Dynamic analysis of speed-dependent friction-induced torque in a nonlinear brake system
Başlık çevirisi mevcut değil.
- Tez No: 400097
- Danışmanlar: PROF. RAJENDRA SİNGH
- Tez Türü: Doktora
- Konular: Makine Mühendisliği, Mechanical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2012
- Dil: İngilizce
- Üniversite: The Ohio State University
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 195
Özet
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Özet (Çeviri)
This study examines a low frequency, friction induced brake vibration problem(often known as the judder phenomenon in automobiles) that is excited by the surfacedistortions in the rotor. A nonlinear brake system is analyzed using experimental,analytical, and numerical approaches, though the main goal is to find new or improvedanalytical solutions for the speed-dependent characteristics of the governing system.Initially, a two degree of freedom torsional model of the brake system with clearancenonlinearity is proposed, where the main excitation is the multiple order frictional torque,as related to the rotor profile imperfections. The nonlinear model is first simplified as aquasi-linear model by ignoring the clearance, and closed form solutions (for adecelerating system) are obtained with and without the viscous damping element. Newsolutions match well with the numerical integration and numerical convolution results.The nonlinear model is then numerically solved using two different methods to calculatethe speed-dependent friction induced torques. The discontinuous curves are firstapproximated with smoothening functions, and then event detection and locationalgorithms are utilized. Both approaches compare well unless the discontinuous functionsare poorly smoothed.Second, quasi-linear and nonlinear models are utilized to calculate the envelopesof the response amplitudes over a range of applicable speeds. The envelope functions arefirst derived from the closed form analytical solutions of the quasi-linear model. Inaddition, a Hilbert transform based envelope curve prediction method is proposed andapplied to both quasi-linear and nonlinear models. Envelope curves are calculated forsingle and multiple order rotor surface excitations, and the estimations match well withanalytical and numerical solutions. Furthermore, the multi-term harmonic balancemethod is successfully adapted to construct the order domain solutions for the nonlinearmodel. The arc-length continuation scheme is successfully implemented and the stabilityof the solutions is checked.Third, a new dynamic friction experiment is designed and constructed with atorsional resonance and clearance nonlinearity. Experimental data clearly show thespeed-dependent behavior of the friction induced torque in the shaft, as controlled by themultiple orders of the rotor surface distortion. Key dynamic events that occur during abraking test are identified by using the time, frequency and order domainanalyses. Measurements are finally used to validate the nonlinear and quasi-linear modelsover the applicable speed ranges. Finally, a nonlinear brake pad model is developed toinvestigate the torque amplitude behavior observed at the higher speeds in the dynamicfriction experiment, and the effects of normal load and frictional constraints acting on thepad are studied. Nonlinear model is solved numerically for many normal load andconstraint combinations, and the peak-to-peak variations in the friction force arecompared. Tractable analytical solutions are obtained as well. Numerical and analyticalsolutions are validated with a bench experiment, where a translating brake band is used toreplace the brake rotor. The trends explain the significance of the center of contact forceconcept.
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