Camshaft work?

In this article, you will find the camshaft of engine performance. You will get a visual impression of the different engine layout. (SOHC)(DOHC)。 As the overhead camshaft (SOHC) and double overhead camshaft (DOHC) the actual work. Then we look at some of the camshaft can be adjusted so that the speed of the engine is running a more efficient way.

If you read "How car engines work" in this article, you will know the valve so that air / fuel mixture entering the engine and let exhaust out. Camshaft with convex angle (known as cams) to promote the camshaft rotates, the valve opens; valve spring so that they return to the closed position. This is a key work on the engine performance at different speeds have a significant impact. In this event the next page you can see a graphical performance to let you know that a standard camshaft and camshaft.

Camshaft lobe is the key to a key part of the cam. In the camshaft rotates, the cam opens the intake valve when the piston and exhaust valve is closed. This shows the shape of the cam camshaft and engine speed in different working conditions are directly related.

To understand why this is so, imagine that our engine is running very slow. - Only 10 or 20 per minute, transfer (RPM) - that the Pistons take a few seconds to complete a cycle. A real slow so it is impossible to launch, but let us imagine that it is so slow. In such a slow speed, we hope that the shape of the cam as follows:

In the intake stroke of the piston to move down to (known as top dead center, or TDC), the intake valve to open. When the piston moved to the top of the intake valve can be closed. The end of the compression stroke the piston moves (called the BDC, or BDC), the exhaust valve to open and complete the compression stroke when the piston off. The construction of the engine is running fine, as long as the engine is running very slow. However, if the speed increase it? Let's solve this problem.

Reduce engine speed when you increase engine speed, 10 to 20 transferred to the camshaft configuration work is not very good. If the engine speed is 4,000 rpm, the valve should open and close per minute 2,000, or 33 times per second. In this speed, the piston quickly, so the air / fuel mixture into the cylinder very fast.

When the intake valve opens, the piston starts its intake stroke, air / fuel mixture in the intake turbine begins to accelerate into the cylinder.In the intake stroke of the piston movement to the bottom of the cylinder when the air / fuel mixture velocity reached quickly. If we suddenly turn off the intake valve, all the air / fuel mixture will speed stop, can not enter the cylinder.

By the time the intake valve open longer, so that the air / fuel mixture into the cylinder while the piston compression stroke. So the faster engine speed, air / fuel mixture velocity is faster, and we hope the intake valve open longer. We also hope to open the valve to the rapid pace of a large number - a parameter called valve lift, is determined by the shape of the cam.

Cam any given time only a certain engine speed is perfect. In other speed, the engine can not run very well. Therefore, the camshaft is usually a stop-gap device configuration. This is why the cam manufacturers design the engine speed changes, a different cam.

Camshaft camshaft engine configuration there are several different configurations. Let's talk about a few common parts. You may have heard these terms:
(SOHC) Overhead camshaft (SOHC)
(DOHC) Double overhead camshaft (DOHC)
Let us first look at putting overhead camshaft.

This configuration is equivalent to an engine has a cam per head. If it is a single four-cylinder or a single six-cylinder engine, there will be a cam. If the V-6 or V-8 engine, there will be two cam.

According to the valve rocker switch on the cam, and open them. The valve spring back to their closed position. These springs have to be very strong because the engine is fast, the valve is pressed quickly, spring rocker and the valve must contact. If the spring is not very strong, the valve may also quickly jump back from the arm. This will result in extra cam and rocker wear.

In the overhead camshaft and double overhead camshaft engine, the cam driven by the camshaft by a belt or chain to, called the timing belt or timing chain. These belts and chains must be replaced at regular intervals or adjust. If the timing belt breaks, the cam will stop rotating, will hit the exhaust valve on the piston.

Double overhead camshaft a double overhead camshaft engine has two cams per head. So there are two separate cam engine, V has four cam engine. Usually double overhead camshaft for each cylinder has four or more engine valves - a camshaft can not drive all the valves. Dual overhead camshafts is the main reason to use more air intake and exhaust valves. More valves means that intake and exhaust flow more freely, because it has more to lift circulation. This increases the engine's power.

As overhead camshaft engine and dual overhead camshaft engine, putting the engine valve is located in the top of the cylinder above the other. The key difference in putting the engine cam in the engine cylinder block is not inside the top of the cylinder.

Cam-driven plunger into the cylinder through the cylinder top box and mobile arm. The putter has increased the quality of the system, thus increasing the valve spring load. This can limit the speed of putting the engine; overhead camshaft engine in the system canceled the putter, so that the faster the engine as possible.
Putting the engine in gear or the cam is usually a short chain drive. Gear drive is usually not easy to break compared with the belt drive, so often seen overhead camshaft engine.

Variable valve timing There are several manufacturers to change the cam valve timing approach. （VTEC） Honda engine used in a system called Variable Valve Timing and Lift Electronic Control (VTEC)
Variable Valve Timing and Lift Electronic Control (VTEC) Honda engine is an electronic mechanical systems, it can allow the engine to have multiple camshafts. VTEC VTEC engine has an extra intake cam and a rocker arm connected to. The shape allows the intake valve cam lift cam shape than the other large. The engine speed is low, the rocker is not connected with any valve. At high speed, extra arm lock piston, so that the two control two intake valve rocker arm.
Some vehicles using advanced valve timing device. This does not make the valve lift more, it opens and closes them later. It achieved by rotating the cam a few degrees.

If the intake valve is usually in the piston reaches top dead center (TDC) rotated 10 degrees, and reaches TDC (TDC) and turn 90 degrees off, the total duration of 200 degrees. Time can be opened and closed by rotating the cam rotates to the front organizations that transfer. Therefore, in the piston reaches top dead center (TDC) rotated 10 degrees, and reaches TDC (TDC) and turn 210 degrees off. In the ensuing close the valve 20 degrees is good, but if it can increase the intake valve open duration will be better.

。 Ferrari already has a good way to do that.。 Cam in the Ferrari engine has a three-dimensional shape can change with the length of the cam. One end of the cam is a cam shape less neat, and at the other end is a neat cam shape. Shape of the cam smoothly combine these two. A body can slide side to the valve to the cam so that different parts of a cam. Axis of rotation remains the same as ordinary cam - but with the gradual increase in engine speed and load side to slide cam, thus valve timing is optimized.

Some engine manufacturers are experimenting with infinitely variable valve timing system. For example, imagine that each valve has a magnetic switch that can control over the computer rather than the cam to open and close the valve. With such systems, you will be able to reach the maximum engine speed of each engine performance. Looks forward to achieve things.