Cummins HPI-TP fuel system introduction
(Second article)
HPI injector structure and working principle
The injector has the following characteristics:
Therefore, it is necessary to ensure that the coolant is drawn out before removing the fuel injector, at least to ensure that the coolant level is lower than the bottom surface of the fuel injector installation hole.
The following figure is the structure diagram of HPI injector:
(1) The ejector rod is pressed down under the action of the cam drive system. The lower plunger located below the inside of the fuel injector is tightly pressed on the nozzle seat surface. The lower plunger will remain in this position until the exhaust stroke of the engine ends (as shown in the figure below).
(2) As the cam starts to move toward the inner base circle, the three plungers are in close contact together and move upwards until the lower plunger reaches its upper pointing point. The lower plunger spring will keep it in the upper pointing position. At this time, the lower plunger reveals the metered fuel inlet hole located on the side wall. The metered fuel will be energized after the metered fuel control valve is energized. Under the action of the pressure wave, the fuel inlet check valve will open, and the metered fuel will enter the metering cavity of the injector.
(3) The upper plunger of the injector continues to move up, and the timing plunger still moves up with the upper plunger until the upper plunger reaches its upper pointing point. The bias spring will keep the timing plunger in contact with the upper plunger. In this position, the timing fuel inlet is exposed. Prepare for the timing of the fuel intake.
(4) The timing fuel control valve is energized, leading to the fuel passage and delivering fuel to the timing fuel inlet. With the injection of timing fuel, the timing plunger moves downward, and the amount of fuel injection advance will be determined by the amount of timing fuel injected. The longer the timing fuel control valve is energized, the greater the fuel injection advance.
(5) The cam starts to drive the upper plunger down, which will immediately close the timing fuel inlet. At this time, a hydraulic link is formed between the upper plunger and the timing plunger, and the timing plunger will be pushed down and in contact with the lower plunger. Subsequently, the three plungers move downward together. As the lower plunger descends, the metering fuel inlet is blocked, and the fuel pressure in the internal cavity of the nozzle rises. When the fuel pressure is greater than the pressure in the cylinder, the injection starts. .
(6) Now that the plunger descends to the bottom, it will fit closely with the seat surface of the nozzle to complete the fuel injection. At this time, the overflow oil passage on the lower plunger will connect the metering chamber with the injector overflow oil passage, and discharge the high pressure inside the metering chamber. The lower plunger will be continuously compressed on the nozzle seat under the action of the compression pressure in the timing oil chamber. The compression pressure is controlled by the overflow gap size of the timing plunger and the overflow pressure holding ring.
(7) When the upper plunger also runs to the bottom, the three pieces of the lower plunger, the timing plunger and the upper plunger will be pressed together and pressed on the nozzle seat under the force of the cam drive system. The timing and metering ports are sealed by the side wall of the plunger. This compaction state will be maintained until the end of the next exhaust stroke of the cylinder.
The above is the structure and working principle of the Cummins HPI-TP injector. The Scania HPI injector is the same as the above introduction.
