Jump to content


Photo

help/advice/comment on my steering column UJ probelm


  • Please log in to reply
6 replies to this topic

#1 mariner

mariner
  • Member

  • 1,359 posts
  • Joined: January 07

Posted 14 August 2012 - 11:08

Yes, I'm begging for practical help with my toy car again - this time steering column UJ angles.

The steering column system on my toy car is , frankly, horrible but it has worked OK for several hundreds of miles now. The actual steering column shaft ( an OEM Ford unit to meet regulations) points roughly at the pinion on the rack housing but a chassis part is in the way! So the linkage has three UJ's and two shafts. One is in free space , the other is held centrally by a uniball joint.

Rough sketch here

Posted Image

It has worked OK, heavy but to be expected with 550kg on 265 section tyres and a dinky stering wheel. Then I had the rack refurbished and when I re-installed it I was "clever" and reduced the UJ angle at the rack end ( UJ3 in the pic). Result - almost impossible to steer and very "lumpy " wheel feel.

Why? - I think because when I reduced UJ3 angle I increased the UJ 2 angle and as this has the biggest angle it has dramaticaly increased the steering wheel load variation.

So I think the right thing to do is to INCREASE the angle of UJ3 next to the rack as much as space will allow so as to reduce the biggest angle in the linkage , UJ 2, as much as possible.

The angles are changed simply by rotating the rack housing around its lateral axis - i.e twist it clockwise in the sketch.

Any commants ( apart from how bad it is - I know that!)


Advertisement

#2 Lee Nicolle

Lee Nicolle
  • Member

  • 5,663 posts
  • Joined: July 08

Posted 14 August 2012 - 11:22

Yes, I'm begging for practical help with my toy car again - this time steering column UJ angles.

The steering column system on my toy car is , frankly, horrible but it has worked OK for several hundreds of miles now. The actual steering column shaft ( an OEM Ford unit to meet regulations) points roughly at the pinion on the rack housing but a chassis part is in the way! So the linkage has three UJ's and two shafts. One is in free space , the other is held centrally by a uniball joint.

Rough sketch here

Posted Image

It has worked OK, heavy but to be expected with 550kg on 265 section tyres and a dinky stering wheel. Then I had the rack refurbished and when I re-installed it I was "clever" and reduced the UJ angle at the rack end ( UJ3 in the pic). Result - almost impossible to steer and very "lumpy " wheel feel.

Why? - I think because when I reduced UJ3 angle I increased the UJ 2 angle and as this has the biggest angle it has dramaticaly increased the steering wheel load variation.

So I think the right thing to do is to INCREASE the angle of UJ3 next to the rack as much as space will allow so as to reduce the biggest angle in the linkage , UJ 2, as much as possible.

The angles are changed simply by rotating the rack housing around its lateral axis - i.e twist it clockwise in the sketch.

Any commants ( apart from how bad it is - I know that!)

Decrease than centre uni angle. I suspect that the support heim may also be binding it. It really us suck it and see. Those steering unis really are not effective over about 15 degrees. I used a similar deal on my old Sports Sedan to get the steering around the starter.Changing the rack to one with a straight input solved all the problems as it straightened all the angles somewhat.
Though now be lateral, has the refurbished rack been adjusted too tight? That will make the steering VERY notchy. If so straighten those uni angles anyway.


#3 gruntguru

gruntguru
  • Member

  • 5,175 posts
  • Joined: January 09

Posted 15 August 2012 - 00:26

Your drawing shows all three joints at the same phase angle. 1 and 3 should be at the same phase and 2 should be 90 deg to both. This is easy to do if all four shafts/axes lie in the same plane, a little trickier if not.

#4 Greg Locock

Greg Locock
  • Member

  • 4,477 posts
  • Joined: March 03

Posted 15 August 2012 - 01:30

I'm not going to get involved in the maths, but UJ phasing of three dimensional shafts rarely involves exact multiples of 90 degrees. Typically my priorities are symmetrical ratio of rack motion to steering wheel angle to the left and right, then, if I can get that, to get the maximum velocity ratio (rack/SWA) at the on centre location, and then, finally to minimise the variation in velocity ratio to less than 10%.

Now, for a play car where the SWA is unlikely to exceed 180 degrees when you are serious, a lot of these criteria can be relaxed, but the first would still be my priority.

This can mean using an an unholy mix of single and double cardans. generally I dislike joints hanging on two unguided shafts as they could toggle.

Edited by Greg Locock, 15 August 2012 - 01:31.


#5 Kelpiecross

Kelpiecross
  • Member

  • 834 posts
  • Joined: October 10

Posted 15 August 2012 - 13:59

[quote name='mariner' date='Aug 14 2012, 21:08' post='5872288']
Yes, I'm begging for practical help with my toy car again - this time steering column UJ angles.

The angles are changed simply by rotating the rack housing around its lateral axis - i.e twist it clockwise in the sketch.

Have you tried rotating the rack to see if it helps or worsens the problem?

#6 mariner

mariner
  • Member

  • 1,359 posts
  • Joined: January 07

Posted 15 August 2012 - 14:22

yes, Kelpie I have done that now, if it ever stops raining here I'll go and test.

We had wonderful weather for the Olympics now back to rain!

#7 mariner

mariner
  • Member

  • 1,359 posts
  • Joined: January 07

Posted 17 August 2012 - 19:31

now tested with much better equalised UJ angles.

Much, much better so shows what quite small changes in things can do!

thank you all