“Variable speed is the key”

Occasional Contributor

Interview with Achim Richartz

Variable speed pump drives are supposed to make hydraulic machines more effcient. If it was up to Achim Richartz, Product Manager for industrial hydraulics control systems at Bosch Rexroth, we would only talk about electro-hydraulic systems instead of electronics or hydraulics in the future.

Stand-alone axis

Mr. Richartz, you are the head of the technical product management of industrial hydraulics control systems. What exactly are your areas of responsibility?

Product management is a job which includes the entire life cycle: from the definition to the end of life, i. e. from the cradle to the grave. It starts with looking far into the future. What will our customers need in five, ten or 15 years from now – but also tomorrow. Then we have to decide how to evaluate these requirements and whether this is an attractive business segment for us, in particular if a new area or new technology is concerned. Subsequently, we have to make a decision together. The sales units and the technical units have to agree according to which plan we will proceed and what we will earn our money with tomorrow and the day after tomorrow.

What are the current challenges in the area of stationary hydraulics?

If we start with pressure generation in stationary hydraulics, there is the following challenge: Various concepts will continue to exists. What we are talking about is the combination of constant and variable displacement pumps with variable speed drive motors. The functionality and performance of these motors is scalable as well. From the asynchronous machine with speed controller to the highperformance synchronous drive.
To some extent, these overall systems are already well established, others still have to be further enhanced or completely industrialized. Regarding the general trend, it is clear to me that variable speed will become indispensable and higher maximum speeds will be a decisive factor. This means, for example, that the pumps we use will be able to pump the medium in a cavitation-free manner at higher speeds. At the same time, we have to keep the system costs in mind. A simple law is: the higher the required pressure, the higher the required drive torque and the higher the currents. This has a signifi cant infl uence on the size of the motor and the power electronics; and on the costs as well. An increase in pump speeds is called downsizing in this context.
Smart system design is the key: What does the machine cycle look like, which overall design is required, which operating points are relevant? Do I aim for corner power or average power? How do I handle the peaks in the cycle? This is what we are concerned with in the engineering and consultation process.
The next big topic is the integration in superior control architectures. At this point, Industry 4.0 comes into play. We have to design the combination of hydraulics and electronics in a reasonable manner for our customers; this means that we have to develop interfaces where users want to interfere or where there is real customer benefit.

Axial press

You are saying that these are the challenges a design engineer faces today.

It starts when a customer describes what they want and what the machine is supposed to do. Translating what the machine is supposed to do into a specification profi le is often already a challenge. The transfer of the customer’s requirements to a technical solution is controlled by the technical and commercial parameters which have to be met. In addition, the machines have architectural aspects which have to be observed.

According to your statement for the panel of fl uid experts, you think that in the future people will talk about electro-hydraulic systems and differentiate less regarding functionality and technology. Have you noticed this already?

For customers or those who have been dealing with the topic for an extended period, these worlds have not been separate for quite a while. Sometimes the term “classical hydraulics” is used. For me, this reduces it too much. People act like there were only hydraulics with on/off valves, hoses and cylinders. These are no doubt widely used but we have put a lot of effort into the development of highly dynamic servo valves or proportional valves which reflect our customer’s needs. The world is not divided into “dirty” hydraulics and shiny electric systems. These dogmas have to be overcome. They will get us nowhere. Electric hydraulics is a term we naturally use at Bosch Rexroth. It starts with proportional valves and continues with the self-contained axis with integrated cylinders, pumps, motors, converters and the corresponding software.

What are the future developments?

We are currently observing a growth trend in the direction of electric hydraulics and self-contained hydraulic axes. I deliberately avoid the word hype which has negative connotations. It implies a nice shell without contents. We, however, are working on the contents and we have customers who value this content. Whether this is a revolution or an evolution has to be considered individually. I say: In some ways it is a revolution because customers suddenly have to build their machines diff erently. This means: There has to be an architectural advantage. Do you want a highly integrated system or a discretely designed system. In our experience and opinion, both systems have merit. We assume that there will be growth in the area of integrated systems and self-contained axes. And this will aff ect a large number of applications. We can talk about the control of wind turbine blades, pitch controls, we can talk about whether it would be reasonable to equip a powder metallurgy press with something like that due to its design, we can think about equipping the carriage motion of a blow molding machine which would otherwise primarily have electrical axes with a hydraulic axis. Neither we nor our customers can foresee how far this will go. Often one axis of a machine is designed in this way at fi rst, then you experience the specifi c advantages and transfer the system to other machines.

What are the drivers?

Integrability is the most powerful driver. There will no longer be as many and proprietary interfaces as there are today. If I imagine a discretely designed system, a hydraulic cylinder, for example, already is a machine element which is designed by the machine manufacturer. And if I talk about an integrated axis with everything attached or integrated, then step by step it also develops the features of a machine element. Thanks to the information we provide together with the product, it is much easier to integrate and the purchase decision can be made based on significantly less assumptions and in a much more targeted manner. I not longer have to coordinate many different elements. This is now done by the manufacturer for the customer or by a specialist at the customer’s.

Pressure and flow control system

The bottom line is that I consider it a step forward that the discussion about different drive technologies, hydraulic and electric, has been somewhat demystified and now has more contents. The dogmas which still existed ten years ago have been eliminated. In this regard we have come a long way and everyone who offers and uses these technologies benefits from that.

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