Abstract:
A resettable torque limiter for installation between two rotary members, which can smoothly disengage upon application of a predetermined torque acting between the members and smoothly reset upon decline of applied torque below the predetermined level. An undulating cam surface formed on one member is engaged by one or more cam followers on the other member which smoothly ride over undulation peaks comprising cam lobes when the torque limit is exceeded and the driving connection between the rotary members is interrupted until the applied torque declines below the preset limit.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional application No. 61/060,288 filed on Jun. 10, 2008. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This invention concerns automatically resetting torque limiting clutches and more particularly automatically resetting torque limiters which can disconnect on overload. 
         [0003]    Resetting torque limiting clutches have been in existence for many years, typically of a friction clutch or ball detent type. The friction type will release or slip at a preset overload torque value, and will reengage when the overload is removed. The disadvantage of this arrangement is that repeated heating of the torque limiter friction linings (as heat is generated the slipping) causes the clutch capacity to fade, as the higher lining temperatures reduces the coefficient of friction, until the torque limiter slips continuously and destroys itself. 
         [0004]    Another long known torque limiter type is the ball-detent reset torque limiter, which uses spring forces to push balls into drill point cavities with the geometry thereof establishing forces and angles to produce a release at a preset torque level. The torque limiter will reengage when the torque demand falls somewhere below the release torque. The disadvantage of this device is the sudden changes in the acceleration of the connected components, which produces shock loads on the components when running disengaged, or when reengaging, which produces high stresses and deformations which greatly reduce the torque limiter service life. 
         [0005]    It is an object of the present invention to provide an automatically resetting torque limiting clutch in which a connected drive member can run with the torque limiter in a released condition without overheating or imposing shock loads during normal operation or when an overload causes relative rotation between driving and driven members. 
       SUMMARY OF THE INVENTION 
       [0006]    The above recited object and others which will be understood by those skilled in the art upon a reading of the following specification and claims are achieved by an automatic resetting torque limiting clutch acting between two rotary members which transmits torque through one or more cam followers carried by one rotary member urged into contact with a cam surface carried on the other rotary member. The cam followers transmit forces to the cam surface which has a smoothly continuous undulating shape which provides a displacement curve for the cam followers to trace so that there are no abrupt acceleration changes imparted to the cam followers as they are displaced by the cam undulations. The cam followers are prevented from overrunning the cam undulation peaks or lobes by spring arrangements producing an engagement pressure and increasing forces resisting displacement of the cm followers by the cam surface contour preventing the cam followers from passing over the cam lobes until a predetermined torque level is applied by the driving member whereupon the cam followers are able to overcome the forces and be displaced sufficiently to overrun the cam lobes and thereby interrupt the transmission of torque through the torque limiter. 
         [0007]    The development of forces necessary to produce the displacement of the cam followers sufficient to release the torque limiter can be set to a selected characteristic providing the release and also the reengagement performance characteristics required. Harmonic motion characteristics, cyclodial motion characteristics and eighth-power polynomial motion characteristics can be used alone or in combinations. Acceleration and velocity curves are matched so that “jerk” is not infinite at any point in the cycle. 
         [0008]    The cam undulation peaks or cam lobes are located radially out from the axis of rotation of the members in order to transmit torque by the engagement of the cam followers and the cam surface but can be arranged to undulate either radially or axially to generate the displacement resisting forces exerted on the cam followers in contact therewith. The undulation can also be formed on internal or external surfaces. 
         [0009]    The cam followers may be mounted in various ways, including on rocker arm assemblies carried by a driving or driven member so as to engage and follow the cam surface and generates forces transmitting the driving torque to the driven rotary cam member. The arrangement can be reversed so that the cam member is the driver and the cam followers are on the driven member. 
         [0010]    Other arrangements include radial slides having cam follower rollers on the ends thereof or rollers rotatably mounted on radially extending pins carried on an axially movable ring urged to engage the rollers with an axially varying cam surface. 
         [0011]    The typical driving load for the reset torque limiter would be about one third to one half the torque release settings for the limiter. The normal “drive torque to release torque ratio” can be varied or adjusted by changes to the cam displacement curve. 
         [0012]    A cam-follower automatic resetting torque limiting clutch according to the invention can be manufactured in various designs depending on application requirements. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a pictorial view of a first embodiment of a torque limiter according to the present invention with an outer rotary member shown in phantom lines to reveal interior details. 
