3-18
3
TRAVEL MOTOR
FUNCTION
Swash plate
The swash plate (5) has three planes of A, B and C, as
shown in the figure, and it is mounted to the flange holder
(6) in such a way that its angle of inclination to the flange
holder (6) can be changed by means of the two steel balls
(7).
When
the 2nd speed control valve is switched to the 1st
speed side, the swash plate control piston chamber (3) is
connected to the tank port. Also, the swash plate (5) is
stabilized at the surface “A” by the forces of the piston as-
sembly
(8), resulting in the angle of “α” that can run the
motor at the 1st speed.
When
the 2nd speed control valve is switched to the 2nd
speed side, the swash plate control piston chamber (3)
is connected to the motor drive pressure port. Also, the
swash plate (5) is stabilized at the surface “B” due to the
equilibrium between the force of the springs (9), (10) and
the force of the 2nd speed control piston (11), resulting in
the angle of “β” that can run the motor at the 2nd speed.
When
the engine is stopped, the pilot pressure of the 2nd
speed control valve is cut off, so the swash plate (5) is sta-
bilized
at the surface of “A” with the angle of “α”, resulting
in
the 1st speed side. For this reason, when starting the
engine, the motor always is set to the 1st speed.
Automatic 2-speed switching system
When a load greater than the set value is applied to the
travel motor during traveling in the 2nd (high) speed, the hy-
draulic
pressure working on the counter balance, passage
(1) and the valve becomes high. This moves the valve (2) to
the left. Once the valve (2) is moved to the left, the pressure
oil that has been flowing through the shuttle valve (12) and
the valve (2) to work on the piston (11) is now flowing into
the tank passage. The piston (11) returns, and the motor is
switched to the 1st (low) speed.
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