The evolution of electric powertrain technologies – with a focus on battery testing and production
Compared to conventional concepts, there’s still plenty of room for improvement in electric vehicle design and production. Given the right instruments, both development and testing as well as manufacturing processes for e-mobility can be rendered more seamless and cost-efficient. For example, there’s huge potential in battery design and production but also in electric powertrain diagnostics and mechanical drivetrain analysis.
Part I: Progresses in powertrain and drivetrain development
With e-mobility and NEVs on the rise, efficiency gains and cost reduction in vehicle development increasingly come into focus. Especially in the passenger car segment, customers tend to be fussy and price sensitive. So how can electric vehicle development and testing be rendered more efficiently, saving time and money in the process? Measurement technology plays an important role here, and recent innovations in this field offer opportunities to optimize development and testing routines especially in the NEV segment. This concerns the whole powertrain from the battery over the drivetrain itself to the mechanical characterization of wheel performance.
Battery monitoring and thermal management with Fiber Segment Interferometry (FSI)
During vehicle development, battery performance must be tested and evaluated thoroughly. Rising temperatures can be an indication for inner malfunctions and pose the threat of thermal runaway, (danger of melting or explosion due to overheating). Thermal management therefore is a key requirement in battery implementation, and it can be handled efficiently with an FSI temperature monitoring system. FSI stands for “Fiber Segment Interferometry” and presents a unique way of measuring battery temperatures accurately and efficiently.
Compared to technologies such as thermocouples, the FSI system is less intrusive and comes with multiple other benefits:
1. The sensors are very compact and lightweight – typically in the low millimeter range, depending on the application.
2. Multiple sensors (up to 88) can be freely arranged and connected to one single processing device, the so-called interrogator, with minimal wiring effort.
3. The system is very robust and immune to electromagnetic interference, so it’s ideally suitable for application in harsh or high-voltage applications.
Temperature measurements with an FSI monitoring system deliver a comprehensive and accurate assessment of the thermal behavior of EV batteries. The gathered data can be visualized as time-resolved heat maps by means of the integrated software. Consequently, simulation models can be improved, and thermal management can be holistically optimized – allowing for a maxed-out battery usage closer to thermal limits, longer battery lifetimes and further improvements in fast charging.
temperature of each cell to easily identify e.g. hot spots.
Efficient powertrain diagnostics – in-vehicle and at the test bench
Depending on the powertrain architecture, electric components such as the e-motor, converters or inverters as well as the battery must be analyzed and evaluated in their interdependent operation. Here, efficiency and performance gains come from a powerful powertrain diagnostics system that can measure these processes comprehensively – in-vehicle as well as on the test bench. The KiBox2 powertrain diagnostics system draws on decades of experience in vehicle testing and offers a broad range of functionalities in one powerful device. It allows for measuring, calculating, and analyzing all relevant electric parameters according to the IEEE1459-2010 standard. As a result, system energy flows can be visualized in real time, eliminating possible energy losses and characterizing propulsion performance in a highly efficient way.
KiBox2 is designed as an open ecosystem and – thanks to a variety of protocols and connectivity options such as DCOM, CAN-FD and XCD, for example – can be connected to both test-bench systems and electronic control units. Available metrics for electric machine characterization include active, reactive and apparent AC power per phase, power factor, phase angle, DC power (inverter input) and power conversion efficiencies. Module integration and channel usage in KiBox2 are highly flexible, and a variety of components is available for specific measurements, e.g. voltage and current probes for AC machine analysis and DC system current flows. In addition to the PEAQ (for piezoelectric sensors), PRAQ (for piezoresistive sensors) and VAQ (voltage input) modules, new high voltage measurement units (>1000 V) will be available in the near future. For on-road testing, KiBox2 is equipped with a complete GPS functionality. Last but not least, KiBox2 is fully “backwards compatible” with combustion engines and their analysis, rendering hybrid vehicle development (MHEV, PHEV) as efficient as BEV testing.
Advanced drivetrain efficiency testing for e-vehicles
The optimization of the drivetrain requires a mechanical characterization and performance analysis of components such as driveshafts, axles and wheels. Therefore, measurements of specific torques and speeds are needed – and even more so for electric vehicles, where a higher number and flexibility of measurements is desired. Especially for this purpose, test engineers apply a unique system to facilitate driveshaft analysis and optimization: KiTorq DS is the world’s first wireless torque measuring system for automotive driveshafts. It consists of a customizable adapter sleeve including transmitter and strain gauge sensor, two half shells for power supply and wireless telemetry, and a receiver unit.
