Faster to SOP: Virtually and with Smarter Testing

Dr. Reik Laubenstein, Engineer, IAV Automotive Engineering Inc.
Dr. Johannes Werfel, Team Manager, IAV GmbH

Batteries are the core component of electrified vehicles. However, conventional approaches, that heavily rely on physical prototyping and extensive testing, are too slow and costly for the pace that is demanded by the market. IAV implemented virtualdriven processes with smart testing achieving development time and cost reductions of up to 30 %.

Methodology
Often the development of EV batteries heavily relies on continuous and frequent hardware updates and extensive durability testing that proves challenging considering timelines and associated costs. Main obstacles are scarce component availability (e.g., cells) in early stages, and expensive & time-consuming testing loops. Shifting towards virtual development can mitigate these challenges, but these methods often fall short on capturing the complex interactions between the different domains (design, thermal management, function). However, IAV developed a project-proven methodology that focuses on early application of predictive component models, which can be coupled and used to predict the behavior of the higher-level system with complex interactions (e.g., module or pack, see Fig. 1) und thus, reduce expensive prototyping and testing during. The foundation of this “shift-left” approach are electro-physico-chemical models (EPCM) that describe the electrical, thermal and mechanical behavior of the cell. Due to the scarcity of physical cells at early stages of development, our internal tools and workflows enable deriving theoretical cell design parameters with minimal input to construct baseline cell models, that are continuously optimized with further progress. To further increase efficiency, we established a smart testing approach based on reinforcement learning to characterize cells in early stages, by utilizing neural networks to balance the testing effort and model accuracy. It has been shown that 60% of all relevant operational points can be sufficient to reach a comparable accuracy of a model that utilizes all measurement points of the measurement matrix. Once established, the EPCM can be seamlessly integrated into the aforementioned domains to enable further development and optimizations by the respective domain experts. This is realized via the versatile virtual battery testbench (VBT) framework developed by IAV and allows for model-in-the-loop (MiL) investigations in various other established toolchains, which are being utilized by various domain experts throughout the whole V-process (e.g., thermal management, BMS function development, exploration of mechanical constraints) and without requiring physical cell samples.

Figure 1

Application
A critical aspect in battery systems development is the ability to accurately understand and predict battery aging under realistic operating scenarios. In our approach the EPCMs are capturing structural changes on particle level (e.g., Li plating, SEI growth, particle cracking) in response to the change of the boundary conditions of the system via interaction through the VBT. This was applied in a representative project: failures in battery modules were detected at roughly half the targeted lifetime. A simulation-driven approach utilizing the cell model, completed within six weeks identified critical pressure accumulation caused by the interaction of cell aging, swelling, and module boundary conditions. Early virtual integration is estimated to have saved more than six months of testing and prototyping.

Effective Solutions for Bearing Insulation to Prevent Electrical Erosion

Philippe Pauchard, Application Engineer at DuPont (Switzerland)
Christoph Berger, Application Development Manager, DuPont (Germany)

Electric erosion in bearings

Undesirable parasitic electrical currents in traction motors can pass through roller bearings and cause damage known as electrical erosion. This phenomenon is characterized by electrical discharges between the rolling elements and the bearing raceways, leading to the formation of spot welds at the contact surfaces. During operation, these spot welds repeatedly break apart, generating abrasive metal debris that accelerates wear and can result in premature bearing failure.

Electrical erosion can affect bearings in various types of electric motors, including AC, DC, servo, and stepper motors, and is most observed in
high-speed motors, electric vehicle regenerative braking systems, and motors controlled by variable frequency drives (VFDs). In severe cases,
electrical erosion can lead to premature motor failure, posing safety risks, increasing downtime, and resulting in significant repair and replacement costs.

Common solution

A common mechanical solution to prevent electrical erosion is the use of hybrid ball bearings with ceramic rolling elements. These bearings provide electrical insulation between the rotor and the housing, thereby eliminating the conductive path required for electrical discharge and subsequent erosion. However, it is important to note that hybrid ceramic ball bearings can be more expensive than standard steel bearings. For roller bearings, or for bearings designed to carry higher loads and therefore employing larger rolling elements, hybrid solutions are either significantly more costly or not commercially available.

A more economical approach is to electrically insulate standard steel bearings. Ceramic-coated bearings, typically using aluminum-oxide coatings applied to the inner or outer ring, effectively block DC and low-frequency stray currents. Coating thicknesses in the range of approximately 100–200 μm are commonly rated for 1–3 kV DC breakdown voltage. However, due to their capacitive behavior and limited mechanical robustness, such coatings may provide reduced protection against high-frequency electrical discharge in modern motors controlled by variable frequency drives (VFDs).

