Is the one-speed transmission the last word?

My Nissan Leaf Forum

Help Support My Nissan Leaf Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
J

jlsoaz

Well-known member
Joined
Jul 8, 2012
Messages
849
Location
Southern Arizona, USA
I keep wondering if there might in the future be any efficiency and-or performance gains to be had by moving to some sort of different transmission. I guess EV makers such as Tesla and Nissan did not necessarily need to install multi-speed or continuously-variable (or variants thereof) transmissions, but if in the future they were to do so, might any weight and complexity trade-offs be offset by energy efficiency and-or performance gains?

The Leaf is a wonderful car, and I like mine including its acceleration from start. I'm not 100% sure ... maybe the acceleration from middle speeds could stand some improvement? I haven't really figured out if any perception of room for improvement on my side is based on always being in ECO mode, maybe D would really change that. In any case, I am wondering about possible future improvements, particularly as they might effect efficiency.

Note: I did search on "transmission" and "one-speed" but didn't at first glance see pre-existing discussion in the forum.
 
Actually, Tesla planned to use a two speed transmission in the Roadster but dropped it after problems arose. I think that a two speed gearbox - or more likely, an elegant form of something like a multi-ratio planetary drive - has some advantages for the future, both for performance and efficiency.
 
jlsoaz said:
Note: I did search on "transmission" and "one-speed" but didn't at first glance see pre-existing discussion in the forum.
Click to expand...

Ok, now I do see this very old thread, will try to come back to it later for improved background understanding of the issue:

http://www.mynissanleaf.com/viewtopic.php?f=10&t=7049
Post subject: Swedes partner to build new EV transmission
PostPosted: Fri Dec 02, 2011 7:49 am
 
I strongly suspect you would lose efficiency adding complexity to the transmission.
You may gain some upper speed performance, however, most people want a commuting/cruising ar, not a race car.

The Tesla issues were that they couldn't find a multi-gear transmission that could stand up to the torque.

Added complexity, lower durability, lower range, increased cost. Nope, I sure hope they don't try to add a multi-gear transmission:)
 
A transmission would realize some efficiency gains. I see a potential for maybe about 5% efficiency improvement. However the increased weight would offset some part of that. Personally I would not want it. The increased complexity and cost are drawbacks, but the biggest one for me is the potential for shift shock. I like never having to feel the transmission shift.
 
Obviously, not needed for utility driving. For racing you'd want a transmission. Not sure where that leaves sports cars. I'd guess there's some "bragging rights" issues. I know I've read criticism of the Tesla Roadster having a top speed of "only" 125mph. Now whether that perceived shortfall is enough to sustain a market is hard to tell. My gut says there'd be a small niche.

Personally, I drove MT ever since I bought my first car. And I enjoyed it. You couldn't sell me an automatic. But all that evaporated with the LEAF. It's just a whole different thing.
 
fiatevmnl
You might want to have a look at this video, if you haven't seen it yet. I think vectoring and multiple motors could be an alternative answer. Isn't the Volt doing something similar by bringing a second motor online at high speeds? It reportedly improves efficiency, much like a gearbox would.


[youtube]http://www.youtube.com/watch?v=IElqf-FCMs8[/youtube]
 
And then there is this:

Ford and GM to jointly develop 10 speed transmission.

http://www.usatoday.com/story/money/cars/2013/04/15/ford-general-motors-gm-transmissions/2083485/" onclick="window.open(this.href);return false;
 
This is the kind of thing where if you had lots of manufacturers all seriously competing for market share in a market where millions of EVs are sold every year you'd see a variety of things tried and the market would sort it out. No telling what inventions are out there waiting to be discovered.
 
Anything you would look to accomplish with a multi speed transmission you can accomplish with more efficiency and reliability with electronics in an EV. Tesla came to this conclusion with the roadster. They thought they needed a 2 speed transmission to get top speed and low end grunt. It turns out they instead geared for top speed and modified the inverter to provide more current at low rpms.
You can do the opposite if the motor is capable of high rpms by increasing voltage at higher rpms to maintain torque and increase HP.
 
Only within limits... There are mechanical, electromagnetic, magnetic,and physical considerations that can not be mitigated by just electronics.

