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The research on the oil quantity control of the micro air compressor used the maintenance of Wang Yuren (Fenghua Tianfeng Automobile Air Compressor Co., Ltd., Fenghua 315500, Zhejiang). After the implementation, good results were obtained. This article is useful for preventing various types of splash-lubricated reciprocating air compressors.
l Bow rumors Micro and small reciprocating compressors are mainly used for industrial instrument control, painting, blowing, tire inflation, brakes for home air sources and large automobile vehicles, starting of ships, etc. Their common feature is structure. Simple, lightweight, low cost, easy to use, and widely used in the market. This kind of micro-miniature compressor is a single-acting structure in which the connecting rod directly drives the piston. Especially in the automotive industry, the oil control of the lubricating oil to the cylinder is very strict. The fuel consumption of the 2.2kW air compressor should be controlled at 1g. /h below. The output of such automotive air compressors in China is about 3 million units per year. For example, the annual output of our company's automotive air compressors has reached about 300,000 units, because if more lubricating oil is exported with compressed gas, it will cause waste of lubricating oil, and at the same time, the lubricating oil will be used for gas objects such as instrumentation and drying. Causes pollution. If the car uses compressed air containing oil, it will cause environmental pollution, and some pipeline accessories will be scrapped due to oil pollution.
In addition, the piston ring with the engine cylinder of the automobile also involves the leakage of the lubricating oil to the working volume of the gas. This leakage not only can make the lubricating oil exhausted for a short time, but more importantly, causes atmospheric pollution, we often go on the road. The car seen on the black smoke, most of which belong to the piston leaking lubricating oil, caused by the burning of lubricating oil. From this point of view, it is of great significance to study how to reduce the oil of the piston.
At home and abroad, we pay great attention to the problem of lubricating oil turbulence in automobile air compressors and engine pistons, and carry out research as a hot topic in the compressor and automobile manufacturing industries. There are many important achievements, such as the widely used tapered ring and twisted ring, which are important achievements. According to our company's practice, these twisted rings use the initial scraping effect, but after hundreds of hours of operation, the tapered part is worn away and the scraping effect is lost. In the past 30 years, our company has cooperated with the Compressor Research Institute of Xi'an Jiaotong University in the research work of controlling piston oil. It has deeply discussed the complex mechanism and influencing factors of piston oil, and accumulated a set of effective control measures. Micro-reciprocating air compressor oil control technology provides benefits.
2 Mechanism analysis of oyster sauce The annual production of automobile air compressors of our company mainly supplies weichai and oyster oil; z. The oil film that passes through the torus when the piston ring is up and down can be calculated as follows, according to the fluid of the piston ring The dynamic lubrication equation has the coordinates of any point along the radial direction of the piston ring, the minimum oil film thickness between the mh ring and the cylinder, the movement speed of the mU* piston ring, m/s using the above equation, according to the automobile air compressor and its piston ring. The structural parameters and operating conditions parameters can be used to calculate the oil film thickness as shown. Dividing the horizontal coordinate in the middle into several equal parts, and subtracting the oil film thickness of the same position from the oil film thickness value of the axial stroke, the oil film thickness difference and the equal width product are accumulated, thereby obtaining a reciprocating stroke. The flow rate of the oil flowing through the piston ring to the cylinder side is 0.12 g/h. It should be noted that this amount of oil is only the amount of oil that is ideally caused by the change of the oil film.
Immediately adjacent to the upper side of the ring groove, the oil is forced into the ring groove through the lower gap of the ring and the ring groove, and when the piston ring is ascending, the high pressure gas force causes the piston ring to abut against the lower side of the ring groove, and the lubricating oil Reciprocating inertial forces relying on the piston are pushed out of the ring groove into the compression volume. This simmering oil is an inertial pump oil, and there is no reasonable way to calculate it.
The other pumping action of the piston ring comes from the difference between the suction pressure and the atmospheric pressure. When the piston is in the suction stroke downward, the pressure in the upper part of the piston ring is lower than the pressure in the lower shaft box of the piston ring due to the resistance of the air valve in the suction process, and the gas under the piston ring is rolled over the interface of the piston ring through the piston ring. The leakage channel at the leak leaks into the working volume of the cylinder and is compressed and discharged with the compressed gas. According to our test, when the suction pressure of the suction chamber is matched from the engines of enterprises such as Shangchai and Xichai. Practice has shown that the vast majority of air compressors can well meet the OEM's oil index. That is to say, most air compressor pistons and cylinders can achieve effective control of oil according to the structure and process technology we designed. However, there are very few air compressors that appear simmering oil at the beginning, and some products go through a section. Oil simmering occurs only after time runs. Through theoretical analysis and product testing, we have summarized a number of factors of oyster sauce: 0) Normally operating compressors or engines are more or less fuel-intensive. According to the results of the study, after the running-in period of the piston ring, its smooth surface will form as shown.
