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Estimates Pro-Braking Velocity of Large-Scale Vehicle from Skid Marks
本研究之實驗場地，選擇路面清潔、平直、交通容易維持的麥寮六輕工業區，以時速50、60、70km/hr等三種車速，作大型油罐車及半聯結車之煞車實驗，從實驗中找出三種車速之阻力係數f值，分別為大型油罐車0.62、0.58、0.69，半聯結車0.58、0.65、0.53。煞車胎痕產生時間 值，大型油罐車分別為0.48、0.48、0.57，半聯結車為0.45、0.49、0.36。煞車胎痕長度ss分別為大型油罐車9.76m、20.5m、17.93m，半聯結車12.89m、14.74m、32.81m。將f、ts、ss分別代入傳統推估公式、Neptune推估公式及交通部運輸研究所改良推估公式，作行車速度之推估比較，其結果以交通部運輸研究所之改良推估法較接近圖形積分。本實驗所得數據與小型車作比較分析，發現大型油罐車之平均阻力係數為0.63、半聯結車之平均阻力係數為0.59，而小型車一般之平均阻力係數在0.8以上，大小型車之間有很大之差異。另大型車輛在煞車過程中，三種車速之加速度曲線皆產生震盪現象，不像小型車加速度曲線那樣平滑，本研究並以快速傅利葉轉換（FFT）作頻譜分析，大型油罐車分別為6.9 Hz、7.1 Hz、6.7Hz，半聯結車分別為4.4 Hz、4.4 Hz、3.2Hz，探討可能原因除受慣性作用外，還有車輛各軸未符合理想煞車力分配條件，即車輛各軸未在同時間產生最大煞車力。
The tests of research located in No.6 Naphtha Industrial Zone, Mailiao where the road surface is clean, straight and the transportation situation maintained easily. The braking experiment was made by large-sized fuel-tank truck and semi-trailer with vehicle speeds of 50, 60 & 70 km/hr. The drag factor f value of these three kinds of vehicle speeds were discovered from the experiment like this:
Fuel-tank truck (large-scale) 0.62 0.58 0.69
Semi-trailer (large-scale) 0.58 0.65 0.53
The time value ts of vehicle begins to leave visible impending skid marks are as follows:
Fuel-tank truck (L) 0.48 0.48 0.57
Semi-trailer (L) 0.45 0.49 0.36
The skid marks length ss are as follows:
Fuel-tank truck (L) 9.76m 20.5m 17.93m
Semi-trailer (L) 12.89m 14.74m 32.81m
Substituting the above three sets of result into the traditional estimated formula, Neptune estimated formula and the improved estimated formula of Institute of Transportation, MOTC. We found the last one is more approached the descriptive integral.
We compared and analyzed the obtained data from this experiment with small-sized vehicles and found the extra differences as listed below:
Fuel-tank truck (L) 0.63 Averaged drag factor
Semi-trailer (L) 0.59
Small vehicle 0.8 above─General drag factor
During the braking process, the acceleration curves of all the three vehicle speeds produced shaking phenomenon, not like the small vehicles with smoothness.
The results of frequency analysis based on Fast Fourier Transform (FFT) were like the following:
Fuel-tank truck (L) 6.9Hz 7.1Hz 6.7Hz
Semi-trailer (L) 4.4Hz 4.4Hz 3.2Hz
Besides the possible reason of inertia effect, it would be the ideal braking force distributed unevenly from various axes of vehicles,
i.e. the maximum braking force were not reached from various axes of vehicles at the same time.
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