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Zorluk: ZorMountain Driving and Steep Downgrades

A freight vehicle with a gross weight of 66000 lb66{}000\text{ lb} is about to descend an 88-mile, 5%5\% downgrade under steady rainfall. The posted maximum safe descent speed for heavy combinations is 35 mph35\text{ mph}. Which operational procedure must the driver execute to ensure safe speed control without causing drive-wheel skids or mechanical brake fade?

  1. A
    Engage the engine retarder at full capacity to reduce service brake friction, remain in a high cruising gear, and apply steady brake pedal pressure to hold the vehicle at 35 mph35\text{ mph}.
  2. B
    Disengage auxiliary retarders, shift to neutral to prevent engine strain, and use continuous light brake applications to prevent the vehicle from accelerating beyond 35 mph35\text{ mph}.
  3. Disengage auxiliary retarders prior to the slope, shift into a gear lower than required to climb the grade before cresting, and perform snub braking down to 30 mph30\text{ mph} whenever the speed reaches 35 mph35\text{ mph}.Cevap
  4. D
    Keep the engine retarder activated on low, descend in top gear until reaching 35 mph35\text{ mph}, then depress the clutch to downshift and brake aggressively to 20 mph20\text{ mph} only if the vehicle exceeds 40 mph40\text{ mph}.

Cevap

Disengage auxiliary retarders prior to the slope, shift into a gear lower than required to climb the grade before cresting, and perform snub braking down to 30 mph30\text{ mph} whenever the speed reaches 35 mph35\text{ mph}.
Safe mountain descent under wet conditions requires three synchronized actions: turning off the retarder to prevent drive wheels from skidding on slick pavement, selecting a low gear prior to cresting so the engine provides primary retarding force, and applying the proper snub braking technique (firmly braking from the 35 mph35\text{ mph} safe speed down to 30 mph30\text{ mph}, then releasing fully to allow cooling).

Adım Adım Çözüm

1
Assess road surface traction and configure auxiliary braking systems.
Auxiliary retarders are deactivated due to wet pavement conditions.
Retarder torque on slippery or wet surfaces causes drive wheels to lose traction, leading to potential drive-wheel skids or jackknifing.
2
Select the correct transmission gear prior to starting down the grade.
The vehicle is placed into a gear lower than what would be needed to climb the grade before beginning the descent.
Engine compression provides primary retarding power, and attempting to shift on the grade can cause transmission lockout in neutral.
3
Execute proper snub braking cycles to maintain speed below the safe threshold.
Brakes are applied firmly until speed drops to 30 mph30\text{ mph} (5 mph5\text{ mph} below the 35 mph35\text{ mph} safe speed), then released completely until speed returns to 35 mph35\text{ mph}.
Periodic application followed by complete release dissipates thermal buildup between cycles, preventing brake fade.

Anahtar Kavram

Integration of traction management, pre-descent gear selection, and snub braking cycles during steep mountain descents.
Tahmini Süre:2m 0s
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Konular

Mountain Driving and Steep Downgrades

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