Abstract:
To make it possible for a rotation angle sensor to be manufactured and assembled more easily and more accurately, the part components of a stator element ( 21 ) made of a ferritic material are held in a sintered stator body, made by a sintering technique, by at least one holding element in a holding recess of a base element made of a non-magnetizable material. A magnetic holding device ( 26, 27 ) is a holding element made by a metal injection moulding (MIM) technique with an at least partly formed magnetic isolation zone and at least one recess. An annular magnetic element ( 24 ) is attached inside the MIM holding device by means of at least one slit-shaped recess and at least one compatible linking element, and positioned at a given angle (α) in relation to a gap, between the sintered stator bodies.

Description:
BACKGROUND OF THE INVENTION 
     The present invention concerns an angle-of-rotation sensor with a stationary component and a rotating component. The stationary component includes a stator accommodated in a housing with at least one base. The stator is in two halves of ferritic material separated by space and each provided with at least one 45° bevel. The rotating component includes an annular magnet accommodated in a holder and rotating around the stator with an airgap left between them. 
     An angle-of-rotation sensor of this genus is known from the WIPO Patent Publication No. WO A 95/14911, which is assigned to the present applicant. It comprises a stationary component and a rotating component that moves in relation to it. The stationary component has two mutually facing stator halves with space between them. Each stator half is a stack of sheetmetal disks secured against the bottom of the housing by a tensioning component. The rotating component includes an annular magnet accommodated in a holder. 
     There are drawbacks to this embodiment. The stacks are expensive to manufacture and secure. The magnet holder is designed such that the magnet is not magnetically insulated from a shaft that the rotating component is fastened to, contaminating the outgoing signals. Furthermore, the poles of the magnet are difficult to position properly with respect to the space between the stator halves while the sensor is being assembled. 
     SUMMARY OF THE INVENTION 
     The principal object of the present invention is accordingly to provide a more accurate angle-of-rotation sensor of the aforesaid genus that will be easier to manufacture and assemble. The stationary component in particular will be simpler, the magnet holder as magnetically insulating as possible, and the annular magnet reliably secured in the holder and easy to position precisely with respect to the space between the stator halves and the stationary component. 
     This object, as well as other objects which will become apparent from the discussion that follows, are achieved, in accordance with the present invention, in an angle of rotation sensor of the type described above, by the following features: 
     (a) the ferritic stator halves are sintered stator halves, with at least one holder secured in a stabilizing cutout in a baseplate of non-magnetic material; 
     (b) the magnet holder is a metal-injection molded holder with at least one partly magnetically insulating section and with at least one cut-out gap; and 
     (c) the magnet is positioned in the holder by at least one cut-out gap and at least one matching web at a specified angle (α) to the space. 
     The present invention has several advantages. Stators are easy to sinter, precise and stable. The complicated stacking procedure is eliminated. One particular advantage is that each sintered stator half can be fastened to the baseplate extremely accurately. The magnet holder can be cost effectively and, in particular, precisely fabricated by metal-injection molding (MIM). Complicated additional shaping, especially machining, of the material is unnecessary. The holder will hold the magnet exactly where it should be within precise tolerances. Measurements will be considerably more precise. The web or space will simultaneously position the magnet precisely in relation to the space during assembly. No complicated readjustments will be necessary. It will accordingly be possible to position the magnet&#39;s pole at a right angle, perpendicular that is, to the space between the two facing stator halves. If any angle other than a right angle is needed in special cases, it can be established ahead of time for all the angle-of-rotation sensors in the same series. Most significant, however, is that the magnet will be secured too tighty to turn. 
     Two alternative embodiments of the stator holders are possible. They can be either sintered bolts or sintered feet. Whether bolts or feet, they can terminate in a sintered cap. This feature ensures that the sintered stator half is secured, stationary, in the baseplate. 
     The baseplate can be a stator baseplate with at least one stabilizing cutout. 
     Two alternative embodiments of the stator baseplate are possible. 
     The stator baseplate can comprise the base of the stationary-component housing and have stabilizing cutouts with sintered stator halves fitting into it along with their feet and caps. 
     The stator baseplate can alternatively be a stabilizing disk with at least one stabilizing cutout and at least partly surrounded by a fastener with at least one fastening cutout. 
     At least the stabilizing disk can be at least partly surrounded by the base of the housing. 
     The second embodiment of the stabilizing cutouts and the fastening cutouts can be round or orange-segment shaped. 
     The stator baseplate can be aluminum, copper, or plastic. 
     The various embodiments of the baseplate can secure the sintered stator halves in two different ways. 
     In the first approach, the halves can be sintered to final dimension, finally positioned, and forced into the base of the housing as a whole. The essential advantage of this approach is the extremely cost-effective stabilization and fastening of the halves. The stationary component can accordingly be finally fabricated in only two basic steps. 
