Petrol–electric transmission (UK English) or gasoline–electric transmission or gas–electric transmission (US English) is a transmission system for vehicles powered by petrol engines. Petrol–electric transmission was used for a variety of applications in road, rail, and marine transport, in the early 20th century. After World War I, it was largely superseded by diesel-electric transmission, a similar transmission system used for diesel engines; but petrol-electric has become popular again in modern hybrid electric vehicles.
Petrol–electric transmission was used in certain niche markets in the early 20th century, such as in the petrol–electric railway locomotives produced in Britain for use on the War Department Light Railways during World War I or for privately owned Arad & Csanad United Railways. In France, the Crochat petrol–electric transmission system was used for standard gauge locomotives (up to 240 kW of electrical power).
Petrol-electric vehicles follow a series hybrid architecture. A spark ignition internal combustion (IC) engine acts as the prime mover, powering a generator which converts the rotational energy into electrical energy. The generator charges a battery pack and drives a traction motor that provides tractive effort for the vehicle to move.
The engine is usually smaller that what would be required for powering a conventional petrol vehicle of the same size. The engine usually runs at its optimum high efficiency RPM, powering the generator. When extra power is needed for acceleration or for climbing gradients, both the engine and the battery pack powers the motor. When the engine produces more power than is required at the road wheels, the surplus is used to charge the battery.
Petrol-electric vehicles typically doesn't require any stepping up or transmission as electric traction motors can operate at a wide rpm range at peak efficiency. The Engine generator pair is a compact unit that isn't connected mechanically to the road wheels. The connection is purely electrical.
Examples of road vehicles using petrol–electric transmission include the Tilling-Stevens bus (UK) and the Owen Magnetic touring car (USA).
Examples of petrol–electric rail vehicles include the North Eastern Railway 1903 Petrol Electric Autocar, Doodlebug (rail car), GE 57-ton gas-electric boxcab, Weitzer railmotor and the petrol–electric locomotives built for the War Department Light Railways by Dick, Kerr & Co. and British Westinghouse. In France, the Crochat-Colardeau system of Henry Crochat and Emmanuel Colardeau was used in some petrol–electric railcars.
Most submarines that served in World War I were diesel–electric. However, some petrol–electric submarines had been built before the war. Examples include: Plunger-class submarine (USA), A-class submarine (1903) (UK), SM U-1 (Austria-Hungary), Russian submarine Krab (1912).
Petrol–electric systems were tested on the British Mark II tank, American Holt gas electric tank and French Saint Chamont in 1917. The latter used the Crochat-Colardeau system of Henry Crochat and Emmanuel Colardeau. This allowed the left and right traction motors to run at different speeds for steering and is detailed in patent US1416611. The 1936 prototype Char G1P was also designed with a petrol–electric drive.
Ferdinand Porsche was the main developer of these drive trains for military vehicles in Nazi Germany. He created the VK 3001 (P) prototype and VK 4501, of which 91 units were produced as the Porsche Tiger. They were later converted into Ferdinand, and subsequently Elefant, tank destroyers. Another noteworthy design was the 188-tonne Porsche type 205 prototypes, commonly known as the Maus super-heavy tank.
In the 21st century, petrol–electric transmission has gained a new lease of life in hybrid electric vehicles. Examples include: Ford Fusion Hybrid; Honda Civic Hybrid; Toyota Prius.
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