Abstract:
The invention relates to a stator arrangement for an electric machine, particularly a DC motor, comprising a stator body having a stator back yoke ring and a number of stator teeth between which stator slots to receive stator windings are formed, the stator teeth extending radially from the stator back yoke ring and stator poles being formed at the free ends of the stator teeth, the stator teeth being coupled to a sleeve, which extends coaxially to the stator body, at their free ends. The invention also relates to a method for the manufacture of a stator arrangement of this kind and a direct current motor that employs such a stator arrangement.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention relates to a stator arrangement for an electric machine, a method for the manufacture of a stator arrangement and a direct current motor that employs a stator arrangement of this kind. The stator arrangement according to the invention can be employed in many different types of electric machines and is particularly intended for DC motors and generators.  
       BACKGROUND OF THE INVENTION  
       [0002]     A preferred field of application for the invention is in brushless DC motors and other permanent magnet motors that are preferably configured as inner rotor motors. Electric motors having a permanently magnetic inner rotor motor configuration have a rotor back yoke that is mounted onto a shaft, one or more permanent magnets being mounted onto the rotor back yoke or embedded in the back yoke. The motors additionally comprise a stator arrangement typically consisting of a number of stacked metal laminations which form an annular stator back yoke from which stator teeth protrude radially inwards. The stator teeth form the stator poles between which stator slots, for receiving stator windings, are formed. The rotor arrangement is inserted coaxially into the stator arrangement. The invention also finds application in outer rotor motors.  
         [0003]     It is common for the rotor and the stator to be accommodated in a housing that has at least one end flange for the purpose of fastening the motor. However, motors are also known in which the outer surface of the stator lamination stack seals the motor to the outside. In most motors, the stator is made up of a slotted stack of laminations, the stator windings, made, for example, from insulated copper wire, being accommodated in the stator slots. The stator teeth are normally widened at their free end and form pole shoes whose purpose is to absorb as much magnetic flux as possible and, through their design, to reduce the cogging torque of the machine. The pole shoes take on the additional function of fixing the windings in position within the slots. In order to minimize the cogging torque of an electric machine and to optimize the magnetic flux, the pole shoes should be as wide as possible. A disadvantage of wide pole shoes, however, is that they only leave a relatively narrow gap open in the stator slots through which the winding wire is led.  
         [0004]     It is thus the object of the invention to provide a stator arrangement for an electric machine that shows good properties with respect to magnetic flux conduction and cogging torque and nevertheless allows a simple winding process for the stator teeth.  
       SUMMARY OF THE INVENTION  
       [0005]     This object has been achieved by a stator arrangement having the characteristics outlined in patent claim  1 . The invention also provides a DC motor according to claim  11  as well as a method for the manufacture of a stator arrangement for an electric machine according to claim  12 .  
         [0006]     The invention provides a stator arrangement for an electric machine, and particularly for a DC motor, which has a stator body having a stator back yoke ring and a plurality of stator teeth. The stator teeth extend from the stator back yoke ring in a radial direction and define stator slots to receive the windings in between each other. Stator poles are formed on the free ends of the stator teeth. In its preferred embodiment of the invention, the stator arrangement is designed for an inner rotor motor, the stator teeth in this configuration extending radially inwards from the stator back yoke ring. The stator teeth do not have any widened pole shoes at their free ends, as would normally be expected in the prior art. The slot openings between the stator teeth are thus wide, making it significantly easier to insert the winding wire into the slot openings to wind the stator teeth than is the case for conventional stator arrangements for inner rotor motors. After the stator teeth have been wound, a sleeve is mounted onto the stator arrangement according to the invention, the sleeve extending coaxially to the stator body and being coupled to the free ends of the stator teeth. In an inner rotor configuration, the sleeve defines the inside diameter of the stator and seals the stator with respect to the rotor.  
         [0007]     In the stator arrangement according to the invention, the sleeve takes on several functions. Firstly, it acts as a slot cover and holds the windings in the stator slots. For this function, it is expedient if the sleeve is given a coating of an electrically insulating material on its surface facing the stator slots, so that it also takes on the function of insulating the slots. Another, more important function of the sleeve is to form pole shoes. To this effect, it is expedient if the sleeve is made of a ferromagnetic material and is magnetically coupled to the free ends of the stator teeth. Moreover, the sleeve is preferably designed in such a way that it has non-magnetic or low-magnetic zones between two adjoining stator teeth that extend in an axial direction in order to separate the pole shoes of adjoining stator teeth from one another. These zones between the pole shoes can be narrow since they merely have the function of magnetically isolating the pole shoes from one another. This provides a stator arrangement that has particularly wide pole shoes which is advantageous for the running performance of the electric machine and, in particular, makes it also possible to reduce cogging torque.  
