Abstract:
A rotational position sensing device includes at least one sensor positioned adjacent a rotating component configured to rotate about an axis of rotation. At least one magnet is positioned at the rotating component such that a magnetic field of the at least one magnet affects the sensor and magnetizes a portion of the rotating component. The at least one sensor is configured to produce an output signal indicative of a magnetic flux, and therefore a position, of the rotating component. A method of sensing a position of a rotating component includes magnetizing a portion of a rotating component with a magnet and measuring a magnetic flux of the rotating component as it rotates about an axis of rotation. An output signal is generated that is indicative of the position of the rotating component.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. provisional application 61/780,057 filed Mar. 13, 2013, the entire contents of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    The present disclosure relates generally to rotational components, such as gears for example, and, more particularly, to methods and sensors for detecting rotational position of a gear, ring, wheel, flexplate, or other rotational component. 
         [0003]    Rotational position sensing of a rotating component may be used in a variety of applications including, but not limited to, angular speed measurement, distance traveled calculation, and absolute position encoding of the rotational component relative to, for example, a fixed component such as a hub or axle. It may also be used to determine a relative position of a first rotating component relative to a second rotating component, whose angular position is also sensed. Further, rotational position sensing may be utilized in other applications, for example, torque sensing, or calculation of applied torque. Thus there remains a need for improved methods of rotational position sensing. 
       SUMMARY 
       [0004]    In one embodiment, a rotational position sensing device includes at least one sensor positioned adjacent a rotating component configured to rotate about an axis of rotation. At least one magnet is positioned at the rotating component such that a magnetic field of the at least one magnet affects the sensor and magnetizes a portion of the rotating component. The at least one sensor is configured to produce an output signal indicative of a magnetic flux, and therefore a position, of the rotating component. 
         [0005]    Additionally or alternatively, in this or other embodiments the rotating component includes a plurality of teeth extending about an outer periphery of the rotating component. 
         [0006]    Additionally or alternatively, in this or other embodiments the at least one sensor is arranged generally perpendicular to and axially aligned with the teeth of the rotating component. 
         [0007]    Additionally or alternatively, in this or other embodiments a spacing between a plurality of adjacent sensors is substantially equal to a spacing between a tooth of the plurality of teeth of the rotating component and an adjacent valley. 
         [0008]    Additionally or alternatively, in this or other embodiments at least one detector is positioned adjacent the rotating component. 
         [0009]    Additionally or alternatively, in this or other embodiments the at least one detector is configured to synchronize a detection method with the teeth of the rotating component. 
         [0010]    Additionally or alternatively, in this or other embodiments an axial and a vertical position of the at least one magnet relative to the at least one sensor varies based on a strength of the at least one magnet and a sensitivity of the at least one sensor. 
         [0011]    Additionally or alternatively, in this or other embodiments a plurality of demagnetizing magnets is positioned about an outer periphery of the rotating component. The demagnetizing magnets are configured to make the rotating component generally magnetically uniform. 
         [0012]    Additionally or alternatively, in this or other embodiments the plurality of demagnetizing magnets are positioned to have an alternating polarity to form an alternating current degaussing pattern. 
         [0013]    Additionally or alternatively, in this or other embodiments the at least one sensor is a fluxgate sensor. 
         [0014]    Additionally or alternatively, in this or other embodiments the at least one sensor is a fluxgate sensor configured as an inductive pickup. 
         [0015]    Additionally or alternatively, in this or other embodiments the at least one sensor is an inductive pickup. 
         [0016]    Additionally or alternatively, in this or other embodiments the rotating component is positioned axially between the at least one sensor and the at least one magnet. 
         [0017]    Additionally or alternatively, in this or other embodiments the at least one sensor is positioned at a first circumferential end of the rotating component, and the at least one magnet is positioned substantially 180 degrees away from the at least one sensor. 
         [0018]    In another embodiment, a method of sensing a position of a rotating component includes magnetizing a portion of a rotating component with a magnet and measuring a magnetic flux of the rotating component as it rotates about an axis of rotation. An output signal is generated that is indicative of the position of the rotating component. 
