Servo-Variable Pump Drives Offer Energy Efficiency & Control


Variable-speed pump drive technology that matches pressure supply to demand is creating the ability for energy-efficient hydraulics to produce energy savings in the range of 30 percent to 80 percent. The technology also provides an option incorporating servo technology into the pump drive that creates a higher performance hybrid control that can be effectively used in traditional hydraulic applications.

Energy consumption is a key factor in the Total Cost of Ownership for machines and plants, and especially in energy-intensive hydraulic machine applications, where the energy cost contribution is often far greater than in standard machines.

New Sytronix technology from Bosch Rexroth is targeting these applications with a scalable range of variable speed pump drives. A frequency-controlled pump drive (FcP 5000) is the base variant suitable for use in constant pressure systems. The DFEn 5000 control system is designed for high power ranges using an axial piston variable displacement pump driven by an asynchronous standard motor and frequency inverter.

A third product utilizing a servo-variable pump drive (SvP 7000) incorporates servo technology to perform axis control tasks and simplify operation of hydraulic systems.

Traditional hydraulic systems have relied on fixed-speed pump technology to generate the power required to operate a machine. These pumps typically rotate continuously without regard to the actual power required by the machine at any given moment. So while innovations have led to efficiencies based on fixed-speed pump technology, there are potential energy savings to be realized by applying variable speed techniques.

Sytronix technology applies a variable-speed electric drive to rotate the pump at the speed optimal for efficiency while supplying only the hydraulic power required by the process at any given moment. They can also be integrated into existing concepts without considerable constructive effort and are suitable for increasing energy efficiency in installed machines subsequently.

Servo-variable pump drives simplify hydraulic circuit
Use of servo-variable pump drives in the SvP 7000 offer maximum performance among variable-speed pump drives to produce better dynamic control and higher precision. These units leverage the power and high dynamics of permanently excited synchronous motors to help increase the efficiency of higher performance applications, including plastics processing machines, die casting machines, and presses, even during short cycle times.

In injection molding series machines, Rexroth reports that manufacturers have consequently realized energy savings of more than 80 percent. Depending on the load cycle, the additional costs for this solution may pay off for the user within the first year of operation. Due to the control loop closed in a decentralized form, Sytronix SvP 7000 offers also possibilities for simplifying the hydraulic circuits. The precise flow rate control allows for a direct control of cylinder movements, without needing the valve technology that has been necessary until now.

The servo-variable drives behave like other electromechanical drives for the control and the Sytronix pump drive software handles all of the details and complexity of interfacing the hydraulic system. This simplifies integration of hybrid servo-hydraulic technology into new machine concepts.

Using fieldbus networking or Ethernet-based protocols, the pump drive technology fits seamlessly into various automation structures. With the drive-based IndraMotion MLD control, Rexroth is able to combine several servo-variable pump drives into one cascading system and generate higher performance. Ethernet-based, real-time cross-communication of several controls using SERCOS III allows users to synchronize an almost unlimited number of SvP 7000 pump drives in line with demand.

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