Bogie



A bogie is a wheeled wagon or trolley. In mechanics terms, a bogie is a chassis or framework carrying wheels, attached to a vehicle. It can be fixed in place, as on a cargo truck, mounted on a swivel, as on a train carriage or locomotive, or sprung as in the suspension of a caterpillar tracked vehicle.

Railway


A bogie in the UK, or a wheel truck, or simply truck in the USA, is a structure underneath a train to which axles (and, hence, wheels) are attached through bearings.

Bogies serve a number of purposes:
 * To support the rail vehicle body
 * To run stably on both straight and curved track
 * Ensure ride comfort by absorbing vibration, and minimizing centrifugal forces when the train runs on curves at high speed
 * Minimize generation of track irregularities and rail abrasion

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

Most bogies have two axles as it is the simplest design, but some cars designed for extremely heavy loads have been built with up to five 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, however, 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, step-less entry low floor trains.

Key components of a bogie include:
 * The bogie frame itself.
 * 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 a bearings and wheel at each end.
 * Axle box suspension to 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 an electrically powered traction motors or a hydraulically powered torque converter.

The connections of the bogie with the rail vehicle allows 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.

The B1 Bogie
The BR Mark 1 coach brought into production in 1950 utilised the B1 Bogie, which was rated to run at 90 mph. The wheels were cast as a one-piece item in a pair with their axle. The simple design involved the bogie resting on four leaf springs (one spring per wheel) which in turn were connected to the axles. The leaf springs were designed to absorb any movement or resonance and to have a damping effect to benefit ride quality.

Each spring was connected to the outermost edge of the axle by means of a roller bearing contained in oil filled axle box. The oil in these boxes had to be topped up at regular maintenance times to avoid the bearing running hot and from seizing.

The Commonwealth Bogie


The SKF or Timken manufactured Commonwealth bogie was introduced in the late 1950’s for all BR MK1 vehicles. The bogie was a heavy cast steel design weighing 6.75 ton with fitted sealed roller bearings on the axle ends, avoiding the need to maintain axle box oil levels.

The leaf springs were replaced with coil type springs (one per wheel) running vertically rather than horizontally. The advanced design gave a superior ride quality to the B1, being rated for 160 km/h / 100 mph.

The side frame of the bogie was usually of bar construction, with simple horn guides attached, allowing the axleboxes vertical movements between them. The axleboxes had a cast steel equaliser beam or bar resting on them. The bar had two steel coil springs placed on it and the bogie frame rested on the springs. The effect was to allow the bar to act as a compensating lever between the two axles and to use both springs to soften shocks from either axle. The bogie had a conventional bolster suspension with swing links carrying a spring plank.

The B4 Bogie
The B4 bogie was introduced in 1963. It was a fabricated steel design as versus cast iron and was hence 1.55 tons lighter than the Commonwealth, weighing in at 5.2 tons. It also had a speed rating of 160 km/h / 100 mph.

Axle/spring connection was again with fitted roller bearings. However, now two coil springs rather than one were fitted per wheel.

Only a very small amount of MK1 stock was fitted with the B4 bogie from new, it being used on the MK1 only to replace worn out B1 bogies. The BR MK2 coach however carried the B4 bogies from new. A heavier duty version, the B5, was standard on Southern Region Mk1 based EMUs from the 1960s onwards. Some of the B4 fitted Mk2s, as well as many B4 fitted Mk1 BGs were allowed to run at 110 mph with extra maintenance, particularly of the wheel profile, and more frequent exams.

The BT10 Bogie
The BT10 bogie was introduced on the British Rail Mark 3 coach in the 1970's. Each wheel is separately connected to the bogie by a swing-arm axle.

There is dual suspension:
 * primary suspension via a coil spring and damper mounted on each axle.
 * secondary suspension via two air springs mounted on the pivot plank. This is connected to the bogie by pendulum links.  A constant coach height is maintained by air valves.

Tramway


Tram bogies are much simpler in design because of lighter axle load, this and tighter curves that are found on tramways means that tram bogies almost never have more than two axles. Furthermore, some tramways also have steeper gradients and vertical as well as horizontal curves, which means that 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 non-pivoting bogies and many tramway enthusiasts see this as a retrograde step.

Tracked vehicles
Some tanks and other tracked vehicles have bogies as external suspension components (see armoured fighting vehicle suspension). This type of bogie usually has two or more road wheels and some type of sprung suspension to smooth the ride across rough terrain. Bogie suspensions keep much of their components on the outside of the vehicle, saving internal space. Although vulnerable to antitank fire, they can often be repaired or replaced in the field.

Hybrid systems


Rubber-tyred metro trains utilise a specialised version of railway bogies. As well as the standard running wheels (rubber instead of steel) there are additional horizontal guide wheels in front of and behind the running wheels.