Someone please help understanding the ratios

[nmikmik]

I know one thing, in exact science like math and physics there is no such thing as miracles

So I am looking at the C&D comparison of EVs

http://www.caranddriver.com/comparisons/final-scoring-performance-data-and-complete-specs-page-8

Spark has the untouchable by other in comparison torque at 400 lbs ft , i will also assume it is at the wheel not at the entrance to the gear box because all other specs are very similar in all the vehicles with the exception of only one thing the gear ratio.
On the Spark it is 3.17 over 2.4 times less of the ratio to the next 7.82 on the Ford Focus.

No da it has such great torque, but is it at the expense of the proverbial range? i.e. if the ratio would be similar in the 7+, would the range increase greatly as well?
Also, does the above ratios have something to do with the regen abilities? Maybe that is the reason the 2015 "should" be getting a greater number for the gear ratio?
Thanks

 

[SteveC5088]

The high torque delivered by the Spark means it can accelerate more quickly. Torque is created by magnetic fields, which is created by current flowing through wires. Higher current = higher torque. So while the car is accelerating quickly, it is using lots of juice. But then, another car accelerating half as quickly would take half the electric current, but over twice the amount of time. So the electric usage is nearly equal.

Range is more affected by the wind drag on the car and the speed the car is traveling. It wouldn't matter which car's motor and drive setup is propelling it down the road. The car with the least drag would get more range. Since wind drag increases exponentially with speed, driving slower is the best way to get more range.

The change in gear ratio may have a slight effect on range, but probably because the different gear ratio allows the motor to run at a more efficient speed.

 

[nmikmik]

Thank you for your reply Steve,

But I was looking at relation between the gear ratios and torque/range.

For example, what dictates the "Higher current = higher torque" if the batteries voltage/motor specifications are the same or similar so will be the current i.e. torque? Yet GM lowers the gear to get that torque.
No offense, but I also don't buy the theory;
"So while the car is accelerating quickly, it is using lots of juice. But then, another car accelerating half as quickly would take half the electric current, but over twice the amount of time. So the electric usage is nearly equal."
If that statement is correct, the quick/aggressive acceleration on any vehicle would have a negligible affect on the fuel economy and subsequently range, but it sure does affect it greatly in the real world applications.

The change in gear ratio may have a slight effect on range, but probably because the different gear ratio allows the motor to run at a more efficient speed.

That is my point/question. If the gear ratio allows the Spark to accelerate on par with Tesla and beat almost all the BEV competition on 0-60, how come reduction of the gear ratio would not have any affect on range?
Thanks again,

 

[SteveC5088]

> If that statement is correct, the quick/aggressive acceleration on any vehicle would have a negligible affect on the fuel economy and subsequently range, but it sure does affect it greatly in the real world applications.

You're talking about fossil fueled engines here, aren't you. Aggressive acceleration causes gasoline etc engines to force lots more air in and lots more exhaust out through the intake and exhaust manifolds. In those engines, that wipes out lots of the power released by the fuel combustion process. Gasoline etc engines can only convert about 30% of the power of the fuel into motion.

Electric motors are way more efficient. Throwing 100% of the battery's capacity at the motor doesn't cause similar losses. Electric systems are way more efficient.

> If the gear ratio allows the Spark to accelerate on par with Tesla and beat almost all the BEV competition on 0-60, how come reduction of the gear ratio would not have any affect on range?

Because greater horsepower and torque will get you from 0 to 60 a lot quicker, but those things don't matter when you're cruising along at 40 or 60 mph. Greater horsepower does require a bigger motor, and therefore more weight. So that would affect range more than tweaking gear ratios.

 

[fengshui]

Spark has the untouchable by other in comparison torque at 400 lbs ft , i will also assume it is at the wheel not at the entrance to the gear box because all other specs are very similar in all the vehicles with the exception of only one thing the gear ratio.
On the Spark it is 3.17 over 2.4 times less of the ratio to the next 7.82 on the Ford Focus.

Don't assume that the 400 ft-lbs of torque is as the wheel. It's not. The Spark EV motor generates 400 ft/lbs at the gear box. However, it has a much lower RPM, so they use the lower ratio gearing.

 

[nmikmik]

Thank you,

Now that makes sense.

 

[FutureFolly]

It's a little bit hard to explain all the reasons they went with such a high torque electric motor.

The convention in electric cars is to exploit the naturally high redline limits of electric motors with modest torque. An electric motor can put out maximum torque from 0 RPM to the RPM where maximum power is available then torque tapers linearly while total available power at the wheels remains the same until redline.

The Spark has about the same power as the competition, but it's noticeably quicker. The reason is that maximum power is reached at a much lower RPM than the competition. Even with much lower gearing the "400ftlbs" is only available at relatively slow speed because power isn't allowed to go above 140hp. If the engine were "unleashed" it could put out as much as the batteries could handle.

In an AC-synchronous motor, the frequency of the electricity determines the speed of the motor. The amount of current varies with the torque on the motor. As explained by an engineer, they considered going with a slightly higher gear ratio because it would reduce the load on the motor thereby increasing efficiency during acceleration, but running at low speeds makes highway travel more efficient. Higher gears help city driving because less torque is demanded from the motor.

The torque of the motor is really an expression of how much current it can handle.

 

[nmikmik]

Thank you for the explanation!

I think this is possibly the reason why they are changing the gearing to a slightly higher number for the 2015 with a "smaller" battery.
So, based on the above, they could have adjusted the current flow a little to compensate for the gears and not loose the "pocket rocket" affect.
I just don't get why they are still playing with the "compliance" vehicle. Adding the QC, different battery.
If they really didn't care, they would stop innovating and just sell as much of the current Spark as they have to and be done with it.
Well, who am I kidding, corporate America doesn't have a clue how to turn on the dime and/or stop, it continues doing what it's doing just because of pure inertia

btw, found this article explaining the reasons for the ratio change, sounds plausible...

http://insideevs.com/2015-chevy-spark-ev-highlighting-changes/

 

[Chocula]

... I just don't get why they are still playing with the "compliance" vehicle. Adding the QC, different battery.
If they really didn't care, they would stop innovating and just sell as much of the current Spark as they have to and be done with it. ...

Engineers want to build the best vehicle possible, even if the executives only care about compliance.

The quick charge is likely very inexpensive to implement, and not excessively expensive to develop. The executives have probably recognizing the writing on the wall, they will need more batteries for more cars in the future, even if they are able to weasel out of CARB requirements again. Bringing this in house reduces cost once you have sufficient demand. The gearing change probably allows them to get the same EPA range with a smaller battery, and a smaller battery reduces cost.