CVT & IVT Gearboxes

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Gow864
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CVT & IVT Gearboxes

Post by Gow864 »

CVT & IVT gearboxes? can these things be used in EV's?

Anyone have any idea of the pro's and con's?


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acmotor
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Post by acmotor »

IVTs have been used maybe 20 years ago in some trials.
The point is that C is for constant and I is for infinite and unfortunately this describes well the losses of these transmission systems compared with fixed ratio(s) gearboxes.
Since the main aim of these transmissions is to make an underpowered motor perform then it is a bit self defeating to have increased losses.

We need to keep thinking no gearbox for the future. This gives a saving in weight and cost and of course complexity (not to mention less oil).

Were you thinking of these transmissions for conversions or OEM ?
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Post by Benonymous »

The CVT gearboxes from Jatco that are used in the Honda Civic and a Japanese only Nissan (I think) are extremely heavy at a bit over 65Kg. I agree with ACMotor. What we need are high torque, low speed motors for direct drive to the wheels. Gearboxes should be eliminated for efficiency gains and weight losses.

However, if you were really keen, you might be able to adapt a Skidoo CVT. These run on V belts and a re similar to those fitted to DAF cars made in the 60's and 70's. From a weight point of view they look good. Efficiency is not as good though and in a high torque application, the belts might not last well.
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Post by Gow864 »

acmotor

for my own conversion, still researching, and probably asking the same questions you've heard a zillion times...

I did find a site that claimed 95% Eff... like I said research.. research...
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Post by acmotor »

If a gearbox spec. is really worthwhile it will state the static friction and rotational loss at rated RPM along with an efficiency at 25% 50% and 100% rated torque.

Single 'efficiency' numbers can be very misleading for an EV application. e.g. a gearbox may be 95% efficient at passing 100kW yet still take that 5kW just to turn it over at cruising speed !

Then there are the wrong numbers... even Bob Brant in his book says a final drive (diff) is 98% efficient.... in your dreams Bob.
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CVT & IVT Gearboxes

Post by soyachips »

acmotor wrote: We need to keep thinking no gearbox for the future. This gives a saving in weight and cost and of course complexity (not to mention less oil).
Hi acmotor,

Does this mean that connecting to the driveshaft of a RWD car is better (in terms of mechanical efficiency) than connecting to the transmission of a FWD car via an adaptor plate?

I like the simplicity of this solution but have read conflicting info on whether of not this is a good idea. The main problem seems to be having a single "gear" to cover the loads when starting off and then having the motor running at non-optimal revs at cruising speed. Do you have any thoughts on this?

Also do you know of anyone who has used a motor designed specifically for this, e.g. NetGain TransWarP?

Thanks!
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Post by acmotor »

Yes.

Both RWD and FWD have diffs. much the same efficiency. It is possible with RWD to go straight to the tailshaft/diff. But not often possible with FWD as the diff / gearbox is usually a combined unit.

You will note that the serious conversions get rid of the gearbox / diff unit of a FWD and drive with their own purpose built unit with single ratio box/diff direct to the half shafts e.g. solectric.

Bypassing the gearbox is not always practicle if there is insufficient motor torque.

Check Zeva.com.au for an MX5 with 11" direct to diff.

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Post by gttool »

Ive been thinking of even building a gearbox of sorts that attaches to the motor shaft with a 1:1 3:1 reduction of sorts
using a single stage planetary gear train and a dog clutch
would be very compact
with the clutch disengaged it would run through the planetry 3:1
clutch engaged 1:1 which would lock the planetry
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Post by Gow864 »

I initially thought that direct drive (motor to prop shaft) would be great, reduce the rotational torque needed, less losses etc.. However, after reading of some DD conversions it seems like not such a good idea,   I don't want to have to draw 1000amps to get away from the lights. Even the DD gearbox, it's still a fixed ratio drive, doesn't this just move the inefficiencies to a different rev band (showing my ignorance here).

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Post by acmotor »

Bottom line is, in wheel hub motors will one day rule the roost.

We can all forget about gearboxes then.

Hub motors at present are too much unspring mass and not really applicable to conversions due to the massive redesign of vehicle dynamics, but they are getting there.

In the mean time, for the present conversion market, direct to diff drive is best but requires suitable motor torque. Failing that, the good old (100 year old) DC motor to the gearbox is quite popular.
Remember, if you need a gearbox then you probably needed a bigger motor in the first place (or one with better low end torque) !

BTW if you don't like 1000A then increase the voltage of the system.
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Gow864
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Post by Gow864 »

Hub motors? what's the difference? Multiple motors yes, but they don't have to be hub motors.
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Post by soyachips »

acmotor wrote: Yes.

Both RWD and FWD have diffs. much the same efficiency. It is possible with RWD to go straight to the tailshaft/diff. But not often possible with FWD as the diff / gearbox is usually a combined unit.

You will note that the serious conversions get rid of the gearbox / diff unit of a FWD and drive with their own purpose built unit with single ratio box/diff direct to the half shafts e.g. solectric.

Bypassing the gearbox is not always practicle if there is insufficient motor torque.

Check Zeva.com.au for an MX5 with 11" direct to diff.

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Hi acmotor,

Thanks for the reply. I checked out the Solectria and they used an AC induction motor in the Sunrise. Are these more suited to direct drive than DC motors? If so could you please explain why?

