PetrolâÂÂelectric transmission (UK English), or gasolineâÂÂelectric transmission or gasâÂÂelectric transmission (US English), is a transmission system for vehicles powered by petrol engines. PetrolâÂÂelectric 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 After World War I, it was largely superseded by dieselâÂÂelectric transmission, a similar transmission system used for diesel engines; but petrolâÂÂelectric has become popular again in modern hybrid electric vehicles.
PetrolâÂÂelectric transmission was used in certain niche markets in the early 20th century, such as in the petrolâÂÂelectric 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 petrolâÂÂelectric transmission system was used for standard-gauge locomotives (up to 240 kW of electrical power).
PetrolâÂÂelectric 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 than what would be required for powering a conventional petrol vehicle of the same size. Internal-combustion engines vary greatly in efficiency at various speeds and power outputs, and in this context can run more often nearer their optimal speeds and power outputs, powering the generator. When extra power is needed for acceleration or for climbing gradients, both the engine and the battery pack power the motor. When the engine produces more power than is required at the road wheels, the surplus is used to charge the battery.
PetrolâÂÂelectric vehicles typically don'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 petrolâÂÂelectric transmission include the Tilling-Stevens bus (UK) and the Owen Magnetic touring car (United States).
Examples of petrolâÂÂelectric rail vehicles include the North Eastern Railway 1903 Petrol Electric Autocar, Doodlebug (rail car), GE 57-ton gasâÂÂelectric boxcab, Weitzer railmotor and the petrolâÂÂelectric 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 petrolâÂÂelectric railcars.
Most submarines that served in World War I were dieselâÂÂelectric. However, some petrolâÂÂelectric 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).
PetrolâÂÂelectric systems were tested on the British Mark II tank, American Holt gasâÂÂelectric 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 petrolâÂÂelectric 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, petrolâÂÂelectric transmission has gained a new lease of life in hybrid electric vehicles. Examples include: Ford Fusion Hybrid; Honda Civic Hybrid; Toyota Prius; Nissan E-power.