A four-stroke internal combustion engine operates with its crankshaft turning at a constan… — Armed Services Vocational Aptitude Battery (ASVAB)

A four-stroke internal combustion engine operates with its crankshaft turning at a constant speed of $3{}200\text{ RPM}$ . At what rotational speed does the engine's camshaft turn?

A
$6{}400\text{ RPM}$
B
$3{}200\text{ RPM}$
$1{}600\text{ RPM}$ Answer
D
$800\text{ RPM}$

Answer

1{}600\text{ RPM}

, because the camshaft rotates at half the rotational speed of the crankshaft in a four-stroke engine.

In a four-stroke internal combustion engine, completing all four phases of the cycle (intake, compression, power, and exhaust) requires two complete rotations (

720^\circ

) of the crankshaft. During this entire sequence, each intake and exhaust valve needs to open and close only once, which corresponds to one complete rotation (

360^\circ

) of the camshaft. Because of this mechanical relationship, the timing drive gears or sprockets ensure the camshaft always turns at exactly half the speed of the crankshaft. Dividing the crankshaft speed of

3{}200\text{ RPM}

2

yields a camshaft speed of

1{}600\text{ RPM}

Step-by-Step Solution

Determine the rotational relationship between the crankshaft and camshaft in a four-stroke engine.

The crankshaft must complete 2 full revolutions (

720^\circ

) for all four strokes (intake, compression, power, exhaust) to occur, while the camshaft completes 1 full revolution (

360^\circ

) to open each valve once per cycle.

Establishing the

1:2

speed ratio between the camshaft and crankshaft is necessary to calculate operating speeds.

Calculate the camshaft rotational speed using the given crankshaft speed.

Camshaft Speed =

\frac{3{}200\text{ RPM}}{2} = 1{}600\text{ RPM}

Dividing the crankshaft speed by

2

determines the exact operating speed of the camshaft.

Key Concept

Camshaft-to-crankshaft 1:2 rotational drive ratio in a four-stroke internal combustion engine

Estimated Time:45s

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Topics

More questions from this topic