Insulating Sleeve Idea

To effectively protect against high-frequency electrical discharge and avoid capacitive effects, a thicker electrical insulation barrier is required.
Polymeric insulating sleeves, typically with thicknesses in the range of 1 to 2 mm, can be used for this purpose. The choice of polymer, however,
is constrained by its dimensional stability at the peak operating temperature of the application. For EV traction motors, peak temperatures typically specified by OEMs are around 150 °C. While many polymers do not melt until higher temperatures, they often exhibit a glass transition temperature below 150 °C, which compromises dimensional stability at elevated operating temperatures.

The use of glass-fiber reinforcement can help mitigate this effect and increase temperature capability; however, the presence of glass fibers may
introduce abrasive wear on metallic counter surfaces, such as aluminum housings. To address these limitations, a high-temperature polymer is required that maintains dimensional stability at elevated temperatures without the need for fiber reinforcement.

Vespel® polyimide: Balancing electrical insulation and dimensional stability

Vespel® S is a sintered polyimide that exhibits no observable glass transition temperature or melting point. Its exceptional high-temperature resistance allows it to be used as an insert in die-cast aluminum components. This unique property is particularly important for applications involving high mechanical loads and elevated temperatures, such as traction motors operating in critical drive modes or under malfunction conditions.

Vespel® polyimide insulating bearing sleeves can be used to electrically insulate the rotor from the housing, thereby suppressing discharge currents. They provide a versatile and cost-effective solution for mitigating electrical corrosion in electric motor bearings and can be installed during final assembly by press-fitting standard ball bearings. A Vespel® polyimide insulating layer with a thickness between 1 and 2 mm offers robust electrical insulation by significantly increasing electrical impedance. This effectively attenuates high-frequency currents traversing the bearing, thereby reducing the risk of electrical erosion. In addition, Vespel® polyimide exhibits mechanical damping properties that may help reduce noise, vibration, and harshness (NVH) in electric motor systems.

Manufacturing Vespel® bearing Sleeve

Vespel® polyimide components are manufactured using a powder-based direct forming process followed by high-temperature sintering. In this process, polyimide powder is compacted at room temperature into a green part, which is then sintered to produce a dense, non-meltable polyimide component. Unlike injection-molded parts, sintered components do not exhibit structural weaknesses such as weld lines or injection points. Depending on the final tolerances required for the assembly, the sintered parts can be machined using conventional metalworking equipment, including grinding operations, enabling the production of high-precision finished components.

Assembly of Vespel® sleeve onto the bearing

The Vespel® sleeves can be installed by press-fitting them onto either the rotor shaft or one of the bearing rings (Figure 1). In all configurations, standard steel ball bearings can be used in combination with the Vespel® sleeve, thereby eliminating the need for costly ceramic rolling elements such as those used in hybrid bearings.

Figure 1: Vespel® bearing insulation sleeves can be installed on the outer diameter (left) or on the inner diameter of the bearing (right)
Figure 2: Assembly of bearing has been done on a 88 mm diameter roller bearing (NU209)

Assemble Bearing Equipped with Vespel® Sleeve

The assembly of bearings equipped with a Vespel® sleeve was evaluated by Durkopp, a manufacturer of roller bearings. In this study, Durkopp ground the outer diameter of several test bearings to achieve press-fit conditions ranging from +5 μm clearance to 50 μm interference. During assembly (Figure 2), the press-in force was measured using a load cell.

The maximum insertion force measured during assembly is shown in Figure 3 for various interferences. An assembly force of up to 9,300 N was recorded at the highest interference fit, with no observable damage to the Vespel® sleeve.

Figure 3: Maximum insertion force measured during assembly for various interference

Electrical Properties Comparison with Ceramic Bearing

Various tests have been conducted to support the use of Vespel® sleeves in addressing electrical corrosion issues. The electrical impedance was measured by IMKT (Institut für Maschinenkonstruktion und Tribologie at Leibniz Universität Hannover). The results indicate that the electrical insulation performance of Vespel® SP-1, while slightly lower than that of hybrid bearings, remains within the same order of magnitude and is
significantly higher than that of ceramic-coated bearing solutions, even when compared with the thickest ceramic coating layer (Figure 4).

Static and Dynamic Load Testing

To demonstrate the mechanical resistance of the Vespel® sleeve, a test was conducted on an 88 mm-diameter roller bearing (NU209). A radial load of 10 kN, which is significant for a standard roller bearing, was applied for 24 hours at a temperature of 140 °C (Figure 5). The circularity
of the Vespel® sleeve outer diameter was measured before and after the test. The results indicate that the circularity increased only from 3.7 μm
to 5.2 μm, remaining well below the supplier’s specified limit of 9 μm for the bearing. These results demonstrate the excellent dimensional stability and mechanical resistance of Vespel® components under demanding operating conditions.

