Abstract:
A torque limiter in which grease passages are provided to enable better lubrication of the wearing components. A disconnect nut is also provided to readily enable release of the torque limiter even for very high release sellings to afford greasing as a part of a maintenance regimen.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional application No. 61/810,855 filed on Apr. 11, 2013. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention concerns torque limiters which are well known devices which act to produce an overload release in a rotary drive train when the torque transmitted exceeds a predetermined level, in order to prevent damage to components in the drive train. 
         [0003]    Resettable torque limiters are also well known in which drive balls are installed in detent pockets and held therein by a plunger urged against the drive ball by spring pressure. When a predetermined maximum torque is reached, the drive ball can force the plunger away and allow the drive ball to climb out of the pocket allowing relative rotation of two interfit parts to interrupt the driving connection therebetween. 
         [0004]    In conventional practice, grease is applied to the wearing components by injection into a passage drilled through the plunger to the drive ball engaged with the plunger end, and passages radially out past a bushing to reach various wear components. 
         [0005]    However, in prior designs grease does not flow past the drive ball to the detent pocket without release of the torque limiter since the drive ball normally blocks the grease flow until the torque limiter releases. Grease flow past the bushing is limited due to the limited clearance. 
         [0006]    For high torque release settings, it is difficult to manually trip the limiter for routine maintenance purposes. 
         [0007]    In such torque limiters there are sometimes also heavily preloaded bearings supporting one interfit part on the other. Normally these parts do not relatively rotate, but both parts rotate together since connected together by the torque limiter drive ball, and these bearings become dry as the grease migrates out overtime due to centrifugal force generated by rotation together of the interfit parts. Due to their location, these bearings are not able to be greased, except when the torque limiter is released. 
         [0008]    It is an object of the present invention to provide improved lubrication for a resettable torque limiter of the type described above by providing enhanced distribution of grease to the wear in components. 
       SUMMARY OF THE INVENTION 
       [0009]    The above object and other objects which will become apparent upon a reading of the following specification and claims are achieved by forming lubricant passages in the plunger and bushing that allow free flow of lubricant to points which will adequately lubricate the moving components in a drive device such as a torque limiter. This includes a central passage extending lengthwise down the plunger which terminates short of the end in contact with the drive ball which central passage is connected to a cross passages extending radially short offset longitudinal passages then distribute lubricant to an open annular space extending around the drive ball, as well as laterally to a clearance between the plunger and the ID of a bore in a bushing in which the plunger is slidably fit. Lubricant from the open spaces further enters cross passages in the bushing which extends to the bushing bore ID as well as lengthwise passages through the bushing to reach the lower regions and the detent pocket. 
         [0010]    In addition, a disconnect nut threadably engages the upper end of a plunger shroud secured to the plunger upper end and when rotated with a wrench causes raising of the plunger to manually elevate the plunger sufficiently to release the torque limiter by driving the locking balls radially outward. 
         [0011]    The torque limiter release enables the lubrication of bearings supporting the interfit drive parts which are included in the torque limiter, which normally cannot be greased when the torque limiter is not in a released condition. Improved lubrication of the torque limiter running parts is also facilitated. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a sectional view of a prior art torque limiter of a type with which the present invention is concerned showing a conventional grease passage pattern. 
           [0013]      FIG. 2  is a view of prior art driving and driven interfit parts combined with a conventional torque limiter to create a driving connection therebetween. 
           [0014]      FIG. 3  is an external pictorial view of a torque limiter according to the present invention. 
           [0015]      FIG. 4  is an enlarged sectional view of the torque limiter according to the present invention shown in  FIG. 3 . 
           [0016]      FIG. 5  is an enlarged sectional view of a plunger included in the torque limiter shown in  FIGS. 3 and 4 . 
           [0017]      FIG. 6  is an enlarged sectional view of a bushing included in a torque limiter according to the invention shown in  FIGS. 3 and 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    In the following detailed description, certain specific terminology will be employed for the sake of clarity and a particular embodiment described in accordance with the requirements of 35 USC 112, but it is to be understood that the same is not intended to be limiting and should not be so construed inasmuch as the invention is capable of taking many forms and variations within the scope of the appended claims. 
         [0019]    Referring to  FIGS. 1 and 2 , a prior art torque limiter  10  of the type which the present invention is concerned is shown. One or more of such torque limiters may be installed circumferentially spaced about the axis of a pair of interfit rotary parts  12  and  14  other arrangements of such torque limiters are well known. 
         [0020]    One interfit rotary part  12  is secured to a drive (or driven) member  16  and the other rotary part  14  is secured to a driven (or drive) member  18 . 
