Patent Publication Number: US-2011073420-A1

Title: High pressure switch

Description:
RELATED APPLICATION 
     This application claims priority to U.S. Provisional Patent Application 61/277,278, which was filed Sep. 23, 2009 and which is incorporated herein by reference. 
    
    
     COPYRIGHT NOTICE AND PERMISSION 
     A portion of this patent document contains material subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyrights whatsoever. The following notice applies to this document: Copyright © 2009 Engineered Products Company, Inc. 
     TECHNICAL FIELD 
     Various embodiments of the present invention concern pressure switches, particularly low-cost pressure switches suitable for high positive or negative pressures. 
     BACKGROUND 
     Many modern systems include pressure switches, devices that turn on or off electrical circuits in response to sensed pressure conditions. For examples, in automobiles or earth-moving equipment, pressure switches sense engine oil pressure or hydraulic fluid pressure and turn on warning lights and/or shut down the engine in response to particular over- or under-pressure conditions, thereby signaling maintenance needs or preventing irreparable damage. Also, air-braking systems in tractor-trailer trucks employ pressure switches to activate brake lights when a driver steps on the brakes and thus provide brake signal to others. 
     The present inventor has recognized that conventional pressure switches suffer from several problems. For examples, for high-pressure applications many conventional pressure switches use a diaphragm—typically a plastic and/or rubber-like disk that flexes in response to differences in the pressures on its top and bottom sides. However, to endure the corrosive nature of some fluids, the diaphragm must be made of expensive materials. Moreover, to withstand the high pressures of some applications, the diaphragm and/or switch housing must be reinforced with thicker materials and flex-limiting features. The use of the special materials, reinforcements, and flex-limiting features increases the cost of manufacturing these switches and makes them more costly to include in vehicles or other systems that need them. Moreover, even with use of these materials and reinforcements, pressure switches in these environments are shorter lived and less reliable than desired. 
     Accordingly, the present inventor identified a need for better pressure switches, particular pressure switches that are suitable for high positive and negative pressure applications. 
     SUMMARY 
     To address this and/or other needs, the present inventor devised, among other things, pressure switches, assemblies, components, and related methods and systems incorporating these innovations. One exemplary pressure switch includes a low-pressure portion and a high-pressure portion. The low-pressure portion, which is formed of plastic for example, includes an electrical switch that can be turned on or off by moving a movable conductor into or out of contact with a pair of stationary contacts. 
     The high-pressure portion, which is formed of metal for example, has first and second barbed or threaded connector ends, with the first connector end engaging an opening in the low-pressure portion, and the second connector end in fluid communication with an external system. An axial bore extending through the high-pressure portion contains a piston. Extending through the opening in the low-pressure portion, one end of the piston is mechanically coupled to the movable conductor of the electrical switch. 
     The piston travels within the bore in response to positive or negative pressure, thereby moving the movable conductor toward or away from the stationary contacts to open or close the switch. In some embodiments, the axial bore and the piston are configured to prevent the piston from escaping from the high-pressure portion of the pressure switch. Some embodiments also include one or more U-seal O-rings between the piston and the interior surface of the axial bore, as well as one or more calibration springs for biasing piston movement. 
     Notably, the exemplary pressure switch omits a diaphragm and uses a piston instead, thereby avoiding the issues related to limiting diaphragm flexure in high-pressure applications and using costly exotic flexible materials to withstand harsh fluid environments. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional diagram of an exemplary pressure switch  100  corresponding to one or more embodiments of the invention. 
         FIG. 2A  is a side perspective view of an exemplary pressure switch  200  corresponding to one or more embodiments of the invention. 
         FIG. 2B  is a cross-sectional view of exemplary pressure switch  200  corresponding to one or more embodiments of the invention. 
         FIG. 2C  is a perspective view of an exemplary switch module portion of pressure switch  200  corresponding to one or more embodiments of the invention. 
         FIG. 2D  is a perspective view of a terminal portion of the switch module shown in  FIG. 2C  and thus corresponding to one or more embodiments of the present invention. 
         FIG. 3A  is a cross-sectional view of an exemplary pressure switch  300  corresponding to one or more embodiments of the present invention. 
         FIG. 3B  is a perspective cross-sectional view of a push plate portion of pressure switch  300  corresponding to one or more embodiments of the present invention. 
