U20-3, U25-3 WSM Hydraulic system (Mechanism section)
IV-M-36
c. Function of negative brake
(1) Negative brake function (Unload condition)
No pressure is applied at the P-port, which means there is no piston driving force.
In this state, the force of negative brake springs pushes down the negative brake piston to get the fric-
tion plate between the piston and the casing. By so doing, the friction plate is held in this poison by a
friction force.
Because the pinion gear and the friction plate are spline-coupled through ring gear, the cylinder block
is held and thus the motor is braked.
(2) Negative brake release (On-load condition)
A pilot pressure is applied at the P-port, generating a driving force to the negative brake piston.
In this state, the piston driving force surpasses the force of negative brake springs to push down the
negative brake piston.
By so doing, the friction plate gets free from the friction force, allowing the motor to run freely.
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