What Does a Camshaft Do? The Purpose of This Car Part

What Does a Camshaft Do

There are many parts in an internal-combustion engine, both moving and fixed. This article discusses one of the most important parts of your automobile's engine and answers the question "What does a camshaft do?"

What Does a Camshaft Do?

auto mechanic figurine on the side of a camshaft

The camshaft has lobes on it that, as the camshaft rotates, opens the valves in your car's engine. The camshaft may have other functions as well, depending on how your car's engine was designed.

The rotational motion of a camshaft is carefully timed to open the valves at exactly the appropriate moment. How it does this, and why it's important, we'll talk about in the following article.

Let's examine some of the physical characteristics of the camshaft itself.

Camshafts are made of either steel or cast iron. Steel camshafts are precisely machined from a rod of steel and then inductively hardened to provide long life.

Inductive hardening is a process where the finished camshaft is heated by induction and then quenched.

This process results in a camshaft that is both harder and more brittle than the native steel.

Cast iron camshafts are produced by pouring a molten iron alloy into a cast of the camshaft's size and shape. The camshaft is then machined precisely.

There is no need to case-harden a cast-iron camshaft because the alloy used is already hardened.

Both kinds of camshafts are precision machined using lasers to ensure the proper shape and position of each of the camshaft's lobes.

This laser measurement ensures that each camshaft in a production line will have the same size and lobe dimensions as others coming off the line.

Simple Camshaft Operation

When considering what does a camshaft do, the first area to examine is, what is its basic function?

Simply put, the camshaft's purpose is to open the intake and exhaust valves at the proper time to maximize the power produced by the engine at a certain number of revolutions-per-minute (RPMs).

Let's examine these valves as we discuss the four-cycle gasoline engine.

Thermodynamics 101

engine camshaft

Image from Pixabay

Internal-combustion gasoline engines operate by the Otto Cycle, named after Nikolaus Otto, the German engineer who in 1876 built the first practical working four-stroke gas-powered engine. Otto cycle engines work as follows:

Compression Stroke

The cylinder now contains air or an air-gas mixture, with both intake and exhaust valves closed.

The piston now moves upward, compressing the air in the cylinder and heating it due to compression. The piston continues upward until it gets near the top of its stroke.

Power Stroke

The cylinder now contains air or an air-gas mixture, with both intake and exhaust valves closed.

The piston now moves upward, compressing the air in the cylinder and heating it due to compression. The piston continues upward until it gets near the top of its stroke.

Exhaust Stroke

The final action of the Otto Cycle is the exhaust stroke. The camshaft rotates until a different lobe pushes the exhaust valve open.

The rising piston then forces the burned fuel-air mixture out through the exhaust valve to the exhaust system, and from there it's expelled past the muffler into the atmosphere.

Where Is the Camshaft?

Learning what does a camshaft do also involves learning where the camshaft is in your car's engine. The answer depends on how your motor was engineered.

There are two standard configurations for a camshaft: either in the engine block itself, or in the cylinder head above the valves.

Compression Stroke

The cylinder now contains air or an air-gas mixture, with both intake and exhaust valves closed.

The piston now moves upward, compressing the air in the cylinder and heating it due to compression. The piston continues upward until it gets near the top of its stroke.

Power Stroke

The cylinder now contains air or an air-gas mixture, with both intake and exhaust valves closed.

The piston now moves upward, compressing the air in the cylinder and heating it due to compression. The piston continues upward until it gets near the top of its stroke.

Exhaust Stroke

The final action of the Otto Cycle is the exhaust stroke. The camshaft rotates until a different lobe pushes the exhaust valve open.

The rising piston then forces the burned fuel-air mixture out through the exhaust valve to the exhaust system, and from there it's expelled past the muffler into the atmosphere.

How Fast Does a Camshaft Turn?

When learning what does a camshaft do, one interesting fact is the speed at which the camshaft rotates.

In the four-cycle engine the camshaft rotates at one-half the speed of the crankshaft, because only every other stroke is a power stroke.

So each valve only has to open during its appropriate stroke, either power or exhaust. In a two-cycle engine, every stroke is a power stroke, and the camshaft rotates at the same speed as the camshaft.

Variable Valve Timing (VVT)

Many of us can recall hearing a high-performance gasoline engine at idle, running so rough that it sounds completely out of tune.

That is because the camshaft is engineered to provide the optimum opening and closing times for the valves based on a particular RPM.

This optimum RPM usually occurs at what's called the power peak, which is the RPM at which the engine is delivering its maximum power.

Particularly in high-performance engines, tuning the camshaft for the power peak means it is not very efficient at low engine RPMs, such as at idle.

It also means the power curve of the engine (the horsepower the engine can deliver at different RPMs, charted on a graph of RPM versus power) is not as smooth as it should be. One way to counter these problems is with variable valve timing.

Camshaft Review

We've covered the topic of what does a camshaft do in our article today. So let's quickly review:

What Is It?

COMP Cams

The camshaft is a lobed rod that opens and closes your engine's intake and exhaust valves in a precisely timed manner to give you maximum power. Camshafts are made of either hardened steel or cast iron.

Where Do They Physically Reside?

Camshafts may reside in the cylinder block, and open/close valves through a pushrod/rocker arm combination, or can reside in the cylinder head and open/close the valves by pushing on a tappet.

What Are VVT and VVL?

Variable Valve Timing (VVT) and Variable Valve Lift (VVL) are techniques to optimize the opening/closing of your engine's valves at widely varying RPMs in order to provide smoother power curves, better fuel efficiency, reduced emissions and better idle performance.

Conclusion

Now that you have a good idea of what does a camshaft do, you'll be able to apply your knowledge the next time you're looking to purchase a new or used car. Knowledge is power!

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