Cost Efficient CO2 Reduction Vehicle Results based on 12V & 48V Architectures

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1 Recuperation Pure Electric Driving Torque Split Boost Advanced Stop/Start esc* BSG esc* 48V BSG 48BSG esc* Cost Efficient CO2 Reduction Vehicle Results based on & 48V Architectures M. Weissbaeck 1, C. Kaup 2, H. Mitterecker 1 1: AVL List GmbH, Graz - Austria 2: AVL Schrick GmbH, Remscheid - Germany Abstract: Starting with an evaluation of the different functionalities that and 48V systems can offer the results of two democars are discussed. Representing the very cost sensitive segment a Renault Megane based on electrical supercharger with the focus on lowest CO2 (75g/km) is compared to a 48V application in a Kia Optima representing top market segment of this brand. In this application a 10kW e-motor in a P0 belt configuration is combined with an electrical supercharger. After the conclusion of the findings an outlook on future potential is given. Keywords: Diesel, Hybrid, 48V, CO2, Friction 1. Introduction Besides achieving legal exhaust emission limits many authorities have also defined CO2 - respectively fuel efficiency - targets. In EU the average fleet value in 2020/2021 is defined with 95g/km CO2 resulting in significant penalty payments if this value is not achieved. Already today the Diesel drivetrain plays an important role in reducing the fleet CO2 level so that it is only the logical next step combining the Diesel with mild hybridisation. By that not only the fuel consumption can be further reduced but also emission compliance is supported by the additional degree of freedom when adding an e- Supercharger or an e-motor to the system. In this paper two different concepts realised in technology demonstrators shall be discussed. On the one hand describing a based solution for the most cost sensitive market segments and on the other hand a 48V application focusing strongly on additional customer benefits by enabling additional comfort and dynamic functionalities. 2. Voltage Level vs. 48V The different degree of electrification offers various functionalities. Fig. 1 shows the main functionalities and a rough rating across the various system architectures. Main Function Comfort Auto Stop Shutdown Assist Comfort Auto Start Enhanced Change of Mind EM** Dynamic Boost EM** Efficiency Generation esc Dynamic Boost o + + o ++ Sailing o o o + + Electric Maneuvering o o o + + Coast down recuperation Braking recuperation *esc: Electric Supercharger **EM: Electric Motor Figure 1: Hybrid Functionalities dependent on degree of electrification The functionalities are defined as follows: Comfort Auto Stop / Shutdown Assist Using electric generator torque to reduce the ICE (Internal Combustion Engine) shut down time and ensure a smooth stop by reducing the engine rebound. Comfort Auto Start Quick starting of the ICE by increasing the engine speed close to idle speed before ICE is fired. Page 1/7

2 Enhanced Change of Mind Restarting of the ICE during the ICE shutdown phase (comfort feature). EM Dynamic Boost Improving engine performance by adding EM torque during vehicle acceleration at low engine speed to enhance transient behavior. EM Efficiency Generation Increasing of load on ICE by adding EM generation torque to increase ICE efficiency esc Dynamic Boost Improving engine performance by increasing combustion engine charge air pressure using an electrical supercharger (esc) especially for vehicle acceleration at low engine speed to enhance transient behavior. Sailing Unfueled engine (motoring or shutdown) at constant velocity and maintaining of velocity using electrical torque assist. 3. Application on Renault Megane 3.1 System description As part of the "Diesel AVL Efficiency Engine Concept" a Renault 1.5L K9K engine was consistently redesigned and developed towards lowest friction values. Starting with a market study it was obvious that the high volume segment needs a cost efficient solution with a rather moderate specific power density; anyway combined with attractive lowend torque performance. Out of those considerations the max power rating was defined with 66kW (same as the series engine at that time) for this 1 st generation of the efficiency engine concept [1] resulting in a maximum peak firing pressure (PFP) of 110 bar (Design 120 bar). The changes to the basic engine carried out thereby were mainly focused on the crank train, the piston group, the air charge system and oil circuit. Due to the limited PFP requirements the cranktrain was significantly modified resulting in smaller bearing diameters, lower compression height of the pistons combined with increased conrod length as can be seen in Fig. 2. Electric Maneuvering Pure electric driving is possible at low vehicle velocities e.g. during vehicle creeping or during stopand-go traffic conditions. Coast down recuperation Converting kinetic energy into electrical energy during vehicle coast down phases. Braking recuperation Converting kinetic energy into electrical energy during vehicle braking phases in addition to the pure coast down recuperation. Dependent on the market segment customers have a different willingness to pay for extended functionalities. The focus of the Renault Megane was on a e- Supercharger best cost concept without hybridization while the Kia Optima utilized the full range of 48V powertrain electrification. This segmentation shall take care on the market needs and customer interests in specific functionalities and the willingness to pay for these extra features. The two solutions serve the complete range of possible solutions from best cost to maximum functionality. Figure 2: Efficiency Engine Gen. 1 Modified Cranktrain The next phase, carried out under the title "Diesel 2020 was based on the results of the "Diesel 2015" program and had a final NEDC CO2 target of 75 g/km in a C-class vehicle without hybridization. Therefore additional friction / consumption optimization measures of the engine and also for the vehicle were defined and implemented. The focus of the Diesel 2020 project was on the representation of a e-supercharger low cost concept, with partial electric auxiliary systems without hybridization. Page 2/7

