Regen reduced when friction brakes are engaged

[SierraQ]

Made a little progress. Found a speed signal *and* what appears to be a battery (or motor) current signal similar to those on the EV bus. The graphs got really messy and hard to follow once I added those but I did confirm that, yes, there can still be some regen even though the "Braking Regen" signal goes to zero. For example, when coasting to a stop in ECO mode, there is no "Target Braking Force" Or "Regen Braking" signals however, there is charge going into the battery. Kinda interesting - appears to be a constant current even though speed is reducing. The amount of regen did however, always drop when the "Braking Regen" signal gave way to friction braking. I was never able to keep strong regen once friction was engaged. I'll post some pics for those interested once I find a good way to plot them that doesn't make your eyes hurt.

I feel that I can tell when regen switches to friction and based on my observations there are three scenarios:

1) Regen while coasting -- this is NOT braking strictly speaking so having no "target braking force" makes sense. TBF sounds like an attempt to balance the sum of all braking contributors to match.

2) Hard braking -- regen is light or non-existent, car changes quickly to friction braking probably because, as Ingineer said, it's in a sort of panic mode and the need for reliable breaking trumps opportunistic regen.

3) Constant braking -- regen active until speed decreases to a certain point where regen is ineffective at which point friction seems to gradually take over.

I would like to see the different between constant brake force and gradually increasing brake force. Perhaps this test: Start at around 50 MPH. Gradually increase the braking pressure on the pedal in one continuous but slow motion with the intent that you will be stopping on friction near the end, but not too abruptly.

And then this test: Start at same speed as above. Press the brake until all regen bubbles are filled and hold it there until the car comes to a stop.

I think seeing this might better define the relationship between the three values.

 

[ghabel]

Ok, newbie question. The regen brakes are only in the front correct? Therefore the rear friction brakes are always engaged when braking correct? Assuming all 4 wheels should be braking for improved breaking.

 

[AP1]

That's a great question ghabel. Maybe the rear brakes are only engaged on hard breaking since that's when you need stability the most and both front and friction brakes are engaged. Otherwise 50% of the energy would be wasted and that's not apparently the case.

 

[TickTock]

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.

If this only occurs a few times in a month, I guess it's nothing much to be concerned about. But looking at these graphs, it seems the car gives-up the regen quite "easily".

Can someone relate this to real life driving ?

To be honest it's a little disappointing. A prius will keep the regen at it's maximum even under pretty sudden/hard deceleration. Only at the very last moment when the ABS is about to engage or is engage does the regen stops.

I grabbed a log of my commute home and did some number crunching. I computed an arbitrary braking power value by multiplying the brake pressure sensor by rpms. I then did the same for the target braking value to get a target braking power and then scaled to match the friction power when under no-regen conditions. Similarly, I scaled the regen power to line up with the target braking power under no-friction conditions. I am not a hyper-miler, but am efficiency conscious. Based on this very loose computation, it looks like I am managing to recover 60% of all applied braking energy.

I may try to hyper mile tomorrow to see if I can improve this. Be cool to get a log from Leaffan or one of our other top hyper-milers to see how well they score. In my entire trip home, there was only one time I managed to sustain both friction and regen for any appreciable time and that was when I was coming to a stop at the bottom of the one hill on my trip.

 

[TonyWilliams]

Based on this very loose computation, it looks like I am managing to recover 60% of all applied braking energy.

The bad part about the regen is that there isn't just one number. I use 50% for planning, just because it's easy. But, any number of variables can change the value quite significantly.

 

[TickTock]

Here's a graph of the drive showing various datapoints. Y axis is only meaningful for mph. X axis is seconds. Target, friction, and regen are all in units of power (brake pressure times rpm) which is why they go to zero when I am at a stop. Third braking spike from the end is that hill where I managed to keep a decent amount of regen even after friction was employed.

