Imagine a hypercar that can go from 0-60 in less than 2 seconds. It sounds impossible, and not just a little uncomfortable. Yet the electric drives in the new C_Two hyper sportscar, developed by Croatian automotive company Rimac Automobili, makes it a reality. Equipped with 1,914 horsepower, the C_Two can accelerate from zero to 100 km/h (62 mph) in 1.85 seconds.
Rimac’s founder, Mate Rimac, began as an entrepreneur trying to electrify his BMW. Today, the technology he developed with his 400-person strong team is one of the leaders in the field. (Photo credit Rimac Automobili, Davor Puklavec.)
However, the most interesting thing about this “monster” of a sports car is the technology under the elegantly shaped external surface. The C_Two is driven by an innovative electric four wheel engine system—one engine for each wheel. Each engine is individually controlled by sophisticated software that allows automatic torque adjustments up to 100 times per second for each wheel.
In light of this, it is no coincidence that Porsche recently bought a 10 percent stake in Rimac. Based in Croatia, the company has developed state-of-the-art electric vehicle powertrain technologies, and Porsche wants to join them on their journey. Rimac is not only well known for its “hyper cars” Concept_one and C_Two. They are also a supplier of full-electric driveline systems to several big automotive players including Aston Martin, Jaguar Land Rover and Renault.
Rimac develops their cars and driveline systems in Dassault Systèmes PLM environments. Initially they used SOLIDWORKS, but as the product complexity grew they moved onto the 3DEXPERIENCE platform.
However, without complementary solutions, PLM platforms in some ways don’t have the capabilities needed to digitally carry them across the finish line. This is where developers like Modelon come into play. The company is dedicated to model-based systems engineering (MBSE); or as CEO Magnus Gäfvert prefers to call it, “model-based system simulation.”
“We usually use the term ’system simulation’ to differentiate us from more requirement-driven solutions,” Gäfvert says, adding that, “It is also important that our software is entirely based on open standards (mainly Modelica and FMI), allowing for the right collaboration and integration with so many PLM platforms.”
Modelon’s Modelica language-based systems are currently supported by more than 100 CAE developers, including ANSYS, Dassault Systèmes and ESI Group. In this article, we look at the Rimac case and how Modelon’s solutions are used in the development of its hyper sports cars and electrical driveline systems.
ELEGANT CURVES. Rimac’s latest hyper sports car model, C_TWO, is developed on Dassault Systèmes’ 3DEXPERIENCE platform.
Rimac leverages the technology it has developed in electric vehicles (EVs) to develop and sell ready-made solutions to global automotive companies. Rimac specializes in high voltage batteries, power transmission, digital interface development and Advanced Driver-Assistance Systems (ADAS) for self-driving cars.
The company’s leader is 39-year-old founder and CEO, Mate Rimac. Over the five years since he founded the firm, he has built a team of 400 employees. His technology is a commercial hit. For example, both the battery in Aston Martin’s Valkyrie hybrid and the electric powertrain in the Jaguar E-Type Zero were developed by Rimac.
Chinese companies are showing interest as well. Under an April 2018 agreement, Rimac will start building electric motors and batteries in a facility in Xiangyang. Beginning this year, the facility is to churn out 50,000 units annually, with construction to cost about €128 million. Rimac holds 40 percent of this joint venture.
So, exactly what created this rising curve of interest in Rimac?
One Engine for Each Wheel with 100 Adjustments Per Second
A few years ago, Rimac introduced its Concept_one electric car, a hypercar that delivers 1,088 horsepower. In March 2018, they released the second version of this vehicle: Rimac C_Two, this time delivering 1,914 horsepower and an innovative 120 kWh battery pack with 1.4 MW power output.
A critical system in this concept vehicle is the Rimac All Wheel Torque Vectoring (RAWTV). Torque Vectoring controls the motors individually through four engines, one per wheel. The system allows for individual and automatic torque adjustment up to 100 times per second for each wheel, independent of each other. For example, one wheel can be accelerated while another is being braked. The engines can also be set to different modes, with available settings to match the drivers’ preferences in given situations.