3 FMEP [%] Based on the previous project (Diesel 2015) following hardware elements were modified to lower the engine friction as much as possible; resulting in the 2 nd generation of the efficiency engine. Cylinder head / camshaft drive On the cylinder head the first camshaft bearing, which has the biggest contribution to the total friction of the camshaft, was converted from plain bearing to roller bearing. This modification also required the adjustment of the drive wheel, since the required installation space for the roller bearing is bigger than for the plain bearing. The change was implemented by means of a modified wheel carrier. Valvetrain The K9K has a drive with mechanical tappets, already representing a friction-optimized solution. For the Diesel 2020 program the tappets were additionally provided with a low friction coating on the surface. Oil circuit At the Diesel 2015 program the oil pressure requirements were already lowered, resulting in a reduction of the oil pump size by 20%. Due to amendments to the camshaft bearing and the conversion to an electrical vacuum pump the oil pump size was further reduced. AVL RPEMS (Rapid Prototyping Engine Management System). LP EGR air cleaner Charge air cooler LP EGR cooler HP EGR esc Intake throttle exhaust manifold esc bypass VG T Figure 3: System layout intake manifold cylinders Alt. AVL RPEMS The engine friction performance for each step is compared in Figure 4 considering the FMEP ratings at 3 different engine speeds. Focusing on 2000 RPM the total friction was reduced by 20% in the first generation while ending up in a total reduction of 33% with the measures described above. Cooling water circuit In the cooling water circuit the mechanical pump was replaced by an electric water pump from Pierburg. In addition, changes to the inlet water pump housing geometry in the cylinder block have been established in order to minimize the flow losses. Accessory drive As mentioned the mechanical vacuum pump was replaced by an electric version which allowed to optimize the belt drive and to install an optimized belt tensioner from INA. % 75% 50% 25% 0% 1500 rpm 2000 rpm 2500rpm -20% -33% E-Supercharger To compensate the effect of the longer axle ratio, an electric charger (esc) from Valeo has been installed (VES Gen 3.1). This made it possible to keep the take-off performance and engine response at the level of the series vehicle. To be suitable with the electrical system architecture of the target vehicle a electrical compressor was implemented. Valvetrain + Accessories* Oilpump standard Piston & Rods Crankshaft * Coolant pump + Vacuum pump + HP Fuel pump + FEAD Figure 4: Friction Reduction for Efficiency Engine As can be drawn from the benchmark comparison in the next diagram (Fig. 5) a friction level similar to gasoline applications was achieved. The system layout, shown in Figure 3, represents both the integration of the esc and the necessary bypass in the air system. The new developed control logic for driving the e-supercharger, the electric water and vacuum pump was implemented in an Page 3/7