With KiTorq DS, the development engineer can measure up to six driveshafts precisely, simultaneously and without contact. The innovative system design provides full reusability and is therefore more efficient and sustainable than conventional driveshaft measurement systems. The adapter sleeve can be tailored to the exact dimensions of each shaft to ensure an optimal fit of the transmitter unit. In combination with a wheel pulse transducer, direct power measurements on driveshafts are possible. KiTorq DS can be calibrated individually to meet the specific demands of the customer’s application, including an optional temperature compensation.
Wireless torque and speed measurement – sustainable and precise
The power delivered by the e-motor is transmitted via the drivetrain to the wheels. For a complete mechanical drivetrain efficiency analysis, resulting torques must be measured directly at the wheel. Here, wheel torque and wheel force transducers from the Kistler RoaDyn series come into play. These measuring hubs replace the rim star of the wheel to integrate seamlessly with the vehicle. They are available in different sizes and measuring ranges – covering a wide variety, from small passenger cars over SUVs and Vans to the point of trucks, tractors and beyond. The new RoaDyn P1 wheel torque transducers even allow for wireless signal transmission to the corresponding on-board unit – signals from all four wheels can be received and processed with one KiRoad Wireless P1 on-board unit. The measured traction torques, and rotational speeds (RPM) enable[RD1] a detailed assessment of the drivetrain’s power output at different development stages. Mounting of the wheel torque transducers resembles a common wheel change and can be completed within less than 15 minutes – for alignment with different vehicles, additional adapters are available.
Fast and comprehensive data analysis with jBEAM
All acquired data can be analyzed quickly and thoroughly with jBEAM Powertrain, the specialized edition for powertrain analysis from the battery to the wheel.
The features include:
- Fast and efficient measurement data analysis, visualization and reporting
- Supports more than 100 file formats incl. automated file content update
- Multiple graphical elements for visualization and interactive control elements
- Flexible reporting incl. multilingual templates and layouts (up to 500+ pages)
- Data synchronization with video and GPS data incl. map server connections
- Extendable with CEA Java components, Groovy or Python scripts, MATLAB functions, and more
- Enables the creation of wizards for complex multi-stage workflows and to ensure quality
jBEAM Powertrain is focused on efficiency gains for test engineers, interacts congenially with KiBox2 and is backed up by software engineers ready to further develop jBEAM for its customers.
Part II: Improvements in battery and component manufacturing
Although looking rather simply, a battery is a complex thing – especially when it comes to large arrays and packs as in automotive applications, for example. Manufacturing of Lithium-Ion batteries for e-mobility includes three main phases (electrode production, cell assembly, formation and aging), and each phase contains different partial steps and sub processes. Depending on the battery architecture (pouch, cylindrical, prismatic) and the size of the battery (cell, module, pack), there are optional further assembly steps to complete – which can be optimized in terms of resource efficiency and cost reduction.
As an example, the buildup of battery modules from single cells requires the so-called “Stacking”: here, multiple cell units are grouped in a cell carrier, optionally including a suitable adhesive. A defined press force is needed to finalize this assembly step (only for prismatic and pouch cells, cylindrical cells don’t have to be pressed) to ensure that the battery does not expand during operation and over its lifetime. Electromechanical joining systems (servo presses) are predestined for such applications: they deliver exact, force-distance-controlled joining processes, and they come with a higher degree of efficiency and lower energy consumption than other technologies. Compared to pneumatical and hydraulic servo presses, an electromechanical joining system such as the NCFN from Kistler is more flexible and variable, offers superior control options and requires much less energy (according to a study by the University of Applied Sciences Ostfalia, Germany, 2024).
Applying such systems – which include a maXYmos process monitoring system for configuration, digital connectivity, and process documentation – also is beneficial for further battery production processes such as tab contacting, the tensioning of the cells and the final (module to pack) assembly. Manufacturing technologies based on robust and reliable measurement technology can also play their part in the ongoing evolution of large batteries: while innovative architectures such as cell-to-pack and cell-to-chassis – skipping the module or even the pack level – promise higher energy densities, they also tend to be more complex and demanding, thus calling for advanced manufacturing with integrated process monitoring and quality control.
David Sagorz, Application Expert EVP and the team from Vehicle Testing, Joint System Business and Advanced Manufacturing, Kistler Instrumente GmbH
