Hydraulic Power Unit - Siemens SINUMERIK 840D Description Of Functions

2 Configuring
2.3 Configuring the hydraulic drive
2.3.5

Hydraulic power unit

Pressure p
Flow Q
Drive power P
Pump type
Filtration
Cooling
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SINUMERIK 840D/SIMODRIVE 611 digital Descr. of Functions HLA Module (FBHLA) – 04.00 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:
This is calculated by the HYDRO 2 computation program on the basis of the
cylinder data, load forces and pressure drop across the servo solenoid valve.
The usual system pressure for machine tool feed drives is within the 40...100
bar range.
The maximum flow rate 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 E motor to the pump drive is calculated from the
product of pressure p and flow Q.
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.
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.
In order to guarantee general operational reliability, but more importantly, to pro-
tect the control edges against premature erosion and 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 means of full flow filters of class β
ranged in the pressure pipe directly before the servo solenoid valve.
The most critical phase is start-up, since contamination which has accumulated
prior to installation often causes failures. For this reason, it is advisable to purge
the system before the servo solenoid valves are fitted.
Since considerable power losses that cannot be compensated for solely
through oil reservoir dissipation occur when the flow is throttled via the control
edges on the valve, additional oil/air or oil/water heat exchangers must be pro-
vided in most cases.
P=p@Q
=75 which must be ar-
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