         [0019]    Additionally or alternatively, in this or other embodiments the magnetic flux is measured using at least one sensor positioned adjacent the rotating component. 
         [0020]    Additionally or alternatively, in this or other embodiments the at least one sensor is a fluxgate sensor. 
         [0021]    Additionally or alternatively, in this or other embodiments the measured magnetic flux is amplified to produce an amplified output signal. 
         [0022]    These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    The disclosed subject matter is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, aspects, and advantages are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0024]      FIG. 1  is a cross-sectional view of a tooth sensing device according to an embodiment; 
           [0025]      FIG. 2  is a cross-sectional view of a tooth sensing device according to an embodiment; 
           [0026]      FIG. 3  is a perspective view of a tooth sensing device according to an embodiment; 
           [0027]      FIG. 4  is another perspective view of a tooth sensing device according to an embodiment; 
           [0028]      FIG. 5  is a cross-sectional view of a tooth sensing device according to an embodiment; 
           [0029]      FIG. 6  is a cross-sectional view of a tooth sensing device according to an embodiment; 
           [0030]      FIG. 7  is an exemplary fluxgate output signal of the tooth sensing device according to an embodiment; 
           [0031]      FIG. 8  is a side view of a tooth sensing device according to an embodiment; 
           [0032]      FIG. 9  is a detailed view of a detector configured for use in conjunction with the tooth sensing device according to an embodiment; 
           [0033]      FIG. 10  is a top view of a tooth sensing device according to an embodiment; 
           [0034]      FIG. 11  is a cross-sectional view of a tooth sensing device according to an embodiment of the invention; 
           [0035]      FIG. 12  is a schematic diagram of a circuit of a tooth sensing device according to an embodiment; 
           [0036]      FIG. 13  is a schematic diagram of a circuit of a detector configured for use with the tooth sensing device according to an embodiment; and 
           [0037]      FIG. 14  is a schematic view of an embodiment of a flux gate sensor configured for use as a tooth sensing device 
       
    
    
     DETAILED DESCRIPTION 
       [0038]    Detection of a tooth of a circular rotating component via a tooth sensing device  20  including fluxgate technology is generally improved by positioning a permanent magnet  25  in proximity to a fluxgate sensor  30  adjacent the rotating component  40  (see  FIGS. 3 and 4 ) such that the magnetic field generated by the magnet  25  affects the teeth  45  of the rotating component  40  as well as the fluxgate sensors  30 . As the teeth pass  45  through the magnetic field, the change between the presence and absence of a tooth  45  is detected by a fluxgate sensor  30 . Referring now to  FIGS. 1-4 , the magnet  25  may be positioned near one or more fluxgate sensors  30 , such as adjacent a first side  32  of the sensor  30  ( FIG. 1 ) or adjacent a second, opposite side  34  of the sensor  30 . The toothed rotating component  40  is oriented generally perpendicularly (see  FIGS. 3 and 4 ). The axial and vertical position of the magnet  25  relative to the at least one fluxgate sensor  30  will vary based on the strength of the magnet  25  and the sensitivity of the fluxgate sensor  30 . In an embodiment, the magnet  25  is positioned such that the output signal generated by the fluxgate sensor  30  has a high amplitude without system saturation. Magnets  25  that are similar in size to the pitch of the teeth  45  and the spacing between adjacent fluxgate sensors  30  generally create a fluxgate output signal having the strongest signal amplitude. 
         [0039]    In another embodiment, illustrated in  FIGS. 5 and 6 , a first magnet  25  may be positioned adjacent the first side  32  of one or more fluxgate sensors  30 , and a second magnet  25  may be positioned adjacent the second side  34  of one or more fluxgate sensors  30 . The polarity of the first and second magnets  25  is generally reversed relative to one another. Similar to the tooth sensing device  20  of  FIGS. 1 and 2 , the position and strength of the magnets  25  relative to the fluxgate sensors  30  may be dynamically adjusted until the fluxgate output signals have high amplitude without system saturation. 
