Abstract:
A tube is provided with an indentation long enough to receive a sensor bulb and having a nominal curvature corresponding to the outer curvature of the sensor bulb whereby, when secured by a clamp, which is suitably tightened, at least one of the members will deform to the curvature of the other member thereby achieving area contact between the members.

Description:
BACKGROUND OF THE INVENTION 
   The sensing bulb of a sensor is often secured to a pipe or tube. For example, the sensing bulb of a thermostatic expansion valve, TXV, is typically secured to the line between the evaporator and compressor of an air conditioning or refrigeration system. The tube and the bulb are cylindrical in cross section such that there is only line contact for thermal conduction between the members if the members are in contact and if their axes are parallel. If the axes are not parallel there would only be a point contact. Poor sensor attachment can result in failure of the TXV and the system. Changing the shape of the tube or bulb will, at best, produce two line contacts absent an exact matching of curvature between the tube and bulb. This is impractical for mass production where sensors and their bulbs come in standard sizes and where modification of the tubing introduces a restriction and would not be made to the necessary tolerances in a mass production situation. 
   SUMMARY OF THE INVENTION 
   A tube to which a cylindrical sensor bulb is to be attached is provided with an indentation long enough to receive the sensor bulb and having a nominal curvature corresponding to the outer curvature of the sensor bulb. The indentation cradles the bulb thereby facilitating assembly while axially and circumferentially locating the sensor with respect to the tube. A strap type of clamp is placed around the tube and sensor bulb and tightened such that at least one of the members will deform to the curvature of the other member thereby achieving area contact between the members. 
   It is an object of this invention to provide area contact between a sensor bulb and a tube. 
   It is another object of this invention to maximize the sensing ability of a thermal sensor. 
   It is an additional object of this invention to axially and circumferentially locate a sensing bulb on a tube. 
   It is a further object of this invention to provide a more reliable air conditioning or refrigeration unit. These objects, and others as will become apparent hereinafter, are accomplished by the present invention. 
   Basically, a tube is provided with an indentation long enough to receive a sensor bulb and having a nominal curvature corresponding to the outer curvature of the sensor bulb whereby, when secured by a clamp, which is suitably tightened, at least one of the members will deform to the curvature of the other member thereby achieving area contact between the members. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a fuller understanding of the present invention, reference should now be made to the following detailed description thereof taken in conjunction with the accompanying drawings wherein: 
       FIG. 1  is a schematic representation of a refrigeration or air conditioning system employing the present invention; 
       FIG. 2  is a partially cutaway side view of the sensor bulb secured in place; 
       FIG. 3  is an exploded sectional view showing the relationship between the tube and the sensor bulb prior to assembly; and 
       FIG. 4  is a sectional view taken along line  4 — 4  of FIG.  2 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   In  FIG. 1 , the numeral  10  generally designates a refrigeration or air conditioning circuit. Circuit  10  includes a compressor  12  which compresses suction gas to a higher temperature and pressure and delivers it via discharge line  14  to condenser  16  which is in a heat exchange relationship with the surrounding air. In the condenser  16 , the hot refrigerant gas gives up heat to the condenser air thereby cooling the compressed gas and changing the state of the refrigerant from a gas to a liquid. Liquid refrigerant flows from condenser  16  via liquid line  18  to TXV  20 . TXV  20  is operated through solenoid  20   a  responsive to temperature sensor  120  which is located between the outlet of evaporator  24  and the suction of compressor  12 . Sensor  120  senses the superheat or quality of the refrigerant vapor leaving evaporator  24  and TXV  20  controls the amount of refrigerant entering evaporator  24  and the superheat of the refrigerant leaving evaporator  24 . As the liquid refrigerant passes through the orifice of TXV  20 , some of the liquid refrigerant vaporizes into a gas (flash gas). The mixture of liquid and gaseous refrigerant passes via distributor tubes  22  to the evaporator  24 . Heat is absorbed by the refrigerant from the evaporator air by the balance of the liquid refrigerant causing it to vaporize in the coil of evaporator  24 . The vaporized refrigerant then flows via suction line  26  to compressor  12  to complete the fluid circuit. The refrigerant circuit described so far is conventional. The present invention improves the securing of the sensor  120  to suction line  26  and hence the reliability of TXV  20 . 
   Referring to  FIGS. 2-4  it will be noted that sensor  120  is of a cylindrical shape. As best shown in  FIGS. 2 and 3 , suction line  26  has an indentation  26   a  formed therein which is of a length greater than the length of sensor  120  and having a curvature which is, nominally, the same as that of sensor  120 . Indentation  26   a  is also curved at the ends to provide a smooth transition as to the restriction of line  26  that it produces. Because indentation  26   a  represents a restriction relative to suction line  26  a balance must be struck between the restriction imposed and the area of contact achieved. For a tube  26  having an outer diameter of 20.0 mm, a maximum indentation depth of 3.2 mm for indentation  26   a  would reduce the cross sectional flow area by 25% which has been found to be acceptable. With sensor  120  having a diameter of 19.0 mm and a length of 55.5 mm this amounts to 8.3 mm to 9.14 mm or 50-55° of circumferential sensor contact. This equates to an area contact of 421.6 to 464 mm 2 . Any area contact is an improvement over point or line contact. Allowing for varying diameters of the tube  26  and sensor  120  as well as limitations on the acceptable pressure drop produced by the indentation  26   a , contact over 30°-60° of the circumference of sensor  120  provides an acceptable balance with 45°-55° being preferred. 
   As noted above, the curvature of indentation  26   a  is nominally the same as that of sensor  120 . Variation is caused by such factors as tool wear, variation in the force applied to form the indentation  26   a , etc. As shown in  FIGS. 2 and 3 , the sensor is located with respect to indentation  26   a  so as to be received therein. With indentation  26   a  facing upward, sensor  120  is placed therein and held in place for assembly due to the cradling effect of indentation  26   a . A strap, or the like,  130  is placed around the line  26  and sensor  120  and tightened as shown in FIG.  4 . The tightening force is sufficient to deform the sensor  120  and/or the indentation  26   a  to achieve the desired area of contact. A BAND-IT® stainless steel tie made by BAND-IT-IDEX, INC. of Denver, Colo. provides the necessary securing force. The installing of a BAND-IT® tie using a pneumatic tool which applies an 80 psig force when tightening has proven acceptable. If necessary, or desired, more than one strap  130  may be used to hold sensor  120  in place in recess  26   a  of tube  26 . 
   Although a preferred embodiment of the present invention has been illustrated and described, other changes will occur to those skilled in the art. For example, while the present invention has been described and illustrated in terms of a refrigeration or air conditioning circuit it may be used in other applications where sensors are secured to pipes or tubes. It is therefore intended that the scope of the present invention is to be limited only by the scope of the appended claims.