Design Of The Electronic Throttle Control System

With the development of automotive industry, measures have been taken to improve the dynamic performance and fuel economy of automobile, now more and more attention has been paid to the security, stability and driveability of passenger car. Conventional mechanism modulation and control method are difficult to optimize the performance of automobile, so electronic control is the trend of steering device. The need for improved performance leads to powerful engine management system, complex software structure and control algorithms. Torque-based engine management system, which could coordinate torque demands of different modules and need better control of the inlet airflow, is regarded as a promising way. Electronic throttle control system, which could control the inlet airflow based on the required torque of engine, is considered as a viable alternative to conventional air management systems. The electronic throttle control (ETC) system is a drive-by-wire system in which the mechanical linkages between the accelerator and the throttle are replaced with pairs of sensors and actuators. The input signal of accelerator pedal is considered as the driver torque demand, all torque demands are coordinated and prioritized by the torque-based control architecture, and the final torque request is output. Also the required airflow is calculated by the engine management system and corresponding control signal is output to the actuator, then the throttle reaches the desired position. ETC systems have entered mass production abroad, while it comes into use only in recent years at home and there is less research in this field. A set of electronic control system has been designed in this dissertation. The main study include analyzing the structure and function of the electronic throttle, calibrating the output voltage characteristic of sensors, developing the hardware and software of the control system, establishing the mathematical model of the electronic throttle, investigating the non-linear characteristic of the throttle, and comparing the results of different control strategy. The electronic throttle control system is composed of throttle body, accelerator pedal module and control unit. The throttle body comprises the throttle plate, a DC motor, return springs, a set of reduction gears and throttle position sensors. The accelerator pedal module is a steering device which combines the pedal function and the mechanical linkage. In order to improve reliability, both the throttle position sensors and the accelerator pedal position sensors have hardware redundancy to make it likely that a hardware fault is detected. It is found that the outputs of TPS potentiometers are complementary so that the sum of the two signals equals the supply voltage, and the output of PPS1 is twice of that of PPS2. The ETC system is a closed-loop control system and the position of the throttle plate is precisely controlled through the DC motor. So the hardware has to meet the required function of the system. In this paper, a 16 bit micro-controller 80C196KC produced by Intel is selected as main processor, external EPROM, RAM and I/O are extended, communication circuit is designed, and different power electronics are applied to control the DC motor. Micro-controller samples throttle position and pedal position and the ETC tracking control running on the micro-controller will generate the proper PWM duty cycle. The PWM signal will be amplified through electrical circuits to drive the motor to rotate so that the throttle plate can be controlled to the desired position. In this paper, a power-MOSFET IRF460 enables the motor to rotate clockwise, while a semiconductor H-bridge TLE6209 enables the motor to rotate bidirectionally. Detailed mathematical model of ETC will play a crucial role in the design of control algorithm. The mathematical model includes the differential equations to describe the electrical dynamics of the motor and the mechanical dynamics of the throttle plate, from which the complete state equation could be established and the block diagram of ETC transfer function could be drawn. The dynamics characteristic of ETC has shown that at different rotation range or tendency the required motor torque is different because the torque of the return spring changes direction at default position, thus the control signal is different. So non-linearity makes it difficult to control the ETC and non-linear control theory must be adopted. In this paper, conventional PID and variable integral PID are designed; concerning the presence of non-linearity in the throttle dynamics, sliding mode controller is designed to realize accurate tracking control and Lyapunov function ensures the stableness of the system. The software, which is programmed with C language for micro-controller, accomplishes control function and serial communication function. The control function achieves closed loop control of throttle plate position, and is composed of pre-treatment part and main-circulation part. The chief modules include sampling of the throttle position and pedal position, diagnosis of TPS and PPS, calculation of control value, and so on. In order to display the state of the system in real time and...