Cologne/Ludwigsburg, Germany, March 13, 2018 - In oil filtration present and future applications have higher demands in regards of performance, chemical and physical resistance. Synthetic filter media made of polymers without glass fibers have excellent properties to face these challenges. The filtrations experts at MANN+HUMMEL have developed a new media portfolio of the MULTIGRADE O-S class, which offers synthetic media made of polymers for a broad range of applications. The chemical resistance of MANN+HUMMEL synthetic media is adapted to the demands of modern oils in engine as well as transmission and coolant oil applications in internal combustion engines, e-axles and batteries of e-mobility applications.
The MULTIGRADE O-S media withstand the chemical degradation of motor oils up to 600 % better than comparable cellulose or mixed fiber media. A similar result is attainable for the resistance against water in oil. Here, the differential pressure loss is near the performance without any water in oil, which is not the case for cellulose media. Based on the way of production, synthetic fibers can be tailor-made. This is a mandatory basis for every development of filter media with numerical approaches. MANN+HUMMEL benefits of valuable know-how about new high performing filter media with regards to performance, costs and limited installation spaces.
In modern motor driven vehicles the demands on high efficient processes increase more and more. With the EURO norms that have and will come up for internal combustion engines (ICE), it is necessary to improve the combustion process and all other contributing processes steadily. Beside the combustion process, also the engine oil has several important tasks that are directly linked to the efficiency of an ICE. One major task of the oil is lubrication, mainly of the pistons and the crankshaft. Here, technology is steadily evolving and current trends are pointing towards new low viscosity oils for better efficiencies. To maintain the motors’ efficiency over many driving hours, cooling is another task of the oil circuit. The space between the pistons and the motor block’s wall has to be sealed, which is achieved by a thin oil film. As the oil is covering the surfaces, it prevents corrosion due to chemical processes and even quiets the motor’s noise. Another task of high importance is to keep the motor clean. Organic particles like soot from the combustion process as well as inorganic particles like metal due to wear have to be transported away from the lubed spots, such that they do not steadily contribute to further wear.
Besides engine oil, transmission oil also contributes to the efficiency of modern vehicles. Here the oil has the tasks to lube, to cool, to protect of corrosion and also to transport dirt, that influences the efficiency of the vehicle. A very present example of transmission oil circuits can be found in e-axles of modern e-mobility drivetrains like in battery electric vehicles (BEV). Especially in BEV that provide a large power, an e-axle has to be lubed and cooled. The batteries in such systems provide a certain amount of dissipated energy, which has to be transported via a cooling system. Due to security issues, usually coolant oil systems are applied to cool batteries.
All these oil circuits have to be cleaned in-situ by filtration, as they directly or indirectly contribute to the efficiency and lifetime of the drivetrain’s components. Filtration is a process that has been included since the early days of ICE and automatic transmissions. The filtration performance is not only driven by the process parameters themselves. The performance parameters efficiency, the dust holding capacity and the differential pressure are influenced by the choice of the filter media. As filter media are influenced by contaminants and the chemistry of the oils due to chemical degradation during the oil’s lifetime, the performance changes over the lifetime of a filter. Contaminants like particles block the free areas of flow, which leads to an increased differential pressure. Oils and especially oil additives (e.g. conductivity enhancers or aggregation agents) change in chemical nature over operating time due to degradation processes. A common indicator for aggressive changes is the total acid number (TAN), and respectively the total base number (TBN). During the ageing of oils, the acid number increases until the crossover of TAN and TBN. Here, the chemical nature of the oils becomes disruptive for certain materials. Filter media as well are influenced by this change of the oils. However, the extent of change of the filter media is dependent on the choice of the filter media base material.
The filter media base materials have changed over the years. From first pleated media until now, cellulose fibers are used in oil filtration. Since several years, the advantages of synthetic fibers like polymers and glass have been discovered such that they are mixed with cellulose fibers or they are used as 100 % base material. A speciality of glass fibers are the very fine and rigid fibers that provide excellent differential pressure behavior, chemical resistance and ultra-fine filtration efficiencies. The costs that come along these advantages are that the fibers are brittle, have to be handled in a special way during production, and the glass fibers can be shed to the clean side if there is no protection. Using filter media containing glass fibers requires an efficient barrier layer against fiber shedding. MANN+HUMMEL has developed a barrier for fuel applications that is located downstream the filter media and ensures the compliance with current requirements for component cleanliness.