         [0008]     In a first embodiment of the invention, the zones to separate the pole shoes are formed by small slits that are die-cut into the sleeve, for example. In this embodiment, the sleeve is preferably made of a ferromagnetic material.  
         [0009]     In another embodiment of the invention, the sleeve is made of a bi-permeable material that is ferromagnetic in a first state and paramagnetic in a second state. In its original state, this material has ferromagnetic properties and after heat treatment it takes on paramagnetic properties. In the region in which the non-magnetic or low-magnetic zones are to be created, the sleeve is locally heated and thus transformed into its paramagnetic state in these zones.  
         [0010]     A material that is suitable for the manufacture of the sleeve according to the invention is an alloy based on Fe—Cr—C that is made by Hitachi Metals Ltd., Tokyo, Japan under the name YEP FA1 steel. This alloy is described, for example, in U.S. Pat. Nos. 6,255,005 and 6,390,443 as well as in the Japanese Laying-open Publications JP 2004 091842, JP 2004 143585 and JP 2004 281737. Reference is made to these publications with regard to the composition of the bi-permeable material and to the temperature ranges revealed in the documents, particularly the temperatures to transform the bi-permeable material from the ferromagnetic to the paramagnetic state. In the above-mentioned publications, the bi-permeable material is used in electromagnetic valves and other magnetic components; its use in stator arrangements is neither described nor considered.  
         [0011]     In a beneficial embodiment of the invention, the sleeve is also coated with an electrically insulating material on its surface facing away from the stator slots to provide electric insulation vis-à-vis the rotor, to prevent, for example, voltage flash-over in case of failure.  
         [0012]     The stator arrangement according to the invention can be manufactured in a very simple and cost-effective process if the sleeve is made of stamped, rolled sheet metal that can be coated if required. In the first embodiment, the sleeve is first die-cut from flat sheet metal, slits to separate the individual pole shoes and cutouts to connect the sleeve to the stator teeth being die-cut at the same time. The sheet metal is then rolled to form a sleeve which is open at a joint and thus flexible. This makes it easier to mount or press the sleeve onto the free ends of the stator teeth. It is expedient if the free ends of the stator teeth are given a fit that engages with the cutouts in the sleeve. A variety of different sleeve designs is conceivable. For instance, the cutouts to connect the sleeve to the stator teeth could take the form of slits that extend in an axial direction along the sleeve and which are closed at both axial ends of the sleeve. In this embodiment, the cutouts are pressed onto the stator teeth. In an alternative embodiment, the cutouts are formed by slits that are only closed at one axial end of the sleeve. In this embodiment, the sleeve can be slid onto the stator body or the stator teeth respectively, in an axial direction. In another embodiment of the invention, lateral slits are formed in the stator teeth close to their free ends allowing the sleeve to be slid onto the stator teeth in an axial direction such that the edges of the cutouts engage in the slits. This has the advantage that the sleeve cannot be pulled off the stator poles as a result of the magnetic attraction of the rotor magnets. In addition or as an alternative, the sleeve can also be fixedly connected to the stator teeth by means, for example, of welding, particularly laser welding, or bonding. To give the sleeve greater stability, it could be practical to seal the joint of the rolled sleeve after it has been mounted onto the stator body. An open joint has the advantage that greater tolerances can be allowed when the sleeve is die-cut and that the sleeve is more flexible.  
         [0013]     An embodiment of the invention is also conceivable in which the sleeve is first pressed or slid onto the stator teeth and in which the sleeve is then severed in the region of the slits separating the pole shoes in order to create pole shoes that are completely isolated from each other. To stabilize this or other embodiments of the invention, provision can also be made for the stator to be injection-molded with plastics.  
