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Evolute Drives test results show 18% reduction in energy consumption with 3-speed MSYS EV transmission compared to single speed

Evolute Drives, incorporated as a separate entity by its sister company Drive System Design (DSD) (earlier post), will present practical test results for its high efficiency 3-speed MSYS electric vehicle transmission (earlier post) at the upcoming CTI Symposium in Shanghai (16-18 Sept).

In independent tests, a B-class demonstrator vehicle fitted with the transmission achieved a reduction in energy consumption of up to 18% over the NEDC test cycle, compared to the single-speed base vehicle.

The results, obtained at the MIRA facility in the UK, endorse our previous expectations of a 10-15 percent improvement when a single-speed drive is replaced by our MSYS transmission. Reducing the energy required by an EV leads to a corresponding improvement in range, which is still a key issue for many EV users

—Alex Tylee-Birdsall, Managing Director of Evolute Drives

News_3787_1_original
3-speed MSYS transmission fitted in B-class tester. Click to enlarge.

Since technical details of MSYS were presented at the 2013 CTI Symposium, development has continued in several areas, towards a production-intent prototype specification. These developments, along with the detailed results from the MIRA tests, will be presented by Tylee-Birdsall in a paper entitled “Next Generation Development - MSYS 3-speed EV Transmission”.

The cone clutches used in MSYS allow much greater torque transmission density than a wet multi-plate clutch, providing more than four times the torque capacity within the same package size. Recent developments include minimizing torque oscillation during engagement to ensure good and consistent shift feel, through the management of concentricity of the assembly.

The presentation will also describe efficiency improvements obtained through a novel twin-mode lubrication system. The lubricant flow rate to the clutches is increased only during shift events, when greater cooling is required, by a simple variable distribution system. At other times the flow rate is reduced to minimise energy requirements.

MSYS allows full torque power shifts to be made but requires no energy to hold the transmission in gear, which improves system efficiency. The key to the technology is the separation of the two functions provided by a synchroniser (friction and latching), while enhancing the friction capacity so it can be used to temporarily drive the vehicle.

—Alex Tylee-Birdsall

Production-intent prototypes of the MSYS transmission should complete their testing during 2016 and validated production units are scheduled for sign-off around mid-2017.

Comments

mahonj

I thought electric cars were 95% efficient.
I must have a very simplistic view of the world if they can get an 18% improvement with a B class car (Focus sized?)

I suppose if you make gearboxes, every problem looks like a gearbox problem.

Brent Jatko

@ mahonj: I agree; I thought the strength of electric vehicles was that no gears are needed because maximum torque occurs at zero RPM.

Brent Jatko

The lack of transmission is an extremely important maintenance advantage as well.

SJC

Fully loaded slow speed/high current 3 phase permanent magnet motors go well below 60% efficient on the performance curves. See UQM or Remy motor charts.

T2


I suppose if you make gearboxes, every problem looks like a gearbox problem.

Yes, Evolute Drives clearly know little about induction motors or must be reading from 30year old textbooks.

Induction motors can be operated at constant rated torque over their complete speed range providing the inverter voltage is made sufficiently high.

For short time durations induction motors can output a Peak torque of up to 350%, perhaps as high as 420%, before electrical constraints step in. Durations are also limited to avoid rotor meltdowns.

Forget about efficiences quoted at 60Hz since automotive grade 4-pole induction motors don't usually spend much time there (~15mph).

The fact is that induction motors are more efficient the faster they spin, perhaps as high as 99%.

The reason is simple, it takes a certain power to establish the stator field. With the setting up of the magnetic flux needed for rated torque, power output becomes simply proportional to the spin rate.

No more power is needed to maintain that torque. Think of it as a fixed tax that has to be paid following which conversion of power from electrical to mechanical is 100% efficient.

Theoretically, unlimited power lasts for as long as the rotor can survive the rpms but in practice, and it's usually somewhere below 60mph, the motor output has to be constrained electrically by the controller in order to prevent thermal distress to the battery pack. This is the problem faced by the Tesla P85D that has some owners riled up.

To recap, since both efficiency and power increase with rpm it should never be necessary to spin down the motor as you would do with an ICE powered car. This should make the need for a multi-ratio gearbox somewhat moot.

SJC

http://www.teslamotorsclub.com/attachment.php?attachmentid=75172&d=1426681019

T2

SJC , understand that although my "Vista" browser is said to be all knowing and all powerful but Ph...tt Just not able to find attachments. Would you mind a cut and paste here so that us lesser mortals can see what smug village has produced in Teslamotor land, please and thank you.

