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Test Beds

Highway Vehicles - Hydraulic Hybrid Passenger Vehicle (Test Bed 3)

  • Hybrid Car Slideshow
  • Hybrid Car Slideshow
  • Hybrid Car Slideshow
  • Hybrid Car Slideshow


See video of the HHPV test bed and learn about the CCEFP's infrastructure for this project.


Prof. Perry Li, University of Minnesota

Statement of Test Bed Goals

The overall goal of this project is to realize hydraulic hybrid powertrains for the passenger vehicle segment which demonstrate both drastic improvements in fuel economy and good performance. As a test bed project, it also drives and integrates associated projects by identifying the technological barriers to achieving that goal.  The design specifications for the vehicle include: (i) fuel economy of 70 mpg under the federal drive cycles; (ii) an acceleration rate of 0-60 mph in 8 seconds; (iii) the ability to climb a continuous road elevation of 8%; (iv) meeting California emissions standards; and (v) size, weight, noise, vibration and harshness comparable to similar passenger vehicles on the market.  Resulting powertrains must demonstrate advantages over electric hybrids to be competitive.

Test Bed Role in Support of Strategic Plan

Test Bed 3 directly supports goal 2: improving the efficiency of transportation.  Efficiency is achieved by utilizing fluid power to create novel hybrid powertrains for passenger vehicles.  The powertrains integrate high efficiency components and hydraulic fluids (thrust 1), compact energy storage (thrust 2) and methodologies for achieving quiet operation (thrust 3) from related CCEFP projects.

Description and Explanation of Research Approach

The high power density of hydraulics makes it an attractive technology for hybrid vehicles since it should be able to provide both high mileage and high performance.  A few hydraulic hybrid vehicles have been developed for heavy, frequent stop-and-go applications such as garbage or delivery trucks. However, hydraulic hybrids have not yet reached the much larger passenger vehicle market. In order to succeed in this market, hydraulic hybrid drivetrains must overcome limitations in component efficiency, energy storage density, and noise. These barriers represent worthwhile challenges that stretch the envelope of existing fluid power technologies. 

Electric hybrids provide the closest competition to hydraulic hybrids.  While hydraulic hybrids cannot match the energy density provided by electric batteries, they have superior power density.  This is particularly valuable for regenerating braking energy.  Furthermore, hydraulic hybrids eliminate the need for batteries, and thereby eliminate the cost, life and environmental concerns associated with them.

Three possible families of architectures for hybrid drivetrains are series, parallel and power split. A series drive transmits all power from the engine to the wheel with hydraulic pumps and motors.  This architecture enables running the engine at its most efficient combination of torque and speed; however, it cannot take advantage of the high efficiency of purely mechanical power transmission through a shaft.  A parallel architecture augments the engine with a pump/motor.  It transmits power to the wheels through the efficient mechanical shaft, but it has less ability to keep the engine at its best operating point. TB3 focuses on power split architectures, which combine the positive aspects of both approaches. 

This test bed is currently developing two hydraulic hybrid passenger vehicles, each of which offers unique research benefits.   The “Generation I” vehicle (see Fig. 1) was built in-house using the platform of a utility vehicle (Polaris “Ranger”).  The vehicle has been outfitted with a modular powertrain.  This enables experimenting with different pump, motor and energy storage technologies, including those developed in complementary CCEFP projects.  However, this vehicle cannot be driven at speeds higher than about 25 MPH due to concerns about vehicle stability.

 TB1 Gen 1 Vehicle

Figure 1: Test Bed 3 Generation I vehicle


Hydraulic Dyno

Figure 2: Hydrostatic dynamometer connected to
the output shaft of the vehicle transmission

The “Generation II” vehicle is being developed in partnership with Folsom Technologies International (FTI).  It is built on the platform of a F-150 pickup truck, which has refined vehicle dynamics capable of highway speeds.  Its power-train utilizes a custom-built continuously variable power split hydraulic transmission developed by FTI which will be complemented with hydraulic accumulators to enable hybrid operation. The powertrain is built as a compact, integrated, self-contained package. However, the integrated package prevents changing the hydraulic pump/motors or instrumenting them individually.  Also, the transmission is not optimally sized for hybrid operation and presents some control restrictions when operated in hybrid modes.  Therefore, the “Generation I” vehicle is being continued despite the pending availability of the roadworthy “Generation II” vehicle.


[1]    Rannow, M., Li, P., Chase, T., Tu, H., and Wang, M., 2010. “Optimal design of a high-speed on/off valve for a hydraulic hybrid vehicle application”. Proceedings of the 7th International Fluid Power Conference, Aachen, Germany.
[2]    Cheong, K. L., Li, P. Y., Sedler, S. P., and Chase, T. R., 2011, “Comparison Between Input Coupled and Output Coupled Power-Split Configurations in Hybrid Vehicles”, 52nd Nat Conf on Fluid Power (Paper 10.2), Las Vegas, NV.
[3]    Richard Stone, “Introduction to Internal Combustion Engines”, SAE International; 3rd Edition, 1999.
[4]    C. T. Li and H. Peng, 2010, “Optimal Configuration Design for Hydraulic Split Hybrid Vehicles”, Proceedings of the American Control Conference, Baltimore, MD, 2010.
[5]    P. Y. Li and F. Mensing, 2010, “Optimization and control of hydro-mechanical transmission based hydraulic hybrid passenger vehicle”, Proceedings of the 7th International Fluid Power Conference (IFK), Aachen, Germany.
[6]    D. R. Grandall, Performance and Efficiency of Hydraulic Pumps and Motors, M.S. Thesis, Department of Mechanical Engineering, University of Minnesota, January, 2010.
[7]    T. P. Sim and P. Y. Li, 2009, "Analysis and Control Design of a Hydro-Mechanical Hydraulic Hybrid Passenger Vehicle", Proceedings of the ASME 2009 Dynamic Systems and Control Conference #2763, Hollywood, CA.
[8]    Haink C. Tu, et. al., “High-speed 4-way rotary on/off valve for Virtually Variable Displacement pump/Motor Applications”, in Dynamic Systems and Control Conference, Arlington, VA, November 2011.
[9]    Cheong, K. L., Li, P. Y., and Chase, T. R., 2011, “Optimal Design of Power-Split Transmission for Hydraulic Hybrid Passenger Vehicles”, 2011 American Control Conference, San Francisco, CA, pp. 3295-3300.
[10]    Herzog, S., Zink, M. and Michael, P., 2009, “Hydraulic Fluid Viscosity Selection for Improved Fuel Economy”, SAE Journal of Commercial Vehicles, 2(2): 61-65.
[11]    Michael, P., Wanke, T., Devlin, M., et al., 2010. “An Investigation of Hydraulic Fluid Properties and Low-Speed Motor Efficiency”. Proceedings of the 7th International Fluid Power Conference, Aachen, Germany, Vol. 3, pp. 341-353.
[12]    Z. Du, K. L. Cheong, P. Y. Li and T. R. Chase, “Fuel Economy Comparisons of Series, Parallel and HMT Hybrid Architectures”, To be presented at the 2013 American Control Conference, Washington D.C., June 2013.  


Polaris Ranger