Locomotive

Locomotive

High-Speed Train

The French high-speed electric train, the Train à Grande Vitesse, travels up to 320 km/h (200 mph).

Locomotive, any type of self-propelled vehicle used by railroads to pull or push other types of rolling stock, including passenger, freight, and work cars. The locomotive differs from other kinds of self-propelled railroad vehicles in that it is used solely as a power unit and is not designed for carrying passengers or freight, as are trolley cars and some electric cars.

II

EARLY HISTORY

Rocket Steam Locomotive

George Stephenson, a self-taught British inventor and engineer, designed the Rocket, an early steam locomotive. In 1829 the Rocket demonstrated that steam locomotion was possible.

The first practical locomotive was constructed in England in 1804 by the British engineer and inventor Richard Trevithick. This locomotive, with four driving wheels, had smooth wheels operating on smooth metal rails; its success proved that sufficient traction could be obtained without using gear wheels and a cogged or toothed track. Equally important, the Trevithick locomotive exhausted its steam into the smokestack of the engine's firebox; this provided a forced draft for the fire in the firebox and was employed on all subsequent steam locomotives.

After the successful trials of the Trevithick locomotive, a number of moderately successful locomotives were built in England, primarily for use in mining. Not until 1829 was a locomotive developed for use in a railway carrying both passengers and freight. In that year the Rocket, a locomotive designed by the British engineer George Stephenson, won a competition sponsored by the Liverpool and Manchester Railroad. The Rocket pulled a load of three times its own weight at the rate of 20 km/h (12.5 mph) and hauled a coach filled with passengers at 39 km/h (24 mph). This performance stimulated the building of other locomotives and the extension of railroad lines.

Also in 1829, the first locomotive to operate in the western hemisphere was given a trial at Honesdale, Pennsylvania. This locomotive, the Stourbridge Lion, had been built in England for the Delaware and Hudson Canal Company. In the following year, the first locomotives built in the U.S. were put into operation: The Best Friend was operated by the South Carolina Canal and Railroad Company, and the Peter Cooper, also known as the Tom Thumb, was operated by the Baltimore and Ohio Railroad Company. The Peter Cooper was little more than an enlarged model, but it outperformed the Rocket. Old Ironsides, built by the American industrialist Matthias William Baldwin for the Philadelphia, Germantown & Norristown Railroad Company, was a four-wheeled locomotive weighing about 5 metric tons. It was given its first road tests in 1832 and put into service almost immediately.

Many mechanical improvements were subsequently made, both in England and in the U.S. These two countries have generally paralleled each other in locomotive development. In 1831 the swiveling locomotive truck, now commonly called a bogie, carrying a set of supporting wheels supplanted the fixed bogie; in 1836 the outside coupling of pairs of driving wheels was introduced; and in 1837 counterbalances were applied to driving wheels and other parts to smooth the operation of the engine. The first locomotive with six driving wheels and a four-wheeled leading bogie, often called a ten-wheeler, appeared in 1847. In 1863 the Mogul type locomotive, with six driving wheels and a two-wheel leading bogie, came into use; and in 1867 the first Consolidation type locomotive with eight coupled drivers and a two-wheeled leading bogie was built. These heavy-hauling types supplemented the standard, so-called American type locomotive in use for the previous quarter century. The American type, equipped with four driving wheels and a four-wheel leading bogie, was excellent for ordinary service but was not adapted to pulling long and heavy freight trains over severe grades.

III

STEAM LOCOMOTIVES

Steam Locomotive

Engine No. 44, a Baldwin 2-8-0 steam locomotive engine built in 1921, has two wheels on the leading truck, eight driving wheels, and no trailing truck. The engine works on the Georgetown Loop Railroad and formerly ran in Central America. Diesel-electric locomotives began to replace steam locomotives in the 1930s and 1940s.

