Supporting technologies for oil filters – Problem solving

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The supporting technologies for filters have the nature of interdisciplinary fields on a small scale, and thus are easily overlooked. In practice, it is common to observe that well-designed filters installed on the main unit fail to perform to their full potential. And the host users are not satisfied with the performance of the selected filter. This is the problem of improper filter matching. This article attempts to discuss the selection, design, installation, and use of oil filters from a supporting perspective, covering the following eleven topics: 1. The flow rate through the oil filter. 2. Operating conditions of internal combustion engines. 3. The quality of the lubricating oil. 4. The skill level of the internal combustion engine operator. 5. Installation location of the oil filter on the internal combustion engine. 6. Connection of the oil filter to the oil radiator. 7. Determination of the bypass valve opening pressure. 8. Application of the maintenance indicator. 9. Structure of the composite oil filter. 10. High-flow oil filter. 11. Pressure regulating valve issue. The oil filter is located in the internal combustion engine lubrication system. Upstream is the oil pump. Downstream is the main oil passage. As modern internal combustion engines evolved toward higher speeds and greater output, the capacity of the lubrication systems increased, and oil temperatures rose. And devices such as oil coolers and piston injection cooling are commonly used, thereby complicating the structure. At the same time, the improvement in the quality of lubricating oils and the increase in the variety of additives have placed new demands on the filtering capabilities of filters. All of these have added new elements to the supporting technologies for oil filters. 1. The flow rate through the oil filter: There are four criteria for determining the appropriate flow rate for an oil filter: A. The flow rate data specified by the user. B. Type, power, and level of enhancement of the accompanying internal combustion engine. C. Oil pump flow rate. D. Main oil passage flow rate. The empirical formula used to calculate the main oil passage flow rate from the internal combustion engine’s power is as follows: Q = (7 – 1υ) L/hphr for gasoline engines; Q = (10 – 20) L/hphr for diesel engines. A lower value should be used under light load conditions. Use a high value for heavy-load operating conditions. The pressure increase in the extra-heavy load belt can be increased by another 10–30%. If the user provides the designed flow rate of the oil pump or the actual measured flow rate of the new oil pump, then the filter flow rate can be taken as 50-60% of the oil pump’s flow rate value. This is because the designers of the oil pump have taken into account that the pump will gradually wear out over time, resulting in a gradual decrease in flow rate. To meet the host’s requirements, he must increase the design flow rate. Some users also provide the design flow rate of the main oil passage in the internal combustion engine to the filter designers. In this case, the flow rate of the filter should be set at 1.5–2.0 times the designed flow rate of the main oil passage. This is because, as the internal combustion engine undergoes normal wear and tear, the flow rate in the main oil passage increases accordingly to maintain normal oil pressure. As for the flow rate of the bypass filter, it can be set at 5–10% of the flow rate of the full-flow filter, or such that all the oil in the engine’s oil pan is filtered once every 10 minutes or so. 2. Operating conditions of internal combustion engines The operating conditions of internal combustion engines are diverse. From city cars to farm trucks. From electrical power generated indoors to construction machinery in oil fields. The usage conditions vary greatly. In terms of load size, there are light load, medium load, heavy load, and extra-heavy load. In terms of the duration of the loading effect. There are continuous loads and intermittent loads. These different operating conditions affect the changes in oil temperature and oil pressure within the lubrication system, which in turn influence the working conditions of the filter. It also determines the properties of the filtering material and the size of the filtering area. Diesel engines operating under continuous heavy load represent the most severe operating conditions. The oil filter must not only withstand high temperatures for long periods of time (120–150°C), but also endure the impact of pressure shock waves millions of times. Therefore, the structure of the filter and its filtering material must possess sufficient mechanical strength. The adhesives used for sealing elements and filter elements must be able to withstand the attack of high-temperature engine oil. For operating conditions with variable loads, if the proportion of time under light load is very small, such as in case of light vehicles. The load on the filter can be set at 50–60% of the maximum load corresponding to the engine’s highest speed. This prevents the filter from becoming too large in size. Some internal combustion engines also operate at full load continuously, but they are in better environmental conditions and are managed at a higher level. Such as power generation equipment in machine rooms and propulsion systems for large ships. In that case, an oil filter with better performance, even if it has a more complex structure or requires more difficult maintenance, can be used. Or, if there is sufficient space for installation, the filtering area can be increased to extend the maintenance cycle and reduce management costs. There are also some internal combustion engines with special operating conditions, such as those used to power harvesters. It is used continuously for only about ten to twelve days each year. But during these ten-odd days, parking accidents are not allowed. The oil filter designed for such machinery must possess excellent short-term reliability. It is able to hold out throughout the harvester’s operating period, even at the cost of some sacrifices in other performance metrics. The replacement of its filter element should also be very simple, allowing the issue to be resolved within a few minutes. The above are several typical examples of the operating conditions for internal combustion engines. The designers of the filter system must conduct a careful and thorough examination and analysis of the specific operating conditions of the main unit. Choose the structure that best meets the usage requirements. The various performance characteristics of the filter when it is in line allow it to adapt to any operating conditions it faces. Even if it is managed to be created, it is either extremely expensive, has an unusually complex structure, or is too large and heavy to be acceptable to users. 