Conclusive proof gearboxes are awesome.

[spinningmagnets]

I can't find the reference right now (tried google, scratched chin, stared into space)...I seem to remember that during the first half of the initial Tesla car development, they were assuming they would use a 2-speed trans, and they were having difficulties getting the trans prototype to work in an acceptable manner. Then, just when they needing to make some big decisions, there was a big development in the improvement in the efficiency (less waste-heat, cooler-running, better range) and current-capability of the type of FETs they needed. This meant that a one-speed became an option, due to an improved controller?

I may have been smoking my socks that day, but the way I remember it, they always had an acceptable design of motor (which could be scaled up/down slightly as needed), and they always had acceptable current from the initial battery (which, of course, rapidly improved), but it was a controller current and efficiency limit that made them even consider a 2-speed, to reach their 0-100 MPH acceleration time goal (it was never the larger size of motor at issue, for a one-speed)

They always wanted a one-speed, but high current at low speed had controller issues. (I don't know if this is true, I hadn't mentioned it before because I wanted to find the reference first). If I'm way off, please tell me, I'm just trying to sort a foggy memory...

 

[liveforphysics]

I hate to sound like a parrot, but the thread seems to have settled for the status quo that practical EV's ....( ignoring bikes for now please) , require a reducttion drive ( transmission) if not a multi ratio transmission.
We have not yet explained why this is so.
if Motors can be made with sufficient torque for DD drive ( not necessarrily "in wheel" motors,) what are the reasons no one has yet produced a car using that configuration ?
I would not expect Tesla etc to reengineer thier drivetrains now, but why didnt they, or GM, etc, go DD originally ?
Is it just cost or is there some other technical barrier yet to be overcome ?

The same thermodynamic cycle that make the newest gen Prius engine so exceptionally efficient (for ICE) have been available to use for the last 100years.

Things only improve and evolve as folks creating them realize the potential to make something better. EVs of today are far from matured commodity technology.

 

[toolman2]

Thanks again Luke for the kind words, and a more understandable discussion that should benefit all.
But could you be pressed just a little further for a yes or no?

I hate to sound like a parrot, but the thread seems to have settled for the status quo that practical EV's ....( ignoring bikes for now please) , require a reducttion drive ( transmission) if not a multi ratio transmission.
We have not yet explained why this is so.
if Motors can be made with sufficient torque for DD drive ( not necessarrily "in wheel" motors,) what are the reasons no one has yet produced a car using that configuration ?
I would not expect Tesla etc to reengineer thier drivetrains now, but why didnt they, or GM, etc, go DD originally ?
Is it just cost or is there some other technical barrier yet to be overcome ?

A direct drive Is being used heaps as we all can see, and is clearly the perfect solution for solar cars etc etc.
So far i believe the hold up to the higher torque levels required to dominate all reduction designs is the issue of size, weight and scaling.
-like the limits on materials that restrict how high a building can be etc, and is no doubt the subject of much development to potentially become the most efficient for all, maby, one day..

 

[DanGT86]

Might be some mixed up terms being thrown around but I dont think anyone is arguing against a final drive ratio like a single stage chain between the motor and wheel. I thought the question was :does an ev need a multi speed selectable gearbox to achieve the whole speed range.

I would consider the tesla to be direct drive in this discussion. Otherwise everything is some kind of reduction unless you are riding the magnetic rail that toolman was talking about.

 

[Hillhater]

Well, i dont see those " heaps " of EV's in every day use ...beyond bike hub motors ?
But if i read you correctly, you are agreeing that it works in theory, ( specific custom applications ), but widespread application for general use is not currently practical due to factors like size , weight, etc....
....which others here maintain are not really barriers ?

Dan, now you really are confusing the terminology by suggesting the Tesla is Direct Drive.
..And actually, i think the whole basis of this discussion comes down to the suggestion that a electric motor does not need to have gearing reduction to perform acceptably.

 

[DanGT86]

Maybe i am mistaken but there is always some kind of effective "gearing" even if its just the tire size selected.

I considered the tesla direct drive as in the ratio of motor to wheel is always the same.

And i hear LFP and Arlo saying one ratio is all an ev should need when optimized.

That was my impression of how the discussion was framed. Fixed gearing vs variable.

I will quit saying direct drive unless talking about hub motors.

 

[major]

In large EVs (cars), the term direct drive has always included a fixed gear ratio.

