New battery shows way forward

WITH a new 48-volt battery optimized for use in mild-hybrid vehicles, MAHLE Powertrain is making it possible to maximize the recuperated energy that can be stored and released. This can significantly increase the efficiency of mild-hybrid vehicles, allowing a fuel saving of between 12 and 15 percent. With this development, MAHLE Powertrain is increasing the capabilities of 48-volt systems, which offer major safety and cost advantages when compared with high-voltage systems.

Mild-hybrid vehicles need to recover energy efficiently and at a relatively high power during deceleration events. High storage capacity is not required for these applications as the recuperated energy can be deployed during the next acceleration. Thus a compact and cost effective battery that is capable of high charge and discharge power levels relative to its storage capacity (high C-rates) is desirable. As there were no suitable low-cost, compact batteries able to deal with the necessary recharge and discharge cycles involving high currents, MAHLE Powertrain decided to develop its own. The LTO chemistry in the selected cells allows continuous charge / discharge rates of 10 kW and peak rates for short periods up to 20 kW from a battery pack that has only a 0.5 kWh storage capacity.

Optimal battery cooling guarantees charge/ discharge performance and battery durability. However, the coolant needed to be electrically isolated from the cells. MAHLE Powertrain settled on a robust cooling strategy, with simulations showing cooling performance to be exactly on target.

MAHLE Powertrain engineers paid a great deal of attention to the design of the busbars and electrical connections within the battery, as any high resistance in these components can be an additional heat source and limit the power capability of the system.

Testing of the first prototype is underway to verify that the pack can meet the performance targets. Initial results indicate that all temperatures within the pack remain within an acceptable range at a continuous discharge rate of over 10 kW and that it is capable of peak power levels in excess of 20 kW. The next step will be to install the prototype pack into MAHLE Powertrain’s 48V eSupercharged extreme downsizing demonstrator vehicle.