Patent Publication Number: US-6655159-B1

Title: Accumulator dehydrator assembly

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The subject invention relates to an accumulator dehydrator assembly for use in a refrigeration cycle of an air conditioning system of a vehicle. 
     2. Description of the Related Art 
     Various accumulator dehydrator assemblies for use in air conditioning systems of vehicles are known in the art. These assemblies have an inner housing for separating a liquid component from a vapor component of a refrigerant and an outer shell surrounding the inner housing. The outer shell is disposed around and spaced from the outer shell to define a chamber therebetween. The chamber provides an insulating layer to insulate the inner housing. 
     One such assembly, shown in U.S. Pat. No. 5,479,790, discloses an accumulator dehydrator assembly having an inner housing and an outer shell. The inner housing and the outer shell define a chamber therebetween. The outer shell is secured in place by a cap that engages inlets extending into the inner housing. However, the &#39;790 patent does not disclose spacers between the inner housing and the outer shell to secure the outer shell onto the inner housing and to establish the chamber defining a predetermined distance between the inner housing and the outer shell. 
     Another such assembly, shown in U.S. Pat. No. 6,041,618, discloses a cylindrical sleeve mounted around an inner housing. The cylindrical sleeve has a corrugated surface for contacting the inner housing to define air pockets between the corrugations. The cylindrical sleeve is open at both ends and has a mounting bracket for engaging an engine compartment of the vehicle to secure the outer shell about the inner housing. Yet another assembly, shown in U.S. Pat. No. 6,378,327, discloses an accumulator insulator bracket having an inner housing and an outer shell. The outer shell is formed from two halves that are connected together to secure the inner housing within the outer shell. The outer shell has air flow directing ribs for directing the flow of air along the length of the inner housing. However, neither the &#39;618 nor the &#39;327 patent disclose spacers positioned between the inner housing and the outer shell being compressible for securing the outer shell onto the inner housing and establishing the chamber having a predetermined distance. 
     Accordingly, it would be advantageous to provide an outer shell that mounts to the accumulator dehydrator inner housing without connecting to the vehicle and that improves the efficiency of the air conditioning system. It would also be advantageous to provide the spacer to establish a predetermined distance between the inner housing and the outer shell to insulate the inner housing. 
     BRIEF SUMMARY OF THE INVENTION AND ADVANTAGES 
     The subject invention provides an accumulator dehydrator assembly for use in a refrigeration cycle of an air conditioning system of a vehicle. The assembly includes an inner housing for separating a liquid component from a vapor component of a refrigerant and an integral outer shell being cup shaped and having a bottom and side walls extending upwardly from the bottom to an upper edge defining an opening. The inner housing is disposed within and spaced from the outer shell to define a chamber therebetween. The assembly includes at least one spacer positioned between the inner housing and the outer shell and positioned annularly around the side walls and being compressed for holding the outer shell onto the inner housing. 
     The subject invention further provides a method of improving an efficiency of the air conditioning system of the vehicle. The system includes the accumulator dehydrator assembly having the inner housing for separating the liquid component from the vapor component of the refrigerant and the outer shell spaced from one another by the spacer and defining the chamber having the predetermined distance therebetween. The method includes the steps of disposing the inner housing within the outer shell, positioning the spacer between the inner housing and the outer shell, and establishing the chamber between the inner housing and the outer shell. The method includes compressing the spacers between the inner housing and the outer shell to hold the outer shell onto the inner housing. 
     The subject invention provides an accumulator dehydrator assembly having the outer shell that mounts to the inner housing without connecting to the vehicle and improves the efficiency of the air conditioning system. The subject invention also provides the spacer being compressible and positioned between the inner housing and the outer shell for holding the outer shell onto the inner housing and establishing the chamber having the predetermined distance between the inner housing and the outer shell to improve the efficiency of the air conditioning system. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEW OF THE DRAWINGS 
     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: 
     FIG. 1 is a side view of accumulator dehydrator assembly according to the subject invention having spacers integrally formed; 
     FIG. 2 is a cross-sectional view of FIG. 1; 
     FIG. 3 is an exploded view of Line  3  in FIG. 2 showing the spacer integrally formed; 
     FIG. 4 is a perspective view of another embodiment of a spacer being positioned on an inner housing with an outer shell being compressibly engaging the spacer to connect to the inner housing; 
     FIG. 5 is a perspective view of yet another embodiment of the spacer of FIG. 4 having a first plurality of raised portions; 