         [0014]     In its second embodiment, the sleeve is die-cut from flat sheet metal in a similar way as in the first embodiment, the sheet metal being made of a bi-permeable material of the kind described above. Cutouts to connect the sleeve to the stator teeth are die-cut at the same time, but slits to separate the individual poles of the stator are not required. The sheet metal is then rolled to form a sleeve which is open at a joint and thus flexible. The sleeve can be slid onto the stator teeth in an axial direction or pressed onto the stator teeth. Before or after the sleeve has been mounted onto the stator teeth, preferably before the sheet metal is rolled to form a sleeve, the sleeve is locally heated within the zones that extend in an axial direction and lie between two adjacent stator teeth in order to transform the bi-permeable material within these defined zones from its original ferromagnetic state to a paramagnetic state. To this effect, the zones are preferably heated to a temperature &gt;1150° C. using, for example, laser or induction welding. Although this second embodiment requires the additional process of locally heating the sleeve, it has the advantage of providing a sleeve with improved mechanical stability compared to the slotted sleeve. Magnetic short circuits in the region of the end face of the sleeve, where the slits of the first embodiment are bridged, can be avoided.  
         [0015]     To stabilize the finished stator arrangement, it can be molded with a plastic or synthetic resin. Moreover, the sleeve itself can be stiffened by beading or edge bending.  
         [0016]     Practical trials using the stator arrangement according to the invention have shown that the sleeve generates a certain proportion of eddy currents, these effects being lesser in the embodiment having the slits than in the embodiment in which the sleeve is made of the bi-permeable material. The problem of eddy current formation can be minimized by building up the sleeve from individual layers that are electrically insulated with respect to each other in a similar way as used in the production of a stator body from a stamped lamination stack. To this effect, it is preferable if a series of laminations made of a ferromagnetic material or of the bi-permeable material is stacked and die-cut into narrow metal strips. The laminations are then joined together. If the laminations are made from the bi-permeable material, it is best if the laminations are transformed into a paramagnetic state in the region of the zones by heating, using, for example, laser or induction welding, and simultaneously connected together within this region. Then the cutouts to slide the sleeve onto the stator teeth are cut out, die-cut for example, and the sleeve is rolled and joined together at its ends, if required. The advantage of this arrangement is that, due to the laminated structure, eddy currents within the sleeve material are almost totally avoided.  
         [0017]     In a particularly preferred embodiment of the invention, at least one axial end of the sleeve projects beyond the end face of the stator body in an axial direction. This embodiment has the advantage that the bridges disposed at the axial end faces that hold the sleeve together and bridge the pole shoes, can be disposed beyond the magnetic field of the rotor. This prevents the sleeve from forming a magnetic short circuit in the region of the rotor. Another advantage of a sleeve that projects beyond at least one end face of the stator body in an axial direction is that it shields the stator magnetic fields towards the rotor. This makes particular sense for those machines in which a magnetic sensor to measure the rotational position is mounted opposite the end face of the rotor on the stator or on the flange. The shielding effect of the axially protruding sleeve means that these magnetic sensors are not influenced by the magnetic field of the stator and can thus determine the rotational position of the rotor more accurately. 
     
    
     SHORT DESCRIPTION OF DRAWINGS  
       [0018]     The invention is described in more detail below on the basis of preferred embodiments with reference to the drawings. The figures show:  
         [0019]      FIG. 1  an external view of an electric machine according to the invention;  
         [0020]      FIG. 2   a  a schematic sectional view through the electric machine of  FIG. 1  along the line X-X according to a first embodiment;  
         [0021]      FIG. 2   b  an enlarged detailed view of  FIG. 2   a;    
         [0022]      FIG. 3  an exploded perspective view of the electric machine according to the first embodiment;  
         [0023]      FIG. 4 a  similar view as in  FIG. 3  but in an assembled state; and  
         [0024]      FIG. 5 a  perspective view of a sleeve according to the first embodiment that is set into the stator arrangement according to the invention;  
         [0025]      FIG. 6 a  schematic sectional view through a part of an electric machine according to a modification of the first embodiment of the invention, which is similar to the view in  FIG. 2   b;    
         [0026]      FIG. 7  an exploded perspective view of a stator arrangement according to a second embodiment of the invention;  
         [0027]      FIG. 8 a  side view of a sleeve according to the second embodiment, which is set into the stator arrangement according to the invention;  
         [0028]      FIG. 9 a  perspective view of the sleeve of  FIG. 8 ;  
         [0029]      FIG. 10   a  a perspective view of the stator arrangement according to a modification of the second embodiment of the invention; and  
         [0030]      FIG. 10   b  an enlarged detailed view of  FIG. 10   a;    
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0031]     The invention is described below on the basis of an exemplary brushless DC motor, although a person skilled in the art would be aware that the principles of the invention can be applied to a large variety of electric machines, including generators.  
