Abstract:
The invention relates to an expansion valve, designed especially for an air conditioning system in a motor vehicle, that comprises a valve housing with a first high-pressure side port, a second low-pressure side port, and a channel disposed therebetween through which refrigerant can flow. The valve includes a sliding element that is arranged in the channel and can move along a longitudinal axis, wherein an aperture restricts the flow of refrigerant through the channel, and the size and shape of the aperture is defined by the size and shape of the sliding element and the position of the sliding element in the channel. The expansion valve is easy to manufacture and can be universally used based in part on the sliding element extending completely through the channel.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention generally relates to an expansion valve that may be used in an air conditioning system, including an automobile air conditioning system, and methods of use therefor.  
       BACKGROUND OF THE INVENTION  
       [0002]     Modern air conditioning systems often use a controllable expansion valve to regulate the mass flow rate of an expanding refrigerant. This type of expansion valve typically can be set to two positions, i.e., to a closed or open state, depending on an operating parameter of the air conditioning system. The proper operation of the valve helps to insure that the refrigerant super heats before entering the compressor so that the efficiency of the air conditioning system is maintained within an optimal range. A properly operating expansion valve may reduce the need for a low-pressure collector to protect the compressor from fluid refrigerant entering the compressor.  
         [0003]     EP 1 001 229 A2 (see also U.S. Pat. No. 6,430,950) describes an expansion valve for an air conditioning system of a motor vehicle in which a sliding needle plunges essentially vertically into an expansion channel, which channel separates the high-pressure side from the low-pressure side of the refrigerant cycle. The cross-section of the channel is partially free, because the sliding needle only partially plunges into the channel. When the needle completely penetrates the channel, the valve is closed. The valve is opened at a maximum when the sliding needle does not extend into the channel at all.  
         [0004]     Prior art expansion valves, however, are difficult to manufacture and/or are limited in applicability. In addition, the desirable operating range of prior art expansion valves can be difficult to set.  
       SUMMARY OF THE INVENTION  
       [0005]     The invention provides an improved expansion valve for use in a refrigeration circuit that is easy to manufacture and can be in a wide variety of applications.  
         [0006]     In preferred embodiment of the invention, a sliding element is fully inserted in a channel at any state of the expansion valve, and the mass flow rate through the valve is dependent on the shape of the sliding element. Due to the resulting flow along the shape of the sliding element, the desirable flow characteristics of the refrigerant in the channel aperture are improved, which correspondingly reduces the noise level caused by the valve.  
         [0007]     An advantage of a valve made according to the invention is that the sliding element, which may include a control section, is located properly and accurately in every position. In addition, the shaping of the control section allows accurate set up of the valve aperture in dependence on the position of the sliding element. The sliding element may be shaped as an elongated body with a constant cross-section at one end and an adjacent control section that, compared to the end section, has a tapered cross-section. The sliding element and an associated control section further may be advantageously placed in a slot (or in a zone near the slot) in the channel that permits the passage of refrigerant from an area of relatively higher pressure to an area of relatively lower pressure. The tapering of the control section of the sliding element may be of a constant diameter so that the change of the aperture in dependence on the motion of the sliding element is constant. However, depending on the technical requirements of each system, the tapering may also have a variable cross-section so that the aforementioned dependence is not constant. This design allows for a precise optimization of the function of the expansion valve according to the invention, which can improve the efficiency and the reliability of an air conditioning system. In addition, it is possible, as regards the usability of the expansion valve in air conditioning systems of various types and sizes, to provide a channel and slot for a sliding element of a sufficiently large diameter, and further to adjust or adapt the dimensions of the tapering in the zone of the control section to a particular type of air conditioning system.  
         [0008]     In order to achieve an acceptable seal between the channel and sliding element, the diameter of the sliding element at the end can be larger than the width of flanges that define a sealable opening into the channel. This design enlarges the sealing surface between the channel wall and the sliding element in various states of the sliding element. It also will be appreciated by persons of skill in the art that the diameter of the channel may be larger, smaller or the same size as the diameter of the sliding element or the aperture into which the sliding element is placed.  
         [0009]     Furthermore, the sliding element may be advantageously shifted by means of a control mechanism in the direction of the axis, whereby the valve is made settable. In an especially advantageous design, the control mechanism includes a spring to bias the position of the sliding element. This spring force defines in a simple fashion, a mechanical condition for the opening of the valve. In order to ensure that the construction of the expansion valve is simple and cost-effective, the spring and the control mechanism may be arranged on the same side as the sliding element.  