The ring profile, the formation mechanism of the grinding surface is as follows: the tilting of the piston in the cylinder; the self-rotation of the piston ring; the thermal expansion and cone wear of the piston and the cylinder; the twisting movement of the piston ring itself; and the size of the machined part Error and geometric tolerances.
These factors generally cause the piston ring to be inclined with respect to the cylinder wall surface such that the upper and lower sides of the ring are worn to form an intermediate projection with a collapsed shape at both edges. According to the theory of fluid dynamic lubrication, this shape is necessary to reduce wear and form an oil film.
Q, as shown in the piston ring grinding surface, the oil effect is not the same when it is up and down. When the gas is compressed upwards, the high pressure in the ring groove pushes the piston ring toward the cylinder wall surface, so that the oil film of the upward stroke is reduced. Small; in the suction phase of the downward stroke, the low-pressure gas in the ring groove has a small thrust on the piston ring, and the oil film layer on the cylinder wall of the compression chamber is thickened through the piston ring, and the piston ring is in the next upward compression stroke. The lubricating oil is scraped into the compressed gas, so that the oil film forming the piston ring increases and decreases the pumping oil.
However, when the piston ring is in the upward stroke of the piston ring, it is lean oil lubrication, and the oil layer on the cylinder wall surface is thin. When the piston descends, the crankcase side supplies more lubricating oil, which is rich in oil lubrication and remains on the cylinder wall surface. The oil film layer is thicker, which also becomes the piston ring 02 (the total oil consumption of the compressor is reduced from 0.3g/h to 2g/h when the total maintenance and repair service is reduced to 0.9bar.
P, the top of the piston A The top of the piston passes through the ring groove gap. The specific pressure of the oil scraping ring and the side clearance have a significant influence on the control of the oil. The installation of the scraper ring on the piston is as shown, the roundness of the scraper ring, the interface clearance of the oil ring, the specific pressure of the scraper ring to the cylinder, the side clearance of the scraper ring and the piston ring groove, etc. Both have significant effects. These values ​​are too tight and can cause the ring to become stuck; if these dimensions are too loose, the amount of oil will increase. Manufacturers of compressors often think that if the effect of the scraper ring is too good, the piston ring of the sealing gas will be short of oil, which is not a problem. In the engine, the contact pressure of the scraper ring reaches more than 10 bar, and the high temperature combustion occurs repeatedly in the cylinder. The lubricating oil is consumed faster than the air compressor, but the lubrication of the engine piston ring can also be ensured. In the piston ring of the air compressor, there is no high temperature combustion in the cylinder, and the situation is much better, that is, the lubrication of the piston ring is sufficient in the air compressor.
The gap between the piston and the cylinder has a significant effect on the amount of oil. The larger the gap between the two, the easier it is to produce oyster sauce; but too small a gap may cause the piston to rise and fall in the cylinder. Because the cylinder is cast iron material, there is external cooling, the amount of expansion is smaller; and the piston is aluminum alloy material, the expansion coefficient is large, and the heat of the piston is not easy to be dissipated, causing the expansion of the piston to be large. Therefore, the gap between the two should be carefully selected.
The practice of more than 0 years shows that the machining accuracy and installation accuracy of various parts of the compressor also have a great influence on the oyster sauce. The accuracy of all these dimensions can cause the piston to skew the cylinder. In the 80s and 90s of the last century, we used general-purpose equipment to manufacture crankcases, cylinders, crankshafts, connecting rods and pistons of air compressors. As a result, the proportion of oil-removing machines was much larger than now, since we installed and processed After the center, the precision of each part is greatly improved, and the proportion of the oil simmering machine is significantly reduced.
* The oil level in the crankcase is appropriate and stable, and the oil stroke of the oil rod or oil ring has an effect on lubrication and oil.
In the past, it was thought that the oil-splitting mechanism must hit the oil into the cylinder. After many years of practice, the oil-splitting mechanism could only suffice enough oil to lubricate the connecting rod size head. At this time, the amount of oil entering the cylinder wall surface was sufficient.
