Lotus Elan

CV joints...General aspects.

PostPost by: billwill » Fri Oct 26, 2012 6:29 pm

Having looked at the descriptions of CV joints on Wikipedia,

Image


I still don't understand why on our Elans, they solve the problem of the seemingly required variable length of the half-shafts, for which when U/Js are used it is necessary to use splined sliding sections.

Can someone enlighten me?
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PostPost by: GrUmPyBoDgEr » Fri Oct 26, 2012 6:41 pm

billwill wrote:Having looked at the descriptions of CV joints on Wikipedia,

Image


I still don't understand why on our Elans, they solve the problem of the seemingly required variable length of the half-shafts, for which when U/Js are used it is necessary to use splined sliding sections.

Can someone enlighten me?


That's a simplistic diagrammatic representation of the basic principle of a constant velocity joint.
Take a look at an actual joint that will provide axial variation & you will see that the shape of the grooves in which the balls move are far complicated than the spherical shape depicted here.
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PostPost by: Chancer » Fri Oct 26, 2012 6:48 pm

Go to GKNservice.com and download the Loebro PDF file and all will be revealed.

There are plunge joints there that will cope with a much wider angle than the Elan ones are failing to cope with, I suspect cost or availability is a determining factor.
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PostPost by: billwill » Fri Oct 26, 2012 7:46 pm

So the answer to my initial question is that the CV joints known as plunge joints contain a sliding spline joint, but it is inside the CV joint, so you don't realise it is there from simple external photos.

I presume that only one of the two joints on a shaft (I quite like that phrase "side shaft") is of plunge type, otherwise the shaft would float in an unpredictable way between the two joints.
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PostPost by: types26/36 » Fri Oct 26, 2012 7:55 pm

billwill wrote:So the answer to my initial question is that the CV joints known as plunge joints contain a sliding spline joint, but it is inside the CV joint, so you don't realise it is there from simple external photos.

I presume that only one of the two joints on a shaft (I quite like that phrase "side shaft") is of plunge type, otherwise the shaft would float in an unpredictable way between the two joints.


1. No there is no sliding spline, the smaller inner race (both ends) is held on the shaft on splines BUT it does not slide as it has a shoulder to press against and a circlip to prevent movement.
2. Yes, It can "float" but only on the ball race grooves.
Last edited by types26/36 on Fri Oct 26, 2012 8:51 pm, edited 1 time in total.
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PostPost by: GrUmPyBoDgEr » Fri Oct 26, 2012 8:36 pm

billwill wrote:So the answer to my initial question is that the CV joints known as plunge joints contain a sliding spline joint, but it is inside the CV joint, so you don't realise it is there from simple external photos.

I presume that only one of the two joints on a shaft (I quite like that phrase "side shaft") is of plunge type, otherwise the shaft would float in an unpredictable way between the two joints.



No nobody has said that!
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PostPost by: collins_dan » Fri Oct 26, 2012 9:27 pm

The movement is predictable by the ball race grooves. You basically have a fixed shaft in the middle of two ends that move. You understand the movement a lot better after you have to take one apart to replace torn boots. The movement possible is twice what your picture depicts, because you have them at both ends. Dan
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PostPost by: billwill » Fri Oct 26, 2012 10:35 pm

OK, OK... I believe you all. It's an easy mistakaA to MakeaA

:lol:

And in my defence.. This one does have sliding splines made with balls.

Image

:twisted:
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PostPost by: AHM » Fri Oct 26, 2012 10:45 pm

!Ok
There are fixed and plunging joints. On a fixed joint the component parts have concentric truncated spherical surfaces which do not allow axial freedom. On plunging joints the outer race has a straight rather than spherical surface and is therefore not constrained axially.

The components are designed to provide "steering" so that the joint operates on the homokinetic plane and does not "float" even in the straight line state.

Constant velocity is achieved by keeping the balls on the bisecting plane so that their angular velocity is uniform - The homokinetic plane. Contrast this with a UJ. Where the trunions are driven on the input and output planes.

Articulation angle is restricted by the interference between the shaft and the outer race. This is restricted further in plunging joints at full plunge and by the balls coming out of the tracks at full extension.
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PostPost by: Andy8421 » Sat Oct 27, 2012 9:28 am

For the reasons mentioned above, non plunging joints work at more extreme angles than plunging joints. On the later minis, the outer CV joint that had to cope with steering angles was non plunging, the inner joint which only had to cope with suspension movement plunged.

Worth noting that in-period Chapman used ball splines if he needed a plunging link. Normal splines lock up under load, and in an Elan significant torque on the rear driveshafts locks the rear suspension. I have TTR UJ/splines on the S3 I race, but suspension travel is nearly zero, so I guess it isn't too much of a problem.
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PostPost by: GrUmPyBoDgEr » Sat Oct 27, 2012 9:36 am

AHM wrote:!Ok
There are fixed and plunging joints. On a fixed joint the component parts have concentric truncated spherical surfaces which do not allow axial freedom. On plunging joints the outer race has a straight rather than spherical surface and is therefore not constrained axially.

The components are designed to provide "steering" so that the joint operates on the homokinetic plane and does not "float" even in the straight line state.

Constant velocity is achieved by keeping the balls on the bisecting plane so that their angular velocity is uniform - The homokinetic plane. Contrast this with a UJ. Where the trunions are driven on the input and output planes.

Articulation angle is restricted by the interference between the shaft and the outer race. This is restricted further in plunging joints at full plunge and by the balls coming out of the tracks at full extension.



Wow!, brilliantly explained; makes my effort look so daft.
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PostPost by: AHM » Sat Oct 27, 2012 9:26 pm

John, Thanks.

... memories from a previous life!
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PostPost by: GrUmPyBoDgEr » Sat Oct 27, 2012 9:33 pm

I guessed that might be the case :wink:
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