Abstract:
A proximity sensor is carried within a small diameter package and includes a magnet for providing a desirable magnetic field for operation of proximity sensing circuitry carried along a central axis to allow for a maximum sensor signal output with no change due to a relative rotation angle between the sensor and a target being monitored. Electrical contact pins include an offset positioned near the central axis for permitting a desirable small gauge insulated wire to be connected the sensor.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of U.S. Provisional Application having Ser. No. 60/524,799 for Offset Compensated Position Sensor, and U.S. Provisional Application having Ser. No. 60/524,919 for Minimized Cross-Section Sensor Package, both having filing date Nov. 25, 2003, the disclosures of which are herein incorporated by reference in their entirety, both commonly owned with the instant application. 

   FIELD OF THE INVENTION 
   The present invention relates to magnetic sensors and more particularly the packaging of said sensor to reduce package size and cost while providing optimum circuit sensitivity and improving durability. 
   BACKGROUND OF THE INVENTION 
   Sensing devices which are used to measure proximity or displacement of an object in a mechanical system are common in industry. As mechanical systems become more complex and costly there has developed a need to reduce the overall sensor package size and cost. Many mechanical systems employ sensors that detect the movement of a magnetically permeable object that is positioned in front of the sensor package. This patent addresses this type of configuration where it is necessary to insert or mount a sensor with a cylindrical package in an confined area and said sensor is required to detect the presence of an object that is moving in front of it. This sensor must have its sensing element located in the package such that it is perpendicular to the length of the package and positioned such it and the magnet are in close proximity to the target to allow for maximum sensitivity. Additionally the wires used to make external connections must be confined within the diameter of the sensor package. 
   Conventionally most magnetic sensors utilize a pre-packaged sensing element. For applications where size is not a consideration a prepackaged device is appropriate as handling the bare die can be costly. This prepackaged sensing element is placed into a larger assembly which then requires an even larger package to house the components. Complexity, size, durability, and cost are all issues for these types of sensors. 
   There have been attempts to simplify the packaging using unpackaged sensing elements but they fall short of addressing all the aforementioned criteria. 
   This patent provides for a sensor package that is designed in such a way that it provides for a minimum of parts thereby reducing the complexity and cost, provides for a unique configuration thereby reducing size while maintaining optimal sensitivity, and using materials that compliment and support each other providing for extreme durability. 
   SUMMARY OF THE INVENTION 
   A sensor according to the present invention may include an elongate magnet having a planar top surface at a proximal end, the planar top surface generally orthogonal to a central axis of the elongate magnet extending to a distal end, and a side wall extending therebetween, proximity sensing circuitry carried directly on the flat surface, the proximity sensing circuitry having at least two bond pads for providing an electrical connection therewith, the proximity sensing circuitry having a sensing element aligned along the central axis for providing a desirable sensor signal output independent of a rotation about the central axis, at least two nonmagnetic, electrically conductive elongate pins extending generally parallel to the central, the at least two elongate pins in a spaced relation to the side wall of the magnet, each of the at least two elongate pins having a proximal end proximate each of the at least two bond pads and a wire connection therebetween, wherein a distal end of the at least two elongate pins includes an offset extending around the magnet distal end and inward toward the central axis, and insulated conductive wires connected to each of the offsets and having at least a portion thereof extending along away from the magnet generally along the central axis thereof. 
   Each of the surfaces of the proximal ends of the at least two elongate pins and each of the at least two bond pads may have the wire connection therebetween lying within a common flat plane extending perpendicular to the central axis. A girth dimension for each offset may be greater than a girth dimension for each elongate pin, thus allowing a smaller gauge connection for each insulated wire to be connected thereto. In one embodiment, a first encapsulation secures the at least two electrically conductive elongate pins in a fixed position relative to the magnet and an enclosing thereof. Alternatively, a second encapsulation may enclose the proximity sensing circuitry and the first encapsulation therein while having only the insulated wires extending therefrom. 
   One embodiment of the invention may include a cylindrical sensor package that has its internal components and materials optimally configured and orientated as to maximize circuit sensitivity, and providing a minimized cross section for use in a mechanical systems which has limited space. The sensor package may contain an sensing element that is mounted directly to the center of a magnet then both are aligned so they are optimally placed in the center of the radial axis of the cylindrical sensor package to allow for the maximum sensor signal output with no change due to the relative rotation angle between the sensor and the target being sensed. 
