1. Oil absorption and pressure oil process

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 is communicated with the oil passage in the pump body, and the fuel chamber is quickly filled with fuel.

When the cam hits the roller of the roller body, the plunger rises. From the beginning of the plunger, it moves upward until the oil hole is blocked by the upper end surface of the plunger. During this period of time, due to the movement of the plunger, the fuel is squeezed out of the oil chamber and flows to the oil passage. So this period of lift is called pre-stroke. When the plunger blocks the oil hole, the oil pressure process begins. As the plunger moves upward, the oil pressure in the oil chamber rises sharply. When the pressure exceeds the spring force of the delivery valve and the upper oil pressure, the delivery valve is opened, and the fuel is pressed into the fuel pipe and sent to the fuel 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 oil supply starting point.

When the plunger continues to move upwards, the oil supply continues, and the oil pressure process continues until the spiral bevel on the plunger lets the plunger sleeve return to the oil hole. When the oil hole is opened, the high-pressure oil flows 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 drops rapidly, the oil outlet valve drops back to the valve seat under the action of the oil pressure in the spring and the high-pressure oil pipe, and the fuel injector stops fuel injection immediately. At this time, although the plunger continues to move upward, the fuel supply has been terminated.

The time when the oil return hole on the plunger sleeve is opened by the bevel of the plunger is called the theoretical oil supply end point.

It can be seen from the above-mentioned oil suction and oil pressing process that during the entire upward movement of the plunger, only the middle stroke is the oil pressing process, and this stroke is called the effective stroke of the plunger.

2. Oil volume adjustment

In order to meet the requirements of the diesel engine load, the fuel supply of the fuel injection pump must be able to be adjusted from the maximum fuel supply (full load) to zero fuel supply (stop).

The adjustment of the fuel supply is realized by rotating all the plungers of the fuel injection pump at the same time through the gear rod and the rotating sleeve.

When the plunger rotates, the start time of oil supply is unchanged, and the end time of oil supply is changed due to the change in the position of the oil return hole of the plunger sleeve caused by the hypotenuse of the plunger. As the angle of rotation of the plunger is different, the effective stroke of the plunger is also different, so the oil supply also changes.

The greater the rotation angle of the plunger with respect to the non-supply level 1, the greater the distance from the upper end of the plunger to the oblique side of the oil return hole opening the plug sleeve, and the greater the oil supply. If the rotation angle of the plunger is greater If it is smaller, the fuel cut will start earlier and the fuel supply will be smaller. When the diesel engine is stopped, the oil must be cut off. For this reason, the longitudinal groove on the plunger can be turned to the oil return hole on the plunger sleeve. At this time, during the entire plunger stroke, the fuel in the plunger sleeve flows back to the oil passage through the longitudinal groove and the oil return hole. There is no oil pressing process, so the fuel supply is equal to zero.

Therefore, when the plunger rotates, the timing of changing the end of the fuel supply is used to adjust the fuel supply. This method is called the fuel supply end adjustment method.

Other adjustment methods can be obtained by changing the position of the bevel on the plunger. The following figure shows the shape of the plunger's slanted edge for the three oil volume adjustment methods.

(A) It is the above-mentioned fuel supply end point adjustment method. It is suitable for use on diesel engines with constant speed, and also on marine supercharged diesel engines.

(B) is the method of supply starting point adjustment. Due to the upward slope of the spiral bevel, when the plunger is turned to adjust the amount of oil, the start point of the oil supply changes while the end of the oil supply does not change. This adjustment method was once thought to be suitable for diesel engines that directly drive the propeller, because when operating according to the propulsion characteristics, the load increases with the speed, and the fuel injection advance angle should also increase. But in fact, it is disadvantageous when working at low load. Therefore, it is rarely used in marine diesel engines with relatively high pressure. It is still hoped to adopt the first method of adjusting the fuel supply end point.

(C) It is the method of changing the start point and end point of the fuel supply at the same time. This kind of plunger meets the requirement of reducing the fuel injection volume by properly shifting the start point and advancing the end point, so it can control the entire combustion process, regardless of low or high load, near the top end point. This adjustment method is suitable for marine diesel engines with high boost pressure and varying speed and load.

In the fuel injection pump oil volume adjustment mechanism, in addition to the rack-rod type oil volume control mechanism described above, there is also a fork type oil volume control mechanism. There is an adjusting arm at the lower end of the plunger. The ball end of the adjusting arm is placed in the groove of the adjusting fork. The adjusting fork is fixed on the pull rod with a locking screw. When the pull rod is moved, the adjusting fork drives the plunger to rotate, thereby changing the supply. The purpose of oil volume. Its advantages are simple processing, easy repair, and small size of the oil pump. Our No. 2 series pumps use this kind of control mechanism.