Three-Mode Steering Circuit Descriptions - JLG sky trak mmv Service Manual

5
9.8.31 Three-Mode Steering Circuit
Descriptions
Vehicle three-mode steering includes front-wheel steer-
ing (see page 9.56 and page 9.58), four-wheel steering
(see page 9.60 and page 9.62) and crab steering
(see page 9.64 and page 9.66).
a. Front-Wheel Steering
When the steer select switch (5) is in the front-
wheel steer (forward) position (6), the front
wheels (7) will steer in the direction the steering
MT3870
wheel is turned and the rear wheels (8) will re-
main fixed.
1. Front-Wheel Steering Left Turn (See page 9.56)
In the front-wheel steering mode, when a left turn is
made, system pressure from the accumulator charge
valve is applied through the intake side of the metering
section of the power steering unit.
Model MMV Rev. 12/04
6
7
5
8
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, where it is chan-
neled through the steer select valve to the left rod end of
the front steering cylinder. Both solenoids in the steer se-
lect valve are de-energized.
Oil from the right rod end of the front steering cylinder
flows to the power steering unit, then to the return filter in
the reservoir.
2. Front-Wheel Steering Right Turn (See page 9.58)
When a right turn is made, the steering unit spool is shift-
ed so that system pressure from the accumulator charge
valve is applied to the intake side of the metering section
of the power steering unit.
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, where it is chan-
neled to the right rod end of the front steering cylinder.
Oil from the left rod end of the front steering cylinder flows
through the steer select valve to the power steering con-
trol valve, then to the return filter in the reservoir. Both so-
lenoids in the steer select valve are de-energized.
Hydraulic System
MM1800
9.81