05-06-2021, 09:30 PM | #1 |
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Coming to a stop / slowing down / braking not smooth, MY21 x40i
Hello everyone,
I would like to inquire other owners if their car behaves like mine. In particular owners with MY21 with the mild hybrid x40i. In case anyone asks I have M-Sport package+brakes and I have turned off ASS with BimmerCode. What I have noticed since I received my car a month ago is that "slowing" down the car is not so smooth. I say slowing down because this issue is not really about the brakes. Let me explain in detail. There are several factors at play when we slow down(brake) our X5; 1) brake friction (rotor + pad) 2) mild hybrid regenerative braking (drag from motor/generator) 3) transmission (down-shift) In my opinion the brakes themselves are fine but it's #2 and #3 that's causing some "jerk" when I slow down my X5. I don't mean a violent jerk but enough that you can clearly feel it. I don't really feel it when the mild hybrid regen brake kicks in(engage), but I definately feel it when it releases(disengage) coming to a stop. This combined with the multiple down-shift of the transmission (especially around 2-4 gear) makes slowing down (braking) a bit harsh in my opinion. Am I overly sensitive or anyone else agree? |
05-07-2021, 09:29 AM | #2 |
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I can't say I felt any jerking but I had a MY21 loaner for a few days while mine was in for some work and was surprised at the difference in coasting between mine (MY19) and it. On mine when I cancel the cruise or leave of the gas it coasts like every other vehicle I have driven. On the MY21 doing the same was like putting on the brakes. It definitely slowed down much faster than I was used to and ended up having to give it gas a few times where I normally wouldn't.
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05-07-2021, 09:47 AM | #3 |
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I noticed something similar when i had a long road trip while driving in sport mode, but when driven in eco, i didnt feel anything. both coasting down hill (7% decline). i havent tested again thinking it was normal. been driving in eco on long road trips since. will need to test it out again on next long road trip in couple weeks.
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05-07-2021, 11:07 AM | #4 |
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I have exact same experience as you described. Don't like it at all. Below is my post where I explained the issue. To me it is a design problem that is only impacting MY21 Mild Hybrid, even though another 45e PHEV owner echoed same experience. Try driving it in Sport Standard mode and see if it improves (my assumption: in sport mode the brake regen doesn't engage).
https://www.bimmerpost.com/forums/sh...php?p=27554731
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05-07-2021, 03:51 PM | #5 | |
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05-07-2021, 08:42 PM | #7 |
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Appreciate all the feedbacks, love this forum.
Just to clarify, I normally drive in Comfort mode. ECO mode almost gets ride of brake regen and lets you "coast/glide", thus is definitely smoother. I haven't tried Sport mode but I expect more harsh down-shifts. Personally, I think it's the "harsh" downshifts (around 2nd -4th gear)that bother me the most. Last edited by ladra; 05-07-2021 at 11:21 PM.. |
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05-09-2021, 05:35 PM | #8 |
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I am trying ECO PRO mode and pulsation feel is less. The name is kinda counter intuitive because one would think this mode would have most brake regen.
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05-09-2021, 06:00 PM | #9 | |
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Or just use the sport mode……….🤣 I like to ease in at the stop or the red light.
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05-09-2021, 07:21 PM | #10 | |
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05-09-2021, 08:40 PM | #11 | ||
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05-09-2021, 09:31 PM | #12 | |||
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05-09-2021, 09:59 PM | #13 |
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Two helpful articles on regenerative brake design and 48V system. The last link is a G20 forum post by a BMW research employee, he tried to clarify some misunderstandings. I was unable dig out any meaningful info on the TIS site.
https://www.brakeandfrontend.com/reg...aking-service/ https://www.greencarcongress.com/202...7-5series.html https://g20.bimmerpost.com/forums/sh...7#post26311167
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05-10-2021, 09:30 AM | #14 |
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I have a MY21 M50i and definitely notice this braking issue. I previously had a My19 40i and it was much smoother. I also have the ASS off bottom, but coded it off with BimmerCode.
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05-10-2021, 10:52 AM | #15 |
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That is interesting since the M50i doesn’t have the mild-hybrid system. Yes, the button is gone from the mild-hybrids.
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05-10-2021, 11:28 AM | #16 |
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I think this issue is related to the regenerative braking system - pulsation feel on the brake pedal. Does M50i have regenerative brake system? If the answer is yes, then it is plausible.
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05-10-2021, 03:46 PM | #17 | |
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05-10-2021, 07:34 PM | #18 | |
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Unless something recently changed, the Brake Energy Regeneration system is not tied to the brakes themselves but rather is a system that decouples the alternator from the engine and only connects it when coasting, decelerating or braking. From what other folks posted, they changed it for the mild-hybrids although I have never seen anything official. https://www.autobytel.com/car-owners...ration-123423/
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05-12-2021, 10:18 AM | #19 |
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I tested braking and decelerating (MY21 40i, 07/2020 iSTEP) by observing energy flow screen. I wanted to see when the battery is being charged and when the electric motor assist kicks in (for all driving modes). Here are my non-scientific findings:
1. When you brake to slow down, ALL driving modes charges battery using brake regenerative system. 2. When you decelerate, ONLY Eco Pro driving mode doesn't charge battery (all other modes does). Eco pro goes into coasting when I decelerate. Didn't see/feel any regen activity on the screen. 3. Interestingly, I didn't notice any instances of assist from the electric motor when I started driving from a standstill. However, the electric motor assistance kicked in many times when I was in may be around 4the to 5th gear (around 50 km mark). When the car is in Ready status and I start to drive, I was expecting the first few seconds the electric motor will assist the car to move forward and then ICE takes over thereafter, but it wasn't the case as per the energy flow screen. Conclusions: When braking, the ECO pro or Eco pro individual mode has the least amount of shudder or brake pulsating feel. Perhaps BMW has different regen algorithms for different driving modes. Really wish we had a choice to set our own regen percentage. When we code the ASS option off, I believe it doesn't stop the regenerative charging process. It simply turns off the auto start stop function (saving fuel), thats about it.
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05-12-2021, 10:38 AM | #20 | |
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I have a MY20 m50i, so can't talk about the regenerative braking. But I do feel the down-shift "jerk" when slow down / coming to a stop. I can see the rev going up when the ZF 9AT automatically down shift. If you move to neutral as you glide, you won't feel the "jerk" from down shift at least. Last edited by zhangyi17; 05-12-2021 at 10:44 AM.. |
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