Transmission gear position sensor using printed circuit element

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.

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.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now toFIG. 1, a transmission10may include a gear selection shaft12extending therefrom to be received by a gear position sensor14. The gear selection shaft12may extend through an opening15in a base of the housing16of the gear position sensor14to connect with a carrier18. The gear selection shaft12may include a key surface interfacing with a corresponding key in the carrier18so that the carrier18may rotate with the gear selection shaft12inside of the housing16. A housing cover20joins with the housing16to define an enclosed volume holding the carrier18. The housing cover20may have a second opening21through which a continuation of the gear selection shaft12may exit.

An arcuate printed circuit board22fits on the underside of the carrier18to rotate therewith above two flexing contacts24. The contacts24are each separately supported by portions of different electrical conductors26within the enclosed volume of the housing16and attached to the housing16.

The electrical conductors26extend from the enclosed volume of the housing16through apertures28in a wall of the housing16into a connector shell30open outside of the housing16to accept a mating electrical connector31. Outside of the housing16, the electrical conductors26are formed as pins that may be received by corresponding sockets of electrical connector31. Inside the housing16, the electrical conductors26provide for flat plates that may be mounted against the base of the housing16to provide a support surface for the flexing contacts24.

Referring now toFIG. 2, the two electrical conductors26may be connected by a breakaway tab32that aligns them for passage through apertures28during assembly and can be removed later to electrically isolate the two conductors26from each other.

Referring now toFIG. 3, plastic alignment pins34may pass upward from the base of the housing16through openings in the conductors26as 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 conductors26to attach the conductors26to a bottom face of the housing16.

Referring now toFIG. 4, the portions of the conductors26extending outward into the connector shell30may initially pass through an outwardly opening pocket36that may be partially filled with flowable epoxy or other sealant or adhesive27(not shown). Referring toFIG. 5, an elastomeric plug38may then slide down over the pin portions of conductors26(the latter fitting through corresponding apertures39of the plug38) to retain the epoxy within the pocket36and to compress the epoxy to fully seal the conductors26as they pass through the apertures28. The apertures39in the plug38further wipe any misapplied epoxy from the outer surface of the conductors26.

Referring now toFIG. 6, the flexing contacts24may have barbed lower extensions40that may be press fit for gastight electrical connection to corresponding apertures42in the conductors26within the housing16. The conductors26may, for example, be brasses stampings. The flexing contacts24may provide for cantilevered bifurcated wiper arms41extending upward from the base of the housing16and 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 housing16.

Referring now toFIG. 7, carrier18may provide for downwardly extending pins44that may fit within corresponding holes46in a semicircular printed circuit board22. The under-surface of the printed circuit board22includes inner and outer electrically independent semicircular traces50coaxial about a rotation axis51(shown inFIG. 1) of the carrier18. Each of the traces50may be divided into different segments, and each segment is spanned by a different electrical resistor52. The resistors52may be connected to the traces50by short radial traces53, allowing the size of the resistors52to be independent of the separation between the traces50. It will be understood that the resistors52and the arcuate extent of the traces50may 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 toFIG. 8, the printed circuit board22may be retained against the carrier18by a heading operation on the pins44after the pins44are fit to the corresponding holes46in the printed circuit board22.

Referring again toFIG. 1, each of the curved traces50may connect to a different one of the flexing contacts24so that the different resistors52are switched between the conductors26with rotation of the carrier18.

Referring toFIG. 9, the passage of the gear selection shaft12through the housing16may be sealed by O-rings55fitting between wells59of the housing16and cover20and cylindrical rotor seal surfaces57extending upward and downward from the carrier18eliminating a seal between the gear selection shaft12and the gear position sensor14when the gear selection shaft12is positioned within the housing16. The sealing of the O-rings55and the interfitting of the flexing contacts24against the traces50may be seen inFIG. 10.

FIG. 11shows a barbed press fit of the flexing contacts24into the conductors26within the housing16.