Tool to find car leakage problems (understand the principle of car leakage detector)
As far as the current technology is concerned, the transmission will encounter leakage, and the operation process of those new multistage transmissions is very complex, once the transmission fluid leakage, it will seriously affect the shift effect. However, if the problem is solved at the initial stage of product manufacturing, that is, after casting and before assembly, the product leak detection will not only save a lot of production costs for transmission suppliers, but also avoid many problems caused by customer complaints and even recalls. Therefore, the research and development of helium leak detection system undoubtedly provides another good solution to these problems.
one Leakage detection of transmission machine after casting
In the past, transmission leaks were not discovered until after assembly. However, if a fixture equipped with a helium leak detector is used, most leaks can be detected after casting, eliminating problematic castings early in the production process, resulting in significant savings in production costs.
The leakage detection process is as follows: First, the transmission is automatically removed from the tooling station, and the holes such as the spiral valve plate (shift channel) and the torque converter cavity are blocked with a specific fixture. The sealing clamp has a very high precision and can effectively prevent the plugging hole leakage; Next, the transmission with a plugging clamp is placed in a fully enclosed device and clamped, sealed and vacuumed. Helium is then injected into the sealed unit and stirred by a fan to form a uniform helium/air mixture with a density of 1%, which is evenly distributed to various parts outside the transmission. The helium leak detector is connected to the device being tested through a "shift channel". If helium enters the transmission from the helium-rich outside through pores, cracks, threaded holes or any other leak point, the helium leak detector detects it immediately, accurately and quickly. At this point, it is possible to determine whether the product is qualified and collect relevant data for later tracking. In addition, all channels and holes in the transmission need to be tested separately.
If there is a porous leak in the 25.4mm diameter range of the cast aluminum surface, then helium molecules may enter the product through hundreds of millions of pores. Air or underwater detection methods cannot detect such pores, but helium detection equipment can do so, which is unique to the device. In contrast, a helium leak detector takes just a few seconds to detect. The entire testing time of the product is also only 30-40s, ensuring that the helium leak detection process is as fast as the production process such as drilling or installing solenoid valves.
At present, the leakage rate allowed in the industry is about 1 sccm, but as the transmission continues to upgrade, the structure is increasingly complex, the liquid used inside it also changes, and the performance requirements are getting higher and higher at the same time, the leakage rate must also be lower and lower. Automotive test engineers familiar with the process said that the leakage rate of the new 9 - and 10-speed transmissions can be as low as 0.1sccm, which is only l0 percent of the original standard.
two Leak detection on finished transmission equipment line
In the second stage, especially later in the production phase, the manufacturer may test the transmission again, this time for leaks from the inside out. After the test chamber is vacuumed, the closed transmission product is placed in it for testing. During the test, once the test chamber cover is closed, vacuum is immediately pumped with a large vacuum pump. The helium leak detector is then connected to the vacuum pump to detect whether helium molecules are leaking out of the finished transmission.
The transmission is vacuumed at the same time as the test chamber, and helium is then injected into the transmission. Because the transmission seal assembly cannot withstand a pressure difference greater than 27.6kPa, the pressure of pure helium inside the transmission was kept within a range of about 20.7kPa during the test. If there is a crack in the transmission, the helium will leak from the inside out - previously it was from the outside in. Insideout leak testing is done in the first place because manufacturers typically require testing within product design standards. For automatic transmissions, the liquid pressure is transmitted from the inside to the outside, so the mold should also simulate the final operating conditions of the product. If the channel squeezes under pressure, or the joint expands. The helium will flow out like a liquid; Second, because of the complexity of the production process - solenoid valves, hydraulic torque converters, "shift channels" and all the bending channels - helium leaks into the vacuum more quickly if the transmission is cracked. Before the product leaves the factory, all channels in the transmission must be tested for leakage to ensure their tightness.
Compared to air testing or pressure decay testing, helium testing offers better repeatability, is not limited by temperature, and is easier to clean after testing. There are many variables in the test equation of the helium leak detector to achieve the measurement effect R&R - repeatability and reproducibility.
Three. Superiority of helium detection method Compared with the traditional air test method, the helium test method has many advantages.First of all, the air detection method is very sensitive to temperature, and the hot parts or parts to be cooled will cause the mass flow rate to be inaccurate or unable to be tested repeatedly;
Second, the volume of the product to be measured has no effect on the tracer gas leak detection test, but the volume will cause many problems for air testing methods such as mass flow or pressure decay detection. Larger products take longer to test and are less sensitive. Among them, the pressure attenuation detection method not only requires several times to obtain stable pressure, but also the multiple pressurization of the product is bound to cause the temperature to rise, thus affecting the accuracy of the pressure test.
The helium detection process requires very low pressure, and because the helium leak detector has a very high sensitivity, even very low concentrations of helium can be detected. The benefits of pressure reduction, on the one hand, not only reduce the production cost, that is, each product each test cost is reduced by about 0.5 yuan, on the other hand, it also improves the safety of production and ensures the operation safety of employees.
Although the helium detection method requires very low pressure, it is more efficient to detect mass, and can also detect pores that cannot be detected by mass flow and pressure decay tests. These fine textures and pores are potential safety hazards in the transmission, and liquid leakage will occur after long-term operation.
The helium detection method is not only suitable for automotive transmissions, but also for any cast aluminum product, including turbocharger housing, transfer case housing, valve sets, valve covers, and even diesel liquid valve housing. In addition, exhaust gas recirculation coolers and charge air coolers (generally stainless steel, but copper components are also used) use similar test methods.