 

[liveforphysics]

-like the limits on materials that restrict how high a building can be etc, and is no doubt the subject of much development to potentially become the most efficient for all, maby, one day..

That's a perfect explanation for the point I was trying to communicate, thank you for making it so well.

I love the building analogy as well. At the time the empire state was built it was the tallest. Now the Burj is over twice as tall, because people learned how to make better choices in combining materials and structural geometry.

This too will happen for EV's from materials and structural design choice improvements. EV's will get lighter, cheaper to make, last a lifetime, and have total system efficiency beyond what has been built today, along with a performance envelope able to spin the tires up to the power maximum of the vehicle. It might be something like short-flux-path switched reluctance transverse flux inboard motors with a CV per wheel, it might be something ironless and so light and efficient it's not a meaningful weight penalty to locate it in the wheel using just the rim as it's heatsink.

However, they won't get there until someone chooses to design it rather than settling for what's off the shelf today. In a world with most builders, even at OEM levels not wanting to look past what EV drivetrain can be pieced together from a catalog, I am choosing to inspire some to recognize there is an alternative if you're willing to put the RnD work into making it happen.

As to yes or no for your question, if you add the right artificial constraints it's "Yes". A situation can certainly exist for the transmission to help something work better in some given context with some given design limitations (like my friends Zero motor powered Insight that can only get around because of the tranny). So, it's definitely possible for the answer to be Yes, but it's equally possible to be "No" the vehicle to use a topology which doesn't eat core loss while coasting down a hill powered off, like induction, or ironless PM motors, or switched reluctance etc.

 

[alan]

A simple two-speed tranny can have an input shaft and an output shaft (exactly like a reduction gearset with the same number of bearings, having the same loading based almost entirely on the torque loads and not the mass of the gears) with two gears on each shaft. Say the input shaft has a large gear A and a smaller gear B, and the output shaft has a smaller gear C and a larger gear D. A and B can be spaced apart and C and D can be close together. C and D move together on the output shaft so that either A and C are engaged or B and D are engaged...

Bullshit. The gears not in use will add drag/inefficiency no matter how you make it the gear not in use will not be turning the same speed as the shaft and that will cause drag. Also those extra gears will cause more oil drag or what ever lube you run as they will fling it around more then not having them.

Please reread my simple two-speed tranny description, and understand that A and B are rigidly fixed to the input shaft and C and D are rigidly fixed to the output shaft. Also note that manual trannies do not require oil baths for thorough lubrication. Then consider replying to me without your very tiresome "bullshit" display of ignorance.

 

[Arlo1]

A simple two-speed tranny can have an input shaft and an output shaft (exactly like a reduction gearset with the same number of bearings, having the same loading based almost entirely on the torque loads and not the mass of the gears) with two gears on each shaft. Say the input shaft has a large gear A and a smaller gear B, and the output shaft has a smaller gear C and a larger gear D. A and B can be spaced apart and C and D can be close together. C and D move together on the output shaft so that either A and C are engaged or B and D are engaged...

Bullshit. The gears not in use will add drag/inefficiency no matter how you make it the gear not in use will not be turning the same speed as the shaft and that will cause drag. Also those extra gears will cause more oil drag or what ever lube you run as they will fling it around more then not having them.

Please reread my simple two-speed tranny description, and understand that A and B are rigidly fixed to the input shaft and C and D are rigidly fixed to the output shaft. Also note that manual trannies do not require oil baths for thorough lubrication. Then consider replying to me without your very tiresome "bullshit" display of ignorance.

Show me a real world example of this and I will edit my comment.

Are you saying the whole shaft slides back and forth?
Are you saying the gear teeth will catch the two different shafts while spinning at different speeds?

 

[Hillhater]

In large EVs (cars), the term direct drive has always included a fixed gear ratio.

True, but i guess that is because it has never been practical to to have a ICE wheel driven by direct connection of the ICE motor shaft to the wheel hub., and that convention has carried over to EV cars also ?
Also in "Our" world of Ebikes we have DD hub motors and "geared" hub motors which actually only have one fixed ratio ( generally)...but we never refer to them as DIrect drive hubs ! :? ...so yes we need to be clear in our definitions
I guess i have to simply accept that current technology , just does not allow the practical application of that ultimate direct 1:1 coupling of an EV motor to the drive wheels

 

[liveforphysics]

I guess i have to simply accept that current technology , just does not allow the practical application of that ultimate direct 1:1 coupling of an EV motor to the drive wheels

Have you seen the EV side of the regera? I think it handily meets most direct drive requirements, is light and packages well and delivers using today's tech.


http://jalopnik.com/how-the-1-500-hp-koenigsegg-regera-hits-248-mph-without-1689181377

 

[flathill]

Assuming 100% efficient infinite gearbox with a less than 100% efficent motor vs load/rpm then a gearbox will be awesome.

