We Need to Talk About the Grounding Ring

Posted on 26th August 2026

Goeff Lewis, Technical Director, Duvelco

OEMs love SiC and GaN [1]; higher switching speeds lead to more efficient motors, which in turn mean greater range or lighter, less expensive batteries for the same BEV range.

Higher switching speeds, dV/dt, can mean increased displacement current coupled onto the motor shaft [2].

For a given common-mode voltage (CMV) amplitude, this causes the floating shaft voltage to reach its limit more quickly. Oil films on the bearing races can break down at around 20 to 50 volts, which in turn can lead to bearing damage through electrical erosion (EDM) and related pitting. Higher-speed, higher-frequency multipole motors mean the number of possible EDM events increases broadly in proportion to the voltage excitation frequency, hastening possible bearing failure.

One widely adopted solution is to fit a shaft grounding ring, which effectively clamps the floating shaft voltage to near zero — typically within a few volts in practice.

Why don’t OEMs love this solution?

• An additional component with associated cost, complexity, and assembly considerations.
• Axial packaging space requirement, which can be challenging in highly integrated e-axle designs.
• Requirement for a dry operating environment (i.e. separation from the lubrication system), which may necessitate additional sealing and space.
• A wear component that may not reliably meet the ~15-year design life expected of BEV drivetrains.
• Potential source of NVH (Noise, Vibration and Harshness), particularly noticeable in inherently quiet electric vehicles.
• Most critically, a hidden degradation mechanism can be difficult to detect and may lead to non-graceful bearing failure, potentially immobilising the vehicle.

Engineers and product managers have therefore sought to design out the risk of EDM entirely – the ideal solution. However, despite the use of advanced filters and common-mode chokes, this has not yet been achieved without compromising the efficiency gains offered by SiC- and GaN-based inverters.

A commonly adopted mitigation strategy is the use of electrically insulated bearings. These may take the form of bearings with ceramic insulating coatings or hybrid bearings with ceramic rolling elements.

Such bearings can be relatively expensive and, to some extent, more fragile. In addition, thin ceramic coatings with a moderate dielectric constant can still support capacitive coupling, allowing displacement currents to flow and reducing the overall impedance at high frequencies.

A dimensionally stable, creep-resistant polymer insulator with a low dielectric constant (e.g. ~2.7 at 1 MHz and 150 °C) could enhance the robustness of such mitigation strategies.

Research from Leibniz Universität Hannover (IMKT) has shown that polyimide coatings can exhibit higher electrical impedance than conventional ceramic coatings, approaching that of hybrid bearings while providing improved robustness [3].

Building on this work, Ducoya — a highly crystalline, PFAS-free PMDA–ODA polyimide from Duvelco — offers excellent flow characteristics, enabling high-precision moulding of thinner-walled sections. Its relatively low dielectric constant also helps reduce parasitic capacitance and associated displacement currents. Together, these attributes enable reduced material usage and improved dimensional control, providing an economically attractive route to enhance the robustness of grounding strategies and mitigate EDM-related bearing damage.

Duvelco Ducoya also exhibits high compressive and tensile strength and toughness at elevated temperatures, which may be advantageous across a wider range of applications.

Duvelco Ducoya is available both as a moulding-grade polymer for use with suitable modern precision processing equipment and as finished components for integration by bearing manufacturers or OEMs.

The preliminary data in the graphs below, demonstrates how Ducoya also exhibits high compressive and tensile strength and toughness at elevated temperatures, which may be advantageous across a wider range of applications.

As electrified powertrains continue to evolve, the focus is increasingly shifting from mitigating EDM risk to addressing it at source. Advancedmaterials such as Ducoya may offer new possibilities for more robust, spaceefficient insulation strategies, helping engineers explore alternatives to traditional approaches. The question is: could a material-led solution play a greater role in future drivetrain design?

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[1] Silicon Carbide and Gallium Nitride.
[2] I=C. dV/dt
[3] Pauchard, P., Berger, C., and Jackowiak, R., “Effective Solutions for bearing Insulation to prevent electrical corrosion in E-Drive Systems” CTI Magazine, December 2025, pp. 25.

Thermal Analysis of Axial-Flux In-Wheel Motors

Posted on 19th August 2026

* Simulation results visualizing free surface flow of the oil jet (injection nozzle indicated by the yellow arrow) on the left side and heat distribution in the rotor on the right side, resulting from one single MPX simulation. The green circle marks the location of an infrared sensor.

