Abstract:
A one-way coupling includes a cam plate including cams, a pocket plate including pockets, struts, each strut located in one of the pockets, and an electromagnet for engaging one of the struts with one of the cams, including a coil, a core and poles that extend from the coil to said strut, a gap between the poles and the pocket plate exceeding a gap between the poles and said strut.

Description:
[0001]    This application is a continuation-in-part of pending U.S. application Ser. No. 13/488,699, filed Jun. 5, 2012. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention This invention relates generally to an overrunning, one-way coupling, such as a brake or clutch, whose engaged and disengaged states are selectively controllable. 
         [0003]    2. Description of the Prior Art Automatic transmissions employ hydraulically-actuated clutches and brakes to control power flow and establish the operating gear. A one-way clutch carries torque in one direction while overrunning in the opposite direction. A selectable one-way clutch can overrun in both directions, and can be commanded to lock clockwise, counterclockwise, or both directions. Electromagnetic clutches use electromagnetism to actuate the locking element or strut, as opposed to hydraulic pressure, a mechanical linkage, or centrifugal force. 
         [0004]    One-way clutches typically include two races and a locking element, sometimes called a strut or rocker. The locking element or strut is a movable component that will wedge between the races and transfer torque in one direction. When torque is reversed, the locking element will “tuck” or rotate out of the locked position. One race (the pocket plate) houses the locking element and can be either rotating or stationary. The other race (the cam plate) contains features to interact with the locking element and transfer torque. This race also can be either rotating or stationary. 
         [0005]    In an electromagnetic one-way clutch, the locking element is controlled through the use of electromagnetism. When current is applied to a coiled conductor an electromagnet is energized to either engage or disengage the locking element. 
         [0006]    In order to function properly electromagnetic one-way clutches require a gap between the locking element and the magnet poles to generate a force necessary to actuate the locking element or rocker When the coil is energized, the rocker must rotate a particular distance to change the engagement state. This rotation closes the gap between the rocker and the poles of the coil. Consequently the gap between the poles and the rocker is greatest prior to energizing. To minimize the size of the coil it is beneficial to manage this gap. 
         [0007]    Magnetically non-permeable material is frequently used to prevent flux leakage, but if too much flux leaks through the race rather than jumping the gap to the rocker the magnitude of the force generated may be insufficient to displace the rocker. 
         [0008]    It is desirable to place the coil of an electromagnetic clutch as close as possible to the locking element. However doing so puts the coil in the area of the race that carries most force and deflection, thereby risking damage to the coil. Moving the coil to a safer location however compromises flux generation. 
       SUMMARY OF THE INVENTION 
       [0009]    A one-way coupling includes a cam plate including cams, a pocket plate including pockets, struts, each strut located in one of the pockets, and an electromagnet for engaging one of the struts with one of the cams, including a coil, a core and poles that extend from the coil to said strut, a gap between the poles and the pocket plate exceeding a gap between the poles and said strut. 
         [0010]    Because pocket plate is static and an electromagnet is located on the pocket plate and acting directly on the strut (i) dynamics issues related to having a strut and a spring, which is loosely contained in a pocket orbiting a centerline at high speed, are eliminated resulting in a significant increase in OWC reliability; (ii) the locking element can be commanded to either the engaged or disengaged position, whereas, if the electromagnet were on the cammed race the strut could only be commanded to engage; and (iii) rather than having a large diameter coil, very small coils can be wound realizing significant cost, material, weight, and package space savings as well as providing an increase in reliability. If one coil were used and it failed, the assembly would not function. If several small coils were used and one fails, degraded function results. 
         [0011]    The scope of applicability of the preferred embodiment will become apparent from the following detailed description, claims and drawings. It should be understood, that the description and specific examples, although indicating preferred embodiments of the invention, are given by way of illustration only. Various changes and modifications to the described embodiments and examples will become apparent to those skilled in the art. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0012]    The invention will be more readily understood by reference to the following description, taken with the accompanying drawings, in which: 
           [0013]      FIG. 1  is a front view of a selectable OWC in which the rings are aligned axially; 
           [0014]      FIG. 2  is side perspective view of the selective OWC of  FIG. 1 ; 
           [0015]      FIG. 3  is a perspective view of the electromagnets, second struts and second pocket plate of the selective OWC of  FIG. 1 ; 
           [0016]      FIG. 4  is a side showing the second struts and coils assembled in the second pocket plate; 
           [0017]      FIG. 5  is a side view showing a disengaged strut and its lever ratio; 
           [0018]      FIG. 6  is a perspective view showing the poles extending radially inboard from the coil toward a disengaged strut; 
           [0019]      FIG. 7  is a side view showing a disengaged strut contacting its stop due to the force of a spring; and 
           [0020]      FIG. 8  is a perspective view showing the flux path from one of the poles, through the locking element and to the opposite pole. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0021]    The selectable OWB  10  shown in  FIGS. 1 ,  2  and  3  includes a radial outer, first cam plate  12 ; a first pocket plate  14 ; a radial inner, second cam plate  16 ; and a radial inner, second pocket plate  18 . A lead frame  20  is removed to show three coils  24  of electromagnets and three second struts  26 . Plates  12 ,  14 ,  16 ,  18  are aligned with an axis  22 . 
