universal joint question

[BGL990]

I thought I once heard/read that a U-joint is OK up to nearly 45 degrees at slower speeds (although I don't know what "slower" really means). If that's true, and roughly judging by the angle of my tiller PTO shaft when in use, I would have thought 20 degrees at each end would be OK ...

 

[Roscoe]

Gday people, Im probably a bit late with this post but the maximum constant velocity angle for a single universal joint is 27 degrees.

Cheers
Roscoe

 

[DaveNay]

</font><font color="blue" class="small">( Gday people, Im probably a bit late with this post but the maximum constant velocity angle for a single universal joint is 27 degrees.

Cheers
Roscoe )</font>

I think I feel pretty confident that the 27 degrees is not a constant and is highly dependant on the physical design of any given U-Joint.

Dave

 

[Cord]

Well, as mentioned above it all has to do with how many RPM's are being turned. Some constant velocity joints can handle 70-80 degrees-but that's at 100rpms. My shaft is turning at 1200rpms so there is a significant angle reduction. A mfr told me that at 20 degrees with a double knuckle joint that it'll start to chatter. As I understand it the chatter comes from the diameter of the knuckle changing as it rotates causing a speed change. Guess it's a problem that really shows up at the higher speeds.

 

[drmiller100]

like they said, a cv joint from the front axle of a FWD car wll do the most angles.
doing a carrier bearing in the middle is another choice. have the carrier bearing will double the u-joints, allowing each to have half the angles, if you do it right.
the old style cv joint, in and of itself, doesn't add much angle, especially at slower speeds.
hydraulic pumps are closer to 90 percent efficient i believe.

 

[Cord]

Ok so lets try describing this layout...

on the left I have a jack shaft which is bearing supported. This is connected to a long shaft with no bearing support with a single cross universal joint. On the right I have another jackshaft which is also supported by bearings. This second jackshaft is connected to the long shaft with a double H style constant velocity joint. This is not a cardan style joint. Does the long shaft need a bearing to support it on the right side?


---B---B--- u joint ------------ u joint H u joint ---B----B---

 

[Defective]

You need a bearing in there somewhere. The problem is the center U-joint. Visualize it this way: If you hold this two-piece shaft by the ends, it will tend to bend at the center joint. If the shaft is spinning, it will wobble. Putting a bearing support on the long shaft, this will effectively lock it in place and make the CV joint the only part free to wobble. Since it is supported at both ends by a U-joint connected to a stationary shaft, it can't wobble.

Of course, this won't work if the long shaft needs to change angle at any time.

Maybe take a look under a large truck or bus for ideas, they usually (or, at least often...) have a 2 shaft setup. The first shaft is fixed at part of the needed angle and the second shaft is allowed to move.

 

[Roscoe]

I put up a reply saying that the max constant angle was 27 degrees, this was for automotive use and since then I have looked at varios websites concerning UJ angles and they all quote differant maximum angles so It dousnt make it easy.

If you look at the drive shaft angle between the drive axles on a truck/tractor unit (Called the "Jack shaft" here), the angles are quite severe, more so when the axles are oscillating over uneven ground.

One thing that has not been mentioned here is that the UJ Yokes must be in line on the same shaft, eg, if the shaft is splined in the middle and can come apart, when assembled, the yokes that hold the universal joint MUST be lined up or "In Phase". All Agricultural shafts that I have seen can only be assembled one way to ensure this happens.

I accidently assembled the rear shaft on my 4WD once, one spline out and when I tried to drive away there was this terrible banging from underneath and the rear of the vehicle was trying to twist on the springs so that alignment is very important.

I think if you are having continuing issiues with shaft angles then a hydraulic motor may be a worthwhile option.
This has the advantage that the motor speed is infinitly variable irrispective of what the tractor engine rpm is.

Cheers
Roscoe

 

[Youare]

I use U-joint couplings for a variety of power transmission applications. The rule of thumb is a 20 degree max. operating angle for the max. recommended operating RPM.

As you increase the operating angle under power the velocity or RPM of the shaft changes as the bearing ends of the joint rotate. This velocity change leads to vibration in the drive shaft which increases as load and RPM increase.

Greater operating angles can be tolerated up to a point as long as load is lighter and RPM's are lower. A constant velocity automotive joint would work well as long as dirt does not get into the joint, a good boot on the joint is necessary.

Randy

 

[ZJ_HR]

I had very good luck with both of my PTO shafts, with wide angle CV joints on one side, used on corn pickers. They were not stopped even at full angle (80-85 degrees), and they survived several hundered hours without any problems, run at 540rpm.