Investigating e-motor thermals as a result of free-surface flow cooling strategies has long been a complex, laborious effort. We demonstrate a novel simulation method – Mesh-Particle Multiphysics (MPX) – which can provide high-fidelity insights from a single simulation run.

Johannes Becker, Dive CAE
Liam Pek, Dive CAE

Automotive drivetrain electrification presents major challenges to engineering teams, as performance, thermal, weight, and packaging requirements drive the need for increasingly efficient and power-dense designs. At the same time, global supply chain volatility drives the need for high-performance motors that do not rely on rare-earth magnets to enable domestic manufacturing and strengthen industrial resilience.

The primary objectives of drivetrain prototyping are to validate performance, efficiency, durability, and system integration before moving to production. Prototypes for e-motors undergo thorough load testing on test rigs and in demonstrator vehicles to confirm structural and thermal stability under expected real-world and extreme conditions. Insufficient cooling and lubrication leading to prototype failure results in costly iterative rework or even changes to the underlying system architecture, significantly impacting time-to-market.

While virtual testing of lubrication and cooling performance via simulation has been industry standard for years, it is often done in isolated domains, as workflows to combine particle-based simulations used for oil flow analysis and structural thermal simulations often involving multiple solvers and laborious processing steps that require deep numerical expertise. A novel solution to this problem, Mesh-Particle Multiphysics (MPX), enables single-run analyses of free-surface flow lubrication and cooling strategies including full conjugate heat transfer (CHT) through structural elements with timescale coupling. Leveraging the strengths of Smoothed-Particle Hydrodynamics (SPH) for the fluid dynamics of jet, spray, or sump cooling, and the Finite Element Method (FEM) for heat propagation through structures in one unified solver architecture reduces complexity and can reduce time-to-result in e-motor studies from weeks to hours.

The ORBIS ELECTRIC HaloDrive is an axial-flux electric motor architecture with a wide range of applications across industries, including as an in-wheel motor for passenger EV or commercial vehicle propulsion. Depending on the intended application, it supports different cooling strategies optimized for the expected load cycles, operational environment, and TCO.

Using Dive’s MPX, we investigate thermal performance of rotor cooling, comparing a passively cooled rotor as a baseline case with multiple intensities of active jet cooling, axially applied to the rotor. Jet cooling is confirmed to reduce rotor temperature at the position of a radial infrared sensor (see green circle) by up to 22% after 100 seconds of runtime at 1,500 rpm. While the 5m/s jet configuration reaches steady-state temperatures after about 70 seconds of runtime, both 10 and 15m/s jet configurations stabilize around 30 seconds into the test, with diminishing returns of going beyond 10m/s.

Importantly, results for this study were obtained in a single afternoon – requiring less than one hour of simulation pre-processing and four to five hours (depending on flow rate) of simulation time. Executing thermal studies on complex free-surface flow phenomena enables simulation-driven design that produces advanced cooling strategies which are well-validated and understood before going into a physical prototype.

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References
› HaloDrive model provided by ORBIS ELECTRIC. www.orbiselectric.com/halodrive
› Mesh-Particle Multiphysics (MPM). www.divecae.com/technology

Interview “Our Future Hybrids are Designed to Fit in All Current BEV Platforms”

Posted on 7th August 2026

Ingo Scholten, CTO, Horse Powertrain

In addition to dedicated hybrid transmissions, Horse Powertrain also supplies dedicated combustion engines and complete drive modules. At the 28th CTI Symposium in Berlin last December, we spoke to Ingo Scholten, CTO of Horse Powertrain, about developments in current and future hybrid technology.

Mr. Scholten, Horse Powertrain has a broad portfolio of hybrid drives, but also produces its own dedicated hybrid engines and ICEs. That’s unusual
for a Tier 1 supplier …

It is. There used to be a lot of ‘transmission-only’ suppliers for manual transmissions, automatics etcetera. But usually, OEMs made their engines and dedicated hybrid transmissions, or DHTs, in-house. Now we offer both – as a system supplier. That makes us quite special to our partners. Instead of just components, we can also offer entire drive systems – plus full integration support, including topics like emissions and homologation.

What are customers asking for?

Firstly and naturally, we still make drives for Geely and Renault, our parent companies. The Renault E-Tech hybrid, for instance, is now in its third generation. For Mercedes, we supply a 1.5-liter combustion engine for mild hybrids. In China, we’re developing our dual-motor DHTs, which now use dual-shaft transmissions instead of planetary gearing in earlier years. And we’re talking to other customers in Europe and the US. The demand there for full hybrids is even stronger than in China, but they also want PHEVs. We are discussing range extenders more and more, too. In China, it’s mostly long-range PHEVs with a parallel option; they have big traction motors, and drive like EVs. In Europe, drivers still use manual transmissions so multi speed system are accepted even in combination with electrification. But in China, multi-speed transmissions can be a problem because customers there expect an EV driving experience.

