What Is a Fuel Injection Pump

by MOU YONG HONG on December 01, 2021

The fuel injection pump is an important part of the automobile diesel engine. The fuel injection pump assembly is usually a whole composed of the fuel injection pump, governor, and other components installed together. Among them, the governor is a component that guarantees the low-speed operation of the diesel engine and limits the maximum speed, and ensures a certain relationship between the injection volume and the speed. The fuel injection pump is the most important part of the diesel engine and is regarded as the "heart" part of the diesel engine. Once it goes wrong, the entire diesel engine will malfunction.

The structure of the fuel injection pump

The fuel injection pump is mainly composed of four parts: pumping mechanism, fuel supply adjusting mechanism, driving mechanism, and fuel injection pump body. Among them, the oil pumping mechanism includes plunger assembly, delivery valve assembly, etc.; oil supply adjustment mechanism refers to rack type oil adjustment mechanism or shift fork-type oil adjustment mechanism; driving mechanism includes camshaft, tappet assembly, etc.; Fuel injection pump body is the installation base of the above three, it is required to have sufficient strength, rigidity, and tightness, and easy to disassemble, adjust and maintain.

Classification of fuel injection pumps

Mechanical fuel pump: The mechanical fuel pump uses a positive displacement with a plunger or diaphragm. In the cyclic action, the pump sucks in fuel, traps it, then moves the fuel to carbohydrates and the engine, and repeats the process.

Electric fuel pump: The electronic fuel injection system on modern vehicles requires higher pressure, which is achieved to some extent by using electric fuel pumps instead of mechanical modules. Here are some examples of electric pumps:

Inside the tank: Most new cars sold today use a fuel pump located in the tank. This helps protect the module, and the gas helps keep the module cool.
Tandem: The tandem pump is easier to replace than the fuel tank pump. It is located between the fuel tank and the engine and is installed in the fuel system rail. These are usually installed under the car or in the engine compartment.

Rotary vane: Like mechanical pumps, rotary vane pumps also use positive displacement to move fuel. Inside the rotary vane pump, a rotor with a "paddle" runs eccentrically in the cavity. Because it is eccentric, a crescent-shaped space is formed, allowing fuel to enter. The blades close a small amount of fuel as the rotor moves and release the fuel after passing through the outlet valve. Different types of vane pumps include rolling vanes, sliding vanes, flexible vanes, and swing vanes.

Gear pumps: Gear pumps also use positive displacement, but use different parts to implement this method. There are two interlocking gears in the gear pump, an internal gear with teeth and an external gear ring with a smooth arc lobe. The internal gear deviates from the external gear. Therefore, when they rotate, a small bag of fuel can be collected, pressurized, and released.

Working principle of the fuel injection pump

Oil suction process: the plunger is driven by the cam of the camshaft. When the convex part of the cam leaves the plunger, the plunger moves down under the action of the plunger spring, the volume of the oil chamber increases, and the pressure decreases; when the plunger sleeve is on When the radial oil inlet hole is exposed, the fuel in the low-pressure oil cavity flows into the pump cavity along the oil inlet hole.

Oil pumping process: When the convex part of the cam pushes up the plunger, the volume in the pump cavity decreases, and the pressure increases. The fuel flows back to the low-pressure oil cavity along the radial oil hole on the plunger sleeve; When the radial oil hole on the plunger sleeve is completely blocked, the pressure on the pump chamber increases rapidly; when this pressure overcomes the pretension force of the outlet valve spring, the outlet valve moves upward; when the outlet valve is up When the decompression ring belt leaves the valve seat, the high-pressure diesel is pumped into the high-pressure fuel pipe and injected into the cylinder through the fuel injector.
Oil return process: As the plunger continues to move upward, when the chute on the plunger communicates with the radial oil hole on the plunger sleeve, the fuel in the pump cavity passes through the axial oil passage on the plunger, obliquely The oil passage and the oil hole on the plunger sleeve flow back to the low-pressure oil chamber, and the pump oil stops.

Fuel injection pump function

1. Increase oil pressure (constant pressure): Increase the injection pressure to 10MPa~20MPa.

2. Control injection time (timing): injection and stop injection at the specified time.

3. Control the fuel injection volume (quantitative): According to the working condition of the diesel engine, change the fuel injection volume to adjust the speed and power of the diesel engine.

This article mainly introduces what is a fuel injection pump, the structure of the fuel injection pump, the classification of the fuel injection pump, and the working principle of the fuel injection pump.


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