C7 Engines for Caterpillar Built Machines Air Inlet and Exhaust System Caterpillar


Air Inlet and Exhaust System
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C7 Engines for Caterpillar Built Machines [SENR9939]
AIR INLET AND EXHAUST SYSTEM
C7 Engines for Caterpillar Built Machines Air Inlet and Exhaust System - Inspect
C7 Engines for Caterpillar Built Machines Air Inlet and Exhaust System
1.1. Turbocharger
2.1. Valve System Components
3.1. Air Inlet Heater
4.2. System Components


Illustration 1g01113108
(1) Exhaust manifold
(2) Air inlet heater
(3) Aftercooler core
(4) Exhaust valve
(5) Inlet valve
(6) Air inlet
(7) Exhaust outlet
(8) Compressor side of turbocharger
(9) Turbine side of turbocharger

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 components of the air inlet and exhaust system are the following components:

  • Air cleaner

  • Turbocharger

  • Aftercooler

  • Cylinder head

  • Valves and valve system components

  • Piston and cylinder

  • Exhaust manifold

Inlet air is pulled through the air cleaner into air inlet (6) by turbocharger compressor wheel (8). The air is compressed and heated to about 150 °C (302 °F) before the air is forced to the aftercooler (3). As the air flows through the aftercooler the temperature of the compressed air lowers to about 43 °C (109 °F). Cooling of the inlet air increases combustion efficiency. Increased combustion efficiency helps achieve the following benefits:

  • Lower fuel consumption

  • Increased horsepower output

From the aftercooler, air is forced into the inlet manifold. Air flow from the inlet chambers into the cylinders is controlled by inlet valves (5). There are two inlet valves and two exhaust valves (4) for each cylinder. The inlet valves open when the piston moves down on the intake 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. The exhaust valves open and the exhaust gases are pushed through the exhaust port into exhaust manifold (1) as the piston rises on the exhaust stroke. After the exhaust stroke, the exhaust valves close and the cycle starts again. The complete cycle consists of four strokes:

  • Inlet

  • Compression

  • Power

  • Exhaust

Exhaust gases from exhaust manifold (1) enter the turbine side of the turbocharger in order to turn turbocharger turbine wheel (9). The turbine wheel is connected to the shaft that drives the compressor wheel. Exhaust gases from the turbocharger pass through exhaust outlet (7), a muffler and an exhaust stack.

The air inlet heater (2) is controlled by the Electronic Control Module (ECM). The air inlet heater aids in engine start-up and reducing white smoke during engine start-up.

Turbocharger



Illustration 2g01113125
Cross section of turbocharger
(1) Compressor wheel housing
(2) Oil inlet port
(3) Bearing
(4) Turbine wheel housing
(5) Turbine wheel
(6) Air inlet
(7) Exhaust outlet
(8) Compressor wheel
(9) Bearing
(10) Oil outlet port
(11) Exhaust inlet

The turbocharger is installed on the center section of the exhaust manifold. All the exhaust gases from the engine go through the turbocharger. The compressor side of the turbocharger is connected to the aftercooler by pipe.

The exhaust gases enter turbine housing (4) through exhaust inlet (11). The exhaust gases then push the blades of turbine wheel (5). The turbine wheel is connected by a shaft to compressor wheel (8).

Clean air from the air cleaners is pulled through compressor housing air inlet (6) by the rotation of compressor wheel (8). The action of the compressor wheel blades causes a compression of the inlet air. This compressor allows the engine to burn more fuel. When the engine burns more fuel the engine produces more power.

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.



Illustration 3g01113130
Turbocharger with wastegate
(12) Canister
(13) Actuating lever
(14) Line (boost pressure)

The operation of the wastegate is controlled by the boost pressure. At high boost pressures, the wastegate opens in order to decrease boost pressure. At low boost pressure, the wastegate closes in order to increase boost pressure.

When the engine is operating under conditions of low boost, a spring pushes on a diaphragm in canister (12). This action moves actuating lever (13) in order to close the valve of the wastegate. Closing the valve of the wastegate allows the turbocharger to operate at maximum performance.

As the boost pressure through line (14) increases against the diaphragm in canister (12), the valve of the wastegate is opened. When the valve of the wastegate is opened, the rpm of the turbocharger is limited by bypassing a portion of the exhaust gases. The exhaust gases are routed through the wastegate which bypasses the turbine wheel of the turbocharger.

Note: The turbocharger with a wastegate is preset at the factory and no adjustment can be made.

Bearings (3) and (9) for the turbocharger use engine oil under pressure for lubrication and cooling. The oil comes in through oil inlet port (2). The oil then goes through passages in the center section in order to lubricate the bearings. This oil also cools the bearings. Oil from the turbocharger goes out through oil outlet port (10) in the bottom of the center section. The oil then goes back to the engine oil pan.

Valve System Components



Illustration 4g01121466
(1) Rocker arm
(2) Pushrod
(3) Valve bridge
(4) Valve spring
(5) Valve
(6) Lifter

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 through an idler gear. The camshaft must be timed to the crankshaft in order to get the correct relation between the piston movement and the valve movement.

