Air Inlet and Exhaust System Components
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| Illustration 1 | g00328151 |
(1) Exhaust manifold (2) Aftercooler (3) Air choke (4) Exhaust inlet to the turbocharger (5) Cylinder (6) Air inlet (7) Turbocharger compressor wheel (8) Turbocharger turbine wheel (9) Exhaust bypass valve | |
Clean inlet air from the air cleaners is drawn through air inlet (6) into the turbocharger compressor by compressor wheel (7). The air is compressed and the air is forced through air choke (3). The air flows through aftercooler (2). The aftercooler reduces the temperature of the compressed air before the air enters the air plenum. The air enters the air inlets in the cylinder heads.
Air flow into cylinder (5) is controlled by the inlet valves. The camshaft controls the opening of the valves. There are two inlet valves and two exhaust valves for each cylinder. Refer to "Valve System Components". The inlet valves and the gas admission valve open when the piston moves down on the intake stroke.
The air is pulled into the cylinder through the air inlet. Gas is also supplied to the cylinder through the gas admission valve. The gas admission valves and the inlet valves close and the piston starts to move up on the compression stroke. When the piston is near the top of the compression stroke, the lean mixture of air and fuel from the cylinder is mixed with the richer mixture of air and fuel in the precombustion chamber. The mixture in the precombustion chamber becomes combustible. The mixture in the precombustion chamber is ignited by the spark plug. This ignites the air and fuel in the cylinder.
The force of the combustion pushes down on the piston for the power stroke. When the piston moves up again the piston is on the exhaust stroke. The exhaust valves open and the exhaust gases are pushed through the exhaust port into exhaust manifold (1). After the exhaust stroke, the exhaust valves close. The four stroke cycle of intake, compression, power, and exhaust continues.
Exhaust gas from exhaust manifold (1) turns turbocharger turbine wheel (8). The turbine wheel is connected to the shaft that drives the compressor wheel. Exhaust gas is directed through the exhaust inlet to the turbocharger or the gas is diverted directly to the exhaust elbow by exhaust bypass valve (9). This depends on the requirements of the load and speed.
An electrohydraulic actuator controls the position of the exhaust bypass valve (9). The actuator provides the desired boost pressure. The position of the actuator is determined by the ECM.
Aftercooler
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| Illustration 2 | g00485390 |
(1) Coolant outlet (2) Coolant inlet | |
Coolant from the water pump on the left side of the engine flows through coolant inlet (2). Coolant circulates through the core assemblies. Inlet air from the compressor side of the turbocharger flows into the aftercooler housing. The inlet air passes the fins in the core assemblies. The aftercooler core reduces the temperature of the air. The cooler air flows into the air plenum and through the inlet ports of the cylinder heads.
The coolant exits the aftercooler through the coolant outlet (1) .
Reducing the temperature of the inlet air increases the density of the air. This results in more efficient combustion and in lower fuel consumption.
Turbocharger
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| Illustration 3 | g00825487 |
Typical example (1) Turbine housing (2) Compressor housing (3) Outlet for the air from the compressor (4) Air inlet for the compressor (5) Outlet for the exhaust from the turbine (6) Inlet for the exhaust to the turbine (7) Outlet for the engine oil | |
Turbine housing (1) is connected between the exhaust manifold and the exhaust elbow. Compressor housing (2) is connected between the air cleaners and the aftercooler.
Exhaust gas flows into the turbocharger through inlet (6). The exhaust gas pushes the blades of the turbine wheel in the turbine housing. The exhaust gas exits the turbine housing through outlet (5) .
The turbine wheel is connected to a compressor wheel in the compressor housing. Rotation of the turbine wheel causes the compressor wheel to rotate.
Clean air from the air cleaner is drawn into air inlet (4) by the rotation of the compressor wheel. The compressor wheel compresses the inlet air. The air exits the compressor housing through outlet (3) and the air flows to the aftercooler. Compression of the air provides the engine with more power because the engine can burn additional fuel with greater efficiency.
Pressurized engine oil enters an inlet to passages in the center section of the turbocharger in order to lubricate the bearings. The engine oil exits through outlet (7) .
