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| Illustration 1 | g02720982 |
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Air inlet and exhaust system (1) Aftercooler core (2) Air filter (3) Clean Emissions Module (CEM) (4) Turbocharger (5) Wastegate actuator (6) Boost pressure chamber (7) Exhaust gas valve (NRS) (8) Wastegate regulator (9) Exhaust cooler (NRS) (10) Inlet manifold (11) Throttle valve | |
The components of the air inlet and exhaust system control the quality of air and the amount of air that is available for combustion. The air inlet and exhaust system consists of the following components:
- Air cleaner
- Exhaust cooler (NRS)
- Exhaust gas valve (NRS)
- Turbocharger
- Aftercooler
- Inlet manifold
- Cylinder head, injectors, and glow plugs
- Valves and valve system components
- Piston and cylinder
- Exhaust manifold
- Clean Emissions Module (CEM)
- Throttle valve
Air is drawn in through the air cleaner into the air inlet of the turbocharger by the turbocharger compressor wheel. The air is compressed to a pressure of about
- Lower fuel consumption
- Increased power output
- Reduced NOx emission
- Reduced particulate emission
From the aftercooler, air is forced into the inlet manifold. Air flow from the inlet manifold to the cylinders is controlled by inlet valves. There is one inlet valve and one exhaust valve for each cylinder. The inlet valve opens when the piston moves down on the intake stroke. When the inlet valve opens, cooled compressed air from the inlet port is forced into the cylinder. The complete cycle consists of four strokes:
- Inlet
- Compression
- Power
- Exhaust
On the compression stroke, the piston moves back up the cylinder and the inlet valve closes. The cool compressed air is compressed further. This additional compression generates more heat.
Note: If the cold starting system is operating, the glow plugs will also heat the air in the cylinder.
Just before the piston reaches the top center (TC) position, the ECM operates the electronic unit injector. Fuel is injected into the cylinder. The air/fuel mixture ignites. The ignition of the gases initiates the power stroke. Both the inlet and the exhaust valves are closed and the expanding gases force the piston downward toward the bottom center (BC) position.
From the BC position, the piston moves upward. This initiates the exhaust stroke. The exhaust valve opens. The exhaust gases are forced through the open exhaust valve into the exhaust manifold.
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| Illustration 2 | g02720984 |
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Typical example | |
The NOx Reduction System (NRS) operates with the transfer of the hot exhaust gas from the exhaust manifold to the assembly of the exhaust gas valve.
The assembly of the exhaust gas valve consists of an exhaust gas valve and an electronically controlled actuator.
As the electronically controlled actuator (7) starts to open the flow of exhaust gas from the exhaust gas valve mixes with the air flow from the charge air aftercooler. The mixing of the exhaust gas and the air flow from the charge air aftercooler reduces the oxygen content of the gas mixture. This results in a lower combustion temperature, so decreases the production of NOx.
As the demand for more exhaust gas increases the electronically controlled actuator opens further. The further opening of the actuator increases the flow of exhaust gas from the exhaust gas valve. As the demand for exhaust gas decreases, the electronically controlled actuator closes. This decreases the flow of exhaust gas from the exhaust gas valve.
The hot exhaust gas is then cooled in the exhaust cooler (6). The cooled gas then travels from the exhaust cooler (6) to the inlet manifold.
Exhaust gases from the exhaust manifold enter the inlet of the turbocharger in order to turn the turbocharger turbine wheel. The turbine wheel is connected to a shaft that rotates. The exhaust gases pass from the turbocharger through the following components: exhaust outlet, Clean Emissions Module (CEM) and exhaust pipe.
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| Illustration 3 | g00302786 |
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Typical example of a cross section of a turbocharger (1) Air intake (2) Compressor housing (3) Compressor wheel (4) Bearing (5) Oil inlet port (6) Bearing (7) Turbine housing (8) Turbine wheel (9) Exhaust outlet (10) Oil outlet port (11) Exhaust inlet | |
The turbocharger is mounted on the outlet of the exhaust manifold. The exhaust gas from the exhaust manifold enters the exhaust inlet (11) and passes through the turbine housing (7) of the turbocharger. Energy from the exhaust gas causes the turbine wheel (8) to rotate. The turbine wheel is connected by a shaft to the compressor wheel (3).
As the turbine wheel rotates, the compressor wheel is rotated. The rotation of the compressor wheel causes the intake air to be pressurized through the compressor housing (2) of the turbocharger.
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| Illustration 4 | g02720975 |
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Typical example (12) Line (boost pressure) (13) Wastegate actuator (14) Actuating lever | |
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| Illustration 5 | g02720981 |
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Typical example (15) Wastegate regulator | |
When the load on the engine increases, more fuel is injected into the cylinders. The combustion of this additional fuel produces more exhaust gases. The additional exhaust gases cause the turbine and the compressor wheels of the turbocharger to turn faster. As the compressor wheel turns faster, air is compressed to a higher pressure and more air is forced into the cylinders. The increased flow of air into the cylinders allows the fuel to be burnt with greater efficiency. The more efficient burning of fuel produces more power.
