This invention concerns automatically resetting torque limiting clutches and more particularly automatically resetting torque limiters which can disconnect on overload.
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.
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.
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.
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.
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.
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.
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.
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.
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.
A cam-follower automatic resetting torque limiting clutch according to the invention can be manufactured in various designs depending on application requirements.
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.
A radially acting external cam torque limiter 10 is shown in
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 16A, the distance from the axis of rotation to points on the cam surface varying about the outer perimeter of the member 12.
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 16A. 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 16A since the spring force resisting movement of the rollers increases as the rollers 20 move up the cam lobe 16A until the applied torque can no longer generate sufficient force to further displace the roller 20.
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 16A, preventing relative rotation until the cam follower rollers 20 can rotate past the lobes 16A on the cam surface 16 which occurs when the applied torque becomes sufficiently high to overcome the spring force.
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 16A. 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 16A against the resistance of the urging spring force acting on the cam follower rollers in opposition to the torque generated component.
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 16A 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 16A 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 16A, which avoids shocks when the torque limiter 10 is running released or when resetting.
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.
The cam follower assemblies 18 and cam surfaces 16 may be variously configured and mounted.
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 16A and a lower rate of torque decline when descending the cam lobes 16A.
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
The cam surface can also be formed on an axial face of a cam member 12A with the cam follower rollers 20 cammed to move axially as in the embodiments of FIGS. 7A through 7E-2 described further below.
In the embodiment of
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 16A but are unable to completely pass over the cam lobes 16A until the transmitted torque exceeds a predetermined level.
Another cam follower configuration is shown in
The rocker arms 22B are pivoted by engagement of the cam follower rollers 20B with the cam lobes 16A formed on the member 12. The rocker arms 22B are pivotally mounted on the outer rotary member 14B by pivot pin 29B-1 held with caps 29B.
As seen in
In the embodiment of
In the embodiment of FIGS. 7A through 7E-2, the cam surface on a rotary member 38 has cam lobes 40 projecting in an axial direction (
The guide rollers 50 move in slots 54 (
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.
As seen in
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.
For inline mounting, the torque limiter 10 may be mounted on the input or output shaft 70A, 70B of the drive as seen in
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. (
Referring to
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.
The carrier ring 88 mounts a plurality of cam follower rollers 92 mounted on radial axle pins 94.
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.
A thrust bearing 102 absorbs the axial thrust generated by the springs 96 and follower rollers 92.
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.
This application claims the benefit of U.S. provisional application No. 61/060,288 filed on Jun. 10, 2008.
Number | Date | Country | |
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61060288 | Jun 2008 | US |