Abstract:
A friction disk clutch with an electromagnet arrangement which has a coil former and a ferromagnetically conductive coil support, which supports the coil former and at least partially surrounds the latter, and, adjacent to the coil support, there are permanent magnet means, by means of which an axially movable friction section of the friction disk clutch can be connected magnetically to the rotor, and the permanent magnet means are arranged on the rotor in such a way that the permanent magnet means are covered by essentially no magnetically conductive section of the rotor on a side which is transverse to the direction of magnetization thereof. Anchoring means for mounting the permanent magnet means on the rotor include a mounting section formed for this purpose on the rotor, by means of which the permanent magnet means are mounted in the correct position on the rotor.

Description:
[0001]    This application claims the benefit under 35 USC §119(a)-(d) of German Application No. 10 2012 009 589.9 filed May 15, 2012, the entirety of which is incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    This invention relates to a friction clutch. 
       BACKGROUND OF THE INVENTION 
       [0003]    Friction clutches for transmitting torques between a drivable rotor and an element to be driven by the rotor are known, allowing parts that are to be coupled to one another, such as disk-type clutch components, to be selectively separated or connected, in particular, by nonpositive engagement. 
         [0004]    Friction clutches of this kind can be designed as magnetic clutches, which comprise an electromagnet arrangement having a coil former or wire coil, which can be connected to an electric voltage source and energized, and a coil support composed of magnetically conductive material. 
         [0005]    These also include arrangements which additionally have permanent magnets, by means of the magnetic action of which, when the electromagnet is not exerting a magnetic effect, a movable clutch element is attracted to a mating section, counter to a spring force or the like, for example, and these components are connected nonpositively for torque transmission. By energizing the electromagnet, it is then possible, by means of the magnetic field produced, to attenuate or cancel out the effect of the permanent magnet to such an extent that the friction clutch disengages, with the movable clutch element leaving the position of nonpositive engagement. 
         [0006]    These clutches are used in vehicles, for example. 
         [0007]    The disadvantage with the arrangements described is the comparatively high outlay involved in the manufacture of such clutches and the components thereof. 
       SUMMARY OF THE INVENTION 
       [0008]    It is the object of the present invention to improve friction clutches of the type stated at the outset technically and in respect of economical manufacture. 
         [0009]    The present invention starts from a friction clutch for torque transmission from a rotor that can be driven about an axis to an element to be driven, comprising a friction disk clutch with an electromagnet arrangement which has a coil former and a ferromagnetically conductive coil support, which supports the coil former and at least partially surrounds the latter, and, adjacent to the coil support, there are permanent magnet means, by means of which an axially movable friction section of the friction disk clutch can be connected magnetically to the rotor, and the permanent magnet means are arranged on the rotor in such a way that the permanent magnet means are covered by essentially no magnetically conductive section of the rotor on a side which is transverse to the direction of magnetization thereof. The element to be driven preferably rotates about the same axis about which the rotor can be rotated. 
         [0010]    The essential aspect of the present invention consists in that there are anchoring means for mounting the permanent magnet means on the rotor, comprising a mounting section formed for this purpose on the rotor, by means of which the permanent magnet means are mounted in the correct position on the rotor. In particular, the permanent magnet means can be anchored rigidly on the rotor by means of the anchoring means. The permanent magnet means can thus advantageously be mounted on the rotor in a simple and easily assembled manner. It is furthermore advantageous that a main body of the rotor is formed by or manufactured integrally with a component. In particular, the permanent magnet means are annular, being a single part, for example, or being formed by a plurality of parts which correspond to sections of a ring shape, e.g. by a plurality of ring segments in the form of ring sections. If there is a plurality of permanent magnet elements on the rotor, these are preferably of the same design as one another. 
         [0011]    In particular, the permanent magnet means can be mounted on the inside of an already existing section of the rotor, e.g. a web region extending in the axial direction. The web region or that side thereof which is fitted with the permanent magnet means is spaced apart here from the electromagnet arrangement and, in particular, the coil support by means of an air gap. 
