"Hybrid drive systems - simulation can give a good prediction of trends"

Simulation models are playing a more and more important role in the development of drive systems. This has resulted in a sharp increase in the requirements that have to be met by such simulation models. Not only are high quality and reliability the preconditions for an efficient implementation of the models, the number of parameters that have to be taken into consideration for increasingly complex calculations has also risen disproportionately. ATZ spoke to Dr. Gotthard Rainer, Vice President Advanced Simulation Technologies at AVL List GmbH, about the possibilities and limitations of modern simulation models and how close their results already are to reality.

To what extent is the current CO2 debate influencing the activities of AVL Advanced Simulation Technologies?
The CO2 discussion is not really so important for the strategic decision on which software we develop or how we develop it. The simulation model "Reduction in Fuel Consumption" is largely covered by existing software modules. What is important is that the properties of alternative fuels are available in order to define the right parameters for simulating the combustion process. Work is still required in this area to allow us to include the chemical components in the simulation in their correct form.The simulation of emissions, on the other hand, is a huge problem that has yet to be solved. The models for simulating emissions and combustion are not yet precise enough to provide accurate predictions. However, they are certainly able to support the engineer in making decisions. Due to these "new" areas of emphasis such as the simulation of emissions, we have continuously expanded our workforce in the fields of chemistry and process engineering in order to develop breakthrough technologies.

Why are these models not yet accurate enough?
The reason is the physical-chemical modelling of the combustion process, which is extremely complex and for which we still do not know the sum of all relationships and parameters. Precisely modelling a combustion process also requires corresponding computing resources. And that's where we come up against our limits at present.

How are test bed testing and simulation linked at AVL?
Since it is not possible to measure all of the quantities that are necessary to evaluate an engine, AVL began at a very early stage to integrate simulation modules into test bed tests. Simulation models that run offline and are relatively time-consuming are either developed in a "trimmed down" version in the direction of real time or real-time models are fed using elaborate simulations. The aim is to establish "hardware-in-the-loop" testing in the future. A further aspect is that complex simulations have to be supported by experience from engineering and always have to be additionally verified with real measurements. The experience of the engineer in evaluating the results also helps to raise the simulation models to a higher level of accuracy.

Therefore, simulation performs a lot of work in a short time and the results are verified by expert engineers and measured values.
Correct. At the beginning of the development process, I make extensive use of simulation in the area of design support. I then accompany the prototype phase and verify the simulation results with the results of measurements. I use simulation wherever it is most effective, and measure those parameters for which simulation is too difficult or even impossible, due to non-linearities or physical/chemical parameters that cannot be determined by simulation.

What reductions in development time will be possible within the next five years?
My question: is a further reduction in development time necessary at all, and would it make sense, assuming development times of 48, 36 or even 24 months?

The marketing departments of OEMs could react more quickly if vehicle models did not have to be fixed four years before their market launch.
That's certainly true, but numerous recalls due to faults that clearly come from the development process quickly raise the question of whether such a change is justified. Does one necessarily have to invest the time saved by using simulation at the beginning of the design phase into shortening the development time or wouldn't it be better to use the time to improve quality?

How has software development changed over the past decade?
About ten years ago, particularly computer-intensive software was used above all by specialists in the area of research. That has changed dramatically. More and more engineers use software only occasionally, as they have to perform other tasks in parallel. Software development had to be considerably simplified and formalised with a view to ergonomics and reliability, making it recordable, repeatable and understandable. The technologies that make this possible originally come from the development of embedded software as software for ECUs must not contain any faults - and are also used today in the process of developing offline software. This considerably improves the quality and reliability, but it also means an extremely high increase in development time and cost per unit of software.

Where has AVL, which has been a specialist for internal combustion engines for many years, gained the knowledge of electric motors and batteries that is required for the simulation of hybrid drive systems?
We have, of course, employed new staff with special expertise in transmissions and powertrains. For the development of simulation software, these were specialists from the fields of electrical engineering and physics as well as from mathematics and mechanical engineering. Of course, we have also outsourced the development of modules (above all electronic components) to external specialists.

How can simulation support the efficient development of hybrid drive systems?
The most important factor in this context is that AVL is in the excellent situation of having engineering, test bed development and mathematical simulation available all under one roof. Synergies allow us to develop new methods and to expand existing calculation models (e.g. transient start-stop systems) in order to take into account as many of the phenomena of hybrid drive systems as possible. Today, simulation is already so reliable that it provides a very good basis for decision-making, even if the application of hybrid technology is currently still being developed to a large extent on the test bed.

Could you please briefly explain the meaning of the abbreviation "DoE"?
It stands for "Design of Experiments" and comes from the field of metrology. In order to correctly represent the influences of different parameters, the entire characteristic map of an engine on the test bed must be covered - from idling to full load (WOT), and from idling speed to maximum speed. As far as accuracy is concerned, it would be ideal if engine speeds, torques and loads could be tested in very small steps. This, however, means that testing becomes extremely time-consuming and costly. DoE helps to reduce the number of tests by selecting those decisive parameters that have to be examined in any case, in order to allow inferences to be made regarding the overall behaviour of the engine in the map. This technology has in the meantime also been adapted to simulation calculations.

How will future powertrain development benefit from modern simulation?
Simulation will mean that product maturity is already relatively high in the design phase or pre-development phase. This makes it possible to implement sub-systems in hardware more quickly and to begin component testing earlier. Since its results can be better verified with test results, simulation will play a more active role in the entire development process and testing will be less dominant, although it will remain indispensable. As far as ECU development is concerned, I expect it to move completely from the hardware-driven side to the software-driven side in the next five to ten years. ECU development will then take place at a very early stage in the development process and will be almost entirely based on results from simulation.

Dr. Rainer, thank you for giving us this interview.



Professional background:
Dr. Gotthard Ph. Rainer, Vice President Advanced Simulation Technologies
1973 - Research Associate, TH Darmstadt
1978 - Research Engineer, AVL
1982 - Head of Department - Mechanics and Strength / Software / AVL
1986 - Head of Main Department - Computer Aided Engineering
1991 - Head of Main Department - Structural Analysis
1996 - Vice President - Advanced Simulation Technologies

Interview by: Thomas Jungmann

Suche: