Der Antrieb von morgen 2017

Climate change is one of the most critical challenges of the 21st century. In order to reduce anthropogenic CO2 emissions, the European Union (EU) has set emission reduction targets for each industry sector. Due to the fact that a major part of anthropogenic CO2 emissions can be traced back to the transportation sector, stringent targets regulating new vehicle CO2 fleet emissions were adopted. In 2020, new vehicles should emit less than 95 g/km CO2 on average. Reducing those targets even further is currently under discussion. Possible targets for 2025 range between 68 g/km and 78 g/km and 2030 targets ranging from 50 g/km to 70 g/km.

The process, methods and tool to design conventional vehicles has been developed, tested and optimized over more than 100 years. For battery electric vehicles (BEV), there is no such experience. In powertrain and energy storage systems (battery vs. fuel tank), but also in chassis and electronics, there are significant differences. Due to this, new design rules for construction need to be developed because developing electric vehicles according to the requirements for driving performance of conventional vehicles is not beneficial for the electric car concept. For example maximum traction power highly depends on temperature, manoeuver duration and State-of-Charge (SoC) of the battery. To design an electric vehicle considering user acceptance, efficiency and economic viability, the layout criteria need to be adapted to the characteristics of, amongst others, powertrain and energy storage.

48V - Where to place the e-machine?

The increasingly stringent statutory requirements for reducing CO2 emissions and pollutants from vehicles, is increasing the necessity for hybridization and electrification of the powertrain.

The DI Diesel engine has gained an increasing market share in the recent 25 years and has converted from a niche application to an established, highly appreciated propulsion system in the Light-Duty vehicle segment, covering passenger car as well as light commercial applications. In vehicle classes with high market penetration this low CO2 concept offers a substantial contribution to minimize Greenhouse gas (GHG) emissions from the transportation sector.

With the S 400 Hybrid in 2009, Mercedes-Benz introduced its first commercial hybrid electric vehicle (HEV). This P1-hybrid system, along with the first fully electric driving ML 450 Hybrid, were the foundation for the upcoming second-generation hybrid system, which first was offered in 2012 in the E 300 BlueTEC Hybrid – the world´s first diesel-hybrid vehicle in the premium segment. This highly efficient P2-hybrid system was able to reduce its CO2 emissions to 99 g CO2/km.

Battery electric vehicles provide an attractive alternative to the internal combustion engine propulsion if they are combined with a fuel cell. There are no toxic emissions, as the hydrogen fuel is solely converted to water. The electricity stored in the battery and generated by the fuel cell is used to supply electric power to an electric traction motor, which also provides some advantages regarding the dynamic behaviour and drivability compared to the internal combustion engine. Further-more, the possibility to recuperate the kinetic energy during braking events offers a convenient strategy to reduce the fuel consumption of the vehicle.

The powertrain of a vehicle hast to meet many criteria. Basically, the requirements can be divided into seven different categories: quality, comfort, environmental compatibility, design, passive safety, active safety and economy.

The whole car industry faces a big change on the way mobility is realized. The combustion engine is no longer the main path for future powertrain. Drivers are mainly government regulations for CO2 emissions, emissions in general and especially in China for license plates of cars. In addition to that “green” thinking of people will play a major role for the future car architectures.

Climate change is one of the major threats to mankind. Acknowledging this, the recent COP21 Conference in Paris has set a target of maximum 1,5°C temperature rise compared to the pre-industrial levels to limit the negative effects of global climate change. CO2 emissions from transport globally account for 23% of the total CO2 emissions. As the COP21 agreement has been ratified by 114 countries (status November 2016), the targets will be transferred into local legislation on CO2 emissions which are expected to become more stringent compared to existing scenarios. The COP21 action paper shows targets for all means of transport globally. Some countries are already planning to ban vehicles powered by Internal Combustion Engines (ICE) completely to achieve the targets (e.g. India, Norway, Netherlands). Consequently, market forecasts show that the production of locally zero-emission vehicles, namely Plug-In Hybrid Electric Vehicles (PHEV) and Battery Electric Vehicles (BEV) will strongly increase. In addition, the rising concern on air pollution caused by ICE (PM2.5, NOx) enforces the use of Real- Driving-Emission measurements of NOx which will lead to the use of more expensive Exhaust Aftertreatment Devices. As the decrease of battery pack cost is faster than expected, OEMs expect a break-even between xEV and ICE which meet the more stringent NOx and PM2.5 emission targets can already be reached in the 2021 – 2023 time frame. As a first step, 48V Hybrids will enable “Electrification for the Masses”.

