 | |
| Illustration 1 | g01356032 |
Air inlet and exhaust system (1) Exhaust manifold (2) Injector (3) Glow plug (4) Intake manifold (5) Aftercooler core (if equipped) (6) Exhaust outlet (7) Turbine side of turbocharger (8) Compressor side of turbocharger (9) Air intake from the air cleaner (10) Inlet valve (11) Engine cylinder (12) Exhaust valve | |
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 air inlet and exhaust system consists of the following components:
- Air cleaner
- Turbocharger
- Aftercooler (if equipped)
- Inlet manifold
- Cylinder head, injectors, and glow plugs
- Valves and valve system components
- Piston and cylinder
- Exhaust manifold
A turbocharger increases the temperature and the density of the air that is sent to the engine cylinder. This condition causes a lower temperature of ignition to develop earlier in the compression stroke. The compression stroke is also timed in a more accurate way with the fuel injection. Surplus air lowers the temperature of combustion. This surplus air also provides internal cooling.
Air is drawn in through the air cleaner into the air intake of the turbocharger (9) by the turbocharger compressor wheel (8). The air is compressed and heated to about 150 °C (300 °F) before the air is forced to the aftercooler (5). As the air flows through the aftercooler the temperature of the compressed air lowers to about 50 °C (120 °F). Cooling of the intake air increases combustion efficiency. Increased combustion efficiency helps achieve the following benefits:
- Lower fuel consumption
- Increased horsepower output
- Increased engine torque
- Increased durability of the engine
- Reduced particulate emission
From the aftercooler, air is forced into the intake manifold (4). Air flow from the intake manifold to the cylinders is controlled by inlet valves (10). There is one inlet valve and one exhaust valve 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 intake port is forced into the cylinder. The complete cycle consists of four strokes:
- Induction
- Compression
- Power
- Exhaust
On the compression stroke, the piston moves back up the cylinder and the inlet valve (10) closes. The cool compressed air is compressed further. This additional compression generates more heat.
Note: If the cold starting system is operating, the glow plugs (3) will also heat the air in the cylinder.
Just before the piston reaches the Top Center (TC) position, fuel is injected into the cylinder. The air/fuel mixture ignites. The ignition of the gases initiates the power stroke. Both the inlet and the exhaust valves are closed and the expanding gases force the piston downward toward the Bottom Center (BC) position .
From the BC position, the piston moves upward. This initiates the exhaust stroke. The exhaust valve (12) opens. The exhaust gases are forced through the open exhaust valve into the exhaust manifold (1) .
Exhaust gases from exhaust manifold (1) enter the turbine side (7) of the turbocharger in order to turn turbocharger turbine wheel. The turbine wheel is connected to the shaft that drives the compressor wheel. Exhaust gases from the turbocharger pass through exhaust outlet (6), a silencer, and an exhaust pipe.
Turbocharger
 | |
| Illustration 2 | g00302786 |
Typical example of a cross section of a turbocharger (1) Air intake (2) Compressor housing (3) Compressor wheel (4) Bearing (5) Oil inlet port (6) Bearing (7) Turbine housing (8) Turbine wheel (9) Exhaust outlet (10) Oil outlet port (11) Exhaust inlet | |
The high-pressure turbocharger is mounted on the outlet of the exhaust manifold. The low-pressure turbocharger is mounted on the side of the cylinder block. The exhaust gas from the exhaust manifold enters the exhaust inlet (11) and passes through the turbine housing (7) of the turbocharger. Energy from the exhaust gas causes the turbine wheel (8) to rotate. The turbine wheel is connected by a shaft to the compressor wheel (3) .
As the turbine wheel rotates, the compressor wheel is rotated. The rotation of the compressor wheel causes the intake air to be pressurized through the compressor housing (2) of the turbocharger.
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, air is compressed to a higher pressure and more air is forced into the cylinders. The increased flow of air into the cylinders allows the fuel to be burnt with greater efficiency. This produces more power.
