Coasting in a Leaf

[gergg]

At some airspeed, there has to be a cutover point where you're better off putting that downhill energy "into the bank" with regen, since air drag increases exponentially and will prevent you from storing it all as momentum; bleeding it off into air turbulence instead.

It would be interesting to hear from some of the Leaf owners who have tried both coasting and eco/drive mode going downhill to see what is the most effective means of increasing range.

 

[bowthom]

Hello,
Unfortunately the leaf motor has permanent magnets embedded into the rotor. This causes it to have drag as the magnetic field eddies around the stator. You can feel it by putting it in N and pushing the car. The upside is, motors designed like this have a flatter torque curve at high RPM's.

 

[Volusiano]

At some airspeed, there has to be a cutover point where you're better off putting that downhill energy "into the bank" with regen, since air drag increases exponentially and will prevent you from storing it all as momentum; bleeding it off into air turbulence instead.

It would be interesting to hear from some of the Leaf owners who have tried both coasting and eco/drive mode going downhill to see what is the most effective means of increasing range.

I don't think the "cut over" point would be any different going downhill as opposed to be on flat terrain. It'd basically be at the optimum speed you want your Leaf to be that also keeps up a reasonable flow with the traffic and condition of the road.

I prefer coasting by adjusting the foot pedal such that you're at 0 positive bubble (lowest energy used). Going to reverse to get to N for coasting then back to D or Eco is too much shifting for me, while can I achieve the same thing by just slightly adjusting my foot pedal. Plus I don't like to get into the habit of getting too comfortable with thinking R=N and become trigger happy and put my car into R while I'm not moving.

 

[planet4ever]

Unfortunately the leaf motor has permanent magnets embedded into the rotor. This causes it to have drag as the magnetic field eddies around the stator.

Oh. I don't know enough about motors to know whether that is true when the wires in the stator are effectively open circuits, but I'll believe whatever the experts say. Before I read that I was about to propose that it coasts better because the motor is spinning. The mass of those permanent magnets would seem to be a fairly effective flywheel.

Ray

 

[Metalman]

Hello,
Unfortunately the leaf motor has permanent magnets embedded into the rotor. This causes it to have drag as the magnetic field eddies around the stator. You can feel it by putting it in N and pushing the car. The upside is, motors designed like this have a flatter torque curve at high RPM's.

I have an electric bike with a brushless motor in the rear hub and that's how it acts at very low speeds. Anything over say 5 MPH and it's not a factor.
I do lot's of coasting in the Leaf.

 

[Herm]

Unfortunately the leaf motor has permanent magnets embedded into the rotor. This causes it to have drag as the magnetic field eddies around the stator.

Oh. I don't know enough about motors to know whether that is true when the wires in the stator are effectively open circuits, but I'll believe whatever the experts say. Before I read that I was about to propose that it coasts better because the motor is spinning. The mass of those permanent magnets would seem to be a fairly effective flywheel.
Ray

What he is talking about is called "cogging", the magnets introduce a jerkyness as they rotate at low speed and they align with the iron slots in the stator.. it does act like a brake but it can be designed away by skewing the angle the windings make with the magnets.. I believe the stator slots are skewed, where the windings go. Bowthon says he has felt this cogging.

 

[LEAFfan]

When I can coast in N for a mile, I seriously doubt there is any regen from the motor. I've never felt unsafe using N instead of featheriing which is difficult for me to hold in neutral.

 

[harryjpowell]

I just wish someone could figure out a switch to turn off the re-gen, set it to 0. then I can really just coast without moving the control to N and back to D. I just want the option !

Can we find the wire to tell the Regen not to come on? It must be there as it tells it not to re-gen when the battery is full....

 

[ebill3]

I just wish someone could figure out a switch to turn off the re-gen, set it to 0. then I can really just coast without moving the control to N and back to D. I just want the option !

Can we find the wire to tell the Regen not to come on? It must be there as it tells it not to re-gen when the battery is full....

Sounds like we are talking about degrees of effort - flip a switch or move the hockey puck. Too little of a difference for me to worry about.

Bill

 

[harryjpowell]

Not really,
With a switch to turn the re-gen off,
I could use Cruise control and let it roll down hills not hold the speed with regen.
I would also have full pedal available to accelerate right from coasting if needed.

 

[gergg]

If I'm understanding how the Leaf works, seems like moving the puck in/out of "gear" would be very similar to the action one would use in a manual transmission to do the same thing....yeah?

