Examkin

Soru

Zorluk: OrtaMountain Driving and Steep Downgrades

A commercial motor vehicle driver is preparing to descend a long, steep mountain grade. Why is it critical to shift into the correct low gear before starting down the hill rather than attempting to downshift during the descent?

  1. A
    Riding the clutch while attempting to downshift allows the driver to maintain continuous light brake pressure without overheating the brake drums.
  2. Increasing road speed downhill makes matching engine RPM and road speed difficult, risking transmission lockout and total loss of engine braking.Cevap
  3. C
    Shifting gears on any downgrade automatically disengages the vehicle antilock braking system (ABS) until the vehicle reaches level ground.
  4. D
    Attempting to shift during a descent forces the engine retarder to engage at maximum capacity, inducing an immediate drive-wheel skid.

Cevap

Increasing road speed downhill makes matching engine RPM and road speed difficult, risking transmission lockout and total loss of engine braking.
Gravity causes the vehicle to accelerate rapidly once the descent begins. When attempting to shift during the descent, the transmission passes through neutral, making it extremely difficult or impossible to match engine RPM to the fast-increasing road speed. This can lock the transmission in neutral, eliminating all engine braking and forcing total reliance on service brakes.

Adım Adım Çözüm

1
Identify the primary speed-retarding force required on steep downgrades.
Engine compression braking is the principal method used to hold speed on a downgrade, keeping foundation brakes cool and functional for supplementary slowing.
Relying exclusively on foundation brakes quickly causes thermal expansion and brake fade.
2
Evaluate the mechanical process of shifting a manual transmission while descending under gravity.
When the transmission passes through neutral during a shift, gravitational momentum rapidly increases vehicle speed.
The driver will be unable to rev the engine high enough to synchronize engine RPM with the rapidly accelerating drive wheels.
3
Determine the safety consequence of failed gear synchronization.
The transmission becomes locked out of gear, leaving the vehicle in neutral with no engine braking available.
Without engine braking, the vehicle rapidly accelerates out of control, overburdening and overheating the foundation service brakes.

Anahtar Kavram

Selecting the proper low gear before cresting a grade to maintain engine braking and prevent transmission lockout
Tahmini Süre:1m 0s
Bu soruyu puanla

Konular

Mountain Driving and Steep Downgrades

Bu konudan daha fazla soru