Recharging w/ gear selctor in "B" enging braking mode

T8INVA · Dec 21, 2015

Recharging w/ gear selector in "B" engine braking modett

I believe i read somewhere that in save mode the car will only charge itself up to 50%.......I have a long steep grade hill near my house, and i am wondering if i leave fully charged and reach the hill with 95% charge remaining, will the car charge back to 100% if i put the gear selector in "B" engine braking mode, or is it similarly governed to 50%?

T8INVA · Dec 21, 2015

Anyone know the answer to this?

Conradi · Dec 21, 2015

Recharging w/ gear selctor in "B" enging braking mode

The number of T8 owners is still limited.

I'm aware about the 50% - I thought it's valid while charing by the petrol engine - but that's not stated in the manual. The same is valid for B.
Unfortunately I live in a allmost flat country, so regenerating is limited to roll-out for traffic lights ;-)

T8INVA · Dec 21, 2015

Thanks for the reply Conradi, are you able to tell if you are recharging on roll out to traffic lights when you are already above 50% charge?

Conradi · Dec 21, 2015

Yes, definately. Just from my VOC log book: 12 km ride, started with full bateries using 2.9 kWh energy and regenerating 1.0 kWh. So it always regenerates ;-)

T8INVA · Dec 21, 2015

Great, thanks for the verification, much appreciated!

GrecianVolvo · Dec 22, 2015

T8INVA said:
Anyone know the answer to this?

Without plugging it in, the battery will charge up to a maximum 46% of its capacity.

T8INVA · Dec 22, 2015

GrecianVolvo said:
Without plugging it in, the battery will charge up to a maximum 46% of its capacity.

So you are saying if the battery is charged above 47%, engine braking will not charge the battery? This is different than what conradi states above from his real world experience. I understand that in save mode, the ICE engine will not charge above that level, but would make sense that you can recapture energy using the engine brake at any charge level.

acb · Dec 22, 2015

In my D6 which I am sure will be the same from what I have seen the battery does recharge under braking whatever level the battery is at. I have a similar hill near me so I use battery to start the journey and when I reach the bottom of the hill the battery is almost back up to full. The 46% limit is only when using the engine to re-charge. You can also tell from the VOC app as it states how much charge you have added. I drive in save mode quite a lot as on longer journeys I need to save charge and when the battery is above 50% you can see the battery level increase not by much but noticeable from braking and free wheeling.

Conradi · Dec 22, 2015

That's correct, my T8 reacts exactly the same as described above already.

Gary-16-Xc90 · Feb 28, 2016

Is it appropriate to in B all of the time to maximize regeneration (e.g., whenever coasting, light braking)? Another poster on Green Car Reports believes that the B on the Volvo is for engine braking. I know that it does that, but is counter production fuel economy wise to leave the gear selector in B all of the time? I am looking for both a better understanding (from what the manual describes) and some practical guidance.

See the article and comments for context: http://www.greencarreports.com/news...02337_2016-volvo-xc90-t8-plug-in-hybrid-an-owners-first-21-days#image=100546929

Thanks in advance.

ntt.ntt · Feb 28, 2016

Here is what the manual says:

Code:

Brake – B
B can be selected at any time during a drive. In this mode, the engine braking function is activated when the accelerator pedal is released, which helps charge the hybrid battery. This means that the hybrid battery is charged even if the brake pedal is not depressed.
 
B mode in the instrument panel
With B selected, manual shifting to lower gears is possible. The gear indicator in the instrument panel shows the gear currently being used (1–8).
Each time the gear selector is pulled rearward, the transmission will shift down one gear.
In order to manually shift to higher gears, the vehicle must be equipped with steering wheel paddles.
Press the gear selector forward to return to D mode.
For smooth shifting and engine performance, the transmission will shift down automatically if the vehicle's speed becomes too low for the selected gear.

GrecianVolvo · Feb 28, 2016

Gary-16-Xc90 said:
Is it appropriate to in B all of the time to maximize regeneration (e.g., whenever coasting, light braking)? Another poster on Green Car Reports believes that the B on the Volvo is for engine braking. I know that it does that, but is counter production fuel economy wise to leave the gear selector in B all of the time? I am looking for both a better understanding (from what the manual describes) and some practical guidance.

See the article and comments for context: http://www.greencarreports.com/news...02337_2016-volvo-xc90-t8-plug-in-hybrid-an-owners-first-21-days#image=100546929

Thanks in advance.

I would not use B all the time. Yes, it can recharge the battery with engine braking but it will also reduce drastically the coasting distance when lifting off; something that most people are not used to.

Gary-16-Xc90 · Feb 28, 2016

Thanks! I had read that, too. It does not tell me if there is any similar regeneration in D. I assume that there is not. Is everyone driving in B with your T8? Is the fuel economy adversely affected when in B say with normal deceleration?

ntt.ntt · Feb 28, 2016

I would guess it decreases fuel economy. It essentially engages regenerative braking as soon as you lift throttle which would mean you don't get the economy benefit of coasting. Normally you only regenerate the battery when braking gently.