         [0012]    Covering of the permanent magnet means as hitherto, e.g. in the manner of a sandwich structure, which is expensive, can be avoided since fastening the permanent magnet means with the anchoring means provides sufficiently high retaining forces. 
         [0013]    The magnetic field lines of the permanent magnet means mounted in a fixed manner on the rotor run perpendicular to main sides of the relevant permanent magnets or the surfaces of the main sides are at least approximately perpendicular to the direction of magnetization of the permanent magnet means, for example. The permanent magnet means can be formed, for example, by a plurality of segment-like permanent magnets or by a continuous, uninterrupted ring composed of a permanent magnet material. 
         [0014]    One advantageous possibility is for the permanent magnet means to be present at different points or in different orientations on the rotor. It must merely be ensured that a suitable magnetic flux can form in each case between the rotor and the element to be driven. It is advantageous if the main sides of the permanent magnet means are oriented in such a way that the normals thereof are oriented in the axial or the radial direction relative to the axis of rotation of the rotor. 
         [0015]    In particular, the permanent magnet means can be fixed on the rotor by means of the anchoring means in such a way that just one main side or main surface of the permanent magnet means rests on the rotor, with the other, opposite main side of the permanent magnet means remaining free or adjoining the air gap and thus advantageously being adjacent to the coil support of the electromagnet arrangement. 
         [0016]    Accordingly, a flat coil side of the ferromagnetic coil support likewise adjoins the air gap, the coil side preferably being oriented parallel and opposite to the free main side of the permanent magnet means. This arrangement is advantageous overall for the desired formation of the magnetic field lines. 
         [0017]    It is advantageous if the anchoring means comprise an offset, against which a stop surface, matched to the offset, of the permanent magnet means rests when the permanent magnet means are mounted in the correct position on the rotor. In the mounted state of the permanent magnet means on the rotor, the offset, by means of adjacent offset surface regions on the rotor that converge with one another at right angles for example, and the stop surface of the permanent magnet means, e.g. a narrow side or end of the permanent magnet means, come into mutual surface contact. In this case, the offset forms a mechanical stop for the permanent magnet means, with the result that the permanent magnet means rest thereon and are secured against movement on the rotor in at least one spatial direction. If the permanent magnet means are mounted by means of a holding element, the holding element can rest with one side against the offset and hence be fixed in position in the relevant direction. 
         [0018]    It is furthermore advantageous that the anchoring means have a contact region set back on one side of the rotor. In this case, the contact region provides a contact surface, for example, which can be a bottom surface of a recess that serves as a fixed contact side or boundary for the permanent magnet means inserted or a holding element. 
         [0019]    In this case, the offset can be present on the rotor so as to encircle the recess, the recess being used for the accommodation or at least partially recessed insertion of the permanent magnet means on the rotor. The recess can, for example, have a bottom surface of basically rectangular shape which is flat or arched in the form of a hollow cylinder and forms the contact surface, the shape and size or a bottom side of the permanent magnet means being designed accordingly to match the shape and size or bottom surface of the recess and hence being capable of being inserted in a well-fitting manner into the recess. The permanent magnet means can be accommodated in the recess so as to be flush or to protrude, for example. In the case of a rectangular recess, the offset, which forms four edge sections of the recess which are at right angles to one another and surrounds the recess, provides a mechanical stop for the permanent magnet means in four different spatial directions. 
         [0020]    It is furthermore proposed, in an advantageous variant of the present invention, that a holding element is provided, on which the permanent magnet means are present, wherein the holding element can be attached releasably, in particular snapped in or latched, to the rotor in order to attach the permanent magnet means. This simplifies the installation of the permanent magnet means. 
         [0021]    It is also advantageous that the holding element comprises an annular main body which is mounted releasably on the rotor. 
         [0022]    In particular, the holding element is matched to the shape of the rotor or of a section thereof, being, in particular, annular or hollow-cylindrical or in the form of at least a section of the shape. It is advantageous if the permanent magnet means are shaped in a corresponding manner, that is to say, for example, are annular or in the form of a ring segment and are mounted on the holding element. 
