Research On Gear-shift Schedules In The Braking Process Of Parallel Hybrid Electric Bus

Hybrid electric vehicles (HEV) owning good advantages of both the pure electricvehicles with motor and the traditional vehicles with internal combustion engine arethe hot research in new energy automotive field. Automatic transmission is the keycomponent of parallel hybrid electric vehicles (PHEV) and gear-shift schedule is thekey technology of automatic transmission. A reasonable gear-shift schedule canimprove the vehicle’s performance of economy, dynamic, security and emission.Taking a PHEV equipped with automated manual transmission (AMT) as researchobject, the control strategy of regenerative braking, gear-shift schedule decisionmethod and gear-shift schedule optimization in the process of the brake are deeplyresearched. The main contents of this paper are as follows:An advanced single-shaft parallel hybrid electric bus was chosen as studyobjective, and a reverse analytical method for braking control strategy was proposed.The control strategy of gear-shift schedule, engine braking and regenerative brakingunder different handles were obtained. The results lay the foundation for research ofgear-shift schedule in the process of braking.The calculation model of motor efficiency and the estimation model of batterystate of charge (SOC) were obtained by analysis of the vehicle test and design ofexperiments (DOE) of Isight. The decision-making method of down-shift schedules ofeconomy, security, dynamic and comprehensiveness and up-shift schedule in theprocess of brake were formulated by analysis of dynamic analysis in the process ofdriving and braking. The objective functions and constraint conditions of alldown-shift schedules were formulated.The joint optimization method using Isight and Matlab was used to analyze theinfluence of various parameters on the objective function of gear-shift decision andthe optimal gear-shift speed, reducing the gear-shift parameters. The gear-shiftconditions and three parameters gear-shift schedules of economy, security, dynamicand comprehensiveness and up-shift schedule in the process of brake were formulatedthrough optimization. Considering the fluctuation of the gear-shift condition factor and the change of gear-shift condition, the fuzzy control was used to eliminate theinstability of gear-shift decision-making and the minimum speed of down-shift wasconfirmed.Finally, PHEV model was built according to the vehicle dynamics analysis,parsing vehicle control strategy, and gear-shift schedules and gear-shift processcontrol strategy of this paper. The simulation results that gear-shift schedules appliedto the conditions of bus driving cycles of typical Chinese city, coasting and differentbraking intensity were analyzed, proving that the proposed gear-shift schedules havethe rationality and superiority by comparing the simulation results of the gear-shiftschedules of original vehicle and other schedules.