Abstract:
A method is provided for producing a magnetic position or path sensor element, the magnetic position or path sensor element having at least one magnetic pathway that extends along a displacement path and that has a plurality of magnetic north-south transitions, as well as at least one magnetic sensor mounted so as to be movable relative to the magnetic pathway. At least one of the magnetic north-south transitions is defined as a critical north-south transition whose position is to be detected with a specified degree of precision. Adjacent to the critical north-south transition are situated magnetic poles having identical polarity. The method provides production reliability by reducing the sensitivity of the magnetic position or path sensor element to positional tolerances.

Description:
FIELD OF THE INVENTION 
     The present invention relates to magnetic sensor elements that can be used for example as linear position sensors and/or path sensors. In particular, the present invention relates to the production of an optimized multipole geometry for magnetic linear position and path sensors. Such magnetic sensor elements can for example be used in automotive technology, in particular as linear position and/or path sensors in automatic transmissions. In various areas of the natural sciences and technology, the recognition of a relative position and/or positioning between two elements that are mounted so as to be movable relative to one another is required. In the following, example embodiments of the present invention are described substantially with reference to position sensors for transmission controlling, for example in automatic transmissions, in which positions of an actuating element (for example of a selector lever shaft, of a selector slide, or of a parking lock cylinder) are to be detected relative to the housing or to some other fixed element. Such position sensors may be used individually and may also be integrated into electronics modules. Position sensors that can also be modified in the present context are described for example in Robert Bosch GmbH, “Sensoren im Kraftfahrzeug,” ed. 2007, pp. 136-137. However, other applications are also possible in principle. 
     BACKGROUND INFORMATION 
     For position recognition, in many cases sensors are used that operate according to the Hall sensor principle. For example, for this purpose application-specific integrated circuits (ASICs) can be used as magnetic sensors that, in addition to one or more sensors, for example Hall sensors, can also include an electronics system, for example an electronics system that processes or pre-processes the signals of the sensors. The sensitive elements in the sensors, or the ASICs, are as a rule excited by a movable multipolar permanent magnet, also called an encoder. The signal in the ASICs is generated by the pole transition of the magnetic field (transition from north to south or transition from south to north, referred to hereinafter as a north-south transition without limitation of the direction of transition). The encoder is moved by a coupling with an entraining piece, for example the above-named selector lever. The detection of the position of the encoder by the ASICs is the function of the magnetic sensor element. 
     For example, in an automatic transmission that is switched manually, the position sensor detects the position of the selector lever and/or selector slide, for example the positions P, R, N, D, S, as well as the intermediate regions, and outputs these to a transmission control device in the form of a code, for example a 4-bit code. For reasons of safety, the coding of the position is as a rule carried out in one step, i.e. two bit changes are always required for the recognition of a new position. The required magnetic field curve (pole transition) is provided to the sensitive elements by the encoder for the correct signal output. However, in the case of a geometrical displacement relative to a specified nominal position, due for example to positional tolerances, distortions of the pole transitions due to the mutual influence of the magnetic poles can cause a deviation of the measured position signal. In order to ensure sufficient sensor precision, the positioning of the slide in all three spatial directions relative to the sensitive elements of the ASICs must have narrow tolerances. 
     As a rule, the positional tolerances between the sensitive elements and the encoder are a consequence of assembly and/or component tolerances. Thus, a tolerance chain of these tolerances includes for example the positioning of Hall elements inside an ASIC, the positioning of the Hall ASIC in the sensor package, a positioning of the sensor package with respect to a reference point in the overall system, the positioning of the sensor package relative to the encoder, and the positioning of the encoder relative to the entraining element, for example the selector lever (measurement object). However, this tolerance chain represents a considerable challenge for the manufacturing tolerances that are to be realized. This can result in high reject rates and a high economic expense for reject reduction. 
     SUMMARY 
     Therefore, a method for producing a magnetic sensor element and a magnetic sensor element are described herein that at least significantly avoid the challenges and disadvantages of known magnetic sensor elements and production methods. Example embodiments of the present invention provide a suitable design of the multipole geometry of the magnetic encoder, which can bring about a significant reduction in the sensitivity of the magnetic sensor element to positional tolerances between the encoder and sensitive elements of the Hall ASICs. In this manner, an increased production reliability can be achieved, and the requirements of precision in the overall assembly process of the magnetic sensor element can be greatly reduced. 