The bearing housing in the turbocharger is cooled by coolant that flows through coolant passages in the bearing housing.
Exhaust Bypass
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| Illustration 4 | g00815802 |
(1) Electrohydraulic actuator (2) Linkage | |
Actuator (1) for the exhaust bypass receives an electronic command signal from the ECM. The command signal is a pulse width modulated signal (PWM). The signal is based on the difference between the average combustion burn time and the desired combustion burn time. The signal causes the actuator to move linkage (2) in order to operate the exhaust bypass.
When the ECM requests a slower combustion burn time or a leaner air/fuel ratio, the actuator moves the exhaust bypass toward the closed position. This directs more of the exhaust gas to the turbocharger turbine wheel. The additional exhaust gas increases the rpm of the turbine wheel and the compressor wheel. A greater quantity of air is compressed for combustion. This increases the amount of air in the air/fuel mixture.
When the ECM requests a faster combustion burn time or a richer air/fuel ratio, the actuator opens the plate of the exhaust bypass. This diverts some of the exhaust gas directly to the exhaust elbow instead of through the turbocharger. The reduction of exhaust gas to the turbine wheel reduces the rpm of the turbine wheel and the compressor wheel. Less inlet air is compressed for combustion. This reduces the amount of air in the air/fuel mixture.
Air Choke
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| Illustration 5 | g00815989 |
(1) Electrohydraulic actuator (2) Linkage | |
Actuator (1) receives an electronic command signal from the ECM. The signal is based on the exhaust port temperatures. The signal causes the actuator to move linkage (2) in order to operate the air choke. Movement of the air choke's plate controls the flow of inlet air from the turbocharger to the aftercooler.
At full load and full speed, the air choke is in the fully open position. This reduces the restriction of the air flow. The engine efficiency is improved.
As engine load decreases, the air choke begins to restrict air flow. This maintains a sufficiently rich mixture of air and fuel for combustion at lighter engine loads.
Exhaust Manifold
The dry exhaust manifold provides maximum heat to the turbine. The exhaust manifold is insulated. The insulation helps retain the heat in the exhaust system. The energy from the heat helps to drive the turbocharger turbine. The insulation also helps protect the components that are outside of the exhaust system from the heat.
| NOTICE |
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The soft wrap must remain on the exhaust manifolds at all times. The soft wrap prevents the wiring from burning. The soft wrap also prevents the oil lines and the water lines from heating up. |
A dry exhaust manifold is possible because of the lower exhaust temperatures of lean combustion. Engine performance is enhanced.
Valve System Components
The valve system components control the flow of the inlet air and fuel into the cylinders and the flow of exhaust gas out of the cylinders during engine operation.
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| Illustration 6 | g00825443 |
(1) Rocker arm (2) Valve bridge (3) Rod (4) Valve rotator (5) Valve spring (6) Gas admission valve (7) Pushrod (8) Inlet valve (9) Valve lifter (10) Camshaft lobe | |
The crankshaft gear drives the camshaft gears through idler gears. The camshafts must be timed to the crankshaft in order to get the correct relation between the movement of the piston and movement of the valves.
The camshafts have three camshaft lobes (10), valve lifters (9), and pushrods (7) for each cylinder. One lobe operates valve bridge (2) that moves two inlet valves (8). One lobe operates the valve bridge that moves the two exhaust valves. The center lobe operates gas admission valve (6). As the camshaft turns, the camshaft lobes cause the valve lifters and pushrods to move up and down.
One pushrod moves rod (3) in order to operate gas admission valve (6). The other two pushrods move rocker arms (1). Movement of the rocker arms cause valve bridges (2) to move up and down on a dowel in the cylinder head. This movement operates inlet valves (6) and the exhaust valves. One valve bridge enables one rocker arm to operate two valves simultaneously. There are two inlet valves and two exhaust valves for each cylinder.
Valve rotator (4) turns the valve during engine operation. The rotation of the valves keeps the deposit of carbon on the valves to a minimum. This provides longer service life for the valves.
When valve lifter (9) moves downward, valve spring (5) closes the valve.