Jump to content


Photo
- - - - -

Driveshaft Angle and Phasing Made Ridiculously Simple


  • Please log in to reply
46 replies to this topic

#1 Magoo

Magoo
  • Member

  • 2,518 posts
  • Joined: October 10

Posted 28 July 2014 - 10:06

Trying to explain driveshaft angle and phasing can be devilishly difficult, but this video demonstration makes it totally easy and simple.

 

This item has drawn a huge response since it was posted, suggesting that there is more need for good, clear tutorials like this than we may suppose. So if you know of any on automotive topics, please shout out. 

 

 

 

 

Video: Driveshaft Angle and Phasing 

 

 

 

 

qfHBcS.jpg

 

 

 



Advertisement

#2 gruntguru

gruntguru
  • Member

  • 5,388 posts
  • Joined: January 09

Posted 29 July 2014 - 05:20

Nice video. Particularly liked the credit card flapper as a velocity indicator.

 

Not mentioned but worth adding - constant velocity does not require the input and output shafts to be parallel, only that the operating angle of each joint be the same. Of course if the input and output shafts are not in the same plane, the phasing will need to varied to suit.


Edited by gruntguru, 29 July 2014 - 05:21.


#3 Lee Nicolle

Lee Nicolle
  • Member

  • 6,062 posts
  • Joined: July 08

Posted 29 July 2014 - 09:31

The phasing of modern [last 30 years!!] triple joint tailshafts is a real drama. Many such as Holden Commodore always have a light 'whip' at low speeds under accelaration. Damned annoying. Most others do not do it,,, until everything gets old and tired

This does truly still confuse me. Even just a std tailshaft which all of us take for granted. 

As does universal joints, simple but complex! That and balancing tailshafts, something many places cannot get right. Yet others can be machined off and shortened with no viabration issues. 

Uni joints are not uni joints though. Some cheap ones seem to bind at high speed. Having suffered horrendous vibes at over 150 mph [race car] the brand name unis were replaced with high performance Spicer ones, shaft balanced [hardly needed it so they said]  and no viabrations at all. Tested to about 175mph. In this instance I will reccomend Spicer for balancing whole heartedly.

Interestingly I was told that having the shaft dead straight at ride height is not a good idea. The rollers dont roll in the trunnions and the uni will get roller marks in the cross at a fairly short service life. In my case I just adjusted the nose of the diff down,which helps hook it up at low speed anyway,  not so easy in most cars. This was because the pinion is so low in a 9" diff in comparison to the GM pinion it straightened out the angle. On my vehicle.



#4 sblick

sblick
  • Member

  • 488 posts
  • Joined: September 01

Posted 29 July 2014 - 20:32

Always been told in NVH that a flat driveshaft is not as good as one with a slight angle. So if you don't want any shaking in the car don't design a flat driveshaft.

#5 Canuck

Canuck
  • Member

  • 1,671 posts
  • Joined: March 05

Posted 29 July 2014 - 20:57

Your timing could be better. In the middle of a driveshaft redesign as we speak. The vendor's casual "oh yeah, no problem, do it all the time" response has me scared enough to be doing lots of homework.

#6 desmo

desmo
  • Tech Forum Host

  • 13,101 posts
  • Joined: January 00

Posted 29 July 2014 - 21:42

All right, 'big bang' traction benefits are misaligned u-joints away!



#7 Greg Locock

Greg Locock
  • Member

  • 4,544 posts
  • Joined: March 03

Posted 30 July 2014 - 05:06

One thing to bear in mind is that your diff pitches under acceleration, ruining your carefully thought out angles. You can only truly optimise a driveline for one propshaft torque, managing the compromise is the name of the game. This has led to the popularity of CV joints in RWD propshafts.

 

According to Hookes Joint manufacturers the optimum angle for durability on a rig is 4 degrees, to avoid False Brinelling as it is often called. In a car that is not needed as much because the engine and the diff are moving around a fair bit.

 

Incidentally, if you think driveshaft angles are tricky, wait until you try and lay out a steering column, with typically 3 UJs and massive angles between the shafts.



