Abstract:
A combination Hall effect position sensor and switch for sensing the position of a moveable object. The sensor has a magnet that is attachable to the moveable object. The magnet has a pair of ends and a central portion. A linear magnetic flux sensor is positioned about the central portion of the magnet. The linear magnetic flux sensor generates an electrical signal indicative of a specific position of the movable object. A switch type magnetic flux sensor is positioned about one of the ends of the magnet. The switch type magnetic flux sensor generates an electrical signal that is indicative of the movable object reaching a pre-determined location.

Description:
BACKGROUND  
       [0001]     1. Technical Field  
         [0002]     This invention relates, in general, to position sensors. More particularly, this invention relates to a sensor that uses Hall effect devices to generate signals indicating positional information.  
         [0003]     2. Background Art  
         [0004]     Position sensing is used to electronically monitor the position or movement of a mechanical component. The position sensor produces an electrical signal that varies as the position of the component in question varies. Electrical position sensors are a part of many products. For example, position sensors allow the status of various automotive components to be monitored and controlled electronically.  
         [0005]     A position sensor needs to be accurate, in that it must give an appropriate electrical signal based upon the position measured. If inaccurate, a position sensor may hinder the proper evaluation and control of the position of the component being monitored.  
         [0006]     Typically it is also described that a position sensor be adequately precise in its measurement. However, the precision needed in measuring a position will obviously vary depending upon the particular circumstances of use. For some purposes only a rough indication of position is necessary; for instance, an indication of whether a valve is mostly open or mostly closed. In other applications more precise indication of position may be needed.  
         [0007]     A position sensor should also be sufficiently durable for the environment in which it is placed. For example, a position sensor used on an automotive valve may experience almost constant movement while the automobile is in operation. Such a position sensor should be constructed of mechanical and electrical components to allow the sensor to remain sufficiently accurate and precise during its projected lifetime, despite considerable mechanical vibrations and thermal extremes and gradients.  
         [0008]     In the past, position sensors were typically of the “contact” variety. A contacting position sensor requires physical contact to produce the electrical signal. Contacting position sensors typically consist of potentiometers to produce electrical signals that vary as a function of the component&#39;s position. Contacting position sensors are generally accurate and precise. Unfortunately, the wear due to contact during movement of contacting position sensors has limited their durability. Also, the friction resulting from the contact can degrade the operation of the component. Further, water intrusion into a potentiometric sensor can disable the sensor.  
         [0009]     One important advancement in sensor technology has been the development of non-contacting position sensors. A non-contacting position sensor (“NPS”) does not require physical contact between the signal generator and the sensing element. Instead, an NPS utilizes magnets to generate magnetic fields that vary as a function of position, and devices to detect varying magnetic fields to measure the position of the component to be monitored. Often, a Hall effect device is used to produce an electrical signal that is dependent upon the magnitude and polarity of the magnetic flux incident upon the device. The Hall effect device may be physically attached to the component to be monitored and thus moves relative to the stationary magnets as the component moves. Conversely, the Hall effect device may be stationary with the magnets affixed to the component to be monitored. In either case, the position of the component to be monitored can be determined by the electrical signal produced by the Hall effect device.  
         [0010]     The use of an NPS presents several distinct advantages over the use of a contacting position sensor. Because an NPS does not require physical contact between the signal generator and the sensing element, there is less physical wear during operation, resulting in greater durability of the sensor. The use of an NPS is also advantageous because the lack of any physical contact between the items being monitored and the sensor itself results in reduced drag.  
         [0011]     While the use of an NPS presents several advantages, there are also several disadvantages that must be overcome in order for an NPS to be a satisfactory position sensor for many applications. Magnetic irregularities or imperfections can compromise the precision and accuracy of an NPS. The accuracy and precision of an NPS can also be affected by the numerous mechanical vibrations and perturbations likely be to experienced by the sensor. Because there is no physical contact between the item to be monitored and the sensor, it is possible for them to be knocked out of alignment by such vibrations and perturbations. A misalignment can result in the measured magnetic field at any particular location not being what it would be in the original alignment. Because the measured magnetic field can be different than that when properly aligned the perceived position can be inaccurate. Linearity of magnetic field strength and the resulting signal is also a concern.  
