Abstract:
A clutch for selective transmission of torque and power, utilizing pairs of coded arrays of permanent magnets affixed respectively to the driving member and the driven member. A shape memory alloy actuator brings to driving member and the driven member into proximity to engage the clutch via a higher-order mutual magnetic correspondence between the coded magnetic regions of the permanent magnet arrays. Also provided is a clutch having a magnetorheological fluid between the driving member and the driven member, to increase the torque and power transfer through the fluid when its viscosity is increased by the magnetic field of the arrays in proximity. Sets of corresponding teeth on the driving member and driven member mesh when the rotation of the members is synchronized, providing positive direct drive to prolong the service life of the fluid.

Description:
BACKGROUND 
       [0001]    Direct current (DC) motor drives in conjunction with Shape Memory Alloy (SMA) actuators are being explored for a wide range of automotive and similar applications ranging from power seats to power sunroofs to power shutters. These drives combine the best attributes of DC motors (low cost, high continuous power output, reversible motion) and SMA actuators (low mass, extremely small package size, high energy density) to allow a single DC motor to be multiplexed across multiple applications thereby yielding compact and low cost alternatives to the current practice of driving each application with a dedicated DC motor. SMA actuators serve to engage/disengage clutches that control the flow of torque and power from the DC motor to various loads. Smooth engagement requires the driving and driven members of the clutch to align properly and attain the same speed before engagement. Typically, friction cone extensions of the mating clutch elements or software based techniques are used to achieve this. Unfortunately, friction cone extensions do not perform well at small length scales, and software solutions introduce an undesirable time lag in clutch response. 
         [0002]    To overcome the above drawbacks, magnetorheological fluids (“MRF”) have been proposed for use in a clutch. An MRF has a viscosity which can be controlled by applying a magnetic field. In the absence of a magnetic field, an MRF has a low viscosity. When a magnetic field is applied, the MRF viscosity increases substantially and can transmit torque and power through the viscous fluid. 
         [0003]    Unfortunately, however, MRFs tend to exhibit long-term degradation when subjected to high shear stress in the viscous state. 
         [0004]    There is thus a need for a clutch that either benefits from the controllable viscosity of the MRF while minimizing the stress on the MRF, or which is able to avoid the need for the MRF altogether. This goal is met as disclosed herein. 
       SUMMARY 
       [0005]    The present application discloses a clutch for selective transmission of torque and power, examples of which utilize pairs of coded arrays of permanent magnets affixed respectively to the driving member and the driven member. Benefits include smooth engagement and disengagement, long life, reduced noise, suitability for small-scale clutches, and better response times than attainable through software solutions. 
         [0006]    Coded magnetic arrays feature a magnetic field that is strong at close range (“near field”), but which falls off rapidly with increasing distance. A coded magnetic array may also be custom-configured with a special coded pattern of magnetic regions to have a particularly strong magnetic interaction when brought into magnetic proximity with another array that has been custom-configured to correspond to the same pattern. The strong magnetic interaction not only can attract the coded arrays toward one another, but can also align them to particular positions and angles, according to the specific pattern. Such corresponding patterns are denoted herein as having a “higher-order mutual magnetic correspondence”, a term which indicates that the magnetic field is of higher multipole order than an ordinary magnetic dipole field. 
         [0007]    According to examples in the present disclosure, when the coded magnetic arrays of the driving member and of the driven member are separated by a variable distance, and when the variable distance is reduced, the coded magnetic arrays are brought into magnetic proximity with each other, at which point their magnetic near-field interaction synchronizes the rotation of the driven member with that of the driving member. 
         [0008]    According to other examples of the present invention, an MRF is disposed between the driving member and the driven member to enhance the effect of the coded magnetic arrays, for synchronizing the rotation of the driven member with that of the driving member. The MRF brings the driven member up to speed, after which the coded magnets align the angular position of the driven member relative to the driving member. 
         [0009]    In further examples of the present invention, the driving member and the driven member have teeth which can be meshed to achieve positive locking of the members after synchronization. In the case of examples utilizing an MRF, shear stress on the MRF immediately vanishes when the teeth mesh, thereby minimizing deterioration of the MRF and prolonging the useful service life thereof. 
         [0010]    In further examples, engaging and disengaging the clutch are performed mechanically by a Shape Memory Alloy (SMA) component, which changes shape when activated, to move the driving member and the driven member together or apart during clutch engagement and disengagement, respectively. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The subject matter disclosed may best be understood by reference to the following detailed description when read with the accompanying drawings in which: 
           [0012]      FIG. 1A  illustrates a disengaged clutch according to an example of the present invention. 
           [0013]      FIG. 1B  illustrates a partially-engaged clutch according to the example of  FIG. 1A . 
           [0014]      FIG. 1C  illustrates a fully engaged clutch according to the example of  FIG. 1A  and  FIG. 1B . 
           [0015]      FIG. 2A  illustrates a disengaged clutch according to another example of the present invention. 
