Chevrolet Spark EV

[JRP3]

Extreme window sticker: Tesla Roadster 2.5 estimated at 119 MPGe

Both the Spark and the 2.5 Roadster are rated at a 119 mpge average, so his last statement is not true, especially since the roadster is at least 5 year old technology. Typical GM BS.

Wasn't the Roadster tested under the old method, which gave higher results?

 

[TonyWilliams]

Wasn't the Roadster tested under the old method, which gave higher results?

Yep, although they could make arbitrary range adjustments of up to 30%, which they did on the 2011-2012 LEAF. It could pass the LA4 EPA test at 100 miles, but EPA adjusted that to 73.

For 2013, with the new 5 cycle test, they averaged an 80% and 100% charge. The same was done to the 2012 - 2013 Toyota Rav4 EV. This was not done on the Tesla Model S, however, with 208 and 265 mile range ratings with 60kWh and 85kWh batteries, respectively.

 

[ChadS]

Wasn't the Roadster tested under the old method, which gave higher results?

I know that is true for the range. But did they change the way they calculated city and highway consumption too? Or the way they calculate mpge from the consumption figures?

They could well have, but I hope not as I like to rationalize keeping the roadster by saying it is more efficient than anything else I could get...of course I could rationalize it by saying it's the most efficient car that can get me to my mom's house and back.

 

[stopcrazypp]

I know that is true for the range. But did they change the way they calculated city and highway consumption too? Or the way they calculate mpge from the consumption figures?

They could well have, but I hope not as I like to rationalize keeping the roadster by saying it is more efficient than anything else I could get...of course I could rationalize it by saying it's the most efficient car that can get me to my mom's house and back.

You can actually calculate this from the numbers.

I'll use the 111mpge, 30kWh/100mile rating from the pre-2.5 Roadster (note that the Roadster 2.5 got 119mpge mainly from charging efficiency improvements, since the range remained the same at 245 miles).
http://green.autoblog.com/2011/05/26/epa-rates-tesla-roadster-at-111-mpge/
The 245 mile range from 56kWh works out to 22.85kWh/100 miles. This works out to a charging efficiency of about 76% if you assume the range and efficiency numbers were obtained under the same criteria.

From Tom's testing of the 2008 Roadster (which got 111mpge rating), it uses ~270Wh per ideal mile (244 ideal miles in range mode), which means 65.9kWh to charge completely full. This works out to a charging efficiency of 85% (you can also work out from 119mpge vs 111mpge, that the Roadster 2.5's charging efficiency is 91%).
http://www.saxton.org/tom_saxton/2010/07/tesla-roadster-charging-rates.html

76% from previously divided by 85%, means for the pre-2.5 Roadster there was a 90% multiplier used for the 111mpge number. So for the efficiency rating at least, this is consistent with what was done for the transitional years (2008-2012), which is to take the pre-2008 2-cycle range and apply a minimum 70% multiplier to it (as I explain in this post, although back then I didn't figure in charging efficiency):
http://www.teslamotorsclub.com/showthread.php/8252-EPA-range/page2?p=131625&viewfull=1#post131625

If you want to be more "fair" and consistent with the 2011 Leaf, you would use a 70% multiplier for the efficiency number which would give you 119mpge * (70%/90%) = 93mpge for the Roadster 2.5.

A more "realistic" number would be to use the actual test results of the Model S: 320 miles 2-cycle EPA, 265 miles 5-cycle EPA, resulting in a 82.8% multiplier, which means 99mpge for the Roadster 2.5.

But for now you can safely say that the 119mpge number is at least "adjusted" 5-cycle (although with a higher 90% multiplier, but they must have chose that higher multiplier with good reason), while the 245 mile range rating is completely unadjusted (pure EPA 2-cycle range).

 

[ChadS]

Thanks, the link to your old post really helped. I somehow thought range was determined separately, rather than calculated from the consumption figures.

 

[scottf200]

2014 Chevy Spark EV Gets EPA Range Rating of 82 Miles; 119 MPGe Combined (in comments section)

Peter Savagian
May 1, 2013 at 12:21 pm

I am the general director for Electric Drives and Electrification Systems Engineering at General Motors. I need to disabuse you 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.
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 extraordinarly low driveline inertia, less than 1/5 of the driveline 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.

