Zoomit wrote:
GM obviously has some rationale to limit the top end of the EV variant. If that rationale was not "motor speed limits", what components of the drive train, or vehicle dynamics, do you think caused them to limit the EV to 90mph?
A couple of things come to mind. First, how many kw's is the motor drawing at 90 mph? Electric motor power ratings are based mainly on the ability to dissipate heat. If this motor is rated "100 kw", that is likely the peak "short term" rating. Long enough to accelerate to desired speed, up an incline, with full weight capacity, but not intended to remain at this load continuously. An IC engine CAN run at it's peak rating for long durations, so it's limitation is based on mechanical stresses (RPM's). (The water cooling jacket of an ICE is a very efficient system) I've seen some GE DC traction motors with a peak rating as much as 6 times its continuous rating. I don't know what the Spark's continuous rating is, but I sure would like to.
Another thing that may factor in is the permanent magnet motor design used. Magnets weaken with exposure to high temperatures. (how about a Leaf with a deteriorating battery AND motor capacity! That would really suck)
Also from what I've read on this forum, the stability of this 3,000 lb car isn't the best at highway speeds (at least not with stock tires). For those of us who aren't skilled high speed drivers, this could be quite dangerous.
Just a few possibilities...
David
ps, that poor Fluke...A few dollars spent on better balancing and bearings would eliminate that situation in the Spark. Some types of motors MUST have a load at all times cause they can spin up uncontrolled until exploding into shrapnel. Some fan motors and vacuum cleaner motors are like that. Quite scarry the 1st time it .... "teaches" you this lesson in motors.