Adiesel–electric transmission, ordiesel–electric powertrain, is atransmission system powered bydiesel engines forvehicles inroad,rail, andmarinetransport. Diesel–electric transmission is similar topetrol–electric transmission, which is powered bypetrol engines.
Diesel–electric transmission is used on railways bydiesel–electric locomotives anddiesel–electric multiple units, as electric motors are able to supply fulltorque from 0RPM. Diesel–electric systems are also used inmarine transport, including submarines, and on some other land vehicles.
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The defining characteristic of diesel–electric transmission is that it avoids the need for agearbox, by converting themechanical force of the diesel engine intoelectrical energy (through analternator), and using the electrical energy to drivetraction motors, which propel the vehicle mechanically. The traction motors may be powered directly or viarechargeable batteries, making the vehicle a type ofhybrid electric vehicle. This method of transmission is sometimes termed electric transmission, as it is identical topetrol–electric transmission, which is used on vehicles powered by petrol engines, and toturbine–electric powertrain, which is used forgas turbines.
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The absence of a gearbox eliminates the need for gear changes, which prevents uneven acceleration caused by the disengagement of aclutch. With auxiliary batteries the motors can run on electric alone, for example when the noise or exhaust from the engine disrupts aclean air zone.[1]
Disadvantages of a diesel electric transmission are the potential complexity, cost, and decreased efficiency due to energy conversion.[dubious –discuss] Diesel engines and electric motors are both known for having high torque at low rpm, this may leave high rpm with little torque. Typically a petrol engine is paired with electric motors for this reason. Petrol engine produces most torque at high rpm, supplemented by electric motors' low rpm torque.
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The first dieselmotorship was also the first diesel–electric ship, the Russian tankerVandal fromBranobel, which was launched in 1903.Steam turbine–electric propulsion has been in use since the 1920s (Tennessee-classbattleships), using diesel–electric powerplants in surface ships has increased lately. TheFinnishcoastal defence shipsIlmarinen andVäinämöinen laid down in 1928–1929, were among the first surface ships to use diesel–electric transmission. Later, the technology was used in diesel poweredicebreakers.[citation needed]
In World War II, theUnited States Navy built diesel–electric surface warships. Due to machinery shortagesdestroyer escorts of theEvarts andCannon classes were diesel–electric, with half their designed horsepower (TheBuckley andRudderow classes were full-power steam turbine–electric).[2] TheWind-classicebreakers, on the other hand, were designed for diesel–electric propulsion because of its flexibility and resistance to damage.[3][4]
Some modern diesel–electric ships, includingcruise ships and icebreakers, use electric motors in pods calledazimuth thrusters underneath to allow for 360° rotation, making the ships far more maneuverable. An example of this isSymphony of the Seas, the largest passenger ship as of 2019.[5]
Gas turbines are also used for electrical power generation and some ships use a combination:Queen Mary 2 has a set of diesel engines in the bottom of the ship plus two gas turbines mounted near the main funnel; all are used for generating electrical power, including those used to drive thepropellers. This provides a relatively simple way to use the high-speed, low-torque output of a turbine to drive a low-speed propeller, without the need for excessive reduction gearing.[citation needed]
Most earlysubmarines used a direct mechanical connection between the combustion engine and propeller, switching betweendiesel engines for surface running andelectric motors for submerged propulsion. This was effectively a "parallel" type of hybrid, since the motor and engine were coupled to the same shaft. On the surface, the motor (driven by the engine) was used as a generator to recharge the batteries and supply other electric loads. The engine would be disconnected for submerged operation, withbatteries powering the electric motor and supplying all other power as well.[6]
In a true diesel–electric transmission arrangement, by contrast, the propeller or propellers are always driven directly or throughreduction gears by one or moreelectric motors, while one or morediesel generators provide electric energy for charging the batteries and driving the motors. While this solution comes with a fewdisadvantages compared to direct mechanical connection between the diesel engine and the propeller that was initially common, the advantages were eventually found to be more important. One of several significant advantages is that it mechanically isolates the noisy engine compartment from the outer pressure hull and reduces theacoustic signature of the submarine when surfaced. Somenuclear submarines also use a similarturbo-electric propulsion system, with propulsionturbo generators driven by reactor plant steam.[7]
