Abstract:
A spring clip is attached to a thermostat bottom wall for attaching the thermostat to tubing in heat exchange relationship. The spring clip has an opening that faces transversely of the thermostat longitudinal axis so that installation forces act in a direction that is more parallel to the bottom wall to avoid denting of the bottom wall. The spring clip has a flat mounting base attached to the thermostat bottom wall to spread forces over a large area of the bottom wall and to reinforce the bottom wall against deformation.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 09/478,160, filed Jan. 5, 2000 which is a continuation-in-part of U.S. patent application Ser. No. 09/227,598, filed Jan. 8, 1999 now abandoned. The entire disclosure of these prior applications is considered part of the disclosure of this application, and is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This application relates to the art of thermostat mounting clips and, more particularly, to spring clips for attaching thermostats to tubing in heat exchange relationship therewith. The invention is particularly applicable for use with thermostats that have a bimetal disc within a thermostat cup and will be described with particular reference thereto. However, it will be appreciated that the invention has broader aspects and the spring clip can be used for other purposes as well as with other types of thermostats. 
     In a known arrangement for attaching thermostats to tubing, a generally U-shaped spring clip is welded to the bottom wall of the thermostat cup. The generally U-shaped clip makes line contact with the thermostat cup bottom wall, and is positioned so that insertion forces during attachment of the clip to the tubing act perpendicular to the thermostat cup bottom wall. These forces tend to permanently deform the thermostat cup bottom wall and this may cause improper operation of the thermostat. In addition, accidental bumping of the clip or dropping the thermostat on the clip can permanently distort the thermostat cup bottom wall in a manner that interferes with proper thermostat operation. 
     A prior art thermostat and clip arrangement of the type described is illustrated in FIG. 7 where a generally cylindrical thermostat cup  2  has a generally U-shaped spring clip  3  welded to its flat bottom wall  4 . Clip  3  makes little more than line contact with bottom wall  4  as generally indicated at  5 . The spaced-apart end portions of the arms of clip  3  define an entrance opening  6  that is centered on thermostat longitudinal axis  7 . Entrance opening  6  opens outwardly in a direction parallel to axis  7  and perpendicular to thermostat bottom wall  4 . Therefore, installation of clip  3  on tubing results in forces being applied to thermostat cup bottom wall  4  in a direction perpendicular thereto. Because clip  3  is welded to bottom wall  4  along a small area, these forces are concentrated and may permanently deform bottom wall  4 . 
     It would be desirable to have an arrangement that minimizes possible damage to the bottom wall of the thermostat cup during attachment of the thermostat to tubing and to otherwise minimize possible deformation of the bottom wall by forces applied thereto through the mounting clip. 
     Additionally, it is well known that tubing manufactured for use in, for example, the refrigeration and HVAC industries is not subject to exacting tolerances for geometric dimensions, including roundness. Furthermore, it is often the case that thermostats, like the one disclosed here, are employed in situations where they are clipped to tubing that is not round, such as when the tubing is bent at an elbow or “kinked” such that the cross-sectional configuration of the tubing is other than substantially circular. Consequently, the need has arisen for a thermostat spring clip that can attach to both tubing that exhibits a substantially circular cross-section and tubing that exhibits a non-circular or “out-of-round” cross-section while still maintaining a low insertion force, high clamping force, and still maintaining good thermal response in the thermostat. 
     SUMMARY OF THE INVENTION 
     A substantially flat mounting base on a spring clip is attached to a substantially flat bottom wall of a thermostat disc cup. The substantially flat mounting base occupies a large amount of the bottom wall area to minimize the possibility of the bottom wall being deformed by forces applied to the clip. 
     In a preferred arrangement, the spring clip has an entrance opening that opens in a direction transversely of the longitudinal axis of the thermostat cup. Therefore, forces applied to the clip during the attachment of same to tubing act generally parallel to the bottom wall of the thermostat cup to further minimize the possibility of bottom wall deformation by installation forces. 
     The spring clip has a spring arm integral with the mounting base and is positioned so that the tubing is received between the mounting base and the spring arm. The spring arm has a tubing receiving portion therein to provide high resistance against displacement of the tubing from the spring clip. The tubing receiving portion may be curved on the radius of a circle that generally corresponds to the external curvature of tubing that is received within the spring clip. In an alternative arrangement, the tubing receiving portion comprises a generally abrupt arcuate portion extending through an angle of approximately 90° and two adjacent non-arcuate portions adjoining either side of the arcuate portion. The resulting tubing receiving portion in conjunction with the mounting base contains the tubing securely at three points about the circumference of the tubing. 
     It is a principal object of the present invention to provide an improved spring clip for attaching a thermostat cup to tubing. 
     It is a further object of the invention to provide an improved thermostat clip that improves the thermal response of the thermostat and that is easier to weld to the bottom wall of a thermostat disc cup. 
     It is another object of the invention to provide an improved thermostat disc cup and spring clip assembly that facilitates attachment of the thermostat cup to tubing while providing high resistance to displacement of the thermostat disc cup from its attachment to tubing. 
