will the new SMRE IET increase travel distances?

[Squizzel99]

i am newcomer to the Brammo Forum and I'm very keen to buy a Brammo Empulse in 2012.  I assume that the 2012 Empulse model will have the recently announced EIT from SMRE?  Does anyone know if the EIT will vastly improve the range to the battery system as you won't be running the generators at top amp draw during city operation or highway operation?  I'm looking for this to become a city transporter, fun day tour vehicle.  Any thoughts on this posting would be greatly appreciated

[protomech]

Look at the efficiency chart, page 2 of the Perm PMS motor brochure:
http://www.perm-motor.de/fileadmin/users_upload/pdf/PMS_Motoren-Generatoren/PM_DS_PMS_15_03-10_E.pdf

The only efficiency chart they give is for the PMS 080, the smallest motor of that family. Presumably it is representative of the entire motor line, especially the PMS 120 L (Enertia 3.1 / Enertia Plus air-cooled) and PMS 150 W (Empulse water-cooled). They list two efficiency lines, presumably for a smaller voltage and a higher voltage. In any case, the motor spins up to 6000 rpm, and from 2000 rpm on it is nearly a flat efficiency curve.

Here's a chart of estimated peak performance for the PMS 150W based on the PMS 156W chart.

Supposing Perm's datasheets are accurate, I expect there will be little efficiency gained by an IET for the PMS series motors. The IET may in fact be overall slightly less efficient than a direct drive transmission, resulting in slightly reduced range.

On page 4 they list the continuous and peak torque as well as peak power curves for the PMS 156 L, the motor used in the Enertia TTR race bike. This is the big brother to the PMS 150 L, the motor used in the Empulse concept bike, and is approximately 35% more powerful. The motor can be operated for a short time (peak power output) with increased torque at low RPMs, before asymptotically approaching the near-constant torque output at high RPMs. For best performance you will probably want to shift the motor so that it operates at 4000 to 6000 RPM.

An illustrative example* - acceleration from 45 mph.

Empulse direct drive - say 95% efficient, geared for 6000 rpm at 100 mph. Total gear ratio 4.516:1.
Motor is operating at 2700 rpm, peak torque ~51.8 Nm, 14.6 kW.
Output at the rear wheel is 598 rpm, torque 222 Nm or 164 ft-lb, power 13.9 kW or 18.6 hp.

Empulse IET - SWAG'ing 92% efficient, 2nd/3rd gear? motor is turning 4000 rpm at 45 mph. Total gear ratio 6.69:1.
Motor is operating at 4000 rpm, peak torque ~46.9 Nm, 19.6 kW.
Output at the rear wheel is 598 rpm, torque 289 Nm or 213 ft-lb, power 18.0 kW or 24.2 hp.

In this particular case, IET improves maximum performance by approximately 30%. In the more general case, IET should significantly improve the Empulse maximum performance at low speeds, with a lesser effect as speeds increase. Note that if you ride at higher power, your range will suffer.

* based on Perm's datasheets. Brammo's specifications for the Empulse claim 40 kW peak motor power, approximately twice the estimated peak power from Perm's datasheets. Double the performance figures above to match Brammo's claims.

[Squizzel99]

Wow, this is a real technical answer to my question . So, just to clarify in the city with reasonable driving style, one should expect a slight but noticeable range improvement.  However, on the highway or aggressive riding style would result in a decreased range.  No different than a gasoline powered bike?  But, there won't be say a 30% increase in range, just because the Empulse is now going to use the EIT.

The more important question is when do you think the Empulse with the EIT will be available?  Early 2012?

[protomech]

I suspect range will decrease slightly with an IET - maybe by a couple of percent. The range decrease probably won't be substantially noticeable - if you're pushing to 98% of maximum range anyway, you probably should reconsider your choice of rides - but the increased power should be quite noticeable.

I'm curious as to whether Brammo will integrate SMRE's IET with the Perm 150W in the Empulse Concept or if they will switch to an SMRE motor/IET combination.

[Squizzel99]

Thats a very good point about the range.  I'm looking for an urban cruiser anyways. I probably won't every get to the range limit. It would be great the match the 150w generator with the EIT from SMRE.

