Secondary-Axle Disconnect Clutch
A secondary-axle disconnect clutch is a coupling that separates an EV’s normally supplementary drive axle from the wheels when its torque is not needed.
How it works
Turning an electric motor’s torque command to zero does not necessarily stop it, its gears, bearings, seals, and lubricant from rotating with the wheels. A disconnect can open the mechanical path and reduce some of those drag losses. Which parts stop rotating depends on where the coupling sits in the drive unit.
The system must reconnect quickly and synchronize rotating parts before torque returns. The clutch, actuator, sensors, and controls add mass, cost, engagement transitions, and another durability requirement. Energy savings therefore depend on the motor type, disconnect position, vehicle duty cycle, and how often the secondary axle is required.
For the wider multi-motor efficiency and control context, see Multi-Motor EV Architectures.