     In the second approach, the basic components of the stator are metal-injection molded of a ferritic material and the stator baseplate metal-injection molded, especially of aluminum, around the stator half. The resulting blank is removed from the mold and both the half and baseplate sintered in a furnace, both metals contracting. This process will ensure that the half fits into the baseplate, tight and precise, and cannot be displaced by even powerful forces. 
     The accordingly sintered molding is then inserted into a molded housing and secured therein, either resiliently or at least to some extent by encapsulation. 
     The housing and its base can be of plastic, preferably injection-molded to ensure that the stationary component constitutes a precisely dimensioned component of the sensor. 
     Two alternative embodiments of the metal-injection molded holder are possible. 
     It can be a cup metal-injection molded in one piece of magnetic material with an essentially round foot, at least two, preferably cylindrical stems rising out of one edge of the foot, and an essentially round and hollow bowl resting on the stems. A one-piece bowl is considerably less expensive to manufacture. Such a cup can be molded of magnetic material in a single mold. The molding will be 30 percent oversize and will need to be heated and sintered to its final dimensions. To allow at least extensive magnetic insulation of the cup from the components to be mounted on it, the stems can magnetically insulate the foot from the bowl. 
     The holder can alternatively be metal-injection molded in two parts, comprising an essentially straight-sided bowl with a round base of metal-injection molded of a non-magnetic material, provided in a second molding stage with a cylindrical wall of magnetic material. The resulting bi-material molding will be 30 percent oversize and will need to be more or less sintered to its final dimensions. The base and wall will accordingly be precisely dimensioned and will fit together perfectly tightly. The wall will be precisely positioned. The non-magnetic material of the base will ensure effective magnetic insulation from any components to be mounted on the bowl. One particular advantage is that the base of the bowl can be provided with a cutout that will readily accommodate a simply inserted valve shaft. This feature will compensate for the extra expense of two-part manufacture. 
     A gap can be cut out of the bowl in either embodiment. If the magnetic wall is provided with at least one matching web, the poles of the wall can be positioned at a right angle, perpendicular that is, to the space between the mutually facing stator halves. If, in a special case, the angle is to be other than a right angle, it can be precisely established for all the products in a single series. 
     The web or webs can be positioned near at least one of the joints between the south-north and the north-south segments of the annular magnet. The web will accordingly be positioned in an already existing uniform magnetic-field region and will not be able to move out of the magnet&#39;s field. 
     The webs can be of the same material as the magnetic component they are mounted on. They can alternatively be of plastic. Plastic is to be preferred when the magnetic component is to be fastened to the space between the stator halves without detriment to the magnetic field. 
     For a full understanding of the present invention, reference should now be made to the following detailed description of the preferred embodiments of the invention as illustrated in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic partly sectional view of a angle-of-rotation sensor coupled to a throttle valve. 
     FIG. 2 a  is a schematic top view of the stationary component of the angle-of-rotation sensor illustrated in FIG.  1 . 
     FIG. 2 b  is a section along the line IIB—IIB through the stationary component illustrated in FIG. 2 a.    
     FIG. 2 c  is a cross-sectional view, similar to FIG. 2 b , of the stationary component with an attached lead frame. 
     FIG. 2 d  is a top view through the stationary component showing the attachment of the lead frame. 
     FIG. 2 e  is a cross-sectional view throughthe component of FIG. 2 d . 
     FIG. 3 a  is a schematic top view of the stator baseplate in another embodiment of the angle-of-rotation sensor illustrated in FIG.  1 . 
     FIG. 3 b  is a section along the line IIIB—IIIB through the stator baseplate illustrated in FIG. 3 a.    
     FIG. 4 a  is a schematic illustration of another embodiment of a stationary component with the stator baseplate illustrated in FIGS. 3 a  and  3   b.    
     FIG. 4 b  is a section along the line IVB—IVB through the stationary component illustrated in FIG. 4 a.    
     FIG. 5 a  illustrates a magnet holder for the rotating component in the angle-of-rotation sensor illustrated in FIG.  1 . 
     FIG. 5 b  is a section along the line VB—VB through the magnet holder illustrated in FIG. 5 a.    
     FIG. 5 c  illustrates another embodiment of a magnet holder for the rotating component of the angle-of-rotation sensor illustrated in FIG.  1 . 
     FIG. 5 d  is a section along the line VD—VD through the magnet holder illustrated in FIG. 5 c.    
     FIG. 6 is a schematic top view of the space inside the stator in the adjustable magnet in the angle-of-rotation sensor illustrated in FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The preferred embodiments of the present invention will now be described with reference to FIGS. 1-6 of the drawings. Identical elements in the various figures are designated with the same reference numerals. 