         [0032]     The invention is described below with reference to the figures, reference first being made to FIGS.  1  to  4 .  
         [0033]      FIG. 1  shows an external view of a DC motor according to the invention. In the external view of  FIG. 1 , a stator body  10  can be seen in which a sleeve  12 , projecting axially at both end faces of the stator body  10 , is mounted on the stator teeth. As shown in  FIGS. 2   a ,  2   b ,  3  and  4 , the stator body  10  comprises a stator back yoke ring  14  from which stator teeth  16  project radially inwards. The stator teeth are coupled to the sleeve  12  at their free ends. The sleeve has slit-like cutouts  18  which engage with the free ends of the stator teeth  16 , the stator teeth  16  in the illustrated embodiment having a connecting section  20  at their free ends that is pressed or pushed into the cutouts  18 .  
         [0034]     Moreover, the sleeve has slits  22  that are arranged approximately in the middle between two adjacent cutouts  18  or associated stator teeth  16 . The sleeve can be stiffened by means of beading or edge bending (not illustrated).  
         [0035]     As can particularly be seen in  FIGS. 1 and 4 , the sleeve  12  protrudes in an axial direction with respect to the end faces of the stator body  10 . It demarcates the stator body  10  with respect to a rotor area.  
         [0036]     A rotor is arranged coaxially within the stator body  10  that is shown schematically in the figures by a rotor body  24 . In the illustrated embodiment, the rotor body  24  has spoke-like recesses  26  to receive permanent magnets, the recesses  26  being connected in pairs. The rotor body  24  is mounted on a shaft  28 . An air gap  30  is formed between the rotor body  24  and the stator body  10 .  
         [0037]     As illustrated in the figures, the stator teeth  16  are substantially rectangular, not being widened at their free ends as is commonly the case in the prior art in order to form pole shoes. This makes it easy to wind the stator body  10  since the slot opening between two adjacent pole teeth  16  is very wide. As an alternative, it is also possible to slide pre-wound coils together with the coil body onto the stator teeth  16  from the inside. After the stator teeth  16  have been wound, the sleeve  12  is mounted on the free ends of the stator teeth  16  and thus also acts as a slot cover. It is expedient if the sleeve  12  is coated with an electrically insulating material on its surface facing the stator slots.  
         [0038]     In the preferred embodiment of the invention, the sleeve  12  is made of a ferroelectric material and magnetically coupled to the stator teeth. In this embodiment, the sleeve  12  forms the pole shoes at the end of the stator teeth  16 , adjoining pole shoes being separated by the slits  22  formed in the sleeve. This makes it possible to produce a stator arrangement having pole shoes whose slot opening is smaller than usual in the prior art. In the known stator arrangements having molded-on pole shoes, the rule is that the slot opening has to be approximately ≧1.5 times the wire diameter that has to be inserted through the slot opening. This limitation does not apply to the stator arrangement according to the invention. This means that a stator is provided which, in operation, has extremely small torque fluctuations and a relatively high flux concentration.  
         [0039]     The sleeve  12  is preferably so designed that it projects at the axial end faces of the stator body  10 . This has the advantage that the axial bridges  34  bridging the slits  22  and necessary to hold the sleeve together, are located beyond the effective range of the rotor and thus cannot create a magnetic short circuit. Moreover, the sleeve  12  at the end face of the stator arrangement  10  shields the magnetic field generated by the stator in the direction of the rotor. The magnetic sensors located opposite the end face of the rotor for the purpose of measuring the rotational position of the electric machine, such as Hall sensors or magnetoresistive sensors, are frequently disposed on the stator or on the flange. To obtain an especially precise rotational position signal, these sensors are preferably arranged in the vicinity of the outside circumference of a rotor. This is particularly the case if the rotor does not have embedded permanent magnets (as in the illustrated embodiment) but rather permanent magnets that are arranged on the outside circumference of the rotor. However, the magnetic field generated by the winding head is also active in the vicinity of the circumference of the rotor, which, in the invention, is extensively shielded by the axially protruding sleeve  12 . A possible position for a rotational position sensor is marked in  FIG. 4  by the arrow S.  
