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This study undertakes an investigation of the effect of battery charge balance in hybrid electric vehicles (HEVs) on EPA fuel economy label values. EPA's updated method was fully implemented in 2011 and uses equations which weight the contributions of fuel consumption results from multiple dynamometer tests to synthesize city and highway estimates that reflect average U.S. driving patterns. For the US06 and UDDS cycles, the test results used in the computation come from individual phases within the overall certification driving cycles. This methodology causes additional complexities for hybrid vehicles, because although they are required to be charge-balanced over the course of a full drive cycle, they may have net charge or discharge within the individual phases. As a result, the fuel consumption value used in the label value calculation can be skewed.

The objective of this work is to provide a relatively simple battery energy storage and loss model that can be used for technology screening and design/sizing studies of hybrid electric vehicle powertrains. The model dynamic input requires only power demand from the battery terminals (either charging or discharging), and outputs internal battery losses, state-of-charge (SOC), and pack temperature. Measured data from a vehicle validates the model, which achieves reasonable accuracy for current levels up to 100 amps for the size battery tested. At higher current levels, the model tends to report a higher current than what is needed to create the same power level shown through the measured data. Therefore, this battery model is suitable for evaluating hybrid vehicle technology and energy use for part load drive cycles.

The Hybrid Electric Vehicle Team of Virginia Tech (HEVT) is participating in the 2005 - 2007 Challenge X advanced technology vehicle competition series, sponsored by General Motors Corporation, the U.S. Department of Energy, and Argonne National Lab. This report documents the Equinox REVLSE (Renewable Energy Vehicle, the Larsen Special Edition) design and specifies how it meets the Vehicle Technical Specifications (VTS) set by Challenge X and HEVT through simulation and test results. The report also documents the vehicle control development process, specifies the control code generation, demonstrates an analysis of hybrid powertrain losses, and presents the REVLSE vehicle balance in its intended market.

For a hybrid electric vehicle (HEV) with an internal combustion engine, simply operating the engine in its regions of high efficiency does not guarantee the most fuel efficient operational strategy. This paper defines an operational strategy for a HEV through calculating individual powertrain component losses and comparing those losses across possible operational modes. The results of these calculations define how the vehicle can decrease fuel consumption while maintaining low vehicle emissions. The results presented are meant only to define a literal strategy; that is, an understanding as to why the vehicle should operate in a certain way given driver demands, vehicle speed, and powertrain limitations.

The Hybrid Electric Vehicle Team of Virginia Tech (HEVT) is participating in the 2005 - 2008 Challenge X advanced technology vehicle competition series, sponsored by General Motors Corporation, the U.S. Department of Energy, and Argonne National Lab. This paper presents the Equinox REVLSE (Renewable Energy Vehicle, the Larsen Special Edition) design, simulation and modeling results to set the Vehicle Technical Specifications (VTS), improvements made to approach the 99 % buyoff level of vehicle readiness, and the HEVT hybrid control strategy that selects vehicle propulsion modes to meet VTS. The paper also compares the REVLSE to the production Equinox.

Fuel cell system models are key tools for automotive fuel cell system engineers to properly size components to meet design parameters without compromising efficiency by over-sizing parasitic components. A transient fuel cell system-level model is being developed that includes a simplified transient thermal and parasitics model. Model validation is achieved using a small 1.2 kW fuel cell system due to its availability. While this is a relatively small stack compared to a full size automotive stack, the power, general thermal behavior, and compressor parasitics portions of the model can be scaled to any number of cells with any size membrane area. With flexibility in membrane size and cell numbers, this model can be easily scaled to match full automotive stacks of any size. The electrochemical model employs a generalized polarization curve to approximate system performance and efficiency parameters needed for the other components of the model.

In the past few years, the price of petroleum based fuels, especially vehicle fuels such as gasoline and diesel, have been increasing at a significant rate. Consequently, there is much more consumer interest related to reducing fuel consumption of conventional and hybrid electric vehicles (HEVs). The “pulse and glide” (PnG) driving strategy is first applied to a conventional vehicle to quantify the fuel consumption benefits when compared to steady state speed (cruising) conditions over the same time and distance. Then an HEV is modeled and tested to investigate if a hybrid system can further reduce fuel consumption with the proposed strategy. Note that the HEV used in this study has the advantage that the engine can be automatically shut off below a certain speed (∼40 mph, 64 kph) at low loads, however a driver must shut off the engine manually in a conventional vehicle to apply this driving strategy.

