Electric drive motors - From concept to series production

Time of India

14-05-2025

The electrification of passenger cars represents a diverse market segment spanning from compact city cars to high-performance luxury and sports vehicles. In addition to conventional performance features, the vehicle's electrical system voltage plays a crucial role, determined by requirements for charging times and system efficiency among others.
In the automotive industry, two main voltage classes have been established: around 400 V in conjunction with Silicon Insulated Gate Bipolar Transistors (Si-IGBTs) and approximately 800 V in conjunction with Silicon Carbide (SiC) transistors. In compact cars, mainly 400 V systems are utilized, while in higher vehicle classes, depending on market positioning, both technologies may be applicable.Figure 1 depicts market data of systems for peak power in relation to torque.
BorgWarner's Integrated Drive Modules
(iDMs) are designed to be utilized in vehicles across various segments from A to D as well as in voltage classes of 400 and 800 V. The basic modular solutions are adjusted according to market requirements, such as when the customer requires more power or torque. To meet the requirements of each drive system, component platforms are defined for all core components of the drive modules, especially gearbox, electric motor, and inverter, and are implemented based on BorgWarner's internal development competencies. For instance, the inverters are based on patented power module technology called Viper.
Mechanical components in focus: Structure and function of the drive system
The mechanical configuration of the drives in current series productions of iDMs encompasses both drive architectures with parallel countershaft and coaxial gearboxes. In most cases, the arrangement with parallel countershaft is preferred due to cost advantages and efficiency. However, for limited installation spaces, a concentric countershaft or coaxial arrangement of the gearbox offers advantages. The range of drive modules extends from the iDM146, used in compact cars, to the iDM180 for the mid-range, up to the iDM220, covering systems from 170 to over 350 kW, thus encompassing a broad spectrum. All systems can be configured either as Permanent Magnet Synchronous Motors (PMSM) or as Induction Motors (IM) with a unified stator.
Additionally, an option with Externally Excited Synchronous Machine (EESM) is offered for the iDM220 module. Starting from iDM180, the stator and rotor of all systems are oil-cooled. A regulated oil cooling for stator and rotor through an electric oil pump meets the demand for higher continuous power. Figure 2 shows the iDM220 module and its components. The oil-cooled system features a heat exchanger and an electric oil pump, enabling on-demand cooling and lubrication, thus increasing efficiency. Furthermore, a variant with an integrated park lock is offered. The Viper power module technology with double-sided cooling enables high power density.
Drive systems with EESM offer the possibility to control the excitation field and are therefore a good choice for secondary drives. However, the packaging challenges for secondary drives are higher. The best solution in terms of packaging is a coaxial arrangement. The requirements of such a system are met with brushless transformer technology. The brushless transformer solution for EESM consists of a single robust printed circuit board transformer with a highly efficient resonant inductive excitation system, thus enabling a compact design. This solution is suitable for all mechanical configurations, including a coaxial arrangement.
Integrating this system into the oil-cooled motor area required a simple design of rotation transformer and rectifier. Figure 3 shows the concept of a brushless system designed for voltages of 800 V, requiring 15per cent less space compared to brush-bearing systems.
Next-gen integrated drive module: Concept and development
The next-generation drive module responds to market demands for ultra-compact systems aimed at reducing costs and offering higher efficiency than traditional systems [4], see Figure 4. The fully integrated high-speed drive module is equipped with a high-speed differential gearbox at the rotor shaft of the electric motor, as well as two gearboxes for low torques. By integrating a differential unit with lower torque capacity, the required space compared to similar concepts has been significantly reduced.
Due to system requirements, the electric motor has been completely redesigned compared to currently produced motors. Taking these requirements into account, new rotor properties have been developed, allowing speeds of over 20,000 rpm. Despite further reduction in rotor losses, such a concept requires additional optimization of motor cooling. The solution involves complete immersion cooling of the stator winding heads in circulating oil flow.
