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Thursday, August 9, 2012

ActiveE Technical Issues(part 1): Splines, Splines Everywhere There's Splines!

The teeth (splines) of this ActiveE gear have been grinded away
What the hell's a spline you ask? Don't feel bad I didn't know what it was either and I'm a fairly "technically competent" guy. So when an ActiveE Electronaut posted in our Facebook group a month ago that he needs a new motor because he had 'spline failure' I had to look it up. Turns out splines are just the technical term for the teeth of both the male and female ends of a gear. Spline: A flexible connection featuring grooves cut in a shaft that mate with corresponding grooves in a connecting member, such as a hub. 

Suddenly everybody in the group was buzzing about splines like it was some advanced technology that BMW somehow under-engineered. It's just a simple gear, nothing complicated about it. Question is why are they failing on so many cars, and on a personal level why hasn't mine failed? I have way more miles than anyone else who has an ActiveE, I'm close to 21,000 miles now and the next person (that I know of) is around 13,000. Plus, many of the gears are failing on cars with less than 5,000 miles! Why would that be?

Possible Causes: (my opinion only)

Abusive driving. Maybe the people that have had the gear failure are just really punishing the car beyond its capabilities. There were a few MINI-E drivers who were known to have really abused their cars which is why BMW tightened up the rules and return policies on the ActiveE, making us more accountable for the condition the car is in when we return it. Probability: 5%

Bad batch of gears. It could be that BMW simply got a bad batch of gears that were defective metal. Probability: 15%

The car is too heavy. The drive system for the ActiveE wasn't designed for the ActiveE. It was designed for the 2013 BMW i3 which will be about 1,300lbs lighter than the ActiveE. Could it be the gear just can't handle the stress of applying 184lb-ft of torque to move a car that is over 4,000lbs before you add the weight of the passengers? Probability: 20%

Improper lubrication from factory. All of the pictures of the gears that ActiveE drivers have received from their service departments show the gears devoid of any grease. Gears like this obviously need an ample amount of lubrication or they will grind themselves away in short order. Did the factory just forget to grease some of the gears? Probability: 25%

Lubrication leak/washed away. Perhaps the factory did properly lubricate the gears, but there is either a design flaw that allows moisture to seep in and wash the grease away or there is some kind of faulty seal that allowed moisture in on some cars and that's why their gears failed and others didn't. Probability: 35%

Rusted & Stripped
Then maybe it's a combination of a couple of these possible causes. Maybe the gear is stressed to its limit because of the extra weight, there's an issue with moisture getting in there somehow and the ActiveE drivers love the feel of the instant torque so much they punch the accelerator every chance they get. Or maybe I'm missing it completely. If you think you have a better cause, please feel free to post your thoughts in the comments section. Of course if a BMW technician who knows the real reason(s) wants to post there also anonymously, I won't mind that either. ;)

Technical issues are expected with the ActiveE. This is a car that is purely a test vehicle, meant to fully vet the components that will be used in the 2013 BMW i3. BMW also gets the CARB credits they need, which personally I'm fine with, and they have never disputed that the ZEV credits are part of the reason they did the MINI-E and ActiveE programs. However as long as these programs allow people like me to drive electric, and help BMW improve the technology so the cars they begin selling next year are the best they can be, then I think they are more than worth while. Just about everything in the ActiveE is new. The motor, the power electronics, the KLE(onboard charger), the battery modules, the active thermal management system and the entire high voltage battery system have never before been used an any vehicle so it would be foolish to think there wouldn't be technical issues like this. I've been a big supporter of the BMW electric vehicle program and sometimes when I take a step back and look at my posts I think I may be too positive without showing all of the challenges we in the program face from time to time. That's why I've decided to add a new series of posts called "ActiveE Technical Issues" that I will mix in with my other posts, highlighting the problems the car (and the people driving them) face.

This by no means is an indication that I don't love the car and regret applying for the program, which I don't for a minute. The ActiveE is really a great electric car and just about everyone I know who has one feels the same way. But it is a test car, and the technical deficiencies as compared to a production car do come out from time to time, and I'm going to do my best to write about them, just as I do for all the great qualities the car has.

This is how the gear should look
Splines Splines Everywhere there's Splines
Failing on the ActiveE, Breaking up my mind
Do This don't do That or you'll Break your Splines...