1. Piston ring 2, 7. Scraper ring 3. Piston 4. Bushing 5. Retaining ring 6. Piston pin type piston assembly 3 measures to control air compressor squeegee (I for intermediate protrusion, bilaterally symmetrical collapse The piston ring grinding surface 5Q) always scrapes the oil to the compression chamber of the cylinder in each reciprocating stroke. If special measures are taken, the piston ring forms an asymmetrical under-slip surface during operation, ie the intermediate projections are offset towards the piston skirt as shown. When the piston moves downward, the oil film on the stroke is thin, and when the stroke is high, the oil film can be stroked even though the sealing pressure is high. In this way, the amount of oil that is scraped toward the compression volume is reduced. In fact, the tapered and twisted ring is the most typical and extreme oil-slip surface *50, (e)). However, the tapered ring that is considered to be processed, after hundreds of hours, the upper portion of the tapered surface is worn away, and the stroke is as close as the symmetrical smooth surface shown, and the oil scraping ability is lost. According to our test and measurement, the ratio of the maximum amount of collapse to the length of the collapse is about 1/200 to 1/500, and the scraping effect and lubrication effect are better. If the amount of collapse is too large or too small, it will not have the effect of oiling upwards and scraping oil downwards.
The Q scraper ring is the key mechanism to reduce the consumption of lubricating oil. The scraper ring needs to have a large elastic force to ensure a good scraping effect. However, excessive spring force can cause ring and cylinder wear and increase power consumption. In addition, the axial clearance between the scraper ring and the scraper ring groove is very important. For the scraper ring with a piston diameter of about 100 mm, the end face flatness should be within 0.02 mm, and the end face gap between the ring and the ring groove should be 0.06~0.08mm. This minimizes the pump oil that passes through the gap between the end faces of the ring groove. However, it should be noted that the gap between the ring and the ring groove should not be too small to prevent the scraper ring from being stuck.
The model Q of the five kinds of grinding surfaces on the crankshaft side reduces the flow resistance loss of the intake valve is an effective means to control the amount of oil in the piston ring. This requires maximizing the flow area of ​​the intake valve, selecting a larger valve lift and selecting a smaller spring force. The design of the gas valve needs to be analyzed and simulated by the law of the valve movement, especially under the condition that the engine speed is greatly changed, and the valve piece is required to have wide adaptability.
(4Crankshaft, crankshaft, connecting rod, piston pin, piston and other parts of the cylinder affect the concentricity of the piston to the cylinder. Therefore, to control the piston oil, actually improve the processing accuracy of the entire compressor, reduce the various components The thermal deformation and force deformation. For example, the structure of a certain air compressor cylinder in our factory is shown in Q. We find that the flange on the cylinder head is thin. During the operation of the air compressor, the cylinder head is stressed. The flange connecting the cylinder head is easily deformed by pulling, which is also a factor that causes the gap between the cylinder and the piston to be uneven. Therefore, we obviously increase the thickness of the flange connecting the cylinder head on the cylinder block 71), and receive a good control of the oil. The effect of the amount.
* In previous design manuals and textbooks, the oil slinger fixed on the big head cover of the connecting rod also has a scoop-like feature, and at least the flat oil surface is used to hit the lower oil surface. In recent years, we have experimented with the oil bar that can be designed as a wing type, with a very small face to hit the oil, still can provide enough oil for the cylinder lubrication. In order to ensure the stability of the lubricating oil surface in the crankcase, we use the engine oil pump to deliver oil to the crankcase. On the other hand, we set a large oil return hole to return excess oil to the engine's gearbox. Going, maintaining a very stable oil level in the crankcase, thereby limiting splashing oil to the piston and cylinder wall. However, it should be noted that the amount of oil supplied to the piston pin should be sufficient to allow the friction between the connecting rod and the pin to travel tropically.
Q original thin flange * thickened flange cylinder head flange structure 4 Conclusion Reduced oil squeezing technology of small air compressor involves the machining accuracy and fit clearance of all parts of the compressor, as well as its wear and tear during operation . In addition, select the appropriate oil scraper ring and piston ring, select the appropriate ring groove and the end face of the ring to match the gap, (the tongue ring is 0.10 ~ 0.15mm, the scraper ring is 0.05 ~ 0.08mn), choose the appropriate The clearance between the piston and the cylinder (0.10~0.16mn), the dimension ring and the twist ring have good oil-scraping effect at the beginning of use, but after more than 100 hours of operation, the tapered cone is smoothed and loses oil scraping. effect. In order to form a long-term cone scraping effect, it is necessary to close the smooth surface of the piston ring to the lower end portion, and the upper end portion is kept in a soft original state, so that the smooth surface of the piston ring automatically forms a permanent process during the work. Cone ring shape.
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