Asynchronous Motor

An automotive asynchronous motor (or induction motor) is an alternating current (AC) motor widely utilised in new energy vehicle powertrain systems. Its operating principle is based on electromagnetic induction: when three-phase AC power is supplied to the stator windings, a rotating magnetic field is generated. This rotating magnetic field cuts across the rotor windings, inducing currents and generating an induced magnetic field within the rotor. The interaction between both magnetic fields drives the rotor to rotate in pursuit of the stator's magnetic field. Because the rotor speed is always slightly lower than the synchronous speed of the rotating magnetic field (a phenomenon known as "slip"), it is termed an asynchronous motor.

Core Operating Principles and Technical Characteristics

The core advantages of an asynchronous motor lie in "slip generation via electromagnetic induction, a permanent magnet-free design, and a broad high-speed operating range":

Electromagnetic induction and slip operation: The rotor typically adopts a squirrel-cage structure (utilising aluminium or copper conductor bars shorted by end rings) and contains no permanent magnets. Torque is generated only when relative motion (slip) exists between the rotor and the stator magnetic field, allowing the rotor to cut magnetic flux lines and induce current.

Drag-free physical characteristics and resistance to high-speed demagnetisation: Because the rotor contains no permanent magnets, the motor does not produce the "back-EMF drag torque" typical of permanent magnet motors during high-speed coasting or unpowered conditions. Furthermore, it is entirely free from the risk of high-temperature demagnetisation, making it ideal for sustained high-speed cruising.

Application Scenarios and Market Value

Asynchronous motors are widely deployed in battery electric vehicles (BEVs) where high-speed performance, cost control, and high-output rear-axle auxiliary drive capabilities are required (such as the rear drive unit in early Tesla models and the secondary drive units in selected high-performance dual-motor AWD models).

Characterised by lower manufacturing costs, zero reliance on rare-earth materials, outstanding high-speed efficiency, and strong overload tolerance, this technology serves as a key powertrain solution for balancing EV production costs with top-speed performance.

Safety Specifications and Physical Limitations

It is strictly prohibited to attempt high-voltage charging or high-current driving if the motor has suffered severe water ingress or has aged, compromised internal insulation. Doing so can easily trigger internal short circuits, burn out stator windings, or cause hazardous high-voltage electrical leakage. 

Due consideration must be given to the inherent physical characteristics of asynchronous motors, namely their relatively lower energy conversion efficiency and higher heat generation during low-speed start-offs or frequent stop-and-go driving conditions. Compared to permanent magnet synchronous motors (PMSM), their energy efficiency in congested urban traffic is typically lower, placing greater demands on the heat dissipation performance of the vehicle's cooling system.