3. Quality of lubricating oil: Experience over the years has shown that, if the quality of the lubricating oil for internal combustion engines is not taken into account, even the best oil filters will fail to perform properly. It is true that high-quality lubricants have been used in some internal combustion engines. Users are already familiar with lubricants of API grades SD, SE, SFCC, and CD. These oils possess good antioxidant stability and resistance to floating and diffusion. Microporous filter paper cartridges perform well when used with these types of oils, but it should also be noted that in rural and remote areas, many users still use oils of poor quality or even substandard quality. Oil contains many impurities, has poor antioxidant properties, and lacks cleaning capabilities; it tends to form gummy substances and asphaltenes during use, leading to clogging of the filter elements. It shortens the service or maintenance life of the filter, which is particularly detrimental to filter elements made of microporous filter paper. In response to this situation, filter designers must take certain measures: either add a metal mesh pre-filter before the paper filter element, use a filter element made of composite materials, or install a centrifugal filter in parallel within the lubrication system. However, users should be informed that the filtration system after implementing the above measures will incur higher maintenance and service costs. If a detailed analysis is conducted on the overall technical and economic benefits of using lubricants of different grades, the conclusion will inevitably be in favor of high-quality lubricants. 4. Technical skill level of the internal combustion engine operator. The oil filter is a component that requires regular maintenance or replacement, at intervals of approximately 5,000–10,000 kilometers, or 150–250 hours. Therefore, the technical level of internal combustion engine operation and management affects the decision regarding which type of filter structure to use. The following explains this issue using the maintenance methods for three types of filters. Replacing a spin-on filter is the simplest. Simply unscrew the old one with your hands or a tool, then screw on a new one by hand to finish. There are no other parts that need to be disassembled or assembled. Even those who are not very familiar with the structure of oil filters can carry out this replacement task. This is one of the advantages that enables spin-on filters to be rapidly adopted. However, a prerequisite for using spin-on filters is that the filter spare parts must be readily available and purchasable at any time. In sharp contrast to spin-on filters are centrifugal filters. It has excellent filtering performance, no parts that need to be replaced, and its lifespan is almost identical to that of the engine. But it has a high-speed rotating rotor (5,000–8,000 r/min). It is reassembled after finishing machining. Such work requires a fairly high level of technical skill to be done well; otherwise, all or part of the advantages of the centrifugal filter will be lost. Between the two structures mentioned above is the replaceable element filter. Since the filter element components need to be replaced, a reliable supply of filter elements is essential. At the same time, when maintaining and replacing the filter element, some parts also need to be removed, installed, and replaced. Therefore, users are required to have a certain level of understanding of the filter’s structure and the function of its components. Otherwise, a wrong installation or omission of a sealing ring, a spring, or a small tray can render the filter ineffective. There are a wide variety of filter structures. There is a large variation in user levels. Designers and manufacturers believe that even the most excellent filters may not receive praise from users in actual use. One of the reasons is that the user’s skill level does not match the requirements for using the filter. 5. Installation location of the oil filter in the internal combustion engine. The filter designer needs to know the installation position of the filter within the engine in order to make the necessary adjustments to the product’s design. There are roughly three ways to install a filter: upright, horizontal, and inverted. The centrifugal filter must be installed upright, with the angle between the centerline of the rotor shaft and the vertical line not exceeding 20°. Other types of filters do not have this limitation. Filters mounted upside down should be equipped with a check valve to prevent the lubricating oil from draining out of the filter after the engine stops. Once it is emptied, there will be a short period of oil shortage when the engine is started again. In mild cases, it increases engine wear; in severe cases, it can cause the main unit to get stuck. Filter designers should also be aware of whether there are other components and accessories in the vicinity of the installation location, or if there is any interference. Therefore, the filter assembly diagram should show the spatial dimensions required for replacing or maintaining the filter, so that the main engine designers can make appropriate arrangements. During filter maintenance, oil inevitably drips. Therefore, filters should be avoided from being installed above electrical motors and appliances as well as rubber and plastic components. For centrifugal and other types of filters installed in an inverted position, the housing and components must be removed upward during disassembly or maintenance; therefore, it is necessary to avoid the engine’s exhaust pipes to prevent burns. 