In Toyota's VVT-i, the engine control unit (ECU), the head and most powerful computer on cars, receives signals from various sensors and uses those signals to adjust an output to an oil control valve. The VVT-i is the Toyota's version of an engine with variable valve timing (VVT). The "i" stands for "intelligence."
The various sensors crucial to the VVT-i engine are the camshaft and crankshaft position sensors. The valve acts as a hydraulic actuator by rotating a rotor inside a housing connected to the crankshaft via a timing chain. According to Toyota, its dual VVT-i engine automatically controls the timing of the engine's intake and exhaust valves to help ensure the engine works to maximum efficiency. An engine's valves are opened with the lobes on a camshaft as the camshaft rotates. On older cars, intake and exhaust valves opened for specific times at specific points in a stroke cycle. Newer cars can change the timing, lift and duration of the valves with the advancement of computer technology. Toyota introduced the VVT-i in 1996, although automakers have been developing VVT systems since the 1960s. Honda manufacturers a similar type of VVT engine, the VTEC engine, for installation in its automobiles.