Vehicle and powertrain modelling in the hole development process

DEVELOPMENT Calculation and Simulation

6 ATZ worldwide 6/2004 Volume 106

By Andreas Riel,

Wolfram Hasewend,

Erik Bogner and

Robert Fischer

Modellierung von Fahrzeug und

Antriebsstrang im gesamten

Entwicklungsprozess

You will find the figures mentioned in this article in the German issue of ATZ 6/2004 beginning on page 522.

Vehicle and Powertrain Modellingin the hole Development Process

The rapidly growing complexity and the highly interdisciplinarystructure of the vehicle and its powertrain are the two majordrivers for an increasingly simulation-centric developmentprocess. Therefore, simulation models of the vehicle and all itscomponents are used not only during the very early phases butthey rather play central roles throughout the whole develop-ment process. The following article shows how AVL List GmbHis implementing simulation models and tools and how it intro-duces effective methodologies for virtual product development.A dual clutch transmission serves as an example to show howthe development process can be supported, accelerated andverified from the concept phase to SOP by simulation.

7ATZ worldwide 6/2004 Volume 106

1 Introduction

The predominant requirement to simula-tion-based vehicle development lies pri-marily in modelling non-existent vehiclecomponents to be able to test or calibrateone or more parts of the whole vehicle atanywhere in the process. This applies to thevehicle manufacturers (OEMs) themselvesas well as to their suppliers and servicepartners both locally and within globallynetworked collaboration. The original de-mand arises from the fact that usable pro-totypes of components become availableincreasingly late in the process, whereassubsystems have to be designed and cali-brated for the whole system earlier and ear-lier. In this context, calibration denotes theoptimal adjustment of parameters of elec-tronic control units like the engine andtransmission control units (ECU and TCU,respectively). Transmission suppliers wantto design and calibrate their transmissionseven before the corresponding engines ex-ist as functional hardware prototypes.There is a trend towards the exchange ofsimulation models instead of hardwareprototypes among manufacturers and sup-pliers, such that each of them has all the re-quired and missing components availablevirtually. This raises particularly strict re-quirements both to the simulation toolsand the modelling itself in terms of quality,modularity, compatibility and repro-ducibility.

2 Use of Models in the Process

Very often in the automobile industry, theterm “Virtual Product Creation“ is used as asynonym for the DMU methodology [1,2,3].The DMU (Digital Mock-Up) is estab-lishedas the “Digital Master” within the process.Up to now, however, it only covers the ar-eas of design and production. It is hardlyused during the long phase of func-tionaldevelopment, since it only mimics the geo-metrical properties of parts and as-sem-blies. The functional development phase re-quires models of the system’s func-tions,i.e., its behaviour. The vehicle is a complexmechatronic system that contains func-tions from a multitude of different disci-plines, like from mechanics, thermody-namics, hydraulics and electronics.

A large number of individual power-train components closely cooperate to real-ize a growing number of increasingly com-plex functions for drivability, driver assis-tance, safety, and others. Consequently,there is a trend from the traditionallystrong part-oriented development to func-tion-oriented development. Already today,the engine and transmission control units

interact so closely, that a holistic view onthem is a prerequisite to be able to fulfillthe growing requirements to the quality,comfort, fuel consumption and emissionsof modern powertrain concepts. Network-ing the engine and transmission develop-ment processes can be achieved by theseamless use of simulation tools and con-sistent simulation models. Closely connect-ed to this is the process of collecting all thedata that are required for the models used[4].

The current and potential future areaswhere simulation models of the vehicleand the powertrain are used or will be usedare manifold. The list below gives onlysome examples:■ Basis for collaboration (departments,manufacturer, suppliers)■ design and pre-calculation■ sensitivity analysis of design and varia-tion parameters■ substitute of missing hardware at vari-ous testbed variants■ validation and decision basis: virtualmilestones and virtual quality gates■ early detection and removal of failures■ (long-term) archiving■ model-based control algorithms in mod-ern electronic control units.

3 The Engine and TransmissionDevelopment Processes

Figure 1 shows the most essential phases ofthe powertrain development process [5].The engine and transmission developmentprocesses run in parallel in very similarphases and they are closely linked by con-

secutive “vertical” tasks if the powertrain isdeveloped in a holistic way [6]. From con-cept simulation via tests and calibrationson various kinds of testbeds to the phasewith the vehicle prototype on the chassisdyno, simulation models with different lev-els of detail are used to mimic real compo-nents that are not yet available. In this sce-nario, it may well happen that the trans-mission exists before the engine has beenbuilt and vice versa. The permanent inter-actions and synchronizations between thetwo processes are sketched with the in-clined arrows in Figure 1.

