What is the biggest challenge when vehicles move towards electrification? Electric drive system responds positively to this question, which plays a key role in terms of energy saving and carbon emission reduction. Besides, it is required to provide excellent driving performance, therefore becoming a hot topic in the automotive field. Hence Automotive Innovation proposed this special issue.

This paper presents a review on the recent research and technical progress of electric motor systems and electric powertrains for new energy vehicles. Through the analysis and comparison of direct current motor, induction motor, and synchronous motor, it is found that permanent magnet synchronous motor has better overall performance; by comparison with converters with Si-based IGBTs, it is found converters with SiC MOSFETs show significantly higher efficiency and increase driving mileage per charge. In addition, the pros and cons of different control strategies and algorithms are demonstrated. Next, by comparing series, parallel, and power split hybrid powertrains, the series–parallel compound hybrid powertrains are found to provide better fuel economy. Different electric powertrains, hybrid powertrains, and range-extended electric systems are also detailed, and their advantages and disadvantages are described. Finally, the technology roadmap over the next 15 years is proposed regarding traction motor, power electronic converter and electric powertrain as well as the key materials and components at each time frame.

Dedicated hybrid transmission (DHT) is the developing trend of hybrid transmissions. This paper studies different types of DHTs regarding the structure, function, and performance. Firstly, the structure and function of different well-known DHTs in the market are discussed and analyzed. Through the analysis, the reasonability and necessity of the different modes and the electric motor power requirements that lie behind different DHTs are derived. Secondly, the dynamics of different DHTs are further compared with the driving areas in different modes under different driving conditions. Then, the basic or minimum dynamic requirements are defined and taken into consideration before the economic comparison. To ensure the effectiveness of the comparison, the optimization of the configurations for each kind of DHT is carried out with the modular simulation model. The economic comparison is conducted under the premise of excluding the influences of the configurations in the results. Finally, the sensitivity and influence of different engine characteristics for different DHTs are studied to find out the sensibilities of the two kinds of DHTs with engine technology. Through these studies, the essential differences and features of different DHTs can be derived to help better understand the decision in choosing the technical route for the original equipment manufacturers.

As a vital vehicle part, the powertrain system is undergoing a fast transition towards electrification. The new integrated electric drive system has been widely used, especially for passenger cars. In this work, a novel electric dual motor transmission is proposed for heavy commercial vehicles. The transmission scheme is firstly introduced, which can achieve 9 different operating modes including 5 single motor modes and 4 dual motor modes. Then, the mode shift map with minimum energy consumption is designed based on the motor efficiency map and the proposed energy management strategy. The driving power is appropriately distributed between the two motors in dual motor modes under the condition of minimum power consumption. In addition, a coordinated control strategy is developed for mode shift control without power interruption. The results show that the electric dual motor transmission has advantages in power consumption and power shift ability compared with the conventional single motor automated manual transmission.

The dual-mode electro-mechanical transmission (EMT) system is a crucial part of power-split hybrid electric vehicles (HEVs), especially for the heavy HEVs. To improve the precision of the system power distribution and the response speed of the electric power supply, a model-based double closed-loop coordinated control strategy is proposed. As the basis of the proposed control strategy, an EMT system model, particularly of an electrical system, is established first. The proposed control strategy includes the power distribution strategy, battery power closed-loop feedback control strategy, and motor coordinated control strategy. To verify the feasibility of the proposed control strategy, simulation and experiment are performed. The results indicate that the proposed control strategy can realize the expected power distribution by coordinating generators and motors and achieve rapid and stable electric power supply.

As a new drive system for electric vehicles, the dual-mode coupling drive system can automatically switch between centralized and distributed drive modes and realize two-speed gear shifting. Because the actuator’s displacement signal affects the mode-switching control, when failure occurs at the angle-displacement sensor, the mode-shifting quality is likely to drop greatly, even possibly leading to shift failure. To address the angle-displacement sensor failure and improve the reliability of the shift control, an adaptive fault-tolerant control method is proposed and verified. First, the effect of the output signal of the angle-displacement sensor in the mode-switching control process is analyzed. Then, an adaptive mode-switching fault-tolerant control method is designed based on the Kalman filter and fuzzy theory. Finally, the feasibility of the control effect is verified through simulations and vehicle experiments. The results indicate that the proposed method can effectively eliminate the signal noise of the angle-displacement sensor and successfully switch the modes when the sensor fails. It provides a reference for ensuring the working quality of similar electric drive systems under sensor failures.

