Komatsu Galeo PC800-8 Shop Manual page 196

SEN00384-02
2) At high speed (automatic 2nd)
• When the pilot signal is ON, pilot pressure PI
from the control pump acts on travel speed se-
lector valve (1) and the capacity is automatically
changed by the drive pressure of the travel mo-
tor.
Balance of force for travel speed selector valve
F1 [Force pushing spool (1a) to right (high-
speed side)] = A (area of spool (1a) receiving
pressure) × PI
F2 [Force pushing spool (1a) to left (low-speed
side)] = A (area of spool (1a) receiving pressure)
× PH (motor drive pressure) + force of spring
(1b)
i) When traveling on level ground, if the travel
motor drive pressure is low, the condition
becomes F1 > F2, and spool (1a) is pushed
to the right.
When this happens, the main oil pressure
(M1, M2) passes through spool (1a) and
goes to the control piston chamber. Rocker
cam (14) overcomes moment Mx with
34
10 Structure, function and maintenance standard
hydraulic force from propulsion force Fc of
control piston (10). It rotates and holds the
moment balance at the high speed surface
and is held in position (Mx < Fc, L).
ii) When operating the steering or traveling
uphill, if the motor drive pressure is high, and
it goes above the set pressure, the condition
becomes F1 < F2, and spool (1a) is pushed
to the left.
When this happens, the main oil pressure
(M1, M2) passes through spool (1a) and is
drained to the motor case. This creates the
low-speed condition in the same way as
when PI = 0.
PC800, 850-8