There is a huge potential in the consis-tency of these models in terms of re-use ofmeasurement data, calculation results andmodel parameters, as well as in the trans-parency of the functionalities of simulationtools regarding arbitrary combina-tionsfrom virtual (i.e., modeled) and real compo-nents. This requirement completely appliesto e.g. AVL Drive [7,8] and AVL Cameo [9].Drive is a tool for the objective assessmentof subjective driving experience and it real-izes the horizontal “Assessment” line in Fig-ure 1. Cameo is a tool for electronic controlunit calibration and thus belongs to the“Optimisation” path in the figure. AVLPuma Open [10] provides the seamless “Au-tomation”-backbone.

4 Example: Dual-Clutch Transmission

Figure 2 shows the phases that will behighlighted in this article using a power onup-shift as an example [11,12]. The drivingcondition “shifting”, i.e., a gear shift, is a

3 The Engine and Transmission Development Processes

Figure 1 : Closely coupled development processes of engine and transmission



complex technical task particularly in thecase of a dual clutch transmission. It seemsto be no less complex to describe and assessthe human perceptions of the people in thevehicle during this usually very short dri-

ving condition to a satisfactory level. Theshifting behaviour, however, is gaining sig-nificance with the increasing automationand the growing number of different en-gine-transmission combinations.

4.1 Concept Simulation of theVehicle and the PowertrainIn the project that serves as the basis forthis article, a vehicle and its powertrainwith dual clutch transmission was mod-elled in AVL Cruise [13].

Figure 3 shows the modelling environ-ment of the simulation tool for the conceptsimulation with the powertrain model. Toaccount for the specific requirements to thedevelopment of a dual clutch transmissionlike shifting comfort and transmissionacoustics, very special effort was investedinto the transmission structure model.

The basic mechanical structure of theengine is comparatively inferior. The quan-tity that is of prime interest in this applica-tion is the engine’s torque behaviour,which was modelled in detail through thesimulation of the charge dynamics and thethermodynamic engine process within thedepicted engine model block with particu-lar focus on potentially critical transientcharacteristics.

The powertrain that was modelled inthis project belongs to the recentlylaunched family of four-wheel drive vehi-cles with dual-clutch transmission. Withinthe model, the gearbox can be recognizedby its two parallel clutches, the sixgearsteps that can be selected via dogclutches, and the two different axle-ratios.The reverse gear was not modelled since ithas no relevance for the investigated ef-fects.

The control logic model can be seen inthe lower part of Figure 3. It is at least as im-portant as the functional structure modelof the powertrain mechanics, since this iswhere the logical links between the indi-vidual information channels of all the vehi-cle components are specified. Just like inthe real vehicle, this enables the TCU totake decisions based on various sensor sig-nals and to subsequently control the shift-ing process via the responsible actors.

The results of a power on up-shift fromthe first into the second gear under full-load conditions and the corresponding Dri-ve marks are depicted in Figure 4 and Fig-ure 5. Due to its high dynamics, this shiftmanoeuvre is very well suited as an illus-trative example. Besides the high enginetorque and the particularly strong influ-ence of moments of inertia in lower gears,the energy that is converted through wheelslip is lower in all-wheel-driven vehiclesdue to their better traction.

A critical issue during a shift without in-terruption of traction is that the engine’skinetic energy has a highly effective influ-ence on vehicle acceleration and thus onthe riding comfort. Due to the facts that es-pecially sporty drivers appreciate short


4 Example: Dual-Clutch Transmission

Figure 2: Process phases for the example dual clutch transmission

4.1 Concept Simulation of the Vehicle and the Powertrain

Figure 3: Concept simulation of the vehicle with dual clutch transmission in Cruise


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4.1 Concept Simulation of the Vehicle and the Powertrain

Figure 4 : Averagely well calibrated power on up-shift in the soncept simulation with Drive-assessment

Figure 5: Well calibrated power on up-shift in the concept simulation with Drive-assessment


shifting times and the transmission’s hard-ware components have to be protected, thetime needed for clutch synchronizationneeds to be adequately short. Therefore theengine speed gradients and thus the torquecoming from the mass inertia are very high.To avoid this, the engine torque has to belowered briefly and in time.

