
Concept explainers
- Explain staged and continuously variable value timing systems.

The explanation of staged and continuously variable valve timing systems.
Explanation of Solution
Staged variable valve timing:
Staged valve timing consists of a central camshaft, where the lobes push against the wall to open when the camshaft is rotated. Crankshaft provides input to drive cam. Both the valves can be opened when there is a single cam. In the case of two cams, one can be used for intake and the second cam is for exhaust.
Valve timing ideal value point changes with a change in rpm. It is related to engine performance and fuel efficiency.
It involves three cams with different timing and lifts profile.
Stage one- low speed.
Stage two- medium speed.
Stage three- high speed.
Example − Honda VTEC system.
Continuously variable valve timing:
Continuously variable valve timing camshaft is fitted with a phaser. It is mounted in place of timing pulley, sprocket, or gear. The principle of phaser is based on a helical gear set or vanes enclosed in a housing. When the engine is running, it helps in changing time from cam-shaft to crankshaft.
It can be electronically or hydraulic controlled.
Example − Toyota’s VVT-i system.
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