4 NEDC cycle CO 2 [g/km] FMEP [bar] 2,0 1,5 1,0 0,5 AVL Friction database - Complete Engine (compressing piston) motored FMEP [bar] over Engine Speed [rpm] 1.5L HSDI - BASE 1.5L HSDI - Efficiency Engine - Gen L HSDI - Efficiency Engine - Gen.2 Diesel Gasoline AVL Friction Scatterband ( ): Diesel HSDI & Gasoline Engines TGDI Complete Engine - compressing pistons Oil temperature = T coolant = 90 C Swept volume 1.4L to 2.0L, I4 Year: Oil Spec. 10W40 to 0W20 0, Engine speed [rpm] Figure 5: Friction scatter band 3.2 CO2 Walk and Vehicle Results To achieve the target value of 75 g/km CO2 in the NEDC following CO2 reducing steps were applied starting from the Diesel2015 vehicle level (Fig. 6): Stop / Start A stop / start system has been introduced which allows to stop the engine at vehicle speeds below 7km/h. With all these listed measures, a CO2 level of 78g/km was proven on chassis roller in the cold NEDC. For the final achievement of the target value of 75g/km CO2 following additional measures are considered to be implemented. Optimization Package 1 FIE update to make use of digital rate shaping, steel pistons and selective coating. Those measures were evaluated on a different engine anyway not yet transferred to the one installed in the vehicle. Optimization Package 2 Further finetuning of the oil circuit like demand controlled oil pump, switchable cooling jets and updated oil specs. Optimized vehicle coast down In order to achieve the ambitious consumption target of 75g/km also vehicle and comprehensive rolling resistance optimizations are necessary. Based on benchmarking of market available vehicles in that class according vehicle measures were defined and carried over for the chassis roller settings. Downspeeding / DCT To reduce the engine speed a 10% longer overall axle ratio was implemented and the shift points of the DCT (dual clutch transmission) were adapted accordingly Friction Reduction The engine friction reduction measures described in chapter 3.1 have been implemented (Efficiency Engine Gen. 2). Engine out recalibration Starting from the Diesel 2015 calibration, which was adjusted to a EU6 emission level without NOx exhaust aftertreatment, the engine out emissions were adapted in order to increase the combustion efficiency. Figure 6: CO2 Walk The measures applied had to be adapted to an existing engine, to a certain extend also considering production boundaries of existing lines. Starting from a clean sheet of paper additional potential in the range of 2% to 4% can be expected. Thermal Management By the usage of the electric water pump described in chapter 3.1, it was possible to optimize the engine thermal management and to ensure a faster engine warm-up behavior, resulting in a fuel consumption benefit. Page 4/7

5 4. 48V Application on Kia Optima 4.1 System description During a cooperation with Hyundai Motors Europe Technical Center the KIA Optima was selected to demonstrate the potential of a 48V application in the image market segment. Additional customer benefits based on improved functionalities as described at the beginning of this paper are here combined with a significant improvement in fuel consumption. The KIA Optima powertrain is based on a 1,7l diesel engine with HP EGR and a 48V mild hybrid system. This system consists of a belt integrated e-motor (BSG) for recuperation and boost support combined with an electrical Supercharger (esc) see Fig. 7 [2]. The 48V Advanced Lead Acid Battery as well as the DC to DC converter complete the electrical architecture. Downspeeding was chosen in this project to further increase CO2 reduction potential. For the functional integration of hybrid controls AVL has chosen a separate controller with ETK interface to the ECU. LP EGR HP EGR cooler air cleaner Charge air cooler 48V HP EGR 48V esc Intake throttle exhaust manifold esc bypass DC DC VGT Figure 7: System description 4.2 CO2 Walk and Vehicle Results intake manifold cylinders 48V BSG HCU Etas 910 reduction measures like low friction oil or variable oil pump were added to improve emissions and also increase performance. These measures are of course independent from the choice of the electrical voltage level and could either be realized with or 48V, whereas the following actions are only possible by utilizing 48V technology. Drivetrain A 15% longer final drive was implement to the gearbox. This measure can be applied because the BSG (Belt-Starter-Generator) and also the electric supercharger support the engine in low end torque area resulting in attractive driving performance of the vehicle more than compensating the transient drawback of downspeeding. Energy Management Due to the fact that the 48V system is able to recover a significant part of the brake energy and use this for torque assist during launching and driving an additional CO2 savings was achieved. Boardnet Support Further CO2 benefit was achieved considering that the required power for the vehicle electric system (200W are assumed during NEDC) can be gained by recuperation and needs not to be generated by a conventional alternator. Extended Start / Stop The fast response time since the BSG is permanently engaged and the high power of the system allow an extension of the Start/Stop functionality. That means the engine can be stopped earlier even during vehicle driving conditions with higher speeds and also be fired up later after the BSG has already accelerated the engine to idle conditions. Shifting Strategy Finally because of the possibility to homologate such system as a hybrid vehicle it is possible to select free shift pattern during NEDC cycle even with a manual transmission. Based on this powertrain architecture the CO2 reduction potential shown in Fig. 8 has been achieved. The following measures have been applied [3]: Engine optimization Increased injection nozzle size by ~18%, turbocharger enlarged and rail-pressure raised from 1600 to 1800bar to cope with the rated power increase of 25%. In addition the compression ratio of the engine was reduced to 15 and several friction Page 5/7

