G
Vehicle Simulation

Vehicle simulation has been referred to several times in this report as part of the fuel consumption assessment and certification process and is described in Chapter 3 as already part of Japan’s heavy vehicle fuel consumption rules. Any simulation relies on the availability of accurate submodels or good-quality test data from the components and on accurate portrayal of the physical and control linkages between the components.

Several key requirements are necessary to answer both industry needs to accelerate the introduction of advanced technologies and regulatory needs to evaluate benefits in the most cost-effective manner.

The simulation tool should provide a set of default models, processes, and postprocessing, but also allow users to integrate any legacy code. Indeed, future regulations might recommend that companies use the same assumptions but might also give the option to use legacy codes (e.g., engine and vehicle models) that have been internally developed. Using the same models regardless of the technology considered might penalize a particular company. However, if proprietary models are used, a validation process should be clearly defined to ensure their accuracy under specific operating conditions.

Due to the large number of power train configurations, which will continue to increase with hybrid electric vehicles, the tool should also be able to quickly simulate any drivetrain configurations. Finally, all the physical equations and control parameters should be open source, at least to the regulator, to ensure transparency of the process. It may be necessary to require that proprietary codes be available to the regulatory body either as soon as they are used for regulatory compliance or after some waiting period.

A review of currently available software reveals that, while the tools all provide a set of existing models, each has existing limitations. Some of the existing tools do not represent realistic vehicle behavior (e.g., ADVISOR), are not open source (e.g., AVL CRUISE, GT-DRIVE, AMESIM) or cannot be compiled to perform model-based design (MBD; e.g., AVL CRUISE), or linkage with database management is not available or incomplete.

Most of the models used throughout the industry to simulate fuel consumption are based on steady-state look-up tables representing the losses of the components. Table G-1 lists the main maps for each component. Some of the look-up tables listed can also be multidimensional (e.g., the transmission will have different maps for each gear, the electric machine losses and maximum torque might depend on voltage). The models also require additional parameters such as mass, inertia, ratios, and fuel characteristics.

Most of the parameters can be directly obtained from manufacturers’ specifications. However, some, like tire losses, require specific testing. Additional testing is also required to characterize the losses of the different components. While some of the test procedures are well characterized, others remain different from one manufacturer to the next and consequently should be clearly defined.

TABLE G-1 Main Vectors for Component Models

Component

X-Axis

Y-Axis

Z-Axis

Engine

Speed

Torque

Fuel Rate

 

Speed

Maximum torque

 

 

Speed

Closed throttle

 

 

 

Torque

 

Transmission

Speed

Torque

Efficiency

Final drive

Speed

Torque

Efficiency

Electric machine

Speed

Torque

Efficiency

 

Speed

Continuous torque

 

 

Speed

Maximum torque

 

Energy storage

State-of-charge

Open-circuit voltage

 

 

State-of-charge

Internal resistance

 



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G Vehicle Simulation Vehicle simulation has been referred to several times in cannot be compiled to perform model-based design (MBD; this report as part of the fuel consumption assessment and e.g., AVL CRUISE), or linkage with database management certification process and is described in Chapter 3 as already is not available or incomplete. part of Japan’s heavy vehicle fuel consumption rules. Any Most of the models used throughout the industry to simulation relies on the availability of accurate submodels or simulate fuel consumption are based on steady-state look-up good-quality test data from the components and on accurate tables representing the losses of the components. Table G-1 portrayal of the physical and control linkages between the lists the main maps for each component. Some of the look-up components. tables listed can also be multidimensional (e.g., the trans- Several key requirements are necessary to answer both mission will have different maps for each gear, the electric industry needs to accelerate the introduction of advanced machine losses and maximum torque might depend on volt- technologies and regulatory needs to evaluate benefits in the age). The models also require additional parameters such as most cost-effective manner. mass, inertia, ratios, and fuel characteristics. The simulation tool should provide a set of default mod- Most of the parameters can be directly obtained from els, processes, and postprocessing, but also allow users to manufacturers’ specifications. However, some, like tire integrate any legacy code. Indeed, future regulations might losses, require specific testing. Additional testing is also re- recommend that companies use the same assumptions but quired to characterize the losses of the different components. might also give the option to use legacy codes (e.g., engine While some of the test procedures are well characterized, and vehicle models) that have been internally developed. Us- others remain different from one manufacturer to the next ing the same models regardless of the technology considered and consequently should be clearly defined. might penalize a particular company. However, if proprietary models are used, a validation process should be clearly defined to ensure their accuracy under specific operating conditions. Due to the large number of power train configurations, TABLE G-1 Main Vectors for Component Models which will continue to increase with hybrid electric vehicles, the tool should also be able to quickly simulate any drivetrain Component X-Axis Y-Axis Z-Axis configurations. Finally, all the physical equations and control Engine Speed Torque Fuel Rate parameters should be open source, at least to the regulator, Speed Maximum torque to ensure transparency of the process. It may be necessary to Speed Closed throttle Torque require that proprietary codes be available to the regulatory body either as soon as they are used for regulatory compli- Transmission Speed Torque Efficiency ance or after some waiting period. Final drive Speed Torque Efficiency A review of currently available software reveals that, Electric machine Speed Torque Efficiency while the tools all provide a set of existing models, each Speed Continuous torque has existing limitations. Some of the existing tools do not Speed Maximum torque represent realistic vehicle behavior (e.g., ADVISOR), are not Energy storage State-of-charge Open-circuit voltage open source (e.g., AVL CRUISE, GT-DRIVE, AMESIM) or State-of-charge Internal resistance 

