Transmission question

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Leafless

Active member
Joined
Jun 18, 2016
Messages
34
Location
SoCal
OK.. The Spark EV has a one speed transmission. As I understand, the low (L) range is not really a lower gear set, but rather, a different calculation that increases the regenerative braking. So, my question: Is the reverse (R) a different gear, or alternatively, does selecting "R" simply reverse the motor?
 
Leafless said:
OK.. The Spark EV has a one speed transmission. As I understand, the low (L) range is not really a lower gear set, but rather, a different calculation that increases the regenerative braking. So, my question: Is the reverse (R) a different gear, or alternatively, does selecting "R" simply reverse the motor?


reverse the motor:

http://gm-volt.com/2013/06/07/my-vision-of-gen-2-0-volt/
 
Yes... that is certainly the way I see it.

There is a nice cutaway view of the driveline in Fig. 3. I have seen something similar in a short video regarding the Spark. Let me see if I can get a link to that video.

Found it here:
http://www.chevynorthridge.com/VehicleDetails/new-2016-Chevrolet-Spark_EV-Hatch_2LT_%28Automatic%29-Northridge-CA/2789824743

The images of the motor/trans appear at about 1:30 - 1:40. You can stop the video to take a closer look.
 
L is just different SW for what happens when you let off the Go pedal.
In D you get a SW generated 'Coast'.
In L you have to keep you foot on that Go pedal at all times. You determine how to slow down.

And the Brake pedal is ALL REGEN until it maxes out then the friction brakes are blended in.
Some EV's don't have 'Blended Brakes' and require you to stay on the Go pedal (like driving in L for us) and the Brake pedal is always just old fashioned friction brakes.

Yes, as said it just spins the motor in reverse, which means in theory you could go 90 MPH in Reverse.

But NO.... We're stuck with the Nanny State always protecting us from ourselves... Thanks 'alot'...
 
NORTON said:
L is just different SW for what happens when you let off the Go pedal.
In D you get a SW generated 'Coast'.
In L you have to keep you foot on that Go pedal at all times. You determine how to slow down.

And the Brake pedal is ALL REGEN until it maxes out then the friction brakes are blended in.
Some EV's don't have 'Blended Brakes' and require you to stay on the Go pedal (like driving in L for us) and the Brake pedal is always just old fashioned friction brakes.

Yes, as said it just spins the motor in reverse, which means in theory you could go 90 MPH in Reverse.

But NO.... We're stuck with the Nanny State always protecting us from ourselves... Thanks Obama....
Yes, I remember lots of cars going 90 MPH in reverse prior to the Obama administration, just like they do in other countries now. Many, many people have called me and told me about their cars being able to go 90 MPH in reverse. The NFL even called me and told me that they wanted to have cars going 90 MPH in reverse during their games, but Obama wouldn't let them.
/sarcasm off
 
You may not be able to go 90 MPH in reverse. Aerodynamics going reverse is different, and probably far worse than forward motion. From torque curve extrapolation, maximum forward speed without electronics limit would be about 96 MPH. See my blog post on performance analysis.

http://sparkev.blogspot.com/2016/06/sparkev-performance-analysis.html

Reverse would be less depending on how bad Cd is. At 0.82 Cd (about that of a long cylinder) vs 0.32 (SparkEV forward), max speed in reverse would have to be analyzed since torque is not constant throughout speed. My guess is that it'd be about 62 MPH if not software limited.

Anyone have large driveway to be able to test max reverse speed?

Oh, and the obligatory "Thanks Obama"
 
SparkevBlogspot said:
... From torque curve extrapolation, maximum forward speed without electronics limit would be about 96 MPH. ...
.....
Oh, and the obligatory "Thanks Obama"
I seriously doubt your theoretical 'top speed'. The motor is rated 130 HP. What's the (?)87 HP gas version good for?
But electric motors also have a 'Red Line' RPM. That may be why there is that 90 MPH limit.

I read there was a goofy 'Reverse Race'. A Porsche 928 Automatic with the hatch bolted open just enough for better visibility won the race series. It was geared the best for this.

Of course, with the front suspension caster working against any top speed runs, it would make for a great video if done on a dry lake bed !!
 
nikwax said:
NORTON said:
But NO.... We're stuck with the Nanny State always protecting us from ourselves... Thanks Obama....


we don't need that sh*t here
Once again the lack of a 'Sarcasm Font' has let me down.......
I'm the most Safety Sensitive, Big Government, Make the world a better place for all (not just me and mine) person you'll ever meet!!

Oh, and the obligatory "Thanks Obama",,, for not allowing a 'Sarcasm Font'... :roll:
 
NORTON said:
I seriously doubt your theoretical 'top speed'. The motor is rated 130 HP. What's the (?)87 HP gas version good for?
But electric motors also have a 'Red Line' RPM. That may be why there is that 90 MPH limit.
It's not about peak power, but of torque at speed. On gas cars with multi-gear transmissions, they can put the torque to wheels to achieve optimal top speed. With single speed of SparkEV, that low end torque doesn't get to high speed. If you read my blog, I extrapolate sloping top end torque and drag force and see where they intersect (96 MPH). That is effectively the physical top speed with that gear setup even without software limit.

Now if you can have multi gear transmission, you can move some of that low end torque to higher speed. Even then, there's a theoretical limit on top speed due to drag force increasing at cube of speed (that's why you feel acceleration even close to 90 MPH while top speed is only 6 MPH away). I put it as homework for the reader to figure out what that top speed might be with optimal gearing. You're welcome to tweak the script in a loop and see which gear ratio will give you maximum speed. Hint: it's under 150 MPH.

An interesting aspect of massless multi-gear transmission is that 3 speed could get you 0-60 MPH in about 6.7 seconds in first gear, same efficiency as now in second, peak speed "almost" 150 MPH in third.
 
Interesting post, only some/all of your numbers may be in question, as: Aerodynamic force is related to the square of velocity -https://www.grc.nasa.gov/www/k-12/airplane/vel.html
True, I do feel this little sucker still pulling hard at 89 MPH!!
SparkevBlogspot said:
..... Even then, there's a theoretical limit on top speed due to drag force increasing at cube of speed ...

We have stopped talking about a simple motor and 1 speed transaxle.... :?
 
My bad, you are correct. Force is proportional to square of speed. Was thinking of power, which is cube of speed. Math in blog post, however, is as I'm using second order polynomial to model the drag force to relate to driving force. Drag force is probably pretty close to actual since modeling the range with those parameters resulted in range estimate close to actual obtained by Tony Williams and others.

Simple motor and 1 speed transaxle is why SparkEV is so much easier to analyze. All schools should have SparkEV in their science department as teaching tool. They can go with cheaper iMiev, but SparkEV will "spark" far more interest from students.
 
Leafless said:
OK.. The Spark EV has a one speed transmission. As I understand, the low (L) range is not really a lower gear set, but rather, a different calculation that increases the regenerative braking. So, my question: Is the reverse (R) a different gear, or alternatively, does selecting "R" simply reverse the motor?

KnQYwmT.jpg
 
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