 

[Smidge204]

TickTock; Any chance you can post some raw data for that last graph? I'd like to be able to zoom in and get a better picture of what's going on. That graph is just a little too squished!

=Smidge=

 

[TickTock]

Here's a graph with all the stopped and moving data hidden so you can see the braking activity with more detail. Ignore the discontinuities in the mph and amps curves due to me chopping out the data between braking events.

 

[TickTock]

I need to study this some more. I don't understand by the amps into the battery doesn't roll off with speed since if you assume the battery votage to be relatively constant for each event, it should be proportional to power which is proportional to rotational speed with constant braking force. I may be (probably am) misinterpreting some of these signals units.

 

[TickTock]

Another photo if I do not multiply the target, friction, and regen values by the speed to convert to power. In this graph I think their units are units of force and the regen better tracks the amps. Don't read into the Y axis for the amps (or anything other than mph) - it is not to scale.

 

[Rusty]

This looks like much more encouraging data (if I'm reading the graphs right, no guarantees there!). These curves seem to show a much better job of blended regen with friction braking. The braking sequence around timestamp 200 seems to especially show this with initial regen, a spike in target braking being fulfilled with friction blended with regen, and then a regen tail out. Or am I really reading that all wrong? Sure the regen/friction might be blended better, but this certainly looks better than the initial all or nothing interpretation of the first data.

It looks like you've cleaned up your timebase, and the bursting nature of reports you were seeing before. Did I miss a report on how you were doing that?

Can you split your graph data into multiple isochronous graph presentations? While I'm still working on getting my graphs to not look like crap, I'd split this presentation into 3 graphs. One for MPH, one for kW (my reported signals gives me HV amps and volts, and I graph the multiple - though I'm tempted to include the raw amps and volts as a footnote since I've recently found some interesting data there too), and one with three combined linecharts (as you have here) for target, regen, and friction?

I don't understand by the amps into the battery doesn't roll off with speed

In these plots it looks to me like there's a hard limit on the amount of wattage they're allowing regen to generate back into the battery (roughly 35-40 amps, though I'll bet you a plug nickel it's watts based, not amps). Anytime brake target goes above that it's implemented with friction. If so, as speed tails off they just increase the amount of regen drag to compensate to maintain a constant (as much as possible) power feed back to the battery. Does that interpretation make any sense?

 

[bowthom]

Hello,
Seems to me there is a signal missing. There is obviously regen occurring that is not "braking" so that is not being added to the graph except for showing up on the battery current trace. I have gotten 30 kW regen without the brake pedal activated on a downhill freeway off ramp in econ mode. I can feel the transition from regen to friction on both the Leaf and our gen 1 Prius.

 

[Smidge204]

Hello,
Seems to me there is a signal missing. There is obviously regen occurring that is not "braking" so that is not being added to the graph except for showing up on the battery current trace. I have gotten 30 kW regen without the brake peddle activated on a downhill freeway off ramp in econ mode. I can feel the transition from regen to friction on both the Leaf and our gen 1 Prius.

A keen observation! It seems the "target" brake force is is also zero at these points, so I'm going to hypothesize that this is coasting regen. This might be a separate signal but it's not really important if we're investigating how regen and friction braking interact - regen braking seems to be reported correctly, or at least consistently.

Edit: More interesting is how the amperage goes slightly positive whenever speed goes to zero. Or is that just before it rises sharply? Really weird resolution issue here... I only see amp spikes for some of the accelerations. Maybe the data collector misses it often because it's too brief a spike?
=Smidge=

 

[evnow]

Here's a graph with all the stopped and moving data hidden so you can see the braking activity with more detail. Ignore the discontinuities in the mph and amps curves due to me chopping out the data between braking events.

You should change the title of the topic to reflect the mixing of regen & friction.

