A newly developed OHC (Over-Head Camshaft) prototype of a six-cylinder in-line diesel engine (with bore size: 114mm, stroke size: 130mm) was studied, comparing with the previous version of OHV (Over-Head Valve) type engine (with bore size: 110mm, stroke size: 130mm). It was found that the new type of cylinder block (with 130.8 kg of mass) has significantly lower natural frequencies than those for the previous type of cylinder block (with 133.2 kg of mass). Furthermore, slightly more predominant engine noise and vibration were induced in the new engine.
The vibration behavior and the excitation force transmission characteristics were investigated by EMA (Experimental Modal Analysis). We performed a series of impact tests for (1) free-free cylinder block, (2) free-free crankshaft substructure with torsional damper and flywheel attached, and (3) the case where (1) and (2) are assembled together. In the testings, we measured the acceleration response for 77 measuring points for (1), and 42 points for (2), each in the X-Y-Z directions, over a frequency range of 0∼2000 Hz.
In addition to the modal parameters (natural frequencies, mode shapes and mode damping factors) for (1),(2),and (3), the transfer functions between the excitation forces applied on the cylinder liners and crankshaft main bearings, and the acceleration responses at the cylinder block surface. For the crankshaft substructure assembled in the cylinder block, we investigated the coupling behavior between the crankshaft vibrations and the cylinder block vibrations, for the cases (a) when the thrust bearing is attached, and (b) when the thrust bearing is removed.
By a series of experiments, we learned substantially important knowledge for the vibration behaviors of (1),(2),and(3). Furthermore we found that the EMA approach is quite straightforward, efficient and reliable for such research.