Hybrid Computer-Aided Design of a Hydrostatic Vehicle Drive With Energy Accumulator

The article presents the use of the hybrid computing technique in the design and optimization of a novel hydrostatic drive for urban vehicles. The vehicle system is modelled on the analog computer whereas the optimization algorithm and overall control is performed in the digital section. The ‘on-line’ features and the high computing speed of the analog model proves very advantageous in both the preliminary design and the system optimization process. The drive system consists of a small IC-engine, a hydrostatic transmission and a hydraulic accumulator energy storage. The hydraulic accumulator assists the engine during acceleration and allows for regenerative braking which results in a high overall efficiency in urban driving, where frequent stops occur. In the first stage of the design, the feasibility of the drive concept was evaluated. Thus preliminary designed system is repeatedly ‘driven’ through a short driving cycle under the control of the digital computer. A direct search optimization routine known as complex method evaluates the drive performance and readjusts four drive controller parameters. The objective of the optimization is to minimize the fuel consumption without any loss of drive dynamics. The comparison of the drive performance before and after optimization is presented and discussed.