Camshaft

Assuming that you know the basics of 4-stroke internal combustion engines (here is my brief introduction) as well as common valve systems I wrote about in this post, you can jump to this next topic. By now you should be aware of the importance of intake and exhaust valves’ timing in the smooth operation of the engine. In this post, we will provide some information regarding valve timing, duration and lift since most of the so called variable valve timing in general, tend to alter this parts of system in order to extract more power, increase fuel efficiency and so on.By now you should know that the valve is opened by camshaft as written on this post, so we will describe more on the camshaft topic in this post. As you can see, it is nothing more than a simple shaft with numerous cams attached to it. In fact, it has as many cams as the number of the valves it is designed to handle. Below you can see an animated figure. Its function is straightforward although crucial for engine’s operation.

The connection of the crankshaft and the camshaft(s) is achieved using a so called timing chain and the ideal timing based on the crankshaft’s rotation is a result of the camshaft gears which are connected to the crankshaft using the aforementioned timing chain. In some cases, the camshaft gears are used for additional tasks such as triggering the ignition system distributor but this is out of the scope of this blog post.

Knowing these, let’s dive into a more detailed look of the cam. By the way, the cam sometimes known by different name such as cam lobe, cam profile and so on. Whatever the name is lets bear in mind that this part holds the power of how the valves work.

Here we have three stages which are identical for both opening and closing of the valves. I will discuss them separately starting from left to right. We have:

- Ramp
The stage when the valve will start opening (for opening) or has just finished closing (for closing cycle).
- Flank
This part of the cam is the factor of how fast of slow the valve will start opening or closing depending on the side.
- Nose
The point where the valve reaches its maximum lift. This part also determines how deep will be that lift.
Although the terminology might differ, the operation remains the same. Speaking of terminology, here is a similar diagram I found on the web which is also very informative.Here you can also see some new terms which are:-
-Duration
The time required (measured in degrees) from the beginning of opening/closing to reaching the maximum/minimum lift of a valve. This is one of the most important characteristics among camshaft technical specifications.
-Overlap The overlap is an interval when both intake and exhaust valves are neither closed nor open.

Valves
Yeah, the next component will be valves and valve train. As in the post, you know that valves open by camshaft. So this is how it connected and act upon camshaft force

Before ending this section about camshafts, here are a couple of well known techniques to increase performance through camshaft.

- Lift Increase
The higher the lift the more air will be provided to the combustion chamber and more exhaust gas will be released. This translates to more power, however, this is highly affected by the duration since the increased duration (because of the cam’s shape) will decrease the performance. For that matter, this is effective but it usually provides limited results.
- Increasing Overlap
This is usually achieved by increasing the lift duration. As a result the combustion chamber will have an interval when the intake valve will provide air and the half-open exhaust valve will allow emptying the combustion chamber from any gases with higher pressure. This will lead to a more powerful ignition in the next engine’s cycle. The downside of this performance tuning is that it is only effective on high RPMs and consequently, it doesn’t provide considerable power increase in low RPMs.