A further tightening of emission legislation with Euro7 is expected. FEV’s hypothesis for the key challenges of the next European emission legislation consist of the following major topics:
- A general reduction of the gaseous emission limits CO: 500 mg/km . HC: 50 mg/km . NOX: 35 mg/km
- Non-allowance of auxiliary emission strategies that can lead to high emissions
- Particle number emissions measured down to 10 nm instead of 23 nm
- Incorporation of further emission components limits for the lab tests
- Extension of the RDE legislation framework to incorporate further emission components and short driving trips
FEV has investigated how ultimately even a zero-impact combustion engine could be achieved, causing less emissions than those contained in the ambient air. In particular the following targets have been set:
- Emissions in WLTC
- NOX: 40 µg/m³ (corresponds to approx. 0.03 mg/km)
- PM (2.5): 25 µg/m³ (corresponds to approx. 0.02 mg/km)
Compared to today’s Euro 6d legislation, this means a reduction of NOX emissions by 99.9 percent and PM emissions by 99.2 percent.
FEV has developed extensive patented and patent-pending development methods in the field of simulation, as well as testing and aging of emission-relevant components, which make it possible to demonstrate high robustness and forecast accuracy at an early stage of development.
RDE emission simulation and identification of worst case cycles
Emission simulation at FEV is an essential pillar in the frontloading of development. Presented
for the first time in 2016 at the Vienna Engine Symposium, and further refined since then, this modular FEV simulation toolchain based on the GT-Suite software environment is now an essential part of FEV development activities. Engine raw emissions are modeled based on stationary and transient measurement data from engine and roller test benches. The simulation models of the exhaust aftertreatment follow a map-based approach. Still, discretization of the catalyst monoliths allows a good description of the warm-up behavior to take into account individual, temperature-dependent conversion rates. Figure 1 depicts the all relevant variables which are included in the calculation of the conversion.
Knowledge of which vehicle- and powertrain-specific cycles can lead to the highest emissions is essential for reliable compliance with all emission limits under RDE conditions. FEV has realized an abstraction of such real driving conditions. The result is a derivation of a concise number of parameters. This parameterization allows machine learning techniques to be applied to identify the worst case RDE cycles based on an analysis of a few hundreds of simulated cycles. This methodology has meanwhile been successfully applied in many development projects.
Catalyst and gasoline particle filter characterization
In the course of the development of FEV’S RDE emission simulation methodology, it was identified that initially catalysts could hardly be modeled with sufficient precision. The reason for this lies in the mostly limited measurement data available from catalyst manufacturers and OEMs. However, for a precise prediction of the emissions under RDE boundary conditions, knowledge of the conversion rate at highest space velocities and in a wide temperature range is of high importance. FEV there-fore developed its own equipment that can be used to characterize catalysts under exactly these conditions. The system shown in Figure 2 is designed and proven for exhaust gas mass flows up to those produced by turbocharged V12 engines to measure the conversion efficiency at high mass flows and cold temperatures, such as they occur in a full load acceleration shortly after an engine start.
Catalyst and gasoline particle filter aging
FEV has established a method for rapid aging of catalysts and GPFs, as well. For GPF aging, the burner test bench is modified allowing oil to be burned in order to generate ash. Different methods have been investigated and finally oil injection was chosen. FEV generated a cycle and oil dosing strategy that is able to reproduce similar aging characteristics as they are found during vehicle durability testing.
Exhaust aftertreatment concept to achieve zero-impact emissions
Five building blocks form the exhaust aftertreatment concept for achieving zero-impact emissions.
- Optimization of NOX raw emissions during cat heating
- Exhaust aftertreatment with readiness immediately after engine start
- HC emission adsorption
- Increase of total catalyst volume
- GPF with improved filtration efficiency
The individual building blocks are discussed below.
NOX optimized catalyst heating
NOX aw emissions can be optimized by an adaptation of cat heating calibration. For very retarded ignition timings, a high amount of fuel is required to generate an IMEP that matches the FMEP. This results in dethrottling and a lower rate of internal EGR. The cylinder peak temperature increases and remains on a high level over a longer period of time. As a result, the NOX emissions increase. To achieve a drastic reduction in NOX emissions, an optimized cat heating calibration would therefore use only a mild spark timing retardation. As a consequence, HC raw emissions would increase, and additional measures need to be implemented to address this.
Electrically heated catalysts
Two electrically heated catalysts are integrated upstream of the main catalyst (4 kW per disc, 8 kW in total). The metallic substrate heats up rapidly achieving light-off after a few seconds. However, an engine start followed by cold exhaust gas flowing across the electrically heated catalysts would drop their temperature below the level needed for sufficient conversion efficiency. Therefore, a secondary air pump is used to flow air across the electrically heated catalysts prior to the engine start in order to heat up the main catalyst as well. Figure 4 illustrates the heat up process of the final system configuration. The convective heat transfer can clearly be seen in the lower half of the diagram. As soon as the engine is started the higher exhaust mass flow leads to even better convective heat transfer but at the same time also a reduction in the temperatures.
Emissions can be further optimized by ensuring that the catalyst system maintains a high temperature level. In a hybrid engine, this can be supported by the operation strategy and re-activation of the electrically heated catalysts.
Emission adsorption before catalyst light-off
One way to achieve emission adsorption is by dedicated coatings. In order to achieve a high adsorption efficiency, low temperatures are necessary. This matches with the lower incoming exhaust gas temperatures due to advanced ignition timings during cat heating. A metal substrate is considered since this allows high thermal inertia and thus low temperature increase in the first seconds of engine operation and an even distribution of the secondary air mass flow to the inlet face of the electrically heated catalyst. With a temperature limit of 850 °C the adsorption catalyst dictates the position of the exhaust aftertreatment system to be not closed coupled which in turn has benefit regarding thermal aging. Figure 5 shows a comparison of cat heating with and without HC adsorption, in this case downstream of the catalyst.
