Essieux

Essieu is the French term for an axle, a central shaft that either rotates with a wheel or serves as a support beam for a wheelset. In road vehicles, the axle carries the vehicle’s load and, when it is a driven axle, transmits torque from the drivetrain to the wheels. Axles may be rigid (a single beam spanning between the wheels) or split into separate hubs, allowing independent mounting in some suspension configurations. A driven (live) axle includes gears and a differential to distribute power to one or more wheels; a dead (non-driven) axle merely carries load and houses bearings.

The axle works in conjunction with bearings and hubs; the wheels are mounted on the ends of the axle, and the axle either passes through a hub or carries a wheel hub. Suspension systems connect to the axle to absorb road irregularities, using leaf springs, coil springs, torsion bars, or air springs. Maintenance focuses on bearing lubrication, inspection for wear, bending, cracks, and proper alignment.

In rail transport, essieux are the axles inside wheelsets. Each wheel is mounted on an end of the axle, and multiple axles are often mounted in pairs on a bogie. Rails impose significant radial and lateral loads, so axle integrity and bearing condition are critical for ride quality and safety.

Beyond transportation, axles appear in various machines and trailers, where design choices depend on load, speed, and duty cycle.