Re: how does an open differential work

[Dave Eaton <dave.eaton@minedu.govt.nz>]

orin,

i'm not trying to insult you, so lighten up....

with an open diff, it will not support any significant torque difference
*between* the drive axles (taking into account bearing friction as you
suggest).  in an open diff, the maximum amount of torque conveyed by the drive
shafts is limited to approximately twice the amount of torque supported by the
shaft having the *least* friction.  put a wheel in the air, and you don't need
any blocks.  been there, done that (4-wheel drives off road).  try it an see.

hth,
dave
'95 rs2
'90 ur-q

>
>>
>>----------
>>From: 	Orin Eman
>>Sent: 	Thursday, February 26, 1998 3:55:50 PM
>>To: 	David Eaton
>>Cc: 	quattro@coimbra.ans.net
>>Subject: 	Re: how does an open differential work
>>Auto forwarded by a Rule
>>
>
>> nope, you're wrong sorry.  easy to test.  take your parents car (fwd or
>> rwd), jackup one wheel and startup, put it into gear, and let out the
>> clutch.
>
>I don't know why I'd want to use my parents' car.  Is that supposed
>to be a veiled insult?  I could use one of my own except I'm
>not that stupid.
>
>> voila, no movement, and one nicely spinning wheel.  $1,000 on it, any
>> day............
>
>Proves nothing.  Result would be as you say with one wheel spinning.
>It would be a very stupid and dangerous test unless you blocked the
>car so that it couldn't move.
>
>The reason the car wouldn't move is that sum of the frictional forces
>in the bearings and axles of the wheels that are on the ground is
>greater than the torque required to spin the one wheel.  I assure you,
>the other driven wheel is still receiving the same torque as the
>spinning
>wheel... IT'S JUST NOT ENOUGH TO DO ANYTHING.
>
>IF there were no torque going to the stationary wheel, then if you
>were to jack up that side too, it wouldn't turn.  Give it enough gas,
>I assure you it will...
>
>If you can disprove the Physics, fine.  I doubt that you can though.
>
>> >-----Original Message-----
>> >
>> >Date: Wed, 25 Feb 1998 15:46:23 -0800 (PST)
>> >From: Orin Eman <orin@wolfenet.com>
>> >
>> >> "This rotation allows the pinions(your bevel gears) to compensate for
>> >> the difference in rotational speed of the side gears(connected to drive
>> >> axles) - while continuing to drive both side gears. This differential
>> >> action is self adjusting to any variation in axle speed - but only until
>> >> one wheel begins to slip.
>> >
>> >> When one wheel  begins to slip or to spin, the case will continue to
>> >> rotate the pinions but, instead of driving both side gears, the pinions
>> >> will take the path of least resistance, rotate on their shaft, and
>> >> "walk" around the axle connected to the wheel with greater traction. All
>> >> the torque will be directed toward the spinning wheel. 
>> >
>> >I disagree, as does the Bosch Automotive Handbook.  The slipping wheel
>> >case is actually better than this.
>> >
>> >What I am saying is that in the slipping wheel case, wheel accelerated
>> >to its maximum speed, then there is an equal amount of torque directed
>> >to the non-slipping wheel.  Has to be.  Moments about any point on any
>> >bevel gear must sum to 0 or it will be accelerating.
>> >
>> >