1. The oil suction and pressure of the fuel injection pump are completed by the reciprocating movement of the plunger in the plunger sleeve. When the plunger is in the lower position, the two oil holes on the plunger sleeve are opened, the inner cavity of the plunger sleeve communicates with the oil passage in the pump body, and the fuel quickly fills the oil chamber;

2. When the cam pushes against the roller of the roller body, the plunger will rise. Move upward from the beginning of the plunger until the oil hole is blocked by the upper end face of the plunger. During this period of time, due to the movement of the plunger, the fuel is squeezed out from the oil chamber and flows into the oil passage. So this section of lift is called pre-stroke. When the plunger blocks the oil hole, the oil pressure process starts. As the plunger moves upward, the oil pressure in the oil chamber rises sharply. When the pressure exceeds the spring force of the oil outlet valve and the upper oil pressure, the oil outlet valve is pushed open, and the fuel is pressed into the oil pipe and sent to the injector;

3. The moment when the oil inlet hole on the plunger sleeve is completely blocked by the upper end face of the plunger is called the theoretical oil supply starting point. When the plunger continues to move upward, the oil supply continues, and the oil pressure process continues until the helical bevel on the plunger leaves the plunger sleeve to return to the oil hole. When the oil hole is opened, the high-pressure oil passes through the oil chamber. The longitudinal groove on the plunger and the oil return hole on the plunger sleeve flow back to the oil passage in the pump body. At this time, the oil pressure in the plunger sleeve oil chamber decreases rapidly, and the oil outlet valve falls back to the valve seat under the action of the oil pressure in the spring and the high-pressure oil pipe, and the injector stops injecting oil immediately. At this time, although the plunger continues to move upward, the oil supply has been terminated.