All locomotives, such as buses, trains, and even sea vessels, apply the same engineering system. All these engines require a specific torque at a given speed at a given moment. The problem is that the petrol or diesel engines do not have the same torque at the same speed in that it has different torque/speed characteristic. Therefore, the main reason why the diesel locomotives would require electric motors to drive the wheels is that it would help in matching the torque/speed characteristics of the two, which are the vehicle and the engine.
The electric motor
In case the power needed to operate a locomotive is not high, it is imperative to match the torque or speed characteristics of the automobile and the engine, which is done through a gearbox. The challenge, though, is experienced when dealing with large diesel locomotives since using the gearbox will be impractical in this situation. Hence, it calls for electric motors using AC and DC to drive each wheel, and the engine driven has an alternator. Solid-state power electronics match the torque/speed characteristic to support the movement.
The system is referred to as diesel-electric transmission. Its benefit is that it helps avoid the need to use the gearbox, which it does by converting the mechanical force of the diesel engine to electrical energy. Without the electric motors, getting the train to move initially would be hard. Making use of a diesel engine only would require a clutch system, and since diesel engines always develop little torque at a low revolution per minute (RPM) and based on the weight of the train, there is a high chance you would destroy the clutch as the train tries to move. Another problem because it would be hard to switch the diesel locomotive without the electric motor is that, on most occasions, diesel engines produce very little idle torque, making it hard to start the train. Since there will be little torque available as the train begins to move, there is a high chance of the clutch getting destroyed instantly.
The solution will therefore be to use an electric motor that can produce maximum torque at 0 RPM when switching locomotives. Heavy locomotives like trains require large electric motors that can produce sufficient torque to move the train in motion. If the movement has been initiated, there will be a minimum torque requirement. The mechanical and engineering system behind the incorporation of the two systems is having the diesel engine drive the generator, which helps produce the needed electricity. After the electricity has been produced, it turns and drives the electric motor used in the locomotive.
Electric motors play a significant role as it uses torque/speed characteristic that helps in powering locomotives to motion. Electric motors are that important because diesel engines produce very little torque at 0 RPM, making it hard to start a stationery train which, if pushed, will lead to the destruction of the gearbox. Therefore, it is right to argue that electric motors provide the solution needed when starting diesel engine locomotives without destroying the gearbox through their high torque and good speed control.
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