Research On Creeping Launch Control Method For AMT Heavy Commercial Vehicle

The Automated Mechanical Transmission(AMT)combines a mechanical manual transmission with electronic control technology.The transmission control unit(TCU)automatically controls the engagement and disengagement of the clutch and the selection and shifting of the transmission.AMT has the advantages of high transmission efficiency and suitable for multi gear transmission,and is currently the preferred automatic transmission form for heavy commercial vehicles at home and abroad.AMT heavy commercial vehicles require the vehicle to be able to drive at the low speed expected by the driver under conditions such as docking trailers,moving into storage,and exceeding the width limit door,so as to achieve accurate control of vehicle displacement by the driver.This low speed driving condition achieved by clutch sliding is a creeping condition.The creeping condition includes three stages: creeping start,low speed driving,and deceleration parking.The control of the clutch during the creeping start phase is to shift it from a disengaged state to a semi linked state,thereby enabling the vehicle to slowly accelerate from standstill to the driver’s desired creeping speed.This poses challenges to the control accuracy of the clutch,the identification of driving intentions,and the estimation of vehicle load,which is a difficult issue in the development of commercial vehicle AMT.This paper takes a domestic AMT heavy commercial vehicle as the research object,and conducts a research on creep start control strategy through a combination of simulation and experiment.The main contents are as follows:(1)The characteristics of the transmission torque of the clutch in the sliding state are analyzed,and a clutch test rig is built to obtain the relationship between the transmission torque of the clutch and the displacement of the actuator,thereby transforming the torque control of the clutch during the creeping start process into the displacement control of the actuator.The longitudinal dynamics and starting dynamics of the vehicle during creeping start are analyzed,and based on this,a complete vehicle powertrain model is built using Simulink software for simulation tests.(2)Based on the accelerator pedal opening test data,the driver’s creeping start intentions were classified into slow,medium,and fast creeping start intentions.The corresponding target creeping speed was established for the three creeping start intentions,and a BP neural network model was established to identify and estimate the start intentions and target speed.The recursive least square method is used to estimate the vehicle mass,the Kalman filter is used to estimate the road gradient,and the starting load torque is estimated based on the vehicle mass and road gradient.(3)According to the four evaluation indicators of creeping start quality,the optimal control amount of the engine and clutch is calculated based on the minimum principle,and the weight coefficients of the four evaluation indicators are determined based on the driver’s intention and load torque.In order to prevent the actual vehicle speed from overshooting relative to the target vehicle speed,the control strategy has been improved,that is,before reaching the target vehicle speed,the clutch changes from engaged control to disengaged control.Based on the improved creep start control strategy,the clutch target displacement trajectory is formulated,and a sliding mode controller for the clutch actuator is designed to accurately track it.A clutch temperature model is built to estimate the clutch temperature in real time,and use this temperature to correct the torque transmitted by the clutch.At the same time,the overtemperature protection function of the clutch is realized.(4)A real vehicle test platform was built with a 12 gear AMT heavy commercial vehicle as the test object.Based on the test platform,experiments related to the vehicle creep start control strategy were conducted.Through the analysis of the test results,the feasibility of its load torque estimation method,clutch displacement control,and creep start control strategy was verified.