Vehicle Interior Noise Analysis Based On Optimization And Simulation Of Power-train Mount System

With the improvement of living standards, consumer’s requirements of automotive quality become more demanding, and good NVH performance appears more important. Excessive vibration and noise not only affect ride comfort, but also distract the drivers, reduce component life, and affect driving safety.The engine vibration is an important source of vehicle’s vibration and noise. The excitation transfers via power-train mount system to the frame and the vehicle body, causing vibration and noise in the cab. In order to reduce the vibration transmitted to the frame and the body, vibration isolation performance of power-train mount system is particularly important. Emerging active, semi-active hydraulic mount has a superior vibration isolation performance, but higher cost. As for the traditional rubber mount and passive hydraulic mount, a reasonable arrangement and parameter matching can affect the performance of vibration isolation, mainly distributed in the natural frequency of the power-train mount system and the merits of decoupling performance.According to positive NVH performance development projects of a domestic light truck, we optimized the decoupling performance of power-train mount system by changing the mount stiffness and installation angle, and the optimization results are verified. The main contents include the following aspects:1. In theory, we deduced the generating mechanism of engine vibration and vibration isolation principle of mount, described the effect of power-train mount system, layout requirements and arrangement. The concept of decoupling was put forward, and several mainstream method was introduced.2. Conducted an impact test on the V-shaped bracket of rear power-train mount, and obtained its natural frequencies and dynamic stiffness. These verified the reliability and simplified the modeling procedure. Six mode frequencies and mode shapes were obtained through modal test, which became the basis to verify the accuracy of the modal in the follow-up work.3. The powertrain was simplified as six degrees of freedom rigid body in space, ignoring the role of the torsion spring. The mechanical model of the power-train mount system was established. The specific calculation formula of natural frequencies and decoupling rate were deduced, and calculated by using MATLAB. The accuracy of the mechanical model was verified by the contract of natural frequencies between test results and the calculated. Based on this, the decoupling rate calculated was credible.4. The mount system was optimized by using an optimization function in MATLAB, with eight variables in total including six axial stiffness and two installation angle. Made Roll motion decoupling rate was over 90% with Bounce motion decoupling rate was close to 80% in premise.5. Establish power-train mount system model in ADAMS, and obtain natural frequencies by simulation. The accuracy of the model was verified by comparing the simulation results, test results and calculated results. Through simulation analysis in idle condition, optimized rear mount suffered significantly reduced Z force, indicating the optimization scheme effective.6. The test vehicle was transform based on the optimization scheme. Measure the interior noise level condition before and after the transformation. According to the test results, two order and four order frequency noise peak decreased significantly after the transformation, which indicating the optimization scheme effective.