We should make a clear commitment to electromobility

Dr Norbert Alt, COO of FEV

There is uncertainty about which drive solutions will be best in the near and longer term. In our interview, Dr Norbert Alt, COO of FEV, an innovation driver in the mobility sector, advocates a technology-open approach but with a clear commitment to electric vehicles. Hybrid BEVs are included, he says – but e-fuels will not be realistic for passenger cars in a market-relevant quantity by 2035.

Dr Alt, what do you think about the current reluctance to buy battery-electric cars?

Looking at BEV sales figures in China, the USA, and the EU, you see continuous growth and an all-time high in absolute terms. If you count BEVs, PHEVs, and REEVs together, the overall market share has grown from 22 in the first half of 2023 to 25 percent in the first half of 2024. In China, for example, New Energy Vehicles – the NEVs – have a market share of 45 percent. In Germany, we did see a decline of 16 percent for BEVs and an increase of 13 percent for PHEVs in the first half of the year. In contrast, 94 percent of new cars registered in August were electric in Norway. These are just examples. So, we should look more at international developments, not so much at ourselves in Europe. When I talk to industry stakeholders, everyone agrees that in the long term, we‘ll mainly drive electric, meaning BEVs with some PHEVs or REEVs and continuously decreasing shares of ICE in passenger cars.

How do you define REEV as being distinct from PHEV?

A while ago, we had REX, which was a Range Extender with a low-power combustion engine. Today’s REEVs – range-extended electric vehicles – have a powerful combustion engine that keeps the electric drive motor operating at full power even when the battery is low. At FEV, we actually call them Hybrid BEVs. So a Hybrid BEV / REEV should be‚ battery-electric born’, meaning it’s an electric car that we then hybridize. You can only have one vehicle platform, a BEV platform because that will be the mainstream. Hybrid BEV / REEV gives you the driving dynamics of a BEV plus additional range from the combustion engine. In China, Hybrid BEV / REEVs have a significant market share. In the spirit of technological openness, we in Europe could learn something from this. Hybrid BEVs would also help people make the transition to pure electric cars.

Interest in REEVs seems to be growing in North America, too …

Under the ACC-II Regulation of the California Air Resources Board, 35 percent of all vehicles must be ZEVs, or zero-emission vehicles, from 2026 – and 100 percent by 2035. Almost one-third of the US states are adopting this legislation. Here‘s the surprising part: Of those ZEVs, 20 percent can be hybrids, provided they have a minimum electric range of 70 miles. So basically, this opens a little window where Europe can say to the authorities: ‚Hey, look at the rest of the world; these concepts are successful in China, and they’re enshrined in law in the USA’. As engineering service providers, we always have our ears to the ground so we know what’s coming down the line. And right now, the Hybrid BEV or REEV topic is in a strongly increasing development focus. We believe that taking a similar approach as China or the USA would make more sense than unproductive debates about banning ICEs.

And what if e-fuels were to become established?

The future will be significantly electric. In Europe, we discuss using e-fuels after 2035, which, in theory, are great. But with an existing fleet of a good 1.3 billion cars worldwide, we’d need them very quickly. In the years leading up to 2035, they cannot help. It takes eight to ten years to approve and build the production
facilities. Even if we built 100 percent of the plants being discussed worldwide, the total amount of e-fuel would cover just 10 percent of German requirements – in areas outside individual mobility! Even the aviation industry is concerned about how to hit its targets. By 2032, the goal is to replace 1,2 percent of aviation fuel with sustainable e-fuels known as RFNBOs, or renewable fuels of non-biological origin’. So, we don’t see a realistic way of getting meaningful quantities of e-fuels on the road in 2035. One option not yet on the table would be similar as in US and China allowing Hybrid BEVs that burn fossil fuels and can drive 150 km electrically for example, to stay on the road longer than planned. If we were to regulate for 70 percent BEV and 30 percent Hybrid BEV, for instance, we would still be driving around 90 percent electric overall.

Moving to vehicle technology – how would you design a Hybrid BEV drive architecture?

