Internal combustion locomotive

The most common type of petrol locomotive are petrol-mechanical locomotives, which use mechanical transmission. The earliest examples of these locomotives used a plate or cone[9] clutch and mechanical gear-box driving the main axle either directly,[10] via a chain drives[7] or using bevel gears.[11]

The interior of a Petrol-electric locomotive showing the engine and dynamo

Petrol–electric locomotives are petrol locomotives that use electric transmission to deliver the power output of the engine to the driving wheels. This avoids the need for gearboxes by converting the rotary mechanical force of the engine into electrical energy by a dynamo, and then powering the wheels by multi-speed electric traction motors. This allows for smoother acceleration as it avoids the need for gear changes, and the power output can be divided amongst multiple motors, which gives greater traction control. However the generating equipment is more expensive, heavier, and often more complex to maintain than mechanical transmission.[12]

Schematic illustration of a Diesel mechanical locomotive

An early Diesel-mechanical locomotive at the North Alabama Railroad Museum

A diesel–mechanical locomotive uses mechanical transmission to transfer power to the wheels. This type of transmission is generally limited to low-powered, low speed shunting (switching) locomotives, lightweight multiple units and self-propelled railcars. The earliest diesel locomotives were diesel-mechanical.

The mechanical transmissions used for railroad propulsion are generally more complex and much more robust than standard-road versions. There is usually a fluid coupling interposed between the engine and gearbox, and the gearbox is often of the epicyclic (planetary) type to permit shifting while under load. Various systems have been devised to minimise the break in transmission during gear changing; e.g., the S.S.S. (synchro-self-shifting) gearbox used by Hudswell Clarke. Diesel–mechanical propulsion is limited by the difficulty of building a reasonably sized transmission capable of coping with the power and torque required to move a heavy train.

In 1906, Rudolf Diesel, Adolf Klose and the steam and diesel engine manufacturer Gebrüder Sulzer founded Diesel-Sulzer-Klose GmbH to manufacture diesel-powered locomotives. The Prussian State Railways ordered a diesel locomotive from the company in 1909. The world's first diesel-powered locomotive (a diesel-mechanical locomotive) was operated in the summer of 1912 on the Winterthur–Romanshorn railway in Switzerland, but was not a commercial success.[13] The locomotive weight was 95 tonnes and the power was 883 kW with a maximum speed of 100 km/h.[14] Small numbers of prototype diesel locomotives were produced in a number of countries through the mid-1920s.

Schematic diagram of diesel electric locomotive

Diesel–electric locomotives are diesel locomotives using electric transmission. In this arrangement, the diesel engine drives either an electrical DC generator (generally, less than 3,000 horsepower (2,200 kW) net for traction), or an electrical AC alternator-rectifier (generally 3,000 horsepower (2,200 kW) net or more for traction), the output of which provides power to the traction motors that drive the locomotive. There is no mechanical connection between the diesel engine and the wheels. The vast majority of diesel locomotives today are diesel-electric.

The important components of diesel–electric propulsion are the diesel engine (also known as the prime mover), the main generator/alternator-rectifier, traction motors (usually with four or six axles), and a control system consisting of the engine governor and electrical or electronic components, including switchgear, rectifiers and other components, which control or modify the electrical supply to the traction motors. In the most elementary case, the generator may be directly connected to the motors with only very simple switchgear.

Originally, the traction motors and generator were DC machines. Following the development of high-capacity silicon rectifiers in the 1960s, the DC generator was replaced by an alternator using a diode bridge to convert its output to DC. This advance greatly improved locomotive reliability and decreased generator maintenance costs by elimination of the commutator and brushes in the generator. Elimination of the brushes and commutator, in turn, disposed of the possibility of a particularly destructive event called a flashover, which could result in immediate generator failure and, in some cases, start an engine room fire.

World's first useful diesel locomotive (a diesel-electric locomotive) for long distances SŽD Eel2, 1924 in Kyiv

In the late 1980s, the development of high-power variable-frequency/variable-voltage (VVVF) drives, or "traction inverters," has allowed the use of polyphase AC traction motors, thus also eliminating the motor commutator and brushes. The result is a more efficient and reliable drive that requires relatively little maintenance and is better able to cope with overload conditions that often destroyed the older types of motors.

In 1914, Hermann Lemp, a General Electric electrical engineer, developed and patented a reliable direct current electrical control system (subsequent improvements were also patented by Lemp).[15] Lemp's design used a single lever to control both engine and generator in a coordinated fashion, and was the prototype for all diesel–electric locomotive control. In 1917–18, GE produced three experimental diesel–electric locomotives using Lemp's control design.[16] In 1924, a diesel-electric locomotive (E^el2 original number Юэ 001/Yu-e 001) started operations. It had been designed by a team led by Yuri Lomonosov and built 1923–1924 by Maschinenfabrik Esslingen in Germany. It had 5 driving axles (1'E1'). After several test rides, it hauled trains for almost three decades from 1925 to 1954.[17] It was the world's first functional diesel locomotive.

A German DB Class V 200 diesel-hydraulic locomotive at Technikmuseum, Berlin

Diesel–hydraulic locomotives are diesel locomotives using hydraulic transmission. In this arrangement, they use one or more torque converters, in combination with gears, with a mechanical final drive to convey the power from the diesel engine to the wheels.

Hydrokinetic transmission (also called hydrodynamic transmission) uses a torque converter. A torque converter consists of three main parts, two of which rotate, and one (the stator) that has a lock preventing backwards rotation and adding output torque by redirecting the oil flow at low output RPM. All three main parts are sealed in an oil-filled housing. To match engine speed to load speed over the entire speed range of a locomotive some additional method is required to give sufficient range. One method is to follow the torque converter with a mechanical gearbox which switches ratios automatically, similar to an automatic transmission on a car. Another method is to provide several torque converters each with a range of variability covering part of the total required; all the torque converters are mechanically connected all the time, and the appropriate one for the speed range required is selected by filling it with oil and draining the others. The filling and draining is carried out with the transmission under load, and results in very smooth range changes with no break in the transmitted power.

The main worldwide user of main-line hydraulic transmissions was the Federal Republic of Germany, with designs including the 1950s DB class V 200, and the 1960 and 1970s DB Class V 160 family. British Rail introduced a number of diesel hydraulic designs during it 1955 Modernisation Plan, initially license built versions of German designs. In Spain RENFE used high power to weight ratio twin engined German designs to haul high speed trains from the 1960s to 1990s. (see RENFE Classes 340, 350, 352, 353, 354).

Hydrostatic drive systems have also been applied to rail use, for example 350 to 750 hp (260 to 560 kW) shunting locomotives by CMI Group (Belgium),[18] and 4 to 12 tonne 35 to 58 kW (47 to 78 hp) industrial locomotives by Atlas Copco subsidiary GIA.[19] Hydrostatic drives are also used in railway maintenance machines such as tampers and rail grinders.[20]