2020 T8 Brake Mode - inconsistent behaviour
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    1. #1
      Junior Member Hawkmoon's Avatar
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      2020 T8 Brake Mode - inconsistent behaviour

      We just recently moved from a 2016 T8 to a 2020 T8 (lease was up on the '16) and I have found that when putting the transmission in Brake Mode "B" that the vehicle behaves inconsistent. Both my wife and I drove our '16 extensively and know how it should feel when in "B" mode.

      With the new 2020 in "B" mode, at times, there is no difference between "B" and "D". You can literally shift between the 2 modes and there is absolutely no change in behaviour. Typically speaking you should feel the vehicle slow down in "B" mode as it uses the kinetic energy to charge the battery. Living at the top of a hill, when in "B" mode we can drive 2- 3 km to get to the bottom and still have a full charge. We have found, at times, this doesn't happen and although in "B" the car behaves as though it is in "D". When we get to the bottom of the hill part of the battery is used (ie 1 or 2 km).

      I know the braking system is changed in the 2020 from our old 2016. I feel like it is a bug in the system. Of course I will take it in to have it looked at, but curious if anyone else with a 2020 T8 has experienced this behaviour?
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    3. #2
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      I'm nearing 3-weeks into my new XC60 T8, but I'm not coming to it from another Volvo, instead from a Tesla Model S (where motor braking and "driving by wire" was my normal modus operandi). I have not yet encountered the problem you describe, driving in "Hybrid Mode" and "B-gear" most of the time. I too live in a hilly area, and find "B" does what I expect -- a slight increase in braking/slow-down as I take my foot off the throttle, compared to if I'm in "D" in the exact same location and speed. Incremental regeneration is noticeable in “B-gear”, as long as my battery doesn't appear full on the IC. Of course, if I go into a different driving mode such as "Polestar Engineered" ("Power" if you don't have the P* Optimization), or go too fast, the ICE will kick-in and regeneration/electrical dynamics change.

      ...a thought, as it does not get cold enough here for me to have proved this to myself quite yet, but in my former Tesla, if it was too cold outside, by design it would absolutely NOT do regeneration of any sort until the battery warmed itself up (taking a few miles of travel, when I had not immediately trip-charged before taking-off.) Is temperature a potential consideration where you’re seeing differences in your case — E.g. do you find the same problem if you first precondition?

      Good luck on your investigation!
      Last edited by BertL; 01-18-2020 at 02:39 PM. Reason: ...a little better English!
      Bert

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    4. #3
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      Quote Originally Posted by Hawkmoon View Post
      We just recently moved from a 2016 T8 to a 2020 T8 (lease was up on the '16) and I have found that when putting the transmission in Brake Mode "B" that the vehicle behaves inconsistent. Both my wife and I drove our '16 extensively and know how it should feel when in "B" mode.

      With the new 2020 in "B" mode, at times, there is no difference between "B" and "D". You can literally shift between the 2 modes and there is absolutely no change in behaviour. Typically speaking you should feel the vehicle slow down in "B" mode as it uses the kinetic energy to charge the battery. Living at the top of a hill, when in "B" mode we can drive 2- 3 km to get to the bottom and still have a full charge. We have found, at times, this doesn't happen and although in "B" the car behaves as though it is in "D". When we get to the bottom of the hill part of the battery is used (ie 1 or 2 km).

      I know the braking system is changed in the 2020 from our old 2016. I feel like it is a bug in the system. Of course I will take it in to have it looked at, but curious if anyone else with a 2020 T8 has experienced this behaviour?
      I have 3 week old 2020 XC90 T8 and came from the same model in a 2017. I am not experiencing your issue...

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    6. #4
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      Quote Originally Posted by BertL View Post
      I'm nearing 3-weeks into my new XC60 T8, but I'm not coming to it from another Volvo, instead from a Tesla Model S (where motor braking and "driving by wire" was my normal modus operandi). I have not yet encountered the problem you describe, driving in "Hybrid Mode" and "B-gear" most of the time. I too live in a hilly area, and find "B" does what I expect -- a slight increase in braking/slow-down as I take my foot off the throttle, compared to if I'm in "D" in the exact same location and speed. Incremental regeneration is noticeable in “B-gear”, as long as my battery doesn't appear full on the IC. Of course, if I go into a different driving mode such as "Polestar Engineered" ("Power" if you don't have the P* Optimization), or go too fast, the ICE will kick-in and regeneration/electrical dynamics change.

      ...a thought, as it does not get cold enough here for me to have proved this to myself quite yet, but in my former Tesla, if it was too cold outside, by design it would absolutely NOT do regeneration of any sort until the battery warmed itself up (taking a few miles of travel, when I had not immediately trip-charged before taking-off.) Is temperature a potential consideration where you’re seeing differences in your case — E.g. do you find the same problem if you first precondition?

