Full Battery & going downhill - Engine coming on?

Why don't you use B? That's what it's there for.

When I lived in Denver, driving an Accord and a Camry V6 LE. I drove like an old lady when it snowed. Too many n00bs from California and Texas with RWD Stupid Utility Vehicles and no experience driving in precipitation.

I saw more than my share of people passing me on I-70, rolled over a few miles ahead, fires from not putting the car into low gear, etc.

This was before the Prius Era, so I don't know what it's like now.

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Yes, but for me, down hill is less than half mile and I don't need engine break at all.

 

The car has no way to know how long your downhill run is. I have one that I take pretty frequently that's nearly 50 miles long.

If you are at a full change and want to force friction braking, put the car in neutral. Dangerous, but the ICE shouldn't start.

 

This is normal behavior, this is to keep the car from coasting out of control. Normally when you coast the battery charges and provides some braking (like a normal car), when the battery is fully charged there wouldn't be any braking and cause excessive speed going downhill (trust me, the prius will coast like a bat out of hell if you let it). So the ICE will fire up and provide the additional braking.

As far as fuel consumption goes, yes gas is being used but somewhere near the equivalent to 300-400 MPG...kind of hard to say since my ODBII scanner calculates fuel economy only by mass airflow. Either way very little fuel is used.

Friction braking on long descents after the battery is charged fully would be unwise, this can cause the brake pads and rotors to overheat and cause you to lose brakes, excessive wear or damage.

Bottom line is, everything is fine, when you see the EV light go off going downhill start braking like your in a normal car and not hybrid...meaning don't ride the brakes.

Do not put the Prius in Neutral, it accomplishes nothing. The Prius can manage itself quite well.

 

It's my understanding that full charge does not mean full battery it means 80% full battery always leaving room for regen. I have had the ICE come on going down hill on full charge as well, but I think it had to do with the climate control system or even just the defrost being on. Still trying to figure this ICE thing out. What seems true so far is that it at times comes on at times you wouldn't predict.

 

Many-most modern cars have DFCO (deceleration fuel cut off), so no fuel is being used.

 

No.

I test this virtually every day since my office has chargers and is at the top of a big hill. If I charge to 100% at work, I have to be very careful down the hill to avoid engine start. If I charge to 95%, it's never a problem.

 

We have plenty of long downhills but no escape ramps. Cars and trucks (and their drivers) are held to a higher technical standard here. Some hills have "low gear"-signs at the top.
I absolutely realize why engine braking is a thing, but forcing it to engine brake (and start a long and wasteful warmup process) prematurely in such an automated primary electric car car is downright inefficient.
How on EARTH can pure EVs be considered safe without an ICE to brake them!?!? Oh dear the fear!!!


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When my battery is almost full, and I brake down a tiny hill during winter time, my engine will f***ING start and won't turn off for like 5-10 minutes. And we're not talking Prius-superduperefficiency during those five to ten minutes. The block is cold and the car dumps fuel into the cylinders, pushing the fuel consumption through the roof.
I bought the car (and it seems designed-) for small errands and quick drives in town. If anything, HOW ABOUT AT LEAST TRYING TO AVOID ENGINE BRAKING WHILE IN EV MODE, TOYOTA? Hmm? It's got a tiny EV range anyway. No one is tackling enormously long downhills with any sizeable EV range.
Let me use the goddamn friction brakes for a bit before you start wasting fuel, you utter retardation of a PHEV.


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This is really annoying. My trip from home starts with 0.7 mile down hill road which would add 1.2 miles of charge. The ICE would be on for almost sure if I charge between 27 miles to full (33 miles). It is really pointless to warm up the engine while I won't use it for rest of the day.

So what I am doing is to stop the car at the stop sign, turn off/on the car and happily drive in EV mode. What a hassle.

 

I have the car on neutral instead. Still a goddamn hassle, but much nicer to the engine compared to letting it start.


iPhone ?

 

So when battery is full, use the brake pads/rotors to avoid ICE on when I am sure I won't use the ICE at all.