For exhaust aftertreatment systems targeting at catalyst pre-heating with a burner instead of electrically heated catalysts, the adsorption of the burner emissions via a small carbon canister positioned downstream of the catalyst might be a good solu-tion as well.
Increased catalyst volume
The catalyst volume is increase by 30 percent compared to the Euro 6d-TEMP base-line which is already using a bigger catalyst volume compared to former Euro 6b/c levels. This includes the volume of electrically heated catalysts. As a consequence, the space velocity at rated power is reduced to values at which high conversion efficiency can be maintained even in aged conditions.
GPF with improved filtration efficiency
Best-in-class Euro 6c and Euro 6d-TEMP engines without GPF already achieve PM emissions in WLTC of only 0.12 – 0.28 mg/km. Compared to the zero-impact target of 25 µg/m³ (approx. 0.02 mg/km), there is the need for a further PM emission reduction by 83 – 93 percent. This can well be achieved with a second generation GPF.
Final results and outlook
The outlined exhaust aftertreatment system is finally assessed in combination with a 2.0 l 4-cyl. turbocharged GDI engine in a plug-in hybrid configuration. Figure 6 shows the final exhaust aftertreatment system.
Extensive DoE investigations have been performed in order to achieve the zero-impact emission level while minimizing the fuel consumption penalty that arises from the electric pre-heating of the catalysts. Figure 7 depicts the correlation between the electrical pre-heating energy and all resulting gaseous emissions. Valid points fulfill the zero-impact target of NOX emissions lower than 40 µg/m³ as well as a balanced SOC of the battery at the end of the cycle. The optimum for meeting the zero-impact target at best possible fuel consumption is found slightly below 0.4 kWh. HC and CO emissions remain well below FEV’s anticipated Euro 7 limits. But, due to the concept, those emissions are not as drastically reduced as the NOX emissions.
The final results for the optimal operation strategy are depicted in Figure 8. The remaining NOX emissions – although hardly visible – mainly result from the first seconds after engine start. The oxygen storage capacity of the catalyst is completely filled at that time and initial rich operation is required to purge the catalyst before full NOX conversion efficiency is achieved. In the remaining part of the WLTC, NOX emission slips remain minimal. The electrically heated catalysts are re-activated for short intervals during the cycle to ensure the temperatures stay on a sufficiently high level at all times. Fuel consumption increases by 4.3 percent compared to the Euro 6d-TEMP baseline.
The zero-impact emission concept presented here is extremely biased towards achieving minimal NOX emissions. For the fulfillment of “just” the Euro 7 emission limit, several conceptual adaptations are possible, e.g. reduction of the number of electrical heated catalysts from two to one. Moreover, the adsorption catalyst could be eliminated, allowing the entire catalyst system to be re-located back to a closed coupled position.
The potential to achieve a simultaneous reduction in both NOx and CO2 emissions via fitting of a pre-turbine exhaust aftertreatment system (PT-EATS) in combination with a mild-hybrid concept was investigated via simulation. The main engine and hybrid system hardware were specified and thereafter, the operating strategies for recuperation and turbocharger control were determined to enable the system to meet a defined tailpipe NOX emissions value of 40 mg/km with a conformity factor (CF) of 1 over all real-world driving cycles. The performance and drivability of the demonstrator are defined to be equivalent to the base vehicle.
The main concept was to locate the exhaust aftertreatment system (EATS) directly downstream of the exhaust manifold, but upstream of the turbine as shown in Figure 1, so that the best CO2 reduction potential and the best aftertreatment performances can be achieved simultaneously.
The engine hardware and PT-EATS were designed and optimized via simulation to identify the best layout of the catalysts and to quantify the potential benefits for CO2 and NOX emissions reduction. The 48V system, made up of a belt starter generator (BSG) with the associated control components, an electric assisted turbocharger (e-TC) and the 48V battery as well as PT-EATS, were integrated to the existing engine model. The simulations optimized EATS component sizes to achieve successfully the integration within the engine bay. The e-Turbo was dimensioned in GT Power and moreover the EGR strategy was optimized to meet the extremely low engine-out NOx emission targets. Furthermore, the recuperation potential was established by using the simulation model. The original exhaust manifold was rotated 180 °C to enable the integration of the turbocharger and a larger EGR cooler was inserted to allow EGR to be used during full-load operation. Additional design modifications were made to the intercooler bracket, the water lines and air lines to allow the complete packaging within the engine bay of the chosen J-Segment demonstrator vehicle.
Placing the aftertreatment system upstream of the turbine results in an altered enthalpy and thermal inertia profile over the turbocharger compared to a conventional arrangement (Figure 2). The introduction of a 48V electric system to the vehicle enables the incorporation of a pre-turbine aftertreatment system via the integration of an e-TC which compensates the loss of pressure and temperature caused by the increased thermal inertia of the PT-EATS.
In the early phases of operation, the temperature before turbine is significantly lower than without the PT-EATS, owing to the increased thermal mass, but as the exhaust system heats up, a thermal lag and overall temperature offset is seen as a result of the higher thermal mass upstream of the turbine. The heat loss profile over the PT-EATS leads to a calculated cumulative enthalpy loss of ~ 4 percent over a WLTC (Figure 2). In order to maintain the boost pressure levels in such low enthalpy phases, the electric turbocharger generates additional boost pressure, it is also used to recuperate excess energy whenever possible.