         [0040]     The sleeve  12  can be coated with an electrically insulating material on its inner surface and/or on its outer surface.  
         [0041]     As can particularly be seen in reference to  FIG. 5 , the sleeve is preferably die-cut from sheet metal and then rolled, it being possible for the sleeve  12  to remain open at a joint  32 . This makes the sleeve  12  flexible enough to be inserted in an axial direction into the inside of the stator body  10  and to be pressed onto the stator teeth  16  using the cutouts  18 . The geometry of the free ends of the stator teeth  16  and the cutouts  18  has to be made to fit each other accordingly.  
         [0042]     In the illustrated embodiment, the cutouts  18  and the slits  22  are bridged by bridges  34  at both axial ends of the sleeve  12 . In an alternative embodiment, it can be provided that the cutouts  18  are open at one axial end of the sleeve  12 . This makes it possible to slide the sleeve  12  in an axial direction onto the stator teeth  16 . Moreover, provision can be made for the slits  22  as well to be open at an axial end of the sleeve which goes to minimize the risk of the sleeve  12  forming a magnetic short circuit. Provision can also be made to sever the sleeve  12  in the region of the slits  22  after it has been mounted onto the stator teeth  16  in order to completely isolate adjacent pole shoes from each other for their magnetic optimization. It can further be expedient to mold the wound stator arrangement after the sleeve  12  has been mounted with a plastic in order to increase the stability of the stator arrangement. Severing the sleeve  12  can be done after the stator arrangement has been embedded in plastic.  
         [0043]      FIG. 6  shows a schematic section through a detail of an electric machine according to another embodiment of the invention, which is similar to  FIG. 2   b . Corresponding parts are indicated by the same reference numbers and not explained in detail again. In contrast to the embodiment described earlier, the stator teeth  16  have lateral slots  36  in the vicinity of their free ends in which the sleeve  12  can be inserted—in an axial direction of the stator. In this embodiment, the cutouts  18  in the sleeve  12  are open at an end face so that the sleeve  12  can be inserted into the slits  36  with the edges of the cutouts  18 . This embodiment has the advantage that the sleeve cannot be pulled off the stator teeth or the poles as a result of the magnetic attraction of the rotor magnets.  
         [0044]     In all embodiments of the invention, it is possible to additionally connect the sleeve  12  firmly to the stator teeth  16 , for example, by welding, especially laser welding, or bonding.  
         [0045]     The sleeve is preferably made of a magnetically conductive, i.e. ferromagnetic, material. However, if its sole function is to provide a cover for the slots, it can be made of a non-magnetic material.  
         [0046]     A second embodiment of the stator arrangement according to the invention is shown in FIGS.  7  to  9  and a modification of this embodiment in  FIGS. 10   a  and  10   b . As far as the stator body  10  and the rotor body  24  are concerned, this embodiment does not differ from the previously described embodiment. Corresponding parts are indicated by the same reference numbers. The sleeve, however, has a different design to the first embodiment.  
         [0047]     In the second embodiment of the invention, the sleeve  40  is made of a magnetic material that is ferromagnetic in a first state and paramagnetic in a second state. This magnetic material is also referred to as a bi-permeable material. The preferred material for the sleeve according to the second embodiment is a YEP FA1 steel that was developed by Hitachi Metals Ltd., Tokyo, Japan. It is an alloy based on FE—Cr—C which contains additional parts of Si, Mn, Ni or Al. This material has an original ferromagnetic state having a relative magnetic permeability of approximately 900 and a paramagnetic state having a relative magnetic permeability down to some 1.01. The material can be transformed from its ferromagnetic state to a paramagnetic state by heating it to a temperature of over 1050° C., particularly over 1100° C. and preferably in the range of 1100° C. and 1200° C. A particularly preferred temperature range lies between 1150° C. and the melting point of the material. Further details are given, for example, in U.S. Pat. No. 6,255,005 as well as in the Japanese laying-open publications mentioned above.  
         [0048]     In the second embodiment of the invention, the entire sleeve  40  is made of this material, the sleeve being preferably die-cut from sheet metal with cutouts  42  being formed during the die-cutting process. The sleeve is then rolled and can initially remain open at a joint  44 . Using the cutouts  42 , the sleeve  40  is slid onto the stator teeth  16  in an axial direction, as described above with reference to the first embodiment. As an alternative, the sleeve  40  can also be pressed onto the stator teeth  16 .  
