Abstract:
A magnetic field sensor, in particular an rpm sensor and/or rotational direction sensor and/or position sensor for the drive train of a motor vehicle, has a sensor array, with a sensor element that responds to a magnetic field, and optionally with a permanent magnet, the latter being sheathed with plastic jointly with the sensor array and parts of terminal conductor tracks, and the conductor tracks are embodied in one piece with a fixing element for the permanent magnet and the sensor array as a stamped grid, wherein stamped grid is shaped as a three-dimensional structure which carries the sensor array and optionally embraces the permanent magnet in the manner of a mount, and the mount and the terminal conductor tracks are first stamped out from a metal sheet as a gridlike developed form, and then deformed to form the mount.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The invention relates to a magnetic field sensor, in particular an rpm sensor and/or a rotational direction sensor and/or a position sensor, preferably for the drive train of a motor vehicle, and to a method for producing such a sensor, of the kind disclosed for instance by European Patent Disclosure EP 0 898 180 A.  
         [0002]     This reference shows a frame for installing a magnetic field sensor that has crossbars for fixing a permanent magnet and also has a plurality of terminal conductor tracks for a sensor array, which in turn upon installation and with a later plastic potting rests on a flat portion of the frame. Such an arrangement on the one hand fails to assure exact positioning of the sensor components and on the other fails to provide an exact association between the permanent magnet and the sensor array, since the permanent magnet and the sensor array are fixed by separate parts of the frame, and furthermore the clamping mounting of the permanent magnet takes place regardless of the positioning of the sensor array.  
       SUMMARY OF THE INVENTION  
       [0003]     It is therefore an object of the present invention to provide a magnetic field sensor, and a method for producing such a sensor, which constitute a further improvement of the known sensors and methods for producing the same.  
         [0004]     More particularly, it is an object of the present invention to provide a magnetic field sensor and a method for producing it which are distinguished by low tolerance fields both in product design and in terms of the manufacturing steps. High product and manufacturing precision are further intended to assure an exact position of the magnetic field sensor relative to a detection target, or in other words, in the preferred application, a small air gap that can be adhered to exactly, compared to a transducer wheel, which on its circumference has ferromagnetic teeth or magnetic poles that move past the sensor and that to ascertain the rpm and/or the direction of rotation and/or the position alternate with tooth gaps or pole gaps.  
         [0005]     Instead of a transducer wheel, a rack or pole rod can serve as the transducer structure; in the case of a transducer array with magnetic poles (multipole structure), there is no magnet in the magnetic field sensor.  
         [0006]     In keeping with these objects and with others which will become apparent hereinafter, one feature of the present invention resides, briefly stated, in a A magnetic field sensor, comprising a sensor array with a sensor element that responds to a magnetic field; terminal conductor tracks; fixing means for said sensor array, sheathing means which sheath said sensor array and parts of said terminal conductor tracks in plastic, said conductor tracks being configured in one piece with said fixing means as a stamped grid, said stamped grid being configured as a three-dimensional structure in a region adjacent to a transducer array and carrying said sensor array on a face-end portion.  
         [0007]     Another feature of the present invention resides, briefly stated, in a method for producing a magnetic field sensor which has a sensor array with a sensor element that responds to a magnetic field, wherein the sensor array and parts of terminal conductor tracks are sheathed in plastic and the conductor tracks are configured in one piece with the fixing means for the sensor array as a stamped grid, the method comprising the steps of stamping out first a grid-shaped developed form of a mount for elements selected from the group consisting of sensor array, the terminal conductor tracks, and both, from a metal sheath; and then shaping the grid-shaped developed form of a mount into the mount in a region of the sensor array, and optionally further components.  
         [0008]     It has proved structurally advantageous if in addition to the sensor array, a permanent magnetic transducer is retained and positioned in the stamped grid structure, and the stamped grid structure at least partly embraces the permanent magnet. It is expedient if the stamped grid, which carries the active parts of the sensor, comprises a copper bronze, such as CuSn6, because such an alloy on the one hand has high stability and elasticity and on the other can be joined with difficulty and securely to the terminals of the sensor array, preferably by welding/bonding. Instead of a copper bronze, aluminum alloys, such as AlMgSi1, and copper-iron alloys with a low proportion of iron, such as CuFe2P, are also suitable as stamped grid materials.  
         [0009]     For harmonizing the magnetic field generator by means of a permanent magnet in the sensor, it is advantageous if a ferromagnetic scattering disk is associated with the permanent magnet, on the face end of the permanent magnet toward the sensor element, and this scattering disk can likewise be securely held and positioned in the mount for the permanent magnet between the magnet and the sensor array. In versions with an external magnetic transducer structure, the scattering disk in the sensor is also omitted.  
         [0010]     For precise bracing and alignment of the sensor array and the permanent magnet, it is also advantageous if the mount parts provided for it have elastically deformable portions for clampingly receiving the permanent magnet and/or the scattering disk and/or the sensor, and the deformable portions embrace at least the permanent magnet, over part of its surface, by form-locking and rest with tension on the surface of the magnet.  
