In an internal combustion engine, the impulse initiated by the combustion of gas within the cylinders is able to put the crankshaft into a rotating movement, thus transmitting a torque to the wheels through the drivetrain. However, the movement of the piston is not uniform, and the transmitted torque is far from being constant at a steady engine regime. Indeed, the important pressure variations on the piston as well as the influence of the alternating masses inertia create a periodic oscillation around an average value in torque. This creates a similar oscillation in angular acceleration, speed, and position, which is commonly referred to as torsional irregularity or rotational irregularity.

This oscillation tends to generate unacceptable noises, such as rattling noise in the gearbox, and fatigues the drivetrain parts, shortening the operating lifetime. For these reasons, such irregularities need to be reduced, which is traditionally done by a flywheel located between the crankshaft and the gearbox. However, due to the downsizing of engines for fuel-consumption reasons, the simple flywheel is not enough anymore for acceptable noise levels.

This rotational irregularity phenomenon can be further amplified when the critical frequency of the crankshaft is a multiple of the current engine average speed. Here again, the downsizing is a problem as a crankshaft length reduction increases the critical frequency, enabling a larger spectrum of engine speeds to excite the resonance.

We develop here a new concept of a damper, based on the generation of a counteracting torque by a set of permanent magnets and coils, as in active ways of reducing torsional irregularities, coupled with the principle of the Tuned Mass Damper (TMD), efficient against resonance issues. The TMD is embedding a permanent magnet that moves in a coil. The variation of magnetic field produces an induced current that will feed the main coils.

The proposed model focuses on the determination of an efficient spatial layout of magnets to generate a corrective torque with the least possible energy consumption, with and without simplifying assumptions for inertia equations, and involving angular and time approaches for cyclic excitations and frequency resonances in order to tackle non-stationary operating conditions.

Keywords: Electromagnetic conversion; Rotating systems; Tuned Mass Dampers

References:

- Acyclisme et vibrations, JL. Ligier & E. Baron, Editions Technip, 2002

- Energieeffiziente aktive Dämpfung von Torsionsschwingungen im KFZ-Antriebstrang, J. Pfleghaar, TU München, 2014

- Design development of Rotational Energy Harvesting Vibration Absorber, F. Infante & Al., SMASIS 2018

- Patent EP 2 910 813 A2, MAN Truck & Bus AG, 2014

- Passive, Adaptive and Active Tuned Vibration Dampers – A Survey, J.Q. Sun, JVA Vol.117, pp 234-242, 1995