A similar test was conducted at a rotational speed of 3,000 rpm. In this case, the test was performed under a higher radial load of 25 kN, but at room temperature. The results indicate that the circularity increased only from 2.9 μm to 7.0 μm after the test, which remains below the supplier’s specified limit of 9 μm.

Summary

Electrical erosion is a major reliability concern in modern electric motors, particularly in high speed and VFD controlled applications where high frequency discharge currents accelerate bearing degradation. Conventional mitigation solutions such as hybrid ceramic bearings and ceramic coated bearings offer partial protection but are often constrained by high cost, limited availability, or reduced effectiveness under high frequency electrical stress.

The results presented in this study demonstrate that Vespel® polyimide insulating sleeves provide an effective and economical alternative for
electrically insulating standard rolling bearings. By introducing a thick polymeric insulation layer, Vespel® sleeves significantly increase electrical impedance, thereby attenuating high frequency discharge currents and reducing the risk of electrical erosion. Electrical testing confirms insulation performance comparable in magnitude to hybrid bearings and clearly superior to ceramic coated solutions.

Mechanical testing under representative load, speed, and temperature conditions further confirms the excellent dimensional stability and mechanical resistance of Vespel® sleeves. Their compatibility with standard bearings and conventional press fit assembly processes makes this solution particularly attractive for scalable industrial and automotive applications. Overall, Vespel® insulating sleeves offer a robust, versatile, and
cost-effective approach to improving bearing durability in electric motor systems.

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Protecting a single profit pillar is not a winning strategy

Global powertrain markets are diverging. BorgWarner CEO Joseph Fadool explains why “making speed the moat”, re-regionalization, and AI will shape the automotive propulsion industry – and why policy shouldn’t push technology

Joe, what does it mean for BorgWarner when, as is currently the case in global markets, propulsion concepts are diverging dramatically?

Maybe some context is helpful here. In the past, let’s say 30 to 40 years ago, much of the powertrain development was driven by emissions and fuel economy improvements, with Japan and Germany leading in part. Each region followed more or less the same path, adopting technology that led in one region and then flowed to others three to five years later. What’s changed now is that each market requires a fundamentally different mix due to a combination of local regulations and consumer behaviors. In China, over 50% of vehicles are hybrids or pure BEVs; Europe is approaching 18-19% EV share; the U.S. is stepping back, with government incentives withdrawn and EV penetration expected to remain around 7-8%. For BorgWarner, as a global company serving all major OEMs around the world, the good news is that we have a resilient portfolio capable of serving all markets, no matter the propulsion type. As an industry, we must return to a customer-first mentality rather than letting governments legislate what people will buy. I think that was a complete disaster. The OEMs know what consumers want to buy. You’re going to continue to see regionalization and differences between the markets. Long term, however, we still believe in electrification; it is the only way to truly decarbonize. But it will happen at different speeds, it is dependent on many factors like infrastructure and rare earth mineral availability, and it won’t be without disruption.

In your plenary speech at the CTI symposium in Novi, you used the term “moat”. What are the decisive factors in stabilizing or widening it, especially in competition with China?

Moat is a term Warren Buffett and others used – a reference to castle moats that slow down or stop the enemy. For our industry, it means a couple of things. First, innovation: more value at lower cost, more efficient powertrains – better fuel economy for combustion, smaller batteries for the same BEV range. Second, and this is what’s changed in the last five years: speed as a moat. China is teaching the rest of the world that you must constantly reinvent and bring better products to market faster. The companies that move at speed will win; the slower ones are stuck in the old paradigm. We see this reflected in the OEM landscape too: when I joined the industry 35 years ago, growth was driven by Ford, GM, Volkswagen, Toyota. Today, the only OEMs really growing are seven or eight Chinese companies, plus Hyundai. Hyundai is still growing and doing well. Everyone else – GM is out of Europe, Stellantis retreating from India, Ford down to 3% in Europe – is shrinking. Retreating to protect a single profit pillar is not a winning strategy, in my opinion.

How does regionalization align with the traditional concept of economies of scale through a “world product”? And what are the risks of speed over scale?