#8 gruntguru

gruntguru
  • Member

  • 5,388 posts
  • Joined: January 09

Posted 30 July 2014 - 06:45

At least the steering column won't vibrate. :)



#9 bigleagueslider

bigleagueslider
  • Member

  • 863 posts
  • Joined: March 11

Posted 31 July 2014 - 00:54

I love the term "false brinelling". As if the damage done to the race surfaces is not a "true" problem. With needle bearings subject to oscillatory motion, there should be sufficient movement to ensure each roller completes one full rotation. This distributes the wear evenly over the race surfaces. If there is little or no rotation of the rollers, they will create small local depressions in the race surfaces. And when the rollers eventually do pass over these surface depressions, it will produce pitting/spalling of the race.



#10 Magoo

Magoo
  • Member

  • 2,518 posts
  • Joined: October 10

Posted 31 July 2014 - 02:53

 

 

Incidentally, if you think driveshaft angles are tricky, wait until you try and lay out a steering column, with typically 3 UJs and massive angles between the shafts.

 

About six months ago I drove a street rod with extremely odd steering feel and response. Looked at the steering column arrangement and.... honestly, the things people come up with. 



#11 Lee Nicolle

Lee Nicolle
  • Member

  • 6,062 posts
  • Joined: July 08

Posted 31 July 2014 - 09:12

One thing to bear in mind is that your diff pitches under acceleration, ruining your carefully thought out angles. You can only truly optimise a driveline for one propshaft torque, managing the compromise is the name of the game. This has led to the popularity of CV joints in RWD propshafts.

 

According to Hookes Joint manufacturers the optimum angle for durability on a rig is 4 degrees, to avoid False Brinelling as it is often called. In a car that is not needed as much because the engine and the diff are moving around a fair bit.

 

Incidentally, if you think driveshaft angles are tricky, wait until you try and lay out a steering column, with typically 3 UJs and massive angles between the shafts.

Three unis in a steering shaft is too many. Very few vehicles use that. And really you need a bearing on an intermediate shaft. Or it just flops everywhere .

Having been there and done just that, RH drive car with a Chev engine. The starter is in the way!

Steering column,, uni, short shaft to a second uni,, another short shaft with a carrier [heim joint] then another short shaft to the rack and the third uni. Far from ideal, safe but only just. 

Later I changed the rack to a  stronger one with a better input angle and then only 2 unis. And no more worry about the rack failing. [Which had happened]

If a manufacturer has to use three it is just plain bad design. 



#12 MatsNorway

MatsNorway
  • Member

  • 2,075 posts
  • Joined: December 09

Posted 12 August 2014 - 16:13

This might be interesting for you guys.

 

"Through using shifted slot parts of the universal ring the user can also tune the angular speed fluctuations to create chatter which can be desirable in some conditions."

 

http://www.redrc.net...tem/#more-84946



#13 gruntguru

gruntguru
  • Member

  • 5,388 posts
  • Joined: January 09

Posted 12 August 2014 - 21:56

Dirt racer - big bang thinking?


Edited by gruntguru, 13 August 2014 - 05:50.


#14 desmo

desmo
  • Tech Forum Host

  • 13,101 posts
  • Joined: January 00

Posted 12 August 2014 - 23:01

See post #6 above.  What, you thought I was joking? So did I.



#15 MatsNorway

MatsNorway
  • Member

  • 2,075 posts
  • Joined: December 09

Posted 13 August 2014 - 12:03

:)

 

I think that the shattering stuff is increasing the resistance on the inner wheel making it aid in turning on tight bends.



#16 MatsNorway

MatsNorway
  • Member

  • 2,075 posts
  • Joined: December 09

Posted 27 September 2014 - 12:53

Does anyone consider driveshaft angle and phasing in steering applications? non linear output despite the same amount applied to the steering wheel and so on.


Edited by MatsNorway, 27 September 2014 - 12:53.


#17 Magoo

Magoo
  • Member

  • 2,518 posts
  • Joined: October 10

Posted 27 September 2014 - 14:19

Does anyone consider driveshaft angle and phasing in steering applications? non linear output despite the same amount applied to the steering wheel and so on.

 

Absolutely. There is some reference to it in the discussion above. You know the feel on the ratchet when you are wrenching on a fastener with a socket, extension, and u-joint at extreme angle? Just like that, and more pronounced with a smaller steering wheel diameter. 



#18 Greg Locock

Greg Locock
  • Member

  • 4,544 posts
  • Joined: March 03

Posted 28 September 2014 - 04:21

There are three main camps on this. There are those  who prefer to have a high ratio on centre, those which prefer a low ratio on centre, and those that don't have the faintest idea what we are talking about. It's possible to make either work, perfectly well with normal geometries, people aren't all that sensitive to it so long as the system is symmetrical and there isn't too much variation in ratio.

