4 – 7 December 2023, Main Days: 5 – 6 December, Estrel Hotel Berlin, Germany
HERE you meet the experts from Europe, America and Asia!
Senior Vice President Purchasing and R&D, Toyota Motor Europe
Director R&D Fellow Automotive Systems, Infineon Technologies AG
Chief Commercial Officer, cellcentric GmbH & Co. KG
Senior Partner, Roland Berger GmbH, Germany
Senior Vice President Strategy & Supply, TotalEnergies Marketing & Services
CTO, Member of the Executive Board, R&D, MAN Truck & Bus SE
An electric Two-Drive-Powertrain using two electric machines is presented, which allows a highly efficient over all usage. The multi-motor approach achieves a downsizing effect, when one motor is deactivated during moderate driving. The novel features of the powertrain are its electric synchronized dog clutches and its two highly overloadable electric machines, each connected to a […]
An electric Two-Drive-Powertrain using two electric machines is presented, which allows a highly efficient over all usage. The multi-motor approach achieves a downsizing effect, when one motor is deactivated during moderate driving. The novel features of the powertrain are its electric synchronized dog clutches and its two highly overloadable electric machines, each connected to a two-speed sub transmission providing a total of four different electric speeds. This arrangement enables full torque support during shifting processes. In addition, the waste heat from the inverters and the electric machines is used for heating the transmission oil under cold environmental conditions, thus increasing efficiency. Furthermore, the possibility and advantages of adding an internal combustion engine mechanically linked to both sub transmissions and its realization in a public founded project is addressed.
Increasing efficiency is a major target in the development of electric drivetrains. In parallel to established BEVs with one electric motor and a fixed transmission ratio, multi-speed [1, 2] and multi-motor [3, 4, 5] con-cepts are gaining importance. At the IMS of the TU Darmstadt, research is focused on multi-motor and multi-speed drives called TDT („Two-Drive-Transmission“). These electric drives combine high efficiency and performance by using a downsizing effect, according to which a highly utilized electric drive can be operated more efficiently than a large one in its corresponding partial load.
The conceptual benefits of an all-electric concept with two small electric machines with two speeds each, called TDT22, have al-ready been outlined in [6]. Efficiency advantages of up to 8.3% were identified for urban use compared to a benchmark fixed speed BEV. For short and slow driving, there is almost no alternative to a BEV from an ecological point of view. When it comes to long range, [7] stated that it is currently not reasonable to realize high ranges by using larger and heavier batteries. The battery capacity of BEVs ca-pable of reliably reaching distances greater than 500 km increases to more than 100 kWh. A current P2 hybrid concept with optimized energy storage sizes and propulsion machines shows poten-tial to reduce the CO2 footprint from cradle to grave because of its smaller battery. To achieve this, however, it must be charged regularly and driven mainly electrical. In addition, there are user benefits such as rapid refueling e.g., using renewable fuels in the future if an even longer distance is to be covered.
With these potentials in perspective, this paper will focus on the de-velopment of a hybrid version of a TDT22 already mentioned in [8]; a TDT4LR („Two-Drive-Transmission for Long Range“). This concept is based on a DRT (Dedicated Range-Extender Transmission) and is cur-rently being developed and built in the public funded Project DE4LoRa for a dedicated use case.
The vehicle being developed in DE4LoRa is designed for a typical German average user and leaves a minimal environmental footprint. According to the “Kraftfahrt-Bundesamt” [9] the 101-110 kW power class contained in 2020 by far the most new-registrations in one of the dis-crete subdivisions. This number was only topped by the open-ended category of more than 151 kW. At the same time, the most frequently registered class was the rather unspecific one of SUVs, closely followed by the C-segment [10]. As the former is not suited for an ecological vehicle, the focus is on the latter. According to a study from the Federal Ministry for Digital and Transport called “Mobility in Germany” sur-veyed in 2017 [11], approx. 80% of passenger car trips covered less than 20 km, with only approx. 30% of the total mileage of a vehicle reached on short distances of less than 20 km in total. Therefore, the develop-ment of the drivetrain was focused on this use case (e.g., daily commute to work and twice a year a long trip on vacation).
