The modular Electric Drive Units (EDUs) from hofer powertrain are attractive. They are compact, scalable, and efficient. Yet, the scope and complexity involved in the development of different EDUs may vary from case to case. In this article, we highlight key engineering and development areas, along with essential skill sets. hofer powertrain experts cover a range of crucial development phases, explaining each step in the process, demonstrating how our customers achieve their aspired results in a cost-efficient manner.

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Our EDUs are designed as building blocks – many functions are standalone and suitable for multiple applications. This makes them ideal for a range of application targets. Individual units are standardized at a certain level of performance and provide the perfect basis for further adaptations. Like Lego building blocks, the modules can be assembled to fit together perfectly. Based on the customer's intentions, they can be either used off-the-shelf or customized further to meet unique requirements (like our autonomous ready EDU130-I-240). Higher or lower performance spectra can be achieved by adapting single components. This design helps achieve certifications quickly, as many integrated functions already comply with the norms.

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When taking customized applications as a starting point, electric drive units' development entails highly interlinked steps. Many aspects need to be considered when moving from the first high-level requirements to fully deployable, volume-ready, and efficient solutions. The development process combines clearly defined and established steps with various flexible methods aimed towards agility, short response times to unforeseen issues, and complexity reduction during the overall development process.

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Specification of requirements are crucial for the development and production goal setting – a basis for all further engineering work

At the heart of every development project lies the collection of precisely described requirements. Sometimes customers have a clear and expansive list of in-depth requirements. Other times they need to be collected from scratch. This is where the foundation is laid for all further actions. Including desired designs and performance goals as well as specific characteristics of the e-motor, the inverter, the transmission, and the software, the requirements are defined initially broadly and later at a granular level, down to the smallest detail. At this stage, a high degree of expertise and experience is essential to identify all relevant, known, and potential unknown parameters.

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Consequently, this first process has a significant influence on the overall development complexity and time. The better the goals are defined at the beginning of the project, the better the engineering specialists can react to and control unexpected circumstances later. Here, engineers make the first sketches, where simple circular disks stand for gears, blocks for the casing, or cylinders for the e-machine. Next, these sketches are turned into concrete and realistic engineering drawings, which lead to the generation of precise 3D models.

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Established process frameworks, such as Automotive SPICE, which map the entire development scope and evaluate the development processes' performance, are needed. They provide support for system and software development for new EDU designs. The overall system development process is the primary process that incorporates other development processes, such as software and EDU development. As a result, definition, and documentation are carried out at different levels. In the case of software development, the entire process is mapped based on specified requirements. It allows the systemic building of ideal systems in line with the electric drive solutions, following the V-process. This process starts with requirements, followed by software architectures and detailed design, delivering unit verification through integration and qualification tests.

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Accurate EDU design through detailed early calculations, simulations and analysis

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At this stage, the engineers design a concrete, realistic concept on the mechanical, electrical, and electronic levels, adapted to the customer's previously defined requirements and requests. The system developers must take many parameters into account to design the models correctly and avoid unnecessary steps during development.

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The simulation measurements can be modeled repeatedly with the design adjusted according to new calculations for identified deviations from estimates. Insights gained in the simulations are transferred into the follow-up design cycles, allowing thorough design verification and quick modification until the perfect result is realized.

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Elaborate computations and precise simulation algorithms continually fine-tune and improve the electric drive solutions, moving them successfully from one evaluation phase to the next. Engineering approaches need to be based on process efficiency. Our experts put theoretical optimums to the test first before moving into implementation. Ongoing trials and design verification steps accompany the entire process until the end of all development phases.

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The top engineering services provided by hofer powertrain in the areas of simulation and design include:

- Dynamic multi-body vehicle simulations 

- FEM analyses

- The computer-aided design of the gearbox, gearing system and bearing with the KISSsys® tool

- Thermal simulations

- Efficiency and fuel economy simulations

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Multi-body vehicle simulations enable dynamic modeling of complex systems. Developers employ dedicated software tools allowing the coupled simulation of both structure and drivetrain dynamics. Also, functions such as ParkLock or Disconnect Clutch and their respective operation characteristics are simulated in the system and modeled according to ideal calculated results.

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Drafts and designs of electric motors and entire drive units are also optimized further, utilizing numerical calculations through early-stage corrections. The simulation programs rapidly analyze different application profiles, depending on the entered parameters. Once initial computations and the pre-optimized designs are made, other simulation methods such as finite element analysis (FEM) deliver further detailed findings of the physical behavior in the electric drive unit, the gearbox, or the response of the shaft under torque load.

