New Technologies and Industry Outlook of Automotive Electric Drive Systems

Development Trend of Electric Drive Technology: User demands determine the evolution direction of electric drive product technology.

Table of Contents

I. High Performance

Dynamic performance: Power/torque, two-wheel drive/four-wheel drive
Off-road capability: Independent four-wheel drive
Space utilization: Vehicle layout/electric drive integration
Driving range: High efficiency/low-temperature range (heating); four-wheel drive auxiliary technologies: asynchronous motors/disconnecting mechanisms
Fast charging: 800V high-voltage electric drive/compatible with 400V pile boost fast charging

II. Low Cost

Platformization: Top-level design, serialized electric drives covering diverse vehicle requirements
Integration: Multi-in-one integration/shaft-tooth integration/structural component integration
Modularization: Standardized subsystems/interfaces between subsystems; modularization of oil pumps, heat exchangers, parking systems, power modules, drive boards, stators, etc.
High-speed operation
Systematization: Voltage upper limit design for high-voltage systems; oil-cooled flat wire design for high-power motors

III. Electric Drive Vehicle Layout and Configuration

Front drive axle: Mainly restricted by collision space, with limited X-direction space; electric drives tend to be tall and slender, while flat designs are also applicable. Matching with suspension (MacPherson/double wishbone), steering gear, and frunk (front trunk) must be considered; the inverter position should account for collision impacts.
Rear drive axle: Mainly restricted by rear passenger compartment space, with limited Z-direction space; electric drives tend to be flat. Z-direction space must be considered, and X-direction space should avoid interfering with the battery.

IV. High-Speed Operation

To achieve goals such as strong power, high speed, and low energy consumption for new energy vehicles, core indicators of electric drive systems (e.g., rotational speed, efficiency, power density) are continuously improved. Enhancements in core performance of electric drive assemblies rely on breakthroughs in key materials and integration technologies.

With technological advancements including high-voltage platforms, silicon carbide (SiC) controllers, low-loss silicon steel sheets, and deep multi-in-one integration, electric drive assemblies have achieved rotational speeds of 25,000rpm~30,000rpm, peak efficiency of 93%~94%, and power density of 3.5kW/kg for high-voltage platforms.

In 2025, high-efficiency, high-density electric drive assemblies with rotational speeds exceeding 20,000rpm will take the lead in mass production for passenger vehicles:

FAW will launch a three-in-one electric drive with a maximum speed of 22,000rpm, entering mass production in 2024;
Huawei has developed a high-speed flat wire motor with a maximum speed of 25,000rpm, and the multi-in-one electric drive integrated with this motor will enter mass production in 2024;
BYD’s 30,000rpm motor will enter mass production in 2025.

V. Integration

Purpose: Cost reduction, weight reduction, volume minimization, compact structure, and improved vehicle layout. Three-in-one electric drive assemblies have become mainstream products; by 2025, their supporting share in domestic passenger vehicles will reach 55%. Multi-in-one products represented by Geely’s 11-in-one and BYD’s 12-in-one have entered mass production.

Common three-in-one electric drive integration;
Multi-in-one integration: Currently dominated by structural integration, following the “3+3+N” model (3 refers to motor + transmission + inverter and OBC + DC/DC + PDU; N refers to VCU + PTC + BMS + …). Higher integration requires higher reliability, demanding stronger technical capabilities and vertical industrial chain integration;
Multi-in-one integration method 1: Integration into the electric drive;
Multi-in-one integration method 2: Integration into the battery (under the passenger compartment, with higher energy density);
Structural integration: Reduces bolt connections, minimizes volume, and enables customized inverters, including integrated built-in cooling pipelines (water/oil circuits) and mounting integration;
Motor shaft/transmission input shaft integration: Reduces bearings, shortens shaft length, and lowers weight, but increases shafting support and installation difficulty;
Typical multi-in-one products:
1. BYD 8-in-one: Motor/Electronic Control/Reducer/DC/DC/OBC/PDU/BMS/VCU
2. Changan 7-in-one: Motor/Electronic Control/Reducer/OBC/DC/DC/DC/AC/PDU
3. Inpower 5-in-one: Motor/Electronic Control/Reducer/DC/DC/PDU
4. GM Ultium 7-in-one: Electronic Control/Reducer/Motor/VCU/DC/DC/OBC/PDU
5. Daoyi Power 9-in-one: Motor/Electronic Control/Reducer/DC/DC/OBC/V2L/PDU/PTC/Super Charging
6. Geely 11-in-one: Motor/Electronic Control/Reducer/VCU/DC/DC/OBC/V2L/PDU/PTC/Super Charging/Heat Pump
7. BYD 12-in-one: Motor/Reducer/Electronic Control/VCU/DC/DC/OBC/PDU/MOS/Boost/Boost/Self-Heating/Energy Management

VI. Motor Oil Cooling

Compared with water cooling, oil cooling offers superior insulation and cooling efficiency, balancing stator winding temperature rise under low-speed, high-torque conditions and magnet temperature rise under high-speed, high-power conditions, thereby improving motor efficiency. Currently, automakers and Tier 1 suppliers have basically switched to oil-cooled motor solutions for next-generation electric drive systems, with the highest penetration rate in B-class vehicles.

