Improving the Energy Density of Hydraulic Hybrid Vehicles (HHVs) and Evaluating Plug-In HHVs

Principal Investigators

  • Dr. Mohammad Elahinia
    The University of Toledo

Co-Principal Investigators

  • Dr. Mark Schumack
    University of Detroit Mercy


  • Dr. Walter Olson
    The University of Toledo
  • Dr. Mark Vonderembse
    The University of Toledo

Project Dates:

10/01/2007 to 12/31/2009

Project year: Year 2

MIOH-UTC Project Identifier: AF 12; Project 1 and 2

Focus Area:

  • Research: Alternative Fuels


Hydraulics (often called fluid power) offers the best solution for hybridizing heavier vehicles such as SUV's, trucks and buses to improve fuel economy.  Using conventional gasoline engines under a parallel hybrid, US EPA/NVFEL testing and modeling programs project a 34% fuel economy improvement for a large 4WD SUV. This research project aims at addressing one of the main limitations of hydraulic hybrid vehicles (HHVs). These hybrid vehicles capture the otherwise-wasted-energy in mechanical batteries (hydraulic accumulators).

The hydraulic accumulators allow for rapid charging and discharging, which translates to very high power density in hydraulic hybrid vehicles.  This feature is the main benefit of these vehicles over electric hybrids.  The energy density of the HHVs on the other hand is limited by the amount of fluid that can be stored in the high pressure accumulators.mentation to address this energy density limitation of the hydraulic hybrid vehicles. A compressed air reservoir will be integrated into the hydraulic hybrid system. In addition to improving the energy density and providing longer operation for the vehicle, this new system will provide the electric plug-in capability for HHVs.

This project is entering the second year of research in 2008-09.

Final Report:


Total Budget: $208,402 for two years


US DOT, MDOT, The University of Toledo, University of Detroit Mercy