Cheers
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Post by antiscab »

Hi Gow,

500A through a warp 11 direct to diff was fairly sufficient acceleration in a mx5 in my experience.

you remove some inefficiency by eliminating the gearbox.
there is no single ratio gearbox.
the differential usually has a built in ratio.
the torque needed is always higher than with a gearbox.

with a direct drive converison, you will need a larger diameter motor.
it doesnt necessarily have to be bigger (heavier) but they usually are.
bigger motors are more efficient at higher loads.
larger diameter motors make the same amount of power, but more torque.
the ratio you usually end up with is as if you are in 4th or 5th all the time.

The gearing does of course affect the efficiency curve to speed relationship.
Most motors are more efficient at rated rpm.
at low speeds efficiency does indeed drop, however, so does power required.
How much of an effect this is depends on the motor and what ur driving pattern is.
for my driving pattern (60kmh zones and a few traffic lights) i expect 70%+ of the energy i use will be used while i am at speed.

I can measure fairly accurately on my emax the energy usage relationship, and that is 70%+ of the energy used is at speed.

for my setup i expect a kostov 11 to have 900 Nm at 2000A, 450 Nm at 1000A, 180 Nm at 500A.
a warp 11 should be much the same.
the A of course are all motor side, because of my high battery voltage, battery side A will be far lower (400A when motor A is 2000 at 20kmh)

hope this clears up some confusion.

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CVT & IVT Gearboxes

Post by Gow864 »

I was referring to the solectria type gearboxes that are bolted to the Azure dynamics motors, ignoring the diff (which isn't in the gearbox of my car). These are a fixed ratio? yes/no?

OK, so here's another question:

1, Direct drive AC 320V 100AH
2, Direct drive DC 144V 200AH
3, Two AC motors (Help with batt pack for this)
3, Two DC motors (Help with batt pack for this)

Which of the above options would deliver the greater efficiencies.

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CVT & IVT Gearboxes

Post by acmotor »

Firstly, Gow864, hub motors (when they get them right) will be the ultimate motor. But yes, one at each wheel for AWD (as all cars should be anyway). This gives the best computer control over ABS, traction control, dynamic cornering etc. All this without the need for gearboxes, diffs, half shafts unis CVs ... how simple (mechanically at least). Then there is the redundancy of 4 motors and so on.

soyachips,
DC motors have good low end torque (if you don't blow them up as smoke is their only limit). They suit direct drive if they are big enough but tend to run out of revs.
AC (and brushless DC) have less starting torque (and don't send up as many smoke signals as you can't just push 'till something breaks). However the torque continues flat to quite high revs whereas DC motor's torque drops off.
DC motors need to be big for direct drive to work well. (and the controller needs to have plenty of current)

Single AC direct drive will deliver the greatest efficiency.
Economy of scale - one big motor is more efficient than two smaller ones. Direct drive is more efficient than gearbox. AC is more efficient than DC. Be aware thought that the most efficient is also likely to be the most expensive.

Having said that, DC with two motors works fine e.g. kilacycle. Image
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Post by Rob M »

[quote="Gow864"] CVT & IVT gearboxes? can these things be used in EV's?

Anyone have any idea of the pro's and con's?


Hi
I have often considered this type of transmission for EV's.
Tuarn has mentioned some of the disadvantages albeit with some overstatement.
Transmissions do vary in their efficiency for sure but it puzzles me why an apparently "highly efficient" AC motor needs water cooling whilst a gearbox rarely does. I have experimented a bit with gearboxes but have yet to do an AC motor conversion.
Cost aside, I would still need a gearbox, fixed ratio at the very least, in order to get some reasonable performance with an AC motor.
The cars with continuos ratio gearboxes don't seem to suffer from huge weight gains or high fuel consumption so they can't be too bad.
One big advantage I can see is that motor speeds can be selected for optimum power and/or efficiency. The benefits of this might even outweigh the other "losses".
I still beleive that a well designed planetary gearbox with at least 2 speeds will deliver better performance in both acceleration and efficiency in an EV than a large motor and lots of amps (AC or DC).
I have tried both and although the transmission was an old 3 speed Borg Warner 40 without the torque converter, the acceleration was outstanding. The weight of the 9" motor plus tranny was similar to the 11.5" GE motor.
I have to add that a weight difference of 30 or 40 Kg represents only 2 to 3% so barely affects acceleration.
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Post by Johny »

Hi Rob
When you used the Borg Warner, what did you do to maintain fluid pressure?
I have read one thread where the guy kept the motor spinning over at about 150-200 RPM when stationary. I have a Borg Warner 35 and am about to ditch it, but your comment interests me.
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Post by Rob M »

Hi Johny,
I drove the pump from the drive motor simultaneously. It meant I had to be careful not to plant my foot from a stationary start or there would be a distinct bump when first gear engaged but the other changes were very smoth. I would consider using a separate oil pump, probably electrically driven if I was to use the system again.
Keeping the motor spinning would also be useful if you wanted to run the power steering pump and/or air conditioner from the drive motor.
I originally had the Triton ute motors driving the steering pump but since it was a direct drive system (motors to diff) there was no steering at low speed or reverse when it was needed most.
cheers
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Post by acmotor »

Stating the obvious and inevitable is never overstatement ! Image

A well designed motor requires neither gearbox nor water cooling.

Cooked any DC motors lately ? Maybe they should be water cooled.Image
You could run an ICE radiator and motor to pump cooling water to the controller as well !

Seriously though, one problem at present is the limited choice of motors at planet earth prices.
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