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The hills I refer to are long, maybe 2 miles long and quite steep.

Not sure about the car automatically engaging B mode as that has never happened to me. But it does the equivalent of B mode in that it will rev the engine like crazy to get ride of the charge. I've also had it where the regen has switched off when the Battery was super full. That was scary - you'd be surprised how much braking force comes from the regen!

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The hills I refer to are long, maybe 2 miles long and quite steep.

Not sure about the car automatically engaging B mode as that has never happened to me. But it does the equivalent of B mode in that it will rev the engine like crazy to get ride of the charge. I've also had it where the regen has switched off when the battery was super full. That was scary - you'd be surprised how much braking force comes from the regen!

The "does the equivalent of B mode" is what I took johalareewi to mean by automatically engaging B mode.

I haven't had the regen switch off on me so far, but have always thought the regen braking force to be significant, hence my original comment back to Timberwolf re brake pad wear.

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On a very long hill, B mode saves the friction brake pads (the pads are thinner than on an ordinary car). Once the HV (High Voltage) battery is full, ...

It would have to be quite a steep hill for the friction brakes to come into effect and a veeeerrrryyyy long decline to fill the HV Battery to 8 full bars.

Personally, I've only seen it once where I was able to completely fill the HV Battery. And it was a very long descent out of some mountains in Germany.

When the drive presses the brake pedal, the Hybrid braking system determines whether to use regenerative or friction? Is it that simple, or can the system use both regenerative and friction?

Ignoring the question above, under what circumstances can the Hybrid braking system use the friction brakes? I can think of three situations.

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That's a tin of worms. Someone on the Priuschat forum had analised it and came up with a graph. The regen is on all the time to varying amounts depending on many factors if I recall. Only below 7 mph does the car use friction only. Or when the HV Battery is totally and utterly full.

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That's the two I was thinking of. Friction brakes are also used when you need to stop quickly. There are probably more, such as when the wheels slip under regenerative braking?

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I was told once by a Toyota Head Office technician that the brakes are very slightly applied any time the brake pedal is pressed, even when almost all the braking is regenerative - this is to make sure they are warmed up and dry in case they are needed (and helps to avoid discs rusting).

Also, they cut in under very heavy braking, if the ABS is invoked (that's what the Gen 3 alleged braking issue was all about), and if (as GC says) the HV Battery is completely full (not just 8 bars showing).

Gen 1 and 2 switch to normal brakes below 7 mph, but the Gen 3 and equivalents seem to have some regen below this speed.

The other time normal brakes only are used is if N is selected whilst moving, sometimes useful to give the discs a clean (having taken due safety precautions, of course!).

BTW: I've never had a totally full Battery on a Gen 2 or 3, but my last Gen 1 took about 4 miles down a 20% gradient in Scotland to get that full, and was very interesting to drive for a little while when the bottom was reached some two miles later!

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That's the two I was thinking of. Friction brakes are also used when you need to stop quickly. There are probably more, such as when the wheels slip under regenerative braking?

Wasn't that what the whole problem was about. When the wheels slipped the regen immediately switched off leaving only very light friction brakes. They keep adjusting it and now it's much more balanced.

At least the Euro versions of the Prius have stronger brakes in that they have more 'bite'. The US versions have harder discs and pads and thus don't wear out as quickly, but at the expense of brake feel.

I'd rather have the Euro version.

Oh and the Emergency Brake Assist thingy works very well. Very well indeed :) You couldn't brake that hard on your own if you tried.

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The problem as I recall was the "let go"/floaty feel after the regeneration was switched off and before the friction brakes took over.

It is also a feature on the Gen 2 but there wasn't a recall.

At the time, it was difficult to work out if the feature was worse on the Gen 3. It didn't help that the media was on a witch hunt.

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Well, that is interesting. I've driven those roads in Brighton and while I can't claim to have driven every road, I never came across any descent that would completely fill my HV battery--they are just not long enough. Sure it certainly got in the green and even 8 bars, but the HSD never automatically engaged B mode. I wouldn't expect it to either, as most of those hills are tiny really-- the height differential, I'm guessing, no more than 250 ft.

The ones I use a lot come down off the A27 from Hollingdean, and from the racecourse through Whitheawk. They are not long (a mile or so) but drop quite quickly and you have to go down slowly to keep under the speed limit. Coming off of the A27, the HV Battery is often at 6 or 7 bars and without B mode, hits 8 bars way before I reach the bottom and can max out.

But with yours and GC's comments, I'm wondering whether the Gen III pumps more energy back into the HV than the Gen II does? I have read that there is a more definite regen braking on the Gen III compared to the Gen II, so maybe it does.

Pretty sure this is correct. The gen3 can regen at slower speeds than the gen2 for sure.
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And doesn't full regen when going down such a hill pump out tens of kw? If you could brake down an infinitely long hill and hook up the car to the grid you could power half your street. Or something like that.

