6. May 2020
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Author Archives: Stefan Kasprowski
NVH
NVH-requirements of Electric Drive Units in the Vehicle Interior
NVH-requirements of Electric Drive Units in the Vehicle Interior
Legislative requirements for emissions and fuel consumption reduction are driving OEMs to develop innovative powertrain and vehicle technologies. In addition to continued development of new technologies with conventional internal combustion engines (ICE), there is an increasing trend toward electrification. These trends make it essential to develop relevant means of assessing the NVH performance of electric drive tunits (EDUs). These components do not generate the amplitudes of noise and vibration observed from internal combustion engines (ICE). As such, the methods used for NVH assessment and target development of IC engines are not sufficient for electric machines: While the objectives of ICE-based NVH development are reduction and refinement of source excitations, EDU-based NVH development focuses on the elimination of potential objectionable noise behavior in the context of ever-changing or missing masking noise content. For example, there is a reduced background noise for masking tonal noise in the absence of a running internal combustion engine.
The expectation for interior noise content from ICE-based vehicles (i.e., “powertrain presence”) depends highly on the vehicle class and target demographic; while luxury cars target low interior noise content, performance vehicles demand some level of powertrain noise feedback (with an emphasis on development of the desired “brand character”). Conversely, the tonal noise typically associated with EDUs is universally considered annoying; hence the goal is to minimize perception of this content in the vehicle. This becomes challenging, given that the reduced overall noise content available to hide (mask) this tonal noise content is lower on electric vehicles than ICE-based vehicles. Figure 1 below illustrates the difference in typical noise levels observed in ICE-powered vs. electric vehicles (EV) in the form of FEV scatterbands. Clearly, significant reduction in overall noise levels on EV are evident, especially at low-to-mid vehicle speeds.
To predict the perceptibility of tonal noise content in-vehicle, masking band analysis can be used. As shown in the figure below, the order content can be compared to surrounding 3rd octave levels to determine how much noise is available in adjacent frequencies to mask the tonal noise. If the order level (of whine noise) is high relative to the corresponding 3rd octave band noise levels, this is an indication that there is insufficient background noise to mask the order, resulting in a perceptible, and hence, objectionable whine noise. Also shown below is a masking surface which illustrates the masking content for various orders over the operating range of an example vehicle. At higher vehicle speeds, wind noise is more prominent; this results in more masking content and an associated reduction in perception of whine noise.
NVH issue root-cause analysis & mitigation
Increased trends in electrification and associated technologies have posed new challenges in NVH development. In addition to minimizing tonal noise content in the vehicle’s interior, there are multiple potential NVH issues related to transient instabilities (e.g., gear rattle or other driveline issues). FEV utilizes a structured approach, with extensive experience in 8D analysis and Design-of-Experiments (DoE) to address such problems. As part of this root-cause analysis, FEV utilizes a combination of industry-standard methods (e.g., Ishikawa diagrams), as well as FEV developed tools and processes. FEV’s Vehicle Interior Noise Simulation (VINS) is an example of a unique methodology that can be effectively utilized in the support of root cause analysis with complex noise issues. The VINS process is a unique time-domain transfer path analysis which provides insights into noise sources and transfer paths which contribute to sound quality issues under steady-state or transient conditions. Any noise issues identified at the vehicle’s interior can be broken down to identify contributions of various structureborne and airborne noise paths. The critical noise paths can be further decomposed to identify any potential opportunities for improvement (mount isolation, attachment point stiffness, vibroacoustic sensitivity, acoustic attenuation, etc.). Because the results generated are in the time-domain, advanced analysis methods or subjective evaluations (listening studies) can be used for assessment of the overall simulated noise or individual path contributions. Figure 2 schematically shows the integration of the VINS methodology in a structured 8D root-cause analysis process.
Component-level EDU NVH assessments
FEV has established standard testing procedures for quantifying radiated noise, sound power, and vibration at the component-level to facilitate assessment of source-level inputs to support electric vehicle NVH development. Analogous to ICE-based powertrain NVH testing, overall EDU radiated noise levels are typically assessed based on average radiated noise, measured at a distance of 1 m from the EDU (e.g., using SAE J1074 standard). Additionally, it is common practice for electric machines and EDUs to augment these assessments with measurement of sound power, utilizing a hemispherical or parallelepiped array (e.g., IS0 3744 or 3745 standards). Structureborne excitations can be assessed by measurement of vibration at the EDU mounting locations (i.e., interface points between the EDU and vehicle).
Comparison of average overall sound pressure levels between ICE-based powertrains and EDUs in the figure below illustrates that noise levels radiated from EDUs are significantly lower than those observed from ICE powertrains. As such, assessment of individual orders excited by the electric machines and/or gear meshing frequencies is more relevant (than overall noise levels) for quantification of EDU NVH performance. An example of order content relative to overall radiated noise levels is illustrated below. This comparison provides information regarding the contribution of orders to overall noise levels. Additional investigation of the frequency content of the component noise levels can provide insights into perceptibility of this noise in a test cell environment. However, component level data analysis alone does little to predict the perceptibility of these orders by the customer in-vehicle. For this, a vehicle-centric data analysis approach is required, as described below.
Vehicle-centric EDU NVH target development
Derived from the VINS methodology, FEV has developed an additional process for interior noise prediction, called dBVINS. Unlike VINS (which utilizes vehicle-specific noise transfer functions), the dBVINS process predicts interior noise based on a combination of source data (noise and vibration, as measured in the test cell) and standardized vehicle noise transfer functions. These “standardized” noise transfer functions are based on median vehicle noise sensitivity performance, derived from the extensive database of vehicles assessed by FEV. By standardizing the transfer functions, the interior noise relevant NVH performance of a given component (e.g., EDU) can be judged based on component-level tests from a NVH test bench. This allows for direct comparison of the expected interior noise performance of different EDUs or design variants of a development EDU. Specific to EDU development, this process allows for prediction of relevant order content at the vehicle interior. Comparison of this order content to the masking noise levels discussed above provides insights into the potential perceptibility of tonal noise issues by the customer. Appropriate design changes using a combination of CAE (e.g., MBS/FEA) and test-based approaches (e.g., calibration changes, NVH countermeasure development) can be employed to improve the component-level NVH performance of the EDU, utilizing such a vehicle-centric approach.
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Powertrain Test Field
Workflow-Based Information Management for Powertrain Testing Facilities
Workflow-Based Information Management for Powertrain Testing Facilities
Compared to the amount of raw measurement data generated and processed by self-driving vehicles, the amount produced during powertrain testing is quite easily manageable. However, the sheer variety of information encountered with powertrain tests and how the pieces interact place high demands on the tools used to process that information. An efficiently organized testing facility therefore needs that information to be structured and standardized sensibly and its information management tools to be networked intelligently. That is the only way to speed up information processing during the testing process and maximize the knowledge gains.
Due to the variety of information, it makes sense to divide information into domains (Figure 1). Then, the flow of information between the domains and an adequate tool chain can be specified and set up.
FEVFLEX™ enables the configuration of project data, such as team definitions and availability, time frames and budgetary conditions, and allows for the transfer of this data from the ERP system and machine data acquisition systems to the first information domain – the testing assignment database. The powerful, graphical user interfaces in FEVFLEX™ enable a reliable planning and coupling of test programs and resources (test beds, measuring instruments, personnel).
