Abstract:
A low profile non-contacting position sensor for rotational engagement with a shaft. A pole piece has a first and a second piece. A backstrap retains the first and second pieces in parallel and opposing relationship. A shaft passes through at least one of the pieces. The pole piece is held to the shaft by a shaft retainer. A first and second magnet is disposed on the first and second pieces, respectively. A magnetic sensor is positioned between the first and second magnets. A magnetic field sensor such as a hall effect sensor is positioned in an gap and operates to provide an output signal representative of the field strength of the magnet as the shaft rotates. The output signal changes magnitude in relation to the relative position of the magnet with respect to the magnetic field sensor.

Description:
BACKGROUND OF THE PREFERRED EMBODIMENT(S) 
     1. Field of the Preferred Embodiment(s) 
     This invention generally relates to position sensing and to a position sensor which is compact, durable and precise. More specifically, the invention relates to a noncontacting low profile position sensor. 
     2. Description of the Related Art 
     Position sensing is used to allow an electrical circuit to gain information about an event or a continuously varying condition. There are a variety of known techniques for angular position sensing. For example, optical, electrical, electrostatic, and magnetic fields are all used in a sensor to measure position. There are many known sensors such as resistive contacting networks, inductively coupled ratio sensors, variable reluctance devices, capacitively coupled ratio detectors, optical detectors using the Faraday effect, photo-activated ratio detectors, and electrostatic ratio detectors. 
     There are many applications for sensors, and a wide variety of technologies to fill these needs. Each of these technologies offers a unique set of advantages and limitations. limitations. Of these technologies, magnetic sensing is known to have a unique combination of long life components and excellent resistance to contaminants. 
     Regardless of the arrangement and method for changing the field about the sensor, the magnetic circuit faces several obstacles which have not been overcome. Movement of the sensor relative to the gap as a result of bearing play will lead to a variation in field strength measured by the sensor. This effect is particularly pronounced in Hall effect, magneto-resistive and other similar sensors, where the sensor is sensitive about a single axis and insensitive to perpendicular magnetic fields. 
     DESCRIPTION OF RELATED ART 
     Examples of patents related to the present invention are as follows, wherein each patent is herein incorporated by reference for related and supporting teachings: 
     U.S. Pat. No. 3,112,464 is a hall effect translating device. 
     U.S. Pat. No. 4,142,153 is a tachometer for measuring speed and direction of shaft rotation with a single sensing element. 
     U.S. Pat. No. 4,293,837 is a hall effect potentiometer. 
     U.S. Pat. No. 4,570,118, is an angular position transducer including permanent magnets and hall effect device. 
     U.S. Pat. No. 4,726,338 is a device for controlling internal combustion engines. 
     U.S. Pat. No. 4,744,343 is a device for controlling an internal combustion engine. 
     U.S. Pat. No. 4,848,298 is a device for controlling internal combustion engine. 
     U.S. Pat. No. 4,942,394 is a hall effect encoder apparatus 
     U.S. Pat. No. 5,055,781, is a rotational angle detecting sensor having a plurality of magnetoresistive elements located in a uniform magnetic field. 
     U.S. Pat. No. 5,115,239 is a magnetic absolute position encoder with an undulating track. 
     U.S. Pat. No. 5,159,268 is a rotational position sensor with a hall effect device and shaped magnet. 
     U.S. Pat. No. 5,258,735 is a multi-pole composite magnet used in a magnetic encoder. 
     U.S. Pat. No. 5,313,159 is a magnetic encoder with composite magnet. 
     U.S. Pat. No. 5,712,561 is a field strength position sensor with improved bearing tolerance in a reduced space. 
     U.S. patent application Ser. No. 08/206982 titled, “dual magnet hall effect position sensor”, filed Mar. 4, 1994 and owned by the same assignee as the instant application. 
     U.S. patent application Ser. No. 08/206474 titled, “molded magnet structure”, filed Mar. 4, 1994 and owned by the same assignee as the instant application. 
     U.S. patent application Ser. No. 08/976879 titled, “molded magnet structure”, filed Nov. 24, 1997 and owned by the same assignee as the instant application. 
