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How Virtual Verification Can Improve Physical Testing

David Kelly, Director, Drive System Design (DSD), discusses how, when applied correctly, simulation or virtual testing can improve and speed up the hardware testing process.

The speed at which the automotive industry is changing has put additional pressure on automakers to reduce their time to market for new products, reduce the cost of prototyping and testing, and identify development risks in systems electrified relatively immature. As this has coincided with the increased availability, accessibility and accuracy of simulation tools, a growing trend is emerging in which early hardware tests are being replaced by sophisticated virtual models.

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Used appropriately, simulation can make subsequent physical testing much more efficient in several ways. A better understanding of the design space early in the process enables faster convergence at a mature design level, which means downstream testing can be more focused, effective and efficient. As a recent example, we used a complex CFD virtual verification to identify thermal performance risks of an electrified “A+” sample system, which enabled a very focused risk-based testing phase that led to a rapid definition of the specifications of the prototype test fleet.

The demand for high quality data to support virtual modeling can also lead to better communication between teams of specialists. The complex relationships in a hybrid/electric vehicle, for example, bring together the thermal, mechanical, electromagnetic, software and other domains. Unlike a traditional approach in which each team brings its material for testing, simulation requires a much more detailed and integrated level of information, earlier in the program, in order to facilitate the construction of mathematical models of the system. This generally leads to greater exchange of critical data on the interfaces between the various system elements and their individual characteristics.

While advances in modeling tools make it possible to run increasingly accurate simulations, that’s only half the story. As vehicles have become more complex, the selection of the individual elements of a powertrain and the optimal organization of the architecture have become increasingly difficult. Unlike traditional powertrain alternatives that were well understood and very mature, today’s options are rapidly evolving, even the core technology of things like motors and batteries are subject to change. Managing the matrix of potential solutions and clearly identifying trends and trade-offs has become a significant challenge in itself. Before any detailed analysis, it is necessary to have a reliable means to establish the optimal concept.

At DSD, we apply a systems engineering approach to establish the effects and requirements of individual subsystems on the overall system. This ensures that the requirements of the complete system are fully understood and protected during any trade-offs between individual elements. In the case of DSD, an in-house developed tool, EPOP (Electrified Powertrain Optimization Process), assesses the complex array of powertrain considerations such as cost, mass, performance, NVH, thermal and energy consumption and autonomy, to deduce the best candidates. for application or “product family” specific architecture and component specification. It is only when the preferred architecture is identified that the more complex and detailed analysis takes place.

Control software is another increasingly important area and differentiator in modern electrified powertrains. For software, simulation is a critical step to achieve high functional maturity before hardware testing, dramatically reducing the time to develop, verify, validate, and deploy a function. At DSD, our hardware-in-the-loop (HIL) test facility incorporates vehicle simulation on real-world scenarios and use cases, network simulation (CAN/Lin/Flexray), fault injection electrical signatures of custom sensors and actuators and powertrain models developed in-house with an accurate representation of electrified system dynamics. Once the hardware is available on the test bench, the same driving scenarios, use cases and vehicle behavior can be linked to a dynamic bench replacing the simulation model of the electrified system. The latest, called ‘rig-in-the-loop’, allows the replication of realistic dynamic driving scenarios allowing for in-depth validation of software and hardware transients.

Ultimately, physical testing will always provide the final validation, but the urgency of the market transition to electrified powertrains has intensified the need to develop new solutions faster. Simulation can provide the insight needed to deliver “greater value for money” per hour of physical testing, which means either shorter time scales or more complete validation within a given time frame. The continuous adjustment of these simulation models with physical test results then creates a “virtuous circle” of virtual verification quality improvement in the immediate product cycle (the so-called “digital twin”) ) and improved processes to apply to the next generation of systems, where performance expectations will be even higher.