     Example embodiments of the present invention are based on the recognition that the precision with which a north-south transition of the encoder can be detected is able to be strongly influenced by the magnetic poles situated immediately adjacent to the north-south transition. Correspondingly, according to example embodiments of the present invention it is provided that particularly critical north-south transitions in the magnetic multipole geometries of the encoder be fashioned such that the magnetic environment of these northsouth transitions enables an optimized detection. 
     A corresponding method is provided for producing a magnetic sensor element. For example, as presented above, the magnetic sensor element can be arranged as a position and/or path sensor, for example as a linear position and/or path sensor. For further possible example embodiments, reference is made to the above description, which can be modified according to example embodiments of the present invention. 
     The magnetic sensor element includes at least one magnetic pathway that extends along a displacement path. A displacement path should be understood as a path stretch along which at least two elements of the magnetic sensor element that are mounted so as to be movable relative to one another can move relative to one another. For example, these two elements mounted movably relative to one another can be an entraining element—for example, a selector lever, a selector slide, or a parking lock cylinder—and a housing that are movable relative to one another, the position of these elements relative to one another defining for example a switching setting, in particular a switching setting of an automatic transmission. The displacement path can in particular be made linear, but in principle curved displacement paths can also be provided. 
     The magnetic pathway, which can extend along the entire displacement path and/or only along parts of this displacement path, and which can also include a plurality of contiguous or non-contiguous partial paths, includes a plurality of magnetic north-south transitions. As explained above, the designation of the north-south transition is not limited to a transition from a magnetic north pole to a magnetic south pole, but rather also includes transitions in the converse direction, so that for example in a direction of movement a magnetic north pole can follow a magnetic south pole, or vice versa. Thus, in the sense of the above description, the magnetic pathway is a magnetic encoder or a part of a magnetic encoder. 
     In addition, the sensor element includes at least one magnetic sensor that is mounted so as to be movable relative to the magnetic pathway. The magnetic sensor can for example be fastened to the entraining element, and the magnetic pathway can be fastened to a housing of the magnetic sensor element, or vice versa. The movable mounting can for example take place by a carriage or a conventional movable bearing. Here, a magnetic sensor should be understood in principle as any sensor capable of detecting a magnetic field with respect to its magnitude and/or its direction. In particular, the magnetic sensor can be a Hall sensor, but in principle other conventional magnetic sensor measurement may also be used. The magnetic sensor can for example include one or more sensor elements. If for example a plurality of magnetic pathways are provided, at least one separate sensor element can be provided for each of these magnetic pathways. In addition, as described above, the magnetic sensor can also include a control and/or evaluation electronics unit, for example in an integrated circuit. Correspondingly, the magnetic sensor can be fashioned completely or partly as an ASIC, for example as an ASIC that also includes one or more or all of the named sensor elements. 
     In the production method, at least one of the north-south transitions is defined as a critical north-south transition whose position is to be detected with an increased degree of precision. In this sense, “critical” thus refers to an increased requirement with regard to the detection of the position of a north-south transition. For example, this critical north-south transition can be a transition whose detection for example brings about a changeover from a parked state into a driving state of a motor vehicle. However, other cases are also possible in which a north-south transition can be defined as a critical north-south transition. In particular, this definition can be a definition specified by a customer and/or user of a particularly critical north-south transition. For example, the magnetic pathway can include at least three north-south transitions, at least two of the north-south transitions being defined as critical north-south transitions. 
     According to example embodiments of the present invention, in order to increase the precision of the detection of the critical north-south transition it is provided to optimize the magnetic environment of this critical north-south transition. Correspondingly, in the method, adjacent to the critical north-south transition there are situated magnetic poles having identical polarity. This means that in a dimension perpendicular to the longitudinal extension of the magnetic path, i.e. perpendicular to the displacement path, adjacent to the critical north-south transition there are situated magnetic poles having identical polarity, i.e. for example north poles on both sides or south poles on both sides. These poles having identical polarity can for example be part of separate magnetic elements that are preferably situated immediately adjacent to the critical north-south transition. For example, the poles having identical polarity can be situated at a distance of less than half the width of the magnetic pathway, i.e. of the extension of the magnetic pathway perpendicular to the displacement path, preferably immediately adjoining the magnetic pathway. 