     FIG. 6 is a perspective view of still another embodiment of the spacer of FIG. 4 having a second plurality of raised portions; 
     FIG. 7 is a perspective view of the spacer having both the first and second plurality of raised portions aligned with one another; 
     FIG. 8 is a perspective view of the spacer having both the first and second plurality of raised portions offset from one another; 
     FIG. 9 is a perspective view of the spacer having a first and a second plurality of recessed portions; 
     FIG. 10 is a perspective view of the tabs of FIG. 11; 
     FIG. 11 is a side view of the spacer being formed as a tab within the outer shell; 
     FIG. 12 is a side view of the spacer being formed as a spacer clip engaging the outer shell; 
     FIG. 13 is a perspective view of the spacer clip of FIG. 12; 
     FIG. 14 is a side view of the spacer being integrally formed with the outer shell as a bump; 
     FIG. 15 is a perspective view of the bump of FIG. 14; 
     FIG. 16 is a side view of the inner housing and the outer shell representing the direction of heat flow and a predetermined distance insulated in the inner housing for calculating the predetermined distance. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the Figures, wherein like numerals indicate like or corresponding parts throughout the several views, an accumulator dehydrator assembly for use in a refrigeration cycle of an air conditioning system (not shown) of a vehicle (not shown) is illustrated generally at  20  in FIG.  1 . The air conditioning system typically cycles a refrigerant from a compressor (not shown) to a heat exchanger (not shown) to a pressure relief valve (not shown) to an evaporator (not shown) and back to the compressor. 
     The refrigerant is compressed by the compressor and leaves as a superheated vapor. The superheated vapor enters the heat exchanger and heat is transferred from the refrigerant inside the heat exchanger to air outside the heat exchanger. This causes the refrigerant to condense to a liquid form. The liquid refrigerant next goes through an expansion device and experiences a significant drop in pressure and temperature. The liquid refrigerant then goes through the evaporator and the air outside the evaporator loses energy to the refrigerant inside the evaporator. The refrigerant gains enough energy to be vaporized and then enters the accumulator dehydrator assembly  20  of the subject invention. The accumulator dehydrator assembly  20  separates any remaining liquid refrigerant from the vapor refrigerant. The vapor refrigerant is then supplied to the compressor. 
     Referring to FIGS. 1 and 2, the accumulator dehydrator assembly  20  includes an inner housing  22  for separating the liquid component from the vapor component of the refrigerant. The inner housing  22  is known to those skilled in the art as an accumulator dehydrator (A/D). The A/D is positioned downstream from the evaporator and upstream from the compressor. The refrigerant that is discharged from the evaporator may have the liquid component that should be removed from the vapor component. The refrigerant enters the A/D and the liquid component is separated from the vapor component as is known in the art. The vapor discharge from the A/D is then supplied to the compressor. The inner housing  22  has connectors  24  as is known in the art for receiving and discharging the refrigerant from the inner housing  22 . 
     The assembly  20  further includes an integral outer shell  26  being cup shaped and having a bottom  28  and side walls  30  extending upwardly from the bottom  28  to an upper edge  32  defining an opening. The opening is large enough to receive the inner housing  22  within the outer shell  26 . It is preferable that the outer shell  26  is formed in a single, continuous piece of material such that the side walls  30  and bottom  28  are continuous. The outer shell  26  may be shaped to fit various inner housings  22 . For example, the side walls  30  may be tapered or straight depending upon the shape of the inner housing  22 . The outer shell  26  may be formed of any type of metal or plastic, but is preferably aluminum. The outer shell  26  defines an aperture  34  for allowing the connectors  24  to pass therethrough to engage the inner housing  22 . 
     The inner housing  22  is disposed within and spaced from the outer shell  26  and defines a chamber  36 , or annulus, therebetween as shown in FIG.  2 . The chamber  36 , or annulus, is bounded by the inner housing  22  and the outer shell  26 . Within the chamber  36 , a fluid is housed between the inner housing  22  and the outer shell  26  such that convection of the fluid is limited. Preferably, the fluid is air, however, it is to be appreciated that other fluids would provide advantageous results when incorporated into the subject invention. 
     The assembly  20  includes at least one spacer  38  positioned between the inner housing  22  and the outer shell  26  and positioned annularly around the side walls  30  and being compressed for holding the outer shell  26  onto the inner housing  22 . The spacers  38  define a predetermined distance  40  between the inner housing  22  and the outer shell  26  to establish the chamber  36 , as shown in FIG.  3 . The predetermined distance  40  is selected from a range of about 0.05 inches to about 0.50 inches, preferably from about 0.10 inches to about 0.35 inches, and most preferably from about 0.15 inches to about 0.30 inches. Additionally, a positioning spacer  31  engages the bottom  28  to ensure that the outer shell  26  has been positioned about the inner housing  22  an appropriate amount, as will be described in more detail below. The positioning spacer  31  may be the same material as the spacer  38 . 
