Power Source and Transmission

Power Source	Transmission	Feature
Electricity	Light weight and high efficiency. The adjustable voltage, adjustable frequency controller enables AC motors as the excellent motive power source. The efficiency is kept high over the wide range of load variations. Recently the permanent magnet motor technology and advanced semiconductor materials such as iii-nitrides and sic increase the train efficiency even more. Just like a reciprocating steam engine, some kind of electric motor can drive axle directly without any reduction gear.
Diesel	Diesel engines are heavy and bulky but low power high speed diesels are relatively light and suitable for regional rail cars. The energy efficiency is high among internal combustion engines and keep efficient over the wide range of engine output. But the exhaust is particulate rich and toxic,, the low frequency noise and the vibration are serious problems and it is not easy to resolve this problem in high output diesels.
	hydraulic converter	The maximum efficiency of the single converter is limited around 80-85% at a narrow range of speed and output. To avoid this disadvantage, Voith type three converter system or Mekydro type multi-speed gearbox is required and the total system becomes complex, large and heavy.
	hydraulic with lock up clutch and multi-speed gear	Recent railcars use hydraulic converters only at starting and low speed to avoid their low efficiency. After the clutch is locked up, the multi-speed (multi-stage) gearbox changes according to the speed and the required traction. The energy loss of this direct drive mode is small over the wide range of speed. As a result, the required hydraulic converter capacity is small and then the weight of total transmission is lighter than the full hydraulic system. The number of shifting steps influences the acceleration and more steps, more fitting to the ideal constant output curve. But the switching gears suspends the acceleration and cause the time loss. To make its minimum, additional devices such as PDK are required. The switching gears also damages transmission system in the high output system and requires very precise revolution control or hydraulic coupling.
	generator and electric motor	Recent advancement of electric transmissions may make the diesel electric drive more popular. The total mass of the driving system is near the hydraulic system and can achieve the higher efficiency.
Gas Turbine	Gas turbines are very light weight, vibration free and has a multi-fuel capability and a clean exhaust. Its torque characteristics are suitable for vehicle use and can drive vehicles without torque converters. Recent gas turbines are relatively efficient but still worse than diesels. Especially at part load and idling. Recuperated gas turbines can improve this to some extent but don't reach diesels. The combined cycle or humid air gas turbine can achieve the efficiency over diesels but many merits of gas turbine, compact and light weight, easy operability are lost and not suitable for vehicles. The high speed revolution of the gas turbine requires sophisticated reduction gears. Also its high volume air flow and high frequency noise require somewhat large air intake and exhaust duct and silencer.
	direct drive	The merit is lightweight and low energy loss. A split shaft gas turbine can achieve the stall torque ratio 2 or more and if 150% over revolution limit is allowed, the starting tractive effort is nearly 4 times against the top speed. Early turbine cars used these characteristics to remove multi-speed gearbox or hydraulic converter from the car. Gas turbines can also be equipped with multi-speed gearboxes to improve the low speed tractive effort, low speed energy inefficiency and high noise level at stall. M1 Abraham tank and Y2K turbine bike are equipped with this system.
	generator and electric motor	The electric transmission compensates for turbine disadvantages such as high speed revolution, fuel loss at part load and high noise at stall. This is prominent especially when the turbine is directly coupled to the high speed alternator. This combination enables very high power density electric generation system.
Hybrid	The on-board battery enables the self-propelled vehicle to regenerate motive energy. This system reduces many defects of internal combustion engines. Engines can operate at most optimum levels and can stop idling. This reduces fuel consumption and emissions.
	Lithium Ion Battery	high energy density
	Ultra capacitor	high power density and high cycle life
	Flywheel	high power density and high cycle life

　

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