         [0023]    It is also advantageous that an adhesive joint is formed for the purpose of mounting the permanent magnet means on the rotor. This is, in particular, a simple possibility for installation. In this case, the permanent magnet means can be bonded directly to the rotor or to the holding element, which may itself likewise be attached to the rotor by adhesive bonding and, if required, additionally secured by further elements. 
         [0024]    It is advantageous if a retaining ring that can be inserted in a groove on the rotor is provided to fix the permanent magnet means on the rotor with respect to at least one direction in the mounted state. In particular, the permanent magnet means are thereby secured on the rotor in an axial direction with respect to an axis of rotation of the rotor. A retaining ring is a reliable and proven retaining element for rotating components. The retaining ring can be a snap ring, for example. It is also possible for the holding element to be secured on the rotor by means of a retaining ring. 
         [0025]    Another advantageous embodiment of the present invention is distinguished by the fact that the permanent magnet means are arranged in a volume of a hollow cylinder. This is advantageous functionally and in terms of construction. It is advantageous if the permanent magnet means are present radially on the inside of an outer part of the rotor, on the outside of which, for example, a belt support of a belt pulley is formed if the rotor is configured as a belt or poly-V belt pulley. 
         [0026]    It is furthermore advantageous that the permanent magnet means are arranged in a volume of a tubular section. The tubular section is part of the rotor or the holding element, for example. It is advantageous if a rotor main body of the rotor, i.e. without the holding element and the permanent magnet means, is formed by a single component or integrally. The rotor can comprise a tubular element, or the rotor main body can be produced from such, if required by connection to further rotor elements. 
         [0027]    According to an advantageous embodiment of the present invention, the permanent magnet means are designed in such a way that the connection of the friction section to the rotor can be canceled in an electrically operated state of the electromagnet arrangement by weakening the magnetic effect of the permanent magnet means. Thus, a “fail-safe clutch” can be obtained, wherein reliable frictional connection of the friction clutch is always achieved in a de-energized state by means of the permanent magnet means. It is thereby possible to avoid critical situations attributable to failure of the power supply by virtue of the friction clutch, which would otherwise not be operated. If the operated friction clutch is necessary, for example, to maintain a cooling system, e.g. that of an internal combustion drive that drives the rotor, cooling is advantageously maintained, even if the electric power supply to the electromagnet arrangement fails. 
         [0028]    It is furthermore advantageous that the permanent magnet means are sintered or injection-molded. 
         [0029]    This is advantageous in respect of production and/or of the properties of the permanent magnet means. 
         [0030]    Finally, it is advantageous that the permanent magnet means are designed as ring segments. In particular, a plurality of similar ring segments are arranged on the rotor at uniform spacings from one another and circumferentially around the axis of rotation of the rotor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    Further advantages and features of the invention are explained in greater detail by means of the illustrative embodiments according to the present invention shown in schematic form in the figures. 
           [0032]      FIG. 1  shows a friction clutch according to the invention in a partial view and in section; 
           [0033]      FIG. 2  shows a rotor of an alternative friction clutch according to the invention in perspective and in section; and 
           [0034]      FIG. 3  shows an enlarged detail of part of another, alternative friction clutch according to the invention in a sectional view. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0035]    In some cases, the same reference signs are used in the figures for corresponding elements of different illustrative embodiments. 
         [0036]      FIG. 1  shows, in section, an arrangement, e.g. for a vehicle powered by internal combustion and having a friction clutch  1  according to the invention, which is designed as a “fail-safe clutch”. The friction clutch  1  according to the invention, which is shown in  FIG. 1  and which is configured for torque transmission from a rotor  2  that can be driven about an axis S to an element to be driven, has permanent magnet means on a section of the rotor  2 , wherein the permanent magnet means corotate with the rotor  2 . 