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 TECHNOLOGIES AND APPROACHES TO REDUCING THE FUEL CONSUMPTION OF MEDIUM- AND HEAVY-DUTY VEHICLES VEHICLE SIMULATION TOOL REQUIREMENTS FOR • Duplication of systems without duplication of models REGULATORY USE stored. For example, a wheel model should be reused numerous times without storing it several times under In a world of growing competitiveness, the role of simula- different names, which would make versioning man- tion in vehicle development is constantly increasing. Because agement difficult. of the number of possible advanced power train architectures • Location of expert models in a single site. For example, that can be employed, development of the next generation an engine system comprised of control, actuator, plant of vehicles requires accurate, flexible simulation tools. Such and sensor models, and initialization file, by being lo- tools are necessary to quickly narrow the technology focus cated under the same folder, would facilitate its transfer to those configurations and components that are best able to to another expert. reduce fuel consumption and emissions. • Open source of the plant and control models (rather With improvements in computer performance, many than compiled) to facilitate understanding of the as- researchers started developing their own vehicle models. sumptions and the modifications of equations to model But often computers in simulation are used only to “crunch new phenomena. numbers.” Moreover, model complexity is not the same as model quality. Using wrong assumptions can lead to errone- Maximum Flexibility ous conclusions; errors can come from modeling assump- tions or from data. To answer the right questions, users need With the consistently increasing number of possible to have the right modeling tools. For instance, one common power train configurations for medium- and heavy-duty ap- mistake is to study engine emissions by using a steady-state plications and the need to select the different level of mod- model or to study component transient behavior by using a eling to properly meet different needs (i.e., fuel efficiency, backward model. emissions, drive quality), the need to quickly simulate any Figure G-1 summarizes the main requirements, discussed application is crucial. A vehicle modeling software should below, for vehicle simulation tools required to fulfill both be able to provide the following features: needs. • Simulation of subsystems, systems, collections or Basic Requirements combinations of systems and subsystems (e.g. power trains), or entire vehicles. Providing a common envi- Maximum Reusability ronment to different experts (e.g., engine and vehicle experts) will facilitate the model’s reusability and While numerous plant and control models exist through- ensure process consistency (e.g., validation, calibra- out companies, it is critical that the work performed during tion). a project can be reused throughout the companies for future • Allow any configuration (assembly of systems) to be applications. Several approaches are necessary to achieve quickly modified and built automatically. For mainte- this goal: nance purposes, saving hundreds of models (a number FIGURE G-1 Vehicle modeling tool requirements. Figure G-1 Vehicle modeling tool requirements.eps bitmap

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 APPENDIX G that can easily be achieved through combination of • Select architecture, model, and data configurations and model complexity) is not feasible. • Check model compatibilities to avoid crash or errone- • Allow users to quickly add their own configurations. ous results • Allow users to implement any test data from sub- • Select simulation type, including component evalua- systems, systems, or entire vehicles in the same tion, vehicle fuel efficiency, or drive quality environment as the models to facilitate the validation process. Generic Processes When evaluating specific technologies, having consistent Selectable Complexity processes is critical for proper comparison. Differences in the Different studies (e.g., fuel efficiency, emissions, drive definitions of processes could lead to discrepancies in results, quality) require different levels of modeling. Throughout a which could become a significant issue for regulatory pur- project, the level of model complexity will increase to take poses. For example, the definition of the term “validation” into accounts new physical phenomena. varies significantly from one engineer to another. In addition clear definition of generic processes (e.g., calibration, valida- • Common nomenclature, including naming convention, tion, tuning) for major tasks throughout a company will lead units. If nomenclature is not consistent, an automated to increased productivity. process should be provided to users to easily integrate U sers should have the ability to easily modify any any legacy code into the agreed upon format. processes or implement new ones. One could assume that • Common model organization to facilitate interactions specific processes would be developed and agreed upon for of different expert models. For example, consistent validation, report generation, and so forth for regulatory format between controllers and plant would allow purposes. integration between both areas of expertise. • Model compatibility check. When used in a large Results Visualization organization, users do not know what models are compatible with each other. For example, a particular The GUI should allow users to quickly analyze the gearbox should be used along with a specific torque simulation. converter. Using another combination could lead to a software crash—or worse—erroneous results. While • Predefined calculation. Since most tools only record the original developers are aware of the potential issue, efforts (e.g., torque, voltage) and flows (e.g., rotational it is necessary to enforce that when one model is used, speed, current), existing calculations should allow us- it is in conjunction with the other one. ers to quickly calculate powers, energies, efficiencies, and so forth. • Predefined plots should be available to quickly analyze Code Neutrality the operating conditions of each component or control While most software companies claim to be able to model strategies. any particular plant with different levels of accuracy, some • Energy balance information should be available. software packages are used mainly for specific applications. • Reports should be automatically generated. As a consequence, different experts will use different pack- • All results should be saved along with the assumptions ages to model specific plants. One needs to have a plug-and- and any files required to rerun the simulation. play platform that allows the user to: • Any existing calculation, plot, or report should be e asily modified by users or new ones should be • Integrate any legacy code from any software package implemented. and • Run all models in the same environment or through Linkage with Other Tools co-simulation. As discussed previously, linkage with other tools is com- pulsory to properly integrate detailed legacy models. While Graphical User Interface numerous tools exist, the list should include at a minimum MathWorks toolboxes, GT-Power, AMESim, TruckSim, Setup Simulation ADAMS, and AVL DRIVE. The graphical user interface (GUI) should be able to allow users to quickly set up different simulations, including:

