I. Introduction

    Electronic throttle (ETC) is the vehicle engine control system is an important subsystem. In this paper, ATmega 16 microcontroller for the control of the core, the German company Bosch Bosch electronic throttle for the study, through the accelerator pedal position sensor signal, and then after a single-chip process control algorithm to drive the throttle body (throttle body) on the DC servo motor, to rotate the disc drive to the specified throttle opening to achieve closed-loop control. Meanwhile, the host computer via USB to RS 232 interface for communication with the MCU to facilitate system debug and run.

    Second, the hardware system design

    The system block diagram of hardware design, which includes the chip and its peripheral circuits, integrated throttle body, DC motor drive circuit, pedal position signal detection circuit. In addition, the microcontroller via USB. RS232 interface, data exchange with the host machine, man-machine dialogue. The following were stated as follows:

    1, ATmega 16 control core

    The system uses a microcontroller to control the core, the model for ATmega 16 (16 MHz crystal). It uses an advanced RISC architecture with a high speed, low-power, anti-interference ability and so on. Because of its own three-channel PWM output and eight 10-bit ADC converter, which is very easy to control the system.

    2, the motor drive circuit

    The system drive circuit using National Semiconductor has introduced a special H-bridge for motion control components LMD18200. The components are integrated on a CMOS control circuitry, and DMOS power devices, the continuous output current of 3 A, and also has a temperature alarm, overheat and short circuit protection, thus making the entire control system has been simplified. Motor drive with single-chip interface circuit.

    3, integrated electronic throttle body

    The throttle system is produced for the German company Bosch, model 06813306, and its structure appearance. Include:

    (1) accelerator pedal position sensor

    This sensor is mounted on the accelerator pedal, the pedal moves into volume with different output characteristics of two types of signal (the step size and the amount of change in rate), transmitted to the microcontroller.

    (2) throttle position sensor

    Throttle position sensor (two potentiometers) and sliding vane and throttle coaxial, when the throttle rotates, simultaneously rotating vane potentiometer, which will be of mutual monitoring throttle opening signal is converted to electrical signals output to the microcontroller.

    (3) DC servo motor

    By PWM control of motor, gear reducer and then after two, you can adjust the throttle opening, the throttle gear reduction ratio is:
   
    The system input is a pedal input θR (t), output is the throttle opening θ (t). Fuzzy parameter regulator is input into the amount of accelerator pedal θR (t) and θ (t) the difference between throttle opening and the rate of change of E Ec. PID controller output is the three control parameters KP, KI, KD. System based on conventional PID controller to get the experience of experts to form the fuzzy control rules for reasoning judgments, and thus the PID controller to achieve three-line self-tuning control parameters, to form different PWM output signal, thus completing the DC motor control valve.

    Third, the control system software design
   
    1, PC software design

    For ease of operation and check the adjustment result, the use of auxiliary control PC software. Matlab 7.0 was chosen to do GUI control, mainly because of strong technical support Matlab platform, its signal processing and graphics, is the superiority of VC # or VB 6. O, the most commonly used PC software can not be replaced. The system GUI Main features include: mode selection, system operation, overcurrent and handshake response display, PC software interface shown in Figure 5.

    Described as follows:

    System, PC and slave serial asynchronous mode communication protocol is as follows: Baud Rate 9 600 b / s, 1 start bit, 1 stop bit, no parity. Serial data is read using the query means, read the serial data, receive data with a continuous soft (continuous) of the default mode, so the next crew to return the data automatically into the input buffer.

    Software serial port initialization settings are as follows:

    Users may need to select the serial port. Design, using pop-up form, the callback function is:
   
    Parameter set, the user through the "parameter" button, the down-bit machine running pass patterns and other related operating parameters. Get a response after the run button to start the user through the system. In the design, in order to achieve interactive input, such as calling the set and get callback function, you should also pay particular attention to data type conversions, otherwise, they can not achieve interactive operation.

    2, lower computer software design

    SCM software system uses CodeVersionAVR programming environment, the program by the former, daemon form. Foreground program including system initialization and loop detection procedures. Daemon program includes the software timer interrupt, serial port and serial port interrupt reception interrupt subroutine to send the program, over-current protection outside the interrupt routine.

    Initialization procedures will include single-chip I / O port initialization, two A / D conversion initialization (pedal sensor A / D conversion initialization and throttle opening sensor A / D converter A / D initial initialization), serial communication port initialization and the initialization of the microcontroller PWM and so on. System initialization is complete, wait for interrupt, the interrupt routine to complete the processing.

    For software timer, using 8-bit T / CO of the CTC mode, the time setting time of 20 ms. Microcontroller to be completed and the throttle pedal position signal read and A / D conversion, fuzzy control algorithm, and the microcontroller PWM signal output function.

    The output of the PWM drive circuit, using the second function of the microcontroller pin PD3 OCl, is used in the phase correct PWM mode. Program design, by changing the input capture register ICRl values ​​to change the PWM frequency, change OCRlA output compare register to change the PWM duty cycle. We found that the motor PWM frequency of the motor has a great influence. Flutter frequency is too low then the motor is too large extent, does not meet the high accuracy electronic throttle control requirements; the motor generates high frequency shrill beep. Through continuous commissioning, found that the motor pulse width modulation frequency of 1 200 Hz or so best.

    IV Conclusion

    Electronic throttle system is a complex nonlinear system, the presence of non-linear factors will affect the system's control accuracy and response characteristics. The system uses fuzzy parameter self-tuning control strategy to achieve precise control of electronic throttle. Throttle control process without jitter, the middle position without oscillation, and the process of opening and closing the throttle, throttle movement was very smooth, so as to achieve the desired purpose.