WEFOUNDIgnition, Valve Timing and Automobile Electric Systems: (Self-Starting and Lighting) a Comprehensive Manual of Self-Instruction On the Operation, ... Self-Starting Mechanisms. Complete Tables an

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In internal combustion engines , variable valve timing ( VVT ) is the process of altering the timing of a valve lift event, and is often used to improve performance, fuel economy or emissions. It is increasingly being used in combination with variable valve lift systems. There are many ways in which this can be achieved, ranging from mechanical devices to electro-hydraulic and camless systems. Increasingly strict emissions regulations are causing [ citation needed ] many automotive manufacturers to use VVT systems.

The valves within an internal combustion engine are used to control the flow of the intake and exhaust gases into and out of the combustion chamber . The timing, duration and lift of these valve events has a significant impact on engine performance. Without variable valve timing or variable valve lift , the valve timing can be the same for all engine speeds and conditions, therefore compromises are necessary. [1] An engine equipped with a variable valve timing actuation system is freed from this constraint, allowing performance to be improved over the engine operating range.

Piston engines normally use valves which are driven by camshafts . The cams open ( lift ) the valves for a certain amount of time ( duration ) during each intake and exhaust cycle. The timing of the valve opening and closing, relative to the position of the crankshaft, is important. The camshaft is driven by the crankshaft through timing belts , gears or chains .

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