A BEV designed for this user profile needs a large and heavy battery, barely using its full capacity. In contrast, the DE4LoRa concept was de-veloped to cover ranges of up to 100 km electric combined with the high efficiency benefits of a TDT22. To reduce complexity, two iden-tical electric machines have been designed, each realizing a continu-ous power of at least 40 kW to enable highly efficient driving with one EM during moderate cycles like the WLTC. Furthermore, they can jointly provide 120 kW peak power for short sporty driving. To enable shifting without interrupting traction even at high accelerations, both electric motors are able to provide 120 kW each for the very short duration of a shifting process. The development of these permanent magnet syn-chronous machine is further described in [12].
Assuming constant transmission efficiencies, as well as a constant bat-tery voltage and temperatures, a simple heuristic operating strategy for electric modes can be created. The resulting shifting map for this TDT22 is shown in Figure 1. The advantages of four different electric gears com-pared to a non-shiftable transmission are described in more detail in [6].
In an overall assessment of the electric consumption, the relatively low transmission losses cause a significant proportion of the total loss-es due to the high efficiency of power electronics, electric machines, and batteries. Therefore, electrically synchronized dog clutches were chosen to avoid friction losses which would occur in mechanical syn-chronization units. Furthermore, the losses of a transmission increase with higher viscosity of the transmission oil e.g., at low temperatures. To keep the efficiency as high as possible after a frequently expected cold start in winter, it can be beneficial to use the waste heat from the electrical components for conditioning the transmission oil. To further increase electrical efficiency, DE4LoRa also uses a rather high voltage level up to 820 V. Since the efficiency drops with the voltage over the state of charge of a battery, the latter should be kept as high as possible. In this concept, the electrical consumption in the WLTC increases by ap-prox. 5% if started at an SOC of 25% compared to 90%.
For the use case described above, highly efficient short-range electric driving alone is insufficient. To improve the concept for occasional long-distance, a monovalent methane gas engine is added. This engine can be connected to both sub-transmissions with different gear ratios, as shown in Figure 2, enabling multiple parallel and serial hybrid modes. This integration combined with the high dynamics and performance of the electric drive allowes the gas motor to be operated in a phlegma-tized manner, thus minimizing emissions and maximizing its efficiency.
In addition, methane provides a high energy density per carbon atom, can be produced synthetically more efficiently than liquid synthetic fuels, and, unlike hydrogen, is easy to store and benefits from an existing infrastruc-ture. Optimizing the gear ratios of this transmission involves a compro-mise between highly efficient electric and SOC-neutral hybrid modes, with SOC-neutral consumption being more sensitive to changes. It has been shown that an electric overdrive provides efficiency benefits, re-sulting in a top speed of 180 km/h in SOC-neutral operation in the third, not fourth gear.
During optimization constant transmission efficiencies were assumed between 96.9 and 97.8% for each mode-dependent combination of two spur gears. In real applications, these effi-ciencies depend not only on the acting speeds and torques but also on the viscosity of the gear oil and thus its temperature. With lower temperatures, the transmission losses increase disproportionately. The inverter and electric machine generate usually unused waste heat. If the lubrication concept of the transmis-sion already uses an oil pump, the heat can be used for conditioning the oil by adding a heat exchanger.
The potential depends on several parameters like the current efficien-cies, the water flow rate, and the oil used. To investigate the possibili-ties for this project, an analytical transmission loss model was created, which includes the viscosity of the gear oil in its calculations of churning losses, meshing losses, sealing losses, and bearing losses. Not only the load-carrying elements but also all co-rotating parts for every mode are considered. This model is supplemented by a lumped-element thermal model of all transmission components. All loss effected transmission parts as well as a water-oil heat exchanger and 30% of the losses of the electric machine at the input shafts are implemented as heat sources. Thus, both the self-heating of the gearbox and the heat transfer from an external water circuit is represented.