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 TECHNOLOGIES AND APPROACHES TO REDUCING THE FUEL CONSUMPTION OF MEDIUM- AND HEAVY-DUTY VEHICLES Database Version Control As models and data evolve with time owing to improved User Access Control data and/or algorithms, or even issues such as new modeling The sharing and distribution of proprietary models can be software version compatibility, the need for version control is achieved successfully only if their producers can trust that mandatory for auditing and regulatory purposes. Any study only the proper users will have access to them. User access done with those models needs to specify which version was control is the cornerstone of that trust. used to ensure 100 percent traceability of the results. User access control can be used in two ways: M oreover, version control can also be used intra- enterprise as a way to get feedback on the original designs. • Intra-enterprise, to define the access at each process For example, the model producer can follow which modifi- steps. For instance, during the design stage, only the cations were needed to his model during the calibration and design team can access the model. Once a version is validation process, which can then be used to create a better ready, access can be granted to a larger group, such as model next time. Version control can also be used to locate calibration, testing, and so forth. the original designer to get more information about some of • Extra-enterprise, to define the access to outside users, the model. including suppliers, regulatory committees, and so User access control applies on versioning as well. Some forth. users should have access to all model versions, when some others have access only to the latest version and others can Access control should be of at least four types: only see the history. • Producer, for the people who can add and/or modify Database Search models and data on the database. • Consumers with full access, for people who can down- To maximize the reusability of models, any user should be load the models and data to run on their computers, but able to search for an existing one available to them. Search not modify them (or at least not upload them on the should be available on name and versions of the files, as well database). as specific criteria, such as, engine technology, displacement, • Consumers with restricted access, who can only run and wheel radius. the models remotely on a dedicated server (no access The search should also be possible by specific vehicle or to the models or data themselves). project, so that all of the models and data used for a specific • Administrator, who manages access control for every- application can be found together and eventually run or one. downloaded on the user’s computer. Only the models and data that the user has access to Users can also be a combination of these types. For ex- should be returned in the search query. As an optional func- ample, some people creating models may need to access ex- tionality, the search could inform the user that other models isting ones, and consumers with full access on some models exist but are not available and could provide the coordinates may have only restricted access on others, or they can access of people to contact to request their access. only low-fidelity versions of some models. SINGLE VERSUS MULTIPLE TOOLS SELECTION FOR REGULATION Enterprise-Wide Solution Another requirement for the sharing and distribution of Numerous tools are currently being used by companies, proprietary models is their enterprise-wide accessibility, in- both internally developed and commercially available. For cluding for producer and consumer teams spread across the regulatory purposes, consistency between all approaches country or even the world for some global companies—for is critical for a fair comparison. As a result, while legacy example, a control design team can have members in the code shall be used, a single platform is necessary to ensure United States and England, or a model calibration and valida- proper integration of the different systems. Indeed, due to tion team might be located hundreds of miles from the model the large number of companies involved, the models used design team. to simulate a specific application will most likely come Up-to-date models should be accessible to all people who from numerous sources. Common tool and formalism are have the right access, wherever they are located. then critical. As shown in Figure G-2, the lack of common This constraint requires a unique and secure point of ac- nomenclature makes reusability of models among companies cess for all users. However, there can be one point of access very cumbersome. for intra-enterprise use only in each company and another global one outside, specifically for regulatory purposes.

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 APPENDIX G FIGURE G-2 Different nomenclatures within each company currently make model exchange very difficult. Figure G-2 Different nomenclatures within each company curre.eps bitmap

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