By the way in case there is misunderstanding about the P85D. It does entirely achieve the 2.8 sec to 60mph ramp as promised but the 85Kwh battery causes the reigning in above that speed. A larger 90kwh is in the offing(at a price) which will significantly improve subsequent acceleration beyond 60mph.

mahonj

@T2, I can read the attachment in Chrome.
Any chance of downloading chrome and trying again?

yoatmon

Well, I agree with Evolute Drives and here is why.
A transmission is not only a speed adapter, it is also a torque converter. With a smaller e-motor and a transmission, you can reach the same torque levels as with a bigger e-motor (excepting high gear where less power and torque is needed for gliding than for acceleration). The bigger the e-motor is, the more current it'll draw under load from the battery. High power density flow is not necessarily of advantage to the battery. On the contrary, the lower the power flow the less strain is exerted on the battery. I could very well imagine that a smaller dimensioned electric motor combined with a 3-gear transmission would suffice general requirements, ease strain on the battery and improve consumption performance.

SJC

http://www.teslamotorsclub.com/showthread.php/44455-motor-efficiency

Bruce Moore

What is the additional weight of this transmission vs a NISSAN LEAF reduction gear? I would rather not add any more moving/shifting parts. Part of the appeal of EVs is the reduction of moving parts.
I would rather have a battery with more capacity.

SJC

Use a planetary CVT with two smaller motors.

T2

mahonj : I'm moving to WIN10 shortly. If that doesn't do it - then I'll try Chrome. In the meantime I was able to reach the thread - thanks SJC much appreciated.

The discussion there runs 3 pages but I didn't see a definitive conclusion. There were comments on data attributed from Tesla being unsubstatiated as far as gear ratios but nothing on whether V/Hz motor characteristics had been changed to suit. It being necessary for the motor design to reflect a change in its V/Hz whenever a gear ratio is changed. You can't change one without changing the other else power peaks will come at the wrong roadspeed, usually too early. That may have been Steve Saleens problem with his P85 enhancement in 2014.

T2

Yoatman, The bigger the e-motor is, the more current it'll draw under load from the battery.

Look, current is not the issue here, rather it is the ability of the motor to deliver power to the load.

At low rpms there can be 1000 amps in the motor but no more than 75 amps being pulled from the battery. So motor current is not a problem to the battery when accelerating from rest.

As the vehicle gathers speed the voltage to the motor is increased proportionally to maintain torque. I think that makes sense. As the controller applies more voltage while still supplying 1000 amps clearly the battery, for its part, has to supply more current.

Simply put the battery voltage times battery draw must equal motor current times motor voltage. In this case since the battery voltage is fixed and we have decided to fix the motor current at 1000 amps, then as the motor voltage rises so must the battery current in order to balance the power IN equal power OUT equation.

Yoatman, I could go on and on because there is considerably more to be written for a complete understanding of the all the issues and I have only touched on one of them here.

There are other issues involved.
These issues concern motor V/Hz, Fixed gear ratio.
Max motor rpm and max vehicle speed.

The first issue is when to allow motor voltage to hit the battery voltage.
The second issue is how soon should the battery current be limited before the first issue takes effect.

Finally my personal favorite "How much do max road speed bragging rights impair system performance with fixed gear systems ?"

T2

I seem to have a complete earlier post wiped thanking Mahonj for the Chrome suggestion, and then SJC reposting a link I could use. Plus comments on the content of that link. ??
Of course that would be the post that I didn't save, because the system told me it had been posted. I began my response to Yoatman almost directly after.

SJC

The point being that electric motors are not always 90% efficient all the time. If you want to get more range around town with lots of starts from stops, a planetary eCVT could help.

T2

SJC , I'll give one more kick of the can to this.

electric motors are not always 90% efficient

Not at slow speed and full torque, I'll grant you your point which is exactly as you stated in your first post earlier in this thread.

But these occurences of slow speed operation (<20mph)do not present a significant loss, in total, of battery energy for several reasons.

They are usually of very short duration when accelerating from rest, sub 3 seconds.

They exist during prolonged slow speed operation where the motor demand is bound to be very low so electrical losses are going to be expected to be proportionally low as well.

Finally within this low speed region, the vehicle may actually be slowing down with or without regen braking.
No losses at all.

Aerodynamic losses, which I consider the biggest battery killer, are almost zero in all these scenarios.

If this was an industrial machine then a CVT may be a good idea if considerable high torque while running continuously at low speed was required. BUT for a road vehicle any heavy demand is only transitory as the motor drives the inertia of the vehicle up to cruise speed. I don't see the need for any further mechanical complication to be added here.

