Why does my 08 Prius use regenerative braking, even when the brake is not pressed ?

pbsriniv · 12-04-2007, 04:37 PM

hi !

I have a 08' prius.. I just noticed that on when I take the foot off the gas, the regenerative braking immediately starts, and I can see the battery charge, in the "power flow" display. When going downhill, I can put the Car into 'N' from 'D' and I can immediately feel the difference of not having the regenerative breaking.

my Highway commute mostly consists of gentle ups and downs' and I would like the car to ideally coast downhill, and engage the ICE only on the uphill.. But it doesn't work this way mainly because of the regenerative breaking, and I end up loosing mpg's as I have to use the gas pedal downhill too..

Does anyone have a way to get around this, other than using 'N' ? Also do other other prius's (07 and earlier) behave identically ?

TIA

qbee42 · 12-04-2007, 04:45 PM

It does this to make the car handle in a way consistent with ordinary cars. The slight regen action simulates engine drag. To avoid this, slightly feather the accelerator peddle.

Tom

David Beale · 12-04-2007, 05:02 PM

The Toyota engineers have built in several things to make us more comfortable with the car. To make it feel like a "normal" automatic transmission equipped car.
1. Simulated engine drag when coasting. As stated above, just feather the accelerator pedal a bit to shut this off. This takes practice.
2. Transmission "creep" when you release the brake pedal when stopped.
There's a third one but I can't think of it right now. It'll come to me the minute I log off.

pbsriniv · 12-05-2007, 12:19 AM

Thanks for the reply..

"Feathering" the throttle is pretty tough.. Seems to me by making this a feature, there is a substantial drop in mpg's, especially on S.California freeways..

Have been experimenting on downslopes, by waiting for the mpg to hit a 100, and then moving into "N" mode.. I am now consistently averaging well over 50 on freeway drives. whereas earlier I used to get less than 50 mpgs.. Will keep the group posted if I see a big jump in mpg's by the end of my next fill up.

Another funny thing, I noticed on a steep downslope, if I put it into "N" mode, and then back to "D", the regenerative breaking doesn't come on..

F8L · 12-05-2007, 12:53 AM

Like stated above, your best bet is to learn how to lightly apply the gas pedal to kick the system out of regen mode. There are write-ups on how to do this. Maybe do a search for "warp stealth". When traveling downhill or approaching off-ramps this technique is very handy.

You will need to learn how to work with the gas pedal anyway to get maximum milage so you might as well practice now.

Here are some links for ya.

Coasting in neutral

patsparks · 12-05-2007, 01:41 AM

If you drive at freeway speeds in neutral you can damage the smaller of the 2 electric motors in your transmission because having the Prius in neutral isn't really neutral but it just cuts electricity flow in the hybrid synergy drive (HSD) transmission. At higher speeds the HSD causes the petrol engine (ICE) to spin over, if this isn't allowed to happen the smaller electric motor (MG1) can overspeed possibly causing damage.

The best way to prevent the over-run regenerative braking is to feather the throttle, easy once practiced and after all when your driving what else do you have to do?

qbee42 · 12-05-2007, 09:20 AM

Quote:

Originally Posted by pbsriniv

Thanks for the reply..

"Feathering" the throttle is pretty tough.. Seems to me by making this a feature, there is a substantial drop in mpg's, especially on S.California freeways..

At freeway speeds there shouldn't be much braking, unless it's stop and go, in which case it's not really freeway speed. Once you get going fast power is required to overcome aerodynamic drag, so there is almost always some draw from the ICE or battery. That should require you to adjust how much power is supplied, but seldom come off the gas enough to cause regen.

I suspect what you are trying to learn are the same high-mileage techniques used in any car: try to keep a steady speed, avoid slowing down, anticipate, accelerate briskly to speed, etc. In that respect, there is nothing unusual about driving a Prius, except for the constant feedback from the MFD.

Tom

narf · 12-05-2007, 10:13 AM

Quote:

Originally Posted by patsparks

If you drive at freeway speeds in neutral you can damage the smaller of the 2 electric motors in your transmission because having the Prius in neutral isn't really neutral but it just cuts electricity flow in the hybrid synergy drive (HSD) transmission. At higher speeds the HSD causes the petrol engine (ICE) to spin over, if this isn't allowed to happen the smaller electric motor (MG1) can overspeed possibly causing damage.

Really? I'd like to see some documentation of that. I can't believe that Toyota engineers would engineer in an operating mode in the Prius that would damage the HSD just by pushing a button. I think it's much more likely that neutral just disables engine braking and motor drive, but doesn't prevent MG2 from spinning so that MG1 won't overspeed.
I've got 55,000 miles on my car and I've been coasting down hills at high speeds in neutral whenever I have the chance. No problems yet.

**efusco** · 12-05-2007, 10:19 AM

Quote:

Originally Posted by narf

Really? I'd like to see some documentation of that. I can't believe that Toyota engineers would engineer in an operating mode in the Prius that would damage the HSD just by pushing a button. I think it's much more likely that neutral just disables engine braking and motor drive, but doesn't prevent MG2 from spinning so that MG1 won't overspeed.
I've got 55,000 miles on my car and I've been coasting down hills at high speeds in neutral whenever I have the chance. No problems yet.