     It is an additional object of the invention to provide an improved arrangement for attaching a spring clip to the bottom wall of a thermostat disc cup in a manner that minimizes the possibility that the bottom wall will be deformed by forces applied to the spring clip. 
     It is a further object of the invention to provide an improved thermostat disc cup and spring clip assembly that requires relatively low installation force while providing relatively high retention force. 
     It is yet another object of the present invention to provide an improved thermostat disc cup and spring clip assembly that can be used with tubing having both substantially circular and non-circular cross-sections. 
     Compared to the previous design of FIG. 7, the design of the present application requires an insertion force that is only approximately 29% of the insertion force of the previous design. At the same time, the design of the present application provides an average increase of approximately 10% in retention force compared to the previous design of FIG.  7 . The large surface area of the mounting base of the clip and the large surface area of engagement between such base and the bottom wall of the thermostat disc cup provides a 22% improvement in thermal response compared to the design of FIG.  7 . Compared to the design of FIG. 7, the design of this application provides about 60 times more dent resistance for the cup bottom wall in a 20 pound deformation test. For drop impact testing at a distance of six feet, the clip of the present application has about 24 times more dent resistance than the arrangement of FIG.  7 . 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The various advantages of the present invention will become apparent to one skilled in the art upon reading the following specification, in which: 
     FIG. 1 is a cross-sectional elevational view of a thermostat disc cup having a first embodiment of the improved spring clip of the present invention attached to a bottom wall thereof; 
     FIG. 2 is a side elevational view taken generally on line 2—2 of FIG. 1; 
     FIG. 3 is a bottom plan view of the thermostat and clip assembly of FIG. 1; 
     FIG. 4 is a side elevational view of a first embodiment of the improved spring clip of the present invention; 
     FIG. 5 is a top plan view of the improved spring clip of FIG. 4; 
     FIG. 6 is an end elevational view of the improved spring clip of FIG. 4; 
     FIG. 7 is a side elevational view of a prior art thermostat disc cup and spring clip assembly; 
     FIG. 8 is a side elevational view of an alternate embodiment of the improved spring clip of the present invention; 
     FIG. 9 is a side elevational view of the improved spring clip of FIG.  8  and showing the spring clip engaging tubing having a cross-section exhibiting an “out-of-round” condition; and 
     FIG. 10 is a side elevational view of the improved spring clip of FIG.  8  and showing the spring clip engaging tubing having a cross-section that is substantially circular. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     It should be understood from the outset that while the following discussion illustrates particular embodiments of the present invention, these embodiments merely represent a best mode of currently practicing the invention and other modifications may be made to the particular embodiments without departing from the spirit and scope of the invention. 
     Referring now to the drawings, wherein the illustrations are for purposes of showing the preferred embodiment of the present invention and not for purposes of limiting same, FIG. 1 shows a thermostat A having a metal disc cup B with a generally cylindrical peripheral wall  10  and a substantially flat circular bottom wall  12  with a substantially flat circular external surface. 
     The bottom portion of disc cup B is stepped as generally indicated at  14 ,  16  to provide a circumferential shoulder on which the peripheral portion of a bimetal disc  20  rests in spaced relationship to bottom wall  12 . A cylindrical plunger  22  is slideably received in a cylindrical hole in a plastic member  24  for cooperation with bimetal disc  20  and with a switch blade  26  that is attached at one end to a post  30  and carries a contact  32  adjacent its other end that cooperates with a fixed contact  34 . Post  30  and fixed contact  32  are attached to a plastic support member  38 , and wires  40 ,  42  are attached to post  30  and to the terminal that provides fixed contact  34 . The cavity within thermostat cup B above plastic support member  38  may be filled with epoxy or another suitable potting compound which then surrounds wires  40 ,  42  and encapsulates the upper end portions of post  30  and the terminal that is associated with fixed contact  34 . 
     Bimetal disc  20  normally is downwardly curved toward bottom wall  12  as shown in FIG.  1  and heat is transferred to bimetal disc  20  through bottom wall  12 . At a predetermined temperature, bimetal disc  20  will snap to an opposite upwardly curved position and move plunger  22  upwardly to close contacts  32 ,  34 . When bimetal disc  20  cools, it will snap back to the position shown in FIG.  1  and contacts  32 ,  34  will separate. 
     Referring to FIGS. 1-3, a spring clip C of stainless steel or other suitable material has a substantially flat mounting base  50  welded or otherwise suitably attached to bottom wall  12  of thermostat disc cup B. Spring clip C includes a spring arm D that extends back along mounting base  50  in a spaced relationship thereto to provide an entrance opening that opens transversely of thermostat longitudinal axis  52 . Spring arm D has a tubing receiving portion  54  therein for inhibiting displacement of cylindrical tubing from its position between spring arm D and mounting base  50 . Mounting base  50  preferably is centered on bottom wall  12 . That is, the center of the area of mounting base  50  is close to or coincides with disc cup longitudinal axis  52  which is also the center of bottom wall  12 . 
     A thermostat and spring clip assembly is attached to cylindrical tubing by aligning the entrance opening of the spring clip with the tubing. Lateral force then is applied to the thermostat and spring clip to bias spring arm D resiliently away from mounting base  50  for allowing movement of the tubing to a position with portion  54 . Spring arm D then closes tightly on the tubing and also urges mounting base  50  into firm engagement with the tubing. A longitudinal axis of the tubing extends perpendicular to thermostat longitudinal axis  52 , and the tubing longitudinal axis either intersects thermostat longitudinal axis  52  or is very close to intersection therewith. 