         [0012]     In determining the position of the item being monitored, it is useful to know when the sensor has reached or moved to a certain location. Once a given position has been reached, a mechanism can provide feedback indicating that the pre-determined position has been achieved. Typically, such a mechanism has taken the form of a separate contact switch. Unfortunately, adding a separate switch complicates the packaging of the position sensor, adds extra cost and increases the overall size of the sensor.  
         [0013]     There is a need for a compact, low cost position sensor that is integrated into a single package and provides position and related information.  
       SUMMARY  
       [0014]     It is a feature of the present invention to provide a combination hall effect position sensor and switch.  
         [0015]     It is another feature of the present invention to provide a sensor that generates signals for indicating the position of a movable object. The sensor includes a magnet attachable to the moveable object. The magnet has a pair of ends and a central portion. A linear magnetic flux sensor is positioned near the central portion of the magnet and a switch-type magnetic flux sensor is positioned about one of the ends. The linear magnetic flux sensor generates an electrical signal indicative of a specific position of the movable object. Further, the switch-type magnetic flux sensor generates an electrical signal indicative of the movable object reaching a pre-determined position. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  illustrates a side view of a combination Hall effect position sensor and switch;  
         [0017]      FIG. 2  illustrates a graph of mechanical position versus output signals for the sensor and switch of  FIG. 1 ;  
         [0018]      FIG. 3  illustrates a side view of the preferred embodiment of a combination Hall effect position sensor and switch;  
         [0019]      FIG. 4  illustrates a graph of mechanical position versus magnetic flux density for the magnet of  FIG. 3 ;  
         [0020]      FIG. 5  illustrates an alternative magnet design for the sensor and switch of  FIG. 3 ;  
         [0021]      FIG. 6  illustrates a graph of mechanical position versus magnetic flux density for the magnet of  FIG. 5 ;  
         [0022]      FIG. 7  illustrates an exploded view of the combination Hall effect position sensor and switch of  FIG. 3  packaged in a housing;  
         [0023]      FIG. 8  illustrates a perspective assembled view of  FIG. 7 .  
         [0024]      FIG. 9  illustrates a perspective view of the assembled sensor and switch of  FIG. 8  mounted to a clutch pedal. 
     
    
       [0025]     It is noted that the drawings of the invention are not to scale.  
       DETAILED DESCRIPTION  
     First Embodiment  
       [0026]     Referring to  FIG. 1 , a combination Hall effect position sensor and switch  100  is shown. Preferably the sensor and switch  100  has a permanent magnet  102  that is polarized such that it has a north end  104 , a south end  106  and a central region or portion  108 . Permanent magnet  102  can be made from several different ferro-magnetic materials such as, but not limited to, ferrite or samarium cobalt or neodymium-iron-boron. Magnet  102  is attachable in a conventional manner to a movable object or member  110  such as by adhesive or mechanical fastening means. Movable object  110  can be a rotatable shaft, a reciprocating lever, a pedal or other movable member. As such, movable object  110  can be adapted to move either linearly, rotationally, or along an arcuate planar path. Sensor and switch  100  are configured to work with the linear, rotational or arcuate motion of the moveable object  110 .  
         [0027]     A switch type magnetic flux sensor, such as a conventional switch-type Hall effect device  112  is positioned adjacent or near the magnet north end  104 . Another conventional switch-type magnetic flux sensor, such as a switch-type Hall effect device  116  is positioned adjacent or near the magnet south end  106 . Switch-type Hall effect devices  112  and  116  are commercially available as model HAL1000 from Micronas company of Zurich, Switzerland. Switch-type Hall effect devices  112  and  116  produce a step output once the gauss level exceeds a certain level. For example, if the magnetic flux level sensed exceeds 300 gauss or 30 milli-tesla (mT), Hall effect devices  112  and  116  will switch output from 0 volts to 5 volts. Accordingly, when Hall effect device  112  or  116  is located about magnet  102  as shown in  FIG. 1 , the Hall effect devices will be turned on and have an output of 5 volts. However, if movable member  110  moves such as to also move magnet  102  to the right Hall effect device  112  will no longer be about the north end  104 , and thus the output of Hall effect device  112  switches to 0 volts. Similarly, if movable object  110  moves to the left such that Hall effect device  116  is no longer about the south end  106  of magnet  102 , then the output of Hall effect device  116  switches to 0 volts.  
