GM Spark 400 ftlb Torque

[VONKIE]

GM’s General Director for Electric Drives and Electrification Systems Engineering, Peter Savagian:

I need to disabuse readers of the mistaken notion that this motor has less than 400 ftlb of Torque. The Spark EV motor is designed and manufactured by GM. This motor makes 540 Nm (402 ftlbf) of Torque at stall and out to about 2000 rpm. This is not gear- multiplied axle torque, but actual motor shaft torque.

Mr. Savagian went on to explain how GM managed that torque-rating, as well as why their EPA ratings are so high:

The very high torque is motor performance that we are very proud of, and customers will notice the difference: (It has a gear reduction of 3.18 to 1, so the axle torque is the product of these two). This is a very low numerical reduction ratio, which has several great benefits

1) Feels much better to drive. 3.18:1 is less than half of the reduction of all other EVs. This makes for extraordinary low drive-line inertia, less than 1/5 of the drive-line inertia of the Nissan Leaf and 1/4 that of the Fiat 500 EV. Their cars feel like you are driving around in second gear all day long; ours feels like fourth gear.

2) Lower gear mesh, spinning losses, and lower high speed electromagnetic losses mean very high drive unit efficiency. The Spark EV efficiency from DC current to delivered Wheel torque is 85% averaged over the city driving schedule and 92% when averaged over the highway schedule. This is the highest in the industry, and that is one of the reasons why the Spark EV sets the benchmark for most efficient car.

 

[nikwax]

That all relates to the 2014. The 2015 has a lighter battery pack, different drive ratio, and lower motor torque figure. Performance specs are the same.

 

[Nashco]

Yes, that's fairly old news, and has already been discussed here:

http://mychevysparkev.com/forum/viewtopic.php?f=2&t=3640&p=6054

...along with many other places.

Bryce

 

[SteveC5088]

And what this really means....

The other day, I made a right turn at a red light, just as the cross-traffic was starting on their green. As usual, the Spark EV ripped down the road way ahead of the following traffic. Had the window open though, and heard the loud sound of a modified muffler from another car. Checked my mirror and saw a new Mustang trying to keep up.

Half a mile down the street, Mustang and Spark EV came to the next red light side-by-side. When the light turned green, Mustang's tires squeaked some, so I knew it was a race. I floored Sparky Jr, the darned front-wheel drive slipped on the white pedestrian crossing lines and did its usual squeaks on uneven pavement. Mustang got a 5-foot lead, but Sparki then caught it and moved ahead slightly. At about 10 over the speed limit, we both let up, both grinning.

I am sure Mustang driver was impressed that he couldn't beat my little 'lectric golf cart, even with his performance mods.

 

[jsca72]

I floored Sparky Jr, the darned front-wheel drive slipped on the white pedestrian crossing lines

This always seems to happen just after a tell a passenger, "Let me show you how it can accelerate!"

 

[nozferatu]

And what this really means....

The other day, I made a right turn at a red light, just as the cross-traffic was starting on their green. As usual, the Spark EV ripped down the road way ahead of the following traffic. Had the window open though, and heard the loud sound of a modified muffler from another car. Checked my mirror and saw a new Mustang trying to keep up.

Half a mile down the street, Mustang and Spark EV came to the next red light side-by-side. When the light turned green, Mustang's tires squeaked some, so I knew it was a race. I floored Sparky Jr, the darned front-wheel drive slipped on the white pedestrian crossing lines and did its usual squeaks on uneven pavement. Mustang got a 5-foot lead, but Sparki then caught it and moved ahead slightly. At about 10 over the speed limit, we both let up, both grinning.

I am sure Mustang driver was impressed that he couldn't beat my little 'lectric golf cart, even with his performance mods.

There's a punk in my neighborhood who has a new Mustang turbo....smoked him a few times and he was PISSED. Come across him again a couple of times and he floors it every time he sees me....lol...kinda funny.

I've lost count how many fast cars I've embarrassed with this thing. I can't imagine how much quicker it'd be if it had 17 or 18 inch rims, better suspension, and a traction control system that doesn't' destroy its off the line acceleration..the Achilles heal of this car IMO.

