Lull 944E-42 Service Manual - Manual (Page 411)

8.159 Model 644E-42/944E-42 Rev. 6/04
Hydraulic System
b. Four-Wheel Steering
When the Steer Select Valve (5) is in the Four-
Wheel Steer (LEFT) position (6), the Front
Wheels (7) will steer in the direction the steering
wheel is turned and the Rear Wheels (8) will
steer in the opposite direction. Return oil from the Steer
Select Valve and Accumulator Charge/Secondary
Function Valve exits the “Drain” Ports and returns to the
Hydraulic Reservoir unfiltered.
1. Four-Wheel Steering Left Turn (See page 8.118)
In the Four-Wheel Steering mode, when a LEFT turn is
made, the Power Steering Unit control valve spool is
shifted so that the system pressure from the Accumulator
Charge/Secondary Function Valve Port “CF” is applied to
the intake side of the power steering unit metering section
“P” Port. A specific amount of hydraulic oil is exhausted
from the metering section and routed to the power
steering control valve, internal to the Power Steering Unit,
exiting through Port “L” where it is channeled through the
Steer Selector Valve Port “R,” exiting through Port “2,”
then flowing to the LEFT rod end of the Rear Steering
Cylinder.
Oil from the RIGHT rod end of the Rear Steering Cylinder
flows to the Steer Selector Valve Port “1” and exits the
Port “P” becoming system pressure and flowing to the
Front Steering Cylinder LEFT rod end.
Oil from the RIGHT rod end of the Front Steering Cylinder
flows to the Power Steering Unit Port “R” and exiting
through Port “T” to the Main Control Valve, through the Oil
Cooler and then to the Return Filter in the Hydraulic
Reservoir.
2. Four-Wheel Steering Right Turn (See page 8.120)
In the Four-Wheel Steering mode, when a RIGHT turn is
made, the Power Steering Unit control valve spool is
shifted so that the system pressure from the Accumulator
Charge/Secondary Function Valve Port “CF” is applied to
the intake side of the Power Steering Unit metering
section “P” Port.
A specific amount of hydraulic oil is exhausted from the
metering section and routed to the power steering control
valve, internal to the Power Steering Unit, exiting through
Port “R” then flowing to the RIGHT rod end of the Front
Steering Cylinder.
Returning oil from the LEFT rod end of the Front Steering
Cylinder flows through the Steer Selector Valve Port “P”
and exits Port “1” to the RIGHT rod end of the Rear
Steering Cylinder. Oil from the LEFT rod end of the Rear
Steering Cylinder flows through the Steer Selector Valve
Port “2,” exiting Port “R” and back to the Power Steering
Unit Port “L,” exiting Port “T” to the Main Control Valve,
exiting the “Outlet” Port and passing through the Oil
Cooler and then to the Return Filter in the Hydraulic
Reservoir.
MU0850
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5
6
7
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MT3880