JLG 1250AJP Service Manual - Manual (Page 52)

SECTION 3 - 1CHASSIS & TURNTABLE
3-4 – JLG Lift – 3121171
4. Ensure the arm will clear the axle (without bottoming
out to 70° stroke of the switch) in the retracted posi-
tion.
5. Check for proper operation. Axle set light is to deac-
tivate when the axle is retracted 0.625 inches (16
mm) maximum from fully extended.
3.4 DRIVE SYSTEM
The drive system utilizes 2 traction pumps so each side is
powered individually. This produces maximum tractive
effort to wheels by minimizing flow divider losses. The
maximum drive speed is modulated with the steered
angle of the wheels to eliminate the whiplash effect of driv-
ing at full speed and maximum steering lock.
3.5 STEERING CONTROL SYSTEM
Each wheel is individually steered by means of a closed
circuit control system utilizing a steer sensor on each
wheel, 4 steer cylinders, and proportional valves.
The control system senses the wheel position in relation
to the steering command (direction and steering mode)
and automatically synchronizes the movement of all 4
wheels to the desired position.
There are three different modes of steering selectable by
the position of the steer select switch on the platform con-
trol panel: conventional two wheel steering, crab and
coordinated. These are shown below.
Each wheel has its own steer cylinder, wheel angle sensor,
and proportional valve, allowing the control system to
position each wheel to the ideal angle for all steering
modes and all steering commands.
Changes in steering modes while the footswitch is
depressed causes the wheels to automatically adjust to
the appropriate angle for the selected steering mode
based on the position of the inside front wheel. If the steer
select switch is changed without the footswitch being
depressed or when the EMS is off, the wheels will not
move until the footswitch is depressed and a steering or
drive command has been initiated.
The steering angles are limited to ±25 degrees anytime
the axles are not fully extended. See the Axle Extension
System (see Section 3.2, Axle Extension System) for inter-
action with the axle extension system.
If a wheel cannot achieve its commanded angle within a
specified time, it is considered jammed. When a wheel is
considered jammed during steering, a fault is reported
and the remaining wheels will continue to their com-
manded position. The fault is cleared when the footswitch
is cycled.
If a wheel is jammed making it significantly out of position,
with regard to the other wheels, the drive motors are
restricted to their maximum displacement (slow speed).
Figure 3-2. Conventional Two Wheel Steer Mode
Figure 3-3. Crab Steer Mode
Figure 3-4. Coordinated Steer Mode