Abstract:
A friction clutch for a driven element that is connected directly to a drive by means of a first friction-disk clutch and being capable of being matched to the speed of the drive. When the first friction-disk clutch is disengaged, the drive of the driven element is adjusted to a relatively low take-up speed by means of an eddy-current clutch which can be engaged by means of a second friction-disk clutch. The driven element is arranged on a shaft or axle, so that, when the first and second friction clutches are disengaged, the drive of the driven element can be adjusted to a further take-up speed by means of the friction of a roller bearing. The eddy-current clutch includes an eddy-current part and a permanent magnet part which can be moved relative to the eddy-current part.

Description:
FIELD OF THE INVENTION 
   The invention relates to a friction clutch and to a drive arrangement for a fan impeller of a motor vehicle. 
   BACKGROUND OF THE INVENTION 
   In so-called two-stage clutches, a driven element can be driven at a drive speed and also at two different, relatively lower take-up speeds. As a result, three different speed stages can be realized. If the driven element, for example a fan impeller of a motor vehicle, is to rotate at the engine speed, a first friction-disk clutch, for example, is provided, so that the driven element can be driven in a non-positive manner. When the first friction-disk clutch is disengaged, a first take-up speed of the driven element is set by means of a second friction-disk clutch and an eddy-current clutch coupled to the second friction-disk clutch. For a take-up speed which is lower still, both friction-disk clutches are disengaged, the driven element is then moved by means of and together with, for example, a rotating driveshaft due to bearing friction. 
   The clutches are driven, in particular, by means of a central driveshaft, or for example when there is a fixed axle, by means of a driving pulley. 
   SUMMARY OF THE INVENTION 
   The invention is based on the object of providing a friction clutch of the type designated in the introduction which is comparatively more advantageous in both technical and economical terms. 
   The invention proceeds from a friction clutch for a driven element, in particular for a fan impeller of a motor vehicle, the driven element being connected directly to a drive by means of a first friction-disk clutch and being capable of being adjusted to the speed of the drive. When the first friction-disk clutch is not engaged, the speed of the driven element can be adjusted to a relatively low take-up speed by means of an eddy-current clutch, which can be engaged by means of a second friction-disk clutch. The driven element is arranged on a shaft or axle, so that, when the first and second friction clutches are not engaged, the drive of the driven element can be adjusted to a further take-up speed by means of the friction of a roller bearing. The eddy-current clutch comprises an eddy-current part and a permanent magnet part which can be moved relative to the eddy-current part. A significant aspect of the invention is that, in spatial terms, the permanent magnet part is arranged in the axial direction between the driven element and a driving flange which, when the first friction-disk clutch is engaged, can be connected directly to the driven element. A compact friction clutch of comparatively simple design which makes use of standard bearings can thus be obtained. In particular, a stepped ball bearing, as used in a known embodiment, is no longer required. 
   A further important aspect of the invention is that the eddy-current part is formed on the side of the driven element. A design which permits simple bearing units is made possible as a result. 
   This approach is based on the awareness that an eddy-current part can be formed entirely within the driven element without running the risk of cooling problems, even if an outwardly-arranged, driven ribbed disk, which was previously necessary for sufficient cooling and which contained the eddy-current part, is dispensed with. When the ribbed disk is dispensed with a stepped ball bearing, which is necessary for the attachment of the ribbed disk can be omitted. 
   The eddy-current part formed on the side of the driven element ensures that the dissipation of heat via the constantly rotating driven element is advantageously assisted in all shift stages. 
   In one advantageous embodiment of the subject matter of the invention, the driven element and the permanent magnet part are each mounted by means of a separate bearing unit at an axial distance. As a result, the driven element and the permanent magnet part can be mounted in an economically advantageous way. On one hand, standard bearing units, for example, can be used which are more cost-effective than so-called stepped or double-ball bearings. In addition, it can be advantageous, for example for service or repair purposes, if the driven element and the permanent magnet part are mounted independently of one another. 
   One advantageous embodiment of the friction clutch is distinguished in that at least one of the two friction-disk clutches is embodied as a clutch which can be solenoid-operated. Clutches which can be solenoid operated are particularly reliable and are low-lag shift clutches which have, for example, been proven extensively in vehicle construction. 
   In one advantageous embodiment of the friction clutch according to the invention, at least one of the two friction-disk clutches is embodied as a pneumatic or hydraulic clutch. The friction clutches can in principle be operated in different ways. In particular, the proposed friction clutch can be matched to, or integrated into, existing pneumatic or hydraulic systems. 
