I'm wondering if it is possible to turn off "engine braking" on the T8. That is, the slight deceleration when you take your foot off the gas pedal.

I'd rather just get regeneration from regen braking, when I actually press the brake pedal. And purely coast at other times.

Is this possible?

Keep the gear selector in “ D” while driving forward and keep it out of “B”.

“D” is free-rolling. However, if you have ACC on and active, ACC will do whatever it needs to do maintain minimum time-distance and max speed.


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Even in "D", I do notice that the recharge line drops below "9 o'clock". So it appears to me that there is some very mild "engine braking" going on. What I'm hoping I can do is turn that off completely, so that it stays at the 9 o'clock position.

The only time I see that there is no "engine braking" is:

1. when coasting in Pure mode over 70 km/h (44mph?).
2. when coasting in Neutral

I don't drive in "B". I don't see the benefit of that. What I'm looking to do is the exact opposite of "B". Turn off all braking and regen, except when I press the brake myself.

 

^ Fair enough. I am not aware of any documented methods to be 100% free wheel and absolute zero re-gen.

Edit: Could the indicator just reflect negligible friction loss rather than reg-gen? The FAQ regarding "B" gear says:

What is the B gear?

With your T8, you have the ability to drive in "D" gear or "B" gear. When you drive in the traditional Drive gear your vehicle works as it would with a traditional engine and only regenerates battery power when applying the brakes. When you drive your T8 in Braking or "B" gear, this harnesses the power of the engine braking (when the engine slows its speed without pressing the brake) which allows the battery to feed off of the extra energy produced when you take your foot off the brake. The most energy is recaptured when you are coasting downhill but you can drive in this mode anytime you drive your T8 to help regenerate your hybrid battery.

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^ Fair enough. I am not aware of any documented methods to be 100% free wheel and absolute zero re-gen.

Edit: Could the indicator just reflect negligible friction loss rather than reg-gen? The FAQ regarding "B" gear says:



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Thanks for the great info.

That could be the case, but in my (albeit few and anecdotal) trials of coasting in D and coasting in N, there is a noticeable slow down in D that isn't there in N. Don't get me wrong, there is some slow down in N (wheel friction and wind resistance), but not as much as D.

 

BTW, @TheWhiteWhale posted some interesting technical information on the XC90 systems which could be, in part, relevant for the SPA 60's models. There is an article on braking here: Brakes.pdf

Maybe there is an article on re-gen and hybrid system hiding amongst us online.

 

First of all, I don't know how you could do that, but I'm not a T8 owner, so I'm not the best person to answer.

Secondly, I'm not sure why you'd want to do that. The whole idea of hybridization is to "harvest" kinetic energy (the energy of the vehicle in motion) and convert it into electrical energy that can be stored for later use. The ONLY way to do this is to use the motors as generators to convert the kinetic energy to electrical energy DURING DECELERATION.

Deceleration occurs when you use the brakes, of course, but also during periods of off-throttle operation. The software engineers make the assumption that when you lift your foot off the accelerator pedal, it means you want to decelerate. A pretty good assumption, I'd say! Thus, off-throttle coasting is an opportunity to regen, and to be most efficient, every opportunity to regen must be taken.

In fact, the holy grail of regen is "one pedal driving" where the coasting regen is so strong that you rarely have to use the brakes. The regen slows the car strongly, even to a full stop. Most hybrids or EVs are not quite capable of this, but it's coming. In many hybrids and EVs the regen power is adjustable.

 

First of all, I don't know how you could do that, but I'm not a T8 owner, so I'm not the best person to answer.

Secondly, I'm not sure why you'd want to do that. The whole idea of hybridization is to "harvest" kinetic energy (the energy of the vehicle in motion) and convert it into electrical energy that can be stored for later use. The ONLY way to do this is to use the motors as generators to convert the kinetic energy to electrical energy DURING DECELERATION.

Deceleration occurs when you use the brakes, of course, but also during periods of off-throttle operation. The software engineers make the assumption that when you lift your foot off the accelerator pedal, it means you want to decelerate. A pretty good assumption, I'd say! Thus, off-throttle coasting is an opportunity to regen, and to be most efficient, every opportunity to regen must be taken.

In fact, the holy grail of regen is "one pedal driving" where the coasting regen is so strong that you rarely have to use the brakes. The regen slows the car strongly, even to a full stop. Most hybrids or EVs are not quite capable of this, but it's coming. In many hybrids and EVs the regen power is adjustable.

I do love regen braking! Convert all that kinetic energy, and save your brakes while you're at it.

But I'm not sure if you should do it all the time though, as not 100% of the energy is converted.

Probably not a big concern for cars with larger batteries, but because of the relatively smaller battery in the T8, it would make sense to not needlessly convert that kinetic energy.

And maybe it's just me, but I don't quite get the fascination with one-pedal driving. It's cool, but not really energy efficient. Plus I like to take my foot off the accelerator sometimes and just coast, especially on long drives.