The recuperation potential of the system was investigated at two part load operating points, shown in Figure 3. The comparison of the brake specific fuel consumption for 2 recuperation strategies was investigated and shown in Figure 3. Recuperation at the turbocharger via VGT is compared with the extraction of the same power over the BSG via an operating point load shift. The latter strategy shows a more energy-efficient path by up to 3.3 percent, as closing the VGT increases the pump losses, as seen in Figure 3, right. It should be noted however that increasing recuperation increases fuel consumption as additional power is needed to generate the same effective power.
The sizing of the e-TC was considered, as a larger turbine could reduce fuel consumption via optimized pumping losses, but, as typical passenger car driving scenarios are not significantly impacted by pumping loss based fuel consumption penalties, there was minimal benefit to upsizing the e-TC as the electrical boost required during transient operation would be increased so a smaller turbine was chosen. The key criteria in determining the size of the e-machine used is the transient response behavior of the vehicle. An acceleration from a standstill to 100 km/h was simulated with different sizes of e-TC to see which could achieve a comparable acceleration behavior to the base vehicle (8.7 s in the sprint to 100 km/h). These simulations are seen in Figure 4. Illustrating that without electrical boost support, the acceleration time increases to 13.0 s, confirming that an e-Turbo is required. An increase in the E-machine power above 11 kW showed no significant reduction in response time (9.0 s to 9.4 s) as acceleration was limited by the electrical machine speed to 180000 min-1.
Regarding the potential to reduce the cost and complexity of the EGR circuit, the use of an HP-EGR-only strategy was investigated which would consist of recuperating excess exhaust gas energy, while controlling the VGT position to achieve the required back pressure to drive higher EGR rates at comparable boost pressure. The results showed, that including the LP-EGR path reduces the required electrical energy over the WLTC by about 30 percent, therefore both HP- and LP- EGR are used. As the PT-EATS volume was found to show only minor impacts on the fuel consumption, compared to the EGR strategy influence, Figure 5, the EATS volumes were chosen to fill the available package space. All the above variables were combined to create an optimised air path strategy. Combining LP and HP-EGR, with a comparatively small turbine and an 11 kW electric motor allows for the lowest possible boost requirement during transient driving conditions. The additional energy requirement for this configuration over a WLTC was approx. 52 Wh when omitting recuperation at the BSG or e-Turbo.
Air path control
The electrical VGT turbocharger requires a dedicated control strategy to optimize the different operating states. For this concept configuration, the electric machine is mainly used for transient support during boost pressure build-up and recuperation during deceleration or in overrun operation. The conventional boost pressure control for the VGT was extended with an advanced model-based control for the power, respectively torque of the electric machine. In this approach the torque of the electric machine is calculated based on the difference between desired and actual turbine torque. An additional e-boost control factor is introduced to balance and adjust the responsiveness of the model-calculated torque demand to the e-machine against the electric energy consumption. The fuel consumption penalty and NOx engine-out emissions as a function of the e-boost control factor are shown, in Figure 6 for the WLTC.
When applying small e-boost control factors, the electric machine only supports during very high differences between desired and actual turbine torque, while for higher control factor values, the e-machine supports for smaller deltas in turbine torque. As such, the NOx engine-out emissions are reduced at higher e-boost control factor values, whereas the fuel consumption increases significantly in consequence of the increased electric power demand. These trends were combined to determine the target operation area.
Overall hybrid strategy optimization
The additional benefits of the 48V mild-hybrid system architecture shown in Figure 7 were evaluated. A 48V belt starter generator replaces the conventional 12V generator, a 48V battery with a capacity of 0.5 kWh, and the electrically supported electrical VGT turbocharger were integrated with the 12V on-board power supply provided via a bidirectional DC/DC converter. When optimizing the control of the electrical VGT turbocharger, a priority manager governs available power for the different consumers, based on the current state of the electric system. The simulation model uses a higher-level energy management strategy to ensure reliable supply for the on-board 12V network under all operating conditions and simultaneously maximizes the potential of the various 48V components to balance transient support during boost pressure build-up and recuperation potential at engine overrun operation and high enthalpy flow upstream turbine.
The balance of the electrical energy within the 48V system over the WLTC is shown in Figure 8. Recuperation takes place almost exclusively by the BSG, whereas the energy consumption is split in roughly equal parts between the supply of the consumers in the 12V network and to support the electrical boosting. As the recuperated energy exceeds the electrical energy consumption, approx. 30 percent is used to charge the 48V battery.
The second part of this paper in an upcoming magazin article will detail the PT–EATS system optimization and the overall system performance over key RDE cycles.
Legislation and public debate on reducing CO2 emissions in the transport sector have centered almost exclusively on nationwide use of battery electric vehicles (BEVs). There are areas of application, however, for which pure battery electric powertrains are not a suitable solution, e.g. for long-distance and heavy-goods transport. Due to their high energy density, liquid and gas fuels will remain the fuel of choice in these areas for a long while yet. This is particularly true for Europe, which will still remain heavily dependent on importing chemical sources of energy. In the future, some of these energy sources will be produced in regions where renewable energy sources are consistently available in large quantities. E-fuels – synthetic fuels made from renewable electricity and carbon dioxide (CO2) – represent a very attractive option here for powering mobility using a closed carbon cycle.
