C-15 On-Highway Engine Caterpillar

Illustration 1	g00451885
Air inlet and exhaust system schematic (1) Inlet manifold (2) Aftercooler core (3) Inlet air line (4) Exhaust outlet from turbocharger (5) Turbine side of turbocharger (6) Compressor side of turbocharger (7) Air cleaner

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

• Turbocharger

• Aftercooler

• Cylinder head

• Valves and valve system components

• Piston and cylinder

• Exhaust manifold

Note: This summary assumes that the engine is developing boost.

The turbocharger compressor wheel pulls inlet air through the air cleaner and into the air inlet. The air is compressed and heated to about 150°C (300°F) before the air is forced to the aftercooler. The air flows through aftercooler core (2) and the temperature of the compressed air lowers to about 43°C (110°F). The combustion efficiency increases because of the cooler inlet air. This helps to provide increased horsepower output. Aftercooler core (2) 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 both cores. This cools the turbocharged inlet air and the engine coolant.

Air is forced from the aftercooler into inlet manifold (1). The airflow from the inlet port into the cylinders is controlled by inlet valves.

Illustration 2	g00615497
Air inlet and exhaust system (2) Aftercooler core (4) Exhaust outlet (5) Turbine side of turbocharger (6) Compressor side of turbocharger (8) Exhaust manifold (9) Exhaust valve (10) Inlet valve (11) Air inlet

Each cylinder has two inlet valves (10) and two exhaust valves (9) in the cylinder head. The inlet valves open when the piston moves toward the bottom center on the inlet stroke. When the inlet valves open, cooled compressed air from the inlet port within the inlet manifold is forced into the cylinder. The inlet valves close when the piston moves toward top center on the compression stroke. The air in the cylinder is compressed and the 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 super heated air. The force of combustion pushes the piston toward the bottom center on the power stroke. The exhaust valves open and the exhaust gases are pushed through the exhaust port into exhaust manifold (8). After the piston moves toward top center on the exhaust stroke, the exhaust valves close and the cycle begins again.

The hot exhaust gases from the exhaust manifold flow into the turbine side of turbocharger (5). The hot exhaust gases cause the turbocharger turbine wheel to turn. The turbine wheel is connected to the shaft that drives the compressor wheel. Exhaust gases from the turbocharger pass through exhaust outlet (4), through the catalytic converter into a muffler, and through an exhaust stack.

Turbocharger

Illustration 3	g00291064
Turbocharger (typical example) (1) Pipe (2) Exhaust manifold (3) Turbocharger

Turbocharger (3) is mounted to exhaust manifold (2) of the engine. All of the exhaust gases go from the exhaust manifold through the turbocharger.

Illustration 4	g00291085
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 gases enter the turbocharger and the exhaust gases turn the turbine blades of the turbocharger. Because the turbocharger turbine wheel is connected by a shaft to the turbocharger compressor wheel, the turbine wheel and the compressor wheel turn together. The turbocharger compressor wheel and the turbine wheel turn at very high rpm. The rotation of the compressor wheel draws clean air through the compressor housing air inlet. 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 burn more fuel. 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. This creates hotter exhaust gases, which will 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 amount 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 5	g00291087
Turbocharger with wastegate (15) Canister (16) Actuating lever

Low boost is a condition that occurs when the turbocharger produces less than optimum boost pressure. There is a spring that is inside canister (15). Under low boost, the spring pushes on the diaphragm in canister (15). 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 in canister (15), 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 inlet port 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.

Wastegate Solenoid

Illustration 6	g00910753
(1) Outlet fitting (2) Inlet fitting (3) Vent (4) Wastegate solenoid (5) Manifold

The wastegate solenoid allows the ECM to fine tune the amount of boost that is generated. A wastegate solenoid is necessary in order to prevent the turbocharger from overspeeding under a high load condition. This will also prevent the boost from exceeding the designed limits.

Illustration 7	g00910769
(6) Turbocharger (7) Wastegate (8) Inlet manifold (9) Inlet manifold pressure sensor (10) ECM (11) Inlet manifold pressure port (12) Air bleed passage (13) Solenoid (14) Manifold (15) Wastegate pressure port

The boost pressure is monitored by the ECM (10) through the inlet manifold pressure sensor (9) that is connected to the inlet manifold (8). The ECM (10) sends a control signal to the solenoid (13) which will allow inlet manifold pressure to actuate the wastegate (7) or the ECM will close the solenoid (13) in order to block the flow of inlet manifold pressure to the wastegate. The default position for the solenoid (13) is open. This will allow the wastegate to function as a standard wastegate. When the desired boost pressure is reached, the solenoid (13) will close. This will cause the pressure to be bled from the wastegate (7) through the air bleed passage (12) to the atmosphere.

Note: Do not tamper with the wastegate solenoid or modify the wastegate solenoid. Bypassing the wastegate solenoid will cause the engine to go into a derate mode and a code will be set. Refer to the Troubleshooting Guide for more information.

Valves And Valve Mechanism

Illustration 8	g00291088
Valve system components (1) Valve bridge (2) Rocker arm (3) Camshaft (4) Rotocoil (5) Valve spring (6) Valve guide (7) Valve

The valves and the valve mechanism control the flow of inlet air into the cylinders during engine operation. The valves and the valve mechanism control the flow of exhaust gases out of the cylinders during engine operation.

Illustration 9	g00291089
Components of the timing gear (8) Timing mark (9) Camshaft gear (10) Adjustable idler gear (11) Idler gear (12) Timing mark (13) Cluster gear (14) 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 occurs as the rotation of the crankshaft causes camshaft (3) to rotate. Camshaft gear (9) is driven by a series of two idler gears (10) and (11). Idler gear (11) is driven by cluster gear (13). Cluster gear (13) is driven by crankshaft gear (14). Timing mark (12) and Timing mark (8) are aligned in order to provide the correct relationship between the piston and the valve movement.

The camshaft has three lobes for each cylinder. One lobe operates the inlet valves. A second lobe operates the exhaust valves. The third lobe operates the unit injector mechanism. The camshaft lobes actuate the rocker arms. Movement of the rocker arms will make the inlet and exhaust valve bridges move. These bridges allow one rocker arm to either open or either close two valves at the same time. Each cylinder has two inlet valves and two exhaust valves. Each valve has a valve spring (5). The spring closes the valve when the camshaft lobe is rotated past the rocker arm.

Rotocoils (4) cause the valves to rotate while the engine is running. Valve rotation provides a longer service life.

Adjustable idler gear (10) is designed to provide the required gear backlash between nonadjustable idler gear (11) and camshaft gear (9). If the cylinder head is removed, tolerances of the components will change. The adjustable idler gear must be relocated if the cylinder head and the head gasket are replaced. For information on setting the correct backlash, refer to Testing and Adjusting, "Gear Group (Front) - Time".

The camshaft drive gear has integral pendulums which act as a vibration damper for the front gear group. These pendulums are designed to counteract the torsional forces from the injector pulses. This eliminates vibration and noise. The engine also runs smoother at all operating speeds.