Research On Matching Method And Control Strategy Of Composite Accumulator Hydraulic Hybrid System

Developing energy-saving and new energy vehicles is one of the important ways to reduce oil consumption and improve the ecological environment.Hydraulic hybrid vehicles(HHV)have the advantages of small size,light weight,no temperature impact and no pollution compared with hybrid electric vehicles.Moreover,there is no need to set up a management system separately,which greatly reduces the development cost of the vehicle.The accumulator volume of an HHV affects the rate of energy recovery and the braking response of the regenerative braking system directly.At present,a single high-pressure accumulator is used in the traditional parallel hydraulic hybrid vehicle(PHHV)to ensure the braking energy recovery ability,however,the braking response of the large accumulator is slow under the condition of high braking intensity,which reduces the braking energy recovery ability.A new configuration of a parallel hydraulic hybrid system based on composite accumulator is proposed in this paper,which not only has the fast braking response,but also has large energy recovery ability.Different volume accumulators are selected and used based on different driving modes,which can meet the requirement of braking characteristics and energy recovery rate.The main contents of this paper are as follows:A new configuration of a parallel hydraulic hybrid system based on composite accumulator is proposed,which is mainly composed of a large volume high pressure accumulator,a small volume high pressure accumulator,a low pressure accumulator,a hydraulic pump/motor and some valves.The power of the hydraulic system is connected with the engine power through a torque coupler.A method of parameter matching of composite accumulator based on genetic algorithm is proposed,which aim is max energy recovery rate considering the cost of accumulators meanwhile.Multi-objective optimization of the working volume and initial working pressure of the composite accumulator is carried out.The control strategy of PHHV based on composite accumulator is proposed.The working time of composite accumulator is determined according to the specific driving conditions to improve the braking performance and fuel economy of the vehicle.The dynamic programming algorithm is used to obtain the optimal control sequence of the torque distribution and energy management for the hydraulic hybrid vehicle.The control rules and logic thresholds of the control strategy are obtained,which gives the switching law of the working time of the composite accumulator.The mathematical model of the PHHV based on composite accumulator is established.The hydraulic regenerative braking system and the vehicle simulation model are established.The braking energy recovery rate of HHV equipped with different volumes and different initial pressure accumulators is compared,and the influence of accumulator volume and initial pressure on braking energy recovery rate is obtained.The simulation of constant braking strength and specific cycle conditions is carried out,which verified the result of the vehicle control strategy and proved the energy-saving principle of the parallel hydraulic hybrid system based on composite accumulator.The test bench of the parallel hydraulic hybrid system based on composite accumulator is designed,which mainly include the design of hydraulic pump/motor system,hydraulic valve block system and hydraulic pump station.The control system hardware of the test bench is selected.The LabView measure and control system is developed.Based on the original Kaimai power transmission test bench,a parallel hydraulic hybrid system test bench based on composite accumulator is built.A new test method of HHV component-in-the-loop for the bench is proposed.The multi-mode operation of HHV is realized on the electric transmission test bench(hydraulic driving only,hybrid driving,engine driving only,regenerative braking and hybrid braking,etc.)The bench test of constant braking strength and NEDC is carried out.The comparison of test and simulation results shows that the vehicle test conditions can be simulated accurately by using this method and the working mode of hydraulic hybrid power,accumulator pressure and engine fuel consumption are basically consistent with the simulation results.The control effect of vehicle control strategy and energy saving principle of parallel hydraulic hybrid power system based on composite accumulator are verified.