Here's the deal...if you go into neutral with the ICE off (ie under 41mph you go into stealth then drop into neutral) then coast down a long steep hill in neutral and then exceed 62mph you'll exceed the 10,000 rpm max. speed of MG1. Presumably doing so will damage/destroy MG1.

If you go into neutral with the ICE turning it will continue to run...since it's running it will prevent MG1 from over spinning at any speed. The engineers did do a lot to prevent us from damaging the car...but you can always build a better moron!

narf · 12-05-2007, 11:30 AM

Quote:

Originally Posted by efusco

Here's the deal...if you go into neutral with the ICE off (ie under 41mph you go into stealth then drop into neutral) then coast down a long steep hill in neutral and then exceed 62mph you'll exceed the 10,000 rpm max. speed of MG1. Presumably doing so will damage/destroy MG1.

If you go into neutral with the ICE turning it will continue to run...since it's running it will prevent MG1 from over spinning at any speed. The engineers did do a lot to prevent us from damaging the car...but you can always build a better moron!

Again, where do you get this information from?

12-04-2007, 04:37 PM	#1
pbsriniv Junior Member Join Date: Oct 2007 Location: San Diego, CA Posts: 5 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	Why does my 08 Prius use regenerative braking, even when the brake is not pressed ? hi ! I have a 08' prius.. I just noticed that on when I take the foot off the gas, the regenerative braking immediately starts, and I can see the battery charge, in the "power flow" display. When going downhill, I can put the Car into 'N' from 'D' and I can immediately feel the difference of not having the regenerative breaking. my Highway commute mostly consists of gentle ups and downs' and I would like the car to ideally coast downhill, and engage the ICE only on the uphill.. But it doesn't work this way mainly because of the regenerative breaking, and I end up loosing mpg's as I have to use the gas pedal downhill too.. Does anyone have a way to get around this, other than using 'N' ? Also do other other prius's (07 and earlier) behave identically ? TIA

12-05-2007, 12:53 AM	#5
F8L Collecting Data on Nature Join Date: Aug 2006 Location: Sacramento, CA. Posts: 3,989 My Car: 2005 Prius Package: #4 Nominated 1 Time in 1 Post TOTM Awards: 0 Friends: 15	Like stated above, your best bet is to learn how to lightly apply the gas pedal to kick the system out of regen mode. There are write-ups on how to do this. Maybe do a search for "warp stealth". When traveling downhill or approaching off-ramps this technique is very handy. You will need to learn how to work with the gas pedal anyway to get maximum milage so you might as well practice now. Here are some links for ya. Coasting in neutral Last edited by F8L; 12-05-2007 at 12:59 AM.

12-05-2007, 01:41 AM	#6
patsparks Uneducated bird-brain Aussie Join Date: Jul 2007 Location: Adelaide South Australia Posts: 4,438 My Car: 2004 Prius Package: Base Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 12	If you drive at freeway speeds in neutral you can damage the smaller of the 2 electric motors in your transmission because having the Prius in neutral isn't really neutral but it just cuts electricity flow in the hybrid synergy drive (HSD) transmission. At higher speeds the HSD causes the petrol engine (ICE) to spin over, if this isn't allowed to happen the smaller electric motor (MG1) can overspeed possibly causing damage. The best way to prevent the over-run regenerative braking is to feather the throttle, easy once practiced and after all when your driving what else do you have to do? __________________ All the warranty I need. And for thrills -> Still averaging 4.4L/100km across town 2004 silver base model Prius Shark fin, genuine mudflaps, colour matched side mouldings, rear bumper scuff guard, sheepskin seats, BT Plate. I love it! Last edited by patsparks; 12-05-2007 at 02:32 PM. Reason: missing letter

12-04-2007, 04:45 PM	#2
qbee42 Senior Member Join Date: Mar 2006 Location: Northern Michigan Posts: 4,865 My Car: 2006 Prius Package: #7 Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 5	It does this to make the car handle in a way consistent with ordinary cars. The slight regen action simulates engine drag. To avoid this, slightly feather the accelerator peddle. Tom

12-04-2007, 05:02 PM	#3
David Beale Senior Member Join Date: Jul 2006 Location: Edmonton Alberta Posts: 1,343 My Car: 2007 Prius Package: B Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	The Toyota engineers have built in several things to make us more comfortable with the car. To make it feel like a "normal" automatic transmission equipped car. 1. Simulated engine drag when coasting. As stated above, just feather the accelerator pedal a bit to shut this off. This takes practice. 2. Transmission "creep" when you release the brake pedal when stopped. There's a third one but I can't think of it right now. It'll come to me the minute I log off.

12-05-2007, 12:19 AM	#4
pbsriniv Junior Member Join Date: Oct 2007 Location: San Diego, CA Posts: 5 My Car: Package: Nominated 0 Times in 0 Posts TOTM Awards: 0 Friends: 0	Thanks for the reply.. "Feathering" the throttle is pretty tough.. Seems to me by making this a feature, there is a substantial drop in mpg's, especially on S.California freeways.. Have been experimenting on downslopes, by waiting for the mpg to hit a 100, and then moving into "N" mode.. I am now consistently averaging well over 50 on freeway drives. whereas earlier I used to get less than 50 mpgs.. Will keep the group posted if I see a big jump in mpg's by the end of my next fill up. Another funny thing, I noticed on a steep downslope, if I put it into "N" mode, and then back to "D", the regenerative breaking doesn't come on..