Abstract:
A magnetic effect sensor system has a target with a first set of regularly spaced tooth/slot transition target features and a second set of different tooth/slot transition target features interspersed within the regularly spaced features. The mix of target features allows a single magnetic effect sensor to output a clocking pulse train for misfire detection and an encoded pulse train for determining absolute mechanical position by utilizing two thresholds on the sensor output waveform.

Description:
This invention claims priority from U.S. patent application Ser. No. 60/078,606, filed on Mar. 19, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention: 
     The present invention relates generally to position sensing apparatus and more particularly to magnetic effect sensing apparatus including linear position sensing as well as the commonly known rotary position “geartooth sensors” wherein a magnetically sensitive device senses a ferrous object or objects generally projecting from a rotating target and resembling the teeth of a gear. 
     2. Discussion of the Related Art: 
     Various sensors are known in the magnetic effect sensing arts. Examples of common magnetic effect sensors may include Hall effect and magnetoresistive technologies. Generally described, these magnetic sensors will respond to the change of magnetic field as influenced by the presence or absence of a ferromagnetic target object of a designed shape passing by the sensory field of the magnetic effect sensor. The sensor will then give an electrical output which can be further modified as necessary by subsequent electronics to yield sensing and control information. The subsequent electronics may be either onboard or outboard of the sensor package per se. In the following explanation the ordinarily skilled artisan will appreciate that adjacent slot and tooth combinations, in whatever order, are necessary to produce the duty cycle required for an intelligible output pulse. Thus, a reference to “slot-to-tooth’ may be deemed equivalent to “tooth-to-slot”, and the obvious or equivalent inverse will not be stated in the text where the two would simply be inversions of each other. 
     For example, geartooth sensors are known in the automotive arts to provide information to an engine controller for efficient operation of the internal combustion engine. One such known arrangement involves the placing of a ferrous target wheel on the crank shaft of the engine with the sensor located proximate thereto. The target objects, or features, i.e. tooth and slot, are of course properly keyed to mechanical operation of engine components. The regularly spaced tooth-to-slot transitions yield a rhythmic, or regular, pulse pattern which determines the timing, or clocking., information necessary to run such functions of the engine as fuel injection and spark plug firing. But those targets designed exclusively with tooth-to-slot transitions at regular intervals and with slot-to-tooth transitions at regular intervals, i.e. regular tooth and slot features throughout the target circumference do not contain any information that would indicate absolute position of the target. 
     Typically therefore, feature, i.e. teeth and slot, widths are lengthened and/or shortened to yield a “signature” or coded pulse that can be distinguished as being different from the rest of the features, and this one signature pulse will yield information that will indicate absolute position of mechanical components, eg. of the engine. Determining the absolute engine position at start up is commonly referred to as “synchronization”. To “synchronize” as quickly as possible, i.e. before a complete revolution of the target, additional “signature” pulse generating features must be added to yield information at more than one place on the target. This is the method by which the internal combustion engine controller determines the absolute position of the pistons within the cylinders, thereby yielding information that can be utilized at startup of the engine to “synchronize” its functions and increase engine efficiency and decrease fuel emissions. 
     However, by eliminating the regularity of teeth or slots to gain the encoded signal, the regular timing pulse is adversely affected. By creating irregular or missing elements within the timing sequence, less timing information is provided. Also, because the feature transitions are not regular, magnetic fringing effects which decrease the accuracy and repeatability of sensor output, can arise. 
     Another desired feature is to be able to detect direction of target movement. One known technique is to utilize a differential sensor which will yield a certain pulse train, or signal, when the target is rotated in one direction and the inversion of that signal when the target is rotated in the opposite direction; with a regular target with wide features of one type and narrow features of the other type, for example, wide slots and narrow teeth. When the target is spinning in one direction the digital output will be high a majority of the time and when the target is spinning in the opposite direction, the digital output will be low a majority of the time; hence duty cycle of the output can be used to determine the direction of target rotation. However, when utilizing this technique a regular type of target does not contain any information with regard to absolute position and will not allow for “synchronization”. 
