An online Chevy Spark EV Forum dissussion group

I think some speculation as to what module(s) actually implements the speed limiter might be more useful than money

If the armature in an electric motor spins too fast the failure can be quite catastrophic. I saw it almost happen once in a power lab in college. The only thing that saved the lives of two undergraduate students was flames shooting out the front of a fluke ammeter that destructively acted as a big old fuse.

The prof was in the room and he heard the motor start to rapidly spin up when someone pulled the wrong power lead. He started yelling hit the breaker at the top of his lungs... I was at the next lab station which was a very large three phase motor generator pair.

When the armature is pushed past it's limits it will come apart and it suddenly stops spinning. It imparts all os it's momentum to the entire motor and rips the entire assembly off its mounts..

Jeff

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.

Why 90mph? It's an interesting question. If GM allows the gas Spark to go 103, it would seem plausible that the Spark EV, with its extra weight and lower center of gravity should be safe up to 120. I've hit the limit a couple times and the transition is abrupt indicating there is lots more umph left they aren't letting us use. According to my calculations, at 90 the motor is spinning less than 5500rpm. That's barely loping for such motors given the Tesla is allowed to spin over 16,000rpm.

Another possibility is the motor diameter. The coaxial drive shaft adds some extra girth, but we're only talking an inch or two. Shouldn't be a problem. And the tires are speed rated for 118; that's not it. Maybe it's just an experiment to see if drivers will be content with a car that only goes 90. After all, the Spark EV is the test run for the upcoming Bolt. Or maybe they set the top speed so low knowing some of us can't help ourselves and won't resist the temptation, and lose our driving privileges.

Personally I think GM set it low so it wouldn't top out faster than a gas Spark, a car they make money on. What to do about it, I haven't a clue.

Another data point is -- the Volt apparently has a similar limit, but it's at 100mph.

and GM changed the final drive ratio in 2015, so 2014 and 2015 are spinning at different speeds at 90 mph.

assumed due to some liability issues.....

I have a 2014 Spark. I think the 90mph limit is a bummer. It would be nice to at least do 100. I did not realize this about the 2014 vs. the 2015, as I actually have both the 14 and a 15. I have noticed my 14 gets significantly more range than the 15.... But I see the ratio on the 14 is 3.17..... I did not even know that EVs had ratios! But I do now.

And why limit it to 90 mph in Forward?

That's my question.
This motor and box O'gears is the same forward or reverse.

I want a SW hack to allow me to go 90 mph in Reverse !!!


Dang Nanny State,,,, Thanks Obama...

You'll need to ask for the "stunt man special."