Conventional engine oil filters effectively remove contaminant particles larger than 40 to 50 microns from the lubricating oil. Some premium filters state filtration efficiency down to 25 microns. The result of the efficiency of these filters is that smaller particles are able to accumulate in the oil, and this is the key reason vehicle oil change intervals remain relatively short. Several studies have concluded that ideal filtration efficiency should include the removal of smaller particulates from lubricating oil, particularly those in the 3 to 10 micron range that can enter into the tight dynamic clearances between moving parts. Such improved efficiency reduces engine wear, increases engine lifespan and improves fuel efficiency. Ultimately, achieving filtration efficiency down to one micron for an extended period of time can extend the oil change interval, but has been available only using bypass filtration units. In industry, there is a need for an oil filter that removes particles down to one micron and can be installed like a conventional spin-on filter. The hybrid spin-on filter may be the answer to the sought-after solution.

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Figure 1. Hybrid Spin-on Filter Assembly

Filter Description
The hybrid spin-on filter is a patented filter design that has been developed for various internal combustion engine capacities and other applications (Figure 1). Housed within a single conventional filter canister, the hybrid filter assembly provides a full-flow filter and a microfilter. The hybrid filter also has a configuration that includes a bypass pressure relief valve but is not shown in Figure 1 due to current patent prosecution.

Because specifications such as filter size and spin-on threads remain the same, the hybrid filter can replace a conventional oil filter without requiring any modifications to the engine or any change in installation technique. The two filtration components of the hybrid filter work in a complementary fashion to improve filtration efficiency. The full-flow filter is designed to capture particles greater than 20 microns while the microfilter captures particles between one and 20 microns. The majority of the oil that enters the filter is processed directly through the full-flow filter. However, the design enables a small amount of oil to be diverted and processed through the microfilter. This hybrid action ensures improvement of filtration efficiency and proper engine lubrication without affecting the oil pressure in the engine.

Impact of Small Particles
Both conventional and hybrid filters have a full-flow filter element that consist of fibers bound to an underlying resin. In an unused filter, the fibers are tightly encased with the resin. As oil passes through this material, the contaminant particles rub against the fiber-resin complex. Over time, the resulting friction erodes the resin and loosens the fibers. This process increases the pore size, and as a consequence, large particles can pass through the loose fibers. This results in a vicious cycle whereby the particles passing through the filter continue to erode the fibers, further reducing filtration efficiency, and causing wear in the engine. Oil contaminated with particulates also results in increased friction, which reduces engine and fuel efficiency. The ultimate outcome is the replacement of both the oil and filter after a relatively short use period. That is why for an automobile, the use of conventional filters typically leads to an oil and filter change after every 3,000 to 5,000 miles of travel.

Hybrid Filter Performance
Testing of the hybrid spin-on filter has been conducted with cars and light-duty trucks, using a variety of engines and lubricating oils. Emphasis was placed on understanding the operation of the filter and the benefits of reducing the level of small particulates in the engine oil.

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Figure 2. Fiber-resin Thickness and Fiber Tightness in Filter Media

Filter Medium
The surface of the full-flow filter medium was observed under a microscope before and after specified test mileage, and the average fiber-resin thickness was measured. Figure 2 shows that due to erosion, the fiber-resin thickness is reduced and the fibers become loose in the conventional filter medium whereas these parameters were practically unchanged in the hybrid full-flow filter medium. This is attributed to the absence of smaller particles in the hybrid filtered oil.

Another demonstration of the impact of particulates in the oil on the conventional filter medium is seen in the oil flow rate. The oil flow rate through the conventional filter medium increases with time due to the enlargement of its pores (Figure 3). In the hybrid full-flow filter medium, the pore size remains relatively unchanged and there is no significant variation in the oil flow rate.

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Figure 3. Oil Flow Rate Through Full-flow Filter Media

Particle Count
As discussed, pore sizes in conventional filters increase during use. Therefore, the concentration of contaminants in the oil is high, as illustrated in Figure 4. On the other hand, with the benefit of the microfilter, the hybrid spin-on filter maintains the initial pore structure of the full-flow cartridge. Even after accumulating more than twice the mileage than that of the conventional filter, the particle count for the hybrid filter is relatively low.

Finally, several vehicles of varying sizes, engine types and driving conditions have accumulated more than 200,000 miles using the hybrid spin-on filter. Many of these vehicles have been driven more than 25,000 miles with the same filter and the same oil while maintaining a five-micron particle count average of fewer than 1,000 per milliliter of oil.

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Figure 4. Particle Count

Benefits of Hybrid Filter Technology
The hybrid spin-on filter improves filtration efficiency leading to the absence of small particles in the engine oil. It prolongs oil filter and engine life and can reduce maintenance and operating costs. It also reduces friction, which increases engine and fuel efficiency. Because the hybrid spin-on filter maintains high filtration efficiency in excess of 25,000 miles, the filter can be used to extend oil and filter change intervals. Improved filtration efficiency and extended oil drains provide direct and indirect savings, which benefits private vehicle owners as well as fleets, high-mileage vehicles and heavy equipment users. In addition, reduced filter and oil consumption leads to a decrease in environmental impacts through a reduction in hazardous waste and use of petroleum.