  1. Tom
    Nice posting!
    A spline shouldn't ever turn, as a gear does, but seeing it dry and without any protection (and obviously rusted surfaces) is not a good sign.

    I suggest there may be multiple issues at work here:
    Improper sealing (rust is odd).

    The prodigious torque output of an electric motor may be what's causing the failure here. The spline may have to get re-engineered with deeper grooves... or for a longer contact area, or something else. (I'm suggesting like threads on a bolt: they could be fine or coarse grade, depending on the application.)

    Based on the photo, the shaft looks kind of short and stubby, if it were longer perhaps that would figure better into the durability equaton. Most high power e-motors have much longer couplings, iirc. At least the ones that last, seem to! ;)

    I wonder how frequent this is?

    Ron (who loves engineering) Freund

  2. Ron,

    I don't have any official data, but at least a couple dozen have had to have this replaced. As I wrote, I have by far the most miles on my car than anyone else and mine is fine.

    It only takes a couple days to have the service done if the dealer has the motor in stock and of course it's all covered (we don't have to pay for any maintenance).

    There is definitely a lubrication issue of some sort, because gears shouldn't look dry and even rusty like these do so I really think there is a moisture penetration issue at the root of the issue.

  3. Thanks for posting some of my pictures... The 3rd picture is actually the old transmission, not the 'motor' as stated in the caption.

    I can tell you that I baby the car as I'm concerned more about mileage than performance. My biggest concern has been to get the highest miles/kWh... This is how I was able to get 110 miles out of a full charge.

    I'm looking forward to getting "Sparkie" back and catching up to you in the mileage contest!

  4. Thanks Stuart. I looked quick and thought it was already connected to the new motor but I can see it's not. That gets bolted to the motor exactly where you see exposed in the picture directly below it.

  5. @Ron Freund:

    After reading your comment where you stated: "Based on the photo, the shaft looks kind of short and stubby, if it were longer perhaps that would figure better into the durability equaton. Most high power e-motors have much longer couplings, iirc" I did some checking. I found some pictures of Tesla's electric motors and the shafts actually looked about the same as the ones pictured here. Short, stubby and about the same thickness. The splines didn't look that much longer or thicker either. The mystery remains...

  6. Interesting. I have heard that there has been e-motor failures and I guess this is the cause. Should be a simple fix I would venture. The absence of lubrication would be a good place to start --- as you point out

    Please let us know what BMW does to remedy the situation and keep up the great reporting!


  7. Too much torque!!!

  8. I'm not buying the too much torque excuse Anonymous. Why didn't this ever happen to the MINI-E I drove for 2 1/2 years? It had almost as much torque as the ActiveE (164lb-ft) and I never once heard of this happening to any of the cars. Heck the Nissan LEAF has 207 lb-ft of torque (Though I'm sure it's dialed down a bit at launch) Also, Teslas cars have more torque and they don't seem to have any issue. There are plenty of EV's with lot's of torque that don't have issues like this. There is something going on here that I bet is an easy fix and has to do with the lubrication.

  9. Interesting stuff please keep up posted. I love reading your blogs, thank you for keeping them up to date with frequent postings like you always do.

  10. After my ~1hr of research on the subject, I'd say that the likely cause would appear to be improperly applied lube at the factory. I'm not seeing much literature on bad seal problems and I'm not reading any reports concerning replacing the seals, only inspecting and re-lubing.

  11. Doug, they should not look rusted like they do after only a couple months of use. I have other pictures that I didn't post of other motors and the gear looks like it's ten years old and had sitting outside in the rain. I definitely think there is some kind of moisture issue there. The gear should not be exposed to moisture like it obviously is.

  12. Hopefully this won't inspire BMW to cut back the power on the upcoming i3 Megacity car. It doesn't matter to me how you figure it out, just make the i3 fun and FAST or it will be out of consideration for my next car purchase/lease in early 2014 when my Volt lease is up!

  13. The half-shafts connecting front-wheel drive car's engines to the drive wheels have splined ends (covered with grease). The joint is covered with a sealed rubber boot which is a maintenance item and one of the items in annual safety inspections, because if the rubber boot is damaged (not-uncommon), water and moisture can get in (located next to the wheel and near the road), leading to premature failure of the spline joint.

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