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摘要: 为有效降低连续长下坡路段汽车交通事故率, 增强车辆行驶的主动安全性, 研究了在发动机制动下汽车下坡制动失效的坡长问题, 通过在汽车试验场进行汽车平路制动试验, 测得汽车紧急制动时制动鼓温升变化数据, 以最小二乘法建立了汽车主制动器制动鼓温升模型, 推导了在山区不同长纵坡路段, 发动机制动下汽车主制动器制动失效的坡长临界值。计算结果表明在5%坡道上, 维持40 km.h-1的安全稳定车速, 采取Ⅲ档发动机制动时, 汽车主制动器制动失效的坡长临界值前轮为15 263 m, 后轮为12 368 m, 既满足了行驶的距离要求, 又满足了运行速度要求, 是一种可行的安全下长坡驾驶方式。Abstract: To lower automobile traffic accident rate effectively on continuous downhill road and enhance its active safety of driving, the slope length of braking inefficacy was studied under engine braking, brake test on flat road in automobile proving ground was done, the elevated temperatures of brake drums under emergency braking case were measured, the elevated temperature model of main brake drums was established by least-squares procedure, the critical slope lengthes of automobile main brake inefficacy under engine braking on various longitudinal slopes in mountain area were deduced.Computation result indicates that when automobile runs at the safe-stable speed of 40 km·h-1 on 5% ramp and driver adopts the No.Ⅲ gear engine braking, the critical slope lengthes of front-and-aft wheel main brake inefficacy respectively are 15263 m and 12368 m, which not only satisfies running distance request, but also meets running speed request, so it is a feasible and safe driving method on long downhill.
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Key words:
- traffic safety /
- engine brake /
- brake inefficacy /
- critical slope length
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表 1 温升变化
Table 1. Elevated temperature variation
℃ 位置 速度v/ (km·h-1) 30 40 50 60 左前轮 3 4 9 10 右前轮 2 6 7 22 左后轮 1 0 8 22 右后轮 3 5 6 13 
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表 2 平均降温速率
Table 2. Average cooling rates
℃·min-1 位置 速度v/ (km·h-1) 30 40 50 60 前轮 1.083 1.667 1.667 3.750 后轮 0.417 1.000 1.333 3.333
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表 3 高差及坡长
Table 3. Height differences and slope lengthes
速度v/ (km·h-1) 高差h/m 坡长L/m 60 14.18 283.6 50 9.84 196.8 40 6.30 126.0 30 3.54 70.8
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表 4 温升与高差
Table 4. Elevated temperatures and height differences
高差h/m 温升ΔT1/℃ 左右前轮平均值 左右后轮平均值 14.18 16.0 17.5 9.84 8.0 6.0 6.30 5.0 2.5 3.54 2.5 2.0
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表 5 散热温度变化
Table 5. Cooling temperatures variation
高差h/m 前轮平均降温速率t/ (℃·min-1) L对应前轮散热温度ΔT2/℃ 后轮平均降温速率t/ (℃·min-1) L对应后轮散热温度ΔT2/℃ 14.18 3.750 1.063 3.333 0.945 9.84 1.667 0.394 1.333 0.315 6.30 1.667 0.315 1.000 0.189 3.54 1.083 0.153 0.417 0.059
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表 6 温度变化
Table 6. Temperature variation
高差h/m 温升ΔT/℃ 左右前轮平均值 左右后轮平均值 14.18 14.937 16.555 9.84 7.606 5.685 6.30 4.685 2.311 3.54 2.347 1.941
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表 7 坡长临界值
Table 7. Critical slope lengthes
行车方式 稳定车速/ (km·h-1) 档位 主制动失效的坡长临界值/m 无持续制动(无发动机制动与排气制动) 40 空档 L前轮为1 547, L后轮为1 253 发动机制动 18 Ⅱ 无需主制动器工作 40 Ⅲ L前轮为15 263, L后轮为12 368 Ⅳ L前轮为3 353, L后轮为2 717
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表 8 不同纵坡下坡长临界值
Table 8. Critical slope lengthes of different gradients
档位 主制动器 纵坡/% 5 6 7 8 9 Ⅲ 前轮主制动器失效坡长L/m 15 263 5 272 2 844 1 946 1 538 Ⅳ 后轮主制动器失效坡长L/m 12 368 3 704 2 009 1 376 1 092 前轮主制动器失效坡长L/m 3 353 2 535 1 792 1 390 1 167 后轮主制动器失效坡长L/m 2 717 1 781 1 266 983 829
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