MAN Nutzfahrzeuge AG / Big Trucks simulated on fast Processors

Thermodynamic Simulation of Combustion Engines in Real-Time

12-Cylinder HiL MAN Nutzfahrzeuge AG | MicroNova
© MAN Nutzfahrzeuge AG (Source: www.man-mn.com, Press & Media)

Is it you who is facing the challenge of continuously rising demands on test systems? Are you confronted with growing expectations in the sphere of real-time? In the simulation of combustion engines, model accuracy and real-time capability are becoming more and more important. The real-time simulation, however, is subject to the narrow time limits of the cylinder clocking. By distributing the simulation work over several processors with NovaSim, there is created freer space – also for future demands.

The following report describes the use of the NovaSim-HiL-Platform for the MAN Nutzfahrzeuge Group dealing with the simulation from Diesel- up to the 12-cylinder-engines. In this application, a multi-processor-system with four processors combined with a thermodynamic simulation model was used.

The Platform NovaSim

NovaSim is the scalable real-time platform of MicroNova AG and covers the range from a simple stimulant up to distributed multi-processors with distributed I/O. The features achievable include:

I/O-Pin-quantity up to several thousand I/Os,
Computing power from the Power-PC up to coupled, distributed real-time systems with up to 16 processors each,
Operating range from the stimulation up to the operation of distributed, high-performance HiL-models,
System without loads up to the highly precise simulation of real loads, such as high pressure magnetic injectors.

Illustration 1 gives you an overview of the scalability options of the NovaSim-Platform.

Scalability of 12-Cylinder HiL MAN Nutzfahrzeuge AG
(Illustration 1: Scalability of the NovaSim-Platform)

MAN Nutzfahrzeuge AG

The MAN Nutzfahrzeuge AG enjoys an excellent reputation as manufacturer of Diesel engines. Their range of products includes 6-cylinder truck engines as well as room-filling 12-cylinder marine engines. The development of Engine Control Units requires a realistic simulation of the engine behavior. The usual map-based mean value models are not able to map all necessary effects without an excessive parameterization effort. The use of a real-time capable thermodynamic engine model produced those high accuracies required. The NovaSim-multi-processor platform provides a powerful running environment to meet these requirements. A typical engine to be simulated is shown below.
For a higher number of cylinders there are used two identical ECUs. The HiL-System used is able to handle the large number of I/Os (several hundred) in real-time.

6-Cylinder-Diesel Engine of the MAN Nutzfahrzeuge AG
© MAN Nutzfahrzeuge AG (Source: www.man-mn.com; Press & Media)

enDYNA Themos

The TESIS DYNAware GmbH, with which MicroNova AG is cooperating, is a provider of real-time capable simulation models which can run on the NovaSim-HiL-Platform.
enDYNA Themos is a professional software package for the simulation of combustion engines. The thermodynamic model approach allows the detailed mapping of physical dependences in the engine.
enDYNA Themos represents a high-quality basis for the development and test of Diesel- and Otto engine control systems. On account of the performance of these models, they are perfectly suitable for the real-time operation on the NovaSim-Platform. The high accuracy of the enDYNA Themos engine models allows ECU-modelers to make exact and reliable statements about the behavior of engines and the relevant Engine Control Units. Even an extensive pre-calibration of the ECUs at the HiL is possible. The simulation models are used, for instance, for the following purposes:

Hardware-in-the-Loop tests of Engine Control Units monitoring the cycle of the cylinder pressure
Concept- and controller design for e.g. two-stage turbo charging, fully variable valve control and exhaust gas recirculation
Test and development of functions for exhaust gas aftertreatment and Onboard Diagnosis.

enDYNA Themos computes the time-dependent pressure cycle in the cylinder based on a null-dimensional combustion model, wall heat dissipation via the cylinders and the piston kinematics.

On account of the physical model approach, coupled effects such as the charge dilution caused by the exhaust gas recirculation on torque evolution and exhaust gas are naturally depicted. The high detail degree of the models with a simultaneous request for real-time requires high-performance hardware and a HiL-Software allowing a parallelization of the computing process. These components are available to NovaSim in the form of a Quadcore-CPU and high-performance Simulink-Blocksets.

Excursus: Thermodynamic Engine ModelThe key element of a thermodynamic engine model is the engine process simulation. In its course, the combustion process and the energy flows generated are computed in a physical-based approach, and time dependent. The crucial advantage compared to previously used mean value models, which mostly log the stationary engine behavior in engine operating maps, is the mapping of complex coherences in accordance with physical active principles and the improved accuracy achieved at the same time. Consequently, the direct effects of reduced air flow on exhaust gas temperature and charging-air pressure, just to give you an example, can be mapped very precisely. As a result of the time dependent computation of the combustion process, the influence of the injection angle and multiple injections becomes obvious in the progression of the internal pressure of the cylinder across the complete working range of the engine. Illustration 2 shows the simulated pressure rates of the cylinder at different loads and injection patterns. Therefore, a thermodynamic engine model is of great importance for tests and the development of increasingly complex controllers for e.g. exhaust gas temperature management, two-stage turbo charging, fully variable valve train, exhaust gas recirculation and the test of the on-board diagnosis functionality.

