08-08-2012, 03:23 PM
I.C. ENGINE VALVE TIMING AND OPERATING MECHANISM
Valve Timing Diagram of Four Stroke Engine.pptx (Size: 1.93 MB / Downloads: 100)
SALIENT FEATURES:-
The Inlet valve open 10 ° - 30 ° before TDC & closes 30 ° - 40 ° after BDC.A longer suction stroke assists in increasing the volumetric efficiency.
Compression start 30 ° after BDC & ends 25° degree before TDC.
Ignition starts 25 ° before TDC & ends 5 ° after TDC.
The opening of Exhaust valve occurs 30 °- 40 ° before BDC & continues 10 ° to 15 ° after TDC.
There is valve overlap also 30 ° to 40 °. Valve overlap is the angle of the crank during which both the inlet & exhaust valves remain open simultaneously.
Valve mechanism for an Overhead Valve engine employing an underhead camshaft
ADVANTAGES:-
Volumetric and compression ratio are good.
Shape of the combustion chamber simple.
DISADVANTAGES:-
Engine height is more as there are parts over the cylinder head.
Lubrication is complicated for valve mechanism.
Noisy working.
More complicated.
Valve mechanism for Side valve
ADVANTAGES:-
Low Engine height is possible as there are no parts over the cylinder head.
Lubrication is easier for valve mechanism.
Working is quieter as there is no rocker arm.
Less complicated.
DISADVANTAGES:-
Volumetric and compression ratio are poor.
Shape of the combustion chamber complicated.
Space for inlet valve is restricted.
OPERATION
1.ADVANCE
When the camshaft timing oil control valve is positioned as illustrated below by the advance signals from the engine control module ,the resultant oil pressure is applied to the vane chamber of advance side to rotate the camshaft in the timing advance direction.
2.RETARD
When the camshaft timing oil control valve is positioned as illustrated below by the retard signals from the engine control module, the resultant oil pressure is applied to the vane chamber of retard side to rotate the camshaft in the timing retard direction.