By Zongxuan Sun, Director of Center for Compact and Efficient Fluid Power, Department of Mechanical Engineering, University of Minnesota
Fluid power is one of the three ways for power transfer: electrical, mechanical or fluid power. The key advantages of using fluid (pneumatic or hydraulic) to transmit power include superior power density and flexibility. These advantages are well demonstrated in mobile applications such as construction machines and agriculture equipment, where large force, linear motion, and fast dynamics are required. However, fluid power systems also face several fundamental challenges, for example throttling loss and component efficiency, etc. Throttling loss refers to the fact that energy loss occurs when pressurized fluid flows through an orifice with significant pressure drop.
Today, the most common way for regulating pressure flow relationship in a hydraulic system is using a valve that is essentially a controlled orifice. The efficiencies of hydraulic pumps and motors are very high at high load and displacement, but drop quickly at low load and displacement. Fluid power researchers and engineers have been working on innovative solutions for those challenges. To name a few: independent valve metering, digital pump/motor, free piston engine pump, etc.
Yet today, the fluid power system is facing a new round of challenges as mobile applications are undergoing two significant transformations: electrification and automation. Those transformations started in the passenger vehicle segment, migrating to the commercial on-road and off-road vehicles. For on-road vehicles, the motivations are better energy efficiency, reduced environmental impact, and enhanced safety. For off-road vehicles, improved productivity is added to the potential benefits. The exact outcome of electrification and automation can be hardly predicated today, but what we know for sure is that they will bring significant changes to both on-road and off-road vehicle markets, and therefore the fluid power industry.
So how do we address the challenges of fluid power systems in the context of electrification and automation? I think a key solution is to focus on the system approach. Rather than only treating fluid power as a power transfer mechanism, we should consider it as an integral part of the whole powertrain system: the energy source, energy conversion, power transfer, and motion control.
Furthermore, we should consider fluid power and the powertrain system in the context of vehicle operation and its interactions with the environment and other vehicles. After all, the driving factors for electrification and automation are to optimize how energy is converted and used in a vehicle and the best way for vehicle operation. The system approach will allow researchers and engineers better understand the relationship of fluid power with other sub-systems for mobile applications and find new opportunities for fluid power systems enabled by electrification and automation.
Given the complexity and the intrinsic multi-disciplinary nature of the transformations driven by electrification and automation, it is important for government, industry, and academia to collaborate for developing innovative solutions. The Center for Compact and Efficient Fluid Power (CCEFP) headquartered at the Department of Mechanical Engineering at the University of Minnesota brings together more than 20 fluid power industry members and multiple universities and collaborates with national labs. The breadth and depth of expertise at the CCEFP will be a key resource for leading the new transformation of fluid power systems.