Abstract:
A radial detent torque overload clutch has a retaining ring inside the outer housing to retain the hub in the housing and a thrust bearing between the ring and pawls to bear thrust loads that tend to pull the hub out of the housing. The pawls exert driving torque in only one direction so that the hub can be turned manually relative to the housing in the opposite direction by the pawls camming on gently sloped surfaces of the housing.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This claims the benefit of U.S. Provisional Patent Application No. 60/567,701 filed May 3, 2004. 
     
    
     STATEMENT CONCERNING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       FIELD OF THE INVENTION 
       [0003]    This invention relates to torque overload clutches, in particular to such clutches for machine drive lines or drive trains. 
       BACKGROUND OF THE INVENTION 
       [0004]    U.S. Pat. No. 6,447,397 discloses a radial detent torque overload clutch primarily suited for a drive line. The clutch has an outer member and an inner member, and three detents between the inner member and the outer member that maintain the members in rotational driving engagement with one another below a certain overload torque between them. Each detent includes a driving member that slides radially in an opening in the inner member between an engaged position in which the driving member is seated in a recess of the outer member in driving engagement with the recess and a disengaged position in which the driving member is retracted from the recess and the outer member is continuously rotatable relative to the inner member. The driving members are moved radially outward to engage in the recesses by a mechanism including a disc spring that exerts an axial spring force that biases the driving members into the engaged position, and the disc spring is regressive so that the spring force it exerts is less in the disengaged position than it is in the engaged position. The disclosure of U.S. Pat. No. 6,447,397 is hereby incorporated by reference for the teaching of the detents in  FIGS. 2-6  and operation in col.  4 , line  12 —col.  5  line  36 , as if fully set forth herein. 
         [0005]    The design of U.S. Pat. No. 6,447,397 is a relatively large diameter mechanism, which is acceptable in many applications. It was a large diameter in part because of the mechanism that permitted it to be free running for a limited angle so as to permit aligning the splines of the hub with the splines of the shaft to which it is to be connected. However, some applications require a more compact design. 
       SUMMARY OF THE INVENTION 
       [0006]    The invention provides a radial detent torque overload clutch that can be made with less material, with good durability, in a smaller size and with fewer separate parts. 
         [0007]    In one form, a radial detent torque overload clutch of the invention has a retaining ring inside the outer housing to retain the hub and pawls axially in the housing. This results in constructional changes that permit the above described advantages. 
         [0008]    Preferably, a thrust bearing is provided between the ring and pawls to bear thrust loads against an axially facing surface of the inner member that tend to pull the hub out of the housing. This helps protect the springs from excessive thrust loads as the thrust bearing will bear them to improve durability of the clutch. 
         [0009]    In another aspect, the pawls exert driving torque in only one direction. In the other direction, the hub can be turned manually relative to the housing by the pawls camming on gently sloped surfaces of the housing. When a pawl reaches one of the driving engagement surfaces when sliding in this direction, the pawl overruns it and keeps going, producing a chattering sound to let the operator know that the clutch is overrunning in the opposite direction. This lets an operator align the clutch with splines on a shaft when installing the clutch to a drive or driven shaft, and also permits the clutch to overrun for example if the power take-off shaft of a tractor is stopped quickly. 
         [0010]    The foregoing and other objects and advantages of the invention will appear in the detailed description which follows. In the description, reference is made to the accompanying drawings which illustrate a preferred embodiment of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a side plan view of a coupler employing a preferred embodiment of a torque limiting clutch of the present invention; 
           [0012]      FIG. 2  is a sectional view of the coupler illustrated in  FIG. 1  as viewed from a radial plane in the engaged position; 
           [0013]      FIG. 3  is an exploded assembly view of the coupler; 
           [0014]      FIG. 4  is a sectional view from the plane of the line  4 - 4  of  FIG. 2  of the clutch in an engaged position; and 
           [0015]      FIG. 5  is a view like  FIG. 4 , but with the clutch in a disengaged position. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0016]    Referring to  FIGS. 1-3 , a torque overload clutch  10  of the invention has a yoke  12  fixed, for example by welding, to an outer housing  14 . An inner hub  16  that is rotatable relative to the yoke and housing has its inner end  18  contained within the housing  14  and its outer end is internally splined to receive a splined shaft. Detents are provided by each of three pawls  20  received in a corresponding radially extending slot  22  in the inner end  18 , each of which is radially slidable therein to normally transmit torque between the hub  16  and housing  14  in one direction, but permit overrunning (relative rotation) if the torque capacity of the clutch is exceeded or if torque is transmitted in the opposite direction. The slots  22  are open at their rear ends. 
