coasting in neutral? can this hurt the engine?

[smkettner]

Nissan does say no to 4 down towing such as behind a motorhome.
Can't see it would hurt anything while driving.

 

[tkdbrusco]

I use N only in the following instances.

(1) When I am at or near 100% charge and no regen is available. Using neutral to coast at the beginning of my commute to known stop signs and stoplights.
(2) On slow gradual downhills. I put it in N to get some speed going, then I shift it into B mode and maximize regen. I find that this is a bit more beneficial as it increases your speed first and thus makes B mode more effective.

Other that the above, I don't use N much.

 

[garsh]

Nissan does say no to 4 down towing such as behind a motorhome.
Can't see it would hurt anything while driving.

It has been done.
It charges up the car nicely.

 

[dgpcolorado]

Coasting is best when you need to carry speed, and regen is best when you need to slow down. Friction brakes are only for emergencies and the last few MPH when coming to a stop, when regen no longer works. If you come into a stop too hot, you have already wasted the energy, and you only heat up the brakes; which is a total waste...

I agree, that's it in a nutshell for nearly all ordinary driving.

 

[kubel]

Correct me if I'm wrong, but the way I understand it, neutral isn't really neutral. If the front wheels are spinning, you are also spinning the reduction gears and the electric motor since everything is fixed. In any other car, putting the transmission into neutral or pressing the clutch will decouple the engine from the drive wheels, allowing the engine to run (or not run) independent of the motion of the wheels. Not so on the LEAF and other EVs.

In other words, the "shifter" is entirely software controlled and is more like a mouse controlling what software does than it is a gear selector mechanically choosing gears. Nothing mechanical happens when you "shift" (except when you go to park, the parking pawl engages if you're going slow enough).

So, no damage will come- though I don't find it particularly beneficial myself. I never shift into neutral unless I'm screwing around or a purse nudges the shifter out of drive and I'm left puzzled for a half second as to why my car lost all power.

 

[dgpcolorado]

Correct me if I'm wrong, but the way I understand it, neutral isn't really neutral. If the front wheels are spinning, you are also spinning the reduction gears and the electric motor since everything is fixed. In any other car, putting the transmission into neutral or pressing the clutch will decouple the engine from the drive wheels, allowing the engine to run (or not run) independent of the motion of the wheels. Not so on the LEAF and other EVs...

While it is true that "neutral" in an EV doesn't involve disconnecting a transmission to an engine, it seems like a reasonable term to describe what actually happens in an EV: no magnetic field is applied to the motor's rotor, so it can spin without any forces being generated.


For those new to EVs, the rotor in the car's electric motor is directly attached, via a reduction gear system, to the wheels (front, for the LEAF). The rotor always spins when the wheels spin. When the battery is used to apply magnetic fields to the motor, a force is generated that causes the rotor to spin forwards or in reverse, depending on the field polarity. The magnetic fields can also be used to turn the motor into a generator so that the kinetic energy of motion causes electricity to be generated and returned to the battery; this is used for "regenerative" braking. If no fields are applied, the rotor (and wheels) spin freely, which we call "neutral". This can be achieved by selecting N on the shifter or by keeping the accelerator pedal positioned at zero power (= no magnetic field).

Regardless of whether or not magnetic fields are applied to the motor, the rotor always turns in one direction if the wheels are moving forward and in the opposite direction if the wheels are moving in reverse. Since the rotor is directly linked to the wheels, its speed of rotation is always proportional to the speed of the wheels.

 

[jpadc]

While it is true that "neutral" in an EV doesn't involve disconnecting a transmission to an engine, it seems like a reasonable term to describe what actually happens in an EV: no magnetic field is applied to the motor's rotor, so it can spin without any forces being generated.

So are there no fixed magnets in the LEAF's motor? Any place on line where they have an inside view of the motor?

 

[TickTock]

You probably should actually read a post before stating it is false. My comment remains correct and yet doesn't contradict anything you stated (which is also correct).

You overestimate the efficiency of regen (Hint: It's not very efficient). There are plenty of anecdotal evidence (here, Tesla forums, etc) that suggests coasting during downhills is more efficient than regen in almost all cases.

In this case, coasting is the clear winner, as 54 vs 50 MPH does not increase drag coefficient very much (probably 5% more). Regen will be much lower than this.

