Dynamic investigation of diesel engine gear train system under fluctuated torque excitation

In last decades trend in automotive industry go towards on a new path due to regulations and high demand of costumers. Most automotive companies downsize and boost their internal combustion engine to have a better fuel economy and emissions. Nowadays, all diesel and most of the gasoline engines have direct injection and turbocharger or supercharger system to get more power with high fuel efficiency. However, this brings new challenges especially for noise, vibration and harshness (NVH) because downsizing and boosting means having higher pressure in the combustion chamber and increasing forces that generated by power conversion systems. There are two main sources of noise for an internal combustion engines; combustion noise and mechanical noise. Rotating systems of engines cause the mechanical noise and one of them is timing drive system. There are different type of timing drive system and geared system generally uses for heavy-duty diesel engine due to its higher load and power capability while reducing durability risks. However, gear systems have worst performance when it comes to NVH, mainly two type of gear noise produces by geared timing drive systems; gear whine and gear rattle. Gear rattle, also known gear impact or hammering noise, is a broadband noise and can be seen in wide frequency range. In this study, the sensitivity of gear rattle under fluctuated torque influence is investigated and computer-aided engineering (CAE) based method applied to get a better timing gear system in terms of NVH. This study can divide into two main chapters; gear dynamic and heavy-duty diesel engine gear system with fluctuated torque source. In the early part of the study, dynamic of a gear pair with different complexity levels is investigated. Firstly, equation of motion of a linear time-invariant gear pair, which has four degrees of freedom governed, and a fluctuated torque applied. Governed equations solved with two different methods, which are analytical and numerical. In addition, a multi-body dynamic (MBD) model built for exactly same system and computationally solved the system. Secondly, same gear pair investigated with backlash. Backlash brings a non-linearity to system. Equation of motion of non-linear system also governed and solved with numerically. Same non-linear system built in computer-based program and results compared with the numeric solution. For all solutions, results are same for different solution for same systems. Thirdly, another gear added to system and degree of freedom increase to six, this system solved only computationally and effect of phasing fluctuated torque presented. A detailed multi-body dynamics model of a six-cylinder heavy-duty diesel engine's geared timing drive system built to calculate gear mesh forces. There are ten gears in this system and two of them have fluctuated torque characteristics; fuel injection pump (FIP) and camshaft. FIP provides fuel to common rail in diesel engines and has highly fluctuated torque demand from the geared system due to his working principle. xxii A metric called impact impulse, which calculated from gear mesh force and used for rattle assessment of the system. Impact impulses calculated for each gear mesh and summed individual impact impulse up to get total impact impulse, which correlated with gear rattle noise. Total impact impulse recalculated after phasing torque curve of fuel injection pump to find best working point of the system in terms of gear rattle noise. In addition, a physical test conducted and radiated noise of engine and acceleration from gear housing measured to compare with computational results. Consequently, both computational measurement results show fluctuated torques has a significant effect on geared timing system of a heavy-duty diesel engine and with phasing of fluctuated torque can reduce gear rattle in a geared timing drive system.