Marginal Column

Enhanced efficiency with integrated drive technology


July 2015


It is possible to measure the advances made in boosting energy efficiency for both stationary and mobile applications. The interaction of innovative software functions with hydraulic and electric drives offers especially high savings potential.

With its power density and ruggedness, hydraulics enjoys unique characteristics among drive technologies. In modern system designs it combines these advantages with high energy efficiency. In the past, hydraulic power units often ran at maximum flow, even if not required by the process at any given moment. Today, increasing numbers of machines and systems make use of variable-speed pump drives, such as those in the Sytronix family. They regulate flow and pressure to meet current needs. When running at partial load, they lower rotation speed and thus attenuate the energy drawn by hydraulic systems in day-to-day operation. In wood processing equipment, for injection molding, and in machine tools this may reach 80 percent. In certain cases, like die casting machines, the savings may be up to 90 percent.

A new generation of hydraulic power units, dubbed the ABPAC and based on a modular design, combines this energy efficiency with tomorrow’s networking capabilities. With decentralized intelligence and optional sensor packages, these units continuously register all the operating conditions and forward them, via open interfaces, to higher-level controls or smart devices – such as smartphones or tablet PCs – that are authorized to access this information.

Hydraulic gearboxes – Electrical power splitting

But development has by no means been completed. The next step will be fully integrated hydraulics. The key word here is Hydro Gear. Regulation of the flow rate, with simultaneous adjustment of pump drive speed and the swivel angle of the pump, gives rise to a hydraulic drive than can be infinitely adjusted. This is already being used by press manufacturers for the entire upper piston drive. To handle linear movements, Rexroth has developed a line of independent axes. Identical servo drives power both electromechanical and hydraulic axes. Servo-hydraulic axes have their own fluid circuit and require no central hydraulic power unit. In this way, for example, machinery makers may achieve a specific performance level within a machinery family simply by choosing the appropriate drive technologies – with nearly identical mechanical design and software, and maximum energy efficiency.

Thanks to intelligent speed regulation, the servo-hydraulic axes attain energy consumption values comparable to axes featuring mechanical power transmission. In addition, an integral pressure accumulator can store a certain volume under pressure – also available with the motor switched off. This is especially interesting where it is necessary to avoid load peaks resulting from simultaneous starting of several large drives.

Power splitting in these fully integrated solutions is purely electrical. The servo drives in the independent axes, regardless of whether electro-mechanical or hydraulic, recover braking energies, which are made available to other using units via an intermediate circuit. In addition, it is possible to put the recovered energy in buffer storage or to return it to the power grid.


Intelligent energy efficiency

Intelligent energy management in the IndraDrive power supply, featuring the Smart Energy Mode, joins the advantages of several feed and recovery variants. Thus as much energy as possible is retained in the system and used multiple times in order to trim peak loads. This regulation system ensures that the voltage in the intermediate circuit is independent of line voltage and, at the same time, makes use of capacitors or kinetic storage. This reduces the connected power of a punching machine, at equal productivity, by as much as 25 percent. In this way all line and power supply components can be smaller.

Rexroth has also developed new concepts for electric drive technology. IndraDrive Mi, requiring no separate controls cabinet, merges the drive electronics and the motor to form an integrated unit. Thanks to continuous refinement, engineers can now place all the line power components at decentralized locations – at the machine. Manufacturers of packaging machines, in particular, utilize this option to modularize their machinery concepts and to save on the required floor space. Installers connect up to 30 IndraDrive Mi units using a hybrid cable providing the power supply and control communications. The drives, connected in series, quite simply exchange energy within their drive circuit. And there’s something else. Cooling for the controls cabinet – a real power guzzler – is also eliminated.

Smart Energy Mode

Open for multi-machine energy management

No matter whether electric or hydraulic drive: Rexroth, with Open Core Engineering, offers numerous options for linking the machines with the upper-level systems in the IT world. This concept includes all the software tools for PLC automation – and more. Rexroth is the first vendor to bridge the gap to the IT world, using the integrated Open Core Interface. Functions programmed in high-level languages make for direct access to the core of the controls and drives. End users can program their control systems to record and exert direct influence on the energy flows. In this way Bosch Rexroth has opened the gate to boosting energy efficiency along the entire value stream – within machines and for entire systems.

Open Core Engineering

Fewer exhaust emissions thanks to intelligent mobile hydraulics

In recent years, new limit values for exhaust emissions generated by mobile working machines have gradually gone into force. In the European Union, discussions have been started on toughening these laws even further. Not only can exhaust gas be cleaned; the manufacturers can often meet specifications simply by downsizing. They use smaller diesel engines and shift maximum torque to lower speeds. This has considerable effects on the hydraulics both for travel and for the implements. Working with less input energy, they have to provide the same output as in the past.

This challenge was solved by Bosch Rexroth by networking the mobile hydraulic controls with engine management. The Diesel Hydraulic Control (DHC) system reports to the diesel engine, in advance, the expected load requirements for both travel and working hydraulics. This is handled by carefully matched control units, one made by Bosch for the engine controls and one made by Rexroth for the travel and working hydraulics. In this way the diesel engine, using the DHC parameters, supplies only as much power as the mobile working machine currently requires. The results: Fuel consumption and thus exhaust emissions are lowered for telehandlers, for instance, by as much as 20 percent.

In auxiliary drives, too, intelligent solutions make for reduced consumption, as is shown by the example of hydrostatic fan drives. Fans that are coupled mechanically with the rotation speed will not provide sufficient cooling when the drive speed drops. In the hydrostatic fan drives, however, the diesel engine controls report current cooling needs to the regulation electronics for the mobile hydraulics. The fan speed is regulated to suit these needs, using a variable displacement pump. In practice, wheeled loaders, excavators, combines and on-road vehicles like buses use up to five percent less diesel fuel. That also lowers operating costs across the entire life cycle.

Diesel Hydraulic Control