Significant reduction of CO2 emissions
Through the Paris Agreement, as well as the social policy goal of combating climate change, all sectors are committed to significantly reducing their CO2 emissions. The electric power supply sector is supposed to become entirely CO2 neutral by 2050. The transport sector is meant to reduce its carbon footprint by at least 80 percent as compared to 1990 – this despite an ever-increasing volume of transport. All conceivable climate-friendly solutions for passenger and goods transport also urgently need to be implemented. Some of these goals are reflected in the increasingly strict CO2 limits for newly registered vehicles in most countries. On December 17, 2018, the European Parliament and the Council of the European Union decided to reduce the fleet CO2 limits for newly registered vehicles again. CO2 emissions from cars are supposed to be reduced another 37.5 percent between 2021 and 2030. This translates to 59 g/km, which is equivalent to about 2.5 l of fossil fuel. When it comes to greenhouse gas reduction in the private transport sector in particular, one technical solution pops up more than most in the public and media debate: BEVs. The number of BEVs will indeed rise dramatically over the next decade. The starting level is still relatively low, however, with BEVs, plug-in vehicles, and range-extender vehicles currently making up roughly 2 percent of newly registered cars. The market penetration of BEVs depends heavily on various local legal parameters and government subsidies, and thus varies significantly in global terms.
The majority of all cars sold in 2030 (close to 90 percent) will still have a combustion engine for various reasons. The most frequent reasons cited for deciding not to buy an electric vehicle are the purchase price, the limited range, long charging times, and inadequate development of the charging infrastructure. In addition to this, only 2.5?–?5 percent of Europe’s vehicle fleet is replaced each year. As such, it will take several more years for BEVs and fuel cell vehicles to have significant market penetration. Relying solely on the growth of the electric fleet to achieve the ambitious CO2 targets is thus not an option. Instead, other effective technologies also need to be used. Using CO2-neutral synthetic fuels (e-fuels) can help in addition to electrifying powertrains and improving the efficiency of combustion engines.
It can be presumed that electrification will provide the largest contribution to CO2 reduction. In this context, electrification means not only pure electric vehicles, but also fuel cell vehicles, hybridizing combustion-powered powertrains, and powertrains with range extenders. An additional 24 percent reduction can be achieved by increasing efficiency through weight, friction, and enhanced aerodynamics as well as changing the modal split (shifting goods to rail). The remaining 31 percent needs to be covered by CO2-neutral fuels, as seen in Figure 2.
Looking at the energy situation in Europe and particularly in Germany, it is clear that the task of creating a system based 100 percent on renewable electricity poses a major challenge. Since renewable power (especially in Europe) is highly volatile and is not easy to store, grid expansion and necessary reserve capacities could involve very high investment costs in the future. The goal of using 100 percent renewable electric energy also means Germany would have to increase its production of renewable energy at least threefold compared to today’s production.
In addition to energy consumption, there is also significantly higher demand for energy for various industrial applications, the heating of buildings, and transport networks, currently total 2,600 TWh per year in Germany. In order to meet these needs using energy from renewable sources, Germany will have to start importing renewable energy on a large scale (Figure 3). Since some of the transmission paths are long, directly importing electric energy is only technically feasible to a certain extent, however. As a result, electric energy harnessed overseas using solar and wind power will need to be converted into chemical sources of energy by means of power-to-fuel. For regions with shorter distances between the production site and consumers, hydrogen or substitute natural gas could also be used as a carrier and transported via pipeline. Conversion into methanol or even Fischer-Tropsch products is a more sensible approach for more remote production facilities. Overall, Germany needs to import up to 29 percent of its energy requirement in the form of power-to-X (PtX) by 2050.
Using CO2-neutral sources of energy is the most efficient way to reduce its carbon footprint. As drop-in fuels, they can also reduce the carbon footprint of existing vehicle fleets. Due to their molecular structures, many prospective PtX fuels have different chemical and physical properties. The candidates that best meet the key criteria (energy density, fuel availability and established production paths, compatibility with the existing fleet) are Fischer-Tropsch fuels and longer-chain alcohols for diesel engines, as well as methanol-to-gasoline (MTG) and methanol for gasoline engines. It is possible to use hydroformylated Fischer-Tropsch fuels containing long and medium-chain alcohols to produce an e-fuel for diesel engines that is compatible with the current EN 590 standard and can thus be mixed into the existing fleet at any ratio. As shown in Figure 4, these fuels also allow for a significant reduction of soot and/or NOx.
Ethanol could be a highly promising candidate for gasoline engines. In 2018, some
110 million tons were synthesized and traded, primarily for the chemical industry. Due its very high knock resistance and good lean-burn characteristics, methanol can be used to significantly improve the efficiency of gasoline engines. As a result, e-fuels can be used to achieve similar tank-to-wheel efficiencies as in fuel cell vehicles. Figure 5 shows the increase in efficiency for engine measures implemented thus far and how the efficiency target of 50 percent could be achieved in the future.
Some countries, such as China, are massively promoting the use of methanol. In Europe, the methanol content in gasoline is currently limited to 3 percent v/v in EN 228, even though most fuel system materials are already certified up to 15 percent v/v. In addition to its direct use as fuel, methanol is also very well suited as a starting material for other fuels. For instance, the methanol-to-gasoline (MTG) process can be used to produce a gasoline-equivalent synthetic fuel that can also be mixed with conventional fuel in large quantities.
Areas of application for e-fuels
In the future, Germany will need to depend heavily on PtX imports. Cost will be the primary factor for the expansion of various technologies, however. Since local circumstances have a critical impact on the availability of renewable energies, the costs of synthesis also vary quite dramatically around the world. Figure 6 shows how greatly fuel production costs depend on the costs of power.
In many countries, e.g. in the Middle East and North Africa (MENA), the costs of synthesis will drop to below 1 euro/l diesel equivalent by 2030 due to low electricity rates. Although the potential for e-fuels has also been discussed outside of Europe, no large-scale PtX plan is currently in the works since legislation still does not acknowledge any CO2 reduction through e-fuels. As a result, market players still do not see a substantial enough business case to invest in e-fuels. A quick market introduction would be possible if one stakeholder were to profit from producing, marketing, or using e-fuels. A certificate trading system could also be introduced to allow carmakers to purchase CO2-neutral fuel and the corresponding certificates. By mixing it into the existing infrastructure, the fuel would be used by all customers.
