Petrol-electric transmission

Petrol–electric transmission (UK English) or gasoline–electric or gas–electric transmission (US English) is a transmission system for road, rail and marine transport which avoids the need for a gearbox. The petrol engine drives a dynamo which supplies electricity to traction motors which propel the vehicle or boat. The traction motors may be driven directly or, in the case of a submarine, via a rechargeable battery.

Petrol–electric transmission was used in certain niche markets in the early 20th century. For example in the petrol–electric railway locomotives produced in Britain for use on the War Department Light Railways during World War I. In France, the Crochat petrol–electric transmission system was used for standard gauge locomotives (up to 240kW of electrical power).

After World War I, petrol–electric transmission was largely replaced by diesel–electric transmission but, in the 21st century, it is making a comeback in hybrid electric vehicles.

Petrol–electric transmission allows smooth, stepless, acceleration without gear changes. The disadvantages are increased cost and weight.

Examples of petrol–electric road vehicles include the Tilling-Stevens bus (UK) and the Owen Magnetic touring car (USA).

Tilling-Stevens petrol–electric bus

Owen Magnetic touring car 1920 advertisement

St. Chamond tank

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.

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