Google search turned up:
Peter Savagian (suh vah’ jhin) - General Motors
SAE International -- mobility engineering
OEM Reports: The Chevrolet Spark EV 1ET35 Drive Unit - Performance, Efficiency, and Drive Quality

Pete serves as Engineering Director of GM’s Electrification Architecture and Electric Motor Release Center. For the past 12 years, in various roles, he has managed product development and advanced engineering for GM’s hybrid systems, including hybrid architecture development, electric drive component development, systems engineering, systems analysis, and control algorithm development. Pete has worked on electric vehicle systems since 1990. Prior to his current assignment, Pete was Chief Engineer for GM’s EV1 Electric Vehicle Drive Unit and Power Electronics at General Motors and at Delco Electronics. In the past, he has worked at Hughes Aircraft Company and Sundstrand Aviation in various engineering roles.
Pete holds a BS in Mechanical Engineering from the University of Wisconsin, a MS in Operations Research Engineering from the University of Southern California, and an MBA from Duke University.

 

[TEG]

One would think that the approach they mentioned could result in a higher top speed (much higher than LEAF) unless their motor has a low redline...

 

[Dave EV]

...unless their motor has a low redline...

It's very likely that they gave up high RPM capability in favor of low RPM torque. Still, seems like a good trade off given the performance they got out of it. A123 batteries don't hurt either - they can take a punishment and still last a long time.

 

[tommolog]

I was one of the people publicly doubting that the 400 lb-ft was a true "at the motor" reading and simply a gear-amplified value, but I was obviously wrong. So it has 100 lb-ft more torque than a Roadster and more than a 60kW or 85kW S does. Only the Model S performance has more. It obviously won't deliver the performance of these vehicles, but it should be an interesting little car to drive. :smile:

 

[GSP]

In the oral presentation that Pete Savagian gave to the SAE (scottf200's link above) he stated that the motor was capable of over 10,000 rpm, but the gearing is designed for 5500 rpm at maximum vehicle speed.

He also described the Model S as "impressive in its own right". :biggrin:

GSP

 

[ElSupreme]

In the oral presentation that Pete Savagian gave to the SAE (scottf200's link above) he stated that the motor was capable of over 10,000 rpm, but the gearing is designed for 5500 rpm at maximum vehicle speed.

He also described the Model S as "impressive in its own right". :biggrin:

GSP

If they are going to keep the top speed motor rpms at 5500 then they will most likely have about half of the gear reduction, thus negating about half of the motor shaft torque.

Engine/Motor torque means nothing, it is all about final drive torque.

 

[scottf200]

If they are going to keep the top speed motor rpms at 5500 then they will most likely have about half of the gear reduction, thus negating about half of the motor shaft torque.
Engine/Motor torque means nothing, it is all about final drive torque.

He tried to address the why in his quote. Not sure if you caught that.

Peter Savagian
May 1, 2013 at 12:21 pm

<snip>
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 extraordinarly low driveline inertia, less than 1/5 of the driveline 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.

 

[ElSupreme]

He tried to address the why in his quote. Not sure if you caught that.

Peter Savagian
May 1, 2013 at 12:21 pm

Yeah. But he only mentioned the benefits, and a lot of people were seemingly wondering how it would perform with so much torque. I was trying to highlight that it doesn't actually put out the torque at the wheels.

The other big drawback that isn't said is this motor will likely be much heavier, and much bulkier than the current motors used in EVs. There certainly advantages, but there are drawbacks also.

 

[Kipernicus]

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 extraordinarly low driveline inertia, less than 1/5 of the driveline 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.

What does lower driveline inertia mean?
It seems like if I'm driving in 4th gear my off-the-line acceleration will be weak but high speed cruising will be smooth and quiet at low rpms (and with less regen at highway speeds).

 

[qwk]

I was one of the people publicly doubting that the 400 lb-ft was a true "at the motor" reading and simply a gear-amplified value, but I was obviously wrong. So it has 100 lb-ft more torque than a Roadster and more than a 60kW or 85kW S does. Only the Model S performance has more. It obviously won't deliver the performance of these vehicles, but it should be an interesting little car to drive. :smile:

Me too, although I'm still skeptical. The only way to settle this, is to put a model S, or roadster, or leaf on a dyno, and then dyno the spark. Rwtq, (or fwtq), will tell the entire story here, as this number is measured the same for both vehicles, and cannot be fudged(like motor hp, tq can).

