Study On The Automatic Control Of Hill-start Assist System For AMT System

Electronic technology in vehicle integrates auto technology with electron technology. So, as technology of auto and electron developing, the application of electronic technology to vehicle becomes more and more extensive and the electronic grade of vehicle becomes higher. Automatic mechanical transmission (AMT) is the outcome of the development of electronic technology. It greatly improves the convenience of vehicle and reduces the intensity of drivers'work and satisfies drivers'requirements.Automatic mechanical transmission (AMT) is based on the structure of the traditional mechanical transmission, through the installation of computer-controlled automatic control agencies, makes the traditional transmission achieve the high efficiency, low cost automatic control. Regarding the hill-start, the mechanical transmission depends on the driver's skilled driving technology to coordinate the brake releasing, the clutch engagement and the engine refueling to achieve a smooth start. But the AMT system has cancelled the clutch pedal, the driver can not apperceive the clutch's position , so that the control of hill starting is to be more difficult. Thus, the control of hill starting becomes one of the key technologies for AMT's merchandization, and difficulty in uphill start is its disadvantage compared to torque convert type automatic transmission. At present, regarding the AMT's hill starting problem, the solution is to install the hill-start assist system (HAS). So which studies on the automatic control of hill-start assist system for AMT has the important practical significance.HAS is a kind of active control function, the driver can choose the active function by HAS switch. HAS can effectively avoid the vehicle's backward motion when driver releases the brake pedal and steps down the accelerator pedal in the process of ramp starting. Typical HAS is primarily through controlling the isolation valve which locates between the brake master cylinder and wheel cylinder to realize the hill-start assist function. When the vehicle starts on the slope way, without using the parking brake to prevent backward motion, the driver steps on the brake pedal and trigger the electromagnetic isolation valve to close the oil pipeline from wheel cylinder to master cylinder. Then maintains the wheel cylinder's pressure and gives drivers enough time to shift and step on the accelerator pedal. When the clutch engages to a certain degree, which its passed torque just can overcome the start resistance, the isolation valve's power loses, relieves the applied braking force rapidly and realizes a smooth start. In the process, the hard point of control is when to relieve braking force. This requires the aid of automatic mechanical transmission (AMT) technology. Furthermore, the identification of hill-start resistance and HAS function triggered by the driver, these limit its scope of application.This article has firstly analyzed the difficulty of hill starting control for AMT, and researches the structure of AMT and control theory and host control procedure, Then proposes the automatic control question of AMT's hill-start assist system, that is to remove the step of driver's gradient judgement and trigger HAS by automatic identification function. Through stress analysis for car with the traditional mechanical type transmission in the process of uphill start, we obtain the questions on which should pay attention. Simultaneously propose the hill-start resistance identification method and the ramp travel condition recognition method based on the automobile travel dynamics, and design the slope way travel state fuzzy identification module. Then we establish the hill starting dynamics model and put forward with the control method of clutch engagement when the vehicle starts on the slope way, which is based on the analysis of the model and the result of hill-start resistance identification. Now the paper analyses the structure of HAS system and its work process. According as the holistic analysis of hill starting assist system, then chooses the kind of HAS electromagnetic valve. According to the research and the application experience, the core problem of HAS's application is the control of the isolation valve, namely when to relieve the brake force. This requires that the work of clutch must real-timely feed back to the ECU .At the same time, the ECU identifies the start resistance. Based on the identification result of start resistance, the ECU judges an appropriate time to send the'off'instruction to the electromagnetic valve. And then the brake is relieved, so the vehicle starts smoothly. Specially the paper proposes the automatic control logic for HAS system, that is, the automatic trigger of HAS function based on the outcome of the fuzzy identification module of ramp travel state, and the automatic release control of HAS electromagnetic valve based on the result of the identification module of hill-start resistance. At the same time, this paper designs the main hardware and software of HAS system, according to the automatic control logic for HAS.At last, this paper applies the MATLAB/Simulink software to establish the vehicle dynamics simulation model equipped with the fuzzy identification module of ramp driving state and the entire vehicle simulation model equipped with the HAS system automatic control module. Through the model simulation, the validity of the fuzzy identification module of ramp travel state is affirmed to be efficaciously, and the feasibility and validity of the automatic control method of HAS system is confirmed.