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This morning (and on one other occasion) I noticed that the regenerative braking wasn't working for a short period of time. http://www.cleanmpg.com/forums/images/icons/icon5.gif I could feel the brakes behaving differently - I had to push harder on the brake pedal - in order to slow down/stop. The green regen bars would not come on during brake pedal movement, but when I took my foot off the gas, the green bars came on. My battery SoCharge was less than full.

Anybody else experience this?

Could I expect the diagnostics to be able to detect this and register an error code that can be read later?

Thanks in advance.

Bob

The only reason apart from a malfunction I can think of is you were going less than 15mph. To discourage extreme downshifting, the regenerative braking cuts out at about 13mph for the Insight.

Could be a cold weather thing. The Prius protects the pack like mad in this weather, even when it's closer to 0C than 0F. Current draw from the pack is limited to practically nothing until it warms up and I suspect that the same is true of charging, though the effects are less apparent. We're both working with the same battery chemistry so I suspect Honda would implement similar protections. Just a guess.

Thanks Bob and Tim.

I called the Honda service dept and they said they would have to actually see the failure in order to diagnose.

Temps were in the mid 30's when this happened. As for speed, at one point I was in a 15 mph zone, but the condition persisted even when I was driving (braking) in a 35 mph zone. And heading home this afternoon, no braking regen even when I got out on the larger secondaries. But then I noticed a 3-4 bar forced charge about 2 miles after starting the drive home. After the forced charge terminated, I noticed the regen braking started working again. Go figure?

I'll note the behavior on the service ticket for documentation purposes when I go in Friday for a tire rotation.

Thanks all.

Bob

I'm curious, did you have either the heater or the front windshield defrost on at the time?

Bob--

I notice this often in my new HCHII here in much-colder Ohio. For probably the first five minutes of my commute (sometimes longer if it's colder) I won't see regen on braking, but I will commonly see one or two bars of forced charge under power for part of that same five minutes. My unproven theory is that the battery management system does this to warm and protect the pack, but I don't know the technical reason this might be.

The behavior you note is consistent and predictable with me. In warmer weather I see behavior more like you've come to expect. Perhaps it's only just now gotten cold enough in Virginia for you to experience this phenomenon? --RN

I'm curious, did you have either the heater or the front windshield defrost on at the time?

Hi Tarabell, I have been leaving the heat temperature control set to 70 degrees or something like that. I almost never turn on the fan, and leave the air vent control to allow outside air to come in. This "ram air" provides a whisp of heat and the fresh air almost always prevents windshield fogging. I'll turn on the fan if passengers request it, but this method keeps me comfortable even down to 10 degrees.

Can't remember when I last turned on the defogger. http://www.cleanmpg.com/forums/images/icons/icon11.gif Keeping the car in the garage helps a whole lot.

Thanks,

Bob

Bob--

I notice this often in my new HCHII here in much-colder Ohio. For probably the first five minutes of my commute (sometimes longer if it's colder) I won't see regen on braking, but I will commonly see one or two bars of forced charge under power for part of that same five minutes. My unproven theory is that the battery management system does this to warm and protect the pack, but I don't know the technical reason this might be.

The behavior you note is consistent and predictable with me. In warmer weather I see behavior more like you've come to expect. Perhaps it's only just now gotten cold enough in Virginia for you to experience this phenomenon? --RN

Thanks, your observations make me feel a little better. And your unproven theory about protecting the battery makes a lot of sense. The drive in yesterday morning was in the low 20 degree range, and the braking thing happened when I drove the car before lunch with ambient temps in the low to mid 30's. Maybe the pack was still cold from the cold soaking out in the parking lot? Is there a way to monitor the pack temp? ScanGage?

Appreciate all your comments and suggestions very much.

Bob

For probably the first five minutes of my commute (sometimes longer if it's colder) I won't see regen on braking, but I will commonly see one or two bars of forced charge under power for part of that same five minutes.
I've also noticed for the first 5 min there's no regen when I take my foot off the gas--only sometimes see the bar or 2 of forced charge at that time.

