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| Illustration 1 | g01914641 |
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Typical Example Air inlet and exhaust system (1) Air-to-air aftercooler (ATAAC) (2) Exhaust manifold (3) Turbocharger (4) Air Cleaner (5) Clean Emissions Module (CEM) (6) NOx Reduction System (NRS) cooler (7) NRS venturi (8) NRS valve (9) Exhaust balance valve solenoid (10) Intake manifold (11) Cylinder head | |
The engine has an electronic control system. The system controls the operation of the engine and the Clean Emissions Module (CEM). The CEM consists of the following components: Aftertreatment Regeneration Device (ARD), Diesel Particulate Filter (DPF) and a muffler.
The system consists of the following components:
- Engine Control Module (ECM)
- Wiring
- Sensors
- Actuators
Inlet air is pulled through the air cleaner . The inlet air is then compressed and heated by the compressor wheel of turbocharger to about
Aftercooler core is a separate cooler core. The aftercooler core is installed in front of the core of the engine radiator. Air that is ambient temperature is moved across the aftercooler core by the engine fan. This action cools the turbocharged inlet air.
From aftercooler core , the air is forced into the cylinder head in order to fill the inlet ports. Air flow from the inlet port into the cylinder is controlled by the inlet valves.
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| Illustration 2 | g02327074 |
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Air inlet and exhaust system (12) NRS cooler (13) Exhaust manifold (14) Aftercooler (15) Exhaust outlet from turbocharger (16) Turbine side of turbocharger (17) Compressor side of turbocharger (18) Air inlet (19) Inlet valve (20) Exhaust valve | |
Exhaust gases from the exhaust manifold enter the turbine side of turbocharger in order to turn the turbine wheel. The turbine wheel is connected to a shaft which drives the compressor wheel. Exhaust gases from the turbocharger pass through the exhaust outlet pipe, the muffler, and the exhaust stack.
There are two inlet valves and two exhaust valves for each cylinder. Inlet valves open when the piston moves down on the inlet stroke. When the inlet valves open, cooled compressed air from the inlet port is pulled into the cylinder. The inlet valves close and the piston begins to move up on the compression stroke. The air in the cylinder is compressed. When the piston is near the top of the compression stroke, fuel is injected into the cylinder. The fuel mixes with the air and combustion starts. During the power stroke, the combustion force pushes the piston downward. After the power stroke is complete, the piston moves upward. This upward movement is the exhaust stroke. During the exhaust stroke, the exhaust valves open, and 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 starts again. The complete cycle consists of four stages:
- Inlet stroke
- Compression stroke
- Power stroke
- Exhaust stroke
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| Illustration 3 | g01945084 |
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Two turbochargers are arranged in a series on some C18 applications. (A) To the aftercooler (B) From the actuator on the balance valve (C) To the Clean Emissions Module (D) From the air filter | |
The low-pressure turbocharger compressor wheel pulls the inlet air through the air cleaner and into the air inlet. The air is compressed by the low-pressure turbocharger. Pressurizing the inlet air causes the air to heat up. The pressurized air exits the low-pressure turbocharger through the outlet and the air is forced into the inlet of the high-pressure turbocharger.
The high-pressure turbocharger is used in order to compress the air to a higher pressure. This increase in pressure continues to cause the temperature of the inlet air to increase. As the air is compressed, the air is forced through the outlet of the high-pressure turbocharger and into the air lines to the precooler.
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. 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 NRS sends hot exhaust gas from the exhaust manifold that is connected to cylinders one, two, and three through the NRS system. In order for exhaust gas to be able to mix with pressurized air from the ATAAC, back pressure is needed in the exhaust system. This back pressure is created by the turbocharger and DPF. The hot exhaust gas is first cooled in the NRS cooler. The now cooled exhaust gas passes through the NRS venturi. The venturi takes a measurement of the flow of exhaust gas through the NRS system. After the gas flow is measured by the NRS venturi, the gas flows through the electronically controlled NRS valve. The electronic controlled NRS valve is hydraulically actuated. When the NRS valve is in the full OFF position, the only source of air for the engine is from the turbocharger compressor. As the valve starts to open the flow of cooled exhaust gas from the NRS cooler mixes with the air flow from the turbocharger. As the demand for more cooled exhaust gas increases, the valve opens wider. This widening increases the flow of cooled exhaust gas from the NRS cooler. As the demand for more cooled exhaust gas increases, the demand for air flow from the turbocharger decreases.
