Browse Topic: Electrically variable transmissions
Electrified powertrains, including Power Splits (Electrically Variable Transmissions), Range Extenders (Series Hybrids), and Electric Vehicles with Disconnect Actuators, offer significant flexibility in managing input actuator acceleration and output torque, drawing power from shared sources. The Hybrid Supervisory Controller (HSC) plays a crucial role in balancing these parameters to meet performance and drivability metrics, yet it often faces challenges under power constraints or sudden high output demands, which can lead to imbalanced control, reduced actuator performance, and unintended vehicle motion. Traditional solutions have typically prioritized one control objective over others, compromising overall system performance. This paper introduces an advanced control strategy that optimally distributes control efforts across multiple actuators with overlapping and conflicting objectives. By resolving these conflicts, the proposed approach ensures system stability and enhances performance. Simulation and vehicle results are provided to demonstrate the effectiveness of this solution in achieving balanced control and improved drivability.
Texas Tech University (TTU) was one of sixteen universities competing in EcoCAR:-The Next Challenge competition. It is a three year collegiate advanced vehicle technology competition where teams are challenged to re-engineer a General Motors(GM) donated vehicle to achieve improved fuel economy and reduced emissions while maintaining consumer acceptability in the areas of stock performance, utility and safety. Two-mode hybrid which is an electrically variable transmission was selected as the Texas Tech team's architecture. The first year of the competition emphasized vehicle design through Powertrain System Analysis Toolkit (PSAT) software. The vehicle design parameters were established through vehicle technical specifications(VTS), development of software-in-the-loop (SIL) and hardware in-the-loop (HIL) techniques, rapid control system prototyping and components selection and sizing. These first year activities were continued for the vehicle development and refinement in subsequent years of the competition. This paper describes the design procedure of SIL, HIL and rapid prototyping. The Mathworks Simulink, SimDriveline, SimScape and Stateflow software provided an environment for modeling selected architecture and powertrain components. Once the model was verified HIL testing was performed with the use of National Instruments PXI and dSpace MicroAutoBox (MABX). In this way the process moved from mathematical models to lab based tests with HIL. A realistic vehicle propulsion controller was developed by moving to in-vehicle testing of the vehicles' on board software.
The new General Motors 2-mode hybrid transmission for front-wheel-drive vehicles has been incorporated into a 2009 Saturn Vue by the West Virginia University EcoCAR team. The 2-mode hybrid transmission can operate in either one of two electrically variable transmission modes or four fixed gear modes although only the electrically variable modes were explored in this paper. Other major power train components include a GM 1.3L SDE turbo diesel engine fueled with B20 biodiesel and an A123 Systems 12.9 kWh lithium-ion battery system. Two additional vehicle controllers were integrated for tailpipe emission control, CAN message integration, and power train hybridization control. Control laws for producing maximum fuel efficiency were implemented and include such features as engine auto-stop, regenerative braking and optimized engine operation. The engine operating range is confined to a high efficiency area that improves the overall combined engine and electric motor efficiency. Simulation results using Powertrain System Analysis Toolkit (PSAT) indicate fuel economy of 28.4/29.4 mpgge over the customized Morgantown Urban Drive Schedule (MUDS)/Route 19 Highway (R19HW), 14.6 second 0-60 mph and 8.6 second 50-70 mph acceleration time. The on-road test results indicated fuel economy of 24.5/31.5 mpgge over the MUDS/R19HW cycles, 16 seconds 0-60 mph and 10 seconds 50-70 mph acceleration time.
