bogie

A bogie is a chassis or framework that carries a pair of wheels on a rail vehicle, such as a train car, tram, or locomotive. It is the wheelset assembly that supports the vehicle’s body, transfers loads to the track, and provides stability and ride quality. A bogie typically consists of a rigid frame, two axles with paired wheels, bearings, and a suspension system, and it may include traction motors on driving bogies.

Most bogies house both the wheels and the suspension that cushions the ride. The wheels are mounted on axles within the bogie frame and rotate freely on bearings. Suspension systems, which can include coil springs, leaf springs, air springs, and dampers, absorb vertical and lateral motions induced by track irregularities. In powered or driving bogies, traction motors or other drive components are mounted to transmit power to the wheels.

Bogies come in various configurations. The common two-axle bogie is widely used on passenger cars and light rail vehicles, while three-axle bogies appear on some heavy freight cars and specialized tramcars. Bogies may be designed to steer or to resist hunting oscillations at speed; radial or self-steering bogies are used to reduce wheel and track wear on curves. Bogie designs also vary in materials (steel, cast or welded frames) and in the arrangement of primary and secondary suspensions.

In practice, bogies are attached to the vehicle body at a bogie mounting point, allowing the bogie to rotate relative to the car body as the vehicle traverses track imperfections. The use of bogies improves stability, handling, and passenger comfort while distributing loads and reducing track wear. Bogies are central to many rail vehicles, including passenger coaches, freight wagons, and trams.