 | |
| Illustration 1 | g01102550 |
(1) Exhaust valve (2) Inlet valve (3) Aftercooler core (4) Precooler (5) High-pressure turbocharger (6) Exhaust inlet for the high-pressure turbocharger (7) Wastegate (8) Outlet for the inlet air on the high-pressure turbocharger (9) High-pressure turbocharger exhaust outlet (10) Inlet for the inlet air on the high-pressure turbocharger (11) Exhaust inlet for the low-pressure turbocharger (12) Wastegate pressure line (13) Exhaust outlet for the low-pressure turbocharger (14) Outlet for the inlet air on the low-pressure turbocharger (15) Low-pressure turbocharger (16) Inlet for the inlet air on the low-pressure turbocharger | |
The engine components of the air inlet and exhaust system control the quality of air and the amount of air that is available for combustion. The components of the air inlet and exhaust system are the following components:
- Air cleaner
- Turbochargers
- Precooler
- Aftercooler
- Cylinder head
- Valves and valve system components
- Piston and cylinder
- Exhaust manifold
The low-pressure turbocharger compressor wheel pulls inlet air through the air cleaner and into air inlet (16). The air is compressed by low-pressure turbocharger (15). Pressurizing the inlet air causes the air to heat up. The pressurized air exits the low-pressure turbocharger through outlet (14) and the air is forced into inlet (10) of high-pressure turbocharger (5) .
The high-pressure turbocharger is used in order to compress the air to a higher pressure. This increase in pressure continues to cause the inlet air temperature to increase. As the air is compressed, the air is forced through the high-pressure turbocharger outlet (8) and into the air lines to precooler (4) .
The pressurized inlet air is cooled by the precooler prior to being sent to the aftercooler. The precooler uses engine coolant to cool the air. Without the precooler, the inlet air would be too hot in order to be cooled sufficiently by the aftercooler. The inlet air then enters aftercooler core (3). The inlet air is cooled further by transferring heat to the ambient air. The combustion efficiency increases as the temperature of the inlet air decreases. Combustion efficiency helps to provide increased fuel efficiency and increased horsepower output. The aftercooler core is a separate cooler core that is mounted in front of the engine radiator. The engine fan and the ram effect of the forward motion of the vehicle causes ambient air to move across the core.
Inlet air is forced from the aftercooler into the engine intake manifold. The airflow from the intake manifold into the cylinders and out of the cylinders is controlled by engine valve mechanisms.
Each cylinder has two inlet valves (2) and two exhaust valves (1) that are mounted in the cylinder head. The inlet valves open when the piston moves downward on the inlet stroke. When the inlet valves open, cooled, compressed air from the intake manifold is pulled into the cylinder. The inlet valves close when the piston begins to move upward on the compression stroke. The air in the cylinder is compressed by the piston. As the air is compressed by the piston, the temperature of the air in the cylinder is heated. Fuel is injected into the cylinder when the piston is near the top of the compression stroke. Combustion begins when the fuel mixes with the hot, pressurized air. The force of combustion pushes the piston downward on the power stroke. The exhaust valves are opened as the piston travels upward to the top of the cylinder. The exhaust gases are pushed through the exhaust port into the exhaust manifold. After the piston completes the exhaust stroke, the exhaust valves close and the cycle will begin again.
Exhaust gases from the exhaust manifold flow into the high-pressure turbocharger exhaust inlet (6). The hot gases that are expelled from the engine are used to turn the turbine wheel of the turbocharger. The turbine wheel drives the compressor wheel that is used in order to compress the inlet air that enters the inlet side of the turbocharger. The exhaust gas exits from the high-pressure turbocharger through the high-pressure turbocharger exhaust outlet (9) .
Wastegate (7) is used by the high-pressure turbocharger to prevent an overspeed condition of the turbocharger turbine wheel during engine acceleration. The wastegate also prevents excessive boost of the engine during engine acceleration. The wastegate is controlled by the boost pressure that is felt in the air hose assembly that connects the inlet side of the two turbochargers. Wastegate pressure line (12) provides the air pressure to the wastegate diaphragm. As the diaphragm reacts to high boost pressure, a valve is actuated. The valve allows exhaust gas to bypass the high-pressure turbocharger turbine, effectively controling the speed of the turbine.
