Engine Basics And More!!

[cyberdoc95]

[SIZE=3]IGNITION SYSTEM [/SIZE]con't

The Coil
The coil is the device that generates the high voltages required to create a spark. It is a simple device -- essentially a high-voltage transformer made up of two coils of wire. One coil of wire is called the primary coil. Wrapped around it is the secondary coil. The secondary coil normally has hundreds of times more turns of wire than the primary coil.

Current flows from the battery through the primary winding of the coil.

The primary coil's current can be suddenly disrupted by the breaker points, or by a solid-state device in an electronic ignition.

If you think the coil looks like an electromagnet, you're right -- but it is also an inductor. The key to the coil's operation is what happens when the circuit is suddenly broken by the points. The magnetic field of the primary coil collapses rapidly. The secondary coil is engulfed by a powerful and changing magnetic field. This field induces a current in the coils -- a very high-voltage current (up to 100,000 volts) because of the number of coils in the secondary winding. The secondary coil feeds this voltage to the distributor via a very well insulated, high-voltage wire.

[cyberdoc95]

[SIZE=3]HOW CAMSHAFT WORKS[/SIZE]

The camshaft uses lobes (called cams) that push against the valves to open them as the camshaft rotates; springs on the valves return them to their closed position. This is a critical job, and can have a great impact on an engine's performance at different speeds. On the next page of this article you can see the animation we built to really show you the difference between a performance camshaft and a standard one.



Lobes are Key
The key parts of any camshaft are the lobes. As the camshaft spins, the lobes open and close the intake and exhaust valves in time with the motion of the piston. It turns out that there is a direct relationship between the shape of the cam lobes and the way the engine performs in different speed ranges.

To understand why this is 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 couple of seconds to complete a cycle. It would be impossible to actually run a normal engine this slowly, but let's imagine that we could. At this slow speed, we would want cam lobes shaped so that:

* Just as the piston starts moving downward in the intake stroke (called top dead center, or TDC), the intake valve would open. The intake valve would close right as the piston bottoms out.

* The exhaust valve would open right as the piston bottoms out (called bottom dead center, or BDC) at the end of the combustion stroke, and would close as the piston completes the exhaust stroke.

[cyberdoc95]

[SIZE=3]HOW CAMSHAFT WORKS[/SIZE] cont

Camshaft Arrangements
There are several different arrangements of camshafts on engines. We'll talk about some of the most common ones. You've probably heard the terminology:

* Single overhead cam (SOHC)
* Double overhead cam (DOHC)
* Pushrod

Single Overhead Cams
This arrangement denotes an engine with one cam per head. So if it is an inline 4-cylinder or inline 6-cylinder engine, it will have one cam; if it is a V-6 or V-8, it will have two cams (one for each head).

The cam actuates rocker arms that press down on the valves, opening them. Springs return the valves to their closed position. These springs have to be very strong because at high engine speeds, the valves are pushed down very quickly, and it is the springs that keep the valves in contact with the rocker arms. If the springs were not strong enough, the valves might come away from the rocker arms and snap back. This is an undesirable situation that would result in extra wear on the cams and rocker arms.

On single and double overhead cam engines, the cams are driven by the crankshaft, via either a belt or chain called the timing belt or timing chain. These belts and chains need to be replaced or adjusted at regular intervals. If a timing belt breaks, the cam will stop spinning and the piston could hit the open valves.


Double Overhead Cam
A double overhead cam engine has two cams per head. So inline engines have two cams, and V engines have four. Usually, double overhead cams are used on engines with four or more valves per cylinder -- a single camshaft simply cannot fit enough cam lobes to actuate all of those valves.

The main reason to use double overhead cams is to allow for more intake and exhaust valves. More valves means that intake and exhaust gases can flow more freely because there are more openings for them to flow through. This increases the power of the engine.

Pushrod Engines
Like SOHC and DOHC engines, the valves in a pushrod engine are located in the head, above the cylinder. The key difference is that the camshaft on a pushrod engine is inside the engine block, rather than in the head.

The cam actuates long rods that go up through the block and into the head to move the rockers. These long rods add mass to the system, which increases the load on the valve springs. This can limit the speed of pushrod engines; the overhead camshaft, which eliminates the pushrod from the system, is one of the engine technologies that made higher engine speeds possible.

