Abstract:
A multiple working surface magnetic particle device for transferring torque between two rotatable members is disclosed. The magnetic particle device includes relatively rotatable members defining a gap therebetween containing a magnetically reactive medium. The magnetically reactive medium stiffens in the presence of a magnetic field interlocking the rotatable members. The multiple working surface design allows for a reduction in the size and weight of the magnetic field source resulting in a more compact, lighter weight magnetic particle device.

Description:
RELATED APPLICATIONS  
       [0001]    This application is a Continuation-in-Part of U.S. patent application Ser. No. 09/702,949, entitled LIGHTWEIGHT MAGNETIC PARTICLE DEVICE, filed Oct. 10, 2000, the disclosure of which is incorporated herein by reference in its entirety. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to magnetic torque-transferring devices and more particularly to those that employ a magnetically reactive medium for coupling together two relatively rotatable members.  
         BACKGROUND OF THE INVENTION  
         [0003]    Magnetic particle devices are known in the art. Generally, magnetic particle devices are based on electromagnetic and mechanical forces that act on a magnetically reactive medium disposed between the working surfaces of a driven member and driving member. The magnetic forces operate to increase the viscosity of the medium to interlock the driven and driving members. Magnetic particle devices are often designed as quick-acting electrically activated brakes or clutches for the transmission of torque. Alternatively, magnetic particle devices may be designed to impart drag between rotatable surfaces to maintain tension.  
           [0004]    Where magnetic particle devices offer many advantages, such as low vibration torque transfer, the ability to operate in the slip condition, and the controllability of torque transfer over a relatively wide range of electrical input, there is a drawback as well. Conventional magnetic particle devices are relatively heavy due to the use of electromagnets as the source of a magnetic field. Known electromagnets generally comprise a shell with known magnetic properties and a coil of conductive wire. The thickness of the shell serves to define the working surface area of the device. Since the working surface is actually being coupled due to the increased viscosity of the magnetically reactive medium, an efficient design is one that maximizes the working surface area. Unfortunately, to increase working surface area in a conventional device, the thickness of the electromagnet shell must be increased, thereby undesirably increasing the weight.  
           [0005]    Accordingly, there exists a need for a lightweight magnetic particle device that does not compromise working surface area or reduce operating life. The present invention provides an effective lightweight magnetic particle device wherein the reduction in weight is achieved without sacrificing working surface area or adversely affecting the operative life.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention recognizes the disadvantages and limitations commonly associated with the operation of conventional magnetic particle devices. By constructing a magnetic particle device in accordance with an aspect of the current invention, the weight of the magnetic particle device can be significantly reduced without adversely affecting the operating life of the device.  
           [0007]    A multiple working surface magnetic particle device for transferring torque between two rotatable members is disclosed. The magnetic particle device comprises relatively rotatable members defining a gap therebetween containing a magnetically reactive medium. The magnetically reactive medium stiffens in the presence of a magnetic field interlocking the rotatable members. In an embodiment of the invention, the rotatable members include include regions of relatively high and low magnetic permeability positioned to create multiple working surfaces through which magnetic flux weaves to activate the magnetically reactive medium. The multiple working surface design allows for a reduction in the size and weight of the magnetic field source resulting in a more compact, lighter weight magnetic particle device. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    The features and inventive aspects of the present invention will become more apparent upon reading the following detailed description, claims, and drawings, of which the following is a brief description:  
         [0009]    [0009]FIG. 1 is a cross-sectional view of a magnetic particle device according to an embodiment of the present invention.  
         [0010]    [0010]FIG. 1A is a cross-sectional view of a magnetic particle device according to another embodiment of the present invention.  
         [0011]    [0011]FIG. 2 is an enlarged cross-sectional view of a magnetic particle gap according to the embodiment of FIG. 1, with no magnetic flux applied across the gap.  
         [0012]    [0012]FIG. 3 is an enlarged cross-sectional view of a magnetic particle gap according to the embodiment of FIG. 1, with magnetic flux applied across the gap.  
         [0013]    [0013]FIG. 4 is an enlarged cross-sectional view of the interface of the electromagnetic and the first and second rotatable members according to the embodiment of FIG. 1, showing a path of the magnetic flux.  
         [0014]    [0014]FIG. 5 is a cross-sectional view of another embodiment of a magnetic particle device.  
         [0015]    [0015]FIG. 6 is a cross-sectional view of another embodiment of a magnetic particle device.  