     With reference to FIGS. 4-6, substantially flat mounting base  50  has a plurality of spaced-apart raised bumps  56  on the surface thereof that faces toward thermostat bottom wall  12  to facilitate welding thereof to the bottom wall. Mounting base  50  is substantially rectangular and has first and second opposite ends  60 ,  62 . The corners adjacent first end  60  are removed to provide 45° peripheral surface portions  64 ,  66 . This allows end  60  to be positioned closer to the circular periphery of bottom wall  12  without having the corners extend radially outwardly beyond the circular outer periphery of bottom wall  12 . Obviously, the end of the mounting base could be curved or otherwise shaped to accomplish the same purpose. 
     Clip C is reversely bent adjacent second end  62  of mounting base  50  as generally indicated at  70  to form spring arm D. Spring arm D has a straight portion  72  adjacent mounting base  50  that makes an angle  74  with mounting base  50  that is between 25-45°. Arm D has a straight terminal end portion  76  that is inclined at an included angle  78  with mounting base  50  that is between 35-55°. Angle  74  may vary depending on the size of the tubing with which the clip will be used. For example, for a clip to be used with a ⅜ inch diameter tubing, angle  74  has been selected to be approximately 38.4°. For a clip to be used with a {fraction (5/16)} inch diameter tubing, angle  74  has been selected to be approximately 30.5°. For all clip sizes, angle  78  has been selected to be approximately 45°. 
     Tubing receiving portion  54  preferably is curved on a radius about a center  82  that is located between mounting base  50  and arm D. Radius  80  preferably is slightly larger than the radius of the cylindrical outer surface of the tubing that is received within the clip by at least several thousandths of an inch. For example, when the clip is for use with tubing having an external diameter of ⅜ inch, radius  80  would be slightly larger than {fraction (3/16)} inch. Where the clip is for use with tubing having an external diameter of {fraction (5/16)} inch, radius  80  would be slightly larger than {fraction (5/32)} inch. Center  82  is located within 20% of the midpoint of the distance between first and second ends  60 ,  62  of mounting base  50 , more preferably within 10% thereof, and most preferably within 5% thereof. 
     Tubing receiving portion  54  has a first intersection  86  with arm straight portion  72  and a second intersection  88  with spring arm end portion  76 . First intersection  86  is located a distance  90  from the inner surface of mounting base  50  and second intersection  88  is located a distance  92  from the inner surface of mounting base  50 . Dimension  90  also corresponds to the distance from the surface of clip mounting portion  50  to center  82  of radius of curvature  80  for tubing receiving portion  54 . The entrance opening  92  to the interior of spring clip C is defined between the interior surface of mounting base  50  and intersection  88 . Downwardly inclined spring arm end portion  76  provides a cam surface that acts against the curved surface of the tubing to cam spring arm D away from mounting base  50  so that the spring clip can be snapped over the tubing. 
     Curved tubing receiving portion  54  extends over an arc of approximately 150° between intersections  86  and  88 . This arc preferably does not vary from that most preferred angle by more than ±10° and more preferably by not more than ±5°. 
     Distances  90  and  92  vary with the size of the spring clip for use with tubing of different diameters. In a clip to be used with tubing having an external diameter of ⅜ inch, dimension  90  is approximately 0.150 inch and dimension  92  is approximately 0.244 inch. In a clip to be used with tubing having an external diameter of {fraction (5/16)} inch, dimension  90  is approximately 0.125 inch and dimension  92  is approximately 0.203 inch. Thus, entrance opening dimension  92  is approximately 65% of the external diameter of tubing with which the clip is to be used. This entrance opening dimension could be between 60-70% of the tubing external diameter or about 0.160-0.260 inch. Distance  90  from mounting base  50  to center  82  is approximately 40% of the external diameter of the tubing with which the clip is to be used. This dimension could be between 35-45% of the tubing external diameter or about 0.115-0.160 inch. However, dimensions  90  and  92  preferably do not vary by more than 10% and most preferably by not more than 5% from the dimensions that correspond to 40% and 65% of the external diameter of the tubing with which the clip is to be used. 
     Clip entrance opening  92  is located closely adjacent the outer periphery of bottom wall  12  and is spaced slightly inwardly of such outer periphery. Entrance opening  92  is located much closer to the outer periphery of bottom wall  12  than to disc cup longitudinal axis  52 . Entrance opening  92  is also spaced from first end  60  of mounting base  50  in a direction toward second end  62 . 
     By way of example, disc cup circular bottom wall  12  has a diameter of 0.6875 inch and an area of 0.371 inch 2 . Clip mounting base  50  has a length of 0.632 inch that is approximately 92% of the bottom wall diameter and a width of 0.330 inch that is approximately 48% of the cup diameter. The area of the mounting base  50  that engages bottom wall  12  is approximately 56% of the area of bottom wall  12 . Preferably, mounting base  50  engages bottom wall  12  over an area that is at least 40% of the bottom wall area and the length of the mounting base is at least 70% of the diameter of the bottom wall. The width of the mounting base is at least 30% of the diameter of the bottom wall. 
     The following is a comparison of the performance of the clip of the present application compared to the clip of FIG.  7 . Measurements were made of the deformation of bottom  12  in response to various loads applied to the spring clip acting in a direction toward bottom wall  12  parallel to the longitudinal axis of the thermostat disc cup. Retention force is measured by pulling on the thermostat in a direction parallel to its longitudinal axis until the clip releases from the tubing. 
     
