A More Efficient EV Motor?

I appreciate what they've claimed but would prefer to see independent confirmation:

• need model numbers of the 18650 cells
• amorphous vs permanent magnet rotor temperature profiles

They may have something but some of this report sounds a little off.

Bob Wilson

 

KLD Energy

 

The tesla motor is already 90%+ efficient. You can't squeeze much more efficiency out of electric motors.

 

What you can squeeze out is a gearbox if you have a motor that doesn't heat up above 2500 rpm. KLD's motor designs have boasted 20,000 rpm.

 

The average inverter/motor efficiency on an induction motor like tesla is typically 91% inverter, 97% induction motor. This comes to 88% efficiency, which is what tesla quoted for the roadster. As you can see the part that will heat up is the inverter, and this could be made more efficient, but still you can't make the inverter/motor drive much more efficient. The inverter in our much lower power prius is liquid cooled.

Tesla's single speed transmission keeps the motor in an efficient range at legal speeds, its only much above the legal speed limit that efficiency drops off. Bellow 90 mph that motor should stay above 90% efficient. If that faster speed range is important a 2 speed transmission could be used.

 

How much is lost in the single speed transmission (gearbox) ?

 

The power loss is minimum possible in a single speed transmission, although there is a reduction gear as the motors are more efficient at higher rpms than 1:1 would need. IIRC if the bearings work properly losses in the drive train will a fixed amount due to friction, which means it should be independant of speed, but per mile. IIRC these losses should be around 10%. The bigger losses will be on tires to the road with largest losses due to rolling resistance and that is one place tesla could improve efficiency. The cold is really the big enemy of tesla efficiency with the losses for heating the cabin. The motors and transmission can't gain much. Batteries and inverters can be improved.

AWD and cold weather packages look to be offered soon. Really at 95mpge on the 65kwh pack, its going to be difficult to get things much more efficient.
As Predicted, Tesla To Launch All-Wheel-Drive Model S For 2014?

 

That 10% loss in the single speed gear box would be encountered in both propulsion and regeneration, correct?

 

IIRC the biggest losses are in the differential when changing speeds and turning. Slow straight deceleration will cause the smallest losses. Losses are larger in quick deceleartion, as the electrical path to charge the battery likely will push into an inefficient range. The only way I know of determining these things well is on a dyno. The 10% is a rough guess on my part. IIRC the prius is only about 25% efficient at converting mechanical motion into battery electricity during regen braking. The gen III prius path through mg2 has one additional universal gear than the tesla and an inverter and battery that can not handle enough power.

To reduce drive line losses individual hub motors might be used and the differential eliminated. This adds to cost, but is unlikely to give you a great increase in efficiency. The tesla's drive line by being rear motor rear drive eliminates some of the inefficiency of front engine rwd, where power must change directions and the drive line is longer and heavier.