Abstract:
In an electronic sensor having a spool with a bore therein for receiving a pole and a magnet adjacent to the pole and a magnet wire wound around the spool forming a coil and the ends of the magnet wire are each coiled around respective electrically conductive legs of a terminal for electrical output from the coil to an external circuit, the legs of the terminal are provided with bumps or protuberances stamped thereon. The bumps have a height greater than the thickness of the magnet wire to protect the magnet wire during installation of a housing covering.

Description:
FIELD OF THE INVENTION 
     The invention relates to electronic sensors, and more particularly to protection of the terminals and wires on electronic sensors. 
     BACKGROUND OF THE INVENTION 
     Electronic sensors, and more particularly, variable reluctance sensors are well known and used in automotive applications such as brake systems, cruise control systems, transmission systems, as well as others. In general, variable reluctance sensors include a bobbin or spool assembly having a non-metal spool which houses magnetic elements and magnet wire. The magnet wire is coiled about a barrel portion of the spool. The end wires of the magnet wire are wrapped around terminal legs for electrical output to an external circuit. The spool assembly is then encapsulated within a metal or plastic housing. The encapsulating process includes sealing the magnetic elements and magnet wire from liquid intrusion, so that the variable reluctance sensor is protected in its environment on the vehicle from corrosive liquids, splash, spill, or other debris. During the encapsulating process, a cap is slid over the spool assembly and the end wires wound around the terminal legs. As the cap slides over the end wires, the wires may be inadvertently damaged or scuffed by the moving cap. A damaged magnet wire can result in an “open circuit” failure condition. Variable reluctance sensors are required to have a reliability and a design life to match warranty target periods of 100,000 to 200,000 miles of the associated vehicle. Failure of the variable reluctance sensor may result in poor engine performance of the vehicle. Consequently, there is a need for designing the variable reluctance sensor, and especially the terminal of the variable reluctance sensor so that the end wires are not damaged upon installation of the cap. 
     SUMMARY OF THE INVENTION 
     The invention is an improvement to an electronic sensor having a spool assembly. The spool assembly includes a spool with a cavity therein for receiving a pole piece and a magnet adjacent the pole piece. A magnet wire is coiled around the spool. Each end of the magnet wire is coiled around a respective electrical conductive terminal leg for electrical output from the coil to an external circuit. A cap slides over the spool assembly and the terminal legs for sealing the components from liquid and debris. The improvement to the electronic sensor includes bumps or protuberances stamped onto the terminal legs. The bumps or protuberances have a height greater than the diameter of the wire or bundle of wires coiled around the terminal leg. 
     Other applications of the present invention will become apparent to those skilled in the art when the following description of the best mode contemplated for practicing the invention is read in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein: 
     FIG. 1 is a perspective view of a portion of a variable reluctance sensor showing a cut-away portion of a cap for sealing the sensor and other characteristics in accordance with the principal of the present invention; 
     FIG. 2 is an enlarged sectional view of a portion of the sensor showing the cap installed over portions of a terminal of the sensor; and 
     FIG. 3 is a front cross sectional view of a conventional fully assembled variable reluctance sensor. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring initially to FIG. 3, there is shown a conventional electronic sensor, and more particularly a variable reluctance sensor  10 . The sensor  10  is shown connected to a conventional electronic harness  12  which ultimately communicates with an exterior circuit (not shown). The sensor  10  includes a bobbin or spool assembly  14  including a spool portion  16  having a barrel  18  around which magnet wire  20  is wound. The magnet wire  20  may be wound as a single strand or as a bundle of wire strands. The spool barrel  18  is generally de-limited at its opposite ends by bottom and top flanges  22 ,  24  respectively. Axially extending completely through the spool barrel  18  and beyond the flanges  22 ,  24  is a bore  26 . In the illustrated embodiment of a conventional sensor  10  shown in FIG. 3, a magnet  28  is disposed within the innermost portion of the bore  26 . A pole piece  30  is inserted through the spool bore  26  to the magnet  28 . The pole piece  30  is preferably constructed of mechanically and magnetically soft ferrous material. The pole piece  30  may include a reduced end  32  at the distal end, spaced from the magnet  28 . The pole piece  30  may be exposed from the housing cover or cap  34 . 
     The magnet wire  20  is wound around the length of the spool barrel  18  between the bottom and front flanges  22 ,  24  to form a coil. The start and finish wire end sections  36  are each wrapped around individual terminal legs  38  of terminals  40  which are molded onto the spool barrel  18 . The wire end sections  36  and the terminal legs  38  are soldered together in a dip solder process. On the opposing ends of the terminals  40  from the terminal legs  38  are connector ends  42 , which are adaptable for connection to an external circuit via the electronic harness  12 . The connector ends  42  may be crimped as shown in FIG. 1 for connection to the electronic harness  12 . 
