Plug In America Wants Automakers to Retool for the Future

[David Dymaxion]

The battery electric Buckeye Bullet (went over 321 mph, over 500 km/hr!) and the under-development fuel cell electric Buckeye Bullet 2 have a five and six speed transmission, respectively.




________________________________
From: matt <[hidden email]>
To: Electric Vehicle Discussion List <[hidden email]>
Sent: Monday, November 24, 2008 6:54:25 AM
Subject: Re: [EVDL] Transmissions or lack thereof was Re: Nuts! WAS:PlugInAmerica Wants Automakers to Retool forthe Future

The conversions that retain a transmission are inherently *slower* than their direct drive counter parts because theyre limited to the low rpm(<3000rpm) (if series DC) of the motor, and the low torque ( less than 500Nm) that a *normal* transmission will accept reliably. That means   max peak value of 150kw or there abouts.....at the motor, not the wheels.

Few ( I have yet to see one, that has) purpose built Evs have a gearbox, and especially not the high performance variants. Even the Tesla guys ditched their gearbox in favour of single ratio, having tried both.


     
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[drowe67]

> As for the throttle control at low speeds, that's an artifact of the
> simple method most EVs use to control throttle. Most have the pedal
> directly control the duty cycle of the motor, which, as you say, won't
> be very controllable for direct drive at low speeds.

That explains something I noticed when driving my EV.  I need to "feed
in" the throttle as I accelerate, i.e. I gradually depress the
accelerator as my speed increases.  In my automatic transmission ICE car
I press it to a constant position until I hit cruise speed to get
constant acceleration.  I think it's also because the ICE develops low
power and torque at low revs.

In my EV I also get a surge of power immediately after I change gear,
which can be unsettling (e.g. for my wife), as there is a lot of torque
at low revs just after the change.  Reverse can also be tricky - push a
little too hard on the pedal and I am flying backwards.

- David


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[Lee Hart]

Joseph Ashwood wrote:
> running off of the target run lowers efficiency, sometimes significantly.

Take a look at the efficiency curves of some typical AC or DC EV
traction motors. You will find that their efficiency remains high over a
very wide range of speed and torques.

For example, the Advanced DC series motor commonly used has a peak
efficiency of 89% at 30hp (138 vdc at 200 amps, 5400 rpm at 32 ftlbs).
But its efficiency stays over 80% from 20-120 ftlbs torque and 3000-8000
rpm.

AC motors can be even better. AC Propulsion's AC-150 combined motor and
inverter efficiency has a peak efficiency of 91%, and stays over 85%
efficient from 2000-11000 rpm and 5-90 ftlbs torque.

This means is that a shifting transmission is not needed. It's not worth
the extra size, weight, cost, and efficiency loss. You're better off
running the motor at a slightly lower efficiency with a fixed-ratio
gearbox. The efficiency savings from eliminating the transmission more
than make up for the efficiency loss in the motor and controller.

Now, if economics matter, you may want to keep the transmission. You may
have gotten it for "free" (because it was part of the donor vehicle). It
may be an inseparable part of the transaxle, so you can't eliminate it
to save weight. And, by shifting, you can get by with a smaller motor
and controller.

--
Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in    --    Leonard Cohen
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net

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[Rick Beebe]

Lee Hart wrote:
  > > For example, the Advanced DC series motor commonly used has a peak
  > > efficiency of 89% at 30hp (138 vdc at 200 amps, 5400 rpm at 32 ftlbs).
  > > But its efficiency stays over 80% from 20-120 ftlbs torque and
3000-8000
  > > rpm.

I've been playing with a spreadsheet to figure ideal direct-drive
gearing for the EV Miata I'm working on. With the stock 4.1:1 rear end,
the car would be going 51 mph at 2000 rpm and 136 mph at 8000 rpm. If I
can find a way to bump that to 7:1 I get a more usable spread of 29 to
80 mph. That's certainly where much of my driving occurs.

  > > AC motors can be even better. AC Propulsion's AC-150 combined
motor and
  > > inverter efficiency has a peak efficiency of 91%, and stays over 85%
  > > efficient from 2000-11000 rpm and 5-90 ftlbs torque.

