Design And Control Strategy Of Parallel Hydraulic Hybrid System In Loader

The contradiction between the rapid increase of energy demand and the lack of oil resources becomes greater, thus people are paying more attention to energy saving and emission reduction in the world. Hybrid technology is currently becoming one of the effective measures to solve the energy crisis and environment pollution. In view of the successful application of hybrid technology in automotive field, it is also gradually introduced into the application of engineering machinery. Wheel loader is one type of main products of engineering machinery. It has some features, such as cyclical work, frequent starting and stopping, more consumption and bad emission. There are a lot of researches about engine oil saving technology and the machine matching technology,it is difficult to improve the fuel economy of the whole machine greatly.The hydraulic hybrid technology uses hydraulic accumulator, which can recycle the brake energy, downhill inertia energy and the engine's redundant energy of the wheel loader and provide the auxiliary power for the restarting and spading of the whole loader, this is important to ensure that the engine works in efficient fuel economic zone. Relative to the electric hybrid technology, hydraulic hybrid can own a higher release and storage capacity for processing high power energy instantly, thus it is more suitable to the frequent starting and stopping and variable load operating requirements, it also is a low cost, high specific power, safe mature technology. In this paper, the parallel hydraulic hybrid technology is used in wheel loader transmission system to realize energy recycling and reuse, realizes energy saving and emission reduction in the end.The author makes a comprehensive thorough research on the loader parallel hydraulic hybrid technology. The mainly work are shown as follows:(1)This paper discusses and analyses the hydraulic hybrid technology's research status and development trend in the world, introducing the structure, working principle, control method and technical characteristics about secondary regulation hydrostatic transmission system.(2)Many types of energy consumption of the loader are analyzed, brake energy and downhill inertia energy are established the main study direction. The drive system and flexible brake system of parallel hydraulic hybrid loader are designed. According to different operating conditions, a variety of operation modes are designed, and conversion conditions are introduced.(3)Key elements selection criteria are determined, such as pump and motor, hydraulic accumulator, and coupler. The model of parallel hydraulic hybrid loader is established on the platform of Matlab and Simulink by backward modeling method. Comparative analysis are provided between simulation results and traditional loader performance.(4)This paper analyzes the influences of distribution way, the operation speed, the coupler ratio, the hydraulic accumulator key parameters and the control strategies on the system efficiency and energy saving effect,and puts forward key parameters selection criteria of parallel type hydraulic hybrid system。( 5 ) This paper designs parallel brake control strategy combining hydraulic regenerative brake and traditional mechanical brake, researches the brake energy recovery rate of different initial brake speed and different road conditions by simulation, also study proportional relation between regenerative brake force and the friction brake force . This paper uses the logic threshold design method to design the control strategy of the parallel hydraulic hybrid loader , distinguish machine operation condition and realize the smooth switching of different working modes .According to the speed and the downlink amplitude of acceleration pedal, this paper also adjustments dynamically active supercharging pressure torsion, optimizes spading drive torque ,ensuring the engine working in efficient fuel economic zone combine with engine load energy saving of the hydraulic accumulator.(6)Parallel hydraulic hybrid system of the loader is made, its structure is discussed and various experiments are conducted, including pump and motor experiment, low brake experiment, compound brake experiment, and the machine experiment.Through theoretical analysis, simulation study and prototype experiment, the results show that parallel type hydraulic hybrid system used on loader can highly efficient recovery braking energy, obviously improve the dynamic properties and the downhill inertia energy.Meanwhile, it is easy to adjust the engine's workload to ensure that the engine can extremely save the fuel. The parallel type hydraulic hybrid technology of this paper will provide theoretical basis for the engineering application, also provide technical guidance for other hosting products of engineering machinery which adopts hydraulic hybrid technology.This dissertation contains 107 diagrams, 13 tables and 135 references.