3054E Industrial Engine Air Inlet and Exhaust System Caterpillar

Air Inlet and Exhaust System
1.1. Turbocharger
2.1. Valve System Components

Illustration 1g01140052
Air inlet and exhaust system
(1) Exhaust manifold
(2) Aftercooler
(3) Exhaust valve
(4) Inlet valve
(5) Air inlet
(6) Exhaust outlet
(7) Compressor side of turbocharger
(8) 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.

Air is drawn in through the air cleaner into air inlet (5) by the turbocharger compressor wheel. The air is compressed and heated to about 150 °C (300 °F) before the air is forced to aftercooler (2). As the air flows through the aftercooler, the temperature of the compressed air decreases to about 50 °C (120 °F). Cooling of the inlet air increases combustion efficiency. Increased combustion efficiency helps achieve lower fuel consumption, increased horsepower output, and reduced particulate emission.

From the aftercooler, air is forced into the inlet manifold. Air flow from the inlet chambers into the cylinders is controlled by inlet valve (4). There is one inlet valve and one exhaust valve for each cylinder. When the inlet valves open, cooled compressed air from the inlet port is pulled into the cylinder.

Each piston makes four strokes for one complete cycle in two revolutions of the crankshaft.

  1. Intake

    During the intake stroke, the piston moves down and air is drawn into the cylinder through the open inlet valve.

  2. Compression

    During the compression stroke, the valves are closed and the piston moves up in the cylinder in order to compress the air. As the air is compressed, the temperature increases. As the piston nears the top of the stroke, fuel is injected into the combustion chamber on top of the piston. The fuel mixes with the hot compressed air in order to cause combustion.

  3. Power

    During the power stroke, the valves are closed as the forces from combustion push the piston and connecting rod down turning the crankshaft.

  4. Exhaust

    During the exhaust stroke, the inertial force of the turning flywheel helps continue the rotation of the crankshaft in order to push up the piston in the cylinder. This action forces the burned gases out of the exhaust valve. This completes the four strokes of the piston.

Exhaust gases from exhaust manifold (1) enter the turbine side of the turbocharger in order to turn turbocharger turbine wheel. The turbine wheel is connected to the same shaft that drives the compressor wheel. Exhaust gases from the turbocharger pass through exhaust outlet (6), a muffler and an exhaust stack.


Illustration 2g01140121
(1) Compressor housing
(2) Oil inlet port
(3) Bearing
(4) Turbine housing
(5) Turbine wheel
(6) Air inlet
(7) Exhaust outlet
(8) Compressor wheel
(9) Bearing
(10) Oil outlet port
(11) Exhaust inlet

The turbocharger can be mounted in two different positions on the engine. All the exhaust gases from the engine go through the turbocharger. 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).

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 (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 passes through oil outlet port (10) in the bottom of the center section. The oil then returns to the engine oil pan.

Illustration 3g01140147
(12) Canister
(13) Actuating lever

The turbocharger has a wastegate. The wastegate helps improve the emissions of the engine. 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 increases against the diaphragm in the canister, 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.

Valve System Components

Illustration 4g01366779
Rocker shaft assembly

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

Illustration 5g01140424
Valve system components
(1) Rocker arm
(2) Spring
(3) Pushrod
(4) Valve
(5) Lifter

The camshaft has two camshaft lobes for each cylinder. The lobes operate the inlet and exhaust valves. Each cylinder has one inlet valve and one exhaust valve. As the camshaft rotates, the lobes cause lifter (5) to move pushrod (3) up and down. Upward movement of the pushrod against rocker arm (1) results in downward movement (opening) of valve (4). Valve spring (2) closes the valves when the lifters move down.

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