     The magnetic poles having identical polarity can for example be, as described above, part of individual magnetic elements situated adjacent to the critical north-south transition. Alternatively, the magnetic poles can however be part of additional magnetic pathways that extend parallel to the magnetic pathway and that each have at least one magnetic pole. For example, the additional magnetic pathway can be a magnetic pathway having at least one north-south transition. To this extent, example embodiments of the present invention can for example also be used in the complex, multipath multipole systems as described above, in which a plurality of magnetic pathways, for example three, four, or more magnetic pathways, are provided, corresponding to the storage depth of the specified bit pattern. For example, multipole systems can be provided that can include for example 3, 4, 5 or more magnetic pathways. 
     The additional magnetic pathways can for example be used exclusively for the purpose of the magnetic optimization of the environment of the critical north-south transition. Such additional magnetic pathways are also referred to as dummy magnetic pathways hereinafter. Their magnetic poles, for example their magnetic north-south transition or transitions, are not detected by the magnetic sensor. Correspondingly, at least one of the additional magnetic pathways can be fashioned as a magnetic pathway such that at least one magnetic pole thereof is not detected by the magnetic sensor. For example, dummy magnetic pathways can have at least one north-south transition that is at least not specifically sought out and detected by the magnetic sensor with the aim of recognizing this north-south transition. According to this aspect, in addition to the method a magnetic sensor element is provided for detecting at least one relative position between two elements that are mounted so as to be movable relative to one another, in particular for use in an automatic transmission that can in particular be capable of being produced, in a method according to an example embodiment of the present invention, in one of the exemplary embodiments described above or in the following. The magnetic sensor element has at least one magnetic pathway extending along a displacement path, the pathway having a plurality of magnetic north-south transitions and at least one magnetic sensor mounted so as to be movable relative to the magnetic pathway. At least one of the magnetic north-south transitions is defined as a critical north-south transition whose position is to be detected with a specified degree of precision. Adjacent to this critical north-south transition are situated magnetic poles having identical polarity that are part of additional magnetic pathways, each having at least one north-south transition, extending parallel to the magnetic pathway. Here it is proposed to arrange at least one of the additional magnetic pathways as a dummy magnetic pathway having at least one magnetic pole, for example at least one north-south transition, which however is not detected by the magnetic sensor. 
     Alternatively or in addition to the arrangement of one or both of the additional magnetic pathways as a dummy magnetic pathway, a design of the method or of the sensor element is however also possible in which one or both of the additional magnetic pathways is also used for the detection and/or the coding of the bit pattern. Correspondingly, the method can be designed such that the north-south transitions of at least one, preferably both, of the additional magnetic pathways are also detected by the magnetic sensor, for example by separate sensor elements of the magnetic sensor. 
     As described above, using the north-south transitions of the magnetic pathway and of the additional magnetic pathways it is possible for example to specify a defined bit pattern along the displacement path. The magnetic sensor can have separate sensors for the magnetic pathway and for at least one of the additional magnetic pathways, preferably for all additional magnetic pathways. In this manner, the named bit pattern can be detected by the separate sensors by traveling along the displacement path. 
     Because in this example embodiment at least one of the additional magnetic pathways is simultaneously used as an information carrier and as an optimization of the magnetic environment of the critical north-south transition, in some circumstances there can result a conflict in goals in the realization of the north-south transitions of this additional magnetic pathway. In order, therefore, to create a greater degree of freedom with regard to the configuration of this additional magnetic pathway, in order to meet the named conditions on the realization of this additional magnetic pathway, it is provided to use the possibility of an inversion of the north-south transitions of this at least one additional magnetic pathway. In this manner, on the one hand the described bit content of this additional magnetic pathway can be ensured, and on the other hand it can be ensured that the magnetic pole, adjacent to the critical north-south transition, of this additional magnetic pathway has the desired polarity. For this purpose, it is provided that the magnetic sensor that detects the north-south transitions of the magnetic pathway and of the additional magnetic pathways have separate sensors for the magnetic pathway and for at least one of the additional magnetic pathways. The signal of at least one sensor can here be inverted. The signal of a sensor for at least one additional magnetic pathway and/or the signal of a sensor for the actual magnetic pathway can here be inverted. This inversion can for example take place through a logical inversion and/or through other types of electronic inverters or software-implemented inverters. For example, the inversion can take place in an ASIC, for example the Hall ASIC of the magnetic sensor. In this manner, through corresponding inversions it is possible to resolve the above-described conflict of goals, in which both the magnetic environment of the critical north-south transition is optimized and also a certain information content must be contained in the additional magnetic pathway. 