     U.S. patent application Ser. No. 08/206568 titled, “flux gradient control”, filed Mar. 4, 1994 and owned by the same assignee as the instant application. 
     U.S. patent application Ser. No. 08/659963 titled, “field strength position sensor with improved bearing”, filed Jun. 7, 1996 and owned by the same assignee as the instant application. 
     U.S. patent application Ser. No. 08/971800 titled, “flux gradient control”, filed Nov. 17, 1997 and owned by the same assignee as the instant application. 
     The foregoing patents reflect the state of the art of which the applicant is aware and are tendered with the view toward discharging applicants&#39; acknowledged duty of candor in disclosing information that may be pertinent in the examination of this application. It is respectfully stipulated, however, that none of these patents teach or render obvious, singly or when considered in combination, applicants&#39; claimed invention. 
     PROBLEMS WITH THE PRIOR ART 
     There are several problems that exist with the prior art that are addressed by the preferred embodiment. One problem with the prior art sensors is that they are too thick and are unable to fit into some engine locations. Engine compartments are becoming more cramped due to more engine functions being added. Another cause of engine room space shortage is the trend toward maximizing the interior space of the car while keeping the overall dimensions of the car the same. This leads to a shrinking of the engine compartment. 
     Another problem is that the prior art throttle position sensors have had to have a shorter input shaft that can not extend through or beyond the device. In some applications, it is preferable to have a longer shaft. 
     This and other problems will be solved by the preferred embodiments of the invention. A review of the specification, drawings, and claims will more clearly teach a skilled artisan of other problems that are solved by the preferred embodiments. 
     SUMMARY OF THE PREFERRED EMBODIMENT(S) 
     It is a feature of the invention to provide a position sensor for rotational engagement with a shaft. The sensor includes a pole piece, having a first and second piece, a backstrap for retaining the first and second pieces in parallel and opposing relationship, and a bore extending through at least one of the pieces for the shaft to be inserted therein. A first and second magnet is disposed on the first and second pieces respectively. A magnetic sensor is positioned between the first and second magnets. 
     A magnetic field varies from a first to a second location on the magnets and extends across the air gap. The magnetic field sensor is positioned in the air gap and operates to provide an output signal representative of the variable magnetic field as the pole piece is rotated. The output signal changes magnitude in relation to the relative position of the magnet with respect to the magnetic field sensor. 
     It is a feature of the invention to provide a first and second magnetically permeable devices with a first and second aperture or bore, respectively. The shaft passes through at least one of the first or second apertures or bore. 
     A further feature of the invention is to provide the magnetically permeable device to be held to the shaft by a shaft retainer. 
     The invention resides not in any one of these features per se, but rather in the particular combination of all of them herein disclosed and claimed. Those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. Further, the abstract is neither intended to define the invention of the application, which is measured by the claims, neither is it intended to be limiting as to the scope of the invention in any way. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features of the invention can best be understood by the following description of the accompanying drawings as follows: 
     FIG. 1 is a perspective view of the low profile non-contacting position sensor with the housing cover on. 
     FIG. 2 is a bottom view of the position sensor of FIG.  1 . 
     FIG. 3 is a exploded view of the position sensor of FIG.  1 . 
     FIG. 4 is a perspective view of a pole piece of the position sensor of FIG.  1 . 
     FIG. 5 is a top view of the pole piece of FIG.  3 . 
     FIG. 6 is a side view of the pole piece of FIG.  3 . 
     FIG. 7 is a cross-sectional view along line A—A of FIG.  6 . 
    
    
     It is noted that the drawings of the invention are not to scale. The drawings are merely schematic representations, not intended to portray specific parameters of the invention. The drawings are intended to depict only typical embodiments of the invention, and therefore should not be considered as limiting the scope of the invention. The invention will be described with additional specificity and detail through the accompanying drawings. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, there is a perspective view of the low profile non-contacting position sensor  10  with the housing cover  12  in place. A housing  14  contains the sensor components. A pair of mounting holes  16  fasten the sensor  10  to another structural support such as an engine or a motor frame. A shaft aperture or bore  18  allows a rotating shaft  19  to extend into and through the sensor housing  14 . Several connector terminals  20  allow the sensor  10  to be connected with a wiring harness (not shown) or other external wiring (not shown). 
