Today at The Mechanical post ! we’ll see about what is vvt engine, its working and advantages of using vvt. So let’s check out What is VVT, i-VTEC or VTVT engine ?
What is meant by vvt engine ?
(Used in latest Honda,Nissan and Ford cars.) – Continuously variable transmission.
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The valves within an internal combustion engine are used to control the flow of the intake and exhaust gases into and out of the combustion chamber. The timing, duration and lift of these valve events has a significant impact on engine performance. Without variable valve timing or variable valve lift, the valve timing is the same for all engine speeds and conditions, therefore compromises are necessary. An engine equipped with a variable valve timing actuation system is freed from this constraint, allowing performance to be improved over the engine operating range.
Piston engines use valves which are driven by camshafts. The cams open the valves for a certain amount of time (duration) during each intake and exhaust cycle. The timing of the valve opening and closing, relative to the position of the crankshaft, is important. The camshaft is driven by the crankshaft through timing belts, gears or chains.
|Image by – Wapcaplet at the English language Wikipedia|
An engine requires large amount of air when at high speeds. However, the intake valves may close before enough air has entered each combustion chamber, reducing performance. On the other hand, if the camshaft keeps the valves open for longer periods of time, as with a racing cam, problems start to occur at the lower engine speeds. Opening the intake valve while the exhaust valve is still open may cause unburnt fuel to exit the engine, leading to lower engine performance and increased emissions.
Types of variations in valve timings
Early/Late intake valve opening Early intake valve opening is another variation that has significant potential to reduce emissions. In a traditional engine, a process called valve overlap is used to aid in controlling the cylinder temperature. By opening the intake valve early, some of the inert/combusted exhaust gas will back flow out of the cylinder, via the intake valve, where it cools momentarily in the intake manifold. This gas then fills the cylinder in the subsequent intake stroke, which aids in controlling the temperature of the cylinder and nitric oxide emissions. It also improves volumetric efficiency, because there is less exhaust gas to be expelled on the exhaust stroke.
Early/late exhaust valve opening Early and late exhaust valve opening timing can be manipulated to reduce emissions. Traditionally, the exhaust valve opens, and exhaust gas is pushed out of the cylinder and into the exhaust manifold by the piston as it travels upward. By manipulating the timing of the exhaust valve, engineers can control how much exhaust gas is left in the cylinder. By holding the exhaust valve open slightly longer, the cylinder is emptied more and ready to be filled with a bigger air/fuel charge on the intake stroke. By closing the valve slightly early, more exhaust gas remains in the cylinder which increases fuel efficiency. This allows for more efficient operation under all conditions. Now you must be thinking what would be controlling all this? The answer to this is ECU or the Electronic Control Unit
Advantages of VVT engine:
Higher RPM – The main advantage of having a variable valve timing technology is the increase it will provide in your engine’s revolutions per minute. When you step on the accelerator, it will require more RPM to sustain this demand.That roaring sound you hear when you step on the gas pedal is the variable valve timing system hard at work to keep your engine running strong.
Better Fuel Economy – As the valves are controlled efficiently the fuel required will decrease considerably. Thus increasing the mileage of the car and reducing the stress on your pocket.
Lower Carbon Emissions – As some amount of exhaust gas is reused again in the combustion process, the emissions of the engine is reduced considerably.
Increased Engine Lifespan – If you continue to maintain an efficient and high performing engine, then you can expect to get a great number of years out of it. A lot of people will wait until their engines go bad before they decide to replace their vehicle. If you have variable valve timing in your engine, then it will help keep it strong for as long as possible. Of course, there are other factors involved in keeping an engine healthy too. Make sure you regularly get oil changes and use the right kind of fuel.
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