U-Joint syncing questions...

I had to calculate this at school once, but thats a long time ago.

So hopefully y'all can help me out.

I know that if you have two U-Joints in a steering column with one, say, going 20 deg down and the other going 20 deg back up they need to be in sync.

Because the rotational speed of the outgoing side is not constant through the whole revolution, compared with the ingoing side.
The second U-joint distorts it back to zero, or even with the ingoing side.

That much is clear to me...

But if you have a U-Joint going down by, say again 20 deg, and the second also 20 deg going the same way?

Do they still cancel each other out, or is the uneven-ness now twice as big?

So do you still sync them as if the second goes back to zero deg?

Or do you put them 90 deg out of sync to cancel out some of the uneven-ness?

 

how fast do you plan of steering this thing?

 

Its a Racecar.

As fast as I can make it go...





Its more about precission than speed...

 

I think the phasing has to do with the angular velocity, so it doesn't matte which way the joints bend...they need to be in phase so the changes in angular velocity happen at the same time at both ends.

 

Cool...

Thats what I thought it might be, but I wasn't able to visualise it.

Thank you.

 

Found the graph...



It goes through a cycle every 180deg, so I think that means you are right.

( like there was any doubt...)

They need to be synced.

 

I doubt U-joint angle would matter in a steering set-up no matter what the angle. Case in point, my Windstar van has a terific angle under the dash and can't feel the
velocity changes in the wheel.

 

Thats true.

In a Windstar it doesnt matter.

 

May depend on the vehicle, we had some new Oshkosh plow trucks that had big angles in both planes in the steering shaft, found they had really strange feel during certain high speed maneuvering.
Engineers revised the joint relationship so they were somewhat out of phase, don't remember how much; but the steering smoothed right out.

 

All kidding aside, yes I think it does matter.

Its a racecar, which means its going to get pushed to its limit.

Having the same degrees of steering input at the R&P as you put in with the steeringwheel, at all times, is probably a good thing.

Plus everything is ultra direct, and none of the components are rubbermounted.


Right now it has the colum a bit too low.

Its too close to the pedals and my feet.

I dont want to use any chaindrives, bevelgears, or that kind of goofyness.

But I can find the space I need with one extra U-Joint and a second support bearing on the column.

Simple, light, and clean.

But I wanted to make sure I wasnt about to make a mistake with my U-Joint syncing.

I think I got the Info I need.

Thanks again guys....

 

Keep them in phase, simple.

 

I'm with Squirrel on this one, angle matters not direction.

 

My point is that in a normal situation, as a street car, You wouldn't know the difference. Sorry,Didn't realise you were referring to a race car.

 

I'm confused how phasing relates to 3 joints? Can they all be in phase?

If they are all curving around an object they wont cancel out. Canceling happens when one is "up" and the other is down the same degree.

 

isn't that graph for a driveshaft? it would make sense that in a drive shaft the velocity would change as the suspension moves up and down. the steering is fixed [i doubt your mounting the rack on a straight axle] so the rpm would stay the same or am i missing something?

 

No sir, the speed on the driven shaft is what changes. The other joint is what corrects the speed or phase. The more angle the more the speed changes. On a hard angle when you turn the u joint the driven shaft speeds up and slows down every revolution because of the differant pivot point on the trunnion. That's why CV joints are called constant velocity joints. The pivot radius is constant no matter what angle they are on. Hope this makes sense, it's pretty early to think.

 

actually cancelling has nothing to do with the angle except for the amount of speed variation. The cancelling comes from how the U-joint halfs are positioned on the shaft in relation to each other (brg caps on each end in line). As one end's speed inc. the opposite end's speed dec. If both angles are equal, theoretically, the speeds at both ends of the shaft will be the same.

 

thought about it all day, kinda get it, the difference in speed must be tiny. i would think the smaller the ujoint the smaller the difference? with the small ujoints used in steering, would you even notice?

 

Went to a driveline seminar once, the rep had a training aid where you could reposition the the ends and vary the angle of the joints. At extreme angle you could see the shaft speed up and slow down, while the tachometers showed the input and output speeds matched.

With three u-joints you need to actually look at it as two shafts, each one using the center
joint.

The speed changes are function of u-joint geometry not size. Big joints and little joints
act the same.

 

thanks, i'm not the sharpest bulb in the box so i'll have to think about that today too.

 

I never understood it until I saw a very slow setup like RICHB describes.

 

if you were using Double D shaft they would always be inphase, therefore Im sure they should be in phase, match up the steering box ( spline ) to be in phase with the other joints.

To simple, maybe but it will work.

Godspeed
MrC.

 

They still cancel each other out. Won't bind and will turn freely. It's easy to confuse driveline torsional vibration to joint-phasing.

 

Yes, double joints are built in-phase but any added in line must be phased with the double joint

 

Actually the joint speeds up 2 times per revolution, once for each cap.