The CO2 savings resulting from the use of e-fuels would then be counted towards the CO2 emissions of the manufacturer’s vehicle fleet. Another option would be to redesign the energy tax by lowering it on renewable sources of energy and gradually increasing the costs for CO2 emissions from fossil fuel combustion. The stakeholders addressed could be the petroleum industry or carmakers. This would yield a sustainable business model with the urgently needed investment security.
All technically feasible options will need to be used to achieve a quick reduction in CO2 emissions. However, the powertrain systems for heavy-load and long-distance vehicles cannot be electrified to the same extent as those for light commercial vehicles and cars. Goods transport will still need to rely on liquid or gas chemical sources of energy. As such, Europe will also rely on substantial imports of chemical sources of energy. The tank-to-wheel accounting currently gives a strong preference to electromobility – which will contribute enormously to lowering fleet CO2 emissions – over alternative technologies.
E-fuels have not been counted toward fleet emissions yet. Legislation thus requires urgent revision. There are various ways to make synthetic fuels more attractive, e.g. a tax on CO2 or carbon from fossil sources. Another option is to count e-fuels toward fleet emissions using a certificate trading system. Regardless of the political instrument used, synthetic fuel absolutely must be compatible with the existing fleet in order to quickly achieve market penetration.
In addition to environmentally friendly drive concepts and automated driving, progress is also being made in other areas of the automotive industry. Lighting design is gaining importance with regard to safety applications and brand differentiation. EDL Rethschulte from Osnabrück, Germany – a subsidiary of FEV – has specialized in this discipline. With this expertise, the FEV Group offers solutions that have a direct influence on the perception, safety, and operation of future cars.
These solutions are based on many years of experience, for example in the development of innovative lighting systems for headlights or transparent OLEDs for rear light applications. The latest development also has the potential to permanently change the view of (and from) the car. The REALEYES Micro-Lens Array (MLA), a further development of the MLA wafer technology, allows for the production of extremely compact and light LED projectors out of plastic the size of a thimble. With their help, images or graphics, for example, can be projected from almost any angle onto any surface, without distorting. Even extremely flat angles of incidence are no problem for the MLA, which in combination with the compact structure allows for high flexibility during installation and reduces costs. Previous solutions mostly consist of projects with just a single lens and cannot execute diagonal projections with sharp contours.
FEV’s development is effective even with high contrast and homogeneous illumination. This opens up entirely new possible uses. On the one hand, these new graphics projections provide an innovative design effect, for example in the form of light carpets, which can already be seen in practice in precursors and offer the driver guidance and a pleasant environment. In mobility concepts, such as the fully-electric, 3-seater, SVEN, which FEV presented as a car-sharing mobility concept at this year’s IAA in Frankfurt am Main (Germany), the new MLA technology offers the possibility of further informative uses. For example, the user can be greeted by an external projection next to the rental car, or receive more information.
This new lighting technology not only offers advantages in terms of additional design aspects but also provides high functional benefits and increased safety, which will become standard in future, especially in electric vehicles. These move almost silently and therefore are hardly acoustically noticeable in their environment and can make other road users notice them with projections on the road surface ahead.
Scenarios are also conceivable in which projecting a pedestrian crossing in front of the vehicle informs pedestrians that the vehicle is stopping and that they can cross the road. Warnings transferred onto the road can notify cyclists that the door of a car parked on the roadside is opening. Also, when reversing or getting out of a parking space, similar visual information for road users could be possible.
Another focal point in the context of MLA technology is the 3D area. Whereas previous 3D processes for displays mostly relied on holography and auto stereoscopy, EDL’s patent is based on light field technology. It can be used to produce high-quality three-dimensional images that can be seen without the need for glasses or other aids.
With autostereoscopic technologies, the 3D effect disappears when you close one eye, because an individual image is projected in front of each eye and it is therefore only a 3D illusion. Another challenge is that the lens of the human eye does not have to be focused on the perceived depth of an object shown but on the distance of the display. This often leads to the viewer experiencing irritations and headaches. Such unpleasant effects do not occur with the light-field technology from EDL. Even with one eye closed, the viewer still perceives a physical, three-dimensional image, since the image points are projected into the space through rays of light, resulting in a real three-dimensional image.
The basis for this patented technology is also the MLA, which consists of numerous micro-lenses the size of a match head; on the surface of a square meter that is 253,000 lenses. These lenses are manufactured with an accuracy of under one micrometer, which is key to producing high-quality 3D displays. This manufacturing process is also part of EDL’s know-how. A special film is used as a storage medium, which is located behind the micro-lenses and is capable of storing large quantities of data. This is necessary, because each of the 253,000 lenses shows the full image, which deviates by a few thousandths from its neighboring lens, and each of these individual images is made up of 65,000 pixels. During manufacturing, the image information for the optic is delivered by an LED exposure unit patented by EDL, which ensures precise orientation. Color errors and distortions do not occur with this method.
The technology gives the viewer the feeling that the objects project up to a meter out of the display.This results in exciting fields of application for the automotive sector. In the vehicle cockpit of the future, it will be possible to create holographic operation elements such as a three-dimensional controller or switch projected virtually from the center console, which the driver can comfortably operate by hand and are captured by sensors.
