Analysis and experimental research on whine noise of the engine balance shaft gear system 2023-01-1152

An Inline 4-cylinder engine is equipped with second-order balance shafts. When the engine is running under a low load acceleration condition, the gear system of the balance shaft generated whine noise. In this paper, an analysis method for reducing the whine noise is presented. First, a flexible multi-body dynamic model of the engine is established, which includes shaft and casing deformation, micro-modification of the balance shaft gears. Taking the measured cylinder pressure as the input, the influence of the micro-modification of the gears’ tooth surface at the balance shaft on the meshed noise was calculated and analyzed. The torsional vibration at the crankshaft nose was measured during no-load conditions, and the measured data was compared with the estimated data, which validate the established multi-flexible body dynamic model of the engine. Secondly, a quasi-static model of the balance shaft gear transmission was established. Taking the calculated load and misalignment of the meshed gears using established flexible multi-body dynamic model of the engine as the input, loaded tooth contact analysis was carried out. The analysis results showed that the transmission error between the crank gear and the bias gear was large if the original tooth surface modification parameters is used, which was the main reason for the whine noise. Based on the proposed quasi-static model, taking minimizing the fluctuation of transmission error and the maximum contact pressure of the tooth surface as optimization objectives, and the tooth surface modification parameters as optimization variables, the NSGA-II (non-dominated sorting genetic algorithm II) method was used to conduct multi-objective optimization. A set of tooth surface modification parameters was optimized, and the fluctuation of transmission error is reduced by 70%. According to the optimized scissor gear parameters, the new scissors gears was fabricated and installed on the balance shaft. An engine noise test experiment with the installation of new balance shaft gears was carried out. The test results showed the whine evaluation index is improved from 5 points to 7.5 points, which solved the problem of gear whine.