The question is, do you want just serial, or do you want series-parallel? Obviously, engineers want the latter because you have high efficiency on the highway, too. But if one has a battery range of 150 or 200 km, maybe one can live with a purely serial drive that consumes a little more fuel at 140 or 150 km/h, which you can only do in Germany anyway. And in the city, the serial hybrid drive is 5 to 7 percent better than a conventional parallel hybrid. Also, we’re continuing our efforts to make combustion engines more efficient. We already have engines with 43 percent efficiency in production, and we’ll soon be heading for 45 percent and more.

How will electric drives and charging technology develop in the future?

There’s a clear trend towards 800V. But market penetration will be top-down for cost reasons, with 400V systems widespread in the lower sectors. In the truck sector, we’re talking about megawatt charging with even higher voltages. Another exciting development path involves optimizing the charging curve for 400V systems. The aim is to minimize losses even when fast charging to 80 percent. We are currently developing 400V systems, which you can charge from 20 to 80 percent in 19 minutes, and which are on a similar level as an 800V system. Several factors make this possible: a special cell chemistry that is well understood, an accurate battery management system, and improved heat dissipation. So, it’s not just about high charging power – you also need the smoothest possible charging curve. That’s something that offers excellent customer benefits.

What about trends in electric motors?

There is a somewhat unexpected trend here. In the past few years, motor speeds have increased – up to 30,000 rpm in the Far East. Higher speeds mean smaller motors, which is good, but also more friction, which is not good for efficiency. Some German manufacturers have now reduced EDU rpm to 13,000 and are seeing excellent consumption at 120 or 130 km/h. You only need higher rpm for sporty applications or when the package is a high priority. Another trend – one we are working on with a German company – is dual-rotor motors, which enable high efficiency at part load, high power and torque density and lower costs. And a topic the whole industry is working on is externally excited electric motors. These require no heavy rare earths and can reduce our dependencies on raw materials.

Which way is battery chemistry heading?

Nickel-manganese-cobalt (NMC) and lithium-iron-phosphate – LFP – batteries are used mainly in passenger cars, especially LFP in the cost-sensitive segment. We’re also developing sodium-ion batteries. Sodium Chloride is available in large quantities in nature, so that’s more favorable concerning raw materials. Also, sodium-ion is already not far behind LFP regarding energy density. And since Hybrid BEVs batteries require less space in a standard BEV platform, they can also cut production costs for Hybrid BEVs. Then, in the high-performance sector, we’re talking about solid state, but that will take a while. Semi-solid-state batteries will come sooner. We’re currently working with manufacturers on joint developments here.

What drive technologies do you foresee in trucks in the next few years?

Surprising as it may seem, there is also a trend towards full electrification in Europe. At the last IAA, almost all major OEMs shared that view. The trend also applies to long-haul trucks because this is an industry where TCO rules. We are talking about 30, possibly 40 percent BEV share in 2035. Hydrogen will also play a role. FEV is working with manufacturers to develop both fuel cells and hydrogen-powered combustion engines. But the majority will be battery-electric trucks. Some OEMs have allied to install 1,700 charging stations along main routes in Europe by 2027. The electric trucks and infrastructure operators are there, but we need support and commitment at the political level.

Some people say China is well ahead of Europe in BEV technology. What’s your view?

The BEV vehicles that German and European manufacturers offer today are on a high level of technology. They have good efficiency, high charging power, system design, drag coefficient, and more. On the other hand, the Chinese are ahead in battery cell technology and production know-how; they have invested strongly in the development and have better access to raw materials. But in the future, more and more processes will be sustainable, through to a circular economy. This will reduce the need to add further raw materials. That will put the issue of „who has the raw materials?“ back into perspective. What’s more, German manufacturers are spending billions on setting up battery cell production. At FEV, we have our own cell chemistry department, too – and as a development service provider, we work with the Chinese. Another topic is automation, which means ADAS systems, autonomous driving, etc. Here, some other countries are nowhere near as advanced as German manufacturers. So, from a technology perspective, the outlook is a lot brighter than some people say, and we will see continuous innovations in all areas. Additionally, one has to mention that low-cost BEVs are very important for the expected market penetration of BEVs, and the capability of the Chinese to produce on low cost is very high which is the major challenge for the European.

