Clunking Vibration type sound

Hopefully, this high visibility catastrophic failure, along with forums and blogs like this one reporting on it, will accelerate Hyundai’s desire to identify the problem and find a fix ASAP. Let’s keep the pressure on.

 

Do we know yet where the problem is, the motor or the reduction gear? My local dealer has the reduction gear part in, and wants to replace mine. I have been holding him off due to the virus, and my 14 day self-isolation after coming back from the US.

 

If you do run a story, I would love to see a poll of some kind to get a better feel for how many cars are affected. I have a poll going in the Niro forum but the total number of participants is too low to draw any statistically significant conclusions. It just seems hard to believe 60% of the cars become defective. We would also need to know how many miles on odometer are required before most of the motors fail. So far it's been all over the map. Some get it just driving off the dealer lot while others seem to require as much as 20,000 miles or more. I'm skeptical it's a transmission issue. That appears to be KIA's/Hyundai's preferred initial repair because these are cheaper and more readily available than new motors. But everyone that has had the transmission swap so far had the problem return eventually. Motor swaps for a new revision appear to offer a longer lasting solution so far. But oddly they have continued to manufacture the original motor revision. Strange choice if they found a design flaw on that older motor.

 

I wonder if the issue is not so much with the motor, per se, but a fundamental design flaw that is causing a misalignment of the drive shaft / motor. Perhaps the current "fixes", whether it's a drive shaft rotation, reduction gearbox replacement or motor replacement sometimes seem to work simply because it's coincidentally realigning the parts as they are reinstalled (at least temporarily).

 

I posted a message on an engineering forum two months ago on this subject but didn't get too many replies past what I already knew. There are a few automotive types there who really know their stuff but the site seems to have fallen out of popularity recently. I've also got some education and industrial experience surrounding the relevant subjects from long ago when working in the automotive test equipment industry.
We don't know much about the Kona/e-Niro motor/gearbox design but it appears to couple two fully constrained shafts together with a splined coupling, just like the Leaf does. The motor shaft has two bearings and is fully constrained in all but rotation. The first reduction stage pinion is mounted in two bearings and is similarly constrained. They are mated with a conventional splined coupling.

The splined coupling is pretty much like male and female gears with shorter teeth and a small running clearance. Normally under torque loading the two sides lock together but can still slide. But any slight angular or parallel misalignment causes the "gear" face contact areas to be highly compromised and fretting can occur if sustained. If lubrication is poor the splines will wear down creating more clearance and presumably noise. A dab of grease may or may not be enough.

I'll speculate and suggest that within their organisation the motor supplier is likely to have been MOBIS while the vehicle design people may have their own "gearbox" department. They would want a simple interface so they can contractually separate their designs and may have understandably expected that a proven method of a splined coupling should allow them to work independently. It's possible that the tight alignment and good lubrication requirements were somehow missed.

BTW, this is classic engineering departmentalization that Tesla are famous for knocking down and this may turn out to be a great example of why that is a good thing.

As I mentioned in the eng-tips query most other EVs don't use this method, specifically the Bolt and Tesla (after the Roadster). They place the first reduction pinion on the motor shaft, either bolted on (ironically the 'Bolt') or integrated on the shaft (Tesla M3). Nissan seem to have made the spline work, perhaps with good design and tight manufacturing tolerances. We shall see ...

 

The minimal info I have does not include the gearbox. I would expect that it's present but haven't made the expense and effort to check since my Kona runs just fine. Perhaps R P can snag a photo of the gearbox opening when the work is carried out.
But it's puzzling as to why gearbox catastrophic failure seems to be one result.

 

Immediate question on the FB report: why would the motor keep spinning
out of control once the driver's foot comes off the pedal? Neither the
go-pedal or the control electronics would have sustained any damage,
presumably, and the motor needs continual control and energizing
of coils in the right order from that external source.

I hope this doesn't start turning into a Prius SUA style storm of bull.
Last kind of thing anyone needs right now.

_H*

 

Well, the plan for them is to replace the gearbox. I am trying to hold off going in to have it done, given the virus situation. Also, would like to know from others if that really does fix the problem. There was talk that it was the motor and I thought some of those were replaced. Which is it? Anybody have more info on that?

 

How many miles or km do you have on your Kona? You may still develop the problem given more time.

Here are some photos of the Niro gearbox and where it attaches to the motor. These were posted on a French forum a long time ago when these issues first started being reported.

 

So, a big wad of grease slathered on the motor shaft and hope for the best.

_H*

 

It's a shame the photographer did not think to snap a photo of the business side of the gearbox.

Well, no one is going to use a grease nipple on anything since 1980. It's an obsolete concept and was widely misused last century. Other than static bearings like ball joints, on many high-speed rotating applications it leads to overfilling and early failure.

This is what I can take away from those photos:
1. It's uncertain if there is fluid sealing between the motor and the gearbox. The black ring around the motor "bearing" flange 'looks' like an O-ring but might just be a gap. Given the relative sizes of everything, if it was an O-ring it seems somewhat thinner than I would pick, but it may be fine.
2a. If there is no sealing then that means the spline and the motor bearings are only grease lubricated. That's not the end of the world.
2b. If there is a seal then oil can wander into that area from the gearbox sump. That's good, and that is what is done on the Prius HSD, but where does it drain out? Toyota have 25 years of experience in details like this. The tail end bearing on the motor may be grease lubed anyway because the motor cannot run flooded with oil.
3. You can see the tubular dowel pins on the motor that align it to the gearbox. Nothing unexpected of course.

Looks like the FB Kona owner in Iceland is getting a new gearbox and will have his car back shortly. That's the first catastrophic failure for Hyundai to sort out. Hope they figure it out soon.

 

I've got an appointment now for next Tues to get my gearbox replaced. Hope to find out more about the cause/fix.

 

You're right. It does look very similar to the leaf. A good teardown of leaf motor in this video. His youtube channel has another teardown of the gearbox.

 

I was curious why he went to the trouble of getting a Leaf motor - he is doing an electric conversion of an old tractor. So I wasted an hour of my time watching his videos where he purchases the tractor, removes the ICE, scrounges for parts, etc. Still a work in progress...

 

That video is certainly more detailed in the area of interest than others I've seen. It's clear both the motor and the gearbox have lip seals to keep gear oil under control and dirt out of the motor bearing. The O-ring on the motor shaft is needed because the pinion gear shaft is hollow, and that feature is certainly provided to expose the splined area to oil. (Note in the photo that the Hyundai/Kia motor also seems to have an O-ring there).
When he placed the pinion shaft on the motor and spun it you could see that the motor turns freely and the shaft didn't wiggle so the motor does have a proper bearing at that end. Also, note the spline has locating diameters at both ends (one at the O-ring), which would certainly match precision bores in the pinion shaft. That would keep the spline halves fully aligned radially to avoid fretting. It's safe to assume that the motor bearings are grease-lubricated and it runs dry internally.

 

Here are a few diagrams from the service manual of the KIA/Hyundai motor and gearbox. Unfortunately nothing shows the gearbox side of the input shaft in any detail.

 

That underbody shot also illustrates how uneven in length the left/right shafts connecting the wheels are. This contributes to increased torque steer seen in front-wheel drive EVs. Much preferred handling of the rear-wheel drive models I test drove but this is only available on a few purpose-built EVs that didn't start with an ICE in the front.