1991-09-01

Reducing Vibration of Reciprocating Engines with Crankshaft Pendulum Vibration Absorbers 911876

Four-cylinder in-line automobile engines are inexpensive to build and economical to operate. However, they produce high crankshaft torsional vibration and high engine block vibration. Traditional ways to reduce this vibration may harm driveability and fuel economy, and may increase the cost of construction. Crankshaft-mounted pendulums have the potential to simultaneously reduce crankshaft torsional vibration and block shake at a reasonable cost without affecting driveability and fuel economy.Described in this paper is a study of the feasibility of applying pendulums to modern four-cylinder engines. The study involved the design, construction and testing of hardware, and an extensive analysis effort. Explored by analysis were optimal trajectories for pendulum motion, strategies for tuning sets of pendulums, the stability of pendulum motion and the shaking behavior of engines equipped with pendulums.Established by both analysis and test was that crank-shaft-mounted pendulums can reduce torsional vibration by over 90%. Vehicle test established that there were subjective improvements in NVH (Noise, Vibration and Harshness) and further that lugging performance - low speed, wide open throttle performance - was dramatically improved. The reduction in block shake observed during test was more modest than the reduction of torsion. Analytical studies of shake performance produced predictions of reductions in the range of 40% to over 70% for realistic pendulum damping and for realistic configurations.Shown by the study is the feasibility of crankshaft-mounted pendulums for reducing torsional vibration in modern four-cylinder automotive engines. Also shown is that crankshaft-mounted pendulums is a promising technology for reducing shake in four-cylinder engines.

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