Driving in hilly terrain, what is the best practice?

Don't put it in Neutral at that speed.

Use Brake option on your gear selector when going down hill. Failing that, just keep it in Drive. Do not put in Neutral as it is illegal in some places to do so, in the Prius you're missing out on all that regen and I also believe it will cause the motors to spin too quickly.

If you're worried about over stressing the HV battery on the way down the hill - don't be. Use B for Brake option and let the car look after itself.

 

Best practices? - just drive it.

DBCassidy

 

+1

The Prius takes care of itself. You can't hurt it.

 

I agree. The best way to drive it is to "drive it."

"Hypermiling" is an illusion; you aren't gaining anything, just losing a bit more than you would by driving normally.

 

Do not put the car in N at speed as this can seriously overspeed MG1 (motor generator 1). With the risk of the rotor exploding under centrifugal force. A very expensive repair not covered under any guarantee. The engine must spin at speeds above 41 mph and in neutral it cannot start. As others have said just drive it the car will look after it's self.

John (Britprius)

 

I'd be surprised if the system weren't protected against doing that. Has this happened for real?

Anyway, "neutral " in a Prius isn't really neutral. The motor-generator has to run very fast to compensate to give you the illusion of coasting. I'd expect that if it were unsafe to shift into "N" the computer wouldn't allow it to shift.

 

No the system is not protected. If the engine is running when you shift to neutral it remains running, but if it is not running it cannot start. This is because mg1 and mg2 or electrically disconnected in neutral to allow the free wheeling (no regen) and that also means they cannot be powered to start the engine. This has been disgust on many occasions in the past here on PC. It is also a fact that leaving the Prius in neutral with the AC on will discharge the HV battery, and then the 12 volt. Again this is because the engine cannot start to recharge the HV battery. The HV battery then in tern can no longer charge the 12 volt battery.
Neutral can be the most damaging selector position.

John (Britprius)

 

I've been in nutural going down long decents. I'd go from b, to nutural then b to nutural, so on so forth, with AC on max to keep battery cool and to not fully charged the bat. So apparently shifiting to N at 75 doesn't damage the car

 

Oh just remembered, I've shifted to N going 85 MPH bbefore, no problem

 

Not all damage you can see...

But the issue is the 42mph threshold. If you start going dowhill in neutral below 42mph, the engine will be off. Once it gets to 42mph, the Prius requires the engine to turn on to prevent over-revving of MG1. But in N, as a safety, it cannot. Damage ensues. If however you are going faster AND the engine is on, you aren't causing any damage because the engine will never shut off. You are just wasting gas.

Using neutral is just stupid in a Prius. The car will shut the engine off for you when it needs to. If it is a long decent, use B mode. Really that simple, no need to try and play games with the car.

 

Stop doing that. You are only fooling yourself. There is no true neutral in the Prius.

 

Well damn, I learn something new everyday! Wasn't doing it to "save fuel" though. I just don't like maxing out all 8 bars on the graph with a battery with 235,500 miles

 

As has been said many times on this forum the Prius has no gear changes of any description. All the gears are in permanent mesh. There are no clutches and at no point is any gear disconnected from the engine or wheels. It also has no reverse gear. Everything depends on the conditions of the electrical state of the two motor generators.
I did state if the engine was running it would stay running, but if it is not and you go over 42 mph the risk is totally yours.

John (Britprius)

 

Then preemptively use B mode. Presumably you know where these hills are that fill up the battery when you start your decent, put it in B. I am hesitant to believe there exists any "hill" in Nashville area where this would not prevent filling up the battery. And on that subject, a "full" battery, isn't. 8 green bars means close to 80% full. Again, the Prius protects itself. Just like when it is "empty" at 1-bar, it is really around 40%.

 

I've driven Monteagle mountain on the way to Chattanooga via I-24 many times. using B all the way down, it will fill up to 8 green bars, and the engine will rev like crazy to burn the excess energy regend. And I am very aware that the battery never goes past 81% charged

 

The "B" position is for situations when there's no place left to put the juice. It burns off the excess energy by compressing air in the cylinders and blowing the extra heat out through the radiator and tailpipe.

 

Engine revving is a good thing. The only reason I use B mode, is to save my brake pads. The battery can fend for itself!

Just looked up that hill, and it is a baby compared to what we have here. My house is a good 1500ft above the main city so I drive that elevation change every day, in a shorter distance, multiple times a day essentially lol.

Just got back from skiing this weekend. Went from 7500ft resting to as low as 5500ft and as high as 11,500ft. All in the Prius. Going down the steep slopes of I-70, higher than the maximum grade allowed on all other interstates, if you put it in B mode, and let the car roll down, it can take a few miles of sharp decent to fill completely if it even does.

 

That battery isn't going to last 235,000 I can tell you that

 

Probably not. Heat and mountains kill Prius batteries. But it does perform as new 130K miles later. Same mpg, and it takes about the same amount of hill to "fill" as it did 70K miles ago.

But we also have a Lexus RX450h hybrid, a Prius C, and then a Leaf so we are tempting the battery gods. If it dies tomorrow, it will have had a great life. Cough up a few hundred bucks and it will be good again for another decade.