A tied-in, digital order management system allows instructions prepared in writing to be issued to laboratories and workshops along with the master data so the necessary measuring tools can be prepared and the test setup be initiated. Information about the subject of testing and the testing program as well as the control unit data sets are supplied by the respective specialist department.
It is clear that reliably functioning information tools also need to promote collaboration and the exchange of information between process partners during testing assignment planning so the information can be combined efficiently and without any loss.
At FEV, our specialist departments and testing facilities do this by using the identical front end of the testing assignment database seen in Figure 2.
The inspection order data is automatically transmitted to the second information domain. FLEX Lab™ creates the configuration of the test bench automation system, MORPHEE™, where it serves as the basis for performing the tests.
In the testing database, individual test steps, such as engine characteristic map measurement, full-load curve, or an emission cycle, are specified, depending on the test types required (Figure 2). Because the information is inherited, only deviations from the planned testing requirements need to be recorded for the subsequent steps and documentation purposes. The test bench operator selects the appropriate step from the testing database via the automation system’s interface, thus creating a connection to the measurement data.
Linking the test assignment data with associated rules, the set points actually achieved during the test, and the time-synchronous measurement data from the various measuring systems produces a complete set of data for calculating test results and for further analyses. Computations are performed as needed. The automation system calculates control deviations or significant quality criteria, e.g. measuring point stability, in real time during measurement. Once the system processes them, they are transferred to the database. Additional calculations based on a standardized list of formulas are performed after the measurement results are imported into the testing database. The results of those calculations are stored separately.
Upon conclusion of each step in testing, we have a pool of informative data available for quality assurance by the testing facility or for additional analyses, even for multiple projects, by the specialist department.
In the third domain – the operational database – the logbook functionality in FEVFLEX™, enables the logging of code-based operating states and error messages of the automation systems and measuring devices in the test field. This makes additional information available.
The test bench operator supplements that information with reports on the error patterns and root causes. If need be, the personnel also prepares 8D reports, as seen in Figure 3, which are forwarded directly to the responsible workshops or laboratories via a messaging system for further follow-up.
This makes the operational database an important tool for supporting operations in addition to the automated productivity analysis of individual projects or entire testing facilities. In the testing facility’s organization, this is handled by various equipment managers, each of whom receives reports about error codes within their purview as well as the anomalies, errors, and the root causes contained in the reports. A powerful interface provides them with extensive information, and they can intervene quickly and selectively if a risk is encountered.
Inheriting the test assignment data links together all information from the test steps and operations. All the information can still be traced, and the preparation of component histories, i.e. load spectra, measurements, and anomalies experienced during the test phase, is simplified considerably.
Quality assurance using online plausibility checks
To verify and examine the plausibility of measurement results while testing is being conducted, the interface between the test bench and testing database offers a data transfer tool with enhanced features, as seen in Figure 5. It successively imports raw data into the testing database during the current measurement process, performing automatic analyses as it does. The test bench operator receives continuous information about the test results via the on-screen visualization (Figure 4) and can, if necessary, intervene to make manual corrections, unless they are already made automatically.
Besides confirming adherence to the testing rules, the plausibility checks involve ensuring the measurement results are complete and comparing the measurements to an expected but not yet critical range of values. They enable early detection of changes or malfunctions in the test item or even the testing equipment. Furthermore, the transfer tool can perform a data-driven analysis of gas travel times when measuring emissions and perform a regression analysis in order to promptly calculate and examine the plausibility of specific emission values. The results of the plausibility check are also stored in the testing database.
Online plausibility checks during data import thus contribute significantly to the quality assurance of testing operations.
Post-processing and reporting
Automated reporting is based on machine-readable report definition, plus standardized report templates and naming. A typical quality measure used by testing facilities is regular, at least daily, taking of reference measurements based on characteristic operating points. The status of the data on the test item and the testing conditions are kept constant at all times. This allows changes or shifting measurements over long periods of testing or after modifications or repairs to be detected quickly. The analysis feature built into the data transfer tool calls up the automated generation of a report in the evaluation tool, UNIPLOT™. The feature supplements data currently being measured with reference measurements already stored since the beginning of the test.
In addition to the quality reports, other project-specific testing reports have been defined. They are available shortly following completion of each test thanks to automatic processing of the test results to be presented. Calculations for individual projects are stored in the database as supplemental computing rules, thereby expanding the contents of the automated testing reports.
Global networking of testing facilities
If test runs are organized across locations, for instance, whenever complicated logistics for test items and components are to be avoided, but a different facility possesses the subject matter expertise, it becomes essential to have rapid and secure exchange of information within the worldwide corporate network.
It is not mandatory for the databases to be situated in the same location as the test execution site or the specialist departments. To ensure efficient testing operations while meeting quality standards, a part of the testing results must be available locally after a short time. This is made possible by replicating the data transfer tool at the local facility. The tool then performs the online plausibility checks and prepares the quality reports. At the same time, the local data transfer tool organizes the data transfer to the central database, where it starts additional alculations and preparation of the project reports, as illustrated in Figure 6. The testing facility, therefore, has a comprehensive report on quality assurance and initial analysis available to it in just a few minutes.
The testing assignment database and testing database are accessed directly using a virtual desktop infrastructure. With it, the expert team can specify new testing assignments or individual test steps, which are made available to the test bench operator as orders on the books in the central testing database. To aid communication and global collaboration, FEV also uses virtual control stations. Comparable to the central control room at a testing facility (Figure 4), a virtual control station is also used to transfer information on online plausibility checks and the status of the automation and the application tool.
Test steps can be continuously assigned and complete test results then promptly communicated between an expert team and a remote testing facility via the testing database. In a series of internationally organized projects conducted at FEV, it was shown that the entire set of test results, including all automated calculations and reports for a test step, can be available worldwide in no more than 15 minutes.
FEV’s shared testing database is thus the central platform for the group’s global network of testing activities.
The necessary standardizations and information management tools were developed by FEV and are being continuously perfected. On that basis, our customers have an attractive range of products available to them – from the automation system MORPHEETM through data management in FEVFLEXTM and FLEX Lab™ to the evaluation in UNIPLOT™ for the information management in testing facilities.
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Expertise and Capacity for e-testing projects
Testing Facilities
Testing Facilities
In the coming year, FEV plans to open two new battery test centers – one in Germany and the other one in France. Additionally, new e-motor and e-axle test benches have been integrated into FEV’s test centers and on customer sites. Based upon long-term planning and construction experience with FEV’s own test cells and test centers, as well as in numerous customer projects, FEV provides an effective methodology for specification development, concept layout and planning for e-mobility test benches, test cells and test centers, this methodology covers hardware (test equipment, technical infrastructure, building), software (data management), logistic and operation aspects.
Based upon FEV’s long-term experience, the sustainable success for the construction of new test cells and test centers is highly influenced from quality and completeness of the specification and planning phases. Precise requirement analysis, complete specification development and well-designed concept development are the key factors which deliver the solid foundation for a successful realization of these projects. Due to the extensive experience acquired by FEV, the described project phases can be actively organized and guided in close collaboration with future users/ customers in order to ensure the development of sustainable and cost-effective solutions which cover future requirements to the highest possible degree.