The design and development process of next generation EV’s requires accurate, realtime capable models of all electric components that are simulated together with the vehicle. Efficiency potential assessment, as the current key driver for system layout, is only complete when incorporating the vehicle cooling system. Adding model fidelity to the necessary thermal component models enables to additionally analyse thermal aging effects, which is a major issue in EV’s durability analysis.

Globally reducing CO2 and emission limits are pushing the rise in vehicle electrification. Increasing electrification also means that powertrains are becoming more complex. Moreover, customers’ mobility needs are changing, as are individual demands on international markets. As a consequence, the range of potential technology solutions is becoming ever broader, and multi-dimensional. Vehicle manufacturers face the highly complex problem of optimising their drive system portfolios despite a high degree of development risk. The manufacturers are responding to that rising complexity by digitising processes and development procedures.

These trends are the background to the collaborative research project being undertaken between AUDI AG and the Institute of Automotive Engineering (IAE) at the Technical University of Braunschweig. Its aim is to create a virtual development chain allowing users to identify and design electrified powertrains for the premium vehicle models of the future. This virtual development chain encompasses five computer tools mapping the steps for the identification, design, evaluation and optimisation of electrified powertrains.

The virtual approach is intended to help meet customers’ requirements of the vehicle and the requirements of the product, while at the same time shortening development lead times and cutting costs.

On the basis of future emission requirements, in particular under the boundary conditions of the RDE legislation, the development, validation and approval requirements will significantly increase.

In this context, the optimization of the tribological system piston, piston ring and cylinder liner in order to minimize oil consumption and frictional losses is in the focus. These partial opposing objectives require a detailed analysis of the functional behavior, taking into account system robustness and the assurance of the overall system with regard to the durability over lifetime.

The effects of fuels and lubricants as well as mixture formation on wear, aging and deposition effects must also be considered. Minor changes in the piston-, piston ring- and gas dynamics or the component geometries can have a significant effect on the sealing effect of the piston group and the resulting particulate and hydrocarbon emissions. Especially transient processes under real driving conditions offer a high optimization potential. The article describes the development method for the analysis and optimization of the piston group based on fundamental research and simulation calculations as well as highly dynamic measurements on the engine test stand. The possible potentials under RDE conditions are shown.

Vehicles are safer and more efficient than ever. This is an important achievement for road users. However, current developments confront the automotive industry with new challenges. The growing diversity of powertrains, the increasing number of vehicle variants, greater depth of system integration and new legal frameworks regarding real driving emissions and energy consumption continuously increase the development effort.

48 V mild-hybrid architectures, currently receiving increasing attention, pave the way for increased levels of engine downsizing. This is facilitated through the ability to achieve a virtually instantaneous and continuous supply of boost air for the engine, even at low engine speeds, via the addition of an electrically powered supercharger (eSupercharger). The ability to increase the level of engine downsizing, while retaining good fuel efficiency across the majority of the engine operating map, would provide manufacturers with a transferable, and scalable, means for meeting these stringent new CO2 targets across their entire fleet.

The Two-Drive-Transmission (TDT) is an innovative and modular powertrain concept. The layout of the specific variant “Two-Drive Transmission with Range-Extender” (called “TDT E-REV 2+2 Gears” in) is shown. The concept combines the advantages of parallel hybrid architectures of plug-in hybrid electric vehicles (PHEV) as well as the benefits of series hybrid drives as found in extended-range electric vehicles (EREV).

Die flächendeckende Elektromobilität ist in naher Zukunft unrealistisch, so der Tenor auf der Fachkonferenz „Der Antrieb von morgen“ in Frankfurt am Main. Die Effizienzsteigerung durch milde Hybridisierung ist naheliegend. Dass es bei der Antriebstopologie keinen Königsweg, sondern vielmehr zahlreiche sinnvolle Konzepte gibt, zeigten die Fachvorträge.