Diesel Fuel Injection Pump BH4Q75R8 Auto Engine Part

Working principle
Low-pressure fuel supply stage: Diesel is first sucked out of the fuel tank by the electric fuel pump, filtered by the filter, and then delivered to the fuel inlet of the high-pressure fuel pump. In this process, the electric fuel pump provides a lower pressure, mainly to overcome the resistance of the fuel pipeline, deliver diesel to the vicinity of the high-pressure fuel pump, and prepare for the work of the high-pressure fuel pump.
High-pressure fuel supply stage: The high-pressure fuel pump is driven by the camshaft, and under the action of the cam, the plunger reciprocates in the pump body. When the plunger moves downward, the fuel inlet opens, and the diesel enters the plunger cavity under the action of low pressure; when the plunger moves upward, the fuel inlet closes, the diesel in the plunger cavity is compressed, and the pressure rises sharply. When the pressure reaches a certain value, the high-pressure diesel enters the high-pressure oil pipe through the oil outlet valve, and then is delivered to the injector.

Structural type
Plunger injection pump: mainly composed of plunger, plunger sleeve, oil outlet valve, oil outlet valve seat, etc. The plunger and the plunger sleeve are a pair of precision parts. The reciprocating motion of the plunger in the plunger sleeve realizes the boosting and metering of diesel. This type of fuel injection pump has a simple structure and reliable operation, and is widely used in some traditional diesel engines.
Distributor fuel injection pump: It adopts a rotor structure, mainly composed of a distribution rotor, a distribution sleeve, a plunger and other components. The distributor fuel injection pump distributes high-pressure diesel to the injectors of each cylinder in turn through the reciprocating motion of a plunger in the rotor. It has the advantages of small size, light weight, and compact structure. It is often used in small diesel engines and some occasions with high space requirements.
High-pressure common rail fuel injection pump: It consists of a high-pressure oil pump, a common rail pipe, an injector, an electronic control unit, etc. The high-pressure oil pump pressurizes the diesel and delivers it to the common rail pipe. The common rail pipe is equivalent to a high-pressure accumulator, which can keep the diesel pressure stable. The electronic control unit accurately controls the opening and closing time of the injector according to the working conditions of the engine, thereby realizing accurate control of the injection amount and injection timing. This type of fuel injection pump has the advantages of high injection pressure, high injection accuracy, and good emission performance. It is a fuel supply system widely used in modern diesel engines.
Function
Establish high pressure: Provide sufficient pressure for diesel injection so that diesel can be sprayed into the engine combustion chamber in a good atomized state, fully mixed with air, and achieve efficient combustion. Generally speaking, the injection pressure of modern diesel engines can be as high as 160MPa or even higher. Such high pressure can only be achieved through the supercharging effect of the diesel pump.
Accurately measure the injection amount: Accurately control the amount of diesel injected into the combustion chamber according to the engine load, speed and other working conditions. For example, when the engine is idling, a smaller amount of injection is required to maintain stable operation; when the engine is working at full load, a larger amount of injection is required to output sufficient power. The diesel pump achieves precise control of the injection amount by adjusting the stroke of the plunger or the opening time of the injector.
Control injection timing: Ensure that the diesel is injected into the combustion chamber at the right time to ensure that the engine's combustion process can proceed in the best condition. Injecting fuel too early or too late will affect the engine's power output, fuel economy and emission performance. The diesel fuel pump cooperates with the engine's timing system to accurately control the injection time, so that the engine can work efficiently and stably.

Common faults and impacts
Oil pump wear: After long-term use, the plunger, plunger sleeve, oil outlet valve and other parts of the oil pump will wear, resulting in a drop in the oil pump's oil supply pressure and insufficient oil supply. This will cause the engine to have problems such as insufficient power, poor acceleration, and difficulty starting. In severe cases, it may even cause the engine to fail to operate normally.
Oil pump jam: Due to impurities, moisture and other reasons in diesel, the plunger or other moving parts of the oil pump may jam, making the oil pump unable to work properly. At this time, the engine will not be able to obtain sufficient fuel supply and will immediately stall, affecting the normal driving of the vehicle.
Oil pump leakage: The oil pump may leak due to aging, damage to the seal of the oil pump or loose oil pipe joints. This will not only cause a waste of fuel, but also make the oil pump's oil supply pressure unstable, affecting the engine's working performance, and there may also be safety hazards.