Traditionally, dry friction non-linear elements have been treated as vibration dampers, in parallel with elastic elements. However, in some practical systems (including automotive drivelines) the dry friction element (with high saturation torque) exists by itself and it functions as a key power transmission path for both mean and dynamic loads. First, to address such path issues, we examine multi-degree of freedom torsional systems with time-invariant normal load. A procedure to predict pure stick to stick-slip boundaries, based on a linear system theory, is developed when the torsional system is excited by harmonic excitation. For non-linear studies, both discontinuous and smoothened friction formulations are examined. The effects of a secondary inertia are analytically and numerically investigated. Results show that the secondary mass significantly affects the quasi-discontinuous nature of the system response. Next, in order to fully understand the non-linear frequency characteristics generated by stick-slip vibration, a new analytical method is developed based on assumed torque and velocity profiles. Super-harmonics are efficiently calculated and effect of the mean torque is qualitatively identified. Further, a refined multi-term harmonic balance proposed and associated computational issues are addressed. Studies show that the mean load significantly affects the response as it could induce asymmetric stick-slip motions.
Second, the effect of time varying actuation pressure (or the normal load) on the dry friction element on transient and steady state responses has been studied. Analytical solution for pure slip motion is obtained based on an approximate linear system model. Effects of time-varying parameters, such as phase, frequency and amplitude of the actuation pressure are observed over several frequency regimes. The negative friction slope is found to be the major cause of judder-induced phenomena such as bifurcations and quasi-periodic or chaotic responses. Some instabilities such as abrupt jumps in the amplitude-frequency maps of relative velocity are also seen around the super-harmonic peak frequencies.
|School:||The Ohio State University|
|School Location:||United States -- Ohio|
|Source:||DAI-B 79/09(E), Dissertation Abstracts International|
|Keywords:||Automotive drivetrain, Dry friction path, Non-linear vibration, Torsional system|
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