         [0011]     With regard to the method of the invention for producing the magnetic field sensor, it is especially expedient if, for embodying the mount of the sensor array and optionally further components, first a gridlike developed form of the mount and the terminal conductor tracks is stamped out of a metal sheet and then shaped into the mount, which continues in one piece into the conductor tracks, by bending, embossing or other suitable methods. It is especially expedient in this respect if both the stamping of the grid and its shaping are done in a follow-on composite tool, in which still other provisions, such as equipping the mount with the permanent magnets, the sensor array, a scattering disk, and optionally other parts, can be done without changing tools. The concluding sheathing and external designing of the magnetic field sensor are expediently done by casting or spray-coating the entire array, except for the conductor track ends, with plastic.  
         [0012]     The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. the invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a perspective view of a completely shaped, assembled magnetic field sensor before its being sheathed with plastic;  
         [0014]      FIG. 2  is a perspective view of the mount of the magnetic field sensor before the assembly;  
         [0015]      FIG. 3  is a side view of the assembled magnetic field sensor, with the plastic potting shown schematically; and  
         [0016]      FIG. 4  is a perspective view of a further version of a stamped grid mount.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]      FIG. 1  shows a magnetic field sensor before it is sheathed with plastic, of the kind that can be used for instance as an rpm sensor and simultaneously as a rotational direction sensor for the transmission of a motor vehicle. Reference numeral  10  indicates a mount for the various components of the sensor, which is stamped out of a metal sheet of copper bronze (CuSn6) as a developed form of the mount  10  in the form of a flat stamped grid  12 . A round or oval, axially magnetized permanent magnet  14  is seated in the mount and is located such that on its left-hand face end, it has a north pole (N), and on its right-hand face end it has a south pole (S). Seated inside the mount  10 , on the north pole face end of the permanent magnet  14 , is a scattering disk  16  of soft iron, which has only a slight thickness and is kept in saturation by the field of the magnet, so that the magnetic field is harmonized, and an extensively constant field intensity in the measurement region preceding the north pole of the magnet is assured.  
         [0018]     Outside the mount  10 , parallel to the end face of the permanent magnet  14 , the actual sensor array  22  is held between two clamps  18  and  20 ; it is embodied as an IC component and includes a sensor element  24 , indicated by dashed lines, in the form of a Hall element.  
         [0019]     The mount  10  is designed in one piece in accordance with the geometry of the original stamped grid  12  and is embodied with two conductor tracks  26  and  28 ; the conductor track  26  forms the ground connection, and the conductor track  28  the signal connection with the sensor element  24 . The permanent magnet  14  is also connected to ground. The internal terminals of the sensor element  24  are indicated only by dashed lines; toward the outside, the sensor array  22  has terminal leads  30  and  32 , which are welded at their ends to the conductor tracks  26  and  28 . In the middle region, the terminal leads  30  and  32 , to protect against overvoltages, are bridged by a capacitor  34 .  
         [0020]     The ends of the conductor tracks  26  and  28 , in the part protruding out of the later plastic potting and for some distance onward into the plastic as well, are reinforced, for instance by folded-over portions  36  and  38 , to twice the thickness of the material of the stamped grid  12 . Moreover, in this stage of manufacture before the concluding potting for stabilizing the array, the conductor tracks  26  and  28  are also held together by webs  40  and  42 ; at least the web  40  is already removed before the concluding potting. Finally,  FIG. 1  also schematically indicates a ferromagnetic transducer wheel  44  that cooperates with the sensor array  22  and that on alternatingly moving past teeth  46  and teeth gaps  48 , as a result of the change in the magnetic field, generates the signals that are output by the sensor array  22 .  
         [0021]     In the following drawings, identical elements are identified by the same reference numerals as in  FIG. 1 .  FIG. 2  shows the unassembled mount  10 , shaped out of the stamped grid  12  in one piece with the conductor tracks  26  and  28 . In its front region, this mount has a flange  50 , bent at a right angle, on which the permanent magnet  14 , with the scattering disk  16  optionally placed on it, is braced on its face end. On the diametrically opposed face end, the permanent magnet  14  is kept under prestressing by a tab  52  and pressed against the flange  50 . The lateral fixing of the permanent magnet  14  in the region of its jacket face is effected by two elastic segments  54  and  56 , whose design is adapted to the shape of the permanent magnet  14 , which in particular may be round, oval, or even rectangular. The two clamps  18  and  20  can be seen on the outer end face of the flange  50  and hold the sensor array  20  by force locking. If needed, however, a further clamp  58  may also be provided in the region of the lower edge of the sensor array  22 , to facilitate the positioning upon insertion of the sensor array  22 .  
