American type bogie serve a number of purposes:
Support of the rail vehicle body.
Stability on both straight and curved track.
Ensuring ride comfort by absorbing vibration and minimizing the impact of centrifugal forces when the train runs on curves at high speed.
Minimizing generation of track irregularities and rail abrasion
Most American type bogie have two axles, but some cars designed for extremely heavy loads have been built with up to five axles per bogie, and single axle bogies can be found owing to their simplicity.[citation needed] Heavy-duty cars may have more than two bogies using span bolsters to equalize the load and connect the bogies to the cars.
Usually, the train floor is at a level above the bogies, but the floor of the car may be lower between bogies, such as for a double decker train to increase interior space while staying within height restrictions, or in easy-access, stepless-entry, low-floor trains.
Key components of a American type bogie include:
The bogie frame: This can be of inside frame type where the main frame and bearings are between the wheels, or (more commonly) of outside frame type where the main frame and bearings are outside the wheels.
Suspension to absorb shocks between the bogie frame and the rail vehicle body: Common types are coil springs, or rubber airbags.
At least one wheelset, composed of an axle with bearings and a wheel at each end
Axle box suspensions absorb shocks between the axle bearings and the bogie frame. The axle box suspension usually consists of a spring between the bogie frame and axle bearings to permit up-and-down movement, and sliders to prevent lateral movement. A more modern design uses solid rubber springs.
Brake equipment: Two main types are used: brake shoes that are pressed against the tread of the wheel, and disc brakes and pads.
In powered vehicles, some form of transmission, usually electrically powered traction motors or a hydraulically powered torque converter
The connections of the
American type bogie with the rail vehicle allow a certain degree of rotational movement around a vertical axis pivot (bolster), with side bearers preventing excessive movement. More modern, bolsterless bogie designs omit these features, instead taking advantage of the sideways movement of the suspension to permit rotational movement.