         [0028]     A ratiometric or linear output type magnetic flux sensor, such as a linear type Hall effect device  114  is positioned adjacent or near the magnet central portion  108 . Hall effect devices  112 ,  114  and  116  are separated from magnet  102  by a gap or open space  118 .  
         [0029]     Linear type Hall effect device  114  is commercially available as model HAL815 from Micronas company of Zurich, Switzerland. Linear type Hall effect device  114  produces a linearly changing output voltage depending upon the polarity of the magnetic field sensed. For example, when the polarity changes from North through the zero point to South, Hall effect device  114  will output a voltage that varies linearly from 0.50 volts to 4.50 volts.  
         [0030]      FIG. 2  shows a graph of mechanical position versus the output signals for the sensor and switch of  FIG. 1 . As stated previously, the electrical output signal of switch Hall effect devices  112  and  114  changes in a step function. Moreover, the electrical output signal of linear Hall effect device  114  changes linearly.  
       Preferred Embodiment  
       [0031]      FIG. 3  illustrates a side view of the second or preferred embodiment of a combination Hall effect position sensor and switch  290 . Sensor and switch  290  has a magnet assembly  300  with a pair of pole pieces or plates including a first plate  301  and second plate  302 . The first plate  301  has a first end  551 , a second end  552 , and a middle  553 . The second plate  302  likewise has a first end  561 , a second end  562 , and a middle  563 . It is to be appreciated that the first plate  301  and second plate  302  may be of any shape, and the reference to “ends” is used for purpose of demonstration, not to limit the scope of configurations possible within the scope of the present invention.  
         [0032]     The first magnet region  321  has a thin end  521  and an opposite thick end  531  with a tapered portion therebetween. The first magnet region  321  is affixed to the first plate  301  such that the thin end  521  is proximate to the middle  553  of the first plate  301 , while the thick end  531  is proximate to the first end  551  of the first plate  301 . The first magnet  321  produces a varying magnetic flux field from the thin end to the thick end, as indicated by vectors  600  in  FIG. 3 . The polarity of the magnetic field generated by the first magnet region  321  is indicated by the upward direction of the vectors  600 . The polarity of the magnetic field generated by the first magnet  321  is denoted the first polarity and defined as positive. Likewise, the strength of the magnetic flux field is indicated by the length of the vectors. As can be seen in  FIG. 3 , the magnetic flux field generated by the first magnet  321  decreases in strength from the thick end  531  to the thin end  521 . Like magnet  321 , magnets  322 ,  323  and  324  are similarly designed as illustrated. As recognized by those having skill in the art, the third magnet region  323  and the first magnet region  321  are described as linearly or symmetrically adjacent, or simply adjacent. Likewise, the second magnet region  322  and the fourth magnet region  324  are described as linearly or symmetrically adjacent, or simply adjacent.  
         [0033]     The four tapered magnets  321 ,  322 ,  323 , and  324  can be formed of bonded ferrite or other magnetic materials. A first gap  581  is shown separating the thin end  521  of the first magnet  321  from the thin end  523  of the third magnet  323 . A second gap  582  separates the thin end  522  of the second magnet  322  from the thin end  524  of the fourth magnet  324 . While the gaps  581  and  582  can be omitted without departing from the scope of the present invention, they serve important functions. In particular, the gaps  581  and  582  increase the consistency of the linearity of the magnetic field within the space or void  516  between the magnets attached to plates  301  and  302 . As a practical matter, the thin end of a magnet will always have a finite thickness and generate a non-zero magnetic field. If the thin ends of two magnets having opposite polarities are immediately adjacent, there will be a discontinuity of the combined magnetic field about the symmetry point  543 . Gaps  581  and  582  allow for a consistent neutral zone, at around point  543  independent of magnetizing property variations, which aids linearity of sensor output. The gaps  581  and  582  can be created during the molding of the magnets. If the magnets are formed individually, the gaps  581  and  582  may be formed by appropriately positioning the individual magnets. Alternatively, magnetic material may be removed to create the gaps after the magnets have been formed.  
