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Horns are an integral part of any automotive vehicle as a warning device. In countries having high vehicle population density like India, honking noise is a major concern at present and in upcoming future. Until now, horn noise pollution parameters have not been given much importance, but understanding the horn at a basic level will help us reduce noise pollution. Two of the major horn types used in passenger vehicles are the shell and disc horns, respectively. From a manufacturing standpoint, vehicle manufacturers prefer to use disc horn as compared to shell horn due to its low cost and high reliability. Among these, shell horns have a better sound quality as compared to disc horn, consequently, horn manufacturers are working to improve the disc horn sound quality to match with shell horn. Hence, it is imperative to develop a simple model to understand vibration and noise generation mechanism. The aim of this paper is to develop an equivalent spring mass damper system of disc horn to estimate the vibration displacement at the centre of the diaphragm. This model will help us understand the relationship between input current and output noise generated. The horn works on the principle of magnetization and demagnetization. The solenoid in the horn is magnetized when the current is switched on, and it pulls down the voice coil attached to the diaphragm. This electromagnetic excitation force (EMF) controlled by the mechanical switch is predicted by solving Maxwell’s equation for given electrical current. During the downward motion, the circuit breaks due to detachment of the mechanical switch which leads to the demagnetization of the solenoid. The voice coil along with the diaphragm goes up due to the spring energy accumulated in the diaphragm during the downward motion. This back and forth motion of the diaphragm produces sound waves. An analytical model of the horn is developed in two cases as - 1. Only the Mechanical switch, 2.Mechanical switch along with diaphragm and the voice coil. For the first case, the mechanical switch is modeled as a cantilever beam under electromagnetic forcing. Vibration response at the point of forcing is predicted, which gives us an estimate of the displacement of the beam as a function of time. In the second case, diaphragm with voice coil and the mechanical switch components are assumed as lumped parameters and their masses, damping coefficients and stiffness are found. Based on experimental observations, horn working cycle in downward motion is divided into three stages of a single degree freedom system. This system is excited with the same EMF as given in the previous case and vibration response at each stage as a function of time is predicted. To validate the analytical results, a test rig is developed, which involves a horn with a provision to observe the motion, high-speed camera setup and two focused LED lights. The vibration displacement at switch contact is measured and compared with analytical results for the two cases. Both the results are in good agreement.
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