Traction Motors

Electric and diesel-electric vehicles carry electric motors onboard, also known as “traction motors” (TM, for short). They are typically located around individual wheel axles, and rely on electricity to be spun and to propel the vehicle .

When the throttle control device is operated in such a vehicle, onboard systems send the desired electrical power to the traction motors. On a diesel-electric vehicle, this indirectly adjusts fuel injection to the engine, changing its spin rate as needed to generate the required electricity.

The faster the TMs spin, the more they generate the counter-electromotive force. This reduces the electric current that flows through them and the power output they produce. So, given the same throttle position, if the vehicle is moving slowly TMs will receive higher current than if the vehicle was moving fast.

The electric current is important because, if it gets too high, it is what heats up the TMs . Depending on the session difficulty settings , when overheated the TMs may pop the breaker , or much worse – short-circuit and set the vehicle on fire . Very high current can pop the breaker even before causing overheating, although at less of a risk for damage.

This is why at low speeds, and especially when climbing positive grades under load, it is critical to apply or reduce the throttle gently, notch by notch and keep the current at a nominal level , by carefully observing the ammeter gauge.

The driver must ensure that the current doesn’t lead to uncontrollable overheating of the drivetrain .

As vehicles with electric drivetrains usually have more than one TM, in case of any one failing its power may be distributed to some of the ones that are still operational. Due to the power being distributed to a smaller amount of wheels, wheelslip is easier to occur. On the other hand, it is possible to add more TMs to a vehicle and improve its traction quality beyond original specifications, by utilizing a slug .

On some diesel-electric vehicles, TMs change their circuits at certain speeds to better optimize the load on the generator. This is called “transition”, and it may result in a brief disengagement of the TMs. This is normal behavior.

TMs can only withstand speed up to a certain amount, usually indicated red on the speedometer. Going above that speed can result in catastrophic failure , regardless of whether the TMs are engaged or not.

For the TMs to be operational, the TM breaker or breakers must be enabled.

Installing an amp limiter or overheat protection gadgets allows prevention of overloading the TMs.