         [0034]     The air gap  516  is formed between the magnet regions  321 ,  322 ,  323  and  324 . Preferably, the air gap or space or void  516  between the magnets  321 ,  322 ,  323  and  324  is essentially diamond shaped, with the central portion of the air gap  517  being larger than both ends  518  of the air gap  516 . A linear magnetic flux sensor such as a Hall effect device  114  is positioned within the air gap or void  516 . A switch Hall effect device  112  is also located in air gap  576  between magnet regions  321  and  322 . The relative lateral movement between the Hall effect device  114  and the magnets causes the position of the Hall effect device  114  within the air gap  516  to vary along plane or line  540 . The magnetic field within the air gap  516  is the sum of the magnetic fields generated by the first magnet  321 , the second magnet region  322 , the third magnet  323  and the fourth magnet region  324 .  
         [0035]     The polarity and strength of the combined magnetic field varies along the axis or line  540 . One end of line  540  is at about position  541  and the other end is at about position  542 . The magnetic field generated by the first magnet  321  and the second magnet  322  is defined as positive. The magnetic field generated by the third magnet  323  and the fourth magnet is defined as negative.  
         [0036]     Magnet assembly  300  can be attached to a movable object that rotates or moves linearly. Magnet assembly  300  can move to the left or right of the position shown. The magnetic field detected by the Hall effect device  114  as it moves along the line  540  will be large and positive at the first end  541  of the air gap and decrease substantially linearly as it approaches the middle  543  of the air gap, at which point the magnetic field will be substantially zero. Magnet assembly  300  is preferably designed and constrained so as to not to move to the left.  
         [0037]     Switch Hall effect device  112  is located at position  541  to start. Hall effect device  112  travels along the line  540  between position  543  and position  544 . At about position  541 , switch Hall effect device  112  will be in the presence of a flux field that is strong enough to keep it switched on. As the magnets move to the right and Hall effect device  112  relatively goes to position  544 , the strength of the flux field rapidly falls off with distance from ends  531  and  532  of the magnet. This flux change is sensed by Hall device  112  and causes device  112  to switch output from a high state of 5 volts to a low state of 0 volts output.  
         [0038]     Hall devices  112  and  114  would be connected to additional signal conditioning circuitry (not shown) that would amplify and condition the electrical signals. It is noted that the switch Hall effect device  112  could be configured to switch from 0 volts at position  541  to 5 volts at position  544  if desired by modifying the signal conditioning circuitry.  
         [0039]     Magnet assembly  300  is preferably designed and constrained so as to not move to the left. This avoids any possible problems with Hall effect switch  112  switching in a region of low magnetic flux such as at position  543 .  
         [0040]      FIG. 4  illustrates a graph of mechanical position versus magnetic flux density for magnet assembly  300 . In  FIG. 4 , the x-axis denotes the position of the Hall effect devices  112  and  114  along line  540  and the y-axis illustrates the magnetic flux density detected. As can be seen, the magnetic flux density measured by the Hall effect device  114  at position  543  is low and goes to high at position  541 . The flux measured by Hall device  114  has a low gradient or rate of change. The measured magnetic flux density is substantially linear between position  541  and position  543 , with the point of substantially zero magnetic flux density being located at position  543 . The magnetic flux density measured by the Hall effect device  112  at position  541  is high and rapidly falls to zero at position  544 . The magnetic flux measured by Hall device  112  has a high gradient or rate of change, resulting in low variability in the switch point position.  
