What are Diesel Mechanical Locomotives? After reading about diesel electric & diesel hydraulic transmission methods you might think why the engine is not directly connected to the gear box as in most of the vehicles. The reason is this. A train is a heavy vehicle. If we supply power from engine directly to the gear box one or both these components might get damaged due to the inertia & it might led to accidents also. Fixing a clutch between the engine & the gear box is not that much suitable. But there are some locomotives with a clutch fixed between the engine & the gear box. This transmission type is known as diesel mechanical transmission & it’s used for low powered & low speed locomotives such as shunting locos.
In diesel mechanical locomotives the power generated from combusting diesel is used to rotate the shaft which is connected to the gear box through a fluid coupling. This fluid coupling is a hydraulic clutch. The mechanical energy output from the gearbox is distributed to the wheels through final drive. The power of an engine in a diesel mechanical locomotive is generally in the range of 300 to 350hp & transmission is similar to a normal automobile with four speed gearbox. Wheels of diesel mechanical locomotives are connected to each other using a rod to increase adhesion.