"Centrifugal pendulum vibration absorbers (CPVAs) are used to reduce engine-order torsional vibrations in rotating systems. They are widely used in light aircraft piston engines and helicopter rotors and have recently been introduced for smoothing torsional vibrations in automotive powertrain applications. These absorbers make use of the centrifugal field due to rotation, in place of elastic elements, for their restoring force, so that they are tuned to a particular engine order, rather than a particular frequency, making them ideally suited for these applications. Increasing demands on fuel economy have led to engine downsizing and downspeeding, resulting in harsh torsional excitations being exerted on powertrain components, which are ultimately felt by passengers. In order to maintain durability and NVH performance specifications for these engines, sophisticated vibration control solutions are required, many of which currently involve CPVAs. The contributions made by this study are in three major topics, all related to the design and performance of CPVAs. The first is the development of a new numerical tool for the rapid analysis of the response of complex CPVA systems. This algorithm recasts the equations of motion in a way that significantly extends the applicability and accuracy of the widely known harmonic balance method. This method essentially automates the analysis of steady state responses of systems with multiple CPVAs, including their stability characteristics. This method is much faster than brute-force numerical simulations, and it allows designers to explore the response of systems that are not amenable to more traditional analysis tools, such as perturbation methods. The capabilities of this new tool are demonstrated through two example systems that are known to exhibit rich dynamical characteristics. The second topic is the investigation of a new configuration that uses CPVAs to eliminate crankshaft torsional resonances under order excitation. This dynamical system is a combination of a frequency based element, a shaft torsional vibration mode, and an order based element oscillator, the CPVA. We show that the linear natural frequencies of this system undergo eigenvalue veering as the engine speed is varied near the resonance point. The structure of this veering suggests that with proper tuning of the absorber, one can eliminate the shaft torsional resonance. We use perturbation methods to show that these results extend to operating conditions where the CPVA amplitudes are large and its response becomes nonlinear. The third topic deals with the design and analysis of a new type of kinematic suspension that increases the effective inertia of the absorber, thereby reducing the packaging space for these absorbers. We show that by employing non-symmetric cutouts for the rollers used in standard bifilar (two point) suspensions of CPVAs, we can specify both the rotational and translation motions of the absorber relative to the rotor. This allows designers to increase the effective inertia of the CPVA, thereby providing better vibration correction for a given amount of absorber mass. The dynamical response characteristics for this system are studied using both perturbation methods and the newly developed harmonic balance method. It is shown that this so-called "rocking" absorber configuration provides an improvement of about 15% when compared to its traditional counterpart."--Pages ii-iii.
Read
