Diesel–electric transmission

Most early submarines used a direct mechanical connection between the combustion engine and propeller, switching between diesel engines for surface running and electric 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, with batteries powering the electric motor and supplying all other power as well.[5]

In a true diesel–electric transmission arrangement, by contrast, the propeller or propellers are always driven directly or through reduction gears by one or more electric motors, while one or more diesel generators provide electric energy for charging the batteries and driving the motors. While this solution comes with disadvantages as well as advantages in comparison with the direct mechanical connection between the diesel engine and the propeller that was initially the most common arrangement, 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 the acoustic signature of the submarine when surfaced. Some nuclear submarines also use a similar turbo-electric propulsion system, with propulsion turbo generators driven by reactor plant steam.[6]

Among the pioneering users of true diesel–electric transmission was the Swedish Navy with its first submarine, HMS Hajen (later renamed Ub no 1), launched in 1904 and originally equipped with a semi-diesel engine (a hot-bulb engine primarily meant to be fueled by kerosene), later replaced by a true diesel.[7] From 1909 to 1916, the Swedish Navy launched another seven submarines in three different classes (2nd class, Laxen class, and Braxen class), all using diesel–electric transmission.[8] While Sweden temporarily abandoned diesel–electric transmission as it started to buy submarine designs from abroad in the mid 1910s,[9] 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 by air-independent propulsion (AIP) as provided by Stirling engines beginning with HMS Näcken in 1988.[10]

Another early adopter of diesel–electric transmission was the United States Navy, whose Bureau of Steam Engineering proposed its use in 1928. It was subsequently tried in the S-class submarines S-3, S-6, and S-7 before being put into production with the Porpoise class of the 1930s. From that point onwards, it continued to be used on most US conventional submarines.[11]

Apart from the British U-class and some submarines of the Imperial 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.[12] 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, the Soviet Navy did not introduce diesel–electric transmission on its conventional submarines until 1980 with its Paltus class.[13]

New Flyer Industries DE60LF diesel–electric bus with rooftop batteries

MCI diesel electric prototype bus with batteries under the floor

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 include Allison Transmission and BAE Systems. New Flyer Industries, Gillig Corporation, and North American Bus Industries are major customers for the Allison EP hybrid systems, while Orion Bus Industries is a major customer for the BAE HybriDrive system. Mercedes-Benz makes their own diesel–electric drive system, which is used in their Citaro. The only bus that runs on single diesel-electric transmission is the Mercedes Benz Cito low floor concept bus which was introduced in 1998.

The diesel–electric powered Liebherr T282 dumper

Examples include:

• Large mining machines, such as the Liebherr T 282B dump truck or LeTourneau L-2350 wheel loader.
• NASA's huge Crawler-Transporters.
• Mitsubishi Fuso Canter Eco Hybrid commercial truck.
• International DuraStar Hybrid diesel–electric truck.[15]
• Dodge is conducting fleet tests of a diesel–electric version of the Dodge Sprinter.[16][17]

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 and General Motors) that developed diesel hybrid cars.

• "Third-Millennium Cruiser", an attempt to commercialize a diesel–electric automobile in the very early 1980s.
• General Motors Precept
• Ford Prodigy
• Dodge Intrepid ESX
• Ford Reflex is a diesel hybrid concept car.[18]
• Zytek develops a diesel hybrid powertrain[19][20]
• Peugeot 307 Hybrid HDi
• Citroën C-Cactus[21]
• Opel Flextreme
• Top Gear Hammerhead-i Eagle Thrust
• Rivian Automotive is developing a diesel–electric engine that should achieve an estimated 90 miles per gallon in the city and over 100 miles per gallon on the highway[22]

Diesel–electric propulsion has been tried on some military vehicles, such as tanks. The prototype TOG1 and TOG2 super heavy tanks of the Second World War used twin generators driven by V12 diesel engines. More recent prototypes include the SEP modular armoured vehicle and T95e. Future tanks may use diesel–electric drives to improve fuel efficiency while reducing the size, weight and noise of the power plant.[23] Attempts with diesel–electric drives on wheeled military vehicles include the unsuccessful ACEC Cobra, MGV, and XM1219 Armed Robotic Vehicle.