Coupling of EV Motor to Reduction Gear Pinion
Coupling of EV Motor to Reduction Gear Pinion
(OP)
Hello,
I'm noting several different approaches to the above detail used on production EVs. The context of my question is that a handful of near-new e-Niro and Kona Electric examples have developed clicking noises reportedly at approx motor shaft frequency. The manufacturers don't seem to have a field solution to this yet, as best as I know, despite replacing both motors and gearboxes. I'm wondering if there is a fundamental flaw in their design related to coupling two fully-constrained rotating shafts which may have small parallel offset errors due to production and mounting tolerances. I'm also wondering how splines outside of oil-wet areas would be lubricated, whether grease is sufficient.
Here's what I have found on several EV designs.
GM EV1: The rotor (induction motor) and pinion are mounted on a single shaft with a bearing at each end. Between them is only an oil seal.
GM Bolt: The pinion is held by a large nut onto the end of the (PM) motor shaft. There is no outrigger bearing.
Nissan Leaf: The motor (PM) has a splined shaft output. The reduction pinion (and parking pawl wheel) is supported at both ends by bearings. The detail of the motor's male and pinion's female splines is not clear.
Hyundai Kona, Kia e-Niro: Not much info is available but the (PM) motor has a splined output shaft like the Leaf. The design detail of that spline and design of the reduction gearbox internals are all unknown. These two vehicles reportedly use the same motor and reduction gearbox but the overall gear ratio is slightly different.
Any insight is appreciated.
thanks,
Paul
I'm noting several different approaches to the above detail used on production EVs. The context of my question is that a handful of near-new e-Niro and Kona Electric examples have developed clicking noises reportedly at approx motor shaft frequency. The manufacturers don't seem to have a field solution to this yet, as best as I know, despite replacing both motors and gearboxes. I'm wondering if there is a fundamental flaw in their design related to coupling two fully-constrained rotating shafts which may have small parallel offset errors due to production and mounting tolerances. I'm also wondering how splines outside of oil-wet areas would be lubricated, whether grease is sufficient.
Here's what I have found on several EV designs.
GM EV1: The rotor (induction motor) and pinion are mounted on a single shaft with a bearing at each end. Between them is only an oil seal.
GM Bolt: The pinion is held by a large nut onto the end of the (PM) motor shaft. There is no outrigger bearing.
Nissan Leaf: The motor (PM) has a splined shaft output. The reduction pinion (and parking pawl wheel) is supported at both ends by bearings. The detail of the motor's male and pinion's female splines is not clear.
Hyundai Kona, Kia e-Niro: Not much info is available but the (PM) motor has a splined output shaft like the Leaf. The design detail of that spline and design of the reduction gearbox internals are all unknown. These two vehicles reportedly use the same motor and reduction gearbox but the overall gear ratio is slightly different.
Any insight is appreciated.
thanks,
Paul
RE: Coupling of EV Motor to Reduction Gear Pinion
For very slight misalignment you might expect a bit of - rocking? along the contact lines of the splines.
For more than slight misalignment, I'd expect issues. Depending on how the two units are mated, there might be a chance of field alignment (or misalignment) when installing.
Seems like this calls for really close inspection of a noisy unit, especially the splines.
And really close inspection /measurement of the mounting arrangements and dimensional variations.
Jay Maechtlen
http://www.laserpubs.com/techcomm
RE: Coupling of EV Motor to Reduction Gear Pinion
RE: Coupling of EV Motor to Reduction Gear Pinion
I found a video showing the relevant details inside the Tesla Model S but the design is not exactly clear. On first glance it appears to have three bearings but it's not certain that the pinion is part of the motor shaft or splined to it.
Found a pic of the Model 3 where the pinion is clearly integrated. It may the same design as the S.
RE: Coupling of EV Motor to Reduction Gear Pinion
RE: Coupling of EV Motor to Reduction Gear Pinion
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Coupling of EV Motor to Reduction Gear Pinion
RE: Coupling of EV Motor to Reduction Gear Pinion
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Coupling of EV Motor to Reduction Gear Pinion
je suis charlie
RE: Coupling of EV Motor to Reduction Gear Pinion
The Tesla Model 3 and Model Y teardown videos by Sandy Monroe indicate that the motor/pinion arrangement is similar with the exception that the gearbox bearing nearest the motor is not present.
Adjacent to the spline coupling in all cases are locating diameters to sensibly center the splined connection when torque is relaxed. In the Teslas, this locating diameter alone appears to support that side of the pinion, effectively utilising the motor's nose bearing. Another interesting feature of the Tesla design is that about the first 1/3 of the motor housing is provided by the reducer housing. So the machining of the motor nose bearing is on the reducer casting. No doubt that's one advantage of manufacturing both units in-house.
My argument is that the Korean design is over-constrained and therefore unnecessarily sensitive to the tolerance stackup between the two shafts. Numerous owners of these EVs are having either or both the reducer and/or motor replaced under warranty due to a ticking noise and one case recently of catastrophic gearbox failure. In a few cases the problem has returned.
RE: Coupling of EV Motor to Reduction Gear Pinion
je suis charlie
RE: Coupling of EV Motor to Reduction Gear Pinion
RE: Coupling of EV Motor to Reduction Gear Pinion
a) misalignment destroying the spline , should be crown spline at the external spine. if free float major diameter fit.
b) not enough lubrication, causing scuffing & fretting, needs oil holes,
and one of the members needs to be coated, eg dry lube, phosphorus, or silver for break in.
c) adding a pilot diameter will also correct misalignment. (this would be a better design)
however if there is not enough lubrication grease will not be enough
it will be only temporary.. it will be pushed out then metal to metal contact.
this has been a hot topic on gear & pulley forum, (Gearcutter)& others
Please search forum on spline being lubed only with grease , high failure rate.