On long downhills (where cops often like to check for speeders) the nice thing about the hybrids is that it's possible to simply let regenerative braking kick in, this will both control your speed and refill the pack. However, I woudl wait until you're already at your desired speed before you start charging -- get over the top, then coast to pick up speed to just at or a little faster than your desired cruising speed, then back completely off the throttle and let the pack charge. The nice thing about the CVTs is that in this situation, the car will automatically downshift for engine braking if the charing is not enough to hold speed. I observed this out going over the Grapevine in Southern California (about 5-6 straight miles of steep downgrade)

Also, at highway speeds, coasting to get extra speed is going to be a diminishing return as there is going to be rapidly increasing drag, so you're probably better off filling the pack to the point where you won't need force-charging later on. This is also the reason why going up a steep grade and down a gradual grade is moer fuel-efficient than the other way around. On gentler grades, it's more efficient to coast than to charge (as there are efficiency losses involved with charging the pack), since the grade is just sufficient to hold a steady legal speed rather than accelerate you past legal speeds.

I live on a hill where I must go up 850 vertical feet, then back down the backside 150 feet when coming home. (This actually kills my overall mileage compared to living at the bottom of the hill by more than 10 percent, thanks to stop signs and low speed limits) so I've got some experience with this type of climbing as well. The key when on the bottom is to pick up speed on the flat part before going into it. If the pack is not topped off, it may be a good idea to drop into "S" when initially accelerating to save some battery power. This will use more gas at first but prevent going into forced charging later on. Then I hold a steady throttle position and let my speed slowly bleed off until I hit each stopsign (I roll up to these rather than braking). I also try to use assist only when accelerating or going up the steepest sections, on parts with more of a gradual grade, I'll feather the throttle until assist backs off, again to prevent the pack from getting low and force-charging near the top.

Also, on the way down, regen braking is not enough to hold my speed, so another idea (if it's hot out) is to run max AC on the coldest setting the entire way down. This will make the cabin very cold, and provide useful braking in the process. It also means the A/C won't need to do as much work later on to keep the cabin at a set temperature.

 

I agree that the design is meant for the average driver and not for us hill people. But the frustrating thing is that the IMA never allows the charge level to go below 4 bars. Is your experience any different in that regard?

I suspect that it also may have to do with how quickly the batteries are drawn down. Just as regen is prevented when the batteries are too cold, assist may be cut off when the batteries are drained very quickly because the batteries over-heat. Just a theory...

 

I have the same experience, living as I do midway up a hill... I usually go down the hill in the morning when the engine is cold, so I get no regen at all for that stretch which is just galling when I spent so much assist power getting up it the previous evening.

So this morning (keep in mind I've only had the car a week) I turned it on, started rolling down the hill, put it in neutral, turned the ICE off, and coasted the rest of the way to the stop sign at the bottom. I'm trying to figure out whether this will be a better strategy (given that it presumably also delays the car's warming up).

Any thoughts?

 

If you're going down a steep hill and you want to force regen on you can shift from D to S. You'll get regen immediately. I don't know if it hurts the battery pack though. Depends how cold it is. I figure that in my area with the temperature usually 50 degrees or more it won't hurt the batteries much.

 

I rarely see my SOC below 5 bars. I think maybe twice it's gotten to 4, but then the thing wants to recharge really badly, so it doesn't stay at 4 for long. Deep discharge is bad for NiMH if you want them to last many years, so Honda's strategy is to limit discharge to preserve the pack through the warranty period.


Packrat

 

I rarely see my SOC below 5 bars. I think maybe twice it's gotten to 4, but then the thing wants to recharge really badly, so it doesn't stay at 4 for long. Deep discharge is bad for NiMH if you want them to last many years, so Honda's strategy is to limit discharge to preserve the pack through the warranty period.


Packrat

 

I misunderstood completely. :-)

My problem is that the pack went from full charge down to 4 bars daily.
My pack never went below 4 either.
The wide pack swings were rumored to decrease battery life if they
occurred frequently. So I experimented with driving that would reduce
the pack swings.

After your post I went reading some more on the NiMH batteries
used in Hybrid cars, and I think they are rated for 100k small
cycles (small like 10% swings). That is ten times the cycle
rating of a normal NiMH battery at 1000 full cycles.

I found a picture of the HCH-I pack on howstuffworks.com,
and found that they are specially made by Panasonic.

I also toyed with the idea of putting a bigger battery pack in my car.
I found some 11000 mah NiMH D cells, and nearly doubled capacity
sounded way cool, but it just wasn't that easy. :-)

 

I wouldn't do that without Honda's approval because it could void the warranty on the whole hybrid system.

 

I wonder if a better strategy would be to let the engine warm up for a while first -- true, you'd burn gas idling, but when the engine is cold, it would burn that same amount of gas anyway when going down the hill. You'd then have the advantage of consuming no fuel when warm going down the hill (fuel cut mode), AND you would be able to accept full regen.

As for me, since I need to go up and over my hill to get home, that means I have significantly climbing to begin with cold. By the time I'm rolling down the big part of the hill, the engine is already warmed up enough that I can charge the whole way down -- I'm usually just topping off as I reach the bottom to get on the freeway.

 

Yea I know its a little risky but I'll only do it on the freeway, I know several state troopers and they have informed me that they won't pull most people over on I-95 unless they are going more than 15 over. Also, I have some police experience and I know some of the tricks and how to read or hide from radar; I was also once radar certified at one time. One rule of thumb to follow, is that as along as you are not the fastest person around you its a safe bet you won't get a ticket but not a guarentee.