     The angle-of-rotation sensor  2  illustrated in FIG. 1 has a stationary component  20  comprising a stator  21  accommodated in a housing  23 . Stationary component  20  is composed of two stator halves  21 . 1  and  21 . 2 . Stator halves  21 . 1  and  21 . 2  are shaped like orange segments and separated by space  21 ″. Their points are beveled, preferably 45°, at the end of space  21 ″. Housing  23  has a base  23 ″ and a cylindrical wall  23 ′. 
     As will be evident from FIG. 1, stationary component  20  is confronted by a rotating component  20 ′. Rotating component  20 ′ includes an annular magnet  24  accommodated in a holder comprising a magnet-securing component  26  and a disk-shape spacer  27 . Spacer  27  is directly connected to a throttle-valve shaft  12 . Spacer  27  and stator  21  are separated, once sensor housing  23  has been secured to a housing  13  by a gap  28  and rotation angle apparatus  1  in FIG.  1 . Cylindrical wall  23 ′ and magnet-securing component  26  are separated by another gap  29 . Magnet-securing component  26  and the annular magnet  24  accommodated therein accordingly constitute in conjunction with spacer  27  a rotor component that can rotate protected inside sensor housing  23 . 
     Once the individual components of rotating component  20 ′ have been properly adjusted and aligned in relation to throttle-valve shaft  12 , sensor housing  23  is thrust over magnet-securing component  26  along with stator halves  21 . 1  and  21 . 2  and a Hall-effect component  22  accommodated in space  21 ″, leaving an airgap  25  and gaps  28  and  29 . Sensor housing  23  is then fastened by its cylindrical wall  23 ′ to valve housing  13 . If the joint between sensor housing  23  and valve housing  13  needs to be sealed, sensor housing  23  will also act as a protective jacket. The whole angle-of-rotation sensor  2  will accordingly be protected against such external conditions as the very high heat in an engine compartment and the effects of oil, water, etc. 
     FIGS. 2 a  and  2   b  illustrate one embodiment of the stationary component  20  in angle-of-rotation sensor  2 . The stator halves  21 . 1  and  21 . 2  are sintered stator halves  80 , individually metal-injection molded of a ferritic material and sintered. Since halves  80  are of the same shape, they can be fabricated continuously and sintered synchronized in batches in a furnace. Each accordingly fabricated sintered stator half  80  will be provided with a foot  82  that merges into a cap  81  which is secured in a stabilizing cutout  32  in a baseplate  30  of non-magnetic material, and with a shoulder  85 . 
     Each sintered stator half  80  will have, along with the aforesaid bevels  84 , a longitudinal bevel  83 , also of 45°. 
     Two such sintered stator halves  80  can be accommodated in a single mold separated by a space  21 ″, acting as a baseplate in base  23 ″ while the plastic sensor housing  23  is being molded. This procedure leaves stabilizing cutouts  52 ( 32 ) in base  23 ″ to accommodate feet  82 . Caps  81  are also secured in base  23 ″. Stator halves  21 . 1  and  21 . 2  are both surrounded by cylindrical wall  23 ′ when sensor housing  23  is molded. Stabilizing components  23 . 1  and  23 . 2  each act to stabilize the apparatus by allowing the apparatus to afix itself to a corresponding female groove, while  21 ′ (FIG. 2 b  is consistent with FIG. 1) also allows the apparatus to be afixed, by a corresponding male attachment. 
     The particular advantage of such a stationary component  20  is that both sensor housing  23  and holders and stops for stator halves  21 . 1  and  21 . 2  in the form of sintered stator halves  80  can simultaneously be produced in a separate molding process, considerably decreasing manufacturing costs and keeping the height of stationary component  20  to a minimum. 
     Another advantage is that Hall-effect component  22  can be positioned in the vicinity of the densest magnetic flux near the parallel and facing surfaces of sintered stator halves  80 , while longitudinal bevels  83  concentrate the flux. The enlarged space between the two sintered stator halves  80  between the facing feet  82  in the vicinity of space  21 ″ keeps the flux less dense. The transverse bevels  84  balance the flow at the orange-segment shaped stator halves due to the absence of edges. 
     FIGS. 3 a ,  3   b .  4 A, and  4   b  illustrate another embodiment of stationary component  20 . 
     This embodiment has a stator baseplate  40  of sintered aluminum. It consists of a stabilizing disk  44  that merges into an annular fastener  45 . Stabilizing disk  44  has a central cutout  21 ′ with tapering ends and confronted by two stabilizing cutouts  42  shaped like orange segments. The are demarcated from central cutout  21 ′ by a cutout web  46 . Annular fastener  45  includes two pairs of mutually facing fastening cutouts  43  in the form of bores. 