The Modular Automotive Technology Testbed (MATT) is a flexible platform built to test different technology components in a vehicle environment. This testbed is composed of physical component modules, such as the engine and the transmission, and emulated components, such as the energy storage system and the traction motor. The instrumentation on the tool enables the energy balance for individual components on drive cycles. Using MATT, a single set of hardware can operate as a conventional vehicle, a hybrid vehicle and a plug-in hybrid vehicle, enabling direct comparison of petroleum displacement for the different modes. The engine provides measured fuel economy and emissions. The losses of components which vary with temperature are also measured.

This paper covers the development of a closed loop transaxle synchronization algorithm which was a key deliverable in the control system design for the L3 Enigma, a Battery Dominant Hybrid Electric Vehicle. Background information is provided to help the reader understand the history that lead to this unique solution of the input and output shaft synchronizing that typically takes place in a manual vehicle transmission or transaxle when shifting into a gear from another or into a gear from neutral when at speed. The algorithm stability is discussed as it applies to system stability and how stability impacts the speed at which a shift can take place. Results are simulated in The MathWorks Simulink programming environment and show how traction motor technology can be used to efficiently solve what is often a machine design issue. The vehicle test bed to which this research is applied is a parallel biodiesel hybrid electric vehicle called the Enigma.

An ADVISOR model of a large sport utility vehicle with a fuel cell / battery hybrid electric drivetrain is developed using validated component models. The vehicle mass, electric traction drive, and total net power available from fuel cells plus batteries are held fixed. Results are presented for a range of fuel cell size from zero (pure battery EV) up to a pure fuel cell vehicle (no battery storage). The fuel economy results show that some degree of hybridization is beneficial, and that there is a complex interaction between the drive cycle dynamics, component efficiencies, and the control strategy.

Proton exchange membrane (PEM) fuel cells are considered to be one of the best alternative power sources for automobiles. For this application, high power and high power density are required. Pressurizing the fuel cell system gives both higher efficiency and higher power density, but that pressure costs a percentage of the fuel cell output power. The compressor used to elevate the pressure has a direct effect on the system efficiency and water balance characteristics, especially at low load. Compressors being developed for fuel cell applications are examined to determine their effect on a fuel cell system. Two compressor technologies are discussed; a positive displacement twin-screw compressor and a turbocompressor, and their effects at low loads and set minimum compressor flows are examined. The turbocompressor proves to be a superior machine in terms of efficiency, and therefore offers the most promising effect on system efficiency of the two compressors.

The impacts of fuel cell system power response capability on optimal hybrid and neat fuel cell vehicle configurations have been explored. Vehicle system optimization was performed with the goal of maximizing fuel economy over a drive cycle. Optimal hybrid vehicle design scenarios were derived for fuel cell systems with 10 to 90% power transient response times of 0, 2, 5, 10, 20, and 40 seconds. Optimal neat fuel cell vehicles where generated for responses times of 0, 2, 5, and 7 seconds. DIRECT, a derivative-free optimization algorithm, was used in conjunction with ADVISOR, a vehicle systems analysis tool, to systematically change both powertrain component sizes and the vehicle energy management strategy parameters to provide optimal vehicle system configurations for the range of response capabilities.

An ADVISOR model of a PNGV-class (80 mpg) vehicle with a fuel cell / battery hybrid electric drivetrain is developed using validated component models. The vehicle mass, electric traction drive, and total net power available from fuel cells plus batteries are held fixed. Results are presented for a range of fuel cell size from zero (pure battery EV) up to a pure fuel cell vehicle (no battery storage). The fuel economy results show that some degree of hybridization is beneficial, and that there is a complex interaction between the drive cycle dynamics, component efficiencies, and the control strategy.

Proton exchange membrane (PEM) fuel cells are considered to be one of the best alternative power sources for automobiles. For this application, high power and high power density are required. Pressurizing the fuel cell system gives both higher efficiency and higher power density, but that pressure costs a percentage of the fuel cell output power. The compressor used to elevate the pressure has a direct effect on the system efficiency and water balance characteristics, especially at low load. Compressors being developed for fuel cell applications are examined to determine their effect on a fuel cell system. Two compressor technologies are discussed; a positive displacement twin-screw compressor and a turbocompressor, along with their effects on overall system characteristics and efficiency. The turbocompressor proves to be a superior machine in terms of efficiency, and therefore offers the most promising effect on system efficiency of the two compressors.

