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Hybrid Electric Powertrain Design Methodology With Planetary Gear Sets for Performance and Fuel Economy

Planetary gear sets (PGs) play a key role in the design of hybrid electric vehicles (HEVs) because they allow the realization of many unique powertrain designs using a limited number of components. By leveraging the capability of this mechanical device, an automated design process for PG-based HEV systems focusing on both fuel economy and performance is introduced in this paper. The design process consists of five major stages. In the first stage, all possible powertrain modes of an HEV design are automatically generated with a given set of powertrain components. In the second stage, all powertrain types that can be formed with a given set of components are mathematically identified, and each feasible mode is classified under one of these powertrain types. In the third stage, computationally efficient linear programming solvers suitable for vector operations are developed for each powertrain type to assess the gradeability, launch torque, overtaking torque, and acceleration time of each mode for all PG gear ratio combinations. In the fourth stage, the combination of modes that meets the performance requirements, and the number and location of clutches that make these mode transitions possible, are explored. As a result, each potent mode combination, the clutches necessary for the mode transition, and the auxiliary modes established as a result of all clutch state combinations constitute a design that meets the performance criteria. In the last stage, the fuel economy improvement potential of each competent design is evaluated. The results show that light-duty truck performance requirements can be met by many two-PG HEV designs without sacrificing fuel economy if the appropriate analysis and synthesis techniques for exploring the entire design space are developed.