     In one embodiment, the predetermined distance  40  is further defined as a function of a mean hot temperature of the fluid outside the outer shell  26  and a mean cold temperature of the fluid inside the inner housing  22 . The predetermined distance  40  is then calculated according to the following equation:        b   ≤       18.2        [         T   r          μ   2           ρ   2          g        (       T   a     -     T   r       )           ]         1   /   3                       
     where, b is the predetermined distance  40  in ft, 
     ρ is a density of the fluid in the chamber  36  in lb m /ft 3 , 
     g is acceleration due to gravity, which is 32.174 ft/s 2 , 
     μ is a dynamic viscosity of the fluid in lb m /fts, 
     T a  is the mean temperature of the fluid on the hot side in ° F., and 
     T r  is the mean temperature of the fluid on the cold side in ° F. 
     In one embodiment, the spacer  38  is further defined as a belt  42 , as shown in FIGS. 3 and 4. Preferably, the belt  42  is formed of a compressible material that includes, but is not limited to, rubbers, plastics, metals, and mixtures thereof. The belt  42  extends continuously around the inner housing  22 . Referring to FIG. 4, the belt  42  may be a separate ring being elastic such that the belt  42  is stretched and positioned around the inner housing  22 . Then, the outer shell  26  is forced onto the inner housing  22  thereby compressing the belt  42  between the inner housing  22  and the outer shell  26 . 
     Referring back to FIG. 3, the belt  42  may be integrally formed with the outer housing and formed of the same material as the outer shell  26 . Accordingly, when the outer shell  26  is forced onto the inner housing  22 , the integral belt  42  compresses and mechanically connects the outer shell  26  to the inner housing  22 . The belt  42  seals the chamber  36  and divides the chamber  36  into at least a first section  44  and a second section  46 . The belt  42  limits the flow of the fluid between the first section  44  and the second section  46  to limit the convection properties of the fluid, as will be described more below. 
     Referring to FIG. 5, the belt  42  may also include a first plurality of raised portions  48  disposed in spaced and parallel relationship around the belt  42  for engaging one of the inner housing  22  and the outer shell  26 . As shown in FIG. 6, the belt  42  may also include a second plurality of raised portions  50  disposed in spaced and parallel relationship around the belt  42  for engaging the other of the inner housing  22  and the outer shell  26 . The first plurality of raised portions  48  and the second plurality of raised portions  50  may be radially aligned to extend in opposite directions as shown in FIG.  7 . Additionally, referring to FIG. 8, the first plurality of raised portions  48  and the second plurality of raised portions  50  may be radially offset from one another about the inner housing  22  and the outer shell  26  to form the mechanical connection. Also, the raised portions allow limited movement of the fluid between the first section  44  and the second section  46 . 
     Alternately, referring to FIG. 9, the belt  42  may include a first plurality recessed portions disposed in spaced and parallel relationship around the belt  42  for allowing fluid to flow therebetween. A second plurality of recessed portions  54  are disposed in spaced and parallel relationship around the belt  42  and facing in an opposite direction from the first recessed portions for allowing fluid to flow therebetween. Similar to the raised portions, the first plurality of recessed portions  52  and the second plurality of recessed portions  54  may be radially offset from one another whereby the first recessed portions and the second recessed portions alternate around the inner housing  22  and the outer shell  26 . The recessed portions allow the fluid to flow between the first section  44  and the second section  46  without allowing additional fluid from outside the outer shell  26  to enter the chamber  36 . 
     With reference to FIGS. 10 and 11, the spacer  38  may also be defined as a tab  56  integrally formed in the side walls  30  and extending therefrom for engaging the inner housing  22 . The tab  56  is formed of the same material as the outer shell  26  and is preferably aluminum. The tab  56  is formed in a punch-type process whereby the side wall  30  of the outer shell  26  is bent inwardly toward the inner housing  22 . The tab  56  is then bent upwardly toward the opening or downwardly toward the bottom  28  to form a generally “L” shaped tab  56 . The tab  56  engages in the inner housing  22  and is compressed to mechanically connect the outer shell  26  to the inner housing  22 . 
     The spacer  38  may further be defined as a spacer clip  58  engaging the upper edge  32  of the outer shell  26 , as shown in FIGS. 12 and 13. The spacer clip  58  is compressed between the inner housing  22  and the outer shell  26 . The spacer clip  58  may be formed of a metal, a plastic, or the like. The spacer clip  58  includes a U-shaped portion  60  for engaging the upper edge  32  and a raised dimple  62  being compressed between the inner housing  22  and the outer shell  26 . An arm  64  extends from the U-shaped portion  60  between the inner housing  22  and the outer shell  26 . The raised dimple  62  extends from the arm  64  for engaging one of the inner housing  22  and the outer shell  26 . Additionally, the spacer clip  58  may be formed with a tab similar to that shown in FIG. 11 in place of the raised dimple  62 . The spacer clips  58  are positioned around the edge of the outer shell  26  and then the outer shell  26  is forced onto the inner housing  22 . The raised dimple  62  or tab compresses and mechanically connects the outer shell  26  to the inner housing  22 . 