           [0016]      FIG. 2B  illustrates a partially-engaged clutch according to the example of  FIG. 2A . 
           [0017]      FIG. 2C  illustrates a fully engaged clutch according to the example of  FIG. 2A  and  FIG. 2B . 
       
    
    
       [0018]    For simplicity and clarity of illustration, elements shown in the figures are not necessarily drawn to scale, and the dimensions of some elements may be exaggerated relative to other elements. In addition, because the figures are intended to be conceptual in nature for illustrative purposes, elements shown therein may not correspond exactly in shape, appearance, or layout to corresponding components intended for production or actual operation. Reference numerals may be repeated among the figures to indicate related or analogous elements. 
       DETAILED DESCRIPTION 
       [0019]      FIG. 1A  illustrates an example of a clutch  100  as presently disclosed, in a disengaged (“idle”) state, where a rotation  109  of a driving member  101  is not transmitted to a driven member  103 . An engagement bias spring  105  is opposed by a disengagement bias spring  107  which in the idle state causes a complete disengagement between driving member  101  and driven member  103 . Mechanically, driving member  101  and driven member  103  can move closer together or further apart along the longitudinal axis of clutch  100  within a predetermined range. The distance between them is thus variable between an upper limit and a lower limit, which are typically provided via mechanical constraints on the relative linear displacement between driving member  101  and driven member  103 . 
         [0020]    A set of teeth  119  on driven member  103  meshes with a corresponding set of teeth  121  on driving member  101  when the variable distance is at the lower limit When teeth  119  and teeth  121  are meshed, driven member  103  is locked rotationally to driving member  101 . In such a configuration, clutch  100  operates in a frictionless manner as a direct mechanical coupling device. However, in the disengaged state shown in  FIG. 1A , teeth  119  and teeth  121  are not meshed. Some residual torque coupling typically exists between driving member  101  and driven member  103  on account of friction from spring  107 . Additionally, in examples utilizing MRF there is also friction from seal  113  and viscous shear from the MRF. However, teeth  119  and  121  are not able to smoothly mesh because driven member  103  and driving member  101  are not yet fully synchronized. 
         [0021]    A coded array of magnetic regions  123  is affixed to driven member  103 , and a coded array of magnetic regions  125  is affixed to driving member  101 . 
         [0022]    In some examples described in the present disclosure, a cavity  111  is filled with a magnetorheological fluid (MRF), which is retained in cavity  111  by a seal  113 , an elastic membrane diaphragm  115 , and an elastic membrane diaphragm  117 . In the disengaged (“idle”) state illustrated in  FIG. 1A  there is no magnetic coupling between driving member  101  and driven member  103 , even when an MRF is used, because the far-field magnetic intensity of coded arrays  123  and  125  is very low on account of the relatively large distance between driving member  101  and driven member  103  when clutch  100  is disengaged as shown in  FIG. 1A . 
         [0023]    Cavity  111  has an axial dimension corresponding to the variable distance between driving member  101  and driven member  103 . 
         [0024]    An actuator  127  is shown in a non-activated state in  FIG. 1A . When activated, actuator  127  engages clutch  100 , as detailed in the following paragraphs. In examples of the present invention, actuator  127  includes a shape memory alloy (SMA) component. In certain examples, the SMA of actuator  127  is activated and deactivated thermally. In other examples, the SMA is a ferromagnetic shape memory alloy (FSMA), which is activated and deactivated magnetically. 
         [0025]      FIG. 1B  illustrates clutch  100  of  FIG. 1A , when actuator  127  is partially activated at a fraction (e.g., 70% to 80%) of full stroke, during the beginning of a clutch engagement action. Actuator  127  partially overcomes disengagement bias spring  107  to bring coded arrays  123  and  125  sufficiently close together to be in partial magnetic proximity with each other, thereby exerting a torque on driven member  103  via the higher-order mutual magnetic correspondence of coded arrays  123  and  125 . 
         [0026]    In examples of the present invention which feature MRF in cavity  111 , the mutual magnetic correspondence of coded arrays  123  and  125  causes formation of fibrils  129  in the MRF, and the consequent shear of the MRF results in increased transmission of torque and power from driving member  101  to driven member  103  through the MRF. Elastic membrane diaphragm  115  and elastic membrane diaphragm  117  are distended to serve as a reservoir to contain the volume of MRF displaced from cavity  111  by the decrease in distance between driving member  101  and driven member  103  by the transfer of the MRF into and out of cavity  111  as the distance between driving member  101  and driven member  103  changes. 
         [0027]    At this stage of partial engagement, a rotation  131  of driven member  103  is not yet synchronized with rotation  109  of driving member  101 , and teeth  119  are not yet meshed with teeth  121 . 
         [0028]      FIG. 1C  illustrates clutch  100  of  FIG. 1A , when actuator  127  is completely activated at full stroke, at the conclusion of the clutch engagement action. Actuator  127  fully overcomes disengagement bias spring  107  to bring coded arrays  123  and  125  close together in full magnetic proximity with each other, thereby aligning driven member  103  with driving member  101  via the higher-order mutual magnetic correspondence of coded arrays  123  and  125 . 
