Resettable pilot operated torque limiter

Volume, weight and complexity difficulties in the fabrication of torque limiters are avoided in a construction including a housing (10), a shaft (20) journalled in the housing (10) and adapted to be connected to a source (22) of rotary power, and a rotary output (28) journalled in the housing (10). A ball ramp coupling (44) is disposed within the housing (10) and includes an axially movable drive element (46) coupled to the shaft (20), a driven element (42) coupled to the output (28), a spring (52) biasing the elements (42,46) towards each other, facing ramps (61,62) in the elements (42,46) at the interface of the elements and balls (64) in the ramps. A first set of teeth (72) is carried by the drive element (46) while a second set of teeth (82) is carried by the housing (10) and aligned with the first set of teeth (72). When resistance to rotation of the output ( 28) is encountered relative movement between the elements (42,46) will occur which in turn will cause the ball (64) to move the drive element (46) axially relative to the driven element (42) causing the teeth (72,82) to engage to halt further torque transmission between the input shaft (20) and the output (28).