Sublime said:
Anything you would look to accomplish with a multi speed transmission you can accomplish with more efficiency and reliability with electronics in an EV. Tesla came to this conclusion with the roadster. They thought they needed a 2 speed transmission to get top speed and low end grunt. It turns out they instead geared for top speed and modified the inverter to provide more current at low rpms. You can do the opposite if the motor is capable of high rpms by increasing voltage at higher rpms to maintain torque and increase HP.
Click to expand...
 
In reading through the old thread, I came across this link:

http://www.gizmag.com/antonov-3-speed-transmission-ev/19088/
Antonov's 3-speed transmission for electric vehicles boosts efficiency by 15 percent
By Noel McKeegan
July 3, 2011
Click to expand...

I don't know as to the exact efficiency increase claim (and at what speed or acceleration, and in what vehicle?) but it does at least give us a reminder that, as at least one person has discussed, even though the EV torque curve may tend to be flatter than an ICV, there is still some room for a transmission to help an EV motor get into its sweet spot.

I am now wondering in particular if a 2- or 3- speed transmission for something like a Leaf could help improve efficiency (and thus range) in the 55-75 mph area. I guess I had been assuming that the seeming rapid drop-off in efficiency from the 40 to 50 to 65 to 75 mph progression was attributable largely or entirely to aerodynamics or something else, but what if some decent amount of it is attributable to gearing? Probably not, but the conversation has me wondering.
 
I've been following EVs since before anyone was manufacturing them (save Tesla), and all those doing home conversions would leave out the transmission entirely if they had a large enough motor, or they would use the car's original transmission and just leave it in 2nd gear all the time. Due to their lower efficiency, automatic transmissions were out of question.

The fact of the matter is that the need for a transmission at all is purely to serve the inherent problems of an ICE. Unlike an electric motor, an ICE cannot operate at 0 RPM. An ICE can only produce its peak power at a small range of RPMs, usually near the point where it would rattle itself to death. And the range at which an ICE is most efficient is also fairly narrow. The Leaf's motor on the other hand, has a wide band of peak power starting at 0 RPM and ending somewhere around halfway towards max RPM of (IIRC; my google-fu fails me) around 11,000 RPM. For reference, most ICE engines top out well before 8,000 RPM.

These engineering problems were evident from the early days of automobiles, which is why so many engineers were developing electrics in those days in the first place.
 
Zythryn said:
I strongly suspect you would lose efficiency adding complexity to the transmission.
You may gain some upper speed performance, however, most people want a commuting/cruising ar, not a race car.

The Tesla issues were that they couldn't find a multi-gear transmission that could stand up to the torque.

Added complexity, lower durability, lower range, increased cost. Nope, I sure hope they don't try to add a multi-gear transmission:)
Click to expand...

Obviously, there are high torque transmissions. Any diesel powered truck, some with about 2000 (yes, two thousand) foot pounds of torque work great. They are grossly heavy and expensive.
 
TonyWilliams said:
Zythryn said:
I strongly suspect you would lose efficiency adding complexity to the transmission.
You may gain some upper speed performance, however, most people want a commuting/cruising ar, not a race car.

The Tesla issues were that they couldn't find a multi-gear transmission that could stand up to the torque.

Added complexity, lower durability, lower range, increased cost. Nope, I sure hope they don't try to add a multi-gear transmission:)
Click to expand...

Obviously, there are high torque transmissions. Any diesel powered truck, some with about 2000 (yes, two thousand) foot pounds of torque work great. They are grossly heavy and expensive.
Click to expand...

Zythryn's comment isn't the first time I've heard that Tesla wasn't able to develop a transmission to stand up to the torque. I don't know if it's the whole story. I think Tesla may have been overly ambitious about the transmission, and they wanted the max speed better to compete with the Ferraris and Porsches of this world. The company, I've heard more than once, almost foundered on this issue and was saved on this issue by going to Borg Warner and getting it done with one speed and sacrificing top speed.

You are undoubtedly correct as to high-torque transmissions being around, but as to the context of the Tesla story, these are the things I've heard.
 
