The Variable Valve Timing and Lift Electronic Control (VTEC) System

The valvetrain is what controls what goes in and out of the cylinder (intake and exhaust). It consists of the camshaft, the rocker arms, and of course the valves. The camshaft is a long rod rotating along with the engine running along the length of the engine. It has a few protrusions (the cam profile) coming out of it which are intended to push a set of rocker arms which then push open the valves. The valves are the “doors” that let the air and exhaust enter and exit the cylinder during the four-stroke combustion cycle.

For a small history lesson; Honda brought the VTEC system to the masses in Japan in 1989 with their Intergra and CRX SiR models. The U.S. was introduced to it in 1991 with the arrival of their everyday supercar NSX which produced 290 horses with only 3.0 liters of displacement. Honda then installed their new tech into the Type R versions of their B16 and B18 engines for an easy 100 plus hp per liter. The B16B built specifically for the Civic Type R boasted an impressive 115.8 hp per liter in a relatively affordable car. The VTEC system culminates in the S2000, which is the only car to use their infamous F20c engine. It produces 240 horsepower with “only” 2.0 liters of displacement and no forced induction. Introduced in 1999 to celebrate the new millenium, the S2000′s F20c still has the highest specific output for a naturally aspirated 2.0 liter car under $100,000.

Let’s get down to the tech side here. V-T-E-C stands for Variable valveTiming and lift Electronic Control. In english, VTEC (and all other variable valve technology) modulates the valves of each cylinder with a computer (just like everything else in this world). VTEC doesn’t modify the valves directly, but rather the camshafts that the valves are connected to. As the engine turns, the camshafts turn in relation and they push the valves open for the cylinder. What VTEC does is change both the duration and lift of the valves as engine speeds change by using different cam profiles. For example, for maximum performance at high RPMs, both valve lift and duration should be relatively longer. But for drivability, comfort, fuel consumption, and emissions, valve duration and lift should be relatively minimal. So for a minivan, larger cam profile is not needed, but for a performance-oriented car that is driven both in traffic on the road and on the track, the best of both worlds are needed. If you want shorter duration and lift, you want your profiles to be smaller, since they won’t push open the valves as far and for as long. If you want longer duration and lift, you obviously want a larger profile. How do we get both smaller AND larger profiles onto one camshaft? For our example, let’s imagine two cam profiles pushing two rocker arms to open two valves. Here’s a simple diagram:

What Honda decided to do was to build a camshaft with two cam profiles and the ability to switch between them. When the time comes to switch from low-RPM comfort mode to high-RPM performance mode, the camshaft makes a small change and switches to its longer duration and lift cam profile. And then the car slows back down to lower-RPM driving, the camshaft profile switches back. So how does Honda change the cam profiles on the fly? Quite simple actually.

What VTEC does is install another rocker arm (let’s call it the VTEC rocker) between the two rocker arms, and a larger cam profile to operate this larger rocker arm. This larger cam profile would obviously push the valves open for a longer duration and lift. The larger cam profile and rocker doesn’t push anything open as there aren’t any valves underneath it, but are just situated between the smaller rockers. Like here:

During low-RPM operation, the valvetrain works normally; ie. the smaller profiles push the smaller rocker arms which then push open the valves. But when the engine enters its higher-RPM range, a hydraulic system pushes a pin that connects the VTEC rocker with the two rockers beside it. When that happens, the larger VTEC cam profile pushes all three rockers even further due to the fact that the VTEC rocker arm is now connected to two non-VTEC rocker arms. When the larger cam profile isn't needed anymore, the pin disengages and unconnected the three rocker arms, reverting back to the smaller cam profile.

The K20A : Honda's first DOHC iVTEC Engine

The K20A used in the new Honda STREAM is the first of the new generation i-VTEC engines. Eventhough the engine does not produce a humongous amount of power in absolute terms, the importance of the engine is that it tells us of the new technologies that Honda is working on, and directly indicates the technologies that will be used on the new generation i-VTEC super high-performance engines that is to come.

Fuel Economy, Ample Torque, Clean Emissions- The i-VTEC provides it all depending on engine load -

The DOHC i-VTEC utilizes smart valve control technology.

The i-VTEC system utilizes Honda's proprietary VTEC system and adds VTC (Variable Timing Control), which allows for dynamic/continuous intake valve timing and overlap control.

The demanding aspects of fuel economy, ample torque, and clean emissions can all be controlled and provided at a higher level with VTEC (intake valve timing and lift control) and VTC (valve overlap control) combined.

Additionally, the intake manifold length can be adjusted.