Even better. 34 mph to 187 mph at 4.1:1. <g> So with AC, getting to 10:1
gives me 15 to 85 mph in that nice efficiency range. Perfect. That Black
Box 2.27:1 underdrive that Tom Alvary found would be perfect IF it can
run 'backwards' at 11,000 rpm!

--Rick

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[Cor van de Water]

AC motors doing over 10,000 RPM are not unheard of,
my truck used a Hughes motor with 9,000 redline.
DC motors doing 8,000 RPM are not common, IIRC the
redline is typically between 4,000 and 5,000 RPM
and too many motors have 'sploded from crossing that
limit, especially when pre-heated.

Regards,

Cor van de Water
Director HW & Systems Architecture Group
Proxim Wireless Corporation http://www.proxim.com
Email: [hidden email]    Private: http://www.cvandewater.com
Skype: cor_van_de_water     IM: [hidden email]
Tel: [phone]        VoIP: [phone] FWD# 25925
Tel: [phone]x109 XoIP: [phone]

Please consider the environment before printing this e-mail.
-----Original Message-----
From: [hidden email] [mailto:[hidden email]] On
Behalf Of Rick Beebe
Sent: Tuesday, November 25, 2008 8:59 PM
To: Electric Vehicle Discussion List
Subject: Re: [EVDL] Transmissions or lack thereof

Lee Hart wrote:
  > > For example, the Advanced DC series motor commonly used has a peak
  > > efficiency of 89% at 30hp (138 vdc at 200 amps, 5400 rpm at 32
ftlbs).
  > > But its efficiency stays over 80% from 20-120 ftlbs torque and
3000-8000
  > > rpm.

I've been playing with a spreadsheet to figure ideal direct-drive
gearing for the EV Miata I'm working on. With the stock 4.1:1 rear end,
the car would be going 51 mph at 2000 rpm and 136 mph at 8000 rpm. If I
can find a way to bump that to 7:1 I get a more usable spread of 29 to
80 mph. That's certainly where much of my driving occurs.

  > > AC motors can be even better. AC Propulsion's AC-150 combined
motor and
  > > inverter efficiency has a peak efficiency of 91%, and stays over
85%
  > > efficient from 2000-11000 rpm and 5-90 ftlbs torque.

Even better. 34 mph to 187 mph at 4.1:1. <g> So with AC, getting to 10:1
gives me 15 to 85 mph in that nice efficiency range. Perfect. That Black
Box 2.27:1 underdrive that Tom Alvary found would be perfect IF it can
run 'backwards' at 11,000 rpm!

--Rick

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[storm connors]

If I try to start off in 3rd gear on a slight uphill, my clutch will
smoke. I replaced the clutch and pressure plate, but it still did it.

> Now, if economics matter, you may want to keep the transmission. You may
> have gotten it for "free" (because it was part of the donor vehicle). It
> may be an inseparable part of the transaxle, so you can't eliminate it
> to save weight. And, by shifting, you can get by with a smaller motor
> and controller.
>
> --
> Ring the bells that still can ring
> Forget the perfect offering
> There is a crack in everything
> That's how the light gets in    --    Leonard Cohen
> --
> Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net
>
> _______________________________________________
> General EVDL support: http://evdl.org/help/
> Usage guidelines: http://evdl.org/help/index.html#conv
> Archives: http://evdl.org/archive/
> Subscription options: http://lists.sjsu.edu/mailman/listinfo/ev
>
>

--
http://www.austinev.org/evalbum/1059
http://stormselectric.blogspot.com/
Storm

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[Jon Bishop-3]

> That's where we differ, I'd use a continually variable transmission, and
> program it for the eletric motor. But at the same time, I am on a "Oh its
> you, nevermind" basis with the local police (he really did say that before
> he got in his car and drove away).

The CVT is the approach I think that the automakers SHOULD take. As
far as you're concerned, you're in go, and the tranny will gear for
peak motor efficiency at whatever speed is desired. We'll see how that
goes, Nissan's doing it now with a couple models, maybe they'll add a
CVTEV in a year or two?

