Research On The Power Characteristics Of Digital Hydrostatic Transmission System And Its Control Strategy

The hydro-mechanical drive dominates the transmission system of vehicles,but its efficiency is low.Hydrostatic transmission has the advantages of high efficiency,continuously variable speed and high driving torque,but its application is restricted by the high cost of core components and the high requirement for fluid cleanliness.Compared with traditional hydraulic technology,digital hydraulic technology has certain advantages in terms of anti-interference,energy saving,fault tolerance and versatility.In this paper,parallel digital hydraulic technology is applied to hydrostatic transmission,a digital hydrostatic transmission system based on parallel digital pump/motor is proposed,the power characteristics of the system are analyzed,an acceleration strategy and an external load adaptive control strategy are developed based on the system,the simulation of the system characteristics and control strategy is carried out in AMESim environment,and the correctness of the simulation and control strategy is verified through experiments.The main research contents and conclusions of this paper are as follows.(1)A digital hydrostatic transmission system consisting of a four-position singlemode parallel digital pump/motor is designed,and a digital model of the digital hydrostatic transmission system is established.(2)The transmission characteristics of the digital hydrostatic transmission system such as speed ratio,torque ratio,efficiency characteristics and gearing are analyzed.An acceleration mode control strategy that takes into account energy saving and acceleration performance is proposed;an external load adaptive control strategy based on digital pump/motor segmentation control and an external load adaptive control strategy based on cost function and two-parameter control are proposed.(3)The physical simulation model of the digital hydrostatic transmission system and the control system model are established in the joint simulation platform based on AMESim-Simulink.The simulation analysis of the conventional/expanded gears of the digital hydrostatic transmission system is carried out to verify the variable speed torque capability of each gear,and it is demonstrated that the expanded gears can make the torque variation of the system more continuous.The mechanism of negative motor speed shock during bad upshift is analyzed,and a switching timing control strategy based on a particle swarm optimization algorithm with variable parameters to identify the optimal delay time is proposed,and its effect of mitigating negative motor speed shock during upshift is verified by simulation.The acceleration mode control strategy is validated by simulation,and its effect of balancing system acceleration capability and energy saving is demonstrated.The two adaptive control strategies for external load are validated by simulation,and both algorithms are proven to be able to adapt to the external load by adjusting the digital pump/motor displacement for variable load conditions.The external load adaptive control algorithm based on the cost function and two-parameter control has better matching effect,can better fit the control target,and the motor speed changes more continuously.(4)Develop a digital hydrostatic transmission system simulation loading experiment bench,write the developed control strategy and control algorithm into the controller,write the data acquisition program through Lab VIEW,and use the dynamometer system to perform loading experiments on it.The experiments verified the torque shifting capability of the system in conventional and extended gears;verified the effect of the switching timing control strategy in mitigating the effect of poor upshifting;verified the effect of the external load adaptive control algorithm based on digital pump/motor segmentation control;and verified the feasibility of the dual-mode digital pump applied to the hydrostatic transmission system.