     Referring to FIGS. 14 and 15, the spacer  38  may also be further defined as bumps  66  integrally formed in the side walls  30  and engaging the inner housing  22 . The bumps  66  may be oval or circular and are compressible. The bumps  66  are preferably integrally formed within the outer shell  26 , but may be formed separately and mounted to either one of the inner housing  22  and the outer shell  26 . It is preferable that the bumps  66  are formed in the outer shell  26  for engaging the inner housing  22  to ease installation of the outer shell  26 . When the outer shell  26  is forced onto the inner shell, the bumps  66  are compressed to mechanically connect the outer shell  26  to the inner housing  22 . 
     The subject invention may further include a cap  68  engaging the outer shell  26  and enclosing the inner housing  22  within the outer shell  26  and the cap  68 . The cap  68  has cap clips  70  extending from the cap  68  for engaging the outer shell  26  and securing the cap  68  to the outer shell  26 . The cap clips  70  may be integrally formed with the cap  68  or secured to the cap  68  separately. Additionally, the cap  68  may include the spacers  38  for establishing the chamber  36  as described above to establish the predetermined distance  40  between the inner housing  22  and the cap  68 . The cap  68  may have dimples in place of the cap clips  70  such that the dimples engage the outer shell  26  for securing the cap thereto. 
     The subject invention further provides a method of improving an efficiency of the air conditioning system of the vehicle. The method includes the steps of disposing the inner housing  22  within the outer shell  26 , positioning the spacer  38  between the inner housing  22  and the outer shell  26 , and establishing the chamber  36  between the inner housing  22  and the outer shell  26 . 
     The method includes compressing the spacers  38  between the inner housing  22  and the outer shell  26  to hold the outer shell  26  onto the inner housing  22 . Compressing the spacer  38  establishes and maintains the predetermined distance  40  between the inner housing  22  and the outer shell  26 . The outer shell  26  is pressed over the inner housing  22  and the force compresses the spacers  38 . The outer shell  26  is pressed until the positioning spacer  31  contacts the inner housing  22 . Once the positioning spacer  31  contacts the inner housing  22 , the outer shell  26  is properly positioned. 
     In order to establish the predetermined distance  40 , a circumambient temperature outside of the outer shell  26 , i.e., in an engine compartment of the vehicle, is measured and an accumulator, or refrigerant, temperature inside of the inner housing  22  is measured. An average temperature of the circumambient temperature and the accumulator temperature is calculated so that a dynamic viscosity for the fluid and a density of the fluid can be calculated at the average temperature. A coefficient of thermal expansion for the fluid is also calculated. These values are then used to calculate the predetermined distance  40  between the inner housing  22  and the outer shell  26  that results in a decreased amount of work being performed by the system. Next, the outer shell  26  is positioned the predetermined distance  40  from the inner housing  22  to decrease the amount of work. 
     The subject invention provides the predetermined distance  40  between the inner housing  22  and the outer shell  26  to serve as an insulation layer. Since the thermal conductivity of air is very low, it can serve as an excellent insulator provided that the free-convection currents are suppressed within the chamber  36 . The predetermined distance  40  around the inner housing  22  is representable by a parallel plate channel enclosed around its edges to form a box, as shown in FIG.  16 . On one side of the chamber  36 , the temperature T r  is the temperature of the refrigerant and on the other side of the chamber  36  the temperature T a  is the temperature of the circumambient air in the engine compartment. It may be noted that in the engine compartment of the vehicle T a &gt; T r  so that the heat transfer takes place from the circumambient air to the refrigerant across the predetermined distance  40  as indicated by the direction of the heat flux q n  in FIG.  16 . 
     The insulative properties of the chamber  36  around the inner housing  22  lowers the refrigerant temperature in the inner housing  22 . The lower refrigerant temperature in the inner housing  22  results in a lower refrigerant temperature at the compressor suction ports. The efficiency of the air conditioning system is improved because less isentropic work of compression, W, is required. The work of compression is directly proportional to a suction temperature T suc  of the refrigerant and is shown in equation (1) as:              W   =         RT   suc       (     n   -   1     )            [         (       P   dis       P   suc       )       n   -     1   /   n         -   1     ]               (   1   )                         