By 2025, the market share of water-cooled motors will be 55%, oil-cooled motors 35%, and air-cooled motors 10%. To address heat accumulation in the middle and deep parts of the motor stator, the industry has launched various oil cooling solutions (e.g., Feifan’s grid cascade type, BorgWarner’s centrifugal type):

Stator bolted fixation with winding spray cooling;
Stator interference fit fixation with built-in oil channels in stator slots;
Feifan’s grid cascade oil cooling technology: Arranges oil pipelines in the stator core, spraying oil onto the flat wire windings of 8-layer Hair-Pin motors. Circulating heat dissipation cools both the motor ends and core simultaneously, increasing peak performance duration by 70%;
BorgWarner’s centrifugal oil cooling technology: Series oil circuit structure that first cools the stator core before spraying the winding ends. Improves volume density by 10%~15% and reduces volume by 10%~15%;
In-slot stator cooling technology: Designs axial cooling oil channels to directly remove winding heat. Despite high technical difficulty, it may become a future trend.

VII. New Stator Windings

To improve motor efficiency and performance, new winding technologies have emerged based on flat wire windings (e.g., X-pin by Continental/BorgWarner/Aion, braided windings by ZF):

X-pin windings: Reduce end height and improve slot fill rate, but excessively short ends affect welding;
ZF braided windings: Reduce length by 6%, copper usage by 8%, and solder joints by 94% compared to Hair-Pin windings;
Yida Drive’s double-layer U-pin-Hair-Pin: Increases winding surface area for better heat dissipation, reduces AC resistance, and lowers winding losses compared to 4-layer windings.

VIII. Axial Flux Motors

Currently available electric vehicles primarily use radial flux motors. In contrast, axial flux motors are smaller, flatter, and lighter, with magnetic force parallel to the motor rotation axis. They significantly reduce axial size and weight while improving power density. Representative enterprises include YASA, Phi-power, and AVID.

IX. Carbon Fiber-Wrapped Rotors

Reducing magnetic leakage and improving motor efficiency have become trends, with the elimination of rotor core magnetic bridges. To counteract centrifugal force during high-speed rotation, protective sleeves are added to the rotor exterior. Carbon fiber has become a research focus due to its low density and high strength.

Advantages: Reduces rotor weight and inertia, improves performance and efficiency; lowers reluctance loss and eddy current loss. Carbon fiber performance: Tensile strength ≥3500MPa, elastic modulus ≥230GPa, density 1/4 that of steel, etc. Typical applications: Tesla Model S Plaid (20,000rpm), SAIC’s 800V SiC motor (21,000rpm), etc.

X. Rare Earth-Free Motors

Compared with permanent magnet motors, electromagnetic motors do not use rare earth materials, reducing carbon emissions. Advantages: Avoids rare earth supply chain risks and lowers emissions. Disadvantages: Requires additional coils/slip rings/brushes, leading to contact losses and pollution, necessitating regular maintenance.

Typical solutions:

BMW: Rated voltage 345V, continuous/peak power 80/220kW;
Mahle: Wireless electromagnetic motor with continuous output exceeding 90% of peak power;
Valeo: Peak power 200kW, upgradeable to 300kW.

XI. Power Modules

Domestic suppliers of IGBT and SiC (represented by BYD) have risen, with SiC-MOS accounting for 10% of the market. Compared to Si, SiC offers 10x higher breakdown field strength and 3x wider bandgap.

Advantages of SiC plastic-encapsulated modules: Easy standardization, thinner size, and good airtightness. Power semiconductor devices are developing toward modularization and low cost.

XII. Motor Losses

Main motor losses include copper loss, iron loss, eddy current loss, and hysteresis loss. Skin effect and proximity effect influence these losses:

Skin effect: Current density is higher on the conductor surface than at the center;
Proximity effect: Interaction between conductors causes current to shift to the far end when currents are in the same direction.

XIII. High-Speed Shaft Voltage/Shaft Current Safety Design

Shaft voltage classification:
- Capacitive voltage: Dominant type of motor shaft voltage, belonging to common-mode voltage;
- High-frequency induced voltage: Generated by common-mode voltage;
Shaft current classification: EDM spark current, circulating current, rotor-to-ground current;
Electrical circuit from motor windings to housing;
DC neutral point reference voltage (common-mode voltage): When the voltage platform increases from 400V to 800V, common-mode voltage rises significantly, increasing shaft current and exacerbating bearing corrosion issues.