         [0037]    For this purpose, the friction clutch  1  has, on the rotor  2 , a belt pulley  3  with permanent magnet means constructed from a permanent magnet ring  4  of permanently magnetic material. It is advantageous if the permanent magnet ring  4  is situated radially on the inside or on a bottom side, opposite a belt support  5  of the belt pulley  3 . 
         [0038]    In order to avoid unwanted thermal stresses due to parts heating up during operation in the region of the permanent magnet ring  4 , in particular due to a flow of electric current through current-carrying parts, the permanent magnet ring  4  can be provided in a form that is divided at one point on the circumference or as an open ring with, for example, just one slot. 
         [0039]    For the same reason, the permanent magnet means in an advantageous embodiment of the friction clutch  1  can be formed not by the permanent magnet ring  4  but by a plurality of ring segments, which are situated on a circumferential line and are positioned spaced apart circumferentially or positioned concentrically with respect to the axis of rotation S of the shaft  6 . The fundamental point for the formation of the desired permanent-magnetic effect of the permanent magnet means is that the direction of magnetization should be the same or is permanently maintained in all the ring segments or segments of the permanent magnet means. This arrangement should be distinguished, in particular, from systems for the formation of eddy currents and, in particular, has nothing to do with an eddy current system, for example. 
         [0040]    By means of an offset A running around the circumference, which is part of the anchoring means and is formed on a radially inner side of a radially outer web  3   a  of radially spaced webs  3   a ,  3   b  of the belt pulley  3 , a stop for an end  4   a  of the permanent magnet ring  4  is provided in a correctly positioned mounted state. It is thereby advantageously ensured that, in the mounted state of the permanent magnet ring  4 , which is mounted on web  3   a  by means of a radially outer longitudinal side, is fixed in position axially in one direction relative to a belt pulley base  3   c  connecting webs  3   a  and  3   b . At its axially opposite end or at the free end of web  3   a , the permanent magnet ring  4  is furthermore secured against displacement during the rotary operation of the belt pulley  3  by means of a prestressed retaining ring  8  inserted removably in a matching encircling groove  7  in web  3   a.    
         [0041]    Webs  3   a  and  3   b  delimit a recess in the form of an annular channel into which an electromagnet arrangement  9  of the friction clutch  1  projects. The electromagnet arrangement  9 , which is fixed in position, has a coil  10  and a coil support  11 , which is U-shaped in axial section and surrounds the coil  10  on three sides. 
         [0042]    It is advantageous if a radially inner longitudinal side of the permanent magnet ring  4  is spaced apart from a radially outer web  11   a  of the coil support  11  by means of a small air gap  12 . The longitudinal sides of the permanent magnet ring  4  are transverse to the direction of magnetization R of the permanent magnet ring  4 . 
         [0043]    The friction clutch  1  according to  FIG. 1  furthermore comprises a friction disk clutch  13  with an armature disk  14 , which can be moved axially in accordance with permanent-magnetic or electromagnetic forces, as described below. 
         [0044]    The rotor  2  can be driven in rotation about the axis S. 
         [0045]    It is advantageous if the permanent magnet ring  4  extends over somewhat more than the axial extent of the coil  10  in the axial direction with respect to the axis S and the shaft  6 . It is also advantageous that the permanent magnet ring  4  is present and formed in the magnetic flux in such a way that, when the coil  10  is not energized, the armature disk  14  is drawn into frictional engagement with a mating section of the rotor  2  or with the belt pulley base  3   c , with torque transmission taking place between the rotor  2  and the armature disk  14  and hence torque transmission taking place from the rotor  2  to the shaft  6 , which represents the element to be driven. 
         [0046]    The arrangement from  FIG. 1  furthermore has an eddy current arrangement  15  in the region of a fan impeller  16  seated on the shaft  6 , with an encircling metal ring  17  being formed in the fan impeller  16  or being enclosed by the material of the fan impeller  16 , for example. A plurality of individual permanent magnets  19 , of alternating polarity, of the eddy current arrangement  15  are present on a flange ring  18  connected to the shaft  6 , in a position axially opposite the region of the ring  17 . The individual permanent magnets  19  have nothing to do with the permanent magnet ring  4 . 