         [0010]     A control mechanism associated with the valve may further include a pressurized membrane. The membrane, which is mechanically connected to the sliding element, allows for a simple motion of the sliding element in dependence on the operating parameters of the air conditioning system.  
         [0011]     In a preferred embodiment, there is a third low-pressure connection for the refrigerant to the valve housing. A membrane of the control mechanism may be exposed to the pressure or temperature of the refrigerant, and particularly to the pressure or temperature in the suction line before the compressor. This design makes it possible to control, in a simple fashion, the sliding element in dependence on a parameter of the refrigerant&#39;s state after its expansion.  
         [0012]     In a further preferred embodiment, there is a fourth low-pressure connection for the refrigerant to the valve housing. Refrigerant flows through the third connection into the valve, without any substantial loss of pressure, and then flows out of the valve through the fourth connection so that the valve housing also forms a part of a low-pressure line of the refrigerant cycle. An expansion valve made according to the invention may be used in a closed volume system, wherein pressure in the system exerts pressure upon the membrane, and wherein the volume is in thermal contact with the third connection. In this manner, the temperature of the refrigerant, which is adjacent to the third connection, can be directly converted, in a mechanical electromechanical fashion, into a corresponding activation/triggering of the sliding element. This conversion occurs in an especially efficient manner if the volume is filled with a defined quantity of a suitable substance, of, for example, the refrigerant of the air conditioning system.  
         [0013]     As an alternative to exerting pressure upon the membrane from a closed volume, the membrane can also be exposed to a force exerted by the air conditioning system&#39;s refrigerant&#39;s pressure, and particularly to a refrigerant under high pressure. Such a design of the control mechanism can be particularly advantageous in the case of CO 2  air conditioning systems, which—compared to conventional air conditioning systems—have somewhat significantly different operation parameters.  
         [0014]     In the interest of a simple construction and reduction of the number of components, the sliding element may be set to a default setting by positioning the control mechanism in a particular relation to the valve housing. In this arrangement there is no need for any additional adjustment of screws, and only the attachment and sealing of the control mechanism in relation to the valve housing requires special design attention.  
         [0015]     Further advantages and features of the expansion valve as designed by this invention become apparent from the subsequent design example and from the claims. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  is a side view of a cross-section of an expansion valve of the invention.  
         [0017]      FIG. 2  is an exploded view of region A of  FIG. 1 .  
         [0018]      FIG. 3  is a top view of a cross-section through the expansion valve from  FIG. 1  along the line B-B in the closed state of the valve.  
         [0019]      FIG. 4  is a top view of a cross-section through the expansion valve from  FIG. 1  along the line B-B in an at least partially open state of the valve.  
         [0020]      FIG. 5  is a top view of an alternative embodiment of the cross-section through the expansion valve from  FIG. 1  along the line B-B in the closed state of the valve. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]      FIG. 1  illustrates an expansion valve in accordance with the invention. This valve includes a valve housing  1 , which may consist of several components in order to simplify its assembly.  
         [0022]     A zone of the valve housing, shown at the lower section of the housing  1  in  FIG. 1 , includes a first port  2  and a second port  3 , which in a preferred embodiment may be located at the same height and preferably in the same axis. The first port  2  is connected with a refrigerant line that comes from the condenser of the refrigeration circuit, and, in general, is part of the high-pressure section of the refrigeration circuit. The second port  3  is part of the low-pressure section of the refrigeration circuit, which, in  FIG. 1 , is also illustrated by means of a larger diameter.  
         [0023]     In a preferred embodiment, ports  2  and  3  are connected through an expansion element of the air conditioning system in which previously compressed refrigerant expands and cools. The expansion element includes a channel  4 , which connects ports  2  and  3 , wherein the common axis of ports  2  and  3  is also the middle axis of channel  4 .  
         [0024]     As illustrated in  FIG. 1 , channel  4  is intersected by a hole  5  that is vertical to the axis of the channel, and in which is disposed a sliding element  6 . Sliding element  6  is shaped as an elongated body and may travel along an axis within hole  5 . The hole  5  extends on both sides of the channel  4 , and a downward-leading part of the hole is designed as a blind hole  5   a  in the valve housing  1 . Channel  4  may have a constant or varying diameter. In addition, the diameter of channel  4  at the intersection of hole  5  may be larger, smaller or the same size as hole  5 .  
