Ventiltiming

Ventil timing, sometimes written as Ventiltiming or known in English as valve timing, refers to the scheduled opening and closing of engine valves to control the flow of air and exhaust gases in piston engines. Valve events are defined with respect to crankshaft position and are commonly expressed in degrees of crankshaft rotation, including intake opening (IO), intake closing (IC), exhaust opening (EO), and exhaust closing (EC). A valve timing diagram or cam profile shows how these events occur over a full engine cycle.

In practice, fixed valve timing uses a permanent camshaft profile, while modern engines often employ variable valve timing (VVT) or variable valve lift (VVL) to adjust timing across operating conditions. Mechanisms include cam phasing, hydraulic or electric actuators, and variable camshaft timing gears. The objective is to optimize air charge, exhaust scavenging, fuel efficiency, and emissions across speed and load.

Valve timing has a direct impact on engine performance: advancing or retarding events changes low- and high-end torque, compression work, and breathing efficiency. Overlap, during which both intake and exhaust valves are partially open, influences idle stability and emissions and can be tuned to balance efficiency and performance. Incorrect timing can cause reduced power, increased emissions, or mechanical interference in interference engines.

Applications span automotive, motorcycle, and industrial engines. Design trade-offs consider engine displacement, compression ratio, rpm range, fuel type, and regulatory standards. Modern engines commonly use adaptive or camless technologies that enable more precise, real-time timing control.

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