         FIG. 3C  is a cross-sectional view of an alternative switching contact arrangement corresponding to one or more embodiments of the present invention. 
         FIG. 4  is a cross-sectional view of an exemplary pressure switch  400  corresponding to one or more embodiments of the present invention. 
         FIG. 5  is a cross-sectional view of an exemplary pressure switch  500  corresponding to one or more embodiments of the present invention. 
         FIG. 6  is a diagram of an exemplary braking system  600  which corresponds to one or more embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     This description, which incorporates the above-identified figures and appended claims, describes one or more specific inventive embodiments. These embodiments, offered not to limit but only to exemplify and teach one or more inventions, are shown and described in sufficient detail to enable those skilled in the art to implement or practice the invention(s). The description may use terms, such as upper or lower in reference to specific features of various as embodiments; however, unless included in the claims, such terms are merely to aid correlating the drawings with the written description. Moreover, where appropriate to avoid obscuring the invention(s), the description may omit certain information known to those of skill in the art. U.S. Pat. No. 7,414,207 is incorporated herein by reference. 
     Exemplary Pressure Switch Embodiments 
     First Exemplary Pressure Switch 
       FIG. 1  shows a cross-sectional block diagram of an exemplary pressure switch  100  which incorporates teachings of the present invention. Pressure switch  100  includes a switch or terminal module  110 , a low-pressure housing portion  120 , a push plate assembly  130 , a calibration spring  140 , and a high-pressure fitting assembly  150 , all of which are centered on an axis  101 . 
     Switch or connection module  110  includes a pair of terminals or leads  111  for connection to an external electrical circuit (not shown), a switch body  112 , and a pair of contacts  113 . Switch body  112  is permanently or removably seated within a switch-module receiving portion  121  of low-pressure housing portion  120 . 
     Low-pressure housing portion  120 , which in the exemplary embodiment is injection molded from a plastic or nylon material, defines an interior chamber  122  and includes an upper opening  123  and a lower opening  124 . Extending through upper opening  123  into interior chamber  122  are contacts  113 . 
     Push plate assembly  130 , which is contained within chamber  121 , includes a circular plate portion  131  and a central pin portion  132 . Circular plate portion  131  has a diameter less than that of chamber  122  to allow free vertical movement of the push plate assembly within the chamber. Central pin portion  132 , which is integrally molded of a non-conductive material such as plastic or nylon, with plate portion  131 , projects perpendicularly from a central region of plate portion  131  toward upper opening  122  and between contacts  113 . Central pin portion  132  includes a conductive portion  133  which in the exemplary embodiment takes the form of a brass or copper bushing. Centered around central pin portion  132  (and contacts  113 ) is calibration spring  140 . 
     Calibration spring  140  has a lower portion  141  seated against plate portion  131  and an upper portion  142  seated against an upper surface  121 A of chamber  121 . Calibration spring  140  biases push plate assembly  130  toward lower opening  123  in low-pressure housing  120 . Extending through lower opening  123  to engage or contact push plate portion  131  is a piston portion  152  of high pressure fitting assembly  150 . 
     High-pressure fitting assembly  150  includes a high-pressure fitting portion  151  and piston portion  152 . High-pressure fitting portion  151 , which is formed of stainless steel and is generally cylindrical in form in the exemplary embodiment, includes upper and lower connection ends  151 A and  151 B that respectively engage in fluid tight coupling, for example via threads or barbs, with lower opening  124  in low-pressure housing  120  and with an opening in a fluid line of an external system (not shown). Extending through fitting portion  151  is a stepped axial bore  153 , which includes a first diameter portion  153 A and a smaller second diameter portion  153 B, which together define an inner annular shoulder  153 C adjacent to upper connector end  151 A. (In some embodiments, fitting portion  151  is molded of a heavy-duty plastic or nylon material and/or molded integral with lower housing portion.) Positioned within axial bore  154  is piston portion  152 . 