     The specified degree of precision with which the position of the critical north-south transition must be detected can be specified in various manners. For example, this precision can be defined by an absolute position of a zero crossing of a magnetic signal that characterizes the transition. Alternatively or in addition, the precision can also be defined for example by an increase in the magnetic signal. For example, this increase can be defined by a change of a magnetic signal by at least a specified amount within a specified maximum stretch along the displacement path. The change in the magnetic signal can for example be specified by a concrete sensor element, for example a sensor IC (for example an application-specific integrated circuit or ASIC). The stretch along the displacement path can for example be specified via requirements on the sharpness of the switching point of the overall sensor, and can be determined for example by a tolerance chain. 
     As described above, the critical north-south transition can for example be specified by customer requirements. It is particularly preferred if the critical north-south transition is allocated to a switching transition in an automatic transmission that moves from a park setting to a non-park setting. Thus, the critical north-south transition can for example be allocated to one or more of the following switching transitions in an automatic transmission: a transition from a park setting P to an intermediate setting Z 1 ; a transition from a neutral setting N to an intermediate setting Z 2  or an intermediate setting Z 3 ; a transition from a reverse setting R to an intermediate setting Z 1  or an intermediate setting Z 2 . These transitions, which in practice must be detected with a particularly high degree of precision in order in particular to avoid accidents, can in this manner be detected particularly reliably, so that the automatic transmission can be realized particularly safely. 
     Overall, using the method and the proposed magnetic sensor element, methods and sensor elements can be realized considerably more economically. At the same time, the reject rates can be greatly reduced with a comparatively low outlay for reject reduction. Future, more stringent market requirements on the measurement precision of the magnetic sensor elements can easily be realized through the example embodiments described herein. 
     Exemplary embodiments of the present invention are shown in the drawings and are explained in more detail in the accompanying description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  show a conventional arrangement and an arrangement according to an example embodiment of the present invention of the magnetic environment of the north-south transition; 
         FIGS. 2A and 2B  show measurement curves of the magnetic field strength along the displacement path for a conventional north-south transition and for a conventional north-south transition; and 
         FIGS. 3A and 3B  show a conventional arrangement and an arrangement according to an example embodiment of the present invention of a magnetic multipole. 
         FIG. 4  shows a magnetic sensor according to an example embodiment of the present invention. 
         FIG. 5  shows a magnetic sensor having separate sensors according to an example embodiment of the present invention. 
         FIG. 6  shows a magnetic sensor having a control unit according to an example embodiment of the present invention. 
         FIG. 7  shows a magnetic sensor movably mounted by a carriage according to an example embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following, example embodiments of the present invention are described with reference to a position sensor as described for example in the above-mentioned publication by Robert Bosch GmbH: “Sensoren im Kraftfahrzeug,” ed. 2007, pp. 136-137. Correspondingly, reference is made to this publication with regard to the possible arrangements of the magnetic sensor element. Example embodiments of the present invention relate only to the arrangement of the multipole system of the magnetic encoder of the position sensor. 
       FIGS. 1A and 1B  show segments of a multipole system  110  of a magnetic encoder  112  of a magnetic sensor element  114 .  FIG. 1A  shows a part of a conventional multipole system  110 , whereas  FIG. 1B  shows an arrangement according to an example embodiment of the present invention of this multipole system  110 . In the depicted exemplary embodiment, multipole system  110  has a magnetic pathway  118  that extends along a displacement path  116 . In general, in the Figures magnetic north poles are designated N, while magnetic south poles are designated S. Magnetic pathway  118  has a plurality of north-south transitions  120 , of which only one is shown in FIGS.  1 A and  1 B. Let it be assumed that this depicted north-south transition is a critical north-south transition  122  whose position along displacement path  116  is to be detected with a specified degree of precision by a magnetic sensor not shown in the Figures, for example with a higher degree of precision than at least one additional north-south transition  120  of magnetic pathway  118 . 
