Takeuchi TB 250, Workshop Manual

Page: 98 / 352

3-17
3
TRAVEL MOTOR
FUNCTION
When the high pressure oil directed to the port P1 is shut
off, the pressure in the port P1 becomes equal to that of
the port P2 and the spool (8) returns to the neutral posi-
tion. This pushes out the oil in the chamber B to the port
P1 side. At this time, the oil flow is narrowed down at the
orifice (9), and thus the spool (8) is slowly returned to the
neutral position. In this way, the motor can be stopped
without having a shock.
2-speed mechanism
2nd speed control valve
When the high pressure oil is directed to the motor port
M1 and the travel 2nd speed solenoid valve (1) is at the 1st
speed side position, the pressure in the chamber C is low
because it is connected to the tank passage via the 2nd
solenoid valve (1). For this reason, the spool (2) is pushed
to the left by the spring (4), and the piston chamber (3)
that controls the swash plate becomes connected to the
tank port (T). There is no force pushes the swash plate (5)
upward.
When the travel 2nd speed solenoid valve is switched to
the 2nd speed side position, the pressure oil from the travel
2nd speed solenoid valve (1) flows into the chamber C to
move the spool (2) to the right. When the spool (2) is moved
to the right, the motor port M1 is connected to the port A,
and the motor port M2 is connected to the port B. This al-
lows the pressure oil from the motor port M1 to move the
shuttle spool (12) to the right and to flow into the piston
chamber (3) that controls the swash plate. Also, the control
piston (11) is activated to push up the swash plate (5).
Since the pressure oil is not supplied when the engine is
stopped, the spool (2) is returned to the 1st speed position
by the spring (4).
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