Two different transmission oils and two different scenarios were consid-ered, using only modes with one EM for simplification. First, a common rather more viscous transmission oil was modeled corresponding to a SAE 80W90. Figures 3 and 4 show the simulation results for a cold start in the Artemis Urban cycle with 0°C ambient temperature.
The efficiency changes of the transmission are shown in Figure 4; in blue without using the heat exchanger, in red with a water flow rate of 1 l/min. In addition, the efficiency with an oil temperature of 60°C at the beginning is shown as a benchmark in gray. Figure 5 shows the most relevant results of the simulations. The heat exchanger in this configuration enables an efficiency advantage of 1.3% which is no-ticeable, but significantly lower than the efficiency with already warm oil. If the gear layout and the acting surface pressures allow the use of an oil with (very) low viscosity, much higher total savings are pos-sible. On the other hand, the benefits of conditioning are hardly notice-able with this lubricant. Finally, the potential in a WLTC at 20°C ambi-ent temperature is evaluated, whereby the heat exchanger leads to an 0.6% lower energy consumption. Prospectively, the usage of additional waste heat by other consumers, such as an internal combustion engine, could achieve greater improvements. Furthermore, the effect could be improved by further optimizing the flow rates and quantity of water and oil.
The concept idea for a hybrid TDT22, the development process as well as the results achieved in the DE4LoRa project so far were stated. It is tailored to fulfill the requirements of an average Ger-man driver with minimized ecological footprint. It covers short distances in highly efficient elec-tric driving due to the advantages of four speeds, uses a comparatively small and thus light battery, a high voltage level, and supplementary oil conditioning. To maximize efficiency, it is rec-ommended to keep the SOC as high as possible. In addition, the effect of transmission oil con-ditioning was examined in more detail, and in summary, the loss reduction potential depends primarily on the oil used. If a conventional trans-mission oil is used, there can be considerable efficiency benefits for short trips and cold am-bient temperatures – 1.3% in this example. How-ever, if the design or maintenance strategy al-lows using a low-viscosity oil, the effect if an oil conditioning decreases significantly and com-bined with longer driving distances and higher ambient temperatures, becomes unnoticeable small.
Gratification We want to thank Max Clauer, Zhihong Liu, and Arved Eßer for theirhelpful feedback and advice.References[1] Biermann, T, “The Innovative Schaeffler Modular E-Axle“, April 2018, Schaeffler Symposium[2] Schmidt, C., Dhejne H., Vallant, W.,
„AVL Two-speed e-Axle – High Efficient and Shiftable Under Load”, November 2021, CTI Symposium, Berlin[3] Xu X., Liang J., Hao Q., Dong, P, et al., “A Novel Electric Dual Motor Transmission for Heavy Commercial Vehicles”, Januar 2021, Automotive Innovation, Springer[4] Hirano, K., Hara, T., “Development of dual motor multi-mode e-axle”, November 2021, CTI Symposium, Berlin[5] Brückner, U., Strop, M., Zimmer, D., „Mehrmotorenantriebssys-teme – intelligente Betriebsstrategie“, May 2017, Antriebstechnik[6] Eßer, A., Mölleney, J., Rinderknecht, S., „Potentials to reduce the Energy Consumption of Electric Vehicles in Urban Traffic”, Juli 2022, VDI Dritev, Baden-Baden[7] Eßer, A., “Realfahrtbasierte Bewertung des ökologischen Potentials von Fahrzugantriebskonzepten“, 2021, Shaker[8] Langhammer, F., Kappes, A., Viehmann, A., Rinderknecht, S., „Novel “Two-Drive-Transmission for Long-Range” Powertrain: Ecology and Efficiency meet Driving Comfort”, October 2021, VDI Dritev, Bonn[9] Kraftfahrt-Bundesamt, „Fahrzeugzulassungen (FZ) Neuzulassungen von Personenkraftwagen und Krafträdern nach Motorisierung Jahr 2020“ – FZ 22; https://www.kba.de/SharedDocs/Downloads/DE/Statistik/Fahrzeuge/FZ22/fz22_2020.pdf?