Also, outside of the vehicle, this 3D development can prove advantageous – for example, integrated in the headlights. In this application case, the use of plastic optics produced by injection molding with the quality of glass optics resulted in entirely new design freedoms, leading to a headlight height of just 11 mm and therefore contributing to significant weight saving. In addition, at dusk the so-called “light-dark limit” could be illuminated on the film material behind the lenses, eliminating the need for visors, which such a narrow design would have made impossible anyway.
This 3D light know-how has already been used to develop vehicle tail lights for prototypes, in which the rear light optically projects from the tail light of the vehicle and is therefore perceived more quickly than with conventional tail lights. In the past, vehicle manufacturers have for example had to work with mirrors to achieve a similar depth effect, which is however nowhere near as pronounced. As a result, with this 3D light technology there is a clear safety benefit for road users with a significantly smaller installation space.
The hybridization of powertrains is an important step toward efficient and clean mobility. In particular, the possibility of shifting the operation of the combustion engine to ranges with a higher efficiency level and representing purely electric driving modes is one of the main advantages of hybrid drives. This shifting of the load point can be further optimized on the basis of route data that includes the expected vehicle speed as well as the road gradient, and is considered to be the state of the art with regard to modern hybrid drives.
Combined with the development of predictive and automated driving functions, further potentials can be tapped. The key factor for an actual reduction of the energy requirement under real driving conditions is a precise forecast of the future development of a traffic situation. This forecast can be based on a multitude of potential sources, such as sensor data, high-resolution maps, and vehicle communication, whereby all the data is fused into a comprehensive environmental model.
Based on the information from this model, the longitudinal guidance of the vehicle and the powertrain control can be optimized. In cooperation with the Institute for Combustion Engines of RWTH University Aachen, Germany, FEV has developed a function structure that is capable of using a multitude of potential data sources. This creates a solution space for predictive speed profile optimization. This speed profile can then be used in order to optimize the operation of torque distribution between the hybrid components.
The function structure was integrated in a hybrid prototype vehicle constructed jointly with DENSO. A robust, real-time model predictive control algorithm is used in order to optimize the longitudinal guidance of the vehicle.
The HYBex3 concept vehicle
The HYBex3 (”HYBrid power exchange 3 modes“) vehicle was developed in order to determine the impact of a cost-effective DHT transmission concept on the driveability of the vehicle and test it under real conditions. It was developed jointly with DENSO AUTOMOTIVE Germany. The base vehicle is a MINI Cooper with a turbocharged 100 kW three-cylinder combustion engine. The serial transmission was replaced with the hybrid transmission to be examined, which was specially developed for the application case. The powertrain topology is equivalent to a mixed hybrid equipped with two electric engines (EE) in a P2/P3 layout. The P2 machine is located between the electrohydraulically powered clutch and the two-stage spur gear component. The synchronization elements are also actuated electrohydraulically. The P3 machine is positioned at the transmission output and therefore has a fixed transmission ratio to the wheel.
Various operating modes can be represented with this DHT transmission. For purely electric driving, the combustion engine is stopped and the clutch is opened. Electric engine P2 can therefore be operated in both transmission stages. In addition to a high starting torque in the first gear, this enables a maximum vehicle speed of 140 km/h in the second gear.
In hybrid operation, serial or parallel driving is possible. In parallel operation, one of the two gear sets is engaged. In serial operation mode, the transmission is shifted to neutral. The combustion engine is then exclusively connected to electric engine P2 while electric engine P3 operates the wheels. All gear changes are synchronized entirely electrically, so that the friction clutch can remain closed even in hybrid operation. The serial operation in the low speed range and the parallel operation at higher speeds enable a significant increase of the system efficiency level.
The operating strategy provides for the combustion engine being operated at a very low dynamic and the implementation of fast load changes by the electric path. The transmission ratios enable a significant reduction of the rotational speed of the combustion engine, without compromising the overall dynamic of the powertrain. The operating strategy was optimized with a Design of Experiments. For this purpose, the parameters of the stop-start strategy of the combustion engine were optimized simultaneously with the parameters of the battery charging strategy. For the final parameterization, a compromise between the layouts for different driving cycles was selected.
The distribution of the torques of the two electric engines, both in parallel operation and in fully electric driving, is determined by an online optimization patented by FEV. The search algorithm varies the torque distribution until the energetically optimal case is found. In doing so, both the battery limits and the power limits of the electric engines are taken into account for the current situation.
The function structure developed for predictive longitudinal dynamic control is designed in such a way that a multitude of data sources, optimization routines, and powertrain structures can be represented in said function structure.
The first step is an aggregation and fusion of the available data into an environmental model, followed by a prediction of the traffic situation. This enables an optimization of the speed profile. On the basis of that, an acceleration control of the vehicle is carried out. The planned speed profile can also be used in order to adjust the charging status strategy. If the desired charging performance is determined, the torque distribution between the powertrain components is carried out on the basis of said performance and the wheel torque requirement.
The precise forecast of the current traffic situation requires the aggregation of all available data. This includes, for instance, RADAR sensors, LIDAR sensors, or optical cameras that traffic participants can identify with the help of image recognition techniques. Usually, these sensors indicate the type (passenger car, truck, pedestrian, etc.), the relative positions and, potentially, the relative speed of the detected objects.Further information can be obtained from the on-board navigation systems, which indicate speed limits, road gradients and curvatures as well as, potentially, intersection data for the most probable path of the vehicle via an “electronic horizon”. If the navigation system is connected to the internet, data on average speeds along the planned route and traffic jams can be provided.
Additional data can be obtained through the future connection of vehicles using 5G or ETSI ITS G5. This Vehicle-to-everything (V2X) communication should include, among other things, the positions, direction, and speeds of other vehicles, as well as the layout of intersections and the status of traffic light systems. The vehicle communication can therefore provide data that goes beyond the horizon detectable via on-board sensors.
