learn me some Leaf regen and braking

[thankyouOB]

After having the car for two months, I have two questions about braking and Eco mode:
- when I am braking and the regen kicks in with bubbles filled to the left of neutral, am I actually engaging the brake or is the computer system in the car reversing the motor so that the electrical system is slowing the car?
and that continues until I need to really stop and then the real brakes kick in?

-Similar question for Eco mode: when I slow in Eco, is the car's electrical system reversing the motor so that it captures the slowing?

 

[DaveinOlyWA]

both. when you lift foot off power, you will regen back to battery. when braking you will initially do the same. now braking is two mode, both regen and friction and the ratio between the two depends on your braking need. slow gradual braking can be nearly all regen which is what you want if you have the room.

i pretty much drive with the energy screen on since it meters power flow. the bubbles are good but i think harder to view at a glance and i like numerical values better anyway.

for max efficiency; drive with as little regen as possible. its better to maintain a steadier speed. now if it not possible and stopping is inevitable, feather the brake to ease into regen to make it last as long as possible.

 

[thankyouOB]

thanks dave.
on your second response, you say that it is most efficient to drive with as little regen as possible;
doesnt that happen best in D rather than Eco?
So, are you saying it is more efficient to be in D, which allows for more coasting and less brakeless regen?

 

[DaveinOlyWA]

thanks dave.
on your second response, you say that it is most efficient to drive with as little regen as possible;
doesnt that happen best in D rather than Eco?
So, are you saying it is more efficient to be in D, which allows for more coasting and less brakeless regen?

no, eco is better in town. on freeway it does not matter.

the reason for my statement is that regen is less efficient that momentum/gravity most of the time. regen may get you back less than 30% of the amount of power it takes to get you to a certain speed. so when traveling with traffic. its better to slowly bleed off speed than it is to speed up and slow down. iow, drive at a speed that requires as less change in velocity as possible

for example; you see a red light, line of cars a few blocks ahead. what you need to decide is how long its going to take you to get to the light.

immediately reduce to no power which bleeds speed off gradually in hopes that traffic will start moving before you get there. the objective is to be going as fast as possible. now this should not be done if on single lane roads.

another situation maybe gentle changes in elevation. use gravity to your advantage. at street speeds, its more efficient to go to no power on downhills even if it requires an increase in speed then bleed that extra speed off on the uphill.

all this requires traffic anticipation and a following distance much greater than what people normally drive. get to know the light timing. it can really help.

city traffic is a make or break. it can either boost your range well over 100 or it can put you into the 60 mile range if that stop and go anticipation is not working well for you

 

[planet4ever]

Similar question for Eco mode: when I slow in Eco, is the car's electrical system reversing the motor so that it captures the slowing?

One semi-technical comment: Perhaps I am just misreading what you wrote, but I wouldn't say the motor is "reversing", either in ECO or when braking. It doesn't suddenly spin in the opposite direction.

There is little if any difference between an electric motor and an electric generator. Essentially, what regen is doing is just applying force on the mechanical end of the motor without voltage force being applied to the electric end so that it starts behaving as a generator. Now, there is a bunch of technical stuff that happens underneath that "essentially" concept, involving phase shifting at the motor and inverting AC back to DC, and most of it I don't even understand (hence the "semi-technical" qualification above). But so far as I know, the motor is always spinning one direction when the car is going forward, and always spinning the other direction when it is going backward, and the motor speed is always proportional to the speed of the wheels. i.e. there are reduction gears, but there is no way to literally shift gears (move them so they connect in different ways), not even in neutral or reverse.

Ray

 

[thankyouOB]

Similar question for Eco mode: when I slow in Eco, is the car's electrical system reversing the motor so that it captures the slowing?

One semi-technical comment: Perhaps I am just misreading what you wrote, but I wouldn't say the motor is "reversing", either in ECO or when braking. It doesn't suddenly spin in the opposite direction.

There is little if any difference between an electric motor and an electric generator. Essentially, what regen is doing is just applying force on the mechanical end of the motor without voltage force being applied to the electric end so that it starts behaving as a generator. Now, there is a bunch of technical stuff that happens underneath that "essentially" concept, involving phase shifting at the motor and inverting AC back to DC, and most of it I don't even understand (hence the "semi-technical" qualification above). But so far as I know, the motor is always spinning one direction when the car is going forward, and always spinning the other direction when it is going backward, and the motor speed is always proportional to the speed of the wheels. i.e. there are reduction gears, but there is no way to literally shift gears (move them so they connect in different ways), not even in neutral or reverse.

