Vvt what does it mean

The high speed cam does not have any effect to the rocker follower because there is sufficient spacing underneath its hydraulic tappet. When speed has increased to the threshold point, the sliding pin is pushed by hydraulic pressure to fill the spacing. The high speed cam becomes effective. Note that the fast cam provides a longer valve-opening duration while the sliding pin adds valve lift.

However, VVTL- i offers variable lift, which lifts its high speed power output a lot. Therefore it is undoubtedly the best VVT today. However, it is also more complex and probably more expensive to build. Continuous VVT improves torque delivery across the whole rev range; Variable lift and duration lift high rev power. More complex and expensive. Toyota Celica GT-S. Variocam Plus uses hydraulic phasing actuator and variable tappets.

Variocam of the Carrera. However, I found their mechanisms virtually share nothing. The Variocam was first introduced to the in It used timing chain to vary the phase angle of camshaft, thus provided 3-stage variable valve timing. Therefore, the Variocam Plus used in the new Turbo finally follow uses the popular hydraulic actuator instead of chain. One well-known Porsche expert described the variable valve timing as continuous, but it seems conflicting with the official statement made earlier, which revealed the system has 2-stage valve timing.

However, the most influential changes of the "Plus" is the addition of variable valve lift. It is implemented by using variable hydraulic tappets. As shown in the picture, each valve is served by 3 cam lobes - the center one has obviously less lift 3 mm only and shorter duration for valve opening. In other words, it is the "slow" cam.

The outer two cam lobes are exactly the same, with fast timing and high lift 10 mm. Selection of cam lobes is made by the variable tappet, which actually consists of an inner tappet and an outer ring-shape tappet. They could by locked together by a hydraulic-operated pin passing through them. In this way, the "fast" cam lobes actuate the valve, providing high lift and long duration opening. If the tappets are not locked together, the valve will be actuated by the "slow" cam lobe via the inner tappet.

The outer tappet will move independent of the valve lifter. As seen, the variable lift mechanism is unusually simple and space-saving. The variable tappets are just marginally heavier than ordinary tappets and engage nearly no more space.

Nevertheless, at the moment the Variocam Plus is just offered for the intake valves. Porsche Turbo. Many experts regard it as the best VVT considering its all-round ability - unlike cam-changing VVT, it provides continuously variable timing, thus improve low to medium rev torque delivery; and unlike cam-phasing VVT, it can lengthen the duration of valves opening and continuously , thus boost power.

Basically, VVC employs an eccentric rotating disc to drive the inlet valves of every two cylinder. Since eccentric shape creates non-linear rotation, valves opening period can be varied. Still don't understand?

Otherwise, Rover won't be the only car maker using it. VVC has one draw back: since every individual mechanism serves 2 adjacent cylinders, a V6 engine needs 4 such mechanisms, and that's not cheap. V8 also needs 4 such mechanism. V12 is impossible to be fitted, since there is insufficient space to fit the eccentric disc and drive gears between cylinders.

Continuously variable timing and duration of opening achieve both drivability and high speed power. Rover 1. EGR Exhaust gas recirculation is a commonly adopted technique to reduce emission and improve fuel efficiency. However, when the car is running at medium speed in highway, in other words, the engine is running at light load, maximum overlapping may be useful as a mean to reduce fuel consumption and emission.

The most noticeable results are: The engine can rev higher, thus raises peak power. Low-speed torque increases, thus improves drivability. For example, Fiat Barchetta's 1. Variable Lift In some designs, valve lift can also be varied according to engine speed. The motor has to be designed for a specific function. Of course, one has to compromise on the other aspects. By now you might have an idea what the variable valve timing would be.

As said before, VVT changes the valve timing when the engine is running. But how does the engine do the same? With that, the VVT tech too reaches new heights. Going by its name, an engine head with VVL allows the valves to have a different sized opening, again, depending upon the revolutions of the engine. Let us know in the comment section below if you have a question regarding VVT.

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Sign up. Password recovery. Recover your password. Friday, November 12, Get help. The GoMechanic Blog. But without going into the detail of VVT we first need to look at what is valve timing. And the valves are like the doors for the ports from which the air or air-fuel mixture enters from the intake and exits the chamber from the exhaust valve when it opens. As said earlier the cam or the lobes on the camshaft control the opening and closing of the valves.

They ride the valves at definite intervals and with utmost extreme precision. Defining the valve timing of an engine is one of the most typical processes. Firstly, the inlet valve opens to let the air or air-fuel mixture enter the combustion chamber. This valve opens a few degrees before the piston reached TDC. This is when the engine is about to complete its exhaust stroke.

The inlet valve closes after the piston reaches tad bit further than the BDC. Also called the suction stroke. The inlet valve closes just before the compression stroke. This is when both the valves are shut inlet as well as the exhaust valve.

For e. Besides, while carrying out activities like swimming or lifting a weight the persons also need to open the mouth to get more air. This is because when the human body is subjected to heavy work, it increases the need for air-intake.

This is because to produce more power , it needs to suck more air-fuel mixture charge for burning. In older conventional engines , the time for which the valves remained open was optimised only for single engine speed.

However, as the engine speed increases, it considerably reduces the time required to fill the cylinders fully. As a result, the engine would receive less amount of charge air-fuel mixture which causes power -loss especially when the engine runs at high speed. The VVT varies the timing of opening and closing of valves for multiple engine speeds.

The Variable Valve Timing system further optimizes the timing of opening and closing the valves for multiple engine speeds. The first-generation VVT design uses two-step variation which optimises the engine for two different engine speeds. In addition, VVT more often improves performance and reduces emissions.