         [0022]    The radial outer surface of first cam plate  12  is formed with spline teeth  28 , by which cam plate  12  is secured against rotation to a stationary component of a transmission assembly, preferably to a transmission case. Similarly, the radial inner surface of first pocket plate  14  is formed with spline teeth  30 , by which pocket plate  14  is secured to a reaction carrier of a transmission gearset. The carrier transmits torque to the OWB  10 , causing the first pocket plate  14  second cam plate  16  subassembly to rotate. 
         [0023]    First pocket plate  14  supports struts  32 , each strut being urged by a respective spring  34  to pivot radially outward into engagement with one of the cams  36  on first cam plate  12 , thereby driveably connecting first pocket plate  14  and first cam plate  12  and holding cam plate  12  against rotation. A retainer plate  21 , located between an axial surface of pocket plate  14  and an axial surface of the second cam plate  16 , prevents interference with the struts  32 . 
         [0024]    Centrifugal force produced on each of the struts  32  overcomes the force of the respective spring  34 , which pivots the strut toward the cams  36 . At high speed, each strut  32  pivots away from the cams  36 , reducing the duty cycle on the spring. The first cam plate  12  must be a complete circle because the first pocket plate  14  can stop rotating at any angular position. 
         [0025]    The first cam plate  12 , first pocket plate  14  and struts  32  comprise a first drive coupling, in this case a one-way brake, which locks or engages when the first pocket plate rotates clockwise (when viewed as shown in  FIG. 1 ) relative to the first cam plate, and overruns when the first pocket plate rotates counterclockwise (when viewed as shown in  FIG. 1 ) relative to the first cam plate. 
         [0026]    The inner surface of the second cam plate  16  is formed with internal spline teeth  38 , which mesh with external spline teeth  39  on the outer surface of the first pocket plate  14 . 
         [0027]    The second pocket plate  18  is bolted to the first cam plate  12 , which is fixed against rotation. A retainer plate  40  connects the opposite ends of the second pocket plate  18 . Each of the second struts  26  is pivotably supported on the second pocket plate  18 . A spring  42 , preferably a helical spring, at each pocket location urges the respective strut  26  to pivot radially outward away from the cams  44  on the second cam plate  16 , thereby opening a drive connection between the second cam plate  16  and the second pocket plate  18 . 
         [0028]    The second cam plate  16 , second pocket plate  18  and struts  26  comprise a second drive coupling, also a one-way brake, which locks or engages when the first pocket plate  14  rotates counterclockwise (when viewed as shown in  FIG. 1 ) relative to the first cam plate and electric current is supplied to coils  24 , and overruns when the first pocket plate rotates clockwise (when viewed as shown in  FIG. 1 ) relative to the first pocket plate  14 . 
         [0029]    In operation, when electric current is supplied to each coil  24  of the electromagnets, the magnetic field carried through the respective strut  26  causes the strut to pivot radially inward toward the cams  44 , thereby closing a drive connection between the second cam plate  16  and the second pocket plate  18 . When at least one of the struts  26  engages one of the cams  44 , the second cam plate is fixed against rotation through struts  26 , second pocket plate  18  and first cam plate  12 . 
         [0030]    When the coils are deenergized and the springs  42  pivot the second struts  26  out of engagement with cams  44 , each second strut contacts a standoff or stop  46 , supported on a radial surface of the second pocket plate  18 . Preferable the stop is of a plastic or another material having relatively low magnetic permeability. 
         [0031]    Because the coils  24  that produce electromagnets are supplied with electric current, they must be in the second pocket plate  18 , which is a static race. Because magnetic flux forces struts  26  into engagement with the second pocket plate  18 , i.e., the static race, unbalance is not an issue and pocket plate  18  may have a shape that is other than a full circle. 
         [0032]      FIG. 4  shows one of the second struts  26  located in a pocket  50  formed in the second pocket plate  18 , the strut being disengaged from the cams  44  of the second cam plate  16  and contacting stop  46  due to the effects of gravity and the force Fs produced by spring  42 . The rotation of the  14 - 16  assembly in the overrun direction for strut  26  will also force strut  26  to disengage. Each spring  42  is located in a cylindrical recess  52  formed in plate  18 . 
         [0033]    Each pocket  50  is formed with concave cylindrical surface  54 , on which a complementary convex surface of strut  26  pivots. Each pocket  50  is also formed with concave cylindrical surface  56 , which guides movement of the strut  26  and limits its radial movement. 
         [0034]    When electric current is supplied to coil  24 , a magnetic field is produced such that its lines of magnetic flux or magnetic induction pass between the opposite poles  60 ,  61  and along the axial width of strut  26  due to its high magnetic permeability. The magnetic field produces distributed force Fm on the strut  26  and magnetically induces a moment on the strut, which causes the strut to pivot clockwise on surface  54  and into engagement with the cams  44  of the second cam plate  16 .  FIG. 1  shows one of the struts  26  engaged with one of the cams  44  and two struts disengaged from the cams  44  and contacting stops  46 . 
