Ten versus 1,000,000,000
Experiences with SCODE at Bosch Powertrain Solutions
Hardly any other software system is as complex as the air system of a combustion engine. Numerous factors have to be considered, many of which influence each other. If the relationships between these factors are looked at incorrectly when starting development, things can quickly become very expensive. The SCODE tools were developed in order to correctly understand and describe complex systems right from the beginning. But do they actually do what the development team expected?
The SCODE development team stepped up to get the steadily increasing complexity in software development under control. After five years in actual use, we can now take stock of function development for Robert Bosch GmbH diesel engine air systems.
The characteristics of modern diesel engines depend largely on the air system. A complex software with many thousands of calibration parameters yields optimized performance characteristics and greater comfort while simultaneously ensuring that increasingly ambitious emissions targets are met – for instance, for real driving emissions (RDE) test cycles.
At Bosch, this is not restricted to just a single engine. The software includes, for example, power ratings, transmission variants, emission standards, and individual market adjustments. A tripledigit number of calibration variants for the same engine is not uncommon. In addition, there are strict time and cost requirements to be observed. This kind of complexity can hardly be realized with conventional methods – let alone provide a flexible response to potential changes.
To get this system under control, we at Bosch gradually replaced static maps with physical models some ten years ago. These models describe system behavior using formulas stored in the ECU and calculate the control model at discrete times.
Now SCODE-ANALYZER lets users describe and validate the complex relationships in control systems. With SCODE-CONGRA, they can then describe these systems using physical formulas, display and validate them as an interactive graph, and transfer them to program code. Integration in MATLAB® and Simulink® environments is possible. The tools are based on functional morphology, which is the study of the structure and relationships of the functions to each other, and on cognitive automation, which is the redesign of information in a behaviorinfluencing system.
SCODE-ANALYZER adds priorities and structure to system description. The tool first asks what is required from each switch and uses this information to describe the entire problem space. Then the process uses morphological analysis as early as the function development stage to break the problem space down into logical subspaces known as modi, such as the exhaust gas return rate in normal operation and the air mass for particle filter regeneration – or the simultaneous control of both parameters for NOX catalytic converter regeneration. This creates a total of about ten specific subspaces to address, rather than the one billion plus that are theoretically possible.
Each mode fully covers all requirements. The ANALYZER eliminates undesired and impossible combinations, and every combination in the problem space is assigned to exactly one mode. The result is a completely and clearly described subspace that covers all requirements and includes nothing that isn’t essential.
SCODE significantly reduces the complexity of the physical models within the software, and thus the calibration effort. An additional benefit is that this process simplifies software design. Using the tools reduces development time for comparable functions by 25 to 30 percent on average. The same is true for calibration effort. Other benefits include design safety, resulting from the clear and precise description and the far greater ease of reusing existing elements. A positive side effect of this is that the process improves documentation all along the control flow by presenting each mode in an extremely compact form.
In conclusion, the new tools have proven highly successful in practice and have even exceeded our expectations. After premiering it in diesel engines, Bosch is now establishing the process as a standard for gasoline engines, too, as well as for electric and hybrid drives.
Dr.-Ing. Thomas Bleile is Senior Expert in air system function development at Robert Bosch GmbH.
Contact at ETAS GmbH: Dr. Markus Behle (Senior Product Manager for software engineering tools and one of the co-inventors of SCODE), Markus.Behle@etas.com