VVT: Variable Valve Timing

VVT: What is Variable Valve Timing And How It Really Works?

 | 5 minutes read

 VVT stands for Variable Valve Timing:

Let's  try to understand in the begining, why to vary the Valve Timing/VVT?

Firstly, read here first what is ‘Engine valve-timing’? An automotive engine actually ‘breaths’ (inhales/exhales) thru’ its valves just like the humans do. The rate at which humans breathe mainly depends upon the work carried out by humans. For e.g., if the person/s are sitting or sleeping, they will breath slowly as compared to when they are walking or running. 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. Thus, it causes faster breathing and/or wider opening of the mouth to receive more air. Similarly, when the engine runs at high speed; it needs to open its inlet valves earlier, faster & for a longer period. 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.

To overcome this deficiency, the engineers developed VVT or ‘Variable Valve Timing’ mechanism. The VVT varies the timing of opening and closing of valves for multiple engine speeds. At high speed, the Inlet valves open quite earlier so that more air-fuel mixture or ‘charge’ enters the cylinders. This helps to increase engine’s breathing which also improves its ‘volumetric efficiency’ to a large extent.

How VVT Works?

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. This design enables two different set of timings which includes one for the ‘part-load’ condition i.e. upto 3500 rpm and other for the ‘full-load’ condition, i.e. above 3500 rpm. In addition, VVT more often improves performance and reduces emissions. Besides, VVT also provides best of both worlds. Thus, it provides smooth idling at low rpm and maximum power at high rpm.

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