It doesn't matter how efficient regen is, in this scenario it is still better even if only 1% efficient. I will restate my post thusly: You are cruising down a mountain, in one scenario you let the drag maintain your speed at 54 mph. You get to the bottom with the same energy in your battery as you had a the top. In the other scenario you let regen recover some of that energy and hold your speed at 50 mph. Now, at the bottom of the hill you have traveled the same distance yet have more energy in your battery than you had at the top. How is the first scenario (coasting) better for efficiency?

Regen really isn't that bad. It is true that you only recover ~39% (according to the Leaf Technicians workbook) of your kinetic energy when you regen to a stop but that is because you are losing energy to frictional losses - all of which are still present when you coast. Removing the frictional losses from the equation since those exist with or without regen, at least 61% recovered based on actual measurements (Hint: eschew anecdotal evidence). Finally, speed is, by a wide margin, the #1 contributor to range. Drag increases square law to speed (double your speed --> quadruple your drag). However, you are also going faster so your losses per distance only increases linearly so 54 mph will cost you 8% more energy than going the same distance at 50 mph.

 

[TimLee]

...Nothing mechanical happens when you "shift" (except when you go to park, the parking pawl engages if you're going slow enough).
...

Other case is if you mess up and shift to Reverse below the speed threshold which I think is 7 mph, the motor will nearly instantly attempt to change direction.
Tires will skid on the pavement and LEAF will attempt to stop abruptly and start moving backwards.
The action is caused by the electric motor though so technically not mechanical.

If you have ever made this mistake you will never forget it

 

[RegGuheert]

It doesn't matter how efficient regen is, in this scenario it is still better even if only 1% efficient. I will restate my post thusly: You are cruising down a mountain, in one scenario you let the drag maintain your speed at 54 mph. You get to the bottom with the same energy in your battery as you had a the top. In the other scenario you let regen recover some of that energy and hold your speed at 50 mph. Now, at the bottom of the hill you have traveled the same distance yet have more energy in your battery than you had at the top. How is the first scenario (coasting) better for efficiency?

In the first scenario, your battery may have the same amount of energy, but you have stored up additional kinetic energy. In the second scenario, you have stored more chemical energy in your battery, but your kinetic energy is unchanged.

The answer to which one leaves you with more total energy at the bottom of the mountain depends on the efficiency of the regen, the amount of aerodynamic drag and the length and slope of the mountain. If your regen is only 1% efficient (your number) and the mountain is short, then you likely are better off coasting.

 

[TickTock]

It doesn't matter how efficient regen is, in this scenario it is still better even if only 1% efficient. I will restate my post thusly: You are cruising down a mountain, in one scenario you let the drag maintain your speed at 54 mph. You get to the bottom with the same energy in your battery as you had a the top. In the other scenario you let regen recover some of that energy and hold your speed at 50 mph. Now, at the bottom of the hill you have traveled the same distance yet have more energy in your battery than you had at the top. How is the first scenario (coasting) better for efficiency?

In the first scenario, your battery may have the same amount of energy, but you have stored up additional kinetic energy. In the second scenario, you have stored more chemical energy in your battery, but your kinetic energy is unchanged.

The answer to which one leaves you with more total energy at the bottom of the mountain depends on the efficiency of the regen, the amount of aerodynamic drag and the length and slope of the mountain. If your regen is only 1% efficient (your number) and the mountain is short, then you likely are better off coasting.

For a short hill and 1% I would agree so, yeah, you're right, it does matter. The difference in kinetic energy at 54 mph and 50 mph comes to .019kWh or ~1/4 gid. OP says the hill is 1/4 mile so his break-even point is if his regen at 50mph produces 3.8kW. If less then coast, if more then regen.

 

[NeilBlanchard]

Correct me if I'm wrong, but the way I understand it, neutral isn't really neutral. If the front wheels are spinning, you are also spinning the reduction gears and the electric motor since everything is fixed. In any other car, putting the transmission into neutral or pressing the clutch will decouple the engine from the drive wheels, allowing the engine to run (or not run) independent of the motion of the wheels. Not so on the LEAF and other EVs...

While it is true that "neutral" in an EV doesn't involve disconnecting a transmission to an engine, it seems like a reasonable term to describe what actually happens in an EV: no magnetic field is applied to the motor's rotor, so it can spin without any forces being generated.


