Patent ID: 7063306

Claim:
An electronic winch monitoring system for a winch mechanism including a gearbox establishing a driving connection of predetermined fixed ratio between a rotatable input shaft and a rotatable output shaft, a primary brake including a plurality of interleaved friction plates and spacer plates operatively connected to the input shaft for selectively resisting rotational motion of the input shaft when activated, a rotatable winch drum operatively connected to the output shaft to rotate therewith for selectively winding on and winding off cable stored on the drum to hoist and lower loads, respectively, and an auxiliary brake including a plurality of interleaved friction plates and spacer plates operatively connected to the output shaft for selectively resisting rotational motion of the winch drum when activated by reducing a pressure in a brake release hydraulic circuit, the electronic winch monitoring system comprising: an input speed sensor for detecting an actual rotational speed of the input shaft and producing input speed signals indicative of thereof; an output speed sensor for detecting an actual rotational speed of the output shaft and producing output speed signals indicative thereof: an electronic control unit including a monitoring section and a brake control section; the monitoring section receiving the input and output speed signals, processing the speed signals to produce a calculated ratio of the actual rotational speed of the input shaft to the actual rotational speed of the output shaft, and producing a fault indication signal when the value of the difference between the calculated ratio and the predetermined fixed ratio exceeds a predetermined acceptable range value; the brake control section, upon receiving the fault indication signal, reducing the hydraulic pressure in the brake control circuit in accordance with a predetermined nonlinear pressure-time profile to engage the auxiliary brake and stop rotation of the winch drum, wherein the predetermined nonlinear pressure versus time profile further comprises: a first profile section having a first time length during which the pressure in the brake release hydraulic circuit is rapidly reduced from a maximum pressure, at which the brake friction plates and spacer plates are at maximum distance from one another, to an intermediate pressure, at which the brake friction plates and spacer plates initially touch; and a second profile section following the first profile section, the second profile section having a second time length during which the pressure in the brake release hydraulic circuit is reduced at a substantially linear rate from the intermediate pressure to a minimum pressure at which the brake friction plates and spacer plates are engaged with maximum force.