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Difference between revisions of "Poppet valve"
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For certain applications the valve stem and disk are made of different steel alloys, or the valve stems may be hollow and filled with sodium to improve heat transport and transfer. | For certain applications the valve stem and disk are made of different steel alloys, or the valve stems may be hollow and filled with sodium to improve heat transport and transfer. | ||
The engine normally operates the valves by pushing on the stems with [[cam]]s and [[Tappet|Cam follower]]s. The shape and position of the cam determines the valve lift and when and how quickly (or slowly) the valve is opened. The cams are normally placed on a fixed [[camshaft]] which is then geared to the [[crankshaft]], running at half crankshaft speed in a [[four stroke cycle|four-stroke]] engine. On high performance engines (e.g., | The engine normally operates the valves by pushing on the stems with [[cam]]s and [[Tappet|Cam follower]]s. The shape and position of the cam determines the valve lift and when and how quickly (or slowly) the valve is opened. The cams are normally placed on a fixed [[camshaft]] which is then geared to the [[crankshaft]], running at half crankshaft speed in a [[four stroke cycle|four-stroke]] engine. On high performance engines (e.g., Ferrari cars), the camshaft is movable and the cams have a varying height, so by axially moving the camshaft in relation with the engine [[RPM]], also the valve lift varies. See [[variable valve timing]]. | ||
Although better heat conductors, aluminum cylinder heads require steel [[valve seat]] inserts while cast iron cylinder heads often used integral valve seats in the past. | Although better heat conductors, aluminum cylinder heads require steel [[valve seat]] inserts while cast iron cylinder heads often used integral valve seats in the past. | ||