[Shinysideup]

While real world stats are in short supply, here's a graph that may help, along with some words that are heavy on marketing:

Words:
http://www.smre.it/eng/propulsore_meccatronico_con_tecnologia_iet/scheda.php

Graphs:
http://www.smre.it/eng/images/ricerca_sviluppo/tec_iet/2.jpg

[protomech]

Yeah. All the graphs show is that with IET you get an increase in wheel torque at low speeds, which means you go at any given time you're travelling faster and have covered more distance from a start than a traditional fixed-gear bike. Nothing about range.

Those graphs also do not start at 0,0 - which can mislead if you're not careful, eg looking at the distance graph and thinking "wow the IET bike is twice as far ahead as the fixed-gear bike!"

Nothing nefarious there, of course.. just a graph that's easy to misread.
[smg id=300 width=396]

[FreepZ]

I.E.T.® permits the engine is functioning in the correct gear under all driving circumstances. Because of this the engine ALWAYS remains in the right range. Because of this, the engine is extremely powerful and offers never before seen performance (Kt 0.34).

That's a curious statement (which probably makes more sense in Italian). The "IET permits ..." In other words, if you know what gear to put the motor in, you could be in the "right" range. Of course, "right" depends on your goals. If you intend on doing a wheelie, the lowest gear is probably the right one. If you're trying to hyper-mile, that's another story.

... thanks to the specially developed motorization, the gear shift makes sure the engine remains in optimal parameters under all driving circumstances ...

I wonder what that is supposed to mean. Is the "gear shift" going to somehow auto adjust itself to try to keep the motor running a peak efficiency? Or are they saying (once again) that you can put the bike into the right gear (assuming that you know what that is)?

This all seems somewhat mysterious to me. I hope that a testable machine will come out soon so that we can get some good reviews about what the implications of the IET really are. Until I see otherwise, I'm going to limit my expectations to:

• Better torque at low speeds.
• Higher top speed.
• No range improvement.

[protomech]

Yes, you're correct about the PR material.

"I.E.T.® stands for "Integrated Electric Transmission", or the integration of a source of electrical motion specially developed for this application"

"Motion" should be "motor". That trips up some of the Italian to English translators I've seen.

I don't expect it to be an automated clutch transmission. I think that's badly translated PR copy.

[Vibetrippin]

Something about all this is bugging me and since my mind is in a painkiller haze I don't think I have the mental capacity to take into account all the variables, but... if you can adjust the top gear ratio so that your back wheel is travelling faster at the same energy efficiency, shouldn't that give you more range?

[protomech]

Basic answer is no. If your car gets 30 mpg at 60 mph or 80 mph, traveling at 80 mph means you cover the same distance but will run out of fuel in a shorter period of time. Same energy per distance (miles per gallon), same distance covered, higher energy per time (gallons per hour).

Efficiency gains from the IET will come from running the motor at a different RPM / torque load point. Basically the motor has "sweet spots" where it's most efficient. Running the motor at high load / low RPM or high RPM tends to be inefficient.

Edit 2012-08-13 PriusChat has removed their images. Changing the image link.
2004 Prius Motor Efficiency Map, from Oak Ridge National Labs via PriusChat.



Assume the following fabrications:
1. 20.0 kw mechanical power at the rear wheel to hold the bike at 100 mph on a level road.
2. Chain is 97.0% efficient. 20.6 kw mechanical power at the transmission output shaft.
3. IET is 95.0% efficient. 21.7 kw mechanical power at the motor output shaft.

At a given power you can draw a curve through an efficiency map. Here's a selection of points along that 21.7 kw power curve:

RPM	Torque	Efficiency
1000	207 Nm	85.0%
2000	104 Nm	93.9%
3000	69.0 Nm	93.0%
4000	51.8 Nm	90.3%
5000	41.4 Nm	87.5%
6000	34.5 Nm	86.2%

The Prius motor is most efficient around 1750-3000 rpm. The most efficient gearing along that curve is around 2400 rpm or a bit over 94% efficient.

4. Motor at 2400 rpm is 94.0% efficient. 23.1 kw electrical power into the motor.
5. Controller is 95.0% efficient. 24.3 kw into the controller, from the battery pack.

Assuming you could draw 10.0 kwh from the battery pack at 2.4C, then your range to empty would be 41.1 miles.


Let's say instead you had a direct-drive transmission and the motor is running at 5500 rpm @ 100 mph, 36.1 Nm.

3. Direct drive transmission is 99.0% efficient. 20.8 kw at the motor output shaft.
4. Motor at 5500 rpm is 87.1% efficient. 23.9 kw electrical power into the motor.
5. Controller is 95.0% efficient. 25.1 kw into the controller from the battery pack.