      Good luck on your investigation!
      I have a similar observation to BertL. I have a Tesla Model S and the regenerative braking can change behavior when it's cold outside. It takes much more effort to engage the same amount of stopping power. However, you should definitely feel something when going from B and D. Does the dash show that the battery is charging when you're on a decline and coasting? It definitely sounds like it needs to go back to the dealer.
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    7. #5
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      I have a 2016. When cold I often have no difference between B and D. Once everything is warmer I start getting some extra breaking from B.

    8. #6
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      Quote Originally Posted by VTbuckeye View Post
      I have a 2016. When cold I often have no difference between B and D. Once everything is warmer I start getting some extra breaking from B.
      +1 for our MY2019T8. I'm going to guess our cold threshold at start where B=D is ~<40F. I'll pay better attention and update, if I remember!
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    9. #7
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      Quote Originally Posted by likeXC90 View Post
      +1 for our MY2019T8. I'm going to guess our cold threshold at start where B=D is ~<40F. I'll pay better attention and update, if I remember!
      That threshold was never true for me. I drove 200 miles under 35F today and B worked as expected. Mine is 2017 T8 R.


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      More details: 10F morning in the garage/outside. Remotely ran parking climate on a fully charged battery plugged into a Level 2 charger for 20 minutes before driving. B=D for about 4 minutes of constant 35mph driving then B behaved normally. I'll update the temperature higher as the days get warmer to find what the threshold is, for my car at least - I'm curious . . .
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    11. #9
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      How does re-generative braking even work if the battery is full?

      My guess is that B doesn't work because the battery is full and since the engine is running, there's to way to take advantage of engine braking.

      I'll willing to bet even though you're not in the orange area of regeneration, the friction brakes are used when the battery is full.

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    12. #10
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      Quote Originally Posted by B0000rt View Post
      How does re-generative braking even work if the battery is full?

      My guess is that B doesn't work because the battery is full and since the engine is running, there's to way to take advantage of engine braking.

      I'll willing to bet even though you're not in the orange area of regeneration, the friction brakes are used when the battery is full.

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      Excellent point. Few comments: what really is "full" or "empty" in the displayed battery status since every company manages the battery differently? Also could any "excess" regeneration energy from braking be dumped to something other than the battery (like a resistor to generate wasted heat for example)?
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    13. #11
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      I can’t imagine Volvo has developed new tricks with what to do if the hybrid battery is fully-charged (regardless how it determines what that is), or that Volvo engineers are willing to accept additional charge e.g. when the L-ion battery is too hot or cold, as it could damage or reduce the lifespan and max charge of the battery. These are things Tesla and others worked-out years ago and have refined since, that I suspect newer mfgrs to the Hybrid/EV game like Volvo didn’t have to rediscover. Teslas do not have a “D vs B” gear concept like a T8. In terms of regen/braking, Tesla “D” operates similarly to a T8 “B” all the time — by design, electric motor regen is always on. My former Model S very clearly displayed on the IC when it was not accepting any regen, and I specifically saw multiple occasions where it would not accept additional regen charge when outside temps were too cold or too hot, or I was already at Tesla’s version of a 100% charge. The way the motors and braking worked in my Tesla didn’t change in those exceptional conditions, only the energy that could have been captured and given back to the battery was discarded. Once those out-of-the-norm conditions were eliminated, regen to the battery automatically resumed. When operating correctly, I expect my T8 does the same sort of basic regen/battery mgmt things, especially in “B-gear”.

      OTOH, I suspect how the car “feels” could be different based on what’s going on at that point-in-time:
      - On my 100% all-the-time electric Model S, when regen to the traction battery was or was not enabled by the car itself, the way it felt to me when going downhill, slowing or braking remained the same.
      - Our T8’s of course are more complex with multiple engine/motors. In Hybrid mode, T8 may change from being RWD all-electric, to FWD ICE, to AWD ICE+Electric under various conditions. We can then change from D-gear to B-gear, with the latter applying more engine braking on the downhill and as you let up on the accelerator pedal. My theory being that B-gear may also feel a little different in slowing/braking with what combination of engine/motors are active — it may also be so subtle it’s hard to distinguish if Volvo has refined everything that closely, IDK, but will leave it to others to explore if they are so inclined.

      Assuming the OP’s T8 is functioning correctly, I still suspect ambient temperature may have something to do with the regen differences he sees upon occasion, and perhaps this new theory about what T8 engine/motor combination may explain part of the “feels different” observation. Hopefully OP gets back to this thread again to set aside or confirm some of our theories, or provides feedback after his T8 comes back from the shop.
      Bert

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    14. #12
      Quote Originally Posted by Hawkmoon View Post
      We just recently moved from a 2016 T8 to a 2020 T8 (lease was up on the '16) and I have found that when putting the transmission in Brake Mode "B" that the vehicle behaves inconsistent. Both my wife and I drove our '16 extensively and know how it should feel when in "B" mode.

      With the new 2020 in "B" mode, at times, there is no difference between "B" and "D". You can literally shift between the 2 modes and there is absolutely no change in behaviour. Typically speaking you should feel the vehicle slow down in "B" mode as it uses the kinetic energy to charge the battery. Living at the top of a hill, when in "B" mode we can drive 2- 3 km to get to the bottom and still have a full charge. We have found, at times, this doesn't happen and although in "B" the car behaves as though it is in "D". When we get to the bottom of the hill part of the battery is used (ie 1 or 2 km).

