From another thread:

I noticed this, as well, and would appreciate validation of my understanding, if it's on the right track.

Question 1: MG2 typically switches from Motor to Generator on pedal lift-off. Regen should depend on road speed when coasting. But if the ICE is at 3000 RPM and I lift off, those "leftover" ICE revs cause MG2 to spin faster for a few seconds than it would if I was just coasting. When I lift off quickly and MG2 switches from M to G, I should see the spike in regen which Gary mentions and which I've seen. Regen should then drop as engine speed drops. Correct? Is this part of why Pulse & Glide generally makes more regen than steady state driving?

Question 2: I know that little or no regen occurs in 'N' in a Prius. Is the same true for the FEH, since they use the same basic planetary drive setup? Mine seems to behave this way, i.e. Neutral allows me to gain free-wheeling coasting ability but I see little or none of the regen I would have gotten if I'd left it in 'D' or 'L'. That's how mine seems to behave, but I wonder if anyone has had the time and equipment to prove this.

I could not find a clear answer when I searched past threads. But if this has already been hammered out, kindly point me to the threads. No need to re-hash. Thanks!

 

I believe from what I've read here is that the Prius will not charge the battery by any means in N. The FEH does NOT charge via regen in N but it will charge the battery in N via the ICE if it is running. N gives you longer coasting because it does not allow for regen in the FEH.

My understanding is this:

Sitting at a stop with the ICE on in N - no charging
Sitting at a stop with the ICE on in D/L - charging via the ICE

Coasting in N with the ICE off - no charging
Coasting in D with the ICE off - some charging via regen
Coasting in L with the ICE off - more charging via regen

Coasting in N with the ICE on - charging via ICE (over about 20mph)
Coasting in D with the ICE on - charging via ICE and regen
Coasting in L with the ICE on - charging via ICE and more regen

 

mtberman — Since MG2 is linked to the wheels through a fixed gear ratio (assuming that the FEH "axle disconnect" is not in effect), the speed at which you lift your foot off the accelerator has absolutely no influence at all on MG2's instantaneous speed. Whether MG2 (and also MG1 for that matter) acts as a motor or as a generator depends solely upon the voltage that the inverter applies to its terminals. If this voltage is greater than the voltage produced by its angular speed, it acts as a motor and consumes power from the source. If this voltage is less than the voltage produced by its angular speed, it generates power. If these voltages are equal, there is no power flow. The direction of power flow depends only on the applied voltage. So, the amount of regeneration will depend upon the decision made by the PCM regarding the load it chooses to apply to MG2, and not directly upon the ICE's speed.

The Toyota hybrids lock out all power flow to or from the MG's when in 'N.' So, there can be no NiMH battery charging or regeneration in 'N.' Discussion is still continuing in the thread "Fuel Injector Shut-Off" as to whether the same is true in the FEH/MMH.

Stan

 

Might it be BA, Brake Assist, that is resulting in heavier regen..?

Brake Assist will assist the driver in appying the brakes if the movement from gas pedal to braking is quick enough. Or maybe even just quick, non-average, release of the gas pedal??

 

Interesting and true. But the effect I was referring to is from the connection between the MG1 and the ICE, not MG2 and the wheels. If I lift and the system changes from M to G, that change is almost instantaneous. If the ICE is off then yes, absolutely, regen starts and happens in proportion to speed based on the fixed ratio you mention.

But if the ICE is at 3000 RPM and I lift fairly quickly, two things should be (momentarily) driving regen: 1: from the wheels acting on the ring gear at a fixed ratio as you say. And also 2:the other MG driven via the ICE's rotation and acting on the planet carrier. For a moment, before the ICE drops from its elevated speed and then shuts down, both should be acting on MG1.

Once the ICE slows and then stops, the fixed ratio you mention applies. But if the ICE is at speed and the wheels are at speed, then a relatively quick lift-off occurs and M changes to G, this would explain the brief spike in regen Gary and I both noticed. Maybe. Sort of. I think. Hmmmm.

 

The spike in charging seems only when the ICE is running and you let off the gas pedal. Both MG1 and MG2 begin to throw juice at the battery is what I think is happening. Quickly the computer adjust the flow to prevent the TBCM from having a fit from the surge. I use the surge all the time to go EV ASAP. In fact, a quick surge and then applying the gas pedal right away prevents overheating the system and helps maintain speed for further acceleration to my target pulse speed.

Tim K, the only thing I see with your list of charging and not charging is sitting at a stop in "N" with the ICE running cannot charge the battery with MG1. This is where passive neutral prevents any charging. When I come to a stop with the ICE running, I shift to "D" or "L" to get charging from MG1 and allow the ICE to shutdown. Staying in neutral at a stop will hold EV or ICE running with no charging.

There is no regen in "N", and don't know why GPSman1 thinks there is. When I was testing coasting, I think I proved this and documented it in this thread: https://www.greenhybrid.com/discuss/...ead.php?t=5395

During my pulse (the best is at 1,800rpm accelerating for me), I have heavy MG1 charging when the battery is low. The first thing I do is a FS in "L" at 25-30mph which slows me down 5mph without a restart most of the time. The second FS is at my target speed and I go EV with that FS. All my gliding is in "N" with no regen possible. If my battery has enough charge to go EV, I do a quick surge like I stated above to prevent EV and maintain speed.

GaryG

 

Okay, this is exactly what I was thought was happening. Thanks! It's ever-so-brief because the MG drag slows the ICE pretty fast. But that needle swings way over to charge for just a moment, doesn't it?

Now if I can only figure out what all this other stuff means. What the heck is an FS? Do I need a Mensa membership to post here ?

 

I'll have to watch more closely over the next few days. I could have sworn I've seen charging in N...

 

FS stands for "Fake Shift" which I named here about 2 years ago. It is exactly what were talking about by letting off the accelerator in drive or low gear to lower RPM's, use regen to charge the battery (heavy in "L"), and go EV in "L". For lack of a better name, I described it like letting off the gas pedal to shift a manual tranny. In addition, I do shift to "N" and sometime "D" to hold my speed as I go EV when the tach bounces.

The charge needle does swing way over like you decribe and I just call it a surge. The charge arrow on the energy screen to the battery gets real thick also for a second.

GaryG

 

Over the last day I've been watching closely. I've edited my post above accordingly and re-posted it here. The thing that suprised me the most is that there is ICE charging while coasting in N but not below 20mph or at a stop. Also, there appears to be NO regen in N at any time.


Sitting at a stop with the ICE on in N - no charging
Sitting at a stop with the ICE on in D/L - charging via the ICE

Coasting in N with the ICE off - no charging
Coasting in D with the ICE off - some charging via regen
Coasting in L with the ICE off - more charging via regen

Coasting in N with the ICE on - charging via ICE (over about 20mph)
Coasting in D with the ICE on - charging via ICE and regen
Coasting in L with the ICE on - charging via ICE and more regen