Assuming 100% efficient motor vs load/rpm with a less than 100% efficient gearbox then a gearbox will be useless

 

[liveforphysics]

Assuming 100% efficient infinite gearbox with a less than 100% efficent motor vs load/rpm then a gearbox will be awesome.

Assuming 100% efficient motor vs load/rpm with a less than 100% efficient gearbox then a gearbox will be useless

This is an available today PM motor from a LEAF (not something exotic or ironless etc).

Show me what operating conditions it's going to be worth the gearbox's mass, cost and added friction. Even though no motors today are 100%, many are already so close to 100% efficient over such a wide envelope, it's tricky to see the area at which the transmission could possibly justify its own losses over simply selecting a logical motor choice.

 

[Miles]

This is an available today PM motor from a LEAF (not something exotic or ironless etc).

Show me what operating conditions it's going to be worth the gearbox's mass, cost and added friction. Even though no motors today are 100%, many are already so close to 100% efficient over such a wide envelope, it's tricky to see the area at which the transmission could possibly justify its own losses over simply selecting a logical motor choice.

It's difficult to argue with that case. The challenge, for most of us, is replicating that wide range of high efficiency with a much smaller motor. There is a significant scaling effect with regard to motor performance.

 

[nutnspecial]

Good evidence Luke. That aspect is inarguable when it comes only to motor efficiency in that case. In real world use, this does not yet completely rule out gearing benefit imo though.
I like flathill's statement too.
To lower both sides of comparison below 100% (like 99% efficient motor > 98% efficient gearing) would be cause for disaster when attempting an absolute statement imo.

Part of this is (imo) isn't just about motors. Any real world examples must include the rest of the portable E system. For stationary power transormation and transmission, there is no problem tapping the Sun or Hydro or Wind or Nuclear directly for E. EV has a common difference though.

I think there are evidences up into current ev application that we'll likely always find at least some benefit in trading some motor efficiency for reductions and/or multiple gears. Many reasons simply have to do with our shortcomings in the ability to transform and store energy, but is also limited to the physical nature of motors as we understand them. Losses in motor design are far less important imo, but also have undeniable room for improvement too.

So that's not to say E doesn't/wouldn't have the potential to do away with all mechanical gearing benefit. . . I consider reference comparison to more 'natural' means of locomotion on a planetary scale down to a microscopic level. No gears there. And for manmade, we have limited gears in the air or sea, and DD is sufficiently advanced to be even more applicable to land vehicles than before.

So for better or worse, logic dictates ev has HUGE potential for technical improvement in energy transformation, which is the same crux of as stationary power. Compare to PV up to Maglev trains. . . One side note- I have not seen much high scholastic study of magnetism on a quantum level. The field is fairly stagnant and held hostage imo by classical laws and thinking. I consider matter, magnetism, light, sound, and electricity to all be potentially the same thing- energetic wavelengths.

We should consider the largest pictures, and consider as manipulation of energy transformation and storage improve, so also will likely improve our ability to manipulate matter. This would include physical aspects of vehicles and drives, and is important to consider in tandem because matter appears to be just energy too.

It's really neat to remember our latest knowledge that atoms are 99.999999999999% empty as far as we can tell, and the remaining observable FRACTION of material and it's action behave quite interestingly at that quantum level, appearing to break many 'laws' that still govern the physical world.

Seems to me that as our ability to harness energy (transform, store, and do work with) increases, so likely will our ability to manipulate matter (motor, vehicle, and 'gearing').
As mastery increases, I'd predict advancement of 'mechanical' and 'electric' to blur into the quantum depths, until previous meanings are completely lost.
Energy efficiency and density could coalesce at 100% (unity), likely also with matter as we currently understand it. Till then, why leave 'neutral gear' (<pun) for an incomplete and unnecessary thought restriction, unless it's necessary?

I think there are many benefits still to mechanical gearing and even variable gearing in electric vehicles today, evidencing E amd EV are not suffiently advanced to rule them out just yet. My opinion.