     Stator halves  21 . 1  and  21 . 2  in the form of sintered halves  70  of a ferritic material are sintered facing each other to the stabilizing disk  44  in the accordingly fabricated stator baseplate  40 . A stabilizing foot  72  is sintered into each sintered stator half  70  as part of the process. The sintered stabilizing foot  72  merges into a sintered securing cap  71 , anchoring the stator half into an aluminum baseplate  41  and securing it thereon. The central cutout  21 ′ between the two halves is as wide as its length in baseplate  41 . 
     This second embodiment is outstanding for strength. Sintered stator baseplate  40  secures sintered stator halves  70  so effectively that they can resist any static or dynamic force. Stator baseplate  40  is then inserted into a sensor housing  23  already fabricated as hereintofore specified or otherwise. 
     FIGS. 5 a  and  5   b  illustrate a magnet-securing component  26 , in this case bowl  61 , which together with disk-shaped foot  63  and two stems  62  and  62 ′ constitute the entire cup  60 . 
     Cup  60  consists of a disk-shaped foot  63  with two stems  62  and  62 ′ extending out of it and supporting a bowl  61 . 
     Mutually facing gaps  64  and  65  have been cut out of bowl  61 . 
     According to the present invention cup  60  is preferably metal-injection molded of a magnetic material in the form of X12CrMol7Si steel. This steel does not corrode and is injected into a mold. The molding is heated in an furnace in a process similar to sintering, reducing the volume of the cup by 30% to its final dimensions. 
     The bowl  61  in this embodiment constitutes magnet-securing component  26 , and foot  63  spacer  27 . Stems  62  and  62 ′ connect magnet-securing component  26  to spacer  27  and at least extensively insulate them magnetically from each other. 
     FIGS. 5 c  and  5   d  illustrate another embodiment of a magnet holder in the form of magnet securing component  26 , in this case cylindrical wall  51  of metal-injection molded and sintered bowl  50 . This bowl  50 , which is rotating component  20 ′, has cutout  53  and cutout gap  54 . 
     Bowl  50  is metal-injection molded in two parts. Its non-magnetic base  52  is molded of X2CrNi1911 steel along with such additives as wax. A cylindrical wall of powdered X12CrNiSi7 steel is then injected around it, also combined with such additives as wax in another mold. 
     The resulting metal-injection molded blank is then at lest partly washed free of the additives, especially the wax, and “baked” at approximately 1000° down to its final dimensions, approximately 30 percent of its original dimensions, in a process similar to sintering. 
     Although metal-injection molding (MIM) is in itself known, using it to fabricate parts like the two embodiments of a magnet holder specified herein is not. 
     As specified hereintofore with reference to FIG. 1, angle-of-rotation sensor  2  has a component  20 ′ in the form of an annular magnet  24  that rotates around stationary component  20 . 
     In FIG. 6, mutually facing webs  90  and  92 , which position the magnet precisely in relation to the space during assembly, can be made of the same material as the magnetic component they are mounted on, or of plastic, and are here mounted on annular magnet  24 , which comprises north-south segment  24 . 1  and south-north segment  24 . 2 . The interior of one segment is north-poled and its exterior south-poled, the interior of the other is south-poled and its exterior north-poled. The overall magnet is accordingly radially two-poled and acts like a bar magnet. The magnetic flux is radial in the areas labeled N and S. The only field irregularities are at interfaces  24 . 3  and  24 . 4 , and the webs are situated in those magnetically neutral regions. The device may on the other hand have only one web  90  or even several webs  91 . Annular magnet  24  can also be provided with a cut-out gap  94  which aids in stabilization. 
     The radially two-pole annular magnet  24  must be positioned at a specified angle α, 90° in the illustrated embodiment, to the two mutually facing halves  21 . 1  and  21 . 2  of stator  21 , which as hereintofore specified, are in the form of fixed sintered stator halves  70  and  80 . 
     In FIG. 6 one of the webs is utilized to establish annular magnet  24  in the gap  54  cut out of bowl  50  at angle α. 
     Additionally in FIG. 6 both webs  90  and  92  are utilized to establish annular magnet  24  in cut-out gaps  64  and  65  at angle α. 
     It should be emphasized that the webs and matching cut-out gaps allow simple and extremely precise positioning of annular magnet  24 . No complicated re-adjustments are necessary. It is essential to the present invention that annular magnet  24  cannot turn inside base  52  or wall  51 . Even the most powerful forces cannot displace or remove the magnet. 
     There has thus been shown and described a novel rotation angle sensor which fulfills all the objects and advantages sought therefor. Many changes, modifications, variations and other uses and applications of the subject invention will, however, become apparent to those skilled in the art after considering this specification and the accompanying drawings which disclose the preferred embodiments thereof. All such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the invention are deemed to be covered by the invention, which is to be limited only by the claims which follow.