     Referring to FIG. 2, a bottom view of the position sensor of FIG. 1 is shown. A shaft retainer  22  is located in the center of the sensor  10 . The shaft retainer  22  holds the shaft  19  of a rotating object and transfers the rotational movement of the shaft  19  to the sensor  10 . 
     FIG. 3 shows an exploded view of the position sensor  10 . Specifically, there is a pole assembly  30  which is made up of a circular pole piece  32  to which a pair of semicircular magnets  34  are attached. The magnets  34  vary in width along their circumference. The magnets  34  are preferably formed out of conventional ferrite. An encapsulant  33  is applied over the magnets  34  after they are attached to the pole piece  32 . The shaft retainer  22  is molded onto the pole piece  32 . A circuit board holder  36  holds a circuit board  38 . The circuit board has mounted on it a magnetic field sensor  37  and its associated circuitry. The magnetic field sensor  37  is typically a conventional hall effect sensor. An air gap  35  is shown located between the magnets  34 . The magnetic field sensor  37  is mounted in the air gap  35 . An electrical connection (not shown) connects the circuit board  38  to the connector terminals  20 . The shaft  19  is adapted to be inserted through the shaft aperture  18  and held by the shaft retainer  22 . The shaft  19  and pole assembly  30  rotate about an axis of rotation  40 . A pair of inserts  15  are located within the mounting hole  16 . 
     The assembly of the position sensor  10  is as follows: The magnets  34  are attached by molding or gluing to pole piece  32  which is then overmolded with a plastic encapsulant  33  forming pole assembly  30 . The shaft retainer  22  is part of the overmolded plastic encapsulant  33 . Next, the circuit board holder  36  is inserted into the pole assembly  30  and then the circuit board  38  is inserted into the circuit board holder  36 . The connector terminals  20  are inserted into housing  14 . The pole assembly  30 , the circuit board holder  36  and the circuit board  38  are placed in the housing  14 . The connector terminals  20  are electrically connected to the circuit board  38 . The inserts  15  are molded into the mounting holes  16 . The cover  12  is placed over the housing  14  to complete the assembly. 
     FIG. 4 shows a perspective view of the pole piece  32 . Pole piece  32  has an upper piece or disc  42  and a lower piece or disc  44  connected together by a backstrap  46 . The backstrap  46  magnetically couples the upper disc  42  and the lower disc  44  to complete a closed magnetic flux path. The pole piece  32  can be stamped out of a single piece or welded together from several pieces. The upper disc  42  is positioned spaced parallel to and opposed from lower disc  44 . The shaft aperture  18  passes completely through the upper and lower discs  42  and  44 , respectively. The pole piece  32  is preferably formed out of a ferromagnetic stainless steel such as  401  stainless. The discs  42  and  44  are formed of a uniform thickness. 
     Referring to FIG. 5, a top view of the pole piece  32  is shown. The magnets  34  are shown in dotted line attached to the pole piece  32 . FIG. 6 shows a side view of the pole piece  32 . FIG. 7 shows a cross-sectional view along line  7 — 7  of FIG. 6 of the pole piece  32 . The magnets  34  are seen in dotted line section. 
     OPERATION OF THE PREFERRED EMBODIMENT 
     The operation of the low profile position sensor is described next. As the shaft  19  rotates and is driven by the rotating object whose position is desired to be sensed, the magnets  34  will be rotationally moved relative to the magnetic sensor  37  mounted on the circuit board  38 . A closed magnetic path exists when flux generated is confined within a high permeability material. The flux path from magnets  34  primarily flows from the lower magnet  34 , through the air gap  35 , through upper magnet  34 , through upper disc  42 , through backstrap  46 , and through lower disc  44  completing the path. It is understood that there are magnetic losses in any magnetic path from fringing flux and other loss sources. As the magnets  34  rotate, the magnetic field strength sensed by the magnetic sensor will change due to the changing thickness of the magnets  34 . When the magnet narrow region is positioned near magnetic sensor  37 , the magnetic field will have a relatively low intensity and the output from the magnetic sensor  37  will be low. As the magnets  34  rotate, a thicker portion of the magnets  34  is located near the magnetic sensor  37  and the magnetic field strength increases proportionally. 