         [0029]    In examples of the present invention which feature MRF in cavity  111 , the mutual magnetic correspondence of coded arrays  123  and  125  increases the formation of fibrils  129 . Elastic diaphragm  115  and elastic diaphragm  117  are further distended to contain the volume of MRF displaced from cavity  111  by the further decrease in distance between driving member  101  and driven member  103 . 
         [0030]    At this stage of full engagement, a rotation  133  of driven member  103  is completely synchronized with rotation  109  of driving member  101 , and teeth  119  mesh with teeth  121 . Once this occurs, driving member  101  and driven member  103  are rotationally locked, so that clutch  100  is in a positive drive mode. 
         [0031]    During the positive drive mode in examples of the present invention which feature MRF in cavity  111 , no more torque is transferred through shear of the MRF. Thus, transfer of torque and power does not depend on the characteristics of the MRF, and the useful life thereof is extended. 
         [0032]      FIG. 2A  illustrates an example of a clutch  100  as alternately disclosed, with features similar to those of  FIG. 1A , except that a reservoir  201  with a freely-moveable (“floating”) piston  203  having a return spring  205  is used to receive MFR displaced from cavity  111  as clutch  100  is engaged.  FIG. 2B  illustrates the position of piston  203  during the beginning of the clutch engagement action, and  FIG. 2C  illustrates the position of piston  203  when clutch  100  is fully engaged. 
         [0033]    It is noted that the distinction between the member which is considered the “driving member” and the member which is considered the “driven member” depends on the direction of torque and power transfer. Certain embodiments of the present invention are symmetrical, in that either member  101  or member  103  may be considered to be the “driving member” depending on the circumstances of use. During service, clutch  100  ( FIG. 1A ) may alternately transfer torque and power in different directions at different times. Thus, it is understood that the terms “driving member” and “driven member” are not fixed to specific elements of the clutch, but are applied to the relevant elements of the clutch according to the circumstances as appropriate. 
         [0034]    It is further noted that embodiments of the present invention also provide for symmetrical rotation of clutch  100  ( FIG. 1A ), in that both clockwise and counterclockwise rotation modes for the driving and driven members are provided. In certain embodiments of the present invention, the speed and/or direction of rotation may be changed at any time, when clutch  100  is disengaged (idle), when partially engaged (startup), or when fully engaged (normal operation). 
         [0035]    When disengaging clutch  100  ( FIG. 1A ), the sequence of actions presented in  FIG. 1A ,  FIG. 1B , and  FIG. 1C  is reversed by deactivating actuator  127 , resulting in a smooth disengagement. 
         [0036]    It is sometimes desirable to be able to keep clutch  100  in either a disengaged condition or an engaged condition without having to continually expend energy to maintain the disengaged/engaged condition. As described above and illustrated in  FIG. 1A , if actuator  127  is not activated, clutch  100  remains in a disengaged “Power-Off hold” condition without continual expenditure of energy, because disengagement spring  107  is able to overcome both engagement spring  105  as well as the far-field magnetic forces between coded arrays  123  and  125 . In an additional embodiment of the present invention, as illustrated in  FIG. 2A ,  FIG. 2B , and  FIG. 2C , a “Power-On hold” is also provided, in which the clutch remains engaged without having to continually expend energy keeping an actuator  227  activated after a clutch engagement operation. 
         [0037]    In this embodiment, actuator  227  is configured to operate in a bidirectional fashion, such as by having two opposing elements  227 A and  227 B which can be independently activated. Thus, an engagement element  127 A is activated to engage the clutch, and a disengagement element  127 B is activated to disengage the clutch. As before, without activating actuator  227  the clutch, when disengaged, remains disengaged, because disengagement spring  107  overcomes engagement spring  105 . 
         [0038]    Unlike the previous embodiment illustrated in  FIG. 1A ,  FIG. 1B , and  FIG. 1C , however, in this embodiment coded magnetic arrays  223  and  225  are configured to hold together with the strong near-field attractive force, so that when the clutch is engaged ( FIG. 2C ), engagement element  227 A can be deactivated without losing clutch engagement. Engagement spring  105  in combination with the near-field attractive force of coded magnetic arrays  223  and  225  sustains the engagement of the clutch even when engagement element  227 A is no longer activated. Thus, the clutch has a “Power-On hold” which keeps the clutch engaged without requiring a continual expenditure of energy to maintain the engagement. To disengage the clutch, disengagement element  227 B is activated. Disengagement spring  107  in combination with disengagement element  227 B then overcomes engagement spring  105  in combination with the near-field attractive force of coded magnetic arrays  223  and  225  to disengage the clutch, and return to the state shown in  FIG. 2A . In embodiments of the present invention, elements  227 A and  227 B are SMA elements.