         [0016]    [0016]FIG. 7 is a cross-sectional view of another embodiment of a magnetic particle device.  
         [0017]    [0017]FIG. 8 is an exploded view of the first and second rotatable members as described in the embodiment shown in FIG. 7.  
         [0018]    [0018]FIG. 9 is a cross-sectional view of another embodiment of a magnetic particle device. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0019]    Referring to FIG. 1, an embodiment of a magnetic particle device  10  in accordance with the principles of the present invention is shown. The device  10  includes a stationary housing member  12  having a duct  14  therethrough for receiving a rotatable shaft  16 . Shaft  16  is rotatably supported within duct  14  by bearings  18  and  20  the positions of which are determined by shoulders  22  and  24  that are formed within duct  14  of housing member  12  and shoulder  25  formed on shaft  16 . Bearing  18  is biased against shoulder  24  by an annular retainer member  26 . Bearing  20  is biased against shoulder  22  by a biasing member (not illustrated) in a device that is driven by the magnetic particle device  10 .  
         [0020]    A first rotatable member  30  of known magnetic properties is fixedly secured to shaft  16 . First rotatable member  30  includes a cylindrical portion  32  located radially outwardly of shaft  16  such that cylindrical portion  32  is substantially parallel with shaft  16 . Cylindrical portion  32  includes an inner surface  34  and an outer surface  36 . Outer surface  36  includes a plurality of grooves  38 , depicted in the FIG. 1 as generally trapezoidal in cross-section, but not intended to be limited thereto. Grooves  38  can also, in the alternative, be located on inner surface  34  or located on both inner surface  34  and outer surface  36  of cylindrical portion  32 , as seen in FIGS. 5 and 6 and explained in further detail below.  
         [0021]    A second rotatable member  40  of known magnetic properties is supported on shaft  16  by a bearing  41 , the position of which is determined by a shoulder  42  located on a distal end  43  of shaft  16  and a foot  44  of first rotatable member  30 . Second rotatable member  40  is positioned on bearing  41  by a shoulder  45  located on a base  46  of second rotatable member  40 . Base  46  further includes a plurality of teeth  48  for engaging the underside of a typical drive belt (not illustrated) found in automotive applications. While the present invention describes a magnetic particle device driven by a belt, it is understood that other suitable mechanisms may be employed to drive the device.  
         [0022]    Second rotatable member  40  further includes a cylindrical portion  50  located radially outwardly of cylindrical portion  32  of first rotatable member  30  and substantially parallel to shaft  16 . Cylindrical portion  50  further includes an inner surface  52  and an outer surface  54 .  
         [0023]    Inner surface  52  further includes a plurality of grooves  56 , depicted in the FIG. 1 as generally trapezoidal in cross-section, but not intended to be limited thereto. Grooves  56  can also, in the alternative, be located on outer surface  54  or located on both inner surface  52  and outer surface  54  of cylindrical portion  50 , as seen in FIGS. 5 and 6 and explained in further detail below. Grooves  56  are positioned on inner surface  52  such that grooves  56  are located radially outwardly of a point equidistantly between grooves  38  in first rotatable member  30 . Grooves  38  on cylindrical portion  32  and grooves  56  on cylindrical portion  50  define therebetween a plurality of working surfaces  58 ,  59 ,  60  and  61 . Working surfaces  58 ,  59 ,  60  and  61  cooperate with a magnetically reactive medium  64  (as best seen in FIG. 2) to interlock first rotatable member  30  and second rotatable member  40  when magnetically reactive medium  64  is subjected to a magnetic field.  
         [0024]    First rotatable member  30  and second rotatable member  40  are not in contact, but define therebetween a uniform gap  66 , generally toroidal in configuration. Gap  66  is of a predetermined width to permit a thin layer of magnetically reactive medium  64  (as seen in FIG. 2), such as a magnetically reactive powder, to reside therein. A magnetically reactive powder is the preferred medium because it has the advantage of being resistant to temperature levels that would degrade oil based magnetorheological fluids. Grooves  38  in first rotatable member  30  and grooves  56  in second rotatable member  40  serve the purpose of providing additional physical volume for receiving magnetically reactive medium  64  when no magnetic field is applied. Removing magnetically reactive powder  64  from gap  66  when no magnetic field is applied decreases friction thereby reducing drag between first rotatable member  30  and second rotatable member  40 . In addition, grooves  38  and  56  aid in concentrating the lines of magnetic flux  68  across gap  66  and substantially through working surfaces  58 ,  59 ,  60  and  61  as seen in FIG. 4.  