The final goal is to develop a technical solution covering building construction aspects, concepts for the test cells and test benches, laboratories, workshops, the technical infrastructure including supply media and energy supply, furthermore operational and logistical issues. Due to long-term, global experience, FEV’s experts provide the right solutions. They have the in-depth knowledge and experience gained in the construction of their own test centers for the mobility of the future to support customers. They use specific calculation and simulation tools to simulate the different scenarios.
Boosting the test center performance
In state-of-the-art test centers, the visible parts, such as the buildings, the building infrastructure and the test benches can no longer be separated from the invisible parts – the comprehensive information system with a high automation degree.
Let’s evaluate how this information system controls the workflow and use cases in a battery test center. When the battery pack, module or cells and (sub-) components are received, a bar code is created that follows the Unit Under Test (UUT) throughout the entire workflow. The UUT is taken from a safe storage room and subsequently equipped with sensors and measuring devices in a preparation area. The availability and maintenance status of resources (equipment, test benches, employees) is documented in a database, thereby supporting an efficient and effective planning and assignment of UUT and resources. After the installation of the UUT at the test bench, the test programme is executed, followed by the post processing of the measurement data being acquired via the automation system and further measuring devices. The measurement data is checked regarding plausibility and finally documented in standardized test reports. The information system allows data on the UUT, the assigned resources, the test program and test results to be logically linked throughout the workflow. The above information system is based on the FEVFLEX™ software suite.
This modular, layer-based suite features dedicated modules for managing the main workflow of a test center, starting from the test demands up to the final test reports:
- Enterprise functionality at the layer of the overall test center:
FEVFLEX™ facilitates experiments in the field of simulation, benchmarking, and component and system test benches up to vehicle fleet tests, as well as combinations of those. At this layer, work orders are created by combining data from ERP and MES systems (e. g. customer and project data, cost centers) with information on the UUT, the test program and the availability and status of resources (equipment, test benches, employees). Tasks are planned and subsequently assigned to test benches and resources. Moreover, FEVFLEX™ allows the UUT and its (sub-) components to be defined in a Build of Material (BOM) list – well known from benchmarking contexts – thereby supporting UUT life cycle control. In the final stage of the workflow, FEVFLEX™ handles test results from any source (benchmark or simulation data and measurement data obtained from the automation system and measuring devices), which are subsequently time-synchronized and pushed to data evaluation tools.
- Host system functionality as binding factor between test center and test benches:
FLEX Lab™ takes care of the overall data handling and parametrization of MORPHEE® automation systems at component and system test benches. At this layer, the FEVFLEX™ work orders are translated into the preparation of the automation system resulting in a base parametrization (including e.g. a measuring plan, channel limits, log lists, integration of measuring devices, test program).
Furthermore FLEX Lab™ supports the management of MORPHEE® configurations, including back-up and versioning. Launching the execution of test programs at the test bench is secured via communication between the FLEX Lab™ host system and the MORPHEE® automation system. Finally, FLEX Lab™ pushes the measurement data, which was acquired via the automation system to data evaluation tools, such as UniPlot.
As a final conclusion, the workflow in FEVFLEX™ is supported by SCADA remote monitoring and run-time statistics:
- Remote monitoring supports immediate alerts and interventions in case of incidents
- Run-time statistics support facility managers to repair weaknesses in their workflow sustainably
With the help of this comprehensive information system based on the FEVFLEX™, an effective test bench usage of 95 percent was reached in FEV’s battery durability test center.
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Interview
Thomas Körfer about the new 3.0L Duramax Diesel Engine
Thomas Körfer about the new 3.0L Duramax Diesel Engine
Dipl.-Ing. Thomas Körfer, Group Vice President Light-Duty-Diesel, about the development of the new 3.0L Duramax Diesel Engine
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Electric Drive Concept
High Performance Through Innovative Two-Speed Gearbox
High Performance Through Innovative Two-Speed Gearbox
The trend towards battery electric vehicles will continue and likely even accelerate in the future. These vehicles will make a significant contribution to meet future targets for fleet fuel consumption and emissions. To be commercially successful, these new vehicles require modern and intelligent solutions for their powertrain, including battery and drive unit.
The optimal drive unit concept has to be developed based on an evaluation of performance, efficiency, and cost on a system level, including all powertrain components, such as a battery, inverter, electric motor, and transmission. This is what FEV and YASA have done with a high-performance D-class passenger car application in mind. The result is a drive unit concept with exceptional power density and efficiency based on YASA’s unique axial flux motor technology and an innovative 2-speed transmission concept by FEV.
Figure 1 shows an external view of the drive unit and its main specifications. With a peak of power of 300 kW and a weight of less than 85 kg, it provides an outstanding power density of 3.5 kW/kg on system level. The maximum axle torque of 6.00 Nm even exceeds typical wheel slip limits for both front and rear-wheel drive applications and ensures superior acceleration performance on a vehicle level.
Electric motor and inverter
The YASA motor is an axial-flux permanent magnet machine and was chosen because of its high power density (up to 15 kW/kg for custom motor designs), high efficiency (especially at part loading) and low-cost manufacturing. In the YASA motor, the oil coolant is in direct contact with the copper windings, providing very efficient and even cooling over each winding.
YASA controllers feature similarly differentiated high-density performance. This is achieved by the use of some of the YASA motor’s proprietary direct oil cooling technologies that provide for very efficient cooling, and substantially reduce the need for heavy and costly heatsinks and power semiconductor packaging. When integrated with a YASA motor, the motor and controller share the same oil cooling circuit, further improving the standard integration benefits of reduced volume, mass and interconnection complexity.
Gearset concept
Based on the above-mentioned findings, a powershift capable 2-speed concept was developed. Figure 3 shows different views of the drive unit.
The 2-speed functionality is realized based on a Ravigneaux planetary gearset. Figure 4 explains the topology of the transmission. The planetary gearset is arranged coaxially to the electric motor. The small sun (SS) does serve as the input, and the ring (R) serves as the output to the intermediate shaft and differential. Two brakes B1 and B2 are used to realize two speeds. Brake B1 is connected to the carrier and paired with a one-way clutch (OWC), B2 is connected to the large sun gear (SL). Despite being mechanically more complex than architectures in a simple planetary gearset, this architecture has a number of technical benefits. As shown in the table “Clutch relative speed matrix”, the delta speed at open brakes is always below the input speed at the small sun, an important quality for minimum drag losses. At the same time, the torque reaction at the brakes is favorable as shown in the table “Clutch torque matrix”. Brake B2 only has to react less than half of the input torque. Brake B1 has to react 1.5 times the input torque but is supported by the one-way-clutch. This allows to size the brake itself smaller, further reducing drag losses. As opposed to clutches, brakes avoid the use of rotary joints or engagement bearings to actuate the gearshift. In addition, the thermal capacity of brakes can be scaled via the thickness of their (stationary) steel lamellae without negatively affecting rotary mass moments of inertia. The exclusive use of brakes was, therefore, an important criterion in the selection of the concept. Both brakes are actuated via an existing series-production, on-
demand actuator from LuK. The unit, also known as HCA (hydrostatic clutch actuator), operates with a brushless electric motor for each gearshift element, which actuates a hydraulic master piston via a spindle. Because of the leakage-free seals, this system is very efficient. Alternatively, electromechanical actuation concepts could be used thanks to the good axial accessibility of the brakes.
