To:               Offroad@offroadlist.com
From:             "Shaw, Steve" 
Subject:          Gearless Locker
Date sent:        Sat, 12 Jun 1999 21:29:27 -0400
Send reply to:    Offroad@offroadlist.com

I had a long chat several months ago with the engineers at Trac-tech about
the Gearless Locker (and their other products) and thought I'd through the
info into the pot.  (A little about myself - I'm a mechanical engineer who
has always been interested in mechanical drive systems and traction aiding
differentials; I work with many types of clutches in my work and do run
Detroits at both ends in my rig)

To start off, my definition of a locker is a differential that ensures that the
output shafts (axles & wheels) travel at least as fast as the differential case
in the direction that the torque is applied (to the diff case).  The well known
Detroit, EZ-locker, and Lock-right do this by using "dog" clutches (toothed
clutch or "gear") that are normally engaged, but disengage when the wheel tries
to drive the axle faster than the diff case (the Detroit unlocks by a cam
pushing the dog clutch apart as the output clutch tries to overrun, and the
other 2 use the applied torque to push the clutches together, releasing due to
the cut angle in the dog clutch sets).  

The new "gearless" locker is actually similar to the EZ-locker and
Lock-right in that it uses the applied torque to apply the clutches.
Instead of using a single "geared" dog clutch, they use a clutch pack using 6
sets (at least with the Dana 44) of metal disks.  The design is such that the
"cam angle" that applies the clutch pushes them together with more force for a
given torque than required to transfer that the same torque.  This means that
the Gearless locker is indeed a true locker, it just uses a clutch pack instead
of a dog clutch.  Ultimately if you apply too much torque something will break,
just like the rest of the auto-lockers.

As far as how well it will survive on the trails, only time will tell.  Jim (I
think that was the engineer's name) said in their tests (about 8 months ago)
they had found clutch wear didn't seem to be a problem.  I've heard from others
on the web that they have had a couple grenade (I assume the clutch apply force
was so high it split the diff case), but can't confirm this.

Another diff that is sort of an auto-locker is the Eaton Gov-Lock
(http://www.torquecontrol.eaton.com/prodinfo/products/index.html
 ).  It
also uses applied torque to lock up a couple of clutch packs.  The clutches are
only applied after a certain RPM difference between wheels (approx. 100 RPM). 
These units do have a problem with failing (usually stripping the governor drive
teeth) if you're heavy on the throttle, but work well if driven gently in
typical snowy conditions or the occasional muddy road. When they work, they lock
up solidly and you can spin a tire on the ground (even dry rocks) with the other
in the air (I've done it).  One major difference with the Gov-lock over other
lockers is Eaton uses a standard "open" differential inside the diff case to
normally transfer the torque, whereas the others provide all of the drive
coupling through the clutches.

An open diff simply splits the torque (typically 50:50) between the two
wheels regardless of traction and the maximum torque applied to both wheels is
whatever it takes to spin the one with the least traction.  

A limited slip has a standard open differential within it, but also has
something to provide potential torque bias.  The bias is limited to some
torque value, hence why it's called a limited slip.  Typically this is done with
clutches (auburn, trac-lock, etc.) and may provide a few hundred foot pounds of
extra torque to the wheel with traction (which isn't much when you talking
off-roading).  The bias does increase with torque applied with these units, but
only due to the side thrust in the spider gears (read not much - I made the
mistake of installing a trac-lock in the front of my truck a year or so ago and
I wasn't impressed off-road).  Some use a cam to apply the clutch (power-lock)
or worm gears to provide friction (true-trac,  torsen, etc.).  These have the
advantage of having a torque bias that is directly proportional to the amount of
torque being applied (the more you step on it the more they lock up - that's why
brake & gas work well) and the ratio can be adjusted in the design.  The higher
the ratio, the better they will work off-road, but the more torque steer you
will see on the street.

Hope that helped.

Steve Shaw
http://www.off-road.com/~ovo/members/sshaw/sshaw.htm
 






To:               Offroad@offroadlist.com
From:             "Shaw, Steve" 
Subject:          Gearless Locker & others
Date sent:        Wed, 16 Jun 1999 08:23:33 -0400
Send reply to:    Offroad@offroadlist.com

Without pictures I can't easily explain how it's possible to lock something up
through friction, but I'll try an analogy.