     where P suc  is the suction pressure of the refrigerant supplied to the compressor, P dis  is the discharge pressure of the refrigerant exiting the compressor, R is the gas constant and n is the polytropic index of the refrigerant. n is further defined in equation (2) as              n   =     1   +       1     1   +       Jc   p   0          (     T   suc     )                (     2     2   -     Z   c   2         )                 (   2   )                         
     where c p   o (T suc ) is the zero-pressure isobaric specific heat of the refrigerant calculated at the suction temperature, T suc , Z c  is the critical compressibility of the refrigerant and J is the mechanical-to-thermal energy conversion factor. Thus, from equation (1), the presence of the fluid in the chamber  36  around the inner housing  22  lowers the work of compression due to the refrigerant having the lower suction temperature, T suc . This results in higher energy efficiency of the air conditioning system and provides a relatively inexpensive way of insulating the refrigerant in the inner housing  22  from the circumambient air temperatures in the engine compartment of the vehicle. However, the predetermined distance  40  must be optimized to provide the maximum improved efficiency of the air conditioning system. 
     The predetermined distance  40  has a desired distance that will provide the maximum improved efficiency of the air conditioning system due to the insulative value of the chamber  36 . For the illustrative system shown in FIG. 16, an overall heat transfer coefficient U in the chamber  36  is expressible as                1   U     =       1     h   r       +     b     k   a       +     1     h   a                 (   3   )                         
     where h r  is the free convection heat transfer coefficient in the chamber  36  on the refrigerant side in Btu/sft 2 ° F., h a  is the free convection heat transfer coefficient in the chamber  36  on the circumambient air side in Btu/sft 2 ° F., k a  is the thermal conductivity of the fluid in Btu/sft° F., and b is the predetermined distance  40  in ft. 
     In equation (3), 1/h r  represents convective resistance on the refrigerant side, b/k a  represents the conductive resistance of the chamber  36  having the predetermined distance  40 , and 1/h a  represents the convective resistance on the air side. When the free convection in the chamber  36  is suppressed due to the spacers  38  secures the outer shell  26  onto the inner housing  22 , then 1/h r =1/h a =0 and the heat flow is by pure conduction alone. For pure conduction, equation (3) yields U=k a /b. 
     The process of free convection of heat transfer in the chamber  36  shows that U=k a /b for              Gr   ≡         ρ   2        g                   β        (       T   a     -     T   r       )            b   3         μ   2       ≤   6000           (   4   )                         
     where Gr is the dimensionless group called the Grashof number representing the ratio of buoyant force to viscous force, ρ is the density of the fluid in lb m /ft 3 , g is the acceleration due to gravity, which is 32.174 ft/s 2 , β is the coefficient of thermal expansion for the fluid defined below in 1/° F., μ is the dynamic viscosity of the fluid in lb m /fts, b is the predetermined distance  40  in ft, T a  is the fluid mean temperature on the hot side in ° F., and T r  is the fluid mean temperature on the cold side in ° F. 
     The coefficient of thermal expansion β for the fluid at any temperature T is defined as              β   =         ρ   r     -   ρ       ρ        (     T   -     T   r       )                 (   5   )                         
     where ρ is the fluid density at temperature T and ρ r  is the fluid density at temperature T r . 
     For an ideal gas, ρ=P/RT where P is the pressure and R is the gas constant. Introducing this into equation (5), β is expressible as              β   =             ρ   r     /   ρ     -   1       T   -     T   r         =             T   r     /   T     -   1       T   -     T   r         =     1     T   r                   (   6   )                         
     Introducing equation (6) into equation (5), the suppression of the free convection is expressible as:                    ρ   2          g        (       T   a     -     T   r       )            b   3           T   r          μ   2         ≤   6000           (   7   )                         
     Solving for b,              b   ≤       18.2        [         T   r          μ   2           ρ   2          g        (       T   a     -     T   r       )           ]         1   /   3               (   8   )                         
     Equation (8) gives the desired distance for the predetermined distance  40  as a function of the properties of the fluid within the chamber  36  and the mean temperatures of the two fluids on the opposite sides of the chamber  36 . Shown below in Table 1 are the results for the predetermined distance  40 , under an idle condition and a traveling condition, or a down-the-road condition. The idle condition is defined as the vehicle engine is operating and the vehicle is stationary. The traveling condition is defined as the vehicle engine is operating and the vehicle is traveling at a 50 miles per hour down the road. The results are presented below in tabular form. The results show that in one embodiment under idle conditions, b≦0.161 inches and under down-the-road conditions, b≦0.150. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Predetermined distance 40 around the inner housing 22 under idle and 
               
