What are the key parts of a Camshaft?

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Key Parts of a Camshaft:

The key parts of any camshaft are the lobes. Because the camshaft spins, the lobes open and shut the intake and exhaust valves in time with the motion of the piston. It seems that there’s a direct relationship between the form of the cam lobes and also the way the engine performs in several speed ranges.

To understand why this can be the case, imagine that we are running an engine extremely slowly — at just 10 or 20 revolutions per minute (RPM) — so that it takes the piston a pair of seconds to complete a cycle. It’d be impossible to truly run a standard engine this slowly, but let’s say that we could. At this slow speed, we’d want cam lobes shaped so that:

  1. Just as the piston starts moving downward in the intake stroke (called the highest spatial relation, or TDC), the valve would open. The valve would close right because the piston bottoms out.
  2. The valve would open right because the piston bottoms out (called bottom spatial relation, or BDC) at the top of the combustion stroke, and would close because the piston completes the exhaust stroke.

This setup would work very well for the engine as long because it ran at this very slow speed. But what happens if you increase the RPM? Let’s understand.


When RPM Increased:

When you increase the RPM, the ten to twenty RPM configuration for the camshaft doesn’t work well. If the engine is running at 4,000 RPM, the valves are opening and shutting 2,000 times every minute, or 33 times every second. At these speeds, the piston is moving very quickly, that the air/fuel mixture rushing into the cylinder is moving very quickly further.

When the valve opens and also the piston starts its intake stroke, the air/fuel mixture in the intake runner starts to accelerate into the cylinder. By the time the piston reaches the underside of its intake stroke, the air/fuel is moving at a reasonably high speed. If we were to slam the valve shut, all of that air/fuel would come to a stop and not enter the cylinder. By leaving the valve open a bit longer, the momentum of the fast-moving air/fuel continues to force air/fuel into the cylinder because the piston starts its compression stroke.

Therefore the faster the engine goes, the faster the air/fuel moves, and therefore the longer we wish the valve to remain open. We also want the valve to open wider at higher speeds — this parameter, called valve lift, is governed by the cam lobe profile.

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