DUAL BRAKE SYSTEM – OPERATION
When hoisting or pulling a load, the brake clutch allows
free rotation of the inner brake race and input shaft. The
sprag cams lay over and permit the inner race to turn
free of the outer brake hub (Figure 1). The friction brake
remains fully engaged. The winch, in raising a load, is
not affected by any braking action during haul-in.
When the haul-in operation is stopped, the load
attempts to turn the input shaft in the opposite direction.
This reversed input causes the sprag cams to instantly
engage and firmly lock the inner brake race to the outer
brake hub (Figure 2).
When the winch is powered in reverse, to pay-out
cable, the motor and gear train will not rotate until
sufficient pilot pressure is supplied to open the brake
valve. The friction brake within the winch will completely
release at a pressure lower than that required to open
the brake valve. The extent to which the brake valve
opens will determine the amount of oil that can flow
through it and the speed at which the load will be low-
ered. Increasing the flow of oil to the winch motor will
cause the pressure to rise and the opening in the brake
valve to enlarge, speeding up the descent of the load.
Decreasing this flow causes the pressure to lower and
the opening in the brake valve to decrease thus slowing
the descent of the load.
When the control valve is returned to neutral or “hold,”
the pilot pressure will drop and the brake valve will
close, stopping the load. The friction brake will engage
and hold the load after the brake valve has closed.
When lowering a load very slowly for precise position-
ing, no oil flow actually occurs through the winch motor.
The pressure will build up to a point where the friction
brake will release sufficiently to allow the load to rotate
the motor through its own internal leakage. This feature
results in a very slow speed and extremely accurate
positioning.
The friction brake receives very little wear in the lower-
ing operation. All of the heat generated by the lowering
and stopping of a load is absorbed by the hydraulic oil
where it can be readily dissipated.
5
Hoisting
Stopped
Holding
Load
Sprag Cams
Permits free sha
ft
rotation
while hoisting.
Sprag Cams
Static friction brake applied
Load attempts to rotate sha
ft
in opposite direction.
Brake clutch locks sun gear sha
ft
to friction brake.
Figure 2
Figure 1
