Research On A Design Methodology For Hybrid Electric Vehicle Powertrain Configuration With Planetary Gear Sets

With the deterioration of the environment and the shortage of petroleum resources,the development of vehicles employing alternative energy has become an inevitable trend for the development of the automotive industry in the world [1-3].Among the alternative-energy vehicles,pure electric vehicles and fuel cell vehicles cannot be widely applied due to crucial shortcomings such as the short driving range and the high manufacturing cost.At present,hybrid electric vehicles are regarded as an effective solution to reduce the demand for petroleum resources and protect the environment.Among a variety of hybrid electric vehicles,the hybrid electric vehicles possessing planetary-gear powertrain configurations are preferred by many automotive manufacturers because they can improve the operating efficiency of engine by achieving rotational speed coupling and torque coupling of electric machines and engine.The typical manufactured vehicle is Toyota Prius and Chevrolet Volt.However,the number of various configurations with planetary gear sets is up to tens of thousands due to numerous connection relationships between the planetary gear sets and power plants / planetary gear sets,which is very large.It is very difficult to receive the configurations possessing excellent performance among the numerous configurations.In order to solve this problem,this paper,supported by a 135 scientific research project(No.2016YFB0101402)“ The research on coupling mechanism and configuration optimization method of plug-in / Extended range hybrid electric vehicle”,focus on the hybrid system powertrain configuration with planetary gear sets and the research is carried out as follows:(1)As the power coupling device of the configurations,in this stage,the rotational speed relationship and torque relationship among the three components of a planetary gear set(ring,carrier and sun gear)will be first analyzed and the finding will be obtained that the torque relationship can be calculated referring to the principle that the input and output power are balanced while the rotational speed relationship is specified.Then,take a configuration with two planetary gear sets as an example,the relationship between the derivation process of the rotational speed equations of configurations and the generation principle of the configurations with any number of planetary gear sets and any number of power sources is explored and the generating principle of the configurations with any number of planetary gear sets and any number of power sources is revealed.(2)On the basis of the principle in Stage 2,the connection relationships in all configurations with any number of planetary gear sets and any number of power sources consist of the connection relationship between all nodes in independent planetary gear sets,the connection relationship between connected planetary gear sets,the connection relationship between the power nodes and planetary nodes and the connection relationship between the brakes and the planetary nodes.Then,the matrices automatically generating the connection relationship between all nodes in independent planetary gear sets,the connection relationship between connected planetary gear sets,the connection relationship between the power nodes and planetary nodes and the connection relationship between the brakes and the planetary nodes,respectively will be derived.Then,in order to compute the physical connection relationships in a hybrid electric vehicle powertrain by a computer,the physical nodes in the powertrain are represented by the number nodes and thus the physical connection relationship can be calculated by a computer.After that,a comprehensive matrix containing the connection relationship and the rotational speed relationship will be created and the systematic generation and dynamic equations extraction of the configurations with multiple planetary gear sets are attained by means of mathematical matrix operations.Finally,a general methodology which can generate the configurations with any number of planetary gear sets and any number of power sources is provided.(4)This stage mainly focuses on the modeling of the components in a hybrid electric vehicle powertrain and prepare for the optimal selection and performance analysis of configurations in the later work.The engine,the electric machine,the planetary sets,the battery and the vehicle dynamic will be modeled,respectively.(5)Apart from that above,in order to avoid the impact of control strategies on the screen of the configurations,various control strategies for hybrid electric vehicles are analyzed and the global optimal control strategy based on dynamic programming is selected as the control strategy of the performance simulation.The optimal selection of numerous configurations automatically generated in Stage 3 will be completed in this stage.Fuel economy is selected as the criterion of economic performance in a powertrain configuration and the accelerating performance is regarded as the dynamic performance.Through considering the economic performance and dynamic performance of the obtained hybrid electric vehicle powertrain configurations under city driving cycle,highway driving cycle and comprehensive driving cycle,the optimal configurations which possess the best fuel economy,accelerating performance and comprehensive performance respectively are acquired.