 

[TickTock]

Hello,
Seems to me there is a signal missing. There is obviously regen occurring that is not "braking" so that is not being added to the graph except for showing up on the battery current trace. I have gotten 30 kW regen without the brake peddle activated on a downhill freeway off ramp in econ mode. I can feel the transition from regen to friction on both the Leaf and our gen 1 Prius.

A keen observation! It seems the "target" brake force is is also zero at these points, so I'm going to hypothesize that this is coasting regen. This might be a separate signal but it's not really important if we're investigating how regen and friction braking interact - regen braking seems to be reported correctly, or at least consistently.

Edit: More interesting is how the amperage goes slightly positive whenever speed goes to zero. Or is that just before it rises sharply? Really weird resolution issue here... I only see amp spikes for some of the accelerations. Maybe the data collector misses it often because it's too brief a spike?
=Smidge=

There are amp spikes on all the accelerations on the first graph which includes all the boring stuff. In the second and third, I chopped out the activity between braking so you aren't seeng the whole picture but can see the brake activity better. Those "interesting" amp spike when the car stops happen even if already stopped and I just modulate the pressure on the brake. My guess is the car is passing through "creep mode" which Nissan added to make the car feel like it has a torque converter (and you can creep forward just by lifting off the brake). So the car is applying a little traction power when you are stopped but brake pressure is below a certain threshold.

Yes, these signals seem to be relevant only to the explicit braking force applied. Coasting regen is not included (might be another signal we haven't decoded yet).

 

[TickTock]

This looks like much more encouraging data (if I'm reading the graphs right, no guarantees there!). These curves seem to show a much better job of blended regen with friction braking. The braking sequence around timestamp 200 seems to especially show this with initial regen, a spike in target braking being fulfilled with friction blended with regen, and then a regen tail out. Or am I really reading that all wrong? Sure the regen/friction might be blended better, but this certainly looks better than the initial all or nothing interpretation of the first data.

That event at 200 on the recent graph is when I was braking to a stop on the way down a hill. Consistent with others observation of sustatained regen under these condition. Shows both are possible however it is still disappinting that regen is diminished once friction kicks in. Would be nice if it stayed at the max and you just feathered in friction on top of it. AND it was able to keep regen on for more of the braking conditions (most of the time it looks like either-or). I think my first observation that regen stops when friction starts is not too far off. Maybe should read regen significantly diminished when friction applied

It looks like you've cleaned up your timebase, and the bursting nature of reports you were seeing before. Did I miss a report on how you were doing that?

Nope. Still seeing the bursty data. I just applied a low pass filter to smooth it out. I suspect the messages are getting queued up at the USB interface.

 

[TickTock]

Here's a graph with all the stopped and moving data hidden so you can see the braking activity with more detail. Ignore the discontinuities in the mph and amps curves due to me chopping out the data between braking events.

You should change the title of the topic to reflect the mixing of regen & friction.

How do I do that?

 

[Rusty]

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?

 

[DaveEV]

You should change the title of the topic to reflect the mixing of regen & friction.

How do I do that?

Just go edit the Subject in the first post of the thread.

 

[bowthom]

Hello,
Seems to me there is a signal missing. There is obviously regen occurring that is not "braking" so that is not being added to the graph except for showing up on the battery current trace. I have gotten 30 kW regen without the brake peddle activated on a downhill freeway off ramp in econ mode. I can feel the transition from regen to friction on both the Leaf and our gen 1 Prius.

A keen observation! It seems the "target" brake force is is also zero at these points, so I'm going to hypothesize that this is coasting regen. This might be a separate signal but it's not really important if we're investigating how regen and friction braking interact - regen braking seems to be reported correctly, or at least consistently.

Edit: More interesting is how the amperage goes slightly positive whenever speed goes to zero. Or is that just before it rises sharply? Really weird resolution issue here... I only see amp spikes for some of the accelerations. Maybe the data collector misses it often because it's too brief a spike?
=Smidge=

Seems to me this would be creeper current. Maybe the brake pedal was not being depressed enough.