The exhaust gases then enter the exhaust inlet for the low-pressure turbocharger (11). The exhaust gases drive the turbocharger turbine. This energy is used in order to compress the inlet air in the same manner as the high-pressure turbocharger. The exhaust gases then exit the low-pressure turbocharger through the exhaust outlet for the low-pressure turbocharger (13). The exhaust gases are then expelled into the vehicle exhaust system.
Turbochargers
 | |
| Illustration 2 | g01102627 |
Turbochargers (1) Wastegate (2) High-pressure turbocharger (3) Low-pressure turbocharger | |
High-pressure turbocharger (2) is mounted to the exhaust manifold of the engine. Low-pressure turbocharger (3) is located below the high-pressure turbocharger on the engine. The exhaust gas from the low-pressure turbocharger is fed into the vehicle exhaust system. Wastegate (1) is used in order to control the amount of exhaust gas that enters the turbocharger turbine during engine acceleration.
 | |
| Illustration 3 | g01102643 |
Typical example of a turbocharger (4) Air inlet (5) Compressor housing (6) Compressor wheel (7) Bearing (8) Oil inlet port (9) Bearing (10) Turbine housing (11) Turbine wheel (12) Exhaust outlet (13) Oil outlet port (14) Exhaust inlet | |
The exhaust gas from the engine enters the turbocharger turbine housing (10) through exhaust inlet (14). The blades of the turbocharger turbine wheel (11) are caused to rotate. As the turbine rotates, the exhaust gas flows around the turbine and exits through the turbocharger exhaust outlet (12). Because the turbocharger turbine wheel is connected by a shaft to the turbocharger compressor wheel (6), the turbine wheel and the compressor wheel rotate at high speeds. The rotation of the compressor wheel pulls clean air through air inlet (4) of compressor housing (5). The action of the compressor wheel blades causes a compression of the inlet air. This compression allows a larger amount of air to enter the engine. With more air in the engine, the engine is able to operate more efficiently. The overall effect is an increase in power.
When the load on the engine increases or when a greater engine speed is desired, additional fuel is injected into the cylinders. The increased engine speed creates more exhaust gases. More exhaust gases cause the turbine wheel and the compressor wheel to turn faster. Additional air is forced into the engine as the compressor wheel turns faster. The increased flow of air allows the engine to produce more power. The engine produces more power because the engine is able to burn additional fuel with greater efficiency.
 | |
| Illustration 4 | g01102644 |
Turbocharger with wastegate (15) Canister (16) Actuating lever | |
The engine does not operate efficiently under conditions of low boost. Low boost is a condition that occurs when the turbocharger produces less than optimum boost pressure. There is a spring that is located inside canister (15). Under low boost, the spring pushes on the diaphragm within the canister. This moves actuating lever (16). The actuating lever closes the wastegate, which will allow the turbocharger to operate at maximum performance.
Under conditions of high boost, the wastegate opens. The open wastegate allows exhaust gases to bypass the turbine side of the turbocharger. When the boost pressure increases against the diaphragm that is in the canister, the wastegate is opened. The rpm of the turbocharger is limited by bypassing a portion of the exhaust gases around the turbine wheel of the turbocharger.
Note: The calibration of the wastegate is preset at the factory. No adjustment can be made to the wastegate.
Bearing (7) and bearing (9) in the turbocharger use engine oil that is under pressure for lubrication. The lubrication oil for the bearings flows through oil inlet port (8) and into the oil cavity in the center section of the turbocharger cartridge. The oil exits the turbocharger through oil outlet port (13). The oil then returns to the engine oil pan through the oil drain line for the turbocharger.
Valves And Valve Mechanism
 | |
| Illustration 5 | g01062836 |
Valve system components (1) Rocker arm (2) Valve adjustment screw (3) Rocker arm shaft (4) Camshaft follower (5) Camshaft (6) Valve bridge (7) Valve rotator (8) Valve spring (9) Valve (10) Valve seat | |
The valve train controls the flow of inlet air into the cylinders and the flow of exhaust gases out of the cylinders during engine operation. Machined lobes on camshaft (5) are used in order to control the following aspects of valve function:
- Height of valve lift
- Timing of valve lift
- Duration of valve lift
The crankshaft gear drives the camshaft gear through the front gear train. The camshaft must be timed to the crankshaft in order to get the correct relation between the piston position and the valve position.
