Ray posted an interested column yesterday (9.13.19) addressing the question of what harm comes to an electric car from flooring the gas pedal. Is that more harmful to an electric car than doing the same thing with a gasoline car? Ray mentions the stress on the car’s suspension system etc … but goes on to say comparing gasoline motors to electric:
“There are no moving pistons, no rings, no crankshaft, no connecting rods or bearings. That’s one of the great advantages of electric motors. Many fewer moving parts.”
While its true there are fewer moving parts in the electric engine overall, electric motors definitely use bearings. And the beefier the motor, and the more power extracted from it, the more forces on the bearings. So I got to wondering if bearing failure is a common problem in electric vehicles? What about other failure modes for the electric motor? Any motor failure patterns showing up yet?
I believe an electric motor develops full torque at almost zero rpm, so it doesn’t need the gears to gain mechanical advantage to get the vehicle moving as a gasoline powered car does. Also, an electric.motor is easily reversed electrically, so there is need for a transmission.
That’s been my assumption. But I do see reference to a gear box for Teslas. I guess there’s still the gears in the differential, maybe that is what they are referring to.
Power makes heat, and torque. Both stress things as they increase, so, Yes driving hard is hard on the motor. It is also hard on the electronics and the batteries. Neither of which is 100 efficient doing their jobs. A Tesla has a 10x speed reduction single speed gearbox so the motor doesn’t spin so fast.
Figure the motor is 96% efficient. The control electronics are similar at about 95% and the Li-Ion batteries are about 95% as well. The transmission is, say 96% efficient as well. Total system efficiency is about 83%. Much better than an I.C. car but less than were are led to believe.
A Tesla Model 3 has 450 hp so that means 18-22 horsepower ends up as heat in each of the 4 sub-systems. All but the batteries are air-cooled. 80 hp is a lot of heat to dissipate at full throttle from stuff buried inside the car. If you hammer the car at a track, it will start dropping power to save itself because it is getting too hot.
The bearings in the electric motor wouldn’t be first and foremost in my mind. What would is the windings in the stator, or field in the motor and all the gadgetry in the speed controller and of course the batteries which have many parameters that come into play when full charging and rapid discharging are at foot. The speed controller is handling all the electrical pixies that make all the fun happen, so they need to be robust.
You do NOT want to “let the smoke out” of those electronics, they aren’t cheap. OEM Tesla smoke is very expensive and very finicky to re-install into those electronics.
I’m sure those electronics are bolstered for daily use, but maybe not so much to be used at their 100% limit… Surely they are designed up to a certain point of duty cycle etc and its safe to say that there would be room for improvements if the goal was to use the vehicle in a “Drag Racing” type of format.
That’s where my head would be initially for this exercise
I’m not sure about Tesla’ internals, but in my Honda hybrid both electronics/inverter and electric generators/motors are liquid-cooled, in the cooling circuit separated from the ICE engine cooling.
Battery is forced-air cooled, but this is the smaller load to compare to the rest of this setup
