Regen reduced when friction brakes are engaged

[TickTock]

Yesterday, I made a more conscious effort to avoid the friction brakes and raised my score (regen braking/total braking) from 57.7% to to a whopping 70.0%. Traffic is too unpredictable(other drivers, untimed stale green lights, etc), I think, to expect to reliably do much better for my commute.

 

[SierraQ]

Can you supplement your next graph with activity information (e.g. hard braking, constant pressure at time 150)? I still feel these graphs are incomplete without some sort of pedal pressure measurement. Or is that correspond to the target braking power? (I was doubting this since that line jumps around a lot.) I realize you may just be recording this on average drives but a series of controlled tests would be interesting.

 

[TickTock]

Can you supplement your next graph with activity information (e.g. hard braking, constant pressure at time 150)? I still feel these graphs are incomplete without some sort of pedal pressure measurement. Or is that correspond to the target braking power? (I was doubting this since that line jumps around a lot.) I realize you may just be recording this on average drives but a series of controlled tests would be interesting.

"target" is proportional to the braking pedal pressure. The higher the target the harder I was pressing. "regen" and "friction" are the two signals indicating how much of that target is met through regen or friction. All three and read from the canbus and regen+friction=target seems to hold reasonably true.

 

[TickTock]

So the car is applying a little traction power when you are stopped but brake pressure is below a certain threshold.

I see exactly this on my car as well (granted, a horse of a different color). For me it can bump into several hundred watts if I actually let the car creep. If I apply a higher brake target (that is, press the pedal harder :- ) it reduces the wattage going to the motor. I can fully modulate the motor power/torque while completely motionless just by adjusting the brake target. Then again, I've had a manufacturing engineer tell me it shouldn't do that, so that may be something that goes away with a software update (something pending on my list to do, after I figure out how to quantify what the car is doing first... so I can tell better what changes with the update!)

Are you seeing the Leaf "torque crawl" power engage as a binary function (full creep power below a certain brake request point, zero after) or does it modulate based on brake request?

I finally remembered to check this. It is a little hard to tell given I only have 0.1kW resolution, but it does appear that there are more than one (or two if you count zero) creep power levels modulated by the amount of pressure.

 

[bowthom]

Hi,
If I am stopped with good pressure on the pedal, as I slowly release the brake I can feel the car "bump" when creeper current comes on.

Don

 

[TickTock]

So the current starts the same time the car starts to move? Creeper current starts before the car actually moves more me. I feel the "bump" (although it's pretty subtle) when the car starts to move. This can be explained by the brakes moving from the (higher) static coefficient of friction to the (lower) kinetic coefficient of friction.

 

[TickTock]

OK. Finally plotted the data versus time. Interestingly, the data got more choppy. It appears the can data is bursty and block of messages are sent together (with close timestamps) even though it seems likely that the actual message content was accumulated over a longer period of time. Anyway, below is more of the same data except now the X axis is time in seconds. The Y axis is only valid for the line lebeled rpm. This is really mph. You will notice groups of spikes on the brake signals. That was my way of getting my bearings in the log. While at a stop, I pressed the brake twice before accellerating to 20mph, three times before the 30mph test, four for 40, and five for 50. At the very end I went to 20mph and allowed eco mode to bring it to a stop. There you can tell that total regen is the sum of braking regen and something else. It appears the regen turn off is less a function of speed then it is amount of brake applied *and how fast you apply it*. That latter part is interesting - along with the evidence that more regen is supported on longer braking down a hill suggests to me that Nissan is using a PID controller to apply the regen.

Thanks for this.

FYI, the CAN frames are occurring at regular intervals, so there must be something wrong with your DAQ setup.

-Phil

Ingineer, Are you referring to the EV-Can or Car-Can (or both)? On my setup, only when I log Car-Can does the data come in bursts. The EV-Can messages arrive more continuously.

 

[Ingineer]

Ingineer, Are you referring to the EV-Can or Car-Can (or both)? On my setup, only when I log Car-Can does the data come in bursts. The EV-Can messages arrive more continuously.

I don't see bursty data on either bus, I wonder if there is some sort of buffer overrun going on on your system?

-Phil

 

[Reddy]

So under certain condition, regen indeed stops when friction brakes are engaged.

My question would be : how often does that happen when driving "normally" on the highway, on a smaller road, in town etc.....snip....Can someone relate this to real life driving ?...snip.....

Yes, I agree. In my experience, I get the most regen by taking my foot off the go pedal in D thereby slowing down a bit, switching to ECO to slow down more, and then if needed, applying the actual brake pedal. Most of the time this method works very well when combined with looking ahead and anticipating traffic behavior and lights. However, by viewing the energy screen, I've noticed that the car stops regen entirely at very low speeds (say below 5 mph) when the brake pedal is applied.

Reddy

 

[TickTock]

Been driving around with a modded SOC meter that chirps at a rate proportional to friction*speed (geiger counter style audio cue - thanks for the suggestion, Herm). By using friction*speed, it doesn't chirp when stopped and the rate of the chirps is proportional to the amount of power you are wasting. This has given me some new insights on Nissan's algorithm. First, friction brakes are engaged *every time* you press the brake no matter how carefully you press. If you are braking gently, it is very short lived and the friction braking is quickly replaced with regen. Usually. After driving a while with the audio cues, I've found that I can eliminate nearly all friction braking by slightly over braking and then very subtly easing off. If you keep static brake pressure or slowly increase pressure, the friction brakes stay engaged so I've learned to do my braking with slightly decreasing brake pressure as I approach the stop. When I do this, I can come to a complete stop with (almost) no friction brakes at all.