6. Connection between the oil filter and the oil radiator: Modern high-speed internal combustion engines increasingly use oil radiators to control the temperature of the lubricating oil. Thus, there is the issue of how to connect the filter and the radiator. One way is to install the filter before the radiator. The advantage is that the filtered, clean oil can flow into the radiator, preventing the channels of the cooling elements from being blocked by impurities in the oil. Another advantage is that when the engine is running properly, oil with a higher temperature passes through the filter first; since the viscosity of oil is lower at high temperatures, the filtering effect is improved. The second method is to place the filter after the water-cooled radiator. Advantage: Hot water can flow into the radiator when starting the engine with a cold vehicle (when hot water is filled into the cooling system). As the oil temperature rises, the oil can pass through the filter more easily. Based on the above analysis, the full-flow oil filter should be connected after the radiator. The oil temperature inside the filter can be controlled, resulting in a relatively stable filtering effect. It is preferable to install a bypass filter in front of the radiator. It’s fine to start the engine even if no oil passes through the filter. When the engine is operating normally, oil with a higher humidity can first pass through the bypass filter, which allows its filtering capabilities to be utilized more effectively. This is especially true for centrifugal filters. As the oil temperature rises, the rotation speed increases, resulting in the best separation effect. 7. Determination of the bypass valve opening pressure: A full-flow oil filter must be equipped with a bypass valve (safety valve). Prevents the oil flow in the lubrication system from being interrupted when the filter element becomes clogged. The magnitude of the pressure difference at which the bypass valve opens has the following effect: regarding the service life of the filter element, a larger pressure difference for opening the bypass valve results in a longer service life for the filter element. Regarding the strength of the filter element, a greater pressure difference required to open the valve necessitates an increased strength in the filter element, as it must withstand a larger pressure difference. For the main oil passage pressure, the bypass valve pressure difference represents the pressure drop from the outlet of the oil pump to the main oil passage. The pressure difference across the valve is set high, and this pressure drop will also increase. It is possible for the oil pressure difference in the main oil passage to be low. Therefore, from the perspective of the overall requirements of the lubrication system, it is advisable to set a lower pressure difference for opening the bypass valve. The only drawback is that the filter has a relatively shorter lifespan. Several more filter elements need to be replaced, but setting the pressure difference too high can cause problems in the lubrication system, such as low oil pressure in the main oil passages or damaged filter elements. The opening pressure difference of the bypass valve in vehicle filters is usually between 70 and 250 kPa. For light vehicles, the smaller value can be used, while for heavy vehicles, the larger value can be used. The bypass valve opens fully when the filter element is completely clogged. Therefore, sufficient large dimensions should be given when designing the oil inlet and outlet holes and passages of the bypass valve. Ensure that 80–100% of the filter’s rated flow rate can pass smoothly through the bypass valve. 8. Application of the maintenance indicator: When the filter needs maintenance or replacement; in other words, how users can know that the bypass valve is about to open or has already opened. This has been a concern for users for a long time. The maintenance indicator was created to meet this need. It is a pressure difference sensor combined with a signal display device. It has already been used in large diesel engines. However, it should be noted that when the engine starts with a cold machine, due to the high viscosity of the oil, the pressure difference inside and outside the filter element is also large. Requiring the indicator to distinguish between cold and hot engines will complicate the design, increase costs, and make it difficult to implement it in small and medium-sized internal combustion engines. Therefore, no maintenance indicator products have yet been released on the market. As electronic technology is increasingly incorporated into internal combustion engine control systems, the practical feasibility of using devices for the installation and maintenance of vehicle filters will surely increase. As filter designers, one should pay attention to these developments. 