For those new to EVs, the rotor in the car's electric motor is directly attached, via a reduction gear system, to the wheels (front, for the LEAF). The rotor always spins when the wheels spin. When the battery is used to apply magnetic fields to the motor, a force is generated that causes the rotor to spin forwards or in reverse, depending on the field polarity. The magnetic fields can also be used to turn the motor into a generator so that the kinetic energy of motion causes electricity to be generated and returned to the battery; this is used for "regenerative" braking. If no fields are applied, the rotor (and wheels) spin freely, which we call "neutral". This can be achieved by selecting N on the shifter or by keeping the accelerator pedal positioned at zero power (= no magnetic field).

Regardless of whether or not magnetic fields are applied to the motor, the rotor always turns in one direction if the wheels are moving forward and in the opposite direction if the wheels are moving in reverse. Since the rotor is directly linked to the wheels, its speed of rotation is always proportional to the speed of the wheels.

It is in neutral. No energy is being used or created.

When you put the Leaf in reverse - is it really in reverse? There is no gear change ...


On the regen question: regen loses at least as much as charging does, so 15-20%, and it is probably losing more than this. You have to consider the whole cycle - if you use energy to get the car rolling, that kinetic energy is always going to lose energy to aero losses and rolling resistance.

When you coast - those are the only losses.

When you use regen, you lose the aero drag and the rolling resistance AND the regen losses.

So, when you need to carry speed to continue your drive, then coasting will always be better.

When you need to slow down, or limit your speed down a slope, then regen is better than friction brakes.

 

[TimLee]

...
When you put the Leaf in reverse - is it really in reverse? There is no gear change ...
...

Why would you think you would need a gear change to be in reverse?

Just because ICE vehicles had to use a transmission to accomplish reverse because an engine cannot spin in the reverse direction, does not mean an electric vehicle needs to do the same thing.

So in an electric vehicle changing the motor rotation and moving the vehicle backwards is reverse.

Similarly when Neutral is selected and the motor is not providing motive power, that is by definition Neutral.
In an electric vehicle there was no need for a clutch to accomplish Neutral.
It is better for the motor to stay spinning at the speed matching the speed the vehicle is moving.
Less stress when the motor is put back into providing motive force.
Only drawback is the slight drag from the single speed transmission gears spinning in the oil bath.
But that is small, and clutches are a chronic maintenance problem on ICE vehicles.
There was no justification to have one on an electric vehicle.

 

[TickTock]

So, when you need to carry speed to continue your drive, then coasting will always be better.
.

This is an over-simplification. As Reguheert pointed out a couple posts up, it really depends on the length of the hill and how much regen. In the OP scenario, you can easily calculate this to be 3.8kW of regen (assuming the driver adds 165 lbs to the total weight of the car). If using regen to slow from 54 to 50 for a quarter mile results in 3.8kW or more, then it is a win to use regen. If not then coasting is better.

 

[lorenfb]

So, when you need to carry speed to continue your drive, then coasting will always be better.

When you need to slow down, or limit your speed down a slope, then regen is better than friction brakes.

This is best answer to the common question asked on this forum unless one wishes to always utilize
the scientific calc app on one's cell phone while driving and before deciding whether to coast or regen!

Remember the acronym KISS - Keep it simple stupid

 

[dgpcolorado]

So are there no fixed magnets in the LEAF's motor? Any place on line where they have an inside view of the motor?

An interesting question. Yes, the LEAF motor uses permanent magnets (the Tesla uses a pure induction motor, so no permanent magnets and the rare earths needed to make them, but it is reported to be less efficient).

However, if the electromagnetic coils are not powered there is no force being applied to the rotor so the motor is in "neutral" and just spins along with the wheels (or stays motionless if the car isn't moving). The motor needs opposing magnetic fields to apply force to the rotor and the wheels.

These pictures aren't the greatest, but they are taken from the LEAF technician's training manual and show the motor type and structure:

 

[NeilBlanchard]

...
When you put the Leaf in reverse - is it really in reverse? There is no gear change ...
...

Why would you think you would need a gear change to be in reverse?

Just because ICE vehicles had to use a transmission to accomplish reverse because an engine cannot spin in the reverse direction, does not mean an electric vehicle needs to do the same thing.

So in an electric vehicle changing the motor rotation and moving the vehicle backwards is reverse.

