What is the full form of VVT?

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Question

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RRB ALP Mechanic Diesel 21 Jan 2019 Official Paper (Shift 1)

Answer 1

Explanation:
Variable valve timing (VVT):

Variable-valve (VVT) technology, became standard in engine design, variable valve timing becomes the next step to enhance engine output, no matter power or torque.
As you know, valves activate the breathing of engine.
The timing of breathing, that is, the timing of air intake and exhaust, is controlled by the shape and phase angle of cams.
To optimse the breathing, engine requires different valve timing at different speed.
When the valve increases, the duration of in take and exhaust stroke decreases so that fresh air becomes not fast enough to enter the combustion chamber, while the exhaust becomes not fast enough to leave the combustion chamber.
Therefore, the best solution is to open the inlet valves earlier and close the exhaust valves later.
In other words, the overlapping between intake period and exhaust period should be increased With variable valve timing, power and torque can be optimized across a wide rpm band.