How to save energy with hybrid hydraulic technology in working machines

Computer control makes it possible to introduce hybrid hydraulic technology into working machines. This will not only save energy but also – in the long term – make autonomous machines possible.

Viktor Larsson in his office at LiU. Photo credit: Mikael Sönne

Fascinating technique

Viktor Larsson has always been interested in tractors and other working machines. As a child, he was allowed to drive tractors on his parent’s farm, and is today proud owner of three tractors himself. He was fascinated in particular by the hydraulics: it was the only part of his childhood tractors he couldn’t quite understand.

As a research student in the Division of Fluid and Mechatronic Systems (FLUMES), Viktor Larsson has concentrated on one part of working machines – the hydromechanical transmission. In his thesis, Control of Hybrid Hydromechanical Transmissions, he describes how computers can control hybrid hydromechanical transmissions in the wheel loaders, tractors and excavators of the future.

Working machines are currently exclusively powered by diesel, but a computer-based solution would make it possible to use hybrid technology in the machines.

“I have done simulations that show that hybridisation can contribute to fuel savings of up to 50% in a wheel loader. So the new technology creates huge possibilities”, says Viktor Larsson.

Computers a must

There are several types of hybrid technology, but they all have in common that an extra energy source is connected into the machine and shares the load with the normal combustion engine, in this way saving fuel. Viktor Larsson has based his work on hydraulic accumulators, in which gas is compressed by oil, and in this way stores energy.

Viktor Larsson in the machine shop.

In order to transfer energy between the accumulator and the driving wheels, a hydromechanical transmission is required, consisting partly of mechanical gears, and partly of hydraulic pumps and motors (hydraulic components). Computers are necessary to control the transmission and its components.

“I would say that this is a necessary condition for the use of hybrid technology. Without computers it may be theoretically possible, but it just wouldn’t work in practice.”

A major advantage of using software control, in addition to opening the possibility of hybridisation, is that flexibility increases. When manufacturing pumps, for example, producers are compelled to develop different variants depending on whether the pump is to be controlled with respect to pressure, flow or power. When using software control, a single component can be controlled and used in different ways.

Simple and robust

Viktor Larsson has looked at commercially available products and shown how they can interact, following small modifications and with the necessary control. Previous research in the field has been more theoretical, and given solutions that have been difficult to carry out in practice, one reason for which may be, for example, that they are far too expensive.

It is a huge challenge to make the computer-based system as simple and robust as the traditional mechanical systems. It must also be easy to implement the control, and to make it easy to combine lower fuel consumption with stability and safety.

“That’s true, and I think I’ve managed it very well. There are physical limitations, but these are the same as for the mechanical systems”, says Viktor Larsson.

Computer control is also a requirement for the development of autonomous, self-driving working machines in the future.

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