Hydraulic Power Unit - Siemens SINAMICS S120 System Manual

Configuration
3.3 Configuring the hydraulics
3.3.5

Hydraulic power unit

The hydraulic power is supplied by a hydraulic power unit installed separately or integrated
in the machine. The power unit is individually configured to meet the requirements of all
hydraulic loads. The following individual factors are of particular importance:
● Pressure p
● Flow rate Q
● Drive power P
● Pump type
● Filtration
● Cooling
Pressure p
The pressure is determined from the cylinder geometry, hydraulic characteristics of the servo
solenoid valve and other data such as load forces and flow resistance 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.
Flow rate Q
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.
Drive power P
The power P output by the electric motor to drive the pump is calculated as the product of
pressure p, flow rate Q and efficiency η.
P = p × Q × η
Pump type
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 flow rate required during the cycle.
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System Manual, 04/2015, 6SL3097-4BA00-0BP1
Hydraulic Drive