NHW20 Prius - Keeping SoC lower for better FE.

[msantos]

Quick question for the Prius experts (IIRC this has been discussed before):

Have you tried to keep the SoC purposely lower in order to attain better overall FE? I understand the architectural why's to a certain extent, but the strategy and technique is where I am a little foggy.

Anyhow, I don't have as many opportunities to discover/verify this as I once did, but any feedback and tips would certainly help... at least on the few instances where I can actually test this.

Cheers;

MSantos

[mparrish]

Hi Msantos,

Oh, we Prius folk love the Prius questions. I'm sure others are typing as we speak.

Edit: Just noticed the Prius on your Vehicle list. I had not before.

I have indeed experimented with a more liberal use of the pack to improve FE, and I've over time come to the fairly extreme (but probably common) position that ANY pack use for whatever reason is bad! The FE pain of refilling the pack eventually overtakes any short term EV gain. As such, I work hard to keep six bars (roughly "equilibrium" with little fill or discharge) at all times.

The only time I would consider lowering SOC is if I knew I would be approaching a situation where significant pack generating regen via braking were unavoidable. Of course, it that were the case, I probably wouldn't take that route at all anyway. haha.

Last summer I certainly tried. I start my commute with a short uphill followed by a LONG downhill, and it was fun to delay ICE warmup, EV-only up before gliding down, and be sitting at some ridiculously high trip figure. But pack refill via the ICE throughout the rest of the trip would drop my trip like a stone.

It's not true, but it's close. Give me a pack & plug, or don't bother at all.

[xcel]

Hi Manuel:

___I used to believe until reviewing Cheryl’s Prius-I last summer that a 3 or 4 bar SoC would allow a higher efficiency of charge and assist but after that review, I am in line with what Marc just posted. Any use for any reason other than a Chicago Style “Stop and Crawl”, to get up to 15 – 20 mph from dead stop or < ½ a block to get over a crest for another glide is an absolute waste of fuel!

___You probably remember how little the NHW 20 assisted by comparison to the HCH-II and I think it was done for two reasons. Pack longevity being the first and real world FE being an additional benefit.

___Good Luck

___Wayne

[msantos]

Hi Marc & Wayne;

Thanks for the awesome and extremely qualified feedback.

That's what I always thought as well. However, I never gave much thought to the claims about working the ICE a little harder for FE... because it appeared a little counter intuitive in most cases and probably only applies to a small number of scenarios (if any ?). I certainly can't think of any ATM.


Cheers;

MSantos

[locutus]

Agreed... I see the best results from staying off the pack completely (except in obvious cases like taxiing around a parking garage or other very short low speed segments where the ICE would be horribly inefficient). If in normal driving I drop to 52% or lower (4 bars), then I notice the ICE revving higher for a given pedal position on pulses with the same thrust and greater (re)charge. At 3 bars (49%) this just becomes more pronounced, with the added problem of no longer allowing forced EV.

I've definitely found the sweet spot to be 55-62% (5-6 bars). I'll let it go down to 4 at the end of a segment, only because S1 (for the next segment) is unavoidable and tends to provide a significant (re)charge back to 5.

[mparrish]

Originally Posted by locutus

I've definitely found the sweet spot to be 55-62% (5-6 bars). I'll let it go down to 4 at the end of a segment, only because S1 (for the next segment) is unavoidable and tends to provide a significant (re)charge back to 5.

That's a good point. I use EV a bit more liberally ascending my parking garage, cause I know headed back down I'll be in a forced S1 yet luckily able to regen back to the pack (instead of driving off of the pack) because I'm going downhill. Another one of those "unavoidable regen situations".

Oh yeah, the Dan method! That's a good use of the pack. If your stops are 10-15 minutes, don't shut down. Turn off the screen and manually lock the car. You may lose a bar or two of SOC over the 15 minutes, but it beats having to power up and endure a (probably) unnecessary and painful S1 again.

Plus it makes your grocery shopping super efficient. "Self-serve checkout honey, I'm probably down to 4 bars". She's learned to cope with my "ways".

I had the following conversation with a buddy:

Him: What are you doing?
Me: Leaving the car on and locking it. It saves gas.
Him: But couldn't somebody drive off after breaking the window?
Me: Yes, but they won't.
Him: How do you know?
Me: Cause they'd probably hit the power button to "power on", but would instead be "powering off"
Him: But what if they knew your trick?
Me: Then I'd drive to Madison and ask Jerad why he stole my car.

OK, the last line I just made up. But it would be an awfully small Cleanmpg criminal lineup.

[xcel]

Originally Posted by mparrish

I had the following conversation with a buddy:

Him: What are you doing?
Me: Leaving the car on and locking it. It saves gas.
Him: But couldn't somebody drive off after breaking the window?
Me: Yes, but they won't.
Him: How do you know?
Me: Cause they'd probably hit the power button to "power on", but would instead be "powering off"
Him: But what if they knew your trick?
Me: Then I'd drive to Madison and ask Jerad why he stole my car.