My holy grail for EV (and hybrid) is how to maximize electric range.

 

I agree that I think intelligently switching between D and B is the most efficient form of driving because coasting is always going to be more efficient then needlessly lowering your speed on e.g., the highway.

I think in this case you're trying to squeeze blood out of a stone, though. If the car is regenerative braking in D when you release the accelerator, it must be extremely light because I don't think I've ever noticed it. It makes me wonder if this is more complex e.g., it only happens when the battery is empty and it's trying to maintain minimum charge for eAWD or something. I wouldn't think too hard on this particular issue but in general agree that one-pedal driving is probably less efficient in some circumstances.

 

Haha, yeah "blood out of a stone".

Maybe it's just me. But while coasting, my regen meter is never at 9 o'clock. It's always a little below that, say 8:45. A little lower than horizontal. Does that not mean it's applying a very (maybe very, very) mild regen braking?

 

"Pure" mode has zero regen until you touch the brakes, only way to do the top post's ask that I'm aware of.

 

I think I've experience that in Pure mode, going 70+ km/hr (45 mph). Where the regen indicator is horizontal (9 o'clock).

But I think when I'm going, say 40 km/hr, it will dip a little below 9 o'clock.

I'll double-check though.

 

There is a saying that applies equally to driving a race car and hybrid regen...

Brakes are like lawyers, every time you use them, you gotta pay.

Heavy coasting regen/one-pedal driving minimizes friction brake use and thus is the most efficient. I can't think of a scenario where it wouldn't be.

That said, I'm not sure how Volvo handles braking regen. They probably do blended braking, where there is a combination of regen braking and friction braking going on when you apply the foot brake.

 

There is a saying that applies equally to driving a race car and hybrid regen...

Brakes are like lawyers, every time you use them, you gotta pay.

Heavy coasting regen/one-pedal driving minimizes friction brake use and thus is the most efficient. I can't think of a scenario where it wouldn't be.

That said, I'm not sure how Volvo handles braking regen. They probably do blended braking, where there is a combination of regen braking and friction braking going on when you apply the foot brake.

My understanding is when the brakes are pressed lightly, it will do some regen braking, until the cars get below 5 km/h, or is that 5 mph. Some low speed. In which case the physical brakes kick in.

The physical brakes will also kick in if the brakes a pressed firmly. As regen braking cannot slow you down as quickly as physical braking.

While I agree that regen braking is better than friction braking, when you actually want to slow down. I would rather it not kick in just because I'm not accelerating.

 

I think one source of confusion here is our good friends over at Tesla and the language/expectations they cause, because they do not have a blended braking system. Touching the brake peddle on a Tesla means loss of efficiency, period. That's why they are generally set up with super-high regen, and you learn to feather the throttle to 'coast' if you want to as you one-peddle-drive.

Volvo's brakes are blended. There's zero difference between decelerating moderately with the brake peddle and with putting her into B mode, it's the same thing, so people asking for "B" mode for more regen to be as efficient as Tesla aren't understanding this difference. Hybrid mode has a tiny bit of throttle-off regen to feel more like a traditional ICE, while Pure will free wheel it at most speeds (I think 2021XC60T8 above is right, it's mostly at mid to higher speeds that this happens).

 

Volvo's brakes are blended. There's zero difference between decelerating moderately with the brake peddle and with putting her into B mode, it's the same thing

Are you sure of this? If I'm in B and I let off the gas, the electric motor regenerates and the front brakes do not actuate. If I'm in D and I hit the brake pedal lightly, are you sure the front brakes are not doing anything? I've noticed my rotors are sometimes hot even when being very careful not to send the braking indicator into the orange zone where it indicates mechanical brakes.

 

I don't know if we'll ever know the details of Volvo's regen blended braking strategy, but here's a generic example...

Note that "Hydraulic braking on non-driving wheels" starts ramping up from the moment you first touch the brake pedal. This means that in this example some kinetic energy is being lost to friction every time you step on the brake, no matter how lightly.

Blending like this is done to provide a normal, natural feel to the brakes. It's a way of managing the hand-off between regen braking and "hydraulic" braking. The engineers that that are charged with extracting the highest possible efficiency from the system are motivated to minimize the use of hydraulic brakes and seek to maximize regen braking. This has been the source of many well-documented driveability complaints.

I'm sure there were a lot of good conference-room arguments around this topic.

 

Is the chart covering up part of the text for you guys? It is on my screen, but not when I Preview the post.

 

Chart displays fine and is clear
That's what I would hope because it reduces front brake but I've not seen anything that clearly explains what it's doing. I agree... The engineering discussions would have been interesting.

 

The engineering discussions would have been interesting.

A bit off topic, but the discussions regarding autonomous driving are even more interesting. Imagine you are a 25 year old software coder and you need to decide what a vehicle does in emergency situations...

https://en.wikipedia.org/wiki/Trolley_problem

It has life-and-death implications.