Long Descents and Regen Techniques

Put it in B at top of descent, keep your speed a little lower, use brakes as needed. Switch back to D if and when there's flat spots, anyplace where you'd otherwise need to use gas.

Don't use cruise. In B it will rev up; keeping the speed down will help some.

 

Just put it in B at the top of the descents. It will spin the ICE up to 2000+ RPM before the battery fills, and 4600-ish RPM after the battery fills. Despite emitting the sound of a jet engine, or a giant vacuum cleaner, or a banshee, the ICE will still be safe. In my experience on 7% grades, and higher altitudes (less air drag and less engine compression), the computer hasn't allowed the engine to redline.

On these steeper hills, if I start the descent at speed limit (60 or higher), B does not have quite enough drag to prevent some acceleration, so some minor friction braking is still needed. If I slow to 50-ish before the descent, then the car can usually maintain speed without the foot brakes. Note that this threshold speed will vary with cargo load, actual slope, altitude, and other factors.

The PiP and Prime do allow far more battery regeneration and longer descents before their batteries fill and force the ICE to start screaming.

 

Never put it in N on descents. You talk about sounding dangerous to continue when the engine revs up: I can tell you, things will get dangerous when you try to coast downhill in N, especially with a shut-off engine. MG1 will over-rev and that may cause serious damage, having the car in N will stop any brakingpower from regen or the engine so you are much likely to overheat your brakes. Just do not do that.

When the engine revs up to "burn off" excess electricity, it does so without burning fuel and with the valve-timing is adjusted so that the maximum engine-braking is achieved. The engine has no problem with that.

I do dislike the fact that you can not tell the Prius to use more electric energy going up a hill. I understand that using the battery as little as possible will extend the lifetime of it, but I'm sure you would get better mileage if you could top up an empty battery when going down as opposed to having to burn more excess energy off.

 

I thought cruise control caused engine breaking on descents to maintain constant speed (i.e., not accelerate over the mph you set in c.c.) ?

 

It does, but it has limits. That little tiny engine has only so much braking capability available, not enough for some of the descents we encounter.

 

Hi I haven't logged on here in many years, I'm getting ready to finally replace my 2004 Prius. I'm looking into buying a certified pre-owned 2014 plug-in Prius. I logged onto here reading this thread trying to understand how it all works.

Recently I drove my Prius up into mountains for the very first time. It really didn't like climbing long inclines. My normal gas mileage is about 48 to 51 mpg per tank (actual, not estimated, I use the trip odometer and divide miles driven by gallons pumped) I had to refill in the mountains and after that climb it put my tank of over 400 miles into averageing about 36 mpg. On the way home it seemed to make up for it but I'm curious...

I read and saw my gen 2 Prius is 110 horsepower combined and the gen 3 Prius is 134 horsepower combined. So I'm thinking it will be a little easier going up that mountain but I'll still need to pull over to let the Osama-mobiles pass me by.

My question is, if I buy this plug-in Prius or as I see here (pip) say I get up the mountain and I'm ready to return and my gas tank is low, I know the regenerative breaking will charge up the traction battery as it does on my gen 2 Prius, but when the land levels out will I also be able to stay in EV mode for the 11 to 16 miles or is the EV mode only available from being charged from an outlet ?

Oh btw, I tried to keep my gen 2 in B for most of the decent to save my brakes, but it really does a high rpm whine. I was concerned I might be screwing up my transmission to save my brakes which would be not smart to say the least. But after reading this thread it appears that's just the ice engine revving up to get rid of excess energy? Did I understand that correctly?

 

Yes, you did. Main thing for anybody worried about the sound: you don't need to invent things to worry about. On your next big descent, shift to B, wait for the battery to fill and the engine to reach its top braking speed, take a good listen, and tell yourself, "this is what Prius engine braking sounds like, and it's fine."

It is all under computer control, and it won't do anything that harms the car. When it reaches the point where the computer isn't going to use the engine any harder, you'll just notice that that's as much engine braking as you get, and then you'll need to touch the friction brakes from time to time to avoid picking up speed.

Anything else you do, out of somehow convincing yourself the normal sound is abnormal or bad, isn't going to improve on just using the car as it was designed.

-Chap

 

Yeah I've noticed more than once people asking, along the lines of "I'm using B but still speeding up, what to do?". Use the brakes, lol.

B mode is a help, but if it's steep enough you still need to brake. Also, if the grade flattens out, to the point you need gas: for sure push it back to D.

 

In my gen i insight I get the car into autostop at the top of the hill and start down the descent in neutral motor off at a very low speed, the hill accelates me, I then shift to 3rd and let regen hold me at the max speed I'm willing to go before friction brakes.

 

The following was concerning:

I recently drove from Cincinnati, Ohio to North Carolina.
Some fairly steep grades.

I almost never needed to use B mode.
I truly didn't accelerate out of control on the long descents.

Is something wrong with my car?

 

I'd say no. Even a vey steep grade doesn't warrant B, as long as it's not too long. Or extremely long downhill grade, but not steep enough that you're constantly braking, same story: just stay in D.

 

Normal cruisecontrol will use regen up to the point that the brakelights would go on (braking on normal CC will never light the brakelights). ACC will use regen beyond that and will also use friction brakes to keep the set speed.
And in both cases: when the battery goes to full, the enginebrake will be used.
So normal CC will not necessarily keep the speed.

 

thank you kind people for answering one of my questions. Hopefully my main question will get answered.

My question is, if I buy this plug-in Prius or as I see here (pip) say I get up the mountain and I'm ready to return and my gas tank is low, I know the regenerative breaking will charge up the traction battery as it does on my gen 2 Prius, but when the land levels out will I also be able to stay in EV mode for the 11 to 16 miles or is the EV mode only available from being charged from an outlet ?

I'll complicate it with a simple second question again, I see ads stating "base plug-in Prius". My understanding is the pip is equivalent to package five meaning it's got everything the four has. I have a package three, at the time three package meant navigation, package four was a three with leather seats. I thought the plug-in was above a four in price and features, if so, why are they calling it a "base"?

Okay simple third question, does the navigation on the plp come with real-time traffic info routing you to avoid congestion? Thank you all in advance for your responses. Take care.

PS new question lol, is there a forum on people selling their Prius? If so please link or direct me to how I can find it. I'm looking into buying a 2014 blue pip with California HOV stickers

 

Your car will be able to charge the traction battery up to about 80% of full charge. This is set in software. You will be able to use that power to push the car.

The packages in each model of Prius can vary and are not really cross comparable. To compare you will have to examine all options available in each model.

I think people are over-thinking the regen. system. The Prius will NOT "overrev." the engine. It will max. out around 4500-5000 RPM. No matter what you do. There are limits set in the software. Yes, it sounds loud, and yes it also sounds unusual. That is only because you don't descend mountains that often, at least most of us don't. You have a choice. You can let the engine waste the excess power compressing air with little extra wear on it, or you can heat up the brakes/hubs with lots of extra wear.

 

Overheated brakes could also end up being dangerous, fail. I suspect it's a very remote possibility, they're over-engineered, but who knows. That's ultimately what this is about; doesn't get mentioned much.

 

What's ACC ?

 

How long, how steep? I'm accustomed to a 7% grade for 7 miles, and have run many others like it. Once you get down to very roughly 4% at interstate speeds, the problem goes away.

 

Bottom line: IF conditions require braking for a "sustained" time, say more than a 2~3 minutes, then B is warranted.

 

I have never overheat breaks unless I'm on racing track....
Normal use of breaks to slow down 10 MPH below posted limit and then let it speed up again...


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