   Electrical contact pins are shaped and positioned to make a connection from the sensing element at the front of the package to the external connecting wires at the opposite end. These pins may be made of a nonmagnetic material as not to cause interference with magnetic field and can be arranged in an circular manner around the sensing element and magnet to maintain an optimal small diameter package. 
   A molding process may be used to encapsulate the assembly providing the final cylindrical shape and giving the assembly a hermetic seal and protection from a harsh environment. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a fuller understanding of the invention, reference is made to the following detailed description, taken in connection with the accompanying drawings illustrating various embodiments of the present invention, in which: 
       FIG. 1  is a partial perspective view illustrating a sensor having an outer encapsulation with the sensor orientated toward a target; 
       FIG. 2  is a partial side elevation view of a sensor illustrated without an inner or outer encapsulation for describing position, configuration, and connection of components; 
       FIG. 3  is a partial top plan view of the sensor without the outer encapsulation illustrating element alignment by way of example; 
       FIG. 4  is a perspective view of one conductive pin useful with the embodiments herein described, by way of example; 
       FIG. 5  illustrates an alternative embodiment for configuring the conductive pins; 
       FIG. 6  is a partial perspective view of a sensor illustrating an alternate pin arrangement; and 
       FIG. 7  is a partial side elevation view of the sensor with the inner encapsulation applied. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout, and prime notation is used to indicate similar elements in alternate embodiments. 
   By way of example, mechanical systems such as internal combustion engines usually contain a significant number of moving objects. For instance, there are usually multiple cylinders in diesel engines utilizing fuel injectors each containing a moving valve or other object that must be monitored for efficient or safe operation. Each injector requires a separate sensor that is wired to a remotely located monitoring system. Referring initially to  FIG. 1 , a sensor  10  is herein described, by way of example, for monitoring a moving object  12 , such as a portion of the fuel injector described above, with the sensor having a housing  14  desirably shaped and having its operating components sealed within the housing. Desirably large (small gauge) insulated wires  16 ,  18  extend from an aft portion of the housing  14  to allow the sensor to be conveniently and effectively located close to the object  12 . By way of the example herein described, the sensor  10  may have a cylindrical shaped housing  14  for locating the housing within a drilled out cylindrical bore within an engine block. 
   With reference now to  FIG. 2 , there is illustrated one orientation and configuration of the sensor  10  according to the present invention that includes an elongate magnet  20  having a planar top surface  22  at a proximal end  24 . The planar top surface  24  is generally orthogonal to a central axis  26  of the elongate magnet  20  extending through a distal end  28 . A side wall  30  extends therebetween. Proximity sensing circuitry  32  is carried directly on the flat planar top surface  22 . As illustrated with reference to  FIG. 3 , the proximity sensing circuitry  32  has at least two bond pads  34 ,  36  for providing an electrical connection therewith. A sensing element  38  is aligned along the central axis  26  for providing a desirable sensor signal output independent of a rotation about the central axis  26 . At least two nonmagnetic, electrically conductive elongate pins  40 ,  42  extend generally parallel to the central axis in a spaced  44  relation to the side wall  30  of the magnet  20 . Each of the pins  40 ,  42  has a proximal end  46  proximate each of the two bond pads  34 ,  36  and a wire connection  48  therebetween. A distal end  50  of the pins includes an offset  52 ,  54  extending around the magnet distal end  28  and inward toward the central axis  26 . The insulated conductive wires  16 ,  18  as above described, are connected to each of the offsets  52 ,  54 . At least a portion  56  of the wires  16 ,  18  extend away from the magnet generally along the central axis  26 . As illustrated with continued reference to  FIG. 2 , a girth dimension for each offset  52 ,  54  is greater than a girth dimension for each elongate pin portion  40 A,  42 A extending generally along the axis  26 , thus allowing a smaller gauge connection  58  for each insulated wire  16 ,  18 . 