       FIG. 1A  shows a conventional multipole system  110  in which the environment of critical north-south transition  122  has been arranged randomly, in that it is surrounded by additional magnetic pathways  124 ,  126  that have magnetic poles  128 ,  130  having opposite polarity situated adjacent to critical north-south transition  122 . Thus, additional magnetic pathway  124  at the left has a magnetic south pole at critical north-south transition  122 , whereas additional magnetic pathway  126  at the right has a magnetic north pole at a critical north-south transition. 
     In  FIGS. 1A and 1B , the dimension parallel to displacement path  116  is designated x, whereas the dimension perpendicular to this displacement path  116  is designated y. Furthermore in  FIGS. 1A and 1B  a curve  132  is shown that characterizes the change in the magnetic field strength as a function of the coordinate y, i.e. as a function of the position perpendicular to displacement path  116 . It follows from this curve that in the system shown in  FIG. 1A  having the asymmetrical realization of magnetic poles  128 ,  130 , the pole transition likewise extends asymmetrically, and the width of the magnetic pole is very strongly distorted. The absolute magnitude of the deviation from a target value, given a deviation from a center position inside magnetic pathway  118 , thus fluctuates comparatively strongly. Thus, due to the strong asymmetry of the pole transition represented by curve  132 , a lateral displacement can cause a significant displacement in the resulting switching point. 
     In contrast,  FIG. 1B  shows a multipole system  110  in which critical north-south transition  122  is surrounded at both sides by magnetic poles  128 ,  130  having identical polarity. In this case, the two magnetic poles  128 ,  130  are realized as south poles, but a realization as north poles is also possible. Here again, in  FIG. 1B  the change in the pole transition  132  as a function of the y coordinate is shown symbolically by curve  132 . It will be seen that in the example embodiment according to the present invention having three magnetic poles of the same type, situated in a U shape around a counterpole, in which this functionally relevant transition forms a curve in the shape of a letter “U,” curve  132  of the pole transition distorts the pole transition significantly less over the width of the magnetic pole. Due to the symmetry of the pole transition, the possible area of displacement of the switching point is also significantly reduced. Due to the symmetrical situation of magnetic poles  128 ,  132  around critical north-south transition  122 , in this manner a minimization can be achieved of the geometric distortion of the pole transition, and the insensitivity of the measurement system to the positional tolerances between the encoder and a magnetic sensor can be increased by up to a factor of 5, depending on the installation space. 
       FIGS. 2A and 2B  show magnetic field measurements at real north-south transitions  120  for a conventional multipole system  110  and a multipole system  110  according to example embodiments of the present invention. The measurements were carried out on a magnetic pathway  118  having a width of 3.3 mm. In each case, magnetic field strength B is shown as a function of the x coordinate in mm along displacement path  116 . 
     First, in both Figures a target curve  134  is shown as an example. This target curve shows that between the beginning and the end of the switching point the magnetic field strength must run through both magnetic switching thresholds of the magnetic sensor in order to trigger a switching process. The beginning and ending of the switching point (location coordinate x) and the switching thresholds of the magnetic sensor (magnetic field B) thus form the target curve. In addition, in each of the Figures a curve  136  is shown that indicates the magnetic field curve for an assumed track center in magnetic pathway  118 . In addition, curves  138 ,  140  are shown that show the magnetic field curve for a displacement in the y direction of −1.25 mm (curve  138 ) and for a displacement by +1.25 mm (curve  140 ). 
     The comparison of the critical north-south transition  122  illustrated in  FIG. 2A  with that illustrated in  FIG. 2B  shows that, given economically producible positional tolerances of the permanent magnet of multipole system  110  relative to the magnetic field sensor, the target curve of the magnetic flux density according to the specifications cannot be maintained, or can be maintained only with difficulty. Thus, curves  138  and  140  of magnetic flux density B lie outside the target curve in the realization shown in  FIG. 2A . In contrast, in the optimized design shown in  FIG. 2B , with economically producible positional tolerances the target curve of magnetic flux density B according to specifications can be maintained. All curves  136 ,  138 , and  140  lie within target curve  134 . 
