If you've read How Car Engines Work for a paper, you will know the valve. Air / fuel mixture entering the engine and go through the engine exhaust gas valve. When the camshaft rotates, the camshaft with a convex angle (cam) to promote the valve to open, the valve spring is responsible for pushing the valve back to closed position. This is a very important item of work, can the engine performance at different speeds have a huge impact.

In this article, you can learn how the camshaft of engine performance. We offer some exquisite animation, to show you the different structure of the engine (for example, single overhead camshaft and double overhead camshaft (DOHC)) of the actual work. Then we come to understand some of the adjustment used in automotive camshaft ingenious ways, these methods are more effective in the cam handle different engine speeds.

The key is that the camshaft cam. When the camshaft rotates, the cam with the piston of the Games in a timely manner to open / close the intake valve and exhaust valve. Therefore, the shape of the cam and the engine speed in different working conditions are directly linked.

To understand why, let us imagine a very slow speed is to run the engine - 10 or 20 rev / min - in this case, the Pistons take a few seconds to complete a run cycle. In reality, the normal operation of the engine may not be so slow, but we imagine it anyway. In such a slow speed, we hope that the cam shape is:

As long as this engine has been running very slowly, which in good working condition will continue. However, if the increase in the speed of the case, how will it? Let us look carefully.

In the speed of 10-20 r / min under the camshaft well-constructed, the increase in speed is no longer suitable for the circumstances. Engine speed to 4000 rev / time-sharing, the valve opening and closing every minute to 2000 times, 33 times per second. This piston movement is very fast, so the air / fuel mixture into the cylinder is running very fast.

When the intake valve opens, the piston starts its intake stroke, air / fuel mixture in the intake tube and began to accelerate circulation, ready to enter the cylinder. Piston during the intake stroke in the end, the air / fuel mixture will be very high velocities. 。 If the intake valve suddenly closed and all air / fuel mixture due to blocked and can not enter the cylinder. By extending the intake valve opening time, when the piston starts the compression stroke, the high-speed operation of the air / fuel mixture will continue the momentum to force mixture into the cylinder. Therefore, the faster the engine is running, the air / fuel mixture to the faster movement, and we hope the time the intake valve open longer. In the case of high speed, we hope that the valve opening larger, this parameter is called valve lift, it is determined by the cam contour.

The following animation will demonstrate and promote the regular operation of the valve cam cam valve timing in terms of the difference. Watch, push the exhaust valve cam (red circle) and intake (blue circle) cycles have more overlap. For this reason, a car equipped with this cam tremor in a stronger sense of idling situations.

Any given camshaft only to a specific speed of the engine running perfect state of operation. When the other speed operation, the engine performance is reduced. Therefore, the fixed cam is not always the best choice. This is why many car manufacturers have formulated development plans, development of variable cam profile to adapt to changes in engine speed.

In the engine camshaft in several different configurations available for adoption. Next, we understand some of the most common way. You may have heard the following terms:

• Single overhead camshaft (SOHC)
• Double overhead camshaft (DOHC)
• Putter

Single overhead camshaft design is characterized by this engine is only one cam per cylinder head. Therefore, inline 4-cylinder or inline 6-cylinder engine is only one cam; and V-6 or V-8 engine has two cams (one each for each cylinder head).

Press and open the valve rocker arm cam driven, spring is the role of the valve back to closed position. These springs must be very strong, because the engine speed operation, the valve is pressed quickly, and the valve is connected through the spring and the rocker. If the spring is not enough strong, the valve may be out of arm and was suddenly sucked back. This bad situation will cause more cam and rocker wear.

Single-and dual overhead cam engine overhead, the cam belt or chain from the camshaft drive through, called the timing belt or timing chain. These belts and chains need regular replacement or adjustment. If the timing belt break, the cam will stop rotating, the piston will hit the open valve on.

Damage caused by the impact piston valve

The picture above shows the valve open when the piston impacts the case.

DOHC engine double overhead cam two cams per cylinder head, so there are two cam engine line, and V-type engine has four. Generally, each cylinder has four or more valves of the engine used dual overhead camshafts, a camshaft can not be installed because the cam enough to drive all of the valve.

The reason why dual-overhead camshaft is to meet the additional intake valve and exhaust valve needs. More air intake and exhaust valve means smoother, because there are more openings for gas flow. Engine power also increases.

The reason why dual-overhead camshaft is to meet the additional intake valve and exhaust valve needs. More air intake and exhaust valve means smoother, because there are more openings for gas flow, engine power also increases.

Push rod engine with single overhead camshaft and dual overhead cam engine like the valve plunger in the cylinder at the top of the engine cylinder head. The main difference is that the ejector cylinder engine camshaft in the engine body, not in the cylinder head.

Push rod engine

Cam-driven plunger to reach through the cylinder block cylinder head, thus promoting the arm. The increase of inertia putter, making valve spring load has increased. This will limit the push rod engine speed, overhead camshaft engine canceled mandrel, so that the engine for higher speeds possible.

Ejector is usually caused by the engine camshaft gear or short chain drive. Typically, the gear drive and belt drive is not easy to break compared, it is often used for overhead camshaft engine.

Variable valve timing cam Here are a few manufacturers to change valve timing of the new approach. Honda engines used in a system called VTEC.

VTEC (Variable Valve Timing and Lift Electronic Control System) is part of the Honda engine used in electromechanical systems, which allow the engine to have multiple camshafts. VTEC engine has an extra intake cam and a rocker arm connected to it. Compared with the other cam profile, which allows the intake valve cam profile open longer. The engine speed is low, the rocker is not connected with any valve; when the engine is at high speed, the piston will be an additional two intake valve rocker and control of the two rocker lock.

Some cars use a special device to improve the performance of valve timing. The device does not extend the valve is open, but to make the valve open time and the closing time back delay, which is rotated by the camshaft a few degrees more to achieve. If the intake valve is usually in the piston reaches top dead center (TDC) rotated 10 degrees before the Open, and reaching the top dead center (TDC) and turn 190 degrees off, then the total rotation of 200 degrees duration of time used. Time can be opened and closed by a cam mechanism to rotate a little more to make adjustments. For example, the valve can point the piston reaches top dead center (TDC) and turn 10 degrees to open, and reached the only point (TDC) and turn 210 degrees when closed. If you can close the valve 20 degrees in the delay based on the increase in the intake valve open duration is more ideal.

Ferrari has been through a clever way to do this.Ferrari engines have a camshaft on a three-dimensional contour lines, with the cam lobe can change the length. One end of the cam is a little curvature of the cam contour, the curvature at the other end is the larger cam profile, the cam contour structures so that the two well together. Make the camshaft using a horizontal sliding mechanism, the valve will be able to bite different parts of the cam. Cam shaft is still the same as normal rotation, but with the increase in engine speed and load, the camshaft will gradually slide horizontally, so to optimize valve timing.

Part of the Ferrari engine with variable cam system of this

Some engine manufacturers are experimenting with infinitely variable valve timing system. For example, for each valve by an electromagnetic switch, allowing the computer rather than through the camshaft to control the valves open and close. With such systems, regardless of how the engine speed, can get the maximum performance of the engine. This is indeed worthy of our common expectations.