Structure Dynamic Design Method Study On Low Noise Diesel Engine

Based on the theory of machinery dynamic design, a systemic dynamic design procedure was practiced aiming to achieve a low structure-borne noise diesel engine. After modeling the major parts of the diesel, their dynamical characteristics were obtained. Engine block dynamic behavior, namely its vibration and noise radiation, can be predicted by computing its dynamic response. Analyzing such prediction result, structure dynamical characteristics and the external load applied on it, structural modification of engine block was conducted and proved to be effective to reduce engine noise radiation.Both engine block and crank shaft dynamic models for an inline 6-cylinder-diesel were established by theoretical and experimental method. Model shape and frequency were obtained and compared, the results from EMA and FEA revealed the reliability of the FEA model.A formulation for modeling a rotating flexible crankshaft coupling with its elastic deformation and component mode synthesis were presented. Crank train kinematical simulation was performed by combining the flexible crankshaft with con-rod, piston and main bearing journal.Structural dynamic response model yielded transfer behavior from major exciting force to surface vibration as well as surface vibrating velocity. Deduction the methodology from surface velocity to noise radiation realized noise power prediction of the engine block.Designing different noise source identification strategy, the intake noise, fan noise, mechanical noise and combustion noise were separated successfully. Their contribution to entire engine noise and correlation to engine load, engine speed were also found.Different modification was made against the noise generation loop. To the exciting force, piston kinematical modeling helps to optimize piston gravity center offset and pin offset, resulted in a minimizing piston slap force. To the load bearing structure, main journal supporting plate and crank case modification reduced engine block skirt vibration. Geometrical shape variation and application of vibration-damping steel plate to the oil pan was attempted. Applying a kit of noise reduction solutions to the sample diesel engine, a 4.1dB(A) overall noise power level reduction was achieved.