__blob=publicationFile&v=5 last checked: 11-10-2022[10] Kraftfahrt-Bundesamt, „Neuzulassungen von Personenkraftwagen nach Segmenten und Modellreihen“ – FZ 11; https://www.kba.de/DE/Statistik/Fahrzeuge/Neuzulassungen/Segmente/n_segmente_node.html?yearFilter=2020 last checked: 11-10-2022[11] infas, DLR, IVT und infas 360, “Mobilität in Deutschland – MiD: Ergebnisbericht,” Im Auftrag des BMVi, 2017;http://www.mobilitaet-in-deutschland.de/pdf/MiD2017_Ergebnis-bericht.pdf last checked: 11-10-2022[12] Clauer, M., Binder, A., “Automated Fast Semi-Analytical Calculation Approach for the Holistic Design of a PMSM in a Novel Two-Drive Transmission”, September 2022, ICEM, Valencia
Ruiping Wang, Geely Auto Senior Vice President, joined CTI SYMPOSIUM GERMANY 2022 as plenary speaker via video from China. See her contribution “Geely’s strategy and practice in powertrain electrification” as video and hear about BEV growth rates, the regulatory context, and Geely´s drive solutions and outlook on HEV, PHEV and BEV in the Chinese market.
Ruiping Wang, Geely Auto Senior Vice President, joined CTI SYMPOSIUM GERMANY 2022 as plenary speaker via video from China. See her contribution “Geely’s strategy and practice in powertrain electrification” as video and hear about BEV growth rates, the regulatory context, and Geely´s drive solutions and outlook on HEV, PHEV and BEV in the Chinese market.
JJE DirectFluxTM Mono-stable and Bi-stable Electromagnetic Clutches for Disconnect and Differential Locker Applications Jing-Jin Electric (JJE) has been developing electromagnetic clutches for various electric drive applications over a decade. Instead of using “reluctance” magnetic force, JJE electromagnetic clutches utilize direct magnetic force – flux in the same direction as the magnetic force – which is […]
Jing-Jin Electric (JJE) has been developing electromagnetic clutches for various electric drive applications over a decade. Instead of using “reluctance” magnetic force, JJE electromagnetic clutches utilize direct magnetic force – flux in the same direction as the magnetic force – which is named “DirectFluxTM”. A mono-stable clutch is engaged by actuation current, and disengaged by spring force when the current is off. A bi-stable clutch will only change its state when there’s an affirmative pulse of command current; otherwise, it will hold its state. Earlier this year, JJE launched industry’s first bi-stable electromagnetic clutch for automotive applications.
The technology roadmap for developing an electromagnetic dog clutch (EMDC) plays a key role in the product’s developing stage. Back to 2009, JJE started to develop the electromagnetic clutch in “DirectFluxTM” concept. The first generation (Gen 1) EMDC product is a circle configuration, mainly applied on hybrid systems as a hybrid mode clutch, which was very successful in China’s commercial market.
In 2017, the 2nd generation (Gen 2) EMDC product was launched, and expanded its application to transmission shifting after optimization over mechanical design. The “crescent” configuration was developed and added in the JJE’s EMDC family.
In early 2019, JJE began the development of 3rd generation (Gen 3) EMDC. The third generation (Gen 3) EMDC features further innovations. It has both mono-stable and bi-stable options. It overcame some limitations of the existing design. Coils evolved to smaller solenoids, and magnetic circuit are further optimized to reduce flux leakage. The Gen 3 EMDC is more capable, faster, functionally safer, and more energy efficient.
JJE’s DirectFluxTM mono-stable electromagnetic clutch has several advantages because of its unique magnetic circuit design and mechanical structure. Compared to the more conventional reluctance flux magnetic circuit design, the DirectFluxTM design greatly reduces flux leakage, therefore it utilizes the magnetic flux to generate force more effectively. The reluctance flux design cannot avoid magnetization of parts near flux circuit, or “flux leakage”, which cause less effective utilization of the magnetic flux.