      I know the braking system is changed in the 2020 from our old 2016. I feel like it is a bug in the system. Of course I will take it in to have it looked at, but curious if anyone else with a 2020 T8 has experienced this behaviour?

      From your description it sounds like you don’t experience ERAD braking when the battery is still fully charged. If that’s when you don’t notice regenerative braking that’s normal. I recall that change via a software update about a year ago or more ago. My driving topography leaving home sounds similar to yours. I don’t get regen braking when leaving home in the morning going down hill unless the battery is not charged. Anytime the charge is below a certain threshold it will regen under B.
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    15. #13
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      Quote Originally Posted by Hawkmoon View Post
      We just recently moved from a 2016 T8 to a 2020 T8 (lease was up on the '16)
      Little off topic question but how much extra electric range are you getting in your 2020 T8 vs 2016 in Pure mode? I'm considering upgrading to the 2021 T8 and was curious, thanks!
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      Two items to add: I was able to drive 24 miles today with the heat off and no other comfort items turned on, simply as an experiment. I was in pure and b modes. Now I do not believe that is the absolute best it can produce as I am in a hilly area. I would imagine someone in a very flat area of the country might be able to travel a longer distance providing they are not going over 45-50 mph where the wind resistance becomes meaningful from a drag perspective. Also when the ERAD braking is experienced, is it only slowing the vehicle down with the rear tires or all four? I am wondering from a tire wear perspective if that would be meaningful over time.
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      I suspect that the rear wheels are where the regen takes place as we do not have electric motors in the front, only in the back. As for wear and tear on the tires I hardly think it is sufficient enough to result in any additional wear. After all the car's regeneration is very mild. Our Chevy Bolt could be driven with one foot as the regenerative function could be adjusted to essentially brake the car. Even in that instance I do not recall any excessive wear or problems with the tires after 22,000 miles.
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    18. #16
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      Quote Originally Posted by drmanny3 View Post
      I suspect that the rear wheels are where the regen takes place as we do not have electric motors in the front, only in the back. As for wear and tear on the tires I hardly think it is sufficient enough to result in any additional wear. After all the car's regeneration is very mild. Our Chevy Bolt could be driven with one foot as the regenerative function could be adjusted to essentially brake the car. Even in that instance I do not recall any excessive wear or problems with the tires after 22,000 miles.
      Got it. When the vehicle is slowing down, are the brake lights activated? I can see other drivers not expecting our vehicles to be slowing and the brake lights are not on at the same time. Could surprise someone who isn't paying attention.
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    19. #17
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      Quote Originally Posted by 2020XC90T8 View Post
      Got it. When the vehicle is slowing down, are the brake lights activated? I can see other drivers not expecting our vehicles to be slowing and the brake lights are not on at the same time. Could surprise someone who isn't paying attention.
      It isn't as agressively slowing down, and people engine brake all the time much more agressively. Typical Jake Brakes on the big rig trucks don't show brake lights when they engine brake either. I don't believe Tesla's agressive Regen shows the brakelights.

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      Quote Originally Posted by B0000rt View Post
      It isn't as aggressively slowing down, and people engine brake all the time much more aggressively. Typical Jake Brakes on the big rig trucks don't show brake lights when they engine brake either. I don't believe Tesla's aggressive Regen shows the brake lights.

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      Confirmed. Many thanks for the info.
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    21. #19
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      Quote Originally Posted by B0000rt View Post
      It isn't as agressively slowing down, and people engine brake all the time much more agressively. Typical Jake Brakes on the big rig trucks don't show brake lights when they engine brake either. I don't believe Tesla's agressive Regen shows the brakelights.

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      Agree that Volvo’s decision with mild hybrid to not show brake lights is not a big deal compared to ICE vehicles that don’t do it either. Other hybrids, even both of my AWD Lexus RXh that had both front and back electric motors didn’t turn on the brake lights because of regen. It’s a non-issue from my POV.

      OTOH, Teslas WILL automatically turn on brake lights as either type of regen is underway — although its a pretty sophisticated piece of software that was implemented several years ago and refined several times since, that does not turn the brake lights on 100% of the time while regen is underway. It turns them on in a way that simulates how an ICE and it’s driver would show the brakes with normal manual braking, so the Tesla more easily fits in with non-EVs on the road. My Model S did not initially have this piece of software when it was first delivered, as it came OTA some months later. Before the automatic feature was provided, given how aggressive regen is in a Tesla compared to any hybrid, and how fast you can come to a full stop just by taking your foot off the accelerator, I was constantly watching my rear view mirror if a driver got too close to me from behind and I would manually put on my brake lights to make sure they saw I was slowing. No problems after it became standard. It’s something many, if not most, Tesla owners probably don’t even realize is happening the way it is, but IMO was one of the most elegant solutions Tesla had in their software.
      Bert

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