         [0035]    Surface  54  applies force Fg to the strut  26  at the pivot, and surface  56  applies force Fp to the strut. 
         [0036]    A transmission controller opens and closes a connection between a source of electric current and the coils  24 , because centrifugal force is not used to pivot the struts  26  into engagement with second cam plate  16 . 
         [0037]    Second pocket plate  18  extends along a circular arc that is less than 360 degrees. Radial lines drawn from axis  22  to the angular extremities of second pocket plate  18  form an included angle, whose magnitude is about 75 degrees. The second pocket plate  18  is large enough to contain the necessary number of struts  26 , thereby reducing the cost and weight of the raceway and minimizing space required in the transmission. 
         [0038]      FIG. 4  illustrates vectors representing forces applied to one of the second struts  26 , wherein Fs is the force of spring  42 , Fm is the magnetic force that is present when the electromagnet is energized, Fc is a force applied at contact surface  56 , Fg is gravitational force due to the mass of the strut  26 , ps is a force applied at pivot surface  54  when the electromagnet is deenergized, and pm is a force applied at pivot surface  54  when the electromagnet is energized. 
         [0039]    As  FIGS. 5-8  illustrate, the locking element or strut  26  is located on the stationary, second pocket plate  18 , thereby allowing an electromagnet to act directly on the locking element, rather than locating the electromagnet on the second cam plate  16 , where each cam  44  act as a pole to attract the locking elements  26 . 
         [0040]    In order to achieve the necessary pivotal displacement at the end  66  of the locking elements  26  that engages cams  44  while minimizing gap  70 , a lever ratio is designed into the locking element. As shown in  FIG. 5 , if the distance B from the pivot center  62  of surface  54  on the locking elements  26  to the center  64  of surface  56  is one unit, the distance C from center  64  to the end  66  is four units. This lever action allows maximum displacement at the end  66 , while minimizing gap before actuation. 
         [0041]    Materials that are magnetically permeable can lead to excessive flux leakage, which results in loss of function.  FIG. 6  shows that the poles  60 ,  61  have the shape of a horse shoe with arms extending radially inward toward the respective strut  26  from a substantially vertical core, which pass through the coil  24  or electrically conductive wire. 
         [0042]    To prevent excessive flux leakage, as  FIGS. 7 and 8  best illustrate, the second pocket plate  18  is formed in the vicinity of the poles  60 ,  61  of the electromagnet such that the air gaps  68 ,  69  between the poles  60 ,  61  and the second pocket plate  18  are greater than the gap  70  between the poles  60 ,  61  and the locking element  26 . Although some flux leakage occurs, the gap  70  to the locking element  26  is the path of least reluctance. Therefore, enough flux jumps this gap  70  to initiate pivoting of the locking element  26  toward the cams  44 . As the locking element  26  pivots and its engagement with a cam  44  occurs, gap  70  reduces causing an increase in the flux density and the magnitude of the magnetically-induced force on the strut  26 . 
         [0043]    In addition to applying a lever ratio to the locking element  26  and managing the gaps  68 ,  69 ,  70 , it is necessary to direct a sufficient amount of flux (represented by the arrows in  FIG. 8 ) to the locking element  26  in order to produce enough force to initiate pivoting of the locking element  26  toward the cams  44 . 
         [0044]      FIGS. 7 and 8  illustrate, the adjacent contour of the respective poles  60 ,  61  encircles and extends around a portion of the contour of the respective strut surface  72 . This encirclement channels more flux into the most critical area  74  of the strut  26  than if the poles  60 ,  61  were simply terminated without extending along the surface  72 , as in conventional electromagnets. 
         [0045]    When the locking elements  26  engage cams  44  and torque is transferred between the second cam plate  16  and the second pocket plate  18 , a significant amount of deflection can occur in the plates, particularly near the cams  44  that are engaged by the struts  26 . Consequently it is important to locate the coil  24  away from the position with the highest deflection, otherwise the coil and its mountings could be damaged. The position with the highest deflection, however, this is usually the most desirable location for the coil  24  for proper flux generation. To address both issues, each coil  24  is located at the radial outboard surface  78  of the second pocket plate  18 . After energizing, the system could contain residual magnetism leading to unwanted lockups. This is resolved by incorporating a degauss cycle at regular intervals. 
         [0046]    As the strut  26  pivots into the engaged position, iron or steel passing through the magnetic field induces a secondary voltage in the coil  24 . By monitoring the coil voltage for a voltage spike, the observer can determine whether the rocker has engaged. Absence of this voltage spike indicates a failure to engage. 
         [0047]    In accordance with the provisions of the patent statutes, the preferred embodiment has been described. However, it should be noted that the alternate embodiments can be practiced otherwise than as specifically illustrated and described.