Because of the more effective flux utilization, the DirectFluxTM clutch has much higher electromagnetic force than reluctance flux clutch, therefore it acts 2-3 times faster, as shown in the charts.
The bi-stable electromagnetic clutch – still based on JJE’s DirectFluxTM electromagnetics – is an innovation beyond JJE’s mono-stable electromagnetic clutch. It uses permanent magnets to hold the clutch in its en-gaged position, while still allowing the electromagnetic coil to “push” the clutch plate away while disengaging. As the clutch can self-hold at both engaged and disengaged positions, there is no need for holding current as the mono-stable clutch does. The operation current curve exactly illustrates the difference between the mono-stable and bi-stable. For bi-stable clutch, the operation only needs to provide a current pulse to switch the clutch’s state (see Fig.).
The bi-stable clutch is inherently fail-safe as it won’t change state in the event of loss of holding current. This feature brings the bi-stable clutch a higher safety level than mono-stable clutch for disconnect, differential lock-er, and transmission shift applications. As far as energy consumption, the bi-stable clutch’s feature of “zero hold-ing current” achieves the zero consumption.
Figure 4: Operation Comparison Between Mono-stable and Bi-stable Clutch
JJE’s mono-stable clutch has already been successfully applied on electric drive disconnect. In an offset, layshaft reduction gearbox, the disconnect clutch is on the output and is integrated with differential. Compared with disconnect on the input shaft or on the layshaft, the output shaft discon-nect cuts out most mechanical losses. JJE is also introducing bi-stable electromagnetic clutch to disconnect application. There is no holding current or power consumption when the clutch is engaged. It is mechanically fail-safe in the event of critical electrical or control fault. When the vehicle is in AWD state, all-wheel power will be maintained for consistency; when the vehicle is in the 2WD state – or secondary axle disconnected – the secondary axle won’t be suddenly engaged, which would cause big jerk, or even wheel lockup at low traction. DirectFluxTM bi-stable clutch has a great performance on the action time. The differential locker and disconnect driven by DirectFluxTM bi-stable EMDC have been tested on JJE’s Dynamometer. The average action time is less than 70ms, and only current pulses are needed for engagement and disengagement. With JJE’s disconnect clutch, the drag loss reduction is remarkable. In a typical 200kW electric drive unit with permanent magnet motor, at 150km/h vehicle speed, the drag loss reduction is greater than 90%, or from nearly 8kW to less than 500W.
JJE debuted industry’s first electromagnetic bi-stable differential locker at 2022 CTI US. Bi-stable’s greatest advantage is still fail-safe – in the event of critical electrical or control fault, this bi-stable feature can prevent sudden locker release and dangerous loss of tractionThis bi-stable DirectFluxTM differential locker will be used in high capability pick-up trucks, SUVs and off-road vehicles in independent electric drive module (EDM) or eBeam axles. It will be launched into production in 2023 in JJE’s newest 6000Nm, 300kW Silicon Carbide EDM for a high-end 4×4 SUV by a leading OEM, which features over 100% gradeability.“JJE has been developing and producing electromagnetic clutch for over a decade”, says Ping Yu, JJE’s Chairman and Chief Engineer, “we have pioneered electromagnetic dog clutch’s application in many areas and generated multiple global patents. The introduction of the bi-stable clutch technology is more exciting – it brings security like a mechani-cal sleeve clutch while maintaining or even improving all other great aspects of an electromagnetic clutch. It will further reinforce our leadership in electric drive technology”.
