Abstract:
A drive device includes a first one-way coupling including a cam plate, pocket plate and struts, a second one-way coupling including a second cam plate driveably connected to the pocket plate, second pocket plate extending in a partial circular arc and secured to the cam plate, and second struts for opening and closing a drive connection between said second plates, and electromagnets for causing the second struts to close said drive connection.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to an overrunning, one-way drive device, such as a brake or clutch, whose engaged and disengaged states are selectively controllable. 
     2. Description of the Prior Art 
     Conventionally a one-way brake (OWB) or one-way clutch requires two circular rings or raceways, because the raceway that transmits input torque contains the locking elements, such as rollers, struts, or rockers. The input race contains the struts because centrifugal forces are used to move the locking elements away from the output race, which reacts torque. The output raceway is annular, because the locking elements may stop at any location against the output raceway. 
     Centrifugal force is used to move the locking elements away from the output raceway to limit the duty cycle on the locking elements and springs during the overrun phase of the OWB. If centrifugal force were not employed in this way, the locking elements would wear prematurely and the spring duty cycle could cause premature failure. 
     The raceways should be annular to satisfy the need to distribute the mass of the rotating components evenly, thereby avoiding an objectionable amount of unbalance. 
     But conventional raceways for one-way clutches and brakes are expensive, heavy and require too much space. 
     SUMMARY OF THE INVENTION 
     A drive device includes a first one-way coupling including a cam plate, pocket plate and struts, a second one-way coupling including a second cam plate driveably connected to the pocket plate, second pocket plate extending in a partial circular arc and secured to the cam plate, and second struts for opening and closing a drive connection between said second plates, and electromagnets for causing the second struts to close said drive connection. 
     The raceways are the largest components in a one-way brake or one-way clutch, the heaviest components, and the most expensive components. 
     The second pocket plate has the form of a circular arc, whose includes angle is substantially less than ninety degree, large enough to contain the necessary number of struts, thereby reducing the cost and weight of the raceway and minimizing space required for it in the transmission. 
     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 
       The invention will be more readily understood by reference to the following description, taken with the accompanying drawings, in which: 
         FIG. 1  is a front view of a selectable OWC in which the rings are aligned axially; 
         FIG. 2  is side perspective view of the selective OWC of  FIG. 1 ; 
         FIG. 3  is a perspective view of the electromagnets, second struts and second pocket plate of the selective OWC of  FIG. 1 ; and 
         FIG. 4  is a side showing the second struts and coils assembled in the second pocket plate. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     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 . 
     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. 
     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 . 
     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. 
     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. 
     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 . 
     The second pocket plate  18  is bolted to the first cam plate  12 , which is fixed against rotation. A retainer plate  40  and a member  23  connect 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 . 
     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 . 
     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 . 
     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. 
     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. 
       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 . Each spring  42  is located in a cylindrical recess  52  formed in plate  18 . 
     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. 
     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 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 . 
     Surface  54  applies force Fg to the strut  26  at the pivot, and surface  56  applies force Fp to the strut. 
     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 
     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 A, 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. 
     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.