Research And Development Of Adjusting Electrical Horn

Vehicle horns can be mainly divided into two types: mechanical horns and electrical horns. Mechanical horn has short life expectancy because of touch of horn which can be easily damaged by high current and the spark. Electrical horn has longer life expectancy than mechanical horn but can not maintain good sound level under environmental changes or after being used for a long time because its frequency can not follow the resonant frequency of horn which is closely related to environment, material and quality of assembly. This project is supported by Shanghai Science Committee. The main task is to design adjusting frequency electrical horn for middle and high class automobiles. Adjusting frequency electrical horn inherits the advantages of mechanical horn such as better environmental adaptability and tracking capability, and it overcomes the disadvantage of shorter life expectancy of mechanical horn. It can be seen in the future that adjusting frequency electrical horn will replace mechanical horn and be applied in a large scale.In this paper, electrical horn products and patents are firstly surveyed, followed by various experiments and validation. With the knowledge of sound, vibration and electronics, three schemes were proposed. Signal generator was used to generate PWM waveforms to drive the horn and the duty ratio was set to 68% equal to that of mechanical horn. Using this method we can get optimal frequency of horn. For scheme imitating touch of mechanical horn and adjusting frequency horn using microphone, great efforts were made to form prototypes. Taking their performances, reliability and cost into consideration, we chose the scheme using microphone for further research. In this project, microphone was used to detect the sound and the output of microphone reflects the movement of diaphragm. After rectifying, filtering, frequency adapting, PWM waveform was generated to drive MOSFET, in that way, the horn speaked. Through this close-loop control system, the frequency of PWM waveform was close to resonant frequency of horn with 70% duty ratio.Samples of adjusting frequency electrical horn using microphone were produced to validate the design, including scheme using analogy circuit and scheme using microcontroller. Numerous tests were implemented to test the electrical horn using analogy circuit. These tests included tracking resonant frequency ability test, reliability under comprehensive environment, durability to succeed 500,000 times'operation. The result showed that the horn operated normally despite of changes in voltage, temperature, environment and assembly conditions. The horn could track the resonant frequency automatically. The sound level and sound effect met the requirement. The life expectancy exceeded 500,000 times with high reliability. The horn could work for a long time under high or low temperature environment. Results demonstrated that the sample horns met the requirements of GM2812 defined by General Motor. Now the patent application is under process.