Research On Characteristics And Control Strategies Of Automatic Mechanical Transmission With Gearshift Assistant Mechanism

Improving the overall efficiency of the automatic transmission has become a crucial research topic on vehicle emission reduction without compromising its dynamic performance and riding comfort.Automatic transmission simplified the operation process,alleviate the driver's driving intensity,and make the vehicle power source work in the high-efficiency area through reasonable gear shift.The growing application of automatic transmission in vehicles is a general trend in the current era,and the performance of automatic transmission directly affects the reliability,dynamic performance,and riding comfort of the vehicle.Automatic mechanical transmission(AMT)is a manual transmission with an automatic gearshift module and an automatic clutch control module.It has the advantages of large torque compacity,high efficiency,low cost,and good production inheritance,which makes it widely applied in heavy commercial vehicles,and has the potential for application in hybrid vehicles and pure electric vehicles.The main problem of AMT is the vibration of the driveline caused by torque interruption and improper clutch engagement and disengagement.Excessive or long-term vibration and torque interruption of the powertrain will deteriorate the riding comfort and restrict the application of AMT in the field of passenger cars.To improve the foregoing disadvantages of AMT,the concept of a gearshift assist mechanism is proposed in this paper and a thorough investigation is carried out on its implementation on AMT.The main research contents include the following aspects:(1)The concept of AMT with a gearshift assistant mechanism is proposed.A synchronizing clutch is applied to replace the roles of the clutch and synchronizer of traditional AMT in the shifting process.The driving plate of the synchronizing clutch is connected with the engine,and the driven plate is connected with the output shaft.If the gear ratio of the epicyclic mechanism meets the design principles,the engagement of the synchronizing clutch can synchronize the pre-shift gear with its coaxial shaft.Once the gear is locked with the output shaft,the engine can directly recover the power supply to finish the gearshift.The proposed structure simplifies the shifting process to some extent.(2)The mathematical model of the whole powertrain system and the gearshift assistant mechanism are established.The models are constructed on MATLAB /Simulink platform.The whole powertrain system model includes the vehicle hardware model,driver model,the driving resistance model,etc.The model of gearshift assistant mechanisms is presented based on the detailed kinematic and dynamic characteristics analysis of gearshift assistant mechanisms for coaxial AMT and biaxial AMT.(3)The optimal launch control of biaxial AMT with a gearshift assistant mechanism is carried out.The LQR controller considering system disturbance is applied to control the launch process of biaxial AMT with a gearshift assistant mechanism.In the launch process,the motor in the gearshift assistant mechanism does not work,and the transmission output torque in phase is completely provided by the engine and transmitted by the synchronizing clutch.In the design process of the LQR controller,a quadratic objective function including the angular velocity difference of synchronizing clutch and sliding friction work is established,and the system disturbance is introduced into the multiplier of Hamilton function to enhance the robustness of the controller.The simulation results demonstrate the magnitude of the torque transmitted by the clutch on different slopes and the robustness of the controller under the corresponding conditions is also presented.The feasibility of the synchronizing clutch applied in the vehicle launch process is verified.(4)The decoupling control scheme of the coaxial AMT with a gear shift assistant mechanism in the upshift process is proposed.To eliminate or alleviate the coupling effect between the motor torque and the synchronizing clutch friction torque during gearshift,and make the clutch engagement process and transmission output torque track the reference trajectory respectively,the decoupling controller,disturbance compensator,and PID feedback controllers are applied.The simulation results show that the control algorithm can effectively decouple the control inputs of the system.The system dynamic in the fast upshift process is demonstrated,and the effectiveness of the proposed gearshift assistant mechanism is verified.(5)A sub-optimal PID parameter self-tuning method based on the system timedomain response is proposed.In order to make the controllers robust to the system parameter perturbation caused by the varying vehicle driving environment and clutch friction coefficient,it is necessary to determine the PID control parameters in prespecified system states under the premise that the according system states are accurately estimated.In this paper,the self-tuning method of PID parameters considers the time series data of the system output and the target value into the objective function and uses the downhill simplex method to automatically search its suboptimal solution.The algorithm can be completely and automatically calculated by the computer,which greatly reduces the workload of PID parameter tuning.The simulation results show the impact of the relevant parameter change on the iterative results.With the perturbed parameters well estimated,the satisfactory PID parameters can be automatically adjusted and effectively improve the robustness of the control strategy.(6)The gear meshing loss analysis model of the gearshift assistant mechanism is established.To accurately evaluate the energy consumption loss caused by the gearshift assistant mechanism,based on the general equation of gear meshing friction loss,Willis equation,and power flow analysis method,a general efficiency analysis model of gear meshing friction loss of transmission employing multiple epicyclic mechanisms is proposed,and the numerical relationship including the meshing loss of the epicyclic mechanism,the working state and the number of teeth of each gear is clarified.The efficiency model is embedded in the whole powertrain model for simulation.The simulation results show that under the FTP-75 driving cycle,the gear meshing loss power caused by the gearshift assistant mechanism only accounts for about 0.23% of the total power loss.(7)Taking the efficiency of the shift assistant mechanism as the research object,a gear ratio matching algorithm is proposed to reduce the friction loss of the clutch plate.Since the gear ratio of the gearshift assistant mechanism is determined by the gear ratio of the epicyclic mechanism and toque complementary gear-pair,the gear ratios may not be able to accurately match the target ratios.The greater the difference between the matched gear ratios and the target ones,the greater the friction loss of the synchronizing clutch will be.The gear ratio matching algorithm simply calculates and stores all possible gear ratios and corresponding working modes of the multi-row simple epicyclic mechanism,and then selects the appropriate ones from them.In this paper,through theoretical analysis and simulation test research,the proposed AMT with a gearshift assistant mechanism is thoroughly studied.The simulation results show that AMT with a gearshift assistant mechanism can simplify the shifting process and compensate power interruption at the cost of low friction loss,which has certain reference value for the future development and application of AMT.