The problem of GWN Niola V., Avagliano V., Quaremba G. Department of Mechanics and Energetics University of Naples “Federico II” Via Claudio 21, 80125, Napoli, ITALY vincenzo.niola@unina.it http://niola.dime.unina.it/ quaremba@unina.it Abstract – The Gear Whine Noise (GWN), as well as the gear rattle noise, is one of the main vibro-acoustic phenomena of gearbox. For that reason GWN is an important problem to solve or to reduce or to "manage" at least in an appropriate way. Running conditions of the gear-box were reproduced by means of an innovative test-bed, which allows to perform the test without using the engine. This means that the noise and vibration due to the engine were not introduced into the system. From this point of view we say that the present study was performed in optical Noise, Vibration and Harshness. Key-Words: - vibro-acoustic emission, gearbox, gear whine noise, automotive, driving comfort. 1 Introduction Recent marketing research, carried out on car buyers, showed that customer expectations have changed on the automobile choice. In fact, since 1990, a statistical study showed that the sources of dissatisfaction, before and after buying the vehicle, also affect the appearance of the vibro-acoustic comfort inside the car. In the past, this factor was almost always overshadowed with reference, for example, to performance as fuel economy, safety and price. In addition, the increasing competition between car manufacturers led, nowadays, a significant reduction of level of noise due to the engine, for example by adopting new design solutions and / or absorbing and damping materials. Then, new important sources of noise, in the past "hidden" from the engine, are important. They are now in a position to affect the perception of sound within the car. A car, in fact, from a vibro-acoustic point of view can be defined as a "complex system", consisting of "primary sources of excitation” which directly generate vibration and noise, and of "passive elements” which transmit acoustic energy and vibration between the sources and the passenger compartment. The diffusion of this kind of energy between the primary sources and the ear of the driver/passenger is transmitted simultaneously by air and by structural elements. In order to get a good acoustic comfort in the cabin we should intervene on both the primary sources, by reducing the primary excitation, and on the "passive" elements by decreasing the transmission of vibro-acoustic phenomena. Continuing advances, in the automotive industry in recent years, lead the manufacturers of automobiles to develop more and more advanced products both from technical and quality point of view. In addition, consumer needs, aligned with the highest standards nowadays achieved, prevent manufacturers to make vehicles of poor quality [1]. This is the reason the major car manufacturers devote significant resources to the Noise, Vibration and Harshness (NVH) which deals with noise and car vibration also the driving comfort [2]. The present work was aimed to analyze two gearboxes, made by the same manufacturer, for the objective assessment of its vibro-acoustic emissions due to the phenomenon of gear whine. This article reports the results of several tests, carried out in optical gear whine noise for evaluating the difference between the vibro- acoustic emission of two gearboxes of the same type, one, in particular, showing a micro- geometrical error located on the side of tooth and characterized by lack of material at the base of the tooth due to a slight drift of the production process. All tests were carried out in the fourth gear [3]. The user of the vehicle, in fact, seems to be particularly attentive to the vibro-acoustic emissions. For that reason the major car manufacturers devote significant resources to solve the problem of Noise, Vibration and Harshness, which deals to improve the standard of driving comfort of the vehicle by reducing noise and vibration. Mathematical Methods and Techniques in Engineering and Environmental Science ISBN: 978-1-61804-046-6 363