~Jon

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[Kelly Hales]

I do have to agree here, if we could hack the electronics to keep the rpm
where we want it
Kelly
----- Original Message -----
From: "Jonny B" <[hidden email]>
To: "Electric Vehicle Discussion List" <[hidden email]>
Sent: Tuesday, November 25, 2008 9:09 PM
Subject: Re: [EVDL] Transmissions or lack thereof was Re: Nuts!
WAS:PlugInAmerica Wants Automakers to Retool forthe Future

>> That's where we differ, I'd use a continually variable transmission, and
>> program it for the eletric motor. But at the same time, I am on a "Oh its
>> you, nevermind" basis with the local police (he really did say that
>> before
>> he got in his car and drove away).
>
> The CVT is the approach I think that the automakers SHOULD take. As
> far as you're concerned, you're in go, and the tranny will gear for
> peak motor efficiency at whatever speed is desired. We'll see how that
> goes, Nissan's doing it now with a couple models, maybe they'll add a
> CVTEV in a year or two?
>
> ~Jon
>
> _______________________________________________
> General EVDL support: http://evdl.org/help/
> Usage guidelines: http://evdl.org/help/index.html#conv
> Archives: http://evdl.org/archive/
> Subscription options: http://lists.sjsu.edu/mailman/listinfo/ev
>

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[Joseph Ashwood]

----- Original Message -----
From: "Lee Hart" <[hidden email]>
To: "Electric Vehicle Discussion List" <[hidden email]>
Sent: Monday, November 24, 2008 1:04 PM
Subject: Re: [EVDL] Transmissions or lack thereof was Re: Nuts! WAS:
PlugInAmerica Wants Automakers to Retool forthe Future

> Joseph Ashwood wrote:
>> running off of the target run lowers efficiency, sometimes significantly.
>
> Take a look at the efficiency curves of some typical AC or DC EV
> traction motors. You will find that their efficiency remains high over a
> very wide range of speed and torques.
>
> For example, the Advanced DC series motor commonly used has a peak
> efficiency of 89% at 30hp (138 vdc at 200 amps, 5400 rpm at 32 ftlbs).
> But its efficiency stays over 80% from 20-120 ftlbs torque and 3000-8000
> rpm.
>
> AC motors can be even better. AC Propulsion's AC-150 combined motor and
> inverter efficiency has a peak efficiency of 91%, and stays over 85%
> efficient from 2000-11000 rpm and 5-90 ftlbs torque.

I would consider both of these relatively low power.

I will use the Nissan GT-R for the comparison, depending on the person's
views it is either the lowest specd supercar or the highest spec
non-supercar.

Top Speed: 192mph

This would require an overall ratio of 11000 rpm/192 mph for the AC-150, or
57.29rpm:1mph. So at a cruising speed of 60mph the AC-150 would be
3437.5rpm, just inside the efficient range. Dropping the speed to the
claimed overall average of 37mph for travel in the US, the motor rpm would
be 2119rpm, just inside the efficiency range. Bringing this to an observed
average for LA traffic during rush hour or about 15mph, a motor rpm of 860
is below the efficiency range. This makes for a significant amount of time
spent below the efficiency range.

0-60mph: 3.5 seconds

Assuming the running gear of the GT-R, and using the ratio necessary for the
192mph. The GT-R has a final drive tatio of 3.700, and a top gear ratio of
0.796. Since the 192mph is achieved at redline of 7000rpm, the math isn't
too difficult. The shaft rpm is 8793.97 entering the final drive at max
speed, so an internal drive ratio of 1.251:1 is necessary for the AC-150.
This means that in a 0-60 run with the AC-150 will peak at 106lbft, compared
to the GT-R's peak of about 480lbft (first gear 4.096, final gear 3.700).
This gearing will not reach anything even close to supercar acceleration.

Changing the ratio to deliver supercar acceleration will leave the vehicle
well below supercar top speed. It is possible to build a motor delivering
both, but such a motor would be simply too large and heavy for use. Instead
using a properly chosen transmission both gears can coexist, so a
transmission is necessary for supercar performance.

These limitations are easily verified. Tesla Motors uses an AC motor of
similar strength to the AC-150, and delivers a claimed "under 4" second
0-60mph, which of course means that it is between 3.9 and 4.0 seconds, about
12% less quick, and a top speed of 125mph is claimed, about 30% slower, this
makes the unverified claims already significantly less than even the lowest
supercar level.

For a normal vehicle the requirements are different, and a geared limit of
100mph is reasonable and a 7second 0-60mph is entirely reasonable. This
level of performance doesn't require a transmission, but it is not supercar
level.
                    Joe

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