Hydraulic Power Unit - Siemens Sinumerik 840D Series Function Manual

10.03
2.3.5

Hydraulic power unit

Pressure p
Flow rate Q
Drive power P
Pump type
Filtration
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SINUMERIK 840D/SIMODRIVE 611 digital, HLA Module (FBHLA) - 10.03 Edition
The hydraulic power is supplied by a hydraulic power unit installed separately or
integrated in the machine. The power unit is configured individually to meet the
requirements of all hydraulic loads. The following factors are of particular impor-
tance:
The pressure is determined from the cylinder geometry, hydraulic characteristics
of the servo solenoid valve and other data such as load forces or flow resist-
ance values in the hydraulic circuit due to the drive speeds and forces required.
The standard value for the system pressure for machine tool feed drives is
around 40... 100 bar.
The maximum flowrate is calculated from the rapid traverse velocity.
If several cylinders are operating simultaneously, the sum of all loads must be
taken into account.
Maximum flow is often reached for only brief periods and can be supplied by an
accumulator.
The pump capacity is selected to satisfy the mean flow rate.
The power P output by the electric motor to the pump drive is calculated as the
product of pressure p, flow rate Q and efficiency η.
P=p@Q@η
Variable displacement pumps with pressure regulators in combination with an
accumulator are generally employed in order to prevent power losses and to
match the energy supply to the fluctuating delivery requirement during the cycle.
Vane pumps have proven successful in the normal pressure range for these
applications of 70 to 210 bar.
Axial piston pumps are commonly used for high-pressure applications up to 350
bar.
Classic servo-valves with fluid converters as initial stages are extremely sensi-
tive to contamination. However, even the control edges of modern servo sole-
noid valves require filtration.
To ensure general operational reliability, but more importantly, to protect the con-
trol edges against premature erosion and to maintain the quality of zero overlap,
the oil contamination must be limited in compliance with
Class 7...9 according to NAS 1638.
This is achieved by using class β
in the pressure line directly upstream of the servo solenoid valve.
The most critical phase is start-up, since contamination which has "accumu-
lated" prior to installation often causes failures. For this reason, it is advisable to
purge the system before the servo solenoid valves are fitted.
2.3 Configuring the hydraulic drive
=75 full flow filters, which must be positioned
10
2 Configuration
2-43