Adaptive Pendulum Damps Low-Speed Engine Vibration

Engine vibration spikes dramatically at low rpm. Traditional methods to control the problem aren't always enough as carmakers shift to powerplants that are smaller but more powerful.

Researchers at Germany's Fraunhofer Institute say one solution may be their prototype adaptive centrifugal pendulum system. Developers will show the technology next month at the country's Hannover Messe 2013 show.

Carmakers often minimize the inherent torsional vibrations in their engines with a split flywheel mounted between the engine and transmission. The system features separate flywheel sections linked by a large spring that allows the halves to shift relative to each other and offset engine vibration.

But flywheel systems become less effective in small engines that produce high torque. Fraunhofer says its pendulum system offers greater control because it is able to damp first- and half-order vibrations.

Engine makers have used centrifugal pendulums for years to control vibration in airplane and ship engines. Such devices use a pendulum attached to a disk that is rotated by the engine. The pendulum oscillates at a frequency that varies directly with engine speed and counters the torsional vibration created by the powerplant itself.

Centrifugal pendulums began to show up in automotive applications a few years ago. But they oscillate only at a frequency set by engine speed. Fraunhofer says its design does the same but also can be made to oscillate at half that frequency, known as the 0.5 order.

The resulting technology simultaneously measures vibration in terms of both amplitude and engine speed. It adjusts to whichever type is dominant. Fraunhofer says this flexibility enables the new design to compensate for vibration over a range that otherwise would require two pendulums a configuration too bulky for small automotive engines.

The researchers say they aim to make their design more compact by optimizing the control system that switches the pendulum between first and 0.5 order frequencies.