中央传动及转向离合器设计-外文资料

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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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摘要：

IntroductiontoLocmotiveAlocomotiveisarailwayvehiclethatprovidesthemotivepowerforatrain,andhasnohydetachedfromtheirtrains,areknownaspowercars.Traditionally,locomotivehualtheirtrains.Increasinglycommonthesedaysinpassengerserviceispush-pulloperation,wherethelocomotivepushthetrainsinonedirectionandareco...

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