Among the pioneering users of true diesel–electric transmission was theSwedish Navy with its first submarine,HMSHajen (later renamedUb no 1), launched in 1904 and originally equipped with a semi-diesel engine (ahot-bulb engine primarily meant to be fueled by kerosene), later replaced by a true diesel.[8] From 1909 to 1916, the Swedish Navy launched another seven submarines in three different classes (2nd class,Laxen class, andBraxen class), all using diesel–electric transmission.[9] While Sweden temporarily abandoned diesel–electric transmission as it started to buy submarine designs from abroad in the mid-1910s,[10] the technology was immediately reintroduced when Sweden began to design its own submarines again in the mid-1930s. From that point onwards, diesel–electric transmission has been consistently used for all new classes of Swedish submarines, albeit supplemented byair-independent propulsion (AIP) as provided byStirling engines beginning withHMSNäcken in 1988.[11]
Another early adopter of diesel–electric transmission was theUnited States Navy, whoseBureau of Steam Engineering proposed its use in 1928. It was subsequently tried in theS-class submarinesS-3,S-6, andS-7 before being put into production with thePorpoise class of the 1930s. From that point onwards, it continued to be used on most US conventional submarines.[12]
Apart from the BritishU-class and some submarines of theImperial Japanese Navy that used separate diesel generators for low speed running, few navies other than those of Sweden and the US made much use of diesel–electric transmission before 1945.[13] After World War II, by contrast, it gradually became the dominant mode of propulsion for conventional submarines. However, its adoption was not always swift. Notably, theSoviet Navy did not introduce diesel–electric transmission on its conventional submarines until 1980 with itsPaltus class.[14]
DuringWorld War I, there was a strategic need for rail engines without plumes of smoke above them. Diesel technology was not yet sufficiently developed but a few precursor attempts were made, especially forpetrol–electric transmissions by the French (Crochat-Collardeau, patent dated 1912 also used for tanks and trucks) and British (Dick, Kerr & Co andBritish Westinghouse). About 300 of these locomotives, only 96 being standard gauge, were in use at various points in the conflict.[citation needed]
In the 1920s, diesel–electric technology first saw limited use inswitcher locomotives (UK:shunter locomotives), locomotives used for moving trains around in railroad yards and assembling and disassembling them. An early company offering "Oil-Electric" locomotives was theAmerican Locomotive Company (ALCO). TheALCO HH series of diesel–electric switcher entered series production in 1931. In the 1930s, the system was adapted forstreamliners, the fastest trains of their day. Diesel–electric powerplants became popular because they greatly simplified the way motive powerwas transmitted to the wheels and because they were both moreefficient and had greatly reduced maintenance requirements. Direct-drivetransmissions can become very complex, considering that a typical locomotive has four or moreaxles. Additionally, a direct-drive diesel locomotive would require an impractical number of gears to keep the engine within its powerband; coupling the diesel to a generator eliminates this problem. An alternative is to use atorque converter orfluid coupling in a direct drive system to replace the gearbox.
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Diesel electric based buses have also been produced, including hybrid systems able to run on and store electrical power in batteries. The two main providers of hybrid systems for diesel–electric transit buses includeAllison Transmission andBAE Systems.New Flyer Industries,Gillig Corporation, andNorth American Bus Industries are major customers for the Allison EP hybrid systems, whileOrion Bus Industries andNova Bus are major customer for the BAE HybriDrive system.Mercedes-Benz makes their own diesel–electric drive system, which is used in theirCitaro. The only bus that runs on single diesel–electric transmission is the Mercedes Benz Cito low floor concept bus which was introduced in 1998.
Examples include:
In the automobile industry, diesel engines in combination with electric transmissions and battery power are being developed for future vehicle drive systems.Partnership for a New Generation of Vehicles was a cooperative research program between the U.S. government and "The Big Three" automobile manufacturers (DaimlerChrysler,Ford andGeneral Motors) that developed diesel hybrid cars.[citation needed]
Diesel–electric propulsion has been tried on somemilitary vehicles, such astanks. The German armored vehiclesVK 45.01 (P),Elefant, andPanzer VIII Maus of the Second World War were petrol-electric or diesel-electric propelled. The prototypeTOG1 andTOG2 super heavy tanks of the Second World War used twin generators driven by V12 diesel engines.[citation needed] More recent prototypes include theSEP modular armoured vehicle andT95e. Future tanks may use diesel–electric drives to improve fuel efficiency while reducing the size, weight and noise of the power plant.[28] Attempts with diesel–electric drives on wheeled military vehicles include the unsuccessfulACEC Cobra,MGV, andXM1219 armed robotic vehicle.[citation needed]