Since the same object can therefore be detected multiple times by various data sources, the data aggregation must also include a functionality for data fusion. This is especially advantageous for hardware setups with different types of sensors, e.g. a RADAR sensor and camera sensor. The RADAR sensor can precisely define the distance to and the relative position of a vehicle driving ahead, but cannot determine the lateral position of the vehicle in relation to the road markings. In contrast, the camera sensor can only provide estimates regarding the relative speed and the distance, but can precisely determine whether the detected object is in the same lane as the vehicle under consideration. After the fusion of several data sources, an aggregated object list is created, which only contains valid and relevant data for all detected objects, and generates a corresponding environmental model.
Before an optimization of the vehicle trajectory can be carried out, there must be a forecast of the development of the current situation. This forecast is based on the relevant objects that the environmental model provides. The first step is the determination of the speed limit along the prediction horizon. Based on that and the current condition of detected vehicles driving ahead, the speed and position trajectory of these vehicles is forecast.
On the basis of this, a solution space is spread out in which the downstream optimization algorithm can operate. The function structure developed by FEV and the Institute for Combustion Engines enables the implementation of different algorithms to this end. Depending on the requirement, simple, rule-based approaches, as well as model predictive control or discrete dynamic programming methods can be represented.
Application in the vehicle
To test the function structure, a real time-compatible model predictive control (MPC) was implemented in the rapid prototyping control unit of the HYBex3 concept vehicle and various test scenarios were carried out. In a first demonstration, the functionality and real-time compatibility of these scenarios for a predictive adjustment of the HYBex3 concept vehicle was proven. With an efficient implementation of the MPC using the qpOASES tool, an optimization of the speed curve for a horizon of 10 s can be carried out within less than 100 µs.
In the future, the modular design of the function structure can be used to expand the forecast horizon of the vehicle – for instance, with traffic lights ahead – or to represent predictive, automated driving functions such as Predictive Cruise Control (PCC).
Automated driving functions and autonomous driving fundamentally influence the way we will move in future. Validating these functions require systems that recognize the various scenarios in road traffic during test drives, evaluate them, and prepare them for the developers. FEV is overcoming this central challenge with a data management and assessment system developed in house, which uses the computing power of the Microsoft Azure, a cloud computing platform.
By today’s estimates, test scopes of 240 million to 16 billion kilometers of road* are needed to validate an automated driving function. However, it is not the quantity of tests that determines the maturity of a system, but the number of road traffic situations “experienced” in which the algorithms have to actively make a decision – for example, during an overtaking maneuver on the highway.
In this regard, the V2I (Vehicle-to-Infrastructure) data management system established by FEV is an efficient solution for the development and validation of such driving functions. This is because aside from the duration and number of test drives, the quantities of data obtained are also a major challenge with regard to the validation. The sensor set installed in the vehicle, consisting of cameras, lidar (light detection and ranging), and radar (radio detection and ranging), quickly generates up to 40 terabytes of data in a single day.
That is precisely what the data management solution from FEV deals with. First, a networked data logger developed in-house takes over the collection of selected vehicle signals and sends them to a back-end in real time during the test drive. FEV once again cooperated successfully with Microsoft for this. With the combination of Azure Cloud Microsoft products and the IOT hub responsible for the data transfer, FEV was able to count on an established, high-performance tool chain. The sent vehicle data is consolidated in the cloud, while algorithms analyze these signals in regards to relevant scenarios. It is therefore possible to send feedback to the relevant engineers even during test drives, and to flexibly coordinate entire fleets according to a predefined plan.
A standardized time stamp also significantly simplifies the cleaning and preparation of all vehicle data. Not least, this scenario-based pre-filtering also enables cost-efficient data storage in the cloud. Only previously-detected data packets or scenarios are loaded into the cloud hot storage, which is the layer with the highest available computing power and access management. Less important sections are saved in lower performance cloud areas that are consequently more affordable.
As an integration and development partner in series production projects of various automotive manufacturers, the efficient assessment and validation of sensor data quickly proved its worth for FEV and its clients. To minimize the general testing time on real streets and the associated costs, the development service provider is increasingly transferring significant test scopes to simulation and laboratory environments.
The data-logger solution, in combination with FEV’s own cloud-based labeling software, is a significant milestone for the construction of a holistic development environment for ADAS/AD environments. The efficient preparation of the data using automated recognition and classification according to driving situation is the basis for all other process steps in this regard.
While the driver assistance systems in series production today are still based on predefined rules, in the future, FEV believes that this will also be possible with the use of machine learning. FEV’s goal is to let artificial intelligence handle even the most complex of situations and accurately anticipate the behavior of road users.
The cooperation with Microsoft is an important component of this. Interdisciplinary collaboration between sections of the automotive industry and IT is enabling groundbreaking, cross-company innovations to be established, which offer critical development benefits. At this year’s IAA in Frankfurt, the German Chancellor and visitors had the chance to view the results of the cooperation at the
FEV expects a high growth potential for the Urban Air Mobility market and sees the opportunity for automotive players to make business in this multi-billion-dollar market and diversify their product portfolio.
Mobility is a determining factor for the quality of life in urban areas. The expected doubling of the urban passenger mobility demand by 2050 will push conventional ground based transportation to their limits. Moreover, their enhancement is limited due to large investments, footprints, and lead-times required. Metropolitan areas and cities will consequently face significant challenges with regards to pollution, noise, and congestion.
