Abstract:
A magnetorheological clutch consists of a stationary part, a primary part and a secondary part, a working space which contains a magnetorheological fluid being formed between primary part and secondary part, in which working space primary discs and secondary discs successively alternate in the radial direction, and a controllable magnetic field acting on the magnetorheological fluid. In order to prevent segregation of the fluid by centrifugal force in a simple type of construction, the working space is L-shaped in longitudinal section, the primary part is a shaft and the secondary part is a pot enclosing the working space, and are of pot-shaped design.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a National Stage of International Application No. PCT/EP2006/005026, filed May 26, 2006. This application claims the benefit of Austrian Patent Application No. GM0358/2005, filed May 31, 2005. The disclosures of the above applications are incorporated herein by reference in their entirety. 
     
    
     FIELD 
       [0002]    The present disclosure relates to a magnetorheological clutch having a stationary part, a rotating primary part having primary disks and a coaxially rotating secondary part having secondary disks, wherein a working space containing magnetorheological fluid is formed between the primary part and the secondary part and in which the primary disks and the secondary disks alternate sequentially in the radial direction and wherein a regulatable magnetic field acts on the magnetorheological fluid. The magnetorheological fluid can be either a liquid or a gas with magnetizable particles suspended therein. 
       BACKGROUND 
       [0003]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
         [0004]    Power consumption and construction size must be minimized for the use of a magnetorheological clutch in the powertrain of a motor vehicle. There are also demands, such as a wide control range of the transmitted torque, as well as a fast and precise response, to satisfy all dynamic driving demands. 
         [0005]    A clutch of this type is known from EP 940 286 A2. The magnetic field is generated by a coil fixed with respect to the housing. The field lines are relatively long due to the manner of construction of the magnetic coil with its yoke, which reduces the size of the active part of the magnetic field that acts on the magnetorheological liquid. An air gap thereby also arises between its yoke and the rotating parts, in particular the disks, and the air gap has to have a substantial width for tolerance reasons. The magnetic field lines are thereby interrupted and the magnetic field acting on the magnetorheological fluid is further weakened. The cylindrical disks give rise to further problems. The suspended particles migrate slowly outwardly, driven by the centrifugal force, cascade-like in serpentine lines between the individual cylindrical disks; the fluid unmixes; and the disks prevent a fast circulation of the fluid which would mix it again. This problem is also addressed in U.S. Pat. No. 6,318,531 which likewise has a magnetorheological clutch of this category as its subject. A further problem is the connection of the cylindrical disks to their axially normal base plates. It is extremely labor intensive and a precise centering and maintenance of the spacings between the individual disks is not possible. 
       SUMMARY 
       [0006]    The present disclosure improves a generic clutch such that a torque can be transmitted which is as high as possible in a very small working space and with a minimal power consumption, in so doing, the problems of the unmixing and of the connection of the disks to their base parts is solved. 
         [0007]    The working space may be L-shaped in longitudinal section, and provides very high density and utilization of the magnetic field lines. The pot-like design of the disks permits a particularly simple shape of the pot which surrounds the working space and which at the same time forms a yoke. Above all, a simple connection to the parts supporting them and a precise centering with an exact maintenance of the intermediate spaces between the disks. In addition, the disks can also be manufactured cheaply and precisely by deep drawing. 
         [0008]    The problem of the unmixing is solved by the interaction of the seals with the pot shape of the disks and the secondary part. The seals are at the cylindrical part of the disks, where the centrifugal force acting on the suspended particles is the largest and thus a migration of the particles into the outwardly adjacent gap is suppressed. Thanks to the pot shape, only every second intermediate space needs a seal. 
         [0009]    The base parts of the disks guided radially to the axis of rotation of the clutch permit a fluid connection of the individual intermediate spaces between the disks at the point of the smallest radius and minimal centrifugal force. No seals are necessary there and a fluid flow can take place which does not result in unmixing. In addition, the fluid connection facilitates (for instance, by the spline, by means of which the primary disks are connected to their primary part) the filling of the clutch with magnetorheological fluid and the pressure equalization between the intermediate spaces. Overall, a working space is created by the pot shape which is L-shaped in longitudinal section and has L-shaped fluid gaps between the disks. 
