Brief Analysis of Diesel Engine High-Pressure Fuel Pump Plunger Seizure Fault (I)

The diesel engine high-pressure oil pump is an important part of the fuel injection system. Its working performance has a great impact on the diesel injection system. It can increase the pressure of diesel and deliver high-pressure diesel to the high-pressure oil rail in a timely and quantitative manner according to the timing and load of the engine. Therefore, the high-pressure oil pump can also be called the "heart" of the diesel engine. When the high-pressure oil pump works normally, it is necessary to ensure that the pump oil pressure can meet the requirements of the injection pressure and atomization of the injector. The oil supply of the high-pressure oil pump accurately meets the amount required for the diesel engine to work. The oil supply and oil supply time of the high-pressure oil pump also need to be able to be adjusted to ensure uniform oil supply in each cylinder.

1. Working principle of plunger pump

The plunger of the plunger pump has a groove on the cylindrical surface of the plunger, which is connected to the axial hole and the top of the plunger through the radial hole on the plunger; the plunger sleeve has an oil inlet hole and an oil return hole, both of which are connected to the low-pressure oil chamber.

The oil outlet valve of the plunger pump is a one-way valve. Due to the force of the spring, the cone surface on the upper part of the valve and the valve seat fit closely. When the oil supply is stopped, the oil outlet valve can isolate the high-pressure oil circuit and the cavity at the upper end of the plunger pair, effectively preventing the oil in the high-pressure oil circuit from flowing back into the oil pump. When the plunger pump is working, the plunger reciprocates up and down under the joint action of the bottom cam and the plunger spring, thereby realizing the oil pumping process.

During the oil inlet stage, the cam mechanism is in the return stage, the plunger moves downward, the space volume above the plunger increases, the pressure decreases, and a certain vacuum is generated. When the plunger moves down to the oil inlet hole, the oil enters the cavity above the plunger (i.e., the oil pumping chamber) through the oil circuit. When the plunger moves to the lowest point, the oil inlet process ends. During the oil supply stage, the cam mechanism is in the lift stage, the plunger moves upward, the fuel pressure increases, and part of the oil flows back to the pump oil chamber through the oil hole. When the plunger moves to the upper end face to block the upper edge of the oil inlet hole of the plunger sleeve, the pump oil chamber on the upper part of the plunger becomes a sealed oil chamber. The plunger continues to move upward, and the pressure in the pump oil chamber increases rapidly. When the pressure reaches a certain value, the oil outlet valve opens, and the high-pressure diesel enters the high-pressure oil rail through the oil outlet valve and is sprayed into the cylinder through the injector for combustion. During the oil return stage, the oil groove on the plunger is connected to the oil return hole on the sleeve, and the oil pressure drops rapidly. Under the action of the spring, the oil outlet valve is quickly closed and the oil supply stops.

As the camshaft continues to rotate, the plunger continues to perform a reciprocating up and down cyclical motion.

2. Analysis of the "bite" mechanism of the plunger pair

The plunger generates heat when working, so the plunger needs to be cooled and lubricated.

The upper part of the plunger is cooled and lubricated by the fuel in the pump oil chamber, the middle part of the plunger is cooled and lubricated by a small amount of fuel flowing in, and the lower part of the plunger is cooled and lubricated by a small amount of lubricating oil flowing in.

According to the experience in actual work, the "seizure" phenomenon of the plunger pair often occurs between the annular surface matching the middle part of the plunger and the internal oil groove of the sleeve. If this part cannot be cooled well or there is dirt accumulation, it is easy to "seizure" failure. The plunger pair is in a high temperature and high pressure working environment when working, and the reciprocating motion will generate a lot of heat. The plunger sleeve is fixed on the pump body, so the heat on the plunger sleeve can be conducted out through the pump body, but the heat on the plunger cannot be transferred. If there is no effective heat dissipation measure, the plunger will be thermally deformed after being heated. The gap between the plunger and the plunger sleeve is very small. After the plunger is thermally deformed and contacts the plunger sleeve, "seizure" will occur.

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