|
Maybe, but I would be surprised if they did that. From a manufacturing point of view, having two different motor types is more expensive. More importantly, the motor drive electronics would have to be designed specifically to support that. A motor's top speed is limited by the supply voltage because a spinning motor generates its own voltage called back-EMF. When back-EMF matches the supply voltage, the motor drive can't push any current through the motor because there's not enough of a voltage difference. When the motor spins even faster than that, its back-EMF exceeds the supply voltage. This does something funny to the motor drive. The voltage across the FETs in its H-Bridge circuit swaps polarity and the FETs become "reverse biased". A reverse biased FET acts like a diode, and allows current to flow through it. As a result, the motor generates a braking torque. The only way for a motor drive to avoid that would be to have an additional semiconductor in series with the H-Bridge circuit. That would make the drive more expensive, and lower efficiency. It could be done, but I doubt it. It's also hard to optimize a motor to work well at low speeds, but then have it be efficient at high speeds, even if not using it. One of the ways motors lose efficiency are in what are called "eddy current losses". Just the fact that the motor is spinning means that metal is moving through alternating magnetic fields, and that induces eddy currents in the metal. Those Eddy currents generate a braking torque, and heat up the metal. This all assumes the motors are permanent magnet brushless motors. I think that's a safe assumption since they are in-hub. There are other types of motors, such as induction, that work differently and don't have the same "speed limit" or Eddy current losses when freewheeling. Most electric vehicles use one or two induction motors. They aren't in-hub, though, because they don't scale down in size well. |