Research On Energy Saving And Control Performances Of Wheel Drive Hydraulic Hybrid Vehicle

With the rapid development of industrial production and transportation industries in the world, energy resources shortage and environmental pollution problem are becoming more and more severe. Hybrid technique is an effective way to alleviate energy resources crisis and environmental deterioration before a new and clean energy technique comes into full play. Hydraulic hybrid system can recycle kinetic energy of the system during braking, which will be stored and used again. Besides, the energy storage units of hydraulic hybrid system can cooperate with the main power source, which will facilitate optimal control of the working points of the main power source. Therefore, the hydraulic hybrid system can improve the energy using efficiency of the whole system and reduce the environmental pollution caused by low efficiency. The parallel actuating elements in the common pressure hydraulic system can work independently, which makes it possible for the hydraulic hybrid system to be applied in wheel drive vehicles, and thus a wheel drive hydraulic hybrid vehicle (WDHHV) comes into being. Its structure layout is more flexible and reasonable, and it can be controlled in a more flexible manner, make better use of road adhesion conditions, and further improve vehicle control stability.The current hybrid technique schemes were compared and the characteristics and advantages of hydraulic hybrid technique were analyzed from such aspects as energy transformation, environment protection effects and safety as well as stability performances. The configuration modes and their applicability of hydraulic hybrid vehicles were compared and analyzed.A new model of WDHHV was proposed and the corresponding mathematical model and simulation model were established after the analysis of the operation principle of WDHHV. The corresponding relationships between parameters of hybrid vehicle model and those of simulation test bench were deduced.Based on the analysis of the main factors that can influence energy saving effects of WDHHV, the matching of the propulsion system's key components and system working parameters was optimized. An adaptive simulated annealing genetic algorithm based on rule-based knowledge base was proposed to solve the possible optimal matching problem caused by the complicated relationship between the design variables and their restrictions. Different optimization results with different optimization emphases were simulated in order to verify the improvements of the optimized hybrid vehicle in such performances as energy saving and propulsion compared with those of the traditional vehicles.The WDHHV regeneration braking strategies were established based on backward model and semi-forward model according to the characteristics of the wheel drive vehicle. Energy saving effect was mainly considered in the strategy made based on the backward model, while in the strategy based on the semi-forward model, the driver and passengers'comfort and safety were emphasized more than energy saving effect. The influences of initial braking velocity and braking force on energy recovery rate were analyzed according to the simulation results.The deficiencies of the power management strategy of"thermostat plus power following"were analyzed. According to the characteristics of the transmission system of WDHHV, stochastic dynamic programming method was used in engine power management strategy, which could help regulate engine working points reasonably and thus improve the engine's fuel economy. Simulation research validated the effects of this strategy on the reduction of fuel consumption and NOx as well as soot emissions by the engine.To deal with the system parameters perturbation problem, a fuzzy predictive control method was introduced to control the rotate speed of the hydraulic pump/motor in WDHHV's propulsion wheel, which effectively improved the control robustness against the parameters perturbation. In order to improve the vehicle operation stability, a wheel drive vehicle electrical differential control strategy, which controlled the slip ratios of four wheels respectively by controlling rotate speed and by referencing vehicle yaw rate and angular acceleration, was proposed and simulated.In the end, in order to validate the proposed strategies and methods, the experimental research on rotate speed control, braking control strategy and power distribution in circulating driving cycle was conducted by using hydraulic hybrid system test bench.