Abstract:
A gear position sensor employs a sliding electrical connection between arcuate conductors and flexible wiper arms held on opposite surfaces that rotate relative to each other with the movement of a gear selector shaft. The traces may have multiple segments joined by resistors to provide flexible change in resistance value and resistance range for different applications.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This Non-Provisional Application is based on International Application No. PCT/US2011/028431, filed Mar. 15, 2011 and claims benefit to U.S. Provisional Application Ser. No. 61/314,903 filed Mar. 17, 2010. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a sensor suitable for sensing a gear position of a mechanical transmission, specifically to a sensor using a printed circuit board element for flexible reconfiguration of the sensor output and sensor range. 
     BACKGROUND OF THE INVENTION 
     A mechanical transmission, for example as used in an all-terrain vehicle, may provide multiple gear positions, for example: high, low, neutral, reverse, and park, as are generally understood in the art. Often it is desirable to provide an electrical signal indicating the gear position, for example, to provide visual feedback to the user or as part of an electrically controlled gear shifting mechanism. 
     An existing sensor for providing this electrical signal indicating gear position uses a set of concentric electrical contacts arranged along arcs about a common center. These contacts may be manufactured as a lead frame insertion-molded into a plastic housing during an injection molding process. A wiper, movable with a gear selection shaft of the transmission, may connect and disconnect different contacts to provide switched signals indicating the gear position. 
     One drawback to the above design is the expense of producing a lead frame and insertion-molding the lead frame into the housing as well as the high tooling costs when changes in the sensor are required, for example, for different transmission models. 
     A second drawback to a switched sensor of the type described above is the need for multiple electrical wires to communicate between each of the different contacts and a remote circuit employing the gear position signal. This latter drawback can be addressed by employing a potentiometer that can be turned by the gear selector shaft to output a variable resistance that can be communicated over a single pair of wires instead of the multiple wires needed for multiple contacts. A potentiometer may provide a resistive trace along which a conductive wiper may travel to produce a varying resistance. Standard potentiometers may be insufficiently robust for the transmission environment and specialty potentiometers can require costly retooling when changes are required. 
     SUMMARY OF THE INVENTION 
     The present invention provides a sensor applying different resistance values between a pair of conductors using a rotating printed circuit board that moves with a shaft such as the gear selection shaft. The printed circuit board may contain a set of discrete resistors joining arcuate, concentric, conductive traces. Wiper contacts mounted on the housing connect to the arcuate traces to provide the different resistance value outputs. The use of a printed circuit board allows the range and resistance values to be readily adjusted for different applications with low tooling costs. 
     Specifically, the present invention provides a transmission gear position sensor for a transmission of the type having a rotatable transmission selector shaft. The gear position sensor includes a housing defining an enclosed volume and supporting a first and second conductive element extending from a first location accessible outside of the enclosed volume for electrical connection to a connector harness to a second location within the enclosed volume and a rotating carrier fitting within the enclosed volume receiving a rotatable transmission selector shaft to rotate therewith about an axis. An insulating substrate having a first face holding conductors arcuate about the axis includes resistors bridging adjacent coaxial ones of the arcuate conductors to provide different resistances between the arcuate conductors and a first and second flexing conductive wiper positioned within the housing to engage and electrically connect to the adjacent coaxial ones of the arcuate conductors throughout a range of rotation of the insulating substrate with respect to the first and second flexing conductive wipers. One of the first and second flexing conductive wipers and the insulating substrate are attached to the rotating carrier so that the insulating substrate rotates with respect to the first and second flexing conductive wipers so that rotation of the rotating carrier changes the electrical resistance across the first and second conductive elements. 
     It is thus a feature of at least one embodiment of the invention to provide a gear position sensor communicating gear position via resistance using a device that permits flexible change in resistances and ranges through the substitution of discrete resistances. It is another feature of at least one embodiment of the invention to eliminate the need for high resistance materials that can resist sliding wear from the flexing conductive wipers. 
     The insulating substrate may be attached to the rotating carrier and the first and second flexing conductive wipers may be attached to the housing. 
     It is thus a feature of at least one embodiment of the invention to simplify the construction of the gear position sensor by permitting the flexing conductive wipers to be supported by the conductive elements retained by the housing. 
     The rotating carrier may be a thermoplastic material having bosses extending outward therefrom to be received by corresponding holes in the insulating substrate so that the latter may be retained by thermoforming ends of the bosses over a surface of the insulating substrate. 
     It is thus a feature of at least one embodiment of the invention to permit separate fabrication of the insulating substrate from the rotating carrier, the latter which may be injection molded. 
     The insulating substrate may be a printed circuit board material and the arcuate conductors are traces on the printed circuit board. 
