Electric Rear Axle Drive Units

An electric rear axle drive unit — sometimes called an eRAD or eAxle — is a complete electric powertrain in a box. It contains an electric motor, a reduction gear set, a differential, and sometimes the power electronics (inverter), all integrated into a single unit that bolts to the rear subframe. It adds all-wheel drive to a front-wheel-drive platform without needing a driveshaft, transfer case, or traditional rear differential.

Plug-in hybrid vehicles (PHEVs) are the most common application. The front wheels are driven by the gasoline engine through a conventional transmission. The rear wheels are driven by the eRAD using power from the hybrid battery. The vehicle can drive in FWD (engine only), RWD (electric only on the rear), or AWD (both together). The ECM coordinates both power sources seamlessly. The driver does not need to select a mode — the system chooses based on driving conditions, battery charge level, and traction needs.

Volvo uses an electric rear axle on their T8 PHEV models — the front is driven by a turbocharged and supercharged four-cylinder, and the rear is driven by an electric motor. BMW uses eAxle units on their iPerformance PHEV models and on the iX and i4 electric vehicles. Hyundai and Kia use them on some PHEV configurations. Many dedicated EV platforms use front and rear eAxle units as the primary propulsion — the Tesla Model 3 Performance, Hyundai Ioniq 5, and Ford Mustang Mach-E GT all use a dual-eAxle setup.

The eRAD is a sealed unit — there is no traditional gear oil service like a conventional differential, though some do have a drain plug for the reduction gear lubricant. Because it contains an electric motor, it is part of the high-voltage system and requires HV safety precautions for service. Cooling is important — most eRADs have a dedicated cooling circuit with coolant lines running to them. Check for coolant leaks at the fittings. Common failures include cooling system issues (motor overheating), bearing noise from the reduction gears (similar to a conventional differential whine), and inverter faults if the power electronics are integrated into the unit.