Thanks for the tip. Don't know why I did not think about that before, maybe my mind was full of energy saving instead of wasing

 

Are the friction brakes any different than a standard automobile in terms of reliability and ruggedness? Ignoring the usual, hot brakes problem in Colorado which happens to all vehicles, are there any additional concerns? Because regen was assumed, did they under design the friction brakes? Of course I am probably succumbing to Prius geekiness overkill as my downhill is about 5 miles/700 feet. Doing this at the rumored roughly 400 mpg rate of the ICE, I am burning 2.5 gallons of fuel/year. Assuming new brake pads cost about $150 and I have to do this twice in the 10 year life of the car I am trading off 25 gallons vs $300. At future gas rates of $10/gallon I still come out ahead compression braking.

 

They aren't allowed to be any less than what is required for a vehicle of this weight, regardless of regen capabilities.


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Just excreting energy, happens to me too, my car that is. It’s sort of a mysterious car, one cannot predict it’s
behavior.

 

Glad I found this thread, thought I was going crazy.

It's one thing that the engine comes on going down hill from our house (doesn't seem to do much engine braking), but then for the next 2-3 miles (@30mph) it is using partial or full engine for acceleration. It will also do this when the pack isn't charged. Very non-EV like behavior.

The other nit is sometimes when the battery pack is low and car is going down a hill, I flick on regen and it will work for a while and then the engine comes on and starts engine braking. The guy at Toyota said "that gives you even more battery voltage!" ... I just shook my head.

I should experiment with the car's speed, see if Toyota's software is looking at road speed limit, amount of braking I'm doing, and deciding things are out of control and they need to step in. ":^)

 

So, downhill, battery fully charged, in B mode for steep down hill driving. Do you also precondition the car and temperature?, I do! My engine shows, coming on for a few seconds, I don’t believe it really is. Driving mode is Eco/ev. now a short run up and a large run down, steep. I put it in brake, for safety, charge comes back to original value again. Now, the next big run up, ~ 1000 feet I attempt to be conservative, but to no avail, Engine comes on, battery needs assistance with load. Charge goes from 26 miles to 20 miles.
Next portion freeway, downhill, getting mild regen, all freeway now, speed up to 65. within 5 miles of destination computers will let me charge, at about 16- 18 range left. Finally arrive, after 22 miles of travel with 18 to 21 miles left // On the return trip I’ll charge on the flats so I can make it up the hills using only Ev. If I’m lucky I’ll have 6-10 miles left after Iv reached the top of the hill. Now a big downhill, hopefully when I reach the bottom I’ll have 6-10 miles to make it up the next big one. Now, on that last leg it’s in charge and B mode.
Safety plus one always has a charge, either from ICE or regen. The ICE mode is always very intermittent and short.
That’s my daily, hope that helps.
I’m averaging over 1000 miles on every tank.

 

When descending a long grade, just set the cruise control and let the computer decide the best way to maintain the speed using a combination of friction braking, regen braking and engine braking. Also, I would never recommend using N to keep the ICE off.

 

see post 57, all steep serpentine curves, I never use N, however on a long grade down, I may use it to get up to speed w/o using ICE or Ev. long grades on freeway.

 

There are different conditions that will cause the ICE to start. If your battery is fully charged and then going downhill, that's probably causing it. Secondly, the software isn't going to be looking at your speed per se, however yes speed can play a role in whether the ICE starts. In the regular prius the ICE starts when the battery pack is near it's maximum charge. The software controls the rate of charge into the battery pack. Once the battery nears its maximum charge the charge rate will drop and to maintain engine braking the ICE will start and the braking will be part ICE and part MG. This is all normal behavior and is to maintain battery life over the long haul.

Don't use N, just lightly press the accelerator, you'll get the same effect. Get an OBDII scanner and see for yourself no current will be going in or out of the battery. I live in the mountains and all can be best managed by the accelerator and brake...and sometimes 'B'