Analyze the working principle of diesel pump

1. Suction and Pressurization of Diesel Pump Suction and Pressurization The priming pump reciprocates the plunger. When the plunger is in the lower position, the two oil holes in the plunger sleeve are opened. The plunger sleeve cavity communicates with the oil passage in the pump body, and the fuel quickly fills the oil chamber.

When the cam is pushed against the roller of the roller body, the plunger rises. Move up from the beginning of the plunger until the oil hole is blocked by the upper end of the plunger. During this period of time, due to the movement of the plunger, the fuel is forced out of the oil chamber and flows toward the oil passage. So this lift is called pre-stroke. When the plunger blocks the oil hole, the oil pressure process begins. As the plunger goes up, 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 valve is opened and the fuel is pushed into the oil pipe and sent to the injector.

The moment when the oil inlet hole on the plunger sleeve is completely blocked by the upper end surface of the plunger is called the theoretical starting point of oil supply.

When the plunger continues to move upwards, the oil supply continues and the oil pressure process continues until the spiral bevel on the plunger opens the plunger sleeve back to the oil hole. When the oil hole is opened, the high pressure oil passes from the oil chamber. The longitudinal groove in the plunger and the oil return hole in the plunger sleeve flow back into the oil passage in the pump body. At this time, the oil pressure in the plunger sleeve oil chamber is rapidly reduced, and the oil valve falls back to the valve seat in the spring and the high pressure oil pipe, and the fuel injector immediately stops the injection. At this point, although the plunger continues to rise, the fuel supply has been terminated.

The moment when the oil return hole of the plunger sleeve is opened by the oblique edge of the plunger is called the theoretical oil supply end point.

As can be seen from the above oil sucking and pressure oiling processes, during the entire upward movement of the plunger, only the middle stroke is the oil pressure process, and this stroke is called the effective stroke of the plunger.

2. Adjustment of diesel pump oil quantity In order to meet the diesel engine load requirement, the fuel supply quantity of the fuel injection pump must be adjustable within the range of maximum fuel supply (full load) to zero fuel supply (stop).

The adjustment of the oil supply amount is achieved by rotating the entire plunger of the fuel injection pump at the same time through the rack rod and the rotating sleeve.

When the plunger rotates, the oil supply start time does not change, and the end of the oil supply time is changed due to the change of the plunger oblique edge to the position of the oil return hole of the plunger sleeve. As the plunger rotates at different angles, the effective stroke of the plunger will be different, so the amount of oil supply will also change.

The greater the angle at which the plunger does not rotate for the oil level 1, the greater the distance from the upper end of the plunger to the bevel edge of the oil return opening of the plug sleeve. The larger the oil supply, the greater the angle of rotation of the plunger. When it is small, the oil cut off starts earlier and the oil supply is also smaller. When the diesel engine is stopped, the oil must be cut off. For this purpose, the longitudinal groove on the plunger can be turned to face the oil drain hole on the plunger sleeve. At this time, during the entire plunger stroke, the fuel in the plunger sleeve always flows back to the oil passage through the longitudinal groove and the oil return hole, there is no pressure oil process, so the oil supply amount is equal to zero.

Therefore, when the plunger is rotated, the amount of oil is adjusted by changing the timing of the end of the oil supply. This method is called the end of supply regulation method.

By changing the position of the ramp on the plunger, other adjustment methods can be obtained. The following figure shows the plunger ramp shape for the three oil regulation methods.

(a) The above-mentioned adjustment method for the supply end point. Suitable for use in diesel engines with constant engine speed, but also for marine diesel engines.

(b) Supply start adjustment method. As the spiral bevel is tilted upwards, when the plunger is turned to adjust the amount of oil, the starting point of the oil supply changes and the end of the oil supply does not change. This adjustment method was considered to be suitable for a diesel engine directly propelled by a propeller, because the load increases with the rotation speed and the injection advance angle should increase when operating according to the propulsion characteristics. However, it is actually unfavorable to work at low loads, so marine diesel engines with relatively high boost pressure have been rarely used, and it is still desirable to adopt the first method of adjusting the end of oil supply.

(c) Methods for simultaneous change of fuel supply start point and oil supply end point. This kind of plunger meets the requirement of reducing the fuel injection amount through proper back-starting start point and advance end point, so it can control the entire combustion process, and it is performed near the top stop point at low and high load. This regulation method is applicable to marine diesel engines with high pressure boost and changes in speed and load.

In the fuel injection pump oil amount adjustment mechanism, in addition to the above-mentioned tooth-rod oil amount control mechanism, there is also a fork type oil amount control mechanism. There is an adjusting arm at the lower end of the plunger. The end of the adjusting head of the adjusting arm is placed in the slot of the adjusting fork. The adjusting fork is fixed on the pulling rod with the locking screw. The moving rod pulls the adjusting rod to rotate the plunger so as to achieve the change of supply. The purpose of the amount of oil. Its advantages are simple processing, easy to repair, small size of the oil pump, and the diesel pump series 2 pumps in China use this control mechanism.

In the above fuel injection pump, the most critical part is the plunger. The structure of the plunger is many, but its basic structure is as follows:

The chute (oil control side) on the plunger has helical (b and d) and linear (a and c) shapes. The plunger of the linear chute returns oil through the center hole and has the advantages of simple processing, etc. China's No. 2 series pumps use this type of plunger.

The spiral groove or linear chute on the plunger can be divided into right-handed (c and d) and left-handed (a and b) according to its inclination. The direction of the spiral groove can be judged by the left and right hand rules. The direction of rotation of the spiral groove is related to the direction or arrangement of the control gear bar. The right-hand spiral groove, which reduces the oil supply when turning to the left, is used in the fuel pump of the governor installed on the right side of the integral pump of the diesel pump. The fuel pump on the left side of the installed governor uses a left-handed spiral groove.