Center Axle Disconnect (CAD) systems are commonly used on part-time four-wheel drive (4WD) internal combustion engine (ICE) vehicles. These systems allow drivers to enjoy the extra traction that 4WD provides, when it is needed, as well as the fuel efficiency of two-wheel drive (2WD) for normal driving. Electric vehicle drivetrain designers are using a similar concept called disconnecting driveline technology to meet some of the unique demands of EVs, which include reducing energy consumption.
The electric motors used in EVs put out a tremendous amount of torque. Using 4WD during vehicle acceleration reduces the stress on the tires and helps the vehicle reach cruising speed quickly and efficiently. Depending on the drivetrain architecture, powering both the front and rear axles can be less energy efficient. On some EV drivetrains, disconnecting the front wheels from the drivetrain during cruising can reduce energy consumption and help maximize range.
On a part-time 4WD ICE vehicle, the CAD uses a shift fork that moves a collar to either engage or disengage the front outer axle shaft from the front inner axle shaft, allowing either 2WD or 4WD operation. Some of these systems, especially on older vehicles, are vacuum operated, but many late-model vehicles have systems that use an actuator driven by a small electric motor and gears.