Electronic engine control units are among the most important components in today’s motor vehicles. Alongside researchers, advanced and series development engineers at DaimlerChrysler are further improving these devices with the help of new regulating procedures.

Achieving high performance at minimal fuel consumption and the lowest emissions possible — the demands placed on today’s engines are without a doubt extremely challenging. Customers want a car that offers them pure comfort and driving pleasure, but at the same time doesn’t guzzle gas. In addition, lawmakers are placing increasingly stringent emission limits on vehicles.

These demands pose a great challenge to engine researchers and developers, who also have to take costs into account. The problem is that although the experts are able to come up with an optimal solution for each demand, every such solution negatively impacts one of the other requirements. Reconciling fuel economy with low emissions is particularly difficult due to physical factors. In fact, measures taken to reduce emissions often actually raise fuel consumption, regardless of whether the engine in question runs on gasoline or diesel. One thing engine experts therefore never have to worry about is a lack of work.

The electronic engine control units and the software they work with are already extremely complex. For example, if you were to print out a document detailing the engine control software used by Mercedes-Benz, you’d easily end up with 6,000 pages of paper.

> Exponential growth

“Each additional challenge — such as a new emissions guideline — which has to be incorporated into the engine control process leads to a huge increase in the functions and data that need to be included in the control unit,” says Josef Steuer, team leader in the Drive System Control department at DaimlerChrysler Research and Advanced Development for Electric/Electronic Systems and Information Technology. “Every new element or alteration also has an impact on all existing software components, and when you introduce new technology, the result is an exponential increase in the complexity of the system.” The engineers working under Steuer’s departmental director, Markus Kern, work closely with the department headed by Hermann Breitbach at Mercedes-Benz Series Development. In addition to developing engine control algorithms for new combustion processes as a means of lowering raw emissions and fuel consumption, their cooperation is focusing on exhaust gas treatment techniques that utilize various catalytic converter and filter systems. Their goal is to use a model-based approach to develop new engine control technologies that will fully exploit combustion possibilities in engines while at the same time minimizing software complexity.

> Thousands of engine characteristics

During operation, electronic engine control units have up until now used specific types of data contained in their software, with the actual data selected depending on engine operating conditions and performance demands. Experts refer to this data as engine characteristics structures, which encompass specific values.
If, for example, a driver depresses the gas pedal to accelerate, the engine control unit not only “knows” that more fuel is now needed but also regulates the fuel dosage and intake air to ensure that emissions do not exceed a certain value. In other situations, the engine control unit might alter the ignition timing, or the position of the throttle valve or camshaft as needed.

The software installed in today’s engine control units contains up to 5,000 engine characteristics covering virtually all driving situations. The associated data is used to control everything from injection valves to exhaust gas recirculation. The data involved is generated through the analysis of numerous test drives, a process that gives rise to a myriad of measurement values.

“If you conduct a test drive at three locations — in Germany, South Africa, and northern Sweden, for example — you’ll end up with three data sets containing different parameters,” says Steuer’s colleague Ulrich Springer. “That’s because the different conditions in the three regions, such as temperature, elevation, humidity, and even fuel quality, have an impact on the engine and its performance. The engine control software basically contains all the values obtained from such tests, which means that the amount of data in the control units just gets bigger and bigger.”

> Combustion monitoring with sensors

Engine control systems also face other challenges throughout the life of a vehicle, one of which involves taking into account production tolerances, since no engine is exactly like another. Aging through wear and tear and dirt has an impact on combustion processes as well. An additional consideration for diesel vehicles is that engine control systems should only allow the regeneration of the particulate filter when it is actually full of particulates. This is because every burning-off operation consumes additional diesel fuel. To this end, a team led by Nicholas Fekete — also from the Drive Systems Control department at DaimlerChrysler Research and Advanced Development — is working on the further development of a model integrated into the engine control unit that monitors the particulate level in the filter.

Despite the increasing complexity, specialists have to date been able to design engine control units in such a manner that the units can fall back on the corresponding data for every driving situation and regulate the engine and its performance/emission behavior in the appropriate manner. Up until now, however, measurement data has been obtained only from outside the combustion chamber. “Engine control systems do not know exactly what goes on in the combustion chamber,” says Steuer.

That’s why he and his colleagues are searching for new ways to ensure that combustion always remains optimal. The key to achieving this goal is an engine control unit that doesn’t simply issue commands to sub-systems — such as the fuel injection unit or spark and glow plugs — but instead uses sensors to monitor whether the combustion process is actually running as it should. If necessary, such a unit could intervene and make adjustments. This would transform the current one-way chain of command into a closed control loop.

For example, the level of emissions produced by an engine depends heavily on the combustion process in the cylinder. “Combustion in diesel engines can be influenced primarily via injection parameters such as fuel amount, injection times, or a synchronized injection process in which several partial injections are made within fractions of a second,” says Rüdiger Pfaff, who is a team leader at Mercedes-Benz Series Development. As part of his work, Pfaff also focuses on combustion regulation.

In order to obtain information on what happens in the combustion chamber — and also influence the combustion process online — DaimlerChrysler engineers are using sensors that measure the pressure in the chamber and transmit their data to the engine control unit. The first such sensors ever used were screwed into an extra hole bored into the cylinder head, whereas today’s pressure sensors are integrated into diesel glow-plugs.

Another model-based approach for innovative engine functions registers all physical processes in both the air intake system and the exhaust tract. These are translated into software data that is combined with processing algorithms and integrated into the engine control unit. Rather than accessing the huge amount of stored engine characteristics data, the control unit instead utilizes the processing algorithm that corresponds to the operation in question.

Bringing innovative functions to motor vehicles requires more than just software, however; the engineers also had to address hardware issues. The prototype for their original control unit was the size of a cardboard moving box. The DaimlerChrysler experts used it to test, optimize, and specify the various algorithms, which they later integrated into a control unit the size of a cigar case. Without this reduction in size, it would have been impossible to get the innovative functions into a passenger car.

> Technological building blocks

The engineers’ new control system operates with an extremely short cycle time measuring only a few milliseconds. In other words, it analyzes engine data up to 300 times per second and can react just as quickly. “We want to use the model-based approach to engine control to directly regulate the combustion process in the cylinder as a means of maintaining an optimal level of emissions,” is how Steuer and Pfaff explain their strategy. “In this respect, we see the innovative engine functions as technological building blocks for lowering emissions — and also for achieving higher performance and ensuring that the engine runs more smoothly.”



Computer simulations and depictions of injection and combustion processes provide new insights into the inner workings of engines.


Engine control systems continuously monitor the combustion process and intervene within fractions of a second if necessary.


Effectively packaged innovative engine functions: Collection and analysis of large amounts of engine data from test drives is part of the everyday routine for researchers and advanced developers. Such data includes measurements taken by an online pressure sensor. The first control unit for the new engine functions took up practically the entire trunk space; today it’s about the size of conventional control units.


Effectively packaged innovative engine functions: Collection and analysis of large amounts of engine data from test drives is part of the everyday routine for researchers and advanced developers. Such data includes measurements taken by an online pressure sensor. The first control unit for the new engine functions took up practically the entire trunk space; today it’s about the size of conventional control units.


Effectively packaged innovative engine functions: Collection and analysis of large amounts of engine data from test drives is part of the everyday routine for researchers and advanced developers. Such data includes measurements taken by an online pressure sensor. The first control unit for the new engine functions took up practically the entire trunk space; today it’s about the size of conventional control units.


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