There are intake and exhaust passages in the cylinder head, and inlet and exhaust valves are installed inside. Fresh charge (ie air or a combustible mixture of air and fuel) is charged into the cylinder via air cleaners, intake manifolds, intake ports and intake valves. The expanded gas passes through the exhaust valve, the exhaust passage and the exhaust pipe, and is finally discharged into the atmosphere through the exhaust muffler. The opening and closing of the intake and exhaust valves are controlled by the intake and exhaust cams on the camshaft, respectively, through the transmission members such as the tappet, the push rod, the rocker arm and the valve spring. This set of parts is called the internal combustion engine. Gas mechanism. The intake and exhaust systems are usually composed of an air cleaner, an intake pipe, an exhaust pipe, and an exhaust muffler.
In order to supply fuel into the cylinder, the internal combustion engine is provided with an oil supply system. The gasoline engine mixes air and gasoline in a certain ratio (air-fuel ratio) through a carburetor installed at the inlet end of the intake pipe, and then supplies it to the cylinder through the intake pipe, and is ignited by the spark timing controlled by the gasoline engine ignition system. The fuel of the diesel engine is injected into the combustion chamber through the diesel fuel injection system, and it is fired by itself under high temperature and high pressure.
The combustion of the fuel in the cylinder of the internal combustion engine heats the piston, cylinder liner, cylinder head and valve and the like, and the temperature rises. In order to ensure the normal operation of the internal combustion engine, the above parts must be operated at a permissible temperature without damage due to overheating, so a cooling system must be available.
The internal combustion engine cannot be turned into the operating state from the parking state, and the crankshaft must be turned by an external force to start it. This device that generates an external force is called a starting device. Commonly used are electric start, compressed air start, gasoline engine start and manual start.
The working cycle of an internal combustion engine consists of processes such as intake, compression, combustion and expansion, and exhaust. In these processes, only the expansion process is a process of external work, and other processes are processes required to better achieve the work process. According to the number of strokes that realize one working cycle, the working cycle can be divided into four strokes and two strokes.
Four-stroke refers to completing one working cycle in four strokes of intake, compression, work (expansion) and exhaust, during which the crankshaft rotates two times. During the intake stroke, the intake valve is opened and the exhaust valve is closed. The air flowing through the air filter or the combustible mixture formed by the mixture of the carburetor and the gasoline enters the cylinder through the intake pipe and the intake valve; when the compression stroke is performed, the gas in the cylinder is compressed, the pressure is increased, and the temperature rises; The expansion stroke is to inject oil or ignite before the compression top dead center, so that the mixture gas is burned, and the high temperature and high pressure are generated to push the piston down and work; when the exhaust stroke is performed, the piston pushes the exhaust gas in the cylinder through the exhaust valve. Thereafter, the intake stroke begins and the next duty cycle is performed.
Two-stroke refers to completing one working cycle in two strokes during which the crankshaft rotates one revolution. First, when the piston is at the bottom dead center, the inlet and exhaust ports are opened, the fresh charge is charged into the cylinder by the air inlet, and the exhaust gas in the cylinder is swept out to be discharged from the exhaust port; then the piston is ascending, and will enter, The exhaust port is closed, and the charge in the cylinder begins to be compressed until the piston approaches the top dead center to ignite or inject fuel, so that the combustible mixture in the cylinder burns; then the gas in the cylinder expands, pushing the piston down to do work; when the piston is under the row When the port is opened, the exhaust gas is discharged therefrom, and the piston continues to descend to the bottom dead center, that is, a working cycle is completed.
The exhaust process and the intake process of the internal combustion engine are collectively referred to as a ventilation process. The main function of the ventilation is to remove the exhaust gas from the previous cycle as much as possible, so that the cycle can supply as much fresh charge as possible, so that as much fuel as possible can be completely burned in the cylinder, thereby emitting more power. The quality of the ventilation process directly affects the performance of the internal combustion engine. To this end, in addition to reducing the flow resistance of the intake and exhaust systems, it is mainly to open and close the intake and exhaust valves at the most appropriate time.
In fact, the intake valve is opened before the top dead center to ensure that the intake valve has a large opening when the piston descends, which can reduce the flow resistance at the beginning of the intake process and reduce the work consumed by the intake. At the same time, it can also be filled with more fresh charge. When the piston runs to the bottom dead center during the intake stroke, the fresh charge can continue to be charged into the cylinder due to the inertia of the air flow, so that the intake valve is delayed to close after the bottom dead center.
The exhaust valve is also opened ahead of the bottom dead center, that is, the exhaust is started after the expansion stroke, in order to utilize the higher gas pressure in the cylinder to automatically exhaust the exhaust gas out of the cylinder, thereby causing the piston to stop from the bottom dead center. The gas pressure in the cylinder is lower during exercise to reduce the work consumed by the piston to exhaust the exhaust gas into the cylinder. The purpose of closing the exhaust valve after top dead center is to utilize the inertia of the exhaust gas flow to eliminate residual exhaust gas in the cylinder.
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