 

[fengshui]

What does lower driveline inertia mean?
It seems like if I'm driving in 4th gear my off-the-line acceleration will be weak but high speed cruising will be smooth and quiet at low rpms (and with less regen at highway speeds).

After some research, here's what I've discerned. Please anyone here who sees flaws in this argument, correct me if I'm wrong.

For an EV, one of the energetic costs of acceleration is altering the inertia of the driveline. If you've got a standard electric motor with a single-gear engine spinning at 6000 RPM into a 9:1 gear reduction, the vehicle is travelling at about 45mph. If you want to accelerate to 55mph, the RPM of the engine needs to be increased to 7300 RPM. Disregarding the energy required to move the car and run ancillary services, it takes energy just to bring the engine itself up by 1300 RPM. On the Spark EV, they use a high-torque/low-speed motor. As such, the Spark motor will only be running at 2000 RPM to achieve speeds of 45mph. For the Spark, accelerating to 55mph only requires 450 additional RPM. By reducing the inertial energy contained in the motor, the energy efficiency of the entire system is increased.

Unfortunately, the side affect of the above is that due to the decreased gear reduction, the Spark EV gets less axle torque out of the 400 ft-lbs of engine torque it generates. If the Spark EV motor had a 7-9:1 gear reduction, it would be faster off the line than other EVs, certainly. However, because its reduction is only 3.18:1 each rotation of the engine has to do more movement of the car. That reduces the effective axle torque, and shows why the motor was built with such a high initial torque. Does that fit with other reader's understanding?

 

[JRP3]

I think you've summed it up well.

 

[ElSupreme]

After some research, here's what I've discerned. Please anyone here who sees flaws in this argument, correct me if I'm wrong.

For an EV, one of the energetic costs of acceleration is altering the inertia of the driveline. If you've got a standard electric motor with a single-gear engine spinning at 6000 RPM into a 9:1 gear reduction, the vehicle is travelling at about 45mph. If you want to accelerate to 55mph, the RPM of the engine needs to be increased to 7300 RPM. Disregarding the energy required to move the car and run ancillary services, it takes energy just to bring the engine itself up by 1300 RPM. On the Spark EV, they use a high-torque/low-speed motor. As such, the Spark motor will only be running at 2000 RPM to achieve speeds of 45mph. For the Spark, accelerating to 55mph only requires 450 additional RPM. By reducing the inertial energy contained in the motor, the energy efficiency of the entire system is increased.

Unfortunately, the side affect of the above is that due to the decreased gear reduction, the Spark EV gets less axle torque out of the 400 ft-lbs of engine torque it generates. If the Spark EV motor had a 7-9:1 gear reduction, it would be faster off the line than other EVs, certainly. However, because its reduction is only 3.18:1 each rotation of the engine has to do more movement of the car. That reduces the effective axle torque, and shows why the motor was built with such a high initial torque. Does that fit with other reader's understanding?

Good summation. But remember that driveline inertia is a miniscule amount of energy compared with moving the vehicle forward. And in an EV you are talking probably half to start with from an ICE. And you only have that increased inertia before the gear reduction. So in the Tesla basically just the rotor, and the motor drive shaft. Not a whole lot of mass with extra inertia (over a slower motor) and that high torque low speed motor is going to be more massive, so you might not come out ahead until at high speed.

I am skeptical that GM has something really great here. I think they started out with a standard 1800/3600 rpm industrial motor, and adapted it for EV use, versus starting from scratch, or a high speed motor.

 

[JRP3]

I doubt they started with an industrial motor, they know how to build EV motors from scratch.

 

[fengshui]

Good summation. But remember that driveline inertia is a miniscule amount of energy compared with moving the vehicle forward. And in an EV you are talking probably half to start with from an ICE. And you only have that increased inertia before the gear reduction. So in the Tesla basically just the rotor, and the motor drive shaft. Not a whole lot of mass with extra inertia (over a slower motor) and that high torque low speed motor is going to be more massive, so you might not come out ahead until at high speed.

Yeah, it seems like a weird place to economize. However, the GM VP seems to feel there's value in it (either actual or marketing):

Lower gear mesh, spinning losses, and lower high speed electromagnetic losses mean very high drive unit efficiency.

​We'll find out how it all shakes out when the car is released later this year.