Electrification and digitalization: The fitness program for hydraulics

A man showing advantages of electrification and digitalization for industrial hydraulics

High power density, robustness and modular design: Even today, hydraulic systems are still an essential factor in the world of production. However, how future-proof is fluid technology?

Fully hydraulic, fully electric, hybrid. These terms are often used in connection with the topology of drives but are only defined more or less exactly. Often, they suggest a competition between hydraulics and electrics that does not even exist in modern machine designs.

Electric, hydraulic hybrid

In industry, practically all machines and applications are supplied with electric energy. For transmission of forces, electrically driven machines use mechanical and fluidic (hydraulic/pneumatic) transmissions. Electro-hydraulic as well as electro-mechanical machines are "fully electric". "Hybrid machines" are applications with mixed types of transmission while no individual axes are featuring classical hybrid drive structures. Industrial hydraulic axes are fully electric: Electric motor, servo controller, sensor technology and software are parts of electro-hydraulic drive systems.

As transmission design, hydraulics is up against mechanical solutions. The seeming reduction in hydraulic systems applied in transmissions does not reduce the relevance of hydraulics for drive technology. Quite the contrary. An example can be found in injection molding machines. At the turn of the millennium, a drastic decrease in fully hydraulic injection molding machines in favor of fully electric machinery was predicted. However, hydraulics remains the most dominant transmission design in the industry. Why is that so?

Automation and energy efficiency are among the reasons for the requirement for modern primarily controlled electrical servo drives. These drives can be equally applied in mechanics and hydraulics. Today, machines are mainly driven by electrical synchronous motors, either mechanically via transmissions and spindles or hydraulically via Sytronix variable-speed pump drives, cylinders and hydraulic motors. Although this technological transition took place, it did not affect the relevance of hydraulics.

Amongst others, the advantages of classical hydraulics include robustness, power density and an easy way of power distribution. The disadvantages of throttle control, fixed speed pumps and analog technology include power consumption, noise behavior and poor automation capability. In terms of mechanics, the situation is the complete opposite: Power consumption, noise behavior and automation capability are among the advantages. Robustness, power density and power distribution come off worse. For technical reasons, mechanics consequently makes use of the advantages of electrics.

Decentralized intelligent drives

Rexroth Sytronix variable-speed pump drives are a good example for the increase in electrification and digitalization in hydraulics. They unite the above mentioned advantages by combining the physical advantages of hydraulics with the functionality of electronics. Thanks to the use of servo motors, the power consumption, noise and automation capabilities of electro-mechanical systems can be achieved without compromising the advantages of hydraulics. This leads to reductions in noise by 20 db(A) and energy savings of up to 80 % in contrast to previous conventional solutions and this is just the beginning of a series of further improvements.

Technology in the course of time

The transition in technology is a combination of numerous factors. Technical basic conditions and timing are playing a decisive role in the market. One example from the field of consumables: In 1993, Apple launched "Newton", its first tablet computer. However, without success: Good displays and batteries and particularly software apps and mobile broadband Internet access had not yet been available. In 2010, the product innovation made its second attempt. Apple released the iPad and achieved a breakthrough in this product category. Other manufacturers followed with similar devices changing the market considerably. The sales of notebooks dropped clearly in favor of tablets.

Another example is the transition to digital photography. Before any transition, new solutions first need to pass the comparison with established technologies. Before digital cameras could match analog photography in basic areas like costs, picture resolution and quality, their market share had been very low. In 2003, the situation changed quickly and irreversibly. The analog basic characteristics were fulfilled. Additionally, the new technology helped to realize functions that had not been possible using the old technology or only with disproportionately great effort including live view, memory cards, copying and post-processing, Facebook, miniaturization or the integration in smartphones, cars or IP cameras. The transition is disruptive and any new development in the previous technology to catch up is bound to fail.

What are the consequences for the transition in technology in electric hydraulics, for example for Sytronix pump drives? The technology has been available for a long time but was not able to stand the comparison with fixed speed pumps before 2000 due to their performance data and costs. Reduced costs and improved performance data in electrics and electronics enabled the increasing application of the technology. Today, energy savings of up to 80 % and noise reductions of 20 db(A) are clear sales arguments.

