Development of a Torque-Based Control Strategy for a Mode-Switching Hydraulic Hybrid Passenger Vehicle 2018-01-1007
An increase in the number of vehicles per capita coupled with stricter emission regulations have made the development of newer and better hybrid vehicle architectures indispensable. Although electric hybrids have more visibility and are now commercially available, hydraulic hybrids, with their higher power densities and cheaper components, have been rigorously explored as the alternative. Several architectures have been proposed and implemented for both on and off highway applications. The most commonly used architecture is the series hybrid, which requires an energy conversion from the primary source (engine) to the secondary domain. From he
re, the power flows either into the secondary source (high-pressure accumulator) or to the wheels depending upon the state of charge of the accumulator. A mode-switching hydraulic hybrid, which is a combination of a hydrostatic transmission and a series hybrid, was recently developed in the author’s research group. This paper focuses on the development of a new controller for the mode-switching hydraulic hybrid prototype. A uniform torque-based control strategy is proposed, which, along-with a supervisory controller decides on the usage of the high-pressure accumulator, thereby switching the vehicle mode from hydrostatic to series hybrid, among others. The supervisory controller analyzes the driving scenario, the system states and the user power demand to select the optimum vehicle-driving mode. This improved control strategy allows the vehicle to operate in higher efficiencies and the uniform control type results in a better “driver-feel”. The development of the control strategies, their implementation on the prototype vehicle and the test results are discussed in this paper.