     Piston portion  152 , which is generally cylindrical and longer in its axial dimension than its diameter or width, includes respective first, second, and third diameter portions  152 A,  152 B, and  152 C. First diameter portion  152 A is slightly smaller than the first diameter portion of axial bore  153 ; second diameter portion  152 B is slightly smaller than the second diameter portion of axial bore  153 . The first and second diameter portions  152 A and  152 B together define an outer annular shoulder that prevents passage of piston portion  152  in an upward direction through upper end  151 A of fitting portion  151 . Third diameter portion  152 C is larger than the second diameter of axial bore  154  and is entirely outside the axial bore, limiting downward travel of piston  152  through axial bore  154 . In the exemplary embodiment, piston portion  152  is injection molded from a plastic or nylon material. 
     In normal operation, pressure switch  100  is electrically coupled via contacts  111  to an electric circuit such as a circuit having a battery and a light and/or computer and fluidly coupled via the lower connection end of high-pressure fitting assembly  150  to an external system having a pump coupled via a fluid line to an engine or to one or more pneumatic or hydraulic devices. Piston portion  152  responds to positive or negative pressures in fluid line by moving upwardly or downwardly within axial bore  154 , assuming sufficient pressure to overcome the bias of calibration spring  140 . Movement of piston portion  152  results in movement of push plate  130  and conductive portion  133  toward or away from contacts  113 . Sufficient movement of the piston will result in making or breaking an electrical connection between contacts  113 , depending on the initial position of conductive portion  133 . If the contacts are connected in series with a light and a battery, making the connection results in illumination of the light, and breaking the connection opens the circuit and results in turning off the light. 
     Second Exemplary Pressure Switch 
       FIGS. 2A and 2B  respectively show side perspective and center cross-sectional views of an exemplary pressure switch  200 , which is similar in form and function to pressure switch  100 . Switch  200  includes a low-pressure housing assembly  210 , a switch or terminal module  220 , a push plate assembly  230 , a calibration spring  240 , and a high-pressure fitting assembly  250 , coaxially arranged along a central axis  201 . 
     Low-pressure housing assembly  210 , which includes an upper housing portion  212 , a lower housing portion  214 , and a collar  216 . In the exemplary embodiment, all components of the housing assembly, except for filter  216 B and collar  216  are molded from Clariant Nylon 6/6 (13% Glass Filled.). Filter  216 B is formed of Teflon PTFE, and collar  218  is formed of aluminum, with edge rolled down after assembly of the switch. More particularly, upper housing portion  212 , which is generally horn-shaped in the exemplary embodiment, includes a breather hole  212 BH, a filtration system  212 FS, a switch module receiving portion  212 SMR. Breather hole  212 BH is in fluid communication with the atmosphere via filtration system  212 FS, which includes a dust cover  212 DC and a filter  212 F. Switch module receiving portion  212 SMR includes a vertical sidewall  212 VS surrounding a switch module opening  212 SMO and including a guide fin portion  212 GF, which engages a slot in switch module  220 . Upper housing portion  212  is attached to lower housing portion  214 , for example via a snap fit, defining an interior chamber  213  analogous to interior chamber  122  in  FIG. 1 . 
     Lower housing portion  214 , which in the exemplary embodiment has a generally cup-like structure, includes a sidewall  214 SW and a high-pressure fitting assembly receiving portion  214 RP. High pressure fitting assembly receiving portion  214 RP includes an opening  214 O. 
     Collar  216  encircles the snap-fit interface between upper and lower housing portions  212  and  214  to add further integrity and aesthetic appeal to the switch. Collar  218  includes upper and lower rolled edges  218 A and  218 B. Some embodiments omit collar  216 . 
     Switch or terminal module  220  fits within switch module receiving portion  212 SMR and extends partially through switch module opening  212 SMO into chamber  213 . Switch module  220 , shown in isolation and perspective in  FIG. 2C , includes a terminal pair  224  and upper and lower portions  226  and  228 . (Module  220  is inverted in  FIG. 2C  relative to its orientation in  FIG. 2B .) Terminal pair  224  includes substantially identical non-contacting terminals  224 A and  224 B. Shown best in  FIG. 2D , terminal  224 B includes a terminal pin  224 BA, a terminal pad  224 BB, and a leaf contact  224 BC. (Only the leaf contacts are clearly visible in the cross-sectional view of  FIG. 2B .) Terminal pin  224 BA, which is sized to engage or mate with a female connector (not shown), is formed of half-hardened brass and tin plated. Substantially covering terminal pad  224 BB, leaf contact  234 BC is formed of beryllium-copper and includes a spring portion  224 BD. Insert-molded around terminal pair  224  are upper and lower module portions  226  and  228 . 
