Torque limiter having over-speed protection

Abstract

An apparatus for connecting a rotational drive member to a rotational driven member brakes rotation when either the torque transmitted between the members exceeds a predetermined torque limit or the rotational speed of the drive member exceeds a predetermined rotational speed limit. The apparatus includes a torque limiter configured to actuate a braking mechanism or disconnect transmission when the torque limit is exceeded, and an over-speed governor configured to trigger the torque limiter when the rotational speed of the input element exceeds the rotational speed limit. The over-speed governor may trigger the torque limiter by reducing the torque limit of the torque limiter, or by introducing rotational drag in the apparatus to increase transmitted torque.

What is claimed is: 
     
       1. An apparatus for connecting a rotational drive member to a rotational driven member, the apparatus comprising:
 a structural ground; 
 an input element rotatable relative to the structural ground; 
 an output element rotatable relative to the structural ground; 
 a torque limiter connecting the output element to the input element for rotation with the input element, wherein the torque limiter is actuated to brake rotation of the input element and the output element, or to disconnect the input element from the output element, when torque transmitted between the input element and the output element exceeds a torque limit; and 
 an over-speed governor configured to cause actuation of the torque limiter to brake rotation of the input element and the output element, or to disconnect the input element from the output element, when rotational speed of the input element exceeds a rotational speed limit. 
 
     
     
       2. The apparatus according to  claim 1 , wherein the torque limiter includes a torque limit setting spring having a preload defining the torque limit, and the over-speed governor causes actuation of the torque limiter by reducing the preload of the torque limit setting spring when the rotational speed limit is exceeded, thereby reducing the torque limit. 
     
     
       3. The apparatus according to  claim 2 , wherein the over-speed governor reduces the torque limit to substantially zero torque when the rotational speed limit is exceeded. 
     
     
       4. The apparatus according to  claim 2 , wherein the over-speed governor includes:
 a preload setting shaft engaging the torque limit setting spring, the preload setting shaft being axially displaceable relative to the structural ground to set the preload of the torque limit setting spring; 
 at least one fly weight arranged on the input element to hold the preload setting shaft at an axial setting position when the rotational speed of the input element does not exceed the rotational speed limit; 
 wherein the at least one fly weight moves by centrifugal force when the rotational speed of the input element exceeds the rotational speed limit to release the preload setting shaft and permit axial displacement of the preload setting shaft away from the axial setting position thereby reducing the preload of the torque limit setting spring. 
 
     
     
       5. The apparatus according to  claim 4 , wherein the at least one fly weight is pivotally mounted to the input element. 
     
     
       6. The apparatus according to  claim 4 , wherein the at least one fly weight directly engages the preload setting shaft to hold the preload setting shaft at the axial setting position when the rotational speed of the input element does not exceed the rotational speed limit. 
     
     
       7. The apparatus according to  claim 4 , wherein the at least one fly weight directly indirectly engages the preload setting shaft through a sear to hold the preload setting shaft at the axial setting position when the rotational speed of the input element does not exceed the rotational speed limit. 
     
     
       8. The apparatus according to  claim 7 , wherein the preload setting shaft includes a sear groove therein and the input element includes a radially extending recess, and wherein the sear is partially received by the sear groove and partially received by a radially extending recess to hold the preload setting shaft at the axial setting position when the rotational speed of the input element does not exceed the rotational speed limit. 
     
     
       9. The apparatus according to  claim 4 , wherein the at least one fly weight comprises a plurality of fly weights angularly spaced about a rotational axis of the input element. 
     
     
       10. The apparatus according to  claim 4 , further comprising a button arranged to push the preload setting shaft into the axial setting position to reset the apparatus after an over-speed event. 
     
     
       11. The apparatus according to  claim 4 , wherein the preload setting shaft is adapted for mating with a tool for moving the preload setting shaft into the axial setting position to reset the apparatus after an over-speed event. 
     
     
       12. The apparatus according to  claim 11 , wherein the preload setting shaft includes a tapped hole for mating with a threaded tool. 
     
     
       13. The apparatus according to  claim 4 , wherein the output element includes a fluid injection port through which pressurized fluid is injectable into a cavity to force the preload setting shaft into the axial setting position to reset the apparatus after an over-speed event. 
     
     
       14. The apparatus according to  claim 1 , wherein the over-speed governor causes actuation of the torque limiter by increasing torque transmitted between the input element and the output element when the rotational speed limit is exceeded. 
     
     
       15. The apparatus according to  claim 14 , wherein:
 the torque limiter includes a rotatable braking member arranged to transmit rotational motion from the input member to the output member and a plurality of disc brakes arranged between the braking member and the structural ground, the braking member being axially displaced relative to the structural ground to engage the plurality of disc brakes when the torque limit is exceeded; and 
 the over-speed governor includes at least one fly weight arranged on the braking member, wherein the at least one fly weight moves by centrifugal force when the rotational speed of the input element exceeds the rotational speed limit such that the at least one fly weight applies axially directed force to the plurality of disc brakes to increase torque transmitted between the input element and the output element. 
 
     
     
       16. The apparatus according to  claim 15 , wherein the at least one fly weight is pivotally mounted to the braking member. 
     
     
       17. The apparatus according to  claim 15 , wherein the at least one fly weight comprises a plurality of fly weights angularly spaced about a rotational axis of the braking member. 
     
     
       18. The apparatus according to  claim 14 , wherein the apparatus is resettable after an over-speed event by commanding reverse rotation of the rotational drive member to impart reverse rotation to the input element.