中央传动及转向离合器设计-外文资料
Introduction to Locmotive
A locomotive is a railway vehicle that provides the motive power for a train,and
has nohy detached from their trains, are known as power cars.
Traditionally,locomotive hual their trains. Increasingly common these days in
passenger service is push-pull operation,where the locomotive push the trains in one
direction and are controled from a control cab at the opposite end of the train in the
other.
Beniefits of locomotives
There are many reasons why the motive power for trains has been traditonally
isolated in a locmotive,rather than is self-propelled vehicles.these include:
Ease of maintenance – it is easier to maintain one locomotive than many self-
propelled cars.
Safety – it is often safer to locate the train’s power system away from passenger.
This was particularly the case for the steam locomtive,but still has some relevance.
Easy replacement of motive power – should the locomotive break down, it is
easy to replace it with a new one . Failure of the motive power unit does not require
taking the whoole train out of service.
Efficiency – idle trains do not waste expensive motive power resources. Separate
locomotives mean that the costly motive power assets can be moved around as
needed.
Obsolescence cycles – separating the motive power from the payload-hauling
cars means that either can be replaced without affecting the other. At some times,
locomotive have become obsolete when their cars are not, or vice versa..
Electric Locomotives
The electric locomotive is supplied externally with electric power, either through
an overhead pickup or through a third-rail. While the cost of electrifying track is
rather high, electric trains and locomotives are significantly cheaper to run than diesel
ones, and are capable of superior acceleration as well as regenerative braking, making
them ideal for passenger service in densely populated areas. Almost all high speed
train systems(e.g..IEC,TGV, bullet train) use electric power, because the power
needed for such performance is not easily carried on board. Fot example the most
powerfu electric locomotives that are used today on the channel tunnel freight
services use 7Mwatts of power.
The first known electric locomotive was buit by a Scotsman, Roert Davidson of
Aberdeen in 1837 and was powered by galvanic cells.
Modern electric locomotive range from small battery-powered machines for use
in mines to large main-line locomotives of 6,000 horsepower(4.5MW) or more.
In reality most modern locomotives are electricaly driven. Pure electric
locomotives take their electrical supply from an external source while diesel-electric
locomotives carry their own generating station.
Main line electric locomotives first appeared at the beginning of the 20th
century.The reason for their introduction was the problem of smoke, especially in
tunnlels caused by steam locomotives. In the UK this was the London underground
system while in the USA, it was under river tunnles and needs to eliminate smoke in
built up areas.
Early electric locomotives all relied on external power sourcing. Once up and
running they tend to be reliable and efficint, but the supply infrastructure is a large
capital expense that does require ongoing maintenance. For this reason only heavily
used lines could justify electrification. For suburban lines the reduction in pollution
from steam locomotives was a benefit all were aware ofl
The world speed record for a wheeled train was set in 1990 ba a French TGV
which reached a speed of 515.3km/h (320mph).
While recently designed electrififed railway systems invariably operate on
alternating current, many existing direct current sytems are still in use –e.g. in South
Africa,Spain,and the United Kingdom(750v and 1500v); Netherlands(1500v); Belgiu,
Italy, Poland (3000 v), and the cites of Mumbia and Chicagio (which will be switched
to AC by 2025).
Early locomotives came in a variety of forms. Generally they were designed to
run off the supplied current. so locomotives with a direct current (DC) supply had DC
motors while a alterntating current(AC) supplied locomotives with AC motors. AC
can be either single or three phase. While the former requies two wire supply, one
overhead the other being the track, three phase require three supply wire.Three phase
locomotives therefore had two overhead supplies,the track being the third.
DC supplies were either overhead or by means of a track level supply, commonly
called the third rail.
AC traction motors tended to be smaller than DC motors. This often meant
electric locomotives with steam engine type cranks. DC motors could be smaller and
set up to drive the axles.usually through a gear ,but in some early examples by being
part of the axle. Even so, some notable DC electric locomotives had large DC motors
driving large driving wheels.
One possibility with electric locomotives is that the motor can be used as a
generator during braking, feeding electricity back into the supply system; this is called
regenerative barking. This is not a new idea, it was one reason for the adoption by
some railways of 3 phase AC suppies. Especially in mountainous aresa where the
locomotive going down would generate much of the suppy for a locomotive going up.
The Swiss railway uses the system; three modern locomotives heading downwards
generate enough power to power a single locomotive in its upward journey.
Today all eclctric locomotives tend to have drive motors close to the axles,
although some still have the motor in the body driving the wheels through internal
drive shafts.
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IntroductiontoLocmotiveAlocomotiveisarailwayvehiclethatprovidesthemotivepowerforatrain,andhasnohydetachedfromtheirtrains,areknownaspowercars.Traditionally,locomotivehualtheirtrains.Increasinglycommonthesedaysinpassengerserviceispush-pulloperation,wherethelocomotivepushthetrainsinonedirectionandareco...
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时间：2024-02-04
