For some people electric mobility is the concept for the future. For others it is at least an important component of a drive mix which is environmentally friendly. MANN+HUMMEL is open to all options and selectively develops products which support emission-free mobility.

Even though more and more European and Asian countries have announced their plans to slowly phase out combustion engines, there remains uncertainty about the alternatives. In addition to the purely battery-powered approach, there are also electric hybrid concepts such as 48 volt hybrids, mild hybrids and full hybrids, which are included in the focus of the development activities of vehicle manufacturers. In purely battery electric vehicles (BEV) the drive energy is derived from the battery cells carried on-board, whereas with fuel cell electric vehicles (FCEV) the drive energy is generated on-board from hydrogen. Both approaches have one thing in common: they require customized solutions for the respective requirements with regard to thermal management and the efficient filtration of cooling circuits. MANN+HUMMEL has now extended its existing range of filter media to include electric mobility (‘eM’) with MULTIGRADE eM-CO and MULTIGRADE eM-CW for the filtration of coolants based on oil and water in battery electric vehicles and fuel cell electric vehicles.

 

It‘s all about cooling

The requirements for new drive concepts with regard to thermal management are very challenging. The lithium-ion cells used in battery electric vehicles which have a high storage capacity can only be operated within a strictly limited temperature range,  whereby the heat distribution has to be as homogeneous as possible. High, inconstant temperatures lead to a loss of storage capacity and therefore to a reduced range for the vehicle. Extreme overheating of the battery pack can even lead to a thermal runaway resulting in the complete destruction of the system.

Heat is also the core issue with fuel cell electric vehicles. In contrast to batteries, fuel cells are not used for energy storage, but for the purpose of conversion. The energy is created through the reaction of hydrogen carried in the fuel cell tank with atmospheric oxygen. Water vapor forms through catalysis. In this process, energy and also heat is generated. It is possible to extract the heat from battery packs and fuel cell packs by means of indirect cooling realized with cooling channels filled with a mixture of water and glycol. However, it is also possible to directly cool individual battery cells using non-conductive media. In this respect, specially developed cooling oils can ensure uniform heat dissipation. For both methods it is essential to make sure that particles in the cooling liquid do not block the fine cooling channels, or contribute to increased wear of the pump.

Designed to reduce differential pressure

The MULTIGRADE eM-CO filter media developed by MANN+HUMMEL especially for use in battery electric vehicles meets the requirements with regard to lower differential pressure and higher dirt holding capacity. The fully synthetic media offer a high chemical resistance to the low viscosity oils and dielectric fluids used in battery electric vehicles. The mechanical stability of the filter element is ensured by a drainage grid on the clean side which serves to maintain the ideal distance of the pleats. As a result, the whole filter surface is permanently available for use. This leads also at low temperatures and high flow rates to a low differential pressure. The filter media class MULTIGRADE eM-CO with a separation efficiency of 99.5 percent currently covers particles in the range of 50 to 180 micrometers. The MULTIGRADE eM-CW filter media class is also efficient when used for the filtration of water-based cooling liquids which find application in the thermal management of fuel cell packs. Due to the fact that flow rates of up to 15,000 liters per hour are required for the purpose of cooling, the filter element has to be stable under pressure and also designed to reduce differential pressure. A stainless steel grid ensures that the filter element is characterized by excellent mechanical stability. The selection of appropriate materials for all components reduces the washing out of ions (dissociation or ion discharge) to a minimum and therefore helps to protect the fuel cell against a loss in performance. The MULTIGRADE eM-CW 180 separates 99 percent of all particles from the size of 180 micrometers.

Challenges and success

In order to bring these new, pioneering filtration solutions to the market, new test benches have to be set up and new test methods have to be developed. Here MANN+HUMMEL can draw on its decades of expertise and quickly create the conditions to already test products during the development stage under conditions which are close to series conditions. In 2017 the first prototypes with MULTIGRADE eM-CW were delivered to customers to enable validation tests on a test bench with virtually field conditions. The filters are currently undergoing vehicle tests for the filtration of cooling oil used to cool battery cells. MANN+HUMMEL has already won series orders for both filtration applications. In addition to the discussed cooling applications the media class MULTIGRADE eM-CO has been successfully tested for its use in e-Axles and is currently in vehicle testing.