Injection pump, also known as high-pressure oil pump, is the most important part of the fuel system. The function of fuel injection pump is to increase fuel pressure and inject a certain amount of fuel into combustion chamber in an accurate time according to the requirements of diesel engine working conditions.

The requirements for fuel injection pumps are as follows:

(1) The fuel supply of fuel injection pump should meet the needs of diesel engine under various working conditions, that is, when the load is large, the fuel supply increases: the fuel supply decreases in load hours. At the same time, it is necessary to ensure that the oil supply to each cylinder is equal.

(2) According to the requirements of the diesel engine, the fuel injection pump should ensure the same starting time for each cylinder.

(3) According to the different combustion chamber form and the method of mixture formation, the fuel injection pump must provide enough pressure fuel to the injector to ensure good atomization quality.

Fuel injection pump can be divided into single pump and synthetic pump according to its overall structure.

Monomer pump

The single pump is mainly composed of a plunger and a plunger sleeve. It does not have camshaft or even roller drive parts. Because the single pump is easy to be arranged near the cylinder head, the high-pressure tubing is greatly shortened, and it is applied to high-power medium and low-speed diesel engines with cylinder diameter of more than 200 mm.

Synthetic pump

The synthetic pump is a plunger couple with the same number of cylinders installed in the same pump body. Each cylinder has a set of fuel injection components, which are driven by the corresponding cams of the camshaft in the pump body.

Now the whole fuel injection pump, take out a pump group to explain. The structure is as follows:

Its main parts are: camshaft, roller body, plunger and plunger sleeve, plunger spring, rotating sleeve and gear ring, oil outlet valve and valve seat, and tight pipe connection, etc. Plunger sleeve and plunger are a pair of main precision couples in fuel injection pump. They are carefully processed and matched with each other. Their diameter clearance is only 0.001-0.003 mm. This pair of parts can only be replaced in pairs, and can not be replaced separately.

There are two holes on the plunger sleeve, which make the inner cavity of the plunger sleeve communicate with the oil passage. There is a longitudinal groove at the oil hole on the right side, in which a screw is inserted, so that the plunger sleeve can not be fixed in the pump body to rotate.

The upper part of the plunger has an annular groove, which communicates with the upper end face of the plunger by a longitudinal groove. The helical bevel starts from the longitudinal groove to adjust the oil supply. The lower part of the plunger has two shoulders and flanges. The plunger shoulder is inserted into the incision of the rotating sleeve. The rotating sleeve is freely mounted on the plunger sleeve. The open ring is fastened to the rotating sleeve with a screw and meshes with the gear rod.

The toothed rod is installed in the longitudinal hole of the pump body and is connected with the governor control rod. When the gear rod moves axially under the action of the control rod and the governor, the rotating sleeve and plunger on each oil pump also rotate at a certain angle. The lower bearing plate of the plunger spring is installed on the flange of the plunger. The spring upper bearing plate is supported on the pump body. The function of the spring is to make the plunger go down. The cam on the camshaft acts on the plunger through the roller body to make it move upward.

The roller body is the transmission between the cam and the plunger, which itself bears the lateral thrust and the plunger is only subjected to the axial force. The lower axle of the roller body is equipped with a roller, which is mounted on a needle roller bearing, and the upper end of the roller body is screwed with adjustment screw and safety nut.