Control Options - Sauer Danfoss 45 Series Service Manual

ContRoL oPtions

(continued)
14
Series 45 G Frame Open Circuit Axial Piston Pumps
Service Manual
Features
LS control
The LS control design matches pump
flow with system demand.The LS control
senses the flow demand of the system
as a pressure drop across the external
Control valve (ECV). As the ECV opens
and closes, the pressure delta across
the valve changes. When opening, the
delta decreases. When closing, the delta
increases.The LS control then increases
or decreases pump flow to the system
until the pressure delta becomes equal
to the LS setting as defined by the LS
adjusting plug (7) and spring (8).
Cross-section LS control
Spring
Spring
8
guide
9
Spool
Plug
Plug
Spring
6
Spool
Spring
(PC heavy)
guide
Ls spool shifts to port system pressure to servo
is applied to the spring end.This arrangement allows the LS spool to act on the delta
between system pressure and LS pressure.The LS spring sets the threshold of operation
(LS setting).
Because the swashplate is biased to maximum angle, the pump attempts to deliver
full flow to the hydraulic system. When the flow being delivered exceeds demand, the
pressure delta across the ECV is great enough to overcome spring force and shift the
LS spool porting system pressure to the servo piston.The pump de-strokes reducing
flow until the delta across the ECV becomes equal to the LS setting. When flow being
delivered is less than demand, the delta across the ECV drops below the LS setting and
the LS spring shifts the spool connecting the servo piston to pump case.The pump
strokes increasing flow until the delta across the ECV becomes equal to the LS setting.
When the external control valve is placed in neutral, it connects the LS signal line to
drain. With no LS pressure acting on the non-spring end of the LS spool, the pump
adjusts stroke to whatever position necessary to maintain system pressure at the LS
setting.The pump is now in standby mode.
Because of the series arrangement of the LS and PC spools, the PC spool will override
the LS spool. If at any time system pressure reaches the PC setting, the PC spool will shift
blocking the passage that connects the LS spool with the servo piston, thus porting
system pressure to the servo piston causing the pump to destroke.
520L0605 • Rev AB • December 2010
Typical load-sensing control valve
2
Load sense
pressure
The LS control consists of two spool
valves that connect the servo piston
either to pump case or system pressure.
The PC spool (6) controls the pressure-
compensating function of the control
LS spring
as previously described.The LS spool (9)
7LS adjusting
controls the load-sensing function.The
plug
PC adjusting PC spool has priority over the LS spool.
plug
Through internal porting, system
pressure (upstream of ECV) is applied
P104 051
to the non-spring end of the LS spool,
and through hydraulic line connected at
piston
port X. LS pressure (downstream of ECV)
Load Return
pressure pressure
Tank
System
2
pressure
Pressure drop across external control valve
defines system demand
P101 665E