Dual-motor hybrid drives are gaining ground. When do you use serial-only, and when is serial-parallel better?

For maximum efficiency, including on highways and rural roads, you’d normally use serial-parallel – mostly P1 and P3. A serial-only drive would cost you 4-5% in efficiency. Parallel or multi-speed transmissions are better for higher tractive force requirements. P2 still has its place for small vehicles in segments A or B. And if you already have an all-wheel-drive system with an electric rear axle, P2 is fine there too; you don’t really need a hybrid drive with two electric motors in the front then. P2 can also work when OEMs design vehicles as ‘BEV native’ or ‘BEV first’, respectively. Space is limited, so a P2 with a single electric motor can be practical when a market needs a hybrid variant of the BEV.

Looking at P1/P3 hybrids, we’re seeing solutions with a single fixed gear, and solutions with two, three, or four gears. What do you think will prevail?

When markets want cars that ‘drive like a BEV’, it makes sense to have fewer gears. Often, just one is enough. For high towing capacity, you can use multiple gears to modulate tractive force. When customers ask us for advice, we often recommend either a large traction motor with one fixed gear or a powertrain with four gears and a smaller traction motor. As I mentioned, Renault has a successful solution that’s now in its third generation.

Many OEMs still need two vehicle platforms; others are moving to ‘BEV first’ and using a BEV platform for hybrids, too. What’s your approach?

That’s currently one of our main topics, as I showed in my presentation here at CTI. Some vehicles still use traditional hybrid architectures, which require certain compromises; others use BEV-only architectures. A hybrid drive with one or two electric motors requires more space than an ICE-only drive, whereas a BEV drive requires much less. So, if you optimize a vehicle’s front end for BEV, the installation space is shorter and, above all, narrower. The subframe mountings are configured differently, the drive shafts sometimes go in front of the axle. And then a traditional hybrid drive won’t fit. You need a hybrid drive design that fits within a BEV vehicle architecture without requiring OEMs to compromise their BEV optimization.

Which of your products meet that requirement?

Firstly, there’s our highly compact HORSE G10 for range extenders. It has a two-cylinder boxer engine with a compact pushrod design and a generator mounted directly on the crankshaft. Then we developed the HORSE C15, a range extender as well. This can be installed either vertically or horizontally. And then we have the Future Hybrid System, which is available in P2 or P1/P3. According to our research, it fits most of the dedicated BEV platforms currently available. So, if European customers with a BEV-first approach want a hybrid derivative for their platform, they can use these powertrains while still meeting all the BEV crash-test requirements.

You also offer dedicated hybrid combustion engines. What are their thermal efficiencies, and how much more is possible?

We are in production with over 44 percent break thermal efficiency. And those are figures from engineering, not marketing. We’re aiming for 49-50 percent. But to get there, we need to implement a few more technologies – for instance, lean combustion. We also then need to design exhaust systems that won’t significantly increase overall system costs. On the other hand, ICE dynamics are lower in serial operation, so that simplifies exhaust after-treatment to a certain extent. For tomorrow’s lean-burn engines, the key is to keep lambda above 2.2 as much as possible so after-treatment doesn’t get too complex.

How do you rate the potential of synthetic fuels in terms of lower CO2 emissions?

Nobody expects all the markets to switch to synthetic fuels in the short term. But it could well be a gradual process. In five years’ time, maybe we could add five percent of synthetic fuels, then later fifteen percent, or twenty. The really good thing is that you can reduce CO₂ across your whole existing fleet. Methanol is another field in which Geely is working. They started selling methanol engines in 2013. Originally, these were 100 percent methanol, designed for taxi fleets in regions where methanol was basically a by-product of coal mining. But now they’re working with biomethanol and trying to create a circular economy there. At last year’s Vienna Motor Symposium, Geely presented onboard CO₂ capture for trucks, for example. Some innovations are just getting started, but we’re already seeing potential here and there.

The EU Commission has just reopened the window slightly for combustion engines after 2035. What do political decisions like this mean for Horse Powertrain?

None of our products is specifically designed for Europe. Our product strategy is very broad, with products we use in the European market, Brazil, India, and elsewhere. So, in terms of capacities and defining technical requirements, decisions about the time after 2035 don’t affect us that much. As a globally operating company, we offer solutions that can meet the requirements of various and changing markets.