         [0025]    As illustrated in FIG. 1, two non-contacting sealing members  70  and  72  cooperate between cylindrical portion  32  and cylindrical portion  50  to impede the escape of magnetically reactive medium  64 . This type of “labyrinth” seal is effective to retain a magnetically reactive powder within gap  66 . Sealing members  70  and  72  include cavities  74  and  76  respectively. During application of a magnetic field when both rotatable members  30  and  40  are interlocked, centrifugal forces pull the magnetically reactive medium  64  in cavities  74  and  76  to the outer surface  77  of cavity  76  whereby the centrifugal forces and magnetic flux pull the powder into gap  66 . When no magnetic field is applied to device  10 , the magnetically reactive powder is allowed to disseminate into cavities  74  and  76 , but is substantially prevented from exiting cavity  74  due to the labyrinth geometry of the interacting sealing members  70  and  72 . Sealing member  72  further includes a cylindrical retaining portion  78  that cooperates with an annular seat  80  in second rotatable body  40  to retain sealing member  72 . Similar non-contacting annular sealing members  82  and  84  are fixedly attached to first rotatable member  30  and second rotatable member  40  respectively. Sealing members  82  and  84  cooperate to impede the escape of magnetically reactive medium  64  in substantially the same manner as sealing members  70  and  72 .  
         [0026]    Magnetic particle device  10  further requires a source of magnetic flux, such as a magnet. As shown in FIGS. 1 and 4, a stationary toroidal electromagnet  86  is mounted on the outside of housing member  12  between first rotatable member  30  an housing member  12 . In the alternative, the magnetic source may be a permanent magnet  87  supplemented by a counteracting electromagnet  86 , as shown in FIG. 1A, so that magnetic particle device  10  will default to being engaged should electromagnet  86  fail. Also in the alternative, the magnetic source may be mounted on outer surface  54  of second rotatable member  40 .  
         [0027]    First rotatable member  30  and electromagnet  86  are not in contact, but define therebetween a uniform gap  88 , generally toroidal in configuration. Electromagnet  86  includes a rigid shell  90 , shown as being C-shaped in cross-section, opening to the outside of the toroid and having known magnetic properties. Rigid shell  90  is shown as comprising two annular elements  92  and  94  joined by a plurality of fasteners  96 . In the alternative, rigid shell  90  could comprise a number of annular elements cooperating to define the C-shaped geometry of the rigid shell as seen in FIG. 5. Electromagnet  86  further includes a typical coil of conductive wire  98 , application of an electric current to the coil generating a known electromagnetic field in the vicinity of electromagnet  86 . Electromagnet  86  is controlled by an electronic controller (not illustrated) designed to provide an electrical current to the coil via wires  99  under predetermined conditions. The controller processes all input, being sensor readings or operator selections, to determine the appropriate current level needed by electromagnet  86  to generate the magnetic field so that the magnetically reactive medium  64  locks into chains to achieve the desired transfer of torque within the device  10 .  
         [0028]    [0028]FIG. 2 shows magnetically reactive medium  64  disposed in gap  66  without application of a magnetic field. In this state, no appreciable torque is transferred between first rotatable member  30  and second rotatable member  40 . Second rotatable member  40  is thus free to rotate relative to first rotatable member  30 .  
         [0029]    It is well known in the art that lines of magnetic flux  68  travel a path substantially through structures with known magnetic properties. As seen in FIG. 4, upon application of a magnetic field in the vicinity of electromagnet  86 , lines of magnetic flux  68  exit rigid shell  90  in electromagnet  86  and traverse gap  88 , whereby flux  68  saturates areas  95  located radially inwardly of grooves  38  in first rotatable member  30 . Upon saturation of areas  95 , lines of magnetic flux  68  follow a path of least resistance and traverse gap  66 , through working surfaces  93 , into second rotatable member  40 . The narrowest width of grooves  38  is best designed to be greater than the width of gap  66  thus preventing flux  68  from traversing grooves  38 . Upon entry into second rotatable member  40 , flux  68  saturates areas  97  located radially outwardly of grooves  56 . Upon saturation of areas  97 , flux  68  traverses gap  66  through working surfaces  58 , into first rotatable member  30 . The process of traversing gap  66  is repeated until the number of grooves  38  and  56  are exhausted. The flux path is completed as flux  68  traverses gap  66  and gap  88  and reenters rigid shell  90  of electromagnet  86 .  