The electronic systems sense factors such as speed, acceleration, traction and steering angle, creating a system of extremely high flexibility that gives a superior grip and an optimal driving experience.
Rimac’s Torque Vectoring technology controls the four motors individually (one motor per wheel), allowing for automatic torque adjustments up to 100 times per second for each wheel. Using data from strategically deployed sensors and advanced control algorithms, maximum grip is attained on each tire.
“Rimac has clearly demonstrated its strength on the electric car side,” said Lutz Meschke, deputy vice chairman of Porsche. ”Through the two full-electric two-seater concept vehicles Concept_one and C_Two, as well as an electrically powered electric vehicle driving system, the company has demonstrated impressive competence in electric mobility. We believe Rimac’s ideas and approaches are extremely promising. That’s why we’ve invested capital and worked in close cooperation with them to form a development partnership.”
What Does Rimac’s PLM Environment Look Like?
Given this background, demand for Rimac’s solutions has increased explosively. This places high demands on development methodology, systems and software.
Generally, the Croatian automotive player has developed its vehicles and systems in Dassault Systèmes environments. The first vehicle designed, The Concept_one, was developed in a record-breaking six months with SOLIDWORKS 3D CAD as a base, including simulation tools for stress analysis.
“SOLIDWORKS was not only the easiest 3D CAD system to use, but also the most cost effective to provide a wide range of functionalities, such as structural and stress analysis. Electric cars need high battery capacity, but at the same time, batteries are very heavy and add weight. With the SOLIDWORKS tools, we developed and validated lightweight solutions for distributing battery power more efficiently using springs. With these types of operations, we were able to optimize the car’s chassis and suspension,” said Boris Tarnovski, mechanical engineer at Rimac, in an interview.
However, the growing complexity of the electrical systems related to the new C_Two model and a growing number of customers meant that requirements increased. To manage that complexity, the company implemented Dassault’s 3DEXPERIENCE Platform at the end of 2016.
Now more than 100 employees in Rimac’s product development can work in CATIA (CAD), ENOVIA (cPDm) and other applications (such as CAE Simulia and Delmia on the digital manufacturing side) on the 3DEXPERIENCE platform. With the suite of digital tools on this platform, they also have access to Dassault’s data-driven (as opposed to file-based) aggregated database in ENOVIA as a product data backbone.
A CRITICAL ASPECT of the full-electric driveline is that each wheel is driven by its own engine. In the picture, the red parts mark the engine compartments, with two motors in each wheelhouse—one in the front and one in the rear.
Dassault Acquired Parts of Modelon in 2015
Today, digital tools and methods are paramount for effective product realization. When a vehicle—which exists only as a digital model—has been tested, validated and is ready, then a physical prototype is built. The point is to create a systems of systems that work together and that can be produced with industrially viable processes. Without today’s PLM solutions or PiP platforms (Product Innovation Platforms), this would be almost impossible because the equivalent physical development costs would become astronomical.
Digitally, it’s a whole different story. You can create, simulate, iterate, verify and test drive your electric vehicle virtually, without the involvement of a single physical part or component. But there are still hurdles to overcome, such as the need for capable hardware, computers with good processor capacity and creative product developers.
BROADER STOCK OF PLM PLAYERS. Selling its then-German department to Dassault Systèmes in 2015 allowed it to develop closer partnerships with other PLM players, says Modelon’s CEO, Magnus Gäfvert.
This is where PLM and PiP come in handy. Companies like the Big Three—Dassault Systèmes (3DEXPERIENCE), Siemens PLM (Teamcenter) and PTC (Windchill)—have solutions that can handle most aspects of modern vehicle design and production to varying degrees. There are several more companies, such as Aras, Arena, SAP and Oracle, but the Big Three dominate with their broad suite of tools for the product development process. But, although their treasure chests hold a broad varieties of tools, that’s not always enough to reach the finish line. Add-ons are needed, which is exactly what Swedish software developer Modelon provides.
The company has developed more targeted solutions for systems development. Modelon’s CEO Magnus Gäfvert says that selling its then-German department to Dassault Systèmes in 2015 allowed it to develop closer partnerships with other PLM players.