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| Illustration 4 | g02213856 |
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Turbocharger (21) Air inlet (22) Compressor housing (23) Compressor wheel (24) Bearing (25) Oil inlet port (26) Bearing (27) Turbine housing (28) Small path (29) Balance valve chamber (30) Large Path (31) Turbine wheel (32) Exhaust outlet (33) Oil outlet port | |
The turbocharger is installed on the exhaust manifold. Most of the exhaust gases flow through the turbocharger. A metered amount of exhaust gases flow through the NRS system. The compressor side of the turbocharger is connected to the aftercooler by a pipe.
The exhaust gases go into turbine housing (27) through the exhaust inlet. The turbine housing of the turbocharger is of the asymmetric design. The asymmetric design consists of the turbine housing that has two different-sized paths for the exhaust to flow. Path (28) receives exhaust gas from cylinders one, two, and three. Path (30) receives exhaust gas from cylinders four, five, and six. The smaller path restricts the flow of the exhaust. This restriction helps force the exhaust gas through the NRS system to the intake manifold of the engine. The energy from the heat in the exhaust gases pushes the blades of turbine wheel (31). The turbine wheel is connected by a shaft to compressor wheel (23). The turbine housing also contains the exhaust balance valve and the actuator for the exhaust balance valve. The actuator for the exhaust balance valve receives boost pressure from the intake manifold. This boost pressure is first regulated by the solenoid for the exhaust balance valve. The exhaust balance valve solenoid will open allowing the boost pressure to act on the exhaust balance valve actuator if the valve needs to open. The actuator then opens the exhaust balance valve. The exhaust balance valve allows the flowing exhaust gas from the small path of the turbine housing to enter the large path. This action causes less exhaust gas to act on the turbine wheel from the smaller flow path. This action slows down the speed of the turbine wheel in order to protect the turbocharger. A secondary effect is reduced flow through the NOx Reduction System (NRS).
Clean air from the air cleaners is pulled through compressor housing air inlet (21) by the rotation of compressor wheel (23). The action of the compressor wheel blades causes a compression of the inlet air. This compression gives the engine more power by allowing the engine to burn more air and more fuel during combustion.
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, more air is forced into the cylinders. The increased flow of air gives the engine more power by allowing the engine to burn the additional fuel with greater efficiency.
Bearings (24) and (26) for the turbocharger use engine oil under pressure for lubrication. The oil comes in through oil inlet port (25). The oil then goes through passages in the center section in order to lubricate the bearings. Oil from the turbocharger goes out through oil outlet port (33) in the bottom of the center section. The oil then goes back to the engine lubrication system.
Balance Valve Solenoid Circuit
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| Illustration 5 | g02407017 |
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(34) Balance valve actuator
(35) Line from the intake manifold (36) Balance valve solenoid | |
The balance valve solenoid circuit is used to control the balance valve actuator (34) on the turbocharger. Line (35) directs the boost air from the intake manifold to the balance valve actuator. Balance valve solenoid (36) either prohibits or allows airflow to the balance valve actuator (34). Additionally, the engine ECM must send an electronic signal to the balance valve solenoid commanding the solenoid to permit airflow.
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| Illustration 6 | g02407018 |
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Balance valve solenoid in closed position (37) Path to balance valve actuator (38) Vent (39) Armature (40) Path from the NRS mixer | |
The balance valve actuator is normally closed. The solenoid must be energized by the ECM to keep the balance valve actuator closed. The armature (1) in the balance valve solenoid is responsible for allowing or prohibiting the pressurizing of the entire balance valve system. The armature physically blocks the boost air from flowing to the balance valve actuator. The vent (2) is responsible for purging residual pressure from the balance valve system once the pressure is no longer needed. Without the vent, there would constantly be pressure on the balance valve actuator and not allow the actuator to close. When the charge air pressure supplied to the balance valve actuator exceeds a predetermined limit, the balance valve actuator will open. The actuator opening causes the turbocharger speed to decrease and protects the engine. Engine speed must be present for in order for the electrical current to command the balance valve solenoid to close. If the key is on but the engine is not running, the balance valve solenoid will remain open.
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| Illustration 7 | g02407019 |
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Balance valve solenoid in open position (37) Path to balance valve actuator (40) Path from the NRS mixer | |
The balance valve solenoid is activated to the open position by the ECM when the conditions of the performance map are met. Typical engine conditions are when the pressure difference between the two turbine paths becomes greater than desired. This conditions can occur during engine powering or engine braking (if applicable). When the balance valve solenoid is open the armature blocks the vent passage, not allowing any leakage.
