Future hydraulic power units will differ fundamentally from the assemblies we are accustomed to today. With its own intelligence and sensor technology, the latest generation already increased flexibility, energy efficiency and availability through condition monitoring. Simultaneously, the design has been changed to an extent previously not imaginable. The latest hydraulic power units are encapsulated, and provide optimized degassing and full capacity in the smallest installation spaces.
Hydraulic power units are self-monitoring, communicative and energy-saving
Morning routine for the maintenance technician: He calls up an app and checks the hydraulic power units in the production from his desk. A signal logic shows at a glance whether everything is OK. The button for oil condition of one power unit is yellow. The technician can now tap the button to obtain more detailed information. In this case, 75 percent of the dirt holding capacity of the filter are used up and a replacement will probably become necessary after 200 operating hours. He will check when the machine stops for the next time and then plan the maintenance works accordingly. Since the aggregate will then be maintained anyway, he will also call up all other parameters. He checks e.g. the number of switching cycles of the valves and possible anomalies of the pump. In case of critical variations, a push message would appear on his smartphone and he can take immediate action.
Condition monitoring: identify wear before it leads to downtimes
This is not a dream of the future, but the current state-of-the-art in technology for modern hydraulic power units. The idea is simple: Identify wear and errors before these lead to machine downtimes. Condition monitoring may thus increase availability and turns unexpected downtimes into planned maintenance measures. For this purpose, the hydraulic power units require sensors, an own intelligence and application experience archived in the software.
Due to the use in large-scale serial production, sensors have become so inexpensive that they now are interesting for mechanical engineering as well. A sensor package for hydraulic power units reasonably collects pressures, temperatures, filter contamination, filling level and oil condition. Further parameters such as switching cycles are also feasible. Nowadays, power units utilize variable-speed pump drives more and more frequently, thus providing us with additional data from which we derive possible wear.
Wanted: connective control systems for hydraulic power units
These data are processed in a compact control directly on the power unit. This offers the advantage that the machine control is not strained with additional computing operations. One particularly common requirement when retrofitting condition monitoring packages in installed machines is the frequently used Brownfield approach. Older control systems hardly have any power reserves and the connection of modern sensors is extremely complex. A solution with distributed intelligence usually requires far less effort – provided that it has open interfaces.
Open interfaces comprise common fieldbuses as well as Ethernet protocols. There are control systems in which all common protocols are covered with one hardware. During commissioning, a checkmark is set for the respective protocol. This reduces efforts and simplifies all logistic processes, from procurement to maintenance and replacement in a service case. In addition to this, the development of new standards enabling an information exchange with systems outside the machine world, from smartphone to the SAP system, is on the increase. OPC UA is currently established as standard for machine-to-machine communication. Web servers integrated into the control system pave the way for internet-based applications and data exchange via smartphone or tablets.
Domain knowledge of the fluid technology emulated by software
In addition to the programming in established PLC languages according to IEC 61131-3, first standard control systems also support high-level languages such as C or Java. This significantly simplifies the commissioning of sensors and new user interfaces. Experience gained during the retrofitting of hydraulic test stands in a Bosch Rexroth plant shows that maintenance technicians are able to implement such solutions within four hours. If PLC programming becomes necessary, then commissioning would take at least one man week.
At the beginning, the compact control will determine the normal condition of the power unit and, on that basis, reports critical variations. It is crucial here to keep the balance between reliably punctual warnings and unnecessary false alarms. For this purpose, the domain knowledge of hydraulics and behavior of power units must be emulated by the software. This can be realized only by suppliers with extensive experience in many hydraulic applications. At the same time, the complexity of the hydraulics must be reduced such that maintenance technicians or operators without any profound knowledge of hydraulics can understand the warning messages and rectify the causes on their service level.
The signal logic represents an approach that works all over the world. It facilitates regular checking of the system condition by technicians or by appropriate IT solutions. In case of warning messages, there are different ways to inform persons or systems. The messages can be sent to the machine control so that the operator can view them immediately on the HMI. They can also be sent to defined persons via SMS, email or a messenger service.
New design for hydraulic power units: compact, powerful, silent
In addition to condition monitoring, the new generation of hydraulic power units provides further visible changes. As installation space is valuable, it is obvious that power units follow basically new design approaches. The features of such innovative design concepts for example include a tank which is optimized for efficient degassing and reduces the oil volume by up to 80 percent. Design engineers can configure their power units online from quickly available standard components and thus reduce the time-to-market.
What is far more decisive, however, is the fact that actually everything is integrated into the housing. The housing without interfering contours accommodates all required hydraulic components as well as frequency converters, motor, pump and sensor technology in a space-saving manner. The speed control of the hydraulic power unit reduces heat introduction into the oil. The extreme compact and patented heat pipe technology is therefore sufficient for cooling in many cases.
The housing should also dampen all sources of noise to the outside. Machine manufacturers do not require any additional space-consuming and cost-intensive enclosures for compliance with international standards and requirements typical for the automotive industry concerning admissible noise emissions. The power units comply with protection class IP54.
The Rexroth CytroPac series gives us a first idea of these new hydraulic power units which are fully networked via open interfaces. This helps machine manufacturers comply with the European Ecodesign Directive 2009/125/EC for power consumption and lower CO2 emissions as well as the sometimes even stricter requirements of the automotive industry. Modern hydraulic power units are thus presenting themselves in a very elegant and networked way.
Variable-speed drives: increased energy efficiency and less noise
The use of variable speed drives is increasingly becoming standard practice. The most obvious advantage is the demand-oriented reduction of the speeds during partial or zero load operation leading to energy savings of up to 80 percent in comparison with the constantly driven power units.
Future hydraulic power units benefit from the advantages of electric hydraulics and interconnection. They are more energy-efficient and available in a more flexible way than all previous generations. In particular, they are available even today for a wide performance range, from small power units for clamping tasks in machine tools and medium power for presses and plastics processing machines to large power units for plant construction.
New design for hydraulic power units: Here more information
The new hydraulics power units CytroPac explained in 40 seconds: Watch the movie here