So I think it's possible that unless the ability to harness energy leaps ahead much faster than our ability manipulate matter, current EV design is unlikely to ever completely rule out at least some tandem benefits from 'gearboxes'. . . until unity is reached. And even more importantly imo, there's no need close down perspective before we have all the proof squarely 'in the pudding'.

 

[alan]

One side note- I have not seen much high scholastic study of magnetism on a quantum level. The field is fairly stagnant and held hostage imo by classical laws and thinking. I consider matter, magnetism, light, sound, and electricity to all be potentially the same thing- energetic wavelengths.
...
It's really neat to remember our latest knowledge that atoms are 99.999999999999% empty as far as we can tell, and the remaining observable FRACTION of material and it's action behave quite interestingly at that quantum level, appearing to break many 'laws' that still govern the physical world.

I'm guessing you would very much love the book by Lawrence Krauss, "A Universe from Nothing: Why There is Something Rather than Nothing." This book is a great, fast read.

For more technical reading about quantum magnetism, see "The Feynman Lectures on Physics" by Feynman, Leighton, and Sands, published in 1963, and mostly still current! Volume 2 covers magnetism predominately from a classical perspective, but also proves in chapter 34 that aspects of magnetism (diamagnetism and paramagnetism) is impossible from a purely classical perspective. Volume 3 directly covers quantum magnetism. The final chapter 21 of this volume is what Feynman says is just for fun, not really part of the physics class lectures, and section 1 is titled, "Schrodinger's Equation in a Magnetic Field."

 

[alan]

I considered the tesla direct drive as in the ratio of motor to wheel is always the same.
... I will quit saying direct drive unless talking about hub motors.

You are correct that a hub motor is a direct drive. Even if the motor is connected to the wheel through a drive shaft with CV joints, I would still consider that direct drive, so long as the motor speed and wheel speed are always the same.

I don't have the numbers on the Tesla, but it is like my BMW i3 BEV in that the motor works through a reduction gearing in the differential unit before driving the wheels (same kind of reduction front and rear in the dual motor version Teslas). My i3 is just under a 10:1 reduction from motor to wheel. That is a fixed-speed drive, but not a direct drive. The BMW i8 uses pure electric drive in front, and a ICE drive in the rear (the hybrid coupling is only through the road!). The front electric drive has a 2-speed automatic transmission, and the rear uses a 6-speed. This is at least one real world example of a major car manufacturer finding a transmission coupled with an electric drive improves performance or efficiency or both (and their literature says both). There are other high-performance electric cars using trannys.

 

[alan]

Show me a real world example of this and I will edit my comment.

Are you saying the whole shaft slides back and forth?
Are you saying the gear teeth will catch the two different shafts while spinning at different speeds?

I have seen such a tranny used, but not in a transportation application (it was for a machine tool). I did not come up with the idea myself. The one I saw had the one pair of gears on one shaft connected on a collar shaft to the drive shaft such that it could slide on the drive shaft, but turned with it. I believe the inside of the collar and the outside of the drive (over the sliding region) were square cross section with rolling bearings between them. There were synchromesh mechanisms between the gears to facilitate shifting. I don't remember the specifics of the synchros, but I suspect they are much the same as used in most manual trannys. There was also a throw-out mechanism that controlled the position of the sliding collar, but it was only in contact with the collar during a shift and there was another locking mechanism on the drive shaft that held the position. I know the throw-out did not stay in contact as it made a distinct sound only when engaged. I saw this in an engineering lab at Purdue about 40 years ago when I was there studying engineering.

 

[Arlo1]

Show me a real world example of this and I will edit my comment.

Are you saying the whole shaft slides back and forth?
Are you saying the gear teeth will catch the two different shafts while spinning at different speeds?

I have seen such a tranny used, but not in a transportation application (it was for a machine tool). I did not come up with the idea myself. The one I saw had the one pair of gears on one shaft connected on a collar shaft to the drive shaft such that it could slide on the drive shaft, but turned with it. I believe the inside of the collar and the outside of the drive (over the sliding region) were square cross section with rolling bearings between them. There were synchromesh mechanisms between the gears to facilitate shifting. I don't remember the specifics of the synchros, but I suspect they are much the same as used in most manual trannys. There was also a throw-out mechanism that controlled the position of the sliding collar, but it was only in contact with the collar during a shift and there was another locking mechanism on the drive shaft that held the position. I know the throw-out did not stay in contact as it made a distinct sound only when engaged. I saw this in an engineering lab at Purdue about 40 years ago when I was there studying engineering.