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| Illustration 8 | g02407056 |
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Valve system components (41) Rocker arm (42) Valve adjustment screw (43) Rocker arm shaft (44) Camshaft follower (45) Camshaft (46) Valve bridge (47) Valve rotator (48) Valve spring (49) Valve (50) 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. Specifically machined lobes on camshaft (45) 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.
Variable Valve Actuator (If Equipped)
The Intake Valve Actuation system (IVA) uses pressurized engine oil to delay the closing of the intake valves. The system is controlled by the Engine Control Module (ECM). The system contains the following components:
Check Valve (53) - Pressurized engine oil flows to a rail inside the valve cover base. A check valve prevents oil from flowing from the rail back to the main oil gallery.
Pressure Sensor (52) - A pressure sensor is threaded into the rail. The sensor converts the rail pressure into an electrical signal. The ECM monitors the signal in order to determine the pressure of the oil in the rail.
Control Valve (51) - A control valve is threaded into the rail. The control valve contains a coil and a cartridge assembly. The cartridge assembly contains a spool. The spool is normally closed. When the spool is closed, the oil is contained in the rail. The ECM sends a signal to the coil in order to fully open the spool. The oil is released into the space underneath the valve cover and the rail pressure is reduced.
Actuator (54) - The actuators are located under the valve covers. Pressurized engine oil flows from the rail to each actuator. The actuators use the pressurized engine oil and electrical commands from the ECM in order to delay the closing of the intake valves.
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| Illustration 9 | g02760139 |
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Component location (51) Control valve (52) Pressure sensor (53) Check valve (54) Actuators | |
System Operation During Engine Start
The ECM performs the following sequence of operations when the engine is started:
- The ECM commands the control valve to open for 17 seconds.
- The ECM checks the temperature of the coolant.
- The ECM commands the control valve to close when the coolant temperature exceeds
20 °C (68 °F) . This allows the temperature of the oil in the rail to warm up. - The ECM commands the control valve to open. The ECM samples the rail pressure. The ECM commands the control valve to close. The ECM takes a second sample of the rail pressure. The ECM compares the two pressure values. The ECM activates a code if the pressure difference is too low.
- The control valve should remain closed during engine operation.
System Operation During Engine Operation
The system does not operate until the engine has reached normal operating temperature.
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| Illustration 10 | g02760158 |
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Section view of the components (54) Actuator (55) Space (56) Solenoid (57) Piston (58) Rocker arm (59) Valve (60) Rail (61) Intake valves | |
Each actuator (54) contains two solenoids (56). Each solenoid is connected to a valve (59). The solenoid is normally de-energized. The valve is normally open. This allows oil to flow between rail (60) and the space (55) above piston (57).
Rocker arm (58) is down when the intake valves are open. Pressurized oil flows from rail (60) to space (55) above piston (57). This causes the piston to move down. The piston contacts rocker arm (58).
The ECM energizes solenoid (56) when the ECM requires intake valves (61) to remain open. The energized solenoid closes valve (59). This traps the oil in space (55). The trapped oil causes piston (57) and rocker arm (58) to remain down. This keeps intake valves (61) open.
The ECM de-energizes solenoid (56) when the ECM requires the intake valves to close. The de-energized solenoid lifts valve (59). Valve springs (59) raise intake valves (61), rocker arm (58), and piston (57). The piston that is rising forces the oil from space (55) into the rail (60).
The flow of oil into the rail changes the pressure of the oil in the rail. The ECM monitors the rail pressure. The ECM determines if the changes in rail pressure are correct for the commands that were sent to a particular solenoid. The ECM activates a diagnostic code for the appropriate cylinder if the changes in rail pressure are incorrect for that solenoid.
Intake Variable Valve Actuation Startup System Operation
Engines equipped with IVA may not achieve full performance until the engine coolant is at operating temperature
Once the minimum temperature is achieved, the engine ECM analyzes the IVA performance. The derate will be removed, if the IVA performance is acceptable or initiates a timer which removes the derate after a prescribed time.
There is not a broadcasted operator warning that this function is active, but a derate may be seen in Cat® Electronic Technician (ET). Customers will be able to operate the engine up to the derate power until the IVA derate has been removed.