Online sessions of CTI Symposium China 2020
Session three: Efficiency Optimization of New Energy Vehicles
15 October 2020
China time: 4:30-6:00 p.m.（CET 10:30-12:00 a.m.）
Presentation language: Chinese
Prof. Dr XU Xiangyang
Executive Deputy Director,
National Engineering Research Center for Passenger Car Automatic Transmissions, School of Transportation Science & Engineering, Beihang University
Chief Engineer Corporation Advanced Engineer,
BorgWarner (China) Investment Co., Ltd.
A market segment approach for optimizing hybrid propulsion systems
- Overview of different propulsion approaches including Dedicated Hybrid Transmission (DHT), embedded in dedicated hybrid powertrains (DHP) and their characteristics
- The optimization process will include cost and efficiency but will also address other considerations such as drive quality and customer use profiles
- A vehicle-segment based landscape for DHP will be provided
To achieve a balance between powertrain costs and CO2 emissions, different levels of hybridization have been developed and will exist in parallel on the market for the mid-term future. Dedicated hybrid transmissions (DHT) are embedded in dedicated hybrid powertrains (DHP) which are used in full hybrids (HEV) and some plug-in hybrids (PHEV).
Driven by fuel consumption and high costs of electric components in the past, DHP’s were optimized in several generations towards high efficiency with a relative low complexity. DHP cost attractiveness is achieved by a combination of electrification, simplified transmissions and reduced content combustion engines. When enough electrical power is applied, it allows for the use of a highly efficient combustion engine while still accomplishing moderate dynamic performance.
HEV DHP’s offer an important low CO2 solution in the midterm future while the plug-in-vehicles volumes are relatively low. Additionally, the increasing battery size in PHEV’s promotes interest in DHP’s in order to reduce complexity and cost, offsetting the incremental cost of the added electrification.
This presentation gives an overview of different hybrid propulsion approaches and their characteristics. Starting from typical segment-related driving requirements a full vehicle simulation with a hybrid controller is carried out. The applied hybrid controller is based on the energy consumption minimizing strategy (ECMS) and is used to evaluate the efficiency in charge sustaining mode. Besides the efficiency results, costs and other considerations such as drive quality and customer use profiles lead into a selection process, which finally provides a vehicle-segment based landscape for DHP.
Ms. XIANG Xinqian
Senior Product Development Director
Advanced Product Engineer
Optimizing electric propulsion with low-loss multi-speed drive unit
- Shifting losses from conventional automatic transmission technologies offset much of the energy savings realized through multi-speed EV.
- Low loss 2 speed gear box with new types of shifting elements has nearly equivalent losses to a one-speed.
- Applying parametric vehicle model to optimize system elements and account for changes in battery, rare-earth metal and other commodity prices over time.
- The study demonstrates that a multi-speed EV propulsion system can delivery added value to OEMs for all types of EVs.
Multi-speed EV transmissions are starting to appear in performance cars commercial vehicles, as there is clear value for those market segments. Prevailing wisdom in the industry is there is no compelling case for multiple speeds in “mainstream” passenger EVs, and the market forecast reflects this. The idea behind this is that losses from the shifting elements offset much of the energy savings realized through the added ratio. This idea, however, is based on the paradigm of conventional automatic transmission technology.
This paper describes a new gearbox concept which uses new types of shifting elements that completely decouple when not in use, resulting in a two-speed gearbox with nearly equivalent losses to a one-speed. Using this gearbox concept, a vehicle levels simulation model was developed to examine the tradeoffs between different elements in the propulsion system, and their impact on range, performance and cost. Multiple scenarios are evaluated, including downsizing various elements in the propulsion system and the impact on range, performance and cost. For each of these scenarios a net value is calculated at the vehicle system level. The result of this work is a parametric simulation model which can be used to find the right balance of all 3 attributes for any given application. This parametric model can also be adjusted to account for changes in battery, rare-earth metal and other commodity prices over time. This study demonstrates that a multi-speed EV propulsion system can deliver added value to OEMs for all types of EVs, not just commercial vehicles and performance cars.
Ms. WANG Lei
Assistant president; Director of R&D and Operation
Automotive Research Institute(Suzhou) ,Tsinghua University (TSARI)
Increasing the range of an EV by improving drive efficiencies at low power
- Geared speed reducers and electric motors are often inefficient when operating at low power
- Traction drive speed reducers and high-speed slot-less motors remain highly efficient at low power
- A traction-based speed reducer is low cost, simple, makes almost no noise and can accept very high motor speeds
- A traction drive and high-speed slot-less motor delivers a significant range improvement when executing real world drive cycles
transmission was physically tested at the Tsinghua Suzhou Automotive Institute laboratories to establish efficiencies from zero power up to the level needed to perform this cycle. The motor was simulated using Motor Solve design software. The efficiencies of the motor and transmission were used to establish the total Energy consumption needed to deliver the WLTC cycle. The average efficiency was determined to exceed 85%. An equivalent Imbedded Magnet Permanent Magnet Motor and geared speed reducer were simulated using known efficiency Levels executing the same drive cycle to establish that systems average efficiency. The average efficiency was determined to be less than 75%. The potential cost reduction of the two systems was evaluated and determined significant cost savings for the traction based transmission and high-speed slot-less motor.
Traction drives are being used as speed reducers in EVs, with NSK recently offering this product to the industry. The SILK drive developed by Ultimate Transmissions is very similar to the NSK solution but uses a more compact, simpler clamping system based on wedging, that can deliver much higher speed reduction ratios. The effectiveness of this solution was proved in physical testing. Slot-less motors are used in many smaller power applications but not so far in higher power EVs. Part of the reason for this is their relatively poor torque density. The SILK traction
transmission can accept very high speeds and deliver single step reductions in excess of 15:1. By combining a high-speed slot-less motor with a noiseless traction based speed reducer it is possible to deliver a highly cost-effective Motor transmission solution. The solution is also significantly more efficient than it is conventional equivalent executing real world drive cycles.
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