University researchers use Dymola to model the real world driver behaviour of hybrid vehicles, and to help reduce their environmental impact

Researchers at the University of Warwick are undertaking a three-year research project to investigate the impact of real world driver behaviour on CO2 emissions and energy use of vehicles. It’s the first time a single modelling framework will be developed for all hybrid vehicle architectures which will link individual vehicle models with driver models, transport models and city electrical energy models with the aim of enhancing understanding and promoting the reduction of energy usage in the transport sector.

The project Sustainable Action on Vehicle Energy (SAVE) at the University of Warwick is led by Professor Paul Jennings and Dr Peter Jones; leading the modelling programme is senior research fellow Dr Andy McGordon and post doctoral research fellow, Dr Caizhen Cheng. They are using Dymola, a multi-domain physical modelling and simulation tool, to study the impact of driver behaviour on vehicle emissions (especially from hybrid vehicles), asking such questions as “how do drivers cruise on a motorway?” and “how do we positively influence behaviour to reduce emissions?”

Vehicle emissions are currently evaluated using simple velocity/time simulations, but as Dr Andy McGordon says: “The problem with drive cycles, such as NEDC, which calculate drive cycle emissions is that no one actually drives like that. In fact it’s almost impossible to drive like the velocity to time simulation. When approaching a set of traffic lights the driver doesn’t think right I’m 20 seconds from stopping. Drivers judge in distance – I need to stop in 200 metres. Replacing time with distance is the first difference in our research.

“Where we’re headed is to be able to model the effect of real world driver behaviour, and integrate this into transport models as well as individual vehicle models. Current transport models, although they are effectively distance based simulations, do not include the effects of real world behaviour- each vehicle is effectively computer controlled and behaves in an idealistic manner. This can result in errors in predicted energy use.

Dr Caizhen Cheng is using Dymola to model the hybrid vehicle architecture. Previously researchers at Warwick have used the university’s own simulation tool called  WARPSTAR, which was a drive cycle-led model used to analyse fuel economy of hybrid vehicle architectures over a range of drive cycles. Dr Cheng explained: “The project team chose Dymola because of its ease of use and the power that it gives us in being able to model and simulate all systems in one tool, for example mechanical, electrical and control systems.

Dr McGordon said: “To include the driver model, the vehicle model has to become forward facing. We had the option to just make WARPSTAR forward facing within the Matlab Simulink environment or to make it forward facing and better in terms of  capability for these highly dynamic real world driving models.

Dr Cheng picked up the reasons why Dymola was chosen for the project: “We felt it would be better to use Dymola to do the physical modelling. It can give different fidelities for vehicle component modelling, and the models can be swapped easily to evaluate the effect of different fidelity components on the whole system.”

“I used to develop in Simulink, which is really time consuming, and also I need to verify everything because it has not been validated by other people, it has only been developed by me.  However in Dymola there are a lot of libraries which have been developed and validated by third parties.”

Dr McGordon continued: “There are other advantages through using Dymola. For example, there is continuous checking of the structure of the model  – it checks all the connections and the equations with the variables. Also, Dymola includes models of complex parts like clutches which were extremely difficult for us to build in WARPSTAR in the Simulink environment. We’ve actually integrated Dymola and Simulink so that they are complementary, and we get the best possible out of the physical model and the controller. And obviously for the driver we’re interested in the outputs from the controller.”

It only took Dr Cheng a few weeks to be able to competently master use of Dymola and just two days of formal training with Claytex. Dr Cheng continues: “On the project we have already saved so much time using Dymola. One big advantage is the libraries that are available. We have used the Powertrain and SmartElectric libraries. Libraries mean significant time savings.”

The project, which is viewed by research staff as medium term research looking out three to five years finishes in September 2011 and is being carried out in collaboration with Jaguar Land Rover, Arup  and Froude Hofmann. The project is supported by the Engineering and Physical Sciences Research Council (EPSRC), UK, through the Warwick Innovative Manufacturing Research Centre.

Dymola is provided to the University of Warwick by Claytex (www.claytex.com)

About SAVE
SAVE is a University of Warwick Innovative Manufacturing Research Centre (IMRC) project.

SAVE Project Synopsis
A project to create tools and aid decision-making for future eco-friendly vehicle technology, it is intended that this work will enhance understanding and promote reduction of energy usage in the transport sector.

For the first time a single modelling framework will be developed for all hybrid vehicle architectures which will link individual vehicle models with driver models, transport models and city electrical energy models.

Currently there is no modelling package that compares different vehicle architectures directly and that includes the capability to study the influence of real-world driver behaviour on energy usage. The project team will create such a capability and integrate it into the vehicle design process.

By developing ways of linking individual vehicle models with transport models and city electrical energy models, it is hoped that researchers may use the resulting knowledge to inform users on wider intelligent transport options using criteria such as minimum energy per person per kilometre. This will benefit not only manufacturers but will enable the optimal reduction of a city’s overall carbon footprint, reducing fossil fuel usage within vehicles and improving emissions of noxious gasses within city centres. Several potential methods for influencing driver behaviour will be considered.

SAVE Project Aims
•    To develop a family of Hybrid Vehicle powertrain models, exercised in a common structure (each having the degree of fidelity required to support a particular design decision).
•    To develop methodologies for control strategy optimisation of individual vehicles based upon likely real world fuel consumption and local and global emissions.
•    To link the vehicle models to transport and city energy models, enabling optimisation of fleet CO2 emissions.
•    To create a model which appropriately represents real world driver behaviour, and to integrate it into the vehicle design process.
•    To understand, assess and demonstrate options for the promotion of reduced energy usage and local emissions from individual vehicles and fleets of vehicles.
•    To disseminate the research results, ensuring that the research process is designed to maximise the impact of outputs across the IEV (intelligent and eco-friendly vehicle) sector.

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