   It is also proposed that the permanent magnet part comprises a flange part which is produced essentially as a casting. A casting, made in particular from aluminum or an aluminum-based material, has for example a relatively low specific weight and high stability values. 
   In one embodiment, which is, moreover, favorable, of the subject matter of the invention, the driven element alternatively or additionally has a flange part which is embodied essentially as a casting. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features and advantages of the invention are described in more detail on the basis of the schematically illustrated figures, in which: 
       FIG. 1  shows a detail of a known prior art friction-disk clutch, which can be solenoid operated; and 
       FIG. 2  shows a detail of a friction clutch according to the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows a known friction-disk clutch, which can be solenoid-operated and is used, for example, as a fan clutch  1  for a motor vehicle. The fan clutch  1  comprises a driveshaft  2 , on which a rotor disk  3  is arranged in a rotationally fixed manner. The drive shaft  2 , and thus the rotor disk  3 , is brought up to drive speed by means of a drive motor (not illustrated). In addition, a fan impeller hub  4  is rotatably mounted on the driveshaft  2 , on to which a fan impeller hub  4  having fan blades (not illustrated) can be screwed, for example by means of screw connections  5 . 
   Three different speed stages of the fan impeller hub  4  can be obtained using the fan clutch  1 . If the fan impeller hub  4  is to rotate at the same speed as the driveshaft  2 , a first electromagnetic clutch  6  is engaged by supplying current to an associated first electromagnet  6   a . This results in a first armature disk  7 , which is connected in an axially moveable manner to the fan impeller hub  4 , being magnetically pulled toward the rotor disk  3  by magnetic forces. As a result, the driveshaft  2 , the rotor disk  3 , and the fan impeller hub  4  rotate at the same speed. 
   When the first electromagnetic clutch  6  is not supplied with current, a relatively low speed, a so-called take-up speed, of the fan impeller hub  4  can be set using a second electromagnetic clutch. For this purpose, a second electromagnet  8   a  is supplied with current, and a second axially moveable armature disk  9  is pulled toward the rotor disk  3 . The armature disk  9  is fixedly screwed to an intermediate ring  10 , which is associated with a double-ball bearing  11 , and said intermediate ring  10  is fixedly screwed to a ribbed disk  12 . The double-ball bearing  11  permits rotatable mounting of the fan impeller hub  4  and the ribbed disk  12 . A radially outwardly situated annular region  12   a  of the ribbed disk  12  is spaced apart by a gap s 2  from an annular section of the fan impeller hub  4 , to which a plurality of permanent magnets  13 , of respectively opposing polarity, are attached in the circumferential direction. The annular region  12   a  has, for example, an enclosed steel ring  12   b . When the second electromagnet  8   a  is supplied with current, the ribbed disk  12  is adjusted up to the drive speed by means of the rotor disk  3 , the second armature disk  9  and the intermediate ring  10 , and as a result an eddy-current clutch  14  is activated, so that the fan impeller hub  4  rotates at the first take-up speed. 
   In order to set a second, lower take-up speed, of the fan impeller hub  4 , the first electromagnetic clutch  6  and the second electromagnetic clutch  8  are disengaged, as a result of which the armature disks  7  and  9  are spaced apart from the rotor disk  3  by, for example, the gap s 1 . The friction, which occurs in the double-ball bearing  11  as the driveshaft  2  rotates, causes the fan impeller wheel  4  to be taken up and rotated at a second take-up speed which is lower than the first take-up speed. 
     FIG. 2  shows a schematic illustration of an arrangement according to the invention having a friction clutch  20  for, for example, a fan impeller of a motor vehicle. A fan impeller hub  21  is mounted, by means of a single-step ball bearing  22  having, for example, two roller body rings, on a driveshaft  23 , which is screwed to a screw element  24 . In addition, a rotor disk  25  is connected in a rotationally fixed manner to the driveshaft  23  by means of a sleeve section  26 . The rotor disk  25  has a friction disk section  27  which runs radially and has friction faces for a friction clutch. 
   In the region of the rear side, which faces away from the friction disk section  27  of the rotor disk  25 , two electromagnets  28 ,  29  are arranged radially one above the other so as not to contact said rotor disk  25 . The two electromagnets  28 ,  29  are held on a positionally fixed flange piece  30  which is mounted on the driveshaft  23  by means of a further ball bearing  31 . 
   A conically widening flange  33 , which is secured axially and serves, for example, to transmit drive forces to the driveshaft  23 , is fixedly connected to the driveshaft  23  on that side of the ball bearing  31  which faces away from the clutch arrangement. 
