2-18
Power shift control
The set horsepower valve is shifted by varying
the command current level of the proportional
pressure reducing valve attached to the pump.
Only one proportional pressure reducing valve is
provided.
However, the secondary pressure Pf (power shift
pressure) is admitted to the horsepower control
section of each pump regulator through the
pump's internal path to shift it to the same set
horsepower level.
This function permits arbitrary setting of the
pump output power, thereby providing the optimum power level according to the operating
condition.
The power shift pressure Pf controls the set horsepower of the pump to a desired level, as shown
in the figure.
As the power shift pressure Pf rises, the compensating rod (623) moves to the right via the pin
(898) and compensating piston (621).
This decreases the pump tilting angle and then the set horsepower in the same way as explained
in the overload preventive function of the horsepower control. On the contrary, the set
horsepower rises as the power shift pressure Pf falls.
(3)
Delivery pressure, (P
1
+P
2
)
Delivery flow, Q
P
f
=MAX.
P
f
=MIN.
651
625
B(E)
897
611
D
Servo piston
Large diameter
chamber
621
652
623
612
601
626
Small diameter
chamber
F
875
C
L
P
1
P
1
P
2
Pf
898
R130RE13