         [0030]    As seen in FIG. 3, magnetically reactive particles  65  in magnetically reactive medium  64  change formation, in relation to the intensity of the magnetic field, by aligning with the lines of magnetic flux  68  as flux  68  traverses gap  66  through working surfaces  58 . Magnetically reactive particles  65  under the influence of a magnetic field will lock into chains  100  increasing the shear force and creating a mechanical friction against the working surfaces  58  facing gap  66 . The increased shear force and mechanical friction result in a corresponding transfer of torque between first member  30  and second member  40 .  
         [0031]    [0031]FIGS. 5 and 6 illustrate two variations of the embodiment of FIG. 1 depicting a modified groove arrangement. Both embodiments operate in a manner substantially similar to the embodiment of FIG. 1. In both embodiments, lines of magnetic flux  68  (not illustrated) generated by electromagnet  86  first exit rigid shell  90  and travel a path across gap  88  into first rotatable member  30 . As seen in FIG. 5, upon entry into first rotatable member  30 , flux  68  saturates areas  95   a . Upon saturation, flux  68  follows the next path of least resistance and traverses gap  66  into second rotatable member  40 . As seen in FIG. 6, upon entry into first rotatable member  30 , flux  68  saturates areas  95   b . Upon saturation, flux  68  follows the next path of least resistance and traverses gap  66  into second rotatable member  40 . The embodiments in FIGS. 5 and 6 differ from the embodiment of FIG. 1 in that the capacity to store magnetically reactive medium  64  in grooves  38  and  56  is substantially or totally reduced, resulting in more medium  64  in gap  66 . The increased amount of medium  64  in gap  66  increases the drag against second rotatable member  40  as member  40  rotates about first rotatable member  30  when the electromagnet is not energized.  
         [0032]    [0032]FIG. 7 is a cross-sectional view of a fourth embodiment of the present invention. In this embodiment, the first rotatable member  30  and second rotatable member  40  include non-continuous apertures  102  and  104  respectively. Apertures  104  in second rotatable member  40  are positioned radially outwardly of a point equidistantly between apertures  102  in first rotatable member  30 . Lines of magnetic flux  68  (not illustrated) generated by electromagnet  86  first exit rigid shell  90  and travel a path across gap  88  into first rotatable member  30 . Flux  68  then travels a path of least resistance through a plurality of bridge portions  106  (as seen in FIG. 8) located between apertures  102  until a level of saturation is reached. Upon saturation, flux  68  follows the next path of least resistance and traverses gap  66  into second rotatable member  40  through working surfaces  93 . Upon entry into second rotatable member  40 , flux  68  saturates a plurality of bridge portions  108  (as seen in FIG. 8) located between apertures  104  until a level of saturation is reached. Provided the width of apertures  102  and  104  are greater than the width of gap  66 , lines of magnetic flux  68  traverse gap  66  through working surfaces  58 . The process of traversing gap  66  is repeated until the number of apertures  102  and  104  is exhausted. The path is completed as flux  68  traverses gap  66  and gap  88  and reenters rigid shell  90  of electromagnet  86 . In this embodiment, an annular sealing element  72   a  includes a cylindrical retaining portion  78   a  that cooperates with a annular groove  80   a  to retain annular sealing element  72   a . Cylindrical retaining portion  78   a  further serves the purpose of inhibiting the escape of the magnetically reactive medium from apertures  104  in second rotatable member  40 . Similarly, a cylindrical retaining member  109  is fixedly attached to inner surface  34  of first rotatable member  30  and serves the purpose of inhibiting the escape of the magnetically reactive medium from apertures  102  in first rotatable member  30 .  