     Additional magnetic pathways  124 ,  126 , which provide magnetic poles  128 ,  130  in the area of critical north-south transition  122 , can, individually or both, be realized either as dummy magnetic pathways  118  without usable information content or, individually or both, can also be used as information carriers. The latter case is shown in  FIGS. 3A and 3B ,  FIG. 3A  again showing a conventional design and  FIG. 3B  showing an optimized design. Shown is a segment of a multipole system  110  in which, arbitrarily, the second path has been designated from below as magnetic pathway  118 , and the other magnetic pathways have been designated as additional magnetic pathways  124 ,  126 , and  142 . Finally, however, all magnetic pathways  118 ,  124 ,  126 , and  142 , with their north-south transitions  120 , can act as information carriers, for example in order to form a bit pattern along displacement path  116 , shown horizontally in  FIGS. 3A and 3B . In the depicted bit pattern, for example one of the north-south transitions  120  of magnetic pathway  118  can be defined as critical north-south transition  122 , for example because the switching process associated with this north-south transition  122  is safety-relevant. For example, the detected switching process can be a transition from a park setting P to an intermediate setting Z 1 , and/or a transition from a neutral setting N to an intermediate setting Z 2  or an intermediate setting Z 3 , and/or a transition from a reverse setting R to an intermediate setting Z 1  or an intermediate setting Z 2 . 
     As follows from the bit pattern of the conventional multipole system  110  in  FIG. 3A , in the conventional situation of the multipole geometry all pole transitions except one are made asymmetrical. Critical north-south transition  122 , which has the narrowest tolerance range, is however here at the same time the transition having the largest asymmetry. 
       FIG. 3B  shows a modification according to an example embodiment of the present invention of the bit pattern according to  FIG. 3A . Here, magnetic pathways  118  and  124  are inverted relative to the system shown in  FIG. 3A . In order nonetheless to represent the same bit pattern as in  FIG. 3A , the signals of the associated sensor elements, which detect magnetic pathways  118  and  124 , can for example be inverted. Through the inversion of the magnetic poles on the two inner pathways  118 ,  124 , all north-south transitions  120  of these pathways except one are made symmetrical. In particular, the pole transition defined as critical north-south transition  122  has in this embodiment the sharpest north-south transition. 
       FIG. 4  shows a magnetic sensor according to an example embodiment of the present invention. The magnetic sensor includes the multipole system  110 , which is shown in detail in  FIG. 1B . The magnetic sensor further includes the magnetic encoder  112  of the magnetic sensor element  114 . 
       FIG. 5  shows a magnetic sensor having separate sensors according to an example embodiment of the present invention. The magnetic sensor  114  of  FIG. 5  includes separate sensors  144 ,  146 , and  148 . Magnetic sensor  114  has a separate sensor  144  for the magnetic pathway  118  and separate sensors  146  and  148  for at least one of the additional magnetic pathways  124 ,  126 , and  142   
       FIG. 6  shows a magnetic sensor having a control unit according to an example embodiment of the present invention. Here, magnetic sensor includes control unit  150 . 
       FIG. 7  shows a magnetic sensor movably mounted by a carriage according to an example embodiment of the present invention. The magnetic sensor  114  is movably mounted by a carriage  152 . 
     The realization of additional magnetic pathways  124 , intended to optimize the magnetic field environment of critical north-south transition  122 , in the form of additional magnetic pathways  124 ,  126 ,  142 , which also act as information carriers, is a realization that is particularly efficient with regard to constructive space. Here, additional magnetic pathways  124 ,  126 ,  142  are no longer simply dummy pathways, but are themselves information carriers that, in a double function, provide the suitable magnetic field environment for critical north-south transition  122 . A possible alternative to this is to provide intermediate pathways each of which is inverted relative to the sensor pathways, but which require larger constructive space. In this alternative embodiment, for example all, or some, of magnetic pathways  118 ,  124 ,  126 , and  142  could be surrounded by dummy pathways, each providing, in the area of north-south transitions  120 , or at least in the area of the at least one critical north-south transition  122 , suitable magnetic poles  128 ,  130  having identical polarity on both sides of critical north-south transition  122 . However, this embodiment has the disadvantage of requiring larger constructive space.