         [0010]    The inner rims of the base parts of the primary disks are rotationally fixedly connected to the primary part and are separated from one another by spacers, and the secondary disks have outwardly directed rims in the manner of a hat brim at their side remote from the base parts, the rims connected to the secondary part in a manner contacting one another in the axial direction. The spacers provide the same axial spacings of the primary disks. The secondary disks are thus clamped between the pot rim and the cover and are equally centered without special measures. Since the connection for all disks is of the same radius, a simple spline is, for example, sufficient. 
         [0011]    To improve the fluid connection between the individual fluid gaps, it is of advantage to provide the base parts of the primary disks, and optionally also of the secondary disks, with passage openings in the vicinity of the inner rims, if the clearances at the spline are not sufficient for this. This facilitates the filling and the pressure equalization. No unmixing can take place through the passage openings because the particles would have to migrate against the centrifugal force for this purpose in order to reach them. It is advantageous for the reduction of the magnetic stray flux if the inner rims of the base parts of the primary disks are seated on an intermediate ring which consists of a material of small magnetic permeability and which is in turn rotationally fixedly connected to the primary part. The material portion of the magnetically conductive disks is thus reduced. 
         [0012]    There are different possibilities for the design of the seals within the framework of the invention. In an advantageous embodiment, the regions of the cylindrical parts of the disks remote from the base parts have restricted portions which extend all around as seals and which at least almost contact the adjacent disk. The restricted portions can be attached either to the primary disks or to the secondary disks. The restricted portions are more favorable from a technical production aspect at the primary disks. A secondary disk is adjacent to the primary disk and vice versa. The sealing gap thus comes to lie such that the particles would have to migrate inwardly due to the restricted portion in order to reach the sealing gap at all. In addition, the contact of the disks at the sealing gaps has a positive effect on the shape and on the distribution of the magnetic field lines. 
         [0013]    Rings made of a slide-friendly material of small magnetic permeability are provided as seals at the rims of the primary disks remote from the base parts. 
         [0014]    There are various base shapes with variants for their design within the framework of the invention with respect to the arrangement of the parts generating and guiding the magnetic field (magnetic coils and yokes). They all produce a particularly dense, closed and uniform shape of the magnetic field lines. 
         [0015]    In a first basic shape, the primary part has a magnetic field generator with at least one first yoke and is surrounded by it, said magnetic field generator forming the inner boundary of the working space, with a second yoke being formed in the outer boundary of the working space and the pot of the secondary part being closed by a cover on its side remote from the base. There is thereby a minimal centrifugal force effect on the coil and yoke. The cover can furthermore be used for the fixing of the flange parts. 
         [0016]    In a second basic shape, the secondary part additionally has an insert part inwardly bounding the working space and contains the magnetic field generator. In a third basic shape, the first yoke of the magnetic field generator is fixedly connected to the housing and the insert part and the cylindrical part of the pot form a second yoke. 
         [0017]    Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0018]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0019]      FIG. 1  is a longitudinal section through a first basic shape; 
           [0020]      FIG. 2  is a variant of  FIG. 1 ; 
           [0021]      FIG. 3  illustrates a first embodiment of  FIG. 1 ; 
           [0022]      FIG. 4  illustrates a second embodiment of  FIG. 1 ; 
           [0023]      FIG. 5  illustrates a third embodiment of  FIG. 1 ; 
           [0024]      FIG. 6  illustrates a cross-section of  FIG. 5 ; 
           [0025]      FIG. 7  illustrates detail A in  FIG. 1  in three different variants (a, b, c); 
           [0026]      FIG. 8  illustrates a longitudinal section through a second basic shape; and 
           [0027]      FIG. 9  illustrates a longitudinal section through a third basic shape. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
         [0029]    In  FIG. 1 , a stationary part  1  with sliding contacts  2  for the power supply to a primary part  3  is shown of a housing (not shown) of a magnetorheological clutch. Primary part  3  is a shaft which is supported in the housing. Primary part  3  may drive or be driven, which depends on the respective load state (traction mode or braking mode) in use in a motor vehicle. In primary part  3 , a power supply line  4  leads from sliding contacts  2  to a magnetic field generator  5  which is described in detail below. Primary part  3  has a first spline  6 . The axis of rotation of primary part  3  and of the entire clutch is marked by  8 . 
