Browse Publications Technical Papers 2019-01-0329
2019-04-02

Robust Design Optimization on an I-3 engine balance shaft 2019-01-0329

The Inline 3-cylinder engine is widely used as an alternative for engine downsizing. Its 120-degree crankshaft phase produces zero, first, and second order forces. However, this configuration produces uneven vertical forces from piston motion. Usually known as Pitch and Yaw moments, they can generate high levels of seat track and steering wheel vibrations. Balance shaft is a countermeasure that can reduce this 1st order excitation to get into the vehicle. Its design consists of two main variables, imbalance mass and angle. These variables need to be tuned so the engine pitch and yaw moments are minimized, which can be achieved by solving a deterministic design optimization problem. However, due to manufacturing tolerances of connecting rods, pistons, and balance shaft itself, the actual vibration level of the optimized balance shaft could fluctuate, and often becomes sub-optimal and even unacceptable. One way of addressing the influence of tolerances on vibration is to conduct a Taguchi parameter design, followed by tolerance design, to pick the optimal settings of imbalance and angle with proper tolerances, so the final designs are the least subject to the influence of manufacturing tolerances on the yaw and pitch moments. Another approach of tackling the robust design issue is to use Robust Design Optimization which is empowered by optimization algorithms, to simultaneously tune the nominal values and tolerances of imbalance and angle, as opposed to the sequential tuning approach Taguchi method performs. In this paper, both approaches are used to find the optimal and robust solutions, and the results from both approaches are compared in terms of convenience of problem setup, overall complexity of procedures and turnaround time, and optimal solution quality. This paper concludes the Multi Objective Robustness Design Optimization (MORDO) augmented by Response Surface Models (RSM), is preferred and recommended to tackle robustness in competitive product designs.

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