Study On The Hydraulic System Of Hydraulic Hybrid Vehicles

Study on the hydraulic system of series hydraulic hybrid vehicles (SHHV) was presented in this dissertation. Based on the theoretic research, the test bench of the hydraulic system for SHHV and the prototype vehicle were developed. Computer simulation and experiments of the hydraulic system for SHHV were performed.(1) Technical scheme of the hydraulic system for SHHV was chosen, and the mathematical models of hydraulic system integrated with vehicle load were established. The key components of hydraulic system such as the hydraulic accumulator and bidirectional variable-displacement motor were analyzed detailedly. Some key parameters influencing dynamic performance of hydraulic system were analyzed. The calculation method of variable polytropic index was proposed.(2) Fuzzy algorithm was applied to identify vehicle operating condition. Four representative driving patterns were selected as vehicle duty cycles. Some self-defined parameters were chosen to characterize the driving patterns. Multilevel comprehensive assessment was applied to evaluate the real duty cycle.(3) The function and working process of SHHV were analyzed. Evaluating indexes, such as average power-supplying rate, maximum power-supplying rate, braking energy regenerative efficiency and utilizing efficiency of hydraulic ststem, were established to direct the design of hydraulic system for SHHV. The fuzzy assessment of vehicle driving cycles was applied to the design of the hydraulic system for SHHV.(4) Simulation was performed on the dynamic characteristic of speed controlling system of the hydraulic system and simulation results were analyzed. Verification experiment was perfomed on the self-developed test bench. The simulation results accorded with the experimental data well. The accuracy of systematic models and simulation algorithm was testified. By using the verified mathematical models, power performance and fuel economy of SHHV were studied; fuzzy PID algorithm based on the auto-tuning of scaling factor and decision-making factor was applied to perform the simulation of fifteen-mode driving cycle, evaluating indexes of hydraulic system on 15-mode driving cycle were analyzed; Mathematical models based on the power flow of braking energy recovery for hydraulic hybrid vehicles were established and simulation was implemented. Evaluation indexes of braking energy regenerative system were defined. Constitute of energy loss and corresponding proportion were studied detailedly during the process of braking energy recovery. Quantitative analysis was made to study the influence of bidirectional motor displacement, pipe diameter, initial braking pressure and volume of accumulator on energy regenerative efficiency and braking performance of the vehicle.(5) The test bench of hydraulic system for SHHV was developed in the lab to study its dynamic characteristic. The test bench based on hydraulic motor controlling system in the constant pressure net used transducer motor to drive pump working, wheel load was simulated and real-time controlled through the combination of magnetic particle brake and fly wheel, and data collecting and controlling scheme were implemented by a computer. Different duty-cylces of hydraulic system were tested on the test bench and its dynamic characteristics was analyzed.(6) The prototype vehicle of SHHV based on hydrostatic transmission was built up. The technical and disposal scheme were developed. The hydraulic system and controlling system tests were carried out. Some experiments based on the prototype vehicle and control system were made.