The combination of electric motor, gearbox and power electronics in the e-axle is a promising concept for vehicles with an electric drive. MANN+HUMMEL has developed special gearbox oil filters for this application which use the new MULTIGRADE eM-CO filter media.

Driving pleasure without emissions is currently in vogue. In view of congested cities, high levels of air pollution and stricter statutory requirements, developers are working all out on sustainable solutions. And car buyers are on board: in Germany and other countries across Europe more and more vehicles are being registered with alternative drives. Developers are focused on the electrification of the powertrain. In this respect the highly-integrated e-axle is an especially promising concept. The e-axle is a system which combines the electric motor, gearbox and power electronics. This saves installation space, components and wiring due to the fact that the e-axle is integrated directly on the drive axle. According to the system suppliers, this enables up to 20 percent less weight and between 5 and 10 percent greater efficiency. What‘s more, the easy scalability of the system makes it suitable for use in compact cars, sports cars up to commercial vehicles.

Lubrication and cooling with the same oil

As all the drive components are integrated in an e-axle, a common oil circuit is sufficient for cooling and lubrication. This advantage, however, has a drawback. Mechanical as well as electronic components are exposed to the same oil and metal particles and chips out of the transmission can penetrate the power electronics and electric motor and cause serious damage. As a result, these particles need to be efficiently, quickly and permanently removed from a reliable working system. In this respect, just as with conventional gearboxes the focus is on the separation of particles. Therefore, a filter can be integrated on the pump suction side directly in the oil sump. This protects the system from the pump to the return flow to the sump.

Lower differential pressure

The filtration experts at MANN+HUMMEL have taken on this challenge and developed suitable gearbox oil filters for the e-axle application. The filters are equipped with the new MULTIGRADE eM-CO filter media. The filter media are specially designed to meet the requirements for the oil with regard to the lubrication and cooling of e-axles. Here MANN+HUMMEL is able to transfer the advantages of fully synthetic filter media used in other oil filter applications. The fully synthetic filter media is free of glass fibers and has a high chemical resistance and considerably lower differential pressure in comparison to conventional gearbox oil filters fitted on the suction side. MANN+HUMMEL utilizes consistent filter media layers without uncontrolled artificial media bypass, something which is required for conventional products due to their high loss of differential pressure. Vehicle owners can therefore depend on reliable particle separation at all times. The use of a depth filter media enables the secure entrapment of the separated particles in the 3D fiber matrix. This prevents the reintroduction of particles or even long chips into the system, a danger which is common with conventional systems. The oil supply can also be permanently ensured without use of an uncontrolled filter bypass, which increases the system reliability.

Low space requirement, maximum filter surface area

The MULTIGRADE eM-CO filter media require less space as the developers at MANN+HUMMEL were able to exploit the company‘s proven pleating technology. An installation space of just 20 millimeter is enough for the pleating. This allows the fitting of a substantial amount of filter media in even the smallest installation space. The result is an enormous increase in the filter surface area and therefore also the dust holding capacity by a factor of almost six. An advantage which is particularly evident in the compact design of the e-axles, but also in the classic automatic transmissions. As a result, a significant increase in operating time and thus filter lifetime can be achieved without a significant increase in differential pressure. Under consideration of the differential pressure, which is important for the suction side operation, the advantages of a pleated solution are also clear to see as there is a further significant decrease in the differential pressure. In comparison to a flat filter media, the pleated variant enables a differential pressure which is up to 75 percent lower already with an installation height of 20 millimeter. This gives the customer a greater degree of freedom with regard to higher filter fineness or dimensioning of the pump.

The filter media always retains its shape and performance, even when exposed to coldness or high differential pressure. Stability is ensured by a drainage grid or adhesive lines which maintain the ideal gap between the pleats. This enables more long-term use of the complete filter surface area.

Housing with efficient flow characteristics

The plastic housing of the gearbox oil filter is also robust. Many years of plastics expertise at MANN+HUMMEL and the use of modern simulation methods such as the finite element method (FEM) and mold filling simulations in the development process ensure that all components are able to withstand the highest mechanical requirements. The developers also exploited the possibilities of simulations with computational fluid dynamics (CFD) to enable efficient flow characteristics for the filter housing in particular in tight installation spaces to minimize loss of differential pressure. All of the materials used are also characterized by a high chemical and thermal resistance. On request, additional functions can be easily and economically integrated in the plastic housing. An example here could be magnets which additionally separate the magnetized particles in order to extend the service life of the filter elements.

With regard to the new requirements which electric mobility places on oil filtration, MANN+HUMMEL already today has a wide range of suitable solutions. And a decisive advantage: the specialists from Ludwigsburg are able to exploit many years of filtration know-how and systems expertise. This is also true for the use of suitable filter media used for coolant filtration. This is a further focus of our development activities. Read more about this in the next issue of Automotive News.