How VVTI works?

It is a variable valve timing innovations from Toyota, where in power and fuel efficiency can be optimized by varying the timing of the camshaft with respect to the crankshaft of an engine,by retarding or advancing the camshaft by a certain phase angles.A conventional engine has it's camshaft rotate half the crankshaft rotation and the performance of a such engine would be in it's peak efficiency for a single speed only.Engineers developed a technology to overcome this in-efficiencies by introducing variable valve timing where camshaft rotation can advance or retard with respect to the crankshaft,hence optimising performance and fuel efficiency.