 | This articledoes notcite anysources. Please helpimprove this article byadding citations to reliable sources. Unsourced material may be challenged andremoved. Find sources: "Cab unit" – news ·newspapers ·books ·scholar ·JSTOR(August 2009) (Learn how and when to remove this message) |
In North Americanrailroad terminology, acab unit is a railroadlocomotive with its own cab and controls.
"Carbody unit" is a related term, which may be either a cabless booster unit controlled from a linked cab unit, or a cab unit that contains its own controls.
With both body styles, abridge-trussdesign framework is used to make the body a structural element of the locomotive. The body extends the full width and length of the locomotive. The service walkways are inside the body.
Carbody units, gaining rigidity from the body trusswork, require less structural weight to achieve rigidity than do locomotives with non-structural bodies. For that reason, carbody construction was favored to increase thepower-to-weight ratio for early diesel locomotives, before the power available with diesel technology was increased. Recent years have seen carbody constructionrevived in the quest for greaterfuel efficiency with passenger locomotives.
The full-width body gives a carbody cab unit poor rear visibility compared with ahood unit. For that reason, cab or carbody units are mostly used in situations where rear visibility is not important, such as power for through freight andpassenger trains. Cab and carbody units are also more aerodynamic than hood units, and pulled many of thestreamliner trains.
A cab unit is a carbody unit with a drivingcab (or crew compartment). Thus, a cab unit is also always anA unit (a locomotive with a cab). By contrast, a carbody unit can be either an A unit, or aB unit (a locomotive without a cab).
Acowl unit is an adaptation of thehood unit design with a full-width body. Despite some visual similarities, cowl units are actually very different from cab units. All structural support on a cowl unit is provided by the frame of the locomotive, rather than in the body as with a cab unit. This allows manufacturers to cheaply and easily create full-width locomotives from their hood unit designs by simply adding cowling. Cowl units were first introduced as a special order from the Santa Fe, which wanted a sleeker design for its passenger equipped hood units. Although the first cowl units (such as theEMD FP45 and theGE U30CG) were meant for passenger service, EMD would later offer freight-only derivatives starting with theF45.
Cab units were not generally used in Great Britain. The traditional makers continued to use heavyweight frames andcowl units instead.
The LMS twins 10000 and 10001 used the design and later locomotive types such as theBritish Rail Class 37, andBritish Rail Class 40 utilised cab units but the term "cab unit" is not used in Britain. The Class 37 and Class 40, like most British diesel and electric locomotives, has a cab at each end.
 | This diesel locomotive-related article is astub. You can help Wikipedia byexpanding it. |