         [0017]    Each pawl  20  is a driving member that has a ramped surface  24  that cams on a mating ramped surface  26  of an actuator ring  28 . The actuator ring  28  is biased axially toward the pawls  20  by a spring made up of three disc springs  30 , that has a regressive spring rate as described in U.S. Pat. No. 6,447,397. A ring shaped thrust bearing  32  is positioned inside the housing  14 , outside of the actuator ring  28  and between the outer ends of the pawls  20  and the axially inner side of a split retainer ring  34  that is snapped into an internal groove  36  in the housing  14 . The thrust bearing bears on the adjacent axially facing surface of end  18  on its left side as viewed in  FIG. 2 , and on the ring  34  on its right side if the inner member  16  is attempted to be pulled out of the outer member  14 . The retainer  34  captures the end  18  and the pawls  20  inside of the housing  14  and reacts against any excessive thrust loads the hub  16  exerts on the housing  14 , that tend to pull the hub  16  axially out of the housing  14 . This helps protect the springs  30  from being subjected to excessive thrust loads. 
         [0018]    The inner radius edges of the springs  30  react against the actuator ring  28 , and the outer radius edges of the springs  30  react against a compression plate  38 , or keeper  38 , that is held axially on the hub  16  by a split retainer ring  40  that is snapped into an external groove  42  in the hub  16 . An o-ring  44  seals the outer circumference of the compression plate  38  against the bore  45  in the end of the housing  14 . 
         [0019]    Referring to  FIG. 4 , the pawls  20  are illustrated in their most radially outward, fully engaged positions. In this position, each pawl  20  has a steeply ramped outer corner that is engaged with a mating steeply ramped surface  50  formed in the interior surface of the housing  14 . If a torque is exerted on the hub  16  to drive the yoke  12  in the clockwise direction as viewed in  FIG. 4 , the torque is exerted from the hub  16 , through the pawls  20  bearing on the surfaces  50  to the housing  14  and therefore, since the housing is fixed to the yoke  12 , to the yoke  12 . If the torque capacity of the clutch  10  is exceeded, the pawls  20  cam on the surfaces  50  and are pushed radially inwardly. In doing so, the pawls  20  cam on the ramped surface  26  of the ring  28 , which urges the ring  28  axially away from the pawls  20  against the bias of the disc springs  30 , permitting relative rotation of the hub  16  and housing  14  when the pawls  20  disengage from the surfaces  50 . Each time a pawl  20  passes a surface  50  as the hub  16  and housing  14  relatively rotate, it attempts to re-engage, producing a chattering noise. When the torque subsides to below the capacity, the re-engagement attempts are successful, arresting relative rotation between the hub  16  and housing  14 , to once again transmit torque from the hub  16  to the housing  14 . 
         [0020]    Significant torque is only transmissible in one rotary direction in the clutch  10 . That is the rotary direction in which the pawls  20  approach the surfaces  50  to abut them. Torque may be transmitted from the hub  16  to the housing  14  in this direction, or from the housing  14  to the hub  16 . In the opposite direction, like if the hub  16  were turned counter-clockwise as viewed in  FIG. 4  relative to the housing  14 , each pawl can slide on a surface  52  that slopes gently radially inwardly to the diameter of the inside diameter surfaces  54  of the cam race surface in the bore  45  of the housing  14 , as illustrated in  FIG. 5 , so that they are in the fully disengaged position on the surfaces  54 . The slope is gentle, meaning that it is such that manual force can be exerted to turn the housing  14  and hub  16  relatively in this direction. As illustrated, in the preferred embodiment, the surface ramps inwardly for somewhat more than 45°, whereas the surfaces  50  traverse the same radial distance in very few degrees. This permits the hub  16  to be turned relative to the housing  14  in this direction (moving the pawls  20  away from the surfaces  50 ) with the application of a relatively low torque, in comparison to the torque capacity in the driving direction. This allows overrunning of the housing  14  relative to the hub  16  in the reverse direction so that if there is a large downstream inertia and the power take off shaft of the tractor driving the clutch slows down quickly when it is turned off, like if there is an automatic brake on it, the driven mass, which may have too large of an inertia to be stopped immediately, can keep on turning until the inertia subsides. Also, for smaller capacity clutches, if the force exerted by the springs  30  is sufficiently small, the friction force between the ends of the pawls  20  and the inside of the housing  14  will be small enough to permit manual turning of the hub  16  relative to the housing  14  so as to allow a user to align the splines of the hub  16  with the splines of a shaft to which it is to be connected. 
         [0021]    These features permit a clutch of a significantly smaller size, for example approximately 4″ in diameter versus approximately 7″. They also simplify and reduce the cost of manufacture, and produce a longer life of the clutch by isolating the springs from excessive thrust loads. 
         [0022]    In addition, a clutch so constructed could have something other than a yoke  12  secured to the housing  14 . For example, the yoke  12  could be replaced with a sprocket for a chain drive application, or a gear for a gear drive application, and the sprocket or gear could have a hole through the center that would allow a shaft to be inserted through it, so the shaft could be inserted through the clutch and the sprocket or gear. 
         [0023]    A preferred embodiment of the invention has been described in considerable detail. Many modifications and variations to the preferred embodiment described will be apparent to a person of ordinary skill in the art. Therefore, the invention should not be limited to the embodiment described.