by drees (Posted Mon, 09 Sep 2013 23:17:02 GMT)
Yes, but properly designed a transmission will improve overall efficiency.
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.
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.
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.