           [0014]      FIG. 2  is an enlarged fragmentary side view of a portion of the torque limiter shown in  FIG. 1 . 
           [0015]      FIG. 3A  is a pictorial view of a rotary cam member included in the torque limiter of  FIG. 1 . 
           [0016]      FIG. 3B  is a pictorial view of a different embodiment of the rotary cam member shown in  FIG. 3A . 
           [0017]      FIG. 3C  is a pictorial view of another embodiment of the rotary cam member shown in  FIG. 3A . 
           [0018]      FIG. 4A  is a pictorial view of a cam follower assembly in engagement with a fragmentary portion of a rotary cam member. 
           [0019]      FIG. 4B  is another pictorial view of the cam follower assembly in engagement with a fragmentary portion of a rotary cam member. 
           [0020]      FIGS. 5A and 5B  are pictorial views of the cam follower assembly and rotary cam member from different angles. 
           [0021]      FIG. 6  is a pictorial view of another embodiment of the torque limiter incorporating a rotary cam member having an internal cam surface. 
           [0022]      FIG. 7A  is an end view of another embodiment of a rotary cam member having an axially varying cam profile. 
           [0023]      FIG. 7B  is a pictorial view of the axially varying cam member shown in  FIG. 7A . 
           [0024]      FIG. 7C  is a fragmentary pictorial view of the components of a torque limiter incorporating a rotary cam member as shown in  FIGS. 7A and 7B . 
           [0025]      FIG. 7D  is an end view of components of the torque limiter shown in  FIG. 7C . 
           [0026]      FIGS. 7E-1  and  7 E- 2  are two different sectional views through a torque limiter incorporating the components shown in  FIGS. 7A-7D . 
           [0027]      FIG. 8  is a pictorial view of an embodiment of torque limiter according to the invention incorporating an external rotary cam member and rocker arm followers with a particular rocker arm spring mounting arrangement. 
           [0028]      FIG. 9A  is an exploded pictorial view of components of a rocker arm cam follower incorporating an internal spring arrangement. 
           [0029]      FIG. 9B  is a pictorial view of the rocker arm assembly shown in  FIG. 9A . 
           [0030]      FIG. 9C  is an end view of the rocker arm assembly shown in  FIGS. 9A and 9B . 
           [0031]      FIGS. 10A and 10B  are fragmentary views in different positions of a torque limiter using the rocker arm assembly shown in  FIGS. 9A-9C . 
           [0032]      FIG. 11  is an end view of an embodiment of torque limiter according to the invention incorporating the internal rocker arm springs shown in  FIGS. 9A-9C  and  10 A and  10 B. 
           [0033]      FIG. 12  is an enlarged sectional view of a rocker arm assembly incorporating a built in lubricating oil pump. 
           [0034]      FIG. 13  is a sectional view through a rocker arm incorporating a built in centrifugal oil pump. 
           [0035]      FIG. 14A ,  14 B are partially sectional, partially diagrammatic views of a direct drive torque limiter according to the invention. 
           [0036]      FIG. 15A and 15B  are partially sectional, partially diagrammatic views of an indirect drive torque limiter according to the invention. 
           [0037]      FIGS. 16A and 16B  are diagrams of the force relationship between an external cam and follower cam roller in normal operation and release conditions. 
           [0038]      FIG. 17  is a pictorial view of a preferred embodiment of an axially cammed torque limiter according to the invention. 
           [0039]      FIG. 17A  is a fragmentary pictorial sectional view of a variation of the torque limiter shown in  FIG. 17 . 
           [0040]      FIG. 18  is an enlarged view of a portion of  FIG. 17A  showing details thereof. 
       
    
    
     DETAILED DESCRIPTION 
       [0041]    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. 
         [0042]    A radially acting external cam torque limiter  10  is shown in  FIG. 1 . 
         [0043]    The automatically resetting torque limiter  10  includes two rotary members  12 ,  14 . One member  12  is formed with a cam surface  16 , which extends circumferentially about the axis of rotation of the member  12 . The cam surface  16  in this embodiment undulates to form one or more peak undulations or cam lobes  16 A, the distance from the axis of rotation to points on the cam surface varying about the outer perimeter of the member  12 . 