Figure 5 summarizes the functions of both the brakes and the one-way clutch. It also mentions an additional advantage of the arrangement, including the one-way clutch: In 1st speed during drive (power-on) condition, B1 can be opened and the reaction torque at the carrier will only be provided by the one-way clutch. Then, the power-on upshift, which is most critical in terms of shift comfort, can be performed by only closing brake B2. This type of shift is easier and more robust than any conventional power shift which typically includes the simultaneous control of two shift elements. The same advantage applies to a power-on downshift when only B2 has to be opened. At zero rpm of the carrier, the one-way clutch will automatically lock-in and engage 1st speed.
Cooling and lubrication concept
As mentioned previously, the electric motor and inverter do share one common oil cooling circuit. Using a dedicated EDU oil which fulfills the requirements of both the electrical and mechanical components, also allows for the transmission to be integrated into that cooling circuit. As of today, such a fluid is not yet readily available, however, several oil suppliers have confirmed that it can be successfully developed within a standard series development of 3 years duration. The obvious advantage of such a highly integrated cooling and lubrication circuit is less complex and more cost-effective, as only one pump, one cooler, and almost no external hosing would be required. In addition, the interfaces to the vehicle would be simplified considerably. Alternatively, separate oil circuits can be used for the electric motor/inverter and transmission. In this case, oils are readily available and can be tailored even better for the requirements of each circuit. The development risk will be reduced, but the complexity and cost of the overall system will be increased.
Figure 6 explains the variant with one common cooling and lubrication circuit. An electric oil pump draws oil out of the transmission sump and feeds it via an oil/water heat exchanger to the inverter. From there, the oil flows through the electric motor and subsequently back into the transmission, where the volumetric flow is divided. One part is fed into the main shaft of the planetary gear set, from where it not only lubricates the gears and bearings but also cools the brakes as required. The remainder is not drained into the sump but buffered in a storage tank inside the transmission. From here, further components are lubricated via various channels, including the gear meshes and the bearings of the intermediate shaft.
An intelligent oil pump control strategy allows to vary the level of the storage tank and thus the oil level in the transmission, which makes a large contribution to a reduction in churning losses and thus an increasing inefficiency. Figure 7 shows two internal views of the transmission including the integrated oil reservoir. A park lock system is arranged on the intermediate shaft and can be actuated by a stand-alone, electro-mechanical park-by-wire actuator.
Summary
The presented 2-speed drive unit does use a high powered, dense yet modular combination of an axial flux electric motor and a coaxially arranged inverter. The transmission is based on a Ravigneaux planetary gearset with two brakes as the shift elements. Together, with a one-way clutch, this arrangement is both favorable in terms of drag losses, as well as controllability and shift comfort. The brakes are actuated on-demand for minimum energy consumption. The electric motor, inverter, and transmission do optionally share a single, common cooling and lubrication circuit which reduces complexity and simplifies the interfaces of the drive unit to the vehicle. With a peak power of 300 kW and a weight of less than 85 kg, the drive unit provides an outstanding power density of 3.5 kW/kg on system level. The maximum axle torque of 6,000 Nm even exceeds typical wheel slip limits for both front- and rear-wheel drive applications and ensures superior acceleration performance on vehicle level.
Final remark
The drive unit concept presented in this article has been jointly developed by YASA and FEV. The motor and inverter technology described in this paper is owned by YASA Limited, a UK-based developer and manufacturer of electric motors and inverters. The 2-speed transmission concept described in this paper is owned by FEV, an independent provider of powertrain and vehicle engineering services.
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Optimized Energy Management for 48V Mild Hybrid Drives
48 Volt
48 Volt
When looking at the current drive developments and market forecasts, 48V technology is gaining considerable significance in the automotive industry. This technology is an important part of many automotive manufacturer’s electrification strategies. With moderate technical effort, vehicle fleet CO2 reductions can be achieved in the short term. At the same time, 48V electrification offers significant potential for the reduction of emissions in real operation (real driving emissions – RDE). Given the many functions, such as brake energy regeneration, load point optimization, engine stop sailing, as well as electrification options for charging, driving dynamics, air conditioning, and exhaust systems, it is already foreseeable that the performance and energy reserves of competitive 48V systems will be limited.
The comparison with high-voltage hybrid systems in Figure 1 demonstrates that the operating range of 48V mild hybrid systems is clearly moving toward the system limits. The growing number of 48V components additionally increases the dynamics of torque requirements and the variances in terms of operating strategy. This comes with interactions, dynamic framework conditions, and a high system complexity that stretch rule-based operating strategies to their limits. The use of predictive energy management is very promising, since the available electrical energy and power is ideally distributed within the 48V on-board circuit, allowing for ideal operation of 48V systems designed to save costs and resources.
Concept vehicle
In cooperation with RWTH Aachen University, FEV has developed a 48V mild hybrid concept vehicle. The vehicle is based on a Mercedes-Benz AMG A45 equipped with all-wheel drive and a seven-speed dual clutch transmission. The series vehicle is equipped with a turbocharged 2.0 l gasoline engine that has a specific output of 133 kW/l. This impressive output is achieved through the use of a large exhaust turbocharger (ETC) that, despite twin-scroll technology, significantly limits the maximum torque in the lower engine speed range and results in a noticeably delayed response. In this context, electrified charging and/or electric torque support can significantly improve elasticity, especially in the economical, lower speed range. The 48V mild hybrid powertrain is schematically represented in Figure 2. The central element is the belt starter generator (BSG) in the belt drive of the combustion engine (CE). The P0 topology enables a variety of hybrid functions such as regeneration, load point shifting, and electric torque support. Since the maximum power that can be transmitted with the belt is limited and there is a permanent connection to the combustion engine, the system is not intended solely for electric driving.
There is also an electric compressor (EC) positioned in the charge air path, upstream of the intercooler. The EC reaches a maximum pressure ratio of 1.45 and can significantly increase the charge pressure, and thus the response behavior, in operating ranges with low exhaust enthalpy, regardless of the operating condition of the BSG. The concept vehicle is operated using a rapid control prototyping (RCP) development control device.
Rule-based operating strategy
A driving performance-oriented, rule-based operating strategy with priority-based power distribution controls the electric charging, as well as the electric torque support of the BSG (Figure 3). The operating strategy is made up of the torque-supporting functions in drive management and the overarching power distribution in electric power management. The electric charging is controlled through the pressure ratio between the desired and the current charge pressure in the intake manifold. As long as the waste gate (WG)-regulated ETC does not provide the desired charge pressure, the pressure is additionally increased in the air path through the EC. The required rotational speed is calculated using the compressor diagram of the EC and then limited in accordance with the available electric power.
In contrast to electric charging, during which the drive power results from the additional air and fuel mass, the BSG directly converts electric energy into mechanical drive power that supports the combustion engine (Figure 2). The torque required by the BSG results from the difference between the current torque of the combustion engine and the driver’s needs. When the accelerator pedal is pushed, this difference is positive, so that the BSG temporarily replenishes the torque deficit. The BSG torque is then limited in accordance with the available electric power.
The electric power limits of the various individual 48V components are prescribed by the electric energy management. During an acceleration, the 48V battery must also power the cooling agent pump and the 12V system via the DC/DC converter, in addition to the EC and the BSG. It is therefore necessary to carry out a situation-based prioritization of the 48V components. The available battery discharge capacity is, in this context, prescribed by the battery management system (BMS). The available electric discharge capacity for the respective 48V components is then calculated depending on their priority and the actual power consumption of elements with a higher priority. In order to ensure reliable driving operation, the engine cooling and the 12V system have a high priority in this context. The remaining power is made available for the EC and the BSG in consideration of a calibratable power ratio.