   For the embodiment herein described by way of example, the proximity sensing circuitry  32 , a sensor chip, includes a sensor chip orientated so that the sensing element  32  is orientated in the direction of the sensor face  60  and thus the object  12  along the central axis  26 , as illustrated with reference again to  FIGS. 1–3 . The sensor chip  32  may be attached to the magnet  20  with thermally conductive epoxy. The size, shape and position of the magnet  20  is such that it will deliver a maximum magnetic field to the sensing element  38 . For the embodiment herein described, no mounting substrate is used between the magnet  20  and the sensor chip  32 . This reduces the package length and provides for maximum magnetic field to the sensing element  38  and the object (a target)  12 . If necessary to prevent shorting, a coating may be applied to the magnet  20  to insulate it from the sensor chip  32  or other components. 
   The conductive pins  40 ,  42  are used to deliver the sensor chip signal output to the insulated wires  16 ,  18 . For the embodiment herein described, the pins  40 ,  42  are made from a non-magnetic material so that during assembly of the sensor components, the magnet  20  will not move the pins out of position or cause the magnet itself to move out of position. In addition, the pins  40 ,  42  will not interfere with the magnetic field of the magnet  20 , and cause a disruption of the magnetic field, reducing the sensor sensitivity and measuring range. 
   As illustrated with reference again to  FIG. 2 , and to  FIG. 4 , a pin wire bonding surface  62  is flat so that the wire connection  48  may be made using standard wire bonding methods such as thermal compression. This pin wire surface  62  is in the same plane as the sensor chip bonding pads  34 ,  36  so that the wire bonds will be short, for providing a reduced package length, increasing the sensor sensitivity, with the amount of wire loop low, to reduce the potential of wire bond failure. 
   As above illustrated with reference to  FIG. 2 , the conductive pins  40 ,  42  runs along the side of and terminate behind the distal end  28  of the magnet  20  in a manner that keeps the overall package girth (diameter for the cylindrical embodiment herein described by way of example) optimized to a minimum. As above illustrated, the pins  40 ,  42  are used to provide a connection between the proximity sensing circuitry  32  to the insulated wires  16 ,  18  through the wire connections  48 . 
   In an alternate embodiment, and as illustrated with reference to  FIG. 5 , the pins  40 ,  42  may be oriented with the offsets  52 ,  54  displaced along the central axis  26  for connecting the insulated wires  16 ,  18  thereto. The offsets  52 ,  54  may also be off-centered to allow for the largest insulated wire  16 ,  18  while keeping the sensor girth to a minimum. The pin offset configuration allows for the external connecting wires to have a maximum diameter for current carrying capacity. By staggering the pins, a larger pin offset may be employed, and thus a larger insulated wire. As illustrated with reference to  FIG. 6 , additional conductive pins  64  may be staggered around the central axis  26  without increasing the sensor package size. 
   With reference again to  FIG. 6  and to  FIG. 7 , for the embodiments herein described by way of example, an inner encapsulation  66  is used to fix the magnet  20  and pins  40 ,  42  (earlier described with reference to  FIG. 2 ) into place. The inner encapsulation  66  also provides for an insulation barrier between the conductive pins  40 ,  42  and the magnet  20  for preventing an electrical short between them. In addition, the encapsulation  66  includes alignment elements  68 ,  70  for providing structural support to the area around conductive pins  40 ,  42  and for alignment in a mold  72  as illustrated with reference again to  FIG. 3  for applying the an outer encapsulation  74 . The mold  72  may remain as the housing  14  outer shell, may be removed to have the outer shell be the outer surface of the outer encapsulation, as may be desired to meet the needs of the sensor use. The alignment elements  68 ,  70  feature provides at least a two axis constraint ensuring that the sensor chip  32  and magnet  20  remain centered within the sensor  10  along the central axis  26  during the application of the outer encapsulation  74 . As earlier described,  FIG. 6  illustrates one alternate embodiment in which another pin  64  is added. 
   With reference again to  FIG. 1 , the outer encapsulation  74 , which encapsulates the entire assembly described with reference to  FIGS. 6 and 7 , may be in the cylindrical form, or as desired, keeping the central axis  26  as a reference. This outer encapsulation  74  bonds to the inner encapsulation  66  in such a manner that creates a bond that is as strong as an encapsulation without a joint which provides for an extremely strong sensor packaging with excellent resistance to extreme environmental conditions and industrial fluids. 
   Many modifications and other embodiments of the invention will come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is understood that the invention is not to be limited to the specific embodiments disclosed, and that modifications and embodiments are intended to be included within the scope of the appended claims.