U20-3, U25-3 WSM Hydraulic system (Mechanism section)
IV-M-43
3) Operating principle of two-speed motor
The swash plate has two faces I and II on the surface opposite to the shoe-sliding surface and
supported by the two balls fixed in the body 2 .
The ball is positioned eccentrically above the central axis. In the 1st speed state, therefore, the
face II is pressed against the body 2 by hydraulic oil force applied to the piston and the spring
force in the cylinder barrel and the swash plate angle becomes α. At this time, the motor is of
large capacity.
When the speed selector lever is switched to the g2nd speed position, the operating pressure is
conducted through the two-speed spool to the control room and the control piston moves until the
face II of the swash plate touches the body 2, fixing the swash plate angle at β. At this time, the
motor is of small capacity.
When the engine is stopped, the control room is connected to the drain port through the two-
speed spool and the swash plate is returned to the 1st speed position by the spring force. At the
time of starting, therefore, the motor is always in the 1st speed state.
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