Active Torque Cancellation for Transmitted Vibration Reduction of Low Cylinder Count Engines

Vibration and noise are common problems in engine-based designs such as generators used in recreational vehicles (RVs). In variable-speed applications, at lower loads, the engine can be run at slower speeds to reduce noise. However, one of the main problems incurred from running an engine at a lower speed is that the vibration modes will shift to lower frequencies, where the mounting system may not produce enough attenuation. Even worse, part of the frequency content may get into the range of the mounting system´s resonance, resulting in an unacceptable vibration level. This is a result of engine torque pulsation, which is pronounced for low cylinder count engines. An active torque cancellation mechanism is proposed and demonstrated for engine and transmitted vibration reduction of generator sets with lower cylinder count engines. Specifically, a controlled torque is applied on the crankshaft of the engine to reduce roll motion. An order of magnitude in vibration reduction is obtained through an approach that does not suffer from the need for oversizing of machine, electrical storage, and power electronics. System simulations are developed based on physical and mathematical models to help with control design. The test setup constitutes a two-cylinder diesel engine, a permanent-magnet synchronous machine, an ac/dc active rectifier, electrical storage, and a dc/ac inverter. The experimental setup is used to investigate several issues related to torque cancellation and transmitted vibration reduction, such as the effectiveness of a small number of vibration mode cancellations, tradeoffs between robustness and performance associated with engine cycle-to-cycle variations, and performance objectives used for comparison.