JLG 340AJ Service Manual - Manual (Page 192)

SECTION 5 - HYDRAULICS
5-34 – JLG Lift – 3121259
5.3 DRIVE PUMP
Description
Sauer-Danfoss H1 tandem closed circuit piston pumps convert
input torque to hydraulic power.The tandem design powers
two independent drive trains for dual-path propel applica-
tions.The two-piece input shaft transmits rotational force to
the cylinder block. A splined coupling connects the front and
rear shafts. Bearings at the front, rear, and center of the pump
support the shaft. Splines connect each shaft to a cylinder
block. A lip-seal at the front end of the pump prevents leakage
where the shaft exits the pump housing.The spinning cylinder
block contains nine reciprocating pistons. Each piston has a
brass slipper connected at one end by a ball joint. The block
spring, ball guide, and slipper retainer hold the slippers to the
swash plate. The reciprocating movement of the pistons
occurs as the slippers slide against the inclined swashplates
during rotation.Via the valve plates, one half of each cylinder
block is connected to port A or C and the other half to port B
or D. Front and rear sections have independent porting in the
center section. As each piston cycles in and out of its bore,
fluid is drawn from one port and displaced to the other
thereby imparting hydraulic power into the system. A small
amount of fluid is allowed to flow from the cylinder block/
valve plate and slipper/swashplate interfaces for lubrication
and cooling.Case drain ports return this fluid to the reservoir.
An external charge pump (not shown) provides clean, cool
fluid to makeup this lubricating flow and to maintain mini-
mum loop pressure.
The angle of each swashplate controls the volume and direc-
tion of fluid displaced into the system.The servo pistons con-
trol the angle of the swashplates. Each pump control, by
varying the pressure at the servo pistons, controls each pis-
ton's position. An electric signal to the control coils transmits
the command from the operator to the pump. Mechanical
feedback of the swashplate position to the control through
the feedback pins allows for very precise displacement control
and increases overall system stability. Non-feedback control
options do not use the mechanical feedback link.
Figure 5-24. Drive Pump - Cross Sectional View