The timing of all the different actions isthe greatest challenge in transmission cali-bration for maximum drivability. As an ex-ample, the effects of an incomplete controlof torque lowering become very well visiblein Figure4 when it is compared to Figure 5.The induced engine speed gradients resultin an acceleration impulse at the end of theshifting process, much to the driver’s dis-comfort.

The earlier mentioned AVL Drive toolwas used for the objective quantitative ver-ifica-tion of simulation results with in-ve-hicle measurements and measurementsfrom the chassis-dyno and various kinds ofcomponent testbeds. Drive can be installedin the vehicle, at the testbed and within theconcept simulation environment, in orderto produce objective assessments of drivingmanoeuvres using marks that range from 1(poorest) over 7 (limit of acceptance, i.e., the


Figure 6: PumaOpen transmis-sion testbed withPrime Mover

4.2 Real-time Simulation of the Vehicle and thePowertrain on the Testbed

Figure 7: Seamless model library to provide support during all process phases


vehicle has minor weaknesses) up to 10(best). In the presented case, Drive rates thepower on up-shift in Figure 4 with 6,53,while it “rewards” the acceleration behav-iour of the vehicle model with the im-proved calibration with 9,08.

The effect that is decisive for the worsegrading is denoted “shock” in Figure 4. It de-scribes the engagement jerk, which isstrongly perceived by the driver due to theparticularly high gradient of the longitudi-nal vehicle acceleration. The second indi-vid-ual criterion that is highlighted in theFigures 4 and 5 is the engagement steadi-ness, which assesses the effective ampli-tude of the high-frequency components ofthe acceleration signal.

With such an investigation it is thuspossible to assess and protect concepts veryearly in the process, and to derive essentialprerequisites and requirements for theirimplementations. For that purpose, a rela-tive Drive assessment is mostly sufficient,since the absolute correspondence of Drive-marks from the vehicle and the simulationis neither possible nor meaningful due tothe enormous amount of factors that influ-ence the drivability.

4.2 Real-time Simulation of the Vehicle and the Powertrain on the Testbed In the next step the transmission was oper-ated on an AVL Puma Open ISAC trans-mis-sion testbed with a simulated combustionengine. Figure 6 shows the schematic test-

bed configuration. A dynamic dynamome-ter was used as the load unit, which alsosimulated the dynamic vehicle behaviour.The engine characteristics that are relevantfor the transmission tests were simulatedusing an AVL Prime Mover, which is a per-manent magnet excited synchronous ma-chine with an extremely low real mass in-ertia and a simulated mass inertia that isequal to the engine’s mass inertia. If com-fort effects whose frequencies exceed thetestbed’s maximum frequency shall be imi-tated, one can extend this testbed configu-ration by the highly dynamic vehicle real-time simulation model VSM [14].

In this process phase it is mostly reason-able to have both the engine and transmis-sion control units available as real hard-ware, even if the engine itself is not yetavail-able. This is due to the fact that boththese electronic control units strongly in-teract – especially during shifting manoeu-vres. In the case at hand, the missing en-gine is simulated in real-time with AVLARES [15]. ARES simulates the engine’s be-haviour based on the laws of thermody-namics. The ECU can thus behave like itwould in a real engine.

AVL Cameo can be used to automateECU and/or TCU parameter optimisationfor drivability calibration in this configura-tion [16,17]. Cameo communicates with thetestbed and the control units, and conductsparameter variations according to config-urable strategies that are targeted towardsthe optimisation of criteria like comfort,

performance, fuel consumption and emis-sions under certain restrictions. Like AVLDrive it can be identically operated withina pure simulation environment, at variouskinds of testbeds, and in the vehicle.

If only the engine is available, and notthe transmission, the whole drivetraincould be simulated on the dynamic enginetestbed with AVL ISAC. The entire transmis-sion including the shifting points and shift-ing process is then simulated. ISAC alsocovers the simulation of all the missingcomponents (vehicle, driver and environ-ment), including the contact between thetyre and the road using a real-time wheelslip model [18].