         [0044]    The other rotary member  14  mounts one or more cam follower assemblies  18  including rolling engagement elements comprising rollers  20  spring urged into engagement with the cam surface  16  with a radially inwardly directed force which increases as the rollers  20  move up a cam lobe  16 A. As long as the torque level transmitted between the members  12 ,  14  is below a predetermined release torque, the spring force prevents the rollers  20  from completely ascending the peaks undulation or cam lobes  16 A since the spring force resisting movement of the rollers increases as the rollers  20  move up the cam lobe  16 A until the applied torque can no longer generate sufficient force to further displace the roller  20 . 
         [0045]    A rotary driving connection is therefore maintained acting between the cam surface  16  and the rollers  20 , and is there is no relative rotation therebetween and the driving relationship between the cam surface  16  and followers  18  is maintained (except for a very minor relative motions due to drive torque variations). This is because the radially directed spring force will prevent movement of the rollers  20  all the way up the cam lobe  16 A, preventing relative rotation until the cam follower rollers  20  can rotate past the lobes  16 A on the cam surface  16  which occurs when the applied torque becomes sufficiently high to overcome the spring force. 
         [0046]    The reaction force between the cam follower rollers  20  and the cam surface  16  produces a tangential component capable of generating a torque if the members do not rotate relative to each other. This relative rotation is prevented as long as the torque level generates a radial or axial component not sufficiently high to be able to move the cam follower elements  20  completely past the peak undulations or cam lobes  16 A. That is resisting spring the torque must be high enough to develop a force component able to overcome the urging force and force the cam follower to move a sufficient distance in a direction away from the cam surface to clear the cam lobes  16 A against the resistance of the urging spring force acting on the cam follower rollers in opposition to the torque generated component. 
         [0047]    Once that torque level is exceeded, the cam follower rollers  20  will overcome the spring force and completely ascend and move past the respective peak undulations  16 A on cam surface  16 , and relative rotation between the members  12 ,  14  continue as long as the applied torque remains at or above that level. If the torque level declines below that predetermined level, drive is automatically re-established between the members  12 ,  14  as the follower rollers  20  can no longer completely ascend the cam surface peak undulations or lobes  16 A due to the resistant of the spring forces. The displacement of the cam followers  18  produced by the curve of the cam surface  16  produces smooth, continuous accelerations of the rollers  20  when ascending the undulations  16 A, which avoids shocks when the torque limiter  10  is running released or when resetting. 
         [0048]    The moving parts may be submerged in an oil bath, the oil held outward by centrifugal force, and heat from churning the oil when the torque limiter  10  in a released state is thereby dissipated to air. 
         [0049]    The cam follower assemblies  18  and cam surfaces  16  may be variously configured and mounted. 
         [0050]    The cam surface shape can be varied to accommodate any number of cam follower assemblies as required to produce the required release torque level, with one lobe for each cam follower. The cam surface shape can also be varied to produce high torque attack, i.e., resistance to radial or axial movement of the cam followers  18  can be made to increase rapidly when ascending the lobes  16 A and a lower rate of torque decline when descending the cam lobes  16 A. 
         [0051]    The cam surface  16  can be on the exterior perimeter of the rotary member  12  with the cam follower rollers  20  moving radially outwardly against inwardly directed spring forces to release as shown in  FIG. 1 , or a cam surface  17  can be formed on an internal surface, with the cam follower rollers  20  spring urged to move radially outwardly as seen in  FIG. 6  to engage the internal surface. 
         [0052]    The cam surface can also be formed on an axial face of a cam member  12 A with the cam follower rollers  20  cammed to move axially as in the embodiments of FIGS.  7 A through  7 E- 2  described further below. 
         [0053]    In the embodiment of  FIGS. 1-5 , one rotary member  12  comprises a rotor having a peripherally extending external cam surface  16  as described above, and the cam followers  18  each include a roller  20  mounted on one end of a pair of rocker arms  22  pivotally mounted on the other rotary member  14  with pivot pin assemblies  29 . 
         [0054]    The other rotary member  14  is formed in an annular shape which encloses the rotary member  12 . The other end of each of the pivoted rocker arms  22  mounts a cross pin  24  which acts to compress a pair of springs  26  disposed in spring seat cavities  27  formed in the member  14 . The rocker the arms  22  pivot up as the cam follower rollers  20  are moved radially outwardly in ascending the cam surface lobes  16 A but are unable to completely pass over the cam lobes  16 A until the transmitted torque exceeds a predetermined level. 
