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Zorluk: ZorEnvironmental Impact and Fuel Efficiency

A driver is descending a long gradient on a single carriageway and observes a red traffic signal 300 metres ahead. To minimise both fuel consumption and exhaust emissions without compromising vehicle control, what is the most effective driving technique?

  1. A
    Shift into neutral and allow the vehicle to freewheel down the incline under its own momentum
  2. Release the accelerator pedal early while remaining in gear to activate the engine's overrun fuel cut-off systemCevap
  3. C
    Depress and hold the clutch pedal fully down while regulating speed using only the footbrake
  4. D
    Keep tyres inflated below recommended pressures to create additional rolling resistance when slowing down

Cevap

Release the accelerator pedal early while remaining in gear to activate the engine's overrun fuel cut-off system.
In modern road vehicles equipped with electronic engine management, releasing the accelerator pedal while the vehicle remains in gear triggers the overrun fuel cut-off system. Because the momentum of the moving vehicle drives the engine through the transmission, the fuel injectors deliver zero fuel until engine speed approaches idle RPM. This technique completely eliminates fuel burn during deceleration while maintaining full steering response and engine braking stability.

Adım Adım Çözüm

1
Analyse the vehicle drivetrain state during deceleration on a gradient.
Identified that modern electronic fuel injection (EFI) engines incorporate an overrun fuel cut-off mechanism.
When the vehicle is moving in gear with the throttle closed, the turning wheels drive the engine, prompting the engine control unit (ECU) to shut off fuel delivery entirely.
2
Evaluate the energy consumption and control implications of coasting.
Disproved the misconception that shifting to neutral or depressing the clutch saves fuel.
Coasting requires the engine to burn fuel at an idle rate (typically 0.5–1.0 litre/hour) to prevent stalling, whilst simultaneously disconnecting engine braking and compromising steering and braking assistance.
3
Determine the optimal driving technique that balances zero fuel consumption with road safety.
Lifting off the accelerator early while staying in gear achieves zero fuel consumption and controlled deceleration.
This complies directly with DVSA eco-safe driving guidelines by reducing fuel burn to zero, reducing brake wear, and keeping the vehicle under full mechanical control.

Anahtar Kavram

Overrun Fuel Cut-off and Engine Braking versus Coasting
Tahmini Süre:1m 15s
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Environmental Impact and Fuel Efficiency

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