Oshkosh JLG 400S, Service And Maintenance Manual

Page: 314 / 462

SECTION 5 - HYDRAULICS
5-26 – JLG Lift – 3120895
5.6 HYDRAULIC PUMP “NEUTRAL” OR NULL
ADJUSTMENT
The pump neutral or null adjustment sets the position of
the servo piston and pump swash plate relative to the con-
trolling mechanism.
THE FOLLOWING PROCEDURE REQUIRES THE MACHINE TO BE
DISABLED (WHEELS RAISED OFF OF THE GROUND, WORK FUNC-
TION DISCONNECTED, ETC.) WHILE PERFORMING THE PROCE-
DURE IN ORDER TO PREVENT INJURY TO THE TECHNICIAN AND
OTHER PERSONNEL.
1. Disconnect machine function.(raise wheels off
ground, or chock wheels and disconnect hubs)
2. Connect a hose between gauge ports M4 and M5 to
equalize the pressure on both ends of the servo pis-
ton.
3. Install pressure gauges in gauge ports M1 and M2
to measure system pressure.
4. Start the engine and operate at Mid speed.
5. Loosen the pump “neutral” or null adjustment seal
lock nut. Turn the pump “neutral” adjustment screw
until the system pressure gauge readings are equal.
6. Turn the adjustment screw clockwise until one of the
gauges registers an increase in system pressure.
Note the position of the adjustment screw. Turn the
screw counterclockwise until the other gauge regis-
ters an increase in system pressure. Note the posi-
tion of the adjustment screw.
7. Turn the adjustment screw clockwise to a position
half-way between the position noted above. The sys-
tem pressure gauges should indicate equal pres-
sures.
8. While holding the adjustment screw in position,
Torque the seal lock-nut 15-19 ft. lb.(20 Nm-25
Nm).L
9. Stop the prime mover and remove the hose between
gauge ports M4 and M5. Remove the pressure
gauges installed in gauge ports M1 and M2. Rein-
stall the plugs in the gauge ports.
10. Reconnect work function.
5.7 NON-FEEDBACK, PROPORTIONAL
ELECTRICAL CONTROL - NFPE
The Non-Feedback Proportional Electric (NFPE) control is
a hydraulic control in which an electric input signal acti-
vates one of two solenoids which port charge pressure to
either side of the pump servo control cylinder.
Series 42 pumps equipped with an (NFPE) control have a
special servo cylinder capable of providing proportional
control with an electric input.
The pump displacement is proportional to the solenoid
signal current, but is also dependent upon the pump input
speed and system pressure. This characteristic provides a
power limiting function by reducing the pump swash plate
angle as system pressure increases. A typical response
characteristic is shown in the accompanying graph.
Features and Benefits of the NFPE Control
1. Electric Control.
2. Eliminates mechanical linkage for flexibility of con-
trol design.
3. Power limiting characteristic reduces machine
power requirements.
4. Smooth operation.
Input Signal requirements
The (NFPE) control requires a pulse-width-modulated
(PWM) input current to optimize performance. The recom-
mended PWM frequency is 200Hz. The minimum PWM
frequency is 80Hz. Coil resistance is 5.6 Ohms at 22
o
C
(72
o
F).
Table 5-3. Pump Flow Direction with NFPE Control
Input Shaft Rotation
CW
CCW
Higher Pressure into Control Port A B A B
Port “A” Flow In Out Out In
Port “B” Flow Out In In Out
High Servo Gauge Port M4 M5 M4 M5