How could decision-makers in politics and the industry advance electric mobility?

We would like the EU to look at the regulatory approaches of the USA and China, and to use them as a model to some extent. At the moment, we are letting car owners hope they can have e-fuels in 2035. That’s not going to happen, only for a very small share of the market. We should also make a clear commitment as a tech community, saying we will drive more and more BEVs, some of them Hybrid BEVs. We should allow a defined percentage of Hybrid BEVs and stop the unhelpful discussion about the ICE ban. By 2045, we may reach the point where filling stations no longer stock fossil fuels, just bio and e-fuels. Another critical point we really need to tackle is electricity prices. You can generate electricity with a photovoltaic system for 10 cents per kWh, or even less. If people could charge their vehicle for 10 cents, electric cars would sell like hot cakes. Hybrid BEVs would benefit, too, because people would prefer electric driving whenever possible.

Interview: Gernot Goppelt

e-NVH Design of Electrical Drives with Collaborative, Multidisciplinary Modeling & Simulation

Tackling noise issues after manufacturing can be expensive and may degrade electric drive performance for efficiency, cooling, and weight. Therefore, an efficient virtual prototyping workflow of e-NVH is critical for accelerating development times, reducing prototyping, manufacturing & testing costs, and improving engineering productivity.

The prediction of acoustic noise and vibration in electric drives requires modeling and simulation of all excitation mechanisms, including mechanical forces (e.g. tire/road, gear friction forces), aerodynamic forces (e.g. windshield, fans), and electromagnetic forces. These three sources of acoustic noise must be considered together due to masking effects. For example, the unpleasant tonalities of magnetic noise produced by inverter switching harmonics might be covered up by windshield noise at high speed.

In electrical drives, magnetic excitations come from the converter and the associated traction motor. The frequencies of magnetic forces depend on slot/pole/phase combination, while their magnitude depends on magnetic circuit geometry and control. This makes electromagnetic noise, vibration, and harshness (e-NVH) a unique discipline that requires dedicated troubleshooting and mitigation tools.

Manatee software, now a part of the SIMULIA brand of Dassault Systèmes, is a specialized computer-aided engineering (CAE) software for the assessment and control of magnetic noise at all design stages of electrical machines and drives. It helps designers identify the best tradeoff between electromagnetic & NVH performance. Manatee expands the SIMULIA multiphysics simulation portfolio, which includes Abaqus, CST Studio Suite, Opera, Simpack, and Wave6. Leading vehicle and powertrain developers use these robust and proven simulation technologies for the virtual prototyping of vehicle components, subsystems, and systems, including electric drives.

e-NVH simulation requires electrical, magnetic, structural dynamics, and acoustic models. The traditional method for evaluating e-NVH has been for a CAE expert to use general-purpose FEA software and manually combine all the physics. This process requires setting-up each solver and their interfaces, such as mesh-to-mesh projections, time vs. frequency domain and discretization. It also requires scripting to call this customized model combination at variable speed and to obtain relevant output quantities such as A-weighting for human ear sensitivity. This complex workflow, which is generally maintained and run by a single CAE expert, results in a bottleneck in the numerical simulation process, preventing the use of NVH metrics in design iterations.

To overcome this issue, Manatee provides a unique algorithm to accelerate variable speed e-NVH calculations without loss of accuracy. It contains its own multiphysics models with predefined couplings, but can also be easily interfaced with other CAE software.

In addition, Manatee comes with predefined workflows adapted to each engineering role. The multiphysics simulation can be set up with the click of a button thanks to standardized interfaces that enable collaboration between electromagnetic and mechanical departments. Electrical engineers can set up the electrical machine and run electromagnetic calculations at variable operating points; the result is a Magnetic Look-

Up Table (MLUT). In parallel, mechanical engineers can import the electric powertrain modal basis. The MLUT can be provided to NVH engineers and the modal basis to electrical engineers. This way, noise mitigation techniques based on electromagnetic and mechanical design can be investigated in parallel. NVH engineers can track if NVH targets are fulfilled at all stages of new product development.