     After the magnet wire  20  coil is attached to the terminal legs  38 , the terminal legs  38  are moved in the direction A shown in FIG. 2 to place the terminals legs  38  parallel to the spool barrel  18 . After the magnet  28  and pole piece  30  are inserted within the spool bore  26 , the spool assembly  14  is ready to receive the sensor housing or cap  34 . 
     The hollow sensor housing or cap  34 , is preferably made of a thermoplastic resin. The housing or cap  34  is generally a cylindrical body having an opening  44  at one end  46  for receiving the spool assembly  14  and preferably a smaller opening  48  at the opposing end  50  for receiving a portion of the pole piece  30  therethrough. The housing or cap  34  may also include a generally threaded cylindrical exterior portion  52  for connection to a harness holder  54  or other connector communicating with an outside circuit. 
     The sensor housing or cap  34  is mounted by sliding the cap  34  over the spool assembly  14  until the first end  46  of the cap  34  comes into contact with an expanded stop flange  56  on the spool assembly  14 . As can be seen in FIGS. 1 and 3, the area between the exposed surface  62  of the terminal and the cap interior  58  is minimal. In the prior art, as the cap  34  was being installed over the terminals legs  38 , the magnet end wire sections  36  were susceptible to be frayed or otherwise damaged by the frictional force of the interior surface  58  of the cap  34  against the wires end sections  36 . 
     The improvement to the electronic sensor  10  is shown more clearly in the schematics of FIG.  1  and FIG.  2 . The terminal legs  38  according to the present invention, have bumps or protuberances  60  formed on the terminal surface  62  exposed to the interior surface  58  of the cap  34 . There is at least one but preferably two or more bumps or protuberances  60  on each terminal leg  38 . The bumps or protuberances  60  are preferably stamped into the terminal leg  38  in a one step process during the manufacturing of the terminals  40 . The bumps  60  have a height (H) at least slightly greater than the thickness or diameter of the single strand or bundle of magnet wire  20  wound around the terminal legs  38 . The height (H) of the bumps  58  is equal to or slightly less than the clearance allowance between the interior surface  58  of the cap  34  and the exposed terminal surface  62  of the terminal legs  38 . The addition of the bumps  60  enables the cap  34  to be mounted over the spool assembly during the encapsulating process without interfering with the wire end sections  36  and thus prevents damage to the magnet wire  20 . 
     The bumps  60  are preferably spaced from each other to allow at least one coil of the magnet wire  20  to be disposed between adjacent bumps  60 . It is also preferred to position a first bump  60   a  (as shown in FIG. 1) proximate to each of the free ends  64  of the terminal legs  38 . The distance between the free end  64  of the terminal leg  38  and the first bump  60   a  allows a few conventional coil wraps of the end wire section  36  therebetween. A second bump  60   b  in axial alignment of the first bump  60   a  on the terminal leg  38  is preferably spaced from the first bump  60   a  to allow a diagonal coil wrap of the magnet wire  20  therebetween. Subsequent bumps  60   c  on the terminal leg  38  are positioned in axial alignment to the second bump  60   b  and spaced from the second bump  60   b  and adjacent subsequent bumps  60   c  to allow one or more conventional coil wraps of the end wire sections  36  of the magnet wire  20  therebetween. As shown in FIGS. 1 and 2, the spacing between the first bump  60   a  and second bump  60   b  is greater than the spacing between the second bumps  60   b  and subsequent bumps  60   c.    
     This configuration of the alignment of bumps  60  on the terminal leg  38  allows the wire end sections  36  and terminal legs  38  to be soldered together at the free ends  64  in a dip solder process but allows the remainder portion of the magnet wire  20  on the terminal legs  38  to remain unsoldered and thereby permits expansion and contraction of the magnet wire  20  at its own rate during thermal cycling of the electronic sensor  10 . In the prior art, if the solder was not accurately applied, the solder could over extend onto most of the wire end sections  36  and terminal legs  38 , which would inhibit the expansion and contraction of the magnet wire  20 . Therefore, the placement of the bumps  60  on the terminal leg  38  provides a guide for the application of the solder. 
     The manufacturing process of the terminal  40  and especially relating to its terminal legs  38  eliminates steps taken in the prior art during the assembly of the variance reluctance sensor  10  to protect the magnet wire  20 . Since the bumps  60  are preferably stamped onto the terminal legs  38  in a one step process during the manufacturing of the terminals  40 , the assembly process of the electronic sensor  10  is not hindered or encumbered by requiring further additional steps to protect the magnet wire  20  and terminals  40 . 
     Although the improvement to the terminal of a sensor is illustrated in the environment of the variable reluctance sensor  10  as shown in the figures, the bumps or protuberances  60  as disclosed may be added to the terminal legs of any electronic sensor embodiment utilizing coiled magnet wire  20 . Further, while the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit. and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.