         [0021]    A drive ball  20  is normally seated within a detent pocket  22  fixed in rotary member  14  and a bushing  24  fixed within a housing  26  is secured to rotary member  12 . The drive ball  20  creates a rotational connection so that the rotary members  12  and  14  normally rotate together. 
         [0022]    Upon the development of a transmitted torque of a predetermined level, the drive ball  20  begins to ride up the sloping sides of the detent pocket  22  and to thereby push up a plunger  28  which has radiused pocket  21  ( FIG. 5 ) at its lower end in contact with the drive ball  20 . The plunger  28  is urged downwardly by the effect of a stiff spring  36 . 
         [0023]    The spring  36  exerts pressure on a set of small locking balls  30  engaged by a rounded shoulder surface  29  on the upper end of the plunger  28  tending to force the balls  30  radially out. 
         [0024]    Any axial movement of the plunger  28  is resisted by the constraining effect exerted by an outer thrust race  32  and an inner thrust race  34  urged together by the preloaded spring  36  applying an axial force to inner thrust race  34 . An adjusting nut  37  allows setting of the spring preload. 
         [0025]    If the transmitted torque level reaches a predetermined release value, the spring force described is overcome to move the outer race  34  down and allow the locking balls  30  to move out radially sufficiently to move onto the outer diameter  36  on the plunger  28 . 
         [0026]    At this point, the drive ball  20  has moved up into the interior bore of the bushing. A snap ring  38  then holds the ball  20  up and out of engagement with the detent pocket  22 , allowing interfit parts  12 ,  14  to freely rotate, relative each other, supported by rotary bearings  40 . 
         [0027]    The torque limiter  10  can be reset by striking the upper end  42  of the plunger with sufficient force in the well know manner. 
         [0028]    In order to keep grease on the torque limiter rotating wear parts, a grease fitting  44  is normally provided which allows injection of grease into an axial central passage  46  in the plunger  28  which passes down to the top of the drive ball  20  which normally prevents any further grease flow. 
         [0029]    Two (or more) pairs of cross passages  48  and  50  branch off from the central plunger passage  48 . The upper pair of passages lubricate the races  32 ,  34  and locking balls  30 . The lower pair of feed cross passages  52  reach the bottom of the bushing and theoretically reach the detent pocket  22  and drive ball  20  via a clearance and small grooves. However, little or no grease will reach the lower components as a practical matter due to the slight clearances. 
         [0030]    Grease will only exit the lower end of the passage  46  when the torque limiter  10  has been released by movement of the plunger  28 . 
         [0031]    Additionally, the bearings  40  can only effectively be greased during routine maintenance when the torque limiter is tripped. This is almost impossible to do manually due to very high torque limit settings often used in some applications. Since the bearings  40  are typically heavily preloaded and do not rotate while the torque limiter remains locked, heavy wear can result as the grease over time tends to migrate out due to rotation of the assembly and consequently the bearings  40  become dry. 
         [0032]    Referring to  FIGS. 3 and 4 , a torque limiter  54  according to the invention is shown. This includes a housing  56  which has a threaded extension  58  which receives a disconnect nut  60  which engages a plunger shroud  66  threaded to the upper end  64  of the plunger  28 . 
         [0033]    A recess  68  in the plunger shroud  66  receives a grease fitting  70 . 
         [0034]    An axial central lengthwise grease passage  72  is provided in the plunger  28 , which terminates short of the drive ball  74 . Instead, there are two cross passages  76  which connect with two pairs of offset longitudinal passages  78  that extend to an annular clearance space  80  adjacent the drive ball  74 . 
         [0035]    The bushing  82  has two cross passages  84 , each receiving grease from the annular space  80  and direct into the same out through down passages  86  through the bushing  82  so that grease can reach the detent pocket  88 . 
         [0036]    The cross passages  76  extend to the inside diameter of the bushing  82  to provide additional grease. 
         [0037]    Thus, the set of grease passages described are able to effectively direct grease to the wearing components without releasing the torque limiter. 
         [0038]    A second aspect of the invention does involve the disconnect nut  60  and plunger shroud  66 . The disconnect nut  60  has a series of wrenching flats  90  thereon so that a wrench can be used to turn the same and advance the disconnect nut  60  up as viewed in  FIG. 4  on the external threads on the housing extension  58 . 
         [0039]    The upper recessed face of the disconnect nut  60  will engage an underside of flange  92  on the plunger shroud  66  so as to pull up the plunger  62  as the shroud  66  is elevated. 
         [0040]    The powerful mechanical advantage exerted by of the threaded engagement of the disconnect nut  60  enables the balls  96  to be forced out until the torque limiter  54  becomes disconnected, even if the torque release level is set to be very high. 
         [0041]    Once released, the bearings  40  can be rotated and greased as a part of a regular maintenance regime. In addition, flow of grease to the torque limiter wear components as described above is enhanced.