The camshaft in a pushrod engine is often driven by gears or a short chain. Gear-drives are generally less prone to breakage than belt drives, which are often found in overhead cam engines.

[cyberdoc95]

[SIZE=3]HOW CAMSHAFT WORKS[/SIZE] cont

[SIZE=3]Variable Valve Timing[/SIZE]
There are a couple of novel ways by which carmakers vary the valve timing. One system used on some Honda engines is called VTEC.

VTEC (Variable Valve Timing and Lift Electronic Control) is an electronic and mechanical system in some Honda engines that allows the engine to have multiple camshafts. VTEC engines have an extra intake cam with its own rocker, which follows this cam. The profile on this cam keeps the intake valve open longer than the other cam profile. At low engine speeds, this rocker is not connected to any valves. At high engine speeds, a piston locks the extra rocker to the two rockers that control the two intake valves.

Some cars use a device that can advance the valve timing. This does not keep the valves open longer; instead, it opens them later and closes them later. This is done by rotating the camshaft ahead a few degrees. If the intake valves normally open at 10 degrees before top dead center (TDC) and close at 190 degrees after TDC, the total duration is 200 degrees. The opening and closing times can be shifted using a mechanism that rotates the cam ahead a little as it spins. So the valve might open at 10 degrees after TDC and close at 210 degrees after TDC. Closing the valve 20 degrees later is good, but it would be better to be able to increase the duration that the intake valve is open.



Ferrari has a really neat way of doing this. The camshafts on some Ferrari engines are cut with a three-dimensional profile that varies along the length of the cam lobe. At one end of the cam lobe is the least aggressive cam profile, and at the other end is the most aggressive. The shape of the cam smoothly blends these two profiles together. A mechanism can slide the whole camshaft laterally so that the valve engages different parts of the cam. The shaft still spins just like a regular camshaft -- but by gradually sliding the camshaft laterally as the engine speed and load increase, the valve timing can be optimized.

[ssaloon]

damn ang haba! you could've left the searching to us in the site ehehehe

for more, you can download the link found on the sticky thread "car hacks, mods for dummies" there's a link to a 380++ page PDF file on all sorts of stuff for your car ;)

[silhouette]

So informative!

[OTEP]

Pwede natin ilagay ito sa Tech Specs and Quick Reference section. :D

[yan_168]

di ba sa www.howstuffworks.com ito?

[cyberdoc95]

damn ang haba! you could've left the searching to us in the site ehehehe

for more, you can download the link found on the sticky thread "car hacks, mods for dummies" there's a link to a 380++ page PDF file on all sorts of stuff for your car

Hey Ssaloon,

Napagkatuwaan ko lang to put all these stuff together. That's self-teaching and learning, then, nababasa rin ng iba, right?!he he he..Yes, I could have left the searching to you and maybe, I'll just stop posting then.

Lately kasi, no new automotive-related topics have been posted. So I just took the initiative to put something that I could re-learn. Although not entirely new but at least something that you can learn from. Then, parang cumulative na knowledge lang na I could add something basic once a week or something until this will accumulate.

If you look at some of the topics posted on the Forum, its all about power, torque, problems about noisy engine sounds, engine designs,etc. With the basic knowledge about engine, you'll see that you can initially diagnose the problem yourself when you have the basic knowledge about the engine. This was what I was aiming to do..I bet, iilan lang siguro sa atin ang talagang alam ang lahat ng parte ng isang sasakyan by heart kundi siguro ang pagpa-load lang ng accessories. Not na there's anything wrong with that but at least hindi man lang maloko ng mga mekaniko na kung ano-ano na ang sinasabi kung nasisira ang sasakyan.

But I think nobody seems to appreciate the effort. Sayang lang din pala time ko nito. Why did I even bother in the first place... he he he...

Ssaloon, Thanks though for pointing that out to me...

Yes Yan168, If you have read from the beginning of this thread, I stated that my source is HOWSTUFFWORKS.COM and as a researcher in the medical field, I always state my source in any claim I have to make them all credible..Thanks for that comment...Really appreciate it.

To THE MODS: KINDLY CLOSE THIS THREAD. THANKS PO!

[gearspeed]

Sa totoo lang kaunti lang alam ko dyan mabasa nga yan mamaya..