Running on elec vs gas

Hi Brodie,

It has to do with the state of charge (SOC) of the battery. If you have been using the battery allot prior to your reference road, its SOC will be low, and the car will accellerate with the engine easier. If the SOC is into the green, the car will hold onto to an electric accelleration longer. What the programing is doing is trying to keep the battery near 60 % SOC, which is within the highest blue bar on the MFD SOC indicator. By doing this, the Prius is maximising the battery life.

 

As I often feel obligated to point out on these threads, the less you use the battery, the better. Charging and discharging the battery is an inherently inefficient process, so you should try to avoid doing either whenever you can. Obviously this is impossible to do all the time with the Prius, but if you view it as a "general philosophy," it will help your MPG.

By the way, this is why "Pulse and Glide" is such an MPG-friendly driving style. You are mostly using the gas engine on the "Pulse" and not doing any charging or discharging of the battery on the "Glide."

 

+1 on donee's post.

I will add that in my experience, the harder I push for max FE/MPGs and
the closer I monitor the ICE/HV battery, the more I become aware of
circumstances and situations where the generally expected behavior doesn't
occur. I'm not talking about anything major, just a reading or an energy path
that makes me wonder, "What the heck was that?" and its back to driving in
the real world. If I had a CanView recording the right readouts, and the time
to review the recordings, maybe I could figure it out, but I have neither -- I
do have a ScanGauge.

Here are a few things that I think contribute to "mystery" HSD responses:
* The HV battery can be in a " very low" or "very high" 6th blue bar -- or any
other "bar" for that matter -- and be at a value that is in the overlap with the next
bar.(There is a cool graphic showing the bar overlaps, but I can't find it. Sorry.)
* Sometimes the ICE runs just to keep the catalytic converter hot even though
the engine coolant is above 154 deg. F.
* Sometimes the CPU(s) run the ICE while conducting tests "in the
background." As an example, IIRC, about every 100 miles the system tests
the airspace between the metal gas tank and resin fuel bladder for evidence
of gas vapors. If it finds some value, it reports a fuel system problem.
[EDIT] * Somtimes the HV battery temps are too high or low

I suspect that there are more of these special conditions that may cause ICE
operation/small unexpected energy flows.

My hope is that members with more experience, or are better read, or have
better memories will come up and remind us what they are.

 

Brodie,

I think your first post is an excellent example of a situation that any attentive
Prius driver might encounter, and then wonder about. Good job. No apologies
needed.

My first post wasn't meant to suggest that the conditions I noted are of
concern to only hypermilers -- I consider myself a "very good miler," and don't
have the inclination or dogged persistence to go "hyper." Rather, I meant that
it is more than likely that it is the higher FE/MPG chasers that notice the HSD's
subtle quirks and oddities and have a suspicion of what the CPU(s) is up to.

 

I agree with Tony. The coolant is a bigger factor for me than SOC. The ICE wants to run with the battery well into the green at times. Having a lot of hills and such can require a bit different optimization. My 2.9 mile trip tonight was with a warm ICE, burned a bar off the battery and exceeded 100 mpg (wish I could see by how much). When the car is run the next time it will be cold, the ICE will want to run, so it will at least have something useful to do.

 

I have not found at all that my car accelerates with battery only during medium loads, definitely not under heavy acceleration. Under medium acceleration from a stop, the ICE kicks in it seems within a few seconds. But, I would need to really watch the energy monitor to be sure and give parameters.

From a stop with engine reasonably warm, I can accelerate with battery only, but only with gentle acceleration, up to about 30 mph.

If I accelerate more quickly, go up an incline anything over a very slow pace, that ICE is on for sure.

Sometimes I've noticed cruising light throttle, even at 35 mph, the ICE in energy screen is shown to be off.

My car started off brand new showing 53.x mpg average. This tank has been 56.x mpg. Better than I expected before purchase. Thought I would be in the forties.

 

It's a lot more complicated than indicated above.

Heating things:
First, the ICE will run to keep the catalytic converter in a warm operational state.
If your interior A/C system is calling for heat, and the engine coolant is below about 55 C, the ICE will run.

Charge control:
The ICE will run if the system senses the traction battery needs a bit more charge.
The ICE will shut off if the system senses the traction battery is too fully charged (as long as the throttle is not aggressively depressed ).

Battery pampering:
The ICE will run and the battery current drawn will be severely restricted if the battery temperature is sensed as too high. Charging will also be restricted, causing the ICE to run "too long" (as perceived by the driver), if the battery temp is too high.

To influence all this (which is all we drivers can do):
Keep the cabin interior at a comfortable temperature, so the battery can keep itself as cool as possible.
Use gentle pressure on the throttle.
Be aware, no matter how nice the temperature is inside the car, charging or discharging the battery generates a lot of heat. So if you just used or recharged the battery heavily, chances are you will not be able to do so again until it has a chance to cool off.

 

It is too bad Toyota doesn't provide the relevant factors on the MFD. I would like to see the amps, the coolant temp, the battery temp, etc.

Mild battery discharge rates haven't seemed to pose much trouble, but the irony is that fast regen (lots of steep slopes often with stops at the bottom) keeps ramping up the battery charge, with little opportunity to burn it off before regenning again. Then, to make matters worse, the coolant can get too cool on extended downhill runs...so that the ICE wants to kick in when you would prefer to rely more on the battery first to clear the accumulated regen charge.

I admit I am developing some envy for those who get to run the Prius in flatter terrain on rural highways. The few times I've gotten to use real pulse & glide the mileage has been phenomenal. Hill P&G is a different critter entirely.

I really wish there was a wider band in the throttle between regen-glide-electric. I hate having the most minor surface imperfections bounce me back and forth through all three although it feels like my foot has never moved. There is no way to be gentle enough with the present throttle.

 

To reduce ICE cool-down install grill blocking. We're just exiting a warm spell, where I observed with both grills blocked, it's safe even up at ambients of 25C. In fact, it was 30C on the highway (100 km/hr) and coolant only got up to a peak of 97C. It stabilized at 93-95C (fan cycling).

To monitor more data get a Scangauge II. You can watch battery voltage and current. You can also watch SOC displayed as a %, not just a bargraph.