EXPERIMENTAL EVALUATION AND SIMULATION OF TORQUE TRANSMISSIBILITY FREQUENCY RESPONSE FUNCTIONS OF VIBRATION ISOLATORS AND ABSORBERS FOR DRIVETRAIN APPLICATIONS

Four studies involving torsional vibration isolation performance of automotive drivetrain components, make up this dissertation. One study features a prototype planetary torsional vibration absorber, a unique device that targets low frequency torsion modes in automotive drivetrains. Two studies feature experiments on several torque converters, clutch locked and open, to validate models of the hardware. The last study details experiments on a centrifugal pendulum absorber in a torque converter, to characterize the viscous friction while submerged in automatic transmission fluid (ATF). The enclosed studies improve the state of the art of drivetrain vibration absorbers and isolators, by introducing a new vibration absorber concept and increasing understanding of the underlying physics of torque converters, lock-up clutch dampers, and centrifugal pendulum absorbers. The design and test of the planetary torsional vibration absorber concept demonstrated the utility of a gear reduction in increasing the apparent inertia of the absorber. By increasing its apparent inertia, the device successfully attenuated a ~20 Hz mode of vibration, and used less packaging volume and mass than a traditional torsional vibration absorber of equivalent performance. Various lockup clutch designs were characterized with torque transmissibility frequency response function (TTFRF) measurements while spinning at simulated vehicle operating conditions. This in situ testing lent itself useful in characterizing the speed dependent friction in a lockup clutch damper, while also confirming other damper parameters—like stiffness and damping. The torque converters were also tested in open mode (lockup clutch not engaged). The open mode testing revealed that the hydrodynamic torque converter transmits enough torsional vibration to excite the damper mode for the turbine damper architectures. The open clutch testing contributes a complete data set—encompassing a wide range of speed ratios—to verify torque converter models with. When comparing the test TTFRFs to model TTFRFs, a discrepancy in the damper mode’s natural frequency was revealed, and it was hypothesized that this error resulted from a reflected inertia effect of the ATF undergoing toroidal flow. The locked clutch testing provoked some questions about the centrifugal pendulum absorber (CPA)—a component of one of the tested torque converter clutch dampers. To validate an existing CPA model, and to characterize the equivalent viscous damping of the CPA mechanism, TTFRFs of custom made torque converters were measured. The custom hardware included: pinned damper (CPA active), pinned CPA (damper active), and pinned straight spring (CPA and arc spring active). The torques due to friction and viscous damping of the damper were effectively eliminated from the CPA, and the equivalent viscous damping of the CPA characterized

Design and test of a torsional vibration absorber in series with a planetary gearset

Traditional vibration absorbers have not often been a practical solution for attenuating low frequency drivetrain modes of vibration because of the combination of the large mass and inertia and/or low stiffness, required to tune to the desired frequency. With the goal of reducing the inertia and size of a torsional vibration absorber, a unique vibration absorber was developed. Using a planetary gearset, the effective inertia of the absorber was increased without changing its physical mass, and a torsional mode below 30 Hz was successfully attenuated with physically realizable inertia and stiffness parameters. By reducing the tuned mass, the total volume claimed by the vibration absorber and planetary gearset was up to three times less than an equivalent traditional vibration absorber. A lumped parameter torsional model was developed to determine the optimal configuration of the planetary gearset input, output, and absorber inertia as well as a method to predict the optimal tuning frequency of the planetary torsional vibration absorber. A drivetrain dynamometer setup which emulates a two-degree-of-freedom torsional system was used to experimentally test and validate the performance of two planetary torsional vibration absorber prototypes built based upon the results of the lumped parameter model. The dynamometer setup was designed to have a first torsional mode around 20 Hz in which the planetary torsional vibration absorber was designed to attenuate. Based upon the experimental results of the planetary torsional vibration absorber, a reduction of over 20 dB was achieved

Measurement methods for evaluating the frequency response function of a torque converter clutch

In developing new torque converter clutch (TCC) technology, it is desirable to have accurate models to have confidence in performance predictions. To develop and calibrate TCC models, a test cell has been developed to measure the torsional vibration isolation performance of TCCs. The isolation performance is defined as the ratio of output torque to input torque, or torque transmissibility. This test cell uses an electric motor as a torsional exciter and a secondary motor (absorbing dyno) to control the output speed of the TCC. This loading condition, input torque-output speed, replicates the loading seen in a vehicle drivetrain where the engine provides a torque to the input of the torque converter and the vehicle’s wheels provide the speed boundary condition to the output. The torque transmissibility plot is acquired using a stepped sine approach with three frequencies per measurement. Two other excitation methods will be investigated to further reduce testing time. Step inputs (both up and down) Pseudo-random excitation (constant amplitude, random phase) The torque transmissibility results of the new excitation methods will be compared to the previous measurement method for validation