The technicals of the Prius are truely marvelous. Someone very switched on designed it.

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And doesn't full regen when going down such a hill pump out tens of kw? If you could brake down an infinitely long hill and hook up the car to the grid you could power half your street. Or something like that.

The technicals of the Prius are truely marvelous. Someone very switched on designed it.

I think you're probably correct with the Tens of KW. My Pip recharges at about 2.2kw from the grid, 30 min gets 5 miles on the EV range, however slowing from 70mph-0 over half a mile can get me anything from 0.5-1 miles depending if down hill etc, so its a fair wack its putting back into the Battery on regen braking.

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And if I recall the li-ion of the PIP can't handle as much regen going into it as the NiMh of the traditional Prius. So imagine what the NiMh is having to absorb in such a short amount of time. No wonder it gets hot!?!

Just looked it up. The max regen on the Prius is 20kw! (a kettle is about 2.5 kw!)

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And if I recall the li-ion of the PIP can't handle as much regen going into it as the NiMh of the traditional Prius. So imagine what the NiMh is having to absorb in such a short amount of time. No wonder it gets hot!?!

Just looked it up. The max regen on the Prius is 20kw! (a kettle is about 2.5 kw!)

It's the other way around GC, the PiP accepts charger faster / better than the conventional Prius with their NiMh cells, which means they also return (according to what I've seen online) better MPG in HV mode than the standard Prius.

Like you say 20kw though is one hell of a charge rate. By my calculations with that 10 min at full regen will give the PiP a full Battery charge. Which doesn't sound impossible, I've seen a good mile gained before now on max regen from high speeds to a stop. I'm going from the East Coast to Sussex tomorrow for a long weekend, and am looking forward to seeing how well the regenerative brakes work and recharge the Battery on some decent hills (something we lack here in East Anglia).

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Well my old non plug in Prius will drive for over a mile as a pure electric car for upto 40 mph after a run down my nearest long hill. It was a strange feeling. The car would get to the bottom of the hill with 8/8 bars and the engine revving off the charge. I'd set off down the road and the car would accelerate faster and even into the Power band on electric only - like EV mode and then some.

The car would move along quickly and very quietly but as the Battery was losing the charge (still at 8/8 bars though) it would switch the engine on if you entered the Power but quickly switch it off when out of it. After half a mile the car was still at 8/8 bars and would drive like EV mode at 40 mph. After a mile (from the bottom of the hill) or just over the first capacity bar would drop to 7/8 and the car was then reacting as normal.

But it was always an interesting experience and shows how well programmed the Prius is and gives a little taste of what you PIP owners get :)

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  • 2 weeks later...

Congratulations on your new car, sounds like you are getting good mileage already.

Be happy with 45mpg in town on short stop start, it's very decent especially as your old car got mpg in the teens. I have another car that gets 12mpg on short journeys.

Drive it normally with some minor adjustments and you will be looking at a nice further boost in mpg.

Do not drive it slow. Get up to speed as quick as possible without over fuelling. Don't be scared to use the pwr band if needed. I use it especially for higher speeds but try not to exceed past the end unless you are joining the m way etc.

Keep speed steady, try not to vary the speed as slight accelerations interrupt the good efficiency.

Then the only adjustment you need to make to your driving style really is the slowing down bit. The prius is pretty aerodynamic and providing the speed is under about 50mph, it will glide for quite some time on the flat and especially downhill.

People practice this imagining they haven't got brakes "driving without brakes". You can do this and not annoy anyone as it looses speed very slowly (unless wind resistance hits and you are doing more than 50mph). You can even begin earlier by slightly reducing the throttle and bleed off tiny amounts of speed before you begin slowing down. As I get up to speed quick, I usually overshoot the posted limit but usually only by enough to keep me roughly within the 10%+2 gps true speed rule. If that makes sense.

All you have to remember is check the hsi indicator and make sure you apply just enough throttle to make the indicator disappear or stay in the first quarter. Don't let it go into regen as the extra drag this creates slows you down more and is only useful downhill.

I gradually got better mileage as I got used to it. Ironically I am now a faster driver and use ev less. It's true what they say, do not force ev. Just let it happen, by all means hang on to it but don't exhaust the Battery extra fast by trying to stay under the middle line going up hill. Just use it when you can stay under about half way on the Eco zone of hsi. With tyres pumped up correctly you will roll/glide for ages on minimal Battery at less than 40mph on good flat road.

I seem to have no issues getting tank averages in the 67-71mpg range. It's incredible to get over 550miles on £48 of petrol. And I repeat you don't have to drive slow either! The only time mpg suffers is motorway. My routes don't include it. Wind resistance is unavoidable. However most motorway trips finish up at at least 64mpg provided there is some normal driving each end.

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