Even though such rule-based approaches can be improved through further dependencies, there are principle-based disadvantages. For instance, the operating strategy merely reacts to the current system status and adjusts the parameters regardless of the expected load status. Since, however, the temporal behavior of torque build-up and the efficiency heavily depend on the load status, the selected operating strategy of the electrified drive (CE with ETC, EC, and BSG), and the electric system limits, this control is usually suboptimal.
Optimized Energy Management
Predictive optimization-based energy management strategies use dynamic route information from the electronic horizon for the long-term optimization of route guidance and the speed trajectory. Based on this information and adequate vehicle sensor systems for surroundings detection, hybrid management considers the electric power limits and load prediction to determine ideal trajectories for gear selection, drive torque, and charge strategies for a medium-term horizon. The predicted system values also enable the derivation of an expectable charge condition evolution of the electric energy accumulator, which adapts an energy weighting factor. This factor represents the importance of electric energy in the energy balance sheet and directly influences energy optimization in drive management (Equation 1).
Equation 1
ETot = ∑N k=0E Chem(kT) + ξE El(kT)
At the same time, the response behavior through the regulation of the drive torque, which is made up from the combustion engine torque and the electric torque (Equation 2), is optimized while complying
with the dynamic system limits of the 48V system.
Equation 2
ΔMAntrieb = ∑N k=0M Antrieb, Soll (kT) − MVM(kT) − iRiemenMRSG(kT)
Nonlinear model predictive control (NMPC) relies on a real time-capable, simplified process model of the 48V mild hybrid powertrain. It works with a time horizon of a few seconds and includes time increments of hundredths or tenths of a second for the representation of the nonlinear system dynamics.
The NMPC will calculate the ideal parameter evolution for the WG and the EC, which influence the combustion engine torque through the air path, as well as the torque of the BSG, which can obtained through the addition of the belt drive. This way, both the differences in the temporal behavior of the charge air path and of the BSG torque and their impact on the overall efficiency of the electrified powertrain are taken into account in the optimization.
Results
The NMPC was more closely examined during a validated co-simulation of a B-segment 48V mild hybrid with turbocharged gasoline, electric compression, and P0 BSG. Figure 4 shows a comparison of the NMPC and the rule-based approach for a full-load run-up for various energy weighting factors ξ. An energy weighting factor of four is equivalent to an overall charging efficiency factor of 25 percent, while the electric energy in the limit case of zero, e.g. due to a high battery state of charge and an upcoming downhill drive, is free of charge. Due to the lack of forecasting, the rule-based operating strategy reacts identically in both cases, while the NMPC adjusts the parameters for the WG, the EC, and the BSG based on the situation in order to achieve a desired drive torque. Beyond that, the variation of the optimization parameters shows that the NMPC reduces the drive torque with increasing weighting of energy (h˜NMPR ↑), in order to reduce energy consumption. If the electric energy is free of charge (ξ=0), the drive torque is shifted to the BSG, while the EC builds up charge pressure with the WG open, in order to reduce charge change losses. In contrast to this, at ξ = 4, the NMPC only briefly provides support through the BSG in order to utilize the rapid dynamics of the electric machine and subsequently save electric energy.
The operating strategy, in such an acceleration scenario, is always a compromise between response behavior and energy efficiency. The response behavior is described through the acceleration time and the energy savings through the inverse of the effective drive efficiency. With a variation of the electric power limitation, the framework conditions are changed.
Additionally, for each of these power trajectories, the prioritization of the rule-based strategy and the weighting ratio of the NMPC optimization were varied. It becomes clear that increasing energy savings are at the expense of the response behavior. However, the NMPC resolves the conflict of objectives significantly better and can describe both the energy consumption and the energy savings through the inverse of the effective drive efficiency. With a variation of the electric power limitation, the framework conditions are changed. The stronger the electric power limitation and the smaller the focus on the response behavior, the more the potential of the NMPC develops.
For more information about 48V mild hybrid drives visit 48v.fev.comAutoren:
Philip Griefnow, RWTH Aachen University
Prof. Jakob Andert, RWTH Aachen University
Dr. Georg Birmes, FEV Europe GmbH
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FEV India
10 Years of Top-Level Engineering Services
10 Years of Top-Level Engineering Services
FEV India was founded in 2006 in Delhi. In 2009, the company opened its technical center in Pune, which is located in the Talegaon region and assumes two hectares of space. Starting with two test benches, one equipped with a direct current load unit for performance and emissions testing and another equipped with an eddy current load unit for endurance testing, the available resources have been continuously increased since then.
Since 2013, FEV India also operates a software center in Chennai that meets the needs of Indian OEMs regarding hybrid and electric drive technology.
In 2016, the upgrade included an additional seven state-of-the-art test benches and since then, a wide variety of services are offered regarding vehicle and engine development, mechanical development and testing, prototype testing, creation, and assessment, as well as engine performance and emissions. In addition to this, there are services in the fields of transmission and OBD calibration.
FEV’s new Vehicle Development Center in Pune opened the following year. The facility has a 250 kW 4×2 chassis dynamometer with three exhaust gas measuring lines (one diluted, two raw exhaust gas measuring lines) that can be upgraded to a 4×4 drive. The facility also enables the execution of measurements in accordance with Indian and European emission regulations including future regulations, such as WLTP (Worldwide Harmonized Light-Duty Test Procedure) and RDE (Real Driving Emissions).
Additionally, through another expansion of company capacities in 2018, stricter requirements due to new emission regulations and electrification were met. To this end, the new facility includes a total of eight test benches meeting the newest requirements, including a dynamic chassis dynamometer with two raw exhaust gas measuring lines and the option of height simulation, and the measurement of Particulate Matter, a PN Counter and soot emissions with a Portable Emissions Measuring System. Furthermore, an advanced powertrain NVH development center for vibration measurement and transmission applications is being implemented.
In May 2019, FEV India expanded its location and inaugurated a new mobility center. The new mobility center, which is located close to the Mumbai metropolitan region, will pave the way for advanced technologies in the Indian market. In addition to state-of-the-art BS6 powertrain test benches and the virtual calibration platform “VCAP”, the center also has a new NVH test bench. The already existing facilities, such as powertrain, vehicle roller with PEMS, HiL and friction test benches are thus ideally complemented. FEV now has a total of 20 test benches at its Pune location.
Additional battery and EDU test benches are planned in a second expansion step until 2021.
Emission Reduction
Cylinder deactivation strategies for diesel engines
Cylinder deactivation strategies for diesel engines
The cylinder deactivation on a diesel engine has showed potentials on the one hand side to further reduced pollutant emissions, while on the other hand to gain some fuel economy in parallel. This has been demonstrated by several investigations in the past. Nevertheless, a static deactivation of half of the cylinders is limited by their operation range. An additional dynamic deactivation of several cylinders delivers further degrees of freedom that could provide an extension of the cylinder deactivation operation range.
The authors have used different simulation tools such as 1D steady-state engine process model and transient mean value model to represent the possibilities of a dynamic cylinder deactivation on diesel engine applications.