6 Figure of Merit [-] Torque [Nm] Energy [%] CO 2 Emissions in NEDC [%] Specific Example KIA OPTIMA CO 2 optimised base (incl. Downspeeding) 105% % 95% 90% 85% 80% 75% Baseline with Stop/Start T/M elongation Recuperation and torque assist by BSG Substitute alternator load by recuperation Figure 8: CO2 Walk 48V extended Stop/Start 13.5% 8.0% Free shift point selection It can be drawn from the diagram downspeeding contributes very strong to the CO2 reduction in this specific example. The listed improvement of 13.5% excluding engine measures mark the upper limit of the scatterband. Typically a CO2 reduction in the range of 6% to 8% is observed when moving towards a 48V application. With respect to full load performance the graph in figure 9 describes the enlarged operating area compared to the performance without e- Supercharger (in red); combining increased rated power performance with improved low end torque performance enabled by the electric boost system (blue line). Even in steady state operation, meaning the electrical power demand of the supercharger is supplied by the BSG (green curve) directly, there is a remarkable increase of low end torque which guarantees repeatable driving performance generation. As a consequence main transient support to the system shall be provided by the electrical boosting while using BSG support only in rather limited operation areas. During real world driving the majority of electrical energy will be generated by recuperation. The recuperation energy will be distributed to supply the electrical auxiliaries of the vehicles system via a DC/DC converter, the electrical Supercharger and the BSG (for engine restart in Stop/Start mode and boost during launch assist). The following graph (Fig. 10) shows the distribution in a RDE cycle in Cologne area with all hybrid functionalities enabled. The power demand of the system is approximately 450W generated by recuperation consumed by BSG-Boost consumed by esc consumed by DCDC total amount consumed Figure 10: Energy Balance in real driving The amount of recuperation energy can be further increased by using different battery technology (e. g. LiIon) and advanced brake systems (brake blending) torque (with VES) [Nm] 6 torque (w/o VES) [Nm] 4 torque (with VES steady state) [Nm] 50 delta Power_mech / P_el [-] Engine speed [rpm] Increased recuperation can also be enabled by installing the e-machine between engine and transmission or directly in the gearbox by that eliminating the engine friction influence which is a limiting factor for recuperation with a belt integrated system. For the described vehicle set-up cost efficiency and modularity where high ranked in the concept phase leading to the described BSG configuration. Figure 9: System description In the lower part of this diagram also the figure of merit is plotted showing a value of around 4 up to 1500 rpm. This means that applying 2 kw electrical power to the E-charger results in a 4 times higher figure to the engine performance since also the thermodynamic effects support the power Page 6/7

7 5. Summary & Conclusion 8. Glossary On as well as on 48V level two very attractive concepts were presented as a first step towards cost efficient electrification. Focusing on different market segments attractive customer relevant attributes are combined with significant benefits in fuel savings. Considering the fact that in addition emission compliance topics are supported by such approaches we will see more coming up in near future. Looking somewhat further ahead it is obvious that a dedicated 48V base engine / drivetrain [4] can lever the next step of potential; considering electrification form the concept phase onwards. esc: electrical Supercharger EM: Electric Motor ICE: Internal Combustion Engine PFP: Peak Firing Pressure VES: electrical Supercharger (Valeo) RPEMS: Rapid Prototyping Engine Management System HP EGR: High Pressure EGR LP EGR: Low Pressure EGR FMEP: Friction Mean Effective Pressure EE: Efficiency Engine DCT: Double Clutch Transmission BSG: Belt Starter Generator 6. Acknowledgement The authors would like to thank the project partners on Renault side, Mr. Ph. Mallet & Mr. A. Lefebvre as well as the partners on HMC side, Mr. S. Hoffmann & Mr. B. Unterberger, both Hyundai Motor Europe Technical Center for their support and contribution. 7. References [1] M. Weissbaeck, M. F. Howlett, S. Krapf, N. Ausserhofer: PC Diesel for EU6 and beyond The Efficiency Engine Concept as a cost-effective Solution, SIA Conference 2012 [2] C. Kaup, S. Hoffmann, B. Unterberger, J. Grimm, M. Weissbaeck: 48V Diesel Hybrid Dynamic and Efficient Powertrain, Part 1 Concept Layout & System Simulation, MTZ 2014/09 [3] C. Kaup, S. Hoffmann, B. Unterberger, M. Weissbaeck: 48V Diesel Hybrid - Fun2Drive at lowest CO2, MTZ 2016/03 [4] H. Sorger, W. Schoeffmann, A. Ennemoser, G. Fuckar, M. Groeger, H. Petutschnig, G. Teuschl, J. Hood: The Ideal Base Engine for 48 Volts Chances for Efficiency Improvement and Optimization of the Overall System Complexity, 24 th Aachen Colloquium 2015 Page 7/7