Chevy Spark EV Forum

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 Post subject: Re: how to disable the speed limiter
PostPosted: Sat Jan 16, 2016 11:00 am 
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Posts: 576
This car needs a torque converter...like the Zombie 222...showing that EVs can out accelerate most cars too at high speeds if they have more than one gear or a converter.


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 Post subject: Re: how to disable the speed limiter
PostPosted: Sun Jan 17, 2016 12:25 pm 
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Posts: 536
Location: Portland, OR
nozferatu wrote:
This car needs a torque converter...like the Zombie 222...showing that EVs can out accelerate most cars too at high speeds if they have more than one gear or a converter.


It's already torque limited at low speeds because it has way more torque than the skinny, high efficiency tires can handle. It doesn't need a torque converter, it needs more traction and less torque limiting (software).

Bryce


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 Post subject: Re: how to disable the speed limiter
PostPosted: Sun Jan 17, 2016 2:26 pm 
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Nashco wrote:
nozferatu wrote:
This car needs a torque converter...like the Zombie 222...showing that EVs can out accelerate most cars too at high speeds if they have more than one gear or a converter.


It's already torque limited at low speeds because it has way more torque than the skinny, high efficiency tires can handle. It doesn't need a torque converter, it needs more traction and less torque limiting (software).

Bryce


No it needs a torque converter to accelerate better at higher speeds....putting the motor back in the higher torque bands at speeds where the motor torque drops off.


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 Post subject: Re: how to disable the speed limiter
PostPosted: Sun Jan 17, 2016 3:30 pm 
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Joined: Sat Jul 27, 2013 9:52 am
Posts: 125
Location: Los Gatos
nozferatu wrote:
Nashco wrote:
nozferatu wrote:
This car needs a torque converter...like the Zombie 222...showing that EVs can out accelerate most cars too at high speeds if they have more than one gear or a converter.


It's already torque limited at low speeds because it has way more torque than the skinny, high efficiency tires can handle. It doesn't need a torque converter, it needs more traction and less torque limiting (software).

Bryce


No it needs a torque converter to accelerate better at higher speeds....putting the motor back in the higher torque bands at speeds where the motor torque drops off.


To get the best acceleration you need to get the motor to its peak POWER point, the torque is not very relevant. The peak power point for the Spark EV is at around the motor speed equivalent to ~45mph, with a slight drop off up to ~80mph and a steeper decline beyond that (MY 2014).

If you were to change the gearing you would need a ratio that does that - a conventional torque converter would be very ill-suited as they only act as a step down where this would need a step-up. Also they are not very efficient - it would probably lose more power than would be gained.

Having selectable gearing might give some advantage - a lower final drive ratio with fixed gearing may also be a good way if the car was going to be used a lot at high speed but range would suffer.

Driving much at high speed would also severely impact range as aerodynamic losses go up as the cube of speed.

kevin


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 Post subject: Re: how to disable the speed limiter
PostPosted: Sun Jan 17, 2016 6:20 pm 
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Joined: Sun Dec 07, 2014 8:46 pm
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Quote:

.... but range would suffer.

Driving much at high speed would also severely impact range as aerodynamic losses go up as the cube of speed.

kevin


I think we're pretty much okay with range loss on this topic.


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 Post subject: Re: how to disable the speed limiter
PostPosted: Sun Jan 17, 2016 8:50 pm 
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Posts: 576
kevin wrote:
To get the best acceleration you need to get the motor to its peak POWER point, the torque is not very relevant. The peak power point for the Spark EV is at around the motor speed equivalent to ~45mph, with a slight drop off up to ~80mph and a steeper decline beyond that (MY 2014).

If you were to change the gearing you would need a ratio that does that - a conventional torque converter would be very ill-suited as they only act as a step down where this would need a step-up. Also they are not very efficient - it would probably lose more power than would be gained.

Having selectable gearing might give some advantage - a lower final drive ratio with fixed gearing may also be a good way if the car was going to be used a lot at high speed but range would suffer.

Driving much at high speed would also severely impact range as aerodynamic losses go up as the cube of speed.

kevin


I think you guys are missing the point....I want REALLY good acceleration at 60 not just from 20. That can be done with a torque converter and range isn't an issue because it's a burst not sustained.

Look at what the Zombie 222 owner did to get an idea of what sort of performance he's getting from the converter.


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 Post subject: Re: how to disable the speed limiter
PostPosted: Mon Jan 18, 2016 8:54 am 
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Joined: Sat Jul 27, 2013 9:52 am
Posts: 125
Location: Los Gatos
nozferatu wrote:
kevin wrote:
...
kevin


I think you guys are missing the point....I want REALLY good acceleration at 60 not just from 20. That can be done with a torque converter and range isn't an issue because it's a burst not sustained.

Look at what the Zombie 222 owner did to get an idea of what sort of performance he's getting from the converter.


>>I want REALLY good acceleration at 60 not just from 20

In that case There is not much you can do - from the power curve @60mph there is about 95kW available. If you change the gearing (even dynamically with a torque converter) the best you could do is about 105kW (The power @ 45mph). Take into account the losses from a torque converter and it would probably be less power to the wheels.

You haven't got the 800HP of the Zombie 222 in the Spark.

kevin


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 Post subject: Re: how to disable the speed limiter
PostPosted: Mon Jan 18, 2016 8:59 am 
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Posts: 928
Location: KC,MO
kevin wrote:
..... at high speed would also severely impact range as aerodynamic losses go up as the cube of speed.
kevin

Aero drag increases with the square of velocity.

_________________
Used '14 2LT w/ DCFC.
In the middle of the country.
Far from any of its sibs.


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 Post subject: Re: how to disable the speed limiter
PostPosted: Mon Jan 18, 2016 10:25 am 
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Joined: Sat Jul 27, 2013 9:52 am
Posts: 125
Location: Los Gatos
NORTON wrote:
kevin wrote:
..... at high speed would also severely impact range as aerodynamic losses go up as the cube of speed.
kevin

Aero drag increases with the square of velocity.


The drag goes up as the square but the power goes up as the cube since you have to multiply the drag by the velocity to get the power required from the motor.

Since you are going faster the time to go a specific distance drops inversely with speed, so the energy to go a specific distance does go up as the square of speed.

kevin


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 Post subject: Re: how to disable the speed limiter
PostPosted: Wed Jun 01, 2016 1:47 pm 
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Joined: Mon May 25, 2015 12:19 pm
Posts: 496
Based on my "highly scientific and extremely accurate academic research on SparkEV blog" (yes, that's sarcasm), power at 90 MPH is about 35 kW on flat road and 90kW on 8% grade.

http://sparkev.blogspot.com/2016/03/ran ... -hill.html

Seeing how peak DCFC is 45 KW to 80% most of the time, sustained drain at higher power may not be good for the battery. It could be that cooling system was designed around 50 kW sustained, and it could exceed that with heater / AC even on slight hill at 90 MPH. I suppose they also have limit based on thermal, but simple speed limiting is also good protection against not being able to drive at all (as in suspended/revoked license).


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