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A 'Diesel Multiple Unit' or 'DMU' is a multiple unit train consisting of multiple carriages powered by one or more on-board diesel engines. They may also be referred to as a railcar or railmotor depending on country.

Contents

Design

Types

Diesel Mechanical

Diesel Hydraulic

Diesel Electric

Benefits

Around the World

North America

Australia

Germany

United Kingdom

Ireland

South Korea

Japan

Gallery

Manufacturers

See also

Design

The diesel engine may be located above the frame in an engine bay or under the floor. Driving controls can be provided at each end of the car, at one end only, or totally omitted, giving pure 'trailer' cars that still have motors which rely on cab cars for control.

Types

DMUs are usually classified by the method of transmitting motive power to their wheels.

Diesel Mechanical

In a Diesel Mechanical Multiple Unit the rotating energy of the engine is transmitted via a gearbox and driveshaft directly to the wheels of the train, much like a car. The transmissions can be shifted manually by the driver, but in most applications gears are changed automatically.

Diesel Hydraulic

In a Diesel Hydraulic Multiple Unit, a hydraulic torque converter, a type of fluid coupling, acts as the transmission medium for the motive power of the diesel engine to turn the wheels. Some units feature a hybrid mix of hydraulic and mechanical transmissions, usually reverting the latter at higher operating speeds as this decreases engine RPM and noise.

Diesel Electric

In a Diesel Electric Multiple Unit (DEMU) a diesel engine drives an electrical generator which produces electrical energy. This current is then be fed to electric traction motors on the wheels or bogies in the same was as a conventional diesel electric locomotive.
In most modern DEMUs, each car is entirely self-contained and has its own engine, generator and electric motors. In older designs some cars within the consist may be entirely unpowered or only feature electric motors, obtaining electrical current from other cars in the consist which have a generator and engine.
Direct-drive diesel locomotives often require an impractical number of gears to keep the engine within its powerband; coupling the diesel to a generator eliminates this problem. Power still needs to be transmitted to the generator or alternator via a simple gearbox but this is advantageous because;

★ Mere cables transmit the power to the axle traction motors, not a complex system of rods

★ Sending power to a generator via a low powerband (i.e. diesel) is analogous to sending power to a propeller, in that one gear ratio is enough, unlike sending power to wheels, where several ratios are necessary. This is because the high friction between wheels and contact surface requires a low gear for takeoff to avoid stalling, and higher gears thereafter, since the output shaft moves relative to vehicle speed and would over-rev the engine if just one gear was available. In a generator or alternator, the force is magnetism, not a high friction surface so a high gear is fine since the magnetism is not great enough to stall the engine. The result is that the diesel-electric system puts the diesel’s low powerband to best use.

★ Rheostatic braking (sometimes called dynamic, electric or regenerative braking) is also available on some DEMUs. By attaching the motors to an electrical load they act as generators and slow the train down. The load is usually resistors which dissipate electrical energy as heat to the atmosphere, though it is sometimes used to heat the interiors. In some cases it is stored for later use or passed back into external power supplies. The advantage for this method of braking is reduced wear and tear on the main service brakes.

Benefits

A train composed of DMU cars scales well as it allows extra passenger capacity to be added at the same time as motive power. It also permits passenger capacity to be matched to demand, and for trains to be split and joined en-route.
Distribution of the propulsion among the cars also results in a system that is less vulnerable to single-point-of-failure outages. Many classes of DMU are capable of operating with faulty units still in the consist. Because of the self contained nature of diesel engines, there is no need to run overhead electric lines or electrified track, which can result in lower system construction costs.

Around the World

North America

One of the first Diesel Multiple Units in North America was the Budd Rail Diesel Car (RDC). The RDC was a single passenger car with two diesel engines and two sets of controls. Any number of cars could be connected together and all the propulsion systems controlled from a single operator's station or cab. Introduced in the early 1940s, the cars were used on rural railway lines that did not warrant full passenger trains, or short commuter services.
In the United States of America only heavyweight DMU systems are permitted on freight rail corridors. This is due to the Federal Railway Administration setting higher buff strength requirements than European regulators, effectively prohibited the use of lightweight European-style light-rail DMUs on main line railways.
Several rail operators in the United States use DMUs suitable for mainline use:

★ The South Florida Regional Transportation Authority has used a Colorado Railcar bi-Level DMU and Coach consist since October 2006 as a technology demonstrator on the 87-mile long Tri-Rail commuter rail line between Miami and West Palm Beach, Florida. In early 2007, three more bi-level DMUs and an additional bi-level non-powered coach were acquired.

