Therefore, hydraulics must also be adapted to better match the properties of electric machines. Switching from a combustion engine to an electric motor imposes entirely new demands on the hydraulic pump.
Ulrik Svedin
Improved efficiency
Hydraulic systems are found in all sorts of places in society, not least in large machines such as loaders and excavators. Essentially, hydraulics work by using pressurised fluid (oil) to transmit and amplify forces.
“In conventional machines, there is a single pump that pushes fluid through the system. The pump’s pressure is then adjusted to the highest pressure in the system, which means a large amount of energy is lost. Efficiency can be around 30 per cent. In an electric system, pumps can instead be placed on each cylinder or actuator. This can greatly increase efficiency” says Thomas Heeger.
At the same time, this creates new demands on the system, particularly on the pump. Thomas Heeger has studied this from several perspectives, including the importance of the pump’s position in relation to the electric motor.
“We have looked at different ways of integrating the hydraulic pump with the electric motor. We studied axial stacking – a more linear arrangement where the pump is aligned with the motor – and radial integration, where the pump is more centrally positioned and the motor surrounds it. We also examined how a gearbox can be used to reduce the motor’s torque.”
Motor position matters
The position of the electric motor affects how compact the entire system becomes. Weight and volume have become even more critical since batteries often take up a lot of space.
Ulrik Svedin
Thomas Heeger has also mapped people’s perception of simulated sound from hydraulic flow pulsations in various configurations of electrified hydraulic systems.
Speed range
“In a variable pump, the amount of oil per revolution can be adjusted. But with an electric motor, it is more natural to change the rotational speed instead. This means a wider speed range – you can run at both lower and higher speeds – which in turn offers advantages for the entire hydraulic system.”
Hidden sounds emerge
The challenge lies in the sound profile. Sounds previously masked by the diesel engine become noticeable, and higher speeds also generate more noise. Thomas Heeger developed a simulation model and converted the flow processes in the hydraulic system into an audio file.
“So that you could hear what the processes might sound like. We conducted a small survey comparing systems with displacement control and speed control – that is, rotational speed. It showed that participants preferred when the machine did not run so fast.”
Ulrik Svedin
“Yes, because higher speeds were bad for noise levels. But they were good for the machine’s compactness. This knowledge, together with the other studies, is therefore useful for the development of future hydraulics” says Thomas Heeger.
What has it been like to pursue a doctorate at Linköping University?
“It has been very rewarding. I have had the opportunity to work on my research during exchanges in South Korea and the USA. There is also strong encouragement to take general courses, such as methodology and ethics, as well as very specific courses – for example on hydraulic pumps or electric motors – which are directly useful for research” says Thomas Heeger.
Read the thesis here:
