bwilson4web
Posts: 704
Joined: Fri Apr 29, 2016 11:59 pm
Location: Huntsville, AL

Re: Well that was not fun . . .

Wed Dec 14, 2016 7:24 am

Hi,

Since my BMW i3-REx is in the shop for a 'broken driver side motor mount bolt', I have some questions:
alohart wrote: . . .
Our 2014 i3 hasn't had its defective motor mount bolt replaced, so I can't offer any personal experience with the updated software. However, what apparently causes the motor mount bolt to crack or break is when the rotation of one drive wheel suddenly accelerates rapidly when the drive wheel briefly loses contact with the road (e.g., when driving over a curb, speed bump, etc.). When that rapidly spinning drive wheel hits the road again, the shock of its rotation suddenly decelerating can crack or break the motor mount bolt. Others have stated that the software fix adjusts traction control to prevent the sudden acceleration of a drive wheel. I'm not sure that any of us knows for sure the details of the fix, but it apparently hasn't changed the i3's performance, so you might not have very strong grounds for suing BMW.
When I got the BMW i3-REx to Huntsville, the 'motor mount bolt' action was performed. So now I'm wondering what would have been done?

Would all of the bolt(s) have been replaced or just inspected and the software patch applied?

During the recent failure, the technician reported he was disconnecting the HV in the motor compartment and saw the broken bolt:
Image
This suggests he would have been looking at the top of the body side of the transmission/motor mount to see one or more broken bolts.

These images suggest there are five bolts holding the transmission/motor assembly to the frame:
Image
Image
The top two should be visible but the lower three may be hard to see.

There is one additional support attached to the anti-sway bar:
Image

In a good design, the bolts are 'mechanical fuses' that fail before damage to the frame or transmission/motor housing. But given the nature of this failure, I would like to know all bolts including the anti-sway bar ones have been replaced. For good measure, inspect the transmission/motor housing and body attachment points to make sure there is no damage.

As for the broken bolt, I've had to deal with them in the past and it is a b*tch! There are specialty tools used to back out the broken bolt part but it isn't fun. It certainly is not something I would want to do with the transmission/motor still in the car.

Looking at this YouTube, the strain, the motion inside the compartment, is impressive:
https://www.youtube.com/watch?v=p9fVuqh5yb0

After the car is repaired, I may look at ways to monitor/record the transmission/motor displacement.

Bob Wilson
20k/27k mi 2014 BMW i3-REx
10k/10k mi 2017 Prius Prime

jadnashuanh
Posts: 4487
Joined: Thu May 22, 2014 2:07 pm
Location: Nashua, NH USA

Re: Well that was not fun . . .

Wed Dec 14, 2016 5:17 pm

Customer field use brought the potential for a broken motor mount bolt to their attention, and all affected vehicles are subject to the free replacement. The stated most common reason for their failure was/is going over a bump while accelerating fairly hard...the wheels unload, potentially speeding up considerably, then hitting the pavement, and rapidly decelerating. The S/W patch changed the logic that detects wheelspin so that the motor controller can catch that symptom sooner, and limit power, preventing that impact by limiting the acceleration.

I don't remember if the fix called for replacing all of the bolts, but I think it did. Then, they tweaked the software to help prevent it from happening again.

So, it's not really movement during normal driving, it's the shock generated by freewheeling then rapid deceleration.

If this was recently done, there were a bunch of other s/w tweaks applied at the same time. FWIW, while BMW used to give the dealers a list of the functions affected, they no longer do, so the dealers are unable to tell you. If you have a problem, they enter it in the computer, and corporate responds with the corrective action...might be s/w, might be an adjustment, might mean replace a part...they do not know in advance except for something like the bolts.
Jim DeBruycker
2011 535i x-drive GT, 2014 i3 BEV

bwilson4web
Posts: 704
Joined: Fri Apr 29, 2016 11:59 pm
Location: Huntsville, AL

Re: Well that was not fun . . .

Wed Dec 14, 2016 11:37 pm

jadnashuanh wrote: . . .
So, it's not really movement during normal driving, it's the shock generated by freewheeling then rapid deceleration.
. . .
Fortunately, I have some recording accelerometers: http://gcdataconcepts.com/x2-1.html

These were left over from the Prius brake-pause investigation:
Image
Image

To have this happen six months after the bolt campaign makes me curious.

Bob Wilson
20k/27k mi 2014 BMW i3-REx
10k/10k mi 2017 Prius Prime

jadnashuanh
Posts: 4487
Joined: Thu May 22, 2014 2:07 pm
Location: Nashua, NH USA

Re: Well that was not fun . . .

Thu Dec 15, 2016 1:36 pm

You probably won't see the acceleration/deceleration when measuring the vehicle's state...it's the rotational energy of the wheels when unloaded/in the air verses when they regain traction that produced the shock that gave issues with the motor mount. The unloaded wheel can accelerate rapidly and this is what the new software is supposed to catch and limit to prevent as severe of a shock. You'd need to be measuring the horizontal g-force as well as the vertical to get an idea of when a wheel was unloaded (unless it was slipping link discussed below). It's hard to be sure, but I do think the operation after hitting a pothole is slightly different now verses previously.

FWIW, I was backing uphill on Tuesday into a curbside parking space covered in snow. The car moved smoothly without spinning the wheels, but the traction warning lamp was flashing consistently. I do have winter tires on the thing, but even then, it was slippery.
Jim DeBruycker
2011 535i x-drive GT, 2014 i3 BEV

bwilson4web
Posts: 704
Joined: Fri Apr 29, 2016 11:59 pm
Location: Huntsville, AL

Re: Well that was not fun . . .

Thu Dec 15, 2016 5:35 pm

jadnashuanh wrote:You probably won't see the acceleration/deceleration when measuring the vehicle's state...it's the rotational energy of the wheels when unloaded/in the air verses when they regain traction that produced the shock that gave issues with the motor mount. The unloaded wheel can accelerate rapidly and this is what the new software is supposed to catch and limit to prevent as severe of a shock. You'd need to be measuring the horizontal g-force as well as the vertical to get an idea of when a wheel was unloaded (unless it was slipping link discussed below). It's hard to be sure, but I do think the operation after hitting a pothole is slightly different now verses previously.
. . .
Source: http://www.gcdataconcepts.com/ham.html
  • HAM-IMU
    • 3-axis accelerometer, gyroscope, magnetometer
      User selectable sample rates of 50, 100, and 200 Hz
      Quaternion orientation solutions based on accelerometer and gyroscope data
This one also has the magnetometer so I should also get some indication of power flow. They have already shipped it so I should see it sometime next week.

I also stopped by the shop:
Image
The motor/transmission attachment broke. Formerly of a structural plastic, the replacement is an aluminum frame. Regardless, the remaining bolt fell to the floor:
Image
Image

The fracture comes from the stress concentrators from the thread. Maximum stress on a thread will lead to stress concentrators, fractures, and eventually, work induced failure.

The stress indicates a fore-aft stress, not a length torsional failure. In effect the ordinary motion resulted in the bolt shearing from front-back motion. Confirmation comes from taking a photo of the body anchor and verification that the final fraction left a vertical bar.

Bob Wilson
20k/27k mi 2014 BMW i3-REx
10k/10k mi 2017 Prius Prime

bwilson4web
Posts: 704
Joined: Fri Apr 29, 2016 11:59 pm
Location: Huntsville, AL

Re: Well that was not fun . . .

Fri Dec 16, 2016 10:18 pm

At the shop, I was able to take more photos including the left and right body anchor points:
Image
Image

I had a 2" receiver hitch installed to carry my wife's folding wheel chair on the back:
Image
Image

When they drop the transmission/motor and REx assembly, these parts may have to come off. I'll contact the vendor to get a copy of their installation instructions.

We also saw four 'pad' spots on the battery suggesting someone in the past raised the car by lifting on the battery. OWCH!!!

Bob Wilson
20k/27k mi 2014 BMW i3-REx
10k/10k mi 2017 Prius Prime

brorob
Posts: 104
Joined: Sat Oct 31, 2015 5:53 am

Re: Well that was not fun . . .

Sat Dec 17, 2016 6:56 am

I've read some posts about a recall for the motor mount screws (bolts are technically a screw that uses a nut for tightening) but I'm wondering if I can have the dealer replace these if I haven't received an official recall letter from BMW, or if there is an official recall. I did receive a letter from BMW recently about bringing the car in for a software update related to the accuracy of the SOC display so I'd like to have these replaced when I bring the car in for that. Wondering how reluctant the dealer will be to do this if I haven't received an official letter from BMW about this. I'm also curious if the letter I received is related to the fixes from the November 2015 software update, which I've already had done by the dealer.

jadnashuanh
Posts: 4487
Joined: Thu May 22, 2014 2:07 pm
Location: Nashua, NH USA

Re: Well that was not fun . . .

