當汽車行駛中發生緊急情況，必須踩煞車減緩車輛速度時，若將煞車立即踩到底易使車輪卡死，此時若車輛有裝載ABS系統便能以近似頻率式的踩放煞車限制煞車的強度，避免車輪卡死導致駕駛無法操控方向反而使車輛煞車距離增加；ABS系統中運用了氣壓式電磁閥控制煞車強度，因此電磁閥的反應靈敏度便極為重要，若能更快速地充放氣，便能以更高的頻率進行煞車控制；電磁閥之壓力上升時間(ts75%)最為關鍵，其是否符合國際 Tier1車廠規範，以及與後續相關種類電磁閥性能比較皆以此做基準。因此本文採用三口二位氣壓式電磁閥為研究對象，並且使用了考量鐵芯移動之動態模擬，其壓力上升時間(ts75%)與實驗數據961 ms之誤差值為8.9 %，而以往固定鐵芯位置752 ms之模擬誤差值為21.7 %；固定鐵芯位置之模擬方式並未考量鐵芯移動過程所影響之物理現象，並且使用了理想氣體進行模擬；而在考量鐵芯移動之動態模擬中，運用了真實氣體進行模擬，能分析更多流場細節以及獲得更正確的壓力上升時間，因此後者之準確度提升許多。經由探討原始電磁閥之壓力、質量流率、馬赫數、以及流場圖後，發現入口噴嘴至鐵芯頂部有壓力振盪現象，此現象影響高壓氣體流入閥體以及氣體流速，而壓力上升時間(ts75%)為875.6 ms；原始鐵芯移動速度為0.133 m/s，將鐵芯移動速度加快(0.166 m/s)時，壓力振盪現象更為嚴重且氣體流速更快，此時壓力上升時間(ts75%)變長至1,040 ms；將鐵芯移動速度減慢(0.100 m/s)，壓力振盪現象減少但是壓力上升時間(ts75%)變長至1,044 ms，不論加快或減慢鐵芯移動速度(0.166 m/s 和 0.100 m/s)均為變差，此現象或許是因為將鐵芯移動速度做過大地改變，必須做細部調整才能找出最佳之鐵芯移動速度。

This research presents an unsteady simulation of CFD effort to realize and estimate the pressure-rising characteristics of a 3/2-way pneumatic solenoid valve, which is used extensively in activating the anti-lock braking system (ABS). The actual pressure-rising action of solenoid valve is accomplished by executing the armature-moving process and the pressure-filling process. At first, the open mode of solenoid valve in ABS is reached by moving the armature to its lowest position, which can block the ventilating holes and the flow leakage completely. Also, a space between the armature and the nozzle is created for allowing the high-pressure air to fill the valve system, which has been reported in previous literatures. Clearly, the course of armature movement is an extremely quick transient process and forms a time-consuming and problematic CFD challenge, which is thus ignored usually. However, the flow pattern at the end of armature movement is the initial condition for activating the actual pressure-charging process. Therefore, this work intends to firstly perform the transient simulation on the armature-moving process to understand the physical phenomenon in details and obtain the correct initial condition for the succeeding pressure-filling process. In addition, the real-gas relation is implemented in all numerical calculations executed here to ensure the accurate and reliable numerical results.
As a result, the transient flow analysis on the entire pressure-charging action indicates that a repeating pressure-oscillation phenomenon exists inside the region between the iron core and the nozzle exit at the original armature speed (0.133 m/s). From the numerical flow visualization, it is found that this fluctuation is contributed to the cyclic resistance on the incoming air mainly generated by the large flow circulation existed between the iron core and the nozzle exit, in which a rapid and huge volume change is induced by the moving armature. Also, the amplitude of pressure perturbation diminishes quickly after six fluctuating cycles since the volume-variation effect becomes smaller as the armature moves away from the nozzle. As regard to the pressure-responding estimation of this solenoid valve, CFD calculations show that 876 ms and 752 ms are needed to reach 75% of the activation pressure from present and old approaches, respectively. Apparently, the deviation percentage is significantly improved from 21.7% to 8.9% based on the actual test data (961 ms).
Furthermore, it is demonstrated that the moving speed of armature has significant influence on the pressure-fluctuation phenomenon and the resulting pressure-rise time needed for this ABS valve. Thus, the unsteady analysis on different armature speeds (0.100 m/s and 0.166 m/s) is carried out to find its corresponding pressure responding time of this valve. The numerical calculations indicate that cycle number and perturbed amplitude of the pressure fluctuation increase for a higher armature speed while no improvement on the responding time is observed. Besides, this result implies that the moving velocity of armature is an important design factor, which can be optimized systematically with the aids of CFD tool. In conclusion, this investigation successfully establishes a rigorous and systematic CFD scheme to reveal the physical mechanism in details and accurately estimate the pressure-rise characteristics of a 3/2-way pneumatic solenoid valve.

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