         [0030]    A secondary part  10  is supported in bearings  7  with respect to the primary part  3 . Secondary part  10  consists of a substantially rotationally symmetrical pot  11  with a cover  12 , which may be substantially an axially normal plate. Pot  11  and cover  12  form end plates in which bearings  7  are seated. Pot  11  here consists in one piece of a cylindrical part  13  and a base part  15  on the side opposite cover  12 . Cylindrical part  13  has a second yoke in its interior, which extends all around and which forms a shoulder  16  and a second spline  17 . Cover  12 , held by a circlip  18 , for example, is seated on the latter. 
         [0031]    Pot  11  and cover  12  bound a working space  20  outwardly and the magnetic field generator  5  bounds it inwardly. Working space  20  is “L”-shaped in longitudinal section and accepts a disk packet which consists of a number of primary disks  21  and secondary disks  22  between which respective fluid gaps  23  remain free. They are part of the working space  20  which is filled with a magnetorheological fluid. Primary disks  21  consist of a cylindrical part  25  and a substantially axially normal base part  26 , which merge into one another with a rounded portion. The rounded portion facilitates the manufacture of the primary disks  21  by deep drawing. The secondary disks  22  equally consist of a cylindrical part  27  and a base part  28  disposed in an axially normal plane. The primary shafts  21  have a section  31  in their base part  26  at an interior rim  38  surrounding primary part  3 , and are seated rotationally fixedly on first spline  6  with the section, separated from adjacent disks by spacers  32 . 
         [0032]    There may be a radial spacing, not shown, between section  31  and spine  6  that permits the passage of fluid. Primary disks  21  may be installed very simply and very precisely using a thickness of spacers  32  and the centration by spline  6 . If play in the first spline  6  is not sufficient, passage openings  33  for the connection of the individual fluid gaps are provided at a lowest possible spacing from the axis of rotation  8 . A seal  34 , here forming the rim of the cylindrical part  25  of the primary disks  21 , may be provided at the side opposite from the base parts  26  and  28  of disks  21  and  22 . Seal  34  here consists of a restricted portion  35  of primary disks  21 , which forms their rim and which extends all round. 
         [0033]    Inner rim  38  of base parts  28  of secondary disks  22  extend up to first spline  6 , but without contacting it. Fluid may thus also pass through there. Additional passage openings  33 ′ may also be provided on the same radius as passage openings  33  of secondary disks  21 . At a side remote from the base parts  28 , disks  22  have a flange part  36  as an outer rim, which lies in an axially normal plane and forms the “brim” of a hat. At its outer rim, flange part  36  has teeth  37  all around which engage into second spline  17  in secondary part  10  and establish a rotationally fixed and centered connection. Flange parts  36  of secondary disks  22  contact one another in the axial direction and are clamped together between the second yoke  14  and cover  12 . Their position with respect to the primary disks  21  can thereby be precisely fixed, and by their centration in the second spline  17 . 
         [0034]      FIG. 2  differs from  FIG. 1  in that the base parts  26 *,  28 * of the disks do not reach up to the shaft forming primary part  3 , but up to an intermediate ring  40 , which has a third spline  41  for the acceptance of primary disks  21  at its outer periphery and whose inner rim is in turn seated on first spline  6  of primary part  3 . Working space  20  thereby does not reach fully up to primary part  3 , but third spline  41  has to lie on a smaller radius than the cylindrical part of the innermost disk with respect to the axis of rotation  8 . The intermediate portion consists of a material of small magnetic permeability and has the purpose of reducing the material portion of the magnetically conductive disks. In this manner, the magnetic stray flux in the disks may be reduced. 
         [0035]    In  FIG. 1 , magnetic field generator  5  is indicated by a rectangle in broken lines. In  FIG. 3 , magnetic field generator  5  consists of a magnetic coil  51  whose winding axis is the axis of rotation  8  and of a first yoke  51  which surrounds it and which only has a zone  52  of less magnetic permeability all around radially outside the coil  50  to prevent short-circuited field lines. The magnetic field created in this manner is characterized by a field line  53 . 
