Analysis and discussion on technical problems of marine engineering training report

Through two weeks of engine disassembly practice, my theoretical knowledge has been sublimated, which makes me have a general understanding of the overall layout of the engine, the appearance and relative position of each component, and the assembly and operation between them.

The outer surface of the engine is equipped with a generator, and the generator has a gear meshing with the flywheel; The starter is used to start the operation of the engine; The distributor and high voltage coil are used to increase the voltage and distribute the ignition sequence of each cylinder; A device for ignition; There are intake manifold and intake branch pipes, some of which are cast as a whole, and some of which are riveted together with rivets. Their upper source has an air filter to filter the air entering the engine, and a sensor is installed at the throttle position to detect the air volume. The intake manifold and the opposite side of the intake manifold are provided with an exhaust manifold and an exhaust manifold, which are used for discharging waste gas generated in the combustion process of the engine; Modern engines usually install a three-way catalytic converter here to detect the content of harmful gases in the exhaust gas, so as to feedback and adjust the intake and injection quantity to ensure that the exhaust gas meets the requirements of environmental protection regulations; Oil inlet pipe and oil return pipe should also be installed; Because the engine injects the combustible mixture into the cylinder, the air and gasoline should be fully mixed in the intake pipe. There are two ways of fuel injection: one is single-point fuel injection and the other is multi-point fuel injection. Single-point injection injectors are located in the intake manifold and then enter the cylinders at the branch pipes assigned to each intake. The multi-point injection injector is located at each intake branch pipe and directly enters the cylinder after mixing with the intake branch pipe; The starting side is also provided with a water inlet pipe and a water outlet pipe, which cool the high-speed running engine through water flow and provide a good working environment for the engine; Generally, there is also a sensor to detect the water temperature, which is used to feed back the working condition of the engine.

The external devices of the engine have been basically introduced. Let's talk about the assembly relationship and operation of the internal parts of the engine.

When you take off the top cover, the first thing you see is the rocker arm and the rocker shaft. The rocker arm is fixed on the rocker shaft and can swing up and down. Adjusting the nut at the top can change the swing amplitude, and adjusting the opening of the valve can adjust the intake/exhaust volume. In modern automobile engines, overhead valves are mostly used. According to the position of camshaft, valves can be divided into three types: lower camshaft, middle camshaft and upper camshaft. The lower camshaft valve is far away from the camshaft, so the valve transmission parts are more complicated and the height of the engine is also increased. The middle camshaft is located in the middle of the cylinder block, and the rocker arm is directly driven by the camshaft through the tappet, thus eliminating the push rod. The upper camshaft is arranged on the cylinder head. The upper camshaft has two central structures: one is that the camshaft directly drives the valve through the rocker arm, so there is no tappet or push rod. The reciprocating motion quality is greatly reduced, and this structure is suitable for high-speed engines. The other structure is that the camshaft directly drives the valve or the hydraulic prop drives the valve. This valve train has less reciprocating mass and is especially suitable for high-speed engines. Remove the cylinder head and turn the cylinder head upside down, you can clearly see the valve and the combustion chamber, in which the valve has one big and one small, the big one is intake and the small one is exhaust. The rest of the engine is reversed. There is an oil drain bolt at the lower end of the oil pan. Before disassembling the engine, it should be unscrewed to let all the internal oil flow out. After the vehicle travels a certain distance, the engine oil should be changed regularly to ensure good engine lubrication. When removing the oil pan, you can see the oil filter, remove the oil filter and oil pump, unscrew the bolt on the crankshaft bearing cover and then remove the bearing cover. Bearing cover and inner bearing bush should be marked, corresponding to bearings one by one. After removing the piston bolt fixed on the crankshaft, you can lift the crankshaft and then remove the piston. The removed pistons should also be marked, corresponding to each cylinder, so that the engine can be removed.