         [0047]    Moreover, there is a rolling contact element bearing  20 , by means of which the rotor  2  is supported rotatably relative to the shaft  6 . Here, the rolling contact element bearing  20  is designed as a two-row rolling contact ball bearing. In this case, it is advantageous that the rolling contact element bearing  20  extends axially over the entire axial extent of that part of the belt pulley  3  which is designed as a belt support  5 . 
         [0048]    By means of the electromagnet arrangement  9 , it is possible to act upon the friction disk clutch  13 , the friction disk clutch  13  serving to transmit torque from the rotor  2  to the shaft  6  in the operated state of the friction clutch. The friction disk clutch  13  comprises the friction disk, which is connected rigidly to the shaft  6 , is configured as a ferromagnetic armature disk  14  and can be moved in the direction indicated by the double arrow P 1 , axially with respect to the shaft  6  and parallel to the axis of rotation S. For this purpose, the armature disk  14  is mounted by means of a resiliently deflectable spring disk  21  made, for example, from spring steel, the spring disk  21  being connected rigidly to the flange ring  18  in a position radially on the inside. 
         [0049]    The friction disk clutch  13  with the armature disk  14  is designed in such a way that, in practice, the armature disk  14  in each case occupies one of two different operating positions. In a first operating position (not shown), the armature disk  14  is drawn against a mating end section or the belt pulley base  3   c  of the ferromagnetically conductive rotor  2  by the magnetic forces produced by the permanent magnet means in accordance with the permanent magnet ring  4 , with the result that the two components  14  and  3   c  interact nonpositively or frictionally and are connected to one another for conjoint rotation. To form a desired magnetic field line profile, the armature disk  14  and the belt pulley base  3   c  are provided with mutually offset openings or gaps in the material. 
         [0050]    If torque transmission to the shaft  6  is to be canceled while the rotor  2  is rotating, the coil  10  of the electromagnet arrangement  9  is energized, producing a magnetic field which counteracts the magnetic field of the permanent magnet ring  4  in such a way that a resultant or possibly almost completely eliminated magnetic field is so weak or negligible that the spring force of the spring disk  21  acting on the armature disk  14  ensures that the armature disk  14  is moved away from the belt pulley base  3   c . As a result, the shaft  6  is no longer driven in rotation directly by the rotor  2  (see  FIG. 1 ). 
         [0051]      FIG. 2  shows a sectional perspective view of a rotor  22  of an alternative friction clutch according to the present invention. The basic construction of the rotor  22  is comparable to that of the rotor  2  shown in  FIG. 1  and, accordingly, has a belt pulley  3  with an outer web  3   a , on which the permanent magnet means are present radially on the inside in the form of a plurality of permanent magnet elements arranged circumferentially with respect to the axis of rotation S, permanent magnet elements  23   a  to  23   f  of the elements being visible in  FIG. 2 . Permanent magnet elements  23   a  to  23   f  are mounted rigidly on an annular holding element  23 , which is part of the anchoring means. Permanent magnet elements  23   a  to  23   f , which are rectangular in plan view, are bent slightly to match the hollow-cylindrical shape of the holding element  23 . 
         [0052]    The holding element  23  is manufactured from plastic and is formed with a plurality of projecting latching tabs  24  capable of slight elastic deflection, which are present on one edge of the holding element  23  in a manner uniformly spaced apart around the circumference. The latching tabs  24  are triangular in section and project from a side of the holding element  23  which lies opposite the side having permanent magnet elements  23   a  to  23   f.    
         [0053]    To enable the holding element  23  together with the permanent magnet elements to be mounted detachably on the rotor  22 , by hand or without tools for example, the latching tabs  24  engage in a continuous encircling groove  25  radially on the inside of web  3   a , the groove being designed to match the latching tabs  24 . The holding element  23  can thus be snapped into the rotor  22 , for example, by the latching tabs  24  being pressed into the groove  25  and latching in there, thus ensuring that the holding element  23  with the permanent magnet elements is mounted in a manner fixed or secured on the rotor  22 , this being shown by  FIG. 2 . 