         [0055]      FIG. 8  shows an alternate mounting for the rocker arm springs  26 A in which the springs  26 A extend generally tangentially to the axis of rotation of the member  14 , and are compressed by pivoting of the rocker arms  22 A pushing half round end pieces  28  together, with a stop feature  30  preventing the far end piece  28  from moving away so that compression of the springs  26 A occurs upon outward movement of the rollers  20 . Other spring configurations can also provide the resisting urging forces on the cam follower rollers  20 A, which establishes the transmitted torque. 
         [0056]    Another cam follower configuration is shown in  FIGS. 9A-9C  and  10 A,  10 B. This configuration minimizes the space required. The springs  26 B force balls  32  along an axis parallel to the axis of pivoting of the rocker arm  22 B. The balls  32  are seated in conical stepped recesses  25  (specifically designed detents), which increasingly compress the springs  26 B as the balls  32  are moved up the recess stepped surfaces to be cammed out as the rocker arms  22 B are pivoted. 
         [0057]    The rocker arms  22 B are pivoted by engagement of the cam follower rollers  20 B with the cam lobes  16 A formed on the member  12 . The rocker arms  22 B are pivotally mounted on the outer rotary member  14 B by pivot pin  29 B- 1  held with caps  29 B. 
         [0058]    As seen in  FIGS. 3A ,  3 B and  3 C, various alternate mountings of the drive member  12  are shown. In  FIG. 3A , an integral shaft can be keyed or splined to an input or output member. In  FIG. 3B  an integral tube  12 B can be keyed or splined to an input or output shaft. In  FIG. 3C , threaded holes are formed in an integral shaft to allow attachment of a flange to connect a sheave, gear, etc. 
         [0059]    In the embodiment of  FIG. 6 , the annular outer rotary member  19  has a circumferentially undulating cam surface  17  on the inside of a cavity, and inner rotary member  15  carries cam followers comprised of sliders  21  having rollers  20 A rotatably mounted on the ends thereof, the sliders  21  movable radially in slots formed in the rotary member  15  and urged radially outwardly by springs  23  into engagement with the cam surface  17 . 
         [0060]    In the embodiment of FIGS.  7 A through  7 E- 2 , the cam surface on a rotary member  38  has cam lobes  40  projecting in an axial direction ( FIGS. 7A ,  7 B), although located spaced radially out from the axis of rotation in order to generate a torque. Tapered cam follower rollers  42  (FIGS.  7 C- 7 E- 1 ) are mounted on a spring ring  44  carried on another rotary member  48 . The tapered rollers  42  are mounted for rotation about radial axes defined by axle pins  46 , and are urged axially into engagement therewith by a set of springs  52  acting in an axial direction on the spring ring  44 . Guide rollers  50  are mounted on pins  53  projecting radially from the spring ring  44 . 
         [0061]    The guide rollers  50  move in slots  54  ( FIG. 7E-2 ) in the other rotary member  48  so as to cause the spring ring  44  to rotate with rotary member  48  while freely allowing relative axial movement thereof necessary to axially displace the spring ring  44  by engagement of the rollers  42  with lobes  40 . 
         [0062]    The driving and driven rotary members are held to be concentric with each other by frictionless bearings (usually ball bearings or tapered roller bearings if thrust forces are applied.) Bearings can be oil or grease lubricated. During the driving mode the entire bearing assembly rotates as a unit with no relative rotation between races so as to not require lubrication. For oil lubrication, the bearing mounting may provide dams which hold oil in the bearings against centrifugal forces. 
         [0063]    As seen in  FIGS. 12 and 13 , oil for the main bearings, in the center of the torque limiter  10 , is pumped from the oil annulus at the outer portion of the torque limiter assembly by small centrifugal pumps  58  mounted within bearings  59  on each end of the pins  60  for the rollers  20 A. The pumps  58  are built into the rocker arms  22  and are driven by the rotation of the rocker arm cam rollers  20 A which occurs only upon relative rotation. The cam follower roller  20 A rotates, driven by (or driving) the engagement with the cam surface  16  when the torque limiter  10  is overrunning in an overload condition. At this time the main bearings begin to function and may require lubrication. Each cam follower roller  20 A drives its attached pin  60  which in turn drives the pump rotors  62 . Oil is conveyed to the bearings  66 ,  67  and other parts by internal drillings  64 . 