 

[nikwax]

Switch off traction control?

 

[Leafless]

OK... Leafless here... new to this forum. Maybe a better handle would have been "Clueless." Well, maybe not 100% clueless, but certainly confused. Here is what I don't understand:

2014 Spark EV specs detail 400 ft. lbs. torque and use the 3.17 final drive ratio.
2015 Spark EV specs detail 327 ft. lbs. torque and use the 3.87 final drive ratio.

I understand that there is a difference in the batteries used for these two model years. And, since I have not been able to find any information relating to a change in the motor, I am assuming that the motors across these two model years are identical. (If I am wrong on this point, please enlighten me.)

So, why the difference in torque?

Also, I saw something indicating the the max rpm for the 14 is 5500 rpm. I haven't seen anything regarding the max rpm for the 15-16 Spark EV. Has this changed?

 

[nikwax]

OK... Leafless here... new to this forum. Maybe a better handle would have been "Clueless." Well, maybe not 100% clueless, but certainly confused. Here is what I don't understand:

2014 Spark EV specs detail 400 ft. lbs. torque and use the 3.17 final drive ratio.
2015 Spark EV specs detail 327 ft. lbs. torque and use the 3.87 final drive ratio.

I understand that there is a difference in the batteries used for these two model years. And, since I have not been able to find any information relating to a change in the motor, I am assuming that the motors across these two model years are identical. (If I am wrong on this point, please enlighten me.)

So, why the difference in torque?

Also, I saw something indicating the the max rpm for the 14 is 5500 rpm. I haven't seen anything regarding the max rpm for the 15-16 Spark EV. Has this changed?

in 2015, GM changed battery suppliers from A123 to LG. The LG battery pack is lighter and has less capacity, which more or less evens out in terms of range. The motor is the same in both, GM designed and manufactured.


Motor torque x gear ratio = torque at the wheel. Again, things more or less even out. As far as we know, the driving factor behind this was the change in battery supplier. And we now know that LG is going to supply most of the drive train for the upcoming Chevy Bolt.

 

[wywa]

> This motor makes 540 Nm (402 ftlbf) of Torque at stall and out to about 2000 rpm. This is not gear- multiplied axle torque, but actual motor shaft torque. [OP]

If true this implies the motors are not the same or are current limited for 2015 by the inverter or some other way.
--

 

[Taxman]

I believe that in both cases, the software is torque limited to just under the amount needed to break the front tires loose on clean dry pavement.

Notice that when you do the math, the front wheel torque (claimed motor torque x gear ratio) is the same.

The software also limits horsepower to 140, so power rises from 0-140hp as speed increases from zero to about 40mph, then power holds constant at 140 while torque decreases with increasing speed.
I suspect the 140 figure is either to maximize motor life, or to keep from frying the motor control circuits.

 

[SparkevBlogspot]

The software also limits horsepower to 140, so power rises from 0-140hp as speed increases from zero to about 40mph, then power holds constant at 140 while torque decreases with increasing speed.

Power to wheels and power to motor are two very different things. It is true that instantaneous power at the wheels are 0 HP at 0 MPH, but the motor is sucking 140 HP at 0 MPH. This is true of all cars (even gassers). As an example, imagine you’re at a hill and holding position using throttle (gas or EV). Power will be drawn out of the battery (or using gas) even if the mechanical power of the wheels is zero: zero movement=zero energy=zero power.

For SparkEV, electric power is constant at 140 HP regardless of speed. Instantaneous wheel power is 0 at 0 MPH to peak at 140 HP at about 42 MPH, then start to taper down along with torque. Just so that there's no confusion, we're talking about full throttle scenarios only.

Curiously, if you recall from your basic power electric course, electric motors made peak torque at 0 RPM and then slope down due to back EMF, yet most EV do not; they hold the torque to some RPM and taper much later, like at 35 MPH. Why would this be?

I suspect it’s due P=I^2 * R and torque=k*P (simple model; more complex in reality). That would make the current exponentially large at low RPM to follow “traditional” motor torque profile. If you extrapolate the slope of SparkEV and this theory is true, it would suck over 4 times the current (over 1000 amps!) at 0 RPM if not software limited, and break things in the process.

