Hydraulic Transmission/en

Diesel-hydraulic vehicles are propelled by an onboard diesel engine and hydraulic transmission. This transmission type is characterized by the use of one or more torque converters, which are enclosed devices filled up with hydraulic fluid, with a pump on one end, driven by the engine, and a turbine on the other end, driving the wheels.

Rather than being mechanically connected, the engine and the wheels transfer energy between each other through the fluid. In this setup, the engine is able to run independently of the wheels (it cannot stall, as the fluid is not dense enough to force it to), yet the wheels are still set in motion by it.

By operating the throttle control, the driver adjusts fuel injection to the engine. If the vehicle is in gear, as the engine spins up the pump, it will spin the hydraulic fluid inside the torque converter, in turn spinning the turbine on the opposite end. As the turbine is mechanically connected to the wheels, this propels the vehicle.

The heavier the train, the harder it is to spin the turbine, and so the more it lags behind the engine pump. This resistance causes friction to the hydraulic fluid and heats it up.

Depending on the session difficulty settings, if overheated, the torque converter can fail catastrophically. To prevent that, it is necessary to adjust the throttle so that the load on the turbine is not contributing to heat in an uncontrollable way.

See also: Internal Combustion Engine, Powertrain Overheating, Mechanical Powertrain Damage, Throttle, Hydrodynamic Brake, Engine & Compression Brake, Difficulty