Abstract:
A modular reed switch assembly and method for making the same are provided. A switch assembly ( 101 ) includes a reed switch ( 206, 106 ) that is enclosed between a primary reed switch cover ( 208 ) and a reed switch base ( 104 ) wherein the reed switch cover and reed switch base are recessed to accommodate the reed switch. A secondary reed switch cover ( 102 ) further covers the primary reed switch cover ( 208 ) and the secondary reed switch cover ( 102 ) connects with the reed switch base ( 104 ). A protrusion ( 106 ) provides access to the electrical contacts ( 302 ) of the reed switch ( 206, 106 ) through the primary reed switch cover ( 208 ) and secondary reed switch covers ( 102 ).

Description:
RELATED APPLICATION 
     This application claims priority under 35 U.S.C §119(e) of U.S. Provisional Application No. 60/327,246 filed on Oct. 5, 2001, the entire contents of which are herein incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to switch assemblies. More particularly, a modular reed switch assembly and method for making utilizes a compliant material that is able to dampen vibrations seen by the reed switch. This helps reduce reed switch failures due to high vibration levels and other environmental factors. 
     BACKGROUND OF THE INVENTION 
     There are many commercial and military applications of reed switches. One specific application is the use of a reed switch to provide valve position feedback information on aircraft. However, a known problem with reed switches is a predisposition towards failing in the high vibration environments that aircraft encounter during operations. Rotating equipment such as motors, engines, actuators and gearing can all generate vibrations and introduce other harmonic disturbances that can cause numerous problems with reed switches and cause them to fail. Deleterious consequences such as switch bounce and hot latching are very environmentally sensitive phenomena, where small changes in response characteristics or differing vibration inputs can significantly affect ultimate performance. 
     One particular application of the reed switch is to provide a positive indication of the status (e.g., open or closed) of a fuel valve that regulates the flow of fuel to an engine. If mechanical latching or sticking occurs between the electrical contacts of a reed switch, an indicator may yield a faulty reading indicating a disagreement or mismatch between an intended command and a valve position. 
     Therefore, it is desirable to have a reed switch assembly that can operate in hostile environments and eliminate or reduce the harmful effects of the operational environment, such as vibration, upon reed switch operation. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, the deficiencies in prior systems are overcome by providing an improved modular reed switch assembly and a method for making the same. 
     A modular reed switch assembly includes a reed switch that is enclosed between a secondary reed switch cover and a reed switch base. The reed switch base is recessed to accommodate the reed switch. The reed switch is further enclosed between a primary reed switch cover and a main housing wherein the primary reed switch cover and the main housing are recessed to accommodate the switch assembly containing the reed switch. A protrusion provides access to the electrical contacts of the reed switch through the primary and secondary reed switch covers. 
     The secondary reed switch cover and the reed switch base snap together around the reed switch. The mating surfaces of the secondary reed switch cover and the reed switch base snap together and form an integrated whole surrounding the reed switch. The material used to enclose the reed switch is compressed upon installation around the reed switch. The material used to enclose the reed switch is a compliant material and has a durometer rating. The material selected can be Viton® or Fluorosilicone®. The material used, as well as any rubber used, yields durometer value (D) ranges from a high value of about 75 D average to a low value of about 55 D average. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete understanding of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a schematic illustration of a perspective view of the reed switch assembly prior to mounting in the main housing; 
     FIG. 2 is an exploded view of the switch of FIG.  1  and how it interfaces with the main housing to form the integrated modular reed switch assembly; 
     FIG. 3 is a sectional view of the modular reed switch assembly; 
     FIG. 4 is another sectional view of the modular reed switch assembly; and 
     FIG. 5 is a flow diagram of a method for making the reed switch assembly. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Aspects of the invention are disclosed in the accompanying description with reference to the attached figures. 
     One embodiment of the present invention is shown in FIG.  1 . In FIG. 1, a reed switch assembly  101  is shown prior to mounting of the reed switch assembly in the main housing. A secondary reed switch cover  102  fits over a reed switch base  104 . The secondary reed switch cover  102  fastens together with the reed switch base  104  in a snap together manner, with interlocking tabs  107  and  108  snapping into slots  109  and  111  respectively. Those skilled in the art will realize that other fastening mechanisms can be used to fasten the components together. 
     In FIG. 1,  110  represents an opening through the secondary reed switch cover  102  through which a fastener can be inserted through the opening and connecting the secondary reed switch cover  102  to a main housing  210  that is shown in FIG. 2. A hole  105  in the secondary reed switch cover  102  allows a protrusion  106  to pass through so that the electrical connectors connecting with the reed switch may be routed through this protrusion as it passes through the secondary reed switch cover  102 . In this embodiment, the reed switch is considered to include the reed switch  206 , the circuit board, the electrical connectors and the protrusion  106  that the connectors to the reed switch pass through. This protrusion  106  is part of the reed switch  206  and is shown in FIG.  2 . The reed switch itself cannot be seen in FIG.  1 . However, the specific location and orientation of the reed switch  206  is shown in FIGS. 2,  3  and  4 . 