If I haven't convinced you by now then at least you are in good company with Evolute Drives they don't see it either.

Alex_C

@T2,
have you heard of any attempt to coat IM rotor and interior of stator with some special materials that are able to radiate and absorb heat much better than those surfaces of current IM motors, so that heat from rotor is extracted faster?

I did a quick search, found this on a forum:
"... there are nanostructure coatings that can remove heat up to four times faster than standard paints. Researchers at Oregon State University and the Pacific Northwest National Laboratory have discovered a way to achieve near-optimal heat dissipation by applying a nanostructured coating.
They have reported the coatings produced a "heat transfer coefficient" ten times higher than with the uncoated surfaces, dissipating heat four times faster than previously possible."

Another thing - to increase torque, common method is to increase number of poles (say 2 pairs per phase instead of one for high speed IM motors).
This assumes doubling the frequency, and you mention in one of your earlier comments that it may be problematic pushing 480 Hz into the motor.

Wouldn't it be worth trying with 5 (or 7) phase system and one pair of poles per phase for motors (say IM ones) spinning above 15,000 rpm, especially those going above 20,000 rpm, to keep the frequency below 400 Hz?

T2

Alex, no I hadn't heard, but a somewhat less sophisticated alternative to avoid rotor overheat is to cut the rotor in half so to speak and then use the two resulting downsized motors to separately power each axle.

Theoretically the effect is to increase surface to volume ratio by 26%. That opens up the possibilities of more power per motor but with the same motor case temperature as the original single motor drive system.

Splitting the drive unit like this also confers AWD something the Evolute isn't offering I notice.

SJC

Not just acceleration from stop but acceleration in general. If you logged around town performance of a straight reduction EV with PM three phase PWM drive, you would see substantially less than 90% efficiency. With a eCVT you can get more range with the same battery pack and less recharge time than a larger pack.

Alex_C

@SJC,
BTW how do you plan to implement eCVT with electric motors only?
In Toyota eCVT system there are 2 e-motors and ICE attached to the planetary eCVT system.
Did you try on paper to connect 2 or 3 e-motors similar to those currently used and run the numbers from 0 to 100 mph, with calculated all gear ratios in such system?
I'd like to see such a system, its pros and cons , never saw any eCVT with only e-motors.

Alex_C

@T2,
agree that 2 downsized motors would be easier to cool (agree on number 26% too, played with formulas myself, after reading your comment earlier).
On the other hand using 2 smaller motors opens opportunity of two (or more) speed gearboxes, where one motor provides infill torque (IM with high overload capability well suited for this), while the other motor changes gear using just a dog clutch, after first quickly matching speed of two spinning surfaces to be clutched.
For both motors it is desirable to have high overload capability during the shift. For the one driving the wheels - in order to provide infill torque. For the other motor (doing gear shift) - to change its speed (up or down, depending if it is downshifting or upshifting) as fast as possible.
Actually WrightSpeed does it already in commercial products (www.WrightSpeed.com).

Here is fast shift demonstration :
http://www.wrightspeed.com/technology/

1. Motor is accelerated to 20,700 rpm in first gear, Upshift (Shift from 1st gear to 2nd gear)
2. Motor torque is reduced to zero
3. Shift actuator is moved to neutral position (mid-stroke)
4. Motor speed is synchronized to the correct speed for second gear, 9000 rpm (80 ms)
5. Shift actuator moves to second gear
....

One thing here is not clear - what is the phase frequency at mentioned 20,700 rpm (350 Hz if one pair of poles, or 700 Hz if two pair of poles per phase). Some companies bought those trucks, so somebody could answer this question by measuring frequency of current going through cables from inverter into motor, relatively easy (while truck moves, or with wheels lifted, just measure highest frequency), without disconnecting cables to motor.

Do you think it would be significantly easier to temporary overload (for gear shift) the induction motor at 350 Hz (21,000 rpm) than at 700 Hz (ie 2 pair of poles, at the same 21,000 rpm)?

The torque fill in WrightSpeed truck system is obviously done by, say, left pair of rear wheels while right wheel pair motor shifts, and then the other way around.

Similar thing could be done with 4WD e-drives (separate motors on front and rear axles as in some Teslas, model S).
On one or on both axles motor can use 2-speed transmission, where motor on the opposite axle provides torque fill while the other does gear change.

T2

See if I've got this right. 20,700rpm to 9000rpm in 80mSecs. So you're thinking you can regen a rotor the size of a 1lb coffee can to give up 75% of its rotational energy in less than a tenth of a second. Sorry, not possible, the physics is just not with you.

