Automotive Engineering Crash Course Part – 2 | Camshaft & Valve

Automotive Engineering Crash Course Part – 2 | Camshaft & Valve


hi welcome to automotive appreciation part 2 in this section we will cover camshafts and valves there are various layouts for the camshafts early engines had the camshaft at the bottom of the engine the valves were operated by push rods via rocker arms hence the name pushrod engine an advantage of this design was that it was easy to lubricate the camshaft but I however at high speeds the rods were prone to lose contact with the cams due to their inertia sohc single overhead cam in this design the camshaft was relocated to the top of the engine and driven by a timing chain or belt one camshaft was used to operate both the inlet and exhaust valves via rocker arms in a dohc or jewelle overhead cam separate cams were used for inlet and exhaust valves with a non-interference engine the valves do not extend into the path of the piston if the timing belt breaks it will not result in damaged fans with an interference engine the valves extend into the path of the piston if the timing belt breaks it will result in damage to the valves valves are used to a no air enter an exhaust gas exit from the cylinder they are open plate the lobe on the camshaft and throws price spring pressure usually in that ports are larger than exhaust ports as it is more difficult to get air into the cylinder early engines had only one inlet and one exhaust per cylinder market an engine usually have two inlets and two exhaust valves the top position of the piston is called top dead center TDC and the bottom position is called bottom dead center of BDC while the volume between the two is called the swept volume the total engine capacity is the swept volume multiplied by the number of cylinders for this engine the compression compression ratio is 10 to 1 a diesel engine will be higher at perhaps 20 to 1 initially one might think that on the intake stroke the inlet valve should open a top dead center and throws at bottom dead center similar with the exhaust stroke the exhaust valve should open at PDC and close at TDC if we look at the inlet valve housing at PDC we see that a flow of air is blocked behind the valve from entering the cylinder it would be much better to delay closing the valve until the increase in cylinder pressure stops the flow then we get more air into the cylinder similarly with the exhaust stroke near bottom dead center the combustion stroke has most of us worked on best to open the exhaust valve early thus expelling more of the waste gas we use a timing diagram to show the valves opening and closing near top dead center of the exhaust stroke both inlet and exhaust panels are open for a short period the flow of air from Inlet to outlet is called valve overlap and it’s scavenging of the exhaust gas a camshaft can operate the valve directly or usually cam-follower or tap it is used between the cam and the valve sometimes the camshaft lobe is offset from the center of the valve and tap it to encourage the tappet and valve to rotate as it is pushed down to allow for expansion as the engine heats up it is necessary to have a small gap between the tapas and cam to ensure the valve is fully closed note the area around the exhaust valve is the hottest part of the engine a further development is the hydraulic tappets this tablet is is extended by high pressure ie through a non-return valve that happened will occupy the available space between the cam and the valve thus eliminating any noise as the cams rights that happen it will also ensure the valve cam those Forli at all times as the result is a small eye leakage from the top earth this will allow it to retract as the top it heats and expands by manufacturing different tape cams engine manufacturers were able to design engines for high efficiency or high power cams for racing cars were called race cams or high lift cams by altering the lobe profile they would open the valve earlier further and for longer usually at the expense of fuel consumption with VTEC the camshaft has two separate lobe profiles the valve is in contact with the blue rocker arm at low speed cam operates on the standard profile for efficiency and at high speed the pin is activated by re and the rockers are joined together when they’re aligned thus altering the timing and lift for maximum power be cam a further development was vvt-i this uses a system her the position of the cam relative to the poly can be adjusted thus altering the valve timing for power and efficiency dependent on driving conditions high pressure oil is fed through the camshaft into a chamber thus rotating the poly on the camshaft when the oil is released the cam advance is removed it is normal to adjust timing on the inlet valves with a double overhead cam engine it is possible to adjust both inlet and exhaust valves independently of each other note Pvt only adjust timing but VTEC adjust both timing and lift we hope you learned from our homework of appreciation


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