Combined with the DOHC i-VTEC, in order to obtain both ample low/mid-end torque and high-end output, a rotary valve is used inside the dual-passage intake manifold.


During low/mid rpm,, the rotary valve is closed, while it opens during high rpm's. By varying the intake path length according to engine rpm, ample torque is gained at all rpm levels. Additionally, the rotary valve design is superior over past butterfly valve (flap) in that it reduces intake resistance.

DISCUSSION

Components Identification.
There are a few components of vtech system .Are

      

·         Rocker Arm

· 

         Lock Pin

·    

     Poppet Valve

·       

  Push Rod

       Cam Sensor

·     

    Cam\Camshaft

· 

•          Hydraulic System  
•      ECM\ECU System

     
    

What does the VTEC system in a Honda engine do?

The camshaft uses rotating lobes that push against the valves to open and close them.It turns out that there is significant relationship between the way the lobes are ground on the camshaft and the way the engine performs in different rpm(rotations per minute) ranges. To understand why this is the case, imagine that we are running an engine extremely slowly -- at just 10 or 20 rpm, so it takes the piston seconds to complete a cycle. It would be impossible to actually run a normal engine this slowly, but imagine that we could. We would want to grind the camshaft so that, just as the piston starts moving downward in the intake stroke, the intake valve would open. The intake valve would close right as the piston bottoms out. Then the exhaust valve would open right as the piston bottoms out at the end of the combustion stroke and would close as the piston completes the exhaust stroke. That would work great for the engine as long as it ran at this very slow speed.


W­hen you increase the rpm, however, this configuration for the camshaft does not work well. If the engine is running at 4,000 rpm, the valves are opening and closing 2,000 times every minute, or thirty to fourty times every second. When the intake valve opens right at the top of the intake stroke, it turns out that the piston has a lot of trouble getting the air moving into the cylinder in the short time available (a fraction of a second). Therefore, at higher rpm ranges you want the intake valve to open prior to the intake stroke -- actually back in the exhaust stroke -- so that by the time the piston starts moving downward in the intake stroke, the valve is open and air moves freely into the cylinder during the entire intake stroke. This is something of a simplification, but you get the idea. For maximum engine performance at low engine speeds, the valves need to open and close differently than they do at higher engine speeds. If you put in a good low-speed camshaft, it hurts the engine's performance at high speeds, and if you put in a good high-speed camshaft it hurts the engine's performance at low speeds (and in extreme cases can make it very hard to start the engine!).













Article credit to http://auto.howstuffworks.com

VIDEO HONDA IVTEC ENGINE...TENGOKLE...

the video of ivtec.....

HISTORY OF VTEC FROM HONDA

VTEC (Variable Valve Timing and Lift Electronic Control) is a valvetrain system developed by Honda to improve the volumetric efficiency of a four-stroke internal combustion engine. The VTEC system uses two camshaft profiles and electronically selects between the profiles. It was invented by Honda engineer Ikuo Kajitani, and was the first system of its kind.Different types of variable valve timing and lift control systems have also been produced by other manufacturers (NeoVVL from NissanMIVEC from Mitsubishi, AVCS from Subaru, V-i/VVTL-iVT from Toyota, VANOSfrom BMW, VarioCam Plus from Porsche, , etc.).



VTEC, the original Honda variable valve control system, originated from REV (Revolution-modulated valve control) introduced on the CBR400 in 1983 known as HYPER VTEC. In the regular four-stroke automobile engine, the intake and exhaust valves are actuated by lobes on a camshaft. The shape of the lobes determines the timing, lift and duration of each valve. Timing refers to an angle measurement of when a valve is opened or closed with respect to the piston position (BTDC or ATDC). Lift refers to how much the valve is opened. Duration refers to how long the valve is kept open. Due to the behavior of the working fluid (air and fuel mixture) before and after combustion, which have physical limitations on their flow, as well as their interaction with the ignition spark, the optimal valve timing, lift and duration settings under low RPM engine operations are very different from those under high RPM. Optimal low RPM valve timing, lift and duration settings would result in insufficient filling of the cylinder with fuel and air at high RPM, thus greatly limiting engine power output. Conversely, optimal high RPM valve timing, lift and duration settings would result in very rough low RPM operation and difficult idling. The ideal engine would have fully variable valve timing, lift and duration, in which the valves would always open at exactly the right point, lift high enough and stay open just the right amount of time for the engine speed in use.

The three rockers are interconnected by the two hydraulically operated pins A and B.
The cam in the middle operates on the valves by the interconnected rockers

The outside cams operate on the valves by outside rockers.

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