NVH Research In The Engine Cold Test

Along with our country automobile industry increasing, more fierce competitionhappened among them, every automobile engine manufacturers start to increase capacity to capture market but at the same time they also pay more and more attention to quality and brand reputation, and due to the traditional hot test in production, test cost, quality control and environmental protection are unable to fulfill the request of engine manufacturers, so the engine Cold Test technique has been paid great attention in industry, started to flourish.And with the continuous development of Cold Test technology, all sorts of new test functions are gradually integrated into the Cold Test, one of the most representative is the engine NVH test. At the beginning there is no vibration test in Cold Test, but with the improvement of customer requirements for vehicle vibration comfort and the government start to control of environmental noise pollution in our country, the engine vibration test as an important monitoring project was added to the Cold Test, start to play the role of cannot be ignored.In this article, through to research both in-line three cylinders engine and in-line four cylinders engine NVH principle, using the failure simulation, image analysis to research the periodic character of engine cold test NVH behavior and Order test principle, to provide the reference and support for the NVH application in online working.Based on NVH curves from different test software and engine principle, changing the NVH curve from time domain signal to frequency domain signal by Fourier transformation calculation and calculating the transmission ratio between engine main parts and the crankshaft, define the NVH monitoring window in the curve for engine main parts which can generate the vibration.Research engine time-domain NVH behavior which abscissa axis in window is time or the angle of crankshaft, through to compare engine vibration curves between the same number of engine cylinders and the different number of engine cylinders, determine the periodic character of engine vibration signal and defines the monitoring window in the different crankshaft angle; Research engine NVH Order, determine monitoring method of the engine periodic vibration and impact vibration, there is a prominent improvement of product defects after optimizing monitoring methods, we can find that the reasonable monitoring window definition is very important for online testing work.