Similarly when Neutral is selected and the motor is not providing motive power, that is by definition Neutral.
In an electric vehicle there was no need for a clutch to accomplish Neutral.
It is better for the motor to stay spinning at the speed matching the speed the vehicle is moving.
Less stress when the motor is put back into providing motive force.
Only drawback is the slight drag from the single speed transmission gears spinning in the oil bath.
But that is small, and clutches are a chronic maintenance problem on ICE vehicles.
There was no justification to have one on an electric vehicle.

You may have missed my attempt at sarcasm? My point was to confirm that an EV can coast in neutral even though the motor is still spinning ...

 

[NeilBlanchard]

So, when you need to carry speed to continue your drive, then coasting will always be better.
.

This is an over-simplification. As Reguheert pointed out a couple posts up, it really depends on the length of the hill and how much regen. In the OP scenario, you can easily calculate this to be 3.8kW of regen (assuming the driver adds 165 lbs to the total weight of the car). If using regen to slow from 54 to 50 for a quarter mile results in 3.8kW or more, then it is a win to use regen. If not then coasting is better.

If the car is traveling too fast, then use regen to slow it down.

If you accelerate too much, and then use regen, then you will use more energy than if you accelerated less, then coasted, and then used regen.

The entire drive has to be considered to see the whole picture - once you have invested energy in getting the car rolling, the best way to use it is to coast - if you want to keep the car moving. If you cannot coast, and have to slow down immediately after accelerating - then you have accelerated too much, and you have already wasted energy.

 

[DaveinOlyWA]

Correct me if I'm wrong, but the way I understand it, neutral isn't really neutral. If the front wheels are spinning, you are also spinning the reduction gears and the electric motor since everything is fixed. In any other car, putting the transmission into neutral or pressing the clutch will decouple the engine from the drive wheels, allowing the engine to run (or not run) independent of the motion of the wheels. Not so on the LEAF and other EVs.

In other words, the "shifter" is entirely software controlled and is more like a mouse controlling what software does than it is a gear selector mechanically choosing gears. Nothing mechanical happens when you "shift" (except when you go to park, the parking pawl engages if you're going slow enough).

So, no damage will come- though I don't find it particularly beneficial myself. I never shift into neutral unless I'm screwing around or a purse nudges the shifter out of drive and I'm left puzzled for a half second as to why my car lost all power.

ok. first of all, we need to understand that a physical connection is only one type of connection

 

[DaveinOlyWA]

You probably should actually read a post before stating it is false. My comment remains correct and yet doesn't contradict anything you stated (which is also correct).

You overestimate the efficiency of regen (Hint: It's not very efficient). There are plenty of anecdotal evidence (here, Tesla forums, etc) that suggests coasting during downhills is more efficient than regen in almost all cases.

In this case, coasting is the clear winner, as 54 vs 50 MPH does not increase drag coefficient very much (probably 5% more). Regen will be much lower than this.

It doesn't matter how efficient regen is, in this scenario it is still better even if only 1% efficient. I will restate my post thusly: You are cruising down a mountain, in one scenario you let the drag maintain your speed at 54 mph. You get to the bottom with the same energy in your battery as you had a the top. In the other scenario you let regen recover some of that energy and hold your speed at 50 mph. Now, at the bottom of the hill you have traveled the same distance yet have more energy in your battery than you had at the top. How is the first scenario (coasting) better for efficiency?

Regen really isn't that bad. It is true that you only recover ~39% (according to the Leaf Technicians workbook) of your kinetic energy when you regen to a stop but that is because you are losing energy to frictional losses - all of which are still present when you coast. Removing the frictional losses from the equation since those exist with or without regen, at least 61% recovered based on actual measurements (Hint: eschew anecdotal evidence). Finally, speed is, by a wide margin, the #1 contributor to range. Drag increases square law to speed (double your speed --> quadruple your drag). However, you are also going faster so your losses per distance only increases linearly so 54 mph will cost you 8% more energy than going the same distance at 50 mph.

the correct answer is highly dependent on the situation. regen is more efficient than people realize because its the ratio of power returned over power generated but each case has gravity and friction to over come which doubles the apparent losses regen sees making 100% regen a physical impossibility.

So efficiency is really based more on how well you know your route than what mode you drive in. I can GUARANTEE I can drive more efficiently than anyone using neutral in my backyard. Regen drivers do not have a prayer.

also, another thing we should consider is making false assumptions since a lot of the negative neutral comments seem to think that we will be speeding...