The shaft that connects the turbine to the compressor wheel rotates in bearings (4) and (6). The bearings require oil under pressure for lubrication and cooling. The oil that flows to the lubricating oil inlet port (5) passes through the center of the turbocharger which retains the bearings. The oil exits the turbocharger from the lubricating oil outlet port (10) and returns to the oil pan.
Crankcase Breather
The engine crankcase breather is a filtered system. The crankcase breather system consists of two main elements, a primary separator in the valve mechanism cover and a filtered canister that is mounted on the cylinder head. The gases exit the engine through the valve mechanism cover. The gases then pass through the primary separator. The primary separator removes most of the liquid oil from the gas. The liquid oil is then returned to the engine.
The gas then passes through the filter element before exiting to atmosphere in an open breather system or back to the induction system in a closed breather system via the breather vent pipe.
Any liquid oil that is captured by the filter drains from the bottom of the canister. The liquid oil is returned by the drain pipe that runs from the bottom of the canister back to the crankcase. A valve connects the drain pipe to the crankcase. This valve prevents the bypass of gas past the filter and oil from passing up the drain pipe.
A pressure relief valve is located in the rear of the canister in the integral mounting bracket. Under normal operation of the engine, this valve will not operate. If part of the system becomes blocked the valve will open at a pressure of 8.5 kPa (1.2 psi). The open valve will allow gas to bypass the filter and the pipes for venting.
The filter element can be accessed from either the top of the canister by removing the top cap or from the bottom of the canister by removing the bottom cap. Refer to Operation and Maintenance Manual, "Engine Crankcase Breather Element - Replace" for the correct procedure.
| NOTICE |
|---|
The crankcase breather gases are part of the engines measured emissions output. Any tampering with the breather system could invalidate the engines emissions compliance. |
Valve System Components
 | |
| Illustration 3 | g01924293 |
Valve system components (1) Bridge (2) Rocker arm (3) Pushrod (4) Hydraulic lifter (5) Camshaft (6) Spring (7) Valve | |
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 (5) must be timed to the crankshaft in order to get the correct relation between the piston movement and the valve movement.
The camshaft (5) has two camshaft lobes for each cylinder. The lobes operate either a pair of inlet valves or a pair of exhaust valves. As the camshaft turns, lobes on the camshaft cause the lifter (4) to move the pushrod (3) up and down.
The lifter (4) incorporates a hydraulic lash adjuster which removes valve lash from the valve mechanism. The lifter (4) uses engine lubricating oil to compensate for wear of system components so that no service adjustment of valve lash is needed.
The engine lubricating oil enters the lifter (4) through a non-return valve. The engine lubricating oil increases the length of the lifter (4) until all valve lash is removed. If the engine is stationary for a prolonged period the valve springs will cause the lifter (4) to shorten so that when the engine is started engine valve lash is present for the first few seconds.
After cranking restores oil pressure the lifter (4) increases in length and removes the valve lash. When load is removed from a lifter (4) during service work by the removal of the rocker shaft the lifter (4) increases in length to the maximum extent. Refer to Systems Operation, Testing and Adjusting, "Position the Valve Mechanism Before Maintenance Procedures" for the correct procedure.
During reassembly of the rocker shaft the engine must be put into a safe position to avoid engine damage. After load is imposed on the lifters by reassembling the rocker assembly, the engine must be left in safe position for a safe period until the lifters have reduced to the correct length. Refer to Disassembly and Assembly, "Rocker Shaft and Pushrod - Install" for the correct procedure.
Upward movement of the pushrod against rocker arm (2) results in a downward movement that acts on the valve bridge (1). This action opens a pair of valves (7) which compresses the valve springs (6). When the camshaft (5) has rotated to the peak of the lobe, the valves are fully open. When the camshaft (5) rotates further, the two valve springs (6) under compression start to expand. The valve stems are under tension of the springs. The stems are pushed upward in order to maintain contact with the valve bridge (1). The continued rotation of the camshaft causes the rocker arm (2), the pushrods (3) and the lifters (4) to move downward until the lifter reaches the bottom of the lobe. The valves (7) are now closed. The cycle is repeated for all the valves on each cylinder.