Toyota has been a leader in innovation for fuel economy for many years now. In 1991, Toyota introduced their Variable Valve Timing in the 4AGE engine. This engine “features 5-valves per cylinder, and a two-stage, hydraulically-controlled cam phasing system.” VVT-i came in 1996 and added intake valve timing to cam phasing. This became the norm in the bulk of Toyota’s engine line-up.
The reason to vary the valve timing is fuel economy. “Introducing VVT to a combustion engine allows for more precise control of engine output and can greatly increase fuel economy.” VVT is measured in either early or late opening or closing of the valve. Later opening of valves allows for reduced nitric oxide emissions while effecting torque very little. Opening the valve earlier results in valve overlap, which means, “the valve will send hot exhaust through the intake valve where it is momentarily cooled in the manifold before returning to the cylinder in the next stroke.”
VVT-i is now used in Toyota’s engines. There are multiple types of VVT-i used in different ways. The i in VVT-i stands for “intelligent.” VVT-i improves the timing more than VVT by controlling the opening and closing height and duration throughout the camshaft and the lifters, and controlling the duration through the changes in the camshaft’s rotation. VVT-i works by using a variable-speed head on the camshaft; this is where the timing system gives the rotational force to the camshaft. This system has shown improvements in engine performance output under different driving conditions, improving fuel economy by double digit percentages in many of Toyota cars, thus becoming well reviewed and received with engineers and mechanics.
Dual VVT-i adds in control of exhaust, and found in the latest V6 engines, and show advantages in catalytic converter heating, compression minimizing (improving the idle fuel economy), and timing to include more variation. Variable Valve Timing and Lift with intelligence (VVTL-i) is enhanced VVT-i that allows valve lift control to go with timing control. VVT-iE (VVT-i by Electric motor) is the exact same as Duel VVT-i with the exception of an electronically-operated actuator adjusts the camshaft timing, rather than hydraulic pressure. Last, the Valvematic system uses an “oscillating camshaft design that gives a rocking motion to a partial camshaft lobe.” This comes from the steam engine and allows continuos lift, as well as duration, adjustment, though they are not separate as in VVT-i.
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