 

However at least one company thinks it is a big deal

 

http://www.designfax...et=motion&pn=01

 

I haven't driven one of these yet but I did attend a good technical briefing by the main inventor of the system, it gives some really useful effects. Lee'll love it.



#19 desmo

desmo
  • Tech Forum Host

  • 13,101 posts
  • Joined: January 00

Posted 28 September 2014 - 04:56

Looks promising doesn't it?

Advertisement

#20 Kelpiecross

Kelpiecross
  • Member

  • 907 posts
  • Joined: October 10

Posted 28 September 2014 - 05:38


What happens if you lose all electrical power to the steering mechanism?

#21 Greg Locock

Greg Locock
  • Member

  • 4,544 posts
  • Joined: March 03

Posted 28 September 2014 - 05:52

The worm drive /motor system locks up, like most worm drives thereby leaving you with a direct connection between wheel and column It's possible to create a worm drive geometry that can be back driven, but it is much easier to design one that isn't. The formula relates the pitch angle and mu, it should be in any gear design manual. 



#22 Kelpiecross

Kelpiecross
  • Member

  • 907 posts
  • Joined: October 10

Posted 28 September 2014 - 05:59


Thank you for that. I thought at first look that it was entirely fly-by-wire. Seems like a very clever idea.

#23 Greg Locock

Greg Locock
  • Member

  • 4,544 posts
  • Joined: March 03

Posted 28 September 2014 - 07:36

I think it is clever, I'm waiting to see if it is useful!



#24 MatsNorway

MatsNorway
  • Member

  • 2,075 posts
  • Joined: December 09

Posted 28 September 2014 - 10:08

Could you not just use gears in the steering? It is a fairly fixed installation after all. I guess the slack is noticable.


Edited by MatsNorway, 28 September 2014 - 10:09.


#25 Greg Locock

Greg Locock
  • Member

  • 4,544 posts
  • Joined: March 03

Posted 28 September 2014 - 21:30

Yes, you have to be very careful with both backlash and friction in the steering system. You can use gears - for example BMW's active steering uses an epicyclic box in the column, but then they have rather lost their class leading ride/handling/steering compromise these days   decades



#26 Kelpiecross

Kelpiecross
  • Member

  • 907 posts
  • Joined: October 10

Posted 29 September 2014 - 05:06


I would have thought that with the motor/worm drive etc. contained within the steering wheel (and turning with the steering wheel) that all the (variable) steering effort would be supplied by the driver's hands. At parking speeds would not the reduced turns on the steering lead to a very high steering effort? Presumably it would need some form of power assistance downstream from the steering wheel?

#27 Greg Locock

Greg Locock
  • Member

  • 4,544 posts
  • Joined: March 03

Posted 29 September 2014 - 05:26

Yes, it is in series with the EPAS, it provides a way of subtly modifying the feel of the handwheel. The EPAS still provides all the assistance.



#28 gruntguru

gruntguru
  • Member

  • 5,388 posts
  • Joined: January 09

Posted 29 September 2014 - 08:08

KC the steering effort (force) will be essentially the same, the extra work (energy) of turning the road wheels further is supplied by the worm drive.



#29 Greg Locock

Greg Locock
  • Member

  • 4,544 posts
  • Joined: March 03

Posted 29 September 2014 - 11:36

Not quite, the wiper motor turns the column more which turns the torsion bar more which tells the epas to turn the road wheels more. So the small power input to the steering wheel motor causes the epas to join in.



#30 mariner

mariner
  • Member

  • 1,384 posts
  • Joined: January 07

Posted 29 September 2014 - 14:22

This sems to be one of those " very simple but very clever" ideas because all the " fly by wire" benefits ar backed up by fail-safe mechanicals.

 

It would be interesting to think about a competiton application where the yaw , lat G and speed sensors could adjust the worm drive motor to enhance the driver feedback loop seperately from normal steering feel from pheumtic trail , slip angle etc.



#31 gruntguru

gruntguru
  • Member

  • 5,388 posts
  • Joined: January 09

Posted 29 September 2014 - 23:48

Not quite, the wiper motor turns the column more which turns the torsion bar more which tells the epas to turn the road wheels more. So the small power input to the steering wheel motor causes the epas to join in.

