A Study On Shift Control Strategy Of Coaxial Parallel Hybrid Electric Bus Based On AMTs

Nowadays,energy crisis,environmental problems and vehicle fuel consumption regulations are becoming more and more serious.Hybrid vehicles,as one of the main products of new energy vehicles,are competition core among the international automobile industries because of its great practical significance.Due to its flexible configuration and wide application range,the coaxial parallel hybrid electric bus based on AMTs becomes a research hotspot.Shift control strategy,as one of the core technologies in automatic transmission field,should reflect the driver's intention in the vehicle dynamic and economy performance and should switch dynamically based on the vehicle's different operation modes.Firstly,this paper established the theoretical coaxial parallel hybrid electric bus model based on bench and vehicle experiments data,including the engine model,the dry clutch model,the motor model,the power battery model,the motor model,the AMT model and the vehicle model.Secondly,to solve the difficulty in recognizing the driver intention,it is divided into five categories,namely,stop,deceleration,maintain,acceleration and urgent acceleration.Then,the relative accelerator opening is defined.Finally,a fuzzy control system is designed to identify the driver's acceleration characteristics in real time.It takes the vehicle speed,the change rate of the accelerator opening degree and the relative accelerator opening degree as inputs and the quantitative driver intention as output.Hybrid vehicles have two power sources,and four driven modes,namely,engine driven alone,motor driven alone,engine-motor driven jointly,and driving charge mode.Hence,it is important to set a reasonable upper torque split strategy to coordinate the operation of transmission parts.To solve the above problems,firstly,the calculation process of the driver demand torque is introduced in detail.Then,the maintaining torque split strategy is designed.According to the two-parameter economy shift strategy and dynamic shift strategy of conventional vehicles,the paper introduces the shift strategy when the hybrid vehicle is driven in the engine alone mode,the motor alone mode,the hybrid mode and the driving charge mode.Furthermore,the quantified driver intention is regarded as a weighing coefficient and involved into the formulation of the shift points.Finally,the designed shift strategy is compared with the conventional methods on the simulation model and verified by road tests in Chinese typical urban cycle working conditions.Results show that the fuzzy inference system can identify the driver's intention well and the dynamic shift control strategy can reflect driver's intention dynamically.