Okay,
I want to start but stating that I understand why an electric motor doesn’t need a transmission in the context of required torque and the lack of need to convert low RPM to high torque.
But in randomly plotting a battery pack for my “planned and likely to never happen” electric bike/moped. I was wondering if there might be ways to extend the battery life without just dumping more cells in. My first thought is that if the power applied to the motor is proportional to the total output of the motor, then higher output means higher power draw (profound, I know but bear with me) so to reduce power draw, you would just have to reduce the work the motor is doing (again, brilliance incarnate, I know)
That brings me back around to transmissions and this might be where my understanding of the way motors and their relationship to power falls apart.
Wouldn’t the momentum of your system reduce the need for certain torque ranges? Until recently, I actually though that was how transmissions worked, they traded the torque energy for high end speed in later gears. You have environmental conditions (drag, friction, etc etc) but the momentum should help alleviate some of the torque requirements, right?
If so, then outside of “top end performance” could a transmission be used to reduce the work load of the motor allowing it to do the same work at lower RPM’s and thus extend the range of the battery?
Obviously a lot of energy would get lost in the new system being added and efficiency would be an issue but throwing the idea of a car transmission out the window, would a transmission of SOME sort help with that?
Your flaw is thinking momentum is a force that’s working with the electric motors. It takes constant force to maintain speed. The faster you go, the more force is needed.
Transmissions are needed on ICE cars because they have a specific power band and have a limited RPM range. The transmission allows the engine to propel the vehicle at any road speed while operating within that specific RPM range. In addition to this, the transmission can be coded to shift at certain RPM’s based on load and speed which can increase power or efficiency. But it has nothing to do with being more efficient in general at higher gears.
Electric motors produce the same power and torque regardless of RPM, thus a transmission is not needed. Transmissions in and of themselves contribute their own drivetrain losses, are an additional wear item, and are heavy. So adding a transmission to an electric car would make it less efficient, produce less range, and be less reliable.
Besides the constant power requirement you have, which basically doesn’t change no matter what you put around there, motor systems used in EVs are quite “sophisticated” in terms of how much you can control them, which doesn’t exist at all for combustion engines. Depending the power demand you have from the car at any given instant, the controller can set the motor to provide the torque and the speed at the highest efficiency point, which is super interesting.
I guess the easiest way to understand it is what converts your rpm to torque in your configuration? In an ICE your torque is generated by rpm and needs to be maintained at a fixed rpm for peak torque. Your motor generates torque by electrons not rpm.
So there you have a mechanical limit vs a electromagnetic limit. One of these converts rpm and torque faster and more efficiently.