VTEC (Variable Valve Timing & Lift Electronic Control) - Working

VTEC (Variable Valve Timing & Lift Electronic Control) - Working

 

“Until you change how you get things done, you'll never know what works best.”
― Roy T. Bennett

 

Engine demands sufficient air-fuel ratio to deliver the brake power that we want. For producing expected brake power, we need to supply that air-fuel ratio depending on various speed conditions only by managing the valve openings accordingly. Valve openings for a low-speed condition are not suitable for high-speed operation because the supply of air is inadequate to deliver more power., (i.e.) valve timing and lifting of cam have fixed for normal speed operations in commercial vehicles, so the engine can't produce enough power at high-speeds. The required output during different speeds can attain precisely by controlling the valves functioning.

Honda introduced VTEC (Variable Valve Timing & Lift Electronic Control) technology to overcome this circumstance gradually by making adjustments in timing and lifting of valves. In VTEC, two different cam profiles had used, a smaller cam profile (actual) for performing at lower rpm and the bigger for performing at higher rpm with hydraulic lever actuation. Both cams had mounted in the same shaft correspondingly.

 

Hydraulic actuation takes place in rocker arm

 When you drive a car at a medium speed, a smaller cam is functioning with an actual valve opening and a bigger cam remains idle, so the car gets enough input to deliver sufficient output. If you increase the speed of the car, the electronic control unit fetches the data from engine speed, temperature, oil pressure, throttle position, and wheel speed with the help of suitable sensors. Instantly it actuates the hydraulic pin which is placed inside the rocker arms. This hydraulic pin switches both rocker arms (get engaged) to function concerning the movement of the bigger cam. Now the bigger cam operates the valves and the smaller cam remains idle., (i.e.) smaller cam is just fixed with a bigger one. If you decrease the speed gradually from higher rpm to lower rpm, the hydraulic pin disengages the cams, now a smaller cam starts controlling the valves and the bigger cam becomes idle.

VTEC can improve volumetric efficiency with increased performance at high-speeds and increased fuel consumption at low-speeds.

 

DOHC Engine with three rocker arm

i-VTEC performs as same as VTEC with an additional improvement called variable valve timing (VVT) that can help to reduce emission by varying the valve timing depending on the speed with increased volumetric efficiency and fuel consumption.

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