Universal joints
Universal joints
(OP)
I need a "primer" on u-joints. I don't even know the nomenclature for a typical cross-type automotive u-joint (steel cross with four needle bearings)? And I've never seen (or tried to derive) the math (output angular position vs. input as a function of running-angles, etc.). For a two-joint drive (typical front & rear of a driveshaft), what orientation of the joints provides maximum cancellation of angular velocity disturbances? Is it true that equal-but-opposite run-angles of the two joints is most desirable?
RE: Universal joints
So... let's cut to the chase. The pickup truck I'm putting together would have the rear u-joint running at about four degrees but the front joint at about one degree in the wrong direction. Would this create noticeable vibration?
RE: Universal joints
Roughly speaking those angles won't kill the transmission/driveline, but may cause booms. Bear in mind that on a live rear axle setup the rear UJ angle is a compromise for the average torque.
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: Universal joints
Get your trans or your rear end shimmed.
rmw
RE: Universal joints
Hence the request for a diagram.
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: Universal joints
My understanding is that the joints should be out-of-phase by 90 degrees and their run-angles should be equal and opposite, to effectively cancel velocity fluctuations. I trust that this is true, and I'll probably change the wedges at the rear axle housing mounts to accomplish this. I'm just curious how bad the situation would be the way it sits right now- noticeable vibration? Self-destruction of bearings? Noisy?
Regarding the rear angle being a compromise: it's less of a concern than with most leaf-sprung rears, since I've built a 48" long torque arm to react differential housing torque to the frame.
RE: Universal joints
eg http:/
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: Universal joints
Hopefully your torque-arm rear suspension is stiff enough so that the axle as a whole doesn't wind up significantly under acceleration, and hopefully you've placed the side-view instant-centre such that the anti-squat geometry cancels out the weight transfer, thus the rear suspension will remain at or close to nominal ride height under acceleration.
Torque-arm rear suspensions (and all other link-type suspensions with non-parallel upper and lower arms in side view, such that they have some anti-squat in them) will always rotate the axle housing with suspension movement, thus sending the U-joint angles out of alignment, but at least if you have it aligned at nominal ride height, the effect will be minimal during normal driving and the amount it goes out of kilter will be equal and opposite (and kept to a minimum) with up or down movement away from nominal ride height.
RE: Universal joints
A mis-aligned U-joint probably isn't too unhappy under those conditions. It is at higher speeds - road speeds, cruising speeds - that you will see the effects of U-joints being out of line (out of angle match). Not too much torque then, but lots of revs and lots of potential for vibes - bad vibes.
rmw
RE: Universal joints
It had weak rear lower control arm bushes and I beat on it a lot spinning wheels towing boats up ramps and tramping the axles with intermittent wheel spin on corrugated roads. It regularly chopped the rubber out of the front bush on the rear longitudinal lower control arms, allowing the back uni to hit the top of the tunnel on hard acceleration. It developed high speed drive line vibrations that no attempts at balance could fix.
At one time the clutch pressure plate bolts backed out enough to lock the engine (I thought it threw a rod by the sound it made).
Shortly after that it destroyed a gear box in spectacular fashion. This was at 13 months old after repeated unresolved complaints to the dealer of these vibrations.
The new gear box fixed everything, but maybe they fitted harder bushes at the same time. hmmmm. I always blamed it on gear box lay shaft bearing clearance/misalignment problems.
Regards
Pat
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RE: Universal joints
There are two separate effects we need to compensate for - pitch of the axle due to vertical suspension travel, and rotation due to torque.
These are controlled by different attributes of the suspension architecture, and as such any setting is a compromise.
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: Universal joints
RE: Universal joints
I am assuming that your front spring eyes are located considerably less than 48" in front of the axle and that your torque arm is not pin-connected on the chassis side.
Norm
RE: Universal joints
Every drive-shaft I've played with had the joints in-phase, or the yokes on each end of the drive shaft lined-up. I'm thinking you'd get a double velocity fluctuation at the pinion if you turned the yokes 90 degrees relative to each other, which would be a very bad thing.
RE: Universal joints
Lionel- yokes lined-up on driveshaft DOES cause the rear joint to be driven 90 degrees out-of-phase with front joint.
RE: Universal joints
Norm
RE: Universal joints
The effective radius resulting from clamping to the springs is approximately infinite (leaf packs are symmetrical ahead-of and behind the clamps).
I tend to think of the 52" radius of the torque arm (front Heim joint to axle centerline) as "almost infinite" in light of the limited travel range of the rear axle during "normal" driving- maybe 5"?
Thus, the lack of coincidence causes merely a small increase in spring rate.
Thanks for listening and for helping.
RE: Universal joints
Norm
RE: Universal joints
This means that to a large degree the leaf spring behvaes much more like a trailing arm than anything else.
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: Universal joints
It's been too many years for me to remember exact measurements, but with almost every leaf sprung, live axled race car of the last 40 years, I have used no tq reaction devices save a short (relatively), stiff front spring section with a solid bushing with a longish rear section on compliant shackles or roller sliders along with a Panhard bar or Watts link. U joints are set parallel and in phase. No extra links. Axle wind up on acceleration is not the big problem but, axle hop on heavy braking can be. All in all, I am not a proponent of adding any additional axle control devices to a leaf sprung live axle.
I know of many who do not like my approach, but I have an awful lot of wins and lap records to make me stick with what works for me.
Rod
RE: Universal joints
RE: Universal joints
http://www.ponysite.de/212777_wattslinkage.jpg
page 16 here, allegedly
htt
allegedly a 1969 trans am car with narrowde leafs and a watts linkage
http:
http:
RE: Universal joints
I think the trick is setting the PHB or WL at the proper height.
Norm
RE: Universal joints
Tmoose, I've competed against Bud Moore cars in vintage racing, including one Palm Springs Grand Prix in the late 80's where they were driven by Parnelli Jones and George Follmer. PJ broke and at the checker I could see Follmer's Mustang coming up to lap me. Good stuff!
Rod
RE: Universal joints
Sorry 'bout that.
Rod
RE: Universal joints
Internet searches let me down, however, on a description of ball-and-trunnion style joints, such as used in my '55 Plymouth (and I'm too lazy to work out the math myself). Anybody know (or direct me to) the expression for output velocity vs. run-angle for such a joint (at constant input velocity)?
RE: Universal joints
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: Universal joints
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: Universal joints
RE: Universal joints
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: Universal joints
RE: Universal joints
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: Universal joints
See the attached paper. It outlines possible instabilities.
Other than that you should be ok.
Fe
RE: Universal joints
RE: Universal joints
Yes you should have no problem. It's more of something to look out for, and to gain some technical knowledge of the subject.
Fe