Gary-16-Xc90 · Feb 28, 2016

Thanks ntt.ntt and GrecianVolvo. That's what I needed to know. It sounds like I would only use B temporarily when I want engine braking such as going down steep hills and on snow and ice. Recharging the battery is a side benefit but it is a trade off because it can adversely impact fuel economy if used all of the time on a typical drive. Does that sound right? Thanks!

rpmccormick · Feb 28, 2016

For my every day use (mostly commuting) I stay off the Interstate highways and use the Pure mode and in B (versus D). I've gotten pretty good at knowing when to just let-off the accelerator and use the drag (either coming to a stop, going downhill or approaching a corner) to do regen. I'm typically seeing between 1 to 2 kWh of regen in a 17 mile +/- 7.5 kWh consumption (max battery range) ... and in an aprox 10 mile commute I use +/- 4.5 kWh and regen 0.4 to 0.5 kWh.

Indeed in D mode the car won't slow down as fast (it becomes a rolls can hardly: rolls really good downhill but can hardly make it up the other side, well, not really

) as it coasts farther. But in doing some experimentation with this - doesn't really save me any time and whatever power the car generates that is power that doesn't have to be supplied by the electric company.

For me - when I use the D mode I can go a week without starting the engine as I charge at home and at work. If I don't use the D mode there are times when the battery may have a low enough charge that the engine kicks on - so for my specific scenario, I believe that D mode improves fuel economy. But I think the important thing is YMMV - every driving scenario may differ (especially if you're trying to really push the limits).

The Save mode seems to really put a noticeable charge back into the battery (as in I can watch the battery charge meter climb while driving) - but if you have an empty battery, running the vehicle in Save mode will only fill it up to 33%. That's frustrating - as I have plenty of scenarios where I may drive an hour or two on high-speed roads ... and then have another 10 to 20 miles of roads that would be great for the EV capabilities. OTOH - if you start out with a full battery and put it in save ...

I can't say that the typical breaking / deceleration regen has ever netted out positive; that is ... the vehicle in either Pure or Hybrid mode seems to always consume more power than I've ever been able to generate with D selected.

I wish Volvo would release more details for owners who would really like to understand the logic to the whole PHEV system.

Zaxxon · Feb 28, 2016

Keep in mind that regenerating battery should not be your overriding goal. (Unless you're aiming to charge the battery for later use in a congestion charge area or something.)

Each time energy is placed in the battery (or taken out), there's a loss incurred. Apologies if I'm stating the obvious here, but as a longtime Prius driver I've found that many people mistakenly think of the battery as a magical efficiency-improving device at first.

Base your desire to regen on what it's replacing: regenerating when coming to a stop is much better than the 100% energy loss incurred when friction braking (to take an extreme example). Regenerating when coasting is not beneficial unless you're going to coast to a stop or you're going downhill and are directing energy into the battery rather than letting yourself accelerate to an undesirable speed. Otherwise, if efficiency is your goal, your target should generally be to coast with as little speed loss as possible so as to displace the need to slow down only to speed up again.

Gary-16-Xc90 · Feb 28, 2016

The use of D v B gear selection is becoming a bit clearer to me. I will use D for normal driving and use B temporarily for exceptional circumstances, subject to rpmccormick's refined techniques.

Yesterday, I only drove in D for 100+ miles and I confirmed that I gained some significant regeneration and that my rollout without power was noticeably longer. After more thoroughly reading multiple parts of the manual, I understand that this was due to "light braking" and "to some extent" when ICE is running.

I understand now that the Gear selection "B" comes into play only when your foot "lifts off of the accelerator". I missed that detail.

At pp. 391-392 of the US owner's manual (PDF) where Drive modes are explained there is no reference to gear selection D or B. One could infer that regeneration is occurring in Hybrid, Pure and Save, but it would be clearer if the relationship to the gear selector position and regeneration were explicitly explained here.

The manual does say under hybrid that "The [instrument panel] gauge also indicates when the battery is being recharged (regenerated) during light braking. See article "Brakes" for additional information." On page 20, this article the manual states that "When the brakes are applied lightly, the electric motor is used for engine braking during which the vehicle's kinetic energy is converted into electric current that is used to help recharge the battery." So here, I believe the reference is to the electric motor in the rear - not the generator in front. The manual goes onto state that "The hybrid battery is also recharged to a certain extent when the gasoline engine is in operation." This last statement could use more a bit more explanation.

Most of MN is relatively flat (compared to mountain states - stating what might be obvious for some). On snow-pack and ice, my plan is to shift into B for safety and better control prior to "lifting off of the accelerator" in order to slow down without touching the brakes. If I find myself going down a steep hill (like in Duluth or Buck Hill

), then I will use B. Finally, I understand that ACC, City Safety, et al will use engine braking when needed regardless of the gear selection.

Hope I have it right now. Thanks for all of the insights.

Mellow Guy · Feb 28, 2016

I use B gear when going down hills or mountains because it eliminates some of the need to brake.
After a full charge, I use Pure mode to use up the charge (I don't see much difference from Hybrid).
I think that AWD mode would work best in nasty weather.

I agree with the previous poster that Volvo should tell us more about the logic of the different modes and B gear.

Recharging w/ gear selctor in "B" enging braking mode

T8INVA

T8INVA

Conradi

T8INVA

Conradi

T8INVA

GrecianVolvo

T8INVA

acb

Conradi

Gary-16-Xc90

ntt.ntt

GrecianVolvo

Gary-16-Xc90

ntt.ntt

Gary-16-Xc90

rpmccormick

Zaxxon

Gary-16-Xc90

Mellow Guy

Top Contributors this Month

Recommended Communities