Fuel injection pump is the diesel fuel supply system, the most important piece, its performance and quality of diesel great influence, known as the "heart" of the diesel engine. Its main function: to raise the diesel pressure, in accordance with the engine's work order, load size, timing and quantitative delivery of high-pressure diesel fuel injector, and the cylinder oil pressure equal. Requirements: (1) pump pressure to ensure injection pressure and atomization quality, (2) fuel supply should be consistent with the exact number of diesel engine work required, (3) to ensure that the work order by the diesel engine, within the specified time Accurate fuel supply, (4) fuel supply and fuel supply time can be adjusted, and ensure uniform fuel supply to each cylinder, (5) the law of fuel supply should ensure complete combustion of diesel, (6) start and end of fuel supply, agile, Off the oil simply to avoid dripping. Its main types: Automotive diesel injection pump according to their different working principle can be divided into plunger-type injection pump, fuel injection pump - injector and rotor dispensing pump three categories. Piston pump pump mechanism includes: Plunger and plunger sleeve is a pair of precision couplings, can not be interchanged after paired grinding, requiring high precision and finish and good wear resistance, the radial clearance of 0.002 ~ 0.003mm. The plunger head cylindrical surface cut with a chute, and through the radial hole, the axial hole and the top of the same, the purpose is to change the circulation of fuel supply; plunger sleeve system has into and back to the oil hole, both with the pump Low-pressure oil chamber connected to the body, the plunger set into the pump body, the positioning screw positioning. Plunger head chute location, change the amount of fuel supply is also different. Outlet valve and the valve seat is also a pair of precision couplings, can not be swapped after grinding, with the gap of 0.01. Outlet valve is a one-way valve, under the action of spring pressure, the upper conical surface of the valve is tightly matched with the valve seat. Its function is to cut off the high pressure oil pipe from the upper cavity of the plunger to prevent the oil in the high pressure pipe Inverted into the injection pump. The lower part of the oil valve is cross-section, both to guide, but also through the diesel. Under the conical surface of the valve, there is a small cylindrical surface, called the vacuum ring, whose function is to quickly reduce the pressure of oil in the high-pressure tubing when the fuel supply ends, so as to avoid dripping oil at the orifice. When the ring falls into the valve seat, the upper volume increases rapidly, the pressure decreases rapidly, and the injection is stopped rapidly. The main working principle of pump oil: (1) work, under the action of the cam and plunger spring on the camshaft of the injection pump, forcing the plunger to reciprocate up and down to complete the pump oil task, the pump oil process can be divided For the following three stages. (2) into the oil process: When the convex portion of the cam turn, under the action of the spring force, the plunger moves downward, the upper space of the plunger (called pump oil chamber) to produce a vacuum, when the plunger upper end surface The plunger sleeve into the oil hole is opened, filled with oil in the upper body of the oil passage through the oil hole into the pump chamber, the piston moves to the bottom dead center, into the oil end. (3) oil supply process: When the cam shaft to the raised part of the cam top wheel body, the plunger spring is compressed, the plunger upward movement, the fuel pressure, part of the fuel flow through the hole back to the injection pump body oil Cavity. When the plunger top cover the upper edge of the sleeve into the oil hole, due to the small clearance between the plunger and sleeve (0.0015-0.0025mm) so that the top of the plunger pump chamber becomes a sealed oil chamber, the plunger Continue to rise, the pump oil chamber pressure rapidly increased, pump oil pressure> spring force of the valve + high pressure tubing remaining pressure, open the valve, high pressure diesel oil into the high pressure tubing through the injector spray Into the combustion chamber. (4) back to the oil process: the plunger upward oil supply, when up to the plunger on the chute (stop for the edge) and the sleeve connected to the oil return hole, low pressure oil pump chamber and the plunger head Of the hole and the radial hole and oblique groove communication, a sudden drop in oil pressure, the oil valve in the spring force quickly shut down, stop the oil supply. After the plunger has to go up, when the convex part of the cam turn, under the action of the spring, the plunger down again. At this point they started the next cycle. (5) Conclusion: Through the above discussion, the following conclusions can be drawn â‘ The total reciprocating stroke of the plunger L is constant, which is determined by the lift of the cam. â‘¡ The amount of oil supplied per cycle of the plunger depends on the supply stroke Oil stroke is not subject to camshaft control is variable, â‘¢ fuel supply start time does not vary with the fuel stroke changes, â‘£ turn the plunger can change the fuel supply end time, thus changing the fuel supply.