Abstract:
A dog clutch, includes a first ring secured to an overrunning brake rotatable race, including first teeth, a first disc, the second ring angularly displaceable relative to the discs, a non-rotating, axially displaceable second ring including second teeth engageable with the first teeth and a second disc engageable with the first disc, a first spring urging the discs into mutual contact, and a second spring urging the first and second rings apart.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates generally to a non-synchronized friction brake for actuating a dog clutch 
         [0003]    2. Description of the Prior Art 
         [0004]    While engaging the teeth of a dog clutch while its components are rotating in an automotive vehicle, an objectionable clash can be heard and felt. This clash can be eliminated if the teeth are engaged while the components are stationary. 
         [0005]    A full synchronizer would represent a conventional solution to the clash problem, but a full synchronizer requires a large number of parts and relatively high cost. Empirical evidence shows that full synchronization is not needed when large clutch apply pressures are available for dog clutch actuation. 
         [0006]    A need exists in the industry, however, for a technique that stops rotation of the dog clutch in the most cost effective manner and minimizes hydraulic drag of a rotating friction element when the dog clutch is open. 
       SUMMARY OF THE INVENTION 
       [0007]    A dog clutch, includes a first ring secured to an overrunning brake rotatable race, including first teeth, a first disc, the second ring angularly displaceable relative to the discs, a non-rotating, axially displaceable second ring including second teeth engageable with the first teeth and a second disc engageable with the first disc, a first spring urging the discs into mutual contact, and a second spring urging the first and second rings apart. 
         [0008]    Since the rotating parts are spinning with inertia force and drag due to an open clutch pack, the energy that must be dissipated is small, and the likelihood of the energy being dissipated is high. 
         [0009]    The dog clutch slows rotation of the first race of the dog clutch prior to engagement of the dog teeth by forcing the discs into frictional contact, one of the discs being held against rotation. 
         [0010]    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: 
         [0011]      FIG. 1  is a cross section side view of a portion of the kinematic arrangement of an automatic transmission; 
           [0012]      FIG. 2  is a perspective view showing the teeth of the dog clutch disengaged and a friction disc is a slot on the first disc; 
           [0013]      FIG. 3  is a perspective view showing the first ring having been displaced angularly relative to its position in  FIG. 2 ; and 
           [0014]      FIG. 4  is a top view of the clutch showing the dog teeth engaged. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0015]      FIG. 1  is a cross section side view of an assembly  10 , which is a portion of the kinematic arrangement of an automatic transmission. The assembly  10  includes a one-way or overrunning brake  12  having an outer ring  14  formed with cams distributed angularly about an axis  16 , a rotatable inner race  18 , and a torque transmitting members  20 , such as rockers, each torque transmitting member being supported in a pocket  22  of the inner race and able to pivot into and out of engagement with one of the cams. When overrunning brake  12  is engaged, race  18  is held fixed against rotation through the rockers and cams due to the outer race  14  being fixed by a spline connection  24  to a transmission housing  26 . When overrunning brake  12  is disengaged, inner race  18  can spin freely relative to the outer race  14 . 
         [0016]    Assembly  10  further includes a dog clutch  30 , which includes an inner or first ring member  32 , driveably connected by an axial spline  34  to the inner race  18  for rotation as a unit with the inner race and fixed against axial displacement by a snap ring  36 . The first ring  32  includes first, axially-directed dog teeth  38 , which are spaced angularly about axis  16  and are aligned with mating axially-directed dog teeth  40  on the second ring  42  of the dog clutch  30 . 
         [0017]    The second ring  42  of dog clutch  30  is driveably connected by an axial spline  44  to the housing  26 . A friction disc  46  is supported on the second ring  42  for axial displacement relative to the first ring member  32 . A coiled compression spring  48  continually urges friction disc  46  toward contact with a friction surface  50 , which is supported on the first ring  32  and aligned with the friction disc  46 . A Belleville spring  52 , secured by a snap ring  54  to the center support  56  of the housing  26  and contacting the second ring  42 , continually urges the second ring rightward away from the first ring  32 . 
         [0018]      FIG. 2  illustrates that friction surface  50  is supported on a disc  60 , which is located and retained in an annular slot  62  formed on the first ring  32 . The radial width of annular slot  62  is greater than the radial dimension of the portion  64  of disc  60  that is located in the slot, thereby permitting angular displacement of the first ring  32  about axis  16  relative to disc  60  and friction disc  46  when the discs are engaged mutually. 
         [0019]    Since the rotating parts are spinning with inertia force and drag due to an open clutch pack, the energy that must be dissipated is small, and the likelihood of the energy being dissipated is high. 
         [0020]    When hydraulic fluid in cylinder  66  is pressurized, the second ring  42  is displaced axially leftward, thereby carrying its dog teeth  40  toward dog teeth  38 . Before the dog teeth  38 ,  40  engage mutually, the first ring  32  may rotate about axis  16  along a radially distance x in the direction of arrow A from the position shown in  FIG. 2 , in order for the crests of clutch teeth  38  to become aligned with the valleys between clutch teeth  40 , while the positions of discs  46 ,  60  and frictional contact between the discs is maintained. 
         [0021]      FIG. 3  shows that first ring  32  has been displaced angularly through radial dimension x, such that the crests of clutch teeth  38  have become aligned with the valleys between clutch teeth  40 , thereby allowing the first ring  32  and second ring  42  to engage, while the radial position of discs  46 ,  60  and frictional contact between the discs is maintained. 
         [0022]      FIG. 4  is a top view of the clutch showing the dog teeth engaged. 
         [0023]    While the one-way brake  12  overruns, the dog clutch  30  and a friction brake are fully retracted from the rotating inner race  18  of overrunning brake  12 , providing a minimum spin loss condition. When engagement of the dog clutch  30  is required, piston  68  is first actuated leftward by pressure in cylinder  66  in order to actuate the friction brake apply spring  48 . The force needed to compress the apply spring  48  is sufficiently greater than the force needed to actuate the second ring  42 ; therefore, the dog teeth  38 ,  40  do not yet engage the rotating, slowing first ring  32 . The hydraulic force on piston  68  is then applied through the second ring  42  and the engaged friction discs  46 ,  60  to the first ring  32 . 
         [0024]    The mass of the rotating assembly  10  is known, as is the approximate starting speed, making the energy of the assembly a known value. The force on piston  68  and its pressurized area are also known, making the length of time needed to bring the first race  18  to zero speed also known. After this length of time has passed, the piston pressure is increased to the point where the force of spring  52  is exceeded, and the dog clutch  30  completes its engagement with the first race  18  at zero speed. 
         [0025]    When the first ring  32  of the dog clutch  30  is rotating, it pulls the friction disc  60  to the side of the annular slot  62 . When the first ring  32  is at zero speed and the second ring  42  starts to engage the first ring, the saw tooth profile of the dog teeth  38  rotates the first ring  32  in the opposite direction relative to its overrunning condition. The annular slot  62  allows the first ring  32  to rotate without altering the angular position of the mutually engaged friction discs  46 ,  60 . 
         [0026]    The dog clutch  30  is disengaged upon venting cylinder  66 , which allows spring  52  to move the second ring  42  rightward away from the first ring  32 , thereby disengaging the meshing dog teeth  38 ,  40 . 
         [0027]    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.