 

[ncerna]

I imagine there would be less tire squeal with some good racing tires.

 

[kevin]

...
It is true that instantaneous power at the wheels are 0 HP at 0 MPH, but the motor is sucking 140 HP at 0 MPH. This is true of all cars (even gassers). As an example, imagine you’re at a hill and holding position using throttle (gas or EV). Power will be drawn out of the battery (or using gas) even if the mechanical power of the wheels is zero: zero movement=zero energy=zero power.

For SparkEV, electric power is constant at 140 HP regardless of speed. Instantaneous wheel power is 0 at 0 MPH to peak at 140 HP at about 42 MPH, then start to taper down along with torque. Just so that there's no confusion, we're talking about full throttle scenarios only.
....

That is completely incorrect.

The motor controller will limit the torque to a specific level that is constant up to about 40mph. Since torque is proportional to torque the current will be approximately constant up to 40mph. I expect for the Spark the current is in the 300-500 Amp range.

The losses in the motor will be significant at full torque and low speed - probably in the region of 10kW at full torque.

In an internal combustion engine vehicle the only way to get full power at zero speed is to slip the clutch while keeping the engine at its peak power RPM - all of the power will be dissipated in the clutch and it won't last more than a few seconds under these conditions.

With an automatic transmission it will not usually even allow the engine to get to full power RPM - again all th engine power has to be dissipated in the torque converter or clutch (depending upon type of automatic transmission).

kevin

 

[SparkevBlogspot]

That is completely incorrect.

What exactly is incorrect?

In a typical motor torque curve, the peak torque occurs at 0 RPM and taper. As you correctly state (which I also stated), current is roughly linear to torque. That means the peak current occurs at 0 RPM.

For SparkEV, peak torque occurs about 5 MPH and roughly holds until about 35 MPH. Since the torque is roughly constant, current is also constant. Given that the battery voltage is also roughly constant, that means power drawn is roughly constant.

But if you hold SparkEV on a hill to not move by using the throttle, you will use energy from the battery but the car gains zero energy. In effect, power from the battery is "something", but the power at the wheels is zero.

Given that the peak power is about 120 kW out of the battery and the battery is about 370V (about 75%), simple math shows the peak current to be 324 amps. But some of that current will be lost in other stuff (ie, inverter), which means the motor would see less, maybe bit under 300 amps (111 kW) or 283 amps (105 kW).

If you extrapolate torque taper like one would see with "typical" motor torque curve, you will see that zero RPM will be 2X to 4X the torque, depending on how you extrapolate. That means if SparkEV motor operating in "typical motor" fashion could draw 1000 amps at 0 RPM.

For full power with gas car, what you say is true, and I wrote a whole blog post on how gas car can be made to behave like EV by destroying their transmission.

http://sparkev.blogspot.com/2015/11/can-stock-corvette-beat-tesla-p90dl-in.html

 

[kevin]

That is completely incorrect.

What exactly is incorrect?

...l

"It is true that instantaneous power at the wheels are 0 HP at 0 MPH, but the motor is sucking 140 HP at 0 MPH."

The power at 0mph will only be the losses - it will not be 140HP.

The torque(current) will be limited to the 400 lb-ft maximum. As you calculate, this is in the region of 300Amps into the motor.

However because of the way the motor controller uses PWM to regulate the motor current the battery current may be much less.

At zero RPM but full torque it is probable that the battery current is only 30-40 Amps resulting in 10-20kW total input that will appear as heat in the motor. In a permanent magnet motor such as the Spark the current needs to be controlled to avoid demagnetizing the magnets.

kevin

 

[SparkevBlogspot]

You can test it yourself if you don't believe me. Fully press the throttle at any speed and see the peak power. I see 120 KW, and that's not 30A.

0 MPH is a bad example, because the motor torque at 0 MPH is about 90% to 95% of peak torque (peak starting about 5 MPH). Still, the torque is related to <b>average</b> current, the current to the motor has to be over 90% of the peak regardless of PWM. But if you're moving at 5 MPH and encounter resistance that prevents any more than 5 MPH, the motor will suck 140 HP (or more) out of the battery on full throttle while the car gains no energy.

