Research On The Vibration Of Structural Parts Affecting Mini Excavator Cab Low-frequency Noise

The vibration and noise of excavator cab have direct impacts on drivers’ riding comfort as well as physical and mental health.With the degree of domestic excavator to participate in international competition is becoming deeply,the requirements for excavator’s NVH(Noise,Vibration and Harshness)performance have become increasingly higher.So it’s of great significance in engineering practices to control the vibration and noise level of excavator cab.The cab’s structural parts which have a decisive influence on the low-frequency noise inside the cab are affected by multiple excitation sources at the same time.So it’s an important means to reduce the excavator cab’s vibration and low-frequency noise level by analyzing these structural parts’ main vibration sources as well as their transfer law.This thesis focuses on the problem that the low-frequency noise inside the mini excavator cab is salient,and uses the method combining ICA and EEMD together to identify the vibration sources of main structural parts which affect the low-frequency noise inside the cab,and the analysis results are useful to attenuate the vibration energy transmitted from the excitation sources to the cab structure.Then we analyze the cab vibration transfer path so as to clear the propagation law of vibration energy.And the results can help improving the vibration and noise performance of the excavator cab.Firstly,in order to solve the problem that the main excitation sources are difficult to be identified,this thesis proposes a vibration source identification method which combines EEMD and ICA together to decouple the single channel signal and extract the most important source signals.The method first uses EEMD to decompose the one-dimensional signal,and selects the effective IMF components according to the screening criteria considering both the correlation coefficient and the energy contribution rate.Then,the virtual multi-channel signal is constructed as the input of ICA to realize the source identification of the single channel signal.At last,the contribution degree of each source is determined according to the estimated hybrid matrix.The simulation results show that the method can separate the source signals of one-dimensional mixed signal correctly,and the energy contribution calculation results are consistent with the actual situation,which verifies that the method is feasible to be used to analyze the excavator vibration signals.Then,this thesis uses the wavelet packet decomposition algorithm to extract the low-frequency components of the excavator cab vibration signals,and analyzes the formation mechanism of the excavator cab vibration and noise as well as the spectral characteristics and frequency domain correlation of the cab’s vibration and noise signals.Afterwards,we identify the vibration sources of main structural parts which affect the low-frequency noise inside the cab and calculates the energy contribution of each vibration source.The analysis results show that the noise inside the cab is dominated by low-frequency components.And the dashboard,the right guard board and the right panel is the main structural parts which affect the low-frequency noise inside the cab.And the first and second order combustion excitation of the engine occupy the main proportion in the vibration signal’s energy composition of each structural parts,which are the main excitation sources affecting the vibration and low-frequency noise level of the cab.Finally,the analysis of the cab vibration transfer path is carried out to determine the engine vibration’s propagation law and the influence on the cab vibration.The performance of the engine and cab damping system is evaluated with frequency domain vibration transmission rate.The vibration characteristics of the upper frame are studied based on the finite element modal analysis method,and the results can help to find the resonating frequency and the area whose structural rigidity is insufficient.At last,the improvement scheme to control the excavator cab vibration and noise level is put forward according to project experience.