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Difficulty: EasyEngine Principles and Internal Components

In a standard four-cycle automotive engine, how many complete revolutions does the camshaft make for every two full rotations of the crankshaft?

  1. 1 revolutionAnswer
  2. B
    2 revolutions
  3. C
    4 revolutions
  4. D
    0.5 revolution

Answer

1 revolution
A four-stroke engine requires two complete rotations (720∘720^\circ) of the crankshaft to complete all four strokes (intake, compression, power, and exhaust). During this cycle, each valve needs to open only once. Therefore, the camshaft is geared to rotate at half the speed of the crankshaft, making exactly 1 revolution for every 2 revolutions of the crankshaft.

Step-by-Step Solution

1
Identify the relationship between the four-stroke operating cycle and crankshaft rotation.
One complete four-stroke cycle requires 720 degrees of crankshaft rotation, which equals 2 full revolutions.
Each stroke (intake, compression, power, exhaust) takes 180 degrees of crankshaft movement (4×180∘=720∘4 \times 180^\circ = 720^\circ).
2
Determine how many times each valve must open per four-stroke cycle.
Each intake and exhaust valve opens exactly once per complete cycle.
The camshaft lobes actuate each valve once per full 360-degree rotation of the camshaft.
3
Calculate camshaft revolutions relative to two crankshaft revolutions.
The camshaft turns 1 revolution for every 2 revolutions of the crankshaft (a 1:2 speed ratio).
The camshaft gear has twice as many teeth as the crankshaft gear, causing it to turn at half the crankshaft's rotational speed.

Key Concept

Camshaft to crankshaft 1:2 rotational speed ratio in four-stroke engines
Estimated Time:45s
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Topics

Engine Principles and Internal Components

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