Precision requirements for the bifilar hinge slots of a centrifugal pendulum vibration absorber

Centrifugal pendulum vibration absorbers (CPVAs) are designed to respond to torsional excitation within a centrifugal field so that their dynamic reaction tends to reduce the torsional oscillation of the system in which they operate. A differentiating feature of a CPVA is that it is tuned not to a single frequency (as are traditional frequency tuned dampers), but rather to a multiple of average rotation speed, or order. Because rotating machinery tends to produce torsional oscillation at a rate that is a multiple of average rotation speed, when tuned properly, CPVAs can correct a specific order torsional vibration at all speeds. In order to function properly, CPVAs must be tuned precisely in relation to the excitation order they are to correct, which in turn implies that the machined pieces that define pendulum motion paths must be cut precisely. This article develops a novel technique for determining the cutting precision required to maintain a prescribed target tuning range for a CPVA. The investigation focuses on the precision required for the most common type of hinge used to create centrifugal pendulums, the bifilar hinge. Two types of machining errors are analyzed: coarse location error for hinge cut-outs, and radius of curvature errors within the cut-outs. Sensitivities for each type of error are derived. Results are applied to analyze CPVAs integrated into the design of an engine crankshaft for the purpose of improving automotive noise, vibration, and harshness (NVH).