Common failure analysis of automotive engine high pressure fuel pipe

Compared with the traditional automotive engine core components, engine high pressure fuel pipes have not received special attention for a long time. However, statistics show that in recent years, the failure cases of high pressure fuel pipes have been increasing, and their proportion has entered the automobile for years. The top ten in the number of engine parts failed, and there is an increasing trend.

The engine high pressure fuel pipe is an important component that connects the fuel injection pump and the fuel injector, and is responsible for delivering high pressure fuel to the engine. Once the high pressure fuel pipe of the engine cracks, causing oil leakage, it not only adversely affects the reliability of the engine, but also, after the high pressure fuel injection leaks, it is likely to come into contact with the high-temperature components of the engine, resulting in a serious fire accident.

Therefore, it is of urgent practical significance to analyze and summarize the various failure modes of high pressure fuel pipes on the market.

1. High pressure fuel pipe raw material internal surface defects

During the manufacturing process of high pressure tubing, the inner surface undergoes a complicated drawing deformation process, in which various inner wall defects are inevitably formed, the most important of which is the inner wall crack defect. At present, the international standard for the control of the inner wall quality of high pressure tubing is ISO 8535.

For the defect level, the general enterprise will have clear regulations in its corporate standards based on the working conditions of the high pressure fuel pipe. At present, the defect level of high pressure fuel pipe control of domestic ordinary automobile engines is mostly Q grade and above. The inner wall strengthening process is a commonly used high pressure fuel pipe inner surface treatment method. The method is to optimize the stress distribution of the surface of the pipe to generate the stress state of the internal pressure and pull out, which can effectively slow down the crack propagation speed, not only improve the pressure resistance of the fuel pipe, but also reduce the data dispersion in the fatigue test.

2. Poor processing quality at the transition between the hoe and the shank

The processing process of the high pressure tubing boring head is complicated, the deformation amount is large, and the metal on the inner and outer surfaces undergoes a strong deformation flow. If the process is improper, the metal streamline may be twisted or even cold-folding defects may occur.

Various process defects at the steamed bread will become the origin of fatigue cracks during use, causing the tubing to crack and leak oil. Therefore, each enterprise will control the shape of this defect in its internal standards, mainly for the steamed bread. The depth of the cold folding crack is controlled.

3. "Inclusions" defects on the outer wall of high pressure fuel pipe

At present, domestic high pressure tubing pipes are almost all imported from abroad, and currently the relevant ISO standards and national standards do not clearly define the micro-quality of the outer wall of the pipe. In recent years, there have been many cases in which fatigue cracks originate from the appearance of inclusion defects on the outer surface of the tubing, resulting in fuel pipe cracking and oil leakage. Even, there have been many occurrences of cracks in the tubing processing process due to such outer surface-like inclusion defects.