【正文】 nd manufacturing tolerances. 2 AN INDUSTRIAL APPLICATION ? TRANSMISSION NOISE REDUCTION Introduction This section briefly describes the activities involved in reducing gear noise from a wheel loader transmission. The aim is to show how the optimization of the gear geometry described in Paper E is used in an industrial application. The author was project manager for the “noise work team” and performed the gear optimization. One of the requirements when developing a new automatic power transmission for a wheel loader was improving the transmission gear noise. The existing power transmission was known to be noisy. When driving at high speed in fourth gear, a high frequency gearwhine could be heard. Thus there were now demands for improved sound quality. The transmission is a typical wheel loader power transmission, consisting of a torque converter, a gearbox with four forward speeds and four reverse speeds, and a dropbox partly integrated with the dropbox is a chain of four gears transferring the powerto the output shaft. The gears are engaged by wet multidisc clutches actuated by the transmission hydraulic and control system. Gear noise target for the new transmission Experience has shown that the high frequency gear noise should be at least 15 dB below other noise sources such as the engine in order not to be perceived as disturbing or showed that if the gear noise could be decreased by 10 dB, this criterion should be satisfied with some margin. Frequency analysis of the noise measured in the driver39。ren Andersson (KTH), and Dr. Lars Br229。Gearbox Noise?Correlation with Transmission Error and Influence of Bearing Preload Doctoral Thesis in Machine Design TRITAMMK 2020:19 ISSN 14001179 ISRN/KTH/MMK/R08/19SE Department of Machine Design Royal institute of Technology SE?100 44 Stockholm, Sweeden 169。the (Volvo).The financial support of the Swedish Foundation for Strategic Research and the Swedish Agency for Innovation Systems – VINNOVA – is gratefully acknowledged. Volvo Construction Equipment is acknowledged for giving me the opportunity to devote time to this S246。s cab showed that the dominant noise from the transmission originated from the dropbox gears. The goal for transmission noise was thus formulated as follows: “The gear noise (sound pressure level) from the dropbox gears in the transmission should be decreased by 10 dB pared to the existing transmission in order not to be perceived as unpleasant. It was assumed that it would be necessary to make changes to both the gears and the transmission housing in order to decrease the gear noise sound pressure level by 10 dB. Noise and vibration measurements In order to establish a reference for the new transmission, noise and vibration were measured for the existing transmission. The transmission is driven by the same type of diesel engine used in a wheel loader. The engine and transmission are attached to the stand using the same rubber mounts that are used in a wheel loader in order to make the installation as similar as possible to the installation in a wheel loader. The output shaft is braked using an electrical brake. Optimization of gears Noiseoptimized dropbox gears were designed by choosing macro and microgeometries giving lower transmission error than the original (reference) gears. The gear geometry was chosen to yield a low transmission error for the relevant torque range, while also taking into consideration variations in the microgeometry due to manufacturing tolerances. The optimization of one gear pair is described in more detail in Paper error is considered an important excitation mechanism for gear whine. Welbourn [1] defines it as “the difference between the actual position of the output gear and the position it would occupy if the gear drive were perfectly conjugate.” In this project the aim was to reduce the maximum predicted transmission error amplitude at gear mesh frequency (first harmonic of gear mesh frequency) to less than 50% of the value for the reference gear pair. The first harmonic of transmission error is the amplitude of the part of the total transmission error that varies with a frequency equal to the gear mesh frequency. A torque range of 100 to 500 Nm was chosen because this is the torque interval in which