3BAB64524-0 Tohatsu PROPELLER (11.5), 3 X 9.25 X 11.5

Illustration 1 g02169274
Typical Example
Basic air inlet and exhaust system
(1) NOx reduction system (NRS) cooler
(2) Exhaust manifold
(3) Aftercooler
(4) Exhaust outlet
(5) Turbine wheel
(6) Compressor wheel
(7) Air inlet
(8) Inlet valves
(9) Exhaust valvesThe 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
DOC
NRS
Turbocharger
Aftercooler
Cylinder head
Valves and valve system components
Piston and cylinder
Inlet manifold
Exhaust manifoldNote: The following description of the operation of the air inlet and exhaust system assumes that the engine is developing boost pressure.Inlet air passes through the air cleaner into the air inlet of the turbocharger compressor (6). A turbocharger is used to increase the flow of air into the engine. This increase in air flow pressurizes the combustion air supply for the engine. The pressure that is placed on the inlet air allows a larger volume of air to be compressed into the cylinder. This compressing of the inlet air is referred to as engine boost.The compressing of air causes the air temperature to rise to about 204 °C (400 °F). As the air flows through the aftercooler the temperature of the compressed air is cooled to about 46 °C (115 °F). The aftercooler utilizes a heat exchanger to cool the inlet air. Cooling the inlet air causes the air to become more dense. Compressing and cooling the inlet air increases the combustion efficiency of the engine. This also increases the horsepower output of the engine .From the aftercooler, air enters the inlet manifold. Air flow from the inlet manifold to the cylinders is controlled by inlet valves (8). There are two inlet valves and two exhaust valves (9) for each cylinder. The inlet valves open at the top center position of the piston. When the inlet valves open, cooled compressed air enters the cylinder through the inlet ports. The inlet valves close as the piston reaches the bottom center position. This is called the inlet stroke of the engine. As the piston begins to travel back to the top center position on the compression stroke, the air in the cylinder is compressed to a high temperature. When the piston is near the end of the compression stroke, fuel is injected into the cylinder and mixes with the compressed air. This causes combustion to start in the cylinder. Once combustion starts, the combustion force pushes the piston toward the bottom center position. This is called the power stroke. The exhaust valves open when the piston moves toward the bottom center position and the exhaust gases are pushed through the exhaust port into exhaust manifold (2) as the piston travels toward top center on the exhaust stroke. The exhaust valves close and the cycle starts again. The complete cycle consists of four strokes:
Inlet
Compression
Power
ExhaustThe exhaust gases from the cylinder are forced into exhaust manifold (2). The flow of exhaust gases from the exhaust manifold enters the turbine side of the turbocharger. The flow of the exhaust gas and the heat of the exhaust gas causes the turbine wheel (5) to spin. The turbine wheel is connected to a shaft that drives the compressor wheel. Exhaust gases from the turbine wheel then exit the turbocharger.Turbocharger
Illustration 2 g02137980
Water-cooled turbocharger
(10) Compressor inlet
(11) Compressor housing
(12) Compressor wheel
(13) Shaft bearing
(14) Oil Inlet port
(15) Shaft bearing
(16) Turbine housing
(17) Small scroll
(18) Exhaust balance valve chamber
(19) Large scroll
(20) Turbine wheel
(21) Turbine outlet
(22) Oil outlet portAll the air that enters the engine passes through the turbochargers compressor. All the exhaust gases from the engine pass through the turbochargers turbine.The exhaust gas enters the turbocharger through the turbine inlet. The flow of the exhaust gas pushes the blades of the turbine wheel (20) and exits through the turbine outlet (21). The turbine housing is asymmetrical in design. This design allows the heat energy from two different volumes of exhaust gas that are from the forward exhaust manifold and the rear exhaust manifold to be used efficiently by the turbocharger.The exhaust balance valve is controlled by the exhaust balance valve solenoid. The solenoid for the exhaust balance valve is electronically controlled by the Electronic Control Module (ECM). When the balance valve is in the open position, the velocity of the exhaust gas in the small scroll is decreased. This equalizes the pressures on the vanes of the turbocharger, and prevents overspeed of the turbocharger. When the exhaust balance valve is in the closed position, the pressure in the two scrolls is unequal. This is due to a higher backpressure in the smaller scroll and a lower backpressure in the larger scroll. The turbine wheel is connected by a shaft to compressor wheel (12).As the compressor wheel rotates, a vacuum is created in the turbochargers compressor housing (11). Air is pulled through the air filters into the compressor housing through the compressor inlet (10). Impeller vanes are manufactured into the compressor wheel. The vanes are used to compress the incoming air. The compressed air is directed to the compressor outlet of the turbocharger into the inlet piping. The air is then directed toward the inlet side of the engine. Boost pressure is created as the flow that is developed by the compressor wheel exceeds the needs of the engine. This results in a positive inlet manifold pressure that exceeds atmospheric pressure. The increased pressure allows the engine to burn more fuel during fuel combustion. Through optimum fuel efficiency, this strategy allows the engine to produce more power and lower emission levels.When the throttle is opened, more fuel is injected into the cylinders. The combustion of this additional fuel produces an increased flow of exhaust and greater exhaust temperature. The additional flow and the increased temperature of the exhaust causes the turbine and the compressor wheels of the turbocharger to turn faster. As the compressor wheel turns faster, air flow into the air inlet system creates an increase in the pressure that is in the inlet manifold. This increased air pressure allows the engine to burn additional fuel with greater efficiency.Valve System Components
Illustration