About the VVT-i Engine
VVT-i, or Variable Valve Timing with intelligence, is an automobile variable valve timing technology developed by Toyota, similar in performance to the BMW's VANOS. The Toyota VVT-i system replaces the Toyota VVT offered starting in 24 December 1991 on the 5-valve per cylinder 4A-GE engine. The VVT system is a 2-stage hydraulically controlled cam phasing system. The Toyota motors CEO has been reported to have said, "VVT is the heart of every modern Toyota!"
VVT-i, introduced in 1996, varies the timing of the intake valves by adjusting the relationship between the camshaft drive (belt, scissor-gear or chain) and intake camshaft. Engine oil pressure is applied to an actuator to adjust the camshaft position. Adjustments in the overlap time between the exhaust valve closing and intake valve opening result in improved engine efficiency. Variants of the system, including VVTL-i, Dual VVT-i, VVT-iE, and Valvematic, have followed.
Wikipedia - http://en.wikipedia.org/wiki/VVT-i
The main difference between this and other engines is that it uses a timing chain rather than a belt. This is is good for the engine economy, and there is less maintenance because the belt does not need changing (which can be expensive), but you have to make extra care to ensure the oil is changed regularly and kept at the right levels.
Funcargo . Yaris Version Toyota VVT-u engine image