What I am saying is the EPAS does the same amount of work (lock to lock) as usual, the driver does fewer turns less angle at the same torque (so less work) and the wiper motor adds the extra turns angle (at the same torque as the driver) so makes up the work shortfall.

 

Of course the system could also increase the turns angle lock to lock in which case the driver would do more work than usual and the wiper motor would be absorbing energy.


Edited by gruntguru, 30 September 2014 - 08:44.


#32 Greg Locock

Greg Locock
  • Member

  • 4,544 posts
  • Joined: March 03

Posted 30 September 2014 - 02:15

Ah, no, the system in the steering wheel doesn't do turns, it does very small numbers of degrees, typically much less than 30. The development systems could do a lot more than that, but I am told that various weird behaviours (such as the steering wheel no longer being straight at straight ahead) very much limits how enthusiastic the calibrators can get. Making the system less capable also reduces its inertia and volume, which is good 


Edited by Greg Locock, 30 September 2014 - 02:27.


#33 Kelpiecross

Kelpiecross
  • Member

  • 907 posts
  • Joined: October 10

Posted 30 September 2014 - 07:06

KC the steering effort (force) will be essentially the same, the extra work (energy) of turning the road wheels further is supplied by the worm drive.


The way I pictured the situation was to imagine (for a test situation) holding the steering wheel stationary and operating the worm drive - clearly all the reaction force from the worm drive turning the front wheels would be supplied by the driver.

I suspect this system is one that you would have to drive to see how it feels. It would have to be a big improvement to justify the extra complication.

To change the subject slightly - worm and wheel drives are very interesting in that they are "digital" (having fixed numbers of teeth) but exhibit some "analogue" properties.

#34 gruntguru

gruntguru
  • Member

  • 5,388 posts
  • Joined: January 09

Posted 30 September 2014 - 08:39

(1.) The way I pictured the situation was to imagine (for a test situation) holding the steering wheel stationary and operating the worm drive - clearly all the reaction force from the worm drive turning the front wheels would be supplied by the driver.

(2.) To change the subject slightly - worm and wheel drives are very interesting in that they are "digital" (having fixed numbers of teeth) but exhibit some "analogue" properties.

1.  - clearly all the reaction force from the worm drive turning the front wheels PAS input would be supplied by the driver.

 

2. Worm drives are very much analog as are spur gears in spite of having integer numbers of teeth.



#35 gruntguru

gruntguru
  • Member

  • 5,388 posts
  • Joined: January 09

Posted 30 September 2014 - 08:42

Ah, no, the system in the steering wheel doesn't do turns, it does very small numbers of degrees, typically much less than 30.  

 

My comments apply regardless of the maximum angle. Sorry if my post gave the impression that the added angle was more than one turn.



#36 Greg Locock

Greg Locock
  • Member

  • 4,544 posts
  • Joined: March 03

Posted 30 September 2014 - 22:35

No worries, it is quite an odd thing to get your head around. Those who have driven it say it is good, but they are people who spend much of their time thinking about the feel of the steering, real people may notice something in the first five minutes and never again. 

 

Anyay, this worksl like most PAS systems  with the driver reacting the steering wheel torque, and the rack (or steering box) reacting the tie rod forces including the direct geared force and the assist force or torque.



#37 Kelpiecross

Kelpiecross
  • Member

  • 907 posts
  • Joined: October 10

Posted 01 October 2014 - 04:31

1.  - clearly all the reaction force from the worm drive turning the front wheels PAS input would be supplied by the driver.

 
2. Worm drives are very much analog as are spur gears in spite of having integer numbers of teeth.

On 1. - I had in mind a test where the engine was not running and the worm drive could be actuated by a switch.

On 2. What I had in mind here was that the gear ratio of a certain pair of spur gears can only varied in distinct steps - numbers of teeth - not continuously - and only by changing the gears. The analog property of a worm refers to the self-locking effect which occurs when the worm system is driven in the reverse direction - here it has a continuously variable range of positions in which it can lock even though the gears are themselves unchanged.

#38 imaginesix

imaginesix
  • Member

  • 5,716 posts
  • Joined: March 01

Posted 01 October 2014 - 04:33

Looks like a poor man's AWS.



#39 Kelpiecross

Kelpiecross
  • Member

  • 907 posts
  • Joined: October 10

Posted 01 October 2014 - 04:40

Looks like a poor man's AWS.