The NovaSim-Hardware used in this Application

12-Cylinder HiL MAN Nutzfahrzeuge AG A 12-Cylinder-Diesel-HiL accommodates, from top to bottom, the following components:

Error activation for 160 Pins. The injectors have a separate error activation.
Break-Out-Boxes for 360 I/O-Pins
Simulated loads for 16 high pressure magnet injectors with current measurement. For the injectors there are LEDs available to display the activation of the injectors.
ECU-activation with additional simulated loads
4-Processor-QuadCore-CPU with 2.4 GHz pulse frequency
PXI-Rack with I/O-cards and signal conditioning
Emergency shut-off unit
Power supply

For the structure of the HiL-Simulator, the tried-and-tested NovaSim-HiL modular system was used once more. Components, such as the simulation of Lambda-sensors, are already included. The dimensioning of the simulation of the used high pressure magnet injectors was adapted to the actual physical facts in the truck sector.

The NovaSim-Software used in this Application

The simple connection of the engine-specific inputs and outputs forms the basis for the successful use of models to simulate combustion engines. For this purpose, NovaSim provides a series of Simulink-Blocksets which are easy to configure. They include:

Analog In- and Outputs,
Digital In- and Outputs,
PWM In- and Outputs,
Table-controlled generation of crank- and camshaft signals,
Injection- and ignition coverage (also multiple injections- and ignition coverage),
Simulink-Blocksets for CAN,
Simulink-Blocksets for LIN.

These blocksets have already been used on numerous NovaSim-HiL-Simulators. Also so-called multirate-models, i.e. models containing parts with different cycle times, are supported by NovaSim and utilize the high computing power of multi-processor platforms.
In the application described, parts of the model are computing in parallel on several processors, so that the time limits required by the simulation were fulfilled. NovaSim contains Simulink-Blocks which allow single computations to be assigned to different processors in graphical manner. Those parts of the models that run on each of the processors just have to be placed into appropriate subsystems by the user. The NovaSim-Platform provides an efficient assignment of computations to single processors and takes care of the synchronization of each of the parallel computations. Thus the use of several processors becomes child’s play for the user.

Model step 12-Cylinder HiL MAN Nutzfahrzeuge AG Illustration 3 shows a model step with a cycle time of one millisecond. The main loop is shown in pink, the combustion processes of each cylinder in red. The computation for four cylinders at a time is compiled in a thread. The computing times for each of the cylinders differ in length because the combustion process, for instance, requires more computing time than the emission of the exhaust gases. The threads shown in blue are so-called idle-threads. They represent the reserves of the computing time at the HiL-Simulator. As you can see, there is still enough leeway for future expansions.

The HiL-Simulator can be operated in two ways:

On the one hand, there is available a comfortable interface, realized in LabVIEW.
On the other hand, a fully automated operation of the simulator is possible via a test automation based on Python.
The user interface for the HiL-Simulator is shown in Illustration 4. All inputs and outputs as well as important model variables and –parameters are arranged on the user interface for easy operation.

MAN Nutzfahrzeuge AG was supplied the HiL-System with a completely parameterized model.

Conclusion
By using tried and tested components from the NovaSim-HiL modular system, MicroNova succeeded in realizing a customized HiL-System within a short period of time and based on standards. The simulation of the real engine was implemented so realistically that no entries in the fault memories of the Engine Control Units emerged any longer. The Engine Control Unit is unable to recognize that there is no real engine in operation.

To achieve a simulation quality like this was possible because:

1. MAN provided engine data of very high quality.
2. The enDYNA engine model qualifies for a simulation with the required detailing. Only does a thermodynamic model approach depict the engine behavior in the accuracy necessary.
3. NovaSim offers the efficient hardware- and software environment that is essential.

In the past those tests had to be carried out at costly and time consuming engine test benches and under less reproducible conditions. Now, the customer will benefit from a big cost advantage because tests can be performed on the HiL-Simulator. You may even start the tests when there is no real engine available yet.

The NovaSim-HiL-Platform is also perfectly suitable for other complex application areas, such as driving dynamics models in combination with driver assistance systems. Through the support of nearly any number of processors in multi-processor-systems, the HiL-applications come close to what was unthinkable a short time ago.