         [0054]    In this case, a further tubular section of the holding element  23  comes into surface contact with a contact region  27  on the inside of web  3   a , the contact region being formed in a recessed or set-back manner. The contact region  27  is bounded by an offset  26  on web  3   a . The contact region  27  formed on the hollow-cylindrical wall of web  3   a , together with the offset  26 , is present circumferentially all around the axis of rotation S. 
         [0055]    Permanent magnet elements  23   a  to  23   f  can be adhesively bonded or firmly fixed in some other way to the holding element  23 , for example. By means of the holding element  23 , which is fitted with permanent magnet elements  23   a  to  23   f  and further permanent magnet elements that are not shown, it is advantageously possible to fix the permanent magnet means on the rotor  22  and to remove them again, if appropriate. 
         [0056]      FIG. 3  shows an alternative anchoring means to that in  FIG. 1  for mounting a permanent magnet element  30  on the inside of a web  3   a  of a rotor  31 , a section of which is shown. Instead of the retaining ring  8  shown in  FIG. 1 , a holding element designed as a plastic strip  28  is provided to anchor the permanent magnet element  30 . Also shown is a section of a web  11   a  of a coil support of an electromagnet arrangement, wherein the web  11   a  is spaced apart from the inside of the permanent magnet element  30  by means of an air gap, with the spacing a. The permanent magnet element  30  is mounted rigidly on the plastic strip  28 . The plastic strip  28  is L-shaped in section and has a sleeve section  28   a , on which the permanent magnet element  30  is mounted, and a ring  28   b , which projects at right angles with respect to the sleeve section  28   a  and is rectangular in section. In the illustrated removably mounted state of the plastic strip  28  on the rotor  31 , the ring  28   b  engages in a self-locking manner in a groove  29  formed for this purpose on web  3   a.    
         [0057]    Moreover, like the holding element  23  shown in  FIG. 2 , on web  3   a , the permanent magnet element  30 , which projects on both sides of the plastic strip  28 , is inserted so as to be held resting flat against web  3   a , radially on the inside, in the region of a set-back region with an offset  26 . Here, one end  30   a  of the permanent magnet element  30  rests against a vertical section of the offset  26 . The decisive holding effect is accomplished with the ring  28  snapped or pressed into the groove  29  and latched there, this being indicated only in a highly schematized or greatly simplified manner in  FIG. 3 . A bottom side  30   a  of the permanent magnet element  30  furthermore rests flat against a contact region  32  set back from a radially inner side of web  3   a  of the rotor  31 . 
         [0058]    In addition to snapping in or as an alternative, the plastic strip  28  with the permanent magnet element  30  can also be bonded adhesively to the rotor  31  or web  3   a.    
       LIST OF REFERENCE SIGNS 
       [0000]    
       
           1  friction clutch 
           2  rotor 
           3  belt pulley 
           3   a  web 
           3   b  web 
           3   c  belt pulley base 
           4  permanent magnet ring 
           4   a  end 
           5  belt support 
           6  shaft 
           7  groove 
           8  retaining ring 
           9  electromagnet arrangement 
           10  coil 
           11  coil support 
           11   a  web 
           12  air gap 
           13  friction disk clutch 
           14  armature disk 
           15  eddy current arrangement 
           16  fan impeller 
           17  ring 
           18  flange ring 
           19  individual permanent magnet 
           20  rolling contact element bearing 
           21  spring disk 
           22  rotor 
           23  holding element 
           23   a  permanent magnet element 
           23   b  permanent magnet element 
           23   c  permanent magnet element 
           23   d  permanent magnet element 
           23   e  permanent magnet element 
           23   f  permanent magnet element 
           24  latching tab 
           25  groove 
           26  offset 
           27  contact region 
           28  plastic strip 
           28   a  sleeve section
         28   b  ring     
           29  groove 
           30  permanent magnet element 
           30   a  bottom side 
           30   a  end 
           31  rotor 
           32  contact region