If there is synchros then the gears are not locked to the shafts.

 

[major]

The BMW i8 uses pure electric drive in front, and a ICE drive in the rear (the hybrid coupling is only through the road!). The front electric drive has a 2-speed automatic transmission, and the rear uses a 6-speed. This is at least one real world example of a major car manufacturer finding a transmission coupled with an electric drive improves performance or efficiency or both (and their literature says both).

In the BMW i8, the electric motor drives the front wheels via a GKN two-speed automatic gearbox which always run in first gear while in eDrive mode but switches directly to second gear in the mixed modes.

http://www.bmwblog.com/2014/12/02/multi-speed-transmissions-coming-electric-vehicles/

Looks to me like an electric motor asked to do two different jobs and given a different ratio for each, yet using a fixed ratio while performing its duty in each mode. One mode being pure electric and the other electric assist (hybrid).

 

[DanGT86]

Good link. It is interesting to read that ZF is heading towards more gears rather than less but they are a transmission company so its to be expected.

The more I read and wrap my head around the points being made in this thread the more I am convinced that the ideal solution for me is a simple changeable final drive. I have an E-bike that will get a 3-5kw fixed rear sprocket mid drive motor that I have no interest in rewinding or re-engineering and I would like to use it for Trials type riding then cruise home with non highway traffic. After reading all of this I am steering away from a 2 speed shiftable transmission that would incur losses from the unused gear. Simply having a changeable motor sprocket seems like the way to go.

I know nobody cares what I am doing but I thought it would be helpful to relate this discussion to what I consider a very typical build from someone using off the shelf ebike parts.

Also that article LFP linked to the Konigsegg Regera was interesting. That thing is insane! 93mph-155mph in 3 seconds I did think it was funny that after all this talk of efficiency and wasted energy through reductions and coupling and that thing uses a hydraulic coupling on the motor output. Nothing says waste energy like a blender full of fluid. I get it though. The transition from electric to gas power would probably be really harsh with a locking zero slip coupling. Also got a kick out of them repeating that it wasn't a hybrid. That's just silly. You don't change peoples negative perception of hybrids by changing the terminology. You change it by building a hybrid with 1500hp that goes 0-250mph in 23sec. I would paint hybrid right up the side of that thing! Or maybe on the back of it since that's were the competitors will be looking.

 

[speedmd]

I also like the idea of a trials setup that can also run higher road speeds for traveling to more distant places to ride. Been there with a ICE setup.

Most universal and simple setup may be to just have two sprockets on each end or two different chains that can be swapped if dropouts or chain tensioners can not adapt. . Something like a combined 12 -18 tooth motor sprocket and a corresponding size rear sprocket pair. There was a interesting expanding chain wheel sprocket that was shown at one of the recent shows that was interesting and may have some application here.

 

[liveforphysics]

I often see folks claiming some very high efficiency for gearing stages.

It's true for a single speed and torque load (when the transmission is carrying near peak torque) that the efficiency can be ~98% per spur stage in a well designed system. This is fine for a racecar that is operating at full throttle or full braking for its use profile.

For something you commute with, using the majority of the energy at cruise loading, all the fluid drag and prevailing torque penalty to rotate the assembly doesn't reduce, only the gear-gear face friction and a small amount of the bearing friction scales proportionally with torque.

In otherwords, if spinning your assembly at X speed while at peak acceleration has say 5hp of fluid drag and 20hp of gear friction while you're outputting 250hp, this means the transmission is only 10% loss and 90% is making it to the wheels. Now when this same assembly is cruising down the highway, and the car needs say 15hp to maintain speed, it's eating the same 5hp fluid drag and maybe 1hp of friction. So now it's 6hp into the tranny for 15hp to move the car 40% loss at cruise. These values selected are actually right in line with a modern Honda K series transmissions losses I've personally measured in my previous ICE hotrodding obsessed days.

Chains are similar, at peak torque they are very efficient. At low torque (but same speed) they don't look very good at all.


Honda already figured out a clever way to skip the very meaningful low power cruising losses. The result is a huge and heavy full size accord that has better performance and economy than the tiny engine lightweight CRX.

https://www.google.com/url?sa=t&sou...4qU5AO8s6rQjAC_fg&sig2=LbjsyshMolgRb3K3zyIZ6w

 

[spinningmagnets]

I never heard about that Honda system, brilliant!