Dan wrote to me privately, but I decided - what the heck, blast the whole list,
others might fint it interesting (but rather long...)
Dan wrote:
>Hello Sir,
I seldom respond to the name Sir... Tim does just fine... :-)
>I read with great interest your posing on the british car list. You seem
>to have quite a solid grasp on how transmissions operate. I am eager to
>learn more about transmission theory, and was wondering if you could
>point me in a direstion for further investigation?
Dan,
I didn't learn about transmissions from theory books; actually, I learned by
having to rebuild my 64 TR4's broken trans. I studied the repair manual, took
it apart, and rebuilt it... spent a lot of time "playing" with it while it
was apart to figure out how it worked. Somewhere along the line (it was
twenty-some years ago), I also spent a lot of time going over the "cut-away"
"functional diagrams" in a Chevy truck manual that we had. The book had
cross-sectional drawings of the trans with the shifting mechanisms "moved"
onto each of the "shifted" positions, with colored arrows showing the
transmission of "power-flow" thru the gears. It gave me some idea, but it
didn't realy make sense until I had a trans apart... I have since rebuilt
several transmissions, and they were all about the same, and actually more
simple than an engine; it does help to have a 12-ton press and a bearing
puller (about $150 for the tools), but I managed the first with just "normal"
tools...
>You mention that
>syncros are a subject for another article, I'll read it if you send it!!
Okay here goes....
Bad ascii art:
Gear NOT Engaged Half of a semi-cut-away
of transmission parts
-----------| |-------------
------- | |__| |
|\ \ \|==> ----\_ _/---------
| \ \ | <--\ \_ _/
|\ \ \|==> | - | |
| \ \ | <-- \ | |
|\ \ \|==> | | | |
| \ \ | <-- | | |
|\ \ \|==> | | | |
|_____| |--------------------
=========--|---------
|---------
--+--+--+--+--+--+--+--+--+--+--+--+--+--+ Center Line
Gear Engaged
-----------| |-------------
------- | |__| |
|\ \ \|=----\_ _/---------
| \ \ |<--\ \_ _/
|\ \ \|==| - | |
| \ \ <-- \ | |
|\ \ \|==| | | |
| \ \ <-- | | |
|\ \ \|==| | | |
|_____| |--------------------
=========--|---------
|---------
--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Parts...
Gear
-------
|\ \ \|==> Sycro slpines... (Steel - part of gear)
| \ \ | Rotates freely on output shaft
|\ \ \|==>
| \ \ |
|\ \ \|==>
| \ \ |
|\ \ \|==>
|_____|
--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Sychro Ring (Sychros) usually made of brass - very light...
<--\ cone shaped friction surface
| -
<-- \
| |
<-- |
| |
<-- |
| |
--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Slider (Engages gear, splined to shaft Must rotate with
shaft, but moves back and forth on shaft.)
-----------| |-------------
| |__| |
----\_ _/---------
\_ _/
| |
Cone shaped | |
Surface matches | |
Sychro Ring | |
| |
--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Output Shaft - gears rotate freely, sliders splined to shaft - cannot
rotate on shaft
|--------------------
=========--|---------
|---------
--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Note that in the follow description, the "teeth" mentioned are not the actual
gear teeth that transmit the power, only little teeth on the side of the gear
and sychro's...
The transmission engages a gear by moving the slider toward the gear. When
this happen, the sychro ring is pushed toward the gear also, and contacts the
gear first. The little pointy brass tips on the sychro ring "hits" matching
points on the side of the gear, and the sychro in forced to *very* quickly
match speed with the rotating speed of the gear (since the ring is *very*
light). As the slider is moved more toward the gear, the cone shaped outside of
the sychro ring is forced into contact with the matching surface of the slider.
Friction between the surfaces, and the engaged "teeth" of the sychro ring cause
the different speeds of the rotating gear and the rotating slider/output shaft
to become the same (the gear changes speed, since the output shaft is connected
to the wheels). Once the speeds are matched, then the slider can continue to
move toward the gear, and splines on the "inside edge" of the slider engage the
matching splines behind the "teeth" on the gear. These splines becoming
engaged is what causes the gear to become locked to the slider and in turn to
the output shaft. When sychro's cone surface wears out, the splines of the
slider hit the splines of the gear before the speed gets matched, and you hear
the "GRUNCH" sound. The brass sychros are designed to wear before the steel
gear and slider, because the sychros are simple and cheap (10 - 40 bucks each)
compared to the $$expensive steel gear and slider (20 years ago, it was $100
for a first gear for my TR4, about $3 for a sychro).
The magic comes in the actual sychro material, additional groves to improve
friction, fewer sychro "teeth" to make the engagement happen faster, etc. but
they all work about the same...
Tim Mullen mullent@ymv5.ymp.gov Chantilly, VA
72 Elan Sprint "For the few who know the difference"
|