     It is thus a feature of at least one embodiment of the invention to provide a simple method of fabricating the resistance element adaptable to changes with minimal tooling costs. By using conventional circuit board fabrication techniques different resistances may be readily added to the printed circuit board and/or the traces changed. 
     The printed circuit board may include traces extending radially from the arcuate conductors for providing solder attachment to the resistors. 
     It is thus a feature of at least one embodiment of the invention to permit flexible separation of discrete resistive devices independent of the determination of mechanical separation of the traces. 
     The transmission gear position sensor may provide multiple arcuate conductors of equal radius separated by gaps. 
     It is thus a feature of at least one embodiment of the invention to provide a simple method of generating stepped resistance changes using a single set of flexing conductive wipers. 
     The first and second conductive elements may be substantially rigid conductors passing through the housing and the first and second flexing conductive wipers may be supported within the housing by the first and second conductive elements. 
     It is thus a feature of at least one embodiment of the invention to provide a simple method of mechanical support of the flexing conductive wipers. 
     The flexing wiper elements may be attached to the substantially rigid conductors by mechanical interference fit. 
     It is thus a feature of at least one embodiment of the invention to provide a simple method of electrical connection between the wiper elements and the rigid conductors. 
     The housing may be a thermoplastic material having inwardly extending bosses fitting through corresponding holes in the substantially rigid conductors to hold the substantially rigid conductors to the housing by thermoforming ends of the bosses over a surface of the substantially rigid conductors. 
     It is thus a feature of at least one embodiment of the invention to provide a method of fixing the first and second conductive elements to the housing without the need for insert molding during injection molding process. 
     The transmission gear position sensor may further include seals positioned between the housing and at least one of the gear shift and rotating carrier and rotatable transmission selector shaft. 
     It is thus a feature of at least one embodiment of the invention to provide a variable resistance element robust against environmental contaminants. 
     The first and second conductive elements may pass through a wall of the housing separating the enclosed volume from the outside into a pocket, the pocket sized to receive a flowable sealing material and an elastomeric seal having openings slidable along the first and second conductive elements to wipe the compound from the first and second conductive elements as the seal is moved to cover the pocket. 
     It is thus a feature of at least one embodiment of the invention to provide a hermetic seal without the need for in-molded conductors assembled during the injection molding process. 
     Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims and drawings in which like numerals are used to designate like features. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view of a transmission gear position sensor per the present invention showing the housing that may hold a printed circuit board carrier for rotation with a transmission selector shaft within an enclosed volume of the housing and electrical conductors which pass through a wall of the housing into a connector shell for receiving a mating electrical connector; 
         FIG. 2  is a perspective view of the housing of  FIG. 1 , open to show the electrical conductors during assembly; 
         FIG. 3  is a figure similar to that of  FIG. 2  showing the electrical conductors staked to the housing with a connecting tab, used for alignment during assembly, removed; 
         FIG. 4  is a view into the end of the connector shell showing the conductors extending through a wall of the housing into a pocket and a pre-measured amount of sealing compound in the center; 
         FIG. 5  is a perspective view of the connector shell showing the insertion of an elastomeric plug over the conductors to compress and retain a flowable adhesive material placed in the pocket; 
         FIG. 6  is a perspective view similar to that of  FIGS. 2-3  showing attachment of flexible contact elements to the conductors; 
         FIG. 7  is perspective exploded view of the underside of the carrier of  FIG. 1  showing positioning of an arcuate printed circuit board to the carrier with downwardly exposed traces and discrete resistors; 
         FIG. 8  is a figure similar to that  FIG. 7  showing an assembly of the printed circuit board to the carrier by staking operations; 
         FIG. 9  is an exploded cross-sectional view similar to that of  FIG. 1  showing placement of O-rings to seal a transmission selector shaft as it rotates within the housing; 
         FIG. 10  is a detailed fragmentary cross-sectional view similar to that of  FIG. 9  showing engagement between the flexible contact elements and the traces of the printed circuit board; and 
         FIG. 11  is a detailed cross-sectional view showing an assembly of the flexible contact elements to the conductors by a press-fit barb element. 
     
    
    
     Before the embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein are for the purpose of description and should not be regarded as limiting. The use of “including” and “comprising” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items and equivalents thereof. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to  FIG. 1 , a transmission  10  may include a gear selection shaft  12  extending therefrom to be received by a gear position sensor  14 . The gear selection shaft  12  may extend through an opening  15  in a base of the housing  16  of the gear position sensor  14  to connect with a carrier  18 . The gear selection shaft  12  may include a key surface interfacing with a corresponding key in the carrier  18  so that the carrier  18  may rotate with the gear selection shaft  12  inside of the housing  16 . A housing cover  20  joins with the housing  16  to define an enclosed volume holding the carrier  18 . The housing cover  20  may have a second opening  21  through which a continuation of the gear selection shaft  12  may exit. 