     In the exemplary embodiment, switch module portions  226  and  228  are formed of Vydyne Nylon 6/6 22 HSP. Upper portion  226  includes guide hole  226 A and module support  226 B. Lower portion  228  has a sleeve portion  228 A with a notch  228 B, with the sleeve portion extending from the opposite side of the module support. Notch  228 B extends along the length of the sleeve portion and engages, as  FIG. 2B  shows, with guide fin  212 GF in the switch module receiving portion  212 SMR of upper housing portion  212  to ensure alignment of guide hole  226 A with central axis  201 . The module support  226 B is sealed around the prongs (terminals) to prevent contaminants from entering chamber  213  via switch module opening  212 SMO ( FIG. 2B ). 
     In the exemplary embodiment, the terminal-module-to-upper-housing interface is not fluid tight; however, a suitable connector adapted to fit within the module-receiving portion of  214  can seal this portion of the cap and restrict breathing of the chamber to filtration system  212 B. The module structure is also attached to the cap, and the module structure does not move with respect to the housing assembly. 
       FIG. 2B  shows that push plate assembly  230 , which is generally a bell-shaped structure molded from Vydyne 22HSP Nylon, includes an annular wall portion  230 B, a plate portion  230 C, a pin portion  230 D, and conductive bushing  230 E. Annular wall portion  230 B includes an upper brim portion  230 BA. Plate portion  230 C is bounded by annular wall portion  230 B, and positioned intermediate upper brim portion  230 BA and piston receiving fingers  230 F. 
     Analogous to pin portion  132  in  FIG. 1 , pin portion  230 D extends orthogonally from a central region of plate portion  230 C, with the upper end of the pin portion encircled by conductive bushing  230 E. In one embodiment, conductive bushing is positioned closer to the end of the pin to define the switch as a normally open switch, and in another, it is positioned further from the end of the pin to define a normally closed contact. The majority of the length of pin portion  230 D extends through a guide hole  226 A of terminal module  220  and between leaf contacts  224 BC and  224 BD. 
     Upper brim portion  230 BA of the push plate assembly serves as seat for a lower end portion  241  of calibration spring  240 . An upper end portion  242  of the spring contacts an upper surface  213 A of chamber  213 , biasing the push plate assembly downward. An underside of plate portion  230 C includes six circumferentially spaced fingers  230 F which engage with a portion of high pressure fitting assembly  250 . 
     More specifically, high pressure fitting assembly  250 , analogous to high pressure fitting assembly  150  in  FIG. 1 , includes a high-pressure fitting portion  251  and a piston portion  252 . High-pressure fitting portion  251 , which is machined from 303 stainless steel in the exemplary embodiment or molded from a plastic or nylon in some other embodiments, includes upper and lower connection ends  251 A and  251 B and an intermediate hex-nut portion  253 C. Upper and lower connection ends respectively engage in fluid tight coupling, for example via external threads, with lower opening  214 O in lower housing portion  214  and with an opening in a fluid line of an external system (not shown). (An O-ring  255  encircles a lower portion of upper connection end  251 A to further seal opening  214 O.) Extending through fitting portion  251  is a stepped axial bore  253 , which includes a first diameter portion  253 A and a smaller second diameter portion  253 B, which together define an inner annular shoulder  253 C adjacent to upper connection end  253 A. Positioned within axial bore  254  is piston portion  252 . 
     Piston portion  252 , which is generally cylindrical and longer in its axial dimension than its diameter or width, includes respective first, second, and third diameter portions  252 A,  252 B, and  252 C. First diameter portion  252 A fits within the first diameter portion  253 A of axial bore  253  and includes grooves or channels  252 AA and  252 AB for holding respective piston seals  252 AC and  252 AD. 
     In the exemplary embodiment these seals take the form of U-seal O-rings, with the cupped or U-portion facing toward the applied pressure. In normal operation as pressure is applied, the U-seal O-rings are forced to expand and apply a seal against the internal wall of the axial bore (piston chamber). The fitting, which is made of stainless steel and serves as a cylinder or piston chamber, is polished, by for example, electropolishing, roller-burnishing or other polishing technique(s) to eight microns to enhance the life of the seals. Some embodiments form the fitting from brass. Exemplary seal materials include Viton Flourosilicone rubber to withstand automotive chemicals, and HSBN or Buna-Nitrile materials depending on the switch operating environment and the pressures involved. In one embodiment, a Buna seal lasted through 500,000+ cycles. 