Later, when both the engine and thetransmission become available, they can becalibrated together at a highly dynamicpowertrain testbed, like again for exampleAVL Puma Open with ISAC. AVL Drive andAVL Cameo can be used in both these con-figurations exactly like it was shown abovefor the transmission testbed.

Figure 7 illustrates the process phasesthat this article is predominantly dealingwith by showing the required componentsof the vehicle and its environment forevery single phase with a colour encodingfor real components, real-time models andnon-real-time models. The simulations inall these phases are heavily coined by thereal-time requirements to the models andtools. The meaning of this term is deter-mined by the way the electronic controlunits are integrated into the simulation

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4.2 Real-time Simulation of the Vehicle and the Powertrain on the Testbed

Figure 8: Method for thederivation of real-timemodels from CAE-models



4.3 In-Vehicle Verification

Figure 9: Averagely calibrated power on up-shift in vehicle test with Drive-assessment

Figure 10: Well calibrated power on up-shift in vehicle test with Drive-assessment


loop. In MIL (Model-in-the-Loop) and SIL(Software-in-the-Loop) environments, allthe control units are simulated. In the for-mer, the control unit’s logic is implementedin simulation models (typically in MAT-LAB/Simulink) that are integrated into thesimulation of the whole system. In the lat-ter, the coding of the unit’s software is al-ready identical to the software in the realhardware unit. Instead of the real ECU-hardware, however, a computer (typically astandard PC) is used as execution platform.MIL is thus primarily used to principallyverify the correctness of ECU functions,while the correctness of implementationcan only be verified in a SIL environment.

In a HIL (Hardware-in-the-Loop) envi-ronment, there is at least one real controlunit integrated into the control loop. With-in this loop all the simulation models haveto be real-time capable, where real-time isdetermined by the cycle time of the fastestcontrol loop. This implies cycle times be-tween 0,5 and 2 ms in engine simulations,and between 2 and 10 ms for transmissioncontrol units. Since neither today nor in theforeseeable future, the processing power ofcomputer systems is – or will be – sufficientto calculate CAE-models in such time steps,dedicated real-time capable models have tocreated for every component that has to besimulated. Aiming at a seamless modellingenvironment, these models should be cre-ated only by derivation from the corre-sponding CAE-models to make sure thatthe CAE-models can be used for their para-meterisation.

The ideal process, Figure 8, dictates thatthe CAE-models that are created early inthe process shall act as the single source forall the models that become available laterin regard of the data and the simulated ef-fects. This approach assures the con-sisten-cy of all the models.

In this context, the derivation of real-timemodels from CAE-models means the target-oriented simplification or re-structuring ofCAE-models with respect to the speed andsecurity of their calculation. This for instanceincludes the mapping of physical laws tomaps that can be instantly evaluated duringsimulation. The maps get their data fromCAE-model calculations. Another meansthat is typically applied is the replacement ofalgorithms that use variable integration stepwidths by fixed-step solvers.

The most important application of HILtestbeds is currently the test of electroniccon-trol units, which already today is veryoften highly automated.

4.3 In-Vehicle VerificationSubsequent to the tests, calibrations andassessments at various kinds of testbeds

the in-vehicle road tests are performed forverification.

Figure 9 and Figure 10 show examplesof measurement results acquired with AVLDrive in the vehicle. The lower assessed cal-ibration was the basis for Figure 9 whilethe higher assessed calibration led to Figure10. Thus, Figure 9 corresponds to Figure 4and Figure 10 to Figure 5 from the conceptsimulation. The quality of the concept sim-ulation is primarily determined by the cor-rect modelling of all the real effects that arerelevant for the phenomenon that shall becalibrated. Both the very good qualitativecoincidence between the decisive quanti-ties vehicle acceleration and engine speedand the very similar Drive marks for thepower on up-shift. The match between themarks for the individual criteria is also con-vincing.

5 Summary

It is of great importance to both the vehiclemanufacturer and his suppliers that all ve-hicle components can be represented at ar-bitrary points within the developmentprocess – either as real hardware or virtual-ly as software. Simulation models have tobe available in multiple modelling depthsto fulfil the different requirements to calcu-lation speed in every phase and to fit to theavailable computer platforms. The syntac-tic and semantic compatibility of the mod-els is an important precondition to assurethe profitability of the virtual product de-velopment process. A further requirementis that the development tools can be usedin real and virtual environments to thesame degree. With respect to this target,proper simulation models, tools and effec-tive methodologies have successfully beenintroduced and implemented in the virtualdevelopment process of modern vehiclepowertrains.