The camshaft has two camshaft lobes for each cylinder. The lobes operate the inlet and exhaust valves. As the camshaft turns, lobes on the camshaft cause lifters (6) to move pushrods (2) up and down. Upward movement of the pushrods against rocker arms (1) results in downward movement (opening) of valves (5).

Each cylinder has two inlet valves and two exhaust valves. The valve bridge (3) actuates the valves at the same time by movement of the pushrod and rocker arm. Valve springs (4) close the valves when the lifters move down.

Air Inlet Heater

The engines are equipped with an electric heater that is located behind the air inlet elbow. The electric heater has two functions:

  • Aid in starting

  • Aid in white smoke cleanup during start-up

Under the proper conditions, the ECM turns on the electric heater.

The system is capable of delivering heat for thirty seconds prior to start-up and during cranking of the engine. After the engine has started, the system is capable of delivering heat constantly for seven minutes, or the system can cycle the heat for thirteen minutes. During the heating cycle, the heat is on for ten seconds and the heat is off for ten seconds.

If the air inlet heater malfunctions, the engine will still start and the engine will still run. There may be a concern regarding the amount of white smoke that is present. Also, there may be a concern regarding the need for an alternative starting aid.

System Components

The system of the air inlet heater consists of the following basic components:

  • Relay of the air inlet heater

  • Heater element

  • Coolant temperature sensor

  • Inlet manifold temperature sensor

  • ECM

  • Indicator lamp


Illustration 5g01134096
(1) Relay for air inlet heater

The relay of the air inlet heater (1) turns the heater ON and OFF in response to signals from the ECM.

The air inlet heater is located between the cover of the air inlet and the air inlet elbow. The heater element has a stud for the ground strap that must be connected to the engine.

The operation of the air inlet heater is determined by five different conditions:

  • Power up cycle

The air inlet heater and the lamp are turned ON for 2 seconds after the ECM is first powered up. This will happen regardless of temperatures and engine speed.

  • Mode of preheat

This check is for low altitude conditions. When the sum of the coolant temperature plus the inlet air temperature is less than 25 °C (77 °F), the ECM will turn on the heater and the lamp for 30 seconds. The ECM will turn off the heater and the lamp after 30 seconds if the engine speed remains at 0 regardless of temperature.

This check is for high altitude conditions. When the sum of the coolant temperature plus the inlet air temperature is less than 53 °C (127 °F), the ECM will turn on the heater and the lamp for 30 seconds. The ECM will turn off the heater and the lamp after 30 seconds if the engine speed remains at 0 regardless of temperature.

  • Mode of cranking

The air inlet heater and the lamp will remain on continuously when engine speed is detected. The air inlet heater and the lamp will remain on when the sum of the coolant temperature plus the air inlet temperature is less than 25 °C (77 °F) for low altitude conditions and less than 63 °C (145 °F) for high altitude conditions.

  • Running of the engine

When the engine achieves low idle the air inlet heater and the lamp will remain on for an additional 7 minutes when the sum of the air temperature plus the coolant temperature is less than 35 °C (95 °F) for low altitude conditions or when the sum of the air temperature plus the coolant temperature is less than 63 °C (145 °F) for high altitude conditions.

  • Post heat cycle

The sum of the air temperature and the coolant temperature is less than 35 °C (127 °F) in low altitude conditions or 63 °C (177 °F) in high altitude conditions. The air inlet heater and the lamp are cycled on and off for an additional 13 minutes. The cycle is 10 seconds on and 10 seconds off.

After the engine has started the inlet air temperature and the coolant temperature will determine the state of the heater. The cycle has two strategies.

The two strategies are continuous and intermittent.

  1. During the continuous strategy, the heater remains activated for seven minutes after the engine is started. If the same conditions exist, the ECM will activate the intermittent strategy.

  2. During the intermittent strategy, the heater is cycled for a maximum of thirteen minutes. During this cycle, the heater is turned on for ten seconds and the heater is turned off for ten seconds. After the thirteen minute time limit, the heater is shut off.

When one of the temperature sensors fails, the system will operate in the following manner:

  • Coolant temperature sensor

When the coolant temperature sensor has an open circuit or a short circuit, the coolant temperature sensor has failed. During this condition, the heater will be activated when the inlet air temperature is less than 10 °C (50 °F).

  • Inlet air temperature sensor

When the inlet air temperature sensor has an open circuit or a short circuit, the inlet air temperature sensor has failed. During this condition, the heater will be activated when the coolant temperature is less than 40 °C (104 °F).

Under the proper condition, the heater will be reactivated. When the sum of the coolant temperature and the inlet air temperature has dropped below 25 °C (77 °F), the heater will be reactivated. This condition could exist after a warm engine has cooled and the operator attempts to start the engine.

When the sum of the coolant temperature and the inlet air temperature does not attain 35 °C (95 °F), the heater will be activated. The heater can be activated no longer than 20 minutes (maximum). The ECM will turn off the heater after the 20 minute time limit.

For additional information on the air inlet heater, refer to Troubleshooting, "Air Inlet Heater Circuit - Test".

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