Simulation Research Of The Idle Control Strategy Based On The Electronic Throttle

With the development of automotive industry, measures have been taken toimprove the dynamic performance and fuel economy of automobile, now moreand more attention has been paid to the security, stability and driveability ofpassenger car. Precise control of air and fuel to the spark-ignited engine is arequirement in meeting the emission regulations, and also in providing goodresponse and driveability. Conventional mechanism modulation and controlmethod are difficult to optimize the performance of automobile, so electroniccontrol is the trend of steering device. The need for improved performance leadsto powerful engine management system, complex software structure and controlalgorithms. Torque-based engine management system, which could coordinatetorque demands of different modules and need better control of the inlet airflow, isregarded as a promising way. Conventional air management systems arecontrolled through mechanical linkages, where the driver is in direct control of theair-throttling valve, so it is difficult to optimize the performance of the engine.Electronic throttle control system, which could control the inlet airflow based onthe required torque of engine, is considered as a viable alternative to conventionalair management systems.The electronic throttle control (ETC) system is a drive-by-wire system inwhich the mechanical linkages between the accelerator and the throttle arereplaced with pairs of sensors and actuators. The input signal of accelerator pedalis considered as the driver torque demand, all torque demands are coordinated andprioritized by the torque-based control architecture, and the final torque request isoutput. Also the required airflow is calculated by the engine management systemand corresponding control signal is output to the actuator, then the throttle reachesthe desired position. ETC systems have entered mass production abroad, while itcomes 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. Themain study include analyzing the structure and function of the electronic throttle,calibrating the output voltage characteristic of sensors, developing the hardwareand software of the control system, establishing the mathematical model of theelectronic throttle, investigating the non-linear characteristic of the throttle, andcomparing the results of different control strategy. The electronic throttle controlsystem 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 ofreduction gears and throttle position sensors. The accelerator pedal module is asteering device which combines the pedal function and the mechanical linkage.The ETC system is a closed-loop control system and the position of thethrottle plate is precisely controlled through the DC motor. So the hardware has tomeet the required function of the system. In this paper, a 16 bit micro-controller80C196KC produced by Intel is selected as main processor, external EPROM,RAM and I/O are extended, communication circuit is designed, and differentpower electronics are applied to control the DC motor. Micro-controller samplesthrottle position and pedal position and the ETC tracking control running on themicro-controller will generate the proper PWM duty cycle. The PWM signal willbe amplified through electrical circuits to drive the motor to rotate so that thethrottle plate can be controlled to the desired position. In this paper, asemiconductor H-bridge TLE6209 enables the motor to rotate in two directions.Detailed mathematical model of ETC will play a crucial role in the design ofcontrol algorithm. The mathematical model includes the differential equations todescribe the electrical dynamics of the motor and the mechanical dynamics of thethrottle plate, from which the complete state equation could be established and theblock diagram of ETC transfer function could be drawn. The dynamicscharacteristic of ETC has shown that at different rotation range or tendency therequired motor torque is different because the torque of the return spring changesdirection at default position, thus the control signal is different. So non-linearitymakes it difficult to control the ETC and non-linear control theory must beadopted. In this paper, conventional PID and fuzzy method is designed;The mathematic model of the throttle is designed and simulated inMatlab/simulink. In this paper, the general PID and fuzzy control method are usedin the simulation. And the dynamic test results show that the model can becontrolled precisely with H-bridge circuit and accurate math model.The control strategies are introduced and separated generally according to thestructure ideas. Related to the throttle control, the strategies of the idle speed andfast idle speed mode are designed. In Matlab, the models of the two modes aresimulated and the results show that it has fast responsibility and good stability andcan meet requirements of the modes control.Both step response and steady state tracking experiment have been done.Experiment results indicate that utilizing conventional gain-scheduled PID withpower-MOSFET as drive IC, the overshoot is great, the hysteresis is obvious andthe transient tracking error is large. Utilizing variable integral PID controlalgorithm with H-bridge as power electronic, the overshoot is reduced, thetransient tracking error is small, and the hysteresis is short. While utilizing thesliding mode controller with H-bridge as power electronic, the overshoot isgreatly reduced, and the transient tracking error is smaller, and the hysteresis isshort. This is because sliding mode control algorithm is a model-based controller,and it takes the dynamics of the ETC into account. In summary, we know thatsliding mode control theory with H-bridge as power electronic and based ondetailed mathematical model of the ETC performs well in terms of both transienttracking and steady tracking.