Hydromechanical Transmissions and Hybrid Motion systems

In today’s society, energy efficiency and environmental friendliness are more important than ever. This is also the case for heavy construction machines, such as wheel loaders and haulers. In turn, these machines rely on hydraulics for the transmission of large flows of energy to propulsion and work functions, which stresses the importance of hydraulic systems with high energy efficiency in these machines. In RHYTHM, therefore, we study how these hydraulic systems can be improved. We focus on hybrid concepts, in which hydraulic accumulators are included in the system. A hydraulic accumulator contains gas that acts as a spring to store energy, during braking for example, and subsequently reclaim it. This technique reduces the energy consumption.

Hybrid hydraulic systems show great potential for heavy construction machines, but limited knowledge is available about how the systems should be assembled and controlled to maximise the energy savings. Computer-based tools such as simulation and optimisation are therefore important to save time and other resources. In RHYTHM, we use a special type of simulation called “hardware-in-the-loop”. This concept means that physical components are included in the simulation in real-time. Thus, some parts of the simulation represent the reality, while other parts may be included as models that can be easily modified if different systems are to be tested.

Central questions in the project:

  • How may hardware-in-the-loop simulations be used to validate a system concept?
  • How should the hydraulic accumulator be filled and emptied in order to maximise energy efficiency?
  • How should a hybrid system be controlled to reach the desired functionality?
  • How much can be gained if the hydraulic system in the transmission is connected to the working hydraulic system, together with a hydraulic accumulator?
Example of a HardWare-In-The-Loop simulation of a wheel loader with a hybrid hydraulic systemExample of a HardWare-In-The-Loop simulation of a wheel loader with a hybrid hydraulic system

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