3116 Truck Engine Caterpillar

Illustration 1	g00692826
Air inlet and exhaust system schematic (1) Aftercooler (aftercooled engines) (2) Air inlet manifold (3) Exhaust manifold (4) Exhaust outlet (5) Turbocharger (6) Air inlet (7) Air cleaner

The components of the air inlet and exhaust system control the quality of the air that is available for combustion. These components also control the amount of the air that is available for combustion. The components of the air inlet and exhaust system are listed below:

• Air cleaner

• Turbocharger

• Aftercooler (aftercooled engines)

• Cylinder head

• Valves and valve system components

• Piston and cylinder

• Exhaust manifold

Illustration 2	g00693191
Air inlet and exhaust system (1) Aftercooler (aftercooled engines) (3) Exhaust manifold (4) Exhaust outlet (6) Air inlet (8) Exhaust valve (9) Inlet valve (10) Compressor wheel (11) Turbine wheel

Inlet air is pulled through air cleaner (7). The inlet air is then compressed and heated by the compressor wheel of turbocharger (5) to about 150°C (300°F). The inlet air is then pushed through one of the following components: air-to-air aftercooled (ATAAC) and air inlet cover. The inlet air is forced to air inlet manifold (2). The temperature of the inlet air at the air inlet manifold is about 43°C (110°F). Cooling of the inlet air increases the combustion efficiency. Increased combustion efficiency helps to lower fuel consumption. Also, increased combustion efficiency helps to increase horsepower output.

The air to air aftercooled (ATAAC) system incorporates a separate air to air aftercooler core. This core is installed in front of the radiator of the engine or the core is installed beside the radiator of the engine. Air that is ambient temperature is moved across the aftercooler core by the engine fan and by the ram effect of the vehicle's forward motion. This cools the turbocharged inlet air.

Inlet manifold (2) is a one-piece casting that also serves as a base for the valve cover. From the inlet manifold, 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.

There is one inlet valve (9) and one exhaust valve (8) for each cylinder. The inlet valve opens when the piston moves down on the inlet stroke. When the inlet valve opens, cooled compressed air from the inlet port is pulled into the cylinder. The inlet valve closes 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 valve opens, and the exhaust gases are pushed through the exhaust port into exhaust manifold (3). After the piston completes the exhaust stroke, the exhaust valve closes and the cycle starts again. The complete cycle consists of four stages:

• Inlet stroke

• Compression stroke

• Power stroke

• Exhaust stroke

Exhaust gases from exhaust manifold (3) enter turbine side of turbocharger (5) in order to turn the turbine wheel (11). The turbine wheel is connected to a shaft which drives the compressor wheel (10). Exhaust gases from the turbocharger pass through the exhaust outlet pipe and the muffler.

Catalytic Converter/Muffler

A catalytic converter may be necessary for some engine models to meet EPA regulations. A catalytic converter is a device that is located in the exhaust stream of an engine. The catalytic converter promotes a chemical reaction in order to reduce emissions. This device is commonly called a converter. The Caterpillar catalytic converter/muffler is combined into a single unit for easier installation and less total system back pressure.

Turbocharger

Illustration 3	g00294193
Turbocharger (1) Air inlet (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 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 go into turbine housing (7) through exhaust inlet (11). The exhaust gases then push the blades of turbine wheel (8). The turbine wheel is connected by a shaft to compressor wheel (3) .

Clean air from the air cleaners is pulled through compressor housing air inlet (1) by the rotation of compressor wheel (3). 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.

Illustration 4	g00425163
Turbocharger with waste gate (12) Actuating lever (13) Canister (14) Line (boost pressure)

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

As the boost pressure through line (14) increases against the diaphragm in canister (13), the valve of the waste gate is opened. When the valve of the waste gate is opened, the rpm of the turbocharger is limited by bypassing a portion of the exhaust gases. The exhaust gases are routed through the waste gate which bypasses the turbine wheel of the turbocharger.

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

Illustration 5	g00693226
Turbocharger oil lines (15) Oil supply tube (16) Oil drain tube

Bearings (4) and (6) for the turbocharger use engine oil under pressure for lubrication. The oil comes in through oil supply tube (15) to oil inlet port (5). 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 (10) in the bottom of the center section. The oil then goes back to the engine lubrication system through oil drain tube (16).

