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What does the Nissan Leaf "neutral" actually do? It would appear that the motor is permanently connected to the drive train/differential, in which case how is the shifter "neutral" different to "drive"?

I am currently converting my 1982 Lotus Esprit S3 to electric using a Leaf motor/charger, but while I am developing the control electronics for the motor, I would like to be able to move the car and installed motor without turning the motor via the transaxle.
 

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What does the Nissan Leaf "neutral" actually do? It would appear that the motor is permanently connected to the drive train/differential, in which case how is the shifter "neutral" different to "drive"?

I am currently converting my 1982 Lotus Esprit S3 to electric using a Leaf motor/charger, but while I am developing the control electronics for the motor, I would like to be able to move the car and installed motor without turning the motor via the transaxle.
I'm not sure you have any choice. Turning the transaxle will turn the motor, assuming both wheels on the ground. It may be possible to turn the transaxle (with at least one wheel off the ground) and thru the differential, have the other wheel spin in the opposite direction without turning the motor. There is no 'neutral' in the sense of a manual/automatic transmission. I'm guessing that shifter neutral removes power for the inverter (or possibly tells it to not generate power). The motor is a permanent magnet motor, and power will be generated if the inverter is powered and the motor is spun. The early Leafs could charge the battery by getting a tow.
 

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Yes - that is what I assumed too, but can't really see the point of it.
I'm assuming the point is to prevent overcharging of the batteries, either by too much current or letting the voltage get too high. Maybe to protect the inverter capacitors and such from too high a voltage. Maybe it simply makes sure no torque signals are sent to the motor. I'm guessing they had a reason, but who knows. Maybe to be more like the ICE machines we're all used too.
 

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Discussion Starter #6
OK - my next question is how to put it "neutral" without the shifter/VCM. I assume there must be a CAN message to the inverter to do this?
 

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There is a locking pawl latch in the gearbox that is engaged when you go to Park position. If you can release the pawl, either mechanically or by energizing the actuator, then it will roll. Sorry i don't have the details of that circuit but might be able to look it up in the FSM. It can be found online and is quite handy for reference.

[edit: it is a motor driven actuator]
120500
 

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Discussion Starter #8
There is a locking pawl latch in the gearbox that is engaged when you go to Park position. If you can release the pawl, either mechanically or by energizing the actuator, then it will roll. Sorry i don't have the details of that circuit but might be able to look it up in the FSM. It can be found online and is quite handy for reference.

[edit: it is a motor driven actuator]
View attachment 120500
Thanks for the info - I have seen it online, but that actuator appears to only operate the parking brake - releasing it still leaves the transmission connected to the motor.
 

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What does the Nissan Leaf "neutral" actually do?
It tells the controller/inverter to not power the motor (in forward or reverse), without engaging the parking pawl.

It would appear that the motor is permanently connected to the drive train/differential, in which case how is the shifter "neutral" different to "drive"?
Yes, the gearing connection is permanent. In Drive the controller/inverter can power the motor; in Neutral it does not.

Yes - that is what I assumed too, but can't really see the point of it.
Neutral exists so that you can do exactly what you want to do, which is roll the car without power.

Thanks for the info - I have seen it online, but that actuator appears to only operate the parking brake - releasing it still leaves the transmission connected to the motor.
True. The information about the parking pawl and its actuator is just to help you ensure that you can freely roll the car, by getting it out of Park.



By the way, almost every production EV has a permanently connected single-ratio transmission like this, although not all have a mechanical parking feature.
 

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Discussion Starter #10
Thanks to everyone for the useful information.

I still need to find out how to tell the inverter to go to neutral, though.
 

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I hope it's that simple, but I suspect there is a dedicated CAN command for neutral.
Yes, but you don't need to get the controller into Neutral mode if it is producing zero torque... although the idea of glitch providing another torque command would make me nervous if I were pushing a powered car around the shop.
 

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To command the Leaf inverter to neutral (aka no creep), simply attack the NM demand message on the EV-CAN. Be aware that you need to modify the response message, otherwise you will trigger fault codes. Attach a CAN-bridge between the VCM and inverter, and go to town on the messages. MotorAmpTorqueRequest and MG_EffectiveTorque

More info here: Dala's Leaf buildthread (2015 Nissan Leaf) - Page 7 - Japtoys.net
 

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Discussion Starter #15
I have come to the conclusion that "neutral" is just disconnecting power to the inverter.
 

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If you turn to the motor with the inverter powered off, does it roll freely (great) or does it try to generate or "cog" (bad)?
Because of the reduction gearing, there is some resistance when trying to move the car.
 

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Because of the reduction gearing, there is some resistance when trying to move the car.
Yes, there will be the significant flywheel effect of the motor: as you start it moving you're spinning the motor up, and when you let go the motor keeps it moving like any flywheel. It's like pushing a heavier vehicle: it doesn't take much more to keep it moving, but it's harder to get it going and to stop it. Without a mechanical neutral (and there definitely isn't one), there's no way around that. The issue isn't really the gearing, it's what the gearing is connected to.

If the motor is acting as a generator, there would be continuing drag or "cogging" (feeling like you're pushing past a series of bumps), in addition to the flywheel effect.
 

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What does the Nissan Leaf "neutral" actually do? It would appear that the motor is permanently connected to the drive train/differential, in which case how is the shifter "neutral" different to "drive"?

I am currently converting my 1982 Lotus Esprit S3 to electric using a Leaf motor/charger, but while I am developing the control electronics for the motor, I would like to be able to move the car and installed motor without turning the motor via the transaxle.
 
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