Regen reduced when friction brakes are engaged

[Ingineer]

If the inverter shuts off creep, and there is a light hydraulic pressure, then this could feel like the "grabby" event. I've felt it many times now, and I'm convinced this is what's going on. On one event thusfar, I did observe the creep is indeed gone by watching motor current.

-Phil

 

[TickTock]

Yup. I watched the display closely while it happened yesterday and, yes, there is some very lite brake pressure during the event. Just not enough to break squelch on the audio cue the way I currently have it programmed (since speeds are very low and brake pressure is very low, this is a very, very low amount of friction power).

 

[coqui]

I just try to use brakes as little as possible anyway, while coming to a stop, to (a) harvest as much as possible of the regen, (b) extend the life of the brakes, and (c) try and time stoplights if possible so that the car isn't expending a lot of energy to get back up to speed from zero mph. :mrgreen:

 

[LTLFTcomposite]

I just try to use brakes as little as possible anyway, while coming to a stop, to (a) harvest as much as possible of the regen, (b) extend the life of the brakes, and (c) try and time stoplights if possible so that the car isn't expending a lot of energy to get back up to speed from zero mph. :mrgreen:

I too am trying to net out the takeaway from all this analysis. Bottom line:

A) If you see a red (or yellow) light ahead and know you are going to have to stop, it is better to set up a long braking run with very light pressure rather than "coasting" (or even worse continuing to apply power) and then braking harder at the last minute? ...Although this may irritate ICE drivers behind you, as you may be between them and a left turn lane threshold, right on red opportunity, or just plain getting to the red light sooner, so if you see a pickup with a rifle rack in the rear view mirror maybe a few wasted watts isn't the worst thing in the world

B) Keep your foot firmly on the brake at a light and not let the car creep forward unnecessarily, because even though they did a good job of simulating that ICE behavior, it's costing you precious watts.

Is that about it or am I missing something?

 

[Rusty]

Is that about it or am I missing something?

Sounds right to me. And that's not just a good idea in a Leaf. Any EV or PHEV that emulates torque converter creep should benefit from observation B.

 

[TickTock]

I just try to use brakes as little as possible anyway, while coming to a stop, to (a) harvest as much as possible of the regen, (b) extend the life of the brakes, and (c) try and time stoplights if possible so that the car isn't expending a lot of energy to get back up to speed from zero mph. :mrgreen:

I too am trying to net out the takeaway from all this analysis. Bottom line:

A) If you see a red (or yellow) light ahead and know you are going to have to stop, it is better to set up a long braking run with very light pressure rather than "coasting" (or even worse continuing to apply power) and then braking harder at the last minute? ...Although this may irritate ICE drivers behind you, as you may be between them and a left turn lane threshold, right on red opportunity, or just plain getting to the red light sooner, so if you see a pickup with a rifle rack in the rear view mirror maybe a few wasted watts isn't the worst thing in the world

B) Keep your foot firmly on the brake at a light and not let the car creep forward unnecessarily, because even though they did a good job of simulating that ICE behavior, it's costing you precious watts.

Is that about it or am I missing something?

Actually bottom line is: don't touch the brake pedal.

 

[planet4ever]

Actually bottom line is: don't touch the brake pedal.

My bottom line is just the opposite: Have your foot resting lightly on the brake pedal as you approach the stop, then push down hard and hold it down hard until you can go again.

The last thing you want -- and quite possibly the last thing you would get, ever -- is to be shoved into cross traffic by someone rear-ending you. The cost of that possibility makes a penny saved on your electric bill a million times less than totally insignificant. This, for me, is why built-in creep needs to be a vital safety requirement.

Sorry, TickTock. No smilies from me on this subject.

Ray

 

[LTLFTcomposite]

The last thing you want -- and quite possibly the last thing you would get, ever -- is to be shoved into cross traffic by someone rear-ending you. The cost of that possibility makes a penny saved on your electric bill a million times less than totally insignificant. This, for me, is why built-in creep needs to be a vital safety requirement.

I don't understand that statement p4e... how does built in creep help prevent you from being shoved into oncoming traffic? Because it forces you to keep your foot on the brake?

 

[TickTock]

Actually bottom line is: don't touch the brake pedal.

My bottom line is just the opposite: Have your foot resting lightly on the brake pedal as you approach the stop, then push down hard and hold it down hard until you can go again.

The last thing you want -- and quite possibly the last thing you would get, ever -- is to be shoved into cross traffic by someone rear-ending you. The cost of that possibility makes a penny saved on your electric bill a million times less than totally insignificant. This, for me, is why built-in creep needs to be a vital safety requirement.

Sorry, TickTock. No smilies from me on this subject.

Ray

I was just over-simplifying. Obviously you cannot drive and never touch the brake. But the main take-away is every time you use it you are using friction to some extent. Your technique of applying more once you are near a stop is good since your speed is low so the wasted power is minimal (zero once stopped). And, unless you obsess over things or are really pushing your range to the extreme, don't even worry about it - the cost of electricity is so cheap the ROI just isn't there. Listen to the radio instead. Sorry, but I will still put smiles since this is just intended as a friendly dialogue.