Sat Dec 17, 2016 3:42 pm

It depends on when your vehicle was manufactured...the fix was applied somewhere in the production history so there are obviously some vehicles that left the factory with the latest tweak and therefore don't need anything. The dealer should check your vehicle against the database of required updates whenever you take it in for service. FWIW, some s/w updates won't be applied unless you have an issue that was addressed in a change, though. If you do get new software, you get everything updated, and some updates are applied to everyone, all of the time.
Jim DeBruycker
2011 535i x-drive GT, 2014 i3 BEV

alohart
Posts: 1675
Joined: Sat Nov 01, 2014 7:36 pm
Location: Honolulu, HI

Re: Well that was not fun . . .

Sat Dec 17, 2016 4:02 pm

brorob wrote:I've read some posts about a recall for the motor mount screws (bolts are technically a screw that uses a nut for tightening) but I'm wondering if I can have the dealer replace these if I haven't received an official recall letter from BMW, or if there is an official recall.
I did not receive any communication from BMW telling me that our July, 2014, BEV had a defective motor mount screw that needed to be replaced, a serious problem compared with the only letter I have received from BMW telling me that our i3 needed its software updated to increase the range estimation accuracy, a very trivial problem. Having the VIN of your i3 would be sufficient for a BMW service department to determine whether your i3 needs to have a defective motor mount screw replaced. Replacing this motor mount screw should not generate any resistance from your dealer.

When I took our i3 in for its first scheduled maintenance 2 years after it was manufactured, I told the service representative that I needed the defective motor mount screw replaced during this same service call. The service representative looked up the VIN of our i3 and confirmed that the motor mount bolt needed replacing. There was no pro-active effort by BMW which is disappointing. I wonder whether the screw would have been replaced had I said nothing about it.

Also disappointing is the structural plastic piece that broke in bwilson4web's i3 and is being replaced by an aluminum piece. I'm pretty certain that this plastic piece was not replaced when the motor mount screw was replaced in our i3, so our i3 still has the plastic piece that is apparently prone to break and for which an updated stronger piece has been designed. All i3's should have had this improved aluminum piece installed when the motor mount screw was replaced. I fear that the original plastic piece will break after our warranty has expired resulting in a very expensive repair. The more I read about these i3 problems, the more likely I am to sell our i3 when its warranty expires despite taking a huge depreciation loss.
Aloha,
Art

2014 BMW i3 Arravani Grey, Giga World, Tech + Driving Assist, Parking Assist, DC Fast Charging, JuiceBox EVSE

bwilson4web
Posts: 704
Joined: Fri Apr 29, 2016 11:59 pm
Location: Huntsville, AL

Re: Well that was not fun . . .

Sat Dec 17, 2016 8:45 pm

I went back the original photo (actually I have three) and focused on just the broken motor mount bolt:
Image
  • No evidence of a mount fracture as the top surface does not show new material.
  • The broken off bolt section is visible extending out the right.
  • It looks like there may be a metal insert in the structural plastic.
I was thinking about this the other day and realize my warranty will be ending in about 18 months. I am thinking I may want to bring the car in and have the mount bolts replaced so I get to keep the old ones for analysis. In particular, a dye penetration test to see if there is evidence of early stress fractures.

The other alternative is to order the bolts; have them tested, and; swap them myself. One speculation is to grind the center section so there are no threads at the maximum shear point. Except the act of cutting the initial threads has the potential of making the initial surface defects. If I grind off or use a lathe to turn off the middle threads, I'll have to dye test them afterwards.

Upon further reading, it appears there may be ways to improve thread stress performance by adjusting the nut characteristics. Apparently the first thread is easily over stressed but by cutting the nut with a different profile, the peak stress can be spread across the bolt threads '30%' reduced. So it makes sense that the part affixed to the transmission/motor may be the key.

Bob Wilson
20k/27k mi 2014 BMW i3-REx
10k/10k mi 2017 Prius Prime

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