CO2 emissions are a hot topic. As the eco-revolution gathers pace, driving a hybrid car has become a trendy symbol for the environmentally concerned customer who is consciously contributing to a greener world. While there are already quite a few hybrid cars on the market, hybrid technology is not yet a mature field and its development still presents considerable challenges.
The hybrid drive can be produced at three different hybridization levels with a progressively more powerful electric motor: micro hybrid, mild hybrid and full hybrid. The interaction between the internal combustion engine and the electric motor is a complex process in which the transmission, the engine management unit, ancillary assemblies and the energy storage unit must be able to react to the exacting energy flows of the combined drive system. Electronic control units ensure that everything functions properly together in all traffic conditions.
Continued research is required to understand and evaluate the entire hybrid system and its individual components. Hybrid drive effectiveness not only depends on the hybrid architecture alone; the size of the vehicle as well as the driving conditions in which it operates, have a substantial impact on fuel consumption and emissions. To optimize the overall hybrid drive efficiency, it is crucial to examine and predict C02 emissions in different driving conditions.
Innovative partnership for C02 reduction
Continental Automotive decided to take up this challenge when it launched its project ‘System concept car for C02 reduction’. For this project, Continental Automotive decided to build a demo car to demonstrate increased fuel economy based on affordable technological choices and enhance its global vehicle system know-how for C02 reduction with regard to thermal management, hybrid technology and various powertrain and chassis components.
Continental Automotive opted to integrate a customer-independent prototype engine in a series vehicle. This approach helped understand the interaction between engine, vehicle architecture and control functions so that innovative system solutions could be further developed. For this purpose, Continental partnered with Lotus Engineering in this project.
“Lotus Engineering took the responsibility for the engine development and vehicle integration and Continental had the overall project lead with the responsibility for the control system – actuators and sensors, electronics and software – as well as the complete engine and vehicle calibration,” commented Hervé Dupont, who works on C02 competence and advanced development at Continental Automotive in Toulouse, France.
Minimizing emissions and maximizing fun-to-drive
The primary research objectives were to reduce C02 emissions of future gasoline vehicles and deliver greatly diminished emissions while maintaining an engaging driving experience from an affordable set of technologies. The project sets out to demonstrate top-down vehicle system simulation and aimed to achieve a C02 emission under 140g/km as well as a maximum fun-to-drive factor for the end customer.
By building a complete vehicle model, the project aimed to identify C02 emission contributors, predict fuel consumption and develop and validate control strategies for powertrain components like electrified auxiliaries, thermal management and the mild hybrid part. Given the multi-physical character of hybrid vehicles, understanding and optimizing the controls of different components is a complex task that cannot be done without simulation support. For this, the project partners turned to LMS International and specifically the LMS Imagine.Lab AMESim platform. Based on the simulation analyses, various powertrain component choices or characteristics of have been defined.
Complete vehicle simulation
For the multi-physical vehicle simulation, the researchers used the LMS Imagine.Lab AMESim platform. This model included all multi-physical processes and subsystems such as: combustion engine, mechanical friction, fuel system, thermal management including water and oil circuit for different electrical architectures. The simulation tool helped to assess the potential of C02 emissions for different vehicle sizes and performances. The components were parameterized thanks to data from Lotus Engineering for the engine and input from Continental Automotive for the hybrid parts.
“The engine submodel that was chosen from the LMS Imagine.Lab AMESim platform mixes maps and physicals models to obtain a more accurate physical representation; it simulates transient conditions by successive steady-state operating conditions,” commented Hervé Dupont.
The control functions for hybridization and thermal management were simulated in Matlab/Simulink. The concept vehicle integrates a mild hybrid system that features Stop & Start, recuperation and torque assist functionalities based on a crank shaft mounted Integrated Starter Generator (ISG).
Since the physical and functional models can be co-simulated, simulations could be performed to predict C02 emissions with the identification of different contributors and validate control functions that were then tested on the vehicle. This specific methodology not only offers a first calibration of the control functions, but is also highly cost-effective since it drastically reduces development time.
“During the development of the complete vehicle model, we received valuable support from LMS Toulouse and in particular from Olivier Robert. His help was instrumental in the thermal aspect of the modeling: the cooling system, engine thermal management, lubrication circuit and the thermal heat external exchange,” added Hervé Dupont.
The simulation models have been developed in parallel to the demo car design and buildup in order to capitalize on the maximum of data and help make project decisions. The measurements performed with the demo car have been used to validate the multi-physical and functional virtual models.
Correlation and validation
When creating the simulation models, certain assumptions had to be made. The first model of the production vehicle was based on extensive experimental investigations, so the behavior of the multi-physical model could be validated.
The complete vehicle models created for this project have been validated with experimental test results at three levels: fuel consumption/C02 emissions, electrical behavior and thermal behavior. The models have been put through two different driving cycles; the official New European Driving Cycle (NEDC), which is the recognized standard for emissions and fuel consumption, and the Artemis driving cycle. This cycle has been developed during a European research project and is longer, more dynamic and more representative for actual driving than the NEDC.
Both cycles are used for correlation purposes. Through the model-in-the-loop approach, the experimental results helped to validate the virtual models. The results of these simulations are very promising and the models are continuously improved through measurement correlations and new component developments.
“The aim was to have a deviation between measurements and simulation results below 5% and capture the effect of architecture or function variants with a relative error of less than 3%,” stated Hervé Dupont.
These virtual models will be used to define optimal hybrid architectures for different vehicles in the future.
Towards hybrid maturity
The use of the LMS Imagine.Lab AMESim platform and the LMS Imagine.Lab Internal Combustion Engine and Thermal libraries has proven invaluable for this project. The energy balance feature in LMS Imagine.Lab platform was particularly useful since it is able to visually represent the contribution of each component to the C02 emissions and specifies where the major energy losses occur. With this information, individual components can be optimized and the global efficiency of the system can be improved. Moreover, this particular knowledge can be applied to propose new technologies to suppliers to advance component design and effectiveness.
The advantages of a validated and accurate multi-physical model are numerous. Not only does it reduce the number of tests that need to be performed, but with the model-in-the-loop it becomes easier to test new functions and make development decisions based on quantitative data specifying C02 reduction potential. All this will lead to better hybrid powertrains in the near future.
About Continental Automotive
Headquartered in Frankfurt am Main, Germany, Continental Automotive Systems is a division of the Continental Corporation and is specialized in integrating active and passive driving safety and developing innovative electric drives and body electronics. It provides intelligent system solutions and future-oriented hybrid technology. Continental Automotive has 60 plants, research centers, offices and test tracks in 19 countries worldwide.
About lotus Engineering
Lotus Engineering, the engineering consultancy division of the Group Lotus Plc., provides engineering consultancy services to customers worldwide with facilities in the UK, Malaysia, China, the USA, Germany and Japan.