BraveLittleToaster said:
I've been following EVs since before anyone was manufacturing them (save Tesla), and all those doing home conversions would leave out the transmission entirely if they had a large enough motor, or they would use the car's original transmission and just leave it in 2nd gear all the time. Due to their lower efficiency, automatic transmissions were out of question.

The fact of the matter is that the need for a transmission at all is purely to serve the inherent problems of an ICE. Unlike an electric motor, an ICE cannot operate at 0 RPM. An ICE can only produce its peak power at a small range of RPMs, usually near the point where it would rattle itself to death. And the range at which an ICE is most efficient is also fairly narrow. The Leaf's motor on the other hand, has a wide band of peak power starting at 0 RPM and ending somewhere around halfway towards max RPM of (IIRC; my google-fu fails me) around 11,000 RPM. For reference, most ICE engines top out well before 8,000 RPM.

These engineering problems were evident from the early days of automobiles, which is why so many engineers were developing electrics in those days in the first place.
Click to expand...

Hi bravelittletoaster,

The point is taken from your post and many others that many EV projects don't need or want any transmission, or more than one speed, but my question definitely stands as to what extent another gear (despite the weight and volume penalties, added maintenance and any other issues) might help add range for the Leaf and other EVs. As best I can tell, it seems a possibility that it would add some range (how much I don't know) even after taking into account energy drawbacks (primarily weight).
 
jlsoaz said:
As best I can tell, it seems a possibility that it would add some range (how much I don't know) even after taking into account energy drawbacks (primarily weight).
Click to expand...

The cars are already grossly overweight compared to an oil burner, plus an oil burner gets lighter as it burns off energy.

The trade offs of weight plus cost (on a car that is already too heavy and too expensive) for some nebulous benefit is pretty easy for me to decide.
 
jlsoaz said:
TonyWilliams said:
Obviously, there are high torque transmissions. Any diesel powered truck, some with about 2000 (yes, two thousand) foot pounds of torque work great. They are grossly heavy and expensive.
Click to expand...

Zythryn's comment isn't the first time I've heard that Tesla wasn't able to develop a transmission to stand up to the torque. I don't know if it's the whole story. I think Tesla may have been overly ambitious about the transmission, and they wanted the max speed better to compete with the Ferraris and Porsches of this world. The company, I've heard more than once, almost foundered on this issue and was saved on this issue by going to Borg Warner and getting it done with one speed and sacrificing top speed.

You are undoubtedly correct as to high-torque transmissions being around, but as to the context of the Tesla story, these are the things I've heard.
Click to expand...


Apparently the problem was not one of actual durability of the transmission itself. Tesla evidently spec'ed out a two speed unit with no clutches. The design intent was to do clutch-less shifting and manage the torque output of the motor during the shifts. Unfortunately the rotational inertia of the motor made this plan unworkable as the torque output couldn't be changed fast enough. According to Siry there were never actually any mechanical failures of the X-Trac transmission, it was simply a matter of Tesla not being able to get their control strategy to work adequately with the hardware. Subsequently Tesla contracted Magna to develop a dual clutch two speed gearbox. Unfortunately, this is the design that had durability issues leading to Tesla's ultimate decision to revise the motor for more power and go with a single speed unit for production.
Click to expand...

http://www.autoblog.com/2008/04/16/tables-turned-tesla-motors-sued-by-transmission-supplier-magna/" onclick="window.open(this.href);return false;
 

Similar threads

knightmb
Leaf Service EV System Adventures with P0AA6-1A and a Suspect 12V Battery
3 4 5
Replies
80
Views
5K
CaptLarry
C
M
2012 Leaf charges on 120V but not 240V Tesla EVSE
Replies
2
Views
1K
Marchogwyn
M
knightmb
Reduction Gear Oil Change - Benefits for Range
11 12 13
Replies
258
Views
70K
knightmb
knightmb
G
GCR: Toyota is poised to make affordability, not range, at the center of its EV play
Replies
3
Views
2K
SageBrush
S
A
Comparison: Why I Chose a Nissan Leaf Plus over a Tesla Model 3
7 8 9
Replies
177
Views
33K
Bombastinator2
B

Latest posts

Back
Top