The Insight system is different, but both follow many of the same control rules.
A look at the regen current into the battery when the battery pack is less than 30F will show a saw tooth wave rather than the normal steady DC. The system will only allow about 20A of regen, and will only allow about 35A of assist. Once the battery gets over 42F, everything settles into normal operation.
This is because the NIMH batteries can not accept charge or produce current as well when cold. Keeping current in and out gentle while the pack warms up helps maintain the SOC balance on the individual cells. I am sure that many other factors are being considered.

The Ford Escape has 250 NIMH D cells in it's pack. Has a separate AC system to keep them cool, and a heater to warm them up if too cold. Thats the type of battery control system that we need on all systems.
I have an indoor outdoor temp display in the car, with the outdoor probe right in the battery pack. The normal operation returns almost exactly at 42F.
This does not mean that your car is ok, just something to watch if the symptoms return.

My HCH 11 never regens during braking until the engine has some heat, probably 50% of normal operating temp.

The "green guy" I meet at the gym discussed how supercaps could really help on regenerative braking. They can take a much larger charge than a battery pack. At the very least, it might be possible to put a supercap to hold the charge from heavy or cold weather braking and steadily feed the battery pack.

A bit off topic, but if the system is designed to work that way, it could recover much more energy, but the cost to the manufacturer of the supercaps + batteries + special controller will likely keep that type of Hybrid energy storage system out of all but the most expensive Hybrids.
We need to remember that the reason all of the wizbang stuff that we see in concept cars is not in the show rooms is mostly due to cost factors.
:( ;)

If it helps at all, the Prius analog is roughly this: when
it's wikkid cold, I can only get up to maybe 40 amps [out of 100]
in or out of the battery. Falls to hydraulics a lot earlier in
the game on stopping; this is just one more reason to plan ahead
and try to stretch the stopping distance. If I don't demand
*any* cabin heat, it'll stay like that for quite a while, only
inching up allowable current in/out as the pack slowly self-
heats from activity. If I bring a little heat in the cabin and
the battery ventilation system pulls some of that in, it will
start giving a little more capability.
.
I don't know if the Prius plays with charge-current modulation;
that might be an interesting one to take some readings on.
.
_H*

This morning (and on one other occasion) I noticed that the regenerative braking wasn't working for a short period of time. http://www.cleanmpg.com/forums/images/icons/icon5.gif I could feel the brakes behaving differently - I had to push harder on the brake pedal - in order to slow down/stop. The green regen bars would not come on during brake pedal movement, but when I took my foot off the gas, the green bars came on. My battery SoCharge was less than full.

Anybody else experience this?


Bob

Hi Bob, some folks already appear to have nailed the issue. That behavior is very common, particularly when it is very cold.

I may even add the following additional regen "quirks":

You may also see 1 or 2 regen bars staying on all the time even when you already got a full State of Charge. Of course, this too is by design. :rolleyes:

The only other time when I may actually see some regen when slowing down is when I switch the transmission to the "sport" setting. In fact, this has become my preferred braking method because it is the only way for me to capture that kinetic energy when coming to a stop.


Cheers;

MSantos

Msantos--

Can you elaborate on your comment regarding the "S" mode? Does regen under "S" recharge the pack more quickly/efficiently than in "D"? Could shifting to "S" on a long downhill coast work something like "B" in a Prius? --RN

Yes, it is exactly like the "B" shifter position in a Prius. And in very cold days, that is the only way for me to add charge to the batteries while slowing down simply because the regen braking is not working.


Cheers;

MSantos

MSantos and all:

Thanks for the feedback. Watching this carefully as this behavior is a change for the car. Asked the dealer to check things out while they rotated the tires. The only thing they noted on the service ticket was the brake pad thickness. Ugh.

Anyway, the lack of regen during braking during the first few miles is becoming more repeatable now. Temps have been in the mid 40's. When we had mid 40's in the past, the regen braking was working all the time.

Thanks all.

Bob