E-Motors: high-voltage hairpin technology
Hairpin technology for electric motors has achieved a power density and maximum efficiency of over 97per cent with the latest Hairpin Stator Winding Technology (HVH) for the high-voltage range, see Figure 5. The motors in the HVH series are available in multiple versions with various configurations of different lengths, cooling methods, and winding options, either as a complete motor with housing or as a rotor-stator unit. The product portfolio starts with an outer diameter of 146 mm (HVH146) and a peak power of 90 kW. The medium-size and power range are covered by several variants of the HVH180 with peak powers up to 190 kW.
For applications requiring higher power, BorgWarner offers several versions of the HVH220 with a peak power of 350 kW. At the top end of the product range for passenger car applications is the high-performance version with an outer diameter of 264 mm (HVH264) and a peak power of 450 kW. Especially in the high-power versions, regulated oil cooling is used for the rotor, where the cooling medium is brought close to the permanent magnets.
This proximity to the magnets is crucial for continuous power and also allows the use of magnets with lower rare earth element requirements. The HVH320 is a novel development for applications requiring high torque at low speeds. This new HVH320 platform, launching in 2024, will be produced in three versions with maximum power/maximum torque of 1280 Nm/485 kW, 1500 Nm/525 kW, and 1650 Nm/575 kW. The motor features innovative wire insulation (single-layer polyetheretherketone) meeting the highest quality standards, as well as immersion cooling of the winding heads to deliver the highest possible continuous torque. Fully bonded laminated core packages in the stator and rotor ensure high efficiency.
The end winding and stator are designed to provide sealing against a thermal protection cover that directs oil flow. In motors with interior permanent magnets (IPM), neodymium permanent magnets are used in the current large series with a low proportion of heavy rare earth elements dysprosium or terbium. The next development focuses on a concept that aims for sustainability without heavy rare earth elements.
Since heavy rare earth elements protect against demagnetization under extreme operating conditions, new magnet techniques, further improvements in stator and rotor cooling, and optimization of motor control, which can limit the current peaks when switching to active short circuit (AKS), are combined in a holistic approach.
S-winding technology
The advancement of S-winding technology for use in electric motors is depicted in Figure 6. The second generation (S-Wind Gen2) is widely employed in P2 drive modules for hybrid vehicles in the EU and Chinese markets, with an outer diameter of 270 mm (SW270). The latest generation (S-Wind Gen3) is utilized in 48-V P3 modules with an outer diameter of 130 mm (SW130) for drive motors.
Compared to hairpin technology, S-winding offers clear packaging advantages due to the length of the winding head, eliminating the need to weld individual pins. This is particularly crucial for P2 module applications. The S-winding technology is based on a stator geometry with open stator slots. A special winding process enables the extension of the formed continuous wire initially wound onto a mandrel into the stator. According to measurements conducted in accordance with the Worldwide Harmonized Light-Duty Vehicles Test Procedure (WLTP), the efficiencies of both concepts differ by 0.8per cent when using a comparable number of slots and conductors per slot.
With the further development of S-winding technology, variants with a higher number of conductors per stator slot and a higher number of stator slots are being developed. This enables consistently high rotational speeds, and with an identical stator diameter, the same efficiency as hairpin technology is achieved according to WLTP. This approach allows for better efficiency than hairpin technology at high torque and high rotational speeds (typical during highway driving) due to significantly lower alternating current copper losses with slightly higher direct current copper losses due to the smaller wire cross-section in conjunction with the large number of wires per slot.
The market demand for various concepts is currently highly heterogeneous and is expected to continue in this diversity over the coming decade. Hairpin technology is projected to continue dominating as it offers the highest efficiency according to WLTP. S-winding technology, with a high number of slots and conductors per slot, ensures excellent performance and efficiency at high speeds, leading to its establishment in the market. Advancements in the sustainability of IPM technology will be a central focus of development in the coming years.