Speaker interview: Mike Bassett, Chief Engineer at Mahle Powertrain
In this speaker interview we talk to Mike Bassett, Chief Engineer at Mahle Powertrain, about second-generation 48V system technology developments, system requirements and future trends.
Mike joined the performance analysis group at Mahle Powertrain in 2007 and is currently Chief Engineer in the Research and Advanced Engineering Group, where he is responsible for leading Mahle Powertrain’s research activities in the UK.
What lessons can we learn from first-generation 48V systems and how will the second generation evolve?
To make the most of the potential benefits of 48V hybridisation, the recuperation power needs to be appropriately matched to the vehicle weight, with heavier vehicles needing proportionally greater recuperation power capability. Attention should also be paid to the efficiency of the components within the system to ensure that potential fuel savings achieved through recuperation are maximised. Looking forward, the more dynamic nature of the WLTC in comparison with the NEDC further drives a higher power requirement. Consideration of real-world usage, and the addition of RDE testing, potentially leads to an even greater increase of the recuperative power requirement.
What are the limits of 48V power supply systems? What functions should be using 48V systems?
The challenge with 48V systems is to maximise power capability to take full advantage of the energy available for recuperation during vehicle deceleration events. This is especially true for mild hybrids, where large battery storage capacity isn’t required, and in fact wants to be kept low to minimise the battery pack cost, weight and package size. It is therefore desirable to have a high-power, low-storage-capacity, battery pack, which leads to the requirement for a very high C-rating capability. This then becomes a challenge for the cell durability and thermal management. In terms of functions using the 48V system, clearly any electrical loads that require high electrical power should take advantage. This is especially true for systems that need short-term high power; for example, electric boosting devices to enhance transient response, or electrical catalyst heating devices that are only used when the vehicle first starts.
What are the emerging trends in 48V and power supply loads?
Obviously, it makes sense to add higher-power electrical consumers onto the 48V system and unload the 12V system. I think we will also see increased electrification of systems/components that were always traditionally mechanically driven, including items such as ePAS, HVAC compressors, coolant pumps and cooling fans. The benefit of such electrical ancillaries is that their power can be readily modulated with need. As more vehicles use these, such as 48V components, the cost of these parts will become competitive with the 12V equivalents and will become attractive, as the cabling requirements and losses are lower.
What will be the long-term future for 48V? Will we see 48V systems in full HEVs and EVs?
48V doesn’t make sense for systems requiring very high power levels, as the current becomes high and drives the electrical connector/contactor requirements to become bulky and expensive. I think that we will settle at around 25-30kW as being the practical limit for 48V systems. We will certainly see 48V HEVs with some degree of electric-only driving. 48V EVs also make sense for small city vehicles, as showcased in Mahle’s MEET 48V EV demonstrator.
What are the fuel economy benefits offered by 48V mild hybridisation?
The benefits that can be achieved depend on many factors. System power and vehicle weight are key parameters, but it is also heavily influenced by the hybrid architecture employed. A P0 MHEV will not be able to give a large fuel economy benefit compared with a P2, P3 or P4 architecture that includes the ability to decouple the engine during deceleration events. For a typical mid-size car with a P0 architecture, a 5% fuel consumption reduction is readily possible. If a P4 layout is used, with the ability to deactivate the engine and deploy recuperated energy via fully electric operation with the engine off, then potentially up to 15% fuel consumption benefit could be achieved.
Mike Bassett will be speaking at Electric & Hybrid Vehicle Technology Conference Europe on '48V Systems: Optimising Next Generation 48V Systems and Architectures To Deliver Fuel Efficiency And Reduced Emissions In The Immediate Term' on Tuesday 07 May 2019.