| The increasing deficiency of petroleum resources has been drawing more and more attention of human beings to the urgent requirement of the low energy consumption and low emission green motors. The rapid development of vehicle technology brings a great opportunity to energy saving and the reduction of pollutant emission, which includes electric vehicle technology, fuel cell electric vehicle technology, hybrid electric vehicle technology, hydraulic energy saving vehicle technology, etc.Hydraulic energy-saving vehicle adopts the hydraulic accumulator as the energy storage element, making full use of its advantage in high power density and rapid dynamic response by recovering the braking and inertial energy to meet the intermittence and high power requirement in the starting and accelerating process of vehicle. Being the energy conversion element of hydraulic energy-saving vehicle, the hydraulic pump/motor can works in the four torque-angle quadrants (as a motor to drive the load and as a pump to decelerate the load) by adjusting the swash plate angle, which has advantages in easy realization of positive inversion, high maneuverability and high reliability. With the energy recovery unit composed of the above elements, the hydraulic energy-saving vehicle recovers the braking and inertial energy and releases the energy in starting and accelerating process according to certain energy recovery strategy to ensure the ride comfort and safety. This design reduces the vehicle installed power in a large scale and has a dramatic effect on improvement of the fuel economy and reduction of emission and noise pollutant. Hydraulic energy-saving vehicle technology has gain a wider and wider application in heavy trucks, transporters, and urban buses, especially in the urban traffic and mountain transportation cases. This paper originates from the JiLin S&T Bureau Fund project-'The application research on the secondary regulation technology in hydraulic energy saving vehicle'and the school-enterprise cooperation project-'The development of concrete mixing truck based on the hydraulic energy saving technology'. The main content of this paper includes transformation of the dynamic and transmission system of the 8m3 concrete mixing truck, design of the energy saving unit and torque distribution unit of the hydraulic energy saving vehicle, and the planning of the vehicle controller to coordinate the above units to provide the torque for the vehicle. Hydraulic energy saving vehicle technology combines the electro-hydraulic control technology, computer technology and automatic control technology to make full use of the high power density of hydraulic elements to recover the braking energy on the base of ensuring the braking efficiency and comfort. This paper also includes: the dynamic regulation of each unit and the design of the braking torque control unit which provides hardware to the implementation of the recovery strategy of braking energy; the modeling and simulation analysis of the vehicle braking strategy which proves that the application of the braking energy recovery strategy can improve the recovery rate of the energy saving unit and the fuel economy of the vehicle effectively; the development of a test bench for parallel hydraulic energy saving vehicle; the experiment research on the multi-mode driving cycle of the parallel hydraulic energy saving vehicle, which proves the correctness of the theory and the feasibility of the control strategy and provides foundation for the improvement of the vehicle control strategy and the optimization of the element parameters.The major research work of hydraulic hybrid vehicle in this paper includes the following aspects:1. Study the parameter matching of the parallel hydraulic energy-saving vehicle power transmission system, which includes the selection of hydraulic pump/motor, accumulator, transmission and coupler, the influence of assembly parameters on the dynamic performance, fuel economy, brake energy recovery efficiency, brake safety and comfort, the parameter optimization of the elements based on the optimal control strategy and the simulation analysis of the vehicle with matched dynamic parameters.2. Perform modeling and simulation analysis of the parallel hydraulic energy-saving vehicle. Based on the theory modeling and simulation modeling method, a dynamic vehicle simulation model is established to real-time simulate the driving process in Matlab/Simulink environment, which includes the model of vehicle, the model of mechanical brake module, the model of energy recovery and control unit and the model of driving system. The control module of each main part of the hydraulic energy-saving energy vehicle and the vehicle energy management control system is designed to provide a necessary simulation platform for the development of the energy recovery and management strategy.3. Study the brake energy recovery control strategy of parallel hydraulic energy-saving vehicle. A comprehensive module including brake energy recovery, vehicle energy management strategy and multi-mode cycle condition vehicle control strategy is developed using the above vehicle simulation platform. This module is also embedded to the platform. The evaluation index of the of the influence of the control strategy and element matching on the vehicle dynamic performance is determined and applied to the vehicle control strategy and matching.4. Study the coordinated control strategy of the brake energy recovery unit and mechanical brake unit. A simulation model of the dynamic coordinated control strategy is built and the control algorithm of the dynamic coordination is development. Optimization of the robustness, interference inhibition and tracking performance of the control unit and the construction of the control algorithm of the torque control strategy and dynamic control are also discussed.5. A simulation test bench is developed to study the multi mode cycle condition of parallel hydraulic energy-saving vehicle. The experiment result shows the correctness of the theory analysis and the feasibility of the control strategy, which provides evidence for the improvement of the vehicle control strategy and optimal matching for the element parameters.The following original works are included in this paper:1. The coupling equipment optimal control strategy of hydraulic energy-saving vehicle is proposed. With the application of energy-saving technology to the 8m3 concrete mixer of CNHTC Special Motor Company, this paper provides the design of the total vehicle construction and optimal matching of elements, taking full consideration of the actual engineering constraint condition and driving condition. The optimal control strategy implements the torque and speed control of the hydraulic pump/motor through the tracking control of the target speed ratio. With the application of this strategy, the hydraulic pump/motor works in high efficiency area all the way, implementing the improvement of fuel economy by increasing the element efficiency as well as the satisfaction of the driving and braking performance.2. An energy recovery strategy is proposed which includes the distribution strategy between the front and rear wheel, among various brake torque, and the dynamic adjustment of the brake force. Edge condition of the brake control strategy is proposed with a consideration of the vehicle performance and the urban condition. Simulation analysis of the vehicle model under various conditions is performed to prove the effectiveness of the brake control strategy. The simulation result shows that this brake energy recovery strategy can improve the recovery efficiency of the energy recovery unit and the consequent fuel economy of the whole vehicle.3. A new brake torque control unit of the hydraulic energy-saving vehicle is developed, which adds brake piston, brake accumulator, vehicle controller, pedal angle sensor and controllable throttle to the original brake system. The brake torque and the driver's intention can be acquired through the pedal travel, pedal velocity and pedal acceleration. The control unit makes maximum use of the recovered energy within the limit of the brake torque according to the vehicle control strategy and ratio of the recovery torque and the mechanical brake torque. The design of the brake torque control unit provides hardware for the implementation of the brake energy recovery control strategy.4. The dynamic control strategy of hydraulic energy-saving vehicle brake system is proposed. The dynamic and control model of the energy recovery brake unit and the mechanical brake unit is established in this paper to solve the torque compensation in the hybrid brake process. Making full use of the rapid response and high control precision of the energy recovery unit, the dynamic control strategy reduces the highly oscillatory tendency around the switch point by compensating the torque deficiency due to the slow response of the mechanical brake system so as to improve the brake efficiency and comfort of the vehicle. Development of the dynamic controller is also conducted, which provides hardware foundation for the implement of the control strategy.
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