Petrol–electric transmission (UK English), orgasoline–electric transmission orgas–electric transmission (US English), is atransmission 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 After World War I, it was largely superseded bydiesel–electric transmission, a similar transmission system used fordiesel engines; but petrol–electric has become popular again in modernhybrid electric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 theWar Department Light Railways during World War I or for privately ownedArad & Csanad United Railways. In France, theCrochat petrol–electric transmission system was used for standard-gauge locomotives (up to 240 kW of electrical power).
Petrol–electric vehicles follow aseries hybrid architecture. Aspark-ignition internal-combustion (IC) engine acts as the prime mover, powering agenerator which converts the rotational energy into electrical energy. The generator charges a battery pack and drives atraction motor that providestractive effort for the vehicle to move.[1]
A schematic representation of the power train of a series-hybrid vehicle
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.
Petrol–electric 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.
The IC engine can be made smaller than what is usually required to move a similar sized pure gas-powered vehicle. IC engines are their ownair pumps and have poor efficiency at low speeds. So IC engines have to be made larger than what is required for conventional gas-powered vehicles. This is not the case for petrol-hybrid vehicles where an electric motor providestraction. Electric motors can deliver peak torque at a wide range of rpms. Small engines result in a compact design and more space.[3]
IC engines can operate at their peak rpm range throughout and improvemileage. IC engines operate at peak efficiency at higher rpms, In petrol–electric vehicles, the engine can keep running at these speeds as the motor is the one delivering traction. This results in lesser fuel usage and harmful emissions. This isn't the case with conventional vehicles where the engine has to slow down when the vehicle brakes.
Petrol–electric vehicles have anidle-stop function where the engine can be shut off during idling or during long deceleration.
Regenerative braking is possible with petrol–electric vehicles. When the brakes are applied, the traction motor can be switched to act as a generator and charge the battery pack. A magnetic resistance force acts on the wheels to slow them, while the battery is charged. Conventional brakes use frictional braking force only, which dissipate and waste rotational energy as heat. Regenerative braking saves energy, they are used in combination with friction brakes foranti lock braking (ABS).[4]
Petrol–electric vehicles can deliver additional power when it is demanded by the driver, like during hard acceleration or climbing a gradient. They also haveautomatic transmission and can deliver step-less power.[5]
Petrol–electric vehicles have manyenergy-conversion steps, which can result in reduced efficiency due to energy loss at each stage of the transition.
Petrol–electric vehicles, and typically most series hybrid vehicles need two electric machines, agenerator coupled to the engine and a motor–generator coupled to the wheels.
Petrol–electric systems were tested on the BritishMark II tank, AmericanHolt gas–electric tank and FrenchSaint Chamont in 1917. The latter used theCrochat-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.[13] The 1936 prototypeChar G1P was also designed with a petrol–electric drive.[14]
Ferdinand Porsche was the main developer of these drive trains for military vehicles inNazi Germany. He created theVK 3001 (P) prototype andVK 4501, of which 91 units were produced as the Porsche Tiger.[15] They were later converted into Ferdinand, and subsequentlyElefant, tank destroyers.[16] Another noteworthy design was the 188-tonne Porsche type 205 prototypes, commonly known as theMaussuper-heavy tank.
^Steven J. Zaloga (2014).French Tanks of World War II (1). Osprey.ISBN9781782003922.
^Thomas L Jentz (1997).Panzerkampfwagen VI P (Sd.Kfz.181): The history of the Porsche Typ 100 and 101 also known as the Leopard and Tiger (P). Darlington Productions.ISBN978-1892848031.
