Abstract:
A clutch mechanism includes a coil of wire for producing an electromagnetic field, a locking ring secured against rotation within a case or housing, a gear engageable with the locking ring, and a lever that pivots in response to the electromagnetic field produced by energizing the coil causing the locking ring to engage the gear and hold the gear against rotation.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to a dog clutch actuation mechanism, and more particularly to a locking differential mechanism for a motor vehicle axle. 
     2. Description of the Prior Art 
     Rotating components often require a clutch to transfer torque and rotation from one rotating component to another. The clutch member can be a friction plate or dog clutch, which does not allow any slipping between rotating components during engagement. 
     Common automotive applications of torque transfer clutches include transmissions, transfer cases, air conditioner compressors, power take-offs and many others. Torque transfer clutches are also commonly used in non-automotive applications such as industrial motors, conveyors, agricultural equipment and lawn mowing equipment. The torque transfer clutches can be engaged via compressed air, hydraulic fluid, mechanical leverage or magnetic actuation. 
     Many electronically-controllable torque transfer clutch use an electromagnetic coil to actuate the locking mechanism. When a small moveable coil is used to engage a dog-clutch locking mechanism, the magnetic force it is capable of generating as a function of the air gap is also small. Therefore, it is necessary to amplify the coil&#39;s movement to provide a larger displacement of the locking mechanism. 
     A need exists for a mechanism that amplifies axial displacement of the coil, such as a lever mechanism, which provides the locking mechanism, such as a dog clutch, to operate over a large displacement stroke. 
     SUMMARY OF THE INVENTION 
     A clutch mechanism includes a coil of wire for producing an electromagnetic field, a locking ring secured against rotation, a gear engageable with the locking ring, and a lever that pivots in response to the electromagnetic field produced by energizing the coil causing the locking ring to engage the gear and hold the gear against rotation. 
     Due to the mechanical advantage produced by use of the levers, the strength of the electromagnetic field produced by the coil is reduced in comparison to conventional applications, allowing use of a smaller coil, having less copper, lower weight, and a much smaller package size. 
     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 an exploded, perspective side view of a moving coil electromagnetic dog clutch applied for use in an automotive axle differential mechanism; 
         FIG. 2  is cross section taken through a diametric plane of a differential case and coil showing the initial air gap; 
         FIG. 3  is a cross section showing the clutch actuation mechanism in position with the coil de-energized and the clutch released; 
         FIG. 4  is a cross section showing the clutch actuation mechanism with the coil energized and the mechanism at the mid-stroke of its axial displacement toward the side gear; 
         FIG. 5  is a cross section showing the coil energized and the clutch mechanism at the end of its engagement stroke fully locked with the dog teeth of locking ring engaged with the dog teeth of the side gear; 
         FIG. 6  is a perspective view of a lever; 
         FIG. 7  is a graph showing the variation of the axial force generated by coil as a function of coil air gap, and the force required by the coil to overcome the return spring force; and 
         FIG. 8  is an exploded, perspective side view showing angled surface on the locking ring and differential case. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, there is illustrated in  FIG. 1  a rear axle locking differential mechanism  10 , in which one or more of the side gears  12 ,  14  is selectively rotationally fixed to a differential case housing  16 . The description refers to side gear  12  being secured against rotation to the left-hand case  16 , but either side gear  12 ,  14  could be secured selectively to either the right-hand case  18  or the left-hand case  16 . The gear teeth of the right-hand side gear  14  are engaged with the gear teeth of one of the bevel pinions  20 . A pinion shaft  22 , which extends through the walls of case  18 , supports the bevel pinions  20  in rotation about the cylindrical surface of the pinion shaft  22 . 
     A locking ring  24 , rotationally fixed to case  16 , can move axially within the differential case  16 . 
     A return spring  26 , located between the locking ring  24  and a spring seat in the right-hand case  18 , provides an elastic force  29 , which keeps the locking ring  24  disengaged from the side gear  12  when an electromagnetic coil  28 , located in a coil assembly  30 , is de-energized. 
     When coil  28  is energized, electric current flows through the coil windings producing a magnetic force, which acts on the LH differential case  16  moving the coil axially and pulling the coil towards the LH diff case  16 . 
     Three levers  32 , spaced angularly about axis  34  and located within the LH diff case  16 , are retained by a circular retainer ring  36 . The three levers  32  can each pivot about their own axis  38 , but are fixed to the LH diff case  16  in the other directions. The levers  32  contact the thrust bearing  33  at the upper cam surface  40  and the locking ring  24  at the lower cam surface  42 , the cam surfaces being formed on the levers  32 . 
       FIG. 3  shows the clutch actuation mechanism  44  with the coil de-energized, the air gap  45  between the coil  28  and the adjacent surface of the case  16  at a maximum, and the clutch disengaged.  FIG. 4  shows the clutch actuation mechanism  44  with the coil energized and the mechanism  44  at mid-stroke in the axial direction toward side gear  12 .  FIG. 5  shows the clutch actuation mechanism  44  with the coil energized and the mechanism  44  at the end of its engagement stroke in the fully locked state with the dog teeth  46  of locking ring  24  engaged with the dog teeth  48  of the side gear  12 . 
     When coil  28  is energized, the coil moves toward the LH diff case  16  and its axial motion is transmitted to the locking ring  24  through the levers  32 . Displacement of the locking ring  24  is a function of the coil displacement and the surface profile of the upper and lower cam surfaces  40 ,  42 . Displacement of the locking ring  24  is, in general, nonlinear as shown in  FIG. 7 . 
       FIG. 7  is a graph showing the variation of the axial force  50  generated by coil  28  as a function of coil air gap  45 , and the force  52  required by the coil to overcome the return spring force  29 . The total locking ring displacement can be significantly larger than the total coil displacement, thus a smaller initial coil air gap  45  can be used. Since the initial coil air gap  45  is small, the size of the coil  28  can also be small resulting in less copper or another electric conductor. 
     When the teeth  46  of the locking ring  24  mesh with the teeth  48  on the back face of the side gear  12 , the side gear cannot rotate with respect to the case  16 , because the locking ring is secured to the case against rotation. Then the differential  10  is in a locked state. When the coil  28  is de-energized, the return spring  26  provides an axial force  29  on the locking ring  24  moving the locking ring out of meshing engagement with the side gear  12 . The return spring force  29  exerted on the coil  28  is amplified as a result of the lever multiplication obtained through the upper and lower cam surfaces  40 ,  42  of the lever element. 
     A mechanical retention feature keeps the locking ring  24  in mesh with the side gear  12  when the coil is energized. As  FIG. 8  illustrates, angled surfaces  60 ,  62  are formed on each radial leg  64  of the locking ring, and angled surfaces  66 ,  68  are formed on each mating recess  70  of the case  16 . The locking ring  24  is secured to case  16  against rotation by fitting each radial leg  64  in one of the recesses  70 , the differential case  16  being bolted to the vehicle structure. 
     When torque is applied to lock ring  24  due to its engagement with the side gear  12 , contact between the inclined surfaces  60 ,  62  of the locking ring  24  with inclined surfaces  66 ,  68  of the case recesses  70  produces a force applied at the case and having an axial component. This axial force component keeps the lock ring teeth  46  in tight meshing engagement with the side gear teeth  48 , whenever torque is transmitted between the side gear  12  and locking ring  24 . 
     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.