Why do you think this?

Advertisement

#40 imaginesix

imaginesix
  • Member

  • 5,716 posts
  • Joined: March 01

Posted 01 October 2014 - 06:16

Was in response to Greg's post linking to the Ford steering system.

 

It's more maneuverable at low speed, and more stable at high speed. Basically a few of the benefits of AWS at (I'm guessing) lower cost.


Edited by imaginesix, 01 October 2014 - 06:18.


#41 Greg Locock

Greg Locock
  • Member

  • 4,544 posts
  • Joined: March 03

Posted 01 October 2014 - 06:27

All wheel steering? Yes, I see what you mean, it is a form of active steer. 



#42 gruntguru

gruntguru
  • Member

  • 5,388 posts
  • Joined: January 09

Posted 01 October 2014 - 08:54

On 2. What I had in mind here was that the gear ratio of a certain pair of spur gears can only varied in distinct steps - numbers of teeth - not continuously - and only by changing the gears. The analog property of a worm refers to the self-locking effect which occurs when the worm system is driven in the reverse direction - here it has a continuously variable range of positions in which it can lock even though the gears are themselves unchanged.

The locking function is only a friction thing. Doesn't even exist at low numerical reductions. Many Peugeot RWDs had a worm gear final drive - no trouble push starting them. Apart from that, worm gear-sets are no different to spur gears in terms of ratios calculated from tooth numbers etc.



#43 Kelpiecross

Kelpiecross
  • Member

  • 907 posts
  • Joined: October 10

Posted 02 October 2014 - 04:36

The locking function is only a friction thing. Doesn't even exist at low numerical reductions. Many Peugeot RWDs had a worm gear final drive - no trouble push starting them. Apart from that, worm gear-sets are no different to spur gears in terms of ratios calculated from tooth numbers etc.


I was actually aware of the reason for the self locking. But this is "friction" with a big "F" - usually with friction systems such as a belt drives clutches etc. you can finally make them slip by exceeding their capacity to grip. However with a worm drive system the "locking-up" is as rigid as a tooth or chain drive etc. The teeth on the worm, wheel, drive shaft etc. will break before it slips - it will never slip.
This fact raises the possibility (at least in theory) of a CVT system in which the gear ratio is genuinely continuously variable due to the analog nature of friction - but which will not and cannot ever slip due to the applied torque.

I think it helps if you have a nerdish interest (obsession?) in odd theoretical mechanical systems - as I certainly do.

#44 gruntguru

gruntguru
  • Member

  • 5,388 posts
  • Joined: January 09

Posted 02 October 2014 - 06:35

There are many examples of "friction with a big F" as you describe it. Door wedges, cam cleats, sprag clutches . . . In each case friction drives a wedge in the direction that increases the wedging action which increases the normal force thus increasing the friction etc. Back-driving a worm gear is similar - think of pushing a door "down" onto a door wedge. If the wedge is steep enough and slippery enough it will squeeze out as the door drops. If not, it won't matter how heavy the door is, friction will win.

 

Not sure how this principle might apply to CVTs?



#45 Kelpiecross

Kelpiecross
  • Member

  • 907 posts
  • Joined: October 10

Posted 02 October 2014 - 07:17


Doesn't really apply to conventional CVTs. The aim is to devise a theoretical mechanism that will give a stepless range of gear ratios but with positive engagement but without involving friction and giving a rigid connection between input and output and (importantly) output and input. This is an age-old aim which as never been achieved. It can be done using worm drive ideas - but although this gives a rigid connection it still involves friction - so I am not sure if this is a true solution to the problem or not.
It is not just odd nerds that take an interest in this subject - the mechanical engineering department at Brigham Young Uni have done a lot of work in this field - essentially without any real success (you can see some of the papers on the internet).

My son tells me there is a porn film called "Bring 'Em Young".

#46 gruntguru

gruntguru
  • Member

  • 5,388 posts
  • Joined: January 09

Posted 02 October 2014 - 07:40

The bit I don't get is how you get a ratio change from a worm drive with a fixed tooth count on each gear.



#47 Kelpiecross

Kelpiecross
  • Member

  • 907 posts
  • Joined: October 10

Posted 03 October 2014 - 04:11


The variable ratio arises from making use of the fact that the worm-and-wheel arrangement will lock up in an infinite range of positions. However this is via a complex and theoretical mechanism which at present is not really practical.