       
         
               
               
               
               
             
           
               
                   
               
               
                 Clip 
                 FIG. 7 
                 FIGS. 1-6 
                 FIGS. 1-6 
               
               
                   
               
             
             
               
                 Tubing size (inch) 
                 ⅜ 
                 ⅜ 
                 ¼ 
               
               
                 Number of samples tested 
                 13 
                 12 
                 12 
               
               
                 Deformation (inch) (small is better) 
               
               
                 20 lbs. 
                 0.0178 
                 0.0003 
                 0.0000 
               
               
                 45 lbs. 
                 0.0350 
                 0.0012 
                 0.0007 
               
               
                 60 lbs. 
                 0.0469 
                 0.0017 
                 0.0001 
               
               
                 Insertion Force (lbs.) (small is better) 
               
               
                 Mean 
                 14.0 
                 4.1 
                 4.7 
               
               
                 Max. 
                 16.3 
                 4.6 
                 5.7 
               
               
                 Min. 
                 12.9 
                 3.4 
                 3.9 
               
               
                 Retention Force (lbs.) (large is better) 
               
               
                 Mean 
                 6.8 
                 7.5 
                 11.0 
               
               
                 Max. 
                 7.4 
                 8.6 
                 12.8 
               
               
                 Min. 
                 6.3 
                 6.6 
                 8.9 
               
               
                   
