Cummins HPI-TP fuel system introduction
(Part Three)
Maintenance points of HPI-TP injector
n the second article of Cummins HPI system introduction, we gave a very detailed introduction to the structure and working principle of HPI injectors. If the working principle of your injector is still unclear, please be sure to return Go to the previous article to learn.
If you have a clear understanding of the working principle of HPI-TP. We will begin to further study the maintenance related knowledge of the injector.
The main content of this article is to make everyone more aware of the role of the various parts of the HPI-TP injector, and at the same time understand the failure modes of each part. These knowledge points are very important for the maintenance of this injector.
The following figure shows the HPI injector structure diagram that is installed on the ISX15 engine. We will mainly introduce based on this.
Below we will introduce the function and failure reason of the important parts of HPI-TP injector:
First: Metered fuel inlet check valve and timing fuel inlet check valve
During the oil intake process, these two valves (Figure 2) will be opened under the action of the pressure pulse to fill the metering oil chamber and the timing oil chamber respectively, and these two valves need to be closed in time when the ejector rod descends. In order to generate high pressure in the internal oil cavity of the fuel injector, if the two one-way valves are severely worn, the sealing will be weak, which will lead to errors in timing and fuel metering, and cause the fuel injector to fail.
Second: Upper plunger
When the metered fuel has been filled, the timing fuel has also been filled. Driven by the cam, the upper plunger will move downward and press the fuel in the timing oil chamber, making the timing plunger go down. When the lower end of the timing plunger contacts the top surface of the lower plunger, the upper plunger It will continue to descend and press the fuel in the timing oil chamber to produce high pressure. This high pressure will push the timing plunger and the lower plunger below to move downwards. At this time, the oil and gas mixture in the metering chamber will be pressurized until the pressure is reached. Above the cylinder pressure, the injection starts.
At this time, if the bottom of the upper plunger (position 1 in Fig. 3) is severely worn, it will cause insufficient pressure in the timing chamber, and subsequently cause the pressure in the metering chamber to rise slowly, and the fuel injection will be delayed, which will result in insufficient engine power. Or the exhaust temperature is too high and other faults.
Third: Timing plunger
The timing plunger will move downwards under the action of the oil pressure of the upper timing oil chamber during the oil pressure injection process, and finally combine with the lower plunger to continue to press down the fuel in the metering oil chamber to generate injection pressure .
If the side wall of the timing plunger (position 2 in Figure 3) is worn, it will cause the fuel in the timing oil chamber to leak quickly along the worn part, which will cause the pressure in the injector to rise slowly, and the fuel injection will be delayed. Problems such as insufficient engine power, black smoke or excessive exhaust temperature.
Fourth: Overflow pressure maintaining valve
When the timing plunger runs to the bottom, the fuel in the timing chamber will flow out through the top of the timing plunger and the overflow pressure holding valve (position 3 in Figure 3). Due to the pressure holding function of these parts, the timing A certain pressure will be maintained in the oil chamber, which will ensure that the nozzle needle valve is pressed against the nozzle sealing surface, preventing the high-pressure gas generated during the combustion process in the cylinder from entering the fuel injector through the fuel injection hole.
If the pressure holding valve does not work normally, it will cause the nozzle to not have enough pressing force to seal normally or produce excessive pressing force and seal too tightly. Failure to seal normally will cause high-pressure combustion gas to enter the injector body and produce carbon deposits in the injector, which will damage the injector; if the seal is too tight, it will affect the life of the injector.
Fifth: Lower plunger
The side of the lower plunger plays a role of sealing the high pressure oil in the metering chamber, and at the same time there is an oil drain channel in the lower plunger. If the side wall of the lower plunger (position 4 in Figure 3) is worn, or the side wall of the corresponding injector is worn, this will cause the fuel high pressure inside the metering chamber to leak, which will lead to insufficient injection pressure and delay the injection time; at the same time; , The injected oil volume becomes smaller.
Sixth: Nozzle
The HPI injector is an open nozzle. The high-pressure gas in the engine cylinder will enter the injector through the nozzle and form a mixture of oil and gas in the oil cup. As the needle valve moves down, the mixture of oil and gas will be It is compressed to form a high pressure. When the pressure is greater than the cylinder pressure, the fuel injection will start.
After the injection, the needle valve will continue to be pressed against the nozzle sealing seat surface to seal the injection hole to prevent high-pressure combustion gas from rushing into the injector.
When the oil nozzle (Figure 4) is worn, it will affect the atomization effect, and then affect the engine performance. At the same time, it will also affect the sealing effect of the needle valve on the injector. If the seal is not good, the combustion exhaust gas will enter the injector and form a serious carbon deposit.
Finally, let’s make a summary of HPI injector repair and inspection together:
1: Check whether the bottom of the upper plunger, the side wall of the timing plunger, the side wall of the lower plunger (with overflow oil passage) and the inner wall of the corresponding injector are severely worn. If there is, it will seriously affect the performance of the injector. Need to be repaired and replaced.
2: Check the timing check valve and check whether the metering check valve seat surface is good.
3: Check whether the sealing surface of the fuel nozzle is in good condition. If the bottom of the lower plunger has a large black area, it means that the sealing is not good and the exhaust gas has been able to flush into the fuel injector. Need to remove the blackened carbon deposits.
I hope this article can help repair stations that currently have HPI service business. We will share it on the official website and other platform websites in the future.