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Using efficiency and fuel economy simulations, engineering teams make conclusions, for example, about speed- and load-dependent efficiency levels and overall energy and fuel consumption. These simulation methods can reveal potentials and compare different modules or entire EDU concepts against each other in the early stages.  

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Moreover, thermal simulation enables evaluation and improvements of the physical behavior of future drive units and individual modules. Here, simulation technologies support the conceptual design of cooling systems, connectors and mechanical connections to maximize efficiency, minimize heat loss or use excess heat in a controlled and targeted manner.  

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Striving for consistent durability of gears and bearings calls for balanced design of components in the gear unit. For this purpose, system approaches are essential to show precisely the impact of individual parameter changes on the overall system. Using tools such as KISSsys, hofer powertrain experts keep track of the entire transmission development and optimize the solution anytime according to the conditions.

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Complete system analysis and error detection with sophisticated test methods

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As market demands grow, OEMs often face conflicting challenges. They include high-performance requirements, reliability of individual components, efficiency increase of the overall solution, compact lightweight design with high-level functional safety and conformity aspects. hofer powertrain focuses on proven and innovative testing methods in all development stages, meeting these challenges.

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Some of the key engineering services provided by hofer powertrain in testing include:  

- EM, PEU, gearbox and EDU function, endurance and performance tests 

- Software component and release tests

- Environmental tests of EM, PEU, EDS/EDU and electric battery

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To maintain high quality and security, tests of all modules in the overall system are fundamental. Our experts employ an agile test approach based on multiple loops. In the beginning, quality assurance tests are performed at the component level and once integrated, at the system level. Strong analysis driven approach and modern testing technologies that meet the latest standards are key to verification of components and the system at various development stages.

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In endurance and functionality tests, specialist teams examine the e-machine, the inverter and the transmission to determine their functional safety, performance, continuous power output and ability to cope with mechanical and electronic loads. Interaction on the component level, united in one housing, including functions such as ParkLock and gear shifter, are put to the test.  

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Due to various environmental and mechanical influences that the systems are exposed to on the road, OEMs must also carry out a series of environmental tests to verify durability and stability of the electric drive system, e.g., under different temperatures and humidity rates. These tests are particularly beneficial in the development phase, as they ensure greater efficiency and more robust systems. Here, developers pay attention to compliance with standards, signs of corrosion, temperature shocks, and any unwanted vibrations that may occur to prevent unpleasant future surprises and build a state-of-the-art solution.

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Inspection and testing of modules and functions throughout the entire development cycle contribute to the cost- and time-efficient realization of the defined milestones, regardless of the individual application purposes. Established tests paired with new test methods enable developers to react to changes quickly and allow room for early adjustments and accelerated electric drive unit development.

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Final calibration and system integration for a perfect fit with the customer's vehicle

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At hofer powertrain, seamless interaction and compatibility of all components in the customer's vehicle are the highest priority to EDU development teams. To tackle this challenge, the technical specialists need a profound knowledge of the electric drive system, plus a significant amount of experience, including in-depth understanding of the latest advances in system development.

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Above all, the integrated solution must run reliably and safely when installed in customers' vehicles. The final solution is tested and calibrated on the test bench, considering all relevant operation parameters for maximum quality and efficiency. Another step in the calibration process takes place directly in the customer's vehicle - in combination with vehicle control systems, our integration engineers test the electric drive unit's stability to avoid negative phenomena such as unwanted vibrations or noise on the road.

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Successful industrialization and all-round production support

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Being a central building block for innovative electric vehicles, our variety of electric drive units covers a wide range of needs, be it for fuel cell vehicles (FCEV) or battery-powered electric vehicles. hofer powertrain teams understand the EDU in detail, considering all individual manufacturing goals starting in the design phase. This proactive strategy allows implementation of the most efficient solutions for the desired quantities based on a long experience. Together with our production partners, hofer powertrain offers customers around the world seamless support in the entire development process all the way to SOP and beyond.

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Expectations for electric drive units and their compatibility with new technologies are growing. Must-have and innovative technologies are in focus, from high-performance inverters that can be optimally integrated into existing concepts to advanced stator manufacturing technologies using hairpin technology. Also, safety and security topics, including over-the-air updates (OTA) and cyber security management, are rapidly gaining importance.

In the next part of our Electrification Weeks, hofer powertrain specialists will go into more details on these and other future and security-relevant topics, sharing their experiences and insights.

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