Date: Fri, 23 Apr 1999 10:03:03 +0200
Reply-To: "Dr. Rainer Woitok" <woitok@RRZE.UNI-ERLANGEN.DE>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: "Dr. Rainer Woitok" <woitok@RRZE.UNI-ERLANGEN.DE>
Organization: RRZE (Regionales Rechenzentrum Erlangen)
Subject: Re: Re : How VC's work
In-Reply-To: Msg <003801be8cd1$313a2420$4730a2d1@dell> of 1999- 4-22 08:02:49
-0700 from wdavidson@THEGRID.NET
Content-Type: text/plain; charset=us-ascii
Hi Syncronauts and all you normal Vanagoneers (if you're at all
interested in VCs :-)
On Thu, 1999-04-22 08:02:49 -0700, Davidson wrote:
> Locks up at 100 degrees???? !!!!!!
Wolfgang probably meant degees centigrade. But it seems the theory of
how viscous couplings work is either not very well understood or there
are several theories which contradict each other. This is a common
practice nowadays when some company is filing a patent, because it makes
it more cost intensive for any competing company to disregard the patent
protection (or to "reinvent" something very similar but still different
enough and thus not patent protected). List member Tim Smith (are you
listening, Tim? :-) claims to have two papers describing two of these
contradicting theories. Ages ago he promised to scan them and to make
them available to the list, but his scanner is still seeming to refuse
to work.
One well known fact about viscous couplings is that they are containing
a series of perforated metal disks which are not contacting each other
and which are alternatingly attached to the input and output shafts.
Another fact is that there is some special viscous liquid (silicone)
floating around and between these disks. These two facts can easily be
proven by opening an old viscous coupling (kids, don't try that at home
... you better just believe me :-). The third fact is that a viscous
coupling realy works, and this can be proven by driving a Syncro in
difficult terrain :-).
Now, on to the theories. On this list (as well as elsewhere) there
basically are circulating three theories:
1-st theory: Differing rotational velocities on the input and output
shafts causes friction in the silicone fluid and thus heat. The heat
causes the silicone to expand which in turn presses the metal disks upon
each other and this direct contact causes the viscous coupling to lock.
In my opinion this is clearly bogus. Pressurising any liquid which
contains submerged metal plates will not force these plates into
contact. This, too, is a simple fact from simple physics which can
easily been proven. What's more, these disks are bare metal, no pads or
such, as in a normal clutch. If the friction caused by bare metal being
pressed on bare metal would be essential for the operation of a viscous
coupling, they would do a poor job. Within very short a time the metal
surfaces would be polished and friction would be reduced to almost zero.
2-nd theory: Differing rotational velocities on the input and output
shafts causes friction in the silicone fluid and thus heat. The heat
causes the silicone to become stiff thus causing the perforated disks
(now the perforation starts to make sense, see?) to rotate at the same
speed.
3-rd theory: Differing rotational velocities on the input and output
shafts causes shearing of the viscous fluid and it's that shearing (and
not the heat) which causes the silicone to become stiff and thus the
disks to rotate at the same speed. Of course, before the viscous
coupling locks up totally, there will be some friction, and thus some
heat.
So the main question to tell these two theories apart is whether this
heat is the cause for the locking of the viscous coupling or just an
inevitable technical by-product. If you ask me, I simply don't know.
But currently I would put my money on the third theory, because I really
can't see how quite a few cubic centimeters of silicone fluid could
change their temperature in such a rapid an uniform way as the operation
of a viscous coupling does indeed require (we're talking about split
second timing here). Perhaps I will know more when Tim will ever get
his scanner ready (hint, hint :-)
Hope this clarified a few things.
Sincerely
Rainer
'89 Caravelle GL Syncro 16"
----------------------------------------------------------------------
| Rainer M Woitok | Phone: (+49-9131) 85-27811,-27031 |
| Regionales Rechenzentrum | |
| Friedrich-Alexander-Universitaet | Fax : (+49-9131) 30 29 41 |
| Martens-Strasse 1 | Telex: d 629 755 tf erl |
| D-91058 Erlangen | |
| Germany | Mail: Woitok@RRZE.Uni-Erlangen.DE |
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