VARIABLE VALVE TIMING AND LIFT ELECTRONIC CONTROL also known as VTEC is a revamped version of camshafts, which are used for valve timing.
WONDERING WHAT IS THE TERM “VTEC” SHOWN ON HONDA CARS?
Before the VTEC mechanism, there used to be a single cam profile shaft which is responsible for valve timing in a gasoline engine. So, there is a similar cam profile throughout the camshaft. At low RPM the charge coming from these inlet valves which are actuated by the narrow and similar cam lobes is just sufficient for an engine to breathe.
But, when the car is rolling at higher speeds, at higher RPM, the charge coming from the valves which are actuated from the same narrow cam lobes is not sufficient enough, because at the higher RPM it is obvious, that the car needs more power, more charge, and more AIR-FUEL ratio, the supply should meet the demand. If the car is fixed with bigger lobes, the economy is lost at the lower RPM and that would be extravagant.
ECONOMY is always juxtaposed with SPEED. This is one of the reasons for a sports car not having a good economy.
By the advent of VTEC, both economy and speed are not the contrast things anymore.
WHAT IT DOES?
VTEC is an electromechanical device, which is used to control the valve timing of the valves of an IC engine screaming at both lower and higher RPMs, which in further increase the EFFICIENCY.
INTRIGUING PART IS AHEAD.
HOW VTEC WORKS?
Generally, the motion is transferred from the camshaft to the rocker arms and from rocker arms to the spring-loaded valves. As shown in the figure, there are two cam profiles in the VTEC mechanism,the shorter one is for lower rpm and the larger one is for higher rpm. At lower RPMs there is no connection between shorter and larger cam profiles’ rocker arms. The engine gets the charge from the shorter and narrower cam profile at lower RPMs as there is no demand for more power, it is nominal for driving on the streets. But, when you go crazy on the freeways there will be a sudden demand for more power, which cannot be attained by shorter cam profiles or lobes.
Now, VTEC KICKS IN!! There is an electronic control unit (ECU) which actuates the hydraulic system, supposed to connect both shorter and larger cam profiles’rocker arms by taking the inputs such as, engine temperature and rpm. The rocker arm gets motion from the larger cam profile leads to a larger valve opening and more charge input, which leads to more combustion and BOOM!! More power can be procured. By taking the same inputs as earlier, the connection between the two cam profiles’ rocker arms is lost at lower speeds where the fuel consumption is less. Finally, the volumetric efficiency of an IC engine is optimized.
So, that’s what happens when VTEC KICKS IN, this phrase is familiar for an automobile admirer.
This is the engineering behind the VARIABLE VALVE TIMING AND LIFT ELECTRONIC CONTROL.
The Japanese Honda Integra-1989 was the first car to come out with VTEC.