 

[TickTock]

Yesterday, I made a more conscious effort to avoid the friction brakes and raised my score (regen braking/total braking) from 57.7% to to a whopping 70.0%. Traffic is too unpredictable(other drivers, untimed stale green lights, etc), I think, to expect to reliably do much better for my commute.

Woo hoo! I tried the same route again now that I can monitor the friction braking pressure real time while driving. On the same trip, I got 91% (regen/total braking) versus my best score of 70% when I just avoided sudden braking. I actually think I can do better - there were two lights that I screwed up and ended up using a lot of friction.

 

[Smidge204]

Woo hoo! I tried the same route again now that I can monitor the friction braking pressure real time while driving. On the same trip, I got 91% (regen/total braking) versus my best score of 70% when I just avoided sudden braking. I actually think I can do better - there were two lights that I screwed up and ended up using a lot of friction.

Nice! Any noticeable impact on overall miles/kWh efficiency?

=Smidge=

 

[nogajim]

If you are braking gently, it is very short lived and the friction braking is quickly replaced with regen. Usually. After driving a while with the audio cues, I've found that I can eliminate nearly all friction braking by slightly over braking and then very subtly easing off. If you keep static brake pressure or slowly increase pressure, the friction brakes stay engaged so I've learned to do my braking with slightly decreasing brake pressure as I approach the stop. When I do this, I can come to a complete stop with (almost) no friction brakes at all.

Now that you know what to look for, do you notice a difference in the regen indicated on the console? I had been braking exactly opposite of what you recommend, so thanks for the tip!

 

[garygid]

TickTock is doing some very nice work.

He has developed (and is using) an experimental firmware version in his SOC-Meter, with added hardware: a pizzo-electric "clicker" to produce "more" clicks when mechanical braking increases.

For the moment, consider it experimental ... but a very nice experiment.

As this new function (and the human factors for using it) get better tested and refined, the function (perhaps with the actual clicker as an extra-cost option) is likely to be included in the next SOC-Meter firmware version.

 

[TickTock]

I cannot really say how much my mileage has improved since I am using the heater off and on a lot these days and I've only had the friction mode for a week.

I have not really notice much inspiring about the regen bubbles. You can actually get a fair amount more regen braking after all five are lit without engaging friction but the bubbles do go away quickly once it starts. There just aren't any long enough hills where I live to ever get to get back to 5 bubbles while friction is active.

Here's something interesting. I have experienced the grabby brake symptom a few times with the box on, and in each case, not a chirp from the box. This suggest that the issue is with the motor controller and not the brakes.

 

[davewill]

... Here's something interesting. I have experienced the grabby brake symptom a few times with the box on, and in each case, not a chirp from the box. This suggest that the issue is with the motor controller and not the brakes.

That fits with Phil's supposition that it's the system turning off the engine creep that's causing the feeling. He claimed the engine creep can't be maintained indefinitely, and we get this "grabby" feeling because hitting the brake also kills the creep power when this occurs.

 

[TomT]

I would have to question that as the brake grab I have felt is much more powerful than the amount of creep force that is normally generated... I hate the creep regardless and wish there was a way to disable it.

That fits with Phil's supposition that it's the system turning off the engine creep that's causing the feeling. He claimed the engine creep can't be maintained indefinitely, and we get this "grabby" feeling because hitting the brake also kills the creep power when this occurs.

 

[davewill]

I would have to question that as the brake grab I have felt is much more powerful than the amount of creep force that is normally generated... I hate the creep regardless and wish there was a way to disable it.

That's what I thought at the time Phil said it, but TickTock's observation made me rethink it. The thing to remember is that it's not just the creep "force" but the way the torque it applies interacts with the braking surfaces. Friction is a funny thing and not necessarily intuitive...at low speeds it doesn't take much pedal to get the brakes to grab. The part I don't get is how the brakes can "grab" if there's no friction force at all as TickTock seemed to observe.

 

[TickTock]

I would have to question that as the brake grab I have felt is much more powerful than the amount of creep force that is normally generated... I hate the creep regardless and wish there was a way to disable it.

That's what I thought at the time Phil said it, but TickTock's observation made me rethink it. The thing to remember is that it's not just the creep "force" but the way the torque it applies interacts with the braking surfaces. Friction is a funny thing and not necessarily intuitive...at low speeds it doesn't take much pedal to get the brakes to grab. The part I don't get is how the brakes can "grab" if there's no friction force at all as TickTock seemed to observe.

I will have to look closer. To avoid the box getting annoying, there is a (very low) threshold pressure below which I do not make a sound. It is possible that there is some very light brake interaction that I wasn't observing.

 

[garygid]

Also, the box might be reporting intended or desired mechanical braking, not the actual (or unintended) braking.

If the creep force was under control, there would not be "noticably faster than creep" speed or acceleration.