         [0025]     As illustrated in  FIG. 2 , the sliding element  6  comprises a lower end section  6   a , which is formed as a dimensionally accurate cylinder. In a preferred embodiment of the invention, the end section  6   a  is coupled to a rotationally symmetrical control section  6   b  of the sliding element  6  that is concentric to the end section  6   a . The diameter of the control section  6   b  is conically tapered and has a cross-section that is smaller than the cross-section of the end section  6   a . Overall, the control section forms a rotationally symmetrical truncated cone. The control section  6   b  may have other shapes and forms, and can also be shaped, for example, as a cylindrical body with an aperture.  
         [0026]     The control section  6   b  is coupled to a cylindrical shaft  6   c  of the sliding element  6 , which, in the example of  FIG. 2 , has the same diameter as the lower end section. It is noted, however, that the diameters of these shafts may differ depending on the desired characteristics.  
         [0027]      FIGS. 3 and 4  illustrate the sliding element  6  in different operating positions. As is apparent from these figures, the movement of the sliding element along its longitudinal axis sets up a variable aperture  14  of the channel  4 .  
         [0028]     As illustrated in  FIG. 3 , in the uppermost shifted position of the sliding element, the end section  6   a  is completely inserted into channel  4 . As one of ordinary skill in the art will appreciate, the dimensions of the components are selected (for example, by finely grinding the hole  5  and the end section  6   a ) such that a sealing closure, at least in the sense of the function of the air conditioning system is established. A complete hermetic sealing in the strict sense of the term is usually not required, however. In order to achieve an appropriate seal, the diameter of the end section  6   a  may be noticeably larger than the diameter of the channel  4 , which creates a particularly large contact surface. An end section  6   a  is arranged only between two flanges  4   a  located in the channel  4 , which also achieves a sufficient seal. In the design of a preferred embodiment, the flanges  4   a  or another insert formed differently but having the same function in the channel  4  can be made of a material with the same properties of thermal expansion as the sliding element  6 .  
         [0029]      FIG. 5  illustrates an alternative structure of lower end section  6   a . In this embodiment, a portion of lower end section  6   a  has been machined to a flat shape, as indicated by reference number  6   d . This structure permits displacement of any fluid or material captured in blind hole  5   a  as sliding element moves into blind hole  5   a . In an embodiment of the invention, the width of the non-circular feature  6   d  is less than the width of the flanges  4   a  in order to reduce the possibility of leakage, as the rotational orientation of the sliding element  6  with respect to channel  4  may change over time.  
         [0030]     If, starting from its closed position (see  FIG. 3 ), the sliding element  6  is moved downward as shown in  FIG. 1 , the control section  6   b  crosses the channel  4 . The end section  6   a  plunges into the blind-hole zone  5   a  of the hole  5 . In this arrangement, the channel  4  is completely penetrated by the sliding element  6  regardless of the operating conditions of the expansion valve. The tapering of the control section creates an aperture  14 , which varies depending on the position of the sliding element. In the area of the aperture, the refrigerant expands in a controlled fashion and flows along the outer circumference of the control section  6   b  of the sliding element  6  in a plane that is essentially vertical to the longitudinal axis of the sliding element  6 . In  FIG. 4 , the flowing of the refrigerant is indicated by means of arrows. Overall, this process results in the low-noise expansion of the refrigerant.  
         [0031]     Due to the conical tapering of the control section  6   b , the aperture  14  is not enlarged in a linear relation to the longitudinal motion of the sliding element  6 , but—as, for example, in a preferred embodiment as illustrated in FIGS.  1 - 4 —in an essentially quadratic relation. Thus, the mass flow of refrigerant does not always depend on an operation parameter in a linear manner. In general, a suitable shaping of the control section  6  allows for the accurate adjustment of an expansion valve to a control parameter.  
         [0032]     The shaft  6   c  of the sliding element passes through various portions of valve housing  1 . A sealing element  7  seals shaft  6   c  at the point of penetration of control channel  8 . An o-ring completely surrounds and seals the shaft  6  from control channel  8 . In this manner, the contact surface between the shaft  6   c  and the wall of hole  5  can be pressure-sealed from control channel  8 .  