The camshaft has three camshaft lobes for each cylinder. Each cylinder has two inlet valves and two exhaust valves. One camshaft lobe operates both of the inlet valves for each cylinder. One camshaft lobe operates both of the exhaust valves for each cylinder. There is also one camshaft lobe that operates the unit injector for each cylinder. Camshaft follower (4) rolls against the surface of the camshaft lobe. The follower is used in order to transfer the lift that is machined into the camshaft lobe to rocker arm (1) .
The camshaft lobe lifts the camshaft follower of the rocker arm to actuate the valve (9). As the camshaft lobe lifts the follower, the rocker arm pivots at the rocker shaft (3) applying the lifting action to valve bridge (6). The valve bridge is used to transfer the lift from the rocker arm to the valves. Valve adjustment screw (2) is used in order to adjust the valve lash.
Valve springs (8) are used to hold the valves in the closed position when lift is not being transferred from the camshaft lobe. The springs provide the force on the valve in order to ensure that the valves will close at high rpm. The springs also ensure that the valves will remain closed under conditions of high boost pressures.
Valve rotators (7) cause the valves to rotate while the engine is running. The rotation of the valves in the valve seat prevents valve damage by constantly changing the contact area of the valve face and valve seat (10). This rotation gives the valves longer service life.
 | |
| Illustration 6 | g01102666 |
Front gear train (11) Timing mark (12) Camshaft gear (13) Adjustable idler gear (14) Idler gear (15) Timing mark (16) Cluster gear (17) Crankshaft gear | |
The inlet valves and the exhaust valves are opened by the valve mechanism. The inlet valves and the exhaust valves are also closed by the valve mechanism. This action occurs as the rotation of the crankshaft causes a relative rotation of the camshaft. Camshaft gear (12) is driven by a series of two idler gears. Adjustable idler gear (13) is driven by idler gear (14). This idler gear is driven by cluster gear (16). The cluster gear is driven by crankshaft gear (17). Timing mark (15) and timing mark (11) are aligned in order to provide the correct relationship between the piston and the valve movement.
The adjustable idler gear is adjusted so that backlash can be adjusted for the front gear train. The backlash adjustment is made between the idler gear and camshaft gear. If the cylinder head is removed, tolerances of the components will change. The components that change are the cylinder head and the head gasket. The adjustable idler gear must be relocated in order to maintain the correct backlash setting. For information on setting the timing gear backlash, refer to Testing and Adjusting, "Gear Group (Front) - Time".
The camshaft drive gear has integral pendulum rollers that act as a vibration damper for the front gear group. These thrust rollers are designed to counteract the torsional forces from the injector pulses, eliminating vibration and noise. The engine also runs smoother at all operating speeds.
Variable Valve Actuator
 | |
| Illustration 7 | g01102680 |
This engine uses variable valve actuators on the inlet valves. There are three housings for the variable valve actuators. Each housing has two variable valve actuators. One variable valve actuator is used for the two inlet valves on each cylinder.
The variable valve actuators are used in order to control the closing of the inlet valves. The variable valve actuators do not operate until the engine oil has reached a desired temperature. The oil for the variable valve actuator flows from the oil filter base to an oil rail that is outside of the head. If the oil temperature is below the desired temperature, the diverter valve in the oil rail is open. The open diverter valve allows the oil to drain back into the head. When the oil temperature is increased, the diverter valve is closed. This closing pressurizes the oil rail and the housings for the variable valve actuators. The pressure in the oil rail will be 250 ± 50 kPa (36 ± 7 psi) higher than the rest of the lubrication system. Purge holes are located in the housing in order to exhaust the pressurized oil.
The variable valve actuators hold the inlet valves open. The valves would normally close with the profile of the camshaft lobe. The solenoid is energized while the inlet valves are open. The solenoid allows pressurized oil to fill the cylinder. The pressurized oil pushes down the piston. As the inlet valve starts to close, the valve rocker arm for the inlet valve contacts the piston. The piston holds the inlet valves open.
In order to close the inlet valve, the solenoid is de-energized and the oil is allowed to leave the cylinder. The valve spring force pushes up on the rocker arm. The rocker arm pushes the piston back into the normal position of the piston. The inlet valves are then closed.