## 3 Results and Discussion
### Excitation Source Contribution Analysis and Critical Transfer Path Identification
#### 3.3.2 Analysis of Vibration Transmission to a Single Target Point on the Chassis Frame  
The preceding analysis indicates that the vertical vibration is most intense at the articulation point between the lifting hydraulic cylinder of the cantilevered conveyor trough and the chassis frame (measurement point 1). This location is also near the combine harvester's operator cabin, making it a critical area for vibration improvement. Therefore, a detailed single-point contribution analysis of this location is essential. In this study, measurement point 1 was selected as a representative case for a detailed analysis of its vibration spectrum characteristics in the vertical (X), longitudinal (Y), and lateral (Z) directions. The vertical acceleration response and power spectral density (PSD) curve for measurement point 1 are plotted in Figure 14.  
Figure 12: Contribution of each excitation source to the vertical vibration of the chassis frame. Figure 13: Total contribution values from each excitation source. To provide a quantitative assessment of the overall vibration intensity at measurement point 1, the root mean square (RMS) values of the triaxial accelerations at this point were first calculated under different operating conditions. The results are presented in Table 4.  
As shown in Table 4, the vibration intensity at measurement point 1 varies significantly under different operating conditions. In Condition 1 (engine-only operation), the RMS value in the X-direction (vertical) is the highest at 6.20 dB, which is substantially greater than in the Y-direction (longitudinal, 1.97 dB) and the Z-direction (lateral, 1.30 dB). This indicates that even with only the engine running, vertical vibration is already the primary component of the chassis frame. When the threshing cylinder and vibrating screen are engaged (Condition 2), the RMS values in all directions increase markedly. The X-direction RMS value climbs to 10.76 dB, the Y-direction value increases to 3.50 dB, and the Z-direction value rises to 1.75 dB. This demonstrates that the excitation introduced by the threshing and cleaning system has a cumulative effect on the chassis frame's vibration, with the most significant impact on vertical vibration. In Condition 3 (all components operating simultaneously), the RMS values in all directions show a further slight increase, and the overall weighted value at measurement point 1 reaches its maximum (7.06 dB). This clearly illustrates that as additional working components like the cutting header are progressively engaged, the cumulative effect of the various excitation sources leads to a continuous intensification of the chassis frame's vibration, with the vertical direction consistently remaining the dominant mode of vibration at measurement point 1. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Condition**} & \multirow{2}{*}{**Axis**} & **RMS Acceleration Level (dB)** &
\begin{tabular}{c} **Weighted Acceleration Level (dB)** \\ \end{tabular} \\ \hline \multirow{3}{*}{1} & \(\quad\)X & 6.20 & \\ \cline{2-4}  & Y & 1.97 & 3.83 \\ \cline{2-4}  & Z & 1.30 & \\ \hline \multirow{3}{*}{2} & \(\quad\)X & 10.76 & \\ \cline{2-4}  & Y & 3.50 & 6.61 \\ \cline{2-4}  & Z & 1.75 & \\ \hline \multirow{3}{*}{3} & \(\quad\)X & 11.49 & \\ \cline{2-4}  & Y & 3.79 & 7.06 \\ \cline{2-4}  & Z & 1.83 & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Vibration data for the chassis frame (measurement point 1). Figure 14: Vertical acceleration response and power spectral density curve for measurement point 1. The power spectral density (PSD) curves for the triaxial acceleration at measurement point 1 under different operating conditions are shown in Figure 15. In Condition 1 (engine-only operation), the primary PSD peak for chassis frame measurement point 1 is concentrated at 29.29 Hz. The amplitude is largest in the X-direction (vertical), followed by the Y-direction (longitudinal), and is smallest in the Z-direction (lateral).