A wastegate is installed on the turbine housing of the turbocharger. The wastegate is a valve that allows exhaust gas to bypass the turbine wheel of the turbocharger. The operation of the wastegate is dependent on the pressurized air (boost pressure) from the turbocharger compressor. The boost pressure acts on a diaphragm. The diaphragm is spring loaded in the wastegate actuator which varies the amount of exhaust gas that flows into the turbine.
The wastegate regulator (15) is controlled by the engine electronic control module (ECM). The ECM uses inputs from a number of engine sensors to determine the optimum boost pressure. This will achieve the best exhaust emissions and fuel consumption at any given engine operating condition. The ECM controls the wastegate regulator, that regulates the boost pressure to the wastegate actuator.
When high boost pressure is needed for the engine performance, a signal is sent from the ECM to the wastegate regulator. This causes high pressure in the inlet manifold to act on the diaphragm within the wastegate actuator (13). The actuating rod (14) acts upon the actuating lever to close the valve in the wastegate. When the valve in the wastegate is closed, more exhaust gas is able to pass over the turbine wheel. This results in an increase in the speed of the turbocharger.
When low boost pressure is needed for the engine performance, a signal is sent from the ECM to the wastegate regulator. This causes high pressure in the air inlet pipe (12) to act on the diaphragm within the wastegate actuator (13). The actuating rod (14) acts upon the actuating lever to open the valve in the wastegate. When the valve in the wastegate is opened, more exhaust gas from the engine is able to bypass the turbine wheel, resulting in a decrease in the speed of the turbocharger.
The shaft that connects the turbine to the compressor wheel rotates in bearings (4) and (6). The bearings require oil under pressure for lubrication and cooling. The oil that flows to the lubricating oil inlet port (5) passes through the center of the turbocharger which retains the bearings. The oil exits the turbocharger from the lubricating oil outlet port (10) and returns to the oil pan.
| NOTICE |
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The crankcase breather gases are part of the engines measured emissions output. Any tampering with the breather system could invalidate the engines emissions compliance. |
The crankcase breather has a centrifugal separator. The centrifugal separator has a special coating. Engine oil that has been separated from the breather gas is returned to the timing case. The crankcase breather is driven by the shaft of the fuel injection pump.
A heated connection may be installed on the pipe for the crankcase breather. The purpose of the heated connection is to prevent the formation of ice in cold climates, that could lead to an obstruction of the pipe.
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| Illustration 6 | g03699000 |
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A typical example of valve system components (1) Bridge (2) Rocker arm (3) Pushrod (4) Lifter (5) Camshaft (6) Valve (7) Spring | |
The valve system components control the flow of inlet air into the cylinders during engine operation. The valve system components also control the flow of exhaust gases out of the cylinders during engine operation.
The crankshaft gear drives the camshaft gear. The camshaft (5) must be timed to the crankshaft in order to get the correct relation between the piston movement and the valve movement.
The camshaft (5) has two camshaft lobes for each cylinder. The lobes operate either the inlet valve or the exhaust valve. As the camshaft turns, lobes on the camshaft cause the lifter (4) to move the pushrod (3) up and down. Upward movement of the pushrod against rocker arm results in a downward movement that acts on the valve bridge (1).
This action opens a pair of valves (6) which compresses the valve springs (7). When the camshaft (5) has rotated to the peak of the lobe, the valves (6) are fully open. When the camshaft rotates further, the two valve springs (7) under compression start to expand. The valve stems are under tension of the springs. The stems are pushed upward. The continued rotation of the camshaft causes the rocker arm, the pushrods and the lifters to move downward until the lifter reaches the bottom of the lobe. The valves are now closed. The cycle is repeated for all the valves on each cylinder.
The rocker arm (2) incorporates a hydraulic lash adjuster which removes valve lash from the valve mechanism. The hydraulic lash adjuster uses engine lubricating oil to compensate for wear of system components so that no service adjustment of valve lash is needed.
The engine lubricating oil enters the hydraulic lash adjuster through a non-return valve. The engine lubricating oil increases the length of the hydraulic lash adjuster until all valve lash is removed. If the engine is stationary for a prolonged period the valve springs will cause the hydraulic lash adjuster to shorten so that when the engine is started engine valve lash is present for the first few seconds.
After cranking restores oil pressure the hydraulic lash adjuster increases in length and removes the valve lash. When load is removed from a hydraulic lash adjuster during service work by the removal of the rocker shaft the hydraulic lash adjuster increases in length to the maximum extent. Refer to Systems Operation, Testing and Adjusting, "Position the Valve Mechanism Before Maintenance Procedures" for the correct procedure.
During reassembly of the rocker shaft the engine must be put into a safe position to avoid engine damage. After load is imposed on the lifters by reassembling the rocker assembly, the engine must be left in safe position for a safe period until the lifters have reduced to the correct length. Refer to Disassembly and Assembly, "Rocker Shaft and Pushrod - Install" for the correct procedure.