Large sport utility vehicles have relatively low fuel economy, and thus a large potential for improvement. One way to improve the vehicle efficiency is by converting the drivetrain to hydrogen fuel cell power. Virginia Tech has designed a fuel cell hybrid electric vehicle based on converting a Chevrolet Suburban into an environmentally friendly truck. The truck has two AC induction drive motors, regenerative braking to capture kinetic energy, a compressed hydrogen fuel storage system, and a lead acid battery pack for storing energy. The fuel cell hybrid electric vehicle emits only water from the vehicle. The fuel cell stacks have been sized to make the 24 mpg (gasoline equivalent) vehicle charge sustaining, while maintaining the performance of the stock vehicle. The design and integration challenges of implementing these systems in the vehicle are described.

Fuel cells are being considered for transportation primarily because they have the ability to increase vehicle energy efficiency and significantly reduce or eliminate tailpipe emissions. A proton exchange membrane fuel cell is an electrochemical device for which the operational characteristics depend heavily upon temperature. Thus, it is important to know how the thermal design of the system affects the performance and efficiency of a fuel cell vehicle. More specifically, this work addresses issues of the initial thermal transient known to the automotive community as “cold start” effects for a direct hydrogen fuel cell system. Cold start effects play a significant role in power limitations in a fuel cell vehicle, and may require hybridization (batteries) to supplement available power. The results include a comparison of cold-start and hot-start fuel cell power, efficiency and fuel economy for a hybrid fuel cell vehicle.

The Hybrid Electric Vehicle Team of Virginia Tech (HEVT) is currently developing a control strategy for a parallel plug-in hybrid electric vehicle (PHEV). The hybrid powertrain is being implemented in a 2016 Chevrolet Camaro for the EcoCAR 3 competition. Fuzzy rule sets determine the torque split between the motor and the engine using the accelerator pedal position, vehicle speed and state of charge (SOC) as the input variables. The torque producing components are a 280 kW V8 L83 engine with active fuel management (AFM) and a post-transmission (P3) 100 kW custom motor. The vehicle operates in charge depleting (CD) and charge sustaining (CS) modes. In CD mode, the model drives as an electric vehicle (EV) and depletes the battery pack till a lower state of charge threshold is reached. Then CS operation begins, and driver demand is supplied by the engine operating in V8 or AFM modes with supplemental or loading torque from the P3 motor.

The Hybrid Electric Vehicle Team (HEVT) of Virginia Tech is currently going through several modeling and testing stages to develop models that represent the P3 PHEV powertrain the team is building as part the EcoCAR 3 competition. The model development process consists of several major steps. First, Model-in-the-Loop (MIL) testing is conducted to validate a conventional vehicle model, down-select a desired powertrain configuration, and generate initial vehicle technical specifications. HEVT is pursuing a performance powertrain that balances high performance with minimal energy consumption. Initial MIL modeling results yield an IVM-60 mph time of 4.9 seconds and an overall UF-weighted 4-cycle energy consumption of 560 Wh/km. MIL modeling provides an initial reference to compare subsequent vehicle modeling. Following the MIL process, Software-in-the-Loop (SIL) is used to develop a vehicle model from the ground-up that facilitates the transition to Hardware-in-the-Loop (HIL) testing.

The Hybrid Electric Vehicle Team of Virginia Tech (HEVT) is participating in the 2008 - 2011 EcoCAR: The NeXt Challenge Advanced Vehicle Technology Competition series organized by Argonne National Laboratory (ANL) and sponsored by General Motors (GM) and the U.S. Department of Energy (DoE). Following GM's vehicle development process, HEVT established goals that meet or exceed the competition requirements for EcoCAR in the design of a plug-in, range-extended hybrid electric vehicle. The challenge involves designing a crossover SUV powertrain to reduce fuel consumption, petroleum energy use and well-to-wheels (WTW) greenhouse gas (GHG) emissions. In order to interface with and control the vehicle, the team added a National Instruments (NI) CompactRIO (cRIO) to act as a hybrid vehicle supervisory controller (HVSC).

The Hybrid Electric Vehicle Team of Virginia Tech (HEVT) is participating in the 2009 - 2011 EcoCAR: The NeXt Challenge Advanced Vehicle Technology Competition series organized by Argonne National Lab (ANL), and sponsored by General Motors Corporation (GM), and the U.S. Department of Energy (DOE). Following GM's Vehicle Development Process (VDP), HEVT established team goals that meet or exceed the competition requirements for EcoCAR in the design of a plug-in extended-range hybrid electric vehicle. The competition requires participating teams to improve and redesign a stock Vue XE donated by GM. The result of this design process is an Extended-Range Electric Vehicle (E-REV) that uses grid electric energy and E85 fuel for propulsion. The vehicle design is predicted to achieve an SAE J1711 utility factor corrected fuel consumption of 2.9 L(ge)/100 km (82 mpgge) with an estimated all electric range of 69 km (43 miles) [1].