Contribution to further eAxle compactness and higher power density Makoto NISHIJI, Senior General Manager / Chief Engineer, Driveline CE Department, Automotive Business Unit, JTEKT Corporation In response to the strong expansion of the battery electric vehicle (BEV) market, JTEKT has developed and just announced “Ultra Compact” product series, JTEKT Ultra Compact BearingTM, JTEKT Ultra Compact […]
Makoto NISHIJI, Senior General Manager / Chief Engineer, Driveline CE Department, Automotive Business Unit, JTEKT Corporation
In response to the strong expansion of the battery electric vehicle (BEV) market, JTEKT has developed and just announced “Ultra Compact” product series, JTEKT Ultra Compact BearingTM, JTEKT Ultra Compact SealTM and JTEKT Ultra Compact Diff.TM aiming for e-axle size and weight reduction. (Fig. 1)
“JTEKT Ultra Compact Diff.TM (hereafter referred to as JUCDTM)”, is new differential proposal for BEV e-axle using very unique/patented differential gearing. JUCDTM is extremely small compared with traditional two pinion – one piece housing bevel gear type differential for the same strength.*JTEKT Ultra Compact Diff. and JUCD are registered trademarks of JTEKT.
Needs for eAxle compactness
Following with automotive electrification growth trend and also high ratio of 4 Wheel Drive BEV trend, development and production of eAxle is growing rapidly worldwide. e-axle is the heart of the eDrive system, and integrated inverter, motor, and reducer including differential. In order to develop a better BEV keeping enough battery capacity installation space, the e-axle is required to be smaller and should have much higher lower density (power/weight ratio) in future. In response to this market need, demand of very compact differential for e-axle is expected to grow, and will replace the typical bevel gear type differential widely used for traditional vehicles.
JUCD Background
JTEKT has developed a very compact size and highly durable differential as “JTEKT Ultra Compact Diff.”, which is suitable for BEV e-axle. A differential is a device that absorbs the rotational speed difference between the left and right wheels that occurs in cornering, and transfer the torque between the drive power source to both wheels.
We have further evolved our “No.1 & Only One” product, the Torsen LSD technology, which is a high-performance differential suitable for high power 4WD/sports vehicles, by adding new knowledge of gear design and machining technologies. Introducing smaller gear module geometry into the unique composite planet gear set, we have made it smaller in radial and axial directions, and reborn as “JUCD” general-purpose differential for wide range of eAxles. * LSD: Limited Slip Differential
JUCD Features and Advantages
Compared to the bevel gear type differential, JUCD has an increased mesh quantity and wider mesh width at larger diameter between planet gear and side gear. This is possible by using smaller diameter parallel axis planet gears which are directly supported by the housing bore similar with journal bearing structure. (Fig. 3) As a result, for the same differential gearing functional volume, the ultimate strength is more than doubled. Consequently, for the same ultimate strength, the required volume is less than half for JUCD. (Fig. 2)
In addition, high durability is ensured by reducing each load of the sliding surfaces between planet gears outside diameter to housing bore, compared with the bevel gear type differential pinion gear hole to drive pin. (Fig. 4)
JUCD can support wide range of torque capacity requirement, by selecting the number of side gear teeth and the size of differential outer diameter and/or additional planet gear set, while keeping the common planet gear sets and differential width. (Fig. 5) With these, JTEKT can now propose the optimum ultra compact differential for various eAxle reducer structures and torque requirements. JUCD contributes to the further eAxle compactness and higher power density, and also improves flexibility of the eAxle mountability to the vehicle.
Improve electricity power consumption and safety performance
JUCD also has mild and stable torque biasing LSD characteristics derived from its unique structure, mainly by planet gears outside diameter to housing bore friction as journal bearing structure. This feature contributes to reducing the vehicle wheel friction brake load that intervenes when the tire slips at vehicle start on slippery road surface or climbing a hill. It also contributes to expand the range of regenerative braking situations by stabilizing vehicle behavior during deceleration. These effects are expected to improve electricity power consumption. In addition, these characteristics also contribute to improve straight-line stability, which will reduce continuous steering wheel angle adjustment during steady straight-line driving, contributing to reduce driver’s fatigue and improve ride comfort. (Fig. 6)
For more detail
JTEKT Ultra Compact Diff.TM: www.jtekt.co.jp/e/news/2022/220831.html
JTEKT Ultra Compact BearingTM: www.jtekt.co.jp/e/news/2022/221018.html
JTEKT Ultra Compact SealTM: www.jtekt.co.jp/e/news/2022/221024_3.html