An efficient collaboration of control, electrical, mechanical & NVH engineers also requires a user-friendly interface, where all physical quantities can be easily visualized and post-processed. Manatee comes with insightful plots to help quickly identify which magnetic force excites which structural mode. New specialized e-NVH solutions are regularly developed, supporting all engineers finding solutions to reduce noise & vibration levels (skewing, notching, Harmonic Current Injection, etc).

Manatee also provides parameter sweeps, global optimization with predefined e-NVH metrics and design exploration tools to find the best tradeoffs between electromagnetic & NVH performances.

The robust and user-friendly features of Manatee provide a unique, collaborative CAE environment specialized in the assessment and control of electromagnetic noise & vibrations. By using Manatee during the design stages, designers and engineers can significantly accelerate the virtual prototyping of electric drives, resulting in shorter development cycles, reduced prototyping costs, and better NVH risk management.

For more information visit: https://www.3ds.com/products/simulia/manatee

Dual Motor 600kW EDU Readied for Niche Volume Production

TREMEC is one of the major players in the aftermarket powertrain business with several generations of manual gearboxes known for their performance and robustness. To continue this tradition, the challenge of developing an electric drive unit (EDU) for aftermarket use was undertaken. The goal was to develop an EDU (named TR-DC6000) with a peak power output of 600kW that would fit many existing chassis, allowing it to be retro fitted in an existing internal combustion (ICE) vehicle converting it to electric drive or to upgrade the performance of existing electric vehicles. This paper will first contain an overview of the development history of this EDU to date together with the current state of the program. The main body will cover the relevant test results from our prototypes and how those were used to define the production design. The key differences between the prototypes (ED), and the production ready (DV) units will be explained. Finally, an outlook is provided on what the expected performance is for different use cases of this EDU.

The selected configuration for the TR-DC6000 is a dual-motor concentric lay-out suited for 800V applications. The two electric motors are placed in the middle and each connect to a planetary gearbox providing the reduction to the wheels, see Figure 1. In order to easily fit in existing chassis, the inverters are connected through phase cables allowing some flexibility in their placement. The motors are surface-mounted permanent magnet (SMPM) machines with a carbon wrap or sleeve. Each motor can deliver up to 300 kW and spin up to 18.000 rpm. The inverters selected use 800V Silicon-Carbide (SiC) power modules to unlock the full potential and efficiency of the 8 pole-pair motors. Both the inverter and motor are water-cooled for ease of integration in existing vehicle coolant loops. The gearbox is passively lubricated and cooled with the use of several oil catchers, diverters, and scoops to ensure all components are well lubricated and remain within their operating temperature range.

In the past year, six prototypes have been built and continue to be extensively tested in the TREMEC lab on a dyno capable of the full torque and speed range. Three of the six units were subsequently installed in vehicles for integration testing, demo drives and performance evaluation. One of which, our in-house EV converted Porsche 996, is also used as a development platform for drivability and torque vectoring. Several more functional tests have been run to characterize the unit and compare with the design predictions, such as: thermal behavior, NVH and efficiency. A shortened durability test has been run to prove the robustness of the design, and a series of safety cases (including load dump) have also been completed.

One of the first major observations during the testing campaign was the sensitivity of the phase cable shield contacts at motor and inverter end. Several of these shield contact points showed signs of overheating. A series of specialized measurements and electrical simulations confirmed this was due to the induced AC current running in the phase cable shield as described in Frei et al¹. The high electrical frequency of the motor, phase cable length and high current in the core during track diving caused the current rating of the original shield contact to be exceeded. Furthermore, the high shield current caused the phase cable itself to heat up over longer drive cycles outside of the nominal operating range. To thoroughly investigate and address the issue, a model was built that included the electrical coupling between the core and the shield of the phase cable, as well as the thermal behavior of the phase cable (thermal behavior modelled similar to the method described in Luttenberger²). This model, which allowed for simulating dynamic drive cycles, correlated well with the measurements without the need for parameter tuning (only physical parameters are used). Armed with this new tool, various design solutions were explored which resulted in a different phase cable / connector combination which would meet our durability and peak performance requirements – both electrically and thermally. The selected design, as well as an alternative solution where one common shield is placed around 3 unshielded phase cables, were then tested on our dyno, where the component temperatures were confirmed within margin even during track driving, see Figure 2 showing several data traces recorded on our dyno. The data shown is from a simulated Nürburgring lap where an average EDU power >300 kW is achieved.  All critical component temperatures (stator, rotor and phase cables) remain well within their respective limits.

