Successful Virtual Sprint
Greater competition and shorter development times strongly impact the testing of new components and systems. Developers at ZF are increasingly reacting by using digital twins, which offer even more advantages.
We are living in fast-moving times. This is not only a subjective feeling – there is plenty of evidence for the increase in speed. Digitalization is definitely one of the drivers as it continues to infuse society and the economy. What we know as digital twins, for instance, has an almost dramatic influence on the processes in technology companies such as ZF. In our first publication you learned interesting facts about how digital twins are used in companies. Let's now take a closer look at how development and testing are changing as a result of this digitalization offensive. Among other things, digital twins can shorten development times, reduce costs and enhance product quality. This increases efficiency and competitiveness.
Experts are therefore expecting a positive outcome from the distribution and revenue growth of these digital tools. According to the Irish market research company "Research and Markets," the global market for digital twins will grow by about $163 billion from 2024 to 2029, accelerating at an average annual growth rate of nearly 65 percent during this period.
More Speed in Testing
Dr. Martin Obermayr is someone who is well aware of the importance of such solutions. He heads the Center of Competence (CoC) "Digital Twin" at ZF. Together with the divisions of the Group, this central department has the core task of virtualizing product testing. Currently, ZF spends a high double-digit percentage of its R&D budget on product validation. The more successfully the number of physical tests can be reduced while generating reliable test data for the creation of digital twins, the more money the company can save.Time savings are just as crucial as cost savings. "We used to complete tasks in 24 months. Now we are expected to finish them in 18 months. What we did in 18 months should now be reduced to 12 months," says Obermayr, describing what the customers demand from ZF developers. This can only be achieved through increasing virtualization.
It suits ZF particularly well, because many ZF products are mechatronic systems, such as chassis and powertrains for passenger cars as well as commercial vehicles or off-highway applications. Simply put, there is a cable attached to all these systems, so they have a control unit. Best prerequisites for digitalizing the testing of software and hardware more than before. “If individual physical prototypes or tests can be eliminated, the associated effort required for procurement, manufacturing, documentation, and test-bench testing is also reduced. Suitable parts of this process can be supported or replaced by virtual validation. That’s a major step forward,” explains Obermayr.
Dr. Martin Obermayr, Head of Competence Center Digital Twin
For about two and a half years, ZF's development teams have been working intensively to establish the digital twin in an increasing number of product groups. They explain to customers how ZF changes testing in individual cases and the benefits customers can gain from it. The purpose of the digital twin is not to eliminate the long-standing practice of physical testing, but rather to reduce it to a necessary minimum.
Simulating Physical Tests Digitally
The topics that a digital twin must cover in the testing of mechatronic systems include among others durability – no cracks, no fractures – as well as acoustics (noise, vibration, harshness), electromagnetic compatibility and efficiency. Software and system tests can also be virtualized. All virtual tests are statistically validated. To achieve this, data from the test bench trials are compared with data from the simulation chain. The more often this comparison is made, the higher the so-called confidence interval, meaning the results obtained with the digital twin become more reliable.
Digital twins cannot completely replace physical tests on test benches, but they can reduce their number. Here the testing of a shock absorber.
Digital Testing on the Rise at ZF
Even though ZF is not yet using the digital twins across the board, there is already a growing amount of experience with them. In consultation with a German vehicle manufacturer, for instance, ZF conducted virtualized climate and environmental tests (HTOE tests) for power electronics. This partially eliminated the usual high-temperature tests in special test cabinets. Without compromising the validity of the data, virtualization reduced the testing time by about a year – the planned start of series production for the customer could be maintained.
For a US car manufacturer, ZF implemented prototype-free development during the design phase for adaptive (active) dampers. In this case, it was possible. "We have a lot of experience with dampers," says Obermayr, adding: "If the changes in software from one generation to the next are only minor, it is possible to dispense with prototypes." This results in significant savings in both cost and time. For this project, ZF provided the virtual performance certificates to the customer as agreed, and the customer was satisfied with them.
One technology where virtual testing has become virtually indispensable is Steer-by-Wire. As a fail-operational system, Steer-by-Wire must continue to operate safely even if a first or even a second fault occurs. This results in an enormous number of possible fault combinations that need to be taken into account during testing. “The tests we run here are so extensive that we are talking about three to four months just to cover the relevant fault combinations for a single software version,” Obermayr explains, illustrating the scale of the testing involved.
At the same time, new software code is being generated every day and needs to be tested continuously. This volume of testing can hardly be handled by conventional hardware-based testing on a Hardware-in-the-Loop (HiL) test bench alone. Virtual testing makes it possible to significantly increase test coverage and to test many more fault combinations at an early stage, automatically and repeatedly. It therefore specifically complements conventional HiL testing with a real control unit, microcontroller and actuators. The technology group is now working to extend this digital testing approach to other product groups as well.