Ray

Right (and I concede that I dont use the right terms) but is this what is going on when we slow down in ECO:
the energy generated from moving forward is captured by the car's EV system and instead of drawing power from the battery to move the car forward (via the motor) it is drawing power from the slowing to turn the generator and recharge the battery;

then, when I apply the brakes, it further channels energy from the slowing to the battery?

 

[johnr]

Yes, applying the brakes increases regen. But anything beyond light application also begins to engage the friction brakes. Where this happens exactly, nobody seems to really know as it varies depending on speed, state of charge, and other factors. Personally, I like to shift into ECO to slow down (think of it like downshifting with a stick-shift), and then lightly apply the brake as necessary to slow further. The idea is to maximize regen if you must slow quickly, while minimizing use of the friction brakes.

 

[kawh]

we live on a hill. we have to go up, then way down hill to get to town.

here's my puzzle. once i'm at the top of the hill, will i get more regen/miles if i use eco mode all the way down the hill (in eco, i use almost no brakes) or in regular drive, where i use the brakes a lot?? either way, i use almost no "gas".

also-- is eco better on the steep uphill portion-- or just regular drive??

would love to know just how to handle our hill.
thanks,
kawh

 

[91040]

we live on a hill. we have to go up, then way down hill to get to town.

here's my puzzle. once i'm at the top of the hill, will i get more regen/miles if i use eco mode all the way down the hill (in eco, i use almost no brakes) or in regular drive, where i use the brakes a lot?? either way, i use almost no "gas".

also-- is eco better on the steep uphill portion-- or just regular drive??

would love to know just how to handle our hill.
thanks,
kawh

You will get more regen/miles using eco mode. However:

For maximum range, you want to maintain your momentum. Regen is not 100% efficient so it is better to avoid it, if possible. When you must slow or stop, you want to use that momentum to regen electricity. Friction brakes use the momentum energy to generate heat and wear.

On a downslope, coast feathering the accelerator (0 electricity use on the Nav energy screen). If you gain too much speed, don't press the accelerator, using regen to control speed. If you still gain too much speed, shift into Eco using the additional regen to control speed. Use brakes as your last choice. It is hard to tell when the brakes transition from only regen to adding friction.

Up hill, eco will make a difference only if you need to slow down quicker than the hill and regular drive cause. This assumes you have a light foot on the accelerator.

 

[abasile]

once i'm at the top of the hill, will i get more regen/miles if i use eco mode all the way down the hill (in eco, i use almost no brakes) or in regular drive, where i use the brakes a lot??

I would definitely recommend the use of ECO mode going down that hill. When you manually press the brakes, there is always a possibility of some fiction/mechanical braking getting blended in, especially if you brake harder. On the other hand, regen in ECO mode is generally more smooth and steady then most folks can achieve with the brake pedal, thereby maximizing efficiency and the amount recaptured. Also, for other motorists, it's nicer if you don't appear to be riding your brakes, as that tends to make some drivers grow more impatient if they want to go faster than you do.

is eco better on the steep uphill portion-- or just regular drive??

In general, I believe that the LEAF loses some efficiency at higher motor power levels, like 30+ kW (4+ "bubbles"). I personally prefer ECO mode all of the time because it gives me finer-grained "throttle" control. If you want to limit motor power and speed for the sake of efficiency, it is easier to do so in ECO mode. You just have to be careful not to inadvertently lose momentum to regenerative braking by completely letting up on the accelerator. (For efficiency, it is wise to avoid regen unless you actually need to slow down or control downhill speed.)

 

[Herm]

Perhaps there is an indication in the CAN bus when the friction brakes are engaged.

 

[garygid]

Before you head down a long hill, usually one does NOT charge their car to 100%. Since "re-generation" NEEDS to CHARGE the battery to work, the LEAF will NOT regen at all, in D or ECO, if the battery is ALREADY full. Any slowing will use just the mechanical disc brakes.

So, least (to most) wasted energy is to:
1. not need to slow.
2. slow by coasting
3. slow using Regen
4. slow using the disc brakes
5. slow using a tree and airbags

Cheers, Gary

 

[garygid]

The fixed gear ratio is near 8:1 so tires turning 1000 rpm means 8000 rpm for the motor, even when coasting or in "neutral".