Imagine a fine threaded bolt and nut with very good lubricated threads.  
Take a single washer and by hand tighten the nut.
Now hold the washer and try to continue to tighten the nut.
The nut and bolt will probably spin, but you can see that some torque is
being applied to the nut to tighten it.

Imagine now that you have splines on the bolt and a bunch of washers that
mate with those splines, plus a bunch of the larger washers you originally
tried.
Place a number of pairs of inner (splined) and outer washers on the bolt and
then tighten the nut by hand. Provided that the nut doesn't bottom out on the
splines and it's compressing the washers you can imagine that by tightening the
nut now while holding the outer washers you will actually continue to tighten
the nut (if you have enough pairs of washers). If you continue to tighten you
will either start spinning the outer washers or break something.

Since the compressive force is proportional to the applied torque and the
coupling torque is proportional to the force if it is locks for a given
torque it will remain locked regardless of the torque applied.

With the gearless locker, instead of using a bolt to tighten the "clutch"
they use the cross pin and a ramp on the back of the inner clutch member to push
it outwards.

I did a couple of searches on IBM's patent server and found the following
that you might find interesting.  I'm not positive about each being the
actual patent for the various lockers (including the Gearless one), but they at
least use very similar technology (and many are correct).

Keep in mind that these are written so that a "good mechanical engineer" can
reproduce the units.  There is an "art" to presenting "preferred embodiment"
(these are the words I keep hearing at work) such that anyone trying to
reproduce the device would have to work fairly hard to get it to work (on the
various patents I have applied for our company lawyers are always trying to make
them more vague). 

Check out the following patents (Click on "View Images" to see the entire
scanned patent):

Gearless Locker (5836220 is an "improvement" over 5727430; I don't know if
Tractech leases the rights from Dyneer or what the arrangement is - could be
patent pending with enough of a change to deem novel?):

http://www.patents.ibm.com/details?pn=US05836220__
 
http://www.patents.ibm.com/details?pn=US05727430__
 

EZ-locker:

http://www.patents.ibm.com/details?pn=US05836220__
 
http://www.patents.ibm.com/details?pn=US05715733__
 

Detroit Locker & improvements over the years:

http://www.patents.ibm.com/details?pn=US04644818__
 
http://www.patents.ibm.com/details?pn=US04557158__
 
http://www.patents.ibm.com/details?pn=US04424725__
 
http://www.patents.ibm.com/details?pn=US03791238__
 

Detroit Soft Locker:

http://www.patents.ibm.com/details?pn=US05524509__
 

Detroit C-locker (I think):

http://www.patents.ibm.com/details?pn=US05590572__
 

Powertrax Lockright:

http://www.patents.ibm.com/details?pn=US05413015__
 


Steve Shaw
http://www.off-road.com/~ovo/members/sshaw/sshaw.htm
 



Al, I rode in that TJ (Dean's) when he gave me a ride from the ferry.  I
didn't think it had a ratcheting problem coasting into a parking spot,
unlike a Lockright or EZLocker type which ratchets and bangs a lot from the
backlash.  However, Dean's TJ did do a lock of banging when mildly accelerating
out of a tight corner (like what you would do in a parking lot maneuver), which
I've never experienced before in a locked vehicle.  Is he still have that
problem?

On the highway around sweeping corners, throttle steer was minimal compared to a
conventional locker.


...lars
Well Lars we were out in it again today and took in up Eye in the Sky for
some pictures for the Magazine, we crawled right up then had to pull Rob
delange up ( Land Cruiser Detroit locker in the rear 4" lift), and again
yes to all the other readers the Gearless is a real locker. when he dropped me
off and turned around  at the end of my road you could hear the locker quite
clearly. But again this seems to be the only time you notice it. If you are on
the power going around a corner it chirps just like your regular lockers though.

If you have any question, remark, comment, want to share some philosophy or just want to express your opinion about these pages, feel free to send email to: w.j.markerink @ a1.nl