The sky however, has been successfully used for safe and time-efficient long-haul transportation for decades. Already today, conventional helicopters operate as air taxis in cities like New York City. An 8-minute flight from JFK Airport to Lower Manhattan costs around $200 USD per passenger using the Uber Copter Air Taxi Service. Also, Blade offers an Airport Pass for an annual fee of $295 USD, with which each flight between Manhattan and NYC airports costing $145 USD. Comparing this with ground transportation, the same trip costs $55 USD for a regular taxi and $120 to $180 USD for a more comfortable Uber Black Service, but takes 55 to 100 minutes.
Recent technological developments allow breakthrough of eVTOL aircraft
The high (operational) costs of a helicopter are the key driver behind the high fares. Next to this, noise emissions limit the uptake of current air taxi services. In the recent past, start-ups and established aviation companies developed new disruptive aircraft concepts: electric Vertical Take-Off and Landing (eVTOL) capable aircraft equipped with Distributed Electric Propulsion (DEP). The number of eVTOL related patents has vastly increased in the last years, with USA, China, and Germany being at the forefront. The enabler for eVTOL technology is based on the recent technology improvements in battery technology, electric motors, and automation technology, leading to several advantages compared to conventional helicopters: They promise a safer, quieter, and significantly less expensive operation. With the availability of eVTOL technology, Uber forecasts significantly less than $5 USD per passenger mile for their Uber Air Service in the near term.
Due to the advantages of eVTOL aircraft, a high growth of the eVTOL market is expected. With FEV Consulting’s background from a major near-term Urban Air Mobility (UAM) program for a megacity’s transport authority and their deep eVTOL industry insights, the company forecasted the global eVTOL fleet size through 2040. The projection takes several parameters such as the economic attractiveness of eVTOL air taxis, environmental conditions, underlying regulations, policies, and infrastructure into account. Furthermore, cultural probability of technology adaption and the number of expected, credible eVTOL manufacturers were considered.
The market of eVTOL concepts is broadly diversified, with a common set of technologies such as electric propulsion. More than 80 start-ups and established aircraft manufacturers are currently developing over one hundred eVTOL aircraft concepts. Having extensively reviewed these concepts, FEV Consulting expects that less than 20 percent are suitable for aerial ride sharing and are developed by credible players which have the capability to drive its concept through full development and certification into operation. Different use-cases are a key driver behind the broad conceptual diversification of the eVTOL aircraft landscape. The main differentiator is the aircraft architecture with the related propulsion concept: It can be distinguished between the multirotor, the lift & cruise and the tilt rotor/wing architecture. While there are also differences in the energy source, i.e. pure electric and hybrid systems, the following paragraphs focus on the electric motor.
Performance related requirements differ between the architecture concepts due to different cruise speeds and Maximum Take-Off Weight (MTOW) requirements, but also due to the number of electric motors. Power and torque densities along with the e-motors’ efficiencies are very important to aircraft due to their direct effect on the overall efficiency, range, and consequently on the overall mission suitability. Figure 5 provides an overview of the power density of electric motor concepts from suppliers with aviation activities compared to aviation certified piston engine or turbine applications. It shows why distributed electric propulsion becomes so popular for eVTOL, but is also attractive for small general aviation applications, since state-of-the-art electric motors can achieve weight savings compared to piston engines.
In addition, electric motors for aviation applications must be highly reliable because malfunctions can directly lead to flight critical emergency situations. Against the background of the operational concept, high availability and long maintenance intervals are required. Since the aircraft are lightweight designs mainly based on composites, the Noise Vibration Harshness (NVH) of electric motors should be at a minimum to avoid transferred vibrations to the fuselage and structural components. Using electric motors for these kinds of new aircraft concepts instead of complex turbines, could offer an opportunity for automotive players with activities in the electrification of powertrains.
Urban Air Mobility is an attractive pathway to enter the aviation industry for automotive players
The aerospace industry is characterized by low quantities and low economies of scale compared to the automotive industry with its cost-efficient mass production. The top-selling Airbus A320 was sold 417 times in 2018, which is less than a tenth of the sales volume a BMW 3 series has per week with 366,475 units in 2018.
Key components such as the propulsion system are flight critical and can lead to emergency situations, catastrophic events, and high liability claims. Therefore, such products must comply to the certification specifications defined by regulatory authorities such as the Federal Aviation Administration (FAA) of the United States of America or the European Aviation Safety Agency (EASA). The certification requires among others, extensive testing, validation, and related detailed documentation and reports. Furthermore, a certificate approving the manufacturing of the type certified product is required and all produced components must be highly traceable. These certification and compliance requirements lead to the high development and industrialization effort which needs to be allocated to the low quantities.
On the contrary, the automotive market is characterized by its high sales numbers and the high competition which demands for a cost-efficient mass production and lean organization and development processes. The effort for obtaining a type approval for a car is different to aviation, but the new eVTOL aircraft are also less complex compared to commercial civil aviation aircraft like the A320. Consequently, the capabilities of the automotive industry can help to reduce the costs, make air taxi fares more affordable for a broader public and can contribute to the expected market growth of the eVTOL industry.
At first, automotive players might perceive the requirements for certification as a high entry barrier. However, the supplier base for technologies, such as batteries and electric motors is less established compared to conventional aviation products. The profound experience automotive players already have from their products being used by end-customers on the road should not be underestimated since they provide real-world durability data. The acquired knowledge might help to establish a high level of confidence for respective authorities to certify products from new players. In addition, automotive players develop their products according to (automotive) ISO and SAE standards, which are similar to related standards of the aviation industry. Furthermore, the automotive industry is well experienced regarding supply chain, logistics, and production processes which will be required for a higher output compared to today’s conventional aviation industry. Consequently, there might be a gap, but not a cold start to bring automotive products into the aviation market.