         [0033]     Control channel  8  extends through valve housing  1  and is separate from channel  4  in a preferred embodiment. It is also possible, however, that channel  8  may be more directly coupled to channel  4 . In the embodiment illustrated in  FIG. 1 , channel  8  includes a third port  8   a  and a fourth port  8   b . The third port  8   a  is connected to an outlet of an evaporator of the refrigerant circuit, and the fourth port  8   b  is connected to the suction inlet of a compressor of the refrigerant circuit. Thus, in relation to the circuit, the refrigerant—when flowing through the control channel  8 —is in its lowest pressure zone, which is also reflected in the larger diameter of ports  8   a  and  8   b  as compared to those of ports  2  and  3 .  
         [0034]     Shaft  6   c  crosses the control channel  8  and terminates in a plunger  6   d  of the sliding element  6 . Plunger  6   d  passes through a hole in the housing area  1   a . An upper end surface of the plunger  6   d  is, at least in one direction, in a non-positive connection with the membrane  9 . The membrane  9  is held in a housing  10 , wherein an upper part of membrane housing  10  and the side of the membrane opposite the membrane&#39;s connection with the plunger  9  hermetically close off a volume  11 . Inside membrane housing  10  is a sealing plug  12 , by means of which the volume  11  can be filled with a defined quantity of a substance under certain defined conditions, e.g., pressure or temperature. A collar  10   a  of the membrane housing is held, by means of a thread, in the hole through the valve housing  1   a , and sealing means (not shown) ensure that the control channel  8  is sealed. The plunger  6   d  longitudinally slides along an internal side of the collar  10   a.    
         [0035]     The plunger assembly may be screwed into place, within a tolerance range, of different depths and in a sealing connection, which allows the depth at which the sliding element  6  plunges into the hole to be pre-set. This arrangement compensates for the tolerances in the manufacture of individual components.  
         [0036]     Sliding element  6  is also supported against the lower side of the control channel  8  by means of a helical spring  13 , wherein the helical spring  13  envelops the shaft  6   c  and rests against the plunger  6   d . The sliding element is thus biased in a direction of the spring force.  
         [0037]     Spring  13 , membrane  9 , membrane housing  10 , and enclosed volume  11  form a control mechanism, by means of which the sliding element  6  is moved, in a controlled manner, in dependence on the operation parameters of the air conditioning system. In this configuration, three forces act upon the sliding element, i.e., the pressure force of the refrigerant in the control channel  8 , the spring force of spring  13 , and the pressure force exerted by the volume  11 . The substance contained in volume  11  exerts a force on membrane  9  and acts in a direction opposite to the two other forces. Thus, in the direction of its longitudinal axis, the position of sliding element will be determined by the interaction of these forces. The pressure force of the refrigerant in channel  4  acting on the sliding element is limited because at that location, the sliding element  6  has a relatively small cross-section.  
         [0038]     Through the surface of membrane  9  and the interstice between the plunger  6   d  and the collar  10   a , volume  11  is in thermal contact with the refrigerant of the control channel  8 . A decrease in the pressure of the refrigerant in control channel  8  (typically, after an evaporator) and an increase in the temperature of the refrigerant in the control channel  8  result in a net increase of the force component acting against the opposing forces in a direction of the spring force. The sliding element  6 , therefore, moves downward in the opening direction. In contrast, a decrease in the temperature in the zone of the control channel  8  results in the aperture  14  being closed. A reduced mass flow of the refrigerant in the evaporator then causes an increase in the temperature of the refrigerant in the control channel  8  and/or in the suction line of the compressor. In this manner, a mechanical control circuit arises, which—after a proper pre-alignment and setting of the control mechanism—ensures that the refrigerant sufficiently superheats after the evaporator. This results in a good efficiency of the air conditioning system and reduces the possibility that condensed refrigerant will enter the compressor.  
         [0039]     It is a matter of course that the properties of the expansion valve as designed by this invention are not restricted to the embodiments as illustrated and described above. The control of the sliding element can be realized in any known form including a purely electromechanical control in conjunction with an electronic control device.  
         [0040]     While the invention has been described with an emphasis upon particular embodiments, it should be understood that the foregoing description has been limited to the presently contemplated best mode for practicing the invention. It will be apparent that various modifications may be made to the invention, and that some or all of the advantages of the invention may be obtained. Also, the invention is not intended to require each of the above-described features and aspects or combinations thereof. In many instances, certain features and aspects are not essential for practicing other features and aspects. The invention should only be limited by the appended claims and equivalents thereof, since the claims are intended to cover other variations and modifications even though not within their literal scope.