         [0036]    In  FIG. 4 , the constellation of  FIG. 3  is doubled. Two oppositely poled magnetic coils  56  and  57  are arranged next to one another and each is surrounded by a first yoke  58  and  59 , which is substantially the same as the first yoke  51  in  FIG. 3 . The adjacent magnetic fields thus generated are again indicated by a respective field line  60  and  61 . As a special feature, the disks are not made of a material of high magnetic permeability, but of a material of moderate magnetic permeability so that weak short-circuit field lines  62  are formed. A uniform distribution of the magnetic field lines may thus also be achieved. The number of coils may also be increased, whereby a plurality of small individual magnetic currents are produced at magnetic field lines, which minimizes the formation of eddy currents. 
         [0037]    In  FIGS. 5 and 6 , a number of alternately oppositely poled magnetic coils  64  and  65  are arranged following one another in the peripheral direction (see  FIG. 6 ). The corresponding yokes  66  and  67  are likewise distributed over the periphery of primary part  3 . The field lines  68  and  69  extend as shown in  FIG. 6 . 
         [0038]    In  FIG. 7 , the seals  34  are shown in three variants. The variant a) corresponds to  FIG. 1 . Primary disks  21  end in an inwardly flanged rim  35 , which forms a restricted portion all around and which contacts the secondary disk  22  lying thereunder—or which almost contacts it in view of hydrodynamic lubrication effects. A particle suspended in the magnetorheological fluid is marked by  70 . It is indicated that it would have to migrate somewhat inwardly against the centrifugal force to move to the sealing gap  71  because seal  34  is actually formed by a restricted portion  71  of the primary disk, and not by a bulge of a secondary disk. In this manner, the passage of particles through sealing gap  71 , and thus a cascading unmixing of the magnetorheological fluid, is reliably prevented. Furthermore, a field line  72  is drawn to show that a collective effect is exerted onto the field lines by the contacting of primary disks  21  and secondary disks  22 . In variant b), a ring  73  extends all round a slide-friendly material, for example a suitable plastic, that is fastened to the rim of the primary disks  21  instead of the restricted portion. It is indicated by the in broken lines arrows  74  that these rings  73  form a field gradient with an applied magnetic field which drives the suspended particles toward the stronger magnetic field and thus away from the sealing gap  75 . In variant c), the variants a) and b) are combined, whereby the effects of the two variants are added. 
         [0039]      FIG. 8  differs from  FIG. 1  (with a reference numeral increased by  100 ) in that the magnetic field generator  105  rotates with the secondary part  110 . Accordingly, the sliding contacts  102  fastened to the housing  101  are conductively connected via conductors  104  to the magnetic field generator  105 , here a coil with the winding axis  108 . The secondary part  110  has, at the side remote from its base  115 , a cover  112 , which is connected to or is in one piece with an insert  119 . The cover  112  accepts the magnetic field generator  105  and, together with the insert  119  and the cylindrical part  113  of the secondary part  110 , forms a yoke, which is only interrupted by the working space  120 . For the guidance of the magnetic field lines  137 , a ring  139  consisting of a material of small magnetic permeability is inserted between the magnetic field generator  105  and the working space  120 . 
         [0040]      FIG. 9  differs from  FIG. 1  (with reference numerals increased by  200 ) in that the magnetic field generator  205  is attached with its first yoke  214  to the housing  201 , that is it is stationary, and by a modification of the seal  234 . The secondary part  210  again has the insert  219  which is part of the secondary part and is connected thereto in a manner which is not shown. The insert  219  and the cylindrical part  213  of the secondary part  210  form a second yoke. The field lines  237  have air gaps  202  to be overcome. For the guidance of the magnetic field lines  237 , a ring  239  consisting of a material of small magnetic permeability may be inserted between the magnetic field generator  205  and the working space  220 . 
         [0041]    The modification of the seal  234  differs from that of  FIG. 1  in that the restricted portions  235  may be attached to the secondary disks  222 . Their cylindrical part  227  forms the restricted portions and then merges directly into the flange part  236  which has, for example, the shape of the brim of a hat. Fluid gaps  223  can thus also be formed which are sealed with a smallest radius.