[diamondlarry]

Originally Posted by mparrish

That's a good point. I use EV a bit more liberally ascending my parking garage, cause I know headed back down I'll be in a forced S1 yet luckily able to regen back to the pack (instead of driving off of the pack) because I'm going downhill. Another one of those "unavoidable regen situations".

Oh yeah, the Dan method! That's a good use of the pack. If your stops are 10-15 minutes, don't shut down. Turn off the screen and manually lock the car. You may lose a bar or two of SOC over the 15 minutes, but it beats having to power up and endure a (probably) unnecessary and painful S1 again.

Plus it makes your grocery shopping super efficient. "Self-serve checkout honey, I'm probably down to 4 bars". She's learned to cope with my "ways".

I had the following conversation with a buddy:

Him: What are you doing?
Me: Leaving the car on and locking it. It saves gas.
Him: But couldn't somebody drive off after breaking the window?
Me: Yes, but they won't.
Him: How do you know?
Me: Cause they'd probably hit the power button to "power on", but would instead be "powering off"
Him: But what if they knew your trick?
Me: Then I'd drive to Madison and ask Jerad why he stole my car.

OK, the last line I just made up. But it would be an awfully small Cleanmpg criminal lineup.

I plead the 5th. I also have been know to be the super efficient shopper. It's kind of like mixing hypermiling and shopping together. Thoughts like, "Can I glide past the chips, grab them, and get them in the cart before coming to a stop or it's time to start the next pulse?" I have heard comments from my wife like, "If you'd just shut the car off we wouldn't have to be in such a hurry!" This is when it's time for the Slowhands confused look.

Jared, I've also noticed the mpg hit at around the 4 bar mark. It's nice to see that I wasn't just imagining it.

My game as of my last clinic with Wayne is to see if I can go all day on 6 bars of SoC. It's really difficult to start out the day at 6 since my drive is between .05 and .1 miles long with about 1/2-1% uphill grade. I have managed to hit that goal for my work only commute of 31.3 miles but I usually end up losing 1 bar on the days that I have more errands or when my trips are at night with the headlight use. I could probably count on one hand the number of times I've been at 4 bars in the last 4-5 months.

[Dan]

I'll throw in here.

There seem to be three pack levels internally. Too Low, OK, Too High.

-I see the TH transition to happen at either 6-6.5 bars. When TH it gets real hard to get the engine to turn on. Always favors pack. On the HW it's also hard to get the ICE up to provide power. It just wants to idle.

-I see TL transition to happen at about 3.75 bars. When the pack is in TL mode (panic mode), the ICE is always running way high RPM. It's real hard to ever get a 75 bar or better if your in TL mode. You can feel the transition from TL to OK because if feels like the engine shifts gears. RPM drops by about 2k.

-OK is everything in between. And I'm with everyone else in the belief that you should stay off the pack unless you know TH is imminent.

Now I think the trick is to hold it in OK. If I fear a TL segment cuz I know I'll hit traffic, I'll try to boost my charge a bit by doing some real low RPM pulses. I will generally use EV from 0-15 mph coming off a dead stop. I also will use EV for for about one second after transitioning into a glide. I only do the latter since I almost always enter glides with my EV button. Once the engine cuts I leave the car in "D" for about a second before transitioning to a NICE-Off glide. Main reason for the 1 second DICE-Off glide is to ensure that the CAM places the cylinder heads in the proper position for the next start. If I drop to N too quick after EV I notice some bumpy starts or bumpy stops. Only reason I "yellow-arrow" glide for that one second instead of ensuring "no-arrow" glide is because my foot is locked in my typical pulse position. This way I don't have to feather much, just punch shift and glide.

One thing I did notice is once you settle on a pulse RPM and a route the pack will always reach it's own equilibrium. When I was doing hard-pulse technique I'd level off at 5 bars. If I do a 1500-pulse technique I level off at 4 bars. If I do a soft-pulse technique I'm back at 5 bars.

11011011

[brick]

Put me on the board with everybody else who says to stay off the pack entirely. My experience is that anything less nominal charge results in just enough trickle charging to ruin iFCD readings while I'm trying to DWL (which is my #1 tool in this environment). Dipping into the pack just a tiny bit might be OK if I happen to have surplus, but if I go too far it can take forever to get back to equilibrium. In ideal conditions we could be talking about the difference between a 60+MPG commute and one in the mid 50s.

Obviously, iFCD readings are great (or infinite) if you happen to have a lot of surplus charge in the pack since HSD bleeds it off until it's close to nominal. But the energy wasted to get that surplus is killer. Regenerative braking may be better than friction brakes, but it's still something to be avoided if at all possible when you're trying to maintain peak FE.