     An arcuate printed circuit board  22  fits on the underside of the carrier  18  to rotate therewith above two flexing contacts  24 . The contacts  24  are each separately supported by portions of different electrical conductors  26  within the enclosed volume of the housing  16  and attached to the housing  16 . 
     The electrical conductors  26  extend from the enclosed volume of the housing  16  through apertures  28  in a wall of the housing  16  into a connector shell  30  open outside of the housing  16  to accept a mating electrical connector  31 . Outside of the housing  16 , the electrical conductors  26  are formed as pins that may be received by corresponding sockets of electrical connector  31 . Inside the housing  16 , the electrical conductors  26  provide for flat plates that may be mounted against the base of the housing  16  to provide a support surface for the flexing contacts  24 . 
     Referring now to  FIG. 2 , the two electrical conductors  26  may be connected by a breakaway tab  32  that aligns them for passage through apertures  28  during assembly and can be removed later to electrically isolate the two conductors  26  from each other. 
     Referring now to  FIG. 3 , plastic alignment pins  34  may pass upward from the base of the housing  16  through openings in the conductors  26  as mounted against the base of the housing and staked by heat, pressure, or ultrasonic energy over the outer surface of the flat portions of the conductors  26  to attach the conductors  26  to a bottom face of the housing  16 . 
     Referring now to  FIG. 4 , the portions of the conductors  26  extending outward into the connector shell  30  may initially pass through an outwardly opening pocket  36  that may be partially filled with flowable epoxy or other sealant or adhesive  27  (not shown). Referring to  FIG. 5 , an elastomeric plug  38  may then slide down over the pin portions of conductors  26  (the latter fitting through corresponding apertures  39  of the plug  38 ) to retain the epoxy within the pocket  36  and to compress the epoxy to fully seal the conductors  26  as they pass through the apertures  28 . The apertures  39  in the plug  38  further wipe any misapplied epoxy from the outer surface of the conductors  26 . 
     Referring now to  FIG. 6 , the flexing contacts  24  may have barbed lower extensions  40  that may be press fit for gastight electrical connection to corresponding apertures  42  in the conductors  26  within the housing  16 . The conductors  26  may, for example, be brasses stampings. The flexing contacts  24  may provide for cantilevered bifurcated wiper arms  41  extending upward from the base of the housing  16  and may be constructed of a springy material such as a bronze or the like to retain an upward spring bias when pressed downward toward the base of the housing  16 . 
     Referring now to  FIG. 7 , carrier  18  may provide for downwardly extending pins  44  that may fit within corresponding holes  46  in a semicircular printed circuit board  22 . The under-surface of the printed circuit board  22  includes inner and outer electrically independent semicircular traces  50  coaxial about a rotation axis  51  (shown in  FIG. 1 ) of the carrier  18 . Each of the traces  50  may be divided into different segments, and each segment is spanned by a different electrical resistor  52 . The resistors  52  may be connected to the traces  50  by short radial traces  53 , allowing the size of the resistors  52  to be independent of the separation between the traces  50 . It will be understood that the resistors  52  and the arcuate extent of the traces  50  may be changed by simple revision of the printed circuit board such as requires very low tooling costs. It is also possible to print the resistors using polymer thick film technology. 
     Referring to  FIG. 8 , the printed circuit board  22  may be retained against the carrier  18  by a heading operation on the pins  44  after the pins  44  are fit to the corresponding holes  46  in the printed circuit board  22 . 
     Referring again to  FIG. 1 , each of the curved traces  50  may connect to a different one of the flexing contacts  24  so that the different resistors  52  are switched between the conductors  26  with rotation of the carrier  18 . 
     Referring to  FIG. 9 , the passage of the gear selection shaft  12  through the housing  16  may be sealed by O-rings  55  fitting between wells  59  of the housing  16  and cover  20  and cylindrical rotor seal surfaces  57  extending upward and downward from the carrier  18  eliminating a seal between the gear selection shaft  12  and the gear position sensor  14  when the gear selection shaft  12  is positioned within the housing  16 . The sealing of the O-rings  55  and the interfitting of the flexing contacts  24  against the traces  50  may be seen in  FIG. 10 . 
       FIG. 11  shows a barbed press fit of the flexing contacts  24  into the conductors  26  within the housing  16 . 
     Various features of the invention are set forth in the following claims. It should be understood that the invention is not limited in its application to the details of construction and arrangements of the components set forth herein. The invention is capable of other embodiments and of being practiced or carried out in various ways. Variations and modifications of the foregoing are within the scope of the present invention. It also being understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text and/or drawings. All of these different combinations constitute various alternative aspects of the present invention. The embodiments described herein explain the best modes known for practicing the invention and will enable others skilled in the art to utilize the invention.