         [0040]    The output signal generated by a fluxgate sensor  30  may become saturated if certain portions of the rotating component  40  have a magnetic field. An exemplary fluxgate output signal, illustrated in  FIG. 7 , includes a drop in amplitude as a result of this unwanted magnetic field acting on the teeth  45 . In an embodiment, a current feedback loop (not shown) may be used to reduce the saturation limits of the fluxgate sensor  30 . For example, if the average output of a circuit of the fluxgate sensor  30  is above or below 2.5 volts, a constant current is summed with an inner loop current at the 2.5 Vdc end of the fluxgate sensor  30 . In an embodiment, the current feedback loop (not shown) has a time constant generally equal to the expected magnetic runout at the slowest operational speed of the rotating component  40 . 
         [0041]    In another embodiment, the robustness of the fluxgate output signal may be improved by making the rotating component  40  substantially magnetically uniform. At least one demagnetizing magnet  50 , as illustrated in  FIG. 8 , is arranged near the outer periphery  42  of the rotating component  40 . In embodiments including a plurality of magnets  50 , the magnets  50  are radially spaced about the outer periphery  42  of the rotating component  40  and have alternating polarities to form an alternating current degaussing pattern. The magnets  50  are utilized to erase previous magnetic history that might have come from the manufacturing process or “hot spots” that can occur from unintentional placement of a magnet on the rotating component. Further, the magnets  50  may be utilized to magnetize the rotating component  40  with a fresh field just before it passes the sensor  30 . The number of magnets  50  used may depend on the sensitivity of the fluxgate sensors  30  and the anticipated magnetic field to which the rotating component  40  may be exposed. In an embodiment, the magnets  50  are spaced away from the fluxgate sensor  30 , for example opposite the fluxgate sensor  30  as illustrated in the FIG. 
         [0042]    In another embodiment, an electronic detection circuit (not shown) including at least one detector  55  (see  FIG. 9 ) is configured to use the speed of the rotating component  40 , detected as the tooth passage frequency, to phase its method of detection to match an expected location of the teeth  45  based on the speed of the rotating component  40 . Any suitable type of detector  55  may be used. The electronic circuitry connected to these detectors  55  is configured to synchronize the detection method to the passing of the teeth  45 . 
         [0043]    The one or more fluxgate sensors  30  may be arranged in any of a number of orientations relative to the rotating component  40  and the shaft  35  supporting the rotating component  40 . When the fluxgate sensor  30  is positioned at the side of the rotating component  40 , the fluxgate sensor  30  is more sensitive to the magnetic state of the teeth  45  and the webbing at the center of the rotating component  40 . In an embodiment, the fluxgate sensors  30  are arranged generally perpendicular to and axially aligned with the teeth  45  of the rotating component  40  (see  FIG. 10 ). In addition, the spacing between adjacent fluxgate sensors  30  may be generally equal to the spacing between a tooth  45  and an adjacent valley  48  between teeth  45 , as shown in  FIG. 11 , to produce a fluxgate output signal having a high amplitude. 
         [0044]    In an embodiment, the one or more fluxgate sensors  30  of the tooth sensing device  20  may be used as an inductive pickup configured to measure permeability rather than magnetic flux. Alternatively, the tooth sensing device  20  may use at least one fluxgate sensor  30  in a combined manner such that the electronic circuitry is configured to use a fluxgate sensor  30  exclusively as a fluxgate sensor, exclusively as an inductive pickup, or as a combination thereof. An exemplary circuit  60  configured to use an inductive pickup or a fluxgate sensor  30  configured as an inductive pickup is illustrated in  FIG. 12 . 
         [0045]    With reference now to  FIG. 13 , a sinusoidal signal may be generated into a filter following the detector  55  as a further means of improving the tooth sensing signal. The connection between C12 and R11 has been broken to demonstrate the ripple on the output without the noise cancellation feature. In an embodiment, the inclusion of additional circuitry consisting of four passive components, R19, C14, R18, and C12 may result in a 10 to 1 reduction in output ripple. 
