Internal combustion engine fundamentals: The diagram that shows the correct crank positions corresponding to the precise opening and closing instants of the intake and exhaust valves (including lead, lag, and overlap) is called what?

Introduction / Context:

Correct valve events are central to four-stroke engine breathing. Designers often represent these events on a circular chart tied to crankshaft rotation so that opening and closing moments can be visualized relative to top dead center (TDC) and bottom dead center (BDC). This question asks you to identify the name of that specific diagram used in engine theory, diagnostics, and camshaft design.

Given Data / Assumptions:

• Four-stroke spark-ignition or compression-ignition engine.
• Events of interest: intake opening/closing, exhaust opening/closing, advance (lead), delay (lag), and overlap near TDC.
• Crank-angle based representation is intended.

Concept / Approach:

The valve timing diagram is a crank-angle diagram showing when the valves open and close with respect to TDC/BDC. It typically indicates intake opening before TDC, intake closing after BDC, exhaust opening before BDC, and exhaust closing after TDC, making overlap explicit. This chart helps explain volumetric efficiency, scavenging, and idle quality.

Step-by-Step Solution:

Verification / Alternative check:

Cam datasheets provide opening/closing in degrees at a given tappet lift; these figures are precisely what populate a valve timing diagram used by tuners and OEMs alike.

Why Other Options Are Wrong:

• Indicator diagram: a p–V diagram showing pressure versus volume during a cycle; it does not plot crank-angle valve events.
• Axial force diagram: unrelated to valve timing; used in machine design contexts.
• Pressure–volume sketch: again p–V, not valve timing.
• None of these: incorrect because the standard term exists.

Common Pitfalls:

• Confusing p–V indicator charts with timing charts; they answer different questions (thermodynamics vs. kinematics).
• Reading cam degrees instead of crank degrees (camshaft rotates at half crank speed).

Final Answer:

valve timing diagram