Torque limiters are used in a number of aircraft systems such as between the power unit and the actuator for control surfaces. Conventional torque limiters include multiple interfaces where friction acts in collaboration with input torque as part of the torque limiter operation. These interfaces are primarily sliding in nature. As a result, repeatability and variance of the product's torque limiter setting is sensitive to the plurality of friction effects. Such torque limiters therefore do not have an exact and consistent torque limit value, but rather have a range of torques in which the limiter's torque limit will lie. Variation occurs in large part due to friction at various points within the torque limiter's mechanism. These will be discussed further below. The torque limiter's range of operation (called its torque bandwidth) will be between a maximum limit value and a minimum limit value. The torque bandwidth dictates the minimum torque that the aircraft manufacturer has to accommodate in the structural design. The aircraft manufacturer needs to use a torque limiter with the minimum limit value sufficiently above the normal operational torque that the limiter is unlikely to cut in during normal operation (as this would then prevent normal operation). However, the manufacturer has to design the equipment to withstand at least the torque at the maximum limit value so as to ensure that it does not break if that torque is actually applied through the limiter. Designing equipment to withstand higher torques requires stronger and usually heavier materials and/or other types of over-engineering (which normally add bulk and weight) and is therefore preferably avoided or minimised. Accordingly, the manufacturer would prefer a torque limiter with a reduced torque bandwidth so as to reduce the required over-engineering.
USPTO Backgrounds
USPTO Backgrounds