     The semicircular magnets shown here are able to sense about 200 degrees of rotation. The circuit board  38  contains circuitry that is able to condition the output of the hall sensor and to supply an output signal. The circuit board  38  also has circuitry that compensates for changes in temperature. When the shaft  19  is inserted into the pole assembly  30  and if the shaft is fabricated out of a magnetically permeable material such as steel, the shaft will alter the magnetic flux path in the assembly. The effect of the shaft  19  on the flux path can be taken into account and compensated for in the design of the magnets  34 . Alternatively, the position sensor will also work if the shaft  19  is fabricated out of a non-magnetically permeable material such as plastic or aluminum. 
     REMARKS ABOUT THE PREFERRED EMBODIMENT 
     One of ordinary skill in the arts of sensors, and more particularly the art of designing non-contacting position sensors, will realize many advantages from using the preferred embodiment. In particular, the low profile non-contacting position sensor assembly allows the sensor to have a thin profile which can be fit into a crowded engine compartment because, the shaft aperture  18  and the shaft retainer  22  allow the rotating shaft  19  to pass into and partially be contained by the position sensor  10  resulting in a thin overall profile of the position sensor  10 . 
     The design of the backstrap  46  is critical to the operation of the position sensor  10 . The backstrap  46  must be positioned at a radius on the upper and lower discs  42  and  44  such that the width of the backstrap has sufficient material to contain the flux density and at the same time must not be positioned to close to the shaft passing through the shaft aperture  18  because it would limit the rotation of the pole assembly  30 . A preferred location for the backstrap is between ⅕ and ⅘ of the radius of the upper and lower discs  42  and  44 , respectively. 
     VARIATIONS OF THE PREFERRED EMBODIMENT(S) 
     One of ordinary skill in the art of making position sensors will realize that there are many different ways of accomplishing the preferred embodiment. For example, it is contemplated to make the housing  14 , out of any suitable material, like plastics, epoxy resin, fiberglass etc. Additionally, the pole assembly  30  could be made out of any magnetically permeable material such as cast iron. The magnets  34  and upper and lower discs  42  and  44  that make up pole assembly  30  could be fastened by other methods such as glue, press fitting, welding etc. 
     Even though, the embodiment discusses the use of two magnets  34 , it is contemplated to use only one magnet on one of the discs. Either the upper or lower disc  42  or  44  could contain a single magnet  34 . 
     Similarly, even though the embodiment discusses the use of a Barium Ferrite magnets  34 , one skilled in the art of magnet design would realize that a Samarium-Cobalt magnets could also be used. It is also possible to make the shape of the magnets  34  differently. For example, the magnets  34  could be made narrower or wider than what is shown. The magnets  34  also could be formed from several small magnets that are arrayed having an increasing or decreasing thickness. 
     Although, the shaft  19  is described as passing completely through the pole piece  32  including the upper and lower discs  42  and  44 , it is contemplated that only one of the discs  42  or  44  have a shaft aperture  18 . 
     Additionally, the shaft could pass through and extend well beyond the sensor  10 . 
     The position sensors  10  could be placed at multiple locations on the same shaft. 
     Additionally, although it is illustrated that the shaft retainer  22  is molded to the pole assembly  30 , it is contemplated to fasten the shaft to the pole assembly  30  by other suitable fastening means such as a key, splined shaft, cotter pin, snap ring, welding, etc. 
     The magnetic sensor  37  shown in the preferred embodiment was a hall effect sensor. It is contemplated that two or more magnetic sensors  37  could be utilized and that other types of magnetic sensors could be utilized such as variable reluctance sensors or other types of magnetic sensors. 
     While the invention has been taught with specific reference to these embodiments, someone skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and the scope of the invention. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.