| The multi-mode continuously variable transmission for vehicles could fully adapt to the complex driving conditions of the vehicle.It greatly expanded the adaptability of the Continuously Variable Transmission(CVT)in terms of expanding the speed range,power capacity,and improving the transmission efficiency.In addition,it was also possible to provide hybrid functions for vehicles by equipping with energy storage devices.However,its design schemes and operation modes were quite complex.The existing analysis methods were aimed at specific structural prototypes and could not handle the diversity of design schemes and operation modes at the design stage.The purposes of this study were to seek general methods for the analysis and design of such devices,to study the driving dynamics,fuel economy and power ow reversibility of the designed multi-mode continuously variable transmission,and to test the steady-state performance of the multi-mode continuously variable transmission.It was expected to provide theoretical and experimental basis for the independent design and development of multi-mode continuously variable transmissions.The main research contents were as follows:(1)Research on power split planetary gear train energy theory.Diferential gear trains,single-loop systems and double-loop systems were the core components of the multi-mode continuously variable transmission.Firstly,according to the kinematic equation,the moment balance equation and the power balance equation,the power distribution coefficient of the differential gear train was established,and then the internal power flow decision criterion of the single-loop system and the double-loop sysctem were established.Using node power method,the efficiency equations of differential gear train,single loop system and double loop system were given.On this basis,the general analysis steps of internal power flow and system efficiency were summarized,which could be used for the third loop and above system devices to analysis of the internal power flow and efficiency characteristics.(2)Research on design guidelines of multi-mode continuously variable transmission.Three kinds of multi-mode continuously variable transmission design schemes were proposed.Theirs structural diagrams,speed regulation characteristics,power flow characteristics and efficiency characteristics were given.The concept of multi-mode continuously variable transmission were proposed.The design guidelines of multi-mode continuously variable transmission were established.Given the CVT speed ratio range,the system speed ratio range,and the continuously variable transmission branch power split ratio limit range,the structural parameters of the differential gear train and the fixed ratio mechanism were determined.Three multi-mode continuously variable transmission design examples were given.The influence of structural parameters on the CVT load were discussed.(3)Research on driving dynamics of vehicle with multi-mode continuously variable transmission.Bond graph model of the vehicle equipped with single-loop system,direct +XP type(clockwise circulation)multi-mode continuously variable transmission,XP + PX type multi-mode continuously variable transmission,Infinitely Variable Transmission(IVT)were established.The state equations of these systems were deduced.The powertrain parameters,the structural scheme and parameters of the transmission were given.The simulation models of the vehicle were established.Given UDDS driving cycles,using the best fuel economy control strategy,the driving dynamics of the vehicle were investigated.(4)Research on performance of parallel hybrid powertrain.The PX type single-loop system was adopted.It could effectively avoid the CVT’s torque and power capacity.By serially connection to 2-speed gearbox,the PX type single-loop system ratio spread was enlarged.For regenerative braking mode,the power flow reversibility of the PX single loop system was verified.The bond graph model of the powertrain was established,and the state equations of the system were given.The vehicle simulation model were established.Given the highway portion of the US06 driving cycles,using rule-based control strategy,the performances of the parallel hybrid powertrain were investigated.(5)Research on fuel economy of vehicle with multi-mode continuously variable transmission.Four multi-mode continuously variable transmissions were proposed.Theirs design parameters,speed ratio ranges and specifications were given.The efficiency model of five transmission schemes were established.According to the engine efficiency model,transmission efficiency model,vehicle dynamics model,and given operating conditions,the optimal transmission ratio could be calculated by the off-line optimization algorithm,and the optimal transmission ratio could be looked up to achieve the control strategy of minimizing equivalent fuel consumption.By establishing a backward-facing vehicle simulation model,under UDDS cycle,the fuel economy of five transmission schemes were evaluated.(6)Performance experimental verification of multi-mode continuously variable transmission.A multi-functional modular power split planetary gear train test bench was built.By adjusting differential gear train module and fixed ratio mechanism module,a multi-mode multi-speed gearbox could be achieved.The multi-mode multi-speed gearbox was used to approximately verify the steady-state performance of the multi-mode continuously variable transmission.As the premise and basis for other performance verification,for the first time,a full tests were conducted for the XP-type and PX-type single-loop systems,under three internal power flow states of power split,counter-clockwise circulation,and clockwise circulation.By comparing the experimental results with the theoretical model results.The energy theory of the power split planetary gear train were verified. |
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