       Third Embodiment  
       [0041]      FIG. 5  illustrates a third embodiment that uses an alternative magnet assembly design. Magnet assembly  700  is similar to magnet assembly  300  except that additional field shaping magnets  702 ,  703 ,  704  and  705  have been added. Magnet  702  adjoins end  531  of magnet  321 . Magnet  703  adjoins the end  532  of magnet region  322 . Magnet  704  is adjoins end  533  of magnet  323 . Magnet  705  adjoins the end  534  of magnet  324 . Field shaping magnets  702 ,  703 ,  704  and  705  are polarized opposite to the polarization of magnets  321 ,  322 ,  323  and  324 . Compared to the magnet assembly  300  of  FIG. 3 , field shaping magnets  702 ,  703 ,  704  and  705  cause the magnetic flux field detected by switch Hall effect device  112  to have a larger gradient with a change in position or to change more quickly as magnet assembly  700  is moved. This allows for more precise switch positions for switch Hall device  112 .  
         [0042]      FIG. 6  shows a graph of mechanical position versus magnetic flux density for magnet assembly  700  and  300  as they move from position  541  to  544 . As can be seen in  FIG. 6 , the flux density for magnet assembly  700  changes more steeply than for magnet assembly  300 . The position switching range for magnet assembly  700  is designated as Q.  300 . The position switching range for magnet assembly  300  is designated as R. The position range R is larger than position range Q. In other words, with nominal tolerances in the switch point of the Hall effect device, magnet assembly  300  will display more variation in switch position than will magnet assembly  700 . The higher flux gradient is due to the pole reversal created by magnets  702  and  703 .  
         [0000]     Clutch Position Sensor and Switch  
         [0043]     In accordance with the present invention, a non-contacting clutch position sensor and switch  800  is shown in  FIGS. 7, 8  and  9 . Clutch position sensor and switch  800  includes a housing  810 , cover  820 , magnet holder  830 , magnet assembly  300 , circuit board  840 , connector shroud  850 , clutch bracket  900  and clutch pedal  910 . Housing  810  has a cavity  812 , a pedal opening  813 , a mounting hole  814  and bearing races  815 . Housing  810  can be injected molded plastic.  
         [0044]     Magnet holder  830  has bearing holders  832 , dovetail portion  833  and magnet cavity  834 . Magnet assembly  300  fits into and is retained by magnet cavity  834 . Magnet holder  830  can be injected molded plastic. Ball bearings  836  are located between bearing holder  832  and bearing races  815 . Magnet holder  830  moves in housing  810  along bearing races  815 . Printed circuit board  840  holds switch Hall effect device  112  and linear Hall effect device  114 . The Hall effect devices have leads that are soldered to the printed circuit board. The printed circuit board holds the Hall effect devices in air gaps  516  and  576 . The printed circuit board has terminals  842  that extend into connector shroud  850 . Circuit board  840  is press fit into connector shroud  850 . Printed circuit board  840  can also have signal amplification and conditioning circuitry mounted on it.  
         [0045]     Cover  820  has an aperture  822  through which the printed circuit board passes. Seal  826  makes a seal between connector shroud  850  and cover  820 . Cover  820  is heat staked to housing  810 . Clutch pedal arm  910  extends through housing opening  813  and is mounted to magnet holder  830 . Dovetail portion  833  fits into a corresponding dovetail receptacle (not shown) on pedal arm  910  in order to retain magnet holder  830  to pedal arm  910 . Clutch sensor  800  is mounted to clutch bracket  900  by bolt  902  through mounting hole  814 . A rod  920  extends through pedal arm  910  and bracket  900 . Rod  920  rotatably supports pedal arm  910 .  
         [0046]     When clutch pedal arm  910  is depressed by a vehicle operator, magnet holder  830  and magnet assembly  300  moves with respect to printed circuit board  840 . With Hall devices  112  and  114  fixed in place, their respective electrical output signals change in response to the position of pedal arm  910 . As the magnetic field generated by the magnets  300  and detected by the Hall effect device  114  varies with rotation, the signal produced by the Hall effect device  114  changes accordingly, allowing the position of the pedal arm to be ascertained.  
         [0047]     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.