★ The Florida Department of Transportation is currently conducting preliminary engineering for a DMU commuter line connecting Orlando, Florida with neighboring communities north and south of its downtown, with service targeted to begin in 2009.[1]

★ The Los Angeles County Metropolitan Transportation Authority approved an allocation of $250,000 for a feasibility study of DMUs for "future transportation options for the region" on July 5, 2006 (Ara Najarian, Metro Board Member).

★ Chicago's commuter rail line, Metra, is studying the use of DMUs on its newly proposed lines (STAR line, SES). They claim these DMUs will have better acceleration, be more fuel efficient, and seat more customers than the current diesel engine cab and double decker rail cars that are currently in use. [2]

★ Amtrak is reportedly encouraging the state of Vermont to buy DMUs for Amtrak's state-subsidized Vermonter service, in order to save money over the current locomotive-pulled arrangement. [3]

★ Boston's Massachusetts Bay Transportation Authority is reportedly considering options to utilize DMUs on the Fairmount Line, currently run by locomotive-pulled carriages, in order to improve service and headways on the line. This plan has become known as the Indigo Line.
Canada generally follows similar buff strength requirements to the USA, but new services are evaluated on a case-by-case basis. As a result several types of lightweight DMUs have been used:

★ The O-Train in Ottawa, Ontario uses European-standard Bombardier Transportation Talent DMUs on conventional railway tracks under a specific safety agreement with Transport Canada.

★ Calgary, Alberta has also used European Sprinter DMUs in demonstration service on conventional railway tracks.

Australia

DMUs were first introduced to Australia in the early 20th century for use on quiet branchlines that could not justify a locomotive hauled service. Today a range of modern DMUs are extensively used across Australia for both commuter and intercity routes:

★ Western Australia's Transwa operates the Prospector, Avonlink and Australind on medium and long country services.

★ In Victoria V/Line operate Sprinter and VLocity DMUs on both commuter and medium distance country services.

★ In New South Wales CountryLink uses Xplorer DMUs on country services, and CityRail operate the 620 / 720 class, Endeavour, and Hunter railcars on commuter services.

★ A DMU variant of Queensland Rail's QR Tilt Train is in use on the long distance Brisbane to Cairns service.

★ TransAdelaide in South Australia use 3000 class and 2000 class DMUs on their suburban rail lines.

Germany

The Flying Hamburger of Germany, introduced 1933, established the then-time fastest regular railway connection of the world. Top speed was 160 km/h, the average speed being 124 km/h on the tracks between Berlin and Hamburg.
The Trans Europ Express travelled international traffic between countries like Germany, France, Italy, Netherlands in the 1950s and 1960s. They were diesel multiple units since the electrical systems varied a lot.
Also from Germany is the CargoSprinter concept. With two motorized units and three flatbed wagons between them, this DMU container train tried to compete with container road trucks by profiting from existing railway access to factories and businesses, but eliminating the need for inflexible locomotive-pulled cargo trains. The payload was 160 tons. Suffering from technical problems and failing political support for short-haul cargo railway connections, the prototypes were sold to Austria.

United Kingdom

DMUs have been widely used in the United Kingdom since their introduction in the mid-1950s by British Rail. At that time there was an urgent need to move away from expensive steam traction which led to many experimental designs using diesel propulsion and multiple units. Today apart from from express journeys, DMUs have become the mainstay of UK passenger operations.
One of the first and most successful designs was the Class 101 which entered service in 1956 and remained in mainstream use until 2003. Several hundred were constructed and many similar units followed, such as the Class 121.
Diesel Electric Multiple Units were also developed during the 1950s and 60s as a stop-gap to cover lines that were shortly to be electrified. Of Class 205 and 207, they were nick-named "Thumpers" by their characteristic sound.
The British Rail "InterCity 125" was a much more powerful DEMU introduced in the 1970s. These trains have always run with 2 power cars and between 5 and 9 intermediate coaches. Although originally classified as DEMUs, the coaches were modified from loco-hauled stock, and the power cars were later renumbered as locomotives under Class 43.

In total, around 30 different DMU types were operating by the 1980s, which lead to spiralling costs with many non-standard units in operation. In order to cut costs British Rail decided to rationalise its DMUs in the 1980s, so called "Sprinterisation" and the older first generation DMUs were replaced by several standardised families:

★ Sprinter a DMU based on the Mark 3 carriage bodyshell

★ Pacer railbus, developed as a low-cost train utilising bus technology and designed for regular stopping services.

★ Network Turbo, of class 165 (commuter version) and longer distance class 166.
Following the privatisation of British Rail in the late 90s, several other DMU families have been introduced:

★ Turbo, 168 Clubman and 170/171 Turbostar units, a development of the earlier Network Turbos.

★ Coradia, class 175 were designed as an alternative to the 170 Turbostar, it met with only limited success.

★ Desiro , introduced in 2007 as Class 185 to replace the Class 158 Express Sprinter.
There has also been a resurgence in Diesel Electric Multiple Units, with the introduction of the high speed Class 220 Voyager, 221 Super-Voyager and 222 Meridian/Pioneer units.

Ireland

Main articles: Multiple Units of Ireland

In the Republic of Ireland the Córas Iompair Éireann (CIE), which controlled the republic's railways between 1945-86, mainly used locomotives and hauled stock for its passenger trains. Since 1987, Iarnród Éireann (IE) have been increasing the use of this type of train, in order to replace older locomotives and carriages.
In Northern Ireland the Northern Ireland Railways used DMUs extensively throughout its system, notably the NIR 80 Class introduced in the early 1970s and currently being replaced (as of 2007).

South Korea

Korail operates many DMUs. The DHC (Diesel Hydraulic Car), which made its debut for the 1988 Seoul Olympics, can reach speeds up to 150 km/h and serves Saemaul-ho trains. The NDC (New Diesel Car) serves Mugunghwa-ho trains and the (Commute Diesel Car) serves Tonggeun trains. The NDC and CDC can reach speeds up to 100 km/h and are not used for mountainous lines such as the Taebaek Line.

Japan

In Japan, railways are a major means of passenger transportation, especially for mass and high-speed transport between major cities and for commuter transport in metropolitan areas. Seven Japan Railway companies, state-owned until 1987, cover most parts of Japan. There are also railway services operated by private rail companies, regional governments, and companies funded by both regional governments and private companies.
Japanese trains are also famous for always being on time. Five stations (Shinjuku Station, Ikebukuro Station, Shibuya Station, Umeda Station, and Yokohama Station) serve more than 2 million passengers each on an average day, making Japan the most railway using nation per capita (see Rail usage statistics by country). Both DMUs and EMUs are widely used on urban lines, Metro services and for local services in many parts of the country. The development of Japan in the 20th century is analogous to that of its rail transport. Throughout the times, railway was the most important means of transportation in the country, and it still is in larger cities. As many of Japanese suburban cities were developed by railway operators, its unchallenged importance is something unique among the world.

Gallery

Image:GB Class 143 dmu 143603 (uncropped).jpg|Wessex Trains Class 143 Pacer DMU 143603 at platform 3 of Bristol Temple Meads station with a service to Avonmouth.
Image:222_passing_through_Loughborough.jpg|A four-car Midland Mainline Class 222 passing through Loughborough on 19 November 2005, one of the latest DEMUs to see service in the UK.
Image:Virgin Voyager on King Edward VII Bridge 2005-10-08.jpg|A Virgin Trains Class 221, their replacement for the HST and used on cross-country services.
Image:Red Japanese DMU.jpg|Japanese DMU "KIHA40"
Image:Buffel Zwolle.jpg|Dutch DMU "DM '90" or "Buffel"
Image:Syntus Lint.jpg|Dutch DMU "LINT".
Image:Lint Interieur.jpg|Interior of a LINT train.
Image:DMU in Vilnius depot.jpg|A former Soviet, now Lithuanian DMU in a Vilnius depot.
Image:Talent Enschede.jpg|German DMU "Talent"
Image:Talent Interieur.jpg|Interior of a Talent
Image:OttawaO-TrainInterior.jpg|The interior of an Canadian O-Train’s carriage.
Image:Fuehrerstand 928676 2004-12-09.JPG|The cab of a German DMU of Class 628.4 origin.

Manufacturers

DMU manufacturers include:

★ Bombardier Transportation of Montreal, Canada

★ Colorado Railcar

★ Niigata Transys of tokyo, Japan

★ Rotem of Seoul, South Korea

★ Siemens Desiro DMU

★ Integral Coach Factory of Chennai, India

★ TÜVASAŞ of Adapazari, Turkey

★ BREL, UK (former, now closed).

See also

★ Electric Multiple Unit

★ Diesel locomotive

★ Multiple unit

★ Railways

★ Multiple Units of Ireland

★ Rail transport in Japan