         [0022]     With regard to the conductor tracks  26  and  28 , in designing the stamped grid  12  the fact has already been taken into account that the conductor track  26  is to establish the ground connection and the conductor track  28  is to establish the signal connection. The conductor track  26  is therefore designed continuously and in one piece with the part of the stamped grid  12  that forms the mount  10 , while the conductor track  28  is retained in the stamped grid  12  by webs  40  and  42  during installation. For improving and facilitating the soldered or welded connections, the stamped grid  12  is either made entirely of a galvanically coated sheet of copper or copper bronze, or a sheet of the same material coated on its surface by hot tin coating. In principle, however, it suffices if only the later welding or soldering points are tinned. The thickness of the material of the stamped grid assures adequate mechanical strength.  
         [0023]      FIG. 2  further shows that in this embodiment, the flange  50  is not closed at the top on the face end of the mount  10  and leaves an opening  60  free in the middle region that corresponds to the size of the sensor array  22 . As a result, the sensor array  22  can extend as far as the face end of the permanent magnet  14 , or the face end of the scattering disk  16 , so that the fixing and centering of the sensor array  22  are further improved, and the axial installed length is reduced.  
         [0024]      FIG. 3  shows a side view of the magnetic field sensor of  FIG. 1 , in which the concluding plastic potting  62  is represented symbolically by a dashed line. The outer contour of the plastic  62  is adapted to the applicable installation conditions and is also optimized in terms of the size and shape of the sensor, in order on the one hand to assure high mechanical strength and on the other to minimize the plastic composition, for reducing the thermal and mechanical load on the sensor during production. Otherwise,  FIG. 3  again shows the three-dimensional location and mounting of the permanent magnet  14 , scattering disk  16  and sensor array  22  in the mount  10  shaped from the stamped grid  12 ; the permanent magnet and the scattering disk  16  are securely and precisely locked in the interior of the mount  10 , while as a result of the installation of the sensor array  22 , the air gap toward the transducer wheel  44 , not shown in  FIG. 3 , on the outside of the flange  50  of the mount  10  is minimized.  
         [0025]      FIG. 4  shows an alternative for designing the stamped grid  12  or the mount  10  and the conductor tracks  26 ,  28 . The mount  10  here is shaped such that it is suited in particular for receiving a rectangular permanent magnet. Upon installation, a framelike tab  52   a , or at least one lateral segment  54   a  or  54   b , is bent upward in the shape shown only after the permanent magnet, not shown, has been introduced. A further distinction is the design of the face-end flange  50   a , which in this case has no opening, but instead only has an indentation  64 . Since the stamped grid  12  is made not of ferromagnetic material but rather from copper or copper bronze, for instance, the field of the permanent magnet can pass through the flange  50   a . The indentation  64  serves to provide exact positioning of the permanent magnet and is especially advantageous whenever the permanent magnet is a so-called gap magnet of substantially U-shaped geometry, so that the indentation  64  reaches into the gap and positions the magnet exactly.  
         [0026]     In terms of the manufacture of the magnetic field sensor of the invention, it has already been stated that first, from a metal sheet, a gridlike developed form of the mount  10  and of the terminal conductor tracks  26 ,  28  is stamped out and is then shaped into the mount  10 , in the region of the permanent magnet  14  and the sensor array  22  and optionally of further components, such as the scattering disk  16 . Expediently, the manufacture of the magnetic field sensor is done in a so-called follow-on composite tool, in which the stamping of the stamped grid  12  out of a band material and the shaping of the mount  10  with the conductor tracks  26  and  28  and their equipping with the individual components of the sensor are done in successive work steps. Only the concluding potting of the magnetic field sensor with a preferably pressure-setting plastic  62  is then done in a separate operation and in a separate tool.  
         [0027]     With the magnetic field sensor of the invention, in the field of sensor systems for engine and transmission management in a motor vehicle, for instance, many different functions can be performed, for instance being used as a phase transducer and/or an rpm transducer. As magnetosensitive measuring elements  24  of the sensor array  22 , besides Hall elements, AMR (Anisotropic Magneto-Resistor) and GMR (Giant Magneto-Resistor) elements as well as field plates are used, and when such IC sensor arrays  22  are employed, the requisite exact positioning, for instance relative to a transducer wheel, can be adhered to very precisely and with relatively little expense for material and components. A reduction in tolerances in all directions is thus attained, while simultaneously reducing the number of manufacturing steps in the production of the sensor.  
         [0028]     Moreover, the range of function can be expanded while the functional length and diameter are simultaneously reduced, so that greater tolerances are acceptable in terms of the air gap. For mass production, the design according to the invention and the associated production process create the possibility of leaving the stamped grid  12  during production on a carrier strip of the band from which the stamped grid  12  is then cut free. This makes it possible for instance to stir the finished stamped grids, at the end of the bending and stamping process, in rolled-up form until further processing, or to transport them in that form to other production sites. In particular, however, by both holding the magnetic circuit and simultaneously carrying current and signals in one component, a compact, stable, and simply manufactured unit is achieved, which is distinguished by increased precision and reduced production costs.  
         [0029]     It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.  
         [0030]     While the invention has been illustrated and described as embodied in a magnetic field sensor, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.  
         [0031]     Without further analysis, the foregoing will reveal fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of the invention.