     Notably two seals are used on separate channels along the piston for added safety in the event one of them fails. The two seals also function to hold the seal lubricant (dry graphite or synthetic oil) between the seals, which is useful for air-brake system applications at low pressure under very low temperatures. Without lubrication, the seals may stick and prevent immediate function of the switch. 
     In the exemplary embodiment, the piston seal assembly moves approximately 0.25″ for a full stroke of the piston. 
     In manufacturing the switch, the piston assembly is inserted into the pressure fitting from the pressure port side. The piston is inserted up to the point where the piston bottoms out on the shoulder of the fitting. As the piston is held in this position, the (Delrin) Alignment Pin is inserted into the cavity at the protruding end of the Piston. The Piston and Alignment Pin are pressed together and securely locked by an interference fit. Delrin material is desirable because of its easy machinability, its resistance to temperature extremes, and its low frictional resistance. 
     The alignment pin also serves the function of seating with the six fingers of the Pushpin/push plate. The two seals also help to maintain the alignment of the piston within the fitting so that in some embodiments the seal is the only portion of the piston assembly in contact with the side walls of the Fitting, further helping to reduce friction. In the exemplary embodiment, having the piston and alignment pin locked together helps maintain alignment of the central pushpin with the switch module. In conventional designs having a diaphragm, the diaphragm would provide this function. 
     In this figure, the U-seals O-rings are oriented downward; second diameter portion  252 B fits within the second diameter portion of axial bore  254 . The first and second diameter portions  252 A and  252 B together define an outer annular shoulder that prevents passage of piston  252  in an upward direction through upper end  253 A. 
     Third diameter portion  252 C is larger than the second diameter of axial bore  253  and is entirely outside the axial bore, limiting downward travel of piston  252  through axial bore  254 . In the exemplary embodiment, the third diameter portion is formed separately as a plunger shape that can be glued or press fit into an axial bore within the second diameter portion  252 B. In the exemplary embodiment, piston portion  252  is injection molded or machined from a plastic or nylon material, such as Delrin plastic 
     Third Exemplary Pressure Switch 
       FIG. 3A  shows a cross-sectional view of an exemplary pressure switch  300 , which is structurally and functionally similar to switches  100  and  200 , with the exception that switch  300  includes a low friction switch configuration  310  and high-pressure fitting assembly  320  includes a barbed fitting on the upper connection end that mates with the lower portion of the low pressure housing assembly. 
     Low friction switch configuration  310  is similar to the switching arrangement in switch  200  comprising leaf contacts  224 BC and  224 BC and conductive bushing XXX, except that leaf contacts  312 A and  312 B are spaced to avoid constant contact with central pin  314  and the conductive bushing has been replaced with a larger flanged conductive bushing  314 . The flange in this embodiment is optional; however, it facilitates handling and installation of the bushing during manufacture.  FIG. 3B  shows a cross-sectional perspective view of flanged conductive bushing  314  mounted to central pin of the push plate.  FIG. 3C  shows another alternative leaf contact and conductive bushing configuration, where the leaf contacts are curved or arcuate. 
     Fourth Exemplary Pressure Switch 
       FIG. 4  shows a cross-sectional view of an exemplary pressure switch  400 , which is structurally and functionally analogous, to switches  100 ,  200 , and  300 , with the exception that switch  400  includes an alternative barbed pressure fitting assembly  410 . In particular, pressure fitting assembly  400  includes a piston portion  412  having a central post or projection  412 A at lower connection end  414  of the fitting assembly. Additionally, a conical bias spring  416 , the smaller end of which engages post  412 A, is sandwiched between piston end face  412 B and a hex set screw  418 . 
     In operation, bias spring  416  and hex screw allow one to adjust the make or break pressure set point of the switch. 
     Fifth Exemplary Pressure Switch 
       FIG. 5  shows a cross-sectional view of an exemplary pressure switch  500 , which is structurally and functionally analogous, to switch  400 , with the exception that switch  500  includes an integrally molded lower housing and high pressure fitting portion  510 , combining the two parts into one for further cost savings. In the exemplary embodiment, this integrated housing and fitting is formed of non-filled nylon. 