     To provide a constant pulse train for timing purposes and an encoded pulse train for absolute engine position and directional information during startup, one could use two sensors and two separate targets, however, this would increase the expense to the automotive manufacturer and is therefore undesirable. 
     Therefore, there exists a need for a target and sensor system which allows the user the ability to determine both regular timing pulses and direction of target movement very quickly without sacrificing “synchronization” performance, while being economical to use 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention is to provide more information from a single sensing apparatus while utilizing the same target footprint. 
     It is another object of the present invention to provide a timing pulse train, and an encoded pulse train for determination of engine position, by applying multiple thresholds to the output of a single sensor which is detecting a target, or targets, designed to have multiple topographies without sacrifice of the constant, or regular timing pulses. 
     It is a further object of the present invention to provide a method and apparatus whereby a constant timing pulse and a variable encoded pulse may be gained from a single target by utilizing multiple thresholds on the output of a single magnetic sensing apparatus in order to yield a constant timing signal and special positional information for a mechanical apparatus. Several embodiments are disclosed which will yield this result. 
     It is a further object of the present invention to determine direction of target movement without reduction of encoding or timing information features on the target. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be more fully and completely understood from a reading of the Description of the Preferred Embodiment in conjunction with the drawings, in which: 
     FIG. 1 is a partial illustration of a first embodiment of the present invention. 
     FIG. 2 is a partial illustration of a second embodiment of the present invention. 
     FIG. 3 is a partial illustration of a third embodiment of the present invention. 
     FIG. 4 is an illustration of the sensor output and electronic pulse train according to the sensing apparatus of the present invention corresponding to the embodiment of FIG.  1 . 
     FIG. 5 is an illustration of the sensor output and electronic pulse train according to the sensing apparatus of the present invention corresponding to the embodiment of FIG.  2 . 
     FIG. 6 is an illustration of the sensor output and electronic pulse train according to the sensing apparatus of the present invention corresponding to the embodiment of FIG.  3 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Throughout the Description of the Preferred Embodiment, like components will be identified by like reference numerals. 
     Referencing FIG. 1, a first embodiment of the present invention provides a regular single element magnetic effect sensor  17 , such as a Hall effect sensor or magnetoresistive sensor, in any of various configurations or compositions. The geartooth target  19  is uniquely configured to provide a regular timing pulse and an encoded engine position pulse by providing varied slot depths between the target teeth. There are shallow slots  23  with deep slots  25  interspersed therein at encoded intervals. As seen in FIG. 4, the output  27 , from the sensor  17 , is a substantially sinusoidal wave with waves of a first magnitude  29  having troughs  31  corresponding to the shallow slots  23  and waves of a second magnitude  33  with second troughs  35  corresponding to deep slots  25 . The sensing electronics, represented by, but not limited to, the comparator  37 , then converts the sensor output wave  29  to a first digital pulse train  39  with a regular clocking pulse square wave function because each trough  31  in the pulse train triggers at a first higher threshold  41 . A second digitally encoded pulse train  43  is emitted which contains only state changes at the deeper troughs  35  owing to a second, lower threshold  45  being set to trigger these pulses. These pulses are then passed on to the engine controller  47  which is a microprocessor based electronics package or the like. It will be appreciated that the comparator  37  may be a single unit or multiple units depending on the number of threshold and pulse trains desired. It will further be appreciated that additional electronic components such as amplifiers, inverters and the like may be utilized as necessary or desirable upon consideration by those having ordinary skill in the art. It will also be appreciated that the location of the components could be either on-board the sensor or outboard as deemed desirable and that the present invention may be implemented in analog or digital electronics or a combination of both. 