For applications like engine oil, coolant oil and transmission oil filtration in passenger cars, synthetic filter media made of polymers show many advantages regarding the differential pressure behavior and chemical resistance against the more aggressive oils with further additives. This is why they can already be found in many truck and passenger car applications, and also in future e-mobility applications. In the following, “synthetic media” describe media that are made of 100% polymer fibers without any glass fibers.
Synthetic oil filter media are typically made of polyester (PES), more precisely polyethylene terephthalate (PET) or polybutylene terephthalate (PBT). These synthetic fibers are around 7-20 µm in diameter, which is about the half of common cellulose fibers. To produce synthetic filtration media, manufacturing processes such as the wet-laid, needle-felting, meltblown or spunbonding processes are employed.
In the production process of oil filters, media have to be pleated. For better pleat stability and in order to avoid bunching of the pleats, which means contact through the entire surface particularly under pressure, a drainage is needed. In case of cellulose based media a corrugation is the general way to avoid direct pleat contact. For fully synthetic media, a grid attached on the clean side of the filter media, is applied.
MANN+HUMMEL fully synthetic oil filter media are highly resistant regarding chemical degradation and oil ageing products. To proof this characteristic the burst pressure of filter elements made of cellulose, mixed fiber (cellulose + synthetic) and a MULTIGRADE O-S media was measured in new state and after storage for 48h at 140°C in used oil (from field test vehicles). As shown in Figure 3, the new and stored elements made of cellulose and mixed fibers are similar in burst pressure characteristics. The comparison of the media in new state showed an increased (~ +50 %) stability of the MULTIGRADE O-S media compared to the cellulose based media.
It is already known that cellulose molecules are partially cleaved under acidic conditions and embrittle more quickly. The impregnation with phenolic resins protects the fibers, but if the material is exposed for a longer time in aged, acidified oil at high temperatures, it has a strong impact on its stability. As shown in Figure 3 after ageing, the burst pressure for cellulose based media dramatically drops. Compared to this effect, the MULTIGRADE O-S media shows a significant higher ageing resistance (+ 600 %) by the higher burst pressure.
On the basis of the buildup of the MULTIGRADE O-S with the drainage grid and spirally glued strips around larger filter elements, the resulting pressure drop at increased oil viscosities (around 500 mm2/s) is lower compared to a mixed fiber media. This lower pressure drop is also the reason why the MULTIGRADE O-S media is particularly suitable when small design spaces are available. Particularly with regard to the demands of pulsations in automatic start-stop systems on filter media, pressure drop plays an important role.
In addition to the increased resistance against aged oils, the MULTIGRADE O-S media have the property to remain stable in contact with water. Alternative fuels with higher ethanol contents result in higher water solubility. Once condensed and above the solubility in fuel, water droplets are in the system. These can be removed by MANN+HUMMEL’s three stage water separation. However, dissolved water from the fuel as well as humidity coming with the intake air for combustion as well as breathing of the crankshaft housing introduces water in the engine oil circuit. During an engine cold start, water is also more likely to enter the oil circuit. In this phase, small amounts of water and fuel condense on the cold cylinder linings and intake system and then penetrate the engine oil via blow-by gas. The effect of free water droplets in the oil is enhanced by a short distance drive behavior and influences the lifetime of the motor’s components. Water is taken up by cellulose filter media as water has a large contact angle on these porous materials. However, water leads to a swelling of cellulose materials and therefore the mean pore size decreases, resulting in a larger pressure drop at same operation conditions.
With growing requirements on future oil filtration applications with regard to higher dust holding capacities (DHC), lower pressure drops (∆p) and increasing filtration efficiencies (η) by reduced design space and costs, new tools are needed to support the development of such sophisticated media. Theoretical approaches can be applied best via numerical simulation tools to achieve new insights into filter media structures and therewith optimize the media according to the mentioned demands.
In particular the CFD-simulation around media structures based on CT (computer tomography) analysis can help to improve existing materials or to develop new materials depending on the capabilities of the manufacturing process. To simulate new media, first an existing media has to be digitalized via CT. The structure of this media then is available for numerical simulations and describes the boundary conditions of the media structure precisely. In a further step, a virtual twin is generated and based on this virtual model, different variations could be designed. Via numerical simulation of filter media, new, very high performing structures can be achieved. These structures are translated into new optimized filter media that achieve unreached performances, as well as technically or in terms of costs.
Printed on 2019-02-23