         [0046]    Referring now to  FIG. 14 , a schematic of a fluxgate sensor  30  used as a tooth sensor in variable reluctance mode is illustrated. The fluxgate sensor  30  contains a high permeability core that amplifies the flux according to B=μH, where B is the magnetic flux density, H is the magnetic field density and μ is the permeability of the core. IN some embodiments, the core may be formed from a highly permeable material such as Permalloy (amorphous), typically having a bulk permeability of &gt;10,000, compared to ferrite rod having a permeability of &lt;1000. The core has a small volume, and in one embodiment measures about 0.010″ wide by 0.001″ thick by 0.50″ long, having a cross-sectional area of about 0.010 square mils. IT is to be appreciated that the dimensions of the core included here are merely exemplary, and that other sizes and configurations of cores may be utilized. In this embodiment, the coil wrapped around the core is 0.062″ in diameter by 0.50″ long (500 turns of #42 wire). That measures about 8 Ohms resistance, compared with 3000 Ohms for a typical variable reluctance sensing coil. The net result is a sensor  30  that weighs a few milligrams, rather than several 10&#39;s of grams. The fluxgate sensor  30  thus produces a flux Ø=BA, where A is a cross-sectional area of a fluxgate sensor coil. As teeth  45  rotate past the coil, a voltage is induced in the coil by the modulation of the H field. This, in turn, produces a modulated voltage expressed as shown in equation (1): 
         [0000]        V=N *( dØ/dT )per Faraday&#39;s law.  (1)
 
         [0047]    Where N is a number of turns in the coil, and
       dØ/dT is a rate of change of the flux, which is proportional to the rotational velocity of the rotating component  40  and the number of teeth  45 .       
 
         [0049]    The voltage V is approximately a sinusoidal wave. The voltage V is then output to an amplifier, for example a differential amplifier as shown, or alternatively an instrumentation amplifier. At the amplifier, the voltage V is amplified by a selected gain factor and level shifted to be symmetric about Vdd/2. The voltage V remains sinusoidal in nature but has a greater amplitude than the pre-amplified voltage. It is then fed into a comparator with Vdd/2 as a threshold point. The comparator has a positive feedback resistor shown in  FIG. 1  as  10 R with an input resistor R, resulting in about a 10% hysteresis. This hysteresis prevents high frequency oscillations when the V out  of the differential amplifier crosses over Vdd/2. 
         [0050]    The resultant output Out+ is a ground referenced quasi square wave that is then fed into an electronic circuit where its phase is compared with another reference square wave of the same frequency. The core in the coil is a high permeability mu-metal alloy, e.g., a high magnetic permeability alloy such as an alloy of nickel, iron, copper, and chromium or molybdenum, that will saturate at some point causing a self limiting output voltage, unlike some variable reluctance sensors that have a linear, non-saturating core. The high permeability of the core material compared with other variable reluctance sensors allows for miniaturization of the detector and fewer turns of copper. 
         [0051]    The fluxgate output signal from the one or more fluxgate sensors  30  of the tooth sensing device  20  may be used as an absolute position encoder such that the stopping position of the rotating component  40 , such as a flexplate  40  of an engine for example, may be determined. The fluxgate output signal (or another tooth sensing method that does not require rotation to detect teeth  45 ) may be used to track the position of the teeth  45  as the rotating component  40  slows to a stop. Another input signal, such as a cam sensor signal for example, may be used to determine the position of the rotating component  40  within the engine cycle and once calibrated, each tooth  45  would be numbered and tracked as the engine stops. This information would be provided to a controller (not shown) or an engine control computer so that the absolute position of the shaft  35  supporting the rotating component  40  would be known. Such information would be useful, for example, for start-stop systems. 
         [0052]    The tooth sensing device  20  and the method of sensing tooth position as described herein may be used for, but not limited to, angular speed measurement, distance traveled calculation, absolute position encoding, relative position encoding, and torque sensing. This is a more robust method of tooth sensing, as the system is less sensitive to the magnetic state of the flexplate (or alternatively the teeth of any toothed wheel). 
         [0053]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims. cm What is claimed is: