Diesel multiple unit Facts for Kids

This DMU, called a SA108, is from the Greater Poland Voivodeship in Poznań, Poland.

The Transwa Prospector is a fast DMU that can go up to 200 km/h. It carries passengers between Perth, Western Australia and the mining town of Kalgoorlie.

A diesel multiple unit, often called a DMU, is a special type of train. It has many carriages, and each part of the train has its own diesel engine. This means the train doesn't need a separate locomotive to pull it. DMUs are sometimes called a railcar or railmotor, depending on where you are in the world.

DMUs are great because they can be shorter trains. They are also flexible and can run on lines where electric trains might not be able to go. Many countries use DMUs for passenger services, especially on routes that are not very busy.

How DMUs Move: The Transmission System
Related Train Types
Images for kids
See also

How DMUs Move: The Transmission System

A DMU's diesel engine makes the train move using a special system called a transmission. This system helps the engine's power reach the wheels. There are three main types of transmission systems used in DMUs:

Mechanical Transmission

Like a Car's Gearbox

Some DMUs use a mechanical transmission. This is similar to the gearbox in a car. The engine's power goes through gears that help the train speed up or slow down. It's a direct way to transfer power.

Hydraulic Transmission

Using Fluid Power

Other DMUs use a hydraulic transmission. This system uses special fluids and a torque converter. A torque converter helps change the engine's power into movement for the wheels. It's a smooth way to get the train moving.

Electric Transmission

Diesel-Electric Power

The third type is electric transmission. In this system, the diesel engine powers a generator. This generator then creates electricity. The electricity is used to power special traction motors. These motors are what actually turn the train's wheels. This type is often called a diesel-electric multiple unit.

Related Train Types

If you found DMUs interesting, you might want to learn about these:

Electric multiple unit: These trains are similar to DMUs but get their power from overhead electric lines or a third rail.
Diesel locomotive: This is a separate engine that pulls other train cars.
Multiple unit: This is a general term for trains where each part has its own power.
Railways: Learn more about how trains and tracks work.
Multiple units of Ireland: See specific examples of multiple unit trains used in Ireland.

Images for kids

An JNR Class KiHa40 in use for Erimo Express service, Hokkaido, Japan
An IE 29000 Class diesel multiple unit on a western commuter service at Dublin Connolly Rail station, Ireland
A British Rail Class 185 diesel hydraulic multiple unit operated by TransPennine Express at Manchester Piccadilly station, United Kingdom
One of the underfloor diesel engines with hydraulic transmission under a car of JR Shikoku 2700 series DMU
"Power Pack" car of Stadler FLIRT DMU with open bay of a diesel-generator. The Jacobs bogies under this car do not have their own traction motors, which are mounted on bogies under other cars.
DMU 7023 at Zagreb Central Station
ČD Class 810
ČD Class 814
Iarnród Éireann DMU 2751 at Limerick Colbert station, 2006
Romanian Class 77 Malaxa DMU in Câmpulung Moldovenesc in 2006
ZSSK Class 813
East Midlands Trains Class 222 at London St Pancras
Central Trains Class 170 at Peterborough station
Northern Ireland Railways C3K at Yorkgate station
Two Bombardier Talent low-floor DMUs on the O-Train Trillium Line in Ottawa, Canada
Apollo 2400 DMU in service in Costa Rica
Budd Rail Diesel Car RDC-1 #407 of the Cape May Seashore Lines, New Jersey
Stadler FLIRT owned by TEXRail in Texas
Siemens Desiro serving Sprinter in San Diego County, California
A V/Line VLocity operating in Victoria, Australia
Ferrovias del Bajio DSU at Phom Penh Cambodia Airport
A DEMU train (right) at Kamalapur railway station, Dhaka
Indian Railways class DMU
Indian Railways class Diesel Electric Multiple Unit (DEMU)
Indian Railways class DEMU
KRDI (Indonesian-built). KRDI Inka produced at Madiun. Sri Lelawangsa DMU, Medan.
KRDI Solo Express, Surakarta
JR Hokkaido KiHa 283 tilting DMU on Hakodate Main Line
Korail DHC-PP with new CI colour
Type of diesel Greek-German train