   A further annular flange  32  is rotatably mounted in the axial direction, by means of a ball bearing  34 , on the driveshaft  23  in the region a between the fan impeller  21  and the rotor disk  25 . A plurality of permanent magnets  35  are attached to the annular flange  32  in the circumferential direction and have respectively opposing magnetic polarity in an alternating pattern. The permanent magnets  35  are associated with an eddy-current clutch  36  having an eddy-current region  37  in the fan impeller hub  21  which is moveable relative to the annular flange  32 . The fan impeller hub  21  is provided with a steel ring  38  in the eddy-current region  37  at the radial height of the permanent magnets  35 , which steel ring  38  is, for example, enclosed in the fan impeller hub  21 , which is embodied as a casting. The permanent magnets  35  are slightly spaced apart from the fan impeller hub  21  by the distance c. 
   An armature element  39  is provided connected in an axially moveable manner to the fan impeller hub  21  by means of an intermediate part  21   a  on that side which faces toward the rotor disk  25 . When the first electromagnet  28  is supplied with current, the armature element  39  is magnetically pulled toward the rotor disk  25  and against a radially outer part of the friction disk section  27 , so that the fan impeller hub  21  rotates under frictional contact at the same speed as the rotor disk  25 . A fan impeller (not illustrated) can also be screwed on to the fan impeller hub  21  in addition to the intermediate part  21   a  by means of a screw connection  43  which is only indicated schematically. 
   When the electromagnet  28  is not supplied with current, the armature element  39  is returned axially, or the armature element  39  is spaced apart from the friction disk section  27  by a distance b, by means of a connected elastic return element, for example a spring element  41 . 
   At the same axial height as the armature element  39 , but further inward radially, a second armature element  40  is likewise present in an axially moveable fashion on the annular flange  32 . If, when the electromagnet  28  is not supplied with current, a second electromagnet  29  is supplied with current, the armature element  40  is placed in frictional engagement with a radially inner part of the friction disk section  27 , so that the annular flange  32  rotates at the same speed as the rotor disk  25 . Eddy currents are induced in the eddy-current part  37  of the fan impeller hub  21  by means of the permanent magnets  35  which rotate together with said eddy-current part  37 , and a torque is transmitted to the fan impeller hub  21  by means of the magnetic fields formed in the process. As a result, when the electromagnet  29  is supplied with current and, at the same time, the electromagnet  28  is not supplied with current, a first take-up speed is transmitted to the fan impeller hub  21 .  FIG. 2  illustrates this state with the armature element  40  pulled toward the friction disk section  27 . 
   If both electromagnets  28  and  29  are not supplied with current, a second take-up speed, which is lower than the first take-up speed, is transmitted to the fan impeller hub  21  via the ball bearing  22  by means of friction when the driveshaft  23  rotates. 
     FIG. 2  shows, by way of example, a compact friction clutch  20 , in which, in addition, a damping element  42  is formed on the intermediate part  21   a  between the armature element  39  or spring element  41  and the base body of the fan impeller hub  21  in order to dampen load peaks, for example when engaging a clutch. In this arrangement, good utilization of space is achieved by virtue of the fact that, the space available radially above and axially adjacent to the annular flange  32  is utilized for the coupling movement between the rotor disk  25  and the fan impeller  21 , in the manner of mutual interlocking of the components  21   a ,  32 ,  35 ,  39 ,  40 ,  41  and  42  in order to keep the axial and radial construction depths as low as possible. 
   LIST OF REFERENCE SYMBOLS 
   
       
       
         
             1  Fan clutch 
             2  Driveshaft 
             3  Rotor disk 
             4  Fan impeller hub 
             5  Screw connection 
             6  Electromagnetic clutch 
             6   a  Electromagnet 
             7  Armature disk 
             8  Electromagnetic clutch 
             8   a  Electromagnet 
             9  Armature disk 
             10  Intermediate ring 
             11  Double-ball bearing 
             12  Ribbed disk 
             12   a  Annular region 
             12   b  Steel ring 
             13  Permanent magnet 
             14  Eddy-current clutch 
             20  Friction clutch 
             21  Fan impeller hub 
             21   a  Intermediate part 
             22  Ball bearing 
             23  Driveshaft 
             24  Screw element 
             25  Rotor disk 
             26  Sleeve section 
             27  Friction disk section 
             28  Electromagnet 
             29  Electromagnet 
             30  Flange piece 
             31  Ball bearing 
             32  Annular flange 
             33  Annular flange 
             34  Ball bearing 
             35  Permanent magnet 
             36  Eddy-current clutch 
             37  Eddy-current part 
             38  Steel disk 
             39  Armature element 
             40  Armature element 
             41  Spring element 
             42  Damper element 
             43  Screw connection