     The secondary reed switch cover  102  and the reed switch base  104  can be made from any materials that possess good vibration dampening and isolation capabilities. Another consideration is the compressibility of the material selected, because it is this material characteristic that will help to secure and seat the reed switch. Upon the installation of the reed switch  206  between the secondary reed switch cover  102  and the reed switch base  104 , the material that makes up the secondary reed switch cover  102  and the reed switch base  104  compresses around the reed switch  206  to secure the switch and provide vibration damping characteristics. 
     One exemplary embodiment of the present invention can use rubber as this vibration dampening material. Any type of aerospace grade rubbers can be used to form the secondary reed switch cover  102  and the reed switch base  104 . Specific examples of appropriate materials are Viton® and Fluorosilicone®. Materials with a higher durometer rating are especially well suited for implementing the present invention. Favorable results have been achieved with materials and rubbers yielding durometer value (D) ranges from a high value of about 75 D average to a low value of about 55 D average. The specific design application and anticipated operational environment, such as vibration levels, are factors to consider when selecting an appropriate durometer rating for a material used to enclose a reed switch operating under the vibration levels encountered during a given operational scenario. 
     The switch assembly shown in FIG. 1 is fastened with a main housing  210  shown in FIG.  2  and comprises the modular reed switch assembly. 
     In FIG. 2, the reed switch  206  is shown in relation to the reed switch base  104  and a primary reed switch cover  208 . The reed switch base  104  has a recess  113  where the reed switch  206  is set into. The primary reed switch cover  208  has a recess  117  that surrounds and encloses the top of the reed switch  206 . Incidentally, magnetically actuated reed switches are well known to those skilled in the art and therefore a detailed description of the reed switch itself and its construction will not be provided. 
     The primary reed switch cover  208  also has a hole  209  in the top to allow the protrusion  106  to pass through it to provide an opening for the electrical connectors of the reed switch  206  to pass through and provide connectivity and access to the interior of the switch assembly. The reed switch base  104  then fits into a recess  212  in the main housing  210 . There should be no gap between the reed switch base  104  and the main housing  210  that requires shimming. However, if the tolerances between the surfaces are such that a gap does exist, then a shim(s) can be used to maintain a maximum force margin between the reed switch base  104  and the main housing  210 . 
     The secondary reed switch cover  102  fits over the protrusion  106  and is then fastened down onto the main housing  210  using fasteners  202 ,  203 , and washers  204  and  205 . The fasteners fasten into the holes  214  and  216  shown in the main housing  210 . 
     In FIG. 3, a sectional view of the modular reed switch assembly is shown. The reed switch  206  is located between the primary reed switch cover  208  and the reed switch base  104 . The switch assembly  101  fits into a recess  212  located in the main housing  210 . Fasteners  202  and  203  fasten together the switch assembly with the main housing  210 . Electrical connectors  302  of the reed switch  206  are shown passing through the protrusion  106 . As mentioned earlier, this protrusion provides the electrical connection means between the switch and an external device connected to the switch enclosed in the modular reed switch assembly. 
     In FIG. 4, another sectional view of the modular reed switch assembly is shown. The reed switch  206  is enclosed between the primary reed switch cover  208  and the reed switch base  104 . This portion of the switch assembly  101  fits into a recess  212  located in the main housing  210 . Fasteners  202 , and  203 , and washers  204  and  205  fasten together the switch assembly with the main housing  210 . These fasteners fasten into two holes  214  and  216  located on the main housing  210 . Electrical connectors  302  of the reed switch  206  are shown passing through the protrusion  106 . Again, this protrusion (the protrusion  106  is actually a protective sleeving, the conductors,  302 , provide the electrical connection) provides the electrical connection means between the switch and an external device connected to the switch encased in the modular reed switch assembly. 
     Those skilled in the art will realize that there are various combinations of materials that may be used to construct the modular reed switch assembly. Factors such as the vibration environment, reed surfaces and performance history should all be considered when evaluating a design. 
     According to another embodiment of the present invention, a method of making the aforementioned modular reed switch assembly is also described. FIG. 5 depicts a flow diagram showing a method for making the reed switch assembly. In step  502  a compliant material is selected to enclose a reed switch. In step  504 , the reed switch is enclosed in the compliant material that was selected in step  502 . In step  506 , the product that resulted from step  504  (a reed switch enclosed in a compliant material) is further enclosed into a modular assembly. 
     More particularly, a reed switch  206  is mounted between a primary reed switch cover  208  and a reed switch base  104 . Both the primary reed switch cover  208  and the reed switch base  104  have recesses that have been hollowed out to accommodate and enclose the reed switch  206 . The material selected for the cover and the base should be compressible and compliant. This forms a secure mount for the enclosed reed switch. This switch assembly  101  is then seated in a recess of a main housing  210  and covered by a secondary reed switch cover  102 . Both the primary reed switch cover  208  and secondary reed switch cover  102  provide access for connecting an external device to the electrical connectors  302  of the reed switch  206 . The secondary reed switch cover  102  and the reed switch base  104  snap together around the reed switch  206 . The mating surfaces of the secondary reed switch cover  102  and the reed switch base  104  snap together and form an integrated whole surrounding the reed switch  206 . The present invention can be used with or without shims to provide optimum compression of the compliant material. An optimum compression is one that best achieves a desired objective given a set of operational, environmental and design constraints. The material used to enclose the reed switch is compressed upon installation around the reed switch. The material used to enclose the reed switch is a compliant material and has a durometer rating. The material used to enclose the reed switch can be an aerospace grade material.