A state-of-the-art diesel engine for passenger cars (PC) and medium duty (MD) truck applications have been used for the investigation program.
For the PC applications a 2.0 l 4-cylinder diesel engine with a single stage boosting system and a compression ratio (CR) of 15.5 has been considered. Further engine applications have been an advanced exhaust gas recirculation (EGR) system (uncooled high and cooled low pressure EGR path) and a 2000 bar fuel injection system (FIS). It has been decided to investigate two different vehicles, a C segment vehicle, as well as a compact SUV. Those have been equipped with a 7- and 8-speed dual clutch transmission (DCT). The exhaust aftertreatment system has installed a closed-coupled DOC, SDPF as well as a passive underfloor SCR. All EATS components have been used as aged system. The cycle investigations have considered the standard WLTC and a RDE operation.
The MD truck has been powered by a 7.7 l 6-cylinder diesel engine. The air path has a standard wastegate turbine (WG) boosting system together with a cooled HP-EGR system installed. The combustion system has considered a 2,400 bar FIS and a CR of 17.7. A state-of-the-art EATS based on closed-coupled DOC, DPF and SCR has been installed. For the MD truck application, the WHTC has been considered.
1D engine process simulation model
The commercial 1D engine process simulation software GT-SUITE has been used to investigate the thermodynamic reactions of the different exhaust gas heating strategies. The 1D engine model has considered the entire engine configuration, such as the boosting system, the air and exhaust path, the EGR path (high pressure and low pressure) and combustion chambers. The burn rate of fuel combustion has been implemented through profile arrays from several engine operation points of the entire engine operation range. Those have been generated by a standard 0D approach of cylinder pressure analysis of steady-state experimental engine measurements. The entire EGR control of the model has been modified from a mass flow control to an oxygen concentration control. The fuel injection pattern and rail pressure as well as boost pressure set points have been kept constant.
This 1D model can operate in the entire map range, and allows simulation throughout the entire engine operation range. Standard PID-controllers have been used to control components like EGR valves or turbocharges in order to regulate EGR rates or boost pressure under steadystate investigations. Finally, a sub-model for engine-out emission predictions had been added to the engine model. This uses the physical correlation approach of in-cylinder O2-concentration to predict engine-out NOx and soot emissions. Thus, transient effects on emission production have been considered, which usually occur at dynamic engine operation. In addition, HC and CO emissions have been implemented by steady-state maps which dependent on engine speed and load. The approach describes the standard at FEV and has been used in the past. To obtain an accurate result, the 1D model has been validated to surrogate data. The accuracy of boost pressure showed a deviation of maximum 1 percent. The calibration level of the emission models were more challenging and provided a maximum deviation of 5 percent.
Map calibration for considered heating strategies
To investigate the exhaust heating potentials of the different exhaust heating strategies within the mean value powertrain model (MVPM), the baseline engine-out maps have to be adjusted, based on the results of the 1D model simulations. For this purpose, differential and factorized maps have been generated and added incorporated into the base engine maps. Together with the differential and factorized maps, a new engine calibration with a specified exhaust heating strategy has been considered.
Mean value powertrain model
The FEV Complete Powertrain Simulation Platform, a precursor of FEV’s advanced VCAP calibration platform was utilized in this study. The powertrain model has integrated five main sub-models for boundary/ambient conditions, vehicle settings, transmission, engine and the aftertreatment system. The boundary/ambient condition sub-model described the different road conditions, emission test cycles and different driver behaviors. Inside the vehicle model the rolling resistance as well as road influence, aerodynamics and gravity were considered to model vehicle longitudinal dynamics. The main transmission and driveline components were modelled with ideal torsional systems, subjected to a distinct efficiency at different oil temperatures. Based on those sub-models, the main objective was to calculate the required inputs for the engine, mainly actual engine speed and load request. The engine model provided than on the specific operation point the corresponding engine out conditions, which were described by calibration maps at different coolant temperature.
Selective cylinder deactivation by Dynamic Skip Firing
Dynamic Skip Fire (DSF) is an advanced cylinder deactivation technology. A DSF-equipped engine has the ability to selectively deactivate cylinders on a cylinder event-by-event basis in order to match the torque demand at optimum fuel efficiency while maintaining acceptable noise, vibration and harshness (NVH). To illustrate this concept, Figure 1 shows an example of DSF operation in a four cylinder engine. A varying torque request is shown in green, which results in cylinders being fired (red) or skipped (grey). The combined firing pulse train for all four cylinders is in blue. As torque demand increases, the density of firing cylinders also increases. When torque demand is zero or negative, no cylinders fire. This is termed DCCO, or deceleration cylinder cutoff.
Evaluation of simulation results
The evaluation process has been substituted into two tasks. The first task has dealt with the steady state simulation investigations of the different heating strategies by means of 1D engine process models. Whereas the second task has focused on transient cycle investigation.
Analysis of steady state 1D engine process simulation results
The 1D steady-state investigation have been obtained for partly loaded operation. Those investigations have been done underfour different fire density (FD) levels, where 1 indicates full cylinder operation. A FD of 0.25 is equal to a single cylinder operation out of this 4-cylinder engine. The steps in between are defined as 0.75 and 0.5.
The engine operation at a FD below 1 has led to an anomalous turbocharger operation due to the changed exhaust gas dynamics. Therefore, reduced boost pressure levels have been achieved and resulted in a limitation of the maximum engine load operation. Figure 2 shows a schematic of maximum engine operation loads that can be achieved at different FD levels.
Since the deactivation of one or more cylinders, the load at the remaining fired cylinders have been increased to hold a constant engine power output. The increased inner load has provided a higher exhaust temperature at a higher engine efficiency. Figure 3 summarizes the relative simulation results at a FD = 0.5 of engine efficiency improvement by BSFC and absolute exhaust temperature increase in the lower part load area. It can be seen, that FD of 0.5 has provided a fuel consumption benefit of 15 percent in average in the shown operation area. At the same time an exhaust temperature increase of almost 130 K at 3 bar of BMEP has been achieved in comparison to a 4-cylinder operation.
Additionally to the mentioned advantages other effects have occurred by a steady-state cylinder deactivation. On the one hand a reduction of the exhaust mass flow rate has obtained by deactivating cylinders. Hence, also a lower emission engine out mass flow rate has been achieved. While this has delivered, on the other some degrees of freedom to lower the steady-state EGR calibration to keep the same NOx engine-out mass flow rate compared to a 4-cylinder operation.
Evaluation and assessment of transient MVPM simulation results
To determine the impact of DSF on relevant cycles, the WLTC and RDE were simulated for the PC application, and the WHTC was simulated for the MD application. Figure 4 shows transient results of C segment and compact SUV application over WLTC. It depicts the fire density, exhaust temperature upstream SDPF as well as the cumulated tail-pipe (TP) NOx emission.
The WLTC begins at an ambient temperature of 23 °C. A minimum coolant temperature limit of 60 °C is imposed to represent hardware constraints, and effectively eliminates DSF operation until 140 seconds. The exhaust temperature traces upstream SDPF have showed only slightly increase after cold start and warm-up phase, due to the thermal mass of the DOC. Afterwards, an exhaust temperature increase by around 20 K has been achieved under DSF operation at segment C vehicle. That increased exhaust temperature has improved the NOx conversion of SDPF and dropped the TP NOx emission down to 43 mg/km. It represents a reduction by
4.4 percent compared to the 4-cylinder operation of segment C. Additionally, these improved results have been achieved with a benefit in CO2 emission by 1.5 percent.