ETO solution SHA250, SHA040 and SHA010 electro mechanical cylinders, Hydraulic drive with electrical power distribution

Figure right: SHA self-contained hydraulic actuator, 100 to 2,500 kN (10 to 250 t)

Electronics open up new possibilities for hydraulics

The disruptive transition in technology is sealed by additional advantages: The digital-electronic servo controller of Sytronix pumps opens up all possibilities of modern electronics. Electric power distribution, software functionality, automation, tele-service and interconnectivity are topics that were hardly realized using old technology or only realized with disproportionately great effort. Numerous additional aspects like staff qualification, know-how protection, storage management, product portfolio or condition monitoring are increasing indicators for digital solutions and replace analog technology. Today, future requirements are still unknown or only partially known. Digital technology is more future-proof, analog technology and Connected Industry are incompatible.

Due to these volatile markets and market requirements, suppliers, machine manufacturers and end users are facing increasing challenges. When selecting their suppliers, the machine manufacturers and end users of today not only ask for costs, product and supply performance. The decisive criterion for selecting a business partner is the question: Do I have the right supplier and development partner for the next years to overcome the challenges in face of the transition in technology? Companies making the wrong decision may be quickly left behind. The innovation cycles have become considerably shorter. This is a particular challenge in the field of classical mechanical engineering.

As a leading supplier of Drive & Control solutions, Bosch Rexroth take up this challenge in its own products and the applications at its own plants. The automation specialists can draw on experience and an extensive network in the parent company.

System layout with a future

For hydraulics, this means: Electrification and digitalization are increasingly applied and analog solutions are replaced. This not only has consequences for the used components. Particularly the general system layout is changing.

This potential transition can be clarified using the example of hydraulic cylinder drives:

Hydraulic cylinder transition to electric and digital components system layout

Figure: From open circuit to direct drive

The power-distributed and valve-controlled cylinder drive in an open circuit with central unit is a proven and widespread topology. High toughness, flexibility and low investment costs are advantages that are gained at the cost of comparatively low energy efficiency. By means of Sytronix pumps, high-response valves and throttling points can be partly avoided. The result is a power-distributed central unit with increased energy efficiency and less noise (see figure above, 2-quadrant pump/valve control, open circuit).

The clearly reduced power loss enables a change in system layout (see figure above, 4-quadrant pump control, with and without pendulum volume). Cylinder direct drives using Sytronix pumps in closed circuits transfer power distribution from the hydraulic circuit to the electric intermediate circuit. The axis does not require a classical cooler or oil tank. Externally, these hydraulic and self-contained axes resemble electro-mechanical solutions. The advantages of hydraulics in comparison to mechanics – power range, toughness, life cycle, overload capacity, speed reduction ratio and transmission adjustability (in steps by surface switching or steplessly using variable displacement pumps), force holding without power consumption, emergency travel properties – remain fully retained.

All these advantages are similarly available for low and medium performance ranges from a few kilowatts up to several megawatts. For example, for linear hydraulic direct drives. For this purpose, Rexroth offers a range of modular products with standardized self-contained axes. Self-contained hydraulic actuators, SHA units, cover applications of 100 to 2,500 kN with a maximum velocity of 1 m/s and a stroke of 1,800 mm. For a force range under SHA units, Bosch Rexroth offers electro-mechanical cylinders, EMC and EMC-HD units, from 10 to 290 kN with a maximum velocity of 1 m/s and a stroke of 1,700 mm. The system layout can be applied for power ranges over SHA250 and is available as ETO solution.

Hydro gear electric scheme with kinetic buffer layout diagram and safety badges

Figure: Main voltage 3~400V

Power press ram with hydrogear and power press without hydrogear position power diagram

Figure: Hydrostatic servo-eccentric press, system structure, energy monitor

The advantages of hydrostatic transmissions in comparison with mechanical transmissions include stepless adjustability, full torque at every operating point of the plunger and reduced electric peak performances by application of the motor pump combination as kinetic accumulator. Just as mechanical drives, hydraulic drives are also implemented into the electric system, automation and connection of machinery.


Using throttle-free power provision and control according to requirements, electrification and digitalization of the hydraulics enable increased energy efficiency and reduced noise. Besides hydraulic power distribution, hydraulics today may also optionally apply electric power distribution. Thanks to digital-electrical functionality, hydraulics are today 100% "Ready for Connected Industry".

Operators do not need to sacrifice the well-known advantages of hydraulics including toughness, maximum forces and power density. Electrification and digitalization make hydraulics fit for the future.

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