There are three types of fuel injection pumps: in-line, distributed and unitary. No matter what type, the key of fuel injection pump is the word "pump". The quantity, pressure and time of pumping oil should be very accurate and automatically adjusted according to the load. The fuel injection pump is a component with fine processing and complicated manufacturing process. At present, the fuel injection pumps of GM diesel engines at home and abroad are produced by a few professional factories in the world.
Each plunger system of in-line fuel injection pump corresponds to one cylinder, and four cylinders have four plunger systems, so it is relatively large in size and is mostly used for medium-sized and above cars. For example, diesel engines on buses and trucks usually use in-line fuel injection pumps.
* The key part of the fuel injection pump is the plunger. If we compare the common syringes in hospitals, then the movable plug is called plunger, and the syringe is called plunger sleeve. Suppose the spring is installed in the needle guide tube, leaning against one end of the plunger, and the other end of the plunger contacts the camshaft. When the camshaft rotates once, the plunger will move up and down in the plunger sleeve. This is the basic movement mode of fuel injection pump plunger.
Fuel injection pumps on diesel engines of cars and light vehicles are generally distributed, which have the advantages of small volume, light weight, few parts and simple structure. It adopts two groups of plunger systems (or one group of plunger systems) to pressurize, and the diesel oil is sent to each nozzle respectively.
Its basic working principle is that two groups of opposite plungers are installed on the impeller in the pump. When the impeller is driven by the engine to rotate, the plunger also rotates. Because the convex part of the cam ring presses the plunger, the plunger acts as a pump to send diesel oil to the oil delivery hole in the center of the impeller. At this time, the delivered diesel oil fills the inlet of the distributor, and then is injected in the order of each cylinder.
Because the working revolutions of two plunger systems (or one plunger system) increase in proportion to the number of cylinders, this fuel injection pump is limited by the number of cylinders and the maximum speed.
That is, the diesel engine generates high-pressure fuel through the distribution pump (the oil pressure of the high-pressure fuel generated by the distribution pump is much lower than that in the * * rail diesel engine), and the fuel is injected into the cylinder of the diesel engine through the oil nozzle. A diesel engine can only have one distribution pump, because the diesel engine is in-cylinder direct injection.
With the development of diesel engine technology, a new type of single fuel injection pump (called single pump or pump nozzle) appears, which actually decomposes the above two fuel injection pumps into parts, and the fuel injection of each cylinder of the engine is completed by its own independent injection unit (single pump or pump nozzle).
For the unit pump, the fuel injection pump and the fuel injection nozzle are connected through a short high-pressure oil pipe, while for the pump nozzle, the fuel injection pump and the fuel injection nozzle are combined into one, directly installed on the cylinder head of the diesel engine and driven by the overhead camshaft. Their greatest advantage is that they can reduce or eliminate the influence of pressure waves formed in high-pressure oil pipes during diesel oil flow and injection. Because this kind of pressure wave will hinder the good matching of fuel injection system with load and speed, and it will increase with the length of high pressure pipe.
Therefore, shortening the length of the high-pressure oil pipe (the design idea of the fuel injection pump) or not using the high-pressure oil pipe at all (the design idea of the fuel injection nozzle) and reducing the high-pressure volume between the plunger and the fuel injection nozzle can obtain the oil supply law close to the cam profile. Pump nozzles, in particular, have been used in general motors as early as ten years ago, and now they are precisely controlled by electronic technology to improve their performance.
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Commonly used diesel engine mechanical fuel injection pumps are: A-type pump, B-type pump, P-type pump, VE-type pump, etc. The first three types are piston pumps; VE pump is a distributed rotor pump.
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4D56 and 4M40 adopt distributed pump diesel engines, that is to say, the fuel supply system of this diesel engine adopts distributed fuel injection pump.
That is, the diesel engine generates high-pressure fuel through the distribution pump (the oil pressure of the high-pressure fuel generated by the distribution pump is much lower than that in the * * rail diesel engine), and the fuel is injected into the cylinder of the diesel engine through the oil nozzle. A diesel engine can only have one distribution pump, because the diesel engine is in-cylinder direct injection.
A diesel engine with * * * rail system for fuel injection system is called * * * rail diesel engine.
The so-called * * rail system is composed of high-pressure * * rail (used for storing high-pressure diesel oil, on which components such as pressure sensor, pressure fluctuation regulator and fuel injector are installed) and high-pressure pump (high-pressure generator). * * * rail system generates enough high-pressure fuel, so that the fluctuation of fuel pressure in * * * rail can be controlled. ECU determines the fuel quantity to be injected into the cylinder according to the fuel pressure of * * * rail and engine working conditions, and the fuel injector (ECU controls the opening and closing of the fuel injector) injects an appropriate amount of diesel into the cylinder.
For the second generation electronic fuel injection system, according to the different high-pressure generating devices, the fuel injection system can be divided into distribution pump, in-line pump, nozzle and unit pump electronic fuel injection system. In other words, the unit pump is used to generate the injection pressure of the injector (or injector). For engines with electronically controlled fuel injection system with unit pumps, each cylinder has several unit pumps.
To sum up, we can draw the difference between them: the unit pump is only a high-pressure generator in the second generation electronic fuel injection system, and it has several cylinders, so it needs several unit pumps; Electronically controlled common rail is the third generation of electronically controlled fuel injection system, its performance is better than the second generation, and it is the mainstream of the development of electronically controlled fuel injection system.
PS:* * * The maximum pressure in the rail can reach 150Mpa. Because of the large volume of the rail and the pressure fluctuation regulator, the pressure in the rail is basically constant during the operation of the engine, which can meet the fuel injection requirements of the engine at any time. The pressure produced by the monomer pump is lower than that of the high-pressure pump, generally around 100Mpa, and the amount of high-pressure fuel produced by the monomer pump is limited.