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Re: Why do electric car motors have constant torque?
edit:
I just had another coff of cuppee this morning
so I'll elaborate a bit. The torque output of the electric motor is dependent on the load presented to the shaft opposing rotation. When that electric motor is mechanically connected to a large mass, the torque output tries to accelerate against that mass and then the magnitude of the motor torque is limited by the controller. Most controllers have a current limit.
So when you jump into your EV and mash the throttle pedal to the floor, the controller goes into current limit and allows that amount of current to flow to the motor. As the car accelerates, that current stays at this current limit until the motor reaches base speed. So for that portion of the acceleration profile, there is a constant current to the motor. Since the motor torque is proportional to current, the motor torque is constant (at its maximum) for that portion of the acceleration event.
But after base speed is reached and exceeded, the motor torque reduces. And if you lift the throttle and accelerate at less than maximum, torque will be less.
So electric motor torque is not constant. There is a region of operation in conjunction with the controller and for certain load conditions which will give the appearance of constant torque.
Regards,
major
They do not.why do electric motors have a constant torque over all RPM ranges?
edit:
I just had another coff of cuppee this morning
So when you jump into your EV and mash the throttle pedal to the floor, the controller goes into current limit and allows that amount of current to flow to the motor. As the car accelerates, that current stays at this current limit until the motor reaches base speed. So for that portion of the acceleration profile, there is a constant current to the motor. Since the motor torque is proportional to current, the motor torque is constant (at its maximum) for that portion of the acceleration event.
But after base speed is reached and exceeded, the motor torque reduces. And if you lift the throttle and accelerate at less than maximum, torque will be less.
So electric motor torque is not constant. There is a region of operation in conjunction with the controller and for certain load conditions which will give the appearance of constant torque.
Regards,
major