The motor can be "driven" by the "inverter" (DC to AC) electronics, taking energy from the BIG battery to TRY and make the motor turn faster.

With Regen, the electronics changes its treatment of the motor, using it as a generator and changing the AC to High-Voltage DC, using that energy to charge the BIG battery. This "generation" causes the motor to tend to turn slower, and thus slow the car. Kenetic energy from the car is converted into electrical energy for the battery to store until the car needs to use it later.

The "Regen" and Re-Use process has significant losses, but it is noticably better than throwing the kenetic energy away as heat in the brakes.

 

[dlich18]

This information is VERY useful. Thanks. Although I had assumed part of this, it is interesting to know what is actually going on.

How do you guys know this stuff? Is it basic engineering knowledge (of which I have none), or is this information specific to the Leaf?

 

[Stoaty]

So, least (to most) wasted energy is to:
...
...
5. slow using a tree and airbags

Have you done a test to verify that this wastes the most energy? :lol:

 

[davewill]

So, least (to most) wasted energy is to:
...
...
5. slow using a tree and airbags

Have you done a test to verify that this wastes the most energy? :lol:

If reshaping the front end is a desired outcome, then it isn't wasting energy at all.

 

[PaulScott]

Thanks to Dave in Oly for the great detail in efficient driving. These techniques, if used religiously, will result in tremendous savings over time. It also reduces wear on the friction brakes enabling those to last the lifetime of the car. Another benefit to efficient driving is that it's inherently safer. If most drivers practiced hypermiling, there would be a huge reduction in traffic accidents.

And thanks to Garygid for that hilarious 5th method of slowing. Of course, it's only funny in theory, not so much in practice.

 

[GaslessInSeattle]

So I've heard several folks on this board in other threads suggesting Eco is a waste of time and stating they only drive in "D". I've found Eco to be useful pretty much all the time. Eco is less valuable at highway speeds but even then it seems from reading the manual that Eco mode limits power to climate control, so even at highway speeds it can improves efficiency overall. I've even wished there was a way to make Eco mode the default instead of the regular drive mode, it just seems silly to have to shift twice every time I get in the car.

I do wish we had some indication of when the friction breaks are applied as it's awfully tempting to gently ride the breaks to come to a stop and I'm just not sure how much there is to gain from trying to stretch that out over a longer distance. Lately I've found myself looking a couple of cars ahead when approaching a light to increase the stopping distance with gentle steady breaks for maximized regeneration without (theoretically) engaging the traction breaks. I even find myself trying to think ahead when exiting the highway to get the most out of regen... I thought this would be too tedious but it turns out it's a fun challenge I just hope I'm not over thinking it and not really gaining much.
G

 

[91040]

This information is VERY useful. Thanks. Although I had assumed part of this, it is interesting to know what is actually going on.

How do you guys know this stuff? Is it basic engineering knowledge (of which I have none), or is this information specific to the Leaf?

Physics.
Not to mention, this forum and http://www.hypermilingforum.com/

 

[91040]

So I've heard several folks on this board in other threads suggesting Eco is a waste of time and stating they only drive in "D". I've found Eco to be useful pretty much all the time. Eco is less valuable at highway speeds but even then it seems from reading the manual that Eco mode limits power to climate control, so even at highway speeds it can improves efficiency overall. I've even wished there was a way to make Eco mode the default instead of the regular drive mode, it just seems silly to have to shift twice every time I get in the car.

I do wish we had some indication of when the friction breaks are applied as it's awfully tempting to gently ride the breaks to come to a stop and I'm just not sure how much there is to gain from trying to stretch that out over a longer distance. Lately I've found myself looking a couple of cars ahead when approaching a light to increase the stopping distance with gentle steady breaks for maximized regeneration without (theoretically) engaging the traction breaks. I even find myself trying to think ahead when exiting the highway to get the most out of regen... I thought this would be too tedious but it turns out it's a fun challenge I just hope I'm not over thinking it and not really gaining much.
G

Eco mode is not a waste of time. It is a tool to be used to your advantage.

You can limit the power used by Climate control manually as well. I don't like what Eco does to the accelerator pedal. I like the lighter more responsive feel. I would rather control my lead foot if I need maximum range.