 

[TickTock]

Trying to get back on topic and summarize. Obviously avoiding braking (or even slowing down) as much as is safe is the #2 strategy to extend range (driving slower is #1).

When you:

• have to brake from high speed (due to inconsiderate drivers, mis-judging a stale green, etc.),
  it's not an emergency situation,
  you want to get that last iota of increased range or you don't want to ever change your brake pads, and
  you don't have a brake monitor,

the best strategy I've come up with is to brake a little stronger than desired and then ease off until you have 5 regen bubbles and try to maintain that. I have found it very hard to keep friction engaged with 5 bubbles lit. As you approach the stop you will want to increase pressure again but hopefully you will be slow enough that you've already recovered most of your energy.

Sometimes, when braking lightly, and usually, when slowly increasing braking, friction stays engaged and only lessening the pressure further eliminates it. I have not yet been able to train myself to detect onset/offset of friction without the hardware monitor. There are a lot of non-linear changes in the feel of the brakes that I thought had to do with the friction brakes but I have yet to correlate them to friction now that I have the monitoring capability (so the regen bubbles remain your best indicator).

 

[TickTock]

TickTock, are you willing to share which CAN frames you found this data in? It would be nice to experiment further and add some more data.

Thanks!

-Phil

Sorry for missing this before. I am logging everything I learn here. There are four tabs. Flow is the table showing what messages go where (from the SM). EVcan and Carcan contain what I was able to deduct for those can busses. The final is a copy of Turbo2Ltr's very detailed notes on the carcan. I plan to eventually encorporate it into the Carcan tab.

Phil,
I noticed you listed "Individual Lithium Ion battery cell parameters" in your list of features for LeafScan. Any chance you can share how you are getting this information? Sounds like you were able to decode a lot of information. I've been trying to figure out how to get this information for some time and it would be a significant break-through if you've found it!

 

[Ingineer]

Phil,
I noticed you listed "Individual Lithium Ion battery cell parameters" in your list of features for LeafScan. Any chance you can share how you are getting this information? Sounds like you were able to decode a lot of information. I've been trying to figure out how to get this information for some time and it would be a significant break-through if you've found it!

I will be able to at some point soon, but unfortunately not right now. There's still ongoing development work to be done.

-Phil

 

[brettcgb]

Interesting data. What speed did you achieve before letting up on the pedal and at what speed did you apply braking? From higher speeds (45-50) the energy screen shows a clear correlation between moderate brake pressure and regen. However, as the speed decreases it seems that the system transitions more and more to brakes and no amount of finesse on the brake will increase regen. Almost appears that regen is (assuming capacity in the battery) a function of speed and deceleration (Gs).

X'actly right. Lets look at the math (physics).

Kinetic energy is calculated using KE=0.5mv^2 and can be calculated in Joules
m=mass (fixed) v=velocity
KE is proportional to the square of velocity

Power can be measured in Joules/Second and Watts. (1W=1J/sec)

Power (measured in watts) is limited by the regeneration power the battery can absorb (for high SOC, somewhere >80%), or whatever the motor controller can return to the battery (30kW max).

Working through the math (an exercise left to the reader), when converting velocity to energy, you find that for any given amount of energy, the change in V for high values of V is less than the change in V for low values of V.

In other words, regeneration braking at freeway speeds doesn't slow you as much as the same regeneration braking at lower speeds.

 

[brettcgb]

thanks for the input. You are right to question theses results since there is a lot off guesswork in which messages correspond to the ones referenced in the service manual. I'll try to corroborate the results with the battery current to see if, indeed, no pwr is going into the battery when friction kicks on. It's possible there is another bit that indicates to use max regen even when this signal goes to zero.

Did you ever capture speed while taking these measurements? Edit: Speed was captured.

I suspect the reg/friction braking mix may vary with speed, tending towards 100% friction at very low speed (5-15 MPH). At low speed, regen braking simply isn't possible.

 

[KeiJidosha]

From the REFUEL 2012 Thread

Thankfully the stock LEAF brakes are quite competent even on the track.

I was braking very hard from ~80mph several times per lap and I notice some slight vibration since the event, so I think the rotors overheated and warped slightly. It's not enough to be a big issue, and I didn't get any brake fade during the event.

The BC2BC LEAF also came away from REFUEL with a bit of brake rotor vibration. What is interesting is it provided a tangible way to know when the friction brakes were active. A long decent down San Marcos Pass behind a slow truck confirmed that every brake application began with friction braking that would moderate as the regen level increased to support reduced friction braking to maintain deceleration. This would explain why the LEAF recovers less energy than the A pedal regen cars like the ActiveE or MINI E. You cannot get pure regen if you are on the brake pedal.

 

[TEG]

...You cannot get pure regen if you are on the brake pedal.

Out of habit, when I approach a stop light, I "shift" to ECO mode just to get enhanced regen and "coast down" until I finally have to hit the (friction) brake pedal.
Once I am stopped, I "shift" back into "D".