Power-split hybrid-electric vehicles (HEVs) employ two power paths between the internal combustion (IC) engine and the driven wheels routed through gearing and electric machines (EMs) composing an electrically variable transmission (EVT). The EVT allows IC engine control such that rotational speed can be independent of vehicle speed at all times. By breaking the rigid mechanical connection between the IC engine and the driven wheels, the EVT allows the IC engine to operate in the most efficient region of its characteristic brake specific fuel consumption (BSFC) map. If the most efficient IC engine operating point produces more power than is requested by the driver, the excess IC engine power can be stored in the energy storage system (ESS) and used later. Conversely, if the most efficient IC engine operating point does not meet the power request of the driver, the ESS delivers the difference to the wheels through the EMs. Therefore with an intelligent supervisory control strategy, power-split architectures can advantageously combine traditional series and parallel power paths. Previous work compared two different power-split HEV powertrains using a 2-term cost function and steady-state backward-looking simulation (BLS). BLS was used to find battery power management strategies resulting in minimized fuel consumption over a user-defined drive-cycle. The supervisory control strategy design approach amounts to an exhaustive search over all kinematically admissible engine and EM operating points, leading to a minimized instantaneous cost function. While the approach provides a valuable comparison of two architectures, non-ideal engine speed fluctuations result, preventing the control strategy from being effectively implemented. In the present work, two approaches are investigated for refining IC engine state transitions for use in an implemented control strategy: i) smoothing the 2-term cost function optimization results, and ii) introducing a 3-term cost function. These approaches are tested and verified in high-fidelity forward-looking simulations (FLSs). It is found that both refinement approaches effectively reduce engine speed transitions, and result in fuel economy (FE) estimates and component operation which compare well to BLS results. It is further found that the 3-term cost function finds more efficient operating points than the smoothed 2-term cost function approach. From the investigations carried out in this paper, a two-phase control strategy development process is suggested where control strategies are first explored using highly-efficient steady-state BLS models, and then further tested and refined in high-fidelity FLS models. Favorable comparison of BLS and FLS results justify the efficacy of the two-phased process, suggesting rapid and effective development of implementable power-split HEV supervisory control strategies.
This paper presents a comparative analysis of two different power-split hybrid-electric vehicle (HEV) powertrains using backward-looking simulations. Compared are the front-wheel drive (FWD) Toyota Hybrid System II (THS-II) and the FWD General Motors Allison Hybrid System II (GM AHS-II). The Toyota system employs a one-mode electrically variable transmission (EVT), while the GM system employs a two-mode EVT. Both powertrains are modeled with the same assumed mid-size sedan chassis parameters. Each design employs their native internal combustion (IC) engine because the transmission's characteristic ratios are designed for the respective brake specific fuel consumption (BSFC) maps. Due to the similarities (e.g., power, torque, displacement, and thermal efficiency) between the two IC engines, their fuel consumption and performance differences are neglected in this comparison. The road-load parameters defining each system are used to calculate the required mechanical power at the driven wheels necessary to follow a given drive-cycle. Admissible engine operating states are sought based on component performance limitations and the required mechanical power at the driven wheels. Each IC engine operating point defines an accompanying battery power consistent with the constraints of the electric machines. The design approach is to exhaustively search all admissible states and minimize an instantaneous cost function based on engine power and battery power, at each time instant of the drive-cycle. Two cost functions are considered which weight battery power usage using either a linear, or an inverse-tangent, function of the current battery state-of-charge (SOC). Selected operational states are then compared against each other based on the flexibility and power delivery capabilities of the powertrains. Fuel minimizing cost functions are determined with the assistance of a charge sustaining index introduced by this paper. Finally, the most fuel efficient choices are used to determine the expected efficiency of both powertrains considered.
West Virginia University (WVU) is a participant in EcoCAR - The NeXt Challenge, an Advanced Vehicle Technology Competition sponsored by the U.S. Department of Energy, and General Motors Corporation. During the first year of the competition, the goal of the WVU EcoEvolution Team was to design a novel hybrid-electric powertrain for a 2009 Saturn Vue to increase pump-to-wheels fuel economy, reduce criteria tailpipe emissions and well-to-wheels greenhouse gas emissions (GHG) while maintaining or improving performance and utility. To this end, WVU designed a 2-Mode split-parallel diesel-electric hybrid system. Key elements of the hybrid powertrain include a General Motors 1.3L SDE Turbo Diesel engine, a General Motors Corporation 2-Mode electrically variable transmission (EVT) and an A123 Systems Lithium-Ion battery system. The engine will be fueled on a blend of 20% soy-derived biodiesel and 80% petroleum-derived ultra-low sulfur diesel fuel (B20). Emissions control is accomplished by a diesel oxidation catalyst, a catalyzed diesel particulate filter and selective catalytic reduction (SCR) with urea injection. Simulation results using the Powertrain System Analysis Toolkit (PSAT) developed by Argonne National Laboratory (ANL) indicate a combined cycle fuel economy of 6.2-liter/100 km, (32 mpg) gasoline equivalent, ≤150 g/km well-to-wheels (WTW) greenhouse gas emissions and ≤0.4 kWh/km petroleum energy use while maintaining an 8.0 second 0-60 acceleration time and 680 kg (1500 lb) towing capacity. Passenger capacity, cargo capacity and utility are not sacrificed by addition of the electrical energy storage and hybrid propulsion systems.
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