VALVE &
VALVE ACTUATING MECHANISMS
Introduction The Cylinder Head is made of a single casting. It
is bolted on the top of the Cylinder Block. It has passages for oil and water circulation. It accommodates valves, spark plugs/ injectors (in case of the diesel engines) and heater plug. A combustion chamber is also provided in some
cylinder heads. In case of the overhead valve system, the
cylinder head supports the rocker shaft assembly.
CYLINDER HEAD
CYLINDER HEAD
CYLINDER HEAD
The lower surface of the cylinder head is machined to the specified accuracy and a gasket is used in between the cylinder head and cylinder block to avoid leakage.
MATERIAL OF CYLINDER HEADS:CAST IRON
ALUMINIUM ALLOY
CYLINDER HEAD
Four types of cylinder heads are used in an automobile engine as per the valve arrangements.
‘L’ head ‘I’ head ‘F’ head ‘T’ head
TYPES OF CYLINDER HEAD
•L-HEAD —The intake and the exhaust valves are both located on the same side of the piston and cylinder. •The valve operating mechanism is located directly below the valves, and one camshaft actuates both the intake and the exhaust valves .(Eg. Dodge)
Arrangement of Valves•The majority of internal combustion engines also are classified according to the arrangement of the intake and exhaust valves, whether the valves are located in the cylinder head or cylinder block.
•I-HEAD —The intake and the exhaust valves are both mounted in a cylinder head directly above the cylinder.
•This arrangement requires a tappet, a pushrod, and a rocker arm above the cylinder to reverse the direction of valve movement. •The valves are operated by a single cam shaft through the tappet, pushrod and rocker arm mechanism. •It was rapidly superseded by the overhead camshaft. •Eg. Ambassador, Ashok Leyland.
‘I’ HEAD
•The intake valves are normally located in the head, while the exhaust valves are located in the engine block.•The valves are operated by single cam shaft.•The intake valves in the head are actuated from the camshaft through tappets, pushrods, and rocker arms. •The exhaust valves are actuated directly by tappets on the camshaft.•Eg. Mahindra Jeep CJ-3V Model
‘F’ HEAD
The intake and the exhaust valves are located on opposite sides of the cylinder in the engine block.Two camshafts are used to operate the valves, one for inlet and the other for exhaust.The valves operated by the tappet directly.each requires their own camshaft. Eg. Ford.
‘T’ HEAD
SINGLE OVERHEAD CAMSHAFT•The camshaft is located in the cylinder head. •The intake and the exhaust valves are both operated from a common camshaft. •The valve train may be arranged to operate directly through the lifters, as shown in view A, or by rocker arms, as shown in view B. •This configuration is becoming popular for passenger car gasoline engines.
DOUBLE OVERHEAD CAMSHAFT • When the double overhead camshaft is used, the intake and the exhaust valves each operate from separate camshafts directly through the lifters. •It provides excellent engine performance and is used in more expensive automotive applications.
Valve Train Components1.Cam Shaft2.Cam Shaft drive3.Valve Tappet4.Push Rod5.Rocker Arm and Rocker Shaft
Cam Shaft Material: Forged from alloy steel or cast from hardenable cast iron and is case hardened.Construction: Consists a number of cams at suitable angular positions for operating the valves at appox. timings relative to the piston movement in a sequence according to the selected firing order.Functions: Provides a means of actuating the opening and controlling the period before closing, both for the inlet as well as the exhaust valves. Also provides a drive for ignition distributor and mechanical fuel pump.
Cam Shaft Drive The Camshaft rotates at half the crankshaft speed so as to open and close the valves once in every two revolutions of crankshaft. Drive is either a chain drive or gear drive. Camshaft gear or sprocket wheel is twice as large as the crankshaft or sprocket wheel, consists of timing marks on the sprockets or gears of the camshaft and the crankshaft to ensure correct valve timing. Latest type of drive is made of toothed rubber belt, since they are relatively silent and need no lubrication.
Valve TappetThe Valve tappet i.e. cam follower follows the shape of the cam lobe on the camshaft. Location: placed in between the push rod and the cam.Function: Converts angular movement of the cam into a reciprocating motion in the valve train. Push RodFunction: Serves to transmit the reciprocating motion of the valve lifter to the rocker arm. It also serves as a passage for oil for lubrication of the valve actuating mechanisms.
Rocker Arm & Rocker ShaftFunction: To reverse the upward motion of the push rod to downward motion of the valve and vice versa.
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