Figure 2: Data traces from Nürburgring lap on dyno with average >300kW power and thermal behavior well within limits

A second notable change to prepare the TR-DC6000 for production can be seen in the gearbox design. The prototypes utilized a stepped planetary gearbox to achieve a total ratio of 9.4. Upon reviewing manufacturability during the procurement phase, we encountered challenges with the initial concept, particularly given the low production volumes targeted for this product. Manufacturing stepped planet gears in small quantities proved to be either costly due to high tooling expenses that could not be offset by larger volumes, or overly complex, involving a welding step to join two simpler gears. In response, we shifted toward a design incorporating a single-stage planetary gearbox, while maintaining the same packaging space. This adjustment resulted in a lower gearbox ratio of 7.0, which lowered output torque, yet allowed for significant cost savings. These savings enabled us to enhance the motor with higher-grade magnets, partially compensating for the reduced torque. As a result, we still surpassed our targeted output torque of 6000 Nm. The alteration in design minimally impacted performance, adding only 0.25 seconds to the quarter-mile run, while notably improving efficiency. Specifically, efficiency increased by 3% over the Worldwide Harmonized Light Vehicles Test Procedure (WLTP) and by 9.3% during track driving, attributed to the generally lower motor speed.

While redesigning the gearbox to a single step lay-out some attention was also given to the ring gear fixation to the housing. Both the ED and DV designs use a splined connection. As this is an interface between a hardened steel gear and a softer aluminum housing, some wear or polishing is always expected. Under uniform loading the contact pressure in the spline is extremely low and would not raise any concerns, however due to the planet gear loads the ring gear deforms to a more triangular shape (see Figure 3). This results in a cyclic load pattern where higher contact pressures are expected and some movement takes place on the interface, causing wear. The limited durability testing confirmed some wear in this area. Though the wear was not at an alarming level, the opportunity was taken to mitigate risk. To minimize the wear, the approach was to both reduce the contact pressure and the movement, which was most easily achieved by increasing the ring gear stiffness (see Figure 3). In addition to increasing the ring gear stiffness, several other smaller optimizations to the housing and spline geometry were included in the new design. A full FEA model was created of the gearbox and housing interface to simulate the cyclic loads from the planet gears, deformation of all components, and the movement. The combination of contact pressure and movement, called work, could then be evaluated. The updated design results in 2.4 times lower work on this critical interface compared to the ED design, which will greatly improve the robustness of the EDU.

Figure 3: difference in ring gear deformation under equal output load: left ED, right DV

The changes listed above combined with multiple other tweaks to improve robustness, manufacturability or performance have prepared the TR-DC6000 design for low volume production. We have reliably demonstrated 0-100 km/h below 3s with our own test vehicle and projected times close to 2.5s with improved traction control. While running track drive cycles on our dyno we were able to run a lap of the Nürburgring with an average EDU power of >300kW resulting in a simulated lap-time below 7:45 for a 2000kg vehicle (see Figure 2). This combination of performance, robustness and flexibility makes this an ideal product for aftermarket EV projects and low volume niche car builders alike.

The first DV units with all their improvements are targeted to be built during Q4 2024, and a complete validation and industrialization plan is scheduled during 2025. Low volume production should then begin early 2026.

References:

1. Frei, A. Mushtaq, K. Hermes and R. Nowak, “Current distribution in shielded cable-connector systems for power transmission in electric vehicles,” 2018 IEEE International Symposium on Electromagnetic Compatibility and 2018 IEEE Asia-Pacific Symposium on Electromagnetic Compatibility (EMC/APEMC), Suntec City, Singapore, 2018, pp. 881-886, doi: 10.1109/ISEMC.2018.8393908.
2. Luttenberger, F., MSc. (2016). Electric components in automotive battery systems above 800 V (By Graz University of Technology, Institute of Automotive Engineering & AVL List GmbH).​