Fluid Power Research News: CCEFP Investigates Vane Pump Power Split Transmission

We’ve written before about the Center for Compact and Efficient Fluid Power (CCEFP)—the network of fluid power research laboratories, academic faculty, graduate and undergraduate students at seven universities—that is making a difference when it comes to preparing a better educated workforce for the fluid power industry. The CCEFP has created a 500% increase in the number of fluid power focused advanced degrees awarded in the United States, with almost half of its graduates going on to work in the fluid power industry.


In addition to increasing interest in fluid power, the CCEFP has also been home to a number of research projects in fluid power. One such project involves investigating vane pump power split transmission.

Biswaranjan Mohantyby Biswaranjan Mohanty
PhD Candidate, University of Minnesota

Vane pump power split transmission is a new type of transmission using a novel vane pump technology. The key component of this transmission is vane pump power split unit (VPSU). The unit splits the input mechanical power into the hydraulic and mechanical paths. The hydraulic power is fed to a variable displacement motor to amplify the torque on the output shaft. Due to smooth shifting of displacement of the variable motor, every possible gear ratio can be achieved. It gives more freedom to operate the engine in the most efficient zone. Hence a better fuel economy. The power split unit has an integral clutch which decouples the output shaft from the input shaft. The transmission is simple in design and cost effective.  The schematic of the transmission is shown in Fig.1.

Fluid power research diagrams

The power split unit is based on a balanced designed double acting vane pump. Therefore it has longer lifetime. It is a quieter in operation and compact too.  In conventional vane pump, the floating ring is fixed. However, in the power split unit floating ring is coupled to the output shaft and allowed to rotate. Some of hydraulic power transmit to output shaft through the rotating floating ring. The power sharing fraction between hydraulic path and mechanical path is adjusted by controlling the hydraulic flow. With a pilot pressure command from the hydraulic system, a tapered pin in the rotor is hydraulically actuated to retract the vanes. This decouples the output shaft from the input shaft, lowering the viscous drag on the rotor, or parasitic loss. By blocking the flow in the hydraulic path, the input and the output shaft rotates at the same speed. This lock up function creates an efficient direct drive for high speed. The components of the power split unit is shown in Fig.2.

About the author:
Biswaranjan Mohanty received his BTech degree in Mechanical Engineering from National Institute of Technology Rourkela, India, in 2009. He has worked as a Design and development engineer in TATA Hitachi Construction Machinery, India from 2009-2013. During his work, he was involved in hydrostatic wheel loader and hydro-mechanical motor grader projects. He is a Ph.D. candidate in Mechanical Engineering under the supervision of Dr. Kim A Stelson. He is interested in design and control of mechanical system. His current focus on hydrostatic transmission for wind turbine and Vane Pump Power Split Transmission for a class 1 pick-up truck.

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