In order to select and design parameters of power source system, based on experimental data, a method which uses the theory of curved surface fitting method and two-dimensional interpolation to make isogams of hydraulic pump was applied. Through a study in the characteristic curves of engine and hydraulic pump, the matching efficiencies between engine and fixed or variable displacement hydraulic pump were analyzed respectively. The mathematical models and efficiency maps of engine and hydraulic pump and accumulator were set up together considering the efficiency of accumulator. The economy was...