“We switched from an almost exclusive and close cooperation with Dassault to broader cooperation with several PLM players, entirely in the sense of transparency and openness in line with standards. As a result of this switch, we don’t have a formal partnership with Dassault today, but we still deliver our solutions to their platforms as a third-party supplier.”
Based on the Modelica Language
Modelon’s solutions are based on the open program language Modelica which had long been supported by Dassault for complex system development within the framework of the company’s flagship product, CATIA.
It was a logical investment for several reasons. Modelica is an open, object-oriented and equation-based language designed to model complex physical systems that include mechanical, electrical, electronic, hydraulic, thermal, control, power or process-oriented subcomponents. Components and system models are available in open and commercial model libraries.
However, a problem in this context involves the ability to share and collaborate around the simulations. Compatibility is crucial for smooth workflows, yet all companies exhibit diversified PLM environments to varying degrees. Users must be able to simulate systems no matter what program environments the major automotive companies work in.
How would this be done? The answer to this question takes us back to Modelon.
Libraries Used by ANSYS, ESI and 98 Other CAE Developers
One goal for Modelon’s model-based system technology is the aim of developing open standards solutions. Users should be able to easily utilize their own tools and share models throughout the product development cycle. Transparency in Modelon’s solutions has proven to be something the world’s users of PLM solutions appreciate, users in the automotive industry included.
Modelon’s solutions circulate around the Functional Mockup-Interface (FMI) and Modelica. Gäfvert explains, “We see Modelica for model development and FMI for model integration as two complementary open solutions, which together offer great opportunities for industry to streamline product development.”
Generally, FMI is a supplier-neutral standard for model exchange and co-simulation of dynamic models at the system and component level. With FMI as a base, you can share models partly between tools, and partly distribute them across the company and partners in product development.
The standard also enables reuse of the same model portfolio in different stages of the development process and is currently supported by more than 100 CAE tools.
“FMI is a fundamental component in our value proposition,” explains Gäfvert. “With FMI, models developed by experts in advanced simulation tools using standard desktop tools can be reused by teams throughout the organization. We provide toolboxes for utilizing FMI in MATLAB/Simulink and Excel, and we also develop tailor-made solutions to integrate FMI smoothly into all workflows.”
THE ELECTRIFICATION LIBRARY. Modelon’s Electrification Library is a Modelica-based library for design, analysis and control of electrified systems. The library is suitable for a wide range of electrification applications, including land vehicles, aircraft, personal mobility, extra power electrical storage systems and other complexly designed systems. The library provides scalable and flexible model architectures with compatible component models for electrified systems.
The models are versatile to support different uses in the same modeling frame and multi-fidelity to capture different levels of electrical, mechanical, thermal and control dynamics. Component models include batteries, machines, converters, loads, routing and controls. Models include thermal interfaces and corresponding thermal models. Battery models contain a range of electrical, thermal and “aging models” to support modeling of everything from the cell to the pack.
Libraries are the Ace Up Modelon’s Sleeve
What’s particularly attractive about Modelon’s solutions are their various libraries of complete modules for systems of systems testing. Dassault Systèmes is mentioned earlier in the article, but there are many other software developers that utilize these modules. ANSYS is a good example of a specialist company using the Swedish developer’s model driven capabilities in their TwinBuilder (part of version 19.1 of ANSYS). French ESI Group, which produces virtual prototyping software, is another. The subsidiary ESI ITI integrates Modelon’s Model-based libraries in SimulationX, a software platform for multiphysics simulation.
There are currently 16 different libraries, mainly focused on automotive, aerospace, industrial equipment, energy and process industries. Examples of these libraries include Engine Dynamics, Vehicle Dynamics, Fuel Systems, Electric Power, Fuel Systems and Jet Propulsion. How do they work? Modelon’s Electrification Library is a good example, and relevant for the Rimac story.
This Modelica based library for the design, analysis, and control of electrified systems is suitable for a wide variety of electrification applications including ground vehicles, aircraft, personal mobility, and auxiliary power electric storage systems.