Valve System Components

Illustration 6	g00425278
Valve system components (1) Rocker arm (2) Spring (3) Valve (4) Pushrod (5) Lifter (6) Camshaft lobe

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 three camshaft lobes for each cylinder. The lobes operate the following components: the inlet valves, the exhaust valves and the mechanical unit injector (MUI). As the camshaft turns, lobes on the camshaft cause lifters (5) to move pushrods (4) up and down. Upward movement of the pushrods against rocker arms (1) results in downward movement (opening) of valves (3) .

Each cylinder has one inlet valve and one exhaust valve. Valve springs (2) close the valves when the lifters move down.

Air Inlet Heater (If Equipped)

The engines may be equipped with an electric heater that is located at the air inlet manifold. The electric heater has two functions:

• Aid in starting

• Aid in white smoke cleanup during start-up

Under the proper conditions, an Electronic Control will turn on the system for the electric heater (if equipped). The following conditions are evaluated prior to activating the electric heater:

• Jacket water coolant temperature

• Oil pressure

• Ignition switch position

• Duration of time

Some of the air inlet heaters will have manual controls, while other air inlet heaters will have automatic controls. The system is capable of delivering heat for 30 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 several minutes. This will depend on the control system that is used.

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.

Typical System Components

Illustration 7	g00835479
(1) Inlet manifold (2) Heater element (3) Ground strap

Lamp Test

The heater element comes on for two seconds when the ignition switch is turned to the RUN position. The indicator lamp in the instrument panel should illuminate at that time. Failure of the lamp to illuminate indicates a system malfunction.

Note: If the coolant temperature is below the lower limit of the temperature switch, the system should go directly from the lamp test into the preheat cycle. The light will not turn off.

Preheat Cycle

Three conditions must exist before the air inlet heater will operate in the preheat cycle:

• The ignition switch must be in the RUN position.

• The coolant temperature is below the lower limit of the coolant temperature switch.

• The air inlet heater has not timed out for 30 seconds in the preheat cycle.

There are three ways to end the preheat cycle:

• The ignition switch is turned to the START position.

• The ignition switch is turned to the OFF position.

• The system reaches the 30 second time limit.

Crank Heat Cycle

Three conditions must exist before the air inlet heater will operate in the crank heat cycle:

• The ignition switch must be in the START position.

• The coolant temperature is below the lower limit of the coolant temperature switch.

• The air inlet heater has not timed out for 30 seconds in the preheat cycle. The 60 second timer starts when the ignition switch is turned to the START position. The 60 second timer will continue if the engine has not started and the ignition is in the RUN position. The 60 second timer is continually reset if the ignition remains in the START position.

There are three ways to end the crank heat cycle:

• The ignition switch is turned to the OFF position.

• The engine starts.

• The system reaches the 60 second time limit with the ignition in the RUN position and the engine is not running. The crank heat cycle will resume when the ignition is returned to the START position.

Regular Heat Cycle

Four conditions must exist before the air inlet heater will operate in the regular heat cycle:

• The ignition switch must be in the RUN position.

• The coolant temperature is below the upper limit of the coolant temperature switch.

• The engine oil pressure is above 240 ± 70 kPa (35 ± 10 psi).

• The air inlet heater has not timed out for seven minutes in the regular heat cycle.

There are four ways to end the regular heat cycle:

• The ignition switch is turned to the OFF position.

• The engine stalls.

• The coolant temperature exceeds the upper limit of the coolant temperature switch.

• The system reaches the seven minute time limit.

Illustration 8	g00837775
Typical system schematic

Illustration 9	g00837778
Flow chart of controller of air inlet heater

Note: There is an optional 7E-9425 Temperature Switch for parts service. The 7E-9425 Temperature Switch will open with ascending temperatures at 48 °C (120 °F) and the switch will close with descending temperatures at 35 °C (95 °F).

Note: There is an optional 4P-6602 Control Module for parts service. The 4P-6602 Control Module has the same functions as the standard control module except that the 4P-6602 Control Module remains ON for ten minutes. In the ten minute cycling, the heater is turned ON for ten seconds and the heater is turned OFF for ten seconds during the regular heat cycle.

Ether Starting Aid

Illustration 10	g00694343
Location of atomizer (1) Air inlet manifold (2) Atomizer (3) Air inlet elbow

Ether can be used in cold weather to aid in the startability of the engine. Ether is injected into the center port of the air inlet manifold (1). If the atomizer is not installed correctly, ether could be directed onto the air inlet heater. Possible extensive damage could occur to the engine, if the ether is directed at the heater element and the air inlet heater is activated.