Do you think is a hypothetical question.

4-pole (2pole-pair/phase) induction motors have twice the torque per unit mass so 2-poles are rarely used except to avoid an inverter. Examine a motor catalog for specs, a 10Hp 2-pole and 4-pole will be seen to have the exact same weight, although the 2-pole will have smaller dia rotor. How do I know ? Compare their rotor inertia constants.

Actually the best way is to run a 230Vac 4-pole on 460Vac @120Hz. The motor will develop twice its nameplate power and run cooler. Has it been done ? Yes.
The Tesla system takes the idea further by winding for @480Hz (~14,000rpm), in this case the stator lams would be made thinner of course and the rotor would be finely balanced to enable it to run with low vibration at that speed.

Alex_C

@T2,
It was not my claim (80 ms sync time in that video). I just passed the link, and posted a few lines of text from there. They have commercial product, so it works, the numbers may not be quite as good as in video.
They may not do it in 80 ms, considering they have torque fill from another motor during shift, so the complete shift can be done a little slower (say within 0.7 sec, it's not a racing car).
Please note high ratio L/D on the motor in picture (being held in hands).
It's extremely beneficial to have high L/D for low rotor angular inertia, as moment of inertia is proportional to R^2.
When I said "Do you think", I expected an educated guess from a very knowledgeable person with lots of hands-on experience, not a definitive answer.

I just made a calculation of angular kinetic energy of a hypothetical rotor, weighing 5 kg, L/D=5 (D=2R), at 21,000 rpm.
Assumed density = 8,000 kg/m^3 (little above iron, lower than copper - and it's laminated).
Found rotor was R=2.7 cm (D=5.4 cm), L=27 cm.

Moment of inertia, I=(1/2) m R^2 = 1.8225 x 10^-3 (All SI units)

Angular kinetic energy, E=(1/2) I (omega)^2
At 21,000 rpm, the rotor has kinetic energy of 4.414 KJ.
To accelerate it to that rpm (or to brake it), in 0.1 sec, power of 44.14 kW needs to be applied. (This is 100% of power, not 75%, for 1/2 of max speed)
So their numbers seem very feasible. Unless I made some mistake somewhere.
I probably assumed too small rotor, but their motor has 250 HP, so it can handle 50% larger diameter of rotor (with about 4x kinetic energy of this from my example).

The reason I assumed just 2 poles, is because of high L/D needed to slowdown/accelerate rotor faster (for multi-speed systems). Also hysteresis loses are probably lower with lower max frequency.
In a small diameter you cannot put too many poles.
What you found in catalogs are probably not high performance motors, for cost reasons they may have used the same stator.

T2

What you found in catalogs are probably not high performance motors, for cost reasons they may have used the same stator.

Alex, the motors in a Eurotherm catalog are Premium Effcy with copper rotors - aluminum is being phased out as more and more newly installed motors are being inverter fed.

I refer you to the catalog to see first hand that 460Vac 10Hp 2-pole and 4-pole weigh the same even though the former puts out only half the torque of the latter. It gives a more poignant look at the situation. I know I am repeating an earlier post, perhaps I wasn't clear enough, but an intelligent person like yourself may opt for a 230Vac 5Hp 4-pole which makes the exact same torque as a 10 Hp 2-pole (but will naturally weigh and cost a whole lot less) and drive it with a 460Vac inverter at 120Hz to reach ~3600rpm and thus match the performance of the larger 2-pole.

Hopefully these facts and ideas will lessen your enthusiasm for the use of 2-pole motors which today is now a dead end as far as I am concerned.

You are probably already aware that catalog motors are unsuitable anyway since their windings have a V/Hz of 480/60Hz = 8.0V/Hz Automobile inverter motors are more likely to be 0.25V/Hz. Just need 32X more current to reach the same torque. That's where the 1500Amp IGBT's come in. Their use completely changed the picture as they effectively extend the useful voltage range because the adoption of an extra low V/Hz motor winding allows the motor to spin 8X faster before the inverter runs out of voltage headroom.

Tesla was among the first to use them with the legendary 2.8sec to 60 ramp with fixed gear P85D. So I am thinking how much more proof do you need ?

Anway congrats on figuring out what is basically turns out to be the equivalent of the cube root of two, it looks like the generic formula is the cube root of the number of divisions you make of the original motor.
As you discovered, the utility of two motors suggests 26% better cooling/or more power. From that perspective I think you will find that four motor systems begin to look even more interesting.

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