               
             
          
         
       
     
     From the above tests of clips for ⅜ inch tubing, it is seen that the mean insertion force of 4.1 for the new design is a reduction of approximately 71% from the mean insertion force of 14.0 for the design of FIG.  7 . The mean retention force of 7.5 for the design of the present application is an increase of approximately 10% over the mean insertion force of 6.8 for the design of FIG.  7 . The large surface area of engagement between the clip mounting base and the disc cup bottom wall also improves heat transfer for better thermal response. The large engagement area also reinforces the disc cup bottom wall against deformation and spreads forces out over a greater area of the cup bottom wall. 
     An alternate embodiment of the spring clip of the present invention is disclosed and shown at FIG.  8 . Spring clip C′ is suitable to accommodate and attach to tubing that is either cylindrical or non-cylindrical, the latter including tubing having cross-sections which exhibit out-of-round conditions. 
     The spring clip C′ possesses the same general configuration of the spring clip C as described above, such as a flat mounting base  50 ′ and a spring arm D′ that extends back along the mounting base  50 ′ in a spaced relationship to provide an entrance opening that opens transversely of the thermostat longitudinal axis  52 . Like features of the spring clips C and C′ are similarly designated with like numerals. However, spring clip C′ includes a tubing receiving portion  54 ′ that varies from the spring clip C to enable spring clip C′ to accommodate tubing that are not round. 
     Tubing receiving portion  54 ′ includes a radius  80 ′ which begins at a first tangent location  86 ′ with arm D′ straight portion  72 ′ and terminates a second tangent location  94  with a second arm D′ straight portion  96 . The radius  80 ′ extends over an arc of approximately slightly greater than 90° between locations  86 ′ and  94 . This arc preferably does not vary from 90° by more than ±10°/−5°. More preferably, this arc is not less than 90°. Second straight portion  96  extends to intersection  88 ′ which intersects w/downwardly extending spring arm end portion  76 ′. 
     Dimension  90 ′ locating the centerline of radius  80 ′ is greater than 70% of the outer diameter of the tubing with which the clip is to be used. More preferably, this dimension is between 85%-95% of the tubing outer diameter. 
     Dimension  92 ′ is greater than 45% of the tubing outer diameter, and preferably between 45% and 65%. 
     Spring clip C′ is designed to engage the tubing at least three locations,  100 ,  102 ,  104 , on the exterior surface of the tubing. As shown in FIGS. 9 and 10, spring clip C′ is thus versatile enough to accommodate and clip to tubing  106  having a circular cross-section and tubing  108  having a non-circular or “out-of-round” cross-section. 
     Although specific mention has been made of clips for use with tubing having an external diameter of ¼, {fraction (5/16)} and ⅜ inch, it will be recognized that the clip of the present application can be used with tubing having an external diameter smaller than ¼ inch and an external diameter larger than ⅜ inch, such as up to at least ⅞ inch. Although other sizes are possible for other purposes, the clip of the present application for use on thermostats will generally be configures for use with tubing having an external diameter between ⅛-1 inch. For clips to be used with tubing having an external diameter of {fraction (5/16)} or ⅜ inch, specific examples of clip dimensions have been given simply by way of illustration. It will be recognized that the example dimensions may vary for those specific sizes and that the dimensions will vary for clips to be used with tubing having other external diameters. 
     For clips to be used with tubing having an external diameter of ¼and ⅜ inch, specific examples have been given of the deformation of a disc cup bottom resulting from different loads on the clip, along with examples of the tubing insertion and retention forces. It will be recognized that the clip of the present application is not limited to those ranges of disc cup bottom wall deformations, tubing insertion forces and tubing retention forces that are given by way of example. The clip of the present application has many advantages and uses for requirements that are below or above those that are given as examples. It will further be recognized that the ranges of disc cup bottom wall deformation, tubing insertion forces and tubing retention forces may vary significantly for clips to be used with tubing having other external diameters. 
     Although the invention has been shown and described with respect to a preferred embodiment, it is obvious that equivalent alterations and modifications will occur to others skilled in the art of the reading and understanding of this specification. The present invention includes all such equivalent alterations and modifications, and is limited only by the scope of the claims. 
     Various other advantages and modifications will become apparent to one skilled in the art after having the benefit of studying the teachings of the specification, the drawings, and the following claims.