         [0064]    If rotational speeds are high and the torque limiter is disengaged, the temperature of the oil will rise above ambient and may exceed the heat rejection rate of the torque limiter. Internal wireless sensors or external fixed sensors (not shown) may provide the high temperature signal. 
         [0065]    For inline mounting, the torque limiter  10  may be mounted on the input or output shaft  70 A,  70 B of the drive as seen in  FIGS. 14A-14C . A flexible coupling  72  is required to provide for shaft misalignment. 
         [0066]      FIGS. 14A-14C  also show a “drop out” mount, in which the torque limiter  10  can be slipped out after removal of bolts  73  as indicated. This eliminates the need to completely disassemble the drive line to remove or replace the torque limiter  10 . 
         [0067]    For indirect drives, sheaves  74 , sprockets  76  or gears etc., can be mounted on the input or output members of the torque limiter as required. ( FIGS. 15A ,  15 B) 
         [0068]      FIGS. 16A and 16B  diagram the forces generated in a driving condition transmitting low torque ( 16 A) and high torque ( 16 B). As torque is applied to the cam member the follower element begins to roll up the undulation increasingly compressing the spring through the rocker arm. The force of the spring (F S ) keeping the cam follower in constant contact with the cam surface (through the rocker arm) causes a reaction force (F N ) normal to the cam surface. A component of (F N ) acting perpendicular to a radial line to the point of contact is shown as (F T ). The magnitude of (F T ) multiplied by the radial distance to the point of contact is the torque transmitted by the follower. The magnitude of (F T ) increases as the follower rolls further up the cam undulation due to the increased spring compression combined with the increased pressure angle between (F N ) and the radial line to the point of contact. As the magnitude of (F T ) increases and the radial distance between (F T ) and the axis of rotation increases, the transmitted torque increases until it equals the input torque. When an over torque situation occurs and the cam follower rolls up and over the cam lobe  16 A, the torque transmitted drops until the follower encounters the next lobe  16 A on the cam in a continuous cycle. 
         [0069]    Referring to  FIG. 17 , a preferred form of the axially varying cam surface torque limiter  78  is shown. 
         [0070]    An input flange  80  and input shaft  81  and output member  82  and output shaft  83  are drivingly connected by interengagement of a cam ring  84  formed with axial undulations  86  located radially outward from the axis of rotation of the assembly. The input flange  80  and cam follower carrier ring  88  have a splined connection  90  therebetween so that the output member  82  and carrier ring  88  can have relative axial movement while maintaining a rotary connection therebetween. 
         [0071]    The carrier ring  88  mounts a plurality of cam follower rollers  92  mounted on radial axle pins  94 . 
         [0072]    The rollers  92  are urged into axially undulating cam surface  86  by a series of compression springs  96  contained in pockets  98  in the carrier ring and an output member flange  100 . 
         [0073]    A thrust bearing  102  absorbs the axial thrust generated by the springs  96  and follower rollers  92 . 
         [0074]      FIG. 17A  shows a variation  78 A of the axial torque limiter  78  which includes a series of axially extending pistons  104  mounted in individual pockets  118  in the cam follower member  106 . A cam follower tapered roller  108  pivoted on pins is disposed in a slot in the end of each of the pistons  104  and is urged to engage undulating surfaces  112  formed on a cam ring  108  fixed to the cam member  110 . Each piston is urged in an axial direction by a compression spring  116  also installed in each pocket  118  in the cam follower  106  and adjustably compressed with threaded plugs  120  received in the ends of pockets  118 .  FIG. 18  shows that each roller  108  is of preferably of a tapered generally barrel shape although having partially spherically curved sides and cam surface  112  is correspondingly shaped. The rollers  108  are each mounted on a pin  119  installed after insertion of the roller  108  in the slot in the end of the respective piston  104 . This configuration minimize the axial length of the pistons and the torque limiter. A piston  104  for each undulation cam lobe balances the axial forces around the axis of the torque limiter  78 A. 
         [0075]    The torque limiters are adjustable and provide variable release torque settings. This is accomplished by varying the number of cam followers or by adjusting the spring forces applied to the rocker arms or other cam follower element supports.