The results of compact SUV have showed a lower NOx reduction potential by DSF operation. This heavier vehicle application has led to a higher engine operation with an increase exhaust temperature level. Furthermore, the DSF operation has been reduced based on the higher load request. Thus, only a slightly exhaust temperature increase has entered the SDPF. Nevertheless, an improvement in CO2 emission by around 1 percent has been obtained.
Figure 5 summarizes the simulation results of WLTC and RDE. The results under RDE have provided than additional improvements at the trade off between NOx and CO2 emissions.
Figure 6 shows the simulation results of the MD truck application under cold stared WHTC. It can be seen, that the activation of DSF has increased the exhaust temperature upstream SCR by 10?–?30 K in a wide range of the cycle. Thus, an improved NOx
conversion has occurred and provided a tailpipe reduction by 15 percent compared to base configuration. Also fuel consumption benefit has achieved of around 1.6 percent due to the dynamic cylinder deactivation.
Fig. 6: Simulation results showing firing density, SCR inlet temperature and cumulated TP NOx emissions over cold stared WHTC for MD truck
Figure 7 shows the summary results of MD truck in weighted WHTC. The weighting factors consider a distribution of 14percent cold started WHTC and 86 percent hot started WHTC.
Fig. 7: Summary results of MD truck application benefits of DSF in weighted WHTC (cold and warm started)
The investigations have shown a tailpipe BSNOx improvement of around 30 percent in parallel to BSFC benefit of 1.6 percent.
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Gasoline Engines
200 kW/L at Lambda = 1
200 kW/L at Lambda = 1
The increasing tightening of global emission legislations promotes the further development of gasoline engines with the aim of clean engine operation under all real driving conditions. At the same time, performance requirements are growing. Gasoline engines compete increasingly with electrical components for package volume, and the displacement of high performance engines is reduced to lower the CO2 emissions. This article covers the trade-off between increasing specific power and switching to Lambda = 1 throughout the engine map.
Why Lambda = 1 throughout the engine map?
Components in the exhaust gas flow of gasoline engines are currently protected from excessive thermal stress at high performance by mixture enrichment (Lambda < 1). At the same time, such an operating strategy is linked to the cross-influences:
- The fuel consumption at high engine output is disproportionately high.
- The CO engine-out emissions are increased considerably by the mixture enrichment, and outside of the operating window with Lambda = 1, the three-way catalyst only provides very low conversion rates.
- CO emissions under RDE conditions are not limited by the Euro 6d legislation, but they are measured and recorded (“monitoring”).
- Apart from the monitoring of CO in the homologation process, non-government organisations also record CO emissions under RDE conditions.
- Since the introduction of RDE Package 4, so-called AES (Auxiliary Emission Strategies which influence emissions as e.g. mixture enrichment) can only receive a time-limited approval.
The switch to Lambda = 1 leads to a loss of performance and reduces the specific power of current representative technology packages of gasoline engines to ~ 65 kW/L. It results in the increasing introduction of technological measures which improve the specific power at Lambda = 1. These include:
- Integrated exhaust manifold (iEM)
- High temperature-resistant turbocharger turbines
- Miller cycle combined with corresponding boosting procedure as variable turbine geometry (VTG) or electrical turbocharger (eTC)
- Cooled exhaust gas recirculation (cEGR)
- Variable compression ratio (VCR)
For volume segments from 85 to 100+ kW/L can well be achieved. The development of drive systems for high performance vehicles allows more freedom with regards to cost and applicable technology. FEV has investigated the following question: “Are 200 kW/L at Lambda = 1 possible?”
Combustion process for 200 kW/L at Lambda = 1
The realization of the specific power of 200 kW/L at Lambda = 1 requires a break-up of the conflict of interests between supercharging and knock tendency. Water injection in the intake port represents the key technology. The reduction of the mixture temperature associated with the high evaporation enthalpy of water at the end of compression allows for a significant increase of the efficiency of the high-pressure cycle. Figure 3 shows a variation of the water-fuel ratio (WFR) at a speed of 7800 min-1 and stoichiometric engine operation. With the selected compression ratio of 9.3:1 the brake mean effective pressure (BMEP) can be increased with the growing water share at only a slight delay of the center of combustion to 30.8 bar, so that the value of 200 kW/L is achieved at a WFR of 55 percent. An absolute boost pressure of approx. 3.3 bar is required, which can be supplied with a single-stage compressor.
The position of the water injector in the intake port has been optimized with the help of 3D CFD simulations. For the distance that is furthest away from the valve, the wall film share is too high, because the water can wet the largest area. For water injection closer to the valve, the share decreases significantly, whereby the improvements for a distance of less than 60 mm are minor.
An analysis of the temperature distribution in the combustion chamber shows that the 60 mm position is preferable to the
30 mm position despite the same mean temperature.
With respect to the high mass flow rate and boost pressure demand, the requirement of a low throttle effect of the intake valves is in contrast to the objective of a high charge motion.
Figure 5 shows how 3D machined valve seat rings are used to achieve a high charge motion with simultaneously increased flow coefficient.
Design for high mechanical and thermal stress
An engine design for a specific power of 200 kW/L must withstand high thermal stress and high mechanical load. The turbine wheel is manufactured from MAR 246 and withstands a maximum temperature of 1,050 °C. In addition to the exhaust gas turbocharger turbine, the exhaust valves are exposed to particularly high thermomechanical stress. Therefore, sodium-cooled exhaust valves are used. An optimized solution is used which directs the sodium into the valve disc and at the same time largely maintains its structure.
The aluminium cylinder block is a rigid closed-deck design with a bed-plate and cast iron cylinder liners. An aluminium spray coating guarantees a good connection between cylinder and crankcase. The high thermomechanical stress with the corresponding pronounced cylinder deformation is addressed with free form honing.
High performance boosting and periphery
The system is equipped with an exhaust gas turbocharger on each cylinder bank. The turbine is equipped with a variable turbine geometry without wastegate. The use of the entire exhaust gas mass flow for the generation of the compressor drive power lowers the turbine pressure ratio and therefore also the pressure upstream of the turbine. This means that lower gas exchange losses and exhaust gas temperatures can be reached at rated power.
Secondly, the added hot wastegate mass flow downstream of the turbine with the associated inhomogeneous thermal stress on the catalyst due to insufficient mixing is eliminated. The compressor is equipped with a variable trim, the turbocharger with an electric motor on the shaft to improve the transient behaviour.
Powertrain architecture and electrification
The high performance engine is embedded in the drive system. It consists of:
- Internal combustion engine 600 kW
- Electric motor EM1 30 kW (peak 90 kW) in P1 hybrid architecture
- 7-speed double-clutch gearbox
- Electric motor EM2 55 kW (peak 160 kW) as electric drive unit (EDU)
- High voltage battery 120 kW and 4.0 kWh
The combustion engine and the electric motor EM1 power the rear axle. The electric motor EM2 is configured as an electric drive unit. For reasons of weight reduction, the high voltage lithium-ion battery is designed as a small unit with a capacity of 4.0 kWh. At the same time, it delivers an output of 120 kW at a high C-rate of 30. The torque characteristics of all three engines are shown in Figure 10.
