Exactly how and what works the hardest in an EV/ IMIEV

[phb10186]

I've had a quick trawl through the forum, and couldn't find a good thread for this after my limited flick through.

I was giving a work colleague a lift today in the IMIEV, and he asked the question: what gives the whirring noise under load - to which I said ' the transmision - 1 fixed gear'. Not sure if I was even right about that.

That got me thinking, and I realised that I can exactly explain what bits of an ICE work hard when you stomp on the gas, but I cant do it as well for the EV.

The questions are as follows:

1. How does the electricity flow from the battery to the motor, and what are the points of maximum resistance.
(I thought that if you push an EV, then obviously the most affected parts are the transmission and the bit that handles all the current through it).

2. How does the regen get power back to the battery, and how is the electricity processed on its journey?

3. Does driving an EV hard adversely effect the car in the same was as a conventional ICE one?

4. What parts are likely to wear out first if you drive gently over the lifetime, vs what changes if you drive the car hard over the lifetime?

I was particularly referring to the EV side, rather than the traditional tyres/ brakes/ suspension.

 

[PV1]

Intriguing post.

1. Battery pack through contactors and current sensors, down some High Voltage wiring to the MCU, inverted to 3-phase AC, and pushed through the motor. The max resistance point is likely the MOSFETs in the MCU. If I have my theory correct, there isn't a PWM current limit in the normal sense, but the inverter varies the timing of the phases to be just ahead of the neutral point in the motor (or just behind for regen/reverse). The more power output or more regen/reverse power advances the timing further away from the neutral point. Putting the car in Neutral shuts the inverter off.

2. Not too sure on how regen works. I have my theory above, but nothing to back it up.

3. I don't think it causes excessive wear, as the entire EV powertrain has smooth power and is all rotary motion, no power stroke being converted to rotary. At the most, it stresses the battery cells more than normal, but given the specs of the LEV50n cells, they should be able to take abuse without much complaint. I recommend to watch the cell temps when driving hard and force cool air through the pack.

4. Tires for easy driving. Tires, and maybe brakes for hard driving. The battery will likely wear faster with higher currents (and the resulting higher temperatures), but should still last quite a while. The gearbox/motor seems to be very well built and will likely last a very long time. There are only three main gears and a differential in the driveline.

As for the whine itself, I think it is gear whine in the gearbox, as it sounds different between Drive, Reverse, and regen braking. One interesting note is that a CB radio on a quiet channel with the squelch turned down will pick up whine from the electric drive through the 12 volt system. But then again, computer hard drives and CD drives are direct drive and make just as much whine, so maybe it is the motor that makes the noise and the gears simply amplify it?

 

[mdbuilder]

Found on the internets:

When the speed of the motor is more than the synchronous speed, relative speed between the motor conductors and air gap rotating field reverses, as a result the phase angle because greater than 90° and the power flow reverse and thus regenerative braking takes place. If the source frequency is fixed then the regenerative braking of induction motor can only take place if the speed of the motor is greater than synchronous speed, but with a variable frequency source regenerative braking of induction motor can occur for speeds lower than synchronous speed. The main advantage of this kind of braking can be said that the generated power is use fully employed and the main disadvantage of this type of braking is that for fixed frequency sources, braking cannot happen below synchronous speeds.

In English, you are trolling along at say 5,000 motor rpm in B mode. You lift off the gas a little and the inverter says "Let's change the rpm to 4,800" the 200 RPM difference between actual motor rpm and commanded rpm results in reversed energy flow. Lift off more, commanded rpm goes down and braking force increases.

 

[phb10186]

I thought regen may be capacatative.

Also, unsure whether my '12 plate has LEV50 or LEV50n

I also notice that in the highest regen setting (thats 'B' for me), there is a slight amount of vibration when going from max regen to application of power - not noticible in the other lower regen settings.


... as far as wear goes: was watching Elon Musk explain that the early Teslas broke all the gearboxes... but assume the high power of their units is a different thing entirely to an I miev.