”It provides a scalable and flexible model architecture with compatible component models for electrified systems,” Gäfvert says, explaining that, ”The models are multi-purpose to support different use cases within the same modeling framework and multi-fidelity to capture different levels of electrical, mechanical, thermal, and controls dynamics. Component models include batteries, machines, converters, loads, routing, and controls. Models include thermal interfaces and corresponding thermal models. Battery models include a range of electrical, thermal and aging models to support modeling from the cell to the pack.”
The Modelon libraries are not limited to electrical systems. The Engine Dynamics library, like the electrical library, is used for modeling, simulation and analysis for internal combustion engine systems, including intake/exhaust flow paths, air coolers, turbochargers and exhaust gas recirculation (EGR) configurations.
Rapid Iterations are Spot-On for Rimac
For Rimac, Modelon was just the right fit. The company’s manager of control and simulation, Kruno Hrvatinić, says they, “needed a simulation tool that would enable quick model-based iterations to determine which components and configurations are best for each customer.”
Rimac’s ideal solution would allow users to model reusable scalable components for applications at different levels of complexity. In addition, they needed a solution that was possible to adapt to existing tools and workflows. “We simply wanted a consistent picture of the systems’ interaction and performance—from product concept to operation,” says Hrvatinić.
CLINICALLY CLEAN. Rimac’s manufacturing plant just outside Zagreb has an almost clinically clean environment.
“More Components in the Libraries Mean Safer Results”
When it comes to ready-made model libraries, the more components they contain, the greater their ability to get a realistic idea of how the different systems interact. In the next phase, they can also exclude inefficient, or develop even more efficient, solutions. This appealed greatly to Rimac.
Rimac chose Modelon as a system vendor, specifically for the libraries, such as Modelon’s Electrification Library, Liquid Cooling Library, Hydraulics Library and Vehicle Dynamics Library, as well as Modelon Training and Services.
“The advantage was, among other things, that these libraries contain many more components than competing libraries. These components are meaningfully different and allow modeling at different levels of abstraction, making them the best libraries we could find on the market,” says Kruno Hrvatinić.
He also notes that a driving factor in the firm’s decision to choose Modelon’s libraries was the advantage of building on the Modelica standard, as this solution also supports FMI, the open standard discussed above. In addition, Hrvatinić believes that these libraries give Rimac the freedom to implement their own detailed component models together with the pre-built models in Modelon’s libraries.
When Rimac started using Modelon’s Electrification Library for battery packs and drive assemblies, they identified several workflows to support product development processes. However, these workflows required modification of key system design parameters, modular battery reconfiguration and battery levels, and additional multi-physical simulation interfaces.
In a perfect world, simulation systems are perfect; in reality, such situations are extremely rare. Whenever you implement new systems, some development and customization efforts are always needed. This was also true in the case of Modelon at Rimac so the companies developed a partnership to capture Rimac’s requirements and expand the library to adapt it to Rimac’s needs.
FAST, COMFORTABLE AND FURIOUS. The drives view in the latest Rimac C_Two model.
“Today, Modelon’s Electrification Library also meets Rimac’s specific requirements,” says Gäfvert, adding that “our companies continue the partnership and will include tested and validated battery packs and drive models from Rimac in an upcoming version of the Modelon Electrification Library.”
Kruno Hrvatinić also says he is pleased with Rimac’s initiative. “Absolutely, their libraries give us more confidence in our early system designs and enable us to build and run simulations faster than ever before. Where we used to apply manual, steady-state analysis, we can now run a full simulation and get a lot more insight, and open new opportunities.”
A Model for Evaluating Battery Performance
With the Electrification Library, Rimac now has a way to evaluate battery performance as part of a complete simulation with multiple physical vehicle systems. Because each component is reusable and scalable, Rimac is able to make quick iterations of the models and easily adjust the model’s fidelity depending on the phase of the project. In addition, they can now connect the powertrain to the cooling systems for heat management simulations—something that previously required several software tools and additional efforts.
In the future, Rimac plans to utilize Modelon’s solutions to simulate its existing powertrain component models, such as gear dynamics. This is expected to include complete and portable multiphysics-powered models.
In addition, Rimac will start using other possibilities in the library, including aging models, more detailed controls and electrical system integration, to improve battery life and durability.