapor bleed hole  52 , which is suitably sized to permit such a flow.  
         [0034]     At this point in the cycle, the refrigerant flowing from the evaporator  20  is united with the refrigerant that entered the fifth conduit  54  via the vapor bleed hole  52  to form a compressor supply flow  72 . Because the refrigerant flowing along the passageway  68  is mixed with the oil, it is not necessary to draw any of the liquid phase portion  44  directly into the fifth conduit  54  as described above with respect to known designs. Furthermore, because the refrigerant flowing into the vapor bleed hole  52  is all or mostly evaporated fluid, the compressor supply flow  72  is all or mostly evaporated fluid; thereby reducing the possibility of damage to the compressor  12 .  
         [0035]     It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to define the spirit and scope of this invention.