| Traditional fuel passenger buses are the mainstream transportation equipment in the public transportation field.They have low fuel efficiency and serious pollution under frequent start-stops and low-speed heavy-load driving environments,which are difficult to meet the energy saving and environmental protection requirements under the background of the times.In addition,due to the extremely high mass when fully loaded,braking safety is difficult to guarantee when the vehicle is only braked by the mechanical braking device,and the braking energy cannot be recycled.The main driving scene of battery city buses which have the advantages of zero emissions and rapid energy recovery is urban public roads.It is an important transportation equipment that solves the energy consumption and environmental pollution problems of traditional fuel passenger vehicles.However,because the electric motor is in the state of peak torque output during starting and strong acceleration,which causes the high current discharge of the battery and severely shortens its service life and driving range,its application status is not optimistic.Hydraulic power technology has the characteristics of high power-density and rapid energy regeneration,and has achieved good application effects in transportation vehicles and heavy engineering vehicles.Based on this,this paper designs an electro-hydrostatic hydraulic hybrid powertrain suitable for battery city buses,which combines the advantages of high energy-density of battery and high power-density of accumulators.The hydraulic powertrain assists the vehicle to complete the starting and accelerating actions.At the same time,a composite braking mode based on hydraulic regenerative braking is formed,which improves energy recovery efficiency while ensuring braking safety,and improves the energy-saving and power characteristics of buses.Firstly,based on the original chassis structure and spatial characteristics of the battery bus,the key components of the electro-hydrostatic hydraulic hybrid powertrain are determined under the premise of minimizing structural changes.The rear axle is electrically driven and the front axle is hydraulically driven.Comprehensively considering the characteristics of different driving conditions of the vehicle,an electro-hydrostatic hydraulic hybrid powertrain with multiple power modes is constructed.Combining the vehicle dynamics model to realize the parameter calculation and selection of key power components and improve the design of the powertrain.Considering the frequent start-stops and low-speed heavy-load characteristics of battery buses,combined with the output characteristics of the hybrid powertrain,the best working modes corresponding to different speed ranges is determined.When driving,the power transfer of the electric motor is realized through three modes of auxiliary acceleration,hydraulic power,and parallel filling,which improves the efficiency of the electric motor’s operating points.When braking,the braking energy is recovered through the accumulator and released during acceleration to improve the energy recovery rate.Secondly,in order to preliminarily verify the energy-saving advantages of the designed electro-hydrostatic hydraulic hybrid powertrain and provide a reference for subsequent real-vehicle driving conditions testing,experimental verification and the formulation of smart energy management strategies,while considering the practical value of rule-based energy management strategies.In this paper,a rule-based multi-mode switching energy management strategy is constructed.With the aid of the joint simulation platform of AMESim and MATLAB/Simulink-stateflow software,the vehicle and control model of the hybrid powertrain is established.Co-simulation analysis is carried out under CCBC cycles.The results show that compared to the electric powertrain,the designed electro-hydrostatic hydraulic hybrid powertrain can effectively avoid the torque shock when the vehicle starts and accelerates by switching the power modes under the control of the rule-based energy management strategy.Under the same driving conditions,the energy consumption of the battery is reduced by 31.72%.Thirdly,because the selection of driving conditions has a great influence on the design of vehicle parameters and comprehensive performance evaluation based on software simulation,this article tested the driving characteristics of battery buses in actual operating scenarios and obtained multiple sets of operating conditions.Through corresponding data processing and analysis,a typical urban driving condition suitable for this type of bus is drawn.Based on the actual driving conditions obtained,a simulation analysis is performed to verify the comprehensive performance of the designed hybrid powertrain in actual driving scenarios.The results verify the power and energy-saving advantages of the hybrid powertrain in actual driving scenarios.Compared with the electric powertrain,the battery power consumption under the same driving conditions is reduced by 32.36%.A corresponding test platform is built to verify the feasibility,correctness and effectiveness of the proposed multi-mode switching ideas and simulation models.The test results show that the proposed switching control of rule-based power modes can achieve the predetermined design goals and effectively improve the overall performance of the vehicle.Finally,in order to further improve the comprehensive energy utilization efficiency of the designed hybrid powertrain,this paper formulates a management strategy of active energy regulation and bidirectional transfer guided by actual operating conditions.The K-means clustering algorithm is introduced to realize the segmentation and clustering of driving cycles in the actual driving scene,and the results are used as samples to train and test the LVQ neural network that can realize online driving pattern recognition and prediction.With the help of fuzzy logic controller,the fuzzy processing of multiple input variables is carried out,and the result of comprehensive driving pattern recognition and fuzzy logic controller realizes the active adjustment and bidirectional transfer of the output characteristics of electric motor and pump/motor.According to the results of online identification and prediction of driving patterns,the auxiliary advantages of hydraulic energy are homogenized when the vehicle continues to accelerate,and hydraulic energy is given priority to create more energy storage space for hydraulic regenerative braking during continuous braking.Through simulation,the formulated energy active regulation and bidirectional transfer management strategy is compared with the control strategy based on certain and fuzzy rules.The results show that the designed energy management strategy can effectively realize the intelligent adjustment and migration of energy between composite power sources,and significantly improve the driving range and service life of the battery. |
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