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babynuke
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potential EV transmission; CRS - controlled rotation system

Sun Sep 08, 2013 6:31 am

http://partsservicesholland.com/
http://controlledrotationsystem.com/

3-d-view-automotive-200mm-06-10-2013.gif


Would not a transmission allow for a smaller motor => same acceleration/top speed => less current draw => greater range ???
Ty
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ericsf
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Re: potential EV transmission; CRS - controlled rotation sys

Sun Sep 08, 2013 7:57 am

I don't think so. The electric motor can deliver max torque at zero speed and can spin way faster than needed (the LEAF's top speed is electronically limited). A fixed ratio gear transmission or no gears at all is all an EV needs. The weakest link is the inverter and the battery. What limits the performance and how much power you can draw through them.
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drees
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Re: potential EV transmission; CRS - controlled rotation sys

Sun Sep 08, 2013 12:43 pm

ericsf wrote:I don't think so. The electric motor can deliver max torque at zero speed and can spin way faster than needed (the LEAF's top speed is electronically limited). A fixed ratio gear transmission or no gears at all is all an EV needs. The weakest link is the inverter and the battery. What limits the performance and how much power you can draw through them.

Motors don't have infinite RPM range, at high RPMs back-EMF prevents you from spinning them faster.

A transmission will definitely allow one to use a smaller motor for a given performance threshold.
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DeaneG
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Re: potential EV transmission; CRS - controlled rotation sys

Sun Sep 08, 2013 3:41 pm

drees wrote:A transmission will definitely allow one to use a smaller motor for a given performance threshold.

At a possible cost in efficiency. It's amazing how inefficient even a simple fixed gear reduction can be.
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LTLFTcomposite
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Re: potential EV transmission; CRS - controlled rotation sys

Sun Sep 08, 2013 7:14 pm

With the secret sauce in the Spark's motor it seems this would be unneccessary long term. Assuming a manufacturer has enough patents to cross license with gm.
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fotajoye
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Re: potential EV transmission; CRS - controlled rotation sys

Sun Sep 08, 2013 9:13 pm

Without getting too deeply in the subject details, suffices to say there is a area of the torque/RPM curve that represents the most efficient rpm and load to run the motor; that area is usually where the motor draws the least amount of current while moving the car. to the best of my memory, I believe that point on the Leaf is about 30-40 mph on level ground with the present drive line.

Adding gearing won't make the car more efficient; but, if you want performance, keep the motor in its peak torque range. For the Leaf that's zero to about 3,000 rpm. so, if you select the proper gears and shift them within that range, you should be able to max out the acceleration of the car. A couple of things to consider: there are friction losses in the transmission so that will reduce performance and be careful not to ramp up the motor too quickly because applying 200 ft/lbs of torque to a stationary gear set could destroy it.

I may be wrong on some of my figures; but, I think you can get the idea.

smkettner
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Re: potential EV transmission; CRS - controlled rotation sys

Sun Sep 08, 2013 9:52 pm

One of the things I like most about LEAF is the simple reduction gearbox.
I would give up some performance for additional range at highway speeds.
Maybe just offer two different ratio options.
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drees
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Re: potential EV transmission; CRS - controlled rotation sys

Mon Sep 09, 2013 11:17 pm

DeaneG wrote:
drees wrote:A transmission will definitely allow one to use a smaller motor for a given performance threshold.
At a possible cost in efficiency. It's amazing how inefficient even a simple fixed gear reduction can be.

Yes, but properly designed a transmission will improve overall efficiency.

LTLFTcomposite wrote:With the secret sauce in the Spark's motor it seems this would be unneccessary long term. Assuming a manufacturer has enough patents to cross license with gm.

While GM's secret sauce in the Spark EV lets it produce about twice as much torque, it runs out of steam at about half the speed. Net result - an improvement in efficiency thanks to having to spin the motor and input gear on the transmission half as fast, but it's no miracle.

fotajoye wrote:Without getting too deeply in the subject details, suffices to say there is a area of the torque/RPM curve that represents the most efficient rpm and load to run the motor; that area is usually where the motor draws the least amount of current while moving the car. to the best of my memory, I believe that point on the Leaf is about 30-40 mph on level ground with the present drive line.

The motor draws the least amount of current when it's not moving anywhere. But the efficiency is also at it's lowest.

30-40 mph at very low load is not where the motor is it's highest efficiency. If you look at the actual motor efficiency charts, the motor is actually most efficient at maximum power from around 45-65 mph or so (over 95%). Of course, while the motor is most efficient there, the inverter is not necessarily the most efficient there, and drawing large amounts of current also results in higher losses in energy coming out of the battery pack. All that said, if you look at the DOE ATVA test results, you'll see that while it is more efficient to drive at 45 mph, the battery/inverter/motor are more efficient at 70 mph.
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