     Referencing FIG. 2, a differential sensor  49 , of the type having multiple sensing elements so as to detect slot to tooth transitions and tooth to slot transitions, communicates with controller  47  (similar to controller  47  illustrated in FIG. 1) and is aimed at the geartooth target  50 . In the second embodiment of the present invention the regular spacing of the timing pulses is achieved by placing a high to low, or tooth to slot transition  51 , as best seen in FIG. 5, at regular intervals throughout the circumference of the target  50 . Normally, the slot to tooth transition is a sharp perpendicular low to high edge  53 . But, in the case of encoded signals, the sharp leading edge  53  is substituted by a shallow ramp  55  for selected teeth which the differential sensor does not detect because of the gradual magnetic gradient. The sensor yields an output  57  of sharp positive going pulses  58  at the sharp tooth-to-slot transitions  51  and sharp negative going pulses  60  at the sharp slot-to-tooth transitions  53  and no pulses at the ramp features  55 . A positive threshold  62  is set for the clock threshold and a negative threshold  64  for the encoded pulses, which occur only irregularly due to the substitution of ramp features for sharp slot-to-tooth features. The comparator  37  then produces a rhythmic or regular clock signal digital pulse  59 . The sensing electronics or comparator may also generate an encoded signal  61  corresponding to the negative going pulse  60  as seen in FIG.  5 . 
     It has been found in practice that the ramp features  55  may still be detected by the differential sensor owing to the difficulty in making the ramp so gradual as to produce an undetectable gradual gradient. However, the embodiment of FIGS. 2 and 5 may be practical in certain applications. For example, a circuit with a high-pass filter may be used to reject the ramp and only detect the tooth/slot edges. 
     Referencing FIGS. 3 and 6, a differential magnetic sensor  49  is aimed at the geartooth target  67 . In this third embodiment of the present invention, the topography of the target teeth is changed to have a regular tooth type  63  and a stepped tooth type  65 . The tooth to slot transitions  51  are again placed at regular intervals to yield the timing pulse  39  by placing a first positive threshold  73  and a second negative threshold  77  on the sensor output  75 . The slot-to-tooth transitions  53  of the first regular tooth type  63  will yield a single pulse  69  while the double “slot-to-tooth transitions”, or low to high transitions of the step tooth type  65  will yield a double pulse  71 . The microprocessor  47 , by counting the double pulses is able to determine the encoded information. A tristate output  79  is shown to illustrate that the multiple output pulses from the two sensor thresholds may be combined on a single output line if deemed necessary. It will thus be appreciated that numerous thresholds may be utilized to yield multiple streams of information and that one or more output lines may be used to carry this information. 
     Also, the present invention can yield information on the direction of travel very quickly, in distinction to the known art target types. In the known targets, where feature length is changed to yield encoding; not all “bits”, defined here as the passage of a tooth and its adjacent slot; are known to have the same tooth-to-slot ratio, i.e. yield the same duty cycle for the output pulse. Therefore, in the known art, a unique sequence of “bits” must be recognized by the controller to determine the direction of target movement. But, as seen in the present invention, because every bit is occupied by more slot than tooth, the controller needs only know the duty cycle information of one bit to determine direction of travel. And no encoding is sacrificed. 
     It will be appreciated that any number of various feature configurations may be used on the target object in conjunction with multiple thresholds to yield increased information from the sensing system described. As an example, multiple-stepped teeth beyond the tooth type shown could be added to yield multistate outputs as necessary for additional encoding or other control information dependent upon the resolution of the sensor and design constraints of the target wheel. Or, side by side target tracks on a single wheel or multiple wheels might also be used if the sensor output is appropriately designed to utilize the teachings of the present invention. Also, magnetic sensing implementations beyond the specific embodiments shown are contemplated. For example, a magnetic target having multiple magnetic signatures, such as a ring magnet incorporating different magnetic densities, are considered to be within the scope of the present invention. It will be appreciated by the ordinarily skilled artisan that, although shown herein as a function of voltage, the sensor output may operate as a function of current as well. Also, although the preferred embodiments utilize differential and single element sensors, the invention is not solimited but may be used with any variety of sensor element configuration, including but not limited to multiple element and bridge configurations. 
     Thus the present invention teaches how to get more control information without increasing target footprint, or decreasing timing information, from a target with multiple features and a single magnetic sensor by utilizing more than one threshold in converting the sensor output to pulse train information for yielding the control information. By following the teachings of the present invention presented herein, many embodiments of the present invention will occur to those persons having ordinary skill in the art. 
     While the present invention has been shown and described with reference to preferred embodiments, many alternatives will become apparent to the ordinarily skilled artisan upon disclosure of the present invention. Therefore the present invention is only to be limited by the claims appended hereto.