Now if the controller is smart enough to detect no movement / energy added to the car, and it decides to back off, that could occur in time. But it won't know until the measurements are made, and instantaneous power out of the battery on full throttle would be full 140 HP (or more).

 

[NORTON]

.... In a permanent magnet motor such as the Spark the current needs to be controlled to avoid demagnetizing the magnets.

kevin

Actually it's harming the magnets by over heating them. Magnets can be 'demagnetized' in several ways. High temp is one of them.
You don't hear this talked about much in hot rodding EV talks, ebikes, EV cars, etc. Some people think you just up the wattage to the stator and everything will be fine. Or you might smoke the stator.
At least our little magnets are oil cooled!

This is the reason some EV's state in the Owner's Manual not to hold your place on a hill with the Go Pedal. The 'System' is putting power to only a few of the magnets in the rotor non-stop.

As for "400 ft/lbs of Torque !" ,,, blah, blah,, It has to be marketing 'bragging rights' that engineering went along with.
It may be there, in the lab, at zero RPM, but no way is it ever transferred to the 185's.... :roll:

 

[kevin]

You can test it yourself if you don't believe me. Fully press the throttle at any speed and see the peak power. I see 120 KW, and that's not 30A.

0 MPH is a bad example, because the motor torque at 0 MPH is about 90% to 95% of peak torque (peak starting about 5 MPH). Still, the torque is related to <b>average</b> current, the current to the motor has to be over 90% of the peak regardless of PWM. But if you're moving at 5 MPH and encounter resistance that prevents any more than 5 MPH, the motor will suck 140 HP (or more) out of the battery on full throttle while the car gains no energy.

Now if the controller is smart enough to detect no movement / energy added to the car, and it decides to back off, that could occur in time. But it won't know until the measurements are made, and instantaneous power out of the battery on full throttle would be full 140 HP (or more).

I don't have my Spark anymore but I'm skeptical that that there is actually 120kW going into the motor below the base speed, I seem to remember it increasing as speed increases.

When I have tried balancing the car on a local extremely steep hill (steep enough so I fall off the back of my bike when trying to ride up it!) the indicated power was in the 10-20kW region when the car was held stationery (admittedly not at full throttle but close)

There is a graph in the paper by Steven Tarnowsky (page 9) showing the power vs speed. - full power is not reached until about 40mph.

As I said the PWM control of the motor current means that the motor current can be a multiple of the battery current by a large factor, probably 10 times at low speed.

I would expect that the controller performs cycle by cycle current limiting so there should not be any perceptible time delay in the current limiting.

kevin

 

[kevin]

.... In a permanent magnet motor such as the Spark the current needs to be controlled to avoid demagnetizing the magnets.

kevin

Actually it's harming the magnets by over heating them. Magnets can be 'demagnetized' in several ways. High temp is one of them.
You don't hear this talked about much in hot rodding EV talks, ebikes, EV cars, etc. Some people think you just up the wattage to the stator and everything will be fine. Or you might smoke the stator.
At least our little magnets are oil cooled!

This is the reason some EV's state in the Owner's Manual not to hold your place on a hill with the Go Pedal. The 'System' is putting power to only a few of the magnets in the rotor non-stop.

As for "400 ft/lbs of Torque !" ,,, blah, blah,, It has to be marketing 'bragging rights' that engineering went along with.
It may be there, in the lab, at zero RPM, but no way is it ever transferred to the 185's.... :roll:

The magnets can be harmed both by over-current in the windings or overheating. In short term scenarios the over-current is the important one.

The motor may produce 400ft-lbs and that will be multiplied by the final drive (about 3 to 1) to give about 1300 lbs-ft at the wheels.

However that is pretty wimpy compared to what an ICE vehicle can do when it is in bottom gear with an additional 4:1 multiplier of the gearbox. A moderate performance car with 250 lb-ft from the engine in low gear may have 3000 lb-ft at the wheels. The main advantage of an EV like the Spark is that the torque delivery is very rapid, has a broad torque range, with no gaps to change gear.

kevin