SHAFT 1M3917 - Caterpillar

Illustration 1 g03793924
(1) Exhaust manifold
(2) Aftercooler
(3) Air choke
(4) Exhaust inlet to the turbocharger
(5) Exhaust bypass (wastegate)
(6) Turbocharger turbine wheel
(7) Turbocharger compressor wheel
(8) Air inlet
(9) Cylinder Clean inlet air from the air cleaners is drawn through air inlet (8) into the turbocharger compressor by compressor wheel (7). The air is compressed and the air is forced through air choke (3). The air flows through aftercooler (2). The aftercooler reduces the temperature of the compressed air before the air enters the air plenum. The air enters the air inlets in the cylinder heads.Air flow into cylinder (9) is controlled by the inlet valves. The camshaft controls the opening of the valves. There are two inlet valves, two exhaust valves, and one gas admission valve for each cylinder. The inlet valves and the gas admission valve open when the piston moves down on the intake stroke. The air/fuel mixture is pulled into the cylinder through the inlet port. For more information, refer to Systems Operation, "Valve Mechanism".The gas admission valve and the inlet valves close and the piston starts to move up on the compression stroke. When the piston is near the top of the compression stroke, the leaner air/fuel mixture in the cylinder is mixed with the richer air/fuel mixture in the precombustion chamber. The combustible mixture in the precombustion chamber is ignited by the spark plug. This ignites the air and fuel in the cylinder.The force of the combustion pushes down on the piston for the power stroke. The piston moves up again on the exhaust stroke. The exhaust valves open and the piston pushes exhaust gases through the exhaust port into exhaust manifold (1). After the exhaust stroke, the exhaust valves close. The four stroke cycle continues: intake, compression, power and exhaust.Exhaust gas from exhaust manifold (1) is directed through exhaust inlet (4) to the turbocharger. The exhaust gas turns turbocharger turbine wheel (6). The turbine wheel is connected to the shaft that drives the compressor wheel.If too much compressed air is supplied by the turbocharger, exhaust gas can be diverted directly to the exhaust elbow by exhaust bypass (wastegate) (5). This depends on the requirements for inlet manifold air pressure.An electrohydraulic actuator controls the position of the exhaust bypass (wastegate) (5). The actuator provides the desired inlet manifold air pressure. The position of the actuator is determined by the Electronic Control Module (ECM).