Multi-physics Coupling Based Research On NVH Performance And Optimization Of Gasoline Engine

Turbocharged direct injection gasoline engine (Turbo DI Engine) is becoming increasingly popular and will be the mainstream gasoline engine in the future. The working condition differences between Turbo DI Engine and naturally aspirated gasoline engine (NA Engine) leads to NVH problems which engineers and researchers of engine have to solve. Based on a certain Turbo DI Engine, this paper studied the influence factors and optimization of combustion noise and NVH optimization of structure parts with multi-physics coupling simulation methods.9-point test method and5-point test method were implemented to test a certain Turbo DI Engine. The differences between9-point test method and5-point test method were studied and proved the conclusion said in national standard that5-point test result would be△LWA higher than9-point test result. The research found that5-point test method could replace9-point test method with the correction in this paper under certain condition. The method could effectively improve the efficiency of the sound power test of Turbo DI Engine.This paper studied influence factors of combustion noise and engine noise of Turbo DI Engine for the first time in China, including spark angle, injection phase, injection quantity, load, fuel quality and proved spark angle and load factors influenced combustion noise most. In certain working condition, spark angle caused3dB(A) sound power change of the Turbo DI Engine. Injection phase, injection quantity influenced less and fuel quality least. All these factors influenced sound power more in low engine speed than that in high speed.Attenuation curves in frequency domain and their differences in different engine speeds of different engine sides of Turbo DI Engine were studied for the first in China and concluded that attenuation curves are different among different engine sides and the relationship between attenuation curve and the engine speed is non-monotonic. This paper proposed a method predicting engine sound power based on attenuation curve under one engine speed. This method avoided the difficulty of separating combustion noise and mechanical noise. It set engine sound power optimization as the goal and studied the relationship between variables and combustion noise and finally optimized combustion noise and engine noise. This method was well applied in a certain Turbo DI Engine combustion noise and engine noise optimization and realized1.9 dB(A) engine sound power optimization at most.Gasoline engine NVH performance was studied with multi-body dynamics and multi-physics coupling simulation methods. Based on the research result of dynamic characteristic of main structure parts, its stiffeners were optimized to make better NVH performance of the engine. The optimized parts were made to do sound power test of the optimized engine. The test realized1.1dB(A) engine sound power optimization at most.This paper collected the latest engines published by car companies all over the world and sorted out the newest design method of structure parts. The newest design method was applied in a gasoline engine oil pan with CAE and proved that the newest method could optimize NVH performance of the engine.