The calibration of conventional, hybrid and electric drivetrains is an important process during the development phase of any vehicle. Therefore, to optimize the comfort and dynamic behavior (known as driveability), many test drives are performed by experienced drivers during different driving maneuvers, e.g., launch, re-launch or gear shift. However, the process can be kept more consistent and independent of human-based deviations by using objective ratings. This study first introduces an objective rating system developed for the launch behavior of conventional vehicles with automatic transmission, dual-clutch transmission, and alternative drivetrains. Then, the launch behavior, namely comfort and dynamic quality, is compared between two conventional vehicles, a plug-in hybrid electric vehicle and a battery electric vehicle. Results show the benefits of pure electric drivetrains due to the lack of launch and shifting elements, as well as the usage of a highly dynamic electric motor. While the plug-in hybrid achieves a 10% higher overall rating compared to the baseline conventional vehicle, the pure electric vehicle even achieves a 21% higher overall rating. The results also highlight the optimization potential of battery electric vehicles regarding their comfort and dynamic characteristics. The transitions and the gradient of the acceleration build-up have a major influence on the launch quality.

The move from internal combustion engine vehicles to electric vehicles is happening rapidly, which demands a stepwise change in priorities for the vehicle design process with rational consideration of emerging technologies. This paper focuses on the efficiency of a particular form of high fixed-ratio (15:1) traction drive speed reducer. This is suitable for use in conjunction with a high-speed electric motor for automotive applications. A general discussion of the characteristics of other fixed-ratio traction drives is provided followed by an analysis of underlying efficiency issues. The paper presents details of the speed reducer prototype called a "Silk Drive" and the vehicle for which it was designed. Data from laboratory testing of the prototype are presented, and an efficiency map for the transmission is developed. The efficiency map and vehicle parameters are used in a simulation to determine the overall transmission efficiency for the world harmonized light vehicles test cycles (WLTC) class 3b drive cycle. The importance of transmission efficiency at low power levels, in specific input speed and torque regions, is demonstrated using a novel method for identifying those speed torque regions that most strongly affect overall efficiency. The method applies to all drivetrain components and pinpoints those regions that need to be the focus in the optimal design of such components. This paper presents evidence that the efficiency of zero-spin, fixed-ratio traction drives is similar to that of conventional gear drives.

Internal short circuit (ISC) is a critical cause for the dangerous thermal runaway of lithium-ion battery (LIB); thus, the accurate early-stage detection of the ISC failure is critical to improving the safety of electric vehicles. In this paper, a model-based and self-diagnostic method for online ISC detection of LIB is proposed using the measured load current and terminal voltage. An equivalent circuit model is built to describe the characteristics of ISC cell. A discrete-time regression model is formulated for the faulty cell model through the system transfer function, based on which the electrical model parameters are adapted online to keep the model accurate. Furthermore, an online ISC detection method is exploited by incorporating an extended Kalman filter-based state of charge estimator, an abnormal charge depletion-based ISC current estimator, and an ISC resistance estimator based on the recursive least squares method with variant forgetting factor. The proposed method shows a self-diagnostic merit relying on the single-cell measurements, which makes it free from the extra uncertainty caused by other cells in the system. Experimental results suggest that the online parameterized model can accurately predict the voltage dynamics of LIB. The proposed diagnostic method can accurately identify the ISC resistance online, thereby contributing to the early-stage detection of ISC fault in the LIB.

Battery packs are applied in various areas (e.g., electric vehicles, energy storage, space, mining, etc.), which requires the state of health (SOH) to be accurately estimated. Inconsistency, also known as cell variation, is considered a significant evaluation index that greatly affects the degradation of battery pack. This paper proposes a novel joint inconsistency and SOH estimation method under cycling, which fills the gap of joint estimation based on the fast-charging process for electric vehicles. First, fifteen features are extracted from current change points during the partial charging process. Then, a joint estimation system is designed, where fusion weights are obtained by the analytic hierarchy process and multi-scale sample entropy to evaluate inconsistency. A wrapper is used to select the optimal feature subset, and Gaussian process regression is implemented to estimate the SOH. Finally, the estimation performance is assessed by the test data. The results show that the inconsistency evaluation can reflect the aging conditions, and the inconsistency does affect the aging process. The wrapper selection method improves the accuracy of SOH estimation by about 75.8% compared to the traditional filter method when only 10% of data is used for model training. The maximum absolute error and root mean square error are 2.58% and 0.93%, respectively.