Dizel motorlarda dişli darbe gürültüsünün incelenmesi

Overall noise level of internal combustion engines has always been an important issue in the automotive industry due to the competition between automotive manufacturers as well as legislative regulations. Thus, automotive manufacturers aim to determine engine noise sources and their root causes before mass production, and also they take applicable precautions in order to prevent engine noise problems within the NVH considerations during design and development phases. It is well known that diesel engines are noisier than gasoline engines since diesel engines have higher gas pressure in combustion chamber during combustion process compared to gasoline engines. This also affects mechanical noise problems in diesel engines, which can cause higher vibration and noise levels compared to those of gasoline engines. Therefore, overall noise levels of diesel engines are more crucial than those of gasoline engines. Mainly, radiated noise of internal combustion engines are examined in two categories as combustion noise and mechanical noise. Geartrain noise is one of the most significant mechanical noise contributors in diesel engines, especially in heavy-duty diesel engines. Fundamentally, there are two important gear noise types in geartrains, which are classified as gear impact (rattle) noise and gear meshing (whine) noise. This thesis aims to focus on geartrain impact noise which is also referred to as gear hammering or rattle noise. Likewise, gear meshing noise is named as gear whine noise in the automotive industry. Gear meshing noise, a kind of tonal noise, frequency of which is proportional to the engine order hence its diagnosis is easier with NVH measurements. Gear impact noise, on the other hand, is known as broadband noise, therefore its root cause analysis is more difficult by gear fault diagnosis compared to root cause analysis of gear meshing noise. The main reason for the occurrence of gear impact is that relative motion between gear teeth leads to loss of contact which in turn results in impact between gears creating impact noise. Moreover, speed and/or torque fluctuations of geartrain members and torsional vibrations of engine crankshaft and geartrain members dominate these gear impacts. Operating conditions in diesel engines are also important factor for radiation of impact noise from engine surfaces. Higher loads in the engine cause higher impacts between gears, hence gear impact noise increases with respect to loads. Especially, the gear impact noise becomes a significant noise source in engine full load conditions. On the other hand, gear impact noise becomes more audible at lower engine speed due to the low levels of combustion noise as well as low levels of other mechanical noise. The main objectives of this thesis are to determine the effective parameters on geartrain impact noise in diesel engines and to understand the background theory of gear impacts. In the second chapter, background theory of gear impacts, dynamics, noise and vibration are introduced, and torsional vibration analysis of crankshaft is described. Furthermore, vibration and acoustic analysis methods for experimental studies are presented. For the determination of effective parameters on geartrain impact noise in diesel engines, numerical and experimental studies, which are respectively presented in chapters three and four, are conducted on a six cylinder heavy-duty diesel engine, geartrain of which are made of spur gears. Numerical analyses of geartrain impact are performed by using impact impulse method which is a special analysis method for the evaluation of impact noise level. Critical gear meshes in engine geartrain is determined by geartrain impact impulse analyses. The analysis results show that crankshaft gear and crankshaft idler gear mesh is the most critical gear mesh for geartrain impacts. Moreover, significant parameters on geartrain impacts, which are backlash, engine speed, gear loading and fuel pump phasing, are determined by the impact impulse analysis. As a result, gear loading and fuel pump phasing are determined as the significant factors on gear impacts rather than backlash effect. Experimental studies of geartrain impact noise are conducted with the help of NVH tests in engine dynamometer and NVH tests on the vehicle. Impact noise source on the heavy- duty diesel engine is detected in acoustic dynamometer by using acoustic camera measurement and "vibration and acoustic measurement comparisons". Results of experimental studies show that geartrain side of the heavy-duty diesel engine has the highest noise contribution to the overall noise level of the engine. Significant parameters on impact noise are experimentally investigated by fuel pump phasing test, backlash iteration test in engine dynamometer and gear loading test, idler backlash test and engine speed test on the vehicle. In accordance with the results of the numerical analyses, experimental results also confirm that fuel pump phasing has strong effect on gear impact noise at full load conditions and gear loading has significant effect on gear impact noise at idle operating condition. Moreover, it is observed experimentally that oilpump backlash has minor effect on geartrain impact noise compared to fuel pump phasing and gear loading effect. However, backlash effect on gear impact noise is clearly seen on the gear mesh between camshaft gear and camshaft idler gear. Pressure variations between cylinders are also measured in engine dynamometer, and results show that cylinder to cylinder pressure variations occur in the heavy-duty engines. It is well known that cylinder to cylinder pressure variation has adverse effects on crankshaft torsional vibrations. Housing FRF test is also another conducted experimental study in order to establish the housing effects on geartrain impact noise. Result of housing FRF tests show that design of housing has crucial effect on structural behavior of housing which can also cause higher noise radiation from housing surface due to the gear impacts. Finally, torsional vibration analyses are carried out by both numerical analyses and experimental studies, and it is observed that combustion order, especially the combustion fundamental order, which is the third engine order for a six cylinder engine, dominates the crankshaft torsional vibrations. Likewise, envelope analysis and the new analysis method developed and named in this thesis as cepslope (cepstrum + envelope) reveal the repetition of the combustion orders. Furthermore, they prove that combustion fundamental order is one of the most important parameter on gear impacts. In the conclusion chapter, numerical and experimental studies are evaluated and compared in order to determine the effective parameters on gear impact noise. At the end, geartrain design recommendations and future research recommendations for the subject of this thesis are expressed in some detail.