Angus Blackford, principal design & analysis engineer at MAHLE Powertrain, explains how the vehicle thermal architecture is a crucial factor in enabling EVs to live up to their specifications and perform in real-world operating conditions.
For the key components in an electric vehicle – such as the battery, power electronics or the motor – to be able to deliver their optimal performance, particularly at sustained high power levels or in extreme temperatures, it is crucial that they are maintained within their operating temperature limits.
At MAHLE Powertrain, thermal management is one of the key disciplines we think about in electrified vehicle programme work. Range, charging speed, sustained power output, battery longevity: each of these, at its core, requires a thermal management solution to ensure reliable operation.
How efficiently a battery pack is conditioned across a full operating year shapes real-world range. How quickly heat can be extracted from cells under high current sets the ceiling on charging speed. Whether the motor and inverter can shed heat effectively enough determines whether the vehicle holds its rated output or derates to protect itself.
It is crucial that the thermal architecture is well engineered to allow the vehicle to achieve its specified performance. Get it wrong and the gap between predicted performance and real-world performance will differ consistently.
MRC Current Density
A more complex challenge than it appears
The problem has grown significantly as vehicle electrification has matured. A modern BEV or PHEV does not present a single thermal management challenge. It presents several, running simultaneously, competing for the same physical packaging space for coolant loops within a vehicle platform.
MRC Heat Generation
Battery cells operate within a tightly defined temperature window. Stray outside of this and battery performance drops, degradation accelerates and, in extreme cases, safety margins are compromised. Power electronics and motors generate heat that must be removed effectively to maintain efficiency. Under sustained high-load conditions, the kind of real-world use that matters to customers, the vehicle will limit its own output if the thermal architecture cannot keep pace. Often, the cabin heating, ventilation and air conditioning system (HVAC) draws from the same energy storage that is used for driving the vehicle, which is why real-world winter range so consistently diverges from published figures if the system does not manage energy and heat flow efficiently.
The optimisation of these thermal management systems is further complicated by the fact that these systems interact. They cannot be designed and validated in isolation and then assembled into a platform and expected to perform predictably. For example, the instantaneous thermal state of the battery affects what the power electronics can do. The demands placed on the HVAC system affect the energy available to the drivetrain.
Understanding how these thermal systems behave together, under the dynamic conditions of real-world driving and charging, rather than controlled test cycles, requires a level of modelling complexity and detailed empirical data that few thermal engineers have experience of, or access to. This is where MAHLE Powertrain has a clear advantage over its competitors in this field. Being part of the MAHLE Group enables it to draw on the experience of MAHLE’s expertise in the field of vehicle thermal components and access the vast library of component performance data, to help guide vehicle manufacturers to the optimal component specification to suit their application.
The performance difference between a well-integrated thermal architecture and a poorly integrated one shows up in range, charging consistency, and in how the vehicle performs across varying conditions throughout the year.
Immersion cooling
One area where we are seeing increasing demand, particularly for high-performance applications and platforms targeting rapid charging, is immersion cooling for battery packs. Immersion cooling brings the fluid into direct contact with individual cells. The engineering case is compelling. As the cooling medium is in direct contact with the cells and cell connectors it helps to eliminate thermal gradients within each cell and to ensure an even temperature distribution between cells, across the pack. Eliminating these temperature differences is important because pack performance is constrained by the hottest cell, and uneven temperatures accelerate degradation unevenly over time.
The precision of control immersion cooling, particularly under the high heat loads that come with high power charging, offers considerable advantages over conventional approaches. For battery architectures where charging speed and sustained performance are primary requirements, immersion cooling warrants serious evaluation.
The case for getting it right early
The layout of a vehicle thermal architecture is one of the most crucial decisions made early on in a new vehicle programme and one of the least revisable in the entire vehicle development process. A thermal architecture that is adequate at nominal conditions but insufficient under real-world peak loading is a problem that is not straightforward to fix once the programme is mature. The structural, packaging, and system integration implications of changing a cooling architecture late in development are significant. Hence why MAHLE Powertrain puts a lot of effort into ensuring this is analysed thoroughly at the concept stage, so that the underlying architecture will be capable of performing under all real world operating conditions, whilst driving or charging.
The thermal decisions made at programme start set the boundaries within which everything else must operate. They determine the maximum charging rates that can be sustained over the vehicle’s service life and shape the battery degradation profile that underpins what warranty commitments are commercially viable. They further govern how consistently the motor delivers its rated output in demanding conditions. Getting those decisions right, which means modelling the interactions between thermal systems under real-world conditions rather than nominal ones and making the architecture choices that follow from that analysis, is where the engineering value is created.
Learn more: www.mahle-powertrain.com
