Bogie

Bogies allow the wheelsets to more closely follow the direction of the rails when travelling around a curve in the railroad.

Displacements of a bogie

Bogies serve a number of purposes:[6]

• Support of the rail vehicle body
• Stability on both straight and curved track
• Improve ride quality 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

Usually, two bogies are fitted to each carriage, wagon or locomotive, one at each end. Another configuration is often used in articulated vehicles, which places the bogies (often Jacobs bogies) under the connection between the carriages or wagons.

Most bogies have two axles,[6] but some cars designed for heavy loads have more axles per bogie. 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 bilevel rail car to increase interior space while staying within height restrictions, or in easy-access, stepless-entry, low-floor trains.

A diagram of an American-style truck showing the names of its parts and showing the journal boxes to be integral parts of the side frame.[7][8][9] The journal boxes house plain bearings.

Key components of a bogie include:[6]

• 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, leaf springs and rubber airbags.
• At least one wheelset, composed of an axle with bearings and a wheel at each end.
• The bolster, the main crossmember, connected to the bogie frame through the secondary suspension. The railway car is supported at the pivot point on the bolster.
• 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 with a single speed gearbox or a hydraulically powered torque converter.

The connections of the 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.[6]

Modern diesel and electric locomotives are mounted on bogies. Those commonly used in North America include Type A, Blomberg, HT-C and Flexicoil trucks.[10]

On a steam locomotive, the leading and trailing wheels may be mounted on bogies like Bissel trucks (also known as pony trucks). Articulated locomotives (e.g. Fairlie, Garratt or Mallet locomotives) have power bogies similar to those on diesel and electric locomotives.

A rollbock is a specialized type of bogie that is inserted under the wheels of a rail wagon/car, usually to convert for another track gauge. Transporter wagons carry the same concept to the level of a flatcar specialized to take other cars as its load.

In archbar or diamond frame bogies, the side frames are fabricated rather than cast.

• Archbar bogie pool
• 
  Japanese archbar bogie with axleboxes
• 
  Diamond frame bogie, elliptical springs and American style journal boxes
• 
  Diamond frame bogie, coil springs and journal boxes
• 
  Archbar bogie with journal bearings in American style journal boxes, as used on some steam locomotive tenders. Archbar bogies (trucks) were also used on freight cars.

Side view of a SEPTA K-Car bogie

Tram bogies are much simpler in design because of their axle load, and the tighter curves found on tramways mean tram bogies almost never have more than two axles. Furthermore, some tramways have steeper gradients and vertical as well as horizontal curves, which means tram bogies often need to pivot on the horizontal axis, as well.

Some articulated trams have bogies located under articulations, a setup referred to as a Jacobs bogie. Often, low-floor trams are fitted with nonpivoting bogies; many tramway enthusiasts see this as a retrograde step, as it leads to more wear of both track and wheels and also significantly reduces the speed at which a tram can round a curve.[11]

In the past, many different types of bogie (truck) have been used under tramcars (e.g. Brill, Peckham, maximum traction). A maximum traction truck has one driving axle with large wheels and one nondriving axle with smaller wheels. The bogie pivot is located off-centre, so more than half the weight rests on the driving axle.

Mockup of the pneumatic bogie system of an MP 89 carriage used on the Meteor metro, showing the two special wheelsets[12]

The retractable stadium roof on Toronto's Rogers Centre used modified off-the-shelf train bogies on a circular rail. The system was chosen for its proven reliability.

Rubber-tyred metro trains use a specialised version of railway bogies. Special flanged steel wheels are behind the rubber-tired running wheels, with additional horizontal guide wheels in front of and behind the running wheels, as well. The unusually large flanges on the steel wheels guide the bogie through standard railroad switches, and in addition keep the train from derailing in case the tires deflate.[12]

To overcome breaks of gauge some bogies are being fitted with variable gauge axles (VGA) so that they can operate on two different gauges. These include the SUW 2000 system from ZNTK Poznań.

The Cleminson system is not a true bogie, but serves a similar purpose. It was based on a patent of 1883 by James Cleminson,[13] and was once popular on narrow-gauge rolling stock, e.g. on the Isle of Man and Manx Northern Railways. The vehicle would have three axles and the outer two could pivot to adapt to curvature of the track. The pivoting was controlled by levers attached to the third (centre) axle, which could slide sideways.[14]