 

[thankyouOB]

If I'm understanding how the Leaf works, seems like moving the puck in/out of "gear" would be very similar to the action one would use in a manual transmission to do the same thing....yeah?

yes, but with the caveat that when in gear in your ICE, you are NOT producing any gasoline/recharge, etc.

 

[TomT]

Actually, no since in a car with a transmission, be it automatic or manual, you are actually mechanically disengaging the drive-line via the transmission. In the leaf, it is simply an electrical consideration and nothing mechanical changes when you shift in or out of gear or in to reverse; it is always mechanically coupled.

If I'm understanding how the Leaf works, seems like moving the puck in/out of "gear" would be very similar to the action one would use in a manual transmission to do the same thing....yeah?

 

[TomT]

It's not a wire, it is software...

Can we find the wire to tell the Regen not to come on? It must be there as it tells it not to re-gen when the battery is full....

 

[TomT]

There is a chart elsewhere on the forum that plots the efficiency of the motor versus rpm...

The upside is, motors designed like this have a flatter torque curve at high RPM's.

 

[dgpcolorado]

If I'm understanding how the Leaf works, seems like moving the puck in/out of "gear" would be very similar to the action one would use in a manual transmission to do the same thing....yeah?

Similar in effect: the car is in neutral. But quite different mechanically, as TomT says above.

In the case of the manual ICE car the engine is disconnected from the wheels when the transmission is in neutral. In the LEAF the motor is never disconnected from the wheels because there is no transmission or clutch. As I understand it, neutral in the LEAF is an electrical setting that means no power to or from the motor windings, allowing the motor rotor to spin with very little resistance/drag. When using regen the motor acts as a generator and the resulting electromagnetic "drag" on the spinning of the rotor helps brake the car. The EEs here can probably explain it better than that.

The driving "feel" for coasting in neutral is the same for both a manual transmission ICE and LEAF in my experience. Which I believe is what you are getting at.

 

[gergg]

The driving "feel" for coasting in neutral is the same for both a manual transmission ICE and LEAF in my experience. Which I believe is what you are getting at.

Yep, you got it.

 

[harryjpowell]

Somewhere the software must send a signal to the re-gen brakes

May just have to upgrade to a Tesla:

Perhaps most exciting, the Model S will now feature adjustable regenerative brakes, which is something we certainly like to see in our EVs. For highway driving, having the brakes grab hold each time we take our foot off the accelerator is annoying, so we look forward to seeing just how much "coasting" the Model S will allow.

http://green.autoblog.com/2012/05/2...eries-will-start-june-22-regen-brake-level-n/

 

[dgpcolorado]

Somewhere the software must send a signal to the re-gen brakes

May just have to upgrade to a Tesla:

Perhaps most exciting, the Model S will now feature adjustable regenerative brakes, which is something we certainly like to see in our EVs. For highway driving, having the brakes grab hold each time we take our foot off the accelerator is annoying, so we look forward to seeing just how much "coasting" the Model S will allow.

http://green.autoblog.com/2012/05/2...eries-will-start-june-22-regen-brake-level-n/

I'd like adjustable regen for a different reason: I'd like more regen braking when going down steep hills. On the LEAF regen in Eco is about the same as third gear in my ICE cars but I need second gear to keep my speed at safe levels. That means having to use the brakes, some of which is likely wasteful friction braking.

 

[padamson1]

I'd like adjustable regen for a different reason: I'd like more regen braking when going down steep hills. On the LEAF regen in Eco is about the same as third gear in my ICE cars but I need second gear to keep my speed at safe levels. That means having to use the brakes, some of which is likely wasteful friction braking.

While definitely possible, as discussed in the 'Cost of ECO" thread (http://www.mynissanleaf.com/viewtopic.php?f=27&t=8925), the Regen logic needs to protect the battery. So the engine braking is disabled when the battery gets around 11bars or if the battery is too cold, meaning it wouldn't always be available.

If you have access to a Prius you can see this in action. With a Prius the electric regen is holding back the car in a similar fashion as ECO in a LEAF, but to a lesser extent (or greater extent when the 'B' gear is used). When the battery gets full the ICE turns on and is used to hold back the car. With this system the car doesn't suddenly loose its engine braking (and lurch forward) when the battery gets full, but you hear the undersized ICE revving loudly. In the LEAF the regen gently tapers off to nothing as the battery reaches 11bars. So you'll feel less engine braking as the battery gets closer to being full and start accelerating as if your were in Neutral, so you'll end up using the brakes.

Since everything is just SW, one would think that variable regen is doable, but its yet another thing to test on a very complicated SW platform (and a difficult test scenario to thoroughly test). As a SW engineer, I'd prefer they keep it simple.