References

[1] Knott, T.; Hopf, M.; Hennig, H.: Der Audi A2 –Wegbereiter des virtuellen Prototypenauf-baus. In: ATZ/MTZ-Sonderheft 3/00 – „Derneue Audi A2“; S. 36-42

[2] Koytek, T.; Gaube, O.: Digital Mockup imweltweiten Entwicklungsverbund zwischenZulieferer und Hersteller. VDI Tagung„Virtuelle Produktentstehung“, 1999

[3] Moebius, T.; Spies, R.: Produktentwicklungmit Digital Mock-Up – Der neue Audi A4. In:ATZ/MTZ-Sonderheft 11/00 – „Der neue AudiA4“, S. 33-35

[4] Krastel, M.: Integration multidisziplinärerSimulations- und Berechnungsmodelle inPDM-Systeme. Darmstadt, TechnischeUniversität, Dissertation, 2002

[5] Fischer, R.; Hasewend, W.; Kriegler, W.;Pfeiffer, K.: Unterstützung der Getriebe-entwicklung durch modernste Methoden und Werkzeuge. 2. Internationales IIR Sympo-sium Innovative Fahrzeug-Getriebe, Mainz,2003

[6] Fischer, R.: Powertrain ist mehr als Motor.15. Internationale AVL Tagung Motor &Umwelt, Graz, 2003

[7] Schöggl, P.; Ramschak, E.; Bogner, E.; Dank,M.: Driveability Design: Entwicklung eineskundenspezifischen Fahrzeugcharakters. In:ATZ 103 (2001), Nr. 3, S. 186-195

[8] Bogner, E.; Dobes, T.; Machtlinger, R.;Schöggl, P.: Objektive Bewertung derSchaltqualität. IIR Fachkonferenz Getriebe-elektronik, Regensburg, 2003

[9] Fortuna, T.; Mayer, M.; Pflügl, H.; Gschweitl,K.: Optimierung von Verbrennungsmotorenmit DoE und CAMEO. HDT - 2. Tagung DoEin der Motorenentwicklung, Berlin, 2003

[10] Apschner, M.; Hauser, G.: PUMA Open: Prüf-system für Motor und Antriebsstrang. In: MTZ103 (2001), Nr. 3, S. 228-234

[11] Herbst, R.: Marktchancen von Doppelkup-plungsgetrieben. In: ATZ 106 (2004), Nr. 2, S. 106-116

[12] Bartsch, C.: Doppelkupplungsgetriebe – DerStand der Entwicklung. In: ATZ 105 (2003),Nr. 2, S. 122-126

[13] Hasewend, W.: AVL CRUISE – Fahrleistungs-und Verbrauchssimulation. In: ATZ 103 (2001),Nr. 5, S. 382-392

[14] Schöggl, P.; Dank, M.: Vehicle and EngineDynamics: Simulation, Objective Evaluationand Virtual Development. SIA 12ème Congrèssur la Dynamique du Véhi-cule, 2003, Lyon

[15] Ellinger R.: Integration of AVL's High-FidelityReal-Time Engine Model into ETAS LabCar –Motivation, Experiences and First Results.ETAS Competence Exchange Symposium2002, Stuttgart, 2002

[16] Fischer, R.; Schöggl, P.; Hasewend, W.;Ellinger, R.: Getriebeentwicklung mit objekti-ven Komfortzielen und Verfahren zur virtuel-len Optimierung. VDI-Tagung „Getriebe inFahrzeugen 2004“, Friedrichshafen, 2004

[17] Ramschak, E.; Schöggl, P.; Gallacher, A.;Brustolin, G.: CAMEO and DRIVE: New Soft-ware Tools for the Calibration of Engine Con-trol Units at the Test Bench. ATA 2001: TheRole of Experimentation in the AutomotiveProduct Development Process, Florenz,Italien, 2001

[18] Brodbeck, P.; Pfeiffer, M.; Germann, S.;Schyr, C.; Ludemann, S.: Verbesserung derSimulationsgüte von Antriebsstrangprüfstän-den mittels Reifenschlupfsimulation. VDI-Tagung „Getriebe in Fahrzeugen 2001“,Friedrichshafen, 2001

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Vehicle and powertrain modelling in the hole development process