Drive Motor

1. What is a Drive Motor

The drive motor is the core powertrain component of a new energy vehicle (NEV). Together with the motor controller and traction battery, it forms the core "Three Electrics" of an electric vehicle (EV). Its fundamental function is to convert electrical energy into mechanical energy to propel the vehicle. During braking or deceleration, it operates as a generator to convert kinetic energy back into electrical energy for storage in the traction battery, achieving regenerative braking.

The drive motor and its electric control system account for approximately 10%–20% of the total vehicle BOM (Bill of Materials) cost. In 2024, the total installed volume of NEV drive motors in China reached 15.229 million units.

2. Working Principle

The operating principle of a drive motor is based on electromagnetic induction and magnetic field interaction. In basic terms, a motor comprises a stator (stationary component) and a rotor (rotating component). When electrical energy is supplied from the battery, the coils in the stator create a rotating magnetic field that drives the rotor, generating the mechanical output required to turn the driven wheels.

The speed relationship between the rotor and the stator's rotating magnetic field serves as the key distinction among different motor types.

3. Main Types

There are four primary types of drive motors commonly utilised in electrified vehicles: DC motors, AC asynchronous motors (induction motors), permanent magnet synchronous motors, and switched reluctance motors. Currently, permanent magnet synchronous motors and AC asynchronous motors represent the two prevailing mainstream solutions.

Type	Working Principle	Advantages	Disadvantages	Market Position
Permanent Magnet Synchronous Motor (PMSM)	The rotor uses permanent magnets to produce a magnetic field that rotates in synchrony with the stator's rotating magnetic field.	High efficiency (peak efficiency reaching 95%–97%), high power density, compact packaging, and lightweight design.	Dependent on rare earth elements, higher production cost; susceptible to demagnetisation at high operating temperatures.	Dominant mainstream, capturing approximately 96.0% of total installed market share in 2024.
AC Asynchronous Motor / Induction Motor (IM)	The rotor rotational speed is always lower than that of the stator's rotating magnetic field (operating with "slip").	Robust and simple construction, high durability, lower manufacturing cost, and a broad speed range.	Relatively lower power density; bulkier and heavier than a PMSM of equivalent power output.	Primarily deployed in performance-focused vehicles or as secondary drive motors in dual-motor AWD setups.
Switched Reluctance Motor (SRM)	Simple structural design; the rotor contains neither windings nor permanent magnets.	Low manufacturing cost, high reliability, and wide speed regulation range.	Higher torque ripple and NVH (noise, vibration, and harshness) levels; complex electronic control required.	Limited commercial adoption; currently under evaluation for niche applications.
DC Motor	Available in brushed and brushless configurations.	High low-end starting torque (brushed design).	Lower operating efficiency and high maintenance requirements (brushed design).	Virtually phased out in modern automotive EV applications.

4. Basic Construction

Taking the mainstream permanent magnet synchronous motor as an example, its core assembly consists of:

Stator: Comprising a laminated iron core and copper windings (insulated with enamelled wire), responsible for generating the rotating magnetic field.
Rotor: Embedded with permanent magnets, this is the rotating assembly that produces driving torque.
Resolver: A high-precision rotary position sensor that measures rotor position and speed in real time, delivering critical feedback to the motor controller.
Temperature Sensor: Monitors operating temperatures continuously to prevent thermal overload.
Cooling System: Typically employs a cooling water jacket (liquid cooling) or an advanced direct oil-cooling circuit for effective thermal management.

5. Performance Requirements and Automotive Characteristics

Unlike general industrial motors, automotive drive motors must satisfy significantly more demanding operating criteria:

High Power and Torque Density: Delivering maximum power and torque output within constrained packaging dimensions and weight limits.
High Efficiency and Broad Operating Range: Sustaining high efficiency across the majority of real-world driving cycles to maximise electric range.
Wide Speed Range and High Low-End Torque: Ensuring responsive performance across diverse driving conditions, including stop-and-go traffic, brisk acceleration, and steep hill climbs.
Stringent Safety and Reliability: Built to operate reliably within high-voltage architectures under harsh conditions.
Low NVH: Minimising noise and vibration to ensure superior cabin quietness and driving refinement.

6. Key Technologies and Industry Trends

Electric drive motor development is advancing rapidly towards higher power density, greater system integration, and maximum efficiency.

Hairpin / Flat-Wire Winding: Replacing conventional round enamelled wire with rectangular flat copper wire. This is one of the most critical trends in the industry, with the adoption rate in mainstream models exceeding 80% by 2026. It substantially increases the slot fill factor, boosting both power density and heat dissipation.
Direct Oil-Cooling Technology: Spraying dielectric cooling oil directly onto heat-generating components (especially stator end-windings and the rotor). Its thermal dissipation efficiency far surpasses traditional water jackets, making it crucial for achieving higher continuous power density.
Ultra-High Rotational Speeds: Elevating motor rpm enables higher power output without increasing physical dimensions. For instance, BYD debuted the world's first mass-produced 30,000 rpm drive motor in 2025.
Multi-in-One Electric Drive Integration: Deeply integrating the motor, reduction gearbox, and inverter/motor controller into a single unit to save space, shed weight, and lower overall production costs.
SiC (Silicon Carbide) Power Electronics: Utilising wide-bandgap silicon carbide semiconductor power modules in motor controllers substantially minimises energy losses and boosts powertrain efficiency.

7. Summary

The drive motor serves as the "muscle" of an electrified vehicle, directly governing performance, energy consumption, and driving refinement. Currently, the permanent magnet synchronous motor (PMSM) has established itself as the undisputed mainstream choice due to its high efficiency and power density. Looking ahead, innovations including hairpin flat-wire windings, direct oil cooling, ultra-high speed designs, and multi-in-one integration will continue driving electric propulsion systems towards greater efficiency, lighter weight, and superior performance.