This is a great question, because for 20 to 25 years, as global vehicle volumes grew from 50 to 90 million, scale was the name of the game. We were investing heavily in technology, developing suppliers, and building factories that needed to run efficiently. What we now see is that beyond a certain point, other factors become more important than scale – specifically speed and local accountability. That doesn’t mean abandoning scale; it means finding a new balance. Housing and mechanical parts, even factory assembly, require far less scale than before because these are readily available products, and suppliers are more regionalized. Semiconductors, on the other hand, remain a scale game – chip companies pay more attention to Tier 1s and OEMs that give them high volume. The downside of scale is loss of local agility. Large global competence centers that push technology out to regions are less effective now – they’re expensive and slow. When a region has to route

decisions back to a distant center of competence, that’s time lost, and people far from the customer are making local market decisions without fully understanding the pressure on the ground. What we find more effective is giving regions greater authority and competence – a democratization of know-how, with regions learning from one another rather than relying on a central hub. BorgWarner has a decentralized operating model for this reason.

Would a concept of “similar but not identical” components across markets work for you as a supplier?

Definitely. Take turbochargers: they spin at 300,000 RPM and can be dangerous if they fail. Engineered for the German market – high speeds, high temperatures, autobahn use – they’re built to be virtually indestructible. In China, the use case is mainly stop-and-go traffic with 1.5-liter engines. The load profile is fundamentally different, so you don’t need the same robustness. We’ve reengineered our turbo line for China accordingly – 20% lower cost than the European or North American equivalents. Five or ten years ago, we would have carried over the European or North American product into China. And we found we were no longer competitive. We were sometimes over-engineering for markets that didn’t need it – and while we told ourselves we were gaining scale, the design simply wasn’t affordable in every market.

How can leadership culture help to handle the change?

Leadership has to start by accepting the uncertainty. A big part of the job is looking around the corner and anticipating the future – that has become much harder. It means thinking in scenarios rather than toward a single point, even while maintaining a true north. The second shift is toward flexibility: a resilient portfolio, a flexible supply chain, and a manufacturing footprint that can serve multiple customers on the same production line rather than running just one. Leading today is about providing clarity on facts and priorities, while helping people navigate the uncertainty. The disruption increasingly comes from outside the industry, and that’s accelerating. In China, many successful automotive players came from consumer electronics – Huawei being the obvious example. In the U.S., Apple, Google, Waymo, and Tesla have demonstrated that companies with no traditional automotive background can become highly relevant because of software competence and systems thinking. These players don’t focus on individual components – they think in terms of the experience they want to deliver to the customer.

BorgWarner has been shaped strongly by powertrain hardware. What does it mean when intelligence is shifting into software – and the SDV?

We’ve seen software grow in the powertrain space for a long time – ECU development, electrification driving demand for complete drive modules with integrated software. The software-defined vehicle is a parallel innovation aimed at reducing development costs and enabling over-the-air updates long after a vehicle has left the dealership. If you think of how a smartphone works, the SDV follows the same logic: new features come through software, not hardware replacement. Electrification and SDV actually accelerate each other. The hardest part of implementing SDV is doing it on a legacy platform with hundreds of distributed electronic modules. The goal is to consolidate to a zonal controller architecture. At BorgWarner, we see a future where the Powertrain controller integrates into the front-end zonal architecture. Some competitors have expanded from their ECU supplier role into zonal suppliers – we’re looking at the same path. Most OEMs currently keep Powertrain as a separate subsystem, but we expect that to change, and we want to drive it.

Where is AI most important for BorgWarner as a company?

We’ve used machine learning and AI in our factories for a long time. Generative AI with large language models adds value in three areas. First, product development: replacing routine engineering tasks with agents and tools – code generation, test automation. The highest benefit

comes from automating the repetitive tasks that consume significant engineering hours, freeing time and resources up to manage more strategic work. Second, factory automation: AMRs and robots are increasingly AI-enabled, and generative AI makes it significantly easier to train them. We expect a step-function increase in automation potential in our factories. Third, personal productivity and end-to-end process improvement: using tools like Copilot or Claude for daily work, and automating manual processes such as monthly financial closes and forecasting. Generative AI is one of the biggest changes we will witness. Personally, I find it liberating – you can delegate the monotonous groundwork, the research, the routine write-ups, and focus on the work that actually creates value.

How will increasingly software-defined vehicles change buyer expectations, particularly in North America, where combustion still dominates?

The two trends are closely linked. SDV is easier to implement on an EV platform. As EV batteries become more affordable, adoption will grow; as EV adoption grows, users will experience more features; that experience will pull more people toward EVs in the future. It’s a reinforcing cycle. We expect SDV to reaccelerate electrification as electric vehicles become cost-competitive. Europe will play this out first; North America will follow. Buyers will demand over-the-air updates, vehicles that have more features and deepen integration with their home and mobile environment. You know, these cars are awesome. So I think these two things are converging, and it will reaccelerate electrification to some degree.

Interview:

Gernot Goppelt