In high-speed range, the combustion engine is the dominant drive source. It delivers more than 85 percent of the total system power of 710 kW. The maximum speed is reached in the sixth gear and is limited to 350 km/h. Acceleration from 0 to 100 km/h is achieved without gear change in less than three seconds and is traction limited by the high torque at the rear axle. The operating strategy of the hybrid powertrain is illustrated using the example of the Nuerburgring race track (Figure 12). During braking and before a curve, the energy is recuperated. The acceleration out of a curve is supported by boosting with the EDU (EM2) at the front axle. All engines drive the vehicle on straight sections at full power demand.
Thermal management
The cooling concept used here in the overall vehicle and the breakdown of the heat fluxes for a system power of 710 kW. The high temperature circuit (HT) of the engine cooling system needs to dissipate 232 kW. For this purpose, it uses two radiators integrated in the side pods. The transmission oil cooler transfers an additional 18 kW to the environment. The cooler for the low temperature circuit of the electric motor EM1 is located in the left rear wheel housing. The heat of the battery is transferred to a cooling circuit via an intermediate water circuit. The cooling circuit transfers the heat (6 kW) to the environment. A second condenser provides for the cooling need of the passenger cabin cooling. The heat of the cooling water of the air-water charge air cooler is transferred to the environment (in total 80 kW) through two low temperature coolers.
Emission control concept for Euro 7
The tightening of global emission legislations promotes the aim of low emissions operation under all driving conditions:
1 The restriction of the permissible particle number emission to 6 x 1011 PN/km x CF under RDE conditions which was introduced with Euro 6d-TEMP.
2 The auxiliary emission strategies which receive less and less acceptance, and the discussion about the introduction of conformity for the pollutant CO under RDE conditions.
3 The significant reduction of the emission limits for gaseous pollutant to ~ 50 percent of the currently applicable Euro 6d-TEMP limits with the simultaneous restriction of CF = 1 expected with Euro 7, and the stricter focus on shorter driving distances after a cold start (< 10 km).
Figure 14 shows the exhaust gas aftertreatment system. The illustrated system is designed for one bank, and is mirrored for the second bank. The exhaust gas aftertreatment is equipped with one adsorber catalyst with a volume of 1.5 L per bank. Its ceramic substrate has a high heat capacity and stores HC emissions after a cold start until the light-off of the main catalyst has been reached. For the main catalyst, a metallic support material with low heat capacity and high heat conductivity has been chosen to reduce the light-off time. The volume of the main catalyst is 3.5 L per bank without adsorber catalyst and without particulate filter. Two electrically heated discs per bank have been integrated into the main catalyst. A coated particulate filter (4WC) with a volume of 4.0 L follows downstream of the catalyst.
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Reliable Partner for Turnkey Vehicle Development
From a Single Source – Part III
From a Single Source – Part III
Part three of the series “Turnkey Vehicle Development From a Single Source”.
You find the first part of the series here.And the second part of the series here.
Within the last decade, FEV has become an engineering service provider capable of covering the entire service spectrum of vehicle development. Three articles take a closer look at vehicle modules, body shell, interior/exterior, light and sight and chassis modules. Vehicle properties, such as NVH, driving dynamics, passive and active safety, and fatigue strength are considered. Virtual and real-life testing are the development tools here. The activities are accompanied by various control tasks such as benchmarking with subsequent target setting, test and prototype planning, weight management and homologation.
FEV assumes responsibility for the complete scope of turnkey vehicle development, as well as for the development of individual modules and for the selective design and calculation scope of individual components. The fact that the development competence for powertrain, transmission and vehicle comes from a single source makes FEV an ideal development partner – also for electrified vehicles. FEV offers particular expertise in the conversion of conventionally powered vehicles into electric vehicles. The ideal results here can be achieved only through the closely integrated and parallel development of powertrain and vehicle. Some turnkey vehicle development tasks will be introduced in the following:
Chassis and driving dynamics
For vehicles of all types, the chassis establishes the connection to the road, making it the assembly that transfers the force and torque which affect the vehicle. The chassis’ key task is therefore to always guarantee this contact, as otherwise the transfer of force is not possible. The fact that the road is never smooth and straight, as well as still having various friction coefficients, makes this task so demanding. Overall, the chassis is responsible for driving safety, driving comfort, and dynamic vehicle behavior, which can be broadly divided into longitudinal dynamics (brakes), lateral dynamics (steering) and vertical dynamics (suspension/absorption). There are conflicts of objectives, particularly in the conflict area between driving comfort and driving safety, which have to be resolved in the field of chassis design.
FEV also covers the complete development process in chassis and driving dynamics development. FEV is able to integrate its experience and skills into projects – from the development of new concepts and target values to the construction of parts and modules, right through to the testing and final approval of prototypes. A team of trained drivers is on hand for the tuning of dynamic driving properties to assess and optimize the vehicle subjectively and objectively with the aid of corresponding measurement technology. The close proximity of FEV to the ATC Testing Center in Aldenhoven (Germany) represents a major advantage here. An increasing number of electronic systems are also finding their way into vehicles. In addition to the ABS and ESP systems legally in force today, many advanced driver assistance systems affect the road holding and stability of the vehicle via the chassis. This again underlines the importance of the chassis for modern vehicles, as well as provides an explanation for FEV’s active role in the development of these new systems.
Alternative drive concepts with one or more electric engines offer a means of developing new chassis concepts that were previously impossible due to the installation space in conventional combustion engines.
Passive safety development
For years, there has been particular focus on passive vehicle safety in terms of development and is also in the special interest of buyers, as life and health depend on it in the event of an accident. In addition to legal provisions that have to be met for the registration and maintenance of a car (homologation), there are consumer protection organizations, such as EuroNCAP (European New Car Assessment Programme), which go beyond the minimum legal requirement – for instance, to assess the passive vehicle safety of cars.
In the past, the Consumer Protection Rating became increasingly important, causing the requirements for achieving a high rating (five stars) to increase steadily. The speed at which new test methods, test equipment, and crash dummies are introduced presents huge challenges for vehicle manufacturers every year. Globally active vehicle manufacturers not only have to meet different legal requirements worldwide, they also have to achieve a top rating in the different regional consumer protection ratings – for example J NCAP in Japan, C NCAP in China, US NCAP in the US and Bharat NCAP in India.
The introduction of the pedestrian protection leg impactor (aPLI) is a representative example of the rate of change of EuroNCAP for the implementation of new test specimens. The decision in favor of this new impactor was made in February 2019, resulting in the development strategy for projects already started with SOP 2022 having to be changed. However, the leg impactor currently exists only in the form of a physical impactor, with a virtual development model for the simulation expected to become available for the first time in the second half of 2019.
Thanks to the knowledge and the network of experts at FEV, customers can make the right adjustments to their projects at an early stage in order to implement farreaching development strategies in their development projects as soon as possible. FEV also provides the functional design during development in the field of passive vehicle safety. In addition to virtual crash simulations, part, component, and overall vehicle tests are organized, performed and evaluated. FEV facilities can be used for part and component tests. The company is working together with longstanding partners in the field of overall vehicle crashes. The integration of safetyrelevant components, such as airbags, is also managed by safety experts – constant and close communication between the virtual functional design, system suppliers, and construction is a given here.
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