Clunking Vibration type sound

The owner in Iceland got his car back ...



I think the ticking is due to failure of the gearbox bearing nearest the motor, as I mentioned in an earlier post. The cage may be breaking apart which causes the ticking when the individual balls bunch up together. Or, the cage scrapes part of the housing as it rotates.

 

It's possible there are a number of cars experiencing it, and not noticing. We've got about 5,000 miles now, and because I've seen these threads, I can occasionally hear a slight tick-tick-tick for a few seconds (as I'm going downhill at about 20 mph in this one spot). It's so minor at this point (and might just be in my head anyways). I plan to keep an ear on it for the next year, and let the dealer know about it when it's more consistent. Tons of time left on the warranty, and I'd rather not get into a goose chase as the first car that my dealer needs to diagnose. I think we've only got a dozen or so cars in this part of Maine.

 

Sounds like asymptomatic Covid-19. Perhaps call it 'tick of death'.

 

Someone on facebook kona group reported a 2020 bought within the last few weeks also having this issue. So its not designed out yet.

 

Well, it's a design that requires a high level of precision machining of the related parts. I doubt even 0.001" runout could be tolerated and the production processes needed to maintain that tolerance must be well controlled.

With both the gearbox input shaft and the motor shaft being fully constrained with two bearings each and then joined together with a straight splined coupling, which inherently centers the two halves under torque, misalignment between the motor and gearbox flanges resulting from the tolerance stackup will result in an additional radial load at the two bearings nearest the splines, that load proportional to the prevailing torque.

If the weakest bearing's load capacity is exceeded, failure will eventually occur.

This is nothing new in the world of power transmission design. Every mechanical engineer understands these principles.

 

OK, but it isn't like this sort of thing is new with the Kona. Any other EV has similar issues. What's unique about the Kona/Niro drivetrain that makes this more susceptible to this type of failure?

Would it be the case that with a traditional ICE, the torque converter essentially allows for some amount of misalignment (even though that also uses a spline)?

 

The ticking was worse with the higher ambient temp last week. Had a service appointment today and of course it was cooler and you could hardly hear the ticking. Both the technician and service advisor initially seemed skeptical about my described concerns, which also included the flat 12v battery I experienced from a couple of days ago.

Just got a call back to let me know that the battery and charging system checked out fine, they offered to keep it overnight. I honestly don't know if me not having a car for work tomorrow would help the cause, so I will just continue carrying my lithium jumper pack in the car and deal with it. I am not sure if my video recording of the ticking helped but they mentioned the tech was able to hear a mild aberrant gear train noise and he feels the reduction gearbox needs replacement. They have opened a case with HYTAC and are waiting to get approval for replacement. I guess we will see. In case anyone is interested the car is a 2020 Kona with 8000 km that we have had for a whopping 4 months.

 

I would be careful about coming to that conclusion based on just one car.

Do we know they have made a change in the design, and when it was implemented? The change might not match up to the change in model year.

 

Only the Leaf has a similar design as I mentioned that in an earlier post, see #125. For manual ICE cars you'll note that the transmission input shaft is long and a slight misalignment with the flywheel pilot bearing is less of a problem, and the clutch floats inside the pressure plate assembly. For autos have a read of paragraph 4 here https://www.carbibles.com/what-is-a-flexplate/
The design used by Hyundai/Kia/Nissan is common in hydraulic motors.
Keep in mind I'm not saying this is the reason for the failure, just that there are risks in using over-constrained designs.

 

I went back and watched youtube videos of the disassembly of a Bolt and Leaf transmission, and I think I finally get what it is that you are saying. For some reason, I had thought the Bolt also used a spline, and I can clearly see this is not the case.

 

Having driven the Bolt almost as long as my Niro, I can tell you that its drivetrain feels much better. The Niro has always felt jerky for some reason. Not sure if it's the throttle response or how it transitions between acceleration and regen. Something about it has never felt right. You can feel there is some "play" or slack in the drivetrain somewhere. The Bolt has super smooth throttle pedal response that is seamless.

It's been years since I drove a Leaf so can't comment too much about it. I know their original motors were much weaker than what is found on the Kona/Niro. Maybe that design was okay when dealing with lower torques. Nissan could just be better at building these things since they've been at it for a long time. This is Hyundai's first iteration of this motor/gearbox design (ignoring the 701 motor revision since it's not in mass production).

 

I see what you did there!

Sent from my Pixel 3a using Tapatalk

 

Admittedly without full details of how the setup is built [or does someone have
the relevant diagrams?], how could such a constrained connection have some
radial float designed into it within the same space? It seems like the right place
for it would be on the reduction-gear input side, as the motor shaft pretty much
*has* to be rigid to keep the rotor clear of the stator.

_H*

 

I am wondering if the design that the Bolt uses is an improvement. There the 1st gear is part of the motor shaft, so there is no spline. The amount of float won't be huge, but probably enough to avoid this problem.

It also has a hollow motor shaft that the drive axle goes through - that caught my interest as well.

 

Checking out some more Model 3 videos I think that's what they've done, leave out the gearbox bearing nearest the motor. Here's a photo of the bare motor shaft. The pinion slides over the spline and has just one bearing at the far end. The hollow pinion has a locating diameter at the motor end to ensure no side play, noting the oil channel grooves. A good design.

Noting that there will still be a spline between the gear and the motor shaft, yes, the pinion 'bolted' to the end of the motor shaft is a good design if one company is building the entire unit, as would be expected in the case of GM.
Hollow motor shafts are used elsewhere as well, I think the Taycan and either the eTron or iPace.

 

Well, less than 400 kms since my reduction drive replacement, am starting to hear that noise again. Not happy...

 

Well, this does not bode well :-(

I wish Hyundai would put some additional resources on this problem and figure it out once and for all.