         [0033]    [0033]FIG. 9 is a cross-sectional view of a fifth embodiment of the present invention. In this embodiment, the first rotatable member  30  and second rotatable member  40  include a plurality of alternating continuous magnetic rings  110  and continuous non-magnetic rings  112 . Magnetic rings  110  and non-magnetic rings  112  are secured to rotatable members  30  and  40  by a plurality of fasteners  114 , although the method of securing rings  110  and  112  is not intended to be limited thereto. The rings are positioned such that non-magnetic rings  112  in second rotatable member  40  are positioned radially outwardly of a point equidistantly between non-magnetic rings  112  in first rotatable member  30 . Fasteners  114 , like non-magnetic rings  112 , are preferred to be of a non-magnetic material, such as aluminum or stainless steel. Upon excitation of electromagnet  86 , lines of magnetic flux  68  (not illustrated) first exit rigid shell  90  and follow a path of least resistance by traversing gap  88  into first rotatable member  30 . Upon entry into first rotatable member  30 , the continuous non-magnetic rings  112  prevent flux  68  from short-circuiting through first rotatable member  30 . Therefore, flux  68  follows a path of least resistance and traverses gap  66  through working surfaces  93  into second rotatable member  40 . Upon entry into second rotatable member  40 , flux  68  travels a path through second rotatable member  40  until flux  68  encounters continuous non-magnetic ring  112  and is forced to traverse gap  66  through working surfaces  58 . The process of traversing gap  66  is repeated until the number of continuous non-magnetic rings  112  is exhausted. The path is completed as flux  68  traverses gap  66  and gap  88  and reenters rigid shell  90  of electromagnet  86 .  
         [0034]    The magnetic particle device  10  of present invention is a torque transfer device in which portions of an input member  40  and an output member  30  are provided with regions of relatively high magnetic permeability and regions of relatively low magnetic permeability. These regions of relatively high and low magnetic permeability are positioned to form a flux path through which lines of magnetic flux, generally denoted by element number  68 , travel. As described above, the regions of relatively low magnetic permeability are formed by introducing non-magnetic materials, such as stainless steel, aluminum or a polymer, into input and output members  40 ,  30  or by removing material from input and output members  40 ,  30  to form a cavity or groove. In the embodiment illustrated in FIG. 1, the regions of relatively low magnetic permeability include annular grooves located in input and output members  40 ,  30 . The grooves may be positioned in the inner or outer surfaces of input and output members  40 ,  30  or, alternatively, in both the inner and outer surfaces of the input and output members  40 ,  30 . In the embodiment illustrated in FIG. 9, the regions of relatively low magnetic permeability include non-magnetic rings of metal such as stainless steel. In the embodiment illustrated in FIG. 7, the regions of relatively low magnetic permeability include circumferentially extending, non-continuous apertures located in input and output members  40 ,  30 .  
         [0035]    The input and output members  40 ,  30  of magnetic particle device  10  preferably include multiple regions of relatively high and low magnetic permeability. However, device  10  may be configured to include any number of alternating regions of high and low magnetic permeability with the most basic configuration being at least one region of relatively low magnetic permeability in output member  30  and at least one region of relatively low magnetic permeability in input member  40 . The at least one region of relatively low magnetic permeability in output member  30  is provided to prevent lines of magnetic flux  68  from “short-circuiting” through output member  30 .  
         [0036]    In operation, the traversing lines of magnetic flux  68  activate magnetically reactive medium  64 . The magnetically reactive particles  65  in medium  64  change formation, in relation to the intensity of the magnetic field, by aligning with lines of magnetic flux  68  as flux  68  traverses gap  66 . Magnetically reactive particles  65  under the influence of a magnetic field will lock into chains  100  increasing the shear force and creating a mechanical friction against input member  40  and output member  30 . The increased shear force and mechanical friction results in a corresponding transfer of torque between input member  40  and output member  30  that is precisely controlled in relation to the strength of the applied magnetic field.  
         [0037]    As will be appreciated, the present invention can transfer a given amount of torque between input and output members  40 ,  30  with a weaker magnetic field due to the greater amount of activated medium  64 . Thus, increasing the number of regions of relatively high and low magnetic permeability permits the use of a smaller source of magnetic flux to provide, inter alia, a substantial weight savings over conventional torque transferring devices.  
         [0038]    The present invention has been particularly shown and described with reference to the foregoing embodiments, which are merely illustrative of the best modes for carrying out the invention. It should be understood by those skilled in the art that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention without departing from the spirit and scope of the invention as defined in the following claims. It is intended that the following claims define the scope of the invention and that the method and apparatus within the scope of these claims and their equivalents be covered thereby. This description of the invention should be understood to include all novel and non-obvious combinations of elements described herein, and claims may be presented in this or a later application to any novel and non-obvious combination of these elements. Moreover, the foregoing embodiments are illustrative, and no single feature or element is essential to all possible combinations that may be claimed in this or a later application.