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A bogie (// BOH-ghee) or truck is a wheeled wagon or trolley. In mechanics terms, a bogie is a chassis or framework carrying wheels, attached to a vehicle, thus serving as a modular subassembly of wheels and axles. Bogies take various forms in various modes of transport. A bogie may remain normally attached (as on a railway carriage/car or locomotive, or on a semi-trailer) or be quickly detachable (as the dolly in a road train); it may contain a suspension within it (as most rail and trucking bogies do), or be solid and in turn be suspended (as most bogies of tracked vehicles are); it may be mounted on a swivel, as on a railway carriage/car or locomotive, or additionally jointed and sprung (as in the landing gear of an airliner).
A bogie in the UK, or a railroad truck, wheel truck, or simply truck in North America, is a structure underneath a train to which axles (and, hence, wheels) are attached through bearings. In Indian English, bogie may also refer to an entire railway carriage.
Bogies serve a number of purposes:
Usually, two bogies are fitted to each carriage, wagon or locomotive, one at each end. An alternate configuration often is used in articulated vehicles, which places the bogies (often jacobs bogies) under the connection between the carriages or wagons.
Most bogies 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. 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 bogie include:
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.
The British Railways Mark 1 coach brought into production in 1950 used the BR1 bogie, which was rated to run at 90 mph (145 km/h). 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 a roller bearing contained in oil-filled axle box. The oil had to be topped up at regular maintenance times to avoid the bearing running hot and seizing.
There was also a heavy-duty version designated BR2.
The Commonwealth bogie, manufactured by the English Steel Corporation under licence from the Commonwealth Steel Company in Illinois, USA. Fitted with SKF or Timken bearings, it was introduced in the late 1950s for all BR Mark 1 vehicles. It was a heavy, cast-steel design weighing about 6.5 long tons (6.6 t), with sealed roller bearings on the axle ends, avoiding the need to maintain axle box oil levels.
The leaf springs were replaced by coil springs (one per wheel) running vertically rather than horizontally. The advanced design gave a better ride quality than the BR1, being rated for 100 miles per hour (160 km/h).
The side frame of the bogie was usually of bar construction, with simple horn guides attached, allowing the axle boxes vertical movements between them. The axle boxes 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 was introduced in 1963. It was a fabricated steel design versus cast iron and was lighter than the Commonwealth, weighing in at 5 long tons (5.08 t; 5.60 short tons). It also had a speed rating of 100 miles per hour (160 km/h).
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 number of Mark 1 stock was fitted with the B4 bogie from new, it being used on the Mark 1 only to replace worn BR1 bogies. The British Rail Mark 2 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 Mark 1 catering cars had mixed bogies—a B5 under the kitchen end, and a B4 under the seating end. Some of the B4-fitted Mark 2s, as well as many B4-fitted Mark 1 BGs were allowed to run at 110 miles per hour (180 km/h) with extra maintenance, particularly of the wheel profile, and more frequent exams.
The BT10 bogie was introduced on the British Rail Mark 3 coach in the 1970s. Each wheel is separately connected to the bogie by a swing-arm axle.
There is dual suspension:
On a steam locomotive, the leading wheels and trailing wheels may be mounted on bogies. Articulated locomotives (e.g. the Fairlie) have power bogies similar to those on diesel and electric locomotives.
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 and 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. The only 100% low-floor tram with pivoting bogies - Škoda ForCity - uses the Jacobs bogie.
In the past, many different types of bogie (truck) have been used under tramcars, e.g. "Brill", "Peckham" and "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.
The retractable stadium roof on Toronto's Roger's 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.
The Cleminson system is not a true bogie, but serves a similar purpose. It was based on a patent of 1883 by James Cleminson, 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.
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.
In trucking, a bogie is the subassembly of axles and wheels that supports a semi-trailer, whether permanently attached to the frame (as on a single trailer) or making up the dolly that can be hitched and unhitched as needed when hitching up a second or third semi-trailer (as when pulling doubles or triples).
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