Assuming you could draw 10.0 kwh from the battery pack at 2.4C, then your range to empty would be 39.8 miles.

At saner speeds (say 45-70 mph) the direct drive transmission would be running the motor at closer to 2500-4000 rpm where it is 90-93% efficient, and likely the IET transmission losses outweigh a small efficiency gain from operating the motor at an ideal RPM.

Anyhow. This is a contrived example, the numbers are plucked from thin air, and the Empulse isn't going to have a Prius motor hooked up to it. But hopefully it's illustrative.

[Brammofan]

Damn, protomech.  Just... damn. 

[860]

The other reason why it is uncertain whether in real life people may or may not see better range with the IET is that it will make it damn hard not to pin the "accelerator" off every stop light just for the holigan factor....  

 

Or in scientific-ish terms, it takes a whole lot of energy to blast like a rocket to your cruising speed, even when using multiple gears to stay in the most efficient rpm range.  Acceleration doesn't come for free, even when the motor is working at peak efficiency.  It will be hard to recoup that energy just by changing the cruising rpm to a more efficient rpm.  

Like everything energy related, YMMV!  If you don't take advantage of any of the additional torque available for faster acceleration, and you don't take advantage of the higher top speed the IET provides, you may be able to beat whatever efficiency differences there are between the IET and the original  single speed by keeping the motor at it's most efficient rpm's.  In effect, you could hypermile the Empulse, and you might be able to counteract any added weight and/or any drivetrain efficiency differences.  

No matter what, you probably won't be able to choose all three:  faster acceleration, higher top speed, AND further cruise distances at efficient rpm's.  But I'd love for some folks smarter than me at Brammo to prove me wrong!

[karlInSanDiego]

Has Brammo ruled out downsizing the motor yet?  Everything I know about transmissions is that they help a smaller motor perform work that would otherwise require a large one.  In the history of ICE engines, I can think of only two examples of a 2 speed transmission: powerglide, usually mated to large GM motors, and the Vector W8 also tremendously endowed with massive displacement.  Small engined cars expected to operate at highway speeds would typically make use of 3, 4 and eventually 5 and 6 speed transmissions, the latter pushing any engine into very low rev range, thus reducing consumption and noise.  Pulse and glide tells us that although there are wind and rolling resistance to overcome at highway speed, the power needed to maintain speed once acceleration has subsided, is minimal. 

Understanding that electric motors exhibit torque differently than ICE, and that ICE will always consume fuel relative to revolutions factored with throttle opening neede to maintain speed, the question is, shouldn't you be able to use a motor rated for much lower (half?) the power and much more effiency to do the same job as a larger motor, if you treat it to a transmission to give it mechanical advantage?  And if that's the case, wouldn't all this postulation about knowing that the IET will reduce and not increase range is really just unjustified speculation?  If the design spec is for 100mph & 100 mile range, I expect that this 1 year delay on the product is due to the fact that there is more than one change to the prototype.  Add six speed, increase low speed acceleration (exhibited to be poor for most TTXGP bikes) refactor motor and batteries and get back to your design criteria, while making your bike a better mousetrap, maybe even building in some more profit margin along the way.  That's my guess.

[protomech]

Look at the motor map of the Prius above.

I wouldn't say that's characteristic of motors in general, but generally a motor under a small amount of load is pretty efficient across the board even if it's producing far less than its peak or continuous power.

Prius motor at 1k rpm 50 Nm of load is about 91% efficient -- about 5 kW, plenty for maintaining 55 mph. Looking at the prius motor, the only times it's really inefficient are at high load / low RPM (essentially when initially accelerating - probably why the Zero is so slow taking off in Eco mode) and at high RPM (4k+ with a 6k max).

A small motor + IET can produce identical torque to a larger direct drive motor at very low and very high speeds, and can generally shift up or down to operate the motor in its peak power band and avoid operating at very low or very high RPMs. But even then you're talking about going from 85% to 92-93% best case, and the transmission itself will introduce additional drivetrain losses.

I suspect IET will be great for street performance (huge help for 0-60 on a highway-capable bike), neutral for efficiency, bad for packaging and weight, and questionable for durability.

We haven't really seen many electric bikes at the races using a transmission, certainly none of the major players. There were a few at the first IOM TTXGP race, not sure if they've made a return. The big dollar teams must have looked at the weight & packaging tradeoff and decided a transmission was not helpful for their application.