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VVT-i is a way to enhance performance, economy and emissions through control of the phasing, or timing, of an engineâ„¢s camshafts.
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(Variable valve timing with intelligence.)
ABSTRACT:
VVT-i is a way to enhance performance, economy and emissions through control of the phasing, or timing, of an engineâ„¢s camshafts.
The valves that admit air-fuel mixture into the engineâ„¢s combustion chambers, and that open to allow the burned gasses to be pushed out as exhaust, are controlled by egg-shaped lobes on these camshafts known as cams.
The shape of those lobes, and their positioning on the shaft, determine a camâ„¢s timing. In most cases, cam timing is fixed, and that means that itâ„¢s a compromise that provides optimal performance only at the speed at which the engine is likely to do most of its work.
But engines operate over a wide range of speeds, from an idle speed of about 600 rpm to a peak speed of more than 6,000 rpm. What if cam timing could be optimized over the engineâ„¢s entire operating range?
Thatâ„¢s precisely what VVT-i does.
Using a combination of electronics and hydraulics, VVT-i allows the intake cam to change phase, or timing, over a range of about 30 degrees. Changing the cam timing improves engine breathing at all rpm because the combustion chambers get an optimized volume of air/fuel mixture over a broader range of conditions. The result is more power, more torque, reduced emissions and enhanced fuel economy.
But what if we were able to change the phase of not just the intake cam, but also the exhaust cam? That™s exactly what Dual VVT-i does. By varying the phasing of the exhaust cam by about 30 degrees, we can vary the phasing of the intake cam by a wider range “ by about 45 degrees. That means there™s a broader range over which we can open and close the intake valves. And that means we can extract still more power, torque, economy and better emissions.
(this abstract is submitted by hellsangels1890)
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