Steam locomotives can be classified in a number of ways. The most generally used classification, however, is based on the number and arrangement of wheels with which the engine is equipped. This classification gives the number of wheels on the leading bogie, the number of driving wheels, and the number of wheels on the trailing bogie. Thus, a 2-4-0 locomotive is one with a two-wheel leading bogie, four driving wheels, and no trailing bogie. Many locomotives are also given special type names. Switch engines, used in railroad yards, are usually of the 0-6-0 or 0-8-0 type. Passenger locomotives include the American, 4-4-0; the Northern, 4-8-4; the Atlantic, 4-4-2; the Pacific, 4-6-2; and the Mountain 4-8-2. Freight locomotives include the Mogul, 2-6-0; the Consolidation, 2-8-0; the Decapod, 2-10-0; the Mikado, 2-8-2; and the Santa Fe, 2-10-2. A special type of locomotive used for heavy freight hauling is the articulated, or Mallet, locomotive, which is made up of two or more separate engines joined together, each with its own set of driving wheels. Among the various Mallet types are 0-6-6-0, 0-8-8-0, 2-6-6-2, 2-8-8-2, 2-10-10-2, and 2-8-8-8-2.

Until about 1940, steam engines provided the driving power of most locomotives used on U.S. railroads. Subsequently, the steam locomotive became largely obsolete. By the late 1980s, only a few of them, such as those on the narrow-gage tourist routes of Colorado, were operating in the U.S.

IV

DIESEL-ELECTRIC LOCOMOTIVES

Diesel-Electric Locomotive

This diesel-electric locomotive hauls a passenger train. Diesel engines spin generators that produce electricity to power the locomotive. They are more efficient than steam locomotives and do not require the overhead power lines needed for electric engines.

Among important locomotives developed in the 20th century are the electric locomotive, which picks up electrical power from an overhead wire or a third rail laid beside the track, and the diesel-electric locomotive. In diesel-electric locomotives, known popularly as diesels, diesel engines are used to drive generators or alternators connected to solid-state rectifiers that power electric motors geared to the axles. This type of locomotive eliminates the need for expensive power-transmission lines. Compared to the steam locomotive, it has a greater availability, meaning a higher average of productive hours per day, because it does not require frequent stops for water, fuel, and other servicing. Other advantages over the steam engine include its relative efficiency in converting fuel into available energy and its ability to develop a much higher proportion of its maximum pulling power at low speeds. Also, while steam locomotives require an engineman and fireman for each locomotive, diesel-electrics can be operated as multiple units by one individual, resulting in longer trains and fewer employees. See also Internal-Combustion Engine.

Diesel-electric locomotives were brought into service in the U.S. in 1925 for yard switching. The first passenger-train diesel unit was put into operation in 1934, and the first unit specifically designed for freight service came into use in 1941. Before World War II, the number of diesel units in service totaled about 800, as against more than 40,000 steam locomotives. In the late 1970s more than 27,000 diesel units were in operation, accounting for almost all U.S. railway motive power. By 1990, advances in technology allowed three new-generation locomotives to do the work of four older ones. Although railroads in 2000 hauled a record 1.5 trillion ton-miles, the locomotive fleet stood at only 20,028. Recent locomotive designs make use of improved turbochargers coupled with more powerful and more fuel-efficient engines. Locomotive control systems have been converted to solid-state electronics, replacing most relay functions. On-board microprocessors control engine speed, fuel injection, and excitation of the alternator. These computers also interconnect with improved systems to detect slipping or sliding of the driving wheels, producing faster correction and improved adhesion. An additional function of the microprocessor is to monitor performance of all locomotive systems, thereby increasing their reliability and making the correction of problems easier. A recent innovation in the locomotive is the introduction of variable-frequency, variable voltage, three-phase alternating-current traction motors in place of direct-current series motors, reducing unsprung weight and improving wheel adhesion.

V

TURBINE-ELECTRIC LOCOMOTIVES

After World War II, extensive research in combustion engineering aided the development of turbine-electric locomotives, in which either gas or steam turbines were used to drive generators powering electric motors. A boiler was required to produce the steam in a steam turbine. In the gas turbine, gas was produced in a combustion chamber directly ahead of the turbine wheel. Either coal or oil may be used as fuel to produce steam or gas for turbine operation. Liquid propane gas has been used experimentally as fuel for gas turbines. All of these types of turbine-powered locomotives have been judged to be uneconomical for general freight rail operations. Only the gas turbine, driving wheels through hydraulic transmission, has continued in service in the 1990s as the motive power in the form of a power car hauling a lightweight passenger train.