Highway Vehicles - Hydraulic Hybrid Passenger Vehicle (Test Bed 3)
See video of the HHPV test bed and learn about the CCEFP's infrastructure for this project.
Prof. Perry Li, University of Minnesota
With a growing number of passenger vehicles worldwide and a subsequent increasing strain on petroleum reserves, demand is increasing for improved vehicle efficiency without a sacrifice in performance. To address this demand, the CCEFP is developing a hydraulic hybrid power-train with drastic improvement in fuel economy and good performance to be competitive with other technologies such as electric hybrid, for the passenger vehicle segment. TB3 focuses on power split architectures which combine the positive aspects of the Series Hybrid (allows engine to operate efficiently independant of vehicle speed) and Parallel Hybrid (transmits power through the efficient mechanical drive shaft).
Test Bed 3 Generation I vehicle at 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 excellent 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) emissions meeting California standards; and (v) size, weight, noise, vibration and harshness comparable to similar passenger vehicles on the market. Power trains produced in the scope of this project 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 hydraulic assist to enable operating the engine at or near its “sweet spot” and regenerating brake energy. The power trains integrate high efficiency components, hydraulic fluids and energy management algorithms (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 them an attractive technology for hybrid vehicles, especially since the battery required for electric hybrids can be eliminated. 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 drive trains must overcome limitations in component efficiency, energy storage density, and noise. These barriers represent worthwhile challenges that stretch the envelopes of existing fluid power technologies.
TB3 focuses on power-split architectures, which are not as well studied as other hydraulic hybrid architectures. Power-splits combine the positive aspects of a series and parallel drive train. This test bed is currently developing two hydraulic hybrid passenger vehicles, each of which offers unique research benefits. The “Generation 1” vehicle (Figure 1) was built in-house using the platform of a utility vehicle (a Polaris “Ranger”) connected to an in-house built hydrostatic dynamometer. The vehicle has been outfitted with a modular power train. This enables experimenting with different pump, motor and energy storage technologies, including those developed in complementary CCEFP projects.
The “Generation 2” 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 power train is built as a compact, integrated, self-contained package. However, the integrated package prevents changing out 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 1” vehicle is being continued despite the pending availability of the roadworthy “Generation 2” vehicle.
Figure 1: Overview of Test Bed 3 HHPV Generation 1 with hydro-static dynamometer. The graphs on the right illustrate the effectiveness of the dynamometer in fuel economy evaluation.