9. Structure of the composite oil filter A composite oil filter refers to a filtering mechanism in the engine lubrication system that includes both a full-flow filter and a bypass filter. There are four structural forms: full-flow filters with replaceable filter elements and bypass filters are installed together on a common base. The full-flow and bypass filter assemblies are installed separately in different parts of the main unit, providing a bit more flexibility compared to the common base design. Depending on the operating conditions of the host, two filters can be installed simultaneously or just one of them. The full-flow and bypass replaceable filter elements are combined within a single assembly housing. The oil inlet holes are common. There is one oil outlet hole per unit, and a flow control orifice plate is used within each oil outlet hole to regulate the flow rate. The full-flow and bypass filters are both located within a spin-on housing. Although the structure is complex, since the entire assembly is replaced, it does not cause any extra hassle for the user. The use of a composite filter improves the level of filtration, thereby enhancing its effectiveness; a full-flow filter serves both the purpose of ensuring a steady supply of oil and that of removing impurities. And ensuring fuel supply is of top priority. The engine lubrication system prefers to have slightly dirty oil rather than running out of oil or having insufficient oil. Therefore, installing only a full-flow filter does not guarantee that the engine will have highly clean lubricating oil. The filtration precision of the shunt filter can reach 2–5 μm, and it does not have a bypass valve. Although its flow rate is only 5–10% of that of a full-flow filter, it is still capable of filtering all the oil in the engine oil pan within 10–15 minutes. This results in the oil entering the full-flow filter being cleaner, thereby extending its service life. Moreover, the oil that flows into the main oil passage when the bypass valve is open is also relatively clean. The two filter elements in the latter two structures mentioned above. From the overall perspective of the filter element, it can also be referred to as a composite filter element. In actual varieties, there are also two separate composite filter elements. One method is to embed a fine filtering material within the \"body\" of the full-flow filter element. If the full-flow filter* has a paper core, a filter block made of deep-pouring material should be inserted at both ends of the filter paper at the joints or clamping points, with its circumferential length being about one-tenth of the circumference of the entire filter fold. This results in a single filter element with two types of filtering materials. The flow ratio of the cash part filters is adjusted automatically according to their respective levels of blockage. Another type of composite filter element is a structure composed of multiple layers of filtering material. For example, the filter layer is formed using a layer of filter paper, a layer of highly breathable thick fibers, and several layers of metal mesh. It features good flowability, low resistance, high accuracy in passing through ports, and high strength. It overcomes the drawbacks such as insufficient deep filtration capability of filter paper, inadequate strength of thick fiber layers, and low filtration precision of metal meshes. Leverage the strengths of various materials passing through the port to complement each other and achieve comprehensive advantages. Centrifugal filters started with a split-flow structure, and later two composite filtration forms emerged. One type is called a full-flow centrifuge, in which the clean oil from the center of the rotor flows directly into the engine’s main oil passage, while the oil ejected by the nozzles returns to the oil pan. Another approach is to install a swirl chamber beneath the rotor; the oil coming from the oil pump is divided into two streams – one stream enters the rotor and then returns to the oil pan, while the other stream enters the swirl chamber before proceeding to the main oil passage. It is evident that by taking advantage of the characteristics of various filtering materials and the different arrangements of oil flow, filter designers can achieve a great deal in meeting the diverse needs of various users. 10. High-flow oil filter: The oil filter is usually installed on the side of the internal combustion engine. The diameter of the filter affects the overall width of the device, especially in vehicle engines. The width of the vehicle chassis is related to the wheelbase and the layout of the steering system, hence there are strict restrictions on it. In internal combustion engines used for other purposes, installing filters that are too large can also disrupt the overall aesthetics of the machine. When designing a high-flow filter, an increased filtering area inevitably leads to an enlarged diameter of the housing. To reduce the horizontal dimension, a good solution is to use two or more filters arranged in parallel. Since high-power engines have less stringent restrictions in terms of the length direction for mounting accessories, it is possible to arrange filters vertically; moreover, using multiple filters of the same size in parallel is beneficial both for filter manufacturers and users. Because it can reduce the number of filter specifications and types. The oil filter for stationary large diesel engines is often installed separately from the main engine, that is, independently of it. There is no limit on the size of the filter. However, from the perspective of production supply and usage management, it is a better choice to adopt a structure in which multiple small filters of the same size are installed within a large housing. 11. Pressure regulator issue: The pressure regulator is not a component of the filter; it is a pressure relief device installed in the main engine lubrication system to regulate the oil pressure in the main oil passage. The pressure regulating valve is usually installed at the outlet of the oil pump. But there are also those installed on the filter holder. Therefore, filter designers sometimes also have to consider the structure of pressure regulating valves. It is important to note that the oil drainage channel of the valve must have a sufficiently large size. Ensure unobstructed oil flow when the valve is open. The excessively high oil pressure can drop instantly. There have been many instances during use where, due to the overly small oil drainage passage in the pressure regulating valve, the filter assembly became deformed and started leaking oil, or the filter element was crushed. The ability of paper filters to withstand pressure differences is only 0.6–0.7 Mpa, whereas the outlet pressure of the oil pump at the moment the engine starts in a cold vehicle can reach 1 Mpa or even higher. Therefore, once the pressure regulating valve fails or oil leakage is poor, the filter will suffer severe damage.