               
                 down-the-road conditions 
               
            
           
           
               
               
               
            
               
                   
                 Idle 
                 Down-the-road 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                   
                 T a , ° F. 
                 200 
                 150 
               
               
                   
                 T r , ° F. 
                 73 
                 40 
               
               
                   
                 {overscore (T)} = (T a  + T r )/2, ° F. 
                 136.5 
                 120.95 
               
               
                   
                 μ ({overscore (T)}), lb m /fts 
                 1.3416 × 10 −5   
                 1.2762 × 10 −5   
               
               
                   
                 ρ ({overscore (T)}), lb m /ft 3   
                 0.0670 
                 0.0717 
               
               
                   
                 b, in., Eq. (8) 
                 ≦0.161 
                 ≦0.150 
               
               
                   
                   
               
            
           
         
       
     
     From these results, the efficiency of the air conditioning system is improved when the predetermined distance  40  is selected from a range of about 0.05 inches to about 0.50 inches, preferably from about 0.10 inches to about 0.35 inches, and most preferably from about 0.15 inches to about 0.30 inches. The spacers  38  are constructed to provide the predetermined distance  40  between the inner housing  22  and outer shell  26 . As a result, the outer shell  26  is repositioned to obtain the most improved efficiency of the air conditioning system. 
     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.