     Exemplary Systems 
     The exemplary pressure switches, components, and operating methods thereof can be used in wide variety of applications, such as air-braking systems, fuel systems, and hydraulic and pneumatic systems.  FIG. 6  shows an exemplary air-braking system  600  which has a normal pressure of 120 PSI and which includes four pressure switches  610 ,  620 ,  630  and  640 , each of which incorporates the teachings of pressure switches  100 ,  200 ,  300 ,  400  and/or  500  described above. The respective set or trip points for pressure switches  610 ,  620 ,  630 , and  640  are 65, 5, 77, and 85PSI. 
     There is minor oil, less than 1%, mixed within the air brake system. Typically this application will operate at −40 deg. F. to 160 deg. F. Dry Graphite has been added as a lubricant to the fitting assemblies of each of the switches to enhance function at these very low temperatures. Additionally, system  600  includes a representative electrical circuit  650  which is coupled to the contacts of pressure switch  620 . Circuit  650  includes a battery  651  (or other electric power source) and an indicator light or a computer  652  coupled in series with the contacts of pressure switch  620 . 
     In operation, each time a brake pedal (foot valve or other brake actuator) in this semi-truck air-brake application is depressed (actuated), the pressure in the air-brake system rises from zero PSI up to 5PSI, moving piston portion of the pressure switch and the pushpin conductor toward the stationary contacts. When the pressure reaches 5PSI, the pushpin conductor contacts the stationary contacts completing circuit  650  and turning on the trucks rear brake lights, i.e., indicator lights  652  and/or causing communication of a logic signal to the computer. 
     This is a safety system with regulations requiring the switch to function very quickly; the exemplary switch turns on before the pressure reaches 6PSI. The exemplary switch must be able to handle a life expectancy of 1.5 million cycles. Conventional switches in the market are unable to achieve this many cycles. 
     Exemplary Advantages 
     One or more of the exemplary embodiments includes or provides one or more of the following features, advantages, or attributes:
         1. High positive and negative pressures are contained within the fitting, keeping fluid and pressure from the more delicate components in the switch portion of the assembly. The fitting effectively serves as high pressure portion of the housing, which allows the remaining portion of the housing to have a less rugged plastic construction.   2. The architecture of the design, which includes a housing that receives separate switch subassembly (or module) and a separate fitting (or switch actuation) subassembly allows for mixing and matching of different switch subassemblies with other fittings or switch subassemblies easily, thus allowing a variety of pressure switch variations at different switch point settings.   3. The exemplary switch includes sliding contacts which in operation keep electrical contact surfaces clean of oxidation and other contaminants. (tested with 1 ts Arizona Dust, also tested with ½ ts dry graphite)   4. The piston is able to handle high amounts of dirt and debris with self cleaning action of the seals. (Tested with ¼ ts of Arizona Dust and large grain sand)   5. The piston assembly contains two U-seals for added leak prevention. Further O-ring seal can be added on the plunger end of the Piston to further prevent any leaks occurring when piston is over-pressurized.   6. The fitting is self contained in that if the switch portion of the assembly broke off or the housing were breached in an accident, the system pressure would not be lost and potentially volatile fluid would not be lost to the atmosphere.   7. The fitting subassembly effectively replaces 1″ diameter diaphragm (effective area 0.785 sqin.) with a 0.310″ diameter piston (effective area 0.075 sqin.). This change in effective area effectively uses the same spring force of a lower diaphragm switch to equal a higher force on the new switch. The pressure of the new switch would be ˜10.5× using the same spring as it would be for use in the diaphragm switch.   8. The exemplary switch assembly has a wide pressure range. It can switch at pressures as low as 2-3 PSI switching function and greater than 5,000 PSI. Because all high pressures are contained in the fitting the pressures this switch can withstand are very large. When the piston is pressurized beyond normal operating pressures, the piston will bottom out against the inner shoulder of the fitting, effectively isolating these high forces from the push plate, pushpin, and switch module, thus preventing damage to the switch.       

     CONCLUSION 
     The embodiments described above are intended only to illustrate and teach one or more ways of practicing or implementing the present invention, not to restrict its breadth or scope. The actual scope of the invention, which embraces all ways of practicing or implementing the teachings of the invention, is defined only by the following claims and their equivalents.