         [0049]     The sleeve  40  is locally heated in the region of axially extending zones  46  transforming the sleeve  40  in the region of these zones  46  into the paramagnetic state. The zones  46  are so chosen that they provide full magnetic isolation for the individual stator poles that are formed by the stator teeth  16  and the adjoining sections of the sleeve  40 , the zones  46  lying symmetrically between two adjacent stator poles.  
         [0050]     The heat can be created by using, for example, laser or induction welding and is preferably in the order of magnitude of 1150° C. The zones  46  of the sleeve  40  can be heated either before or after the sleeve is rolled; heating preferably takes place before rolling.  
         [0051]     As explained in reference to the first embodiment, the sleeve is preferably so designed that it protrudes at the axial end faces of the stator body  10 . In the second embodiment, the bridges  48  at the end faces of the sleeve  40  that bridge the cutouts  42  and are necessary to keep the sleeve together, can also be heated and thus transformed into the paramagnetic state. This makes it possible to totally prevent short circuits in this region.  
         [0052]     The sleeve  40  can be coated with an electrically insulating material on its inside surface.  
         [0053]     In the illustrated embodiment, the cutouts  42  are only bridged by the bridges  48  at one axial end of the sleeve  40 . In an alternative embodiment provision can be made for the cutouts  42  to be bridged at both axial ends of the sleeve  40  to give the sleeve additional stability. In this case, it would not be possible to slide the sleeve onto the stator body  10  in an axial direction but it could be pressed onto the stator teeth  16  from inside. It could be expedient to mold the wound stator arrangement with plastics after the sleeve  40  has been mounted in order to improve the stability of the stator arrangement.  
         [0054]     In the embodiment in FIGS.  7  to  9 , the sleeve  40  is slid onto the stator body  10  from one axial end of the stator body. A modification of this embodiment is shown in  FIGS. 10   a  and  10   b , the sleeve being formed in two parts in this modification so that it can be slid onto the stator body from the two opposite axial ends of the stator  10 . The two halves  40 ′ of the sleeve can basically be constructed in exactly the same way as the single-piece sleeve  40  shown in  FIGS. 8 and 9 , the sleeve merely being shortened in the axial direction to allow the two halves  40 ′ to be slid onto the stator body from both sides in such a way that they complete each other to form a sleeve that extends substantially over the entire axial length of the stator.  
         [0055]     While a gap  50  between the sleeve halves  40 ′ is shown in  FIGS. 10   a  and  10   b , the halves are preferably slid so far over the stator body  10  that they touch each other at their end faces, with a small gap being tolerable.  
         [0056]     The second embodiment has the advantage of increased mechanical stability combined with complete magnetic isolation of the individual poles of the stator arrangement. However, it does generate a certain amount of eddy currents which can be suppressed by the measures described below.  
         [0057]     In another modification of the invention that is not shown in the figures, the sleeve is built up of individual layers that are electrically insulated from one another. To this effect, sheet metal made of a bi-permeable material is preferably stacked and die-cut into metal strips, which are initially linear and act as a basic body for the sleeve. Then the regions that are to form the de-magnetized zones are de-magnetized by heating using, for example, laser or induction welding, and the individual laminations are simultaneously joined together by these means. The cutouts for the purpose of sliding the sleeve onto the stator teeth are cut out, for example, by die-cutting, and the sleeve is rolled and connected together at its ends if required. Due to the laminated structure of the sleeve, eddy currents within the sleeve material can be avoided.  
         [0058]     The features revealed in the above description, the claims and the figures can be important for the realization of the invention in its various embodiments both individually and in any combination whatsoever.  
       IDENTIFICATION REFERENCE LIST  
       [0000]    
       
           10  Stator body  
           12  Sleeve  
           14  Stator back yoke  
           16  Stator teeth  
           18  Cutouts  
           20  Connecting section  
           22  Slits  
           24  Rotor body  
           26  Recesses  
           28  Shaft  
           30  Air gap  
           32  Joint  
           34  Bridges  
           36  Slots  
           40  Sleeve  
           40 ′ Sleeve halves  
           42  Cutouts  
           44  Joint  
           46  Paramagnetic zones  
           48  Bridges  
           50  Gap  
          S Sensor position