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Valve Train (Camshaft, Rocker arm, Pushrods) By: Hewett Sze. Objective: To give an overview of how these components function in an engine and how their configurations affect engine performance. Valve Train.
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Valve Train (Camshaft, Rocker arm, Pushrods) By: Hewett Sze Objective: To give an overview of how these components function in an engine and how their configurations affect engine performance.
Valve Train • The valve train consists of the valves and a mechanism that opens and closes them. The opening and closing system is called a camshaft.
Camshaft http://static.howstuffworks.com/gif/camshaft-ch.jpg http://www.familycar.com/classroom/Images/Engine_Camshaft.gif
Cams continued… • The camshaft uses lobes (called cams) that push against the valves to open them as the camshaft rotates • Springs on the valves return them to their closed position
A pictorial representation of intake and exhaust valves http://www2.gsu.edu/~bioasx/engine.gif
Rocker Arm • Works as an intermediary between the camshaft and the valves • Camshaft cam pushes up on the rocker arm (via a push rods) which in turn pushes down on the valves
Piston Engines • Some older engine models placed the camshaft below the pistons • Pushrods actuated rocker arms above the cylinder head to actuate the valves. • Lifters or tappets reside in the engine block between the camshaft and pushrods.
Overhead Cam Systems • Place the camshaft above the cylinder heads and drive the valves or lifters directly instead of using pushrods. • This arrangement is more complex, and relies on a timing belt or chain, but allows for greater valvetrain flexibility.
Single Overhead Cam (SOHC) • One Camshaft is located above the valves • The one camshaft controls both the inlet and exhaust valves
Dual Overhead Cam (DOHC) • Two camshafts for each bank of cylinders • DOHC engines have separate camshafts for inlet valves and exhaust valves • DOHC allow for more valves in each cylinder than SOHC • More valves allow for greater intake and exhaust flow and greater engine power
Conclusion • 3 types of engines that use different valve train configurations are Piston Engines, Single Overhead Camshaft Engines, and Dual Overhead Camshaft Engines • Modern Engines use overhead camshaft configurations
Sources • http://www.familycar.com/engine.htm • http://auto.howstuffworks.com/camshaft3.htm • http://en.wikipedia.org/wiki/Dual_overhead_camshaft • http://www2.gsu.edu/~bioasx/engine.gif