MAN Truck & Bus


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Valve gear with overhead camshaft (OHC Engine) This depicts a valve train with overhead camshaft (OHC engine). The functional diagram shows 1) camshaft 2) rocker arm for exhaust valves 3) rocker shaft 4) rocker arm for inlet valves 5) inlet valve manifold 6) valve spring 7) inlet valves 8) piston 9) cylinder liner 10) exhaust valves 11) exhaust valve manifold with MAN EVB engine brake 12) MAN EVB holder 13) MAN EVB adjusting screw.

The camshaft is an integral part of the valve train in the engine. Tappets and push rods press the cams on the camshaft against the valve stem by means of rocker arms. The valves are opened against the spring force from the valve springs depending on the cam position. The camshaft obtains its drive from the crankshaft via gears, roller chains, toothed belts or vertical shafts. Camshafts on diesel engines in heavy commercial vehicles are generally driven by gears. In addition to tappet and push rod control, rocker arm or drag lever controls are also frequently used in diesel engines. 

Engines are referred to as follows depending on camshaft position and valve control: 

OHV Engine

A lower camshaft controls overhead valves. 

OHC Engine

An overhead camshaft controls lower valves by means of a drag lever. 

DOHC Engine

Double overhead camshafts each control a series of valves by means of hydraulic tappets.