Variable Valve Timing (VVT) is a technology used in internal combustion engines to optimize performance and economy under changing driving conditions by modulating aspects of the intake or exhaust valves. VVT allows cam profiles to change dynamically to optimize low-RPM torque and high-RPM power. Honda’s VTEC was the first implementation of VVT, and since then, almost all major automakers have developed and produced variable valve timing engines.
A type of technology employed in internal combustion engines, Variable Valve Timing (VVT) allows modulation of various aspects of the intake or exhaust valves, including lift, duration, and timing, while the engine is running. The purpose of variable valve timing is to alter engine characteristics as necessary to optimize performance and economy under changing driving conditions. It has grown in popularity with automakers as a way to meet more stringent emissions standards, while continuing to meet customer demand for power.
In an internal combustion engine, air and vaporized fuel are supplied to the combustion chamber by parts known as cams. These are located along the camshaft and open the valves for a certain period of time during each intake and exhaust cycle. The height the valves open is known as lift, the length they open is known as duration, and the timing between the opening of the intake and exhaust valves is known as timing.
In traditional non-VVT engine configurations, the position and shape, collectively known as the profile, of the cams and camshaft is static, and is set for certain revolutions per minute (RPM). This is usually a balance between low RPM torque and high RPM power. Variable valve timing allows cam profiles to change dynamically to optimize low-RPM torque and high-RPM power. Most VVT systems work by advancing or retarding intake or exhaust valve timing.
Variable valve timing has been around as a viable technology in automobiles since the 1960s, when patents for VVTs were first filed. However, it was not adopted on a large scale until the 1980s, when Japanese automakers began adopting variable valve timing on production cars. The first production vehicle to feature a VVT engine was the 1987 Nissan 300ZR.
The most prolific implementation of VVT is Honda’s Variable Valve Timing and Lift Electronic Control (VTEC), which was completed and put into use beginning in 1989. VTEC was initially capable of modulating between a low-speed setting of the engine to save fuel and a performance setting that engages at high engine speeds to improve power. Honda’s updated VVT technology, known as i-VTEC, can continuously alter intake valve timing and isn’t limited to two specific profiles. Since the introduction of VTEC by Honda, almost all major automakers have developed and now produce variable valve timing engines.
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